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Title:
PROCESSES FOR OBTAINING SUBSTANCES FROM BARK AND A COMPOSITION CONTAINING BARK FOR USE IN THE PROCESSES
Document Type and Number:
WIPO Patent Application WO/2020/263170
Kind Code:
A1
Abstract:
Processes for obtaining substances from bark, especially bark high in suberin and lignin, which substances can be used for preparing biofuels are disclosed. The processes use a solvent system for dissolving the substances, which system can be recycled in the process. The solvent system comprises a base selected from tertiary aliphatic amines A composition comprising bark and the solvent system, which can be used in the processes, is also disclosed.

Inventors:
SAMEC JOSEPH (SE)
KUMANIAEV IVAN (SE)
Application Number:
PCT/SE2020/050670
Publication Date:
December 30, 2020
Filing Date:
June 26, 2020
Export Citation:
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Assignee:
KAT2BIZ AB (SE)
International Classes:
C08H7/00; C08L97/00; C10G1/04
Domestic Patent References:
WO2007045728A12007-04-26
Other References:
IVAN KUMANIAEV ET AL: "Valorization of Quercus suber Bark toward Hydrocarbon Bio-Oil and 4-Ethylguaiacol", ACS SUSTAINABLE CHEMISTRY & ENGINEERING, vol. 6, no. 5, 30 March 2018 (2018-03-30), US, pages 5737 - 5742, XP055725044, ISSN: 2168-0485, DOI: 10.1021/acssuschemeng.8b00537
PINTO P C R O ET AL: "Quercus suber and Betula pendula outer barks as renewable sources of oleochemicals: A comparative study", INDUSTRIAL CROPS AND PRODUCTS, ELSEVIER, NL, vol. 29, no. 1, 1 January 2009 (2009-01-01), pages 126 - 132, XP025712758, ISSN: 0926-6690, [retrieved on 20080609], DOI: 10.1016/J.INDCROP.2008.04.015
KUMANIAEV, I.SUBBOTINA, E.SAVMARKER, J.LARHED, M.GALKIN, M. V.SAMEC, J. S. M.: "Lignin depolymerization to monophenolic compounds in a flow-through system", GREEN CHEM., vol. 19, 2017, pages 5767 - 5771
Attorney, Agent or Firm:
BRANN AB (SE)
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Claims:
Claims

1. A process for at least partly dissolving in a solvent system substances of bark, which bark contains a suberin component, and for at least partly depolymerising the suberin com- ponent, comprising the following steps: providing bark; providing a solvent system comprising water, and a base selected from tertiary aliphatic amines; treating the bark with the solvent system by subjecting the bark to the solvent system at a temperature of at least I QO'Ό, thereby obtaining a composition containing at least partly dis solved substances of bark, of which substances the suberin component is at least partly de- polymerised.

2. The process of claim 1 , wherein the tertiary aliphatic amine is a simple tertiary ali phatic amine, preferably a trialkylamine, more preferably an amine selected from the group constisting of triethylamine (Et3N), trimethylamine (Me3N), dimethylethylamine, and diethyl- methylamine, and most preferably triethylamine (Et3N).

3. The process of claim 1 or 2, wherein the bark is Quercus suber (oak) or Betula Pen- dula (birch) bark, preferably Betula Pendula bark.

4. The process according to any one of the previous claims, wherein the heating tem- perature is at least 180qC, and preferably up to 260 °C, more preferably at the most 220 °C, and most preferably in the range of 200 °C to 220 °C.

5. The process according to any one of the previous claims, wherein the heating is per formed for at least 0.3 hours, preferably for 1 to 3 hours, most preferably for 1.5 to 2.5 hours.

6. The process of any one of the previous claims, wherein the solvent system further comprises an alcohol, preferably a low boiling alcohol such as methanol, ethanol, or propa nol, or a mixture of low boiling alcohols, most preferably the alcohol is methanol.

7. The process of any one of the previous claims, wherein the solvent system com prises: water at a content of at least 40 % by volume; - triethylamine at a content of 4-20 % by volume, preferably 4-15 %, more preferably 7- 12 % by volume; and,

- methanol at a content of 40-50 % by volume of the total volume of the solvent system.

8. The process according to claim 6, wherein the ratio of Me0H:H20 in the solvent sys tem is from 2:1 to 1 :2 v/v.

9. The process according to any one of the previous claims, wherein the bark is in the form of finely divided bark, such as milled bark particles, preferably having a particle size of not more than 3 mm, preferably 1 mm or smaller.

10. The process according to any one of the previous claims, additionally comprising, af ter the treatment step, the following step of: recirculating, at least once, the composition obtained after the treatment step, back to the treatment step, for use as solvent system for the next portion of bark to be subjected to treat ment conditions in a next treatment step.

1 1 . The process of claim 10, wherein recirculation of the composition obtained after the treatment step us carried out until a total amount of bark has been added to the solvent sys tem corresponding to a lower limit of solvent to bark ratio of V » 7 L kg-1 has been reached in the composition.

12. The process according to anyone of the previous claims, additionally comprising, after the treatment step, the step of: subjecting the composition resulting from the treatment step to filtration so as to separate from the composition any solid bark residues.

13. The process according to claim 12, additionally comprising, after the filtration step, the step of: separating by evaporation the solvent system from the composition resulting from the treat ment step, and recirculating the separated solvent system for use in the treatment step.

14. A process for preparing a fuel, comprising the following steps: providing bark; providing a solvent system comprising water, an alcohol, and a base selected from tertiary aliphatic amines; treating the bark with the solvent system by subjecting the bark to the solvent system at a temperature of at least 160qC, thereby obtaining a composition containing at least partly dis solved substances of bark, of which substances the suberin component is at least partly de- polymerised; subjecting the composition resulting from the treatment step to filtration, so as to separate from the composition any solid bark residues; separating by evaporation the solvent system from the filtrate obtained in the filtration step, so as to obtain a product mixture; and, hydrotreating the product mixture, thereby obtaining a fuel. 15. The process of claim 14, comprising the additional step of: admixing the product mixture to be hydrotreated with, as a carrier liquid, a plant-derived oil, preferably tall oil fatty acid (TOFA) or rapeseed oil.

16. The process of claim 15, wherein the product mixture to be hydrotreated is sus pended in the carrier liquid. 17. The process according to any one of claims 14-16, wherein the hydrotreatment is per formed by hydrodeoxygenation.

18. A composition comprising a mixture of bark in a solvent system, the solvent system comprising:

- water at a content of at least 40 % by volume;

- triethylamine at a content of 4-20 % by volume; and

- methanol at a content of 40-50 % by volume, of the total volume of the solvent system.

19. The composition of claim 18, wherein the bark is in the form of finely divided bark, such as milled bark particles, said particles preferably having a particle size of not more than 3 mm.

20. The composition of claim 18 or 19, wherein a ratio V of solvent system to bark, in terms of volume of solvent system to weight of bark, is less than « 20 l/kg.

Description:
PROCESSES FOR OBTAINING SUBSTANCES FROM BARK AND A COMPOSITION CONTAINING BARK FOR USE IN THE PROCESSES

FIELD OF THE INVENTION

The present invention generally relates to processes for obtaining substances from bark, especially bark high in suberin and lignin, which substances can be used for preparing biofu els, and more particularly to such processes wherein a solvent system for dissolving the sub stances is used, which system can be recycled in the process. The invention also relates to a composition comprising bark and the solvent system, which can be used in the processes of the invention.

BACKGROUND OF THE INVENTION

Bark is an external tissue of plants. In the current technologies of biomass processing, such as Kraft pulping in paper industry, it is separated from trunks and treated as waste. Higher heating value of bark 21 -24 MJ-kg -1 justifies its burning for electricity production, un less more advanced procedures are developed.

Bark tissue consists of various biopolymers, tannins, lignin, suberin, suberan and poly saccharides. Up to 40% of the bark tissue is made of lignin. While lignin is very abundant in other tissues as well, suberin is a specific component of bark and serves as a protective bar rier of plant. Lignin is an aromatic polyether formed by oxidative coupling of sinapyl and co- niferyl alcohols. Suberin is a poorly functionalized aliphatic polyester composed of hydrox- ylated fatty acids. Lignin and suberin domains are highly crosslinked and form an insoluble rigid network.

In any process for conversion of bark into chemicals and/or fuels, these polymeric sub stances must be partially depolymerized and solubilized in order to make them accessible to chemical modification. Methods of lignin extraction have been widely studied for other types of biomass. In particular, the organosolv procedure has been developed with an intention to provide a more environmentally friendly technique as an alternative to traditional Kraft pulp ing. In this type of processes, the biomass is treated with organic solvents (MeOH, EtOH, di- oxane) mixed with water in presence of acids and other additives at 180-200 °C. To address the emerging issues of lignin repolymerization, so-called lignin-first methodologies have been developed. The extracted lignin is subjected to in situ catalytic transformations and forms sta ble products, i.e. intermediates are directly trapped. A common example of lignin-first ap proach is metal-catalyzed hydrogenolysis where lignin is reduced into stable phenolic mono- mers. In general, lignin-suberin complex is not depolymerized under typical organosolv extrac tion conditions and its cleavage requires alkaline treatment. The known procedures do not allow to recycle the solvent and thus make the process energetically inefficient. Moreover, the extracted bio-oil is contaminated with salts. There is thus a need for a solution where these drawbacks could be eliminated.

SUMMARY OF THE INVENTION

The present invention provides a solution that eliminates the drawbacks of the prior art that includes avoiding the use of metal catalyst and implementing a volatile base instead of alkaline salt.

The invention uses a solvent system comprising water, a base selected from tertiary ali phatic amines, and optionally a low boiling alcohol. The composition of the solvent system allows for recirculating the solvent system in the process. Moreover, the composition of the solvent system also allows for the solvent system to be evaporated in the process, e.g. for the purpose of separating the solvent system, for use in a second, and further cycles, of the process.

Accordingly, in a first aspect the invention relates to a process for at least partly dissolv ing in a solvent system substances of bark, which bark contains a suberin component, and for at least partly depolymerising the suberin component, comprising the following steps: providing bark; providing a solvent system comprising water, and a base selected from ter tiary aliphatic amines; treating the bark with the solvent system by subjecting the bark to the solvent system at a temperature of at least 160°C, thereby obtaining a composition contain ing at least partly dissolved substances of bark, of which substances the suberin component is at least partly depolymerised.

In a second aspect the invention relates to a process for preparing a fuel, which process, in addition to the above steps, also comprises the following additional steps: subjecting the composition resulting from the treatment step to filtration, so as to separate from the compo sition any solid bark residues; separating by evaporation the solvent system from the filtrate obtained in the filtration step, so as to obtain a product mixture; and, hydrotreating the prod uct mixture, thereby obtaining a fuel. In this aspect an alcohol is included in the solvent sys tem.

In preferred embodiments of the inventive processes, the solvent system is recycled back to the treatment step. The used solvent system can be recycled by evaporation of the used system from the composition, however it is preferred that the solvent system is not evaporated from the composition until bark has been added to the solvent system corresponding to a lower limit of solvent to bark ratio of V « 7 L kg -1 . Accordingly, in the in ventive processes, the composition is preferably recirculated back to the bark addition and treatment step until a total amount of bark has been added to the solvent system correspond ing to a ratio of solvent system to bark of V « 7 L kg -1 in the composition, at which point the solvent system is evaporated from the composition. Any solid bark residues in the composi tion is preferably separated by means of filtration from the composition before being recircu lated to the treatment step.

In a preferred embodiment of the inventive process for preparing a fuel, the product mix ture is mixed with, as a carrier liquid, a plant-derived oil, such as tall oil fatty acid (TOFA) or rapeseed oil. More preferably, the composition is a suspension of said mixture in TOFA.

Preferably, the hydrotreatment is performed by hydrodeoxygenation. In a preferred em bodiment the hydrotreatment produces C9-C27 hydrocarbons, preferably C15-C19 hydrocar bons. The hydrotreatment may suitably be carried out at a temperature within a range of 300- 400 °C, preferably 340-380 °C, and at a hydrogen pressure within a range of 40-100 bar, e.g about 50 bar. The duration of the hydrotreatment may e.g. be 1 -3 hours.

In a third aspect the invention relates to a preferred composition, which can be used in the inventive processes, which composition comprises a mixture of bark having a particle size of not more than 3 mm in a solvent system, the solvent system comprising: water at a content of at least 40 % by volume; triethylamine at a content of 4-20 % by volume; and, methanol at a content of 40-50 % by volume of the total volume of the solvent system.

In the inventive processes the substances of bark are at least partly dissolved in the sol vent system, and of which substances the suberin component of bark is at least partly depol- ymerised.

Primary and secondary aliphatic amines are not suitable for use in the invention, since these form amides when reacting with esters. Ammonium is not suitable either.

The tertiary aliphatic amine is preferably a simple tertiary aliphatic amine, more prefera bly a trialkylamine, such as triethylamine (Et 3 N), trimethylamine (Me 3 N), dimethylethylamine, or diethylmethylamine, and most preferably triethylamine (Et 3 N).

Preferably, the inventive solvent system further comprises an alcohol, preferably a low boiling alcohol such as methanol, ethanol, or propanol, or a mixture of low boiling alcohols, most preferably the alcohol is methanol. In further preferred embodiments of the inventive processes, the degree of solubilization of the bark in the solvent system is at least 65%, preferably at least 90% and more preferably 90-95%.

In yet further preferred embodiments of the inventive processes, the composition ob tained after the treatment step comprises a variety of oligomeric products of suberin and lig nin, each molecule being composed of 4-10 monomeric units of lignin and/or suberin, and the whole mixture having the number-average molecular weight 900 Da and the weight-aver age molecular weight 2600 Da, according to SEC data.

Upon further treatment in alkaline conditions the bark containing composition affords a mixture of fatty acids having a chain length of 18-22 carbons, the fatty acids being saturated or unsaturated, and optionally substituted by at least one hydroxy group. Preferably the mix ture of fatty acids includes at least two of 18-hydroxyoctadec-9-enoic acid, 1 ,18-octadec-9- enedioic acid, 1 ,18-octadecanedioic acid, 20-hydroxyeicosanoic acid, 1 ,20-eicosanedioic acid, 1 ,22-docosanedioic acid, 9,10-dihydroxyoctadecane-1 ,18-dioic acid, and 22-hy- droxydocosanoic acid.

The inventive solvent system used preferably comprises from 4-20 % by volume of the amine, more preferably 4-15 %, even more preferably 7-12 % by volume, and most prefera bly no more than 10% by volume of the amine.

The solvent system used according to the invention preferably comprises a low boiling alcohol. When present, the low boiling alcohol is preferably in an amount of up to 60% by vol ume, more preferably up to 50%. Preferably the alcohol is included in an amount of at least 40% by volume of the solvent system.

It is preferred that the solvent system comprises at least 40 % by volume of water.

Preferably, the combined amounts of amine, water, and, when present, alcohol, consti tute 100 % by volume of the solvent system.

In a preferred embodiment the inventive solvent system comprises:

- water at a content of at least 40 % by volume;

- triethylamine at a content of 4-20 % by volume, preferably 4-15 %, more preferably 7- 12 % by volume; and

- methanol at a content of 0-50 % by volume, preferably 40-50 % by volume of the total volume of the solvent system. The bark used in the invention is preferably bark having a high content of suberin and lignin, such as Quercus Suber (oak) or Betula Pendula (birch) bark, preferably Betula Pen- dula bark.

In the inventive processes, the treatment temperature is preferably at least 180 q C, and preferably up to 260 °C, such as within a range of 200-240 °C, more preferably within a range of 200-230 °C, preferably at the most 220 °C, and most preferably in the range of 200 °C to 220 °C.

In the inventive processes, the heating is preferably performed for at least 0.3 hours, preferably for 1 to 3 hours, and most preferably for 1 .5 to 2.5 hours.

The ratio of MeOH:H 2 0 in the solvent system is preferably from 2:1 to 1 :2 by volume, such as 1 :1 by volume.

According to the invention, the bark is preferably in the form of finely divided particles, such as milled bark particles, preferably having a particle size of not more than 3 mm, more preferably around 1 mm or smaller. Preferably, the bark is a bark having a high content of su berin and lignin, such as Quercus Suber or birch bark, preferably birch bark. It is also prefer able that the composition obtained as a result of the depolymerization reaction performed on the finely divided bark, for depolymerizing the suberin component of bark at least partly, in the process is subjected to filtration and any solid bark residues are separated and dis carded. Preferably, the filtrate obtained by the filtration is recycled at least once and used as solvent system for the next portion of bark to be subjected to depolymerisation conditions for at least partly depolymerising the suberin component in the bark.

Preferably, the solvent system, after completion of the depolymerisation treatment of the bark for depolymerising at least partly the suberin component in the bark, is separated from the resulting reaction mixture by evaporation and recycled for use as solvent system for new portions of bark to be subjected to depolymerisation treatment for depolymerising at least partly the suberin component.

The inventors of the present invention have surprisingly found that by using the solvent system of the invention, it is possible to provide a salt- and metal-free solvent system that is recyclable and affords to solubilize bark, such as e.g. bark of birch (Betula Pendula) to a very high degree (for birch bark 94% (91 % of wax-free bark)). This clearly solves the problems of the prior art solutions. DETAILED DESCRIPTION OF THE INVENTION

In the following, the present invention is explained in more detail, by way of example only, and should not be construed as limiting the scope of protection sought in the appended claims. In this detailed description it is referred to the following figures, wherein:

Figure 1 depicts a reaction scheme describing the process steps of preparing biofuel from bark;

Figure 2 is a diagram showing the influence of time, temperature, and content of water and triethylamine on bark solubilization;

Figure 3A is a diagram showing the results of HSQC NMR analysis of bark-derived gum;

Figure 3B is a diagram showing the results of GC-MS analysis of methanolysated bark- derived gum;

Figure 4A is a diagram showing the results of a simulated distillation of the bio-oils ob tained by the process of the invention; and,

Figure 4B is a diagram showing the 2D GC analysis of the distribution of obtained bio-oil components by carbon atom number.

The present inventors have developed a two-stage process and system for bark conver sion into biofuel. According to a preferred embodiment the bark is birch bark. First, in a pre ferred embodiment, milled birch bark is treated with Me0H-H 2 0-Et 3 N solvent system in a re actor or the like. The obtained mixture, containing bark solubilized in the solvent system and solid bark residue is filtered. The filtrate may be returned into the same reactor and thus play the role of the next portion of solvent system. The solid bark residue obtained in the filtration is discarded. The filtrate consists mainly of gum, comprising at least partly depolymerized su- berin and other substances of bark (“depolymerized bark”) dissolved in the solvent system.

After several runs of using the gum solution solubilized in the solvent system as solvent for new portions of milled bark, the solvent system Me0H-H 2 0-Et 3 N is recycled by evapora tion and returned to be used again as a pure solvent system consisting of MeOH, H 2 0 and Et N. As a result of the evaporation a semi-solid gum is obtained. This semi-solid gum is sub jected to hydrotreatment by hydrodeoxygenation, for example in the presence of a suitable hydrodeoxygenation catalyst, such as Pt/Ti0 2 /Mo , and H 2 gas or HCOOH. This second stage of the process leads to a reaction mixture comprising a variety of different hydrocarbon oils in the diesel-range that may be separated from each other through distillation. The reac tion mixture resulting upon hydrotreatment is then distilled in order to obtain different hydro carbons boiling at different temperatures. The inventors of the present invention found that certain amines work surprisingly well in the invention. Ammonia, primary and secondary amines cannot be used because they form amides when reacting with esters.

For the purpose described herein, the simple tertiary aliphatic amine Et 3 N (pKa 10.7) was found to be a surprisingly good choice as a component of the solvent system. In the presence of Et 3 N in organosolv pulping conditions, suberin was found to undergo alkaline hy drolysis (cf. Fig. 1 A). After the solubilization of the substances of bark in the solvent system has been accomplished, Et 3 N can be easily removed by distillation (bp dq'Ό) together with other components of the solvent system.

Mixtures of alcohols with water are suitable for the extraction of nonpolar components of biomass, such as lignin and suberin. Mixtures are more efficient than alcohol or water alone. MeOH can be recycled easier than any other alcohol due to its low boiling point (65°C).

Optimization of the 1st stage

Solubilization of the bark with the Me0H-H 2 0-Et 3 N solvent system was optimized with regard to minimization of the mass of solid bark residue. The degrees of solubilization (%) are reported in relation to the mass of extractive-free bark (content of EtOH-extractives plus moisture is 29%). As a starting point, we treated the bark with MeOH-H 2 0 (1 :1 v/v or 46 vol.% H 2 0) at 220 °C for 1 h in absence of Et 3 N, in which conditions only 27% were solubil ized (Fig. 2). Addition of 4 vol.% of Et 3 N improved the result toward 69%. Increase of Et 3 N concentration to 7 vol.% led to 91 % solubilization. Further increase (12 vol.%) caused a de cline of the solubilization degree (73%).

Using the optimized Et 3 N concentration (7 vol.%), we explored the role of water as com ponent of the solvent system. If no water was added (i.e., Et 3 N-MeOFI mixture was used as the solvent system), the solubilization degree was lower than in case of MeOFI-FI 2 0 1 :1 v/v, but still significant (70%). Addition of 30 vol.% of water did not affect this result (72%). When water became the major component with concentration of 60 vol.%, the degree of solubiliza tion hits the maximum (93%). A FI 2 0-Et 3 N solvent system without MeOFI led to a small de cline of the result (89%) and was more difficult to handle during filtration. Therefore, if the content of water is higher than 46 vol.% its change does not affect the process. We decided to use 46 vol.% of water because presence of MeOFI makes recycling of the solvent system as well as other operations such as filtration easier.

We also investigated the effect of temperature. When the process was carried out for 1 h with the optimized solvent system (MeOFI-FI 2 0 1 :1 ,7 vol.% Et 3 N) at I QO'Ό, very poor solubilization was observed (13%). Increase of the temperature afforded better results: from 45% at 180°C to 54% at 200°C and, finally, 91% at 220°C.

Solvent system recycling (evaporation)

The solvent system was recycled 3 times by distillation in vacuum. The recycling and bark solubilization data are presented in Table 1 below. Composition of the solvent system after each recycling step was determined by NMR in acetone-d 6 . It was observed that con centration of Et 3 N slightly decreases at each step, therefore it makes sense to start with higher concentrations of Et 3 N (-10%) when optimizing the process for industry. The recycled solvent was used for solubilization of new samples of bark. The data were in accordance with the obtained during optimization.

Table 1. Recycling of the solvent system by evaporation

Solvent system recycling (no evaporation)

Due to the low density of bark packing in a reactor (150 kg rrr 3 ), the lower limit of solvent system to bark ratio is V « 7 L kg -1 . It was found that until that point, for V = 20, 15, 10 and 7 L kg -1 , solubilization degree does not depend on this parameter, coming to 91 , 92, 91 and 90%, respectively. Handling is more convenient with larger ratio V. However, evaporation of solvent system demands a sufficient amount of energy, -1.7 MJ per liter of the solvent sys tem. Therefore, and also because solvent system recycling by evaporation causes a slight decline of the yield (cf. Table 1 ), it would be beneficial to decrease V by using the solvent system several times before evaporation, i.e. using the solution for processing each portion of bark like in a looped flow system. Indeed, the presence of bark components in the solution did not affect its ability to solubilize new portions of bark: in three consecutive experiments with V = 10 L-kg -1 , degrees of solubilization came to 91%, 90%, 90%. Thus, the efficient sol- vent system to bark ratio was reduced to 3.3 L-kg -1 . It must be noticed that filtration slows down significantly with each time as the solution becomes more concentrated and viscous, and it might lead to problems when putting the process on industrial scale. Analysis of gum

The gum obtained by“bark depolymerization” (i.e. bark wherein suberin component of bark has been at least partly depolymerized) contains a variety of oligomeric products of su berin and lignin cleavage. M w = 2630 Da, M N = 932 Da (PD = 2.8), according to SEC data, i.e. an average dissolved molecule is composed of 4-5 monomeric units of lignin and/or su berin. Elemental composition of the material differs insignificantly from the composition of bark, however 1-2% of residual nitrogen is present. The material is insoluble in hexane, moderately soluble in toluene (28% of the gum weight) and well soluble in methanol (87% of the gum weight).

Noteworthy, the gum forms a suspension in tall oil fatty acid (TOFA) at 120 °C which re mains practically stable at room temperature, therefore TOFA can be used as a carrier liquid in an industrial process of the gum hydrotreatment. Viscosity of the suspension at room tem perature is 15-500 mPa-s for the concentration range 7-33 wt.% and temperature range 25- 70 °C.

HSQC NMR (cf. Fig. 3A) demonstrated presence of typical structural motifs of suberin.

In order to analyze monomeric fatty acids, the gum was subjected to alkaline methanolysis, and the extract was studied by means of GC (Fig. 3B). A variety of C16-C22 hydroxylated car boxylic acids and diacids was identified, with the main components being 22-hydroxydocosa- noic (26% TIC as silylated derivatives) and 1 ,18-octadec-9-enedioic (14%) acids. In addition, ferulic acid (3%) was detected.

Hydrodeoxygenation. Simdis and 2D GC

The gum was subjected to hydrodeoxygenation in the presence of Pt/Mo0 /TiC> 2 catalyst at 360 °C. Simulated distillation study of the obtained bio-oil showed that it contains hydrocar bons within the diesel range. The lightest components have boiling points of 70 °C and 90% of the mixture boils away before 350 °C (Fig. 4A).

2D GC technique allowed to study different types of components of the mixture (Fig.

4B). The most abundant molecules are C15-C19 hydrocarbons. In the natural suberin, only fatty acids with even carbon atom numbers are present. Therefore, hydrocarbons with une ven chain length emerge due to cracking and/or decarboxylation processes. Higher aromatic compounds such as naphthalenes (20 wt.%) are probably also the products of cracking since their carbon atom numbers are generally lower than the ones of other observed hydrocar bons (average 14.4 versus 16.8 for the whole mixture). Unsaturated and monounsaturated hydrocarbons account for up to 73 wt.%, however, due to the presence of aromatic compounds the average number of double bonds and/or cycles per molecule for the whole mixture is 2.4 and H/C ratio is 1.83.

Yield of the obtained bio-oil is 40% of initial bark weight (56% of extractive-free bark). Carbon content in the bio-oil is 86%, as calculated through 2D GC data, and the carbon yield (the ratio of carbon which has been transferred from bark to the product) is 62%. Various types of bio-oil components and their content are presented in Table 2.

Table 2. Various types of bio-oil components and their content

Experiment 1

1. Analysis of the bark feedstock The bark of birch (Betula Pendula) was analysed.

1.1 . Extractives & moisture

A sample of bark was extracted with EtOH in Soxhlet extractor for 12 h and then dried in air at 50 °C for 12 h. Weight loss: 29% of bark weight. Mass of the EtOH-solubilized material: 26% of bark weight. 1.2. Suberin

Extractive-free bark sample (0.347 g) was treated with 3% MeONa solution in MeOH (25 ml.) under reflux for 2 h. The solution was centrifugated and the residue was washed with MeOH and water. Centrifugation and washing were repeated until the pH became neutral. Solid residue was dried (0.131 g, 38% of extractive-free bark, 27% of total). Solution was acidified to pH 3 with H2SO4 and extracted with DCM (3 x 10 ml_). The organic fraction was dried, filtered and concentrated to afford suberin oil (0.160 g, 46% of extractive-free bark, 33% of total). 1.3. Lignin

The solid residue which remained after alkaline methanolysis (extractive-free desuber- ized bark) was dried in air at 70 °C for 12 h. A sample (91 mg) was treated with 72% aque ous H 2 S0 4 (1 mL) at 30 °C for 1 h. Then the mixture was diluted with water (30 mL) and re- fluxed for 3 h. After cooling to rt, the mixture was filtered through paper filter. The filter was washed with water until a neutral pH was reached, and the residue was dried in air at 70 °C for 12 h to afford acid-insoluble lignin (51 mg, 21% of extractive-free bark, 15% of total).

1.4. Lignin S/G ratio

A sample of untreated bark (50 mg) was placed into a stainless-steel reactor together with 3% aqueous KOH (3 mL) and nitrobenzene (0.1 mL). The reactor was heated with stir ring at 170°C for 1 h. After cooling, the mixture was acidified with HCI to pH 1 and extracted with DCM (3x5 mL). Combined organic fraction was dried with Na 2 S0 4 , diluted with Et 2 0 and subjected to GC-MS. Method: Syringol and guaiacol units were detected as syringaldehyde and vanillin. Though the reproducibility of the method is low, syringol to guaiacol ratio was determined to be 2.2-2.7 based on three runs.

1.5. Carbohydrates

Analysis for carbohydrates was carried out according to previously published procedure; Kumaniaev, I.; Subbotina, E.; Savmarker, J.; Larhed, M.; Galkin, M. V.; Samec, J. S. M. Lig nin depolymerization to monophenolic compounds in a flow-through system. Green Chem. 2017, 19, 5767-5771. No carbohydrates were detected.

The results of the analysis of composition of the birch bark feedstock used are presented in Table 3 below.

Table 3. Composition of birch bark feedstock

1.6. Elemental analysis

The direct elemental analysis by combustion was performed on the birch bark feed stock. The following results were obtained: C, 70.1%; H, 9.2%; N, 0.3%; O, 19.5%. 2. Solubilization of bark (stage 1 )

2.1 . Experimental procedure

Grinded birch bark (~1 mm particle size, 0.30 g) was placed into a stainless-steel reactor (internal volume 7 ml.) together with a mixture of triethylamine (0.35 ml_), methanol (2.32 ml.) and water (2.33 ml.) and a magnetic stirring bar. The reactor was heated at 220 °C in an oil bath for 2 hours with 800 rpm stirring. After cooling, the mixture was filtered through paper filter. The solid residue was dried at 60°C for 12 hours and weighted (0.02 g, 6% of initial bark weight). The filtrate was distilled to recover the solvent system. The residual brown gum was dried in air at 60°C or 130°C for 12 hours (0.28 g, 94% of initial bark weight) and sub- jected to analyses.

2.2. Optimization

The procedure was optimized with regard to minimization of weight of the solid residue. Each experiment was repeated at least twice to address possible issues of samples’ hetero geneity. The experimental data of these experiments are presented in Table 4 below. For graphical representation of the results, see Fig. 2.

Table 4. Bark solubilization in Me0H-H 2 0-Et 3 N

2.3. NMR spectroscopy

0.1 g of the gum was suspended in 0.6 ml. of CDCI at 60°C, the mixture was cooled to room temperature without filtration and subjected to NMR analysis. The spectra were rec orded with a Bruker 400 (400 MHz) spectrometer as solutions in CDCI3. Chemical shifts are expressed in parts per million (ppm, d) and are referenced to CHCI3 (d = 7.26 ppm) as an in ternal standard. 13 C NMR spectra were recorded as solutions in CDCI3 with complete proton decoupling. Chemical shifts are expressed in parts per million (ppm, d) and are referenced to CDCI3 (d = 77.0 ppm) as an internal standard. 2D-NMR spectra were acquired on an Agilent 400-MR spectrometer. The standard Agilent implementations of gHSQCAD experiments were used. The results of the NMR spectroscopy analysis are presented in Fig. 3A.

2.4. Size exclusion chromatography

Size exclusion chromatography (SEC) was performed using a YL 91 10 HPLC-GPC sys tem with three Styragel columns (HR 0.5, HR 1 , and HR 3, 7.8x300 mm each) connected in series (flow rate: 1 mL-min -1 ; injection volume: 50 pl_; THF), a UV detector (254 nm), and an auto-sampler. The system was calibrated using ReadyCal-Kit poly(styrene) (M P 266, 682, 1250, 2280, 3470, 4920, 9130, 15700, 21500, 28000, 44200, 66000 Da). Samples were dis solved in THF to a concentration of 0.5 g-L _1 .

The detected oligomers possess the following properties:

• Molecular weight of the most abundant species M P = 1584 Da

· Number average molecular weight M N = 932 Da

• Weight average molecular weight Mw = 2630 Da

• Polydispersity index PD = M W /M N = 2.82 Table 5. Solubility of the bark gum in various solvents (ca. 0.05 g in 1 ml.)

2.5. Elemental analysis Gum dried at 60°C in air: C, 66.7%; H, 10.2%; N, 2.1%; O, 21 .4%.

Gum dried at 130°C in air: C, 71.4%; H, 9.9%; N, 1 .1%; O, 17.2%. 2.6. Tests for solubility of the gum

Solubility of the gum in various organic solvents was measured as follows. The gum (0.05 g) was treated with a solvent (1 ml.) at 60-70°C for 30 min, the solution was cooled 20°C and filtered through a 0.2 pm syringe filter. Mass of the filtrate was measured. Then the filtrate was concentrated in vacuum and the residue dried in air at 60°C for 12 hours. Mass of the residue was measured. The results of the tests on solubility of the bark gum in various solvents are presented in Table 5 below.

2.7. Suspension of the gum in tall oil

Tall oil is a naturally occurring liquid mixture of fatty acids and rosins which has been demonstrated to be useful carrier liquid for hydrotreatment of biomass derivatives. For this purpose, viscosity of the mixture is crucial. The gum forms a suspension in tall oil fatty acids mixture (TOFA) at 120°C which remains practically stable at room temperature. Viscosity of the suspension was measured with Anton Paar Rheolab QC rotational rheometer with a CC10 sensor (stirring rates 50 to 1400 s -1 ). The viscosity data of the gum suspension in TOFA at different temperatures and concentrations is given in Table 6.

Table 6. Viscosity of the gum suspension in TOFA at different temperatures and concentra tions (mPa-s)

2.8. 1 D GC-MS of the gum methanolysate

1 D GC was used for analysis of monomeric composition of the gum. A sample of the gum (0.1 g) was refluxed with 3% KOH/MeOH (5 ml.) for 1 h. The mixture was acidified with HCI, diluted with water and extracted with CHCI (3 x 10 ml_). Combined organic phases were dried with Na S0 , filtered and concentrated. A sample of the residue (10-20 mg) was dissolved in THF (1 ml.) and silylated with bis(trimethylsilyl)acetamide (50 mI_) in the pres ence of pyridine (50 mI_). The solution was subjected to GC. GC measurements were per- formed on a Shimadzu Shimadzu GC-MS-QP2020 equipped with a HP-5 MS capillary col umn (30 m x 0.25 mm c 0.25 pm) and an MS detector. Compounds were identified by com paring the observed fragmentation patterns to literature data. MS spectra of each identified derivative are given in Fig. 3B. Conclusions from Experiment 1

The inventors of the present invention have thus surprisingly found and shown in Exam ple 1 that Me0H-H 2 0-Et 3 N (46 / 47 / 7% v/v) forms a salt- and metal-free solvent system that is recyclable and affords to solubilize bark of birch (Betula Pendula) to the degree of 94% (91 % of wax-free bark). The obtained gum is composed of organosolv lignin and su- berin oligomers and was characterized with HSQC NMR, elemental analysis, gas chromatog raphy, and size exclusion chromatography. Hydrotreatment of the gum affords a hydrocarbon oil of diesel range (40% yield, bp 271 °C, H/C = 1 .83, theoretical higher heating value 45-48 MJ-kg -1 ) which was studied by means of simulated distillation and 2D GC.

Itemized listing of examples of aspects and embodiments of the invention

Item 1 : A composition comprising bark and a solvent system, wherein the substances of bark are at least partly dissolved in the solvent system, and of which substances the suberin component of bark is at least partly depolymerised, and wherein the solvent system com prises water, and a base in the form of an amine.

Item 2: The composition of iteml , wherein the aliphatic amine is a tertiary aliphatic amine.

Item 3: The composition of item 2, wherein the tertiary aliphatic amine is a simple tertiary aliphatic amine, preferably triethylamine (Et 3 N), trimethylamine (Me 3 N), dimethyl ethyl amine, diethyl methyl amine, most preferably triethylamine (Et 3 N).

Item 4: The composition of any one of items 1 -3, wherein the solvent system further comprises an alcohol, preferably a low boiling alcohol such as methanol, ethanol, or propa nol, or a mixture of low boiling alcohols, most preferably the alcohol is methanol.

Item 5: The composition of any one of items 1 -4, wherein the degree of solubilization of the bark in the solvent system is at least 65%, preferably at least 90% and more preferably 90-95%.

Item 6: The composition of any one of items 1 -5, comprising a variety of oligomeric prod ucts of the suberin and/or lignin, each molecule being composed of 4-10 monomeric units of lignin and/or suberin, and the whole mixture having the number-average molecular weight 900 Da and the weight-average molecular weight 2600 Da, according to SEC data.

Item 7: The composition of any one of items 1 -6, wherein the bark after further treatment in alkaline conditions affords a mixture of fatty acids having a chain length of 18-22 carbons, the fatty acids being saturated or unsaturated, and optionally substituted by at least one hy droxy group. Item 8: The composition of any one of items 1 -7, wherein the mixture of fatty acids in cludes at least two of 18-hydroxyoctadec-9-enoic acid, 1 ,18-octadec-9-enedioic acid, 1 ,18- octadecanedioic acid, 20-hydroxyeicosanoic acid, 1 ,20-eicosanedioic acid, 1 ,22-docosanedi- oic acid, 9,10-dihydroxyoctadecane-1 ,18-dioic acid, and 22-hydroxydocosanoic acid.

Item 9: The composition of any one of items 1 -8, wherein the bark is bark having a high content of suberin and lignin, such as Quercus suber (oak) or Betula Pendula (birch) bark, preferably Betula Pendula bark.

Item 10: A process for preparing a composition of any one of items 1 -8, comprising treat ing finely divided bark with the solvent system as defined in any one of items 1 -9 in order to at least partly depolymerise the suberin component of bark.

Item 1 1 : The process of item 10, wherein the treatment with the solvent system is per formed at a temperature of at least 160 °C to obtain bark dissolved in the solvent system.

Item 12: The process of any one of items 10 and 1 1 , wherein the treatment temperature is at least 180°C, preferably at the most 220 °C, and most preferably in the range of 200 °C to 220 °C.

Item 13: The process of any one of items 10 to 12, wherein the heating is performed for at least 0.3 hours, preferably for 1 to 3 hours, most preferably for 1.5 to 2.5 hours.

Item 14: The process of any one of items 10 to 13, wherein the ratio of MeOH:H 2 0 in the solvent system is from 2:1 to 1 :2 v/v.

Item 15: The process of any one of items 10 to 14, wherein the bark is in the form of finely divided particles, preferably milled bark particles preferably having a particle size of not more than 3 mm, preferably 1 mm or smaller.

Item 16: The process of any one of items 10 to 15, wherein the bark is bark having a high content of suberin and lignin, such as Quercus suber or birch bark, preferably birch bark.

Item 17: The process of any one of items 10 to 16, wherein the composition obtained as a result of the depolymerisation reaction performed on the finely divided bark in the process is subjected to filtration and any solid bark residues are separated and discarded.

Item 18: The process of any one of items 10 to 17, wherein the filtrate obtained by the filtration is recycled at least once and used as solvent for the next portion of bark to be sub jected to depolymerisation conditions for at least partly depolymerising the suberin compo nent in the bark. Item 19: The process of any one of items 10 to 18, wherein the solvent system after completion of the depolymerisation treatment of the bark for depolymerising at least partly the suberin component in the finely divided bark is separated from the resulting reaction mix ture by evaporation and recycled for use as solvent system for new portions of finely divided bark to be subjected to depolymerisation treatment for depolymerising at least partly the su berin component.

Item 20: A mixture comprising a variety of oligomeric products of suberin and lignin, each molecule being composed of 4-10 monomeric units of lignin and/or suberin.

Item 21 : The mixture according to item 20 comprising fatty acids having a chain length of 18-22 carbons, the fatty acids being saturated or unsaturated, and optionally substituted by at least one hydroxy group.

Item 22: The mixture according to item 21 , the mixture of fatty acids including at least two of 18-hydroxyoctadec-9-enoic acid, 1 ,18-octadec-9-enedioic acid, 1 ,18-octadecanedioic acid, 20-hydroxyeicosanoic acid, 1 ,20-eicosanedioic acid, 1 ,22-docosanedioic acid, 9,10-di- hydroxyoctadecane-1 ,18-dioic acid, and 22-hydroxydocosanoic acid.

Item 23: A composition suitable for preparation of fuel, comprising a mixture according to anyone of items 20-22 and a carrier liquid suitable for use in fuel preparation.

Item 24: The composition according to item 23, wherein the carrier liquid is a plant-de rived oil, such as tall oil fatty acid (TOFA) or rapeseed oil.

Item 25: The composition according to item 24, wherein the composition is a suspension of said mixture in TOFA.

Item 26: A process for preparing fuel, comprising a step of hydrotreating the mixture of anyone of the items 20-22 or the composition of anyone of the items 23-25.

Item 27: The process according to item 26, wherein the hydrotreatment is performed by hydrodeoxygenation.

Item 28: The process according to item 26 or 27, wherein the hydrotreatment produces C9-C27 hydrocarbons, preferably C15-C19 hydrocarbons.

Item 29: The process according to any one of items 26 to 28, wherein the process prior to the hydrotreatment step incorporates the steps of the process according to anyone of the items 10-19.

Item 30: A biofuel obtainable by the process of anyone of the items 26 to 29.