Method for treating lignocellulosic biomass by impregnation

Abstract

The invention relates to a process for treating lignocellulosic biomass by means of an acidic liquor in order to produce “second-generation” (2G) sugary liquors. These sugary liquors may be used to produce other products via a biochemical pathway (e.g. alcohols such as ethanol, butanol or other molecules, for example solvents such as acetone, etc.). This process comprises analysis of the liquid streams withdrawn during the process and adjustment of the composition of the impregnation liquor so as to keep the acidic power of said streams constant.

Claims

1. A process for the continuous treatment of a lignocellulosic biomass for the production of sugary liquors, said process comprising: a) impregnating the biomass using an impregnation liquor with a pH of between 0.1 and 7, by placing said biomass in contact with said impregnation liquor, b) separating the impregnated biomass obtained in a) so as to produce a wet biomass with a solids content of at least 15% by weight, and a separated liquor, c) pretreating the wet biomass obtained in b) to produce a pretreated biomass, in the course of which one or more liquid streams are withdrawn, d) analyzing (i) the composition of the separated liquor obtained from b), (ii) the composition of one or more of the liquid streams withdrawn during c) the pretreating of the wet biomass, or (iii) the composition of the separated liquor obtained from b) and one or more of the liquid streams withdrawn during the pretreating of the wet biomass in c), and e) adjusting the composition of the impregnation liquor used in a) so as to keep constant the acidic power, corresponding to the amount of H.sup.+ ions present, of (i) said separated liquor obtained from b), (ii) said one or more liquid streams withdrawn during the pretreating of the wet biomass in c), or (iii) both, throughout the process, wherein the impregnation liquor comprises at least one acid, and optionally water, and wherein adjusting of the composition of the impregnation liquor is performed by adding water, acid, or both to said impregnation liquor used in a), so as to keep constant, throughout the process, the acidic power of the separated liquor obtained from b) or the acidic power of the one or more liquid streams withdrawn during pretreating of the wet biomass in c), or both.

2. The process as claimed in claim 1, further comprising a step of preparing the impregnation liquor prior to a).

3. The process as claimed in claim 1, wherein a) is performed at a temperature ranging from 10 to 95° C., and the residence time of the biomass in said impregnation step is between 20 seconds and 12 hours.

4. The process as claimed in claim 1, wherein the impregnation liquor has a pH of between 0.1 and 6.

5. The process as claimed in claim 1, wherein the impregnation liquor is an aqueous solution of sulfuric acid, hydrochloric acid, or nitric acid, having an acid content of between 0.5% and 8% by weight of acid relative to the total weight of the liquor.

6. The process as claimed in claim 1, wherein b) is performed by draining, decantation, centrifugation, or pressing of the impregnated biomass.

7. The process as claimed in claim 1, wherein the solids content of the wet biomass obtained in step b) is between 25% and 70% by weight.

8. The process as claimed in claim 1, wherein pretreating the wet biomass in c) is performed by cooking.

9. The process as claimed in claim 1, wherein d) comprises measurement of the acidic power of said separated liquor obtained from b), one or more of said liquid streams withdrawn during pretreating of the wet biomass in c), or both, throughout the process.

10. The process as claimed in claim 9, wherein measurement of the acidic power is performed by measuring the pH or by measuring the conductivity, the measurements being performed either continuously or at a given frequency.

11. The process as claimed in claim 1, wherein said liquid streams withdrawn during pretreating of the wet biomass in c) are liquid streams withdrawn downstream of a) and upstream of subsequent biomass treatment steps.

12. The process as claimed in claim 1, further comprising recycling (i) the separated liquor obtained from b), (ii) the one or more liquid streams withdrawn during pretreating of the wet biomass in c), (iii) liquid streams withdrawn during subsequent biomass treatment steps, or (i), (ii), and (iii) into a).

13. The process as claimed in claim 1, further comprising, after the pretreating in c), treating at least a part of the pretreated biomass, by enzymatic hydrolysis, to produce said sugary liquors.

14. The process as claimed in claim 1, wherein at least one portion of the sugary liquors is subjected to an alcoholic fermentation.

15. The process as claimed in claim 1, wherein the impregnation liquor has a pH of between 0.1 and 2.

16. The process as claimed in claim 1, wherein the solids content of the wet biomass obtained in step b) is between 40% and 65% by weight.

17. The process as claimed in claim 1, wherein pretreating the wet biomass in c) is performed by steam explosion.

18. The process as claimed in claim 1, wherein adjusting of the composition of the impregnation liquor is performed by adding water or acid to said impregnation liquor used in a), so as to keep constant, throughout the process, the acidic power of the separated liquor obtained from b) or the acidic power of the one or more liquid streams withdrawn during pretreating of the wet biomass in c) to within ±10%.

19. The process as claimed in claim 1, further comprising recycling (i) the separated liquor obtained from b) into a).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 to 4 of the present patent application illustrate, in a nonlimiting manner, the implementation of the process according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(2) As shown in FIG. 1, the milled biomass is introduced via pipe 1 into the impregnation zone 2. This zone contains the impregnation liquor, composed of acid introduced via pipe 3, and optionally water introduced via pipe 4.

(3) The milled biomass is introduced via pipe 1 into the impregnation zone 2. This zone contains the impregnation liquor, composed of acid introduced via pipe 3, and optionally water introduced via pipe 4.

(4) In the embodiment illustrated in FIG. 2, the impregnation liquor is prepared in a step prior to the impregnation, in a liquor preparation zone 9, by introducing acid (3) and optionally water (4). The liquor thus prepared is introduced into the impregnation zone 2 via pipe 10.

(5) The impregnated biomass obtained is then transferred to a separation zone 5 so as to produce a wet biomass and a separated liquor 6.

(6) According to one embodiment, the features of the separated liquor 6 are measured by means of sensors (pH, conductivity, flow rate, etc.) and the amounts of acid and/or of water introduced via pipes 3 and 4 are adjusted so as to keep constant the acidic power of said separated liquor 6 throughout the operation of the process.

(7) The wet biomass obtained during the separation is then pretreated in a pretreatment zone 7, from which one or more liquid streams 8 are withdrawn.

(8) According to a particular embodiment, the features of the liquid streams 8 are measured by means of sensors (pH, conductivity, flow rate, etc.) and the amounts of acid and/or of water introduced via pipes 3 and 4 are adjusted so as to keep constant the acidic power of said liquid streams 8 throughout the operation of the process.

(9) FIGS. 3 and 4 illustrate the possible recycling of the separated liquor 6 and/or of the liquid streams 8 into the impregnation zone 2.

EXAMPLES

Example 1

(10) Example 1 presents the procedure according to the prior art. The biomass (wheat straw) is placed in contact with an acidic liquor (water+sulfuric acid) of controlled acidity (1.1 wt %). The biomass thus impregnated is pretreated by cooking in a steam explosion reactor (190° C., residence time of 5 minutes). By controlling only the acidity of the liquor introduced into the impregnation step, the variations in the quality of the biomass induced variations in the quality of the pretreated product. The following table illustrates this phenomenon. The two tests were performed on wheat straw under the same conditions: the results demonstrate the intrinsic variability of the feedstock.

(11) TABLE-US-00001 Straw Test 1 Straw Test 2 Acidity of acidic liquor 1.1 wt % 1.1 wt % pH of press liquor 1.6 1.8 Conductivity of press liquor (mS/cm) 12 20 Content of monomeric and oligomeric 50.3% 64.8% sugars in the pretreated biomass

(12) For an acidity at 1.1 wt %, the production of monomeric and oligomeric sugars may range from 50 wt % to 65 wt % after the pretreatment step, due to the variability of the treated biomass. A substantial variation in the quality of the spent impregnation liquor (press liquor), of 0.2 pH unit and 8 mS/cm on the conductivity, is also observed. This variation in the quality of the spent liquor is directly responsible for the variability in the sugar content of the finished product.

Example 2

(13) Example 2 presents the procedure according to the invention. The biomass (wheat straw) used in example 1 is placed in contact with an acidic liquor (water+sulfuric acid). The impregnated biomass is introduced into the pretreatment reactor by means of a screw, generating a liquid stream known as the press liquor. In the implementation according to the invention, the acid content of the impregnation liquor is adjusted so as to keep the quality of the press liquor (pH or conductivity) constant.

(14) The table below illustrates the results of this procedure for a production of several days.

(15) TABLE-US-00002 Test 3 variation pH of press liquor 0.61 ±0.1 Conductivity of press liquor (mS/cm) 33.5 ±3.2 Content of monomeric and oligomeric 68.7% ±5% sugars in the pretreated biomass

(16) Regulating the press liquor (pH to ±0.1 or conductivity to ±10%) made it possible to limit the variability in the quality of the pretreated biomass to ±5 points of yield of sugars (monomeric and oligomeric). The use of the method of regulating the acidic liquor according to the invention thus makes it possible to ensure a constant quality of the finished product.