METHOD AND CATALYST FOR PRODUCING PHENOLIC BUILDING BLOCKS FROM LIGNIN

Abstract

The invention relates to a method for the catalyzed decomposition of lignin with a high yield and high selectivity for phenolic building blocks and with minimal formation of the coke fraction, and to a catalyst suitable for the method. The catalyst contains a basic carrier material, platinum at a weight percentage of 1-10 wt. % and nickel at a weight percentage of 0-5 wt. %. The method comprises: providing a reaction mixture comprisinglignin, the catalyst and a solvent; and heating the reaction mixture so as to obtain a mixture comprisinga product mix, the catalyst and the solvent.

Claims

1. A method for the catalyzed decomposition of lignin, 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 mix, the catalyst and the solvent; wherein the catalyst contains a basic carrier material, platinum at a weight percentage of 1-10 wt. % and nickel at a weight percentage of 0-5 wt. %.

2. The method according to claim 1, wherein the lignin is selected from the group containing organosolv lignin, kraft lignin, lignin obtained by alkaline digestion, lignin obtained by the sulfate method, lignin obtained by the sulfite method, lignin obtained by extraction with water, lignin obtained by hydrolysis with acids, lignin obtained by enzymatic hydrolysis, lignin obtained by saccharification of wood, lignin obtained by treatment with micro-organisms, lignin from biorefinery process streams containing lignin, and mixtures thereof.

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

4. The method according to claim 1, wherein the catalyst is present in the reaction mixture A in an amount of less than 30 wt. % based on the total amount of catalyst and lignin.

5. The method according to claim 1, wherein the reaction mixture A is heated to a reaction temperature of below 400? C.

6. The method according to claim 1, wherein the reaction temperature in method step b) is maintained over a period of less than 240 min.

7. The method according to claim 1, wherein the product mix contains less than 30 wt. % of a coke fraction.

8. The method according to claim 1, wherein at least 50 wt. % of the lignin used in the reaction mixture A is converted into monomeric and oligomeric products.

9. The method according to claim 1, wherein the product mix comprises at least one monomeric product containing a phenolic building block.

10. The method according to claim 1, wherein the product mix comprises at least one oligomeric product of which the monomer building blocks contain a phenolic building block.

11. The method according to claim 1, wherein the basic carrier material contains a mixture of divalent and trivalent cations.

12. The method according to claim 1, wherein the basic carrier material contains at least one type of divalent cation M.sup.2+ selected from the group consisting of magnesium (Mg.sup.2+), nickel (Ni.sup.2+), iron (Fe.sup.2+), cobalt (Co.sup.2+), copper (Cu.sup.2+), zinc (Zn.sup.2+), calcium (Ca.sup.2+), tin (Sn.sup.2+), lead (Pb.sup.2+) and combinations thereof.

13. The method according to claim 1, wherein the basic carrier material contains at least one type of trivalent cation M.sup.3+ selected from the group consisting of aluminum (Al.sup.3+), iron (Fe.sup.3+), chromium (Cr.sup.3+), manganese (Mn.sup.3+) and combinations thereof.

14. A product mix obtainable by a method according to claim 1, comprising monomeric and oligomeric products.

15. A catalyst which can be used in a method according to claim 1, containing a basic carrier material, platinum at a weight percentage of 1-10 wt. % and nickel at a weight percentage of 0-5 wt. %.

Description

INVENTION EXAMPLE 1 (IE1)

[0177] 145.5 g hydrotalcite (Sasol, BET surface area 19 m.sup.2/g) was suspended in 800 mL deionized water and 4.5 g Pt was added as hexachloroplatinic acid (H.sub.2PtCl.sub.6 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 overnight at 70? C. 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 as 7 m.sup.2/g.

INVENTION EXAMPLE 2 (IE2)

[0178] 5 g Pt as platinum(II) nitrate (Pt(NO.sub.3).sub.2 solution with 15.2% Pt, Heraeus) was diluted to 30 mL and homogenized. The solution was added to 95 g hydrotalcite (Sasol, BET surface area 19 m.sup.2/g) and the mixture was homogenized. The mixture was dried overnight at 110? C. in a nitrogen atmosphere in vacuo. This was followed by thermal treatment for 14 h in an oxygen-containing atmosphere, during which the temperature was increased stepwise to 250? C. Finally, the material was treated for 16 h with forming gas (95 vol. % nitrogen, 5 vol. % hydrogen) at up to 250? C. The noble metal surface area of the catalyst was determined as 10 m.sup.2/g.

INVENTION EXAMPLE 3 (IE3)

[0179] The production was carried out in the same way as IE2. In addition, 1 g Ni was added as nickel(II) nitrate hexahydrate (Ni(NO.sub.3).sub.2*6H.sub.2O with 20% Ni, Merck) to the platinum(II) nitrate solution, which was diluted together and homogenized. This solution was added to 94 g hydrotalcite and the mixture was homogenized. The noble metal surface area of the catalyst was determined as 5 m.sup.2/g.

INVENTION EXAMPLE 4 (IE4)

[0180] The production was carried out in the same way as IE2. In addition, 2 g Ni was added as nickel(II) nitrate hexahydrate (Ni(NO.sub.3).sub.2*6H.sub.2O with 20% Ni, Merck) to the platinum(II) nitrate solution, which was diluted together and homogenized. This solution was added to 93 g hydrotalcite and the mixture was homogenized. The noble metal surface area of the catalyst was determined as 11 m.sup.2/g.

[0181] Depolymerizations

[0182] Standard conditions for depolymerization are specified below. 20 g organosolv lignin (ChemicalPoint, average molecular weight 6,200 Da) was mixed with the catalyst and suspended in 200 mL solvent (45.9 vol. % ethanol in water).

[0183] 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.

[0184] After the mixture was cooled to room temperature, the catalyst was separated and then the product fractions were separated from one another. For this purpose, the mixture was adjusted using conc. hydrochloric acid (HCl 37 wt. %) to a pH of 2 to precipitate the lignin tar fraction (containing the oligomeric products). The solid constituents 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 over sodium sulfate, and filtered. The ethyl acetate was removed in a rotary evaporator, and the resulting solid was the lignin-oil fraction (containing the monomeric products). The solids obtained after vacuum filtration were slurried in THE to dissolve the oligomeric products, and the remaining solid constituents (the coke fraction, containing polymeric rearrangement products of lignin and further solid insoluble products) were again separated by vacuum filtration. The organic phase was evaporated off in a rotary evaporator to obtain the oligomeric product fraction.

[0185] The proportions of the yield for the various product fractions were calculated as follows:

yield of monomeric components (in wt. %)=(weight of lignin-oil fraction/weight of lignin used)?100;

yield of oligomeric components (in wt. %)=(weight of lignin-tar fraction/weight of lignin used)?100;

coke proportion (in wt. %)=(weight of coke fraction/weight of lignin used)?100.

[0186] FIG. 3 shows the composition of the product mix of representative depolymerizations with 4 catalysts according to the invention (IE1-IE4) compared to a hydrotalcite without metal loading (CE1). The ratio of lignin and catalyst used was constant (20 wt. % catalyst), and all reactions were performed at 200? C. for 30 min. FIG. 4 also compares example GPC chromatograms used to analyze the average molecular weight of the lignin used, and the monomeric and the oligomeric product fractions of the depolymerization with IE3.

TABLE-US-00001 TABLE 1 OH groups OH groups M.sub.w [g/mol] [mmol/g] M.sub.w [g/mol] [mmol/g] Monomer Monomer Oligomer Oligomer Catalyst fraction fraction fraction fraction CE1 HTC 600 5.3 12582 3.5 IE1 3% Pt/HTC 485 4.5 1585 3.3 IE2 5% Pt/HTC 462 5.1 1909 3.2 IE3 5% Pt + 1% Ni/HTC 838 5.2 3282 3.1 IE4 5% Pt + 2% Ni/HTC 754 5.4 3544 3.2 IE5 5% Pt + 1% Ni/HTC 809 4.2 2810 3.5

[0187] Table 1 summarizes the average molecular weights of the monomer and oligomer product fractions. The results illustrate that the conversion of the lignin used can be significantly increased using the catalysts according to the invention. The phenolic OH groups were titrated for both the lignin used and the product fractions according to the Folin-Ciocalteu method. Table 1 also contains these results. For all catalyst systems shown here, the concentration of the OH groups, which is representative of the presence of phenolic building blocks, was comparable to that of the lignin used (3.7 mmol/g), suggesting that these building blocks were retained during the decomposition reaction.

[0188] In IE5, the same catalyst as in IE3 was used, except that only 1.2 wt. % catalyst was used relative to the weight of lignin to be reacted. The depolymerization was performed at 230? C. for 90 min. IE5 illustrates that a high yield and the desired selectivity of the reaction can be achieved using small amounts of a catalyst according to the invention and under mild reaction conditions.