Process for depolymerizing a lignin compound

Abstract

The present invention relates to a process for the depolymerization of a lignin compound and to a composition obtained from such process.

Description

Borregaard ASPROCESS FOR DEPOLYMERIZING A LIGNIN COMPOUNDFIELD OF THE INVENTION

[0001] The present invention relates to a process for “lignin valorization”, more specifically to the conversion of a lignin compound into valuable aromatic molecules. The molecules produced are useful in a variety of industrial fields such as cosmetics, foods or pharmaceutical industries, or as chemical intermediates for the synthesis of organic compounds.BACKGROUND OF THE INVENTION

[0002] Most of today’s world supply of organic commodity chemicals originates from fossil-based petrochemical feedstocks. Fossil-based chemicals, however, are considered unsustainable and, thus, do not meet the growing demand for sustainable and “green” industrial solutions. Hence, there is an urgent and growing need for sustainably sourced chemicals and processes based on renewable bio-based raw materials for producing the same.

[0003] Lignin is one of the most abundant natural polymers found in the cell walls of plants, primarily in wood and other vascular tissues. Lignin serves as a crucial component for providing structural support and rigidity to plants. Chemically, lignins are biopolymers composed of three crosslinked phenylpropanoid building blocks, coniferyl alcohol (G), sinapyl alcohol (S), and paracoumaryl alcohol (H).

[0004] Lignin is often considered a waste product in industries such as paper and biofuel production, where its presence complicates processing and reduces the quality of end products. Usually, lignin by-products are simply burnt at an industrial production site.

[0005] Several attempts have been made to use lignin as a source for higher value organic chemicals. Such attempts include pyrolysis, gasification, heterogeneous catalysis, and biochemical processes.

[0006] As an early example, depolymerization of lignin to vanillin is disclosed in US 2,598,311. An aqueous reaction mixture and sodium hydroxide is exposed to an increased temperature and pressure. Air or oxygen are continuously introduced into the reactor. A high yield of vanillin is reported, but since a thin film / falling film type reactor is used, low concentrations of lignin are required to ensure low viscosity of the starting material composition. This, in turn, translates into a low volumetric productivity rate.

[0007] In US 8,563,791 , a process for solubilizing organic solids is disclosed, where an organic solid is reacted with an oxidant in superheated water to form at least one solubilized organic solute. The organic solids listed are coal, lignite, kerogen and lignin containing biomass, such as wood, grasses or grains. It is hypothesized that the solubilized organic solutes included carboxylic acids of monoaromatic and aliphatic products. While the carboxylic acid functional groups are essential to solubilize the organic compounds in water, they also entail severe, unspecific degradation of the organic material. Fractionation and isolation of the solubilized organic solutes from the aqueous phase proves difficult due to the wide range of polarity and volatility of the compounds.

[0008] EP 3 072 874 describes the depolymerization of lignin in black liquor at increased temperature and pressure. However, the reported batch process requires long reaction times (30 minutes to 2 hours) and leads to low yields and low selectivity for important monomeric aromatic compounds.

[0009] WO 2014 / 068590 describes a process for the depolymerization of lignin to obtain substituted aromatic compounds. The reaction uses copper nitrate as a homogenous catalyst and hydrogen peroxide as an oxidizing agent. The use of a copper catalyst is supposed to lower the cost of the process, making the same more economical. However, no catalyst recovery and recycling scheme is described. Copper emissions are strictly regulated, and significant downstream processing will be required for copper catalyst recovery and recycling. This, in turn, will entail significant increases in cost.

[0010] While several known lignin depolymerization processes are performed under alkaline conditions, it has been thought that lignin depolymerization is a base-catalyzed reaction, i.e. a reaction where a base is not consumed. As a consequence, insufficient amounts of base are traditionally used, which very often leads to the formation of undesired insoluble organic materials (also referred to as “char”).

[0011] Further, low substrate concentrations have been used to reduce condensation reactions and the formation of insoluble materials. However, this also entails low concentrations of the valuable aromatic products and low volumetric productivity rates.SUMMARY OF THE PRESENT INVENTION

[0012] Overall, currently known processes suffer from several drawbacks, among others from a low load of starting materials, dilute and complicated product mixtures of low purity of single aromatic monomers, as well as a significant portion of non-soluble residual material precipitated together with other oligomeric fractions.

[0013] Also, the use of transition metal catalysts is undesired (both from an economical and ecological point of view) due to a high cost of catalyst and the requirement for cumbersome and expensive downstream catalyst recovery processes.

[0014] Further, when an oxidant is used, excessive consumption of alkali at a high cost may be a problem.

[0015] Accordingly, despite its abundance and potential utility, lignin has basically remained commercially unutilized for the production of valuable aromatic molecules.

[0016] Based on the above, it is an object of the present invention to mitigate one or more of the above-mentioned drawbacks associated with the prior art processes.

[0017] In particular, it is an object of the present invention to provide for an improved process for the depolymerization of a lignin compound.

[0018] It is a particular object of the present invention to provide for a high yield of high- value lignin-derived valuable aromatic compounds, in particular vanillin. It is also an object to avoid degradation and recondensation, both leading to the generation of undesired byproducts.

[0019] These objects are achieved by the process of the present invention as described in the appended embodiments, Items, and claims.

[0020] Among others, the present invention is based on the finding that the depolymerization of lignin is not a base-catalyzed but a base-consuming process. In particular, it has surprisingly been found that base concentration is an important parameter in the production of vanillin and other functional monomers from lignin compounds. As noted above, a base has previously been considered as a catalyst. However, the inventors of the present invention have found that although a base aids in catalyzing the degradation reaction of lignin compounds, a base is (also) an important stoichiometric reagent for the production of monomeric aldehydes. Accordingly, it has surprisingly been found that comparatively high amounts of base are needed / highly advantageous.

[0021] Accordingly, in a first aspect, the present invention relates to a process for the depolymerization of a lignin compound, wherein the process is as defined in the claims.

[0022] In a second aspect, the present invention relates to a composition comprising an aromatic aldehyde (p-hydroxy benzaldehyde, vanillin, and / or syringaldehyde depending on relative abundance of the aforementioned phenylpropanoid building blocks in the lignin) in an amount of more than 6 g / L and the corresponding aromatic methyl ketone (p-hydroxy acetophenone, acetovanillone, and / or acetosyringone) in an amount of 0.001-1 g / L.DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention is at least partly based on the surprising finding that the depolymerization of lignin is not a base-catalyzed but a base-consuming process, and that base concentration and the base-to-lignin ratio are important parameters for achieving an improved process for depolymerizing lignin compounds.

[0024] Accordingly, in a first aspect, the present invention relates to a process for the depolymerization of a lignin compound as defined in the claims. The process comprises at least the following steps:(1) providing a composition, the composition comprising:• one or more lignin compounds,• one or more alkaline compounds, and• water, wherein the composition has an alkaline pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0, and wherein the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- / weightugnin compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds.(2) heating the composition to a defined peak temperature,(3) keeping the composition at substantially the peak temperature for a defined time, wherein substantially means ± 5 °C,(4) cooling the composition.

[0025] As noted above, it has been found that using comparatively high amounts of a base and a comparatively high base-to-lignin-ratio (expressed as moloH- I weighty compounds) is highly advantageous. Without wishing to be bound by theory, it is believed that the alkaline species added to the reaction must exceed the molar amount of all protons with a pKa below 7, as well as that of all phenols present and generated during the reaction. In addition,additional alkaline might be necessary to compensate for acidic species present at the beginning of the reaction and those formed during the course of the reaction. In particular, it has been found that the alkaline loading should be so that the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- 1 weighty™ compounds) is at least 1 mol of hydroxide ions per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg. Preferably, the weight ratio of the one or more alkaline compounds to the lignin compounds (weightaikaiinecompounds I weighty compounds) is at least 0.05, preferably at least 0.1 , more preferably at least 0.2.

[0026] The process of the present invention allows for the use of high substrate concentrations, thereby obtaining high concentrations of valuable aromatic monomers such as vanillin in a short time with a minimum amount of undesired by-products.

[0027] Overall, the process of the present invention holds great potential due to its simplicity and generation of a reaction mixture with high concentration of vanillin. The reaction mixture from this process is compatible with most of the conventional alkaline alcohol extraction procedures known to date.

[0028] Also, the present process leads to compositions comprising an aromatic aldehyde (p-hydroxy benzaldehyde, vanillin, and / or syringaldehyde depending on relative abundance of the aforementioned phenylpropanoid building blocks in the lignin) and the corresponding aromatic methyl ketone (p-hydroxy acetophenone, acetovanillone, and / or acetosyringone). Preferably, the process leads to compositions comprising p-hydroxy benzaldehyde and / or vanillin and / or syringaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and p-hydroxy acetophenone and / or acetovanillone and / or acetosyringone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L.

[0029] Preferably, the process generates compositions where the weight ratio of vanillin to acetovanillone (weightvaniiiin / weightacetovaiiione) is at least 10, preferably at least 20, more preferably at least 30 and / or where the weight ratio of p-hydroxy benzaldehyde to p-hydroxy acetophenone (weightp.hydroxy benzaldehyde I weightp-hydroxy acetophenone) is at least 10, preferably at least 20, more preferably at least 30 and / or where the weight ratio of syringaldehyde to acetosyringone (weightsyringaidehyde / weightaCetosyringone) is at least 10, preferably at least 20, more preferably at least 30.

[0030] The simple process also allows for a modular scale up using parallel systems, yielding a process with high redundancy and robustness. The process could easily be scaled up to multi ton scale.

[0031] Apart from the step of providing the actual reaction mixture, the process of the present invention comprises three steps. First, the reaction mixture (herein referred to as “composition”) is heated to a peak temperature within a given heating time. Second, the (heated) composition is maintained at substantially the peak temperature for a defined reaction time. Third, the composition is cooled from peak temperature to a final temperature.

[0032] The process is preferably performed in a continuous mode. This is advantageous, because continuous processes allow for a precise control over reaction time and can be performed at reduced depolymerization times and, thus, high volumetric productivity rates and high yields. This is strongly desired from an industrial point of view.

[0033] Preferably, the process is performed in a tubular reactor.

[0034] As noted above, the use of transition metal catalysts is economically and ecologically undesired due to a high cost of catalyst and the requirement for cumbersome and expensive downstream catalyst recovery processes. Accordingly, it is preferred that the process is performed in the absence of transition metals or in the presence of only trace amount of transition metals. Preferably, the process is performed in the absence of transition metals. “Trace amounts”, as referred to herein, refers to amounts of less than 0.1 wt.%, preferably 0.05 wt.%, more preferably less than 0.01 wt.%, based on the overall weight of the reaction composition.

[0035] In step (1) of the process of the present invention, a composition is provided.

[0036] In an embodiment, the composition provided in step (1) is fed to a reactor. This means that the composition of step (1) is preferably provided outside of a reactor and is then (after it has been prepared) fed to a reactor. If an oxidant (for example H2O2) is used, the oxidant may be separately introduced into the reactor.

[0037] The composition comprises one or more lignin compounds, one or more alkaline compounds, and water. The composition has a basic pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0. Further, the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- 1 weighty™ compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg.

[0038] The term “added hydroxide ions” refers to hydroxide ions derived from the one or more alkaline compounds added to the composition. It is referred to “added” hydroxide ions, because upon introduction into the composition hydroxide ions may react, with the result that the amount of hydroxide ions “added” to the composition and the amount of hydroxide ions “present” in the composition may not be identical at any point in time.

[0039] Lignin (also referred to as “native lignin”) is one of the most abundant organic materials in nature and provides strength and support to trees and other plants. Lignin is a biopolymer, more precisely a mixture of biopolymers, that is / are present in the support tissues of plants, particularly in the cell walls providing rigidity to the plants. Lignin is a phenolic polymer, more precisely a mixture of phenolic polymers. The specific structure and composition of lignin depends on the plant and therefore varies depending on the plant from which it is derived. Lignin is sometimes also referred to as the “glue” in the cellulosic skeleton.

[0040] Lignin is a byproduct of the pulp and paper industry, produced at a volume of around 100 million tons per year, the vast majority of which is burned at the site. Lignin is a complex biopolymer with hydrophobic and hydrophilic components, consisting primarily of aromatic structures linked via oxygen containing groups such as esters and ethers. Lignin in its native form is insoluble in water except under highly alkaline conditions, but can be made water-soluble by introducing hydrophilic groups such as charged sites (e.g. sulfonate, carboxylate, amines) or polar groups (e.g. polyethoxylates). The most abundant types of lignin produced industrially are the water-insoluble Kraft lignin (from the Kraft pulping process) and the water-soluble lignosulfonate (from the sulfite pulping process). These products can be further modified to change their properties, e.g. by introducing or removing charged sites, oxidation, fractionation, grafting, etc.

[0041] Since there is not only one lignin with a well-defined chemical structure, but lignin exists as a mixture of phenolic polymers, the chemical structure of which depends on the plant from which it is derived, the present invention generally refers to a “lignin compound”. The term “lignin compound” encompasses native lignin, i.e. a lignin polymer or mixture of lignin polymers in its / their native structure, as well as lignin derivatives such as sulfonated lignin (such as lignosulfonate), Kraft lignin, oxidized lignin, organosolv lignin, soda lignin, hydrolysis lignin, biorefinery lignin, steam explosion (SE) lignin, ammonia fiber explosion (AFEX) lignin, hydrothermal lignin, and lignin resulting from reaction conditions including use of super critical water and / or sonication.

[0042] According to a preferred embodiment, the one or more lignin compounds is / are water-soluble. This helps preventing char formation and avoiding build-up of insoluble product aggregates. For imparting water-solubility, the one or more lignin compounds preferably comprise / s charged functional groups, preferably sulfonate and / or carboxylate groups. Within the meaning of the present invention, the term “water-soluble,” means that the lignin compound / s has / have the ability to dissolve in water at a neutral pH to some extent. As examples, a calcium lignosulfonate can demonstrate complete solubility in water while the solubility of a typical Kraft lignin is low or negligible.

[0043] In one embodiment, the one or more lignin compounds comprise sulfonated lignin. Preferably, the one or more lignin compounds are sulfonated lignin. The sulfonated lignin may be, for example, lignosulfonate or sulfonated Kraft lignin. In another embodiment, the one or more lignin compounds comprise oxidized lignin. In a preferred form of this embodiment, the one or more lignin compounds are oxidized lignin. The oxidized lignin may be oxidized Kraft lignin. In another embodiment, the one or more lignin compounds comprise organosolv lignin, preferably are organosolv lignin.

[0044] In an embodiment, the one or more lignin compounds are obtained by treating native lignin in a sulfite pulping process. The sulfite pulping may be followed by one or more post-pulping sulfonation or oxidation steps, preferably oxidation steps. In another embodiment, the one or more lignin compounds are obtained by treating native lignin in a Kraft pulping process followed by one or more post-pulping sulfonation steps. In another embodiment, the one or more lignin compounds are obtained by treating native lignin in a Kraft pulping process followed by one or more post-pulping oxidation steps.

[0045] In an embodiment, the one or more lignin compounds are lignosulfonate or oxidized Kraft lignin. In a preferred embodiment, the one or more lignin compounds are lignosulfonate. The lignosulfonate may be lignosulfonate as obtained from sulfite pulping. In another embodiment, the one or more lignin compounds are oxidized Kraft lignin.

[0046] It is particularly preferred that the one or more lignin compounds are lignosulfonate. It has been shown that lignosulfonate is a particularly good substrate for the depolymerization process of the present invention.

[0047] In an embodiment, the one or more lignin compounds do not contain calcium and / or magnesium, or contain calcium and / or magnesium in an amount of less than 0.1 wt.%, preferably less than 0.05 wt.%, based on the weight of the lignin compounds. The terms “calcium” and “magnesium” encompass calcium and magnesium ions that may be associated with negatively charged groups on the lignin compound. The reason for the preferred low amounts of calcium and magnesium, if any, is that calcium and magnesium create scaling in the reaction and reduce uptime for the process.

[0048] As referred to herein, “sulfonated lignin” is a lignin derivative that is obtained from native lignin by introducing sulfonate groups. Sulfonate groups, as defined herein, are functional groups of the structure -SOs", wherein the sulfur atom is bound to a carbon atom of the lignin backbone. The negative charge of the -SOa' groups is typically balanced by positively charged counter ions. -SO3H groups are also covered by the term “sulfonate groups”, as used herein.

[0049] The term “lignosulfonate”, as used within the context of the present application, refers to any lignin derivative which is formed during sulfite pulping of lignin-containing material, such as, e.g., wood, in the presence of sulfite ions and / or bisulfite ions. For example, during the acidic sulfite pulping of lignin-based material, electrophilic carbon cations in the lignin are produced which are a result of the acid catalyzed ether cleavage. Thus, lignin may react, via these carbo-cations, with the sulfite or bisulfite ions under the formation of lignosulfonates. In an embodiment, the lignin compound used in the present invention is lignosulfonate.

[0050] “Sulfite pulping” is known in the art of wood / plant material processing. Sulfite pulping may be used for producing almost pure cellulose fibers from lignocellulosic biomass (i.e. plant matter). This “pulping” is typically achieved by extracting lignin from lignocellulosic biomass in large pressure vessels called digesters by using various salts of sulfurous acid. During sulfite pulping, lignin molecules are sulfonated and thereby rendered water-soluble. In accordance with the present invention, “sulfite pulping” refers to the process of reacting lignocellulosic biomass or derivatives thereof with at least one salt of sulfurous acid. The salts used in said pulping process are preferably sulfites (SO32") or bisulfites (HSO3"). Depending on the pulping conditions, feed material, and potential post processing, the lignosulfonate polymer can have varying structures and chemical functionalities, such as molecular weight, degree of sulfonation, degree of conjugation, carboxylate groups (-COOH), phenolic groups, etc. Lignosulfonate therefore represents a highly diversified class of materials.

[0051] The degree of sulfonation may be suitably adjusted by varying the pulping conditions, with higher sulfite salt content and a higher temperature generally yielding a higher degree of sulfonation.

[0052] Sulfite pulping may generally be divided into four main groups: acid, acid bisulfite, weak alkaline, and alkaline sulfite pulping. In an embodiment, cellulosic biomass is cooked with a sulfite, preferably a sodium, calcium, ammonium or magnesium sulfite under acidic, neutral, or basic conditions. This sulfite pulping dissolves most of the native lignin present in the cellulosic biomass as sulfonated lignin (lignosulfonate; water-soluble lignin), together with parts of the hemicellulose.

[0053] With regard to the sulfite pulping, the respective disclosure of WO 2010 / 078930 with the title "Lignocellulosic Biomass Conversion" as filed on December 16, 2009, is incorporated by reference into the present disclosure.

[0054] In an embodiment, the one or more lignin compounds are sulfonated lignin, preferably lignosulfonate, and have an amount of organic sulfur which is associated with the sulfonate groups attached to the lignin of less than 8% w / w, preferably less than 7% w / w, morepreferably less than 5% w / w, more preferably less than 4% w / w. Preferably, the amount of organic sulfur which is associated with the sulfonate groups attached to the lignin of 0-8% w / w, preferably 1-7% w / w, more preferably 2-5% w / w, more preferably 2-4% w / w.

[0055] The amount of “organic” sulfur [%S(org), i.e. the amount of sulfur which is associated with the sulfonate groups attached to the lignin], i.e. the degree of sulfonation, is determined based on the difference between total sulfur %S(tot) and the inorganic sulfur %S(inorg) using the following relation: %S(org) = %S(tot) - %S(inorg). Total sulfur is determined with an element analyzer, for instance a ThermoQuest NCS 2500, Appropriate sample amounts (for instance 1-2 mg) are placed in tin capsules with a suitable catalyst (for instance Vanadium pentoxide). Total sulfur in the sample is then quantified using the 2,5-Bis(5- tert-butyl-2-benzo-oxazol-2-yl)thiophene (BBOT) standard, or other suitable sulfur standards. The samples are combusted at 1400°C and all sulfur is oxidized to SO2 and quantified. Inorganic sulfur is determined by measuring sulfate in oxidized samples using ion chromatography with conductivity detection (for instance Dionex instrument using an lonPac AS11-HC column with 13 mM OH- eluent), 30 mg samples are weighed into 50-ml volumetric flasks. 10 ml of 0.5 % NaOH and 5 ml of 3 % H2O2 are added to oxidize sulfurous inorganic anions into sulfate. Samples are then left 12-16 h to give time to react. Milli-Q water is added and pH neutralized by adding 2 ml of 5 % CH3COOH and diluted to the mark with Milli-Q water. Sulfate standards are prepared between 5 mg / l and 80 mg / l. The sulfate content in the oxidized samples is then determined using ion chromatography according to the instrument manual.

[0056] The amount of “carboxylate”, i.e. COOH groups can be determined by potentiometric titration as described in subchapter 7.5.2 (“Determination of carboxyl Groups by Nonaqueous Potentiometric Titration") by C.W. Dence in the reference book “Methods in Lignin Chemistry’, S. Y. Lin and C. W. Dence, Springer-Verlag Berlin Heidelberg, 1992, p 458- 464. The amount is expressed as the weight % of carboxylate relative to the overall dry solids weight of the lignin derivative.

[0057] As noted above, in an embodiment, the one or more lignin compounds are lignosulfonate as obtained from sulfite pulping. As referred to herein, “lignosulfonate as obtained from sulfite pulping" is lignosulfonate that is the direct product of sulfite pulping. Or, in other words, “lignosulfonate as obtained from sulfite pulping" is lignosulfonate directly obtained from a sulfite pulping process without the application of any post-pulping functionalization steps. Thus, lignosulfonate obtained as a by-product of cellulose production by means of sulfite pulping is a “lignosulfonate as obtained from sulfite pulping” within the meaning of the present invention.

[0058] In another embodiment, one or more post-pulping sulfonation or oxidation steps can be performed for obtaining the lignin compound used in the present invention. The oxidation step can be selected from at least one of the following: oxidation with air (oxygen) and / or a periodate, peroxide, ozone or the like, optionally at elevated temperature, TEMPO oxidation, optionally in the presence of an oxidation catalyst and other methods and agents known to the skilled person for oxidizing biomass.

[0059] As referred to herein, a “post-pulping functionalization step", a “post-pulping step” or the like is a chemical, electrochemical, or physical treatment step that is applied subsequent to sulfite pulping or Kraft pulping and that alters the molecular structure of the lignin derivative subjected to said “post-pulping functionalization step". However, any step applied after sulfite pulping or Kraft pulping that does not alter the chemical structure of the lignin derivative, for example, a step for increasing the purity of the lignin product (e.g. a washing step, a filtration step, and the like) is not a “post-pulping functionalization step”, “post-pulping step” or the like within the meaning of the present application.

[0060] As used herein, “Kraft lignin” refers to the lignin product as obtained from a Kraft pulping process. Kraft lignin as such does not comprise sulfonate groups and is not water- soluble. However, Kraft lignin can be rendered water-soluble, for example by applying a postpulping functionalization step, in particular sulfonation or oxidation. Hence, as mentioned above, in one embodiment, the lignin compound is sulfonated lignin obtained from Kraft lignin (also referred to as “sulfonated Kraft lignin”). In embodiments, such sulfonated Kraft lignin may be obtained when Kraft lignin is treated in a post-pulping sulfonation reaction, for example with alkali sulfite and alkylaldehyde at elevated temperature and pressure. In other embodiments, sulfite pulping may be used for sulfonating Kraft lignin. If such sulfonated Kraft lignin is used in the present invention, the amount of organic sulfur which is associated with the sulfonate groups attached to the lignin is preferably less than 8% w / w, preferably less than 7% w / w, more preferably less than 5% w / w, more preferably less than 4% w / w. Preferably, the amount of organic sulfur which is associated with the sulfonate groups attached to the lignin of 0-8% w / w, preferably 1-7% w / w, more preferably 2-5% w / w, more preferably 2-4% w / w.

[0061] As noted above, the one or more lignin compounds may be oxidized Kraft lignin, i.e. Kraft lignin that has been subjected to a post-pulping oxidation reaction. In preferred embodiments, said oxidation step is selected from at least one of the following: oxidation with air (oxygen) and / or a periodate, peroxide, ozone or the like, optionally at elevated temperature, TEMPO oxidation, optionally in the presence of an oxidation catalyst and other methods and agents known to the skilled person for oxidizing biomass.

[0062] “Kraft pulping” (also referred to as “sulfate pulping”) entails treatment of wood chips with a hot mixture of water, sodium hydroxide, and sodium sulfide, known as white liquor, that breaks the bonds that link lignin, hemicellulose, and cellulose. Kraft lignin can be described as precipitated, non-sulfonated alkaline lignin. Kraft lignin differs structurally and chemically from lignosulfonate, e.g. in that Kraft lignin is not water-soluble. Sulfite pulping or other sulfonating reactions may be used for sulfonating Kraft lignin and thereby rendering the same water- soluble.

[0063] Examples of post pulping methods to modify the sulfonate / carboxylate content without introducing non-biobased carbon (i.e. carbon not originating from the lignin) into the lignin include sulfonation and various types of oxidation (e.g. thermal treatment, oxygen, peroxide, ozone, etc.).

[0064] In accordance with the above, the one or more lignin compounds can be obtained by treating native lignin in a Kraft pulping process followed by one or more post-pulping sulfonation steps or oxidation steps. The oxidation step can be selected from at least one of the following: oxidation with air (oxygen) and / or a periodate, peroxide, ozone or the like, optionally at elevated temperature, TEMPO oxidation, optionally in the presence of an oxidation catalyst and other methods and agents known to the skilled person for oxidizing biomass.

[0065] “Organosolv lignin”, as referred to herein, is a type of lignin obtained through the organosolv process, which is a biomass fractionation method used to separate lignin, cellulose, and hemicellulose from lignocellulosic biomass such as wood, agricultural residues, or dedicated energy crops. The term “organosolv” is derived from “organic solvent”, indicating that this process involves the use of organic solvents to dissolve lignin and extract it from the biomass.

[0066] In an embodiment, the one or more lignin compounds have, prior to step (1) of the process of the present invention, been treated in a way that facilitates depolymerization. The lignin may have been extracted by a method in which a blocking agent, such as an aldehyde, has been used to prevent condensation reactions. Oxidative or reductive pretreatment may have primed the lignin to facilitate depolymerization. The one or more lignin compounds may also have been selected or tuned to contain syringyl-lignin (S units) which are less susceptible to repolymerization reactions. Alteration of lignin biosynthesis in biomass cells may make substrates more susceptible to chemical depolymerization.

[0067] In an embodiment, the one or more lignin compounds are present in an amount of at least 4%, preferably at least 6%, more preferably at least 8%, more preferably at least 10%, more preferably at least 12%, more preferably at least 14%, even more preferably at least16%, based on the total weight of the composition. These rather high concentrations of lignin starting material are not only beneficial for producing the product, but also aid in down-stream processing. For example, high dry matter is beneficial in a liquid-liquid alkaline alcohol extraction process.

[0068] According to the present invention, one or more alkaline compounds are present and the composition has an alkaline pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0. Further, the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- 1 weightiignin compounds) is at least 1 mol of hydroxide ions per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg. Thus, the one or more alkaline compounds are provided in an amount such that the amount of added hydroxide ions (in mol) is at least 1 per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg.

[0069] The alkaline base is used for several reasons. It is required for the dissolution of non-water-soluble lignin (such as Kraft lignin or native lignin), it promotes the depolymerization of the lignin compound and it stabilizes the generated hydroxyl and carbonyl groups on the depolymerized product. An incomplete deprotonation of the free hydroxyl groups, caused by an insufficient concentration of alkaline base, significantly reduces the monomeric yield, favors recondensation, and increases the formation of char. Carbon dioxide and organic acids such as formic acid and acetic acid are formed during the lignin depolymerization reaction. Thus, the depolymerization reaction is a base-consuming process (see also above).

[0070] The alkaline concentration should be sufficient not only to deprotonate the free hydroxyl groups on the lignin, but also for the reaction of newly formed hydroxyl groups of the monomers. In addition to that, there should be enough alkaline base to neutralize the generated carbon dioxide and organic acids. The alkali base / lignin weight ratio is, therefore, an important parameter.

[0071] Accordingly, as noted above, in the process according to the present invention, the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- 1 weightiignin compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg. This provides for a sufficient amount of base in the reaction mixture.

[0072] The composition provided in step (1) may further comprise an oxidant, for example oxygen or H2O2. In a preferred embodiment, however, the composition provided in step (1) does not comprise an oxidant.

[0073] In step (2) of the process of the present invention, the composition is heated to the reaction temperature (also referred to herein as “peak temperature”).

[0074] The inventors of the present invention have found that a fast heating rate (and also a short reaction time) is advantageous for solving at least a part of the above-mentioned problems. In particular, it has been found that short residence and reaction times reduce the degree of recondensation reactions of the aromatic monomers as well as the polymeric lignin and, thus, reduce issues associated with the formation of insoluble byproducts. It further allows for fine-tuning of reaction conditions to optimize the yield for the specific feedstock.

[0075] Moreover, it has particularly been found that a reaction temperature (peak temperature) between 180 °C and 500 °C is advantageous for solving at least a part of the above-mentioned problems. Thus, in one embodiment, the peak temperature is between 180 °C and 500 °C, or between 250 °C and 500 °C, or between 300 °C and 500 °C, or between 320 °C and 420 °C. According to a preferred embodiment, the peak temperature is between 260 °C and 500 °C, more preferably between 280 °C and 500 °C, more preferably between 300 °C and 500 °C. A peak temperature of between 280 °C and 500 °C has been found to give good results.

[0076] Further, it has been found that reaching the peak temperature in a short period of time is advantageous for solving at least a part of the above-mentioned problems. Or, in other words, it has been found that rapidly heating the reaction mixture (or “composition”) to peak temperature is advantageous. In particular, it has been found that it is advantageous if the time to go from 100 °C to peak temperature does not exceed 240 seconds. Preferably, the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 180 seconds, more preferably 5 to 180 seconds.

[0077] In step (3) of the process of the present invention, the composition is kept at substantially the peak temperature for a defined period of time. “Substantially the peak temperature” refers to the peak temperature ± 5 °C, preferably ± 3 °C.

[0078] As noted above, it has been found that short residence and reaction times reduce the degree of recondensation reactions of the aromatic monomers as well as the polymeric lignin and, thus, reduce issues associated with the formation of insoluble byproducts. In particular, it is advantageous to keep the time at peak temperature relatively short to avoid degradation of desirable methoxy groups and para-functionalized phenols. In particular, using comparatively short times at peak temperature reduces the degree of recondensation reactions of the aromatic monomers as well as the polymeric lignin and, thus, reduce issues associated with the formation of insoluble by-products.

[0079] Preferably, in step (3), the composition is kept at substantially the peak temperature for a time of not more than 30 seconds, preferably between 1 and 30 seconds, more preferably between 5 and 30 seconds. It has been found that such short reaction times lead to particularly good results.

[0080] After this base-promoted depolymerization of lignin, the result is a product mixture containing monomers with a structural backbone such as coumaryl, guaiacyl, and / or syringyl and an oligomeric fraction, and due to the excess base, all fractions of the product mixture are solubilized. This distinguishes the inventive process from prior art processes, which usually result in char formation, caused by recondensation of the aromatic moieties due to insufficient amounts of base. In addition, the short reaction times reduce the degree of recondensation reactions of the aromatic monomers as well as the residual polymeric lignin and, thus, reduce issues associated with formation of insoluble materials.

[0081] Preferably, the heating time as well as the time at peak temperature are both kept comparatively short. In particular, a fast heating rate in step (2) and a short reaction time in step (3) reduce the degree of recondensation reactions of the aromatic monomers as well as the residual polymeric lignin and, thus, reduce issues associated with the formation of undesired insoluble materials.

[0082] Thus, in a preferred embodiment, the process of the present invention is defined as follows:Process for the depolymerization of a lignin compound, the process comprising at least the following steps:(1) providing a composition, the composition comprising:• one or more lignin compounds,• one or more alkaline compounds, and• water, wherein the composition has an alkaline pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0, and wherein the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- / weighty compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg,(2) heating the composition to a defined peak temperature, wherein the heating is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than240 seconds, preferably not more than 180 seconds, more preferably 5 to 180 seconds,(3) keeping the composition at substantially the peak temperature for a time of not more than 30 seconds, preferably between 1 and 30 seconds, more preferably between 5 and 30 seconds, wherein substantially means ± 5 °C,(4) cooling the composition.

[0083] In a further preferred embodiment, the process of the present invention is defined as follows:Process for the depolymerization of a lignin compound, the process comprising at least the following steps:(1) providing a composition, the composition comprising:• one or more lignin compounds,• one or more alkaline compounds, and• water, wherein the composition has an alkaline pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0, and wherein the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- / weighty™ compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg,(2) heating the composition to a defined peak temperature, wherein the peak temperature is between 180 °C and 500 °C, preferably between 250 °C and 500 °C, more preferably between 320 °C and 420 °C, wherein the heating is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 240 seconds, preferably not more than 180 seconds, more preferably 5 to 180 seconds,(3) keeping the composition at substantially the peak temperature for a time of not more than 30 seconds, preferably between 1 and 30 seconds, more preferably between 5 and 30 seconds, wherein substantially means ± 5 °C,(4) cooling the composition.

[0084] In a further preferred embodiment, the process of the present invention is defined as follows:Process for the depolymerization of a lignin compound, the process comprising at least the following steps:(1) providing a composition, the composition comprising:• one or more lignin compounds,• one or more alkaline compounds, and• water, wherein the composition has an alkaline pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0, and wherein the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- / weighty™ compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg,(2) heating the composition to a defined peak temperature, wherein the peak temperature is between 260 °C and 500 °C, preferably between 280 °C and 500 °C, more preferably between 300 °C and 500 °C, wherein the heating is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 240 seconds, preferably not more than 180 seconds, more preferably 5 to 180 seconds,(3) keeping the composition at substantially the peak temperature for a time of not more than 30 seconds, preferably between 1 and 30 seconds, more preferably between 5 and 30 seconds, wherein substantially means ± 5 °C,(4) cooling the composition.

[0085] In a further preferred embodiment, the process of the present invention is defined as follows:Process for the depolymerization of a lignin compound, the process comprising at least the following steps:(1) providing a composition, the composition comprising: one or more lignin compounds, one or more alkaline compounds, andwater, wherein the composition has an alkaline pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0, and wherein the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- / weighty™ compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds, preferably at least 3 mol per kg, more preferably at least 5 mol per kg,(2) heating the composition to a defined peak temperature, wherein the peak temperature is between 280 °C and 500 °C, wherein the heating is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 240 seconds, preferably not more than 180 seconds, more preferably 5 to 180 seconds,(3) keeping the composition at substantially the peak temperature for a time of not more than 30 seconds, preferably between 1 and 30 seconds, more preferably between 5 and 30 seconds, wherein substantially means ± 5 °C,(4) cooling the composition.

[0086] It is preferred that steps (2) and (3) are at least partially performed under pressure. Preferably, steps (2) and (3) are at least partially performed under a pressure of at least 10 bar and / or above the pressure at the boiling point of water at a given temperature. This avoids that the reaction turns into a wet-air-oxidation, which would yield a less selective reaction.

[0087] In an embodiment, the composition obtained in step (3) comprises vanillin and / or p-hydroxy benzaldehyde and / or syringaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L. Also, the composition obtained in step (3) preferably comprises acetovanillone and / or p-hydroxy acetophenone and / or acetosyringone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L.

[0088] In step (4) of the process of the present invention, the composition is cooled. Preferably, the composition is cooled to a target temperature below 95 °C, preferably to a target temperature below 75 °C. It is also preferred that the composition of step (3) is cooled quickly. Preferably, the cooling in step (4) is performed in a way such that the time for cooling the composition from peak temperature to target temperature is not more than 240 seconds, preferably not more than 180 seconds, more preferably between 0 to 180 seconds.

[0089] Generally, the process of the present invention can be performed with or without the use of an oxidant, in particular H2O2. Thus, in one embodiment, the process is performed in the presence of an oxidant, preferably H2O2. Preferably, if an oxidant is used, the oxidant is fed into a reactor separately from the composition provided in step (1). In a preferred embodiment, the process is performed in the absence of an oxidant, in particular H2O2.

[0090] An “oxidant” within the meaning of the present invention is to be understood as a compound added or a measure performed for providing an oxidative environment or for increasing the oxidative potential. The reason is that, in principle, oxygen (O2) dissolved in the aqueous composition provided in step (1) also exerts a certain oxidative effect. However, if its concentration is not purposefully increased (for example by air or oxygen bubbling), dissolved oxygen is normally present only in low amounts and does not play a significant role in the depolymerization reaction. Thus, naturally occurring dissolved oxygen is not considered as an “oxidant”. A measure that is performed for providing an oxidative environment is, in particular, bubbling air or oxygen through the composition of step (1) or through the water used for preparing the composition of step (1).

[0091] In a second aspect, the present invention relates to a composition comprising p- hydroxy benzaldehyde and / or vanillin and / or syringaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and p-hydroxy acetophenone and / or acetovanillone and / or acetosyringone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L. Preferably the weight ratio of vanillin to acetovanillone (weightvaniiiin / weightacetovaiiione) is at least 10, preferably at least 20, more preferably at least 30 and / or the weight ratio of p-hydroxy benzaldehyde to p-hydroxy acetophenone (weightp.hydroxy benzaldehyde / weightp-hydroxy acetophenone) is at least 10, preferably at least 20, more preferably at least 30 and / or the weight ratio of syringaldehyde to acetosyringone (weightsyringaidehyde I weightacetosyringone) is at least 10, preferably at least 20, more preferably at least 30.

[0092] In an embodiment, the composition is obtained from the process according to the present invention.

[0093] The present invention is also described by the following Items, also in combination with each other and in combination with features or embodiments described throughout the present disclosure.1. Process for the depolymerization of a lignin compound, the process comprising at least the following steps:(1) providing a composition, the composition comprising:• one or more lignin compounds,• one or more alkaline compounds, and• water, wherein the composition has an alkaline pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0, and wherein the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- / weighty™ compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds,(2) heating the composition to a defined peak temperature,(3) keeping the composition at substantially the peak temperature for a defined time, wherein substantially means ± 5 °C,(4) cooling the composition. The process according to Item 1 , wherein the composition of step (1) is fed to a reactor. The process according to Item 1 or 2, wherein the composition of step (1) is provided outside of a reactor and is then fed to reactor. The process according to any one of the preceding Items, wherein the process is performed in a continuous mode. The process according to Item 4, wherein the reaction is performed in a tubular reactor. The process according to any one of the preceding Items, wherein the process is performed in the presence of only trace amounts of transition metals, preferably in the absence of transition metals. The process according to any one of the preceding Items, wherein in step (1), the composition is prepared, before heating step (2) is started. The process according to any one of the preceding Items, wherein the one or more lignin compounds are water-soluble.9. The process according to any one of the preceding Items, wherein the one or more lignin compounds comprise charged functional groups, preferably sulfonate and / or carboxylate groups.10. The process according to any one of the preceding Items, wherein the one or more lignin compounds comprise or are sulfonated lignin, preferably lignosulfonate or sulfonated Kraft lignin; oxidized lignin, preferably oxidized Kraft lignin; or organosolv lignin; wherein preferably the one or more lignin compounds are sulfonated lignin, preferably lignosulfonate or sulfonated Kraft lignin; oxidized lignin, preferably oxidized Kraft lignin; or organosolv lignin.11. The process according to any one of the preceding Items, wherein the one or more lignin compounds are obtained by treating native lignin in a sulfite pulping process, optionally followed by one or more post-pulping sulfonation or oxidation steps, preferably oxidation steps; or wherein the one or more lignin compounds are obtained by treating native lignin in a Kraft pulping process followed by one or more post-pulping sulfonation steps; or wherein the one or more lignin compounds are obtained by treating native lignin in a Kraft pulping process followed by one or more post-pulping oxidation steps.12. The process according to any one of the preceding Items, wherein the one or more lignin compounds are lignosulfonate or oxidized Kraft lignin.13. The process according to Item 12, wherein the one or more lignin compounds are lignosulfonate.14. The process according to Item 13, wherein the one or more lignin compounds are lignosulfonate as obtained from sulfite pulping.15. The process according to Item 12, wherein the one or more lignin compounds are oxidized Kraft lignin.16. The process according to any one of the preceding Items, wherein the one or more lignin compounds do not contain calcium or contain calcium in an amount of less than0.1 wt.%, preferably less than 0.05 wt.%, based on the weight of the one or more lignin compounds.17. The process according to any one of the preceding Items, wherein the one or more lignin compounds are present in an amount of at least 4%, preferably at least 6%, more preferably at least 8%, more preferably at least 10%, more preferably at least 12%, more preferably at least 14%, even more preferably at least 16%, based on the total weight of the composition.18. The process according to any one of the preceding Items, wherein the weight ratio of the one or more alkaline compounds to the one or more lignin compounds (weightaikaiine compounds / weightiignin compounds) is at least 0.05, preferably at least 0.1 , more preferably at least 0.2.19. The process according to any one of the preceding Items, wherein the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 240 seconds, preferably not more than 180 seconds, more preferably 5 to 180 seconds.20. The process according to any one of the preceding Items, wherein in step (3) the temperature is kept at substantially the peak temperature for a time of no longer than 30 seconds, preferably between 1 and 30 seconds, more preferably between 5 and 30 seconds, wherein “substantially” means ± 5 °C.21. The process according to any one of the preceding Items, wherein peak temperature is between 180 °C and 500 °C, or between 250 °C and 500 °C, or between 300 °C and 500 °C, or between 320 °C and 420 °C, wherein preferably the peak temperature is between 260 °C and 500 °C, more preferably between 280 °C and 500 °C, more preferably between 300 °C and 500 °C.22. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 240 seconds, andin step (3) the temperature is kept at substantially the peak temperature for a time of no longer than 30 seconds.23. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 240 seconds, and in step (3) the temperature is kept at substantially the peak temperature for a time of between 1 and 30 seconds.24. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 240 seconds, and in step (3) the temperature is kept at substantially the peak temperature for a time of between 5 and 30 seconds.25. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 180 seconds, and in step (3) the temperature is kept at substantially the peak temperature for a time of no longer than 30 seconds.26. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 180 seconds, and in step (3) the temperature is kept at substantially the peak temperature for a time of between 1 and 30 seconds.27. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 180 seconds, andin step (3) the temperature is kept at substantially the peak temperature for a time of between 5 and 30 seconds. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is 5 to 180 seconds, and in step (3) the temperature is kept at substantially the peak temperature for a time of no longer than 30 seconds. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is 5 to 180 seconds, and in step (3) the temperature is kept at substantially the peak temperature for a time of between 1 and 30 seconds. The process according to any one of the preceding Items, wherein: the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is 5 to 180 seconds, and in step (3) the temperature is kept at substantially the peak temperature for a time of between 5 and 30 seconds. The process according to any one of Items 22-30, wherein the peak temperature is between 180 °C and 500 °C, or between 250 °C and 500 °C, or between 300 °C and 500 °C, or between 320 °C and 420 °C, wherein preferably the peak temperature is between 260 °C and 500 °C, more preferably between 280 °C and 500 °C, more preferably between 300 °C and 500 °C. The process according to any one of the preceding Items, wherein at least steps (2) and (3) are at least partially performed under pressure.33. The process according to Item 32, wherein at least steps (2) and (3) are at least partially performed under a pressure of at least 10 bar and / or above the pressure at the boiling point of water at a given temperature.34. The process according to any one of the preceding Items, wherein the composition obtained in step (3) comprises p-hydroxy benzaldehyde and / or vanillin and / or syringaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and p-hydroxy acetophenone and / or acetovanillone and / or acetosyringone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L.35. The process according to any one of the preceding Items, wherein in the composition obtained in step (3), the weight ratio of vanillin to acetovanillone (weightvaniiiin / weightacetovaiiione) is at least 10, preferably at least 20, more preferably at least 30.36. The process according to any one of the preceding Items, wherein in the composition obtained in step (3), the weight ratio of p-hydroxy benzaldehyde to p-hydroxy acetophenone (weightp-hydroxy benzaldehyde I Weightp-hydroxy acetophenone) iS at least 10, preferably at least 20, more preferably at least 30.37. The process according to any one of the preceding Items, wherein in the composition obtained in step (3), the weight ratio of syringaldehyde to acetosyringone (weightsyringaidehyde I weightacetosyringone) is at least 10, preferably at least 20, more preferably at least 30.38. A combination of Items 34 and 35.39. A combination of Items 34 and 36.40. A combination of Items 34 and 37.41 . A combination of Items 34, 35, 36, and 37.42. The process according to any one of the preceding Items, wherein the cooling in step (4) is performed so that the composition is cooled to a target temperature below 95 °C,preferably to a target temperature below 75 °C, preferably cooled quickly, preferably so that the time for cooling the composition from peak temperature to target temperature is not more than 240 seconds, preferably not more than 180 seconds, more preferably between 0 to 180 seconds. The process according to any one of the preceding Items, wherein the depolymerization of the one or more lignin compounds is conducted in the presence of an oxidant, preferably hydrogen peroxide. A composition comprising p-hydroxy benzaldehyde and / or vanillin and / or syringaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and p-hydroxy acetophenone and / or acetovanillone and / or acetosyringone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L. The composition according to Item 44, comprising p-hydroxy benzaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and p-hydroxy acetophenone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L. The composition according to Item 44, comprising vanillin in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and acetovanillone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L. The composition according to Item 44, comprising syringaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and acetosyringone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L. The composition according to any one of Items 44-47, wherein the weight ratio of vanillin to acetovanillone (weightvaniiiin / weightacetovaiiione) is at least 10, preferably at least 20, more preferably at least 30, and / or wherein the weight ratio of p-hydroxy benzaldehyde to p-hydroxy acetophenone (weightp.hydroxy benzaldehyde I weightp-hydroxyacetoPhenone) is at least 10, preferably at least 20, more preferably at least 30 and / orwherein the weight ratio of syringaldehyde to acetosyringone (weightSyringaidehyde I weightacetosyringone) is at least 10, preferably at least 20, more preferably at least 30.49. The composition according to any one of Items 44-48, wherein the composition has an alkaline pH.50. The composition according to any one of Items 44-49, wherein the composition is obtained from the process according to any one of Items 1-43.EXAMPLES

[0094] The present is now further described and illustrated by the following examples.

[0095] The examples were conducted in continuous mode using a 920 mm long, 8mm internal diameter tubular reactor with a static mixer straight before the inlet. The system was equipped with a heating system delivering 2.5-1000 W / cm3and with the possibility to introduce gases. Of the 920 mm reactor, 600 mm was exposed to the heating mantle and the final 220 mm was the reaction volume at the desired temperature (316 stainless steel). The pressure limits were set between 10-300 bar and due to reaction times shorter than 1 min (21-32 s), a liquid pulsation dampener was used to increase the lifetime of the equipment.Example 1 :

[0096] 8 kg of sodium hydroxide (50 wt.%) was diluted with 5.71 kg water in a 25 L plastic container. 11.29 kg of lignosulfonate solution (Na lignosulfonate, 31 wt.%) was added and stirred until a homogenous mixture was obtained. The mixture was transferred to the feeding tank. Initially, a flow of water (8 kg / h) in the reactor was heated to 300 °C before the starting material was fed into the reactor with a speed of 8 kg / h. Following 2 hours of continuous reaction a sample was collected.

[0097] The mixture was analyzed for aromatic monomers and organic acids (see Table 1 , Entry 1).Example 2:

[0098] 8.3 kg of sodium hydroxide (50 wt.%) was diluted with 4.91 kg water in a 25 L plastic container. 11.76 kg of lignosulfonate solution (Na lignosulfonate, 31 wt.%) was addedand stirred until a homogenous mixture was obtained. The mixture was transferred to the feeding tank. Initially a flow of water (10 kg / h) in the reactor was heated to 320 °C before the starting material was ted into the reactor with a speed of 9.6 kg / h along with 0.4 kg / h of 10 wt.% H2O2. Following 2 hours of continuous reaction a sample was collected.

[0099] The mixture was analyzed for aromatic monomers and organic acids (see Table 1 , Entry 2).Example 3:

[0100] 8 kg of sodium hydroxide (50 wt.%) was diluted with 5.71 kg water in a 25 L plastic container, 11.29 kg of lignosulfonate solution (Na lignosulfonate, 31 wt.%) was added and stirred until homogenous. The mixture was transferred to the feeding tank. Initially a flow of water (10 kg / h) in the reactor was heated to 300 °C before the starting material was fed into the reactor with a speed of 10 kg / h. Following 2 hours of continuous reaction a sample was collected.

[0101] The mixture was analyzed for aromatic monomers and organic acids (see T able 1 , Entry 3).Example 4:

[0102] 8 kg of sodium hydroxide (50 wt.%) was diluted with 8.94 kg water in a 25 L plastic container, 8.06 kg of lignosulfonate solution (Na lignosulfonate, 31 wt.%) was added and stirred until homogenous. The mixture was transferred to the feeding tank. Initially a flow of water (12 kg / h) in the reactor was heated to 280 °C before the starting material was fed into the reactor with a speed of 12 kg / h. Following 2 hours of continuous reaction a sample was collected.

[0103] The mixture was analyzed for aromatic monomers and organic acids (see Table 1 , Entry 4).Example 5:

[0104] 8 kg of sodium hydroxide (50 wt.%) was diluted with 5.68 kg water in a 25 L plastic container, 11.36 kg of lignosulfonate solution (Na lignosulfonate, 22 wt.%) was added and stirred until homogenous. The mixture was transferred to the feeding tank. Initially a flow of water (10 kg / h) in the reactor was heated to 240 °C before the starting material was fed into the reactor with a speed of 10 kg / h. Following 2 hours of continuous reaction a sample was collected.

[0105] The mixture was analyzed for aromatic monomers and organic acids (see Table 1 , Entry 5).Example 6:

[0106] 8.7 kg of sodium hydroxide (50 wt.%) was diluted with 3.95 kg water in a 25 L plastic container, 12.35 kg of lignosulfonate solution (Na lignosulfonate, 22 wt.%) was added and stirred until homogenous. The mixture was transferred to the feeding tank. Initially a flow of water (10 kg / h) in the reactor was heated to 240 °C before the starting material was fed into the reactor with a speed of 9.2 kg / h along with 0.8 kg / h of 10 wt.% H2O2. Following 2 hours of continuous reaction a sample was collected.

[0107] The mixture was analyzed for aromatic monomers and organic acids (see Table 1 , Entry 6).Example 7:

[0108] 8.3 kg of sodium hydroxide (50 wt.%) was diluted with 13.12 kg water in a 25 L plastic container, 3.55 kg of lignosulfonate solution (Na lignosulfonate, 22 wt.%) was added and stirred until homogenous. The mixture was transferred to the feeding tank. Initially a flow of water (10 kg / h) in the reactor was heated to 200 °C before the starting material was fed into the reactor with a speed of 9.6 kg / h along with 0.4 kg / h of 10 wt.% H2O2. Following 2 hours of continuous reaction a sample was collected.

[0109] The mixture was analyzed for aromatic monomers and organic acids (see Table 1 , Entry 7).Example 8:

[0110] 8.7 kg of sodium hydroxide (50 wt.%) was diluted with 8.28 kg water in a 25 L plastic container, 8.03 kg of lignosulfonate solution (Na lignosulfonate, 22 wt.%) was added and stirred until homogenous. The mixture was transferred to the feeding tank. Initially a flow of water (10 kg / h) in the reactor was heated to 200 °C before the starting material was feed into the reactor with a speed of 9.2 kg / h along with 0.8 kg / h of 10 wt.% H2O2. Following 2 hours of continuous reaction a sample was collected.

[0111] The mixture was analyzed for aromatic monomers and organic acids (see Table 1 , Entry 8).Table 1Entry Vanillin Acetovanillone Vanillic Acetic acid Formic acid (mg / L) (mg / L) acid (mg / L) (g / L) (g / L)

Claims

Borregaard ASClaims1. Process for the depolymerization of a lignin compound, the process comprising at least the following steps:(1) providing a composition, the composition comprising:• one or more lignin compounds,• one or more alkaline compounds, and• water, wherein the composition has an alkaline pH, preferably a pH of greater than 8.0, more preferably a pH of greater than 9.0, even more preferably a pH of greater than 10.0, and wherein the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- / weighty compounds) is at least 1 mol of added hydroxide ions per kg of the one or more lignin compounds,(2) heating the composition to a defined peak temperature, wherein the peak temperature is between 260 °C and 500 °C,(3) keeping the composition at substantially the peak temperature for a defined time, wherein substantially means ± 5 °C,(4) cooling the composition.

2. The process according to claim 1, wherein the mol / weight ratio of added hydroxide ions (OH-) to the one or more lignin compounds (moloH- 1 weighty™ compounds) is at least 3 mol of added hydroxide ions per kg of the one or more lignin compounds, preferably at least 5 mol of added hydroxide ions per kg of the one or more lignin compounds.

3. The process according to claim 1 or 2, wherein the composition of step (1) is provided outside of a reactor and is then fed to reactor.

4. The process according to any one of the preceding claims, wherein the process is performed in the presence of only trace amounts of transition metals, preferably in the absence of transition metals.

5. The process according to any one of the preceding claims, wherein the one or more lignin compounds are water-soluble.

6. The process according to any one of the preceding claims, wherein the one or more lignin compounds comprise or are sulfonated lignin, preferably lignosulfonate or sulfonated Kraft lignin; oxidized lignin, preferably oxidized Kraft lignin; or organosolv lignin; wherein preferably the one or more lignin compounds are sulfonated lignin, preferably lignosulfonate or sulfonated Kraft lignin; oxidized lignin, preferably oxidized Kraft lignin; or organosolv lignin.

7. The process according to any one of the preceding claims, wherein the one or more lignin compounds are lignosulfonate or oxidized Kraft lignin.

8. The process according to any one of the preceding claims, wherein the weight ratio of the one or more alkaline compounds to the one or more lignin compound (weightaikaiine compounds I weightiignin compounds) is at least 0.05, preferably at least 0.1 , more preferably at least 0.2.

9. The process according to any one of the preceding claims, wherein the heating in step (2) is performed in a way such that the time for heating the composition from a temperature of 100 °C to the peak temperature is not more than 240 second, preferably not more than 180 seconds, more preferably 5 to 180 seconds.

10. The process according to any one of the preceding claims, wherein in step (3) the temperature is kept at substantially the peak temperature for a time of no longer than 30 seconds, preferably between 1 and 30 seconds, more preferably between 5 and 30 seconds, wherein “substantially” means ± 5 °C.11 . The process according to any one of the preceding claims, wherein the peak temperature is between 280 °C and 500 °C, preferably between 300 °C and 500 °C.

12. The process according to any one of the preceding claims, wherein the composition obtained in step (3) comprises p-hydroxy benzaldehyde and / or vanillin and / or syringaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and p-hydroxy acetophenone and / or acetovanillone and / or acetosyringone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L.

13. The process according to any one of the preceding claims, wherein the composition obtained in step (3) has a weight ratio of vanillin to acetovanillone (weightvaniiiin I weightacetovaiiione) of at least 10, preferably at least 20, more preferably at least 30; and / or a weight ratio of p-hydroxy benzaldehyde to p-hydroxy acetophenone (weightp-hydroxy benzaldehyde I weightp-hydroxy acetophenone) of at least 10, preferably at least 20, more preferably at least 30; and / or a weight ratio of syringaldehyde to acetosyringone (weightsyringaidehyde / weightacetosyringone) of at least 10, preferably at least 20, more preferably at least 30.

14. A composition comprising p-hydroxy benzaldehyde and / or vanillin and / or syringaldehyde in an amount of more than 6 g / L, preferably more than 8 g / L, more preferably more than 10 g / L, and p-hydroxy acetophenone and / or acetovanillone and / or acetosyringone in an amount of 0.001 to 1 g / L, preferably 0.01 to 0.6 g / L, more preferably 0.05 to 0.3 g / L.

15. The composition according to claim 14, wherein the composition(i) has an alkaline pH, and / or(ii) has a weight ratio of vanillin to acetovanillone (weightvaniiiin / weightacetovaiiione) of at least 10, preferably at least 20, more preferably at least 30; and / or a weight ratio of p-hydroxy benzaldehyde to p-hydroxy acetophenone (weightp.hydroxy benzaldehyde I weightp-hydroxy acetophenone) of at least 10, preferably at least 20, more preferably at least 30; and / or a weight ratio of syringaldehyde to acetosyringone (weightsyringaidehyde / weightacetosyringone) of at least 10, preferably at least 20, more preferably at least 30.

16. The composition according to claim 14 or 15, wherein the composition is obtained from the process according to any one of claims 1-13.

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