Method for processing cellulose-containing biomass

Abstract

Described are a method for processing cellulose-containing biomass and the use of methanesulfonic acid for processing cellulose-containing biomass, especially for the pretreatment of cellulose-containing biomass prior to saccharification.

Claims

1. Method for processing a cellulose-containing biomass, comprising subjecting a treatment mixture comprising 15% wt.-% to 75 wt.-% cellulose containing biomass based on the total weight of said treatment mixture, water, and methanesulfonic acid to a temperature in the range of from 100° C. to 200° C. at a pressure in the range of from 1 to 20 bars (100 to 2000 kPa) wherein the pressure is selected so that at least a part of the water is in the liquid state to generate a treated cellulose-containing biomass comprising cellulose, hemicellulose and lignin as major components with decreased amounts of hemicellulose and/or lignin, (i) wherein said treatment mixture further comprises one or more compounds selected from the group consisting of compounds of formula (I) ##STR00009## and a surfactant which is not a compound of formula (I), wherein in formula (I) R.sup.1 and R.sup.2 are independently selected from the group consisting of hydrogen, unsubstituted and substituted alkyl with 1 to 22 carbon atoms (C.sub.1- to C.sub.22-alkyl) and unsubstituted and substituted aryl, wherein in said substituted Cr to C22-alkyl and said substituted aryl each substituent is independently selected from the group consisting of —OSO.sub.3H, —SO.sub.3H, —COOH and —OPO.sub.3H.sub.2 and salts thereof each R.sup.x in said x groups is independently of each further Rx selected from the group consisting of hydrogen and alkyl with 1 to 20 carbon atoms (Cr to C20-alkyl) x is an integer from 1 to 2400 or (ii) wherein said treatment mixture does not comprise any compound selected from the group consisting of compounds of formula (I) as defined above and does not comprise any surfactant which is not a compound of formula (I) as defined above.

2. Method according to claim 1, wherein the one or at least one compound of formula (I) is selected from the group consisting of compounds of formula (I′) wherein ##STR00010## R.sup.1 and R.sup.2 are as defined for formula (I) R.sup.3 and R.sup.4 are independently selected from the group consisting of hydrogen and alkyl with 1 to 3 carbon atoms (C.sub.1- to C.sub.3-alkyl) R.sup.5 is selected from the group consisting of hydrogen and alkyl with 1 to 20 carbon atoms (C.sub.1- to C.sub.20-alkyl) wherein preferably R.sup.4 is not identical to R.sup.3 and R.sup.4 is not identical to R.sup.5 n, m, o independently of each other are integers from 0 to 800 with the proviso that the sum of m, n and o is 1 or more.

3. Method according to claim 1, wherein said cellulose-containing biomass is selected from the group consisting of plant biomass, agricultural wastes, forestry residues, sugar processing residues, paper waste, and blends thereof.

4. Method according to claim 1, wherein the temperature in the range of from 100° C. to 200° C. at a pressure in the range of from 1 to 20 bars (100 kPa to 2000 kPa) wherein the pressure is selected so that at least a part of the water is in the liquid state is maintained for a duration of not less than 1 minute and not more than 120 minutes.

5. Method according to claim 1, wherein the temperature is in a range of 110° C. to 180° C.

6. Method according to claim 1, wherein the pressure is in a range of from 1 to 16 bars (100 kPa to 1600 kPa).

7. Method according to claim 1, wherein said treatment mixture comprises 25 wt.-% to 75 wt.-% of cellulose-containing biomass, based on the total weight of said treatment mixture.

8. Method according to claim 1, wherein in the treatment mixture the total amount of acids selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid is 100 wt.-% or less, based on the weight of the methanesulfonic acid present in the treatment mixture.

9. Method according to claim 1, wherein the treatment mixture consists of (i) cellulose-containing biomass, water, methanesulfonic acid, one or more compounds selected from the group consisting of compounds of formula (I) and surfactants which are not compounds of formula (I), and optionally one or more substances selected from the group consisting of sulfuric acid and salts thereof, hydrochloric acid and salts thereof, organochloro compounds, nitric acid and salts thereof, and metals or (ii) cellulose-containing biomass, water, methanesulfonic acid, and optionally one or more substances selected from the group consisting of sulfuric acid and salts thereof, hydrochloric acid and salts thereof, organochloro compounds, nitric acid and salts thereof, and metals wherein in each case the total amount of substances selected from the group consisting of sulfuric acid and salts thereof, hydrochloric acid and salts thereof, organochloro compounds, nitric acid and salts thereof and metals in the treatment mixture is not more than 1 wt.-% based on the weight of the methanesulfonic acid present in the treatment mixture.

10. Method according to claim 1, wherein the compound of formula (I) or one, more, or all of the compounds of formula (I) are selected from the group consisting of compounds of formula (I) wherein R.sup.1, R.sup.2 and each Rx is hydrogen, x is an integer in the range of from 1 to 800, and compounds of formula (I′) wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.5 are hydrogen and R.sup.4 is methyl, m is an integer in the range of from 15 to 100, and n and o each are integers in the range of from 1 to 100.

11. Method according to claim 1, wherein the treatment mixture is obtained by adding an aqueous treatment solution containing (i) methanesulfonic acid and one or more compounds selected from the group consisting of compounds of formula (I) and the surfactant which is not a compound of formula (I) or (ii) methanesulfonic acid and no compound selected from the group consisting of compounds of formula (I) and no surfactant which is not a compound of formula (I) to said cellulose-containing biomass.

12. Method according to claim 11, wherein in said aqueous treatment solution the concentration of methanesulfonic acid is in the range of from 0.1 wt.-% to 5.5 wt.-%, and the total concentration of compounds selected from the group consisting of compounds of formula (I) and the surfactant which is not a compound of formula (I) is (i) in the range of from 0.01 wt.-% to 5 wt.-%, or (ii) 0 wt.-% in each case based on the total weight of said aqueous treatment solution.

13. Method according to claim 1 comprising preparing an aqueous treatment solution containing 0.1 wt.-% to 2.0 wt.-% of methanesulfonic acid and 0.01 wt.-% to 1 wt.-% of one or more a compound of formula (I) adding said aqueous treatment solution to said cellulose-containing biomass so that a treatment mixture comprising said cellulose-containing biomass, water and methanesulfonic acid and one or more compound of formula (I) is obtained, said treatment mixture comprising 30 wt.-% to 45 wt.-% of cellulose containing biomass, based on the total weight of said treatment mixture subjecting said treatment mixture to a temperature in the range of from 120° C. to 175° C., wherein said temperature is maintained for duration of not less than 1 minute and not more than 40 minutes to generate a treated cellulose-containing biomass.

14. Method according to claim 1 further comprising a step selected from the group consisting of saccharification of the treated cellulose-containing biomass so that glucose and/or other sugars are formed, and optionally fermentation and/or chemical processing of the formed glucose and/or other sugars, and further processing of the treated cellulose-containing biomass to obtain dissolving pulp.

15. Method according to claim 14, wherein the composition of the treatment mixture and the temperature and pressure to which said treatment mixture is subjected and the conditions of the saccharification of the treated cellulose-containing biomass so that glucose is formed are selected such that a higher yield of glucose is formed in comparison to a processing wherein all conditions and compositions are identical with the exception that in the treatment mixture methanesulfonic acid is replaced by the same weight of sulfuric acid.

16. Treated cellulose-containing biomass obtained by the method of claim 1.

Description

EXAMPLES

(1) 1. Pretreatment of Cellulose-Containing Biomass at 120° C.

(2) An autoclave with baffles and a stirrer is filled with a treatment mixture comprising 4 g chopped straw, 100 g of an aqueous treatment solution containing deionized water, an acid as specified in type and concentration according to table 1 and 2, optionally one or more compounds selected from the group consisting of compounds of formula (I) and surfactants which are not compounds of formula (I), as specified in type and concentration according to table 1 and 2. Hereinbelow and in tables 1 and 2, the compounds selected from the group consisting of compounds of formula (I) and surfactants which are not compounds of formula (I) are commonly referred to as additives. For the chemical structure of said additives, see table 5 hereinbelow.

(3) For preparing the above-defined aqueous treatment solution, sulfuric acid was used in the form of an aqueous solution comprising 96 wt.-% sulfuric acid, and methanesulfonic acid was used in the anhydrous form (>99.5 wt.-% methanesulfonic acid).

(4) The autoclave is purged three times with nitrogen gas and the treatment mixture is heated to 120° C. at a pressure of 1.6 bar (160 kPa) under stirring (800 rpm). After 30 minutes, the heating is turned off, the mixture is allowed to cool to ambient temperature, the autoclave is relaxed and is emptied. The content of the autoclave is transferred to a container. The autoclave is rinsed with approximately 50 mL of deionized water and the resultant aqueous mixture is filled into the container too. The obtained mixture comprising treated cellulose-containing biomass is removed from the container and filtered through a frit (pore size 2), and the weight of the liquid phase obtained as filtrate is determined, see table 1 and 2. The treated cellulose-containing biomass obtained as filtration residue is dried overnight in air, and its weight is determined, see table 1 and 2, and then it is subjected to enzymatic saccharification as described herein below.

(5) 2. Enzymatic Saccharification of Cellulose-Containing Biomass Treated at 120° C.

(6) 1.25 g of the treated cellulose-containing biomass obtained according to tables 1 and 2 are weighed into a 50 mL tube and are treated with deionized water containing 0.1 wt.-% sodium azide to a volume of 20 mL. A pH-value of 5.5 is adjusted by adding 100 mM phosphate buffer and an enzyme formulation comprising one or more enzymes selected from the group consisting of beta-glucosidases, exo-cellobiohydrolases, endo- and exo-glucanases, glucoside hydrolases and xylanases is added. The mixture is incubated in an Eppendorf-Thermomixer at 300 rpm and 53° C. (50° C. internal). At certain intervals, 1 mL samples were withdrawn and diluted 1:1 with water. After centrifugation the clear supernatant is analyzed by HPLC for the concentrations of glucose and xylose.

(7) 3. Pretreatment of Cellulose-Containing Biomass at Temperatures in the Range of from 145° C. to 175° C.

(8) An autoclave with baffles and a stirrer is filled with a treatment mixture comprising 7.5 g chopped straw, 100 g of an aqueous treatment solution containing deionized water, an acid as specified in type and concentration according to table 3, where the acid is methanesulfonic acid, optionally a compound selected from the group consisting of compounds of formula (I) as specified in type and concentration according to table 3 (hereinbelow and in table 3 referred to as an additive. For the chemical structure of said additive, see table 5 hereinbelow.)

(9) For preparing the above-defined aqueous treatment solution, sulfuric acid was used in the form of an aqueous solution comprising 96 wt.-% sulfuric acid, and methanesulfonic acid was used in the anhydrous form (>99.5 wt.-% methanesulfonic acid).

(10) The autoclave is purged three times with nitrogen gas and the treatment mixture is heated to the target temperature according to table 3 at a pressure of max. 9.0 bar (900 kPa) under stirring. After the respective hold time at target temperature according to table 3, the heating is turned off, the mixture is allowed to cool to ambient temperature, the autoclave is relaxed and is emptied. The content of the autoclave is transferred to a container. The obtained mixture comprising treated cellulose-containing biomass is removed from the container and filtered through a frit (pore size 2), and the weight of the liquid phase obtained as filtrate is determined, see table 3. The weight of the treated cellulose-containing biomass obtained as filtration residue is determined, see table 3, and then it is subjected to enzymatic saccharification as described herein below.

(11) 4. Enzymatic Saccharification of Cellulose-Containing Biomass Treated at Temperatures in the Range of from 145° C. to 175° C.

(12) 4.50 g of the treated cellulose-containing biomass obtained according to table 3 are weighed into a 50 mL tube and are treated with 25.5 g deionized water containing 0.1 wt. % sodium azide. A pH-value of 5.5 is adjusted by adding 100 mM phosphate buffer and an enzyme formulation comprising one or more enzymes selected from the group consisting of beta-glucosidases, exo-cellobiohydrolases, endo- and exo-glucanases, glucoside hydrolases and xylanases is added. The mixture is incubated in an Eppendorf-Thermomixer at 350 rpm and 53° C. (50° C. internal). At certain intervals, 1 mL samples were withdrawn and diluted 1:1 with water. After centrifugation the clear supernatant is analyzed by HPLC for the concentrations of glucose and xylose.

(13) TABLE-US-00001 TABLE 1 Generation of treated cellulose-containing biomass in the absence of additives (examples No. 1-3) Example No. 1 2 3 Pretreatment of chopped straw to give treated cellulose-containing biomass Mass of chopped straw/g 4.0 4.0 4.0 acid type and conc./wt.-% of aqueous / 1% 1% MSA treatment solution H.sub.2SO.sub.4 Additive type and conc./wt.-% of aqueous / / / treatment solution Temperature/° C. 120 120 120 Time/min 30 30 30 Liquid phase/g 135.8 150.2 147.1 Treated cellulose-containing biomass/g 14.8 6.6 8.1 Enzymatic saccharification Used treated cellulose-containing 1.25 1.25 1.25 biomass/g Calculation factor cellulose-containing biomass 11.84 5.28 6.48 ‘treated/used in saccharification’ Yield of glucose from used treated cellulose-containing biomass Glucose/absolute 23 h enzymatic saccharification 28.65 50.05 72.06 96 h enzymatic saccharification 34.10 61.46 88.06 Norm: Glucose, 23 h enzymatic 28.65 28.65 28.65 saccharification Glucose/normalized absolute 23 h enzymatic saccharification 1.00 1.75 2.51 96 h enzymatic saccharification 1.19 2.14 3.07

(14) TABLE-US-00002 TABLE 2 Generation of treated cellulose-containing biomass in the presence of additives (examples No. 4-11) Example No. 4 5 6 7 8 9 10 11 Pretreatment of chopped straw to give treated cellulose-containing biomass Mass of chopped straw/g 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 Acid type and conc./wt.-% of aqueous / 1% 1% 1% 1% 1% For- 1% For- 1% For- treatment solution MSA MSA MSA H.sub.2SO.sub.4 mic acid mic acid mic acid Additive type and conc./wt.-% of aqueous / 2% 2% 2% 2% 2% 2% 2% treatment solution Pluriol Pluronic Tween Tween Pluriol Pluronic Tween E6000 PE6800 20 20 E6000 PE6800 20 Temperature/° C. 120° C. 120° C. 120° C. 120° C. 120° C. 120° C. 120° C. 120° C. Time/min 30 30 30 30 30 30 30 30 Liquid phase/g 144.4 141.7 133.9 135.9 139.0 135.7 129.3 130.8 Treated cellulose-containing biomass/g 16.6 12.8 13.6 15.1 15.1 18.8 23.0 16.5 Enzymatic saccharification Used treated cellulose-containing biomass/g 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 Calculation factor cellulose-containing biomass ‘treated/ 13.28 10.24 10.88 12.08 12.08 15.04 18.40 13.44 used in saccharification’ Yield of glucose from used treated cellulose-containing biomass Glucose/absolute 24 h enzymatic saccharification 14.42 49.34 50.17 47.12 38.67 20.97 22.17 19.71 48 h enzymatic saccharification 15.70 53.96 53.11 50.08 43.67 23.42 24.44 21.44 Norm: Glucose, 24 h enzymatic 14.42 14.42 14.42 14.42 14.42 14.42 14.42 14.42 saccharification Glucose/normalized absolute 24 h enzymatic saccharification 1.00 3.42 3.48 3.27 2.68 1.45 1.54 1.37 48 h enzymatic saccharification 1.09 3.74 3.68 3.47 3.03 1.62 1.70 1.49

(15) TABLE-US-00003 TABLE 3 Generation of treated cellulose-containing biomass under varying conditions (examples No. 12-20) Example No. 12 13 14 15 16 17 18 19 20 Pretreatment of chopped straw to give treated cellulose-containing biomass Mass of chopped straw/g 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 Acid type and conc./wt.-% of aqueous 0.25% 0.25% 0.25% 0.10% 0.10% 0.30% 0.30% 0.50% 0.50% treatment solution H.sub.2SO.sub.4 MSA MSA H.sub.2SO.sub.4 MSA H.sub.2SO.sub.4 MSA H.sub.2SO.sub.4 MSA Additive type and conc./wt.-% of aqueous / / 0.25% / / / / / / treatment solution Pluriol E6000 Temperature/° C. 165° C. 165° C. 165° C. 175° C. 175° C. 160° C. 160° C. 145° C. 145° C. Time/min 20 20 20 40 40 20 20 0 0 Liquid phase/g 120.8 125.2 114.5 121.9 126.0 119.7 121.3 117.1 117.4 Treated cellulose-containing biomass/g 21.9 18.8 28.0 22.7 16.9 18.6 22.5 27.1 27.3 Enzymatic saccharification Used treated cellulose-containing biomass/g 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 Calculation factor cellulose-containing biomass ‘treated/ 4.87 4.18 6.22 3.76 5.04 4.13 5.00 6.02 6.07 used in saccharification’ Yield of glucose from used treated cellulose-containing biomass Glucose/absolute 24 h enzymatic saccharification 39.37 49.34 89.60 45.82 60.78 40.09 58.42 39.14 56.90 Norm: Glucose, 24 h enzymatic 39.37 39.37 39.37 39.37 39.37 39.37 39.37 39.37 39.37 saccharification/example 12 Glucose/normalized absolute 24 h enzymatic saccharification 1.00 1.25 2.28 1.16 1.54 1.02 1.48 0.99 1.45

(16) TABLE-US-00004 TABLE 4 Properties of the acids used Acid MSA H.sub.2SO.sub.4 Formic acid pk.sub.A −1.9 −3.0 (first pKa) 3.8 1.9 (second pKa) Corrosivity* 3 4 2 Oxidizing* 1 3 1 Reducing* 1 2 5 Vapor pressure* 1 1 5 Temperature stability 1 1 3 *1 = excellent 5 = poor

(17) TABLE-US-00005 TABLE 5 Compound of Additive name formula (I) Chemical structure Pluriol E6000 yes polyethylene glycol having an average molecular weight of 6000 g/mol Pluronic PE6800 yes block copolymer having a central polypropylene glycol block (molar mass = 1750 g/mol) flanked by two polyethylene glycol blocks wherein the percentage of said polyethylene glycol blocks of the molar mass of the molecule is 80%. Tween 20 no polyoxyethylene(20) sorbitan monolaurate

(18) Tables 1 and 2 show the conditions of the generation of treated cellulose-containing biomass from wheat straw at 120° C. for 30 min, using different acids (sulfuric acid, methanesulfonic acid, formic acid, see table 1) in the absence (table 1) or presence of an additive (see table 2), and show the yields of glucose after the enzymatic saccharification of the treated cellulose-containing biomass.

(19) Table 3 shows the conditions of the generation of treated cellulose-containing biomass from wheat straw at different temperatures in the range of from 145° C. to 175° C. using different acids (sulfuric acid or methanesulfonic acid, see table 3) in the absence (examples 12, 13 and 15-20) or presence of an additive (only for methanesulfonic acid, see example 14), and show the yields of glucose after the enzymatic saccharification of the treated cellulose-containing biomass. Due to the higher treatment temperature, in examples 12-20 the duration of the treatment and the acid concentration in the treatment mixture are reduced, compared to the treatment at 120° C. of examples 1-11.

(20) The “yields” indicated in tables 1, 2 and 3 are either absolute yields stated in arbitrary units or normalized absolute yields. Thus, the yields are not based on a theoretical yield. The yields of glucose obtained after the enzymatic saccharification are extrapolated to the quantity of treated cellulose-containing biomass and normalized in tables 1 and 2 with respect to the reference of example No. 1 or No. 4, respectively (pretreatment with water at 120° C.), and in table 3 with respect to the reference of example No. 12 (pretreatment with sulfuric acid at 165° C.).

(21) Surprisingly, in the absence of any compounds selected from the group consisting of compounds of formula (I) and surfactants which are not compounds of formula (I) the use of methanesulfonic acid as acid in the pretreatment of the present invention described above results in a higher yield of glucose after 23 h and 96 h of enzymatic saccharification compared to the use of the same weight of sulfuric acid in the pretreatment (example No. 2 compared with example No. 3, table 1; example No. 12, 15, 17, 19, resp., compared with example No. 13, 16, 18, 20, resp., in table 3).

(22) A pretreatment using a combination of methanesulfonic acid with a compound of formula (I) (Pluriol E6000 or Pluronic PE6800) or a surfactant which is not a compound of formula (I) (Tween 20) results in an even higher yield of glucose after 24 h and 48 h of subsequent enzymatic saccharification (examples No. 5-6, table 2 in comparison with example 3 in table 1, example No. 14 in comparison with example No. 13, table 3).

(23) In more detail, table 2 shows yields of glucose after 24 and 48 h of enzymatic saccharification of treated cellulose-containing biomass obtained by using combinations of acid (selected from the group consisting of sulfuric acid, methanesulfonic acid, formic acid) and an additive in the pretreatment. In every case, the combination of methanesulfonic acid with either a compound of formula (I) (Pluronic PE6800 or Pluriol E6000) or a surfactant which is not a compound of formula (I) (Tween 20) according to the present invention in the pretreatment results in a much higher yield of glucose than a combination of formic acid with the respective additive, and in a higher yield of glucose than a combination of sulfuric acid with the additive Tween 20 (Example 8).

(24) Table 4 shows the chemical properties of the used acids and attributes a value to selected properties between 1 and 5 (1 for excellent and 5 for poor) based on their practicability in the method described above. The problem of corrosivity of sulfuric acid (value 4) can be solved by replacing it with formic acid (value 2), but the yields are poor in comparison to methanesulfonic acid (examples No. 5-7 vs. examples No. 9-11), and therefore the use of formic acid appears not acceptable. Surprisingly, however, the use of methanesulfonic acid in the pretreatment of the present invention as described above results in similar or higher yields of glucose than the use of sulfuric acid and alleviates the problem of high corrosivity. In addition, methanesulfonic acid provides the advantages of low vapor pressure and excellent temperature stability similar to sulfuric acid, in contrast to formic acid.

(25) It is noted that in the above-described examples the concentration of cellulose-containing biomass based on the total weight of the treatment mixture is rather close to the lower limit of the above-defined preferred range of 3 wt.-% to 75 wt.-%. However it is common practice in the technical field of the present invention that the effect of an additive with respect to biomass is initially studied in the presence of a low concentration of biomass. Based on the results gained from the examples described herein, the skilled person based on his knowledge is capable of routinely scaling up the method of the present invention to higher concentrations of cellulose-containing biomass.