Method for producing ethanol from lignocellulosic feedstock

Abstract

Provided is a method for producing ethanol with improved permeation flow rate in membrane separation. More specifically, provided is a method for producing ethanol, the method comprising: a first step for producing ethanol by saccharifying and fermenting in a reaction system containing a lignocellulose-based raw material, a saccharifying enzyme, yeast, and water; and a second step for treating the first mixture containing ethanol, water, yeast, saccharifying enzyme, and lignocellulose-based raw material reaction residue obtained in the first step using a separation membrane to obtain a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water, and lignocellulose-based raw material reaction residue; the solid content concentration of the first mixture is 4-9.5 mass%.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority based on Japanese patent application No. 2022-212741 filed on December 28, 2022, and the entire disclosure of the prior patent application is incorporated by reference into this specification. Technical Field

[0003] The present invention relates to a method for producing ethanol from lignocellulosic raw materials. Background Art

[0004] Since the technology for producing sugars from non-food lignocellulosic raw materials can be used as a fermentation substrate for microorganisms to produce fuels such as alcohol, which can serve as gasoline substitutes, and does not compete with people for food, it is extremely beneficial for building a recycling-oriented society.

[0005] As a method for producing sugars such as monosaccharides and oligosaccharides serving as fermentation substrates from polysaccharides in lignocellulosic raw materials, enzymatic saccharification methods involving hydrolysis using saccharifying enzymes such as cellulolytic enzymes or microorganisms producing such saccharifying enzymes are known.

[0006] In addition, as methods for producing ethanol from lignocellulose using enzymatic saccharification, semi-synchronous saccharification and fermentation and parallel simultaneous saccharification and fermentation are known. In semi-synchronous saccharification and fermentation, after adding a lignocellulose-based raw material and a saccharifying enzyme to a single reaction tank for saccharification, an ethanol fermentation microorganism is added to the same reaction tank for enzymatic saccharification and ethanol fermentation. In parallel simultaneous saccharification and fermentation (also known as simultaneous saccharification and fermentation), the ethanol fermentation microorganism and the aforementioned saccharifying enzyme coexist, and the enzymatic saccharification reaction and ethanol fermentation proceed simultaneously.

[0007] Compared to production methods using starch, molasses, and other raw materials, ethanol production from lignocellulosic feedstocks has the problem of high production costs. Therefore, research is underway to efficiently produce ethanol from lignocellulosic feedstocks. Enzymes contribute significantly to the production cost, necessitating their effective utilization for practical application.

[0008] Patent Document 1 describes a method for producing a sugar solution by hydrolyzing cellulose using cellulase derived from filamentous fungi as a saccharifying enzyme. The method includes the following steps: adding a saccharifying enzyme to the cellulose for primary hydrolysis, followed by solid-liquid separation of the primary hydrolyzate into a primary sugar solution and a solid; adding water to the solid for secondary hydrolysis, followed by solid-liquid separation of the secondary hydrolyzate into a secondary sugar solution and a residue; and filtering the primary and / or secondary sugar solutions through an ultrafiltration membrane, recovering the saccharifying enzyme from the non-permeate side, and recovering the sugar solution from the permeate side. The method also describes increased sugar production and enzyme recovery with this technology.

[0009] As described in Patent Document 1, enzyme recovery and reuse using separation membranes is being explored as one method for effectively utilizing enzymes. However, as described in Non-Patent Document 1, it is known that solid matter in treated water during membrane separation operations can clog membrane pores or accumulate on the membrane surface, thereby reducing membrane performance. Even when using separation membranes to filter ethanol fermentation broth, there are problems with solid matter clogging the pores and accumulating on the membrane surface, resulting in reduced permeate flow, reduced ethanol permeation per unit membrane area, and reduced enzyme recovery.

[0010] Therefore, it can be said that efficient production of ethanol from lignocellulosic raw materials is still being sought.

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: International Publication No. 2011 / 115039

[0014] Non-patent document 1: MEMBRANE, 39(4), 209-216 (2014) Summary of the Invention

[0015] The present inventors have discovered that by performing saccharification and fermentation in a reaction system containing a lignocellulosic feedstock, a saccharifying enzyme, yeast, and water, and thereby obtaining a first mixture containing ethanol, water, a saccharifying enzyme, yeast, and a lignocellulosic feedstock reaction residue, the solids concentration of the obtained mixture is within a predetermined range, thereby increasing the permeation flux through the separation membrane in the solid-liquid separation step. The present invention is based on this finding.

[0016] Therefore, the present invention provides a method for producing ethanol from a lignocellulosic raw material, in which the permeate flux is increased in membrane separation.

[0017] The present invention includes the following [1] to

[16] .

[0018] [1] A method for producing ethanol from a lignocellulosic raw material, comprising:

[0019] In the first step, saccharification and fermentation are performed in a reaction system containing a lignocellulosic raw material, a saccharifying enzyme, yeast, and water to produce ethanol; and

[0020] In a second step, the first mixture containing ethanol, water, yeast, saccharifying enzyme, and the lignocellulosic raw material reaction residue obtained in the first step is treated using a separation membrane to obtain a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water, and the lignocellulosic raw material reaction residue;

[0021] The solid content concentration of the first mixture is 4 to 9.5% by mass.

[0022] [2] The method for producing ethanol according to [1], further comprising a third step of supplying at least a portion of the second mixture to the reaction system.

[0023] [3] The method for producing ethanol according to [1] or [2], wherein the first step, the second step, and the third step are repeated.

[0024] [4] The method for producing ethanol according to any one of [1] to [3], wherein the separation membrane is an organic membrane.

[0025] [5] The method for producing ethanol according to any one of [1] to [4], wherein the separation membrane is an ultrafiltration membrane.

[0026] [6] The method for producing ethanol according to any one of [1] to [5], wherein the separation membrane is an organic membrane and an ultrafiltration membrane.

[0027] [7] The method for producing ethanol according to any one of [1] to [6], wherein the solid content concentration of the first mixture is 5 to 9.5% by mass.

[0028] [8] The method for producing ethanol according to any one of [1] to [7], wherein the solid content concentration of the first mixture is 5.5 to 9.5% by mass.

[0029] [9] The method for producing ethanol according to any one of [1] to [8], wherein the solid content concentration of the first mixture is 6.5 to 9.5% by mass.

[0030]

[10] The method for producing ethanol according to any one of [1] to [9], wherein the solid content concentration of the first mixture is 7 to 9% by mass.

[0031]

[11] The method for producing ethanol according to any one of [1] to

[10] , wherein the separation membrane is in the form of a tubular membrane.

[0032]

[12] The method for producing ethanol according to any one of [1] to

[11] , wherein the fermentation is a parallel simultaneous saccharification and fermentation.

[0033]

[13] A system for producing ethanol from a lignocellulosic raw material, comprising:

[0034] A reaction tank, wherein saccharification and fermentation are performed in a reaction system containing a lignocellulosic raw material, a saccharifying enzyme, yeast, and water to produce ethanol; and

[0035] a membrane separation device comprising a separation membrane for separating the first mixture containing ethanol, water, yeast, saccharifying enzyme, and lignocellulosic raw material reaction residue obtained in the reaction tank into a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water, and lignocellulosic raw material reaction residue;

[0036] The solid content concentration of the first mixture is 4 to 9.5% by mass.

[0037]

[14] The system for producing ethanol according to

[13] , comprising:

[0038] In the first step, saccharification and fermentation are performed in a reaction system containing a lignocellulosic raw material, a saccharifying enzyme, yeast, and water to produce ethanol; and

[0039] In the second step, the first mixture containing ethanol, water, yeast, saccharifying enzyme and lignocellulosic raw material reaction residue obtained in the above-mentioned first step is treated using a separation membrane to obtain a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water and lignocellulosic raw material reaction residue.

[0040]

[15] The system for producing ethanol according to

[13] or

[14] , further comprising a third step of supplying at least a portion of the second mixture to the reaction tank.

[0041]

[16] The system for producing ethanol according to any one of

[13] to

[15] , further comprising a concentrating device for concentrating the mixture containing ethanol and water obtained in the membrane separation device.

[0042] According to the present invention, saccharification and fermentation are performed in a reaction system containing a lignocellulosic feedstock, a saccharifying enzyme, yeast, and water, and the resulting first mixture containing ethanol, water, yeast, saccharifying enzyme, and a lignocellulosic feedstock reaction residue has a solids concentration within a predetermined range, thereby increasing the permeate flux through the separation membrane in the solid-liquid separation step. The present invention is advantageous in that increasing the permeate flux through the separation membrane increases the enzyme ratio on the retentate side of the second mixture containing yeast, saccharifying enzyme, water, and a lignocellulosic feedstock reaction residue, thereby improving enzyme recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a diagram showing a schematic configuration of an ethanol production apparatus according to the system of the present invention. DETAILED DESCRIPTION

[0044] A feature of the method of producing ethanol from a lignocellulosic raw material of the present invention is that it comprises: a first step of carrying out saccharification and fermentation in a reaction system containing a lignocellulosic raw material, a saccharifying enzyme, yeast, and water to produce ethanol; and a second step of treating a first mixture containing ethanol, water, yeast, a saccharifying enzyme, and a residue from the reaction of the lignocellulosic raw material obtained in the first step using a separation membrane to obtain a mixture containing ethanol and water and a second mixture containing yeast, a saccharifying enzyme, water, and a residue from the reaction of the lignocellulosic raw material; the solid content concentration of the first mixture is 4 to 9.5% by mass.

[0045] According to one embodiment of the present invention, the method further includes a third step of supplying at least a portion of the second mixture to the reaction system.

[0046] According to a preferred embodiment of the present invention, the first step, the second step, and the third step are repeated.

[0047] Hereinafter, each step will be described in detail.

[0048] (First process)

[0049] The first step involves saccharification and fermentation in a reaction system containing a lignocellulosic feedstock, a saccharifying enzyme, yeast, and water to produce ethanol. This step produces a first mixture containing ethanol, water, yeast, saccharifying enzyme, and the residue from the lignocellulosic feedstock reaction. Alternatively, this first mixture may be an aqueous ethanol solution containing yeast, saccharifying enzyme, and the residue from the lignocellulosic feedstock reaction.

[0050] In the first step, through the saccharification and fermentation in the above-mentioned reaction system, the lignocellulose raw material is saccharified by saccharifying enzyme (enzyme saccharification reaction), and the generated sugars are converted into ethanol (ethanol fermentation) by yeast-based fermentation. In the above-mentioned reaction system, part or all of the saccharification process can be carried out simultaneously with the fermentation process. Therefore, as the first process, a semi-synchronous saccharification and fermentation process and a parallel synchronous saccharification and fermentation process can be mentioned, preferably a parallel synchronous saccharification and fermentation process. Here, in the semi-synchronous saccharification and fermentation, after a saccharification reaction (saccharification process) is carried out using a lignocellulose raw material and a saccharifying enzyme in a reaction tank, yeast is added to the same reaction tank, and an enzymatic saccharification reaction and ethanol fermentation (saccharification and fermentation process) are carried out simultaneously. In the parallel synchronous saccharification and fermentation, yeast is made to coexist with the above-mentioned saccharifying enzyme, and an enzymatic saccharification reaction and ethanol fermentation (saccharification and fermentation process) are carried out simultaneously.

[0051] According to one embodiment of the present invention, in a parallel simultaneous saccharification and fermentation process, a lignocellulosic feedstock, a saccharifying enzyme, and yeast are first supplied to a reaction tank. In the present invention, the lignocellulosic feedstock, saccharifying enzyme, and yeast may be premixed and supplied to the reaction tank, or they may be supplied separately. Preferably, the saccharifying enzyme and yeast are added to the lignocellulosic feedstock pre-supplied to the reaction tank. The lignocellulosic feedstock is saccharified by the saccharifying enzyme, and the resulting sugars are converted into ethanol through fermentation by the yeast.

[0052] (Lignocellulose-based raw materials)

[0053] The lignocellulosic raw material is a raw material containing pulp or lignocellulose other than pulp. The lignocellulosic raw material may be used alone or in combination of two or more.

[0054] Examples of pulp include wood pulp obtained from conifers, broadleaf trees, forest residues, construction waste, and the like; non-wood pulp such as cotton linters, cotton linters, hemp, wheat straw, and bagasse; wastepaper pulp and deinked pulp derived from wastepaper. Pulp production methods that achieve a high degree of lignin removal, such as chemical pulping methods such as alkali extraction and alkaline cooking, are preferred. Among pulps produced by chemical pulping methods, papermaking pulp is preferred due to its availability. Examples of pulp for papermaking include hardwood kraft pulp (e.g., bleached kraft pulp (LBKP), unbleached kraft pulp (LUKP), and oxygen-bleached kraft pulp (LOKP)), softwood kraft pulp (e.g., bleached kraft pulp (NBKP), unbleached kraft pulp (NUKP), and oxygen-bleached kraft pulp (NOKP)), chemical pulps such as sulfite pulp (SP) and soda pulp (AP), and semi-chemical pulps such as semi-chemical pulp (SCP) and chemical groundwood pulp (CGP). Pulps are preferably hardwood kraft pulp, softwood kraft pulp, sulfite pulp, and semi-chemical pulp; more preferably, hardwood kraft pulp and softwood kraft pulp; and even more preferably, hardwood bleached kraft pulp (LBKP).

[0055] Examples of lignocellulosic raw materials other than pulp include woody materials such as papermaking trees, forest residues, thinning materials, bark, shoots from woody plant stumps, sawdust or sawdust from sawmills, pruned branches and leaves of street trees, and construction waste. Examples of the lignocellulosic raw materials of these woody materials include plants of the genera Eucalyptus, Salix, Poplar, Acacia, and Cryptomeria. As herbaceous materials, agricultural wastes such as kenaf, rice stalks, wheat straw, corn cobs, and bagasse, residues and wastes of industrial crops such as oil crops and rubber (for example, EFB: Empty Fruit Bunch, OPT: Oil Palm Trunk, OPF: Oil Palm Frond, MCF: Meso Cap Fiber), and herbaceous energy crops such as Erianthus, Miscanthus, and Napiergrass can be cited. In addition, lignocellulosic raw materials other than pulp can be biomass. As biomass, paper from wood, waste paper, pulp sludge, and the like can be cited. These biomasses can be used alone or in combination. In addition, the biomass can be a dry solid, a solid containing water, or a slurry.

[0056] According to one embodiment of the present invention, the concentration of the lignocellulosic raw material at the start of the reaction of the first mixture (fermentation liquid) in the reaction tank in the parallel synchronous saccharification and fermentation process is preferably 5 to 30 mass / volume%, and more preferably 10 to 20 mass / volume%. It is advantageous to make the concentration of the lignocellulosic raw material 5 mass / volume% or more in order to avoid the problem that the concentration of the final product is too low and the cost of ethanol concentration becomes high. In addition, it is advantageous to make the concentration of the lignocellulosic raw material 30 mass / volume% or less in order to avoid the problem that the stirring of the raw material becomes difficult and the productivity decreases as the concentration is high. According to another embodiment of the present invention, the concentration of the lignocellulosic raw material at the start of the reaction of the saccharification process in the semi-synchronous saccharification and fermentation process is the same as described above.

[0057] (glucoamylase)

[0058] The saccharifying enzyme is not particularly limited as long as it is a cellulolytic or hemicellulolytic enzyme. Examples of the cellulolytic enzyme include enzymes collectively referred to as cellulases, which have cellobiohydrolase activity, endoglucanase activity, β-glucosidase activity, and the like. Each cellulolytic enzyme can be added in an appropriate amount as an enzyme having its own activity. Commercially available cellulolytic enzyme agents often have the various cellulase activities described above and also hemicellulase activity, so commercially available cellulolytic enzyme agents can be used.

[0059] Commercially available cellulolytic enzymes include those derived from the genera Trichoderma, Acremonium, Aspergillus, Phanerochaete, Trametes, Humicola, Bacillus, and Irpex. Examples of commercially available cellulolytic enzymes include, for example, Cell Leucine AL8 (manufactured by HPI), Cellic CTec2 (manufactured by Novozymes), Cellulase Y-NC (manufactured by Yakult Pharmaceutical Industry Co., Ltd.), and Meicelase (manufactured by Meiji Seika Pharma Co., Ltd.).

[0060] The saccharifying enzymes used may be used alone or in combination, taking into consideration the properties of the cellulolytic enzyme agent and the like.

[0061] The activity of the saccharifying enzyme in the present invention is defined as follows.

[0062] To 8 mL of an aqueous solution (pH 4.8) containing 1.5 mL of 1 M acetic acid buffer, 375 μL of an enzyme solution and 0.5 g of a total of 10 mL of bleached kraft pulp (LBKP) were added to the system and reacted at 33 ° C for 4 hours, and then heated at 95 ° C for 10 minutes to stop the reaction. It was analyzed using a differential refractive index (RI) detector using high performance liquid chromatography (HPLC) (Prominence, manufactured by Shimadzu Corporation) to measure the glucose concentration. Based on the measurement results, the amount of enzyme protein that produces 1 μmol of glucose in 1 minute was taken as 1 unit (U).

[0063] The measurement conditions of HPLC are as follows.

[0064] Column: 80Shodex SUGAR SP0810 (manufactured by Showa Denko Co., Ltd.)

[0065] Mobile phase: ultrapure water

[0066] Flow rate: 0.8 mL / min

[0067] Temperature: 80℃

[0068] According to one embodiment of the present invention, the amount of saccharifying enzyme added to the fermentation liquid in the reaction tank is not particularly limited, but is preferably 50 to 500 U / L, more preferably 100 to 300 U / L.

[0069] According to one embodiment of the present invention, the ratio of the amount of saccharifying enzyme added to the fermentation liquid in the reaction tank in the parallel synchronous saccharification and fermentation process to the lignocellulosic raw material (initial content of saccharifying enzyme (U) / initial content of lignocellulosic raw material (kg)) is preferably 500 to 5000 U / kg, and more preferably 1000 to 3000 U / kg. According to another embodiment of the present invention, the ratio of the amount of saccharifying enzyme added to the fermentation liquid in the reaction tank in the saccharification and fermentation process of the semi-synchronous saccharification and fermentation process to the lignocellulosic raw material is the same as described above.

[0070] (yeast)

[0071] Yeast is not particularly limited, but is preferably capable of fermenting sugars (hexose, pentose). Specifically, yeasts include yeasts of the genus Saccharomyces such as Saccharomyces cerevisiae, Scheffersomyces stipitis (formerly known as Pichia stipitis), Candida shihatae, and Pachysolen tannophilus, and are preferably yeasts belonging to the genus Saccharomyces, more preferably Saccharomyces cerevisiae. In addition, yeasts produced using genetic recombination technology can also be used. As yeasts produced using genetic recombination technology, yeasts capable of fermenting hexose and pentose simultaneously can be used without particular limitation. Preferred yeast produced using genetic recombination technology includes yeast with enhanced ability to produce ethanol from xylose. More preferred are yeasts into which genes encoding xylose reductase, xylulose phosphorylase, xylitol dehydrogenase, transaldolase, transketolase, and alcohol dehydrogenase have been introduced in an expressible manner. Even more preferred are yeasts described in International Publication No. 2016 / 060171. These genes may be endogenous genes of the yeast.

[0072] According to one embodiment of the present invention, the pH of the fermentation liquid in the reaction tank in the parallel fermentation step is not particularly limited, but is preferably maintained in the range of 3 to 10, more preferably in the range of 4 to 8. According to another embodiment of the present invention, the pH of the fermentation liquid in the reaction tank in the saccharification and fermentation step of the semi-synchronous saccharification and fermentation step is the same as described above.

[0073] According to one embodiment of the present invention, the temperature of the fermentation liquid in the reaction tank in the parallel simultaneous saccharification and fermentation step is not particularly limited as long as it is within the optimal temperature range of the saccharifying enzyme and / or yeast, and is preferably 20 to 40° C., more preferably 30 to 40° C. According to another embodiment of the present invention, the temperature of the fermentation liquid in the reaction tank in the saccharification and fermentation step of the semi-simultaneous saccharification and fermentation step is the same as described above.

[0074] According to one embodiment of the present invention, the number of cells in the reaction tank in the parallel simultaneous saccharification and fermentation process is not particularly limited, but is preferably 10 7 cells / mL or more, more preferably 10 8 cells / mL or more. In addition, the preferred range of bacterial cell count is 10 7 ~10 9 cells / mL, and the more preferred range of bacterial cell count is 10 8 ~10 9 According to another embodiment of the present invention, the number of bacterial cells in the reaction tank in the saccharification and fermentation step of the semi-synchronous saccharification and fermentation step is the same as described above.

[0075] According to one embodiment of the present invention, the number of inoculations into the reaction tank in the parallel simultaneous saccharification and fermentation step is not particularly limited, but is preferably 10 6 cells / mL or more, more preferably 10 7 cells / mL or more. In addition, the preferred range of bacterial cell count is 10 6 ~10 8 cells / mL, and the more preferred range of bacterial cell count is 10 7 ~10 8 According to another embodiment of the present invention, the number of inoculations in the reaction tank in the saccharification and fermentation step of the semi-synchronous saccharification and fermentation step is the same as described above.

[0076] The solid content (suspended solid: hereinafter also referred to as SS) of the first mixture (fermentation liquid) in the first step (preferably the parallel simultaneous saccharification and fermentation step) of the present invention refers to the solid content present in the fermentation liquid, and includes yeast, saccharification enzyme, and lignocellulosic raw material reaction residue.

[0077] The lignocellulosic raw material reaction residue in the first mixture may contain, for example, wood.

[0078] In addition, in addition to ethanol, water, yeast, saccharifying enzyme and lignocellulosic raw material reaction residue, the first mixture may further contain unreacted raw materials, glucose, xylose, mannose, etc. When they are solid in the first mixture (fermentation liquid), they are included in the solid component of the above-mentioned first mixture.

[0079] In addition, the method of measuring the solid content concentration is not particularly limited, and for example, it can be measured using an integrating sphere turbidimeter "PT-200" manufactured by Nittoseiko Analytech Co., Ltd.

[0080] The solid content concentration of the first mixture (fermentation broth) is not particularly limited. From the perspective of increasing the permeation flux of the separation membrane in the solid-liquid separation step, it can be in the range of 4 to 9.5% by mass, preferably 5 to 9.5% by mass, more preferably 5.5 to 9.5% by mass, even more preferably 6.5 to 9.5% by mass, and even more preferably 7 to 9% by mass. The method for adjusting this concentration is not particularly limited, and for example, it can be achieved by repeating the first, second, and third steps described above.

[0081] The parallel simultaneous saccharification and fermentation process is preferably continuous, but may also be semi-batch or batch. Continuous refers to, for example, a method in which the raw material supply and ethanol production are continuous.

[0082] In the parallel synchronous saccharification and fermentation process, it is preferably regulated in a manner that the concentration of the lignocellulose raw material of the fermentation liquid is maintained within a prescribed range. As the above-mentioned prescribed range, 5 to 30 mass / volume % can be cited, preferably 10 to 20 mass / volume %. The above-mentioned regulation can be carried out, for example, by supplying lignocellulose raw material to the reaction tank. As shown below, in the solid-liquid separation process, when the second mixture (solid content concentrated fermentation liquid) after the separation of the mixture containing ethanol and water is recovered and transferred to the reaction tank, it is preferred that the supply rate of the total of the solid content concentrated fermentation liquid and the lignocellulose raw material to the reaction tank is the same as the discharge rate of the fermentation liquid from the reaction tank.

[0083] According to one embodiment of the present invention, in the parallel synchronous saccharification and fermentation process, it is preferred to adjust the concentration of the saccharifying enzyme in the fermentation liquid in a manner that is maintained within a prescribed range. As the above-mentioned prescribed range, 50 to 500 U / L can be cited, preferably 100 to 300 U / L. The above-mentioned adjustment can be carried out, for example, by supplying saccharifying enzyme to the reaction tank. Furthermore, in the solid-liquid separation process, the recovered saccharifying enzyme can also be supplied by recovering the second mixture (solid content concentrated fermentation liquid) after separation of the mixture containing ethanol and water and transferring it to the reaction tank.

[0084] (Second process)

[0085] The second step is a solid-liquid separation step in which the first mixture containing ethanol, water, yeast, saccharifying enzyme and reaction residue of lignocellulosic raw materials obtained in the first step is treated using a separation membrane to obtain a mixture containing ethanol and water (e.g., a mixture of ethanol and water, an ethanol-water solution, etc.) and a second mixture containing yeast, saccharifying enzyme, water and reaction residue of lignocellulosic raw materials.

[0086] According to a preferred embodiment of the present invention, the second step is the following step: taking out a first mixture containing ethanol, water, yeast, saccharifying enzyme and lignocellulosic raw material reaction residue from the reaction system, separating a mixture containing ethanol and water from the first mixture using a separation membrane, and recovering the second mixture containing yeast, saccharifying enzyme, water and lignocellulosic raw material reaction residue together with the mixture containing ethanol and water.

[0087] The second mixture may be the remainder obtained by removing the mixture containing ethanol and water from the first mixture. The second mixture may further contain unreacted raw materials, glucose, xylose, ethanol, etc. in addition to yeast, saccharifying enzyme, water, and lignocellulosic raw material reaction residue.

[0088] More specifically, the fermentation liquid (first mixture) discharged from the reaction tank in the second step can be separated by a membrane separation device into a solid-content concentrated fermentation liquid (second mixture) and a mixture containing ethanol and water, for example, a solid-content concentrated fermentation liquid (second mixture) and an ethanol-water solution. The resulting mixture containing ethanol and water can be further distilled or concentrated using various separation membranes, such as a zeolite membrane, to produce high-purity ethanol.

[0089] (Separation membrane)

[0090] The separation membrane used in the second step is not particularly limited as long as it can pass through ethanol and can block enzymes. An organic membrane is preferred. Specifically, polyethylene (PE), polysulfone (PS), polypropylene (PP), polyolefin (PO), polyethersulfone (PES), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), regenerated cellulose (RC), cellulose acetate (CA), tetrafluoroethylene (PTEF), sulfonated polysulfone (P-PS), sulfonated polyethersulfone (P-PES), polyvinyl alcohol (PVAL), polymethyl methacrylate (PMMA), cellulose ester and other materials can be used, and polysulfone is more preferred.

[0091] According to a preferred embodiment of the present invention, the separation membrane used in the second step can include an ultrafiltration membrane (UF membrane) and a nanofiltration membrane (NF membrane), and is more preferably an ultrafiltration membrane. The molecular weight cutoff of the separation membrane is preferably in the range of 10,000 Da (Dalton) to 1,000,000 Da, and more preferably in the range of 20,000 Da to 500,000 Da. According to another preferred embodiment of the present invention, the molecular weight cutoff of the separation membrane is preferably in the range of 0.001 micrometer (μm) to 0.5 micrometer, and more preferably in the range of 0.005 micrometer to 0.1 micrometer. In addition, the separation membrane can be a membrane separation device comprising the separation membrane.

[0092] According to one embodiment of the present invention, the separation membrane used in the second step may have a tubular membrane, a hollow fiber membrane, a flat membrane, a spiral membrane, or the like, and is preferably a tubular membrane.

[0093] According to one embodiment of the present invention, the transmembrane pressure difference (the difference between the pressure at the membrane inlet and the pressure at the membrane outlet on the non-permeate side) of the separation membrane used in the second step can be appropriately set according to the type of separation membrane and is not particularly limited, but is preferably in the range of 0.001 to 1.0 MPa.

[0094] According to one embodiment of the present invention, the membrane surface linear velocity (flow rate / membrane area) of the separation membrane (preferably a separation membrane module) used in the second step is not particularly limited, but is preferably in the range of 0.01 to 5.0 m / s.

[0095] According to a preferred embodiment of the present invention, the permeation flux of the separation membrane can be increased by setting the solid content concentration of the first mixture within a specified range. Here, the permeation flux refers to the amount of permeate permeated per unit membrane area per unit time. By increasing the permeation flux of the separation membrane, the enzyme ratio on the second mixture side (non-permeate side) containing yeast, saccharifying enzyme and lignocellulose-based raw material reaction residue can be increased, which is beneficial in improving the recovery rate of the enzyme. For example, in the case of a high permeation flux, the enzyme ratio of the first mixture (fermentation liquid) is 20%, and the flow rate on the inlet side (first mixture side) of the separation membrane is 100m 3 / h, and the flow rate of the permeate (containing a mixture of ethanol and water) on the separation membrane side is 50m 3 / h, and the flow rate of the non-permeate liquid (second mixture; solid content concentrated fermentation liquid) side is 50m 3 / h, the enzyme ratio in the permeate is 0%, and the enzyme ratio in the non-permeate is 40%. On the other hand, when the permeate flow rate is low, the enzyme ratio of the first mixture is 20%, and the flow rate at the inlet side of the separation membrane is 100m 3 / h, the flow rate of the permeate through the separation membrane is 10m 3 / h, the flow rate of non-permeable liquid is 90m 3 / h, at this time the enzyme ratio in the permeate is 0%, so the enzyme ratio in the non-permeate is 22%.

[0096] According to a preferred embodiment of the present invention, the permeation flow rate of the separation membrane can be, for example, 33 L / (m 2 ·h) or more, preferably 40L / (m 2 ·h) or more, more preferably 45L / (m 2 ·h) or more, more preferably 50L / (m 2 The permeation flow rate of the separation membrane is not particularly limited as long as the effect of the present invention is achieved, and is, for example, 100 L / (m 2 According to another preferred embodiment of the present invention, the permeation flow rate of the separation membrane of the present invention is, for example, 33 to 100 L / (m 2 h), preferably 40 to 90 L / (m 2 ·h), more preferably 50 to 80 L / (m 2 ·h).

[0097] (Third Process)

[0098] The third step is a step of supplying at least a portion of the second mixture to the reaction system. That is, the third step can also be said to be a step of transferring part or all of the solid content concentrated fermentation liquid (second mixture) separated from the fermentation liquid (first mixture) to the reaction tank.

[0099] According to one embodiment of the present invention, the reaction system for supplying the second mixture may be the reaction system of the saccharification and fermentation step in parallel synchronous saccharification and fermentation, and may be either the reaction system of the saccharification and fermentation step in semi-synchronous saccharification and fermentation. According to another embodiment of the present invention, the reaction tank for supplying the second mixture may be the reaction tank for performing the saccharification and fermentation step in parallel synchronous saccharification and fermentation, and may be either the reaction tank for performing the saccharification and fermentation step in semi-synchronous saccharification and fermentation.

[0100] (Ethanol Concentration Process)

[0101] According to one embodiment of the present invention, the mixture containing ethanol and water obtained in the second step can be further concentrated by distillation or rectification, or using various separation membranes, such as zeolite membranes, to produce high-purity ethanol. Alternatively, the mixture containing ethanol and water can be transferred to a reaction tank after the ethanol is removed.

[0102] According to one embodiment of the present invention, hydrous ethanol concentrated by distillation, rectification, or various separation membranes can be dehydrated. Examples of such dehydration procedures include water adsorption using a water adsorbent and azeotropic methods using a third solvent other than water and ethanol. The dehydration procedure removes water from the hydrous ethanol to produce anhydrous ethanol. The anhydrous ethanol is recovered and the removed water is drained.

[0103] The ethanol production method of the present invention can efficiently produce ethanol from lignocellulosic raw materials. The ethanol obtained by the above-mentioned ethanol production method can be used as fuel ethanol, industrial ethanol, food additive ethanol, etc.

[0104] According to another aspect of the present invention, a system for producing ethanol from a lignocellulosic feedstock is provided. One feature of the ethanol production system of the present invention is that it comprises: a reaction tank for performing saccharification and fermentation in a reaction system containing a lignocellulosic feedstock, a saccharifying enzyme, yeast, and water to produce ethanol; and a membrane separation device comprising a separation membrane for separating a first mixture containing ethanol, water, yeast, saccharifying enzyme, and a lignocellulosic feedstock reaction residue obtained in the reaction tank into a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water, and the lignocellulosic feedstock reaction residue; the first mixture having a solids concentration of 4 to 9.5% by mass.

[0105] According to one embodiment of the present invention, the ethanol production system of the present invention preferably further comprises a concentrator for concentrating the mixture containing ethanol and water obtained in the membrane separation device.

[0106] Figure 1 This diagram schematically illustrates the configuration of an ethanol production apparatus according to the ethanol production system of the present invention. To facilitate understanding of the features of the present invention, the following diagrams may be enlarged for convenience, and the dimensions and ratios of the various components may not necessarily correspond to the actual dimensions. Furthermore, only the essential components are shown; the diagrams do not illustrate equipment for supplying lignocellulosic raw materials, yeast, and other components upstream of the reaction tank, pretreatment equipment, the reaction tank, analyzers in the membrane separation unit, and dehydration equipment downstream of the concentration unit.

[0107] In the production apparatus 10 of the present invention, a reaction tank 11 and a membrane separation device 13 are interconnected via a pipe 12. The first mixture obtained in the reaction tank 11 is transferred to the membrane separation device 13 via the pipe 12. Furthermore, the mixture containing ethanol and water separated by the separation membrane in the membrane separation device 13 is transferred to a concentrator 16 via a pipe 14, and the second mixture separated by the separation membrane in the membrane separation device 13 is transferred to the reaction tank 11 via a pipe 15. A pretreatment device or the like may be provided before the reaction tank 11. Furthermore, the equipment following the membrane separation device 13 can be appropriately selected depending on the intended use of the fermentation broth. For example, a concentrator 16 for performing distillation treatment may be provided.

[0108] According to a preferred embodiment of the present invention, the ethanol production system of the present invention includes: a first step of carrying out saccharification and fermentation in a reaction system containing a lignocellulosic raw material, a saccharifying enzyme, yeast and water to produce ethanol; and a second step of using a separation membrane to treat a first mixture containing ethanol, water, yeast, saccharifying enzyme and a reaction residue of the lignocellulosic raw material obtained in the above-mentioned first step to obtain a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water and a reaction residue of the lignocellulosic raw material; preferably including a third step of supplying at least a portion of the above-mentioned second mixture to the above-mentioned reaction tank.

[0109] Therefore, according to a preferred embodiment of the present invention, in the ethanol production system of the present invention, saccharification and fermentation are carried out in a reaction system containing a lignocellulosic feedstock, a saccharifying enzyme, yeast, and water in a reaction tank 11, thereby producing a first mixture containing ethanol, water, yeast, saccharifying enzyme, and a residue from the lignocellulosic feedstock reaction. The resulting first mixture is transferred to a membrane separation device 13 including a separation membrane and treated using the separation membrane to produce a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water, and a residue from the lignocellulosic feedstock reaction. The resulting mixture containing ethanol and water can be transferred to a concentrator 16 for concentration. Alternatively, at least a portion of the second mixture separated from the first mixture can be transferred to the reaction tank 11. For example, by repeating the above steps of obtaining the first mixture in the reaction tank 11, separating the ethanol and water mixture from the second mixture in the membrane separation device 13 including a separation membrane, and transferring at least a portion of the second mixture to the reaction tank 11, the solids concentration of the first mixture can be adjusted to 4 to 9.5% by mass.

[0110] According to another embodiment of the present invention, the ethanol production system of the present invention is preferably used in a continuous manner.

[0111] The embodiment of the ethanol production system can be implemented according to the description related to the method for producing ethanol of the present invention.

[0112] Example

[0113] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. In addition, unless otherwise specified, the units and measurement methods described in this specification are based on Japanese Industrial Standards (JIS).

[0114] Determination of SS concentration

[0115] The SS concentration in the first mixture (evaluation solution) in the examples was measured using an integrating sphere turbidimeter (PT-200, 10 mm cell, Nittoseiko Analytech Co., Ltd.).

[0116] Method for measuring bacterial count

[0117] The bacterial count of the yeast Saccharomyces cerevisiae used in the Examples was observed and measured using a Thoma blood cell counter under an optical microscope (magnification: 400 times).

[0118] Method for measuring permeation flow rate

[0119] The permeation flow rate in the examples was calculated from the permeation rate per unit time and the membrane area by measuring the amount of liquid received in a container.

[0120] Example 1: Study on the relationship between SS concentration and permeation flow rate

[0121] In order to operate the membrane separation system with a constant ethanol permeation rate (production rate), it is necessary to know the relationship between SS concentration and permeation flow rate. In the examples, evaluation solutions with multiple SS concentrations were prepared, passed through the membrane, and the permeation flow rate was measured.

[0122] (1) Pulp (bleached kraft pulp (LBKP)) 5 mass / vol% (based on dry weight), saccharifying enzyme 19771U, urea 0.22 mass / vol%, CSL (corn steep liquor) 1 mass / vol% and antibacterial agent 10 ppm were added to a 150 L culture tank (reaction tank) to a final concentration of 1.0 × 10 7Yeast Saccharomyces cerevisiae was inoculated at an amount of cells / mL. The liquid volume was adjusted with sterile water so that the reaction weight was 142.5 kg. Then, the reaction was controlled at 33°C, a stirring speed of 72 rpm, and a pH of 4.8 (controlled by sodium hydroxide and sulfuric acid) so that it remained constant for 24 hours. After 24 hours of reaction, pulp was added in an amount of 10 mass / volume% (equivalent to 7.5 kg on a dry weight basis) to a total of 150 kg. The reaction was continued for another 24 hours, and the SS concentration in the evaluation liquid was measured. (2) After the reaction was completed, the mixture was allowed to stand for 72 to 96 hours and solid-liquid separation was performed in a culture tank. (3) 75 L of the supernatant was discarded, and the remaining evaluation liquid was added with 5 mass / volume% of pulp (on a dry weight basis), saccharifying enzyme 9885U, urea 0.11 mass / volume%, CSL 0.5 mass / volume%, and antibacterial agent 5 ppm as additional evaluation liquid. The total amount was made into 150 kg with sterile water, and the reaction was continued for another 24 hours. The SS concentration in the evaluation liquid was measured. The above steps (2) and (3) were repeated to prepare eight evaluation solutions having SS concentrations of 1, 6, 7, 8, 9, 10, 11, and 12 mass %, and each solution was used for membrane evaluation.

[0123] The preparation conditions of the evaluation solution are shown below.

[0124] [Table 1]

[0125] project value Temperature, °C 33 Stirring speed, rpm 72 pH 4.8 Evaluation liquid volume, L 150 Response time, hours 48

[0126] The composition of the evaluation liquid is shown below.

[0127] [Table 2]

[0128] project value Pulp, mass / volume % (on dry weight basis) 10 Glucoamylase addition amount, U 19771 Urea, mass / volume % 0.22 CSL (corn steep liquor), mass / volume % 1 Antimicrobial agent, ppm 10

[0129] Calculation of permeation flow rate at various SS concentrations

[0130] In the membrane evaluation, a membrane module (TU-30100-P18A, UF membrane, made of polysulfone, tubular membrane with a molecular weight cutoff of 100,000 Da, manufactured by DAICEN MEMBRANE-SYSTEMS Ltd.) was connected to a 150 L culture tank. Under the conditions of a differential pressure across the module membranes of 0.4 MPa and a linear velocity across the membrane surface of 2.0 m / s, a mixture containing ethanol and water (permeate) and a solids-enriched fermentation liquid (non-permeate) were returned to the 150 L culture tank while the liquids were circulated. The permeate flow rate (L / (m 2 h)), the permeation flow rate value at which the temporal change in the permeation flow rate disappears is measured.

[0131] Table 3 shows the calculation results of the permeation flow rate at each SS concentration.

[0132] [Table 3]

[0133]

[0134] According to Table 3, an increase in the permeation flow rate was observed when the SS concentration exceeded 1% by mass and was less than 10% by mass. Furthermore, the permeation flow rate reached its maximum value when the SS concentration was between 7% and 9% by mass.

[0135] Explanation of symbols

[0136] 10 Manufacturing equipment

[0137] 11 reaction tank

[0138] 12, 14, 15 piping

[0139] 13 Membrane separation device

[0140] 16 Concentration device

Claims

1. A method for producing ethanol from a lignocellulosic raw material, comprising: In the first step, saccharification and fermentation are carried out in a reaction system containing lignocellulosic raw materials, saccharifying enzymes, yeast, and water to produce ethanol; as well as In a second step, the first mixture containing ethanol, water, yeast, saccharifying enzyme, and the lignocellulosic raw material reaction residue obtained in the first step is treated using a separation membrane to obtain a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water, and the lignocellulosic raw material reaction residue; The solid content concentration of the first mixture is 4 to 9.5% by mass.

2. The method for producing ethanol according to claim 1, wherein: The method further includes a third step of supplying at least a portion of the second mixture to the reaction system.

3. The method for producing ethanol according to claim 2, wherein: The first step, the second step, and the third step are repeated.

4. The method for producing ethanol according to any one of claims 1 to 3, wherein The separation membrane is an organic membrane.

5. The method for producing ethanol according to any one of claims 1 to 4, wherein The separation membrane is an ultrafiltration membrane.

6. The method for producing ethanol according to any one of claims 1 to 5, wherein The separation membrane is an organic membrane and an ultrafiltration membrane.

7. The method for producing ethanol according to any one of claims 1 to 6, wherein The solid content concentration of the first mixture is 5 to 9.5% by mass.

8. The method for producing ethanol according to any one of claims 1 to 7, wherein The solid content concentration of the first mixture is 5.5 to 9.5% by mass.

9. The method for producing ethanol according to any one of claims 1 to 8, wherein The solid content concentration of the first mixture is 6.5 to 9.5% by mass.

10. The method for producing ethanol according to any one of claims 1 to 9, wherein The solid content concentration of the first mixture is 7 to 9% by mass.

11. A system for producing ethanol from a lignocellulosic raw material, comprising: A reaction tank, wherein saccharification and fermentation are performed in a reaction system containing a lignocellulosic raw material, a saccharifying enzyme, yeast, and water to produce ethanol; and a membrane separation device comprising a separation membrane for separating a first mixture containing ethanol, water, yeast, saccharifying enzyme, and a lignocellulosic raw material reaction residue obtained in the reaction tank into a mixture containing ethanol and water and a second mixture containing yeast, saccharifying enzyme, water, and a lignocellulosic raw material reaction residue; The solid content concentration of the first mixture is 4 to 9.5% by mass.

12. The system for producing ethanol according to claim 11, wherein: include: In the first step, saccharification and fermentation are carried out in a reaction system containing lignocellulosic raw materials, saccharifying enzymes, yeast, and water to produce ethanol; as well as In the second step, the first mixture containing ethanol, water, yeast, saccharifying enzyme and lignocellulosic raw material reaction residue obtained in the first step is treated using a separation membrane to obtain a mixture containing ethanol and water, and a second mixture containing yeast, saccharifying enzyme, water and lignocellulosic raw material reaction residue.

13. The system for producing ethanol according to claim 11 or 12, wherein: The method includes a third step of supplying at least a portion of the second mixture to the reaction tank.

14. The system for producing ethanol according to any one of claims 11 to 13, wherein: The present invention further comprises a concentrating device for concentrating the mixture containing ethanol and water obtained in the membrane separation device.

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