TECHNICAL FIELD

[001] The present invention relates to a process for preparing a lignin ester, processes for forming lignin oil and lignin oil compositions comprising the lignin ester, lignin oil and lignin oil compositions and use thereof.

BACKGROUND ART

[002] Lignin can be extracted in large scale from black liquor from a Kraft pulping process. This is enabled by precipitation of lignin in solid form instead of incineration of the black liquor in the soda boiler for energy generation. This procedure has enabled for a large supply of lignin as a raw material. The potentially large supply of lignin has led to an increased interest in research for value addition of lignin.

[003] Lignin could to some extent replace fossil oil-based plastics. However, lignin needs to be modified or blended with other materials such as plasticizers to achieve acceptable mechanical properties. Modified lignin is currently used as a base for injection molded or extruded material.

[004] WO2017048424 shows a lignin composition suitable for processing in a refinery to make fuel. In the process for making the composition, an aqueous lignin composition comprising lignin, cooking chemicals, water and an added carrier liquid is provided. Water is removed from the composition. The lignin composition is processed to make the lignin more soluble in the carrier liquid in order to transfer more of the lignin to the organic phase.

[005] Coating experiments have been carried out with a mixture of lignin and starch that indicate the possibility of coating with lignin. Although these attempts have shown the possibility of applying lignin on a pilot scale, the barrier properties have been mediocre. Successful experiments with derivatized lignin have been made, but the process to modify the lignin requires both expensive and toxic chemicals.

SUMMARY OF THE INVENTION

[006] It is an object of the present disclosure to provide a process for preparing lignin ester from lignin material. Further objects are to provide processes for preparing lignin oil and lignin oil compositions from the lignin ester, and uses of such lignin oil and lignin oil compositions. [007] According to a first aspect, there is provided a process for preparing a lignin ester, the process comprising: providing a lignin material, and mixing the lignin material with an esterification reagent in a molar ratio of 1 :0.1 to 1 :20, without a carrier liquid or solvent, wherein the esterification reagent is a straight chained or branched chained, aliphatic or aromatic, C2-C18 acyl chloride, C4-C36 acyl anhydride, C2-C18 acyl acid or any combination thereof. The mixture is allowed to react, whereby a product comprising lignin ester is formed, water is added to the mixture to stop the esterification reaction, the formed product comprising lignin ester is washed in an alkaline solution, thereby changing esterification by-product being corresponding acid from the esterification reagent into its salt form, and the formed product comprising lignin ester is washed with water.

[008] The lignin used may be obtained directly from a Kraft pulping process after separating the lignin from black liquor, optionally after washing and drying the lignin material.

[009] Lignin is a family name of polymeric components in different types of biomass and these polymeric components are possible to separate from different processes operating on biomass. Hence, the lignin family comprises both natural polymers and modified natural polymers.

[0010] Lignin is an amorphous polyphenolic material created through the enzymatic polymerisation of coniferyl-, sinapyl- and p-coumaryl-alcohols in lignocellulosic materials such as wood. The lignin for use in the present invention may be obtained from any lignocellulosic source material. These include wood, annual crops and agricultural waste. Suitable woods may include softwoods and hardwoods. The softwood tree species can be for example, but are not limited to: spruce, pine, fir, larch, cedar, and hemlock. Examples of hardwood species from which lignin suitable as a starting material in the present invention may be derived include, but are not limited to: birch, oak, poplar, beech, eucalyptus, acacia, maple, alder, aspen, gum trees and gmelina. The raw material for lignin production may comprise a mixture of different softwoods, e.g. pine and spruce. The raw material may also comprise a non-wood raw material, such as bamboo, sugar beet pulp, wheat straw, soy hulls, corn stover, sugarcane bagasse and grasses such as switchgrass and elephant grass.

[0011] Since the lignin can be produced from various green resources, such as wood, agricultural residues and annual crops, it is thus abundant, renewable and biodegradable. [0012] The lignin may be isolated as a by-product of a pulping process for the manufacture of paper or board. Common pulping processes are the kraft (sulphate) process, soda process and organosolv processes that may utilize a variety of solvents including but not limited to ethanol, methanol, butanol, ethylene glycol, acetic acid, formic acid, acetone and mixtures thereof. The lignin may be obtained from a LignoBoost process whereby high-quality lignin is obtained by at least partially neutralising kraft black liquor using carbon dioxide in order to precipitate the lignin. The LignoBoost process is further described in: Tomani, Per; The LignoBoost Process; Cellulose Chem Technol., 44(1-3), 53-58 (2010).

[0013] The lignin may be isolated as a by-product of cellulosic ethanol production. When fermenting a lignocellulosic biomass feedstock to produce ethanol, typically 15 to 30 percent of the biomass remains unconverted after fermentation. This residual biomass comprises primarily lignin. [0014] The lignin used here may be non-derivatised lignin. By non-derivatised lignin it is meant lignin that is not subject to any extensive derivatisation either during isolation or through postisolation modification. Non-derivatised lignins may be subject to some degree of hydrolysis or oxidation during isolation, depending on the process used for isolating the lignin, but this is an unintentional consequence of the isolation process and the primary lignin structure remains substantially intact and unmodified. For example, lignins isolated by the kraft and soda pulping processes are considered to be non-derivatised. Lignosulfonates isolated as a by-product of the sulphite pulping process are not considered to be a non-derivatised due to the abundance of sulfonate groups formed on the lignin primary structure. Organosolv lignins may or may not be considered non-derivatised depending on the extent of derivatisation (e.g. acetylation) occurring during isolation.

[0015] The lignins used may be fractionated by any means known in the art, e.g. ultrafiltration or precipitation, in order to provide a purer lignin or a lignin with reduced dispersity.

[0016] The lignin material may be provided in pulverized form for use in the process.

[0017] Mixing of lignin and the esterification reagent: C2-C18 acyl chloride, C4-C36 acyl anhydride, C2-C18 acyl acid, or any combination thereof, in a molar ratio of 1 :0.1- to 1:20, optionally in the presence of a catalyst, forms, apart from the lignin ester, a by-product being remaining esterification reagent and the conjugated base of the esterification reagent (such as hexanoate if hexanoic anhydride is used as the esterification agent) and C2-C18 acyl acid as by-product.

[0018] The lignin material is mixed with an esterification reagent in a molar ratio of 1 :0.1 to 1 :20 (lignin:esterification reagent) without a carrier liquid or solvent, wherein the molar ratio is based on the hydroxyl group content of the lignin.

[0019] Carrier liquid is here meant a liquid used to assist the esterification reagent for improved mixing or reaction. With solvent is here meant a liquid used to assist lignin dissolution.

[0020] The reaction is an acylation and the esterification reagent is added to the lignin material.

[0021] The lignin material used in the process may originate from different types of processes and different types of raw material. The lignin may be of any type and any purity, including any moisture content.

[0022] The C2-C18 acyl chloride, C4-C36 acyl anhydride or C2-C18 acyl acid used in the esterification may have a straight chain structure. Difference in chain length gives different properties (a longer alkyl chain would give a “softer less viscous product).

[0023] The acyl chloride used may be a C2-C4 acyl chloride, a C4-C6 acyl chloride, a C6-C8 acyl chloride, a C8-C10 acyl chloride, a C10-C12 acyl chloride, a C12-C14 acyl chloride, a C14-C16 acyl chloride, a C16-C18 acyl chloride, a C2-C12 acyl chloride, a C4-C10 acyl chloride, a C5-C8 acyl chloride, a C4 acyl chloride, a C5 acyl chloride, a C6 acyl chloride, a C7 acyl chloride, a C8 acyl chloride, a C9 acyl chloride, or a C10 acyl chloride.

[0024] Some straight chain alkyl C2-C18 acyl chlorides used as the esterification reagent may be: acetyl chloride (C2H3CIO), propionyl chloride (C4H5CIO), butanoyl chloride (C4H7CIO), pentanoyl chloride (C5H9CIO), hexanoyl chloride (CeHuCIO), heptanoyl chloride (C7H13CIO), octanoyl chloride (CsHisCIO), nonanoyl chloride (C9H17CIO) and decanoyl chloride (C10H19CIO).

[0025] If the esterification reagent is one of the mentioned C2-C18 acyl chlorides, the use of a catalyst may not be necessary, as the esterification process is fast without any catalyst addition.

[0026] The C4-C36 acyl anhydride used as the esterification agent may be a C4-C8 acyl anhydride, C8-C12 acyl anhydride, C12-C16 acyl anhydride, C16-C20 acyl anhydride, a C20- C24 acyl anhydride, a C24-28, a C28-C32 acyl anhydride, a C32-C36 acyl anhydride, a C4- C24 acyl anhydride, C8-C20 acyl anhydride, or a C10-C16 acyl anhydride. The acyl anhydride may be selected from: acetic anhydride (C4H6O3), propionyl anhydride (CeH Os), butyric anhydride (CsHuOs), pentanoic anhydride (C10H18O3), hexanoic anhydride (C12H22O3), heptanoic anhydride (C14H26O3), octanoic anhydride (C16H30O3), nonanonic anhydride (C18H34O3) and decanoic anhydride (C20H38O3).

[0027] If the esterification reagent is one of the mentioned C4-C36 acyl anhydrides, a catalyst may be used to speed up the esterification. The catalyst used may for example be a strong acid, such as HCI, H2SO4, HNO3, H3PO4. Alternatively, the catalyst may be an acyl anhydride, such as a C4-C6 acyl anhydride. The catalyst used may for example be 1 -methyl imidazole, pyridine or 4-(N,N-Dimethylamino)pyridine (DMAP).

[0028] The C2-C18 acyl acid used as the esterification agent may be a C2-C4 acyl acid, a C4- C6 acyl acid, a C6-C8 acyl acid, a C8-C10 acyl acid, a C10-C12 acyl acid, a C12-C14 acyl acid, a C14-C16 acyl acid, a C16-C18 acyl acid, a C2-C12 acyl acid, a C4-C10 acyl acid, a C5- C8 acyl acid. The C2-C18 acyl acid may be selected from: acetic acid (C2H4O2), propionic acid (C3H6O2), butyric acid (C4H8O2), pentanoic acid (C5H10O2), hexanoic acid (C6H12O2), heptanoic acid (C7H14O2), octanoic acid (C8H16O2), nonanoic acid (C9H18O2), and decanoic acid (C10H20O2).

[0029] If the esterification reagent is one of the mentioned C2-C18 acyl acids, a catalyst may be used to speed up the esterification. The catalyst used may for example be a strong acid, such as HCI, H2SO4, HNO3, H3PO4. Alternatively, the catalyst may be an acyl anhydride, such as a C4-C6 acyl anhydride. The catalyst used may for example be 1 -methyl imidazole, pyridine or 4-(N,N-Dimethylamino)pyridine (DMAP).

[0030] The liquid solution may comprise lignin (calculated as dried lignin) and acyl acid, acyl anhydride or acyl chloride in a mole to mole (Molar) ratio of (wherein the molar ratio is based on the hydroxyl group content of the lignin): 1 :0.1 to 1:20, or 1:0.1-1 :18, or 1 :0.1-1 :16, or 1 :0.1- 1 :14, or 1 :0.1-1:12, or 1 :0.1-1 :10, or 1 :0.1-1 :8, or 1 :0.1-1 :6, or 1 :0.1-1 :4, or 1 :0.1-1 :2, or 1:0.1- 1 :1 , or 1 :0.1-1 :0.5, or 0.5-1:20, or 1:0.7-1 :20, or 1:1-1 :20, or 1:2-1 :20, or 1:3-1 :20, or 1:4-1:20, or 1:5-1 :20, or 1:6-1 :20, or 1:7-1 :20, or 1:8-1 :20, or 1:9-1 :20, or 1 :0.5-1 :9, or 1 :0.5-1 :8, or 1 :0.5-1 :7, or 1 :0.5-1 :6, or 1 :0.5-1 :5, or 1 :0.5-1 :6, or 1 :0.5-1 :5, or 1 :0.5-1 :4, or 1 :0.5-1 :3, or 1 :0.5-1 :2, or 1 :0.5-1 :1 , 1:0.5-1:07 or 1 :1-1 :6, or 1 :2-1 :4, or 1:0.2-1 :10.

[0031] A full esterification of the lignin material may be obtained with a ratio of 1:2-1 :4. A full esterification is, however, not necessary for all applications, where a ratio of 1 :0.1-1 :20 also may give a lignin ester with desired properties.

[0032] In the above described process there is a liquidization of lignin, wherein phenolic groups and other hydroxyls of the lignin are blocked to avoid lignin’s ionic and hydrogen bonding types of self-interactions, so that lignin would turn from solid aggregates into liquid. The phenolic groups and other hydroxyls of the lignin material are blocked by the esterification during neutral (non-acidic) conditions. In the process, the hydroxyls are blocked without use of a solvent or carrier liquid. The chemicals used are non-toxic.

[0033] The formed product is washed to remove excess esterification reagent and/or esterification by-products of corresponding acid from the lignin ester. The formed product is washed using water, to stop the esterification reaction. An alkaline solution (such as different hydroxides, carbonates or bicarbonates, e.g. NaOH, Na2COs, or NaHCCh) is used to change esterification by-product being corresponding acid from the esterification reagent into its salt form. The water and alkaline solution can dissolve esterification reagents and/or by-product but not lignin ester. Using alkaline washing, the esterification by-product, acid, is changed into its salt form, which has much higher solubility than the acid and is thus much easier to remove. [0034] The washing aims at a purer lignin ester product. The acyl acid by-product is commonly difficult to wash away by water due to limited solubility. Using alkaline washing, the acid is changed into acyl anion salt, which has a higher solubility and is thus much easier to remove. The alkaline solution may be e.g. NaOH, Na ₂ CO ₃ or NaHCOs. Any of these alkaline solutions will increase the washing efficiency as compared to water. The pH of Na2COs and NaHCOs is about 11 and 8 respectively. NaOH has a higher pH and is even more efficient. A very efficient washing can be obtained with an alkaline NaOH solution having a pH of 13-14. The conjugated base of the decomposed esterification reagent has an alkaline pH, e.g. hexanoate. The esterification reagent or its decomposed structure, e.g hexanoic acid, has an acidic pH. Theoretically, therefore, the washing effluent’s pH could be used as an indicator for the washing performance. A stable measured alkaline pH means a complete conversion of all acid by-product to its conjugated base in/on the product. A pH of 6 means a complete washing away of all conjugated base. It should be noted that practically, both the acid and the conjugated base may be trapped by the oily lignin ester so false pH may be observed. The lower the pH here, the lower amount of residual conjugated base and the purer the lignin ester. [0035] Methods such as Py-GC-MS analysis and other analyses (like HPLC) to determine the residual acid content could reveal the level of the washing effect and the purity of the product comprising lignin ester.

[0036] In one example of the process, product analysis revealed that the resulting product from a process in which lignin material was treated with the esterification reagent hexanoic anhydride in a 1:3 ratio, followed by washing with NaOH solution, the washed product comprises lignin ester and also about 2-5 wt.% hexanoic acid and its salt (sodium hexanoate), mostly in the free acid form. This implied a content of about 95-98% lignin ester in the formed product. (The purity of the lignin ester was measured in terms of the contents of residual hexanoic acid and sodium hexanoate.) When the very same process was used but without any washing (only water addition to destroy the hexanoic anhydride), the formed product had a lignin ester content of at least 40 wt.%.

[0037] The product may be washed by NaOH and then by water until surface of the product has a pH of 6-10. This could be done by chemical analysis or more practically by monitoring the surface of the product.

[0038] The pH may be measured using pH paper. It could also be measured using a pH- meter, which may be more accurate. As discussed above, pH indicates for example the acid change to its salt and the removal of any excess amount of the washing alkaline solution used and salt. The lower the pH, the lower amount of residual salt and the purer the lignin ester. [0039] Depending on application, different degrees of purity of the product comprising lignin ester may be used or required.

[0040] With the process described above, it is possible to obtain a lignin ester that has a high degree of purity (as high as up to 98% (measured in terms of the total content of residual acid by-product in the formed product)). The process is further cost effective due to its simple setup without using any carrier liquid or solvent. Further, no organic solvent is used to extract or wash the formed lignin ester, which is an advantage since the organic solvent that dissolves lignin ester could also dissolve the by-product organic acid at the same time, reducing the lignin ester's purity.

[0041] The reaction temperature may be 20°C to 100°C.

[0042] Increasing the temperature of the mixture may speed up the reaction. The temperature used may be 20-100°C, 25-100°C, 30-100°C, 40-100°C, 50-100°C, 60-100°C, 70-100°C, 80- 100°C, 90-100°C, 20-90°C, 20-90°C, 20-80°C, 20-70°C, 20-60°C, 20-50°C, 20-40°C, 30-60°C, 50-100°C or 50-80°C.

[0043] The esterification reagent may be preheated before mixing with the lignin material. An esterification reagent solution may for example be preheated to a temperature of 40-100°C, 50-100°C, 60-100°C, 70-100°C, or 80-100°C, before being mixed with the lignin material. The mixture may be allowed to react during stirring or blending.

[0044] The mixture may be allowed to react in the presence of a catalyst.

[0045] If the esterification reagent is one of the mentioned C2-C18 acyl chlorides, the use of a catalyst may not be necessary, as the esterification process is fast without any catalyst addition. When using C4-C36 acyl anhydride or C2-C18 acyl acid as the esterification agent a catalyst may be used to speed up the esterification. The catalyst used may as discussed above be a strong acid or any acyl anhydride.

[0046] When acyl chloride or acyl anhydride is used as the esterification reagent, the reaction might be stopped by destruction of the reagent. This could be made by addition of water.

[0047] The lignin ester product formed in the process may commonly present as an oily, solid or semisolid form. Such product may appear as highly viscose, milky, soft and slippery clogs, or sand-like solids.

[0048] The formed product comprises lignin ester and by-products of the esterification. The corresponding acid from the esterification reagent, acyl chloride, acyl anhydride or acyl acid itself is the main by-product. Theoretically, the product comprising lignin ester and by-products can be used as it is without any washing or very little washing of the product, leaving a product with esterification reagent or its corresponding acid as impurity.

[0049] The process may further comprise washing the formed product in water, in an alkaline solution and/or in an organic solution (such as alcohols e.g. methanol, ethanol or propanol) to remove the by-product.

[0050] The process may further comprise a step of drying the product comprising lignin ester. [0051] For some uses of the product comprising lignin ester, no drying may be needed when a small amount of moisture is tolerated. Drying may be preferred when water is detrimental for the application.

[0052] The drying may be performed at a temperature of 20-80°C.

[0053] The material may be dried at a temperature of 20-60°C or 20-40°C, preferably at room temperature. The material may be dried in air.

[0054] The process described above may provide a product comprising lignin ester, wherein the product comprises 40-100 wt. % lignin ester.

[0055] The solid product may comprise 40-100 wt. % lignin ester, or 45-100, 50-100, 55-100, 60-100, 65-100, 70-100, 75-100, 80-100, 85-100, 90-100, 95-100, 98-100, 40-98, 45-98, 50- 98, 55-98, 60-98, 65-98, 70-98, 75-98, 80-98, 85-98, 90-98, 95-98, 45-95, 50-95, 55-95, 60-95, 65-95, 70-95, 75-95, 80-95, 85-95, 90-95, 40-60, 60-80, 70-90, or 80-90 wt. % lignin ester.

[0056] A polarity of the lignin ester depends on the chain length of the esterification reagent used for preparing the lignin ester [0057] Apart from lignin ester, the product may comprise the corresponding acid from the esterification reagent used when forming the lignin ester, acyl chloride, acyl anhydride or acyl acid itself.

[0058] In one example, the product comprises 95-98 wt.% lignin ester and about 2-5 wt.% acid by-product. The purity of the lignin ester is measured in terms of the total content of residual acid by-product.

[0059] According to a second aspect, there is provided a process of forming a lignin oil, comprising preparing a lignin ester according to the process described above, and increasing the temperature of the formed product comprising lignin ester until a lignin oil is formed.

[0060] By increasing the temperature of the formed solid product comprising lignin ester, which is hydrophobic, a liquid lignin ester is formed, a lignin ester oil. There is a liquidation of the lignin ester itself when increasing the temperature above the melting point of the lignin ester so that lignin ester turns from solid aggregates into liquid.

[0061] The higher the concentration of lignin ester in the formed solid product and the lower the concentration of the by-products (the purer the product is), the higher the temperature required for turning the solid product comprising lignin ester into lignin ester oil.

[0062] In one example, with a product comprising a lignin ester amount of about 85 wt.% a temperature of about 65°C may be needed to turn the solid product into a lignin ester form. With a lignin ester concentration of about 95 wt.%, a temperature of at least 80°C may be needed.

[0063] The liquidized form of the lignin ester turns into a solid form or semi-solid form if the temperature is decreased again. Therefore, to form the lignin oil, the temperature of the solid product comprising lignin ester is increased to a needed temperature and thereafter kept at the temperature such that the formed lignin oil is kept in its liquid form and does not turn into a solid or semi-solid form.

[0064] Repeated heating and cooling of the lignin ester might affect the melting point of the lignin ester. Lignin ester aggregates differently upon heating-cooling. When heating to a too high temperature, it might decompose.

[0065] The formed lignin ester oil can be kept at an elevated temperature and used directly as is in water barriers on packaging material, as primer, as adhesive, as additive, as plasticizer, and in resins.

[0066] According to a third aspect, there is provided a process of forming a lignin oil composition, comprising preparing a lignin ester according to the process described above, and blending the solid product comprising lignin ester with an additional oil.

[0067] The additional oil may be a natural oil or fat, or a modified oil or fat.

[0068] The lignin ester has a polarity depending on the acyl chain length, and is thus hydrophobic to be homogenously mixed with a hydrophobic oil or fat. This will decrease the viscosity of the lignin ester and give an oily homogenous substance at room temperature. The viscosity and the rheological behaviour of an oil or fat, hence, can be adjusted by mixing with different amounts of lignin ester.

[0069] The product comprising lignin ester and produced by the above described process, provides, as described, a product with high concentration of lignin ester, at least 40 wt.%, which enables for a homogenous blended oil with high stability.

[0070] The product comprising lignin ester and the additional oil may be blended by mixing/stirring. The temperature during blending may be 20-100°C, such as 20-30°C, 40-50°C, or 60-100°C. Using an elevated temperature during the blending may speed up the lignin oil composition formation. Too high a temperature should be avoided, such as >180°C. This is due to the fact that many oils decompose at temperatures above 180°C.

[0071] The formed lignin oil composition can be kept at room temperature, as it keeps its oil form at temperatures below the melting point of the lignin ester.

[0072] The formed lignin oil composition can be used in water barriers on packaging material, as primer, as adhesive, as additive, as plasticizer, and in resins.

[0073] The blending of the product comprising lignin ester with the additional oil may be performed at a temperature of 20-100°C.

[0074] The blending may be performed at a temperature of 40-100°C, or 60-100°C.

[0075] When a lignin oil composition according to the third aspect, is prepared, the process may further comprise blending the lignin oil with an additional oil, forming a lignin oil composition.

[0076] In one example, the temperature of the lignin oil is at least 65°C, at least during the onset of the mixing with the additional oil to keep the lignin oil in oil form.

[0077] The resulting lignin oil composition has similar properties to the lignin oil composition produced by blending the product comprising lignin ester with an additional oil (e.g. triglyceride type) according the fourth aspect above.

[0078] The formed lignin oil composition can be used in water barriers on packaging material, as primer, as adhesive, as additive, as plasticizer, and in resins.

[0079] The additional oil may be selected from midoleic sunflower oil, canola oil, soybean oil, sunflower oil, corn oil, rapeseed oil, linseed oil, alkyd oil, olive oil, tung oil, tall oil or any combination thereof.

[0080] The additional oil may be a functionalized or modified oil.

[0081] Alternatively, the additional oil may be a non-natural oil, i.e. a petroleum- or synthetic polymer-based oil, such as castor oil, mineral oil, silicon oil etc. In yet an alternative, the additional oil may be replaced with one or more waxes. [0082] The functionalization can provide a reactivity, e.g. by comprising epoxy groups. The functionalization chosen may for example provide the ability to crosslink the lignin oil composition, or to chemically bind the lignin oil composition to surfaces as e.g. barrier coating. [0083] The lignin oil composition developed, as well as the concept of controlling the functionality and viscosity of the oil, offers completely new opportunities for this new concept to apply barriers. In the long run, such a technology could for example pave the way for replacing polyethylene as a water barrier with a waterborne bio-based barrier that can be applied on-line in a paper or board machine.

[0084] The functionalization may be a triglyceride epoxidation.

[0085] In one example, the modified triglyceride is an epoxidized soybean oil. The epoxidized soybean oil is an alkylating agent. The lignin ester in the lignin oil composition is, however, not active any more for any alkylation.

[0086] The product comprising lignin ester may be blended with the additional oil such that a (weight) ratio of lignin ester to additional oil is 1 :20 to 1 :1 (lignin esteradditional oil) in the lignin oil composition.

[0087] Such a formed lignin oil may be in viscous form at room temperature. In one example, a lignin oil composition with a ratio of lignin ester to additional oil, being a modified glyceride, may be up to 1 :1 and will have a high viscosity reaching 55 000 cP (centipoise) as measured using Instrument Brookfield CAP 2000.

[0088] The lignin oil composition can be adjusted for different viscosities by e.g. adjusting the ratio of lignin ester to additional oil in the lignin oil composition. By lowering the proportion of lignin ester in the lignin oil composition the viscosity may be lowered.

[0089] A lignin oil composition comprising lignin ester and an additional oil in a (weight) ratio of 1 :20 to 1 :1 may be produced using the above described lignin ester.

[0090] Such a lignin oil composition may be in viscous form at room temperature.

[0091] According to a fourth aspect, there is provided a use of the product comprising lignin ester produced in the process of the first aspect, use of the oil produced according the process of the second aspect, the lignin oil composition produced in the processes as discussed above in water barriers on packaging material, as primer, as adhesive, as additive, as plasticizer, and in resins.

[0092] The lignin ester or the oil may be used as additive in plastics or asphalt. The lignin ester or oil may be used as plasticizer in elastomers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Fig. 1 shows the reaction scheme between lignin and hexanoic acid anhydride, in which reaction lignin ester is formed. [0094] Fig. 2 shows schematically an exemplifying process of preparing lignin ester from lignin and thereafter forming a lignin oil composition comprising the lignin ester.

[0095] Figs 3 and 4 show the melt and crystallization temperature for poly(3-hydroxybutyrate) (PHB) with different amounts of a lignin oil composition added as a plasticizer.

[0096] Fig 5. shows the stress-strain relationship measured during uniaxial tensile tests for PHB with different amounts of a lignin oil composition added as a plasticizer.

DETAILED DESCRIPTION

[0097] Lignin in solid form can be extracted in large scale from black liquor from a Kraft pulping process, which has enabled for a large supply of lignin as a raw material. Thereby, there is an increased interest in finding value addition of lignin. Lignin could to some extent replace fossil oil-based plastics. However, lignin needs to be modified or blended with other materials such as plasticizers to achieve acceptable mechanical properties.

[0098] Below is described a process for preparing lignin ester from a lignin material. The lignin ester may be used in a lignin oil or a lignin oil composition. Such lignin oil or lignin oil composition can be used for example in water barriers on packaging material, as primer, as adhesive, as additive, as plasticizer, and in resins.

[0099] The general process for preparing a lignin ester comprises to provide a lignin material, mixing the lignin material with an esterification reagent being a C2-C18 acyl chloride, a C4-C36 acyl anhydride, a C2-C18 acyl acid, or any combination thereof, in a molar ratio of 1 :0.1- to 1 :20, optionally in the presence of a catalyst, and allowing the mixture to react, whereby a product comprising lignin ester is formed.

[00100] The lignin material may for example be from a Kraft pulping process.

[00101] The esterification reagent may be a C2-C18 straight or branched, aliphatic or aromatic chain acyl chloride, e.g. acetyl chloride (C2H3CIO), propionyl chloride (C4H5CIO), butanoyl chloride (C4H7CIO), pentanoyl chloride (C5H9CIO), hexanoyl chloride (CeHuCIO), heptanoyl chloride (C7H13CIO), octanoyl chloride (CsHisCIO), nonanoyl chloride (C9H17CIO) and decanoyl chloride (C10H19CIO) or any combination thereof. If the esterification reagent is an acyl chloride, the use of a catalyst may not be necessary, as the esterification process is fast without any catalyst addition.

[00102] The esterification reagent may be C2-C18 straight or branched, aliphatic or aromatic chain acyl acid, which may be selected e.g. from: acetic acid (C2H4O2), propionic acid (C3H6O2), butyric acid (C4H8O2), pentanoic acid (C5H10O2), hexanoic acid (C6H12O2), heptanoic acid (C7H14O2), octanoic acid (C8H16O2), nonanoic acid (C9H18O2), and decanoic acid (C10H20O2). If the esterification reagent is an acyl acid, a catalyst may be used to speed up the esterification. The catalyst used may for example be a strong acid, such as HCI, H2SO4, HNO3, and H3PO4. Alternatively, the catalyst may be an acyl anhydride, such as a C2-C18 acyl anhydride. The catalyst used may for example be 1-methyl imidazole, pyridine or 4-(N,N- Dimethylamino)pyridine (DMAP).

[00103] The esterification regent may be a C4-C36 straight or branched, aliphatic or aromatic chain acyl anhydride, which may be selected e.g. from: acetic anhydride (C4H6O3), propionyl anhydride (CeH Os), butyric anhydride (CsHuOs), pentanoic anhydride (C10H18O3), hexanoic anhydride (C12H22O3), heptanoic anhydride (C14H26O3), octanoic anhydride (C16H30O3), nonanonic anhydride (C18H34O3) and decanoic anhydride (C20H38O3). If the esterification reagent is an acyl anhydride, one of the catalysts discussed above may be used to speed up the esterification

[00104] In Fig. 2 is schematically illustrated an example of the process of preparing lignin ester from lignin. In this example, the esterification reagent used is hexanoic anhydride (added in excess). A catalyst, 1-methyl imidazole, is used to speed up the process. Thereby a solid product comprising lignin ester is formed with hexanoic acid as by-product.

[00105] In Fig. 1 is shown the reaction scheme between lignin and hexanoic acid anhydride, in which reaction lignin ester is formed.

[00106] The mixture of esterification reagent and lignin material may be allowed to react at room temperature or at an elevated temperature of up to 100°C. A higher temperature may speed up the esterification reaction.

[00107] As illustrated in Fig. 2, the process may further comprise a step of washing the formed product comprising lignin ester to destroy and remove excess esterification reagent and/or esterification by-products from the lignin ester. The formed product may be washed in water, in an alkaline solution (such as different hydroxides, carbonates or bicarbonates, e.g. NaOH, Na2CC>3, or NaHCOs) or in an organic solvent to remove the esterification by-product (such as alcohols e.g. methanol, ethanol or propanol.), i.e. not for dissolution of the lignin ester. In Fig. 2 is shown washing with water followed by NaOH and thereafter water again.

[00108] Theoretically, the formed solid product comprising lignin ester can be used as it is without any washing or very little washing of the product, leaving a product with esterification reagent and/or by-product as impurity. To stop the esterification reaction, water may be added to the solution to destroy the esterification reagent of acyl anhydride. In addition, or alternatively, a more thorough washing may be performed using water or other washing solutions as discussed above to remove the acyl acid by-product.

[00109] Water, any alkaline solution or an organic solvent can dissolve such by-product but not lignin ester. The product may be washed in water, even though the acyl acid byproduct has a limited solubility in water, thus the washing efficiency is limited. A more effective washing solution to use is an alkaline solution or an organic solvent. Using alkaline washing, the acyl acid is changed into its salt form; the latter has a much higher solubility than the acid and is thus much easier to be removed. [00110] As illustrated in Fig. 2, the process may further comprise a step of drying the solid product comprising the lignin ester. Drying may be performed at a temperature of 20- 80°C and may be performed in air.

[00111] The formed solid product comprising lignin ester may be used to form a lignin oil. The oil may be formed by increasing the temperature of the solid product comprising lignin ester to a temperature of at least 65°C (/.e. above the melting point of lignin ester). By increasing the temperature of the solid product comprising lignin ester, there is a liquidation of the lignin ester and a liquid lignin ester is formed, a lignin ester oil.

[00112] The liquidized form of the lignin ester turns into a solid form or semi-solid form if the temperature is decreased again. Therefore, to form the lignin oil, the temperature of the solid product comprising lignin ester is increased to a temperature of at least 65°C and thereafter kept at a temperature of at least 65°C, such that the formed lignin oil is kept in its liquid form and does not turn into a solid or semi-solid form. Such lignin oil may be used as exemplified above.

[00113] A lignin oil composition may be prepared as illustrated in Fig. 2 by blending the product comprising lignin ester with an additional oil, a natural or modified oil or fat. The blending may take place at room temperature or at an elevated temperature (20-100°C) to speed up the lignin oil composition formation.

[00114] The additional oil may be midoleic sunflower oil, canola oil, soybean oil, sunflower oil, corn oil, rapeseed oil, linseed oil, alkyd oil, olive oil, tung oil, tall oil or any combination thereof. The oil used may be a functionalized natural oil, for example an epoxidized triglyceride. In Fig. 2 is illustrated the use of an epoxidized soybean oil. The lignin oil composition may comprise a ratio of lignin ester to additional oil of 1 :20-1 :1. Such lignin oil composition may have a viscosity of 400-55000 cP at room temperature and may be used as exemplified above.

[00115] Below follows a recipe for the process of producing lignin ester and subsequently a lignin oil composition. Below is also discussed a few applications of the lignin oil composition. The recipe and process below are mere examples of how to produce a specific lignin ester and lignin oil composition. As discussed above, many of the parameters, such as the use of elevated temperature, the use/choice of catalyst are optional measures, which may speed up the process, but which are not crucial for the process. As also is discussed above, the choice of washing solution and washing procedure can be chosen based on the requirements, e.g. purity, of the resulting solid product comprising the lignin ester. Further, the choice of additional oil and the ratio of lignin ester to additional oil used in the lignin oil composition can be chosen based on the intended use and required properties of the lignin oil composition. Lignin ester preparation

1. Charge 4 kg liquid form hexanoic anhydride (concentration of hexanoic anhydride >97%).

2. Heat the hexanoic anhydride to 50°C.

3. Under stirring, add 1.3 kg lignin (here dried lignin) to the liquid hexanoic anhydride.

4. Add 78 mL 1 -methyl imidazole (catalyst) to the mixture.

5. Keep heating and stirring for 6 hours.

6. Add 7kg water to the mixture to stop the reaction.

7. Separate water from the formed solid product.

8. Wash the solid product thoroughly with 24L 1M NaOH to reach a stable alkaline pH (pH 13-14 ) to convert all hexanoic acid (by-product of hexanoic anhydride) into sodium hexanoate. (Stepwise washing until no pH reduction is observed after a fresh NaOH addition.)

9. Filtrate and wash repeatedly with 8L water to reach a pH of 6-10. (The more washing times, the lower the pH and the more complete the removal of sodium hexanoate.)

11. Drying the formed solid product comprising lignin ester in air at room temperature. [00116] The solid product comprising lignin ester and being the result from using this recipe weigh about 1.8 kg. Product analysis revealed that the solid product contains about 2-5 wt.% hexanoic acid (a total amount of both hexanoic acid and sodium hexanoate), implying a purity of ca. 95-98 wt.% of lignin ester. (The analysis was performed by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) analysis.)

[00117] Generally, more washing in step 9 will remove more of the by-products of hexanoic anhydride, i.e. sodium hexanoate, and result in a more pure lignin ester product.

Lignin oil composition preparation

[00118] Solid product comprising lignin ester (which may be produced as described above) may be blended with an additional oil, a fatty acid oil, or a functionalized such oil. In one example the solid product comprising lignin ester is blended with epoxidized soybean oil in for example a 1 :1 weight ratio under stirring into a homogeneous oil, forming a lignin oil composition. If needed, gentle heating to 60°C or more, can be applied.

Examples of different uses of lignin oil compositions Water barrier

[00119] Emulsions can be prepared from the lignin oil composition (produced as exemplified above) and water. The emulsions may be used for coating onto different substrates as a water barrier.

[00120] As water and oil are mutually immiscible substances, a third component, an emulsifying agent might be required that can associate with both water and oil. There are practically hundreds of different emulsifiers, some of them responding to very stringent legislative regulations, e.g. pharmaceuticals. Some examples are soy lecithin and non-ionic surfactants (Triton X-114 and X-110). Soy lecithin is fat soluble and therefore suitable to be used in emulsions with oil as continuous phase (water-in-oil (W/O)-emulsion). The non-ionic representatives (Triton-X) are water-soluble and used in oil in water (O/W)-emulsions.

[00121] O/W -emulsions were prepared by mixing low amounts of Triton X-114 or X-110 into cold (+5C) water followed by step-wise addition of the lignin oil composition, up to 15 wt-% oil with Triton X-114 and 25 wt-% with Triton X-110. Lignin oil compositions comprising 35 wt.% or 40 wt% esterified lignin, respectively, and 65 or 60 wt.% epoxidized soy bean oil, were used.

[00122] A W/O emulsion with a ratio of W/O of about 1 :18 (based on weighing the excess water that remained on the surface of the emulsion mixture and did not go into the emulsion or was expelled from it) was used with the lignin oil composition comprising 35% esterified lignin. A lower amount of lignin composition was used in the W/O emulsion comprising the lignin oil composition comprising 40% esterified lignin.

[00123] A commercial board substrate was coated in a laboratory bench coater using wire-wound Mayer rod, with a wet film deposit between 6 pm and 24 pm. The coated substrates were then dried in an oven at 120°C for 30 min.

[00124] Barrier properties were then measured as Water Vapour Transmission Rate, WVTR, according to ASTM F1249 - 13 Standard test method for water vapor transmission rate through plastic film and sheeting using modulated infrared sensor in a Mocon instrument Permatran-W 3/33 MG+. The WVTR measurements were performed at 23°C and 50% relative humidity (RH).

[00125] All emulsion-coated samples showed an improved water barrier compared to the reference substrate (without coating). As the amount of coating increased, the barrier properties improved, resulting in a decrease in WVTR (water vapor transmission rate). With these initial methods, WVTR between 50 and 100 g/m ² /day may be obtained with the above coating.

[00126] Based on these experiments, it is apparent that lignin ester and lignin oil/lignin oil compositions comprising lignin ester show very promising characteristics as a futureproof, biodegradable barrier material in a wide range of products, e.g. food packaging.

Plasticizer for poly(3-hydroxybutyrate) (PHB)

[00127] Poly(3-hydroxybutyrate) PHB is a polyhydroxyalkanoate (PHA), a polymer belonging to the polyester class, which is of interest as bio-derived and biodegradable plastics. [00128] Lignin oil compositions comprising 20 wt.% (L20) or 40 wt% (L40) esterified lignin, respectively, were used. The lignin oil composition further comprised 10-90 wt.% epoxidized soy bean oil.

[00129] Different proportions of the lignin oil composition and PHB were mixed: PHB:L20: 90:10; 80:20; 70:30; 60:40 PHB:L40: 90:10; 80:20; 70:30; 60:40

[00130] The mixtures were compared to PHB without added lignin oil composition, using differential scanning calorimetry (DSC) to determine melt temperature and crystallization temperature. The results, shown in Figs 3 and 4, showed that the added lignin oil composition decreased the melt and crystallization temperature of PHB compared to PHB without any added lignin composition. In these experiments, it was shown that a higher lignin ester content (L40) showed generally better results. This might be due to that pure epoxidized soy bean oil is not compatible with PHB.

[00131] Uniaxial tensile tests were also performed on L20 and L40. The samples were prepared with similar content of lignin oil composition, i.e. the PHB:L20 was mixed at a ratio of 80:20 and PHB:L40 was mixed at a ratio of 90:10. The results from these tests are shown in Fig. 5. Addition of lignin oil composition decreased the stiffness of the PHB and increased the strain at break, see Fig. 5. This indicates a much more ductile material, which is typical for the plastization. The elongation and toughness were favored by a high viscosity lignin oil composition (j.e. a lower degree of soybean oil in the lignin oil composition).

Plasticizer for polyvinylchloride (PVC)

[00132] Polyvinylchloride (PVC) is a common plastic material. Plasticizers may be added to PVC to obtain the desired mechanical properties. In these experiments, a lignin ester composition comprising 40 wt.% lignin oil (L40) and 60 wt.% epoxidized soy bean oil was added to the PVC. The mixtures were compared to PVC without added lignin oil composition, using differential scanning calorimetry (DSC) to determine melt temperature and crystallization temperature. The results showed that the glass transition temperature (Tg) decreased from 78 °C for the pure PVC to 26 °C for the PVC and lignin oil composition mixture. Hence, it is clear that the lignin oil composition is an effective plasticizer of PVC.