Method for treating a lignocellulosic biomass
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-02
- Publication Date
- 2026-04-01
Smart Images
Figure EP2024062128_28112024_PF_FP_ABST
Abstract
Description
[0001] PROCESS FOR TREATING LIGNOCELLULOSIC BIOMASS
[0002] Technical field
[0003] The invention relates to a method for treating lignocellulosic biomass to produce so-called second generation (2G) sweet juices. These sweet juices can be used to produce other products biochemically, in particular by fermentation (for example alcohols such as ethanol, butanol), or other molecules, for example solvents such as acetone, etc.).
[0004] Prior art
[0005] Lignocellulosic biomass represents one of the most abundant renewable resources on Earth. The substrates considered are very varied, they concern both woody substrates such as different woods (hardwoods and softwoods), co-products from agriculture (wheat straw, corn cobs, etc.) or other agri-food industries, paper mills, lignocellulosic waste, etc.
[0006] The lignocellulosic biomass treatment process generally involves
[0007] - pretreatment of the biomass by cooking possibly coupled with a steam explosion and generally preceded by impregnation of the biomass with an acidic, basic, neutral or oxidizing liquor,
[0008] - enzymatic hydrolysis, leading to the production of sweet juices, generally based on C5 and C6 sugars (i.e. sugars with 5 or 6 carbons),
[0009] - and possibly fermentation of these sugars by yeast, to convert them into alcohol of the ethanol type.
[0010] The process also includes steps of separation and / or purification of the targeted final product (sugar, alcohol, solvent, etc.).
[0011] Lignocellulosic biomass is composed of three main polymers: cellulose (35 to 50% by weight), which is a polysaccharide consisting mainly of hexoses; hemicellulose (20 to 40% by weight), which is a polysaccharide consisting mainly of pentoses; and lignin (10 to 30% by weight), which is a polymer with a complex structure and high molecular weight, composed of aromatic alcohols linked by ether bonds. These different molecules are responsible for the intrinsic properties of the plant wall and are organized into a complex tangle.
[0012] Among the three basic polymers that integrate lignocellulosic biomass, cellulose and hemicellulose are those that allow the production of 2G sweet juices. Most often, hemicellulose is mainly broken down into sugar during pretreatment, and cellulose is converted into sugar (glucose) by enzymatic hydrolysis. However, access to raw cellulose remains difficult for enzymes, hence the need for pretreatment. This pretreatment makes it possible to modify the physicochemical properties of lignocellulosic biomass in order to improve the accessibility of cellulose to enzymes and its reactivity to enzymatic hydrolysis.
[0013] Many technologies of interest to the invention for carrying out this pretreatment exist, which will be grouped hereinafter under the generic term of "cooking": acid cooking, alkaline cooking, cooking by auto-hydrolysis, steam explosion, processes called "organosolv pulping" according to the known English term (or treatment with organo-solvent in French). This last process concerns a pretreatment in the presence of one or more organic solvents and generally water. The solvent can be an alcohol (ethanol), an acid such as acetic acid, formic acid, or even acetone. The "organosolv pulping" processes lead to at least partial solubilization of the lignin, partial solubilization of the hemicelluloses. There are then two output streams: the pretreated substrate with residual cellulose, hemicellulose and lignin and the solvent phase which contains the solubilized lignin and a portion of the hemicelluloses.There is generally a solvent regeneration step that allows a lignin stream to be extracted. Some "organosolv pulping" treatments (particularly with ethanol) are coupled with the addition of a strong acid (such as H2SO4). It is also possible to consider contacting the biomass with the solvent via an impregnation reactor before the cooking phase or contacting the biomass with the acid catalyst before carrying out "organosolv pulping" cooking.
[0014] Different configurations are reported for example in the document “Production of bioethanol from lignocellulosic materials via the biochemical pathway: A review”, M. Balat, Energy Conversion and Management 52 (2011) 858-875, or in the document “Bioethanol production from agricultural wastes: an overview”, N. Sarkar, S. Kumar Ghosh, S. Bannerjee, K. Aikat, Renewable Energy 37 (2012) 19-27.
[0015] One of the most effective pretreatments is steam explosion, especially under acidic conditions, which allows almost complete hydrolysis of hemicellulose and a significant improvement in the accessibility and reactivity of cellulose to enzymes. This pretreatment may be preceded by other treatment(s).
[0016] Whenever a treatment requires a pressure step (impregnation, pretreatment of the cooking type or other), it is necessary to use means for introducing solid biomass compatible with these pressure steps. This is for example the case of compression screws, one embodiment of which is described in US patent 4,599,138. Patent FR 3 075 203 describes a process with impregnation of the biomass with an acid liquor, then cooking and steam explosion of the impregnated biomass, with adjustment of the acidity of the acid liquor and recycling thereof. Patent FR 3 075 201 also describes a process for pretreating biomass by acid impregnation then steam explosion, with in addition washing of the reactor feed means and recycling of the wash water in the process.
[0017] These different types of process, starting from lignocellulosic biomass, generate solid residues based on lignin, in particular after enzymatic hydrolysis, and / or after fermentation if the conversion of sugars into alcohol is continued in particular. These solid residues, which will be called in this text "unconverted solid residue" or "lignin cake" are rich in lignin, which does not react or reacts little to the action of the enzymes used for the hydrolysis of biomass and which are generally cellulases and hemicellulases. These woody residues can be used, in particular as fuel, or be integrated as a filler in resin or bitumen-based products for example. However, these unconverted residues are not made up (apart from a certain quantity of water) only of lignin: they can also contain hemicellulose and / or cellulose which have not reacted to hydrolysis.And removing these residues from the biomass conversion process means losing these unreacted polymeric sugar fractions, which impacts the conversion efficiency of biomass into sugar (or alcohol).
[0018] It has already been proposed to reuse these types of solid residues in the biomass treatment process: patent EP 2 516 661 proposes a biomass treatment process with pretreatment of the biomass in an alkaline medium, enzymatic hydrolysis, fermentation of the resulting hydrolysate to obtain a fermentation must containing an alcohol, separation / purification of the alcohol, and separation of a residue cake. This residue cake is sent to a separate cellulose regeneration reactor where the cake is mixed with an alkaline solution and heated before being recycled downstream of the pretreatment. This solution is interesting because it chooses to recover the remaining cellulose contained in this woody cake, to reintegrate it into the process, in order to increase the overall biomass conversion efficiency.On the other hand, it requires separate treatment of this cake, with an additional reactor dedicated to it and which will carry out alkaline cooking of the cake before recycling it, which increases the installation and operating costs of the process as a whole, and which increases the complexity of its implementation.
[0019] Another solution was proposed in patent EP 2 430 171, quite similar to the previous one, but providing for an acidic rather than alkaline cooking of the wood residue, with the same drawbacks. These solutions for reusing these residues are interesting, but remain complex to implement.
[0020] Furthermore, pretreatment reactors using cooking, particularly those with steam explosion, encounter problems of progressive fouling, with deposits of solid residues on its walls which accumulate and which can gradually cause operational problems (blocking of the reactor inlets / outlets, greater difficulty in circulating the biomass, reductions in reactor performance in general). Solutions have been proposed, in particular by carrying out cleaning operations with interruption of production, with emptying of the reactor, and scraping of the walls.
[0021] A cleaning technique using a basic aqueous solution and steam injection was thus proposed in patent WO2020 / 126916.
[0022] Other solutions have been proposed, which carry out cleaning without stopping production, which is more interesting industrially. This includes the technique described in patents WO 2020 / 126918 and WO 2020 / 126917, which propose cleaning the pretreatment reactor with a basic aqueous solution in the presence of biomass, which, de facto, produces an impregnated then pretreated biomass which is basic, which can then continue the conversion treatment such as enzymatic hydrolysis. This basic pretreated biomass is however less reactive towards enzymatic hydrolysis than the biomass impregnated and pretreated in an acidic or neutral medium, which is produced outside the cleaning phase which will tend to mix the two types of pretreated biomass before continuing its conversion.This technique is therefore interesting, but can still be improved to be able to clean the pretreatment reactor with the least possible impact on the pretreatment performance carried out on the biomass during cleaning.
[0023] The invention aims to improve the treatment of lignocellulosic biomass with a view to its conversion into sugar(s) or alcohol. Its particular aim is to increase biomass conversion yields, or to reduce the energy consumption of the treatment or to better recover any by-products of the treatment.
[0024] Summary of the invention
[0025] The invention firstly relates to a method for treating lignocellulosic biomass comprising: b) a step of acid or neutral pretreatment of the biomass previously placed in acidic conditions or at neutral pH in a pretreatment reactor, to produce an acid or neutral pretreated biomass, said step b) being carried out alternately with b') a step of basic pretreatment of the biomass previously placed in acid, neutral or basic conditions, with possible addition of base, to produce a basic pretreated biomass, then c) a step of enzymatic hydrolysis in a hydrolysis reactor (16) of the acid or neutral pretreated biomass resulting from step b) and / or of the basic pretreated biomass resulting from step b'), to obtain a hydrolyzed biomass,d) a step of solid / liquid separation of the hydrolyzed biomass from step c) in the form of sugar(s) or a step of solid / liquid separation of the hydrolyzed biomass in the form of sugar(s) from step c) then treated in one or more other steps subsequent to step c) of enzymatic hydrolysis, in order to obtain a separated juice and an unconverted solid residue, e) a step of recycling at least a part of said unconverted solid residue obtained in step d) to step b') of basic pretreatment.,
[0026] For the purposes of the present invention, the term “unconverted” “solid” residue means a residue which comprises at least 20% by weight of solid, in particular at least 30 or 35% by weight of solid. This proportion of solid and soluble compounds in a sample of the product can be evaluated by measuring its Dry Matter (acronym “DM”) content, which is measured according to the ASTM E1756 - 08(2015) “Standard Test Method for Determination of Total Solids in Biomass” standard.
[0027] The invention therefore combines two characteristics:
[0028] - on the one hand, it offers a pretreatment that alternates acid or neutral pretreatments for the biomass, which makes it possible to obtain pretreated biomasses that are very reactive with respect to the enzymatic hydrolysis that follows the pretreatment and basic pretreatments, which aim to clean the pretreatment reactor while continuing to produce a basic pretreated biomass, a little less reactive, (this results in continuous cleaning of the reactor, without having to stop the pretreatment),
[0029] - on the other hand, it proposes the recycling to the basic biomass pretreatment stage of all or part of the unconverted solid residue which is obtained by solid / liquid separation, either after enzymatic hydrolysis (separation on sugar juice), or after fermentation (separation on alcoholic juice), by introducing it specifically into the basic biomass pretreatment stage.
[0030] It turned out, surprisingly, that this unconverted solid residue had very interesting abrasive properties, and that using it during basic pretreatment made it possible to clean the walls of the pretreatment reactor at least as effectively, and even more effectively, than with biomass alone.
[0031] What is also surprising is that the addition of this residue to the rest of the biomass being treated did not in fact raise any problems in the operation of the pre-treatment tools: it did not complicate the smooth running of the devices used, whereas one might have feared that the addition of this residue, which has a texture very different from that of the biomass, would lead in particular to problems of fouling of the devices, problems of the residue being carried from one device to another or within a device, etc. This was not the case.
[0032] And this combination is very advantageous and synergistic between the two characteristics. Indeed, using this residue to "replace" all or part of the biomass during its basic pretreatment allows to save biomass during the basic pretreatment, to have more biomass available for the acid pretreatment, for the same total mass of biomass to be converted. The efficiency of the periodic cleaning in basic medium of the pretreatment reactor is maintained, by producing less less reactive basic pretreated biomass, and it is even possible to consider replacing the biomass entirely with this residue during these basic cleanings, while ultimately increasing the conversion efficiency of the biomass to be converted.
[0033] Furthermore, this unconverted solid residue is reused in the production line, which allows, if necessary, the extraction of any reactive compounds still trapped in the lignin, for the following stages of the biomass conversion process, which also helps to increase the biomass conversion efficiency.
[0034] The unconverted solid residue thus recycled will gradually become enriched in lignin: in fact, the ultimate unconverted residue obtained at the end of production is depleted in cellulose / hemicellulose which were trapped in the lignin, and enriched in lignin compared to a residue which has not undergone recycling according to the invention: this ultimate residue thus has a higher calorific value, making it more efficient as a fuel for generating heat via a combustion step of this ultimate residue. The heat produced can be used in the biomass conversion process, in one or more steps requiring heating of a fluid (for example the impregnation liquor), a reactor (for example cooking during pretreatment) or a reboiler of a distillation column (for example to purify an alcohol obtained by fermentation, etc.).This final unconverted residue can also be recovered outside the biomass conversion line, for uses external to it. It has thus surprisingly proven that reintroducing this residue into the impregnation or cooking device, with the biomass being treated, made it possible.
[0035] - to extract from this residue at least part of the cellulose and / or hemicellulose which were retained there, the enzymatic hydrolysis reaction not allowing the total conversion of these compounds,
[0036] - and to convert it at least in part by making it follow the path of “fresh” biomass again in its pretreatment and then enzymatic hydrolysis stages, which, in fact, ultimately increases the production of sugars (or alcohol) in the process.
[0037] As indicated above, step b') producing the basic pretreated biomass can, in fact, be a cleaning step for the impregnation reactor. The pretreatment will then be periodically stopped in a neutral or acidic medium, in particular, and the biomass will be brought into contact with an alkaline medium to enable the residues fouling the walls of the pretreatment reactor to be detached and removed, both by the effect of the alkaline medium capable of dissolving / detaching the residues and by the mechanical effect of friction of the biomass, and, according to the invention, of the solid residue not converted in the steps subsequent to the pretreatment.
[0038] Preferably, pretreatment steps b) and b') comprise cooking of the biomass, in particular accompanied by a steam explosion of said biomass.
[0039] Advantageously, it is possible to recycle in step e) to step b') of basic pretreatment a quantity of unconverted solid residue corresponding to at least 10%, in particular at least 20%, preferably at least 30% or 40% by weight of the total supply of residue and biomass to said pretreatment reactor during said step b'). It is even possible to use much more residue to "replace" the biomass, or even to replace it completely in this step b').
[0040] Preferably, the acid or neutral pretreatment step b) and / or basic pretreatment b') includes a prior step a) and / or a') of impregnation, in particular in an impregnation reactor, of the biomass with an acid, neutral or basic aqueous solution.
[0041] And in this case, in a first embodiment, the basic pretreatment step b') includes a prior step a') of impregnation, in particular in an impregnation reactor, of the biomass with an acidic, neutral or basic aqueous solution, and at least a portion of the unconverted solid residue is recycled in step e) to the pretreatment step b') by introducing said residue into the impregnation reactor during the impregnation step a'). This embodiment is advantageous because it facilitates the extraction of the minority reactive compounds contained in the unconverted solid residue and which had been trapped. However, the presence of this residue in the impregnation reactor may induce additional consumption of impregnation liquor.
[0042] In a second embodiment of the invention, (with or without prior impregnation in an impregnation device) it is possible to recycle in step e) at least a portion of the unconverted solid residue to the pretreatment step b') by introducing said residue into the pretreatment reactor, in particular of the cooking type, in particular with steam explosion. This embodiment is advantageous, because the solid residue is carried into the pretreatment reactor by the biomass which has generally been impregnated with impregnation liquor beforehand, and it does not induce additional consumption of impregnation liquor.
[0043] Preferably, step a') of impregnation of the biomass and step b') of basic pretreatment of the impregnated biomass are carried out in reactors each equipped with a biomass feed device, and step e) of recycling the unconverted solid residue is carried out by introducing at least a portion of said residue with the biomass being treated in at least one of said feed devices. "During the treatment" means that the residue is introduced before the biomass or with the biomass for at least part of the time it feeds the reactor in question, or after the reactor has been fed with the biomass while the reactor is in operation.
[0044] At least one of the feeding devices may thus be a feeding screw, in particular at least partly conical, comprising a fairing provided with a cage provided with openings which allow the extraction of the solid-liquid residue from the biomass and possibly the circulation of a washing fluid. This compression screw, in a known manner, creates a hermetic plug of biomass in the downstream portion of the screw, which creates a compression on the biomass resulting in a pressure difference between the inlet of the biomass and the outlet of the biomass from the screw. But any other known device may be used. For the impregnation step, a reactor operating continuously or in batch mode may be used, or other means than a dedicated reactor, in particular a conveyor belt which is sprayed with liquor, etc.
[0045] Advantageously, step b') of basic pretreatment comprises an addition of base in the pretreatment reactor: in this case, the biomass is brought into contact with a basic medium not during its prior impregnation, for example, but during the cooking pretreatment itself. This addition of base in the pretreatment reactor is of course compatible with a prior impregnation of the biomass by an acidic, neutral or basic impregnation liquor: the addition of base is adjusted according to the acidity / basicity of the biomass which feeds the pretreatment reactor. According to one embodiment, the method according to the invention aims at the production of sugar juice only, the separation step d) being carried out on the sugar juice at the outlet of the enzymatic hydrolysis.
[0046] According to another embodiment, the method aims to transform all or part of the sweet juice obtained by enzymatic hydrolysis. It can then also comprise:
[0047] - a step f) of fermentation of the hydrolyzed biomass in the form of sugar(s), in order to obtain a fermented biomass comprising at least one alcohol, step d) of solid / liquid separation being carried out on said fermented biomass.
[0048] In this latter mode, it is possible, according to the invention, to recycle both the unconverted residue at the end of the enzymatic hydrolysis and / or at the end of the fermentation:
[0049] The enzymatic hydrolysis steps c) and fermentation f) can be carried out simultaneously on the pretreated biomass, in which case we speak of SSF for the acronym of the English term "Simultaneous Saccharification and Fermentation" or SSCF for the acronym of the English term "Simultaneous Saccharification and Co-Fermentation". They can also be carried out one after the other, in separate reactors in particular.
[0050] The method according to the invention may also comprise:
[0051] - a step g) of separation or purification, in particular distillation, of the fermented biomass, the step d) of solid / liquid separation being carried out before or after said step g) of separation or purification.
[0052] Carrying out separation d) before step g), when step g) is a distillation, is advantageous, because this avoids introducing a liquid phase containing this residue, which could foul the column or at least hinder its operation.
[0053] But it may also prove interesting to carry out separation d) according to the invention after or during the stage of concentration / purification of the hydrolysate or fermentation wine, because the solid residue may contain a fraction of sugars or alcohol, and passing it into the concentration / purification stage may make it possible to extract at least part of this fraction of sugar or alcohol trapped in the solid residue.
[0054] As mentioned above, the method according to the invention can also comprise:
[0055] - a step h) of combustion of the ultimate unconverted solid residue obtained at the end of the treatment of the biomass, the heat produced from which is used in a step of said process requiring heating, in particular the heating of a fluid, in particular in step b) or b') of cooking or a step g) of separation by distillation.
[0056] The ultimate residue obtained with the invention has an improved calorific value, due to a lower content of cellulose / hemicellulose, which are polymeric sugars with low calorific value, unlike lignin.
[0057] Optionally, combustion step h) may be preceded by a step i) of drying the residue, in particular so that the residue reaches a water content lower than a given threshold, for example less than or equal to 40% by weight, in particular less than or equal to 30% by weight.
[0058] Step d) of solid / liquid separation can be carried out by filtration, in particular using a pressing or draining device, such as a filter press or a vacuum filter, a belt filter, a belt press or a centrifugation, decantation, wringer device or a combination of different devices.
[0059] The unconverted solid residue obtained in step d) of solid / liquid separation generally contains, in addition to water, a majority compound in the form of lignin, and minority compounds among cellulose and / or hemicellulose and possibly one or more alcohols of the ethanol type when the solid / liquid separation d) is carried out after a fermentation step f).
[0060] The unconverted solid residue obtained in step d) of solid / liquid separation may contain, for example, between 40 and 70% by weight of water, in particular between 50 and 60% by weight of water, between 2 and 35% by weight of cellulose, in particular between 5 and 20% by weight of cellulose, and between 0 and 15% by weight of hemicellulose, in particular between 1 and 10% by weight of hemicellulose. It may also comprise other minor compounds, such as mineral compounds (which can be measured by analysis of their ash after combustion).
[0061] The different contents of lignin, cellulose and hemicellulose can in fact vary, in particular depending on the type of biomass used and its reactivity during enzymatic hydrolysis in particular.
[0062] Step e) of recycling the unconverted solid residue reduces the content of at least one of its minor compounds, cellulose and hemicellulose, in the final solid residue obtained at the end of the biomass treatment, and increases its calorific value, which is beneficial both for the biomass conversion efficiency and for the thermal integration of the process.
[0063] The dry basis composition of the ultimate solid residue obtained at the end of the biomass treatment generally comprises mainly lignin, and less than 20% DM of cellulose and less than 8% DM of hemicellulose. The treatment method targeted by the invention can convert the lignocellulosic biomass into sugar juice, in particular C5 and C6 juices, after enzymatic hydrolysis, or into alcohol(s), in particular ethanol, after fermentation of said sugar juice.
[0064] The invention also relates to any installation implementing the method described above.
[0065] The invention also relates to the installation for implementing the method which comprises: a) an impregnation device, in particular an impregnation reactor, for the biomass with an aqueous solution, in particular acidic or neutral b) a reactor for pretreatment by cooking the impregnated biomass coming from the impregnation device, said cooking being optionally accompanied by a steam explosion, to obtain a pretreated biomass, said reactor being provided with means for injecting a basic aqueous solution, c) a reactor for enzymatic hydrolysis of the pretreated biomass, to obtain a hydrolyzed biomass such that said installation also comprises d) a device for solid / liquid separation of the hydrolyzed biomass or of the hydrolyzed biomass then treated in one or more other reactors or devices arranged downstream of the reactor c) for enzymatic hydrolysis, in order to obtain an unconverted solid residue,e) means for recycling at least part of said solid residue not converted in the impregnation reactor a) to the impregnation reactor and / or to the pretreatment reactor when the pretreatment reactor is operated under basic conditions.,
[0066] The means of recycling the unconverted solid residue are conventional, and may include any suitable conveying system (e.g. conveyor, screw, hopper or belt).
[0067] Preferably, the installation according to the invention is such that the impregnation device a) and the pretreatment reactor b) are provided with feed devices, and such that the recycling means e) comprise fluidic connection means between the solid / liquid separation device d) and at least one of said feed devices for conveying the unconverted solid residue from the separation device to the or at least one of said feed devices.
[0068] The invention also relates to the use of the method or installation described above for the treatment of lignocellulosic biomasses, such as wood, straw, agricultural residues, paper residues, and all dedicated energy crops, in particular annual or multi-annual plants such as miscanthus, with a view to producing sugars, alcohol-type biofuels or bio-sourced molecules.
[0069] The invention will be described in detail below, using figures and non-limiting examples.
[0070] List of figures
[0071] Figure 1 is a schematic representation of a first variant of a lignocellulosic biomass conversion plant where the method according to the invention can be applied.
[0072] Figure 2 is a schematic representation of a second variant of a lignocellulosic biomass conversion plant where the method according to the invention can be applied.
[0073] Figure 3 is a schematic representation of a third variant of a lignocellulosic biomass conversion plant where the method according to the invention can be applied.
[0074] Figure 4 is a schematic representation of a lignocellulosic biomass conversion plant applying the invention.
[0075] Note that the same references concern the same flow, the same device, from one figure to another.
[0076] The description of the references is presented below:
[0077] 1: Water inlet into the liquor preparation tank
[0078] 2: Acid entry into the liquor preparation tank
[0079] 3: Tool (tank) for preparing the liqueur
[0080] 4: Acid liquor to impregnation tool (reactor)
[0081] 5: Crushed biomass
[0082] 6: Impregnation tool feeding device
[0083] 7: Wash water from the impregnation tool feeder
[0084] 8: Washing liquid outlet from the impregnation tool feeder
[0085] 9: Impregnation tool (reactor)
[0086] 10: Impregnated and drained biomass
[0087] 11: Pretreatment tool feed device
[0088] 12: Wash water from the “plug screw feeder” of the pretreatment tool
[0089] 13: Press of the pre-treatment tool feed device
[0090] 14: Pretreatment cooking tool (explosion reactor)
[0091] 15: Steam injection for pretreatment
[0092] 16: Pretreated biomass and steam
[0093] 17: Tool (cyclone) for separating steam and pretreated biomass
[0094] 18: Steam 19: Pretreated biomass
[0095] 20: Enzymatic hydrolysis reactor
[0096] 21: Hydrolyzate containing sugars
[0097] 22: Alcoholic (ethanolic) fermentation reactor
[0098] 23: Fermentation wine containing ethanol (alcohol)
[0099] 24: Ethanol recovery device, for example a distillation column(s)
[0100] 25: Concentrated alcohol
[0101] 26: Liquid residue: crude vinasse
[0102] 27: Solid (lignin) / liquid separation, e.g. filter press
[0103] 28: Liquid residue (vinasses)
[0104] 29: Unconverted solid residue (lignin cake)
[0105] 30: Clarified fermentation wine (without solids)
[0106] 31: Clarified hydrolyzate (without solids)
[0107] Description of the embodiments
[0108] The invention proposes to recycle the unconverted solid residue from the process of converting lignocellulosic biomass into sugars or alcohols. This residue is mainly composed of lignin, a compound not converted during the process. This residue is generally separated to be burned in conventional biorefineries; lignin can also be used as a compound of interest for specialty products (resins, bitumen, etc.). The invention proposes to recycle this compound upstream in the process, because the extracted lignin is not pure: it contains a fraction of unconverted polymeric sugars (cellulose and / or hemicellulose). The recycling of these sugar polymers then makes it possible to increase the yield of the process.
[0109] The invention relates to the recycling of at least a portion of a solid residue, referred to as "lignin cake" or "unconverted solid residue" in the present text. This solid is advantageously recycled in the pretreatment step under basic conditions of the lignocellulosic biomass, which, here, also serves as a cleaning step of the pretreatment reactor, which is a biomass steam explosion cooking reactor.
[0110] The preferred embodiment of the invention will be described here, where the pretreatment by explosive cooking is preceded by impregnation of the biomass with an acid liquor: periodically, the biomass passes into an alkaline medium in the cooking reactor in order to clean the reactor.
[0111] Lignin is one of the major components of lignocellulosic biomass (up to 30% DM). In a lignocellulosic biomass conversion process that uses sugars (cellulose and hemicellulose), the lignin cake is a co-product of the process that is composed of water (water can represent 50% to 60% by weight of the cake) and solids from the biomass that are not converted during the process, namely mainly lignin but also cellulose and hemicellulose. Thus, Table 1 below, as an example, indicates the flow rate entering the process and the composition of a typical example of biomass (wheat straw) to be treated and a lignin cake obtained after separation at the end of the alcohol production line:
[0112] Table 1
[0113] And table 2 below indicates, for the same biomass and the same lignin cake, their flow rates and composition of solid compounds, expressed here in dry matter content MS: Table 2
[0114] It can be seen from these tables that two unconverted sugar polymers (cellulose and hemicellulose) are present in the lignin cake, for a total of 11% by weight (or 28% by mass). The invention recycles at least part of the lignin cake (unconverted solid) to convert these polymers and thus increase the yield of the process, since 11% of the polymeric sugars in the biomass are found in the unconverted solid, without adding a treatment step dedicated to this lignin cake.
[0115] In addition, the calorific value of the lignin cake (measured by the value of the Higher Calorific Value PCS of the unconverted solid residue) increases if the sugar polymers it contains are converted. Indeed, sugar polymers contain oxygen molecules that decrease the average PCS of the solid.
[0116] Below are briefly examples of operating conditions for the key stages of biomass processing:
[0117] The process
[0118] Below is a more detailed description of the various key stages of a biomass conversion process using such an installation and to which the invention can advantageously be applied: (this is an example to which the invention is not limited).
[0119] Lignocellulosic biomass conditioning stage
[0120] The treatment process may include in its first step, and conventionally, a step of conditioning the lignocellulosic biomass with at least one grinding so as to obtain biomass particles having a size of at most 300 mm. It is of course possible to carry out several successive grinding steps in order to achieve the target particle size. Generally, the ground biomass has a particle size (the largest size) of at most 300 mm, most often at least 1 mm, and often between 2 and 200 mm. Any method known to those skilled in the art can be implemented to carry out this step. Most often, the grinding of straw is done with screens of 5 to 100 mm. As for the wood, it is generally shredded into parallelepiped plates with a length between 20 and 160 mm, a width between 10 and 100 mm and a thickness between 2 and 20 mm.The crushed lignocellulosic biomass is brought to the next stage by any means known to those skilled in the art, in particular a transfer screw. Stage of impregnation with an acid liquor.
[0121] The treatment method according to the invention comprises a step a) of impregnating the lignocellulosic substrate with an acid liquor so as to obtain an impregnated lignocellulosic substrate whose pH is between 0.1 and 3. This step aims to prepare the lignocellulosic substrate for the pretreatment step.
[0122] The impregnation is carried out in an impregnation reactor at a temperature between 10 and 90°C and preferably at atmospheric pressure. The residence time of the lignocellulosic substrate in the impregnation reactor is usually from 10 seconds to 180 minutes, preferably between 30 seconds and 60 minutes and even more preferably between 30 seconds and 15 minutes. Preferably, the impregnation step is carried out in a single step.
[0123] The impregnation reactor or impregnator is equipped with one or more screws that transfer(s) the lignocellulosic substrate from its inlet to the outlet opening. The impregnator is also equipped with one or more pipes to supply the acid liquor and, if necessary, one or more pipes to withdraw acid liquor. Said acid liquor inlet and outlet pipes are generally installed so as to operate in co-current or counter-current recycling.
[0124] Acid liquor is an aqueous solution of a strong acid, which is for example chosen from sulfuric acid, hydrochloric acid, nitric acid, for example at an acid content of between 0.5 and 4% by weight.
[0125] Solid / liquid separation step on the lignocellulosic substrate impregnated with acid liquor The lignocellulosic substrate impregnated with acid liquor is subjected to a solid / liquid separation step in order to obtain a lignocellulosic substrate having a dry matter content of between 15% and 70% by weight and a spent acid liquor. Preferably, the lignocellulosic substrate impregnated with acid liquor is first drained in order to extract at least a portion of the free acid liquor before being treated by solid / liquid separation.
[0126] The solid / liquid separation step can implement any technique known to those skilled in the art, which can be, for example, decantation, centrifugation or pressing.
[0127] Preferably, the lignocellulosic substrate is pressed concomitantly with its transfer to the pretreatment step when the latter implements the steam explosion method described below. This method of conducting the step is for example ensured by a compression screw called a "plug screw feeder" whose operation has already been described above. The formation of a plug of pressed lignocellulosic substrate ensures the pressure tightness of the steam explosion reactor, thus preventing dangerous steam leaks. The transfer screw is also provided with one or more lines for withdrawing the used liquor (called pressate) separated during pressing. The pressate can be recycled to the impregnation step and / or to the washing step by the washing liquid 12 passing through the feed screw 11.
[0128] The wet biomass obtained at the end of the solid / liquid separation step, which can be designated by the term "washed and acidified lignocellulosic substrate" has a dry matter content preferably between 15% and 70% by weight, and more preferably between 40 and 65% by weight.
[0129] Pretreatment stage of washed and acidified lignocellulosic substrate
[0130] The washed and acidified lignocellulosic substrate undergoes a pretreatment step.
[0131] Cellulose (and possibly hemicelluloses) which are the targets of enzymatic hydrolysis are not directly accessible to enzymes. This is why a pretreatment of the biomass is implemented before the enzymatic hydrolysis step. The pretreatment aims in particular to modify the physical and physicochemical properties of the cellulose fraction, such as its degree of polymerization and its state of crystallinity.
[0132] Various types of pretreatment are known to those skilled in the art, combining chemical and thermal treatment. Examples include acid or basic cooking, the Organosolv process, ionic liquid treatments, and the steam explosion process.
[0133] The preferred pretreatment process is steam explosion ("Steam Ex" or "Steam Explosion" in English terminology) carried out in an acidic environment. This is a process in which the lignocellulosic substrate is rapidly brought to a high temperature by injecting pressurized steam. The treatment is stopped by abrupt decompression.
[0134] The operating conditions of the steam explosion process are as follows:
[0135] - the steam is injected directly into the reactor;
[0136] - the reactor temperature is generally between 150 and 220°C, preferably between 170°C and 210°C,
[0137] - the pressure is between 5 and 25 bars absolute (0.5 and 2.5 MPa), more preferably between 8 and 19 bars absolute (0.8 to 1.9 MPa),
[0138] - the residence time before the relaxation phase varies from 10 seconds to 90 minutes, and preferably between 3 minutes and 30 or 40 minutes.
[0139] Steam explosion can be carried out in batch or continuous mode, and the depressurization step which allows the biomass to be deconstructed can take place in one or more stages.
[0140] At the end of the steam explosion pretreatment stage, a pretreated lignocellulosic substrate with a high dry matter content, generally between 20 and 70% by weight, and a vapor phase which can be condensed is obtained.
[0141] Following steam explosion under acidic conditions, the pretreated lignocellulosic substrate generally has a pH lower than that compatible with the medium for enzymatic hydrolysis. Thus, the lignocellulosic substrate is subjected to a neutralization step to bring its pH to a value between 4 and 6.
[0142] For the neutralization step, an aqueous solution containing a neutralizing agent is used which can be chosen from any weak or strong base known to those skilled in the art. By the term base, we mean any chemical species which, when added to water, gives an aqueous solution with a pH greater than 7. Preferably, the neutralizing agent is chosen from potassium hydroxide, sodium hydroxide, ammonia, lime. Even more preferably, the neutralizing agent is chosen from potassium hydroxide and ammonia, alone or in combination with each other. Preferably, the neutralizing agent is used in aqueous solution, with a mass concentration of between 2% and 75%, and even more preferably between 20% and 70%.
[0143] Neutralization is carried out at a temperature between 15°C and 95°C, and preferably between 20°C and 70°C. In general, the temperature of the neutralization step is not precisely controlled and is simply governed by the heat released by the acid-base neutralization reaction.
[0144] The neutralization step can be carried out continuously, batchwise or fed-batch.
[0145] It should be noted that a possible washing step can be carried out before or after the neutralization step, on all or part of the pretreated lignocellulosic substrate.
[0146] If washing is applied, a liquid stream is brought into contact with the pretreated lignocellulosic substrate, then the liquid is separated from the solid. The washing step can be carried out by percolation, by successive mixing operations and liquid / solid separation, by washing on a belt filter or by any other technique known to those skilled in the art. The washing liquid used can be water or a process stream. The mass ratio between the added washing liquid and the liquid contained in the substrate to be washed is generally between 0.5 and 4. The washing step generates a sugary washing juice containing a portion of the hemicelluloses solubilized during the pretreatment. This washing juice can, for example, be used as a carbon source for the production of biocatalysts (enzymes and / or microorganisms). The washing step is generally carried out at a temperature between 10°C and 95°C.
[0147] The pretreated lignocellulosic substrate, optionally neutralized and washed, is sent to the enzymatic hydrolysis stage of the process.
[0148] The pretreated lignocellulosic substrate that is sent to the enzymatic hydrolysis stage has a dry matter content generally between 15% and 70% by weight. The objective of enzymatic hydrolysis is to hydrolyze (depolymerize), by means of biocatalysts, hemicelluloses and cellulose into fermentable sugars, preferably xylose and glucose.
[0149] The enzymatic hydrolysis step is carried out under mild conditions, at a temperature of the order of 40°C and 55°C, preferably between 45°C and 50°C and at a pH of 4.0 to 5.5, and even more preferably between 4.5 and 5.2. The dry matter content of the enzymatic hydrolysis medium is between 2 and 45% by weight, preferably between 10 and 30% by weight. It is carried out using enzymes produced by a microorganism. Natural or genetically modified microorganisms, such as fungi belonging to the genera Trichoderma, Aspergillus, Penicillium or Schizophyllum, or anaerobic bacteria belonging for example to the genus Clostridium, produce a cocktail of enzymes containing in particular cellulases and hemicellulases, suitable for extensive hydrolysis of cellulose and hemicelluloses.
[0150] Enzymatic hydrolysis can be carried out in continuous or batch mode, or in fed continuous mode, in one or more reactors. The residence time is between 5 hours and 200 hours and preferably between 24 hours and 120 hours and even more preferably between 48 hours and 120 hours.
[0151] At the end of this stage, a hydrolysate containing fermentable sugars is recovered from the bioreactor and is then treated in the fermentation stage.
[0152] It should be noted that the hydrolyzate obtained may optionally undergo one or more treatment steps before the fermentation step. For example, this may involve a pH adjustment, a partial purification in order to limit the content of inhibitory compound for the fermentative microorganism, or at least a partial separation of the solid residues contained in the hydrolyzate (and thus obtain the unconverted solid residue to be treated according to the invention).
[0153] Fermentation stage of the hydrolyzate, when we want to continue the conversion of the sugars obtained into alcohol(s)
[0154] Depending on the step of the process for producing solvents and / or alcohols, the optionally treated hydrolyzate is sent to the fermentation step allowing the conversion by means of one or more microorganisms of different genera of the fermentable sugars into solvent and / or alcohols of interest. The fermentation methods are known to those skilled in the art and are described in particular in document US 8,456,633.
[0155] The term "solvent" means organic compounds other than alcohols, for example organic compounds having a ketone function such as acetone.
[0156] The term "alcohol" includes, in particular, ethanol, propanol, isopropanol and butanol.
[0157] Natural or genetically modified microorganisms can be chosen for example from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Saccharomyces uvarum, Saccharomyces diastaticus, Kluyveromyces fragilis, Candida shehatae, Pichia stipitis, Pachysolen tannophilis or the bacteria Zymomonas mobilis, Clostridium acetobutylicum, Escherichia coli.
[0158] In the context of the invention, the fermentation step makes it possible, for example, to produce ethanol alone or in a mixture with butanol, propanol, isopropanol and / or acetone. For example, the fermentative microorganism may be capable of producing a mixture called "ABE (acetone-butanol-ethanol)" or "IBE (isopropanol-butanol-ethanol)".
[0159] Preferably, the chosen microorganism is a natural or genetically modified yeast of the genus Saccharomyces capable of producing ethanol.
[0160] At the end of the stage, a fermentation must diluted in products of interest is recovered.
[0161] According to one embodiment of the method, the hydrolysis and fermentation steps can be carried out at the same time in at least one bioreactor so that the enzymatic hydrolysis and the fermentation are carried out simultaneously according to a process designated by the term "Simultaneous Saccharification and Fermentation (SES)" or "Simultaneous Saccharification and Fermentation (SSF)" according to the English terminology. When the hydrolysis step is combined with the fermentation step, the operating conditions, in particular temperature, can be adapted to adapt to the tolerances of the fermentation microorganism. For example, the temperature can be lowered to between 28°C and 45°C, and preferably between 30°C and 35°C when the fermentation is carried out with a yeast of the genus Saccharomyces. The pH is preferably adjusted to between 5 and 5.5 in order to promote the performance of the yeasts.
[0162] The production unit implementing the method according to the invention may comprise, in addition to the installations already described, in situ production units for enzymes and / or yeasts.
[0163] Stage of concentration and purification of solvents and / or alcohols from the fermentation must.
[0164] The process according to the invention finally comprises a step of concentration and purification of the product(s) of interest from the fermentation must, which is preceded or followed by a step of solid / liquid separation in order to eliminate at least a fraction of the solid matter contained in the fermentation must, and to produce the unconverted solid residue which will be treated according to the invention.
[0165] Preferably, the concentration and purification step of the product(s) of interest, for example ethanol, uses one or more distillations which is a technology well known to those skilled in the art. The: biomass lï
[0166] According to the invention, the feedstock of the process may be biomass alone or in a mixture. The quantity of water contained in the raw feedstock is generally at least 10%, in particular between 10 and 70% by mass.
[0167] The raw biomass is chosen from any type of biomass, preferably solid biomass, and in particular lignocellulosic biomass. Non-limiting examples of types of biomass include, for example, agricultural residues (in particular straw, corn cobs), forestry residues, forestry products, sawmill residues, dedicated crops, for example short-rotation coppices.
[0168] Preferably, the raw biomass, also called native biomass, is lignocellulosic biomass. It essentially comprises three natural constituents present in varying quantities depending on its origin: cellulose, hemicellulose and lignin. The lignocellulosic biomass feedstock is preferably used in its raw form, i.e. in all three of these constituents: cellulose, hemicellulose and lignin.
[0169] In a preferred embodiment of the invention, the lignocellulosic biomass is chosen from grass biomass, agricultural residues such as straw waste, corn cobs, sugar cane bagasse, forestry or sawmill residues such as wood chips or any other type of woody residue.
[0170] The impregnation fluid:
[0171] The optional fluid injected for impregnation is an aqueous liquid solution containing or not acid, at a temperature between 10 and 95°C and at atmospheric pressure. The pH of this chemical solution is between 0.1 and 12.0, preferably between 0.1 and 7, preferably between 0.3 and 2. According to a preferred embodiment, the liquor used is an acid-catalyzed liquor, and the pH of the liquor is adjusted between 0.1 and 4, in particular between 0.3 and 2. As acid, it is possible, for example, to use at least one acid chosen from sulfuric acid, hydrochloric acid, nitric acid, oxalic acid. Their content, in the aqueous phase, is preferably between 0.2 and 8% by weight.
[0172] The invention applies similarly to different methods and installations, in particular to:
[0173] - installations which only aim at the production of sugars, and which therefore do not provide for alcoholic fermentation, - installations which provide for pre-treatment by cooking without prior impregnation with a liquor (auto-hydrolysis for example),
[0174] - installations which provide pre-treatment by cooking with prior impregnation with a neutral liquor (including auto-hydrolysis of the biomass in contact with water, naturally releasing an acid, particularly acetic acid)
[0175] Figure 1 very schematically represents a non-limiting variant of a lignocellulosic biomass conversion plant in which the invention can be applied, an installation which provides for pretreatment of the biomass including impregnation with an acid liquor then cooking / explosion with steam, then enzymatic hydrolysis followed by alcoholic fermentation, to transform the biomass into ethanol.
[0176] Figure 1 therefore represents a biomass conversion carried out in the following way: the crushed biomass 5 (impregnated or not with a catalytic liquor) is introduced into an impregnation reactor 9 by a feed device 6. This may be a pressurized feed means, for example a compression feed screw, the terminal portion of which is conical, which has a fairing with a drainage grid, a wash water inlet 7 and a wash water outlet 8. A hermetic biomass plug is created in the downstream portion of the screw, which creates a compression on the biomass resulting in a pressure difference between the biomass inlet and the biomass outlet of the screw of at least 0.05 MPa. The compression applied to the biomass can lead to the expulsion of part of the liquid contained in the biomass, in particular when the MS of the biomass is less than 80% before it enters the pressurized feed means 6.The liquid thus extracted mixes with the wash water and is drawn off with the used wash water 8.
[0177] The impregnation reactor 9 is also supplied with acid liquor 4 (water with added sulfuric acid) from a liquor preparation tank 3, itself supplied with sulfuric acid 2 and water 1.
[0178] The impregnated and drained biomass 10 leaves the reactor 9 to feed a steam explosion cooking reactor 14 via another feed device 11, for example of the compression type, such as the feed device 6. In the device 11, due to the compression exerted on the biomass, a liquid 13 resulting from this pressing, also called pressate, is recovered, which is composed of water and acid. The device 11 is washed, using a dedicated inlet, by a washing liquid 12 (water and / or a recycled liquid, as seen below), which is then discharged through the outlet through which the pressate 13 is also discharged. The reactor 14 is also supplied with steam 15. At the outlet of the reactor 14, the biomass-steam mixture passes into a tool 17 for separating the biomass 19 and the steam 18.The biomass 19 is then treated in an enzymatic hydrolysis reactor 20, then once hydrolyzed into sugars, the hydrolyzed biomass 21 (also called hydrolysis must) passes into an alcoholic fermentation reactor 22. The biomass fermented into alcohol 23, also called fermentation must) is then brought into one or more distillation columns 24 to obtain concentrated alcohol 25 and crude vinasse 26, which are solid / liquid residues, mixed or separated depending on the arrangement of the columns 24.
[0179] A solid / liquid separation is carried out using a filter press type device (not shown), and a liquid residue (not shown) and a residue (not shown) are obtained at the outlet, which is the lignin cake of interest in the invention.
[0180] This is just one example of a plant, which can also have many variations. For example, enzymatic hydrolysis and fermentation can be carried out jointly in the same reactor; this is known as SSCF, which stands for "Simultaneous Saccharification and Co-Fermentation."
[0181] Figure 2 is a variant of the method according to Figure 1, where, all other things being equal, the solid / liquid separation by a filter press 27 is carried out on the fermentation wine 23 before the distillation column(s) 24: a lignin cake 29 is extracted, and the liquid residue, i.e. the fermented wine without solid residue, 30 is then brought into the distillation column(s) 24.
[0182] Figure 3 is a variant of the method according to Figure 2, where, all other things being equal, the solid / liquid separation device of the filter press type 27 is arranged between the enzymatic hydrolysis reactor 20 and the fermentation reactor 22: here the separation is carried out on the still unfermented hydrolysate 21, and the liquid part of the hydrolysate (sweet juice) 31 then goes into the fermentation reactor 22.
[0183] In a variant not shown of the process according to figure 3, only the production of sweet juice 31 is targeted, the conversion of which by fermentation is not continued on the same production line.
[0184] In all these variants, the object of the invention is to treat the lignin cake 29, which is ultimately intended to be burned to produce energy.
[0185] Figure 4 represents two alternative or cumulative implementations of the invention, starting from the variant of Figure 2. The invention will recycle this solid residue, this lignin cake, during the cleaning phase of the cooking reactor 14 by adding base (KOH) in the cooking reactor 14.
[0186] This cooking of the biomass in a basic medium, alternating with the cooking of the acid-impregnated biomass, aims to periodically clean the cooking reactor, following the technique described in the aforementioned patents WO 2020 / 126918 and WO 2020 / 126917.
[0187] To give an example of this alternation of pretreatment in acidic and basic conditions, it is possible, for example, to operate the cooking reactor 14 in two alternating modes:
[0188] - in acidic conditions, with impregnation with an acid liquor in the impregnation reactor for 100 hours, then transfer to the cooking reactor 14
[0189] - in basic conditions, with direct injection of a base into the cooking reactor 14, in particular via a dedicated inlet. Alternatively, the base can also, at least in part, be injected into the cooking reactor before feeding the unconverted wood residue (lignin) into the reactor. One possibility is to feed the cooking reactor with only this unconverted wood residue, via the impregnation device upstream of the cooking reactor. In this case, it may not be necessary to inject a base into the cooking reactor, and it is also possible to cut off the acid supply to the impregnation device upstream of the cooking reactor, or to carry out a basic impregnation.
[0190] Implementation of the invention by recycling the lignin cake 29 to the feed device 6 of the impregnation reactor 9
[0191] This recycling before impregnation is advantageous, because the lignin cake 29 (stream 29') (Figure 4) will be brought back into contact with the impregnation liquor (acid) in reactor 9, which will help to extract the residual polymeric sugars contained in the cake and subsequently make them react more easily during enzymatic hydrolysis. One might have feared that the lignin cake would crumble and settle at the bottom of reactor 9, without being able to be entrained with the biomass. But this was surprisingly not the case, even when the biomass was entrained into the reactor from its injection point to its outlet point by screws inside the reactor.
[0192] Implementation of the invention by recycling the lignin cake 29 to the feed device 11 of the cooking reactor 14.
[0193] The lignin cake is recycled at least in part (stream 29” in Figure 4) into the feeder 11 of the steam cooking / explosion reactor 14. In this case, the lignin cake is not re-impregnated with liquor, but is carried along by the biomass that is already impregnated.
[0194] In either embodiment, possibly part of the lignin cake (stream 29'” of Figure 4) is not recycled: The lignin cake may only be partially recycled.
[0195] At the end of production, the non-recycled 29” cake (the so-called ultimate residue) is stored to be used as fuel, either on the production line or for another use outside the production line, as fuel or to be incorporated into various products.
[0196] The same types of recycling apply analogously to lignin cakes according to the processes in Figures 1 and 3.
[0197] Examples of achievements
[0198] Example 1 (comparative)
[0199] This example, which does not conform to the invention, separates the unconverted solid 29 without recycling it. The biomass 5 is a lignocellulosic biomass: wheat straw. The characteristics and composition of the feedstock in the form of wheat straw are as follows:
[0200] Dry matter: 91.07%
[0201] Sugar potential: 67.5 g / 100 g
[0202] Biomass flow rate: 65 kg DM / h
[0203] Particle size: 50 mm
[0204] Biomass is processed according to the process shown in Figure 2. After hydrolysis, cellulose is converted into glucose or glucose oligomers, and hemicellulose is converted into xylose or xylose oligomers. For this, the cellulose or hemicellulose flow rates are expressed as potential glucose or potential xylose.
[0205] The term "potential sugar" (e.g. xylose, glucose) used below defines the addition of the different sugars, regardless of their form: monomeric or polymeric sugar, and corresponds to the theoretical quantity of sugar that can be produced from the composition of the raw material, here biomass. Indeed, after pretreatment by cooking, part of the sugars remains in the form of sugar polymers (e.g. cellulose or hemicellulose), and part of the sugars is in the form of sugar monomers (e.g. glucose or xylose). This measurement can be carried out using the ASTM E1758-01 (2020) standard "Standard Test Method for Determination of Carbohydrates in Biomass by High Performance Liquid Chromatography". As defined in the standard, to express this quantity of sugars in polymer form (e.g. cellulose), the water of hydrolysis must be subtracted from this quantity.
[0206] The procedure is as follows:
[0207] The operating conditions are detailed below:
[0208] Mode 1 = production:
[0209] - Impregnation for production in impregnation reactor 9:
[0210] Acid solution flow rate: 1.5 kg / h (H2SO4)
[0211] Impregnation temperature: 80°C
[0212] - Steam explosion of the impregnated biomass in the pretreatment reactor 14:
[0213] Stay time: 5 min
[0214] Steam temperature: 190°C
[0215] Production time: 20 hours
[0216] After 20 hours of production, the cleaning sequence is carried out under the following conditions:
[0217] Mode 2 = production + cleaning:
[0218] - Impregnation in the impregnation reactor 9:
[0219] Acid solution flow rate: 1.5 kg / h (H2SO4)
[0220] Impregnation temperature: 80°C
[0221] - Steam explosion of the impregnated biomass in the pretreatment reactor 14:
[0222] Stay time: 10 min
[0223] Temperature in the reactor: 200°C
[0224] KOH temperature: 130°C
[0225] KOH flow rate: -300 kg / h
[0226] Cleaning time: 2 hours Concentration of KOH used in the liquor: 7.7% by weight
[0227] Number of cycles: 3 cycles of mode 1 (production) and 1 cycle of mode 2 (production + cleaning)
[0228] - Cleaning cyclone 17 (separation device)
[0229] Number of water flushes: 2, after each cleaning
[0230] After 3 cycles of mode 1 + mode 2, for a total production time of 66 hours (60 hours of production and 6 hours of cleaning), the cleaning proved effective.
[0231] The mass of material cleaned from the reactor at the end of the procedure (after these 3 cycles) does not exceed 3 kg. Carrying out a cycle required:
[0232] - 1300 kg of biomass for production (20h)
[0233] - 130 kg of biomass for production and cleaning (2h) to produce 325 kg of ethanol with a MS yield of 22.7%
[0234] Example 2 (according to the invention)
[0235] This example in accordance with the invention proposes to recycle the unconverted solid 29 at the inlet of the cooking reactor 14 via the feed screw 11 in the cleaning phase. The biomass used for this example is the same as for example 1.
[0236] The biomass is treated according to the process shown in Figure 2. After hydrolysis, cellulose is converted to glucose or glucose oligomers, and hemicellulose is converted to xylose or xylose oligomers.
[0237] The operating conditions are detailed below:
[0238] Mode 1 = production:
[0239] - Impregnation for production in impregnation reactor 9:
[0240] Load: wheat straw at a flow rate of 65 kg DM / h
[0241] Acid solution flow rate: 1.5 kg / h (H2SO4)
[0242] Impregnation temperature: 80°C
[0243] - Steam explosion of the impregnated biomass in the pretreatment reactor 14:
[0244] Residence time: 5 min Steam temperature: 190°C
[0245] Production time: 20 hours
[0246] After 20 hours of production, the cleaning sequence is carried out under the following conditions:
[0247] Mode 2 = production + cleaning: (100% recycling of lignin residue 29) - Impregnation in the impregnation reactor 9:
[0248] Load: 65 kg DM / h of recycled lignins (= unconverted wood residue 29)
[0249] The acid supply to the impregnation reactor is stopped. Impregnation temperature: 80°C.
[0250] - Steam explosion of the impregnated biomass in the pretreatment reactor 14:
[0251] Stay time: 10 min
[0252] Temperature in the reactor: 200°C
[0253] KOH temperature: 130°C
[0254] KOH flow rate: -300 kg / h
[0255] Cleaning time: 2 hours
[0256] KOH concentration in the liquor: 7.7% by weight
[0257] Number of cycles: 3 cycles of mode 1 (production) and 1 cycle of mode 2 (production + cleaning)
[0258] - Cleaning cyclone 17 (separation device)
[0259] Number of water flushes: 2, after each cleaning after 3 cycles of mode 1 + mode 2, for a total production time of 66 hours (60 hours of production and 6 hours of cleaning).
[0260] The completion of a cycle required:
[0261] - 1300 kg of biomass for production (20h)
[0262] - 0 kg of biomass for production and cleaning (2h) replaced by recycled lignin to produce 325 kg of ethanol with a DM yield of 25.0%. This example shows that by replacing the biomass with lignin (the unconverted residue) at a content of 100%, the cleaning was as efficient as in Example 1. Biomass consumption was also reduced to produce basic pomace with a 100% reduction during the cleaning phase, which represents an increase in ethanol yield of 9% over the cycle time.
[0263] In conclusion, compared to the state of the art, the present invention leads to the following advantages:
[0264] - Cleaning the cooking reactor in an alkaline medium is at least as effective when all or part of the biomass is replaced by the unconverted solid residue (lignin cake 29)
[0265] - The overall sugar / ethanol yield of the process can also be improved by recycling the unconverted polymeric sugars (cellulose and hemicellulose) contained in this woody residue. After recycling in the pretreatment, these polymeric sugars are partly converted into monomeric sugars or are made more accessible to the enzymes used in the enzymatic hydrolysis step. In any case, even if the celluloses and hemicelluloses trapped in the lignin are not extracted from it by this recycling, particularly when the recycling takes place to the cooking reactor rather than to the impregnation reactor, the overall yield is improved due to the fact that the same quantity of alcohol / sugars is produced with less biomass, the lignin cake replacing part of the biomass during cooking in a basic medium in reactor 14.
[0266] - The quality of the lignin in the final residue is improved, since the conversion of sugars has made it purer / richer in lignin, the PCS of the solid is therefore increased since polymeric sugars have a lower PCS than lignin
[0267] - Less biomass is “consumed” during the cleaning phase in the basic medium of the cooking reactor 14, since all or part of this material can be replaced by the lignin cake, which allows, for an equal quantity of biomass, to produce more sugars / alcohol.
Claims
Claims 1. Process for treating lignocellulosic biomass comprising: b) a step of acid or neutral pretreatment of the biomass previously placed in acidic conditions or at neutral pH in a pretreatment reactor, to produce an acid or neutral pretreated biomass, said step b) being carried out alternately with b') a step of basic pretreatment of the biomass previously placed in acid, neutral or basic conditions, in the pretreatment reactor, with possible addition of base, to produce a basic pretreated biomass, then c) a step of enzymatic hydrolysis in a hydrolysis reactor (16) of the acid or neutral pretreated biomass resulting from step b) and / or of the basic pretreated biomass resulting from step b'),to obtain a hydrolyzed biomass d) a step of solid / liquid separation of the hydrolyzed biomass from step c) in the form of sugar(s) or a step of solid / liquid separation of the hydrolyzed biomass in the form of sugar(s) from step c) then treated in one or more other steps subsequent to step c) of enzymatic hydrolysis, in order to obtain a separated juice and an unconverted solid residue, e) a step of recycling at least part of said unconverted solid residue obtained in step d) to step b') of basic pretreatment., 2. Method according to the preceding claim, characterized in that step b') producing the basic pretreated biomass is a step of cleaning the impregnation reactor.
3. Method according to one of the preceding claims, characterized in that the pretreatment steps b) and b') comprise cooking of the biomass, in particular accompanied by a steam explosion of said biomass.
4. Method according to one of the preceding claims, characterized in that a quantity of unconverted solid residue corresponding to at least 10%, in particular at least 20%, preferably at least 30 or 40% by weight of the total supply of residue and biomass to said pretreatment reactor during said step b') is recycled in step e) to step b') of basic pretreatment.
5. Method according to one of the preceding claims, characterized in that at least part of the unconverted solid residue is recycled in step e) to the pretreatment step b') by introducing said residue into the pretreatment reactor.
6. Method according to one of the preceding claims, characterized in that the acid or neutral pretreatment step b) and / or basic pretreatment b') includes a prior step a) and / or a') of impregnation, in particular in an impregnation reactor, of the biomass with an acid, neutral or basic aqueous solution.
7. Method according to the preceding claim, characterized in that the basic pretreatment step b') includes a prior step a') of impregnation, in particular in an impregnation reactor, of the biomass with an acidic, neutral or basic aqueous solution, and in that at least part of the unconverted solid residue is recycled in step e) to the pretreatment step b') by introducing said residue into the impregnation reactor during the impregnation step a').
8. Method according to one of claims 6 or 7, characterized in that step a') of impregnation of the biomass and step b') of basic pretreatment of the impregnated biomass are carried out in reactors respectively for impregnation and pretreatment which are each equipped with a biomass feed device, and in that step e) of recycling the unconverted solid residue is carried out by introducing at least part of said residue with the biomass at the start or during treatment into at least one of said feed devices.
9. Method according to one of the preceding claims, characterized in that step b') of basic pretreatment comprises an addition of base to the pretreatment reactor.
10. Method according to one of the preceding claims, characterized in that it also comprises: - a step f) of fermentation of the hydrolyzed biomass in the form of sugar(s), in order to obtain a fermented biomass comprising at least one alcohol, and in that step d) of solid / liquid separation is carried out on said fermented biomass.
11. Method according to the preceding claim, characterized in that the enzymatic hydrolysis steps c) and fermentation f) are carried out simultaneously on the pretreated biomass.
12. Method according to one of claims 10 or 11, characterized in that it also comprises: - a step g) of separation or purification, in particular distillation, of the fermented biomass, and in that step d) of solid / liquid separation is carried out before or after said step g) of separation or purification.
13. Method according to one of the preceding claims, characterized in that it also comprises: - a step h) of combustion of the unconverted solid residue known as the ultimate residue obtained at the end of the treatment of the biomass, the heat of which is used in a step of said process requiring heating, in particular the heating of a fluid, in particular in step b) and / or step b') of pretreatment by cooking or a step g) of separation by distillation, - and which is optionally preceded by a step i) of drying said residue.
14. Method according to one of the preceding claims, characterized in that step d) of solid / liquid separation is carried out by filtration, in particular using a pressing or draining device, such as a filter press or a vacuum filter, a belt filter, a belt press, a centrifugation, decantation or wringer device or the combination of different devices.
15. Method according to one of the preceding claims, characterized in that it converts the lignocellulosic biomass into sugary juice, in particular C5 and C6 juices, after enzymatic hydrolysis, or into alcohol after fermentation of said sugary juice.
16. Installation for implementing the method according to one of the preceding claims, characterized in that it comprises: a) an impregnation device, in particular an impregnation reactor, for the biomass with an aqueous solution, in particular acidic or neutral b) a reactor for pretreatment by cooking the impregnated biomass coming from the impregnation device, said cooking being optionally accompanied by a steam explosion, to obtain a pretreated biomass, said reactor being provided with means for injecting a basic aqueous solution, c) a reactor for enzymatic hydrolysis of the pretreated biomass, to obtain a hydrolyzed biomass, and in that said installation also comprises d) a device for solid / liquid separation of the hydrolyzed biomass or of the hydrolyzed biomass then treated in one or more other reactors or devices arranged downstream of the reactor c) for enzymatic hydrolysis, in order to obtain an unconverted solid residue,e) means for recycling at least part of said unconverted solid residue obtained in step d) to the impregnation device and / or to the pretreatment reactor when the pretreatment reactor is operated under basic conditions.,