Process and catalyst for producing phenolic building blocks from lignin

Abstract

The invention relates to a process for the catalytic decomposition of lignin with high yield and high selectivity to phenolic building blocks and with minimal formation of a coke fraction, and to a catalyst suitable for use in the process. The catalyst comprises a basic support material, 1-10 wt% platinum and 0-5 wt% nickel. The process comprises providing a reaction mixture comprising lignin, the catalyst and a solvent, and heating the reaction mixture so as to obtain a mixture comprising a product mixture, the catalyst and the solvent.

Description

[0001] Due to the limited global supply of conventional fossil resources, the production of chemical building blocks from renewable resources is becoming increasingly important. Thus, the use of biomass from renewable raw materials as a basis for obtaining a wide range of chemicals is the subject of intensive research work. Lignocellulosic material, which can be obtained from agricultural and forestry sources such as wood, is available in almost unlimited and renewable supply. This lignocellulosic material consists of three main components: cellulose, hemicellulose and lignin. While the potential use of the first two components for the synthesis of basic chemicals or fuel components has been relatively well researched, the use of lignin as a raw material has not been researched to the same extent.

[0002] Lignin is one of the most abundant biopolymers and is the only biopolymer consisting of aromatic monomeric building blocks. It is an amorphous 3-D polymer, which is mainly present in plant cell walls. The monomeric building blocks, called monolignols, mainly comprise phenylpropanols, mainly comprising coniferyl alcohol, pinoresinol and secoisolariciresinol. The aromatic rings can carry different substituents, such as hydroxyl groups, alkoxy groups, ether groups, alkyl groups, aldehyde groups or ketone groups; the exact composition as well as the molecular weight varies with the plant. The individual building blocks are connected by different types of bonds, such as alkyl, aryl and ether bonds; the beta-O-4 linkage is the most common. Figure 1 An overview of the various types of bonds in lignin is given.

[0003] The potential polyphenolic structure makes lignin an ideal candidate for use as a starting material for the synthesis of high-value aromatic fine chemicals, which can be used as a basis for the synthesis of other chemical products. Figure 2 Phenolic components are shown by way of example, which show different structural motifs of such desirable phenolic components. However, the heterogeneity of the lignin structure makes it difficult to develop efficient and selective methods for obtaining low molecular weight components.

[0004] Lignin can be isolated from wood (e.g. pine, poplar, birch), annual plants (e.g. wheat straw, miscanthus, switchgrass) or agricultural residues (e.g. sugar cane bagasse) by various extraction methods and the macromolecular structure of lignin is highly dependent on the plant source, location, season and isolation method. There are many methods for the decomposition of lignin, including pyrolysis, acid or base hydrolysis and more selective catalytic reactions, as well as biological methods using enzymes. An overview of such methods in the context of biorefining processes can be found, for example, in "Biorefineries - Industrial Processes and Products" (Kamm et al., Ullmann's Encyclopedia of Industrial Chemistry, Electronic Release, 7th Edition, WILEY-VCH, 2007). Isolation of lignin prior to depolymerization can be necessary for which purpose, for example, an organic solvent process has been established in which the lignocellulosic starting material is separated into lignin and other carbohydrate-containing components.

[0005] Unwanted decomposition products in the depolymerization of lignin can be polymeric components formed by radical rearrangement reactions. These components are generally referred to as "coke fractions", such as "coke", "char" and / or "tar", and are amorphous, inhomogeneous product fractions that cannot be further processed. The formation of this fraction reduces the yield of the desired products, in particular in uncatalyzed reactions or when using catalysts with inadequate selectivity, as shown, for example, in "Catalytic Transformation of Lignin for the Production of Chemicals and Fuels" (Li et al., Chem. Rev., 2015, Vol. 115, pp. 11559-11624).

[0006] One type of catalytic decomposition reaction is base-catalyzed depolymerization (BCD), in which, in its homogeneous version, the lignin to be decomposed is treated with a solution of a mineral base at high temperature and high pressure. Although this reaction is suitable for producing at least partially desired products, such as phenol and catechol derivatives, it cannot be used on an industrial scale due to the large amount of strongly alkaline solution residue generated. An alternative is the use of heterogeneous catalysts which can be easily separated from the reaction mixture after the reaction and reused.

[0007] Generally, such reactions are carried out in an inert gas and / or hydrogen atmosphere, which significantly increases the requirements on the process technology used compared to methods which can be carried out under atmospheric conditions.

[0008] Chaudharya et al. (Green Chemistry, 2017, vol. 19, pp. 778, 788) describe a range of transition metal-free catalysts suitable for BCD of lignin, including zeolites, metal oxides, hydrotalcites and hydroxyapatite. The reaction conditions described enable the production of relevant monomer and oligomer building blocks, but with low yields and high catalyst loadings.

[0009] Support materials provided with transition metals are another class of catalysts suitable for the decomposition of lignin. For example, US 9631146 B2 describes a process in which nickel on a layered double hydroxide is used as catalyst. However, studies on this system show that the yield of the desired product is relatively low due to a high proportion of a coke fraction in the reaction product.

[0010] It is an object of the present invention to provide a process for the catalytic decomposition of lignin with high yield and high selectivity for phenolic building blocks and with minimal formation of a coke fraction. It is also an object of the present invention to find a process for the decomposition under mild reaction conditions (i.e. low temperature, low pressure) and without an inert gas or hydrogen atmosphere. Furthermore, it is an object to minimize the amount of catalyst required.

[0011] It is also an object of the present invention to provide a catalyst suitable for use in the process to be found.

[0012] According to a first aspect of the invention, this object is achieved by a process comprising

[0013] a) providing a reaction mixture A comprising lignin, a catalyst and a solvent;

[0014] b) heating the reaction mixture A so as to obtain a mixture B comprising a product mixture, a catalyst and a solvent;

[0015] wherein the catalyst comprises

[0016] - a basic support material,

[0017] - platinum in a weight percentage of 1 - 10 wt.%, and

[0018] - nickel in a weight percentage of 0 - 5 wt.%.

[0019] In the process according to the application, a catalyst comprising platinum and optionally nickel on a basic support material is used. In the context of the present application, it has been found that the use of platinum or a combination of the two transition metals leads to a high conversion of the lignin used and a selectivity to the formation of low molecular weight constituents. In this respect, the conversion is to be understood as the total amount of product fractions formed. This is also associated with an increased yield, i.e. the proportion of reusable oligomeric and monomeric product fractions relative to the lignin used is increased. In this context, the selectivity means that mainly monomeric and oligomeric phenolic building blocks are formed as low molecular weight product fractions and the formation of the aforementioned coke fraction is avoided.

[0020] Preferably, a product mixture having a small proportion of coke fraction is obtained by the process according to the application.

[0021] For the purposes of the present application, the coke fraction is understood to mean a product fraction which is neither soluble in water nor in the organic solvents THF and ethyl acetate. These are mainly polymeric fractions which are formed by the radical rearrangement reactions of the lignin to be decomposed. However, low molecular weight carbon components or short-chain hydrocarbons which can be formed by competing reaction pathways can also be included. Since this fraction is not soluble in almost all common solvents, further characterisation is problematic or even impossible. In the context of the present application, insoluble is understood to mean that the substance dissolves to less than 0.1 g / L in the corresponding solvent at 25°C and 1013 hPa.

[0022] The present application relates to a process for the catalytic decomposition of lignin.

[0023] Lignin is understood here to mean lignin model components, untreated biomass containing lignin, lignin-containing fractions from treated biomass, and lignin from treated biomass. The biomass can consist of lignocellulose, but the cellulose and hemicellulose can be completely or partially separated. The biomass can include, for example, wood, straw, bagasse, recycled wood, or late-cut grass.

[0024] The treatment can be carried out by chemical pretreatment, by physical methods or by biological methods.

[0025] In a preferred embodiment, the lignin is derived from biomass, wherein the biomass can be selected from the group comprising wood, straw, bagasse and late-cut grass. The lignin is preferably selected from the group comprising organic solvent lignin, kraft lignin, lignin obtained by alkali digestion, lignin obtained by kraft process, lignin obtained by sulfite process, lignin obtained by extraction with water, lignin obtained by hydrolysis with acid, lignin obtained by enzymatic hydrolysis, lignin obtained by wood saccharification, lignin obtained by treatment with microorganisms, lignin from a biorefinery process stream comprising lignin, and mixtures thereof.

[0026] The lignin preferably has an average molecular weight in the range of 3,000 g / mol to 20,000 g / mol, more preferably in the range of 4,000 g / mol to 15,000 g / mol.

[0027] “Disintegration” is to be understood to mean the deconstruction of polymeric lignin into lower molecular weight oligomeric or monomeric building blocks, wherein the bonds between the building blocks are completely or partially broken. The term “depolymerization” can also be used as a synonym.

[0028] The process according to the present application comprises providing a reaction mixture A comprising lignin, a catalyst and a solvent.

[0029] The catalyst is preferably a supported catalyst. A supported catalyst is generally understood to mean a catalyst comprising a support material, the surface of which is provided with a catalytically active material in highly dispersed form. The support material should provide a stable platform for the catalytically active material and be stable under the selected reaction conditions.

[0030] The catalyst comprises a basic support material suitable for dispersing the catalytically active material in the reaction mixture. A basic support material is understood to mean those support materials which have basic sites, i.e. can act as Bronsted bases (Base) (proton acceptors) or Lewis bases (Electron Pair Donors). The basic support material is for example a metal oxide, a mixed hydroxide, a mixed oxide, a zeolite or a clay mineral.

[0031] In a preferred embodiment, the basic support material has a BET surface area of less than 150 m 2 / g, preferably less than 100 m 2 / g, particularly preferably less than 50 m 2 / g. The basic support material preferably has a BET surface area in the range of 5 m 2 / g to 150 m 2 / g, preferably in the range of 10 m 2 / g to 100 m 2 / g. The BET surface area is also referred to as specific surface area and can be determined according to ISO 9277:2010 using nitrogen as adsorbate.

[0032] The preferred basic support material comprises a mixture of divalent and trivalent cations.

[0033] The basic support material preferably comprises at least one type of divalent cation M 2+ : magnesium (Mg 2+ ), nickel (Ni 2+ ), iron (Fe​2+ ), cobalt (Co 2+ ), copper (Cu 2+ ), zinc (Zn 2+ ), calcium (Ca 2+ ), tin (Sn 2+ ), lead (Pb 2+ ) and combinations thereof. In a preferred embodiment, the divalent cation M 2+ is magnesium (Mg 2+ ).

[0034] The basic support material preferably comprises at least one type of trivalent cation M 3+ : aluminum (Al 3+ ), iron (Fe 3+ ), chromium (Cr 3+ ), manganese (Mn 3+ ) and combinations thereof. In a preferred embodiment, the trivalent cation M 3+ is aluminum (Al 3+ ).

[0035] The ratio of divalent cations to trivalent cations is variable, preferably in the range of 1 :7 to 7:1, preferably in the range of 1 :5 to 5:1, most preferably in the range of 1 :3 to 3:1.

[0036] A preferred basic support material is a layered double hydroxide (LDH) of the formula

[0037] [M 2+ 1-w M 3+ w (OH)2] w+ (A n- w / n )·m H2O, wherein

[0038] M 2+ represents a divalent cation,

[0039] M 3+ represents a trivalent cation, and

[0040] A n- represents an anion with a charge n.

[0041] m represents the number of water molecules, and w represents the molar ratio between the trivalent cations and the total amount of cations.

[0042] Preferably, the layered double hydroxide is a crystalline material consisting of a layered structure.

[0043] In a preferred embodiment, the layered double hydroxide comprises exactly one type of divalent cation.

[0044] In a preferred embodiment, the layered double hydroxide comprises exactly one type of trivalent cations.

[0045] Preferably, the divalent cations are magnesium (Mg 2+ ) and the trivalent cations are aluminum (Al 3+ ).

[0046] The layered double hydroxide preferably comprises at least one type of anions selected from the group consisting of hydroxide (OH - ), carbonate (CO3 2- ), nitrate (NO3 - ), sulfate (SO4 2- ) and chloride (CI - ).

[0047] The basic support material can be a hydrotalcite or a hydrotalcite-like compound. Hydrotalcite is understood by the person skilled in the art to mean aluminum-magnesium hydroxycarbonate.

[0048] In a preferred embodiment, the basic support material is a hydrotalcite of the formula Mg6AI2(OH) 16 (CO3)4H2O.

[0049] The catalyst comprises platinum and optionally nickel, which are hereinafter referred to individually or jointly as metal species. The metal species form the catalytically active sites of the catalyst. The term “metal species” does not represent any statement about the oxidation state of platinum or nickel. In other words, it does not represent the presence of an elemental state with an oxidation state of 0. The term “oxidation state” as used herein and known to the person skilled in the art refers to the formal charge of an atom within a compound or the actual charge of a monatomic ion. By definition, an atom in elemental state has an oxidation state of 0.

[0050] In the case of base-catalyzed depolymerization of lignin, the basic support material alone can also catalyze. However, this reaction is not selective as defined by the present invention and cannot achieve the desired high yield of the phenolic components. Surprisingly, the provision of platinum and optionally nickel to the basic support material makes it possible to achieve the desired selectivity of the catalytic depolymerization of lignin and to increase the yield of the desired product fraction.

[0051] Preferably, the catalyst contains not more than 15 wt.-% of metal species, particularly preferably not more than 12 wt.-%, in particular not more than 9 wt.-%, based on the total weight of the support material and the metal species.

[0052] In a preferred embodiment, the catalyst comprises metal species in the range of 1 wt% - 15 wt%, for example 15 wt% metal species, 10 wt% metal species, 9 wt% metal species, 8 wt% metal species, 7 wt% metal species, 6 wt% metal species, 5 wt% metal species, 4 wt% metal species, 3 wt% metal species, 2 wt% metal species, or 1 wt% metal species.

[0053] The catalyst can comprise platinum in the range of 1 wt% - 10 wt%, for example 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or intermediate levels thereof. This means that 1% - 10% of the total weight of the catalyst comprising the support material and the metal species consists of platinum species. In a preferred embodiment, the catalyst contains 2 wt% - 8 wt%, more preferably 3 wt% - 7 wt% of platinum in weight percentage.

[0054] The platinum is preferably present as metallic platinum, i.e. in oxidation state 0.

[0055] The catalyst can comprise nickel in the range of 0 wt% - 5 wt%, for example 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or intermediate levels thereof. This means that 0% - 5% of the total weight of the catalyst comprising the support material and the metal species consists of nickel species. In a preferred embodiment, the catalyst comprises 0.1 wt% - 5 wt%, more preferably 1 wt% - 4 wt% of nickel in weight percentage.

[0056] In a preferred embodiment, the catalyst comprises 5 wt% platinum and 1 wt% nickel.

[0057] In another preferred embodiment, the catalyst comprises 5 wt% platinum and 2 wt% nickel.

[0058] In another preferred embodiment, the catalyst comprises 5 wt% platinum and does not contain nickel.

[0059] Preferably, the metal species are present on the basic support material in particulate form.

[0060] The surface area of the platinum-containing particles of the metal species can preferably be at least 1 m 2 / g, more preferably at least 2 m 2 / g, and even more preferably at least 4 m 2 / g. The surface area of the platinum-containing particles of the metal species can be determined using the method of CO adsorption described later, which comprises a reduction step.

[0061] In a preferred embodiment, the catalyst has a particle size of less than 50 m2 / g, preferably less than 40 m 2 / g, particularly preferably less than 20 m 2 / g. The basic support material preferably has a BET surface area in the range of 3 m 2 / g to 50 m 2 / g, preferably in the range of 4 m 2 / g to 40 m 2 / g. The BET surface area of the catalyst can likewise be determined according to ISO 9277:2010 using nitrogen as adsorbate.

[0062] Suitable catalysts can be prepared by various methods known to the person skilled in the art, such as a precipitation method, an impregnation method, an adsorption method or an ion exchange method.

[0063] Suitable catalysts are preferably obtained by impregnation of a basic support material with a solution of at least one compound of at least one metal of a metal species, followed by reduction. Optionally, a heat treatment can be carried out before or after reduction.

[0064] Suitable catalysts can be prepared, for example, by a method comprising the following steps:

[0065] I) impregnation of a basic support material with a solution comprising at least one compound of at least one metal of a metal species and a solvent;

[0066] II) reduction of step.

[0067] In step I), the basic support material is impregnated with a solution of at least one compound of at least one metal of a metal species. In this step, the material to be impregnated, in the case of the present application the basic support material, is brought into contact with a solution of one or more compounds of at least one metal of a metal species.

[0068] As a result of the impregnation step, an impregnated, i.e. loaded, basic support material with at least one compound of at least one metal of a metal species is obtained. The preferred result is that the basic support material is provided homogenously or uniformly with at least one compound of at least one metal of the metal species.

[0069] Various impregnation methods are known to the person skilled in the art, such as capillary-controlled impregnation (so-called "incipient wetness" method) and diffusion-controlled impregnation (so-called "adsorption-controlled" method). In principle, both methods are suitable for preparing suitable catalysts of the present application.

[0070] Impregnation is generally understood to mean that the support material is combined with the compound and leads to adsorption of the compound on the surface of the support material. In the case of a porous support material, this is in particular also the inner surface, i.e. the surface located within the pores.

[0071] The binding is carried out, for example, by adding a solution of at least one compound of at least one metal of the metallic substance to a suspension of the basic support material in a solvent and mixing the mixture. However, it is also possible to spray such a solution onto the basic support material or to add the basic support material to such a solution, followed by mixing this mixture. Methods for mixing such systems are known to the person skilled in the art and include, for example, stirring or kneading, and use can be made of forced mixers, free-fall mixers, stirrers, kneaders, flow mixers or mixing pumps.

[0072] Preferably, the solution and the composition comprising the basic support material are mixed continuously during the impregnation step.

[0073] In a preferred embodiment, the basic support material is present in the solution in a suspended form during the impregnation step. For the purposes of the present application, a suspension is a mixture of a solid and a liquid, wherein the solid is uniformly dispersed in the liquid in the form of finely dispersed solid matter.

[0074] In an alternative embodiment, the basic support material and the solution are present in the form of an impregnated powder during the impregnation step. This means that the solution is added to the basic support material only to the extent that it is wetted.

[0075] If the basic support material is to be impregnated with several compounds of at least one metal of the metallic substance simultaneously, the relevant compounds can preferably be provided in one solution. However, it is also possible for the relevant compounds to be provided preferably in separate solutions. Both variants are suitable for providing, for example, platinum and nickel to the basic support material simultaneously.

[0076] According to the present application, the amount of metallic substance in the solution can vary within a wide range. By "amount of metallic substance" is meant the content of platinum plus optionally nickel in the solution. Particularly good results are obtained when the solution comprises the metallic substance in an amount of at least 1 % by weight, in particular at least 2 % by weight, preferably at least 5 % by weight, more preferably at least 10 % by weight, based on the amount of solvent. In particular, the solution can comprise the metallic substance in an amount in the range from 1 % to 80 % by weight, in particular in the range from 2 % to 70 % by weight, preferably in the range from 5 % to 60 % by weight, more preferably in the range from 10 % to 50 % by weight.

[0077] The impregnation step can be carried out at room temperature. However, the impregnation step can also be carried out at temperatures below or above room temperature. During the impregnation step, the temperature of the mixture comprising the basic support material and the solution can be, for example, from 10 °C to 90 °C, more preferably from 20 °C to 80 °C.

[0078] The duration of the impregnation step is chosen such that at least one compound of at least one metal of the metal species can precipitate on the basic carrier material in sufficient amounts. Based on routine experiments, the skilled person can determine a suitable duration.

[0079] Preferably, at least one compound of at least one metal of the metal species is completely precipitated from the solution onto the basic carrier material. After the impregnation step, the solvent thus does not contain compounds of at least one metal of the metal species. The skilled person understands by “does not contain compounds” to mean that no longer detectable concentrations can be detected in a hydrochloric acid environment by using tin chloride for noble metal detection, which is a method known to the skilled person in principle.

[0080] The amount of the basic carrier material used during production depends on the desired amount of the metal species to be precipitated on the basic carrier material and thus also on the concentration of the used solution of at least one compound of at least one metal of the metal species.

[0081] During the impregnation step, the basic carrier material is present, for example, in the range of 5 to 95% by weight, more preferably in the range of 10 to 90% by weight, based on the total amount of the solution and the basic carrier material.

[0082] At least one compound of at least one metal of the metal species can preferably be converted into the elemental state via thermal decomposition or by wet-chemical reduction.

[0083] Suitable compounds of at least one metal of the metal species are, for example, salts, complex compounds or organometallic compounds.

[0084] The platinum compounds which can be used for impregnating the basic carrier material are known to the skilled person. For example, the platinum compounds are Pt(II) or platinum(IV) compounds (for example, Pt(II) or Pt(IV) salts or Pt(II) or Pt(IV) complex compounds or Pt organometallic compounds). Examples of platinum compounds which can be mentioned are platinum halides or acids thereof, hexachloroplatinic acid or salts of this acid, potassium tetrachloroplatinate, platinum nitrate, platinum acetylacetonate, platinum oxalate or mixtures of at least two of these compounds.

[0085] The nickel compounds which can be used for impregnating the basic carrier material are also known to the skilled person. For example, the nickel compounds are Ni(II) compounds, for example, Ni(II) salts or Ni(II) complex compounds or Ni organometallic compounds. Examples of nickel compounds which can be mentioned are nickel nitrate, nickel hydroxide, nickel halides or mixtures of at least two of these compounds.

[0086] The solution also comprises at least one solvent.

[0087] The solution can also comprise further components, such as acids.

[0088] The at least one solvent can be selected from the group consisting of water and organic solvents. The organic solvent can be, for example, an alcohol, such as methanol or ethanol.

[0089] Optionally, the impregnated basic support material obtained according to step I) can first be dried before the reduction in step II) is carried out and thereby partially or completely remove the solvent.

[0090] The impregnated basic support material can preferably be filtered off and dried.

[0091] The impregnated support material is dried, for example, at a temperature below 250 °C, more preferably below 200 °C, even more preferably below 150 °C.

[0092] In particular, the drying can be carried out under reduced pressure, preferably at a pressure below 300 mbar.

[0093] Preferably, the drying is carried out for a period of 0.5 hours to 24 hours, more preferably for a period of 2 hours to 20 hours.

[0094] Optionally, the method can further comprise a heat treatment of the impregnated support material after step I) and before step II). Such a heat treatment is also referred to by the person skilled in the art as calcination.

[0095] In a preferred embodiment, the heat treatment of the impregnated basic support material leads to a decomposition of at least one compound of at least one metal of the metal species.

[0096] The heat treatment is preferably carried out in the presence of oxygen.

[0097] In one embodiment, and if no drying is carried out, the optional heat treatment leads to an evaporation of the solvent. In one embodiment, the heat treatment evaporates the solvent and completely decomposes at least one compound of at least one metal of the metal species.

[0098] The heat treatment can be carried out at a temperature of less than 1000 °C, 900 °C, 800 °C, 700 °C, 600 °C, 500 °C, 400 °C, or less than 300 °C. In one embodiment, the impregnated basic support material is heat treated at a temperature of 150 °C to 250 °C.

[0099] Preferably, the impregnated basic support material is heat treated in multiple stages. This is to be understood to mean that the impregnated basic support material is first heat treated at a first temperature and then heat treated at at least one further temperature. Preferably, the first temperature is lower than the at least one further temperature. Preferably, the first temperature is in the range of 100 °C to 200 °C. Preferably, the at least one further temperature is in the range of 200 °C to 300 °C.

[0100] In another preferred embodiment, the temperature is increased during the heat treatment. The increase in temperature can be stepwise or continuous, or a combination of stepwise and continuous increase.

[0101] Preferably, the heat treatment is carried out for a period of 0.5 hours to 24 hours, preferably for a period of 2 hours to 18 hours.

[0102] In step II) of the process for preparing a suitable catalyst, a reduction is carried out. This is to be understood to mean that at least one compound of at least one metal of the metal species present on the basic support material after impregnation is converted into a lower oxidation state.

[0103] In the case of platinum compounds, it can be preferred, for example, to convert platinum from the Pt(II) or Pt(IV) oxidation state into the Pt(0) oxidation state.

[0104] In the case of nickel compounds, it can be preferred, for example, to convert nickel from the Ni(II) oxidation state into the Ni(0) oxidation state.

[0105] The reduction method and suitable reducing agents are in principle known to the person skilled in the art. The reduction step can be carried out, for example, under a reducing atmosphere or wet-chemically. In particular, the reduction step can be carried out under a synthesis gas atmosphere with a reducing acid, a salt thereof or a reducing boron compound. Synthesis gas is understood by the person skilled in the art to be a gas mixture comprising nitrogen and hydrogen (for example 95% by volume nitrogen and 5% by volume hydrogen). In the case of wet-chemical reduction, it is preferred to use formic acid or a salt of formic acid, for example sodium formate, as reducing agent.

[0106] In the case of wet-chemical reduction, the reduction step can be carried out directly in the impregnation solution, i.e. the impregnated support material obtained after step I) is not separated from the solvent. In other words, it can be preferred to add the reducing agent directly after step I).

[0107] The reduction step is carried out, for example, at temperatures below 400°C, more preferably below 350°C, particularly preferably below 300°C. In the case of wet-chemical reduction, it can be preferred to carry out the reduction at temperatures below 100°C.

[0108] Preferably, the reduction step is carried out for a period of 0.5 hours to 24 hours, more preferably for a period of 2 hours to 15 hours.

[0109] It can be preferred to subject the material obtained in step II) to a further process step.

[0110] For example, it can be preferred to dry the material obtained after step II) and thereby partially or completely remove the solvent.

[0111] In a preferred embodiment, the material obtained in step II) is filtered off and dried.

[0112] Drying is for example carried out at a temperature below 250°C, more preferably below 200°C, even more preferably below 150°C.

[0113] In particular, drying can be carried out under reduced pressure, preferably at a pressure below 300 mbar.

[0114] Preferably, drying is carried out in the absence of oxygen.

[0115] Preferably, drying is carried out for a period of 0.5 hours to 24 hours, more preferably for a period of 2 hours to 20 hours.

[0116] In the process according to the application, the reaction mixture A in process step a) comprises a solvent in addition to the lignin and the catalyst.

[0117] The solvent can comprise a plurality of chemical substances, i.e. the solvent can also be a solvent mixture. The solvent can comprise water and / or an organic solvent. The organic solvent can be an alcohol such as methanol, ethanol, propanol, isopropanol, or a ketone such as acetone.

[0118] The reaction mixture A can comprise the solvent in an amount of at least 60 wt.-%, more preferably at least 70 wt.-%, even more preferably at least 80 wt.-%.

[0119] The solvent preferably comprises at least 10 wt.-%, more preferably at least 20 wt.-%, most preferably at least 30 wt.-% water, based on the total weight of the solvent. For example, the solvent comprises water in a range of 10 wt.-% to 80 wt.-%, more preferably in a range of 20 wt.-% to 70 wt.-%, even more preferably in a range of 30 wt.-% to 60 wt.-%.

[0120] The solvent preferably comprises water and an alcohol, preferably water and methanol, water and ethanol, water and propanol, or water and isopropanol. The solvent preferably comprises the alcohol in a range of 5 wt.-% to 95 wt.-%, more preferably in a range of 15 wt.-% to 85 wt.-%, even more preferably in a range of 25 wt.-% to 75 wt.-%, most preferably in a range of 30 wt.-% to 60 wt.-%.

[0121] The use of the catalysts described herein allows the selective catalytic depolymerization of lignin using lower amounts of catalyst than described in the prior art. In a preferred embodiment, the catalyst is present in the reaction mixture A in an amount of less than 30 wt.-%, preferably less than 20 wt.-%, more preferably less than 10 wt.-%, particularly preferably less than 5 wt.-%, based on the total amount of catalyst and lignin. In a preferred embodiment, the catalyst is present in the reaction mixture A in the range of 0.1 wt.-% to 30 wt.-%, preferably in the range of 0.5 wt.-% to 20 wt.-%, more preferably in the range of 1 wt.-% to 15 wt.-%, based on the total amount of catalyst and lignin.

[0122] In method step b), the process according to the application comprises heating the reaction mixture A.

[0123] The exact conditions of the decomposition depend on the lignin used, the catalyst used and the desired product composition.

[0124] The reaction mixture A can be stirred during the process.

[0125] The reaction mixture A is heated to the reaction temperature. This is to be understood to mean the temperature reached after the phase of heating the reaction mixture. The reaction temperature is preferably reached after a heating phase of not more than 90 minutes, more preferably not more than 60 minutes.

[0126] Preferably, the reaction mixture A is heated to a reaction temperature of less than 400°C, more preferably less than 300°C, most preferably less than 250°C. Preferably, the reaction mixture A is heated to a reaction temperature in the range of 50°C to 400°C, preferably to a reaction temperature in the range of 100°C to 300°C, more preferably to a reaction temperature in the range of 150°C to 250°C.

[0127] In a preferred embodiment, the reaction temperature in method step b) is maintained for a period of less than 240 minutes, more preferably for a period of less than 180 minutes, in particular for a period of less than 150 minutes. Preferably, the reaction temperature is maintained for a period of 5 minutes to 240 minutes, particularly preferably for a period of 20 minutes to 180 minutes, in particular for a period of 30 minutes to 150 minutes.

[0128] Methods for heating reaction mixtures are known in principle. In a preferred embodiment, the heating is carried out by jacket heating.

[0129] The process according to the application makes it possible to decompose lignin without the application of elevated pressure.

[0130] In a preferred embodiment, the process is carried out in a closed vessel.

[0131] Since gaseous products can also be formed during the heat treatment of the reaction mixture A, the pressure in the vessel in which the heat treatment is carried out can increase. The pressure during step b) can be less than 150 bar, preferably less than 100 bar, particularly preferably less than 50 bar. The pressure during step b) is preferably between 0.1 bar and 35 bar, more preferably 1 bar to 10 bar, in particular 1 bar to 5 bar.

[0132] A further advantage of the process according to the application is that it is not necessary to operate in a hydrogen atmosphere or in an inert gas atmosphere.

[0133] By the process according to the application, a mixture B comprising the product mixture, the catalyst and the solvent is obtained.

[0134] The product mixture comprises monomeric and oligomeric products which are soluble in organic solvents. The product mixture can also comprise further products, such as polymeric lignin rearrangement products or gaseous products. The gaseous products usually comprise CO2 and H2. In addition, the product mixture can comprise products which are water-soluble and are referred to as water-soluble product fraction.

[0135] For the definition of the terms "monomeric product", "oligomeric product" and "polymer", reference is made in principle to the IUPAC definition. "Oligomer" is understood to mean a medium molecular weight molecule which consists of a plurality of smaller repeating units. Medium molecular weight means that the properties of the molecule do not change when one or a few smaller units are removed. The term "oligomer" preferably comprises compounds having at least three and / or at most 20 monomeric units.

[0136] In the context of the present application, such products are referred to as monomeric or oligomeric components which are obtained from lignin by the process according to the application.

[0137] The monomeric products are preferably soluble in ethyl acetate. The oligomeric products are preferably soluble in THF.

[0138] The monomeric and oligomeric products preferably comprise structural units which comprise at least one aromatic ring and at least one oxygen-containing substituent. In other words, the monomeric and oligomeric products preferably comprise predominantly phenolic structural units. The presence of phenolic structural units can preferably be determined by Folin-Ciocalteu titration of the OH groups.

[0139] Preferably, the monomeric and oligomeric products comprise at least 40% by weight, more preferably at least 50% by weight, of phenolic structural units, based on the total weight of the monomeric and oligomeric components.

[0140] Preferably, the process according to the application produces a product mixture, wherein at least 50 wt.-%, more preferably at least 60 wt.-% of the lignin used in the reaction mixture A has been converted into monomeric and oligomeric products. In other words, in the process according to the application a yield of at least 50 wt.-% of the target products is obtained and the proportion of undesired side products is minimized. For the purposes of the present application, undesired side products are to be understood as meaning the coke fraction, the water-soluble product fraction and the gaseous product fraction.

[0141] The yield is determined using the following formula:

[0142] Yield in wt.-%

[0143] = (weight of monomeric products + weight of oligomeric products / weight of lignin used) x 100.

[0144] Preferably, a product mixture comprising less than 30 wt.-% of the coke fraction is obtained by the process according to the application. This means that less than 30 wt.-% of the resulting product mixture, which comprises the polymeric, monomeric and oligomeric components, and possibly the water-soluble fraction and the gaseous products, consists of this insoluble fraction. More preferably, less than 25 wt.-%, even more preferably less than 20 wt.-%, most preferably less than 10 wt.-% of the coke fraction is obtained.

[0145] Preferably, a product mixture comprising at least 5 wt.-%, more preferably at least 10 wt.-% of monomeric products is obtained by the process according to the application. Preferably, a product mixture comprising 1 wt.-% to 30 wt.-%, more preferably 5 wt.-% to 20 wt.-% of monomeric products is obtained by the process according to the application.

[0146] Preferably, a product mixture comprising less than 20 wt.-%, more preferably less than 15 wt.-%, even more preferably less than 10 wt.-% of monomeric products having no aromatic moiety is obtained by the process according to the application.

[0147] Preferably, the monomeric products comprise no more than 20 carbon atoms, preferably no more than 15 carbon atoms.

[0148] The monomeric products preferably have an average molecular weight of less than 1500 g / mol, more preferably less than 1000 g / mol. The average molecular weight can be determined by gel permeation chromatography (GPC).

[0149] The product mixture preferably comprises at least one monomeric product which contains a phenolic structural unit. The presence of such products having phenolic OH groups can be determined by the Folin-Ciocalteu method.

[0150] Preferably, the total weight of the monomeric products comprises at least 40 wt.-%, more preferably at least 50 wt.-%, even more preferably at least 60 wt.-% of monomeric products comprising an aromatic system with at least one oxygen-containing substituent. The proportion of these monomeric products can be determined by gas chromatography-mass spectrometry (GC-MS).

[0151] The monomeric products preferably comprise at least one product selected from the group comprising alkylated phenols, alkylated alkoxyphenols, catechols, alkylated catechols and alkylated alkoxy catechols. The monomeric products can be characterized by GC-MS.

[0152] Preferably, the product mixture comprising at least 40 wt.-%, more preferably at least 50 wt.-%, even more preferably at least 60 wt.-% of oligomeric products is obtained by the method according to the application.

[0153] The oligomeric products preferably have an average molecular weight of less than 10,000 g / mol, more preferably less than 8,000 g / mol.

[0154] Preferably, the average molecular weight of the oligomeric products is not more than 70%, more preferably not more than 60%, even more preferably not more than 55% of the average molecular weight of the lignin originally used.

[0155] The product mixture preferably comprises at least one oligomeric product, the monomeric building blocks of which comprise phenolic building blocks. The presence of such products with phenolic OH groups can be determined by the Folin-Ciocalteu method.

[0156] The oligomeric products preferably comprise at least one oligomer, the monomers of which are selected from the group comprising alkylated phenols, alkylated alkoxyphenols, catechols, alkylated catechols and alkylated alkoxy catechols.

[0157] In a preferred embodiment, the catalyst is separated from mixture B after the method according to the application has been carried out. This separation can be carried out, for example, by filtration.

[0158] The method can also comprise a method step in which the product mixture is separated from mixture B. The entire product mixture or part of the product mixture can be separated, for example, by filtration, evaporation, distillation, centrifugation, decanting, sedimentation or other methods known to the person skilled in the art.

[0159] In a preferred embodiment, the method according to the application can comprise a step of fractionating, isolating or purifying mixture B.

[0160] In a preferred embodiment, the method according to the application is part of a process in which the biomass is divided into different streams and the lignin fraction is partially broken down. In a preferred embodiment, the method according to the application is part of a process in which the biomass is divided into different streams and the lignin fraction is partially broken down.

[0161] In a preferred embodiment, the process comprises the additional step, wherein a phenol-formaldehyde resin is prepared from at least one of the components of the product mixture.

[0162] The present application also relates to a product mixture obtained by the process according to the present application and comprising monomers and oligomeric products. For preferred embodiments, reference is made to the above description.

[0163] The present application also relates to a catalyst suitable for use in the process according to the present application. For preferred embodiments, reference is made to the above description.

[0164] In the following, the present application is described by way of example embodiments in specific terms, however these example embodiments are not to be understood as limiting.

[0165] Measurement methods

[0166] Platinum and nickel content of the catalyst

[0167] The platinum and nickel content was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0168] BET surface area

[0169] The BET surface area was determined according to the BET theory (multi-point method) according to ISO 9277:2010 using nitrogen as adsorbate at 77 K.

[0170] CO adsorption (noble metal surface)

[0171] The noble metal surface of the catalyst was determined by CO adsorption. For this, the catalyst was first reduced in a closed vessel at 400 °C for 20 minutes in a synthetic gas consisting of 95% argon and 5% hydrogen. Subsequently, carbon monoxide (CO, with helium as carrier gas) was dosed in pulse form into the vessel in which the catalyst was located. This was done until a constant CO peak was detected downstream of the catalyst. By determining the peak area of the dosed CO and by determining the peak area of the reacted CO, the amount of CO that was adsorbed by the catalyst was determined. For this, the integral of the area of the reacted CO was subtracted from the integral of the area of the dosed CO. The amount of CO that was adsorbed in this way was used to calculate how much CO was stored per amount of catalytically active composition used. Using the conversion, the surface area of the active noble metal sites (often also referred to as CO surface area or noble metal surface area) can be determined from the measured amount of CO stored at the active sites.

[0172] Gel permeation chromatography (GPC)

[0173] The molecular weight of the various components was determined by gel permeation chromatography (GPC, Thermo Scientific, Dionex ICS-5000+ with PSS MCX analytical 100A+1000A+100 000A columns; 8 mm x 300 mm, also Thermo Fischer). The characterization was performed at 30 °C with 0.1 mol / L NaOH as eluent at a flow rate of 0.5 mL / min. The detection was performed at 280 nm.

[0174] Before injection, the samples were dissolved in 0.1 mol of L-1 NaOH and filtered through a membrane filter (0.45 pm). SEC calibration was performed using PSS standards (Polymer Standard Service, Mp: 976 000, 679 000, 470 000, 258 000, 194 000, 152 000, 78 400, 29 500, 10 200, 3 420, 891) and vanillin. The standards were also dissolved in NaOH (1 mg mL-1 in 0.1 mol / L NaOH).

[0175] Gas chromatography-mass spectrometry (GC-MS)

[0176] Qualitative and quantitative analysis was performed using gas chromatography-mass spectrometry (GC-MS, SHIMADZU GC-MS-QP 2020, HP-SM5 capillary column, 60 m x 0.25 mm x 0.25 pm). The temperature of the system was raised from 50 °C to 300 °C at a heating rate of 10 °C / min. A hold time of 5 min at 120 °C and 8 min at 280 °C was chosen. Helium was used as carrier gas. The injection temperature was 250 °C. 5 mg of sample was dissolved in 1 mL of ethyl acetate, mixed with 100 pL of toluene with internal standard and injected directly. 41 monomeric components were used as standards for external calibration and calibration was performed in each case in 10 steps at concentrations of 300 mg / L to 0.3 mg / L. In addition, toluene with internal standard was used.

[0177] Determination of phenolic groups

[0178] Phenolic groups were determined by the Folin-Ciocalteu method, in which the hydroxyl groups are titrated with a colored indicator substance. The indicator system used is a complexing system consisting of molybdenum phosphoric acid and tungsten phosphoric acid (3H20-P205-13W03-5M03-10H30 or 3H20-P205-14W03-4M03-10H20). The intensity of the blue complex after reduction is proportional to the concentration of the phenolic OH groups and is quantified by UV-VIS spectroscopy. The calibration substance used is vanillin, a substance with a known proportion of OH groups.

[0179] Inventive Example 1 (IE1)

[0180] A suspension of 145.5 g hydrotalcite (Sasol, BET surface area 19 m 2 / g) was prepared in 800 mL deionized water and 4.5 g Pt was added as hexachloroplatinic acid (H2PtCI6 solution with 33% Pt, Heraeus). The suspension was stirred at 80°C for two days. Subsequently, 22.5 g sodium formate was dissolved in 30 mL water at 70°C and added to the suspension. The suspension was stirred at 70°C overnight. The suspension was then diluted with 1 L deionized water and filtered after cooling to room temperature. The residue was washed and finally dried at 120°C. The noble metal surface area of the catalyst was determined to be 7 m 2 / g.

[0181] Inventive Example 2 (IE2)

[0182] 5 g Pt as platinum (II) nitrate (Pt(N03)2 solution with 15.2% Pt, Heraeus) was diluted to 30 mL and homogenized. This solution was added to 95 g hydrotalcite (Sasol, BET surface area 19 m 2 / g) and the mixture was homogenized. The mixture was vacuum dried at 110°C overnight under a nitrogen atmosphere. It was then heat treated in an oxygen-containing atmosphere for 14 hours, during which the temperature was gradually increased to 250°C. Finally, the material was treated with synthesis gas (95 vol% nitrogen, 5 vol% hydrogen) up to 250°C for 16 hours. The noble metal surface area of the catalyst was determined to be 10 m 2 / g.

[0183] Inventive Example 3 (IE3)

[0184] Prepared in the same way as IE2. In addition, 1 g Ni was added as nickel (II) nitrate hexahydrate (Ni(NO3)2*6H2O with 20% Ni, Merck) to the platinum (II) nitrate solution, which was diluted and homogenized together. This solution was added to 94 g of hydrotalcite and the mixture was homogenized. The noble metal surface area of the catalyst was determined to be 5 m 2 / g.

[0185] Inventive Example 4 (IE4)

[0186] Prepared in the same way as IE2. In addition, 2 g Ni was added as nickel (II) nitrate hexahydrate (Ni(NO3)2*6H2O with 20% Ni, Merck) to the platinum (II) nitrate solution, which was diluted and homogenized together. This solution was added to 93 g of hydrotalcite and the mixture was homogenized. The noble metal surface area of the catalyst was determined to be 11 m 2 / g.

[0187] Depolymerization

[0188] The standard conditions for depolymerization are specified as follows. 20 g of organosolv lignin (Chemical Point, average molecular weight 6,200 Da) was mixed with the catalyst and suspended in 200 mL of solvent (45.9 vol-% ethanol in water).

[0189] The lignin was decomposed in an autoclave (PARR, 4871 Process Controller, software: SpecView3) at a stirring speed of 300 rpm. The reaction mixture was heated to the target temperature and kept at this temperature for the desired time.

[0190] After cooling the mixture to room temperature, the catalyst was separated and the product fractions were then separated from each other. For this, the mixture was adjusted to pH 2 using concentrated hydrochloric acid (HCl 37 wt-%) to precipitate the lignin tar fraction (containing oligomeric products). The solid components were then separated by vacuum filtration. The solid was washed 3 times with dilute hydrochloric acid. The water-soluble phase was extracted 3 times with ethyl acetate and the organic phases were combined, dried with sodium sulfate and filtered. The ethyl acetate was removed in a rotary evaporator and the resulting solid was the lignin-oil fraction (containing monomeric products). The solid obtained after vacuum filtration was slurried in THF to dissolve the oligomeric products and the remaining solid components (coke fraction, containing polymeric rearrangement products of lignin and additional solid insoluble products) were separated again by vacuum filtration. The organic phase was evaporated in a rotary evaporator to obtain the oligomeric product fraction.

[0191] The yield ratio of the various product fractions was calculated as follows:

[0192] Yield of monomer fraction in wt.%

[0193] = (weight of lignin-oil fraction / weight of lignin used) x 100;

[0194] Yield of oligomer fraction in wt.%

[0195] = (weight of lignin-tar fraction / weight of lignin used) x 100;

[0196] Coke ratio in wt.%

[0197] = (weight of coke fraction / weight of lignin used) x 100.

[0198] Figure 3 The composition of the representative depolymerized product mixtures using the 4 catalysts according to the application (IE1-IE4) is shown in comparison to the hydrotalcite without metal loading (CE1). The ratio of lignin used and catalyst was constant (20 wt.% catalyst) and all reactions were carried out at 200°C for 30 minutes. Figure 4 Exemplary GPC chromatograms for the analysis of the average molecular weight of the lignin used as well as the monomer and oligomer product fractions of the depolymerization using IE3 were also compared.

[0199]

[0200] Table 1

[0201] Table 1 summarizes the average molecular weight of the monomer and oligomer product fractions. The results show that the use of catalysts according to the application can significantly increase the conversion of the lignin used. The phenolic OH groups of both the lignin used and the product fractions were titrated according to the Folin-Ciocalteu method. These results are also included in Table 1. For all catalyst systems shown here, the concentration of OH groups representing the presence of phenolic structural units is comparable to the concentration of the lignin used (3.7 mmol / g), indicating that these structural units are retained during the decomposition reaction.

[0202] In IE5, the same catalyst as in IE3 was used, with the difference that only 1.2 wt.% of catalyst was used relative to the weight of lignin to be reacted. The depolymerization was carried out at 230°C for 90 minutes. IE5 illustrates that a high yield of the reaction and the desired selectivity can be achieved using small amounts of catalyst according to the application and under mild reaction conditions.

Claims

1. A process for the catalytic decomposition of lignin, the process comprising a) providing a reaction mixture A comprising lignin, a catalyst and a solvent; b) heating the reaction mixture A so as to obtain a mixture B comprising a product mixture, the catalyst and the solvent; wherein the catalyst comprises - a basic support material, - 1 wt% to 10 wt% of platinum by weight, and - 0.1 wt% to 5 wt% of nickel by weight, wherein the basic support material is a layered double hydroxide of the formula: wherein m denotes the number of water molecules and w denotes the molar ratio between trivalent cations and the total amount of cations, wherein platinum and nickel are referred to as metal species and form catalytically active sites, wherein the catalyst comprises the metal species in the range of 1 wt% to 15 wt%, and wherein the product mixture comprises less than 20 wt% of a coke fraction.

2. The process according to claim 1, wherein the lignin is selected from the group comprising organic solvent lignin, kraft lignin, lignin obtained by alkaline digestion, lignin obtained by kraft process, lignin obtained by sulfite process, lignin obtained by extraction with water, lignin obtained by hydrolysis with acid, lignin obtained by enzymatic hydrolysis, lignin obtained by wood saccharification, lignin obtained by treatment with microorganisms, lignin from a biorefinery process stream comprising lignin, and mixtures thereof.

3. The process according to claim 1, wherein the solvent comprises water and an alcohol.

4. The process according to any one of claims 1 to 3, wherein the catalyst is present in the reaction mixture A in an amount of 0.1 wt% to 30 wt% based on the total amount of catalyst and lignin.

5. The process according to claim 4, wherein the catalyst is present in the reaction mixture A in an amount of 1 wt% to less than 5 wt% based on the total amount of catalyst and lignin.

6. The process according to any one of claims 1 to 3, wherein the reaction mixture A is heated to a reaction temperature of 50°C to 400°C.

7. The process according to claim 6, wherein the reaction temperature in process step b) is maintained for a period of 5 minutes to 240 minutes.

8. The process according to any one of claims 1 to 3, wherein at least 50 wt% of the lignin used in the reaction mixture A is converted into monomeric and oligomeric products. [M 2+ 1-w M 3+ w (OH)2] w+ (A n- w / n ) • m H2O, wherein M 2+ represents a divalent cation, M 3+ represents a trivalent cation, and A n- represents an anion with a charge n, 9. The process according to any one of claims 1 to 3, wherein the product mixture comprises at least one monomeric product containing a phenolic structural unit.

10. The process according to any one of claims 1 to 3, wherein the product mixture comprises at least one oligomeric product, the monomeric structural units of which comprise phenolic structural units. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 11. The method according to any one of claims 1 to 3, wherein the basic support material comprises at least one type of divalent cation M selected from the group consisting of all of the following: 2+ Magnesium (Mg) 2+ ), nickel (Ni 2+ ), iron (Fe) 2+ ), cobalt (Co) 2+ ), copper (Cu) 2+ ), Zinc (Zn) 2+ ), calcium (Ca 2+ ), Tin (Sn) 2+ ) and lead (Pb 2+ ).

12. The method according to any one of claims 1 to 3, wherein the basic support material comprises at least one type of trivalent cation M selected from the group consisting of all of the following. 3+ Aluminum (Al) 3+ ), iron (Fe) 3+ ), chromium (Cr) 3+ ) and manganese (Mn 3 + ).

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