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1. (WO2017171652) PROCESS FOR THE DEPOLYMERIZATION OF LIGNIN UNDER NEUTRAL OXIDATIVE CONDITIONS
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Description

Title of Invention: Process for the depolymerization of lignin under neutral oxidative conditions

Technical Field

The present invention generally relates to a process for depolymerizing lignin to monomers and/or oligomers wherein the lignin is reacted under oxidation conditions at a neutral pH in the presence of a polar aprotic solvent at elevated temperatures. The process is especially useful to make aromatic aldehydes and acids from lignin.

Background Art

Biomass becomes a more interesting source for making fine chemicals, because it is a low-cost, abundant, environmentally benign and renewable material. Biomass comprises algae and vascular plants whose support tissue consists to a large degree of lignin. Chemically, lignins are cross-linked phenolic polymers forming larger molecules of complexity. Unfortunately there are many challenges to use lignin in order to derive fine chemicals therefrom. Harsh reaction conditions and low yields often pose severe limitations. It is difficult to depolymerize and break down the complex structures of the molecules.

Lignin depolymerization is therefore a key process for an efficient use of biomass. Especially the synthesis of fine chemicals from lignin poses high requirements with regard to selectivity and yield.

Lignin due to its chemical structure may especially offer the synthesis of aromatic aldehydes and their oxidation products, if a depolymerization is done under oxidizing conditions. In this regard lignin may be a source to make vanillin and vanillic acid. The global consumption of vanillin is around 12000 tons per year (tpa). While its price is around $15 kg, if the vanillin is made from petrochemicals such as phenol derived guaiacol, prices for lignin based vanillin can reach $100-200 kg, because it is in high demand in certain market sectors (fragrance industries, chocolate manufacturers etc.). Around 2300 tpa of vanillin are produced from lignosulfonates which are the sulfonated lignin byproducts from the production of wood pulp via the sulfite pulping process. However, modern paper and pulp industries prefer Kraft pulping over sulfite pulping and hence there is only minimal availability of lignosulfonate for vanillin synthesis. Moreover, most of the vanillin plants based on sulfite liquor were closed down; also due to disposal issues of the large amounts of caustic soda wastes (-160 kg/kg of vanillin) generated during this process. Therefore there is a need for making vanillin from other sources such as the Kraft pulping processes and from the many emerging biorefineries.

Processes to make vanillin from Kraft lignin are known, such as e.g. from Wood. Sci. Tech. 2001, 35, 245; Ind. Eng. Chem. Res. 2010, 49, 520; Holzforschung, 2011, 65, 203; US 0089046 Al and US 8,808,781 B2. All these prior reported methods require highly alkaline or acidic conditions and the solubility of Kraft lignin under neutral conditions is a major issue in these

methods. The reaction medium is extremely corrosive and causes significant waste disposal challenges. Improved, more environmentally benign, efficient and selective methods for the oxidative depolymerization of Kraft lignin to vanillin or other aromatic aldehydes and their oxidatition products as fine chemicals are therefore desirable.

There is therefore a need to provide a process that overcomes, or at least ameliorates, one or more of the disadvantages the processes for the depolymerization of lignin as disclosed above and that can proceed under neutral conditions and be considered more environmentally benign, efficient and selective over the present state of the art.

Summary

In a first aspect, there is provided a process for depolymerizing lignin to monomers and/or oligomers characterized in that the lignin is reacted with an oxidation agent at a pH between about 5.0 and about 8.0 in the presence of a polar aprotic solvent at elevated temperatures.

Advantageously this process is suited for use in the production of monomers or oligomers from lignin, such as aromatic phenols, particularly aromatic aldehydes or acids in good yields avoiding the use of highly alkaline or highly acidic agents which are corrosive and cause significant waste disposal challenges.

Advantageously the use of a polar aprotic solvent allows for lignin to be dissolved well at elevated temperatures. The use of a polar aprotic solvent is further advantageous in the depolymerization process, because it allows the depolymerization under pH-neutral oxidative conditions, such as at a pH value between 5.0 and 8.0.

Advantageously, the process disclosed above further allows the product composition to be altered depending on the concentration of oxidation agent in the matrix used as well as the total pressure.

Accordingly, a high percentage of an aromatic aldehyde may be obtained by use of a diluted mixture of oxidation agent within a gaseous matrix or lower pressures, while a high percentage of an aromatic acid may be obtained by use of an undiluted mixture of the oxidation agent or higher pressures. Further advantageously, the yield of the process as disclosed above, depending on the employed reaction conditions, can be as high as 7.3 wt% in the case of Kraft lignin.

In one embodiment, the process can proceed without the use of any metal catalyst.

Alternatively the process may comprise a transition metal complex to achieve improved yields particularly in the case of non-treated or partially pretreated lignin precursors. Advantageously, the process can be used for processing a wide variety of lignins obtained from natural sources.

In another embodiment the process comprises the steps of

a) reacting lignin or lignin containing biomass with an oxidation agent under pH neutral conditions in a polar aprotic solvent at elevated temperatures,

b) separating the reaction mixture to obtain a first product mixture comprising the monomers and/or oligomers and the solvent and a second product mixture comprising the remaining lignin and by-products.

Advantageously, this process allows for easy separation of the reaction products in an industrially upscalable way.

Accordingly, the inventors have surprisingly found a process for the depolymerization of lignin as disclosed above, which can proceed under neutral conditions and therefore can be considered more environmentally benign, efficient and selective over the present state of the art.

Definitions

In this specification a number of terms are used which are well known to a skilled addressee. Nevertheless for the purposes of clarity a number of terms will be defined. The following words and terms used herein shall have the meaning indicated:

As used herein, the term "lignin" refers to any lignin or lignin derivative which include Brauns' lignin, cellulolytic enzyme lignin, dioxane acidolysis lignin, milled wood lignin, Klason lignin, periodate lignin, kraft lignin, softwood kraft lignin, hardwood kraft lignin, lignosulfates, lignosulfonates, organosolv lignin, and steam explosion lignin and other lignin's mentioned in the decription. It also refers to any substances made in whole or in part from lignin or any subunits, monomers, or other components derived therefrom. Thus, lignin is meant to include lignin, and/or any compound comprising lignin or the residue thereof and refers to any polymer comprising p-hydroxyphenyl units, syringyl units, and guaiacyl units.

As used herein, the term "biorefinery" refers to a facility that integrates biomass conversion processes and equipment to produce fuels, power, heat, and value-added chemicals from biomass.

As used herein, the term "oligomer" refers to a molecular complex that consists of a few monomer units, in contrast to a polymer, where the number of monomers is, in principle, not limited. Preferably the oligomer comprises 2 to 8, more preferably 2 to 5 monomer units.

As used herein, the term "polar solvent" refers to a solvent wherein the solvent molecules have an uneven distribution of electron density.

As used herein, the term "aprotic solvent" refers to a solvent that has no hydrogen atom bound to an oxygen (as in a hydroxyl group) or a nitrogen (as in an amine group).

The word "substantially" does not exclude "completely" e.g. a composition which is "substantially free" from Y may be completely free from Y. Where necessary, the word "substantially" may be omitted from the definition of the invention.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means ±10% of the stated value, more typically ±7.5% of the stated value, more typically ± 5% of the stated value, more typically ± 4% of the stated value, more typically ± 3% of the stated value, more typically, ± 2% of the stated value, even more typically ± 1% of the stated value, and even more typically ± 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Brief Description of Drawings

The accompanying drawings illustrate a disclosed embodiment and serve to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

Fig. l

[Fig. 1] shows a typical reaction scheme for depolymerization of lignin according to the invention.

Fig.2

[Fig. 2] shows an example of an upscalable version of the inventive process including separation and purification steps.

Fig.3

[Fig. 3] shows typical GC spectra of the reaction product.

Fig.4

[Fig. 4] A, B and C show the Gel Permeation Chromatography (GPC) results of Kraft Lignin (Lignin Alkali, 370959 Aldrich) and the oil before and after the oxidative depolymerization in a representative example.

Fig.5

[Fig. 5] shows the typical linkages and functional groups in lignins that have been made the basis of the NMR analysis to measure the G/S ratios.

Detailed Description of Embodiments

In a first aspect, there is provided a process for depolymerizing lignin to monomers and/or oligomers characterized in that the lignin is reacted with an oxidation agent at a pH between 5.0 and 8.0 in the presence of a polar aprotic solvent at elevated temperatures.

The lignin is not limited to any specific type of lignin. Also a lignin precursor can be used. According to one embodiment Kraft lignin, wheat straw lignin and lignin from empty palm fruit bunch (EFB lignin) also can be depolymerized. Kraft lignin may be particularly mentioned.

The lignin or its precursor may be selected from any kind of cellulosic biomass, wherein the cellulosic biomass is optionally selected from any kind of wood, for example from softwood and hardwood, or grass type biomass and agricultural/industrial wastes such as empty palm fruit bunch EFB, Cornstover, wheat straw, woodchips or Kraft lignin or mixtures thereof and wherein the cellulosic biomass is chemically or enzymatically pretreated or not pretreated. The lignin can be from any kind of cellulosic biomass e.g. any kind of wood, softwood/hardwood, or grass type biomass or agricultural/industrial wastes (empty palm fruit bunch EFB, Cornstover, Wheat straw, Woodchips, Kraft lignin etc.) chemically or enzymatically pretreated or not pretreated. The process according to the invention may be also useful for the production of syringaldehyde, syringic acid, p-hydroxybenzaldehyde and p-hydroxy benzoic acid which depends on the type of biomass used.

The process according to the invention allows to use lignins such as Kraft lignin or lignins from biorefineries which otherwise are non usable in the aqueous or organic solvents of other known processes under neutral conditions. According to one embodiment higher yields of the desired reaction products may be achieved, if suitable soft wood lignins from biorefineries are used which are extracted under relatively mild processing conditions compared to the Kraft processing.

In the present application the term "monomers and/or oligomers" means molecules or oligomers derived from depolymerization of lignin, preferably under oxidative conditions. These molecules or oligomers may be a result of chemical modification or degradation of lignin during the process. The obtained depolymerized lignin monomers and oligomers may have an average molecular weight (Mw) of less than 1600 g/mol, or less than 800 g/mol.

The depolymerization of lignin according to the process converts the complex polymer molecules of the lignin into its monomers, oligomers or a mixture of monomers and oligomers. Typical monomers and oligomers include aromatic phenols, and under oxidative conditions particularly aromatic aldehydes or acids. The monomers may be oxidized in the presence of the oxidation agent. Preferred monomers and/or oligomers that can be obtained according to the process are therefore aromatic aldehydes, ketones and/or acids. The process is especially well suited to make aromatic aldehydes and acids. Vanillin, vanillic acid and acetovanillone may be particularly mentioned as such lignin depolymerization products of the instant process. The process may be preferably used to produce vanillin. Figure 1 shows a typical reaction scheme.

The pH during the polymerization is a in a neutral range such as for instance about pH 5.0 to about pH 8.0. Other ranges that can be mentioned include pH 5.0 to about pH 7.5, pH 5.0 to about pH 7.0, pH 5.5 to about pH 8.0, pH 6.0 to about pH 8.0, or pH 6.5 to about pH 7.5. Further pH values that can be mentioned are about pH 5.3, 6.1, 6.3, 6.8, 7.2 and 7.7. The process avoids the use of highly alkaline or highly acidic agents which are therefore absent in the reaction medium.

The reaction is run in the presence of a polar aprotic solvent. The solvent may be used in admixture with other aprotic solvents and/or water. Aqueous mixtures may be particularly mentioned. The reaction may occur in a solvent that comprises at least 50 %, at least 70 % or 90% by volume, preferably about 95, 97 or 99 % by volume of an aprotic polar solvent or a mixture of polar aprotic solvents. The reaction may alternatively occur in a solvent which substantially consists of a polar aprotic solvent or a mixture of such solvents.

The lignin may be fully or partially dissolved in the solvent. In one embodiment it is substantially dissolved. Usually the reaction is performed using about 1 to about 500 g lignin per liter of solvent. A range of about 5 to 100 g/1, or 8 to 80 g/1 may be particularly mentioned. Typical use rates are 10, 20 ,40 or 80 g/1.

Various polar aprotic solvents can be used. Typically the polar, aprotic solvent is selected from the group consisting of polar aprotic solvents that have a lactam, lactone, carbamate, urea, and carbonate functionality. Preferred polar aprotic solvents include NMP, other N-alkyl pyrrolidinones, 2-pyrrolidone, ethylene carbonate, propylene carbonate, γ-valerolactone (GVL), γ-butyrolactone, dimethylacetamide (DMA), N- methyl-2-piperidone, 2-piperidone, other N-alkyl piperidones, caprolactam, dimethylbenzamide, diethylbenzamide, other dialkylacetamides, and combinations thereof.

According to another embodiment the polar aprotic solvent is selected from dichloromethane, tetrahydrofuran, acetone, N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, ethylene carbonate, butylene carbonate and propylene carbonate, γ-valerolactone (GVL), γ-butyrolactone, and preferably is propylene carbonate or , γ-valerolactone (GVL). Such solvents are distinguished by their relatively high dielectric constants, high dipole moments, and solubility in water.

Preferred solvents have a high boiling point and flash point and hence lower vapor pressure and flammability, such as propylene carbonate and γ-valerolactone (GVL). They are relatively safer to work under thermal oxidative conditions compared to highly flammable alcohols such as methanol and ethanol as solvents.

In one embodiment the polar aprotic solvent has dielectric constant of at least 6, preferably at least 20, more preferably at least 50, and most preferably at least 60, at least 65 or at least 70. The dielectric content may be preferably chosen in the range of 20 to 72 or 30 to 69. The propylene carbonate used according to the examples has a dielectric constant of about 65, a high boiling point 242 °C of about and a flash point of about 132 °C and γ-valerolactone (GVL), has a dielectric constant of about 36, a high boiling point of about 207 °C and flash point 96 °C.

The reaction is performed under oxidative conditions by utilizing an oxidation agent. An oxidation agent is therefore present. Various oxidation agents can be used. Typical oxidation agents comprise molecular oxygen, hydrogen peroxide or mixtures thereof. The use of oxygen is preferred.

In some embodiments the oxidation agents are used in the absence of a catalyst. Depolymerization of lignin using such a catalyst free system according to the invention provides good yields of monomers. For instance treatment of Kraft lignin with propylene carbonate as the solvent at 120 to 220 °C and 6 to 30 bar of 8% 02 in nitrogen matrix resulted in yields of up to about 2.1 wt% (w.r.t lignin) of vanillin. The vanillin was obtained together with trace amounts of vanillic acid, acetovanillone and homovanillic acid. Similarly, treatment of Kraft lignin with propylene carbonate or GVL as the solvent at 120 to 220 °C and 6 to 30 bar of pure 02 resulted in total yields of about 5-7.3 wt% (w.r.t lignin) of vanillin, vanillic acid and acetovanillone .The yields and selectivity of vanillin may be further optimized.

In some embodiments, the reaction occurs in the presence of a metal catalyst. The metal of the metal catalyst may be selected from a transition metal. Preferably the transition metal is selected from the group V to group IX elements, optionally from the transition metals rhenium, vanadium, cobalt, ruthenium and molybdenum.

According to some embodiments the metal catalyst is a metal oxide or a metal complex. The catalyst may be selected from the group consisting of rhenium trioxide, vanadium pentoxide, molybdenum di-or trioxide, rhenium (IV) oxide, rhenium (VII) oxide, ammonium perrhenate, potassium perrhenate, tetrabutylammonium perrhenate and methyl rhenium trioxide. Methyl rhenium trioxide (MeRe03 or MTO) may be particularly mentioned. The catalyst can be used in a wide concentration range. It may be used in a concentration of about 0.1 to about 50 wt. % (determined as metal wt% of the lignin). Other concentrations that can be used are 0.5 to about 20 wt. %, 1 to about 40 wt. %, 1 to about 20 wt. %. A concentration of 0.5 to about 5 wt. % may be particularly mentioned.

Using catalyst higher yields may be obtained particularly when using diluted oxygen as the oxidant and/or non-preated or partially pretreated lignin precursor. In this regard a pretreated lignin precursor refers to any biomass which is chemically or biologically pretreated removing hemicellulose and cellulose or both.

For instance, a reaction of Kraft lignin in the presence of methyl trioxo rhenium (MeRe03 or MTO) as the catalyst in propylene carbonate as the solvent at 160°C and 10 bar 8% 02 in nitrogen yielded 4.2 wt% (w.r.t lignin) of vanillin, compared to 2.1 wt% in the case of the reaction in the absence of metal catalyst.

If oxygen is used as the oxidation agent, with or without catalyst, oxygen may be present in at least 2%, optionally at least 5%, optionally at about 8% or in about 2% to 40 % or in about 2% to 15 %, optionally in about 5 to 30 % by volume of an ambient gas/matrix gas. Typical oxygen ratios that can by mentioned include 1,2, 4, 8, 12, 22, 36, 67, 75, 80, 95, 97, 99 % by volume of an ambient gas/matrix gas. In other embodiments oxygen may be used in substantially undiluted form. Diluted oxygen may be particularly useful in embodiments for making vanillin. The use of a catalyst and diluted oxygen may be another preferred embodiment for making vanillin. Substantially undiluted oxygen may be preferred for making vanillic acid.

The oxygen may be also used in the form of air or mixtures of air with oxygen. In other embodiments it is used in the form of oxygen gas diluted in a matrix gas. The matrix gas may be selected from an inert gas, such as nitrogen or argon. Nitrogen gas is particularly mentioned as matrix gas.

The oxidation agent may be added in various forms. It may be added as a solution with the polar aprotic solvent or may be bubbled into it as a gas, in pure form or in admixture with other gases. In another embodiment the oxidation agent may create an autogenous pressure in a closed or sealed container (autoclave) filled with lignin and optionally the catalyst in a solvent. The autoclave is then pressured with the oxidation agent.

The process according to the invention may be generally performed under pressure. Typically the pressure is at least 3 bar, preferably at least 5 bar. It can be in the range of about 3 to 40 bar or of about 5 to 35 bar, preferably of 8 to about 15 bar. The pressure can be about 2, 4, 6, 8, 10, 15 or 20 bar. The reaction can be also performed without applying a pressure (about 1 bar). In such

embodiment a tube reactor may be used wherein a mixture of the lignin, catalyst, oxidation agent and solvent is brought to reaction at elevated temperatures.

The process according to the invention is run at elevated temperature. Heating to at least room temperature, at least 25° C, at least 30° C, at least 40° C, at least 60° C, at least 80 °C may be suitable. The temperature during the reaction may be in a range of between about 80 and about 300 °C, preferably between about 100 and about 250 °C, and most preferably between about 150 and 200 °C. Temperatures of about 35° C, 85° C, 110° C, 160 ° C, 260° C may be particularly mentioned.

In certain embodiments, the process described herein comprises preparing vanillin from lignin, whereby vanillin is obtained in a yield of about 1% to about 4% and 1 to 7.3% total yield of aromatic carbonyl compounds by weight of the lignin used as starting material. In some embodiments, vanillin is prepared from the lignin in a yield of about 2% to about 4% and 2 to 6 % total yield of aromatic carbonyl compounds by weight of the lignin. High yields may be obtained by using a transition metal catalyst in certain cases as described herein.

The process of the invention may be performed under agitation, such as mixing and stirring.

In certain embodiments, the process described herein comprises preparing vanillin and vanillic acid from lignin. The process provided further allows the product composition to be altered depending on the concentration of oxidation agent in the matrix used as well as the total pressure. Accordingly, a high percentage of an aromatic aldehyde, such as vanillin, may be obtained by use of a diluted mixture of oxidation agent within a matrix or lower pressures, while a high percentage of an aromatic acid, such as vanillic acid, may be obtained by use of an undiluted mixture of the oxidation agent or higher pressures. Accordingly substantially undiluted oxygen or a matrix comprising at least 70 %, at least 80 %, at least 90 % or at least 99 % by volume of oxygen in a diluted form is preferred to obtain higher vanillic acid yields. A typical pressure may then be 8 to 20 bar.

Typically the depolymerization reaction according to the process of the invention is performed in a reaction time of about 1 h to 12 h, or optionally of about 5 h to 7 h. Typical reaction times that can be mentioned are about 1, 2, 3, 4, 5, 6, 7 8, 9, 10 or 11 hours.

After the depolymerization reaction lignin may be isolated by filtration, evaporation, distillation or centrifugation or any suitable separation technique.

The process according to the invention may be combined with further process steps. According to one embodiment the steps of (a) reacting lignin or lignin containing biomass with an oxidation agent under pH neutral conditions in a polar aprotic solvent at elevated temperatures, and (b) separating the reaction mixture to obtain a first product mixture comprising the monomers and/or oligomers and the solvent and a second product mixture comprising the remaining lignin and by-products.

The separating step may be performed by filtration. The monomers and oligomers remain in the solution of the first reaction mixture and can be processed further.

Another embodiment of such process comprises a purification step to remove the solvent of the first product mixture from the monomers and/or oligomers. The purification step may be a distillation. It may be preferred to purify the first reaction mixture by distilling the monomer together with a high boiling solvent (azeotropic distillation) followed by fractional distillation. Alternatively the

purification step may be a membrane separation. In another embodiment the solvent may be recycled back to step (a) after this purification step.

In yet another embodiment of the process the process may comprise a catalyst removal step, wherein the catalyst is removed from the product mixture. This purification may be performed by an aqueous extraction and subsequent removal of solvent.

A typical industrially upscalable process is shown in Fig. 2.

Examples

Non-limiting examples of the disclosure will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Materials Used:

Examples 1 to 23

Depolymerization experiments were conducted in a 50 or 300 ml Parr batch autoclave reactor. A weighed amount of Kraft lignin (Product number 370959, Sigma-Aldrich) was added to the autoclave along with the catalyst and the solvent. The reactor was pressurized to the desired pressure with 8% 02 in a nitrogen matrix and the reaction was performed at the desired temperature for the desired time (t) with stirring. The reactor was then cooled down to room temperature and depressurized. The reaction mixture was diluted with acetone and passed through sintered glass filter. Internal standard (9-acetylphenanthrene) was added to the crude product and the yields of the products were determined by gas chromatography (GC) analysis (see Fig. 3). In representative experiments the solvent was removed by distillation to get the product as a mixture of monomers and oligomers. In the case of propylene carbonate as the solvent vacuum distillation at 130 °C also co-distilled part of the vanillin. The remaining oil was found to be highly soluble in organic solvents such as acetone, DMF, THF and partially soluble in dichloromethane, ethyl acetate and acetonitrile. A gel permeation chromatography (GPC) of this material in DMF showed significant reduction in molecular weight compared to the original Kraft lignin (see Fig. 4). The results of the oxidative depolymerization of Kraft Lignin (Product number 370959, Sigma-Aldrich) using 8% 02 as the oxidant in a nitrogen matrix are shown in Table 1. The Guaiacyl/Syringyl (G/S) ratio for the lignin starting materials (see Fig. 5) has been determined by 31P NMR. For this lignin the G/S ratio was determined as 7 and the maximum possible amount of vanillin from this Kraft lignin was determined as 9.5 wt% by nitrobenzene oxidation. Table 9 shows the various analysis results for different lignins.

Examples 24-30

The experiments were conducted in a 50 ml or 300mL hastelloy Parr batch autoclave reactor. During a typical experiment a weighed amount of Kraft lignin (Product number 370959, Sigma-Aldrich) was added to the autoclave along with the catalyst and the solvent. The reactor was pressurized to the desired pressure with the oxidant and the reaction was performed at the desired temperature (t) for the desired time with stirring. After reaction, the reactor was cooled down to room temperature and depressurized. The reaction mixture was diluted with acetone and passed through sintered glass filter. Internal standard (9-acetylphenanthrene or 4-methoxybenzophenone) was added to the crude product and the yields of the products were determined by gas chromatography (GC) analysis. Table 2 shows the results of the oxidative depolymerization of Kraft Lignin (Lignin Alkali, 370959Aldrich) using pure 02 or 22% 02 as the oxidant in a nitrogen matrix.

Example 31

The reaction was conducted in a 50 ml hastelloy Parr batch autoclave reactor. A weighed amount of the Kraft lignin (Indulin AT, MeadWestvaco) was added to the autoclave along with the catalyst and the solvent. The reactor was pressurized to the desired pressure with 8% 02 and the reaction was performed at the desired temperature for the desired time (t) with stirring. The reactor was cooled down to room temperature and depressurized. After reaction, the reaction mixture was diluted with acetone and passed through sintered glass filter. Internal standard (9-acetylphenanthrene) was added to the crude product and the yields of the products were determined by gas chromatography (GC) analysis. Table 3 shows the results of the oxidative depolymerization of Indulin AT (MeadWestvaco) using 8% 02 as the oxidant in nitrogen matrix. The G/S ratio for this lignin was determined by 31P NMR as 7.5 and the maximum possible amount of vanillin from this lignin was determined as 9.1 wt% by nitrobenzene oxidation.

Example 32

The reaction was conducted in a 50 ml hastelloy Parr batch autoclave reactor. A weighed amount of Wheat straw lignin (Protobind soda lignin) was added to the autoclave along with the catalyst and the solvent. The reactor was pressurized to the desired pressure with 8% 02 and the reaction was performed at the desired temperature for the desired time (t) with stirring. The reactor was cooled down to room temperature and depressurized. After reaction, the reaction mixture was diluted with acetone and passed through sintered glass filter. Internal standard (9-acetylphenanthrene) was added to the crude product and the yields of the products were determined by gas chromatography (GC) analysis. Table 4 shows the results of the oxidative depolymerization of Wheat straw lignin using 8% 02 as the oxidant in nitrogen matrix. The G/S ratio for this lignin was determined by 31P NMR as 0.8.

Example 33

The reaction was conducted in a 50 ml hastelloy Parr batch autoclave reactor. A weighed amount of EFB lignin (organosolv) was added to the autoclave along with the catalyst and the solvent. The reactor was pressurized to the desired pressure with 8% 02 and the reaction was performed at the desired temperature for the desired time with stirring. The reactor was cooled down to room temperature and depressurized. After reaction, the reaction mixture was diluted with acetone and passed through sintered glass filter. Internal standard (9-acetylphenanthrene) was added to the crude product and the yields of the products were determined by gas chromatography (GC) analysis. Table 5 shows the oxidative depolymerization of EFB lignin (organosolv) using 8% 02 as the oxidant in a

nitrogen matrix. Other than the above mentioned products some amounts of other carbonyl compounds such as 4-hydroxybenzaldehyde, methyl and ethyl esters 4-hydroxybenzoic acids were also detected by GC-MS. The G/S ratio for this lignin was determined by 3 IP NMR as 0.5.

Example 34-35

The reaction was conducted in a Syrris Flow reactor. A solution of Kraft Lignin (Lignin Alkali, 370959 Aldrich) in propylene carbonate was taken in a reagent bottle and bubbled with 02. This solution was then infused through a 4 ml tube reactor and heated to the desired temperature. The product was then collected after the desired residence time and analyzed by GC. Table 6 shows the results of the oxidative depolymerization of Kraft Lignin (Lignin Alkali, 370959 Aldrich) under flow conditions.

Example 36-45

The experiments (Table 7) were conducted in a 300mL hastelloy Parr batch autoclave reactor under metal catalyst free conditions using pure 02 as the oxidant. During a typical experiment a weighed amount of Kraft lignin (Lignin Alkali, 370959 Aldrich) was added to the autoclave along with the solvent. The reactor was pressurized with pure 02 to the desired pressure and the reaction was performed at the desired temperature for the desired time under stirring. After reaction, the reactor was cooled down to room temperature and depressurized. The reaction mixture was diluted with acetone and passed through sintered glass filter. Internal standard (4-methoxybenzophenone) was added to the crude product and the yields of the products were determined by gas chromatography (GC) analysis.

[Table 1]

o Lignin Solvent Catalyst Temp Press. t Vanillin Vanillic Aceto Homo

(mg) (10 mL) (3 wt% of (°C) (bar) (h) Yield acid vanillone vanillic metal) (wt%) Yield Yield acid

(wt%) (wt%) Yield

(wt%)

400 Propylene - 160 10 1 1.2 0.2 0.3 0.4 Carbonate

400 Propylene 160 20 6 2.1 0.2 0.4 Carbonate

(50mL)

400 Diglyme - 160 10 1 0.7 - - - 400 Dimethyl - 160 10 1 1.0 0.2 0.3 0.3 carbonate

400 Propylene MeRe03 160 10 6 3.6 0.6 0.4 0.5 carbonate

400 γ-valero- MeRe03 160 10 6 2.5 0.5 0.2

lactone

(GVL)

400 Propylene MeReOs 160 10 2 2.3 0.6 0.2 0.5 carbonate

400 Propylene MeRe03 120 10 6 1.6 0.2 0.2 0.5 carbonate

400 Propylene MeRe03 200 10 6 3.0 0.3 0.3 0.5 carbonate

0 200 Propylene MeRe03 160 10 6 4.2 1.0 0.5 0.2 carbonate

1 400 Propylene MeRe03 160 20 6 3.7 1.7 0.4 - carbonate

2 400 Propylene MeRe03 160 30 6 3.6 1.5 0.4 - carbonate

3 400 Propylene Re02 160 10 6 2.4 0.2 0.8 0.4

Carbonate

4 400 Propylene v2o5 160 10 2 3.2 0.3 0.9 0.4 carbonate

5 400 Propylene Mo04Na2 160 10 2 1.5 0.2 0.6 0.4 carbonate

6 400 Propylene M0O3 160 10 2 3.7 0.3 0.5 0.5 carbonate

7 400 Propylene (Ru(Ph)Cl2)2 160 10 2 1.7 0.2 0.2 0.4 carbonate

8 400 Propylene Zr02 160 10 2 1.8 0.6 0.2 0.4 carbonate

9 400 Propylene C03O4 160 10 2 2.4 0.5 0.2 0.5 carbonate

0 400 Propylene KRe04 160 10 6 2.8 0.8 0.3 0.3 carbonate

1 400 Propylene Re207 160 10 6 3.2 0.9 0.3 0.3 carbonate

2 400 Propylene NH4Re04 160 10 6 3.7 - 0.3 - carbonate

3 400 Propylene NBu4Re04 160 10 6 2.2 0.3 0.2 0.2 carbonate

Example 46-47

The experiments (Table 8) were conducted in a 300mL hastelloy Parr batch autoclave reactor under metal catalyst free conditions using 22% 02 in N2 as the oxidant. During a typical experiment a weighed amount of Kraft lignin (Lignin Alkali, 370959 Aldrich) was added to the autoclave along with the solvent. The reactor was pressurized with 22%02 in N2 to the desired pressure and the reaction was performed at the desired temperature for the desired time under stirring. After reaction, the reactor was cooled down to room temperature and depressurized. The reaction mixture was diluted with acetone and passed through sintered glass filter. Internal standard (9-acetylphenanthrene or 4- methoxybenzophenone) was added to the crude product and the yields of the products were determined by gas chromatography (GC) analysis.

[Table 2]


[Table 3]

o Lignin Solvent Catalyst Temp. Press. t Vanillin Vanillic Aceto Homo

(mg) (mL) (3 wt% of (°C) (bar) (h) Yield acid vanillone vanillic metal) (wt%) Yield Yield acid

(wt%) (wt%) Yield

(wt%) 1 400 Propylene MeRe03 160 10 6 4.0 0.5 0.7 0.6 carbonate

[Table 4]

[Table 5]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

Lignin G/S Ratio Yield of Vanillin by nitrobenzene oxidation (wt %)

Kraft Lignin ( Lignin 7.0 9.5

Alkali, 370959 Aldrich )

(pH 6.5)

Indulin AT-Kraft 7.5 9.1

MeadWestWako

Empty Palm Fruit Bunch 0.5 - (EFB) Lignin

Industrial Applicability

The process as defined above may find a multiple number of applications in which lignin shall be depolymerized to fine chemical of value, such as for instance vanillin and vanillic acid. The process may be upscalable for industrial processes make use of Kraft lignin or lignin from biorefineries. By the use of the polar aprotic solvent the process is more environmentally benign and allows for efficient and selective methods for the oxidative depolymerization of lignins. It may replace existing technologies for lignin depolymerization. The process may find use to make vanillin and vanillic acid for the fragrance and flavor industry from naturally available materials.

This process also may be useful for the production of syringaldehyde, syringic acid, p-hydroxybenzaldehyde and p-hydroxy benzoic acid which relay on the type of biomass used. Additionally these products can be used for further chemical and bio -conversions to form p-terephthalic acid and muconic acid and monomers for bio-based polymers. The oligomers obtained may be used for the existing applications of lignosulfonates, as resins for polymers, as polyphenols, precursors for carbon fibres, lube additives and UV absorbers.

It will be apparent that various other modifications and adaptations of the invention will be available to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.