PROCESS FOR TREATING LIGNOCELLULOSIC BIOMASS

Abstract

The present invention relates to a process for treating lignocellulosic biomass, successively comprising b) a step of pretreatment of the biomass placed beforehand under acidic or neutral pH conditions in a pretreatment reactor (3), to produce an acidic or neutral pretreated must (AM), alternating with b′) a step of pretreatment of the biomass placed beforehand under acidic, neutral or basic conditions, with optional sufficient introduction of a basic aqueous solution (EB) into the pretreatment reactor (3) to produce a basic pretreated must (BM), and then c) a step of enzymatic hydrolysis in a hydrolysis reactor (16) of a mixture of the acidic or neutral pretreated must (AM) obtained from step b) with the basic pretreated must (BM) obtained from step b′).

Claims

1. A process for treating lignocellulosic biomass, successively comprising b) a step of pretreatment of the biomass placed beforehand under acidic or neutral pH conditions in a pretreatment reactor (3), to produce an acidic or neutral pretreated must (AM), alternating with b′) a step of pretreatment of the biomass placed beforehand under acidic, neutral or basic conditions, with optional sufficient introduction of a basic aqueous solution (EB) into the pretreatment reactor (3) to produce a basic pretreated must (BM), and then c) a step of enzymatic hydrolysis in a hydrolysis reactor (16) of a mixture of the acidic or neutral pretreated must (AM) obtained from step b) with the basic pretreated must (BM) obtained from step b′).

2. The process as claimed in claim 1, characterized in that, during step c) of enzymatic hydrolysis of the mixture of acidic or neutral pretreated must (AM) with the basic pretreated must (BM), said mixture is replaced with only acidic or neutral pretreated must (AM) for a portion only of the duration of said step c).

3. The process as claimed claim 1, characterized in that the mixing of the acidic or neutral pretreated must (AM) obtained from step b) with the basic pretreated must (BM) obtained from step b′) in step c) is performed upstream of the hydrolysis reactor (16), or directly in the hydrolysis reactor (16).

4. The process as claimed claim 1, characterized in that the mixing, in step c), of the acidic or neutral pretreated must (AM) obtained from step b) with the basic pretreated must (BM) obtained from step b′) is performed by withdrawals from a zone for temporary storage (13) of the basic pretreated must (BM) at the outlet of the pretreatment reactor (5).

5. The process as claimed claim 4, characterized in that step b′) producing a basic pretreated must (BM) is a step of cleaning the pretreatment reactor (5).

6. The process as claimed claim 1, characterized in that a step of adjusting the pH of the pretreated must (AM, BM) or of the mixture of pretreated musts before or during the enzymatic hydrolysis step c), notably an adjustment of the pH to between 4 and 6, is implemented.

7. The process as claimed claim 1, characterized in that, over a given production time, the sum of the durations of the steps b) of pretreatment of the biomass placed beforehand under acidic or neutral pH conditions in a pretreatment reactor, to produce an acidic or neutral pretreated must (AM), is greater, notably at least 2 to 5 times greater, than the sum of the durations of the steps b′) of pretreatment of the biomass placed beforehand under acidic, neutral or basic conditions, with optional sufficient introduction into the pretreatment reactor of a basic aqueous solution (EB), to produce a basic pretreated must (BM).

8. The process as claimed claim 1, characterized in that a separation is performed between pretreated must (AM, BM) and aqueous phase in the liquid or vapor form at the outlet of the pretreatment reactor (5), by a separation device (8) or several separation devices in parallel, notably two separation devices, operating alternately.

9. The process as claimed claim 1, characterized in that, during the enzymatic hydrolysis step c) in the hydrolysis reactor (16), the mixing of the acidic or neutral pretreated must (AM) obtained from step b) with the basic pretreated must (BM) obtained from step b′) is performed in an AM/BM weight ratio of at least 80/20.

10. The process as claimed claim 1, characterized in that the pretreatment step b) is preceded by a step a) of impregnating the biomass with an acidic or neutral aqueous solution, in an impregnation reactor (3).

11. A facility for treating lignocellulosic biomass, comprising, from upstream to downstream, a biomass impregnation reactor (3) in fluid connection with a vessel (31) for preparation of acidic aqueous solution, a reactor for pretreatment (5) of the impregnated biomass, in fluid connection with a vessel (51) for preparation of a basic aqueous solution, a pretreated must separation device (8) downstream of the pretreatment reactor (5) and which is optionally combined with means for rinsing with an aqueous solution (E), and which is in fluid connection with a zone for intermediate storage (13) of basic must (BM), and optionally a zone for intermediate storage (11) of acidic must (AM), and an enzymatic hydrolysis reactor (16) fed with musts from said/at least one of said storage zones (11, 13).

12. The facility as claimed claim 11, characterized in that it comprises a zone (14) for adjusting the pH of the pretreated musts between the/at least one of the storage zones (11, 13) and the enzymatic hydrolysis reactor (16), notably a pH adjustment zone that is common for said musts.

13. The facility as claimed claim 12, characterized in that the adjustment zone is a vessel or a hopper which ensures the mixing of the musts obtained from at least the or one of the storage zones (11, 13).

14. The facility as claimed in claim 11, characterized in that it comprises two impregnation reactors (3) and/or two separation devices (8) and/or two pretreatment reactors (5) operating alternately depending on whether the pretreatment is performed on biomass placed beforehand under acidic or neutral pH conditions to produce an acidic or neutral pretreated must (AM), according to step b), or on biomass placed beforehand under acidic, neutral or basic conditions, with sufficient introduction into the pretreatment reactor of a basic aqueous solution (EB) to produce a basic pretreated must (BM) according to step b′).

15. The process as claimed in claim 1, wherein said biomass is selected from wood, straw, agricultural residues, and all dedicated energy crops, notably annual or perennial plants such as miscanthus, and said process produces sugars, biofuels or biobased molecules.

Description

LIST OF FIGURES

[0100] FIG. 1 is a block diagram of an embodiment of a process for treating lignocellulosic biomass according to the invention.

[0101] FIG. 2 shows a portion of the facility suitable for performing the process according to FIG. 1.

[0102] FIG. 3 shows the facility implementing a first variant of the first sequence T1 of the process according to the invention shown in FIG. 1.

[0103] FIG. 4 shows the facility implementing a second variant of the first sequence T1′ of the process according to the invention shown in FIG. 1.

[0104] FIG. 5 shows the facility implementing a first variant of the second sequence T2 of the process according to the invention shown in FIG. 1.

[0105] FIG. 6 shows the facility implementing a second variant of the second sequence T2′ of the process according to the invention shown in FIG. 1.

[0106] FIG. 7 is a graph of monitoring of ethanol production according to an example not in accordance with the invention.

[0107] FIG. 8 is a graph of monitoring of ethanol production according to an example in accordance with the invention.

[0108] FIG. 9 is a graph of monitoring of ethanol production according to an example in accordance with the invention.

[0109] FIG. 10 is a graph of monitoring of ethanol production according to an example in accordance with the invention.

[0110] FIG. 11 is a graph of monitoring of ethanol production according to an example in accordance with the invention.

DESCRIPTION OF THE EMBODIMENTS

[0111] FIGS. 1 to 5 are very diagrammatic: the same references correspond to the same components from one figure to another. FIG. 1 is a block diagram. In the following figures, the reactors and other equipment are represented in the spatial position that they occupy substantially in the operational position, without the details or equipment that are of lesser importance for the purposes of the invention.

[0112] The lignocellulosic biomass treatment process including the continuous cleaning of a biomass pretreatment reactor under basic conditions alternating with a conventional pretreatment under acidic or neutral conditions is illustrated here in the context of a biomass treatment process intended to produce alcohols, notably bioethanol-type biofuel. The major steps of this process are described in FIG. 1, and rapidly described below. An embodiment of this process is described in greater detail, for example, in patent WO 2018/015227, to which reference will be made if necessary.

[0113] It should be noted that the process of the invention may be applied in the same manner to any pretreatment followed by an enzymatic hydrolysis of biomass, and to any reactor which is intended for treating a lignocellulosic biomass.

[0114] The biomass treatment process illustrated here and represented in FIG. 1 schematically involves the following major steps: a first step of impregnating the biomass in a vertical reactor, followed by a step of pretreating the biomass, once impregnated, in a horizontal steam explosion reactor 4, then a step of enzymatic hydrolysis, then an alcoholic fermentation (the hydrolysis and fermentation possibly taking place simultaneously in the same reactor or one after the other) and then fractionation by distillation. It is into this sequence of steps that the invention is integrated, as represented in FIG. 1 described below.

[0115] The references of FIG. 1 correspond to the following equipment and compounds, from upstream to downstream, in the biomass treatment facility:

[0116] 1: native biomass (i.e. biomass before any treatment)

[0117] 2: conditioning of the native biomass (grinding, stone removal, removal of dust, if any, etc.)

[0118] 3: zone for contacting the conditioned biomass with an acidic (aqueous phase) liquor (impregnation)

[0119] 4: acidic liquor (H.sub.2SO.sub.4 in aqueous phase)

[0120] 5: reactor for pretreatment by cooking—continuous functioning

[0121] 6: steam injection—continuous functioning

[0122] 7: injection of aqueous solution of base—functions during sequence T2 only (detailed later)

[0123] 8: cyclone-type separation equipment—functions continuously

[0124] 9: vapors separated from the pretreated biomass substrate—evacuated continuously

[0125] 10: exiting of the must produced under acidic conditions—functions during sequence T1 only (detailed later)

[0126] 11: acidic must buffer zone, fed only during sequence T1 and withdrawn during T1 and during T2

[0127] 12: exiting of the must produced under basic conditions—functions during sequence T2 only

[0128] 13: basic must buffer zone, fed only during sequence T2 and withdrawn at least partly during T1

[0129] 14: zone for must neutralization to reach a pH of between 4 and 6

[0130] 15: neutralization solution

[0131] 16: enzymatic hydrolysis reactor

[0132] 17: cocktail of enzymes and other necessary nutrients+pH readjustment

[0133] 18: zone for ethanolic fermentation (separate from or concomitant with the hydrolysis)—CO.sub.2 removal not shown

[0134] 19: fermentation yeasts and other necessary nutrients+pH readjustment

[0135] 20: ethanol recovery device, for example distillation

[0136] 21: ethanol product

[0137] 22: residues (solid and liquid, as mixtures or separated depending on the arrangement of 20)

[0138] Returning to FIG. 1, the conventional steps of the process are first described: The native biomass 1 is first conditioned in step 2, notably to give it a given particle size (grinding), to remove the stones and other components that do not form part of the biomass itself. It is then impregnated with an acidic aqueous solution 4 in an impregnation reactor 3.

[0139] The acid-impregnated biomass is then conveyed into a pretreatment reactor 5 at high temperature with injection of steam 6 to undergo cooking therein by steam explosion. A vapor phase 9 is then separated from the pretreated biomass, also known as must, in this case an acidic must AM, in cyclone-type separation equipment 8. Next, this acidic must is conveyed into a neutralization zone 14 to adjust the pH to a slightly higher value, to go from a pH of the order of 2 to 3.5 to a pH of the order of 4 to 6 by adding a neutralizing agent 15, and this neutralized must NM then undergoes enzymatic hydrolysis in an ad hoc reactor 16 fed with a suitable enzymatic cocktail 17, followed by ethanolic fermentation 18 (which may be concomitant with the hydrolysis), in the same reactor or in a different reactor, with a supply of suitable fermentation yeasts 19. Finally, provision is made to recover the alcohol 21 by separating it from the solid and liquid residues 22 in a device 20, which may be a distillation column.

[0140] The contribution of the invention to this sequence of conventional steps is now described: The invention proposes functioning in two sequences T1 and T2 which alternate. [0141] Sequence T1 is the conventional sequence, also illustrated by FIG. 2, with, at the outlet of the pretreatment reactor 4, an acidic must 10, but, in this case, instead of being sent directly into the neutralization zone 14 after separation in the separating device 8, this must AM passes via a buffer zone 11 for acidic must 10, for example a hopper, which is fed with must only during the sequence T1, [0142] The sequence T2 is the sequence in which the pretreatment reactor is fed with basic aqueous solution 7, notably by means of a preparation vessel connected to the pretreatment reactor 5, from which is then withdrawn a basic must 12, which feeds a buffer zone 13 for basic must 12 (or BM). [0143] The neutralization zone 14 is fed independently of the sequences T1 and T2. During a sequence T3, it is fed only with acidic must 10 coming from the buffer zone 11 and/or directly with the must at the outlet of reactor 10 when said reactor is functioning according to the sequence T1. During a sequence T4, it is fed with a mixture of acidic must 10 (or AM) coming from zone 11 and of basic must 12 (or BM) coming from zone 13, in a defined proportion. The neutralization to be performed in zone 14 is then less pronounced than during the sequence T3, since the must mixture is at a higher pH than that of the acidic must alone; it may even possibly be no longer necessary to perform neutralization by supplying base at this stage. The following steps remain unchanged. Alternatively, if the ratio between the two types of must in the mixture is chosen in consequence, it is possible to bypass the neutralization zone 14 during the sequence T4 and to inject directly the must mixture or each of the musts separately, coming from their respective buffer zones, into the enzymatic hydrolysis reactor 16.

[0144] In an implementation variant, the neutralization zone 14 may be located in the enzymatic hydrolysis reactor 16. Said reactor then receives the musts and the neutralization solution 15 in addition to the enzymatic solution 17.

[0145] The facility that is suitable for performing the invention according to the process of FIG. 1, up to the separation step with the device 8, is shown in FIG. 2. These steps of the process are performed continuously and are described in detail below using the description of the equipment used to implement it: [0146] A vessel for preparation 31 of an impregnation liquor containing a chemical catalyst is provided, which liquor is formed from water E and from catalyst A which feed it; the catalyst in this instance is a strong acid of concentrated sulfuric acid type in an aqueous phase, this vessel making it possible to feed the impregnation reactor 3 with a mixture of water E and of chemical catalyst A, [0147] A conical screw 2a (also known as a plug screw or sealing screw) for feeding fresh biomass 1 (in this instance wheat straw) into the impregnation reactor 3, [0148] A line for feeding the reactor with impregnation liquor connecting the liquor preparation vessel 31 and the impregnation reactor 3, [0149] An impregnation reactor 3 equipped with two ascending transportation screws (not shown) making it possible for the biomass to pass from the impregnation zone in the lower part of the reactor to the draining zone in the upper part of the reactor, and to convey the impregnated and drained biomass to the reactor outlet located at the top of the reactor.

[0150] This impregnated and drained biomass is subsequently sent for pretreatment by means of a feed line emerging in a second conical screw 2b. [0151] This second conical screw 2b feeds impregnated biomass to the pretreatment reactor 5, [0152] The pretreatment reactor 5 treats the impregnated biomass by steam explosion, [0153] A water circuit for washing the conical screws 2a,2b of the impregnation reactor 3 and of the pretreatment reactor 5, represented symbolically in FIG. 1 by water inlets E at said screws, is provided. [0154] A means for separation of the steam 8 is fed by the reactor 5 with biomass which has undergone cooking by steam explosion, for example of cyclone type, with at the top outlet steam V and at the bottom outlet the pretreated/exploded biomass, also called the acidic must (or acidic must) AM.

[0155] This must AM has at this stage a sufficient accessibility of the cellulose to enzymes to be treated by enzymatic hydrolysis for the production of 2G sugars. The conditions of the enzymatic hydrolysis and of the consecutive or simultaneous fermentation which follow this separation (not shown in FIG. 1) are suitable for the desired products and are known to those skilled in the art.

[0156] The use of the pretreatment technique described above results in the deposition of different types of biomass (wheat straw here, but also miscanthus, poplar, and the like), which accumulate on/adhere to the surface of the screw 2b and of the pretreatment reactor 5. These deposits undergo cooking over times longer than the normal residence time of the biomass in the reactor, and are transformed into a residue, which can be called here “coke”. This “coke” can cause various operating problems, such as blockages of the outlet orifice of the reactor 4 or an increase in the frictional actions of the screw 2b on the wall of the chamber in which it is housed, and this may result in a reduction in the performance characteristics of the pretreatment unit as a whole as shown in FIG. 1.

[0157] The definition of the composition of the “coke” proved to be problematic because it concerns a residue whose appearance and composition change over time: at the start of a production cycle, the material which is deposited is biomass; it thus has essentially the same characteristics as the biomass which continues its journey through the reactor 4 and toward the downstream steps. The deposit which is formed by adhesion to the internal wall of the reactor 4 will remain for a much longer time under the cooking conditions (notably the temperature) than desired. The effect of the temperature affects the composition and morphology of the residue, which will change toward an increasingly “cooked” residue. The more the residue is “cooked”, the more compact it is and the more it adheres to the walls of the reactor.

[0158] These “coke” deposits are cumulative: the longer the continuous operating time of the tool, the greater the amount of coke deposited, and the more the “layers” of coke close to the wall will change into a very hard solid. These deposits thus cause fouling, by increasing the thickness of the walls and reducing the working volume of the reactor. Depending on the configuration of the cooking reactor, and notably the type of inserts in place, certain elements may be seen to have their rotation affected, such as the screw conveying the biomass undergoing cooking. This interference is notably observed by an increase in the power of the motor rotating the screw.

[0159] Throughout production, it is also possible that a more or less hardened section of this residue breaks off from the wall of the reactor, under the effect, for example, of the rotation of the screw or of the passage of the biomass through the reactor: accordingly, particles with a density much greater than the bed of biomass undergoing cooking may be caused to become detached and be carried toward the outlet orifice of the reactor, and this may give rise to clogging or operational problems downstream. Despite these detachments, it is found that the deposits continue to increase over time during a given production cycle.

[0160] After stopping, cooling and opening the cooking reactor 4, it was observed that the coke is present in two forms: a hard form in direct contact with the internal walls of the reactor and a more friable form which covers the hard coke. The difference between these two cokes is found in their elemental compositions, as shown in table 1 below.

TABLE-US-00001 Friable coke Hard coke Carbon content (%) 44.57 65.07 Hydrogen content (%) 5.85 4.67 Oxygen content (%) 34.63 24.58

[0161] It is observed that the percentage of carbon contained in hard coke is higher than that in friable coke, while an opposite trend is noted for the oxygen content, and similar values are noted for the hydrogen content. It emerges from this that the friable coke is, as it were, the precursor of the dense coke.

[0162] The invention consists in continuing the operation of the two impregnation 3 and pretreatment 5 reactors, while performing the chemical cleaning of the reactor 5 so as to extract this coke C and/or to slow down its formation, without “losing” the must produced during this cleaning under basic conditions.

[0163] This cleaning does not require the opening of the reactor and the mechanical cleaning of the interior of the reactor, as was previously the case. This cleaning according to the invention, described in detail below, is thus faster, more economical and safer, since it makes it possible to limit the operating risks associated with the assembling and dismantling of the unit and, above all, since it makes it possible to not have to stop the production.

[0164] An example of implementation of the process according to the invention requires the following additional equipment, with respect to those already described, in the light of FIG. 1: [0165] A vessel for preparation 51 of a cleaning liquor/basic liquor EB containing a base. This vessel 51 makes it possible to feed the pretreatment reactor 5 with basic solution at a certain concentration. It is fed with water E and with base B (for example from a base B in the form of a concentrated aqueous solution of KOH), the supply of which is adjusted to obtain a liquor with the desired concentration of base and the desired pH. [0166] A line for feeding the reactor 5 with cleaning liquor, connecting the cleaning liquor/basic liquor preparation vessel 51 and the pretreatment reactor 5 to be cleaned, where appropriate preheating it by ad hoc items of equipment (heating resistors surrounding the pipes, for example), with items of equipment suitable for injecting the cleaning liquor into the reactor 5 under pressure, [0167] An optional rinsing water inlet ER for the cyclone 8. [0168] Also provided, but not shown, are one or more temporary storage vessels or hoppers or other temporary storage means, the “buffer zones” mentioned above suitable for recovering, in one of the vessels, the conventional acidic must AM and, in the other vessel, the basic must BM obtained during cleaning of the pretreatment reactor 5 under basic conditions.

[0169] The procedure of an implementational example of the cleaning process/sequence T1 according to the invention comprises two consecutive sub-sequences: [0170] sub-sequence 1: Injection of the preheated basic liquor EB into the reactor 5 while the reactor is being fed with the acidic biomass.

[0171] The injection conditions are as follows: [0172] the basic solution EB is an aqueous KOH solution, with a KOH concentration of from 1% to 50% by weight of KOH, preferably from 5% to 12% by weight of KOH, relative to the water [0173] the flow rate of the solution EB into the reactor is between 100 and 500 kg/h, notably about 300 kg/h [0174] the degree of filling with the solution EB of the reactor 4 is from 20% to 50%, notably about 30% [0175] the temperature at which the solution EB is injected into the reactor 4 is between 80° C. and 200° C., notably about 130° C. [0176] the temperature of the reactor 4 is between 150° C. and 220° C., notably about 200° C. [0177] the duration of this sequence is between 15 minutes and 8 hours; it is notably 2 hours [0178] the residence time of the solution EB in the reactor 4 is between 5 and 15 minutes, and notably about 10 minutes [0179] sub-sequence 2 (optional): Cleaning of the cyclone 8 by rinsing with the water ER to complete the cleaning. The term “water flush” can be used, insofar as the rinsing consists, in this implementational example, in spraying water under pressure into the cyclone, which water is subsequently rapidly removed.

[0180] The operating conditions of this sequence, if it is performed, are as follows: [0181] number of rinses: from 1 to 10, for example equal to 2 [0182] temperature of the rinsing water: 20° C. to 80° C., for example 20° C. (i.e. either ambient temperature or close to ambient temperature, or a higher temperature requiring preheating of the ER rinsing water)

[0183] In the cleaning phase=sequence T2, a must is obtained at the outlet of the cyclone 8, which is no longer the conventional acidic must AM but a basic must BM.

[0184] The frequency of the cleaning procedure/of sequence 2 can vary widely depending on the type and size of the pretreatment reactor 5, on the type of biomass being processed, and the like. For example, the cleaning can be triggered when the torque of one of the transportation screws internal to the reactor increases by more than 15%, with respect to the torque observed at the start of production. It can also be triggered after a given period, which can range from 2 hours to 4 months of production.

[0185] FIG. 3 describes a mode of functioning of the process according to the sequence T1, from the pretreatment reactor up to the ethanolic fermentation: after the separation by the cyclone 8 (or any other liquid/gas separation device), the acidic must obtained AM is sent for enzymatic hydrolysis, with adjustment of the pH by supplying base B directly into the hydrolysis reactor, so as to obtain, after fermentation, a fermentation wine FW.

[0186] FIG. 4 is a variant of the process of FIG. 3: the difference here is that the adjustment of the pH of the acidic must AM is performed before introduction into the hydrolysis reactor, notably by passing into a neutralization zone/vessel with a supply of base, or by introducing a supply of base into the pipe for transfer from the cyclone to the hydrolysis reactor.

[0187] FIG. 5 describes a mode of functioning of the process according to the sequence T2, from the pretreatment reactor up to the ethanolic fermentation: after the separation by the cyclone 8 (or any other liquid/gas separation device), the acidic must obtained BM is added to temporarily stored acidic must AM to make a mixture AM+BM which is sent for enzymatic hydrolysis, with adjustment of the pH by supplying base B directly into the hydrolysis reactor, so as to obtain, after fermentation, a fermentation wine FW. Alternatively, as shown in FIG. 6, the supplying of base may be performed upstream of the hydrolysis reactor. In both cases, the supply of base will be less than the supply of base required during the sequence T1, since the must mixture AM+BM is globally less acidic than the acidic must AM, depending on the proportion of basic must in the mixture.

[0188] Different variants can be applied to the example of cleaning process/sequence T2 described above, while remaining within the scope of the invention, some of which variants are described in detail below (some at least of these variants can be alternative or cumulative):

[0189] A—During cleaning, the concentration of acid A of the impregnation liquor preparation vessel 31 can be reduced to a zero concentration optionally, that is, ultimately, an impregnation which is then performed only with water.

[0190] B—The washing water E for the screw 2b conveying the impregnated biomass into the reactor 4 can be recycled into the vessel for preparation 51 of the basic solution EB during cleaning, which makes it possible to reduce the additional water consumption due to the cleaning.

[0191] C—The biomass can be impregnated with a basic liquor during the cleaning sequence, either with the same basic liquor EB as that prepared in the vessel 6 or a different basic liquor, notably in terms of concentration of base B. This variant makes it possible to reduce the amount of pure basic solution to be introduced into the pretreatment reactor 4, since there will no longer be, or will be less, acid to be neutralized in order to reach the target basic pH. However, a certain amount of basic liquor will be removed in the pressate (which corresponds to the water extracted from the screw 2′).

[0192] Thus, it may remain necessary to supply basic liquor EB directly into the reactor 4 (via the vessel 51): the vessel 51 for preparation of basic liquor EB still has two inlets, one for the concentrated base B (concentrated KOH), the other for the water, but here it also has two outlets: one outlet to the pretreatment reactor, as previously, and one outlet to the impregnation reactor 3. With this configuration, it is possible to feed the impregnation reactor 3 either with the acidic solution EA from the vessel 31 during the sequence T1, or with the basic solution EB from the vessel 6 during the sequence T2. The vessel 6 can thus simultaneously feed the two reactors 3 and 4, or at least for a common period during the cleaning of the reactor 4. It is also possible to anticipate and begin to feed one of the reactors with basic solution EB before the other, notably the impregnation reactor 3, before the start of cleaning with the EB solution of the pretreatment reactor 4.

[0193] D—It is also possible to combine the two preceding variants, with, at the same time, the recycling of the pressate at the outlet of the screw 2b into the vessel 61 for preparation of basic liquor EB, and the feeding via this same vessel 51 of the two reactors 3 and 4 during at least a part of the sequence T2.

[0194] E—It is also possible to use two impregnation reactors 3,3′ operating alternately. As in the variant C, the biomass is impregnated not with an acidic liquor EA but with a basic liquor EB during at least a part of the cleaning/sequence T2 of the reactor, or even also a little before, in the following manner: in production mode, the biomass is brought into the pretreatment reactor 3 fed with acidic liquor via the vessel 2, and in production+cleaning mode (during all or part of the cleaning), the biomass is rerouted to the impregnator 3′, which itself is fed with basic liquor EB from the vessel 51. A second dedicated impregnation reactor 3′ is thus used for the cleaning. This embodiment has the advantage, in comparison with the variant C, of reducing the transition times between acidic impregnations and basic impregnations.

[0195] F—The variants E and B can be combined, that is to say the two impregnation reactors 3,3′ can be used and the water extracted from the screw 2′ can be recycled into the vessel 6 for preparation of basic liquor EB.

[0196] G—The must (also called the must) can be recycled, notably in the context of the variant E with two impregnation reactors: the basic pretreated biomass M1 which exits from the separation device 8 during the cleaning of the pretreatment reactor 4. This is because, during this period, it is basic. It is then possible to wash this must BM at the outlet of the separation device 8 with water: it becomes a washed basic must BM′, and to extract therefrom a basic aqueous phase E1 which is recycled into the vessel 51 for preparation of the basic liquor.

[0197] H—Another variant consists in using two separation devices 5,5′ (cyclone) operating alternately: a cyclone is added which is dedicated to the treatment of the basic must BM. In production mode/sequence T1, the first cyclone is operational, it treats an acidic must AM; in production+cleaning mode/sequence T2, the output of the reactor 4 is switched to the second cyclone 5′, which will thus separate only basic must BM. The advantage of this variant is that it reduces the transition time between the two modes. It is also possible to combine this variant with the variant G: the basic must BM, once separated in one of the cyclones, is also washed in order to recycle the basic washing water E1 into the vessel for preparation 51 of basic liquor.

[0198] J—This variant emerges from the preceding variant E with two impregnation reactors 3,3′, with the following difference: In production mode, use is made of the conventional impregnation reactor 3 fed with acidic solution EA via the vessel 1. In production+cleaning mode, the system is switched here to the second impregnation reactor 3′ which is fed only with water: during the cleaning/sequence T2, the biomass is thus impregnated only with an aqueous solution at neutral pH (and not a basic solution EB).

[0199] K—The invention also applies to processes for the pretreatment of biomass without prior preimpregnation with a liquor (this is then referred to as self-hydrolysis): in this case, the biomass P, after having optionally undergone a treatment of mechanical (grinding, etc.), thermal (drying) or humidification type, is introduced directly into the pretreatment reactor 4.

[0200] L—This variant combines the recycling of the pressate E1 of the variant E with that of the washing water for the screw 2b of the variant B to the vessel 6 for preparation of the basic liquor EB. Both the consumption of water and of base required for the cleaning according to the invention are thus more substantially reduced.

[0201] M—This variant recommends a thermal integration of the process, by condensation of the steam V at the outlet of the cyclone 8. This steam V is used to heat the basic liquor EB circulating in pipes between the vessel 51 and the pretreatment reactor 4 via a heat exchanger (not shown). It also serves to reduce the amount of water used in the vessel 6 by recovering the condensate obtained from the cooling of the steam exiting from the cyclone, via a condenser (not shown).

[0202] N—According to another variant, it can be chosen to inject biomass impregnated with acidic liquor EA into the pretreatment reactor 4 from the impregnation reactor 3 in production mode, and to directly inject non-impregnated biomass P into the pretreatment reactor 4 in sequence T2 (production+cleaning mode), then stopping the feeding of biomass impregnated with acidic liquor.

[0203] O—According to yet another variant, which can be combined with all the others, it can be chosen to inject, into the pretreatment reactor, a given impregnated biomass in production mode (sequence T1), and to inject another biomass, impregnated or not with a liquor, in production+cleaning mode (sequence T2). For example, in production mode, a straw-type biomass is chosen and, in production+cleaning mode, a more abrasive poplar-based biomass is chosen: a temporary increase is thus brought about in the cleaning time, the abrasive nature of the biomass, in order to assist in more easily detaching the solid coke residues from the walls.

EXAMPLES

[0204] Example 1 not in accordance with the invention: use of a basic must BM alone in SSCF (“Simultaneous saccharification and co-fermentation”, i.e. concomitant enzymatic hydrolysis and alcoholic fermentation)

[0205] A batch of wheat straw is pretreated by steam explosion under acidic conditions. To do this, the straw is ground to 50 mm and then introduced into a first impregnation reactor 3. The characteristics and composition of the wheat straw are as follows:

[0206] Solids content: 91.07%

[0207] Biomass flow rate: 65 kg SC/h

[0208] The straw is introduced into a first impregnation reactor 3 so as to be placed in contact with an acidic liquor before being sent into a steam-explosion pretreatment reactor 4. The operating conditions during production (sequence T1) are as follows: [0209] Impregnation:

[0210] Flow rate of concentrated acid solution: 1.29 kg/h, i.e. a pH of about 1

[0211] Acidity of the acidic liquor: 1.1 g H.sub.2SO.sub.4/100 g

[0212] Impregnation time: 1 min [0213] Steam explosion (cooking reactor 4):

[0214] Residence time: 5 min

[0215] Production time: 20 hours

[0216] After a period of 20 hours of functioning under these conditions, a sequence T2 of cleaning of the steam-explosion pretreatment reactor 5 is commenced: [0217] Impregnation:

[0218] Flow rate of concentrated acid solution: 1.29 kg/h, i.e. a pH of about 1

[0219] Acidity of the acidic liquor: 1.1 g H.sub.2SO.sub.4/100 g

[0220] Impregnation time: 1 min [0221] Steam explosion sequence T2/cleaning:

[0222] Residence time: 10 min

[0223] Flow rate of basic liquor: sufficient to lower the SC to the value for saturation of the pressate recycling biomass (mixture of water for washing the feed means of the cooking reactor 5 (“plug screw” 2b) and of spent acidic liquor): 100%

[0224] Duration of the cleaning/sequence T2: 2 h

[0225] Concentration of the KOH in the basic liquor: sufficient to change the biomass from a pH of 3 to a pH of 13

[0226] After the cleaning sequence T2, a cycle of 20 hours of production T1 and 2 hours of cleaning T2 was performed. The total number of cycles performed is three production/cleaning cycles (sequence T1/sequence T2).

[0227] In total, 54 kg SC/hour (operating time=66 hours; m (straw)=3540 kg) of wheat straw were consumed to produce:

[0228] 50 kg SC/hour of substrate pretreated under acidic conditions (operating time=60 hours, m (acidic substrate)=3029 kg)

[0229] 78 kg SC/hour of substrate pretreated under acidic conditions (operating time=4.5 hours, m (basic substrate)=353 kg)

[0230] 70 kg SC/hour of “transition” musts treated under variable pH conditions during the cooking (operating time=1.5 hours; m (transition substrate)=106 kg)

[0231] The musts treated under AM acidic conditions and under BM alkaline conditions are sampled. SSCF tests are performed in the laboratory with: [0232] An SSCF test fed only with AM must produced under acidic conditions, with a final SC (solids content) of 24% of must [0233] An SSCF test fed only with BM must produced under alkaline conditions, with a final SC of 19% of must.

[0234] The SSCF conditions are conventional, and will not be presented in further detail. They involve neutralization to reach the desired pH in order to maximize the activity of the enzymes. The test is performed in fed-batch mode: a first portion of the must is placed in contact with the biocatalysts, and the rest of the must is then added portionwise over a period of 6 hours so as to control the viscosity of the medium in the first hours.

[0235] FIG. 7 is a graph with, on the x-axis, the duration of the SSCF step in hours and, on the y-axis, the amount of ethanol produced in g/kg. The production of ethanol obtained from the acidic must AM corresponds to the curve with diamond-shaped points, and the production of ethanol obtained from the alkaline must BM corresponds to the curve with square points. By expressing these results as ethanol concentration, the following are obtained: [0236] final titer of the acidic must AM: 56 g/kg of ethanol, [0237] final titer of the alkaline must BM: 6 g/kg of ethanol.

[0238] By expressing these results as conversion yield, the following are obtained: [0239] on the acidic must, AM, the yield is 30.4% by weight of ethanol/sugars present at the inlet [0240] on the alkaline must BM, this yield is 7.5%.

[0241] It is clearly seen, on reading this graph and these data, that the alkaline must BM used alone does not make it possible to obtain a satisfactory production of ethanol.

Example 2: In Accordance with the Invention

[0242] The acidic musts AM and alkaline musts BM produced in example 1 are used as a mixture in the SSCF test in the same protocol as for example 1. The test is fed with an AM+BM mixture of acidic and alkaline musts produced in a mass proportion of 80% of acidic must AM and 20% of alkaline must BM (crude weight). This mixture is prepared before introducing into the SSCF reactor 16/18. The final SC introduced is 24% SC coming from the must mixture. The feeding with must(s) is partly done in an initial batch phase, and partly in fed-batch mode for the first six hours of reaction.

[0243] The ethanol production kinetics are shown in the graph of FIG. 8, which shows the same data on the x-axis and the y-axis as in the graph of FIG. 7, the curve corresponding this time to the production of ethanol using the AM+BM must mixture.

[0244] The following are obtained: [0245] a final titer of 55.3 g/kg of ethanol, which is similar to the results obtained with the acidic must AM alone (it is considered that a difference of less than 1 g/kg of ethanol is not significant since it is within the precision of the test); [0246] a yield of 32.7% by weight of ethanol/sugars present at the inlet.

[0247] It should be noted that it was necessary to readjust the pH of this mixture with sulfuric acid during the initial batch phase and the fed-batch phase.

[0248] This example thus demonstrates that with a significant proportion (20%) of alkaline must in the must mixture, it is possible to continue to obtain an ethanol production substantially identical to that obtained with a 100% acidic must: it is thus possible to perform continuous cleaning of the impregnation reactor without having an impact on the ethanol yield for all the production of the facility, by using all the must obtained after pretreatment, whether it is acidic or alkaline, by means of prior mixing of the two types of musts.

[0249] Example 3 in accordance with the invention: use of an acidic must AM, of an alkaline must BM and of a washed must M1 obtained from an SRC (Short Rotation Coppice) poplar wood substrate

[0250] A batch of SRC poplar wood is pretreated by steam explosion under acidic conditions. To do this, the SRC poplar wood is ground to 50 mm and then introduced into a first impregnation reactor 3.

[0251] The characteristics and composition of the wood are as follows:

[0252] Solids content SC: 55.50% by weight

[0253] Operating flow rate: 64 kg SC/h

[0254] The wood is introduced into a first impregnation reactor 3 so as to be placed in contact with an acidic liquor before being sent into a steam-explosion pretreatment reactor 5. The operating conditions during production are as follows: [0255] Impregnation for the production and cleaning (sequences T1 and T2):

[0256] Flow rate of concentrated acid solution: 2.6 kg/h

[0257] Conductivity of the acidic liquor at 80° C.: 103 mS/cm

[0258] Impregnation time: 1 min [0259] Steam explosion (sequence T1/production):

[0260] Residence time: 7.5 min

[0261] Steam feed: 100% at the top

[0262] Pressate recycling: 100%

[0263] Production time: 58.5 hours

[0264] After a period of 60 hours of functioning under these conditions, a sequence of cleaning/sequence T2 of the steam explosion reactor 5 is commenced: [0265] Impregnation for the production and cleaning/sequence T2:

[0266] Flow rate of concentrated acid solution: 2.6 kg/h

[0267] Conductivity of the acidic liquor at 80° C.: 103 mS/cm [0268] Steam explosion cleaning/sequence T2:

[0269] Residence time: 10 min

[0270] Basic liquor flow rate: sufficient to lower the SC down to the biomass saturation value

[0271] Pressate recycling: 100%

[0272] Duration of the cleaning: 1.5 h

[0273] Concentration of the KOH in the liquor: sufficient to change the biomass from a pH of 3 to a pH of 13

[0274] Number of cycles: Three production and cleaning cycles (3×sequence T1+sequence T2)

[0275] In total, 116 kg SC/hour (operating time=60 hours; m (straw)=6960 kg) of SRC poplar were consumed to produce:

[0276] 119 kg/hour of substrate pretreated under acidic conditions (operating time=58.5 hours, m (acidic substrate)=6962 kg)

[0277] 361 kg/hour of substrate pretreated under alkaline conditions (operating time=1 hour, m (basic substrate)=361 kg)

[0278] 178 kg/hour of transition musts treated under variable pH conditions during the cooking (operating time=30 min; m (transition substrate)=89 kg)

[0279] A portion of the must treated under acidic conditions is filtered on a belt filter, with counter-current washing, to separate a sugary liquor (serving for the yeast propagation) from a partially washed must known as M1 which will be reintroduced in the liquefaction.

[0280] SSCF tests are performed on the musts pretreated under acidic conditions, under alkaline conditions, and on the partially washed musts (the transition musts were not differentiated here):

[0281] An SSCF test with AM must produced under acidic conditions, with must produced under alkaline conditions BM, with partially washed pretreated must M1, 20 mg of enzymes/g SC, for a final SC of 22.2% by weight. This test required 23.7 kg of neutralization solution (containing 2.5% by weight of NH.sub.3).

[0282] The SSCF protocol commences with a “liquefaction” step performed in fed-batch mode.

[0283] The initial reaction mixture is composed of water, basic must, partially washed must and a portion of the must produced under acidic conditions (up to 12.5% SC in the feedstock) and supplemented with nutrients for the yeasts. The pH is adjusted to 5.3 with an alkaline solution (containing 23.5% by weight of NH3). When the pH is at 5.3, the enzyme biocatalysts and yeasts are added. This addition corresponds to the starting of the enzymatic hydrolysis reaction, and of the concomitant fermentation reaction. After a short time, addition in fed-batch mode of the rest of the must produced under acidic conditions is performed over a period of 2 hours.

[0284] When the rheology of the mixture permits it, the mixture is transferred into an SSCF vessel where the hydrolysis and fermentation reactions are continued. The total duration of the SSCF is 144 hours (total in the two reactors).

[0285] The graph of FIG. 9, with the same conventions as the graphs of the preceding figures, corresponds to the production of ethanol produced from this must. This implementation affords: [0286] For the SSCF, a final titer of 59.2 g/kg of ethanol [0287] For the SSCF, a yield of 41.3% by weight of ethanol/sugars present at the inlet

[0288] Example 4 in accordance with the invention: acidic must AM and alkaline must BM obtained from a straw substrate

[0289] A batch of wheat straw is pretreated by steam explosion under acidic conditions. To do this, the straw is ground to 50 mm, freed of dust and then introduced into a first impregnation reactor.

[0290] The characteristics and composition of the wheat straw are as follows:

[0291] Solids content: 88.30% by weight

[0292] Operating flow rate: 65 kg SC/h

[0293] The straw is introduced into a first impregnation reactor 3 so as to be placed in contact with an acidic liquor before being sent into a steam-explosion pretreatment reactor 5. The operating conditions during production are as follows: [0294] Impregnation for the production and cleaning (sequences T1 and T2):

[0295] Flow rate of concentrated acid solution: 2.5 kg/h

[0296] Conductivity of the acidic liquor at 80° C.: 103 mS/cm

[0297] Impregnation time: 1 min [0298] Steam explosion production (sequence T1)

[0299] Residence time: 5 min

[0300] Steam feed: 100% at the top

[0301] Pressate recycling: 100%

[0302] Production time: 78 hours

[0303] After a period of 80 hours of functioning under these conditions, a sequence of cleaning/sequence T2 of the steam explosion reactor 5 is commenced: [0304] Impregnation for the production and cleaning (sequence T2):

[0305] Acidic solution flow rate: 2.5 kg/h

[0306] Conductivity of the acidic liquor at 80° C.: 103 mS/cm [0307] Steam explosion cleaning/sequence T2:

[0308] Residence time: 10 min

[0309] Basic liquor flow rate: sufficient to lower the SC down to the biomass saturation value

[0310] Pressate recycling: 100%

[0311] Duration of the cleaning: 2 h

[0312] Concentration of the KOH in the liquor: sufficient to change the biomass from a pH of 3 to a pH of 13

[0313] Number of cycles: Four production and cleaning cycles: 4 cycles T1+T2

[0314] In total, during the four production/cleaning cycles, 73 kg/hour (operating time=320 hours; m (straw)=23 360 kg) of wheat straw were consumed to produce:

[0315] 138 kg/hour of substrate pretreated under acidic conditions (operating time=312 hours, m (acidic substrate)=43 056 kg)

[0316] 342 kg/hour of substrate pretreated under alkaline conditions (operating time=8 hours, m (basic substrate)=2732 kg)

[0317] SSCF tests are performed on the AM musts pretreated under acidic conditions and under alkaline conditions BM, without differentiating the transition musts:

[0318] An SSCF test was performed with AM must produced under acidic conditions, with BM must produced under alkaline conditions, for a final SC of 22.5% by weight. This test required 42.7 kg of neutralization solution (containing 23.5% by weight of NH3).

[0319] The SSCF protocol commences with a “liquefaction” step to arrive at a mixture of 92% by weight of must produced under acidic conditions/8% by weight of must produced under basic conditions. The liquefaction is performed in fed-batch mode. The initial reaction mixture is composed of water, basic must, and a portion of the must produced under acidic conditions (up to 12.5% SC in the feedstock) and supplemented with nutrients for the yeasts. The pH is adjusted to 5.3 with an alkaline solution (containing 23.5% by weight of NH.sub.3). When the pH is at 5.3, the enzyme biocatalysts and yeasts are added. This addition corresponds to the starting of the enzymatic hydrolysis reaction, and of the concomitant fermentation reaction. After a short time, addition in fed-batch mode of the rest of the must produced under acidic conditions is performed over a period of 6 hours.

[0320] When the rheology of the mixture permits it, the mixture is transferred into an SSCF vessel where the hydrolysis and fermentation reactions are continued. The total duration of the SSCF is 144 hours (total in the two reactors).

[0321] The ethanol production kinetics are described in the graph of FIG. 10, with the same conventions as for the preceding graphs.

[0322] This implementation in accordance with the invention makes it possible to obtain: [0323] a final titer of 54.8 g/kg of ethanol [0324] a yield of 36.2% by weight of ethanol/sugars present at the inlet.

[0325] With an addition of 8% by crude weight of BM must into the AM acidic must, the SSCF double reaction thus takes place satisfactorily.

[0326] Example 5 in accordance with the invention: acidic must AM, alkaline must BM and washed must M1, obtained from a straw substrate (pretreatment and washing conditions different from those of example 4, with a reduction in the reactor temperature)

[0327] A batch of wheat straw is pretreated by steam explosion under acidic conditions. To do this, the straw is ground to 50 mm, freed of dust and then introduced into a first impregnation reactor 3.

[0328] The characteristics and composition of the wheat straw are as follows:

[0329] Solids content: 88.30% by weight

[0330] Operating flow rate: 50 kg SC/h

[0331] The straw is introduced into a first impregnation reactor 3 so as to be placed in contact with an acidic liquor before being sent into a steam-explosion pretreatment reactor 5. The operating conditions during production are as follows: [0332] Impregnation for the production and cleaning (sequence T1):

[0333] Flow rate of concentrated acid solution: 2.5 kg/h

[0334] Conductivity of the acidic liquor at 80° C.: 103 mS/cm

[0335] Impregnation time: 1 min [0336] Steam explosion in production/sequence T1:

[0337] Residence time: 5 min

[0338] Steam feed: 100% at the top

[0339] Pressate recycling: 100%

[0340] Production time: 78 hours

[0341] After a period of 80 hours of functioning under these conditions, a sequence of cleaning/sequence T2 of the steam explosion reactor 5 is commenced: [0342] Impregnation for the production and cleaning/sequence T2:

[0343] Acidic solution flow rate: 2.5 kg/h

[0344] Conductivity of the acidic liquor at 80° C.: 103 mS/cm [0345] Steam explosion cleaning/sequence T2:

[0346] Residence time: 10 min

[0347] Basic liquor flow rate: sufficient to lower the SC down to the biomass saturation value

[0348] Pressate recycling: 100%

[0349] Duration of the cleaning: 2 h

[0350] Concentration of the KOH in the liquor: sufficient to change the biomass from a pH of 3 to a pH of 13

[0351] Number of cycles: one production and cleaning cycle (T1+T2)

[0352] In total, during this production/cleaning cycle, 58 kg/hour (operating time=80 hours; m (straw)=4640 kg) of wheat straw were consumed to produce:

[0353] 109 kg/hour of substrate pretreated under acidic conditions (operating time=78 hours, m (acidic substrate)=8502 kg)

[0354] 372 kg/hour of substrate pretreated under alkaline conditions (operating time=2 hours, m (basic substrate)=744 kg)

[0355] An SSCF test was performed in the pilot plant on the musts pretreated under acidic conditions AM and under alkaline conditions BM, for a final SC of 22.5% by weight. This test required 33.8 kg of neutralization solution (containing 23.5% by weight of NH.sub.3).

[0356] The SSCF protocol commences with a “liquefaction” step to arrive at a mixture of 90% by weight of must produced under acidic conditions AM/10% by weight of must produced under basic conditions BM.

[0357] The liquefaction is performed in fed-batch mode. The initial reaction mixture is composed of water, basic must, and a portion of the must produced under acidic conditions (up to 12.5% SC in the feedstock) and supplemented with nutrients for the yeasts. The pH is adjusted to 5.3 with an alkaline solution (containing 23.5% by weight of NH.sub.3). When the pH is at 5.3, the enzyme biocatalysts and yeasts are added. This addition corresponds to the starting of the enzymatic hydrolysis reaction, and of the concomitant fermentation reaction. After a short time, addition in fed-batch mode of the rest of the must produced under acidic conditions is performed over a period of 6 hours.

[0358] When the rheology of the mixture permits it, the mixture is transferred into an SSCF vessel where the hydrolysis and fermentation reactions are continued. The total duration of the SSCF is 118 hours (total in the two reactors).

[0359] The ethanol production kinetics are described in the graph of FIG. 11, which repeats the same conventions as for the preceding graphs.

[0360] This implementation in accordance with the invention makes it possible to obtain, at 118 hours: [0361] a final titer of 50.0 g/kg of ethanol [0362] a yield of 32.2% by weight of ethanol/sugars present at the inlet.

[0363] The ethanol production remains, here also, at a satisfactory level even with addition of a significant amount (10%) of basic must to the conventional acidic must AM.