[0001] The present invention relates to an improved process for the isolation of high- purity lignin from an organosolv liquor. In a preferred embodiment, the invention also concerns the production of a light-coloured lignin and the thus produced lignin. The invention thus first of all concerns post treatment of the liquor after organosolv treatment of biomass, but in a preferred embodiment also concerns the organosolv treatment itself. The invention also concerns the isolated lignin obtainable by the process according to the invention and the use thereof.

Background

[0002] Biomass, especially lignocellulosic biomass, is a valuable resource for the production of (bio)fuels, chemicals, performance products and energy. Lignocellulose is the most abundant renewable biomass available on land, and therefore relatively cheap. Many research efforts have been devoted to the development of processes for the cost- effective conversion of biomass, especially lignocellulosic biomass, to valuable compounds. The main structural components of biomass are cellulose, hemicellulose and lignin (see Table 1 for approximate compositions of some biomass types). The cellulose component of biomass may for example be converted to glucose, which in turn may serve e.g. as a precursor for 'second-generation' bioethanol (by fermentation of glucose), and is thus suitable for the production of biofuels. However, to render such process economically attractive, the further components of biomass should preferably also be converted into valuable compounds, having a higher value than combustion to generate heat and/or power. In this respect, especially lignin has not found widespread application that would valorise the large amounts that would be coproduced during lignocellulosic biomass conversion for second-generation biofuels and chemicals from sugars. To facilitate value-added and large-scale applications of lignin, biomass valorisation preferably starts with separating the cellulose and lignin components in order to generate lignin with sufficient quality for these applications. [0003] Table 1: Structural components of biomass (wt% based on dry weight)

[0004] Lignin is a complex polymeric structure of aromatic alcohols, which is built up from three distinct monomers (monolignols), being paracoumaryl alcohol or para- hydroxyphenyl (denoted H), coniferyl alcohol or guaiacyl (4-hydroxy-3-methoxyphenyl; denoted G), and sinapyl alcohol or syringyl (4-hydroxy-3,5-dimethoxyphenyl; denoted S). Variation of lignin occurs between different types of biomass, wherein the three monomers are present in varying amounts. Monocot angiosperm (herbaceous biomass) lignin typically contains all three subunits, while dicot angiosperm (hardwood) often contain a mixture of G and S lignin with very little H present. The lignin of gymnosperms (softwood) on the other hand is almost exclusively built from the G monomer with trace amounts of H lignin (see Boerjan et al. , Annu. Rev. Plant Biol. 2003, 54, 519-546).

[0005] Fractionation of biomass may be accomplished by the so-called organosolv process, which delignifies lignocellulosic biomass and thereby improves the accessibility of the cellulose polymers for hydrolytic enzymes converting cellulose to glucose. Without pre-treatment, such as organosolv, the cellulose within lignocellulosic biomass is poorly accessible for the hydrolytic enzymes, as it is shielded by other structural components in the biomass, such as lignin. Conventional organosolv involves high- temperature treatment (typically between 180 and 220 °C) of the biomass with a (water- miscible) organic solvent (e.g. ethanol) and optionally an (acidic) catalyst. During organosolv, the lignocellulose biomass is fractionated into a cellulose-enriched solid product stream (pulp) and a liquid product stream (liquor) comprising dissolved lignin and hemicellulose derivatives.

[0006] A major drawback of current commercial pulping processes for lignocellulosic biomass, such as Kraft, sulphite and soda pulping, is that isolation of lignin from the liquor typically provides isolated lignins with substantial amounts of impurities, such as carbohydrate residues and ash. Although organosolv fractionation typically provides lignins with lower amounts of residual carbohydrates, these lignins still may contain a significant amount of sugar impurities. Also, the lignins retrieved are dark-coloured (dark-brown to black) and typically have a strong odour, which hampers specific application thereof (see e.g. Vishtal and Kraslawski Bioresources, 2011, 6(3), 3547- 3568). Potential application of isolated lignin (also referred to as technical lignin in the art) is mainly in performance products such as paints, resins, binders, plastics and composite materials (see e.g. Stewart, Ind. Crop. Prod. 2008, 27, 202-207 and Lora and Glasser, J. Polym. Environ. 2002, 10, 39-48). The impurities present in technical lignins may limit the use of lignins in specific applications. Moreover, the use of dark-coloured lignin typically results in a strong colouration of the final product. For example, Pan and Saddler {Biotechnology for Biofiiels, 2013, 6: 12) found that organosolv lignin performed better than Kraft lignin in rigid polyurethane foams, but despite that organosolv lignin was lighter in colour than Kraft lignin, the foam turned from yellow to brown upon lignin incorporation. The colour of such lignins can often not be hidden or masked in an economic way when applied in the above fields, especially when a light-coloured final product is desired or required. Thus, the colour of prior art technical lignins is often considered a show-stopper for applications in performance products, and thus for the large-scale valorisation of lignin and eventually lignocellulosic biomass. Hence, research has strived to find a method for producing "white lignin" for many years.

[0007] Some processes for decolouring dark lignins obtained by prior art fractionation of biomass have been reported. Reduction of the colour of sulphonated lignins by virtue of chlorine dioxide oxidation is described in US4454066. Oxidation of sulphonated lignins can also be achieved by air, 0 ₂ or H2O2 when the free phenolic hydroxyl groups of sulphonated lignins are alkylated prior to oxidation (see US4184845). Saritha et al. (J. Environ. Res. Manage. 2010, 1(1), 1-4) discloses the fungal degradation of lignin to obtain a reduction in colour. However, the obtained lignin degradation products cannot be considered light-coloured.

[0008] Extraction of milled wood lignin (MWL) is a well-known analytical method to yield a lignin with properties most closely resembling those of native lignin in the plant. MWL is obtained by excessively milling wood in a bowl mill until a very fine powder is obtained in which the biomass cells are broken. From this powder, lignin is extracted with an organic solvent at room temperature. As such, hardly any chemical modification of the lignin occurs. MWL has an _w well above 5000 g/mol and a broad dispersity D. In view of the mild conditions applied to extract MWL from biomass, this type of lignin is considered to most closely resemble native lignin as it occurs within the biomass. Up to a maximum of 50 wt% of the lignin present in the biomass can be extracted this way. Importantly, the isolation of milled wood lignin requires extensive milling, leading to very high capital costs and energy consumption making the procedure economically unsuitable for large-scale industrial production of lignin. Isolation of milled wood lignin is only performed at lab-scale for research purposes. Moreover, milled wood lignin typically contains significant amounts of impurities, such as carbohydrates, which are co-extracted with the lignin.

[0009] Also known is sulphite pulping of biomass, wherein the biomass is pulped for about 4 - 14 h at a temperature of 130 - 160 °C in the presence of sulphite and/or bisulphite salts. During sulphite pulping, ether bonds of lignin are broken by formal addition of sulphurous acid (H2SO3), and sulphonic acid (-S(0)20H) moieties are incorporated in the lignin, which are referred to as lignosulphonates, which typically instigates an organic sulphur content of 3 - 10 wt%. Although often brownish, lignosulphonates can sometimes be lighter-coloured (yellowish) than isolated lignins obtained in Kraft and conventional organosolv processes. Although ether bond cleavage of lignin does occur during sulphite pulping, the lignin is broken down to a smaller extent than during the organosolv process. Also, lignosulphonates typically have broader molar mass distributions than organosolv lignins. Due to the presence of sulphonyl hydroxide (S(02)OH) groups, lignosulphonates are soluble in water in contrast to organosolv lignins. Organosolv lignins are thus typically employed in different applications as lignosulphonates. Large scale application of lignosulphonates is hampered by their sulphur content, their limited production and their typically broad molar mass distribution. A further drawback of lignosulphonates is that the isolated lignins from sulphite pulping comprise large amounts of impurities, typically 10-25 wt% based on dry weight of the isolated lignin. Organosolv lignins, in view of their narrow molar mass distribution and low levels of impurities, have a far greater potential to be used in performance products. The greater potential of organosolv lignins over lignins obtained via other biomass fractionation processes is e.g. known from Kubo and Kadla, Macromol. 2004, 37, 6904-6911. The present invention provides in the need for light- coloured, high purity and sulphur-lean lignins.

[0010] Softwood organosolv pulping using 40 - 60 wt% ethanol in water is known from Pan et al. {Biotechol. Bioeng. 2005, 90:473-481), wherein organosolv was performed at a temperature of 185 - 198 °C. Lignin having an _w of 2.9 kDa and a dispersity D of 1.6 was obtained. In another study (Ind. Eng. Chem. Res. 2007, 46, 2609-2617), Pan et al. investigated the pretreatment condition for lodgepole pine killed by mountain pine beetle. Treatment at 170 °C for 60 min using treatment liquid containing 65 wt% ethanol and 1.1 wt% sulphuric acid gave optimal results. Organosolv at reduced temperatures based on volatile solvents such as ethanol is known from WO 2012/000093 and WO 201 1/097720, which describe treatment of biomass at 140 - 170°C, at a pH of 1.5 - 2.5, and with ethanol as preferred organic solvent, wherein pulp and lignin-containing black liquors are obtained. Isolation of lignin from organosolv liquors has for example been described by Huij gen et al. {Ind. Crops Prod. 2014, 59, 85-95), wherein the organosolv liquor is added to chilled water to precipitate lignin. Precipitated lignin particles were sedimented by centrifugation, separated by decantation and the resulting lignin was dried to a dry matter content of 96 to 98 wt%, without any further purification. Similar methods are disclosed in US 5010156 and by Huijgen et al. {Ind. Eng. Chem. Res. 2010, 49, 10132-10140) and Felissia et al. {Cellulose Chem. Technol. (2010, Jan 1), 31 1-318).

Summary of the invention

[0011] The invention relates to an improved process for the isolation of lignin from an organosolv liquor, and to the product thereof. Surprisingly, the inventors have found that by implementing a specific heating step of the lignin obtained in an organosolv treatment of biomass, the purity of the obtained lignin significantly improves. According to a preferred embodiment of the process according to the invention, the inventors were even able to obtain lignin having a colour characterised as light-coloured to white. Both the effect on purity and colour of the lignin obtained by the process according to the invention provides a marked improvement over prior art processes of isolating lignin from an organosolv liquor. Large-scale formation of lignin of such light colour is unprecedented in the art and is a marked improvement over known isolated lignins. No industrially applicable processes that afford such high-purity, light-coloured lignin are known from prior art.

[0012] The process for the isolation of lignin according to the invention comprises:

(a) precipitating lignin from an organosolv liquor;

(b) separating the precipitated lignin from the liquor;

(c) heating the separated lignin until it undergoes a phase separation by expelling moisture to obtain partly-dried lignin and a liquid phase;

(d) separating the partly-dried lignin from the liquid phase; and

(e) drying the separated partly-dried lignin to obtain the isolated lignin. [0013] The invention further pertains to isolated lignin obtainable by the process according to the invention. Alternatively or additionally, the isolated lignin according to the invention is characterised by a molar mass distribution having a _w of 1000 - 10000 g/mol. The weight-averaged mean molar mass of the isolated lignin is lower than that of e.g. milled wood lignins. Furthermore, the lignin according to the invention has a sulphur content of at most 1 wt% and is preferably light-coloured.

[0014] Without being bound by a theory, it is believed that the process according to the invention, in particular the implementation of step (c), affords high-purity isolated lignin, since the excreted liquid phase, that is separated in step (c), contains impurities which would otherwise end up in the isolated lignin. The inventors have found that removing this excreted liquid from the lignin being dried removes such impurities and increases the purity of the isolated lignin.

[0015] Furthermore, the process for isolating lignin from an organosolv liquor according to the invention, and preferably the process for obtaining the organosolv liquor, is implemented such that those chemical modifications of the native lignin that affect the colour are reduced as much as possible. Such chemical modification typically includes the elongation of chromophores within the lignin structure, e.g. extension of the conjugated system of chromophores by chromophore condensation, dehydration and/or oxidation, such that visible light is absorbed by these elongated chromophores, and by condensation of lignin particularly with carbohydrate degradation products. It is believed that the present process prevents condensation reactions of lignin with non-structural biomass components (e.g. proteins, fatty acids) or carbohydrate degradation products (e.g. (hemi)celluloses degradation products such as furfural formed during organosolv at more severe conditions) from happening to a large extent, thus preventing colouring of the lignin.

Detailed description

[0016] The present invention first and foremost relates to an improved process for the isolation of lignin. The invention thus first of all concerns post treatment of an organosolv liquor (i.e. isolation of lignin) after organosolv treatment of biomass, but in a preferred embodiment also concerns the organosolv treatment itself. The invention also concerns the isolated lignin obtainable by the process according to the invention and the use thereof. Process for isolating lignin

[0017] The present invention relates to a process for the isolation of lignin from an organosolv liquor. In a preferred embodiment, the invention also concerns the production of a light-coloured lignin and may thus be referred to as a process for the isolation of light-coloured lignin. The process according to the invention comprises:

(a) precipitating lignin from an organosolv liquor;

(b) separating the precipitated lignin from the liquor;

(c) heating the separated lignin until it undergoes a phase separation by expelling moisture to obtain partly-dried lignin and a liquid phase;

(d) separating the partly-dried lignin from the liquid phase; and

(e) drying the separated partly-dried lignin to obtain the isolated lignin.

Step (a)

[0018] Precipitation of lignin from an organosolv liquor is known in the art, and any means to accomplish lignin precipitation may be used. Typically, step (a) involves decreasing the organic solvent content of the liquor, to e.g. below 40%, preferably below 30% or even below 20% (w/w). This is typically accomplished by evaporation of the organic solvent and/or by dilution with (optionally acidified) water or another solvent in which lignin does not dissolve, such as hexane. Also membranes that are selective for organic solvents may be used. The skilled person understand that the optimal parameters at which step (a) is performed may vary between the various possibilities at which step (a) is performed. Step (a) is preferably performed by dilution of the liquor with water or by selectively evaporating at least part of the organic solvent, most preferably by dilution. Dilution is preferably accomplished with water, in which case it is preferred that the organosolv liquor is added to the water. The water may be acidified prior to addition of the organosolv liquor thereto, e.g. by addition of an acid, typically H2SO4, until a pH of 1 - 5, preferably pH 1.5 - 3, such as a pH of about 2, is reached. However, since excellent results have been obtained with neutral water, it is preferred that the water is non acidified, i.e. has a pH in the range of 6 - 8. Best results were obtained using an amount of water that is 2 - 5 times, preferably about 3 times the weight of the liquor. It is especially preferred that lignin is precipitated by addition of water preferably having a temperature of 0 - 15 °C, more preferably 2 - 10 °C. The inventors found that this procedure for precipitating the lignin by dilution with water affords the lightest-coloured lignin. Prior to step (a), the liquor is optionally concentrated using membrane filtration techniques or partial solvent evaporation.

[0019] Precipitation of lignin by evaporation of the organic solvent may be performed at a temperature close to the temperature at which the liquor is discharged from the organosolv reactor and/or a pressure close to the pressure within the organosolv reactor. Preferred conditions of the organosolv reactor are defined below. Alternatively, evaporation of the organic solvent is achieved at lower temperature and pressure than those of the organosolv reactor, e.g. by vacuum distillation, preferably at 20 - 80 °C, more preferably 30 - 60 °C, and 40 - 120 mbar, more preferably 60 - 80 mbar. Using vacuum distillation in step (a) reduces the colour of the isolated lignin compared to evaporation at higher temperatures and pressures. Further guidance how to employ evaporation of organic solvents such as ethanol in order to precipitate lignins can be found in Schulze et a/. (Biores. Technol. 2016, 199, 128-134). Step (b)

[0020] In step (b), the precipitated lignin is separated from the liquor. Such separation is known in the art and is typically accomplished by filtration, flotation, or centrifugation/settling and subsequent decantation. The skilled person is aware how to perform such separation efficiently and what conditions preferably apply for each of the possibilities at which step (b) is performed.

[0021] The separation of step (b) affords a semi-solid lignin precipitate, which is subjected to step (c). This semi-solid lignin is also referred to as "separated lignin" in the context of the present invention. The lignin obtained in step (b) is typically in the form of a pellet having a total solid content of typically 5 - 15 wt%. The semi-solid lignin precipitate thus contains significant amounts of solvent.

Step (c)

[0022] In step (c), the separated lignin is subjected to a heating step. At a certain moment during such heating, a phase separation occurs, wherein the semi-solid lignin precipitate excretes (or expels) a liquid phase. The lignin is typically heated to a temperature of at least 30 °C, such as 30 - 120 °C or 35 - 100 °C. Such heating may be performed by placing the separated lignin in an environment having an elevated temperature (i.e. the environment is pre-heated), such as an oven, dryer, stove or water bath, preferably in an oven or water bath. Alternatively, such heating may be performed by placing the separated lignin in a non-pre-heated environment, e.g. room temperature, and subsequently heating the environment or by providing external energy to the separated lignin in form of, for example, microwave irradiation or addition of pre-heated water. The heating is preferably performed by placing the separated lignin in a pre-heated environment. The separated lignin may be heated open to its surrounding atmosphere or within a closed containment. Step (c) is preferably accomplished by heating at a temperature of 30 - 100 °C, preferably 35 - 60 °C, more preferably 40 - 55 °C, optionally with concurrent reduction in pressure to 0 - 200 mbar, preferably 10 - 100 mbar. Preferably, no such reduction in pressure is applied and the heating of step (c) as performed at ambient pressure. Step (c) is typically continued for at least 5 min, preferably at least 10 min, more preferably at least 15 min or even at least 30 min. The initial stage of heating, which is typically the first 30 min of step (c), is preferably performed at a rate of 0.1 - 10 °C/min, more preferably at a rate of 0.3 - 5 °C/min, most preferably at a rate of 0.5 - 2 °C/min. It will be appreciated that the rate of heating does not need to be constant but may vary over time. Typically the rate of heating will decrease over time and the swiftest heating is observed at the start of step (c). The above defined preferred heating rates apply to the initial stage of heating, as after the first 30 min have lapsed the rate of heating may drop to 0 °C/min.

[0023] The inventors have found that using higher temperatures for the heating of step (c) shortens the time until phase separation occurs. However, keeping the temperature below 60 °C, or even below 50 °C, has a positive effect on the colour of the isolated lignin, and even though phase separation typically occurs more slowly, high levels of excreted water could also efficiently be obtained at temperatures below 60 °C. Most optimal results have been obtained when step (c) was executed at 50 °C, especially when combined with addition of water prior to step (c), as defined further below, when lignin shrink occurs relatively swiftly (i.e. completed in about 45 min from the start of step (c)) while the colour remained desirably light. Thus, in an especially preferred embodiment, step (c) is performed at 45 - 55 °C, most preferably at about 50 °C. It has been found that phase separation takes place when the lignin has reached a certain temperature, which may slightly vary between different samples, but typically is in the range of 30 - 40 °C. Although the heating of step (c) should be carried out until at least the temperature at which phase separation occurs is reached, the heating may also be performed at a higher temperature. The skilled person is capable to determine for a particular sample of separated lignin at which minimum temperature it should be heated to effectuate phase separation.

[0024] In one embodiment, the lignin is cooled prior to step (c), to ensure that the initial temperature of the lignin is not at or above the temperature of phase separation, preferably to a temperature below 30 °C, more preferably to room temperature. No cooling step is required in case the separated lignin originating from step (b) has a sufficiently low temperature. The cooling of the lignin could be performed prior to step

(a) , during step (a), in between step (a) and step (b), during step (b) or in between step

(b) and step (c). Preferably, such cooling is performed prior to step (a) or during step (a). Any means for cooling known in the art can be employed.

[0025] During phase separation, the solid phase of the lignin precipitate shrinks, thus excreting the major part of the liquid that was embedded within the lignin matrix prior to phase separation. The amount of excreted water depends largely on how long the heating is continued after phase separation has commenced. Although the phase separation typically takes only a few minutes, mainly depending on the temperature at which step (c) is performed, it is defined herein as the moment at which the separated lignin starts to excrete water. Phase separation is thus the point in time at which the first water appears outside the solid mass of the separated lignin. This moment is clearly identifiable with the naked eye. Typically within 30 minutes, the volume of the separated lignin is reduced to such an extent that more than 80 wt% of the embedded water is excreted, while the majority of the water is excreted in the first 10 minutes. In most instances, the majority of the liquid is expelled within 5 minutes or even within 1 minute. At lower temperatures, such as 30 - 50 °C, water excretion may take somewhat longer, without negative effects on the resulting partly-dried lignin. Preferably, the heating is continued until at least 25 wt% of the total weight of the liquid phase embedded in the precipitated lignin is excreted, preferably at least 40 wt%. At such levels of excreted water, the improvement in purity of the isolated lignins is already significant, although higher purities may be obtained when at least 75 wt%, preferably at least 90 wt%, most preferably at least 95 wt% of the total weight of the liquid phase embedded in the precipitated lignin is excreted in step (c). In a preferred embodiment, the heating of step

(c) is stopped when 25 - 75 wt%, preferably 40 - 70 wt%, more preferably 45 - 60 wt% of the total weight of the liquid phase embedded in the precipitated lignin is excreted. Based on total volume of the separated lignin, the amount of excreted liquid when step (c) is stopped preferably amounts to 20 - 70 vol%, more preferably 40 - 60 vol %, most preferably 45 - 55 vol%. As a rule of thumb, optimal results can be obtained when step (c) is stopped when the lignin has shrunk to about 50 % of its original volume at the start of step (c). The inventors have found that such lower levels of excreted water in step (c) have a positive effect on the resulting colour of the isolated lignin, while the purity thereof is still markedly improved. It was surprisingly found that removal of the expelled liquid in step (d) prevents further liquid excretion and colouration of the lignin during step (e).

[0026] Without being bound to a theory, it is believed that the semi-solid lignin precipitate obtained in step (b) contains some of the remaining liquor, containing water, possibly organic solvent and components dissolved therein, such as carbohydrates (notably hemicellulose and its degradation products such as furfural), organic acids, salts and possibly other compounds, embedded within the lignin matrix. In view thereof, this liquid phase is not separated during step (b), but is excreted from the lignin structure during step (c). This phenomenon is also referred to as "shrink". During lignin shrink, a significant part of the remaining solvent with components dissolved therein is excreted. The inventors have found that the purity of the isolated lignin is significantly improved when this liquid phase is separated from the lignin, instead of continuing to dry the mixture. As such, impurities are removed with the liquid phase, which otherwise would end up in the isolated lignin.

[0027] At the end of step (c), the lignin is referred to as partly-dried, even though the expelled water is still present, typically as a layer separate of the partly-dried lignin, such as on top of or next to the partly-dried lignin. Partly-dried refers to the reduced water content of the lignin at the end of step (c), compared to the separated lignin form step (b). The partly-dried lignin may also be referred to as "shrunk lignin" or "condensed lignin", "contracted lignin", "densified lignin", "compacted lignin" or "the lignin originating from step (c)". The two phase system of partly-dried lignin and the expelled liquid phase are together subjected to step (d). Thus, instead of continuing the heating of the lignin, the process according to the invention separates in step (d) this liquid phase from the solid lignin, before drying is performed in step (e). Especially when higher temperatures are used, such as above 50 °C or even above 100 °C, some solvent may already evaporate during the heating of step (c), especially in case step (c) is executed open to the atmosphere. Although some evaporation is well tolerated, the extent thereof should not be such that precipitation of impurities dissolved within the liquid phase starts to occur. At lower temperatures, typically 50 °C and below, such spontaneous evaporation hardly occurs within typical heating times of step (c), and the point at which the heating is halted and step (d) is performed is less crucial. Continuing with step (c) at 50 °C for up to 5 hours after phase separation has occurred has been found not to negatively affect the purity of the isolated lignin. In a closed vessel, step (c) could even be performed up to 18 hours at 50 °C without any effect on lignin purity. Generally speaking, also from a process economy point of view, it is preferred that step (c) is interrupted at most 5 h after phase separation occurs. However, as indicated above, the colour of the isolated lignin is negatively affected in case the amount of expelled water is too high. For reducing the colour intensity of the isolated lignin, it is thus preferred that step (c) is halted within 60 min after phase separation is observed, preferably within 45 minutes or within 30 minutes, most preferably within 10 minutes or even within 5 minutes. In one embodiment, step (c) is continued for at most 24 h, or at most 16 h, or at most 10 h, preferably at most 8 h, or at most 5 h, or at most 3 h, more preferably at most 2 h, or at most 1 h, most preferably at most 0.5 h, calculated from the start of the heating.

Step (d)

[0028] It is thus important that the heating of step (c) is not continued until the lignin is dry, but halted in order to separate the liquid phase from the lignin in step (d). When step (d) would be skipped, the solvent of the excreted liquid phase would be evaporated and all impurities dissolved therein would end up in the isolated lignin, reducing the purity and increasing the colour intensity thereof. In addition, in case no water was added prior to step (c), skipping of step (d) would result in continued shrinking of the lignin and thereby further colouration of the lignin during step (e). The process according to the invention is thus a great improvement over prior art processes, wherein drying by heating is continued without intermediate separation of the liquid phase.

[0029] During step (d), the liquid phase which is excreted at the end of step (c) is separated from the solid partly-dried lignin. Such separation can be accomplished by any means known in the art, such as filtration or decantation. In case the lignin would be dispersed throughout the sample, centrifugation may be used to help the separation of step (d), although this is typically not required. For process efficiency, filtration is generally the preferred means of separation. As indicated above, it is preferred that step (d) is executed within 60 min after phase separation during step (c) occurs, preferably within 45 minutes or within 30 minutes, most preferably within 10 minutes or even within 5 minutes. The separation of step (d) separates substantially all of the excreted liquid phase from the remaining solid phase, the partly-dried lignin. The partly-dried lignin from which the excreted liquid phase is separated (removed) is then subjected to the drying of step (e), while the separated liquid phase is not subjected to the drying step. The separated liquid phase may be discarded or used in any way deemed fit.

[0030] The separation of step (d) typically occurs relatively instantaneously. Acts like filtration or decantation generally are completed in a short time period, which mainly depends on the size of the batch. In view of this instantaneous nature of step (d), it is not required that halting of step (c) involves a reduction in temperature. The end of step (c) may thus be defined as the moment at which step (d) is executed. Typically, the temperature of the lignin at the end of step (c) is sufficiently low that hardly any evaporation of the solvent of the liquid phase occurs, and even if step (c) would be performed at higher temperatures, such as at least 50 °C or even at least 100 °C, the duration of step (d) is short enough that any evaporation that may occur is well tolerated. Preferably, the partly-dried lignin is maintained at the temperature it has at the end of step (c), at which temperature step (d) is executed and the separated partly-dried lignin is immediately further dried during step (e). In other words, preferably the partly-dried lignin is not actively heated or cooled from the moment step (c) is halted to the start of step (e).

[0031] An additional advantage of separating the excreted liquid phase is that this liquid phase is not subjected to the drying of step (e). As such, the operating costs of the lignin drying are greatly reduced in the process according to the invention.

Step (e)

[0032] Once the excreted liquid phase is removed, the separated partly-dried lignin is (further) dried, in order to obtain isolated lignin. Such drying of lignin is known in the art and may be accomplished as deemed best fit. A typical procedure involves heating the lignin to a temperature of 20 - 120 °C, preferably 30 - 60 °C, more preferably 40 - 50 °C, for 0.5 - 48 h, preferably 1 - 12 h, at a pressure of 0 - 250 mbar, preferably 10 - 100 mbar.

[0033] The drying of step (e) may be continued until the desired dryness is obtained. Preferably, the water content of the isolated lignin at the end of step (e) is as low as possible, typically 1 - 5 wt% water. At the end of step (e), lignin is afforded with high purity and - according to certain preferred embodiments of the process as indicated herein - of unprecedented light colour. In view of these excellent characteristics of the isolated lignin, the present invention also concerns the lignin obtainable by the process according to the invention.

Optional farther features

[0034] Where appropriate, two or more of steps (a) - (e) may be combined in single action, as will be understood by the skilled person. For example, steps (b) and (c), or even steps (b), (c) and (d), may be combined by centrifugation at elevated temperature, as defined for step (c) above, and subsequent decantation. As such, the precipitated lignin is separated from the liquor during centrifugation and simultaneously lignin shrink is effected by heating. Both the liquor and the excreted liquid are then removed from the centrifuged lignin, referred to as partly-dried lignin in the context of the present invention, by decantation. Alternatively, steps (c) and (d), or even steps (c), (d) and (e), may be combined by subjecting the separated lignin from step (b) to heating in a tumbler (optionally rotating drum permeable for water but not for lignin). Excreted liquid is thus immediately separated from the lignin by filtration through the wall of the tumbler. In case the temperature within the tumbler would be set sufficiently high and/or the pressure would be set sufficiently low, the drying of step (e) could even be performed within the tumbler. Alternatively, the temperature and/or pressure could be adjusted after lignin shrink is (nearly) completed. Such combinations of steps as described herein will be apparent to the skilled person and do not depart from the inventive concept of the present invention.

[0035] In an especially preferred feature, the temperature of the lignin is kept at 60 °C or below, preferably at at most 55 °C, more preferably at at most 50 °C, most preferably at at most 40 °C, from step (a) onwards. The inventors surprisingly found that keeping this temperature such low provides optimal light-coloured isolated lignin. Without being bound to a theory, it is believed that increasing the temperature to above 60 °C causes chemical reactions to occur between reactive groups on the lignin and often present traces of impurities. Also oxidation of the lignin is accelerated at increased temperature, which may also cause colouring of the lignin.

[0036] In a preferred embodiment, some water is added to the precipitated lignin obtained as semi-solid precipitate or pellet at the end of step (b). In other words, this water is added in between step (b) and step (c). The amount of water that is added to the precipitated lignin ranges from 0 (no water added) to preferably 10 times the total weight of the precipitated lignin, preferably 0.5 - 10 times, most preferably 1 - 5 times the total weight of the precipitated lignin. Thus, preferably 0 - 1000 wt%, more preferably 50 - 1000 wt%, most preferably 100 - 500 wt% water is added, based on the total weight of the separated lignin. The water added in between step (b) and step (c) may contain minor amounts of other liquids (at ambient conditions), such as water-miscible organic solvents, but it is preferred that the amount thereof is kept low, i.e. at most 5 wt% based on the total weight of the water, more preferably at most 1 wt%, most preferably water is used without additions. The heating step (c) is then performed with the two-phase system of the precipitated lignin and the water added thereto. The isolated lignins obtained in step (e) after addition of water prior to step (c) were lighter in colour as when no water was added. However, it was found that using water containing 10 wt% ethanol had a darkening effect on the colour of the isolated lignin. The addition of water prior to step (c) is especially advantageous when step (c) is performed at a temperature of 45 - 55 °C, preferably about 50 °C, as most optimal results were thus obtained in terms of lignin shrink rate and colour of the isolated lignin.

[0037] In a preferred embodiment, a washing step is implemented in between steps (b) and (c). Herein, the precipitated lignin is washed with a solvent in which it does not dissolve, preferably with water. The inventors surprisingly found that washing the lignin prior to the initial heating of step (c) afforded isolated lignin with reduced colour intensity in addition to increased lignin purity. Typically, the semi-solid lignin pellet is rinsed with water having a weight of 0 - 10 times the total weight of the precipitated lignin, preferably 0.5 - 5 times, most preferably 1 - 4 times the total weight of the precipitated lignin. Such rinsing may be performed 0 (no rinsing performed) - 5 times, preferably 1 - 3 times.

[0038] The lignin obtained in step (e) may be post-treated as known in the art, for example to enable application thereof in one of the uses according to the invention.

Organosolv process

[0039] The organosolv liquor that is subjected to step (a) of the process according to the invention is obtained by organosolv treatment of biomass. In a preferred embodiment, the organosolv liquor that is subj ected to step (a) of the process according to the invention is obtained by organosolv treatment as described hereinbelow. In a preferred embodiment, the process according to the invention comprises a step of subjecting biomass to an organosolv treatment as described hereinbelow and subsequently subjecting the liquor obtained thereby to step (a). The process according to the latter embodiment may also be referred to as process for obtaining isolated lignin and cellulose pulp.

[0040] Any type of lignocellulosic biomass may be used in the organosolv treatment, such as softwood, hardwood, and herbaceous biomass, including grasses and straws, and can be supplied in the form of e.g. forestry residues, agricultural residues, yard waste, animal and human waste (e.g. biodegradable municipal waste). Preferably, softwood is used as biomass, as isolated lignin having the most optimal colour is obtained with softwood as biomass. The specific nature of softwood lignin is believed to have an influence on the reduced colouring of the lignin, especially during organosolv but also during isolation of the lignin from the liquor. This influence has not been recognised in the art. Softwood lignins almost exclusively contain the guaiacyl (G) monomers, with trace amounts of /?ara-hydroxyphenyl (H) and no syringyl (S) monomers, in contrast to other types of biomass, the lignins of which contain the H- and S-monomers in greater amounts. Softwood refers to the wood of gymnosperm trees, and includes cedar wood, pine wood, fir wood and spruce wood. Mixtures of different types of softwood are also suitably used. Preferably, pine wood or spruce wood, most preferably spruce wood is used as source of the lignin. The biomass subjected to the process according to the invention may be fresh or dried biomass, optionally after removal of large impurities such as stones and pieces of metal, and optionally chopped or milled to pieces for ease of handling (e.g. pieces of 0.01 - 50 cm, in particular 0.1 - 10 cm in length or diameter).

[0041] During organosolv, the biomass is contacted with a treatment liquid in order to separate the biomass into a cellulose-enriched product stream (also referred to as 'cellulose pulp' or just 'pulp') and a lignin-enriched product stream (liquor), which is to be subjected to step (a) of the process according to the invention. A typical organosolv temperature is in the range of 100 - 250 °C. The organosolv process is optimally performed at a temperature of 100 - 160 °C, preferably 1 10 - 155 °C, more preferably 1 15 °C - 150 °C, most preferably 120 - 145 °C. The duration of the organosolv step is preferably 10 - 360 min, more preferably 15 - 180 min, even more preferably 20 - 150 min, most preferably 30 - 120 min. Herein, the duration refers to the time period the biomass/treatment liquid mixture is at the desired temperature, excluding any time needed for heating to reach that temperature or cooling after completion of the organosolv step. In an especially preferred embodiment, the organosolv process is performed on softwood at a temperature of 130 - 150 °C for a duration of 45 - 80 min. Optimal results were obtained by organosolv of spruce at a temperature of 140 °C for 60 min. The autogenic pressure that occurs during the organosolv step, e.g. within the organosolv reactor, typically ranges from 1 - 15 bar(a), preferably 5 - 10 bar(a). Herein, autogenic pressure refers to the pressure built up by the treatment liquid in the reactor at the process conditions, and any externally applied pressure is not accounted for in the above range. Typically, the biomass is suspended in the liquid by mixing at most 50 L and at least 0.1 L of treatment liquid per kg dry weight of the softwood, preferably 1.0 L - 20 L, most preferably 3 L - 10 L. Thus organosolv treatment of biomass uses 1 L of treatment liquid as defined below per between 20 g and 10 kg of biomass, preferably per between 50 and 1000 g, most preferably per between 67 and 333 g of biomass (dry weight). For procedural economy, the liquid to solid weight ratio (L/S) of the organosolv step is preferably as low as possible, preferably lower than 20/1, more preferably lower than 12/1, even more preferably lower than 8/1, most preferably lower than 6/1.

[0042] The treatment liquid comprises an organic solvent fraction, water and an acid catalyst. The organic solvent fraction may consist of one organic solvent or a mixture of different organic solvents. A compound is considered to be a solvent in the context of the present invention, when it is liquid under the process conditions of the organosolv reaction, preferably it is also liquid under ambient conditions. Suitable organic solvents for the organosolv step are known in the art and include alcohols, ketones and ethers, such as methanol, ethanol, (iso)propanol, butanol, ethylene glycol, methoxyethanol, dimethoxyethane, dioxane, acetone, methyl ethyl ketone. Preferably, lower alcohols, ketones and ethers, i.e. having 1 - 6 carbon atoms, preferably 1 - 4 carbons atoms, are used. Conveniently, the organic solvent is easily removed from the organosolv liquor for recycling, e.g. during or after step (a). Hence, it is preferred that the organic solvent is volatile (i.e. has a boiling point below 200 °C at ambient pressure, preferably below 100 °C (boiling point of water), most preferably below 80 °C). In one embodiment, ethanol, acetone or a mixture thereof is used as organic solvent fraction. In one embodiment, at least one alcohol should be present in the organic solvent fraction. Suitable alcohols include all alcoholic organic solvents which are known in the art to be suitable for organosolv. Preferably, the alcohol is selected from methanol, ethanol, (iso)propanol, butanol, ethylene glycol, methoxyethanol and mixtures thereof, more preferably the organic solvent fraction comprises at least ethanol, most preferably consists of ethanol. Using ethanol as organic solvent in the treatment liquid was found to afford optimally coloured lignins. The treatment liquid typically comprises 20 - 80 wt%, preferably 30 - 75 wt%, more preferably 35 - 70 wt%, most preferably 40 - 65 wt% organic solvent fraction, based on total solvent contained in the treatment liquid. It is preferred that the total organic solvent fraction as contained in the treatment liquid comprises at least 50 wt% alcoholic solvent(s), more preferably at least 80 wt%, even more preferably at least 95 wt%, most preferably 100 wt% alcoholic solvent(s).

[0043] The treatment liquid further comprises water, typically 20 - 80 wt% water based on total solvent contained in the treatment liquid. The presence of water in the treatment liquid allows hydrolysis reactions to take place during organosolv, in order to hydrolyse hemi cellulose, break ether bonds within the lignin fraction and break up the network of structural components (the lignocellulose complex). Preferably, the treatment liquid comprises 25 - 70 wt%, more preferably 30 - 65 wt%, most preferably 40 - 60 wt% water, based on total solvent contained in the treatment liquid. The weight ratio of organic solvent(s) to water is preferably 20/80 - 80/20, more preferably 30/70 - 75/25, even more preferably 35/65 - 70/30, most preferably 40/60 - 60/40.

[0044] During the organosolv reaction, acid may be added to the treatment liquid in order to reduce the pH. Conventional organosolv can either be performed autocatalytically (without acid added, at a pH of 4 - 5 mainly as a result of formation of acetic acid from the acetyl side groups of hemicellulose) or acid-catalysed (at a pH of 1.5 - 4.5, preferably 2 - 4.5, most preferably 2.5 - 4). In a preferred embodiment, the pH is typically 0.5 - 7.0, preferably 1.0 - 5.0, most preferably 1.5 - 3.0 in case the organosolv is performed at a temperature below 170 °C. For optimum fractionation to cellulose pulp and lignin- containing liquor, the amount of acid that is added to the treatment liquid preferably amounts to 5 mmol - 1.5 mol per kg dry weight of the biomass, more preferably 50 mmol - 1.0 mol, most preferably 100 - 750 mmol. Otherwise defined, the amount of acid is preferably 0.5 - 100 g per kg dry weight of the biomass, more preferably 5 - 75 g, most preferably 10 - 50 g. Conveniently, the acid is comprised in the treatment liquid, but the acid may also be added separately to the suspension of biomass in the treatment liquid or to the biomass before the remainder of the treatment liquid is added. Preferably, the concentration of the acid in the treatment liquid is 0.5 - 300 mM, more preferably 5 - 200 mM, even more preferably 17.5 - 170 mM, most preferably 20 - 120 mM. In case a monoprotic acid is used, preferred molarities thereof are 1 - 300 mM, more preferably 10 - 200 mM, even more preferably 35 - 170 mM, most preferably 40 - 120 mM. In case a diprotic acid is used, preferred molarities thereof are 0.5 - 150 mM, more preferably 5 - 100 mM, even more preferably 17.5 - 85 mM, most preferably 20 - 60 mM. Alternatively, the amount of acid can be defined as acid equivalents, i.e. between 2 and 300 meq, preferably 20 - 200 meq, more preferably 70 - 170 meq, most preferably 80 - 120 meq, a meq being defined as a mmol of hydrogen ions per L of treatment liquid. In terms of weight, it is preferred that the treatment liquid comprises 0.01 - 1.4 wt% acid, more preferably 0.05 - 1.25 wt%, most preferably 0.1 - 1.0 wt%. Amounts of acid in the treatment liquid above the upper limits may result in more lignin condensation with e.g. carbohydrate degradation products and thus colouring of the lignin during organosolv. Lower amounts of acid, on the other hand, reduce the extent of fractionation and lignin yield realised by the present process. The inventors found that the above acid concentration ranges provide optimal results in terms of minimal lignin colouring while lignin yields remain sufficiently high. As the skilled person will appreciate, the amount of acid which is used for optimum performance of the organosolv reaction may vary depending on the strength of the acid (pKa) and the acid neutralisation capacity of mineral part of the biomass, as well as on the process conditions.

[0045] It should be noted that the higher the temperature during organosolv, the lower the amount of acid required for optimal results in terms of lignin yield, purity and colouring. Hence, it is preferred that the acid concentration is dependent on the temperature at which organosolv is performed. As such, the amount of acid in the treatment liquid preferably is in the range of 0.5 to x g per kg of dry weight of the softwood, wherein x is defined as -2 ^χ J(°C) + 360. Alternatively, the acid concentration can be defined separately for temperatures at which the organosolv is performed of below and above 130 °C. Thus, when organosolv is performed at a temperature of 130 °C or above, the amount of acid comprised in the treatment liquid preferable ranges from 0.01 - 0.80 wt% or 1 - 90 mM, more preferably 0.05 - 0.75 wt% or 10 - 75 mM, most preferably 0.1 - 0.60 wt% or 35 - 63 mM. Likewise, when organosolv is performed at a temperature below 130 °C, the amount of acid comprised in the treatment liquid preferable ranges from 0.1 - 1.4 wt% or 30 - 300 mM, more preferably 0.3 - 1.25 wt% or 40 - 200 mM, most preferably 0.5 - 1.0 wt% or 50 - 170 mM. When defined per kg biomass, it is preferred when organosolv is performed at 130 °C or above that the amount of acid is 0.5 - 50 g per kg dry weight of the biomass, more preferably 5 - 45 g, most preferably 10 - 40 g, and when organosolv is performed below 130 °C the amount of acid is preferably 10 - 100 g per kg dry weight of the biomass, more preferably 20 - 75 g, most preferably 40 - 60 g.

[0046] Suitable acids include organic acids and inorganic acids. Preferred acids have a pKa value of 4.5 or lower, preferably a pKa value of 3.0 or lower, most preferably a pKa value of 1.0 or lower. Acids with such low pKa values are preferred, as a lower amount is needed to enable efficient organosolv fractionation of the biomass, when compared to acids having a higher pKa value. Suitable acids include sulphuric acid, hydrochloric acid, phosphoric acid, perchloric acid, sulphonic acids such as methanesulphonic acid and /?ara-toluenesulphonic acid, formic acid, oxalic acid, benzoic acid, lactic acid, malonic acid, maleic acid, dichloroacetic acid, trichloroacetic acid, trifluoroacetic acid, and combinations thereof. As carboxylic acids are more prone to side-reactions than acids which do not comprise a carboxyl group, such as inorganic acids, the use of non- carboxylic acids or even inorganic acids is especially preferred. Thus, preferably the acid is selected from sulphuric acid, hydrochloric acid, phosphoric acid, para- toluenesulphonic acid, and combinations thereof. Most preferably, sulphuric acid is used. Herein, "acid" may refer to a single compound, or to a mixture of different acids. Preferably, a single acid is used.

[0047] In a particularly preferred embodiment, the organosolv process is performed at a temperature of 100 - 160 °C, preferably 120 - 150 °C for a duration of 30 - 150 min, preferably 60 - 120 min, using a treatment liquid comprising 40 - 60 wt% ethanol and 40 - 60 wt% water, based on total solvent, and 10 - 100 mM, preferably 35 - 85 mM acid, preferably sulphuric acid. Most preferably, softwood is used as biomass.

[0048] A major advantage of the organosolv process as described herein is the formation of a liquor from which light-coloured lignin can be isolated according to the process according to the invention. The organosolv liquor typically contains lignin, carbohydrates (notably hemicellulose and its degradation products such as furfural), organic acids, salts and optionally other compounds, from which the lignin is separated.

[0049] Organosolv treatment of biomass affords, next to a lignin-containing liquor, also a cellulose-enriched product stream (pulp). This pulp may be used or further processed as deemed fit, e.g. subj ecting to enzymatic hydrolysis to produce glucose by contacting the pulp with an enzyme or combination of enzymes capable of hydrolyzing cellulose, referred to as hydrolytic enzymes, preferably cellulases.

[0050] In one embodiment, the conditions of the organosolv step are set as such that 20 - 50 wt%, preferably 25 - 40 wt%, of the lignin present in the biomass ends up in the liquor, and thus that significant amounts of lignin are still present in the cellulose pulp. The skilled person knows how to adjust the organosolv conditions in order to achieve such delignification. Isolated lignins obtained from organosolv at such delignification degree was found of further increased lightness, compared to lignins isolates from organosolv liquors that originate from complete delignification (i.e. as high as possible, typically in the range of 70 - 90 wt% delignification) of the cellulose pulp during organosolv treatment. Optionally, the cellulose pulp obtained in the organosolv step is subjected to a further organosolv step, preferably at a higher temperature (e.g. between 170 - 220 °C) and pretreatment severity, in order to delignify the pulp even further. The treatment liquid of this second organosolv step may be the same as defined for the treatment liquid in the first organosolv step. The further delignified pulp is then suitably subjected to enzymatic hydrolysis to increase biomass valorisation. Pre-extraction

[0051] In one embodiment, the process according to the invention comprises one or more extraction steps, prior to the organosolv process. In the context of the present invention, one or more extraction steps prior to organosolv are also referred to as "pre-extraction". Pre-extraction includes at least one aqueous extraction step and/or at least one organic extraction step. Without being bound by a theory, it is believed that extraction of the biomass prior to organosolv removes non- structural biomass components (extractives) which may influence the purity and colour of the lignin produced. In view of the many side-reactions that might occur, performing such a pre-extraction may be preferred.

[0052] In the context of the present invention, "organic extraction" refers to extraction with an extraction liquid comprising at least 50 wt% of one or more organic solvents, preferably at least 70 wt%, more preferably at least 80 wt%, most preferably at least 95 wt%, and thus at most 50 wt% water, preferably at most 30 wt% water, more preferably at most 20 wt% water, most preferably at most 5 wt% water. Likewise, "aqueous extraction" refers to extraction with an extraction liquid comprising at least 50 wt% water, preferably at least 70 wt%, more preferably at least 80 wt%, most preferably at least 95 wt%, and thus at most 50 wt% of one or more organic solvents, preferably at most 30 wt% organic solvent, more preferably at most 20 wt% organic solvent, most preferably at most 5 wt% organic solvent.

[0053] In one embodiment, only one extraction step is performed prior to organosolv, preferably an aqueous extraction. Alternatively, pre-extraction involves multiple extraction steps, preferably each with a different extraction liquid comprising water, one or more organic solvents or mixtures thereof. Thus, in case extraction is performed prior to organosolv, extraction may involve at least one, at least two, at least three, or at least four separate extraction steps. In one embodiment, at least one aqueous extraction step is performed prior to organosolv, using an extraction liquid comprising at least 80 wt% water, preferably the extraction liquid is water. In an alternative embodiment, at least one aqueous extraction step is performed prior to organosolv, using an extraction liquid comprising at least 80 wt% water, preferably the extraction liquid is water, and at least one organic extraction step is performed using an extraction liquid comprising at least 50 wt%, more preferably at least 70 wt% organic solvent(s), most preferably the extraction liquid is a (mixture of) organic solvent(s).

[0054] It is preferred to use the same (mixture of) organic solvent(s) during optional organic pre-extraction and in the treatment liquid during the organosolv process. Suitable organic solvents to be used in pre-extraction include, but are not limited to, lower alcohols, lower ethers, ketones, lower amides, lower alkanes, carboxylic acids. Herein, "lower" means containing 1-6 carbon atoms (Ci-C ₆ ), especially C2-C4 for alcohols, and especially C3-C5 for other solvents including ketones, ethers, esters and amides. Preferred organic solvents to be used in pre-extraction include methanol, ethanol, propanol, isopropanol, butanol and its isomers, ethylene glycol, propylene glycol, methoxy ethanol, dimethoxyethane, diethylene glycol, dioxane, acetone, methyl ethyl ketone, tetrahydro- furan, dimethyl formamide, dimethyl acetamide, N-methylpyrrolidone and mixtures thereof, preferably methanol, ethanol, propanol, butanol or acetone is used, most preferably ethanol. Further polar or apolar (co)solvents can be used as well, although these are slightly less preferred.

[0055] An aqueous pre-extraction step is conveniently performed using (non- demineralised) tap water or filtered, relatively clean water, while demineralised water is also suitable, preferably without added organic solvents or other additives. The aqueous liquid may contain agents assisting in the dissolution of extractives, such as acids, bases, salts and surfactants. The pH may be from slightly alkaline to acidic, e.g. between 2 and 10, preferably between 4 and 8. If desired minor amounts of an organic solvent (e.g. as described above for the organic extraction) may be added to the aqueous extracting liquid. However, the level of organic solvents is preferably kept low, e.g. below 20 wt%, more preferably below 10 wt%, most preferably below 2 wt%.

[0056] The extracting liquid has a temperature between its melting temperature and its boiling temperature (or higher if pressurised), i.e. is in liquid form. Preferred extracting temperatures are from 10 to 100 °C. For aqueous extraction steps, the extraction temperature is more preferably from 15 to 75 °C, most preferably from 20 to 60 °C, and for organic extraction steps more preferably from 15 to 80 °C, most preferably from 30 to 75 °C. For extraction steps using a mixture of water and organic solvent(s), the skilled person will appreciate how to manipulate the temperatures for optimal results.

[0057] For each individual extraction step, the amount of extraction liquid is preferably between 0.1 L and 25 L of liquid per kg of biomass. For single stage organic extraction, the preferred amount of extraction liquid is between 0.1 L and 12 L, most preferred between 0.5 L and 6 L of solvent per kg of biomass. For single stage aqueous extraction, the preferred amount of extraction liquid is between 0.1 L and 12 L, most preferred between 0.5 L and 10 L of solvent per kg of biomass. For counter-current extraction, the preferred amount of extraction liquid is between 0.1 L and 6 L, especially between 0.5 L and 4 L solvent per kg biomass. The biomass weight is understood herein as the dry weight, without adherent water.

[0058] Each individual extraction step of the extraction may be performed using any extraction technique known in the art. Conveniently, extraction is performed by washing the biomass with the extraction liquid, or by soaking the biomass in the extraction liquid. In this embodiment, the biomass preferably soaks at least 1 minute in the extraction liquid, more preferably between 5 minutes and 600 minutes, most preferably between 10 minutes and 120 minutes. The extraction may also be performed stage-wise, in a counter- current mode. In such a staged mode, relatively clean extraction liquid is used for a second or later stage of the extraction and the extract of the second or later stage is used as an extraction liquid for the preceding (or first) stage. In this way the residual amount of extractives in the biomass is minimised while keeping the amount of extraction liquid relatively low. Counter-current extraction allows a reduction in the total amount of extraction solvent.

[0059] The mixture of biomass and extraction liquid may be filtered after each extraction step of the extraction, using a filter having small enough pores to retain the chopped and washed or soaked biomass, and large enough pores to allow the extract comprising extractives to pass. Typically, the pores of such a filter are between 10 μπι and 10 mm in diameter, preferably between 100 μπι and 1 mm. The retentate comprising biomass is used for further treatment by organosolv as described hereinabove.

Preferred embodiments

[0060] In a first aspect, the invention pertains to a process for the isolation of lignin from an organosolv liquor, comprising steps (a) up to (e) as defined above. In a second aspect, the invention pertains to a process for the isolation of lignin from an organosolv liquor, comprising steps (a) up to (e) as defined above. In a second aspect, the invention pertains to a process for organosolv treatment of softwood as defined above. In a third, especially preferred, aspect, the invention pertains to a process for organosolv treatment of softwood as defined above, and for the isolation of lignin from the organosolv liquor obtained therefrom, comprising steps (a) up to (e) as defined above.

[0061] In a first preferred aspect, the invention pertains to a process for the isolation of lignin from an organosolv liquor. In embodiment 1 of the first preferred aspect, the process comprises:

(a) precipitating lignin from an organosolv liquor;

(b) separating the precipitated lignin from the liquor;

(c) heating the separated lignin until it undergoes a phase separation by expelling moisture to obtain partly-dried lignin and a liquid phase;

(d) separating the partly-dried lignin from the liquid phase; and

(e) drying the separated partly-dried lignin to obtain the isolated lignin.

[0062] Preferred features of the process according to first aspect are:

2. Process according to embodiment 1, wherein step (a) is performed by dilution of the liquor with water.

3. Process according to embodiment 1 or 2, wherein step (d) is performed within 30 minutes after the phase separation occurs.

4. Process according to any one of the preceding embodiments, wherein 50 - 1000 wt% of water, based on the total weight of the precipitated lignin, is added to the precipitated lignin between step (b) and step (c).

5. Process according to any one of the preceding embodiments, wherein the temperature of the lignin is kept at 50 °C or lower from step (a) onwards.

6. Process according to any of the preceding embodiments, further comprising a step of subjecting biomass to an organosolv step to obtain a liquor which is subjected to step (a).

7. Process according to embodiment 6, wherein the organosolv step is performed by organosolv treatment of lignocellulosic biomass with a treatment liquid at a temperature T of 100 - 160 °C, wherein the treatment liquid comprises:

(i) 20 - 80 wt% of organic solvent, based on total solvent,

(ii) 20 - 80 wt% of water, based on total solvent, and (iii) an amount of acid which is in the range of 0.5 to x g per kg of dry weight of the biomass, wherein x is defined as -2 ^χ J(°C) + 360,

to obtain a pulp and the liquor.

8. Process according to embodiment 7, wherein the lignocellulosic biomass is softwood.

9. Process according to embodiment 7 or 8, wherein the organic solvent is an alcohol.

10. Process according to any one of embodiments 7 - 9, wherein the biomass is pre- extracted using at least one aqueous extraction step and/or at least one organic extraction step.

[0063] In a second preferred aspect, the invention pertains to a process for the production of lignin from softwood. In embodiment 1 of the second preferred aspect, the process comprises:

(a) subjecting the softwood to an organosolv step wherein the softwood is treated with a treatment liquid at a temperature T of 100 - 160 °C, wherein the treatment liquid comprises:

(i) 20 - 80 wt% of alcoholic organic solvent, based on total solvent,

(ii) 20 - 80 wt% of water, based on total solvent, and

(iii) an amount of acid which is in the range of 0.5 to x g per kg of dry weight of the softwood, wherein x is defined as -2 ^χ J(°C) + 360,

to obtain a pulp and a liquor.

[0064] Preferred features of the process according to second aspect are:

2. Process according to embodiment 1, wherein lignin is isolated from the liquor in step (b), preferably by the process according to the first aspect as described above.

3. Process according to embodiment 1 or 2, wherein the softwood is pine wood and/or spruce wood.

4. Process according to any one of embodiment 1 - 3, wherein the alcoholic solvent is ethanol.

5. Process according to any one of embodiment 1 - 4, wherein step (a) is performed at a temperature of 100 - 150 °C.

6. Process according to any one of embodiment 1 - 5, wherein step (b) is performed by decreasing the organic solvent content of the liquor. 7. Process according to any one of embodiment 1 - 6, wherein the pulp obtained in step (a) is subjected to a further organosolv step, preferably at a temperature of 170 - 220 °C. Isolated lignin

[0065] The invention also pertains to the isolated lignin, which is obtainable by the process according to the invention. The isolated lignin according to the invention is distinguishable from conventional isolated lignins by their increased purity and preferably by their lighter colour. According to an especially preferred embodiment, the isolated lignin according to the invention is characterized as light-coloured, as further defined hereinbelow. In one embodiment, the isolated lignin according to the invention is defined as being white, off-white or beige in colour. In one embodiment, the isolated lignin according to the invention is defined as having a colour in accordance with RAL 1001 or lighter. In one embodiment, the isolated lignin according to the invention is defined as reflecting at least 25 % of the light in the wavelength region of 380 - 750 nm. The isolated lignin according to the invention has a molar mass _w of 1000 - 10000 g/mol and a sulphur content of at most 1 wt%. Furthermore, the isolated lignin according to the invention is preferentially characterized as having no significant odour.

[0066] The isolated lignin according to the invention has a low weight-average molar mass ( _w ), compared to native lignin as embedded in biomass. Such reduction in molar mass is accomplished by fractionating the biomass using an organosolv step. During organosolv, the lignin is separated from the cellulose part of the biomass and at the same time chemical modifications such as hydrolysis of ether linkages between aromatic structures within the lignin occur. Consequently, the extended polymeric native lignin structures are broken down into smaller structures. The advantage of using organosolv to separate the lignin from the other structural components of the biomass is that lignin is obtained not only with a reduced _w but also with a narrow molar mass distribution. The w of the isolated lignin according to the invention is in the range of 1000 - 10000 g/mol, preferably 1500 - 8000 g/mol, more preferably 2000 - 7000 g/mol, even more preferably 2500 - 6000 g/mol, most preferably 3000 - 5000 g/mol. Such values for _w are determined by alkaline size exclusion chromatography (SEC) according to example 2, in the context of the present invention.

[0067] The isolated lignin according to the invention typically has a narrow molar mass distribution, compared to milled wood lignin and lignosulphonates. The narrow molar mass distribution of the isolated lignin according to the invention is characterised by a dispersity D, defined as _w / _n , which is preferably at most 4.5, preferably at most 4, more preferably at most 3.5, even more preferably at most 3 and most preferably at most 2.5. Dispersities are determined by size-exclusion chromatography (SEC) as described in Huijgen et al, Ind. Crop. Prod. 2014, 59, 85-95. 50 mg of lignin was dissolved in 50 ml of an aqueous 0.5 M NaOH solution. The SEC column was packed with Toyopearl HW-55 beads (TSKgel) and a HP1100 HPLC (Agilent) equipped with UV detector (254 nm) was used. Phenol (94 g/mol) and various sodium polystyrene sulphonates (1100 - 666000 g/mol) were used as standard. In the definition of the dispersity, _w represents the weight-average molar mass and _n represents the number-average molar mass. The closer D approaches 1, the narrower the molar mass distribution of the lignin. D is thus at least 1, although D is usually at least 1.2 or even at least 1.5. Preferred ranges for D include thus 1 - 4.5, more preferably 1.2 - 3.5, most preferably 1.5 - 2.5. Narrow molar mass distributions are preferred for reducing the variability of performance in application of the lignin of the invention. Organosolv lignins having a low value for D are potentially suitable for a wide variety of application, e.g. as anti-oxidant (see Pan, in The Role of Green Chemistry in Biomass Processing and Conversion, first edition, 2013, chapter 7, and Pourteau et al., Polym. Degrad. Stabil. 2003, 81, 9-18).

[0068] The isolated lignin according to the invention has a total sulphur content of at most 1.5 wt%, preferably at most 1.0 wt%, more preferably at most 0.6 wt%, even more preferably at most 0.4 wt%, most preferably at most 0.2 wt% based on dry weight of the lignin. The total sulphur content of a lignin sample is readily determined by e.g. Inductively Coupled Plasma (ICP) or ion chromatography (Dionex IC25, column Dionex AS 18) according to NEN-EN-ISO 10304-1 following bomb combustion in a calorimeter to determine the higher heating value (HHV) (Parr 6300) and subsequent water washing of the combustion residues, according to example 2. In principle, no sulphur containing moieties are incorporated in the lignin structure during organosolv, as typically sulphur- containing solvents are avoided, or during the process of isolating lignin according to the invention. However, the presence of sulphuric acid may account for trace amounts of sulphur in the product. The isolated lignin according to the invention typically has an organic sulphur content of at most 1.0 wt%, preferably at most 0.8 wt%, more preferably at most 0.6 wt%, even more preferably at most 0.4 wt%, most preferably at most 0.2 wt%, based on dry weight of the lignin. An as low as possible organic sulphur content (i.e. 0.0 wt%) is preferred, although minor amounts of organic sulphur may be present, such as at least 0.05 wt% or even at least 0.1 wt%. Typical ranges for the organic sulphur content of the isolated lignin according to the present invention are 0.0 - 1.0 wt%, or 0.05 - 0.6 wt% or even 0.1 - 0.4 wt%, based on dry weight of the lignin. The use of lignin having a low or negligible sulphur content is preferred in terms of potential application, since lignins having a sulphur content of 1 wt% or higher have different characteristics rendering them less suitable for the envisioned applications of the lignins according to the invention. The drawbacks of sulphur-containing lignins for potential material applications are discussed in Lora and Glasser, J. Polym. Environ. 2002, 10, 39- 48. For example, the presence of (significant amounts of) sulphur, which is typically incorporated as -SO3 ^" moiety, increases the polarity of lignin, which would hamper application thereof in apolar polymeric materials, such as in resins. In addition, the presence of sulphur in lignin may hinder downstream chemocatalytic modification, conversion and/or depolymerisation of lignin, as sulphur typically coordinates to and thus inactivates the catalyst used.

[0069] Most preferably, the isolated lignin according to the invention is characterised as light-coloured, or in other words white, off-white or beige. The colour of the isolated lignin according to the invention can be identified in several alternative or additional manners. The colour is preferentially defined according to its reflection spectra. Reflection spectra have been obtained by the inventors using a halogen lamp, a UV-VIS detector (BLACK CXR-SR-50 BW-16 from StellarNet) and a VIS-NIR detector (NIR- 25 BW-ND from StellarNet) against a reflectance reference standard (SRS-99-010 from Labsphere), see also example 2. Reflectance spectra show a plot of the light reflection (in % of incident light) of a surface as function of wavelength. For the perception of light colour, reflections in the visible light region is particularly relevant. The isolated lignin according to the invention is preferably characterised as reflecting at least 12 %, preferably at least 20 %, more preferably at least of 25 %, of the incident light throughout the 380 - 750 nm spectrum, i.e. the reflectance is above 12%, preferably above 20 %, more preferably above 25 % for the entire 380 - 750 nm region. Although it is preferred that as much light as possible is reflected, the amount of reflected visible light is typically below 90 %, or below 80 %, or even below 70 %. Such reflectances do not significantly intensify the perceived colour of the isolated lignins. Prior art lignins typically exhibit a reflectance of below 12 % in the entire visible region, or at least in the major part thereof.

[0070] The light-coloured isolated lignins according to the invention typically exhibit increased reflection over the entire visible wavelength spectrum, compared to conventional isolated lignins. Typically, the light-coloured isolated lignins according to the invention reflect at least 25 %, preferably at least 35 %, more preferably at least 40 %, most preferably at least 45 %, of the light having a wavelength of 380 - 750 nm. As each colour in the visible light spectrum contributes differently to the perception of an (off-)white colour, the visible light spectrum may be subdivided into various colours to characterize the colour of the lignins. In this respect, it is preferred that the light-coloured isolated lignins according to the invention reflect at least 15 %, preferably at least 20 %, most preferably at least 25 %, of the violet light (i.e. having a wavelength of 380 - 450 nm). Additionally or alternatively, it is preferred that the light-coloured isolated lignins according to the invention reflect at least 20 %, preferably at least 25 %, most preferably at least 30 %, of the blue light (i.e. having a wavelength of 450 - 475 nm). Additionally or alternatively, it is preferred that the light-coloured isolated lignins according to the invention reflect at least 25 %, preferably at least 30 %, most preferably at least 35 %, of the cyan light (i.e. having a wavelength of 475 - 495 nm). Additionally or alternatively, it is preferred that the light-coloured isolated lignins according to the invention reflect at least 25 %, preferably at least 30 %, most preferably at least 38 %, of the green light (i.e. having a wavelength of 495 - 570 nm). Additionally or alternatively, it is preferred that the light-coloured isolated lignins according to the invention reflect at least 30 %, preferably at least 40 %, most preferably at least 45 %, of the yellow light (i.e. having a wavelength of 570 - 590 nm). Additionally or alternatively, it is preferred that the light- coloured isolated lignins according to the invention reflect at least 30 %, preferably at least 40 %, most preferably at least 45 %, of the orange light (i.e. having a wavelength of 590 - 620 nm). Additionally or alternatively, it is preferred that the light-coloured isolated lignins according to the invention reflect at least 35 %, preferably at least 45 %, most preferably at least 55 %, of the red light (i.e. having a wavelength of 620 - 750 nm). By investigating the reflectance spectra of the lignins according to the invention and comparative lignins, the inventors found that the blue-to-yellow part of the reflectance spectrum contributes most to the perception of light colour. Particularly, increased reflectance in this region (λ = 450 - 570 nm) sets the isolated lignins of the invention apart from known darker lignins. The light-coloured lignins according to the invention are thus conveniently characterized by their reflectance at a certain wavelength. It is thus preferred that the reflectance R at λ = 450 nm is least 24 %, i.e. R{ = 450 nm) > 24 %, more preferably R( = 450 nm) > 27 %, most preferably R( = 450 nm) > 30 %. Additionally or alternatively, it is preferred that R(A = 500 nm) > 29 %, more preferably R(X = 500 nm) > 31 %, most preferably R(X = 500 nm) > 34 %. Additionally or alternatively, it is preferred that R(X = 550 nm) > 35 %, more preferably R(X = 550 nm) > 40 %, most preferably R(X = 550 nm) > 45 %.

[0071] Additionally or alternatively, the isolated lignin according to the invention may be characterised as having a colour in accordance with RAL classic colour RAL 1001 or lighter, preferably a colour in accordance with RAL 1001, RAL 9001 or in between. RAL colours included in this range are RAL 1000, RAL 1001, RAL 1013, RAL 1014, RAL 1015, RAL 1034, RAL 3012, RAL7032, RAL 7035, RAL 7038, RAL 7044, RAL 7047, RAL 9001, RAL 9002, RAL 9003, RAL 9010, RAL 9016 and RAL 9018. Preferably, the colour of the lignin corresponds to RAL 1001, RAL 1013, RAL 1014, RAL 1015, RAL 1034, RAL 7044, RAL 7047, RAL 9001, RAL 9002, RAL 9003, RAL 9010 or RAL 9016, most preferably to RAL 1013, RAL 7047 or RAL 9002. It should be noted that prior art lignins typically have a colour corresponding to RAL 101 1 (brown beige), RAL 3007 (black red) or RAL 8xxx (entire brown range). Assignment of a RAL colour code to an isolated lignin sample is readily accomplished by visual comparison of the sample with a reference chart of RAL colours, which are available from www.ralcolor.com.

[0072] Additionally or alternatively, the isolated lignin according to the invention is preferably characterised as having a colour in accordance with the RGB colouring system, wherein the R-value is 200 or higher, i.e. 200 - 255, preferably 210 - 250, more preferably 230 - 240, the G-value is 150 or higher, i.e. 150 - 255, preferably 200 - 250, more preferably 220 - 240, and the B-value is 70 or higher, i.e. 70 - 255, preferably 130 - 230, more preferably 200 - 220. The B-value may be somewhat lower than the R- and G-values, which is in line with reflectance spectra wherein blue light was typically reflected to a somewhat lower extent, although it is preferred that also the B-value is high, most preferably above 200, as the colour of those lignins is the closest to pure white. Since an object is perceived as (off-)white when all colours are contributing in more or less equal amounts, it is preferred that the highest and the lowest of the R-, G- and B- values are not more than 100 points apart, more preferably not more than 50 points apart, most preferably not more than 20 points apart.

[0073] The isolated lignin according to the invention preferably originates from softwood. In other words, the isolated lignin according to the invention is preferably softwood-derived. Softwood refers to the wood of gymnosperm trees, and includes cedar wood, pine wood, fir wood and spruce wood. Mixtures of different types of softwood are also included. Using softwood as source of the lignin, particularly light-coloured lignin could be obtained with the process according to the invention. Preferably, pine wood or spruce wood, most preferably spruce wood is used as source of the lignin. Lignin as embedded within biomass is not part of the invention, thus the lignin according to the invention is referred to as "isolated lignin", which is a well-known term of art and is considered synonymous with "technical lignin". Since the isolated lignin according to the invention is readily obtained by organosolv, it may also be referred to as "organosolv lignin", i.e. lignin isolated by an organosolv process.

[0074] Using the process according to the invention, isolated lignins are obtained having a significantly increased purity. In one embodiment, the isolated lignin according to the invention may be interpreted as a composition consisting essentially of the lignin as defined herein, optionally together with minor impurities that originate from the biomass or the treatment liquid and end up in the lignin fraction. Possible impurities include carbohydrate residues and ash. The isolated lignin according to the invention typically comprises at most 5 wt% carbohydrate residues, more preferably at most 3 wt% carbohydrate residues, even more preferably at most 2 wt% carbohydrate residues, and most preferably at most 1 wt% carbohydrate residues, based on dry weight of the isolated lignin. The isolated lignin according to the invention typically comprises at most 1 wt% ash, more preferably at most 0.5 wt% ash, even more preferably at most 0.3 wt% ash and most preferably at most 0.1 wt% ash, based on dry weight of the isolated lignin. Such carbohydrates and ash contents are a marked reduction compared to the carbohydrates and ash contents when the lignin would not have been isolated with the process according to the invention. The isolated lignin may further comprise minor amounts of water and/or solvent. Preferably, the isolated lignin comprises at least 85 wt% lignin, more preferably at least 90 wt% lignin, most preferably at least 95% lignin based on dry weight of the isolated lignin. The lignin content is conveniently determined as the sum of Klason lignin (or acid insoluble lignin) and acid soluble lignin, a well-known measure of lignin content. The skilled person finds guidance in how to determine the lignin content of organosolv lignins in Huijgen et al., Ind. Crop. Prod. 2014, 59, 85-95. Such a high lignin content is achievable when biomass fractionation is performed using the process according to the invention. Typically, the dry weight content of the lignin according to the invention is at least 90 wt%, more preferably at least 95 wt%, most preferably at least 97 wt%, based on total weight. [0075] In an especially preferred embodiment, the lignin according to the invention is characterised as obtainable by the process according to the invention as described hereinbelow. Herein, the given values for _w , D and the sulphur content are inherently obtained.

Uses

[0076] The isolated lignin of the invention and the lignin produced by the process of the invention, in particular the light-coloured lignins, is particularly suitable as a precursor of or a component in paints, adhesives, resins (e.g. as phenol replacement in phenol- formaldehyde resins), binders, (bio)plastics (e.g. polyurethanes for foams and flexible sheets), composite and polymeric materials (e.g. as dispersant, emulsifier, stabiliser, sequestrant, filler, UV stabilising agent, antioxidant), carbon fibres and special chemicals such as food additives and pharmaceuticals. Lignin-based resins can advantageously be applied in e.g. oriented strand board (OSB), plywood and particleboard manufacturing. For the majority of these applications, it is important, if not prerequisite, that the lignin is light-coloured. Such potential applications of organosolv lignins are known to the skilled person, e.g. from De Wild et al. (Biofuels, Bioprod. Bioref. 2014, 8(5), 645-657).

Preferred embodiments of the isolated lignin according to the invention

[0077] In a third preferred aspect, the invention pertains to isolated lignin and use thereof. In embodiment 1 of the third aspect, the isolated lignin has a molar mass _w of 1000 - 10000 g/mol determined using alkaline size exclusion chromatography (SEC) and a sulphur content of at most 1 wt%, wherein the lignin is white, off-white or beige in colour.

[0078] Preferred features of the isolated lignin according to third aspect are:

2. Isolated lignin according to embodiment 1, which is obtainable by the process according to the process according to the first aspect of the invention.

3. Isolated lignin according to embodiment 1 or 2, reflecting at least 25 % of the light in the wavelength region of 380 - 750 nm.

4. Isolated lignin according to any one of embodiments 1 - 3, having a colour in accordance with RAL 1001 or lighter.

5. Isolated lignin according to any one of embodiments 1 - 4, having a dispersity D of at most 4. 6. Isolated lignin according to any one of embodiments 1 - 5, comprising at most 5 wt% carbohydrate residues.

7. Use of an isolated lignin according to any one of embodiments 1 - 6 in paints, resins, binders, plastics or composite materials.

Brief description of the figures

[0079] Figure 1 depicts the reflectance spectra of selected batches of lignin obtained in examples 2 and 4. (a) example 2, batch 1 ; (b) example 2, batch 2; (c) example 2, batch 6; (d) example 2, batch 7; (e) = example 4, lignin according to the invention; (f) example 4, Alcell lignin; (g) example 4, sodium lignosulphonate; (h) example 4, Kraft lignin.

[0080] Figure 2 depicts the pyrolysis-GC/MS spectrum of the isolated lignin of batch 1 of example 2. RT = retention time. Identified peaks correspond to: (a) acetic acid; (b) furfural; (c) guaiacol; (d) 4-methyl guaiacol; (e) 4-ethyl guaiacol; (f) 4-vinyl guaiacol; (g) isoeugenol; (h) catechol.

[0081] Figure 3 A and 3B are photographs of the isolated lignins obtained in example 5, from which the striking difference in colour is immediately apparent. Batch numbers are indicated in the figures.

[0082] Figure 4 depicts the reflectance spectra of selected batches of lignin obtained in examples 5. (a) batch 1-1 ; (b) batch 1-2; (c) batch 1-3; (d) batch 1-4; (e) batch 1-6; (f) batch 2-1 ; (g) batch 2-5; (h) batch 2-6; (i) Alcell lignin (example 4).

[0083] Figure 5 depicts lignin samples that are being heated during step (c), corresponding to example 6. The lignin is heated at 20 °C (figure 5A), 40 °C (figure 5B), 50 °C (figure 5C and 5E) or 60 °C (figure 5D). Water is added to the lignins in figures 5A - 5D, before heating is commenced. Values for time t and temperature T corresponding to each picture a - h are given in Table 6.

Examples

[0084] The following examples are intended to illustrate the invention. Example 1

[0085] Wheat straw was chopped into pieces of < 1 cm. The moisture content of the wheat straw was determined to be 12 wt%. Wheat straw was subjected to organosolv fractionation in an autoclave (Biichi Glas Uster AG, volume = 2 L) as described in Wildschut et al, Bioresource Technol. 2013, 135, 58-66. Organosolv conditions: 60% w/w aqueous ethanol, 10 L/kg straw (dry weight), 30 mM H2SO4, 190 °C, 60 min. The resulting pulp was separated from the liquor by filtration and subsequently washed with (1) 60% w/w aqueous ethanol and (2) water. The pulp yield was 44.7% on dry weight basis.

[0086] The organosolv liquor and the first washing liquor were combined and split into three equal portions. Each portion was subjected to a different procedure for lignin isolation from the liquor. Portion 1 was added to a threefold excess of cold (4 °C) water. The resulting suspension was centrifuged and the above-standing liquor was decanted. The wet precipitated lignin was dried overnight at 50 °C in vacuo. Portion 2 was treated similarly as portion 1 except for the drying step. The wet precipitated lignin was first placed at 50 °C in a closed vessel for 1 h at ambient pressure. During this initial heating, lignin shrink with the excretion of moisture was observed. This moisture was decanted and drying of the lignin was continued by overnight heating at 50 °C in vacuo. Portion 3 was treated similarly as portion 2 with the addition of a washing step (three times with water) prior to the initial heating. All dried lignins were crushed by hand with a mortar into a powder.

[0087] The effect of shrinking and drying on the lignin composition is shown in Table 2. The lignin compositions were determined according to Huijgen et al, Ind. Crop. Prod. 2014, 59, 85-95. The colour of the lignin was determined by visual inspection.

[0088] Table 2. Composition and colour of lignins.

[a] Dry weight of the lignin after (A) centrifugation and decanting; (B) heating (lignin shrink); (C) drying.

[b] After threefold washing with water.

[c] Lig = lignin (sum of acid insoluble (Klason, AIL) and acid soluble (ASL) lignin);

Glc = glucan; Xyl = xylan; Carb = other carbohydrates.

[0089] During the shrinking phase of lignin, the majority of its adhering moisture is expelled. Separation of this expelled moisture substantially increased the dry weight (5.9 to 62.7 wt%) and purity of the lignin. Increased purity is demonstrated by a reduced amount of residual carbohydrates (from 5.8 wt% to 1.6 wt%) and ash (from 0.4 wt% to 0.1 wt%) in the final lignin product. Washing the lignin precipitate with water prior to the lignin shrinking and drying did not significantly affect the lignin composition, but substantially decreased its colour.

Example 2

[0090] Spruce wood was chopped into pieces of < 3 cm or pieces of < 4 mm. The moisture content of the spruce wood was determined to be 48.9 wt%. Pine wood was chopped into pieces of < 1 cm. The moisture content of the pine wood was determined to be 10.8 wt%. Part of the pine wood was subjected to pre-extraction by washing (soaking for 60 min at 50 °C and subsequent decanting) the pine three times with pure acetone (10 L acetone/kg biomass (dry weight)) and subsequent drying under vacuum for 16 h at 50 °C. Pre-extraction led to a 1.54 % weight loss of the pine biomass. These softwood feedstocks were subj ected to organosolv in an autoclave (Biichi Glas Uster AG, volume = 0.5 L or 2 L) at the indicated temperature for the indicated treatment time (see Table 3), using a treatment liquid containing a solvent system of water/ethanol in a weight ratio of 40/60 (except for batch 7 (see Table 3); corrected for water present in the feedstock). The liquid/solid ratio was 10 L per kg biomass (dry weight). The indicated amount of sulphuric acid was added to the treatment liquid.

[0091] Table 3: Organosolv conditions of softwood

[0092] After the indicated time period had elapsed, the reactor was cooled to room temperature and the content was filtered over a 90 mm GF/D filter (Whatman). The reactor and the pulp were washed with the solvent system. The combined liquid streams (liquor and washing liquid) were subjected to lignin precipitation by diluting them in water having a temperature of about 10 °C. The total weight of the water added was 3 ^χ the total weight of the combined liquid streams. The precipitated lignin was separated by centrifugation and decantation of the supernatant. The wet lignin product was placed in an oven at 50 °C and atmospheric pressure until phase separation was observed (typically for 30 - 60 min), when the lignin shrunk into a pellet and expelled most of its adhering moisture. The expelled moisture was decanted and the partly-dried lignin pellet was further dried overnight at 50 °C in vacuo. The dry lignin was crushed by hand with a mortar into a powder. Pulp yields and lignin yields are given in Table 4. The isolated lignins were subjected to colour identification according to the RAL classic colour system. Herein, a test panel of three independently assigned a RAL colour to each of the isolated lignins. The colour associated with the code is available via http://www.ralcolor.com/. The results of the RAL colour assignment are also given in Table 4, together with the corresponding approximate RGB values. The lignin colour of batch 3 was only visually assigned.

[0093] Table 4: Results of organosolv treatment of the biomass

a] In wt%, based on dry weight of the biomass, before pre-extraction.

[b] In wt% lignin present in the combined liquid streams, based on total weight of the biomass feedstock (lignin content in feedstock: 27.5 wt% (spruce); 17.7 wt% (straw); 22.3 wt% (birch); 26.0 wt% (pine)).

[0094] Performing the organosolv step at a reduced temperature (140 °C) using ethanol as organic solvent afforded light-coloured lignin according to the invention. Decreasing the particle size of the biomass did not affect these results, nor did performing a pre- extraction step. Light-coloured lignin was obtained from both spruce and pine wood. The high temperature organosolv of batch 2 afforded high lignin yields and concurrent low pulp yield, suggestive of high delignification. However, the more severe conditions of the organosolv step needed for more extensive delignification led to dark coloured lignin. Furthermore, all light-coloured lignins (from batches 1, 3, 4 and 5) were odourless, while the lignin obtained in batch 2 had a strong odour. The lignins obtained in batches 4 and 5 exhibited thermal decomposition at about 400 °C (TGA850 (Mettler Toledo), heating rate: 15 °C/min, N ₂ atmosphere), and did not melt at a temperature up to 250 °C (M565 (Biichi), air atmosphere).

[0095] The molar mass distribution of the lignins obtained in batches 1, 4 and 5 was determined in duplicate by size-exclusion chromatography (SEC) as described in Huijgen et al., Ind. Crop. Prod. 2014, 59, 85-95. 50 mg of lignin was dissolved in 50 ml of an aqueous 0.5 M NaOH solution. The SEC column was packed with Toyopearl HW- 55 beads (TSKgel) and a HP1100 HPLC (Agilent) equipped with UV detector (254 nm) was used. Phenol (94 g/mol) and various sodium polystyrene sulphonates (1100 - 666000 g/mol) were used as standard. _w values were 6.4 kg/mol (batch 1), 4.2 kg/mol (batch 4) and 4.3 kg/mol (batch 5), and _n values were 1.8, 1.1 and 1.1 kg/mol respectively. As such, the dispersities D amounted to 3.6, 3.7 and 3.8 for batch 1, 4 and 5 respectively. The hydroxyl content of the lignin was determined via the wet chemical method as described by Zakis etal, "Functional analysis of lignins and their derivatives", TAPPI Press, Atlanta, 1994, page 94, and amounted to 5.5 mmol OH moieties per gram lignin for batch 4 and 5.8 mmol/g for batch 5.

[0096] The sulphur content of lignin batch 1 and 4 was determined to be 0.32 and 0.12 wt% on dry weight basis, respectively. The total sulphur was determined as sulphate using ion chromatography (Dionex IC25, column Dionex AS 18) according to EN-EN- ISO 10304-1 following bomb combustion in a calorimeter to determine the higher heating value (HHV) (Parr 6300) and subsequent water washing of the combustion residues. The residual carbohydrates content of lignin batch 1 and 4 was determined to be 3.2 wt% and 1.2 wt% on dry weight basis, respectively. The major carbohydrate in both lignins was mannan (1.6 wt% in batch 1 and 0.5 wt% in batch 4) corresponding to the softwood origin of the lignins. The residual carbohydrates were determined according to Huijgen et al., Ind. Crop. Prod. 2014, 59, 85-95. [0097] The lignins of batches 1, 2, 6 and 7 were further analysed by reflectance spectroscopy. The reflectance of the lignin samples was determined in the wavelength region of 310 to 1700 nm, using a halogen lamp, a UV-VIS detector (BLACK CXR-SR- 50 BW-16 from StellarNet) and a VIS-NIR detector (NIR-25 BW-ND from StellarNet) against a reflectance reference standard (SRS-99-010 from Labsphere). The visible part of the spectrum (380-750 nm) was used and the resulting spectra are depicted in Figure 1.

[0098] The lignins of the present invention are thus promising candidates to be incorporated into performance products and the like, wherein the appearance of the lignin containing product is important for its commercial value.

Example 3

[0099] Spruce lignin batch 1 of example 2 was analysed by pyro GC/MS analysis. Pyro GC/MS analyses were carried out on a GC/MS Thermal Desorption Unit MPS Autosampler and a pyrolysis module with sample transport adapter. Pyrolysis was performed at 500 °C and a polar GC column was used (ZBWAXPlus). The spectrum is depicted in Figure 2. The GC/MS data confirmed that a large percentage of guaiacol subunits is present in the lignin, which is typical for softwood lignin. It is thus concluded that the precipitate from the organosolv liquor is indeed lignin. Additionally, the GC/MS spectrum indicates that the lignin is indeed of high purity, since very few components originating from residual carbohydrates were detected. It should be noted that a given peak could resemble a component of the primary lignin fractions or could be related to fragments that are formed during pyrolysis or GC-MS analysis. Example 4

[0100] Pine wood (moisture content: 10.8 wt%) was chopped into pieces of < 1 cm and subjected to organosolv in an autoclave (Biichi Glas Uster AG, volume = 20 L) at 140 °C for 60 min), using a treatment liquid containing a solvent system of ethanol/water in a weight ratio of 60/40 (corrected for water present in the feedstock). The liquid/solid ratio was 5 L per kg biomass (dry weight). 40 mM sulphuric acid was added to the treatment liquid. After the organosolv treatment, the reactor was cooled to room temperature and the content was filtered over a 90 mm GF/D filter (Whatman). The reactor and the pulp were washed with the solvent system. The combined liquid streams (liquor and washing liquid) were subjected to lignin precipitation by dilution with water having a temperature of about 10 °C. The total weight of the water added was 3 ^χ the total weight of the combined liquid streams. The precipitated lignin was separated by centrifugation and decantation of the supernatant. The separated lignin product was placed in an oven at 50 °C and atmospheric pressure until phase separation was observed (typically for 30 - 60 min), when the lignin shrunk into a pellet and expelled most of its adhering moisture. The expelled moisture was decanted and the lignin pellet was dried overnight at 50 °C in vacuo. The dry lignin was crushed by hand with a mortar into a powder.

[0101] Pulp and lignin were obtained in 66.5 wt% and 8.5 wt% yield, respectively, both based on dry weight of the biomass. The isolated lignin contained 0.08 wt% sulphur and 2.0 wt% residual carbohydrates of which 1.0 wt% mannan (both based on dry weight of the biomass, for methods see example 2). The molar mass distribution was determined as _w = 4.1 kg/mol, _n = 1.5 kg/mol and D = 2.7 (for methods see example 2). The colour of the isolated lignin, determined according to the colour identification protocol as described for example 2, was light ivory (RAL1015; RGB = 230-214-144). The colour was compared to that of isolated lignin prepared via the Alcell process, see Pye and Lora, Tappi J , 1991, 74, 1 13-1 18 (feedstock: mixed hardwoods (birch, maple, poplar); T = 180 - 210 °C; 40 - 60 vol% EtOH/H ₂ 0, 0 mM H ₂ S0 ₄ (autocatalysed, pH around 4)), as well as with Kraft lignin (feedstock: pine, Indulin AT, MeadWestvaco) and sodium lignosulphonate (feedstock: softwood, Borregaard). According to the colour identification protocol of example 2, the Alcell lignin was nut brown (RAL8011 ; RGB = 091-058-041), Kraft lignin was chocolate brown (RAL8017; RGB = 069-050-046) and sodium lignosulphonate was ochre brown (RAL8001 ; RGB = 149-095-032). The sulphur content of Alcell lignin and Kraft lignin was determined to be 0.02 wt% and 1.7 wt%, respectively.

[0102] Figure 1 shows the reflection spectra of the lignin according to the invention (e) and of Alcell lignin (f), sodium lignosulphonates (g) and Kraft lignin (h). Notably, the lignin according to the invention reflects greater parts of the light over the entire wavelength span, particularly in the visible light region, ranging from 380 nm to 750 nm. Since light of all wavelengths is reflected significantly, the lignin according to the invention appears much lighter in colour, when compared to the prior art lignins. Additionally, the Alcell lignin had a characteristic strong odour, which was not the case for the lignin according to the invention. Example 5

[0103] Pine was milled into pieces of < 1 cm. The moisture content of the pine was determined to be 10.3 wt%. Pine was subjected to organosolv fractionation in an autoclave (Biichi Glas Uster AG, volume = 20 L) using the following process conditions: 140 °C, 60 min, 60% (w/w) aqueous ethanol, 5 L/kg pine (dry weight), 40 mM H ₂ S0 ₄ . The resulting pulp was separated from the organosolv liquor by filtration and washed using 60% (w/w) aqueous ethanol. The organosolv liquor and washing liquor were combined and added to a threefold excess of cold (4 °C) demineralized water in order to precipitate lignin. After centrifugation (4000 rpm, 4 min) in 250 mL centrifuge bottles, the above-standing liquid was decanted.

[0104] The resulting semi-solid lignin precipitate was divided into various batches. Each lignin batch was incubated in a closed bottle (initial heating step) for duration t and temperature T (see Table 5). Water (1/1, 2/1 or 4/1 (w/w)) was added to the lignin precipitate of some of the batches prior to this initial heating step. During incubation, lignin shrink with expel of adhering moisture was observed. After shrinking, the expelled moisture was decanted and the lignin was dried overnight at 50 °C in vacuo, except for batches 1-6 and 2-6, wherein only overnight drying was performed without intermediate separation of the expelled liquid. The incubation parameters used for each batch of the precipitated lignin are given in Table 5. The dried lignin pellets were crushed and photographed, see Figures 3A and 3B. The colour of the isolated lignin was determined according to the colour identification protocol as described for example 2 and given in Table 5.

[0105] Table 5: Overview of incubation parameters and resulting lignin colour.

Batch H ₂ 0 ^[a] expel† ^[b] t (h) ^[c] J (°C) ^[c] Lignin color (RAL; RGB)

1-1 * 0: 1 Yes 0.5 50 ivory (1014; 225-204-079)

1-2* 0: 1 Yes 1 50 brown beige (101 1 ; 138-102- 066)

1-3 * 0: 1 Yes 2 50 clay brown (8003; 1 15-066-034)

1-4* 0: 1 Yes 4 50 clay brown (8003; 1 15-066-034)

1-5 0: 1 Yes 16 50 clay brown (8003; 1 15-066-034)

1-6* 0: 1 No NA NA ochre brown (8001 ; 149-095- 032) 2-1* 2:1 Yes 0.5 50 light ivory (1015; 230-214-144)

2-2 2:1 Yes 1 50 light ivory (1015; 230-214-144)

2-3 2:1 Yes 2 50 beige (1001; 217-186-140)

2-4 2:1 Yes 4 50 beige (1001; 217-186-140)

2-5* 2:1 Yes 16 50 beige (1001; 217-186-140)

2-6* 2:1 No NA NA sand yellow (1002; 198-166-100)

3-1 0:1 Yes 16 40 ochre brown (8001; 149-095- 032)

3-2 1:1 Yes 16 40 beige (1001; 217-186-140)

3-3 2:1 Yes 16 40 beige (1001; 217-186-140)

3-4 4:1 Yes 16 40 beige (1001; 217-186-140)

3-5 0:1 Yes 5 50 clay brown (8003; 115-066-034)

3-6 1:1 Yes 5 50 beige (1001; 217-186-140)

3-7 2:1 Yes 5 50 beige (1001; 217-186-140)

3-8 4:1 Yes 5 50 beige (1001; 217-186-140)

3-9 0:1 Yes 4 60 nut brown (8011; 091-058-041)

3-10 1:1 Yes 4 60 clay brown (8003; 115-066-034)

3-11 2:1 Yes 4 60 brown beige (1011; 138-102- 066)

3-12 4:1 Yes 4 60 beige (1001; 217-186-140) a] Parts of water added prior to the initial heating step per part of wet lignin pellet

(w/w). "0:1" indicates no addition of water.

[b] Separation of the expelled liquid.

[c] Duration t and temperature Jof the initial heating step.

* The lignin of these batches has been further analysed by reflectance spectroscopy.

[0106] Without the addition of water, the lignin shrunk to a (dark) brown dense pellet at the conditions applied during incubation in case the expelled liquid is not separated from the lignin pellet. Timely removal of the expelled liquid and subsequent further drying afforded light-coloured lignin. Addition of water to the lignin pellet resulted in a lighter final lignin product. In addition, a lower temperature applied during the incubation phase also reduced colouration of the lignin. [0107] Reflection spectra were obtained of the indicated lignin samples as described in Table 5. Figure 4 shows these reflection spectra. All lignin batches according to the invention have a lighter colour than the reference Alcell lignin. Moreover, isolated lignins from which expelled water is timely separated are lighter than isolated lignins from which no expelled water was separated or from which expelled water was separated after 1 h or more in the oven (batches 1-2 up to 1-6 and 2-6). Both with and without water addition prior to incubation, a shorter duration (t) of the initial heating step, during which the lignin expels its adhering moisture, was found to result in samples that were lighter as they reflected more light. However, the darkening of the lignin samples upon prolonged incubation was found to be much more pronounced when no water was added prior to incubation, than with addition of water (cf. series 1 and 2). In case of water addition, even after 16 h (i.e. 15— 15.5 h after phase separation) the colour of the lignin was still remarkably light (batch 2-5). Example 6

[0108] Separated semi-solid lignin products were obtained by organosolv, precipitation, centrifugation and decantation as described in example 4. Five batches of about 20 g in volume of the semi-solid lignin product were placed in test tubes. To batches A - D, 30 mL of water was added on top of the lignin product. To batch E, no water was added. The test tubes were closed with a cap. For the execution of step (c), all batches were placed in a pre-heated oven with circulating air at temperature T ₀ (see Table 6) at t = 0 min for a duration of 60 min and subsequently placed in a water bath at the same temperature. The temperature Jof the lignin being heated was measured periodically (at t as indicated in Table 6), by submerging a thermometer in the liquid on top of the semi- solid lignin or for batch E by measuring the temperature in a dummy test tube with water placed under the same conditions. At the same time pictures of the lignins were taken. The pictures are depicted in figures 5A to 5E for batches A to E respectively, wherein designators a through g correspond to a certain point in time as indicated in Table 6. The corresponding point in time t and temperature Jof the lignin are given in Table 6.

[0109] Table 6: Temperature of lignin T at point in time t for batches A - E.

A B C D E

(To = 20 °C) (To = 40 °C) (To = 50 °C) (To = 60 °C) (To = 50 °C) t T t T t T t T t T

(min) (°C) (min) (°C) (min) (°C) (min) (°C) (min) (°C) a 0 21 0 20 0 21 0 21 0 20 b 15 21 15 29 15 35 15 41 15 36 c 30 21 30 34 30 40 30 46 30 45 d 45 21 45 36 45 45 45 51 45 50 e 60 21 60 38 60 46 60 54 60 50 f 90 21 90 39 90 48 90 56 90 50 g 120 21 120 39 120 48 120 58 120 50 h 1080 21 1080 50 1080 60

[0110] No lignin shrink or discoloration was observed when no heating was applied (batch A, T = 20 °C). The temperature of batches B - D slowly increased towards the temperature of the environment. At a certain point between t = 0 min and t = 15 min (for batches C, D and E) or between t = 15 min and t = 30 min (for batch B) phase separation was observed and the lignin started to shrink. In view of the water addition to batches A - D, the water level remained above the upper edge of the picture.

[0111] Batches B and C did not show any colouring during the heating. 120 min at 40 °C or even 1080 min at 50 °C has no effect on the colour of the lignin, when water was added prior to the heating. When heating at 40 °C, lignin shrink was slow and not completed at t = 120 min. Heating at 50 °C afforded substantially complete lignin shrink at t = 45 min, after which hardly any additional water was excreted. Lignin shrink of batch D at 60 °C was near completion at t = 30 min and until t = 90 min no discolouration was observed. From t = 90 min onwards, the lignin clearly became continuously darker in colour. Darkening in colour was also observed at T= 50 °C when no water was added prior to the heating, see batch E. From t = 30 min onwards, the colour of the lignin gradually intensified. Lignin shrink was near completion at t = 30 min. Without water addition (batch E), the lignin was found to shrink to a substantially smaller end volume than with water addition (batch C) and was significantly darker in colour.