Ethanol production method

Abstract

To provide a method for producing ethanol, which is capable of efficiently obtaining ethanol from a cellulosic raw material.SOLUTION: A method for producing ethanol comprises: a first step of supplying a cellulosic raw material to a reaction system containing saccharifying enzymes, yeast, and water to saccharify and ferment the cellulosic raw material to produce ethanol; a second step of removing a first mixture containing ethanol from the reaction system and reaction residue separating the ethanol from the first mixture to collect a second mixture containing a reaction residue; a third step of supplying at least a part of the second mixture to the reaction system; and a forth step of treating at least a part of the second mixture with a screw decanter type centrifuge to obtain a third mixture having a lower solid content concentration than the second mixture, followed by supplying the third mixture to the reaction system.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing ethanol. [Background technology]

[0002] In recent years, as part of measures to combat global warming, attempts have been widely made to produce ethanol from cellulosic raw materials such as biomass and use it as various fuels and chemical raw materials. Ethanol production from cellulosic raw materials is carried out, for example, by a process of decomposing the cellulosic raw materials into sugars such as monosaccharides and oligosaccharides, and a process of fermenting the sugars using microorganisms.

[0003] For example, Patent Document 1 discloses a method for continuous saccharification of lignocellulose, which includes recovering unreacted lignocellulose material and saccharification enzymes from a continuous reaction solution, using lignocellulose material from which lignin has been removed as a substrate, and maintaining the ratio of the total substrate mass to the amount of saccharification enzymes in the dispersion solution supplied to a continuous saccharification reaction tank at a rate such that at least 96% by mass of the total substrate is saccharified within the residence time, thereby preventing the accumulation of unreacted lignocellulose and allowing for continuous saccharification reactions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-087319 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a method for producing ethanol that can efficiently obtain ethanol from cellulosic raw materials. [Means for solving the problem]

[0006] One aspect of the present invention relates to a method for producing ethanol, comprising: a first step of supplying a cellulosic raw material to a reaction system containing a saccharifying enzyme, yeast, and water, and producing ethanol by saccharification and fermentation of the cellulosic raw material; a second step of removing a first mixture containing ethanol and a reaction residue from the reaction system, separating the ethanol from the first mixture, and recovering a second mixture containing the reaction residue; a third step of supplying at least a portion of the second mixture to the reaction system; and a fourth step of treating at least a portion of the second mixture in a screw decanter centrifuge to obtain a third mixture having a lower solids concentration than the second mixture, and supplying the third mixture to the reaction system.

[0007] According to the above production method, by removing a portion of the reaction residue in the fourth step, accumulation of the reaction residue in the reaction system can be suppressed. Furthermore, in the above production method, the reaction residue is treated using a screw decanter centrifuge in the fourth step. Since a screw decanter centrifuge tends to selectively remove large particle size solids, it is possible to remove the large particle size solids while leaving the small particle size solids in the third mixture. Therefore, the above production method makes it possible to reuse the yeast present in the reaction residue and the saccharifying enzyme adsorbed to the small particle size solids, which is expected to improve ethanol production efficiency and the use efficiency of the yeast and saccharifying enzyme. For these reasons, the above production method can efficiently obtain ethanol while suppressing accumulation of the reaction residue and increasing the continuity of the reaction.

[0008] In one embodiment, the reaction cycle may include a first reaction cycle in which the first step, the second step, and the third step are repeatedly performed without performing the fourth step, and a second reaction cycle in which the fourth step is performed.

[0009] In one embodiment, the fourth step may be carried out so that the solids concentration of the first mixture is maintained within a predetermined concentration range.

[0010] In one embodiment, the fourth step may be carried out so that the viscosity of the first mixture is maintained within a predetermined viscosity range.

[0011] In one embodiment, the treatment using the screw decanter centrifuge may be performed so that 95.0 to 99.9 mass% of the solid content supplied to the screw decanter centrifuge is removed and 0.1 to 5.0 mass% remains in the third mixture. [Effects of the Invention]

[0012] According to the present invention, there is provided a method for producing ethanol that can efficiently obtain ethanol from cellulosic raw materials. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram of the reaction steps in the examples. [Figure 2] 1 is a graph plotting the number of bacteria in the No. 1 reaction tank against the time elapsed since the start of the reaction in an example. [Figure 3] 1 is a graph plotting the rate of increase in the solid content in the No. 1 reaction tank versus the elapsed time from the start of the reaction in an example. [Figure 4] 1 is a graph plotting the viscosity of the solid content in the No. 1 reaction tank against the elapsed time from the start of the reaction in an example. [Figure 5] 1 is a graph plotting the relative value of the concentration of ethanol in the No. 1 reaction vessel against the elapsed time from the start of the reaction in an example. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0015] The method for producing ethanol according to this embodiment includes a first step of supplying a cellulosic raw material to a reaction system containing a saccharifying enzyme, yeast, and water to produce ethanol by saccharification and fermentation of the cellulosic raw material; a second step of removing a first mixture containing ethanol and a reaction residue from the reaction system, separating the ethanol from the first mixture, and recovering a second mixture containing the reaction residue; a third step of supplying at least a portion of the second mixture to the reaction system; and a fourth step of treating at least a portion of the second mixture in a screw decanter centrifuge to obtain a third mixture having a lower solids concentration than the second mixture, and supplying the third mixture to the reaction system.

[0016] According to the production method of this embodiment, by removing a portion of the reaction residue in the fourth step, accumulation of the reaction residue in the reaction system can be suppressed. Furthermore, in the production method of this embodiment, the reaction residue is treated using a screw decanter centrifuge in the fourth step. Since a screw decanter centrifuge tends to selectively remove large particle size solids, it is possible to remove the large particle size solids while leaving the small particle size solids in the third mixture. Therefore, in this embodiment, it is possible to reuse the yeast present in the reaction residue and the saccharification enzyme adsorbed to the small particle size solids, which is expected to improve ethanol production efficiency and the use efficiency of the yeast and saccharification enzyme. For these reasons, the production method of this embodiment can efficiently obtain ethanol while suppressing the accumulation of the reaction residue and increasing the continuity of the reaction.

[0017] The ethanol production method according to this embodiment may include a first reaction cycle in which the first step, the second step, and the third step are repeatedly performed without performing the fourth step, and a second reaction cycle in which the fourth step is performed.

[0018] Each step will be described in detail below.

[0019] (First step) The first step is a step in which a cellulosic raw material is supplied to a reaction system containing a saccharifying enzyme, yeast, and water, and ethanol is produced by saccharification and fermentation of the cellulosic raw material.

[0020] In the first step, a cellulosic raw material is saccharified with a saccharifying enzyme (enzymatic saccharification reaction), and the resulting sugars are converted to ethanol by fermentation with yeast (ethanol fermentation). The first step may be, for example, a parallel multiple fermentation process in which the enzymatic saccharification reaction and the ethanol fermentation are carried out simultaneously.

[0021] (Saccharification enzymes) The saccharifying enzyme is not particularly limited as long as it is a cellulolytic enzyme or a hemicellulolytic enzyme. Examples of cellulolytic enzymes include enzymes collectively known as cellulases, which have cellobiohydrolase activity, endoglucanase activity, beta-glucosidase activity, etc. Each cellulolytic enzyme may be added in an appropriate amount, but since many commercially available cellulolytic enzyme preparations have the above-mentioned various cellulase activities as well as hemicellulase activity, commercially available cellulolytic enzyme preparations may also be used.

[0022] Commercially available cellulolytic enzyme preparations include those derived from the genera Trichoderma, Acremonium, Aspergillus, Phanerochaete, Trametes, Humicola, Bacillus, and Irpex. Commercially available cellulolytic enzyme preparations include, for example, Celluleucin T2 (manufactured by HPI), Novozym 188 (manufactured by Novozym), Multifect CX10L (manufactured by Genencor), and GC220 (manufactured by Genencor), all of which are trade names.

[0023] The saccharifying enzymes used can be used alone or in combination, taking into consideration the properties of the cellulolytic enzyme preparation, etc. In this embodiment, two types of saccharifying enzymes may be used: a saccharifying enzyme added at the beginning of parallel multiple fermentation, and an additional saccharifying enzyme added continuously or intermittently after a certain period of time has passed, and these saccharifying enzymes may be the same or different types.

[0024] In this embodiment, the activity of a saccharifying enzyme is defined as follows. 375 μL of enzyme solution and 0.5 g of bone-dry weight of hardwood bleached kraft pulp (LBKP) were added to 8 mL of aqueous solution (pH 4.8) containing 1.5 mL of 1 M acetate buffer, and the resulting mixture was reacted at 33°C for 4 hours. The reaction was then stopped by heating at 95°C for 10 minutes. This mixture was analyzed by high-performance liquid chromatography (HPLC) (Prominence, Shimadzu Corporation) using a refractive index (RI) detector to measure the glucose concentration. Based on the measurement results, the amount of enzyme protein that produces 1 μmol of glucose per minute is defined as 1 unit (U). The HPLC measurement conditions are as follows. Column: 80 Shodex SUGAR SP0810 (Showa Denko K.K.) Mobile phase: ultrapure water Flow rate: 0.8mL / min Temperature: 80℃

[0025] The initial content of the saccharifying enzyme in the fermentation liquid in the reaction tank is not particularly limited, but is preferably 50 to 500 U / L, and more preferably 100 to 300 U / L.

[0026] Furthermore, the ratio of the initial content of saccharifying enzyme in the fermentation liquid in the reaction tank to the initial content of cellulosic raw material (initial content of saccharifying enzyme (U) / initial content of cellulosic raw material (kg)) is preferably 500 to 50,000 U / kg, and more preferably 1,000 to 30,000 U / kg.

[0027] (yeast) The yeast is not particularly limited, but is preferably one that can ferment sugars (hexoses and pentoses). Specific examples of yeast include Saccharomyces yeasts such as Saccharomyces cerevisiae, Pichia yeasts such as Pichia stipitis, Candida yeasts such as Candida shihatae, Pachysolen yeasts such as Pachysolen tannophilus, and Issatchenkia yeasts such as Issatchenkia orientalis. Yeasts belonging to the genera Saccharomyces and Issatchenkia are preferred, with Saccharomyces cerevisiae and Issatchenkia orientalis being more preferred. Genetically modified yeasts produced using genetic engineering techniques can also be used. The genetically modified yeast can be any yeast that can ferment sugars (hexose and pentose) without any particular limitation, and preferably yeast that can ferment hexose and pentose simultaneously can be used.

[0028] The yeast used in the multiple parallel fermentation process is preferably a yeast culture medium. Such a yeast culture medium can be cultured in stages using culture tanks of different sizes so that the amount added is appropriate for the process. For example, the yeast can be first cultured in 100 to 300 mL, then cultured in 10 to 30 L using the culture medium obtained, and then cultured in 500 to 1,000 L using the culture medium obtained, and the culture medium obtained can be used in the multiple parallel fermentation process.

[0029] The pH of the fermentation liquid in the reaction tank in the parallel multiple fermentation process is not particularly limited, but is preferably maintained in the range of 3-10, and more preferably in the range of 4-8.

[0030] The temperature of the fermentation liquid in the reaction tank in the parallel multiple fermentation process is not particularly limited as long as it is within the optimum temperature range for the saccharifying enzyme and / or yeast, but is preferably 20 to 40°C, more preferably 30 to 40°C.

[0031] The number of bacteria in the reaction tank in the parallel multiple fermentation process is not particularly limited, but is preferably 10 7 cells / mL or more is preferable, and 10 8 The preferred range of bacterial cell count is 10 7 ~10 9 cells / mL, and the more preferable range of bacterial cell count is 10 8 ~10 9 cells / mL.

[0032] The rate of increase in the solid content (reaction residue, sustained solid: SS) of the fermentation broth in the parallel multiple fermentation process is not particularly limited, but may be in the range of −1 to 5 kg / h, and preferably in the range of 0 to 5 kg / h.

[0033] The glucose concentration in the parallel multiple fermentation step is not particularly limited, but may be in the range of 0 to 0.2 mass / volume %.

[0034] The parallel multiple fermentation process may be, for example, a semi-batch or batch process, and is preferably a continuous process. Here, continuous refers to, for example, a mode in which raw material supply and ethanol production are continuous. The reaction time varies depending on the enzyme concentration, but in the case of a batch process, it is preferably 12 to 240 hours, more preferably 24 to 120 hours. In the case of a semi-batch or continuous process, the average residence time is preferably 12 to 240 hours, even more preferably 24 to 120 hours. Here, the average residence time refers to the average residence time from when the cellulosic raw material is supplied into the reaction tank until it is transferred out of the reaction tank.

[0035] In this embodiment, the parallel double-fermentation process may include continuously or intermittently adding an additional saccharifying enzyme to a fermentation liquor containing a cellulosic raw material, a saccharifying enzyme, and a yeast so that the physical properties of the fermentation liquor itself are maintained within a predetermined range. Such physical properties are not particularly limited, but from the viewpoint of maintaining the required amount of enzyme per amount of ethanol produced at a constant level, the ethanol concentration and / or viscosity of the fermentation liquor are preferred.

[0036] When the physical property of the fermentation broth is the ethanol concentration, it is preferable to add additional saccharifying enzymes so that the ethanol concentration (relative value) of the fermentation broth is maintained at 80% or higher relative to the ethanol concentration at steady state after the start of fermentation. The ethanol concentration is more preferably 85% or higher. The time point for measuring the ethanol concentration is not particularly limited and can be set appropriately, but is, for example, 300 to 500 hours after the start of fermentation. The ethanol concentration of the fermentation broth can be measured by sampling at least 1 mL of the fermentation broth from the reaction vessel, stopping the reaction, and then analyzing the supernatant by HPLC. Such measurements can be easily performed using a Prominence (Shimadzu Corporation).

[0037] Here, the above-mentioned "when a steady state is reached after the start of fermentation" preferably means the time when the ethanol concentration first reaches a maximum value after the start of fermentation and the fluctuation range of the ethanol concentration remains below 20% thereafter. The time when a steady state is reached after the start of fermentation can be appropriately changed depending on the reaction conditions, etc., but is, for example, 12 to 240 hours, preferably 24 to 120 hours, after the start of fermentation.

[0038] The amount of additional saccharifying enzyme to be added is preferably such that the enzyme consumption rate (U / L) in the fermentation broth is maintained at 0.1 to 30% relative to the enzyme consumption rate, for example, 1 to 12 hours after the start of fermentation, preferably 1 to 8 hours after the start of fermentation. Here, the enzyme consumption rate refers to the amount of enzyme required to produce a unit volume of ethanol. The enzyme consumption rate is used as an index of enzyme cost and can preferably be calculated using the following formula: Enzyme consumption rate (U / L) = total amount of saccharification enzyme (U) / total amount of ethanol produced (L) From the viewpoint of reducing enzyme costs, it is particularly advantageous to carry out the enzymatic reaction so that the enzyme consumption rate continuously decreases, as this enables efficient ethanol production. The amount of additional saccharifying enzyme is preferably set so that the enzyme consumption rate (relative amount) of the fermentation broth is, for example, 0.1 to 30%, preferably 0.1 to 10%, and more preferably 0.1 to 2% of the enzyme consumption rate 1 to 12 hours after the start of fermentation. The time point for calculating the enzyme consumption rate is not particularly limited and can be set appropriately, but is, for example, 300 to 500 hours.

[0039] The amount of additional saccharifying enzyme added can be, for example, 20 U or less per liter of fermentation liquid, preferably 1 to 15 U, and more preferably 3 to 10 U. The amount of additional saccharifying enzyme added can be calculated as the amount of additional saccharifying enzyme added per day. The amount of additional saccharifying enzyme can be appropriately determined depending on the temperature, pH, time, enzyme properties and combination, etc. of the parallel multiple fermentation process.

[0040] The mass ratio of the amount of additional saccharifying enzyme added per day to the initial content of saccharifying enzyme in the fermentation liquid (amount of additional saccharifying enzyme added per day: initial content of saccharifying enzyme in the fermentation liquid) is not particularly limited, but is preferably 1:10 to 1:100, more preferably 1:15 to 1:80, and even more preferably 1:15 to 1:50.

[0041] The additional saccharifying enzyme is added continuously or intermittently. When the additional saccharifying enzyme is added intermittently, the additional saccharifying enzyme is added preferably every 2 to 192 hours, more preferably every 6 to 96 hours, and even more preferably every 12 to 48 hours.

[0042] The addition of the additional saccharifying enzyme is preferably started by measuring the physical properties of the fermentation liquid itself and starting the addition so that the measured values ​​are maintained within a preset range.

[0043] The viscosity of the fermentation liquor can also be used as an indicator for adding additional saccharifying enzymes. It is conceivable to use the viscosity as an indicator of the degree of progress of saccharification of the cellulosic raw material. When the physical property value of the fermentation liquor is the viscosity of the fermentation liquor, the viscosity can be appropriately determined depending on the stirring conditions, reaction conditions, etc., but it is preferable to add the additional saccharifying enzymes to the fermentation liquor when the viscosity exceeds 140 cP. The viscosity indicator can be used particularly advantageously when the reaction in the parallel multiple fermentation process is continuous. When the parallel multiple fermentation process is semi-batch or batch, the viscosity of the fermentation liquor can be appropriately determined depending on the stirring conditions, reaction conditions, etc., but it is preferable to add the additional saccharifying enzymes to the fermentation liquor when the viscosity exceeds 4 cP.

[0044] Furthermore, when the physical property of the fermentation liquor is viscosity, the viscosity can be appropriately determined depending on the stirring conditions, reaction conditions, etc., but the aforementioned preset range is preferably 300 cP or less in terms of the viscosity of the fermentation liquor. The viscosity is more preferably 250 cP or less. The above viscosity range can be advantageously used when the reaction in the multiple parallel fermentation process is continuous. When the reaction in the multiple parallel fermentation process is semi-batch or batch, it is preferable to add the additional saccharifying enzyme to the fermentation liquor so that the viscosity of the fermentation liquor is 20 cP or less.

[0045] The viscosity of the fermentation broth can be measured by sampling at least 10 mL of the fermentation broth from the reaction vessel and directly subjecting it to viscosity measurement using a viscometer. Such measurements can be easily performed using a viscometer (analog B-type viscometer LV-T, Brookfield).

[0046] Furthermore, in the parallel multiple fermentation process, it is preferable to adjust the concentration of the cellulosic raw material in the fermentation liquor so that it is maintained within a predetermined range. The predetermined range can be 5 to 30% by mass, preferably 10 to 20% by mass. This adjustment is carried out, for example, by supplying the cellulosic raw material to the reaction vessel. Here, the supply rate of the cellulosic raw material to the reaction vessel is not particularly limited. However, when the parallel multiple fermentation process is continuous and the fermentation liquor is discharged from the reaction vessel, it is preferable that the supply rate of the cellulosic raw material to the reaction vessel and the discharge rate of the fermentation liquor from the reaction vessel are approximately the same. Furthermore, as described below, when the solid-content concentrated fermentation liquor after separation of the aqueous ethanol solution is recovered and transferred to the reaction vessel in the second step, it is preferable that the combined supply rate of the solid-content concentrated fermentation liquor and the cellulosic raw material to the reaction vessel and the discharge rate of the fermentation liquor from the reaction vessel are approximately the same.

[0047] From the viewpoint of yeast growth or preventing the risk of raw materials being transferred from the reaction tanks without reacting, it is preferable that the reaction tanks in which parallel multiple fermentation is performed are at least two reaction tanks connected to each other. It is preferable that the at least two reaction tanks are connected in series. In such an embodiment, for example, the reaction tanks can be connected in series so that the first fermentation broth discharged from the first reaction tank is injected into the second reaction tank via a line. Here, it is preferable that the first reaction tank contains a fermentation broth and is continuously supplied with additional cellulosic raw materials. The amount of cellulosic raw materials supplied is preferably adjusted so that the concentration of the cellulosic raw materials in the fermentation broth in the first reaction tank is maintained within a predetermined range, which may be 5 to 30% by mass, and preferably 10 to 20% by mass. Furthermore, it is preferable that the fermentation broth in the second reaction tank is obtained by continuously transferring a portion of the fermentation broth from the first reaction tank.

[0048] When at least two connected reactors are used for performing parallel multiple fermentation, the physical property values ​​of the fermentation liquor from the first reactor are preferably used as indicators for the addition of additional saccharification enzymes. The fermentation liquor from the first reactor contains a high proportion of unreacted cellulosic raw material, and a decrease in enzyme activity is likely to affect the physical property values. This is advantageous for use as an accurate indicator for the addition of additional saccharification enzymes.

[0049] (Cellulosic raw materials) Cellulosic raw materials refer to raw materials containing cellulose as the main raw material. Cellulose may be, for example, lignocellulose, which contains cellulose, hemicellulose, and lignin. That is, cellulosic raw materials may be, for example, lignocellulose raw materials. Lignocellulose raw materials are pulp or raw materials other than pulp that contain lignocellulose. One type of lignocellulose raw material may be used alone, or two or more types may be used in combination.

[0050] Examples of pulp include wood pulp obtained from conifers, broad-leaved trees, forest residues, construction waste, etc., non-wood pulp such as cotton linter, cotton lint, hemp, straw, bagasse, etc., waste paper pulp made from waste paper, deinked pulp, etc. Preferred pulp production methods are chemical pulp production methods such as alkali extraction and alkali cooking, which remove lignin to a high extent, and among pulps produced by chemical pulp production methods, papermaking pulp is preferred in terms of ease of availability. Examples of papermaking pulp 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 chemi-groundwood pulp (CGP). Pulp is preferably hardwood kraft pulp, softwood kraft pulp, sulfite pulp (SP), or semi-chemical pulp (SCP), and more preferably bleached hardwood kraft pulp (LBKP) or oxygen-bleached softwood kraft pulp (NOKP).

[0051] Lignocellulose raw materials other than pulp include woody materials such as chips or bark of trees for papermaking, forest residues, thinned wood, etc., sprouts from stumps of woody plants, sawdust or sawdust from sawmills, etc., pruned branches and leaves of roadside trees, construction waste, etc. Examples of woody lignocellulose raw materials that can be used include plants of the genus Eucalyptus, willow (Salix), poplar, acacia, and cedar (Cryptomeria). Of these, plants of the genus Eucalyptus, acacia, and willow are preferred because they can be easily harvested in large quantities as raw materials. Examples of herbaceous materials include agricultural waste such as kenaf, rice straw, wheat straw, corn cobs, and bagasse; residues and waste from industrial crops such as oil crops and rubber (e.g., EFB: Empty Fruit Bunch); and herbaceous energy crops such as Erianthus, Miscanthus, and Napier grass. Lignocellulosic raw materials other than pulp may also be biomass. Examples of biomass include wood-derived paper, waste paper, pulp sludge, sludge, sewage sludge, and food waste. These biomasses can be used alone or in combination. Biomass may be a dry solid, a wet solid, or a slurry. The above-mentioned lignocellulosic raw materials other than pulp are preferably used after pretreatment (such as delignification treatment).

[0052] The concentration of the cellulosic raw material in the fermentation broth in the reaction tank is preferably 5 to 30% by mass, more preferably 10 to 20% by mass. A cellulosic raw material concentration of 5% by mass or more is advantageous in avoiding the problem of the final product having a too low concentration, resulting in high costs for ethanol concentration. Furthermore, a cellulosic raw material concentration of 30% by mass or less is advantageous in avoiding the problem of increased productivity due to difficulty in stirring the raw material as the concentration increases.

[0053] (Second step) The second step is a step of removing a first mixture containing ethanol and a reaction residue from the reaction system, separating the ethanol from the first mixture, and recovering a second mixture containing the reaction residue.

[0054] The reaction residue may include, for example, lignin, enzymes, yeast, and the like.

[0055] The first mixture may further contain unreacted raw materials, glycerol, xylose, xylitol, acetic acid, and the like, in addition to ethanol and the reaction residue.

[0056] The rate at which the first mixture is removed is not particularly limited. For example, the amount of the first mixture removed per hour may be 1 / 240 to 1 / 12 of the total retention volume (total volume of the fermentation broth retained in the reaction tank), and from the viewpoint of ethanol production efficiency, is preferably 1 / 120 to 1 / 24 of the total retention volume.

[0057] The second mixture may be a residue obtained by removing ethanol from the first mixture. The second mixture may further contain unreacted raw materials, glycerol, xylitol, acetic acid, etc. in addition to the reaction residue.

[0058] More specifically, the fermentation broth (first mixture) discharged from the reaction vessel in the second step may be separated into a solids-enriched fermentation broth (second mixture) and an aqueous solution, for example, a solids-enriched fermentation broth (second mixture) and an aqueous ethanol solution, using a separation device such as a vacuum distillation device or a membrane separation device. When the reaction vessel has two vessels, it is preferable that the fermentation broth be discharged from the second reaction vessel and transferred to an ethanol separation device. Examples of vacuum distillation devices that can be used include a rotary evaporator and a flash evaporator. Under reduced pressure, ethanol can be separated at low temperatures, preventing enzyme deactivation. The resulting aqueous ethanol solution can be further concentrated by distillation or using various separation membranes, such as a zeolite membrane, to produce high-purity ethanol.

[0059] (Third step) 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 a portion or all of the solid-concentrated fermentation liquid (second mixture) separated from the fermentation liquid (first mixture) to a reaction tank. When there are two or more reaction tanks, it is preferable to transfer a portion or all of the solid-concentrated fermentation liquid (second mixture) to the first reaction tank.

[0060] In the third step, if the entire second mixture is supplied to the reaction system, the fourth step is not carried out. On the other hand, in the third step, if a portion of the second mixture is supplied to the reaction system, the other portion of the second mixture (or a further portion of the other portion) may be supplied to the fourth step. Furthermore, in this embodiment, the third step may be carried out intermittently. When the third step is not carried out, part or all of the second mixture may be supplied to the fourth step.

[0061] (Fourth step) The fourth step is a step of treating at least a portion of the second mixture in a screw decanter centrifuge to obtain a third mixture having a lower solids concentration than the second mixture, and supplying the third mixture to the reaction system.

[0062] In the fourth step, at least a portion of the second mixture is treated in a screw decanter centrifuge to remove a portion of the reaction residue, thereby obtaining a third mixture having a lower solids concentration than the second mixture. The obtained third mixture is supplied to the reaction system. This prevents the accumulation of reaction residue in the reaction system.

[0063] That is, the fourth step can be said to be a step of treating a part or all of the solids-enriched fermentation liquid (second mixture) separated from the fermentation liquid (first mixture) with a screw decanter centrifuge to obtain a low-solids fermentation liquid (third mixture), and transferring a part or all of the low-solids fermentation liquid to a reaction tank. When there are two or more reaction tanks, it is preferable to transfer a part or all of the low-solids fermentation liquid (third mixture) to the first reaction tank.

[0064] The processing speed using the screw decanter centrifuge is not particularly limited. For example, the amount of the second mixture processed in the screw decanter centrifuge per hour may be 1 to 90% by mass of the total retention volume (the total amount of the second mixture recovered in the second step), and from the viewpoint of achieving both the reactivity of the yeast and the enzyme recovery, it is preferably 1 to 50% by mass, more preferably 1 to 30% by mass.

[0065] In this embodiment, the fourth step may be performed continuously or intermittently. For example, the fourth step may be performed so that the solids concentration of the first mixture is maintained within a predetermined range.

[0066] The predetermined range of the solid content concentration may be set appropriately depending on the apparatus conditions, etc., and may be determined, for example, based on the allowable concentration range of the apparatus. The predetermined range of the solid content concentration may be, for example, 1 to 20 mass%, and from the viewpoint of achieving both reactivity and fluidity in the first reaction tank, is preferably 3 to 18 mass%, more preferably 5 to 15 mass%.

[0067] The method for measuring the solid content concentration is not particularly limited, and for example, it can be measured using "SS Turbidity System ST-100" manufactured by Central Scientific Co., Ltd.

[0068] The fourth step may also be carried out to maintain the viscosity of the first mixture within a predetermined range.

[0069] The predetermined viscosity range may be set appropriately depending on the apparatus conditions, etc., and may be determined, for example, based on the allowable viscosity range of the apparatus. The predetermined viscosity range may be, for example, 0 to 1000 cP, and from the viewpoint of achieving both reactivity and fluidity in the first reaction tank, is preferably 0 to 500 cP, more preferably 0 to 300 cP.

[0070] The method for measuring the viscosity of the first mixture is not particularly limited, and the viscosity can be measured using, for example, an analog B-type viscometer LV-T manufactured by BROOKFIELD.

[0071] In the fourth step, for example, the treatment with the screw decanter centrifuge may be performed so that 95.0 to 99.9 mass% of the solid content supplied to the screw decanter centrifuge is removed and 0.1 to 5.0 mass% remains in the third mixture. By performing the treatment with the screw decanter centrifuge so that 0.1 to 5.0 mass% of the solid content remains, the effect of selectively removing the large particle size solid content described above is more pronounced.

[0072] The proportion of the solids removed from the solids supplied to the screw decanter centrifuge is preferably 97.0 to 99.9 mass%, more preferably 99.0 to 99.9 mass%. That is, the proportion of the solids remaining in the third mixture from the solids supplied to the screw decanter centrifuge is preferably 0.1 to 3.0 mass%, more preferably 0.1 to 1.0 mass%. [Example]

[0073] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0074] Example 1 <Yeast cultivation> The yeast used for the fermentation broth was prepared in three stages: (1) 200 mL in a 500 mL flask, (2) 20 L in a 30 L fermenter, and (3) 800 L in a 900 L fermenter. At each stage, an aqueous solution of 1% by mass of corn steep liquor (CSL) and 2% by mass of glucose was prepared, and 1 × 10 ×7 The cells were inoculated at 100 cells / mL and cultured for 12 hours.

[0075] <Ethanol production> A schematic diagram of the ethanol production in this example is shown in Figure 1. In Figure 1, solid arrows indicate the flow of processes that are always performed, and dashed arrows indicate the flow of processes that are temporarily performed.

[0076] 400 kg of sterilized water was charged into the No. 1 reactor 11, which had a maximum capacity of 12,000 L. After adding 14 kg of urea and 63 kg of CSL, the supply of hardwood bleached kraft pulp 1 (LBKP, biomass solids concentration: 10% by mass) was initiated at a rate of 15.2 kg / h (bone-dry weight). Three hours after the start of the LBKP supply, 3N sulfuric acid and 3N aqueous sodium hydroxide were added to adjust the pH to 4.8, and then 966,608 U of enzyme 2 prepared in enzyme tank 8 and the entire culture of yeast 3 prepared in the 900 L fermenter 10 were added to initiate the reaction. The reactor was controlled to a constant temperature of 33 °C, agitation speed of 24 rpm, aeration rate of 0.016 vvm, and pH of 4.8. After 48 hours, half of the total volume (7,300 kg), 3,650 kg, was transferred to the No. 2 reactor 12, which had a maximum capacity of 12,000 L. After the transfer to the No. 2 reactor 12 was completed, the fermentation broth was transferred from the No. 2 reactor 12 to the vacuum distillation column 14 via the buffer tank 13 at a rate of 150 kg / h. The aqueous ethanol solution 4 was distilled off at a rate of 40 kg / h, and the concentrated solids fermentation broth was collected in the reactor 15 at a rate of 110 kg / h. This operation was continued until the operation was stopped. During this time, the LBKP was continuously supplied at a constant rate. (Phase 1)

[0077] After 354 hours had passed since the start of the reaction, a small amount of enzyme was added, with 49,210 U of enzyme added every 24 hours (Phase 2).

[0078] After 558 hours had elapsed, in addition to the enzyme addition, a portion of the reaction residue was extracted using a screw decanter 16 (Tanabe Willtec Corporation, decanter-type centrifuge, model number: Z1LL-KV-BS2). Specifically, 6 kg / h of the 110 kg / h of concentrated solids fermentation liquid after distillation was fed to the screw decanter 16, and the reaction residue 5 was removed. The mixture after removal of the reaction residue was recovered in the No. 1 reaction tank 11 (Phase 3). The operating conditions for the screw decanter were a ball rotation speed of 4800 rpm, a differential (differential speed between the "ball" and "screw" inside the screw decanter) of 10 rpm, and a centrifugal effect of 3000 g.

[0079] The reaction solution in the No. 1 reactor 11 and the No. 2 reactor 12 was sampled every 12 hours, and the viscosity was measured using a viscometer ("Analog Type B Viscometer LV-T" manufactured by Brookfield) and the solids concentration was measured using a turbidity meter ("SS Turbidity Meter ST-100" manufactured by Central Scientific Co., Ltd.). The bacterial cell count was measured using a Thoma hemocytometer and observed under an optical microscope (magnification 400x). The results are shown in Figures 2 to 4. These results confirmed that the viscosity of the reaction solution could be reduced by reducing the solids content while maintaining the bacterial cell count at a level necessary for ethanol production.

[0080] The sample was heated to 95°C for 10 minutes to stop the reaction, and then analyzed using an HPLC (Shimadzu Corporation, Prominence) with a differential refractive index (RI) detector to measure the ethanol concentration. The ethanol concentration 48 hours after the start of the reaction was set to 1, and a relative value was calculated. The results are shown in Figure 5. These results confirmed that partial removal of solids using a screw decanter can reduce the solid concentration and viscosity while maintaining ethanol productivity.

[0081] The amounts of solids subjected to the screw decanter treatment and the amounts of solids remaining after the treatment were determined at 570, 594, and 618 hours after the start of the reaction. The results are shown in Table 1.

[0082] [Table 1]

[0083] (Reference Test 1) <Residual reaction residue rate by particle size> The fermentation liquid (5 L fermenter, 30 mL of continuous fermentation liquid) was centrifuged using a small tabletop centrifuge (Tomy Seiko Co., Ltd., "MX305") under the following conditions equivalent to those of a screw decanter centrifuge, and reaction residue was removed. 200 μL of the supernatant after centrifugation was removed with a pipette, and the particle size distribution was measured. The results are shown in Table 2. Centrifugal force: 3000G Processing time: 1 minute

[0084] [Table 2]

[0085] These results confirmed that the screw decanter centrifuge easily removes large-particle solids (solids with a particle size larger than 10 μm) and tends to leave small-particle solids (solids with a particle size of 10 μm or less). [Explanation of symbols]

[0086] 1...hardwood bleached kraft pulp, 2...enzyme, 3...yeast, 4...ethanol aqueous solution, 5...reaction residue, 6...condenser, 7...vacuum pump, 8...enzyme tank, 9...30L culture tank, 10...900L culture tank, 11...No. 1 reaction tank, 12...No. 2 reaction tank, 13...buffer tank, 14...vacuum distillation column, 15...reaction tank, 16...screw decanter.

Claims

1. a first step of supplying a cellulosic raw material to a reaction system containing a saccharifying enzyme, yeast, and water to produce ethanol through saccharification and fermentation of the cellulosic raw material; a second step of removing a first mixture containing ethanol and a reaction residue from the reaction system and separating the first mixture into a second mixture containing the reaction residue and an aqueous ethanol solution; a third step of supplying at least a portion of the second mixture to the reaction system; a fourth step of treating a treatment liquid containing the reaction residue, which is at least a part of the second mixture, in a screw decanter centrifuge to obtain a third mixture having a lower solid content concentration than the second mixture, and supplying the third mixture to the reaction system; A method for producing ethanol, comprising:

2. a first reaction cycle in which the first step, the second step, and the third step are repeatedly performed, but the fourth step is not performed; a second reaction cycle in which the fourth step is carried out; The method of claim 1 , comprising:

3. The method according to claim 1 or 2, wherein the fourth step is carried out so that the solids concentration of the first mixture is maintained within a predetermined concentration range.

4. The method according to any one of claims 1 to 3, wherein the fourth step is carried out so that the viscosity of the first mixture is maintained within a predetermined viscosity range.

5. The processing using the screw decanter centrifuge is performed so that 95.0 to 99.9% by mass of the solids supplied to the screw decanter centrifuge is removed and 0.1 to 5.0% by mass remains in the third mixture. The manufacturing method according to any one of claims 1 to 4.

6. An apparatus for producing ethanol for carrying out the production method according to any one of claims 1 to 5, a reaction vessel for saccharifying and fermenting the cellulosic raw material; a separation device that separates the first mixture transferred from the reaction tank into the second mixture and the aqueous ethanol solution; a first transfer means for transferring a part or all of the second mixture to the reaction vessel; a screw decanter centrifuge for processing the processing liquid to obtain the third mixture; a second transfer means for transferring a portion of the second mixture to the screw decanter centrifuge; a third transfer means for transferring the third mixture to the reaction vessel; An apparatus for producing ethanol comprising:

7. An apparatus for producing ethanol as described in claim 6, wherein the separation device is selected from the group consisting of a vacuum distillation device and a membrane separation device.

8. An apparatus for producing ethanol as described in claim 6 or 7, wherein the reaction vessel includes a first reaction vessel and a second reaction vessel connected in series to the first reaction vessel.

9. An apparatus for producing ethanol as described in claim 8, wherein cellulosic raw material is continuously added to the first reaction tank.

10. An apparatus for producing ethanol as described in any one of claims 6 to 9, further comprising a concentrating device for concentrating the aqueous ethanol solution.

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