Field of the Invention

The present invention relates to sorbents based on lignocellulosic materials. In particular, the present invention concerns oxidized lignin-containing materials, derivatives made from lignin-containing material, methods of purifying aqueous fluids, methods of purifying solids permeable to aqueous fluids and to novel uses of lignin-containing material.

Description of Related Art

In industry there is a need to treat contaminated effluents and waste waters. Examples of such situations include the purification of industrial sludge, process water, aqueous waste fluids, municipal waste water, and contaminated water or soil after leakages, spills or accidents. To take one particular example, in papermaking, metal ions, especially calcium (Ca ²⁺ ) dissolved at high concentrations, are unwanted substances in process waters. Calcium ion concentrations in typical process streams such as clear filtrate in paper mills which use CaC0 ₃ or CaS0 ₄ as filler or coating pigment or de-inked pulp as raw material, are on the order of 500 to 1000 ppm. Both high and fluctuating concentration of dissolved calcium induces unwanted inorganic and organic precipitation which can abate the efficiency of paper production. Usually, process chemistry can be stabilized by cutting the concentration of dissolved calcium. Also, by reducing the hardness in the process water the functioning of added paper chemicals, such as retention and sizing agents can be enhansed.

Traditional methods of removing contaminants from industrial effluents include chemical precipitation, ion exchange, chemical oxidation or reduction, reverse osmosis, electrodialysis and ultrafiltration. Also biological methods are used. Various sorption methods are used especially for charged contaminants, such as metal ions or charged organic molecules. In the paper and pulp industry Ca-ion concentration control has been achieved primarily by inhibiting the dissolution of the solid substance containing Ca-ions. Chelants are also used in pulp and papermaking to reduce the concentration of harmfull metal ions, sudh as Mn, Cu and Fe prior to or in the pulp bleaching stages. Synthetic ion-exchange materials can be used but they consume fossil fuels. One potential source of absorbents is provided by plant based lignocellulosic materials. Plant carbohydrates cellulose, hemicelluloses and lignin are the most abundant biomass components on the planet. Due to the limited resources of fossil fuels and to the greenhouse effect there is a need for using renewable biomass as a source of energy. In a lignocellulose-to-ethanol process the lignocellulosic material is first pretreated either chemically or physically to make the cellulose fraction more accessible to hydrolysis. Methods known in the art include steam explosion, with or without chemicals, such as sulphuric acid, ammonia, etc., hot water treatment, mild acid hydrolysis, CaO treatment, wet oxidation, organic solvent treatment, ammonium treatment, etc. Lignin is then separated from the pretreated material using conventional methods. The cellulose fraction is hydro lysed to obtain sugars that can be fermented by yeast into ethanol. Also the paper industry uses corresponding pre-treatment methods before separating lignin from cellulosic fibres.

Conventionally lignin is a low-value by-product, which typically is used as a solid fuel. However, lignin derivatives have also found a number of applications. In particular, compounds such as lignosulphonates or lignophosphonates can to some extent replace the use of synthetic sorption materials because they are generally negatively charged and provide numerous binding sites for positively charged compounds, especially for cationic metal ions. The negative charge of the lignosulphonates and lignophosphonates stems essentially from sulphonic or phosphonic groups.

A problem associated with sorbents containing renewable lignin, such as lignosulfonates or lignophosphonates, is their low charge density due to the large bulk of the charged group and, thus, low loading capacity. As a result the material has to be changed or regenerated often. Regeneration of lignosulphonates or -phosphonates requires very acidic and harsh conditions (pH«2). If hazard contaminants, such as heavy metals, are sorbed, the material cannot be combusted for energy production without regeneration. When burned, lignosulphonates produce sulphur oxides, which require sulphur recovery from the gas stream. Lignophosphonates cause increased catalyst deactivation, increased slagging in boilers and they give rise to a phosphorous-rich ash which has very little use in the cement industry. The ask has to be disposed of by landfills which, in turn, causes eutrophication of the water environment.

There are some publications which deal with renewable sorbents. Thus, WO2005/012194 describes systems for air and water purification using charged sorbent mediums including also lignin, and methods for their use. The publication generally concludes that lignin typically carries negative charge on its surface and can thus remove cationic compounds from aqueous phase. Sud et al. (2008) discuss the use of agricultural waste material as a potential adsorbent for sequestering heavy metal ions from aqueous solutions.

As will become evident, in the art there is no suggestion of using lignin remaining after using cellulosic fraction in paper industry or biofuel processes. There is also a need for improved materials and methods for efficient biological sorbent materials to improve the process economics and reduce environmental burden, especially use of fossil fuels. The present invention aims to meet at least a part of these needs.

Summary of the Invention

It is an aim of the present invention to provide a novel kind of sorbent material made from renewable sources. In particular, it is an object of the invention to provide an oxidized lignin-containing material such as oxidized lignin and derivatives thereof, capable of sorbing positively charged components, such as metal ions, from aqueous fluids, such as industrial effluents.

Thus, according to a first aspect, the present invention provides an oxidized lignin- containing material which exhibits a negative charge primarily due to carboxylic groups present on the material. It has been found that the sorbtive capacity of the material is surprisingly good and it can be used as a biosorbent. Typically, the charge of the material, based on the content of the carboxylic groups, is at least 500 μιηοΐ/g dry weight at pH 8. More specifically, the oxidized material according to the present invention is characterized by what is stated in the characterizing part of claim 1.

It is another aim of the present invention to provide a derivatised sorbent material based on a lignin-containing material which is capable of sorbing negatively charged components from aqueous fluids, such as industrial effluents. Further, by modifying the carboxylic groups on the material, e.g. by chemical modification, it is possible to provide a derivative of oxidized lignin having a positive net charge. Preferably said net charge is at least 200 με per gram dry weight of the material.

The chemical derivative of an oxidized lignin material is characterized by what is stated in the characterizing part of claim 8.

It is a third object of the present invention to provide a method of purifying aqueous fluids containing charged components.

The invention also provides a process for removing charged compounds from aqueous fluids and is usable also for high amounts of material to be treated. Accordingly, according to a third aspect, the invention concerns a method of purifying an aqueous fluid containing charged components, comprising the steps of contacting the aqueous fluid with a sorbent comprising a lignin-containing material or a derivative thereof, and sorbing charged components having an opposite charge to that of the sorbent so as to effectively reduce the content of the charged components in the fluid.

It is a fourth object of the present invention to provide a method of purifying solids permeable to aqueous fluid, said solids containing charged components.

In a fourth aspect, the invention provides for purification of solids or solid materials permeable to aqueous fluid, which contain containing charged components. First, at least a part of the charged components are leached out of the solids into an aqueous phase, and then the aqueous fluid so obtained is contacted with a sorbent comprising an oxidized lignin-containing material or a derivative thereof exhibiting a relatively high negative or positive charge to bind at least a part of the charged components. As a result, the content of the charged components is reduced in the aqueous fluid. The spent material is subjected to sequestering. The methods of purifying aqueous streams and of purifying contaminated solid materials are characterized by what is stated in the characterizing parts of claim 10 and 11, respectively.

A further aim of the present invention is to provide biosorbents which have high carboxylic charge density, preferably at least 1 meq/g, more preferably at least 2 meq/g , more preferably at least 3 meq/g most preferably at least 4 meq/g at neutral pH. Generally, high charge of sorbent results in high purification capacity of charged components.

A further object of the present invention is to provide biosorbents which can be easily regenerated to remove (hazardous) compounds, e.g., before combustion or use as a landfill material. After regeneration with acid, the hazard compounds can be recovered.

These and other objects, together with the advantages thereof over known products and processes, which shall become apparent from specification which follows, are accomplished by the invention as hereinafter described and claimed.

The present invention is based on the surprising finding that oxidized, essentially carboxyl- charged lignin-containing materials can be used as effective biosorbents for purifying industrial sludge, process streams, aqueous waste fluids, municipal waste waters, contaminated natural waters or any other aqueous fluid including paint residues from car industry.

Considerable advantages are obtained by means of the present invention. The lignin- containing material described here is highly charged. Since the major charge stems from carboxylic acids, it is easy and safe to regenerate compared to lignosulphonates or lignophosphonates. It is essentially sulphur free and can thus be incinerated without an express need to purify the combustion gases. In addition, carboxyl charged lignin- containing biosorbent has good pH and thermal stability. As such, oxidized lignin is negatively charged with carboxylic groups and usable, e.g., as biosorbent for positively charged components. Such material can be used for removing charged components from fluids by various mechanical implementations. One interesting application relates to pretreatment before paper manufacture or hydrolysis to sugars for fermenation results in two fractions, a solid fibre fraction containing mainly cellulose (for paper manufacture or hydrolysis to sugars) and a soluble fraction containing lignin, hemicellulases and degradation products. Lignin can be separated by e.g. acid precipitation. The lignin-based or lignin-containing sorbtion material can be used, e.g., as a crude filtrate or lignin precipitate obtained from pretreated bio mass or TMP-reject. In this context, lignin precipitate means a lignin fraction that is separated after a pulping process or after pretreatment in bio fuel process. In another application the oxidized lignin- containing material is used as a sorbent for calcium in the same pulping process without precipitation.

Thus, the material is based on renewable sources and can be obtained as byproducts of processes for biorefming of cellulosic or hemicellulosic materials. Since such processes will, in the future, to an increasing extent be integrated with the pulp or paper production (integrated biorefmeries) and with lignocelluloses-to-fuel -processes, there will be an oversupply of separated lignin. For this reason, the present sorbent materials will be available at low-cost and in great abundance.

Specific embodiments of the invention are set forth in the dependent claims. Other objects, details and advantages of the present invention will become apparent from the following drawings, detailed description and examples.

Brief Description of the Drawings

Figure 1 is a schematic presentation of principles of obtaining the carboxyl charged lignin- containing material.

Figure 2 is a graph showing the decrease in calcium as a function of addition of oxidized lignin-containing material or 0.005 M EDTA (reference). An increase in the Ca ²⁺ concentration in the beginning of the experiment is a Ca electrode detection error due to the pH adjustment from 2 to 6. Initial volume of calcium solution was 800 ml, amount of Ca ²⁺ was 100 ppm. Figure 3 is a graph showing the decrease in calcium as a function of addition 0,005 M EDTA, 0,1 M NaOH (two parallel samples) and oxidized lignin-containing material. Initial volume of calcium solution was 800 ml, amount of Ca ²⁺ was 100 ppm.

Figure 4 is a graphic depiction showing the decrease of Ca ²⁺ as a function of added EDTA (control) or oxidized lignin-containing material. Lignin samples were reveived by oxidation with copper catalyst (CatOx) and without a catalyst (AlkOx). Initial volume of calcium solution was 700 ml, amount of Ca ²⁺ was 100 ppm.

Figure 5 is a graph showing the pH of the solution as a finction of added oxidized lignin- containing material or 0.1 M EDTA. Lignin samples were reveived by oxidation with a copper catalyst (CatOx) and without a catalyst (AlkOx).

Figure 6 is a graph showing the decrease of calcium as a function added oxidized lignin- containing material added as a filtrate and given as added volumes. Initial volume of Calcium solution was 200 ml, amount of Ca ²⁺ was 100 ppm and pH of the filtrate reweived by oxidation with a copper catalyst (CatOx) and withouh a catalyst (alkOx) was 4,1.

Figure 7 is a graph showing the decrease of calcium as a function added oxidized lignin- containing material given as dry solids. Two filtrate samples (CatOx and AlkOx) have been tested in pH's 4,1 and 6,5. Initial volume of Calcium solution was 200 ml, amount of Ca ²⁺ was 100 ppm.

Figure 8 is a graph showing the molecular weight distribution of material present in filtrates reveived by oxidation with a copper catalyst (CatOx) and without a catalyst (AlkOx). Definitions

As used in the present context, the expressions "sorbent" and "sorbent material" signify a material that has a capacity to host charged contaminants, e.g., by adsorption or absorption. The sorption can be based on any kind of interaction, including, but not limited to, coulombic attration (e.g. Donnan partitioning, ion exchange), and chemisorption (e.g. complexation, chelation). Regardless of the sorption mechanism, the expression covers all materials that can reduce the activity of the free form of a charged solute by an interaction to some but not all solutes.

The term "biosorbent" covers sorbent materials made from renewable biomass, essentially any lignocellulosic material except living cells. Such material may be for example a polyelectrolyte or chelate. Biosorbtion is generally a process in which material originating from renewable biomass is used for sorption.

"Oxidized lignin" refers to any lignocellulosic material treated with an oxygen-containing oxidizing agent or a fraction thereof. If made from a source containing native lignin, the oxidation will convert most, or at least part, of the aromatic substructures into carboxyl- containing constructions.

For the present purposes the "carboxyl charged" lignin can be obtained by any method capable of achieving oxidation of the phenolic groups to corresponding carboxylic acids. Examples of agents that can be employed in oxidation are any oxygen containing agents such as C"2, Η ₂ 0 ₂ and organic peroxides.

In this context, the expressions "carboxyl charged" and "essentially carboxyl charged" are used synonymously and mean that most of, or at least some, of the charge of the material stems from carboxylic acids. Known charged lignin-based materials include lignosulphonates and lignophosphonates. However, this invention concerns lignin material where the major ionizable functional group comes from carboxylic groups. Also an amphoteric material, i.e., one having both negative and positive charges, is covered with the expression. It is to be understood that other components, such as hemicelluloses, have an effect on the net charge of lignin-containing material. Preferably at least 50 % of the charge at pH 8 stems from carboxylic groups, more preferably 70 %, and most preferably 90 %.

In this context "lignin-containing material" means any plant derived material including lignin and/or oxidation products thereof. Examples of lignin-containing materials are crude filtrate obtained from pretreatment and lignin precipitate obtained from said filtrate. Lignin-containing material exists both in filtrate and precipitate. Half of the dry matter in the titrate is lignin. Most of the precipitate is lignin-containing material.

Description of Embodiments

One purpose of this invention is to provide an oxidized lignin-containing material to lower the activity of positively charged components in aqueous fluids, thus acting as a biosorbent.

This invention is directed especially to sorption of positively charged compounds in aqueous fluids. Sorption of an impurity may include any kind of taking and holding of an impurity, possibly by the actions of absorption or adsorption or a combination thereof.

In one embodiment of the invention, the biosorbent consist essentially of lignin. Lignin can be obtained as a low- value by-product from pulping and bio fuel, especially bioethanol, processes. It is renewable and safe to handle, use and recycle. In another embodiment of the invention, the biosorbents further contain cellulosic and hemicellulosic components. There is no need to separate lignin from other plant derived materials but usually lignin is deemed a waste product and is separted due needs of e.g. pulping process or hydrolysis to sugars for fermentation. In a further embodiment of the invention, the lignin-containing biosorbent is an oxidized filtrate of pulping process. Such material is readily available at pulping sites and could be used to reduce the hardness of process waters, e.g., by removing calcium ions. In a still further embodiment of the invention, the charged lignin- containing material is an oxidized material from a bio fuel process.

In one embodiment of the invention the oxidized lignin- containing material has a negative charge of at least 500 μQq/g per dry weight at pH 8. The net charge can be measured e.g. by quantifying the adsorptive capability of select divalent ions like Ba ²⁺ at pH 8. The net charge is defined as the positive charge less the negative charge, completely ignoring any small counterions. The net charge may also be synonymous with the amount of carboxylic moieties, including derivatives of the same.

Furthermore, in one embodiment of the invention, the negative charge of lignin- containing material at neutral pH stems mainly from carboxylic groups. In this context, neutral pH means a pH between 4 and 10, preferably between 5 and 9 and most preferably between 6 and 8.

The pKa of carboxylic acids range from 2 to 6, largely depending on the electron density of the atoms in their vicinity. An isolated and non-interacting carboxylic acid group has a pKa of about 4. The oxidative degradation of lignin usually creates carboxylic acid moieties close to each other, which typically alter their pKa values. The close interaction between formed carboxylic acids and remaining aromatic structures also alter the pKa values. These two phenomena make this material different from the carboxylated lignin, where the carboxylic acids are introduced by synthesis of a carbon-carbon bond.

Carboxylic acids have a negative charge at pH values above their pKa value. This means that the material has maximum adsorptive capability at pH values above 5, where all carboxylic acids are readily available for sorption. At pH near the pKa, some of the acid groups tend to be protonized and the metal ion needs to compete with the proton for the carboxylate groups. With pKa values spread out over a range of pH values, the ionic charge and therefore the sorptive capability, is not abruptly lost at one specific pH, but only reduced. It is also true that partial regeneration can be made if the pH of the regeneration solution is not below all pKa values within the material. Considering that there are chemically different sorption sites, evidenced by the differing pKa values, some sites may preferentially bind some metal ions. It has not been investigated, but the selective regeneration may have limited use in metal separation.

According to one embodiment the carboxyl oxidized lignin is obtained by process as described in WO2009/034325, the content of which is herewith incorporated by reference. In the known process the lignocellulo lytic raw-material is treated in alkaline aqueous medium in the presence of a catalyst and dioxygen. Catalyst may be a transition metal catalyst comprising copper coordinated with at least one aliphatic or aromatic nitrogen donor ligand. According to another embodiment the carboxyl oxidized lignin is obtained by process as described in WO2009/034325 but catalyst is not used.

According to another embodiment the carboxyl oxidized lignin is obtained by suspending a sample into a solution of 26.5 g/L (0.25 mol/L) Na ₂ CC"3 and stirring under 10 atm 0 ₂ pressure and kept at 120 °C for 20 hours.

According to still a further embodiment of the invention the carboxyl charged oxidized lignin is obtained from pulping process where lignocellulo lytic mass is pretreated in order to seprate lignin before paper manufacturing process.

In a further embodiment of the invention the carboxyl charged oxidized lignin is obtained from process where lignocellulo lytic mass is pretreated before mass hydrolysis to provide sugars for fermentation. If necessary, the lignin-containing material can be further oxidized. Cellulosic fraction and carbohydrates are preferably separated or fermented to yield alcohol, that is then recovered.

The charged lignin material or charged lignin-containing material can be used as such as oxidation product (filtrate containg cellulose and soluble fraction of lignin and hemicellulases) or it can be isolated by conventional methods such as precipitation by acid. The material is water soluble or soluble in other aqueous fluids.

The amount of carboxylic groups is at least 500 μιηοΐ/g, preferably over 2 mmol/g, and most preferably over 4 mmol/g. The amounts are expressed per dry matter of the lignin. In one embodiment, the carboxyl charged material is chemically modified to have a net positive charge at pH 8. The resulting material may be amphoteric. A positive net charge allows the sorption of negatively charged components. The net charge of a derivative may be more than 0.5 meq/g, prefereably more than 1 meq/g, and most preferably more than 2 meq/g. Higher charge results in enhanced capacity to purify the fluid from anionic compounds.

In one embodiment of the invention, the lignin or lignin-containing material is functionalized by small organic molecules such as diamine compounds. Such material is usable as biosorbent for anions depending the needs of purification.

In one embodiment of the invention, the lignin or lignin-containing material is modified to have cationic charge and/or combined with another sorbtion material. Positive charge may stem from e.g. amines or amides.

According to another embodiment of the invention a carboxyl charged process filtrate containing lignin, hemicelluloses and alternatively cellulose is provided for use. Charged lignin can function as a polyelectrolyte or as a chelate depending on its molecular size.

Both lignin and any lignin-containing material can be further fractionated into fractions with different molecular size distributions for use in various applications. The size distributions affect the sorption properties of the materials and can therefore be more suitable for some applications.

The lignin-containing material or derivative thereof can be fractionated according to molecular weight and said fractions are used as polyelectrolytes or chelates allowing to optimize the sorbtion properties for each application.

Fractionating can be performed using conventional methods such as partial precipitation, filtration, kromatographic methods, dialysis or electrophoresis. Fractions with high molecular weight components ranging typically between 500 and 5000 Daltons (in practice up to even 150 kDa) are especially usable as polyelectrolyte applications whereas fractions having low molecular weight components ranging typically between 150 and 1000 Da have chelate characteristic. Filtrates containing suitable material for both applications can be obtained by oxidation process descibed in WO2009/034325; the oxidation can be conducted both with or without a catalyst. The average molecular weight (Mw) measured from the filtrates obtained with a copper catalyst (CatOx) was ca. 3900 Da whereas without a catalyst (AlkOx) ca 1500 Da. Softwood and hardwood kraft lignin (precipitated from black liquir) will be degraded to small components (to alifatic acids and finally to carbon dioxide) if the time of the oxidative treatment at elevated temperatures is long enough. It has been noted that relatively short oxidation time of 10 min - 2,5 hours, preferably, 20 min - 2 hours, more preferably 40 - 60 min is sufficient for evolvement of total charge but molecular weight of the components still remains suitable for use as a sorbent material.

Fractions with high molecular weight molecules (having high hydrodynamic radius) are suited for sedimentation and flocculation whereas fractions with fractions with chelating properties can be separated from the fluid by flocculation, sedimentation, filtration, centrifugation or flotation. In addition, various fractions may have different tendency to colour the material to be treated. Different fractions of lignin may be used for different applications: typically small molecules have characteristics of chelate and they remain in a soluble form also after sorbtion.

As a polyelectrolyte lignin-containing biosorbents are usable e.g. as a chelating agent, as a flocculant in water purifications, as thickener, emulsifier, conditioner, dispersion agent, as a filler in composites, as additive in soap, shampoo or other cosmetics, in a battery, in cement, or in oil recovery or chromatography.

A chelate can be removed from the treated aqueous solution by conventional methods such as flocculation, sedimentation, filtration, centrifugation or flotation.

The charged lignin fraction is akin to a polyelectrolyte, i.e. it has molecules with medium or high molecular weight of 1000 to 5000 Da and high charge density. It can be used for removing charged components, especially metal ions, such as divalent calcium ions from process water streams as a sorbent or an ion exchanger.

An embodiment of the invention is to provide a method of purifying an aqueous fluid containg charged components, comprising the steps of contacting the aqueous fluid with a sorbent comprising a ligning containing material or a derivative thereof as described here and sorbing charged components having an opposite charge to that of the lignin-containing material or the derivative thereof, respectively, to the sorbent in order to reduce the content of said oppositely charged components in the aqueous fluid.

In another embodiment of the invention is a method of purifying solids permeable to aqueous fluid, said solids containing charged components, comprising the steps of

- contacting the solids with an aqueous fluid in order to dissolve at least a part of the charged components into the fluid,

- contacting the fluid thus obtained with a sorbent comprising a lignin-containing material according to any of claims 1 to 7 or a derivative thereof according to claim 8,

- sorbing charged components having an opposite charge to that of the lignin- containing material or the derivative thereof, respectively, to the sorbent in order to reduce the content of said oppositely charged components in the aqueous fluid, and

- sequestering the spent material.

In one embodiment the sorbed material is recovered together with the aqueous fluid having a reduced content of charged components.

One special embodiment of the invention is removing dissolved calcium in process waters in papermaking industry and thereby reducing the hardness of water. In further special embodiment the oxidized ligning containing material is recycled in a pulping process by returning part of the oxidized material to TMP-phase to be used as a sorbent for especially calcium ions.

Experiments carried out in connection with the present invention indicate that by using highly charged lignin fractions as ion exchange materials for metal ion removal from industrial process waters, the hardness of the process filtrates can be greatly reduced. As will be evidenced by the below examples, a lignin fraction having a minimum charge of 2 meq/g will have a theoretical sorption capacity exceeding 40 g Ca ²⁺ ions/kg. For example, with a half kg of this kind of material it is possible to treat a volume of lm ³ calcium solution to reduce Ca-ion concentration almost by 50 %, from 100 ppm to 58 ppm. These values can be considered to stand for a high calcium removal capacity and indicate respective results also with other metal ions. These calculations were made using the results shown in figure 4 (BS200209, CatOx). In one embodiment, said charged compounds are metal ions with any positive charge such as M1+, M2+, M3+ or M4+. Examples of such ions, without limitation are, Pb, Cr, Cd, Ca, Mg, Mn, Zn, Co, Ni, Cu,' La. In the preferred embodiment the metals are heavy metals or Ca. Especially the heavy metals are hazard for the environment and typically the material to be purified is large. This invention provides safe and economic means for purifying large amounts of contaminated material.

In another embodiment, the compounds so be sorbed are positively charged metal oxides such as vanadium oxide or organic molecules such as amines, amides or other ammonium derivates not excluding the ammonium ion. Nitrogen containing compounds must be removed from waste streams in order to prevent eutrophication of nature waters.

According to one embodiment of the invention the oxidized ligning containing material is used in a process of removing charged compounds or components, especially positively charged components such as ions from soil or other solids permeable to aqueous fluids. Contaminated soil is contacted with an aqueous suspension of charged lignin- containing material for sorption of the charged compounds. In on embodiment the sorbent materialused has a content of the carboxylic groups of at least 500 μιηοΐ/g dry weight and at least 750 μeq/g, preferably at least 1 meq/g, suitably at least 1.5 meq/g, for example 2 meq/g.

Lignin-containing material and sorbed components may be removed from the process with the aqueous fluid fraction or recovered by suitable separation methods such as flocculation, sedimentation, filtration, centrifugation or flotation.. Lignin-containing material can be used in combination with other sorption materials or other functional materials.

In one embodiment,said lignin-containing material or a fraction thereof is linked to a carrier, a membrane, or any other support material. This may be useful, e.g., in the creation of ion exchange materials, resins, functionalized beads, or adsorption columns.

In one embodiment of the invention the carboxyl charged oxidized lignin is combined with a support material to be used for ion exchange. Charged lignin-containing material can be confined between two membranes or bound to a carrier material by e.g. grafting.

The lignin recovered after sorbent use can be burned for energy or used as a land filling material or as component of cement or concrete. In further embodiment said lignin is regenerated before further use or in order to recover sorbed ionic compounds. This is needed when hazardous components such as heavy metals are sorbed. Regeneration also allows recovery of sorbed ionic compounds.

The invention is illustrated by the following non-limiting examples. It should be understood, however, that the embodiments given in the description above and in the examples are for illustrative purposes only, and that various changes and modifications are possible within the scope of the invention.

Examples

Example 1. Sample preparation

Principles of obtaining the carboxyl charged lignin-containing material are schematically shown in Figure 1. The Figure also shows part of the measurements and analyses conducted during the procedure. TMP -reject pulp was obtained from Finnish thermomechanical pulping plant and oxidized in Parr reactor equipped with mechanical mixer as described in WO2009/034325 except for shorter reaction time (4 hours, 120 °C, 10 bar initial 0 ₂ , and catalyst components: 300ppm o-phenanthroline monohydrate + 200 ppm CuS0 ₄ *5H ₂ 0). After the treatment the filtrate and the solid material (fibre fraction) were separated by vacuum filtration. Lignin in the filtrate was precipitated by adding 12 M HCl until pH was 2.5. The precipitate was collected by centrifugation for 15 minutes at 4000 rpm, washed with water at pH 2.5 and centrifuged again. Thereafter lignin precipitate was freeze-dried. Two parallel samples were prepared and designated as BS311008 and BS 101108. In recovering the lignin fraction dissolved material mainly originated from hemi-celluloses mostly remains in the supernatant.

Spruce (Norway spruce, Picea abies) saw dust obtained from Hankasalmi saw mill was treated as described in WO2009/034325 except for shorter reaction time (5 hours, 120 °C, 10 bar initial 0 ₂ , and catalyst components: 300ppm o-phenanthroline monohydrate + 200 ppm CuS0 ₄ *5H ₂ 0). A parallel oxidation treatment was also conducted without the presence of catalyst (5 hours, 120 °C, 10 bar initial 0 ₂ , no catalyst). The filtrates were treated as described above. The samples were designated as BS200209 (treatment conduced with Cu catalyst, CatOx) and BS230209 (treatment conduced without Cu catalyst, AlkOx).

Table 1. Fractionation (Yield %) of the raw material in the oxidizing treatments. Yield of lignin (dry solids precipitate) as g/kg filtrate and % (=g/kg raw material).

Example 2. NMR-analysis of the structure of the lignin precipitates

The precipitated lignins were phosphitylated with 2-chloro-4,4,5,5-tetramethyl- 1,3,2- dioxaphospholane and analysed according to Granata et al. By the ³¹ P NMR analysis the different types of hydroxyl groups can be quantified separately. The analyses showed that the lignin precipitate BS311008 contains clearly more phenols and less carboxylic acid groups when compared to the precipitates BS200209 and BS230209 revealing that lignin in TMP reject pulp might be less reactive in the oxidizing treatment than lignin in saw dust. The precipitate BS230209 (treatment conduced without Cu catalyst) contains slightly more aliphatic and phenolic hydroxyls and slightly less carboxylic acids, when compared to the precipitate BS200209 (treatment conduced with Cu catalyst).

Table 2. Amount of hydroxyl groups in the lignin samples relative to the internal standard 1.00 (e-HNDI, 0.01 mmol).

Table 3. Amounts of different hydroxyl group species (mmol/g) in the lignin samples.

Carboxylic group contents of lignin precipitates obtained when applying the oxidation treatment described in WO2009/034325 with or without the catalyst to spruce saw dust have been measured to be higher by Tamminen et al. (2.37 - 2.35 mmol/g) than presented in Table 3. above. Depending on the raw material used in the oxidation treatment described in WO2009/034325 the carboxylic group content may also remain under 1 mmol/g, which is the case in TMP -reject pulp i.e. BS311008 (Table 3). The processing history of the lignocellulosic raw material most likely effects the reactivity and the dissolution of lignin in the oxidation treatment.

Lignin-containing material obtained applying the oxidation treatment described in WO2009/034325 (with or without the catalyst) to raw material not pre-processed with high temperatures (> 130 °C) contains carboxylic acid groups in equal or in higher amount when comparing e.g. to that of lignosulphonates (a by-product of pulp and paper processes). Table 4 shows the functional group content of purified sodium lignosulphate (SL) and fractions obtained from SL (Yang et al). The measurements of the functional groups were not conducted by ³¹ P NMR analysis. Therefore, the results shown in Table 3 and 4 are not absolute comparable. Table 4. Functional group content of purified sodium lignosulphate (SL) and fractions obtained from SL (Yang et al.).

The functional group content of SL

Example 3. Analyzing the total charge Le. the sum of all acids of the samples ; Other measurements and analyses of the samples

The formation of acidic products in the oxidizing treatments was detected by pH measurements before and after the treatment, by conductometric titration of the filtrate and the lignin precipitate (latter dissolved in 1 M NaOH) and also by capillary electrophoresis (CE) analysis. By the titration method the total charge i.e. the sum of all acids was obtained and by the CE analysis small molecular weight acids (e.g such as formic, acetic, glycolic, and oxalic acids) formed both from lignin and hemicelluloses. In the titration the conductivity of the sample was registered as a function of time during titrate addition (both 0.1 M HC1 and 0.1 M NaOH; pH range 2.5-11.5). The total charge of the sample was calculated by using the time difference between the equivalent points of acid and base titration curve. This VTT method is a modification of the method described by Zakis. In the CE analysis, which is similar to that presented by Adler et al., alkaline background electrolyte and indirect UV detection were employed for analyzing aliphatic acids. The content of lignin in the filtrate was calculated based on the UV absorbance at 280 nm using absorptivity 20 1/g cm (Tamminen & Hortling). Table 5. H and lignin content of the filtrate. In all treatments the initial pH after raw material and Na ₂ C0 ₃ solution was above 11.

Table 6. Total charge of the filtrate and the lignin precipitate. Sum of all small molecular weight acids of the filtrate.

Example 5. Chelating experiments

The chelate experiments showing the sorption ability of the lignin-containing material were conducted both with the filtrate samples and dry solids lignin precipitates. pH of the filtrate samples were adjusted to a level of 4.1 with 12 M HC1 and the dry solids lignin samples were dissolved 0.1 M NaOH before contacting with 100 ppm Ca ²⁺ solution. Lignin samples BS311008 and BS101108 to 200 mL, and BS200209 and BS230209 to small amount (ca. 4 mL) of 0.1 M NaOH. pH of the Ca ²⁺ solution was adjusted in a range of 5-6 with 0.1 M NaOH.

The samples were analyzed for their ability to chelate Ca ²⁺ -ions by measuring changes in free calcium concentration of the standard solution as a function of added lignin-containing sample-solutions prepared as described above. Na ₂ EDTA solution prepared from standard solution (9992 Titrisol , 0.1M, obtained from Merck) was used as a reference. Calcium selective electrode was used to detect the changes in the Ca ²⁺ solution. The electrode is not for detecting the absolute values, but follows the changes satisfactorily. In addition, also pH was measured. At the beginning of the test the calcium content was 100 ppm. Calculated value for calcium binding by 0.372g EDTA was 40 ppm. In the case of the experiments conducted with BS311008 and BS101108 dilution of sample volume from 800 ml to 1000 ml was due to the 200 mL volume of lignin sample-solution and reduced calcium content by 20 ppm. The results are shown in figures 2, 3, 4, 5 for lignin precipitates dissolved in NaOH and 6, 7 for filtrate samples used as such after pH adjustment to 4.1 or 6.5.

Example 6. Molecular weight measurements

Molecular weight measurement was conducted for filtrate samples BS200209 and BS230209. PSS MCX column, 0.1 M NaOH as mobile phase (T=25C), UV detector (280 nm), and polystyrene sulphonate standards were used in the processing method. Graph of the results is shown as figure 8.

Table 7. Results of the molecular weigt measurements. Dilution ratios of the filtrate samples are presented in SampleName column.

SampleName Mn Mw Mz MP Poly- Area Result Id

(Da) (Da) (Da) (Da) dispersity ^V*sec)

AlkOx-filtrate 793 1487 3856 835 1.873724 72985871 2909 a 1 :5

CatOx-filtrate a 1125 3919 17092 857 3.484517 171729312 2911 1 :5

AlkOx-filtrate 806 1522 4049 853 1.889352 73034529 2913 b 1 :5

CatOx-filtrate 1146 3901 16818 868 3.405026 86985509 2915 b 1 :10

AlkOx-filtrate 831 1575 4295 875 1.895273 73546056 2917 c 1 :5 CatOx-filtrate a 831 1551 3985 875 1.866974 73253309 2937 1 :5

CatOx-filtrate a 1179 4012 17223 891 3.403245 86227375 2939 1 :5

References

Adler, H., Siren, H., Kulmala, M., Riekkola, M-L., Capillary electrophoretic separation of dicarboxylic acids in atmospheric aerosol particles, Journal of Chromatography A, 990 (2003), p. 133-141.

Granata, A. Argyropoulos, D. S., "2-Chloro-4,4,5,5-tetramethyl-l,3,2-dioxaphospholane, a Reagent for the accurate determination of the uncondensed and condensed phenolic moieties in lignins", J. Agric. Food Chem., 43 (1995), 1538-1544.

Sud et al. "Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions - A review" Biosource Technology 99 (2008) p. 6017-6027

Tamminen, T., Hortling, B., "Lignin reactions during oxygen delignification of various alkaline pulps", in: Fundamentals and catalysis of oxidative delignification processes, ed. D. Argyropoulos, ACS Symp. Ser. 785 (2001), Chapter 4, 73-91.

Tamminen, T., Alakurtti, S., von Weymarn, N., Repo, T., Lahtinen, P., Hakola, M., Riekkola, T., Leskela, M., Chemistry of catalysed oxygen delignification, Oral presentation in ISWPC, Oslo, Norway, June 2009.

Zakis, G.F., Functional analysis of lignins and yheir derivatives, TAPPI Press 1994.

Yang, D. Qiu, X., Zhou, M., Lou, FL, Properties of sodium lignosulfonate as dispersant of coal water slurry, Energy Conversion and Management 48 (2007), p. 2433-2438.