Production of monomers from lignin during depolymerization of lignocellulose-containing composition

Abstract

The present invention relates to a method for preparing monomers via depolymerisation from lignocellulose-containing biomass.

Claims

1. A method for producing fragments of lignin comprising the steps of: a) providing a lignocellulose-containing composition, suspended in an organic solvent comprising less than 50% v/v of water; b) heating the composition of step a) under acidic conditions together with an aldehyde, boronic acid or a compound selected from 2-methoxypropene, dimethyl carbonate and 2,2-dimethoxypropane to achieve a mixture; and c) separating fragments of lignin from the mixture of step b), wherein the aldehyde, boronic acid or compound selected from 2-methoxypropene, dimethyl carbonate, and 2,2-dimethoxypropane is present in a weight ratio of at least 1:25 relative to the lignocellulose-containing composition, wherein the aldehyde, the boronic acid or the compound selected from 2-methoxypropene, dimethyl carbonate and 2,2-dimethoxypropane weight is based on the weight of formaldehyde.

2. The method according to claim 1, wherein in a step d) the fragments of lignin of step c) are converted into monomers.

3. The method according to claim 2, wherein the organic solvent is selected from the group consisting of alcohols with 1 to 6 carbon atoms, cyclic ethers, and lactones.

4. The method according to claim 2, wherein the lignocellulose-containing composition has a lignin content of 20-40 wt. %.

5. The method according to claim 2, wherein the monomers are selected from Formulae M1 to M24 ##STR00022## ##STR00023## ##STR00024## ##STR00025##

6. The method according to claim 1, wherein the acidic conditions of step b) are achieved by adding one or more acidic components to the composition of step a) and wherein the acidic components are selected from the group consisting of organic carboxylic acids or mineral acids.

7. The method according to claim 6, wherein the acidic conditions of step b) are achieved by adding 1 to 10 mmol of the acidic components per gram of lignocellulose-containing composition.

8. The method according to claim 1, wherein in step b) the composition is heated under acidic conditions together with an aldehyde according to formula (I) ##STR00026## wherein R is a hydrogen or an organic residue with 1 to 10 carbon atoms.

9. The method according to claim 8, wherein R is an aromatic residue being substituted with one or more substituents selected from the group consisting of alkyl groups with 1 to 4 carbon atoms, halogen, nitro, nitrile, carboxylic group, carboxylic esters, carboxylic amide, methoxy and ethoxy.

10. The method according to claim 9, wherein in step b) the composition is heated under acidic conditions together with an aldehyde according to formula (I) ##STR00027## wherein R is selected from the group consisting of phenyl, o-tolyl and p-tolyl.

11. The method according to claim 8, wherein R is an aliphatic substituted or unsubstituted residue.

12. The method according to claim 11, wherein in step b) the composition is heated under acidic conditions together with an aldehyde according to formula (I) ##STR00028## wherein R is selected from the group consisting of methyl, ethyl, propyl and butyl.

13. The method according to claim 11, wherein in step b) the composition is heated under acidic conditions together with an aldehyde according to formula (I) ##STR00029## wherein R is selected from the group consisting of cyclopropyl, isopropyl and tert-butyl.

14. The method according to claim 1, wherein in step b) a temperature of 50 to 120° C. is applied for 1 to 8 hours.

15. The method according to claim 1, wherein the lignocellulose-containing composition and aldehyde, boronic acid or compound selected from 2-methoxypropene, dimethyl carbonate and 2,2-dimethoxypropane are present in a weight ratio of 25:1 to 1:1, wherein the aldehyde, the boronic acid or the compound selected from 2-methoxypropene, dimethyl carbonate and 2,2-dimethoxypropane weight is based on the weight of formaldehyde.

16. The method according to claim 1, wherein the organic solvent is selected from the group consisting of alcohols with 1 to 6 carbon atoms, cyclic ethers, and lactones.

17. The method according to claim 1, wherein in step b) the composition is heated under acidic conditions together with an aldehyde according to formula (I) ##STR00030## wherein R is selected from the group consisting of methyl, ethyl, propyl and butyl.

18. The method according to claim 1, wherein in step b) the composition is heated under acidic conditions together with an aldehyde according to formula (I) ##STR00031## wherein R is selected from the group consisting of cyclopropyl, isopropyl and tert-butyl.

19. The method according to claim 1, wherein in step b) the composition is heated under acidic conditions together with an aldehyde according to formula (I) ##STR00032## wherein R is selected from the group consisting of phenyl, o-tolyl and p-tolyl.

20. The method according to claim 1, wherein the lignocellulose-containing composition has a lignin content of 20-40 wt. %.

21. A method for producing fragments of xylan via depolymerization comprising the steps of: a) providing a lignocellulose-containing composition, b) heating the composition of step a) under acidic conditions together with an aldehyde, boronic acid or a compound selected from 2-methoxypropene, dimethyl carbonate and 2,2-dimethoxypropane to obtain a mixture, c′) separating the fragments of xylan from the mixture of step b), wherein the aldehyde, boronic acid or compound selected from 2-methoxypropene, dimethyl carbonate, and 2,2-dimethoxypropane is present in a weight ratio of at least 1:25 relative to the lignocellulose-containing composition, wherein the aldehyde, the boronic acid or the compound selected from 2-methoxypropene, dimethyl carbonate and 2,2-dimethoxypropane weight is based on the weight of formaldehyde.

22. The method according to claim 21, wherein step b) involves heating the composition of step a) under acidic conditions together with an aldehyde, according to formula (I) ##STR00033## wherein R is selected from the group consisting of methyl, ethyl, propyl and butyl.

23. The method according to claim 21, wherein step b) involves heating the composition of step a) under acidic conditions together with an aldehyde, according to formula (I) ##STR00034## wherein R is selected from the group consisting of phenyl, o-tolyl and p-tolyl.

24. The method according to claim 21, wherein step b) involves heating the composition of step a) under acidic conditions together with an aldehyde, according to formula (I) ##STR00035## wherein R is selected from the group consisting of cyclopropyl, isopropyl and tert-butyl.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Validation of Effective Carbon Number (ECN) rule for lignin monomer quantification (X axis: ECN based on empirical rule (Table S3); Y axis: ECN calculated based on FID response using decane as an internal standard). Compound 1 (guaiacol), compound 2 (syringol), compound 3 (guaiacylethane), compound 4 (guaiacylpropanol), compound 5 (guaiacylpropane) and compound 6 (propylbenzene).

(2) FIG. 2: Precipitation of lignin by adding water into the pretreatment liquors; (A) 0 h after the addition of water, and (B) 15 h after the addition of water. (The dark color suggests a severe condensation of lignin; the light color suggests limited condensation in lignin).

(3) FIG. 3a: GC chromatogram of lignin monomers obtained by the method according to the present invention.

(4) FIG. 3b: Corresponding mass spectra of the lignin monomers obtained by the method according to the present invention. (M+ is the molecular ion peak, representing the molecular weight of lignin monomers; the highest peak with arrow pointed represents the molecular weight of the most stabilized fragment ion from each lignin monomer).

(5) FIG. 4: NMR characterization of hexane-extracted lignin monomers. (A) 2D HSQC NMR spectra (the side chain region of lignin monomers), (B) .sup.13C and .sup.13C-DEPT NMR spectra (the side chain region of lignin monomers), (C) 2D HSQC NMR spectra (the aromatic region and methoxy region of lignin monomers), and (D) .sup.13O and .sup.13C-DEPT NMR spectra (the side chain region of lignin monomers). The appearance of methyl group in FIGS. 4A (red) and 4B and tertiary carbon (121 and 128 ppm) in FIG. 4D proved the reaction of lignin aromatic ring with formaldehyde.

(6) FIG. 5: Comparison of monomers from lignin from different processes; (A) Reference Example R.E. 2.2, (B) Reference Example R.E. 2.2, and (C) Example 2.1. Direct hydrogenolysis of native lignin (A and B) generated five major lignin monomers (highlighted with star); the peaks highlighted with arrow refer to the lignin monomers with methyl group on the aromatic ring which derived from the reaction of lignin monomeric units with FA).

(7) FIG. 6: Identification of diformyl-xylose. (A) 2D HSQC NMR spectra of purified diformyl-xylose, (B) 13C and 13C-DEPT-135 NMR spectra of diformyl-xylose, (C) GC chromatogram of diformyl-xylose, and (D) mass spectra of diformyl-xylose.

DETAILED DESCRIPTION OF THE INVENTION

(8) The invention will now be illustrated with reference to the following examples.

EXAMPLES

I. Materials

(9) All commercial chemicals were analytical reagents and were used without further purification. 5% Ru on carbon (Ru/C), guaiacol (2-methoxyphenol, 98%), 4-ethylguaiacol (>97%), 4-propylguaiacol (>99%), syringol (2, 6-dimethoxyphenol, 99%) and propylbenzene (98%) were purchased from Sigma Aldrich. Methanol (>99%), tetrahydrofuran (THF, >99%) and dichloromethane (>99%) were purchased from ABCR. 4-Propanolguaiacol (3-(4-hydroxy-3-methoxyphenyl)-1-propanol, >98%), 1,4-dioxane (98%) were purchased from TCI chemicals. Beech wood (Fagus sylvatica) was harvested in Zollikofen (Switzerland) in October 2014 and air dried for storage. Prior to experiments the beech chips were reduced in size to pass through a 18 mesh sieve.

II. Analytical Methods

(10) (1) Composition Analysis of Biomass

(11) The composition analysis of biomass and substrate after lignin extraction followed the TAPPI method. The, wood particles (0.25-0.50 g) were loaded into 50 mL beakers with the addition of 7.5 mL of a 72 wt. % H.sub.2SO.sub.4 solution. The mixture was left at room temperature for 2 h and stirred with a glass rod every 10 minutes. Afterwards the slurry was transferred into a round-bottom flask and 290 mL of water were added to reach a H.sub.2SO.sub.4 concentration of 3 wt. %. The glass bottle was sealed with a screw cap and sterilized at 120° C. for 1 h in an autoclave. The resultant solution was filtered and the filtrate was used for sugar analysis on an HPLC and the precipitate was washed with water and dried at 105° C. and weighed to determine Klason lignin.

(12) For the analysis of pretreatment liquor, the slurry after lignin extraction was filtered and washed with 30 mL water and analyzed by high performance liquid chromatography (HPLC). To hydrolyze possible oligomers or acetalized sugars into monomeric sugars, 20 μL concentrated sulfuric acid was added to 1 mL of the filtrate and heated to 120° C. for 1 h in an autoclave. The resulting mixture was analyzed by HPLC.

(13) Analysis of the sugars was conducted using an Agilent Infinity 1260 HPLC system equipped with a Refractive Index Detector and a Bio-Rad Aminex HPX-87P column at 80° C. using water as the mobile phase and a flow rate of 0.6 ml/min.

(14) Analysis of Furfural and HMF was conducted using an Agilent Infinity 1260 HPLC equipped with UV-Vis Detector and a Bio-Rad Aminex HPX-87H column at 80° C. using 5 mM H.sub.2SO.sub.4 in water as the mobile phase and a flow rate of 0.6 ml/min.

(15) The composition analysis of beech wood particles resulted in the following:

(16) TABLE-US-00001 arab- galac- Klason Compound glucose Xylose inose tose mannose lignin Content 34% 14% 2% 2% 2% 22%
(2) Lignin Monomer Analysis

(17) To analyze lignin monomers after hydrogenolysis, 1 mL of the resultant solution was directly sampled for analysis without any further treatment other than the addition of 100 μL of prepared internal standard (8 mg decane in 5 mL dioxane). The solution (˜1.1 mL) was analyzed with a GC (Agilent 7890B series) equipped with an HP5-column and a flame ionization detector (FID). The injection temperature was 573 K. The column temperature program was: 313 K (3 min), 30 K/min to 373 K, 40 K/min to 573 K and 573 K (5 min). The detection temperature was 573 K. Sensitivity factors of the products were obtained by using estimates based on the effective carbon number due to lack of commercial standards. The monomer yield was calculated as followed:

(18) $\begin{array}{cc}{n}_{\mathrm{decane}}=\frac{W_{\mathrm{decane}in\mathrm{sample}}}{M{W}_{decane}}& \left(\mathrm{S1}\right)\\ n_{m\mathrm{onomer}}=\frac{A_{\mathrm{monomer}in\mathrm{sample}}}{A_{d\mathrm{ecane}in\mathrm{sample}}}\times n_{\mathrm{decane}}\times \frac{EC{N}_{decane}}{EC{N}_{m\mathrm{onomer}}}& \left(\mathrm{S2}\right)\\ W_{\mathrm{monomer}}=n_{\mathrm{monomer}}\times M{W}_{\mathrm{monomer}}& \left(\mathrm{S3}\right)\\ Y_{\mathrm{monomer}}=\frac{W_{\mathrm{monomer}}\times V}{W_{\mathrm{extracted}\mathrm{lignin}}}\times 100\%.& \left(\mathrm{S4}\right)\end{array}$

(19) In the equations,

(20) W.sub.decane in sample (mg): the weight of decane as internal standard in each analyzed sample;

(21) MW.sub.decane (mg mmol.sup.−1): the molecular weight of decane (142 mg mmol.sup.−1);

(22) n.sub.decane (mmol): the molar amount of decane in each analyzed sample;

(23) n.sub.monomer (mmol): the molar amount of monomer in each analyzed sample;

(24) A.sub.monomer in sample: the peak area of monomer in GC-FID chromatogram;

(25) A.sub.decane in sample: the peak area of decane in the GC-FID chromatogram;

(26) ECN.sub.decane: the effective carbon number (10) of a decane molecule;

(27) ECN.sub.monomer: the effective carbon number of the lignin monomer molecule;

(28) W.sub.monomer (mg): the molecular weight of dehydrated monomer units (guaiacyl glycerol (196 mg mmol.sup.−1) or dehydrated syringyl glycerol (226 mg mmol.sup.−1)) depending on the analyzed monomer;

(29) Y.sub.monomer: the yield of monomer based on the weight of extracted lignin;

(30) W.sub.extracted lignin (mg): the weight of extracted lignin;

(31) V (mL): the total volume of the sample, 1 mL of which was used for GC analysis.

(32) Identification of monomer peaks in the GC-FID chromatograms was performed initially by GC-MS using an Agilent 7890B series GC equipped with a HP5-MS capillary column and an Agilent 5977A series Mass Spectroscopy detector. The peaks in the GC-MS chromatogram appear in the same orders as those in GC-FID chromatogram due to the use of a similar capillary column. The following operating conditions were used: injection temperature at 523 K, a column temperature program of 323 K (1 min), 15 K/min to 573 K and 573 K (7 min) and a detection temperature of 563 K.

(33) (3) NMR Analysis of Lignin

(34) A dried sample was dissolved in 600-1000 μL D-chloroform and transferred into NMR sample tubes. NMR spectra were acquired on a Bruker Avance III 400 MHz spectrometer. The chloroform solvent peak was used as an internal reference (δ.sub.c, 77.2 ppm; δ.sub.H, 7.24 ppm).

(35) (4) Gel Permeation Chromatography (GPC) Analysis

(36) A dried sample was dissolved in 600-1000 THF and GPC analysis was conducted using an Agilent Infinity 1260 HPLC equipped with a Refractive Index Detector and an Agilent PLgel MIXED C column at 40° C. using THF as the mobile phase and a flow rate of 1 ml/min.

III. Monomer Identification and Quantification

(37) Validation of the Effective Carbon Number Method:

(38) The effective carbon number (ECN) rule has been widely used to quantify carbon-containing products based on its response in GC-FID when an authentic standard compound is not available or available only in limited quantities. ECN is the sum of the contributions made by the individual carbon atoms modified by their functional group contributions. Due to the structural differences of different molecules, the accuracy of this rule can vary. In order to verify the accuracy of this rule applied to lignin monomer quantification, the effective carbon numbers of six different lignin model compounds were measured based on their known quantity and their GC response compared to that of decane. The ECN calculated based on FID response using decane as an internal standard was compared to the theoretical ECN based on this empirical rule. For this purpose it is referred to following FIG. 1. Based on the empirical rule, carbons connected only to hydrogen and carbon atoms add 1 unit to the ECN, carbon atoms in a methoxy group (ether) are predicted to not add to the FID response, carbons connected to primary hydroxyl group add 0.5-0.6 units to the ECN and carbon connected to phenolic hydroxyl typically add 0.5 units to the ECN. The only inconsistency we found is that carbon connected to phenolic hydroxyl in lignin monomers did not contribute to the ECN. The contributions of carbon in lignin monomers to ECN (corresponding to increments to calculate the ECN) are summarized in the table below:

(39) TABLE-US-00002 Atom/group ECN contribution Carbon-aliphatic 1 Carbon-aromatic 1 Oxygen-primary alcohol −0.5 Oxygen-phenol −1

(40) Based on this adjusted ECN rule, the ECNs calculated experimentally matched those based on the ECN rule with errors below 1% for all compounds. This demonstrated the high accuracy of using decane as an internal standard and using the factor ECN.sub.monomer/ECN.sub.decane (Equation S2) to quantify lignin monomers. Based on these results, we followed the empirical rule with the modified phenolic carbon connected to the hydroxyl group contribution of 0 for calculating the ECN of biomass-derived lignin monomers. All effective carbon numbers of lignin monomers (ECN.sub.monomers) used for quantification are listed in the following Table:

(41) TABLE-US-00003 TABLE Effective carbon number for lignin monomers Effective carbon number used based Lignin monomer structure on adjusted ECN rule (ECN.sub.monomer) 7 8 7.5 7 8 8 8 9 0 9 8.5

IV. Experimental Procedure

1. Pretesting: Lignin Extraction (Steps a) and b) with Visual Comparison Example 1 According to the Present Invention

(42) In a 50 mL glass vial, 1 g of air-dried beech wood particles, 9 mL of dioxane, 420 μL HCl-solution (36.5-37% in water) (180-185 mg HCl and 315 μL water) and 1 mL formaldehyde solution (36.5% in water) (400 mg FA and 690 μL water) were added. The reaction was conducted in an oil bath set at 80° C. for five hours and stirred by a stir bar at a stirring speed of 300 rpm. After the reaction, the slurry was filtered and washed with acetone until the filtrate was colorless. The filtrate was then neutralized by addition of a sodium bicarbonate solution (˜420 mg in 5 mL water) and further diluted with water to precipitate the “fragments of lignin”.

Reference Example 1 (without Addition of Formaldehyde)

(43) In a 50 mL glass vial, 1 g of air-dried beech wood particles, 9 mL of dioxane, 420 μL HCl-solution (36.5-37% in water) (180-185 mg HCl and 315 μL water) and 690 μL water were added. The reaction was conducted in an oil bath set at 80° C. for five hours and stirred by a stir bar at a stirring speed of 300 rpm. After the reaction, the slurry was filtered and washed with acetone until the filtrate was colorless. The filtrate was then neutralized by addition of a sodium bicarbonate solution (˜420 mg in 5 mL water) and further diluted with water to precipitate the extracted lignin. Pictures were taken directly after the addition of water and 15 hours after the addition of water.

(44) As can be seen from FIG. 2, the color of the “fragments of lignin” obtained by Example 1 according to the present invention is light, suggesting a limited condensation, while the darker color of the “fragments of lignin” obtained by Reference Example 1 indicates an undesirable, severe condensation.

2. Producing Monomers (Steps a)-d))

Examples 2.1 to 2.6 According to the Present Invention (Steps a)-c))

(45) In a 50 mL glass vial, 1 g of air-dried beech wood particles, 9 mL of dioxane, 420 μL HCl-solution (36.5-37% in water) (180-185 mg HCl and 315 μL water) and 1 mL formaldehyde solution (36.5% in water) (400 mg FA and 690 μL water) were added. The reaction was conducted in an oil bath set at the corresponding specified temperature and stirred for corresponding specified hours by a stir bar at a stirring speed of 300 rpm. After the reaction, the slurry was filtered and washed with acetone until the filtrate was colorless. The filtrate was then neutralized by addition of a sodium bicarbonate solution (˜420 mg in 5 mL water). The solvent was removed in a rotatory evaporator set at 60° C. The dried residue was dissolved in 25 mL THF to extract lignin, leaving the salt and carbohydrates as precipitates.

Examples 2.1 to 2.6 According to the Present Invention (Step d); Hydrogenolysis)

(46) 20 mL of the obtained lignin-THF solution along with 100 mg of catalyst (5 wt % Ru/C) was added to a 50 mL high-pressure Parr reactor. The reactor was stirred with a magnetic stir bar and heated with high-temperature heating tape (Omega) connected to a variable power supply controlled by a PID temperature controller (Omega) with a K-type thermocouple that measured the reaction temperature through a thermowell. Once closed, the reactor was purged 3 times and then pressurized with 40 bar of hydrogen. The reactor was heated to the corresponding specified temperature and then held at that temperature for a corresponding specified residence time. After reaction, the reactor was cooled with an external flow of compressed air at room temperature. A sample of the resulting liquid was taken for GC analysis.

Example 2.7

(47) The conditions for the lignin extraction as described in Examples 2.1 to 2.6 are correspondingly applied as described above. The slurry after reaction was filtered and washed with 10 mL dioxane. The filtrate was then neutralized with a sodium bicarbonate solution (˜420 mg in 5 mL water). Dioxane was added to the neutralized solution to reach 25 mL and centrifuged to remove any precipitated salts.

(48) 20 mL of the resulting lignin-dioxane solution along with 100 mg of catalyst (5 wt % Ru/C) were added to a 50 mL high-pressure Parr reactor and the remaining procedure was preformed as described above, wherein the reactor was heated to the corresponding specified temperature and then held at that temperature for the corresponding specified residence time.

Example 2.8

(49) The same conditions as described in Examples 2.1 to 2.6 (steps a)-d)) are applied, wherein after removing the solvent the dried residue was dissolved in 25 mL methanol before being submitted to the hydrogenolysis.

Example 2.9

(50) The same conditions as described in Examples 2.1 to 2.6 (steps a)-d)) are applied, wherein in the lignin extraction only 1/10 of the formaldehyde loading is used.

Example 2.10

(51) The same conditions as described in Examples 2.7 are applied, wherein in the γ-valerolactone (GVL) was used for steps a)-c) as well as for step d).

(52) FIG. 3a shows a GC chromatogram and FIG. 3b a mass spectrum of monomers from lignin (aromatic compounds) obtained by the method of the present invention. FIG. 4 shows data with regard to the NMR-characterization of the monomers from lignin. With regard to all of this data it can be seen that the method of the present invention provides ten different aromatic compounds which were identified.

Reference Example 2.1 (Step a)-c) without Adding of Formaldehyde)

(53) In a 50 mL glass vial, 1 g of air-dried beech wood particles, 9 mL of dioxane, 420 μL HCl-solution (36.5-37% in water) (180-185 mg HCl and 315 μL water) and 690 μL water were added. The reaction was conducted in an oil bath set at 80° C. for five hours and stirred by a stir bar at a stirring speed of 300 rpm. After the reaction, the slurry was filtered and washed with acetone until the filtrate was colorless. The filtrate was then neutralized by addition of a sodium bicarbonate solution (˜420 mg in 5 mL water). The solvent was removed in a rotatory evaporator set at 60° C. The dried residue was dissolved in 25 mL THF to extract lignin, leaving the salt and carbohydrates as precipitates.

Step d) (Hydrogenolysis)

(54) 20 mL of the obtained lignin-THF solution along with 100 mg of catalyst (5 wt % Ru/C) were added to a 50 mL high-pressure Parr reactor and the remaining procedure was preformed as in Examples 2.1 to 2.9, wherein the reactor was heated to 200° C. and then held at that temperature for 6 hours.

Reference Example 2.2 (Only Step d))

(55) 1 g of wood powder was mixed with 20 mL of tetrahydrofuran and 200 mg of the 5 wt % Ru/C catalyst. The slurry was added to a 50 mL high-pressure Parr reactor and the remaining procedure was preformed as in Examples 2.1 to 2.9, wherein the reactor was heated to 250° C. and then held at that temperature for 15 hours.

Reference Example 2.3

(56) The procedure is carried out as in Reference Example 2.2, wherein methanol instead of tetrahydrofuran is used.

(57) The amount of extracted lignin was determined by subtracting the amount of Klason lignin in the extracted residue from the amount of Klason lignin in untreated wood.

(58) Table 1 shows the specific reaction conditions with regard to extraction and hydrogenolysis and the yields of monomers from lignin (aromatic compounds) obtained by the corresponding specific reaction conditions. From said Table it can be seen that every one of present Examples 2.1 to 2.10 shows a significantly higher monomer yield based on extracted lignin than Reference Example 2.1 wherein the extraction step is conducted in the absence of formaldehyde.

(59) TABLE-US-00004 TABLE 1 Yields of monomers from in different reaction conditions. Monomer Monomer yield yield based on based on Extracted extracted native Steps lignin M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 lignin lignin Example a)-c) Step d) yield (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) 2.1 80° C., 200° C., 80 0.76 0 8.36 2.71 2.44 1.28 15.88 11.26 6.77 4.30 53.77 42.82 5 h 6 h 2.2 80° C., 250° C., 50 4.82 0.48 11.05 1.99 14.85 3.75 23.00 4.70 0 0.52 65.17 32.44 1.5 h 15 h 2.3 80° C., 250° C., 80 0.36 0.77 7.47 2.72 11.59 6.74 14.48 8.38 0 0.48 52.98 42.19 5 h 15 h 2.4 100° C., 250° C., 73 3.43 0.60 9.29 2.53 11.64 5.26 18.72 7.89 0 0.53 59.89 43.52 2 h 15 h 2.5 120° C., 250° C., 77 2.71 0.39 5.24 2.03 7.84 6.21 10.47 8.21 0.99 1.38 45.46 34.84 1 h 15 h 2.6 100° C., 250° C., 79 3.17 0.69 5.00 2.40 8.88 7.56 9.51 8.14 0.57 0.92 46.85 36.84 3 h 15 h 2.7 100° C., 250° C., 73 6.88 0.78 6.50 1.80 20.12 7.49 12.30 4.97 0 0.34 61.72 44.85 2 h 15 h 2.8 80° C., 230° C., 80 1.22 0 4.76 1.51 2.73 1.84 9.38 9.07 9.66 5.61 45.77 36.45 5 h 15 h 2.9 80° C., 250° C., 78 5.21 0 3.51 1.02 18.46 0.18 8.64 0.90 0.32 0.39 38.62 29.99 5 h 15 h 2.10 100° C., 250° C., 65 0.3 0 6.5 2.7 0.5 0.5 13.6 8.9 5.1 3.2 63.4 41.30 2 h 15 h RE 2.1 80° C., 200° C., 78 0.67 0 0.81 0 2.54 0 2.23 0 2.45 0 8.70 6.75 5 h 6 h RE 2.2 / 250° C., / 0.51 0 9.60 0 1.24 0 23.05 0 11.66 0 / 45.86 15 h RE 2.3 / 250° C., / 7.79 0 1.78 0 21.62 0 3.22 0 0 0 / 34.25 15 h M1-M10 correspond to the following monomers. M1: guaiacylethane, M2: methylated guaiacylethane, M3: guaiacylpropane, M4: methylated guaiacylpropane, M5: syringylethane, M6: methylated syringylethane, M7: syringylpropane, M8: methylated syringyipropane, M9: syringylpropanol, M10: methlated syringylpropanol. Further, front Reference Examples 2.2 and 2.3 it can be seen that direct hydrogenolysis of the sample leads to a high yield of monomers from lignin. However, the yield is not the only decisive factor. The direct hydrogeholysis bears the disadvantages as described above. In addition, with reference to FIG., 5, only a small variety of aromatic compounds is obtained under direct hydrogenolysis applied in both Reference Examples 2.2 and 2.3, The present method, on the contrary, provides a larger diversity of aromatic compounds.

(60) Further, from Reference Examples 2.2 and 2.3 it can be seen that direct hydrogenolysis of the sample leads to a high yield of monomers from lignin. However, the yield is not the only decisive factor. The direct hydrogenolysis bears the disadvantages as described above.

(61) In addition, with reference to FIG. 5, only a small variety of aromatic compounds is obtained under direct hydrogenolysis applied in both Reference Examples 2.2 and 2.3. The present method, on the contrary, provides a larger diversity of aromatic compounds.

Example 3

Examples E3.1 to E3.10; Steps a) to c) According to the Invention

(62) E3.1 In a 50 mL glass vial, 1 g of air-dried birch wood particles, 9 mL of dioxane, 420 μL HCl-solution (36.5-37% in water) (180-185 mg HCl and 315 μL water) and 1 mL formaldehyde solution (36.5% in water) (400 mg FA and 690 μL water) were added. The reaction was conducted in an oil bath set at 90° C. for 3.5 hours and stirred by a stir bar at a stirring speed of 300 rpm. After the reaction, the slurry was filtered and washed with acetone until the filtrate was colorless. The filtrate was then neutralized by addition of a sodium bicarbonate solution (˜420 mg in 5 mL water). The solvent was removed in a rotary evaporator set at 60° C. The dried residue was dissolved in 25 mL THF to extract the lignin, leaving the salt and carbohydrates as precipitates.

(63) E3.2 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of acetaldehyde in addition with 690 μL water.

(64) E3.3 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of propionaldehyde in addition with 690 μL water.

(65) E3.4 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of benzaldehyde in addition with 690 μL water.

(66) E3.5 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of acetone in addition with 690 μL water.

(67) E3.6 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of 2-butanone in addition with 690 μL water.

(68) E3.7 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of phenylboronic acid in addition with 690 μL water.

(69) E3.8 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of 2-methoxypropene in addition with 690 μL water.

(70) E3.9 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of dimethyl carbonate in addition with 690 μL water.

(71) E3.10 was carried out as E3.1, wherein the formaldehyde solution was substituted by a molar equivalent of 2,2-dimethoxypropane in addition with 690 μL water.

Control Examples CE3.1 and CE3.2

(72) In a 50 mL glass vial, 1 g of air-dried birch wood particles, 9 mL of dioxane, 420 μL HCl-solution (36.5-37% in water) (180-185 mg HCl and 315 μL water) and 690 μL water were added. The reaction was conducted in an oil bath set at 90° C. for 3.5 hours and stirred by a stir bar at a stirring speed of 300 rpm. After the reaction, the slurry was filtered and washed with acetone until the filtrate was colorless. The filtrate was then neutralized by addition of a sodium bicarbonate solution (˜420 mg in 5 mL water). The solvent was removed in a rotatory evaporator set at 60° C. The dried residue was dissolved in 25 mL THF to extract lignin, leaving the salt and carbohydrates as precipitates.

Step d) Hydrogenolysis

(73) 20 mL of every of the obtained lignin-THF solutions from E3.1 to E3.10 as well as CE3.1 and CE3.2 as described above and each along with 100 mg of catalyst (5 wt % Ru/C) was added to a 50 mL high-pressure Parr reactor, respectively. The reactor was stirred with a magnetic stir bar and heated with high-temperature heating tape (Omega) connected to a variable power supply controlled by a PID temperature controller (Omega) with a K-type thermocouple that measured the reaction temperature through a thermowell. Once closed, the reactor was purged 3 times and then pressurized with 40 bar of hydrogen. The reactor was heated to 250° and then held at that temperature for 15 hours. After reaction, the reactor was cooled with an external flow of compressed air at room temperature. A sample of the resulting liquid was taken for GC analysis.

(74) Table 2 shows the specific Examples with regard to and the yields of monomers from lignin (aromatic compounds) obtained by the addition of the specific aldehydes, ketones, boronic acids and compounds selected from 2-methoxypropene, dimethyl carbonate and 2,2-dimethoxypropane.

(75) TABLE-US-00005 TABLE 2 Yields of monomers from lignin Yield M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14 M15 M16 M17 M1-M17 Example (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) [wt. (%)] 3.1 3.35 0.50 2.91 1.07 16.29 6.79 6.66 5.68 0.36 0.53 0.16 0.27 0 1.36 0.47 0 0.23 46.55 3.2 4.93 0 1.79 0 22.83 0 4.22 0 0 0 0.24 0.58 0 2.01 2.13 0 0 38.737 3.3 5.80 0 0.89 0 27.64 0 3.07 0 0 0 0 0.95 0 3.29 0.91 0.35 0.19 43.10 3.4 1.35 0 1.23 0 6.20 0 4.81 0.30 0.32 0 0.87 0.70 3.11 2.68 2.45 0.79 2.63 27.45 3.5 1.48 0 0.62 0 7.63 0 1.64 0 0.37 0 0.18 1.40 0.92 5.26 0.50 0.32 1.48 21.80 3.6 1.52 0 0.87 0 7.24 0 1.98 0 0.51 0 0.67 1.54 1.11 5.98 1.12 0.51 3.89 26.96 3.7 3.08 0 1.33 0 15.32 0 4.86 0 0 0 0.17 0.27 0.57 0.97 0 0 0 26.56 3.8 1.81 0 0.40 0 7.21 0 1.26 0 0 0 0.21 1.31 0.96 4.73 2.88 0.13 026 21.15 3.9 0.54 0 1.19 0 2.31 0 4.09 0.81 1.94 0 0.79 0.53 2.36 1.76 1.56 0.19 2.96 21.03 3.10 1.86 0 0.46 0 9.63 0 1.05 0 0 0 1.06 1.03 0.65 3.64 0 0 0 19.37 CE3.1 1.14 0.84 0.42 0 5.49 0.22 1.48 0 0.13 0 0.21 0.92 0 4.31 0.37 0.14 1.01 16.67 C. E3.2 1.21 0 0.40 0 5.47 0 1.41 0 0.25 0 0.17 0.84 0 3.92 0.30 0.150 1.17 15.30

(76) The yields are calculated based on the amount of Klason lignin in 1 g birch (18% Kalson lignin).

(77) As can be seen from Table 2 all Examples in which aldehydes (E3.1 to E3.4), ketones (E3.5 and E3.6), boronic acid (E3.7) and compounds selected from 2-metoxypropene, dimethyl carbonate an 2,2-dimethoxypropane (E3.8 to E3.10) were used provide a statistically significantly enhanced total yield of monomers from lignin compared to the control Examples (CE3.1 and CE3.2).