Method for producing bioethanol and apparatus for producing bioethanol

Abstract

Provided is a method for producing second-generation bioethanol with reduced production costs. 【Solution means】A method for producing bioethanol from cellulose, comprising a saccharification step of adding an enzyme to the cellulose and saccharifying it to obtain a sugar solution, a step of concentrating the obtained sugar solution to obtain a concentrated sugar solution, a fermentation step of adding yeast to the concentrated sugar solution and fermenting it to obtain hydrous bioethanol, and a concentration step of concentrating the hydrous bioethanol to obtain bioethanol, in this order. After the saccharification step, at least one of a step of recovering the enzyme using a ceramic membrane and a step of recovering unreacted yeast using a ceramic membrane after the fermentation step is further included, and / or in the step of obtaining the concentrated sugar solution, the sugar solution is concentrated using a protein-supported polyamide RO membrane. A method for producing bioethanol.

Description

Technical Field

[0001] The present invention relates to a method for producing bioethanol and an apparatus for producing bioethanol.

Background Art

[0002] In recent years, the consumption of fossil fuels has increased the concentration of carbon dioxide (CO2) in the atmosphere, and global warming caused by it has become a serious problem. Therefore, bioethanol has been studied and promoted as an eco-friendly fuel with a lower CO2 emission in the life cycle compared to fossil fuels.

[0003] The raw materials for bioethanol are mainly plant-derived raw materials such as starchy raw materials like corn, sweet potato, wheat, tapioca, and sugary raw materials like sugarcane. By fermenting the sugars contained in these plant-derived raw materials using microorganisms and then distilling them, high-purity ethanol can be obtained.

[0004] On the other hand, since the above plant-derived raw materials are also edible raw materials, if the demand for eco-friendly fuel increases and its consumption volume increases, the amount supplied as food may decrease, leading to a rise in food prices.

[0005] Therefore, in recent years, the development of second-generation bioethanol using cellulosic raw materials such as lignin and herbs, which are non-edible raw materials, has been progressing. Since the above cellulosic raw materials are not easily affected by the action of enzymes and yeasts that have been conventionally used to obtain bioethanol, a manufacturing technology combining pretreatment, saccharification, fermentation, concentration, etc. is required. Therefore, the production cost is higher compared to conventional bioethanol.

[0006] Therefore, in order to widely spread second-generation bioethanol, the development of technology for cost reduction is expected.

[0007] Since the manufacturing technology of second-generation bioethanol is diverse, there are various means to achieve cost reduction. For example, Patent Document 1 discloses a method for producing bioethanol that can increase the concentration of hydrous bioethanol and reduce the distillation load without requiring special equipment. In addition, Patent Document 2 discloses a fermentation method for promoting the progress of an enzymatic degradation reaction when decomposing and saccharifying cellulose with an enzyme.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] In contrast, the present inventors have explored a method for producing second-generation bioethanol with reduced production costs through a new approach. That is, the object of the present invention is to provide a method for producing second-generation bioethanol with reduced production costs. In addition, it is also an object of the present invention to provide a production apparatus for second-generation bioethanol with reduced production costs as described above.

Means for Solving the Problems

[0010] In response to the above, the present inventors have conducted intensive studies and come up with a method for solving the above problems using membrane separation technology. Specifically, by using a ceramic membrane to suitably recover enzymes and unreacted yeast, the above enzymes and unreacted yeast can be used again, and by using a protein-supported polyamide RO membrane, it was conceived that the concentration of the sugar solution can be efficiently realized with low energy, and the present invention has been completed.

[0011] The gist of one embodiment of the present invention is shown below. [1] A method for producing bioethanol from cellulose, comprising: A saccharification step of adding an enzyme to the cellulose and saccharifying it to obtain a sugar solution, A step of concentrating the obtained sugar solution to obtain a concentrated sugar solution, A fermentation step of adding yeast to the concentrated sugar solution and fermenting it to obtain hydrated bioethanol, and A concentration step of concentrating the hydrated bioethanol to obtain bioethanol, which are sequentially included, Further including at least one of an enzyme recovery step performed after the saccharification step and an unreacted yeast recovery step performed after the fermentation step, The enzyme recovery step includes a step of recovering the enzyme using a ceramic membrane, The unreacted yeast recovery step uses a ceramic membrane, a method for producing bioethanol. [2] A method for producing bioethanol from cellulose, comprising: A saccharification step of adding an enzyme to the cellulose and saccharifying it to obtain a sugar solution, A step of concentrating the obtained sugar solution to obtain a concentrated sugar solution, A fermentation step of adding yeast to the concentrated sugar solution and fermenting it to obtain hydrated bioethanol, and A concentration step of concentrating the hydrated bioethanol to obtain bioethanol, which are sequentially included, In the step of obtaining the concentrated sugar solution, the sugar solution is concentrated using a protein-supported polyamide RO membrane, a method for producing bioethanol.

[0012] [3] The method for producing bioethanol according to [1] above, wherein the enzyme recovery step further includes a step of recovering the enzyme using a UF membrane after the step of recovering the enzyme using the ceramic membrane. [4] The method for producing bioethanol according to [3] above, wherein a UF membrane having a molecular weight cut-off of MW-3000 to 7000 is used as the UF membrane. [5] The method for producing bioethanol according to [1], [3] or [4] above, wherein in the enzyme recovery step, undegraded cellulose is also recovered together with the enzyme. [6] The method for producing bioethanol according to any one of [1] and [3] to [5], which performs both the enzyme recovery step and the unreacted yeast recovery step. [7] The method for producing bioethanol according to any one of [1] and [3] to [6], wherein in the step of obtaining the concentrated sugar solution, the sugar solution is concentrated using an RO membrane. [8] The method for producing bioethanol according to [7], wherein a protein-supported polyamide RO membrane is used as the RO membrane. [9] The method for producing bioethanol according to any one of [1] and [3] to [8], wherein in at least one of the enzyme recovery step and the unreacted yeast recovery step, a ceramic membrane having a filtration accuracy of 1.2 to 1.6 μm is used as the ceramic membrane.

[10] The method for producing bioethanol according to any one of [1] to [9], wherein in the concentration step, the aqueous bioethanol is concentrated by distillation.

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

[10] , further comprising a step of recovering protein-containing waste liquid after one or more steps of the saccharification step, the fermentation step, and the concentration step.

[12] The method for producing bioethanol according to

[11] , further comprising a step of producing and recovering methane gas using the recovered protein-containing waste liquid.

[0013]

[13] An apparatus for producing bioethanol from cellulose, a saccharification tank that adds an enzyme to the cellulose and saccharifies it to obtain a sugar solution, a sugar solution tank to which the concentrated sugar solution obtained by concentrating the obtained sugar solution is supplied, a fermentation tank that adds yeast to the concentrated sugar solution and ferments it to obtain aqueous bioethanol, and a bioethanol tank to which the bioethanol obtained by concentrating the aqueous bioethanol is supplied. A bioethanol production apparatus further comprising at least one of a ceramic membrane for separating the enzyme provided between the sugar solution tank and the fermentation tank and a ceramic membrane for separating unreacted yeast provided between the fermentation tank and the bioethanol tank.

[14] An apparatus for producing bioethanol from cellulose, a saccharification tank for adding an enzyme to the cellulose and saccharifying it to obtain a sugar solution, a sugar solution tank to which the concentrated sugar solution obtained by concentrating the obtained sugar solution is supplied, a fermentation tank for adding yeast to the concentrated sugar solution and fermenting it to obtain hydrous bioethanol, and a bioethanol tank to which the bioethanol obtained by concentrating the hydrous bioethanol is supplied. A bioethanol production apparatus having a protein-supported polyamide RO membrane for concentrating the sugar solution between the sugar solution tank and the fermentation tank.

[15] The bioethanol production apparatus according to

[13] , having a protein-supported polyamide RO membrane for concentrating the sugar solution between the sugar solution tank and the fermentation tank.

Advantages of the Invention

[0014] According to the present embodiment, second-generation bioethanol can be produced at a low production cost. More specifically, by using a ceramic membrane, the recovery of enzymes and unreacted yeast can be suitably carried out, and the recovered enzymes and unreacted yeast can be reused. Also, the amount of saccharification residue waste liquid and the amount of fermentation residue waste liquid can be reduced. Furthermore, by using a protein-supported polyamide RO membrane, the concentration of the sugar solution can be efficiently realized with very low energy. As a result, the production cost of bioethanol can be made significantly lower than before.

Brief Description of the Drawings

[0015]

Figure 1

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described. It should be noted that the present invention is not limited to the embodiments described below. In this specification, "~" indicating a numerical range is used to mean that the numerical values described before and after it are included as the lower limit value and the upper limit value.

[0017] 《Method for Producing Bioethanol》 One aspect of the method for producing bioethanol according to this embodiment includes the following steps in order. A saccharification step of adding an enzyme to cellulose, saccharifying it to obtain a sugar solution, A step of concentrating the obtained sugar solution to obtain a concentrated sugar solution, A fermentation step of adding yeast to the concentrated sugar solution and fermenting it to obtain hydrous bioethanol, and A concentration step of concentrating the hydrous bioethanol to obtain bioethanol.

[0018] In addition to the above, the production method according to this embodiment preferably further includes an enzyme recovery step after the saccharification step, preferably further includes an unreacted yeast recovery step after the fermentation step, and more preferably includes both. Here, the enzyme recovery step preferably includes a step of recovering the enzyme using a ceramic membrane. Also, it is preferable to use a ceramic membrane for the unreacted yeast recovery step.

[0019] In addition to the above, the production method according to this embodiment further preferably performs the concentration of the sugar solution using an RO membrane (reverse osmosis membrane) in the step of obtaining the concentrated sugar solution, and it is more preferable that the RO membrane is a protein-supported polyamide RO membrane.

[0020] Another aspect of the method for producing bioethanol according to this embodiment includes the following steps in order. A saccharification step of adding an enzyme to cellulose, saccharifying it to obtain a sugar solution, A step of concentrating the obtained sugar solution to obtain a concentrated sugar solution, Adding yeast to the concentrated sugar solution and fermenting it to obtain hydrated bioethanol, and A concentration step of concentrating the hydrated bioethanol to obtain bioethanol. In the step of obtaining the concentrated sugar solution, it is preferable to concentrate the sugar solution using a protein-supported polyamide RO membrane.

[0021] In the production method according to this embodiment, it is preferable to use a ceramic membrane in the enzyme recovery step after the saccharification step and the unreacted yeast recovery step after the fermentation step. Thereby, enzymes and unreacted yeast can be suitably recovered. As a result, the above-mentioned enzymes and unreacted yeast can be reused in the saccharification step and the fermentation step, the amount of enzyme used and the amount of yeast used can be reduced, and further, the amount of saccharification residue waste liquid and the amount of fermentation residue waste liquid can also be reduced. From such a viewpoint, this embodiment can produce bioethanol at a lower production cost.

[0022] Further, in the production method according to this embodiment, in the step of obtaining the concentrated sugar solution, it is preferable to concentrate the sugar solution using an RO membrane. It was conceived that by using an RO membrane for the above concentration, concentration can be achieved with low energy, and by using a protein-supported polyamide RO membrane, concentration can be achieved with even lower energy. From such a viewpoint as well, this embodiment can produce bioethanol at a lower production cost.

[0023] Hereinafter, with reference to FIG. 1, the above two aspects will be summarized and described step by step. However, the embodiments described in the drawings are schematized for clearly explaining the present invention, and do not necessarily accurately represent the size and scale of actual devices and the like. Also, the production method according to this embodiment is not limited to the embodiments described in the drawings.

[0024] 〈Saccharification step〉 The saccharification step in this embodiment is a step of adding an enzyme to cellulose and saccharifying it to obtain a sugar solution.

[0025] Specifically, for example, cellulose and an enzyme as raw materials are introduced into the saccharification tank T-1 (arrows 3 and 4 in FIG. 1). At this time, in addition to cellulose and the enzyme, other conventionally used components may be further introduced into the saccharification tank T-1. Examples of the other components include water (industrial water), a pH adjuster, antifoaming agent vapor, etc. (arrows 1, 2, and 5 in FIG. 1).

[0026] In this embodiment, as the cellulose, for example, lignocellulose is preferably used, and raw material pulp, wood, or those extracted from other plants can be used. The extraction source of the cellulose may be one type or two or more types. From the viewpoint of sustainable raw material supply, NUKP (unbleached softwood pulp) and LBKP (bleached hardwood pulp) are preferable as the raw material pulp.

[0027] The above cellulose may be pretreated as necessary to loosen the bonds of cellulose, hemicellulose, and lignin. This makes saccharification and fermentation proceed more easily. Conventionally known methods can be adopted for the above pretreatment. For example, steam explosion using water, hydrothermal treatment, concentrated sulfuric acid method or dilute sulfuric acid method using an acid, ammonia cryogenic explosion method using an alkali, ammonia new method, alkali digestion method or lime method, acetic acid method or ethanol method using an organic solvent, etc. These may be carried out by one method or in combination of two or more methods. On the other hand, considering the increase in energy required for the above pretreatment and the increase in chemical consumption, the above pretreatment may not be carried out from the viewpoint of production cost. Also, as a pretreatment, centrifugation may be carried out, and more specifically, centrifugation using a decanter type centrifuge may be carried out. Centrifugation has no concerns such as the above-mentioned energy increase.

[0028] In this embodiment, conventionally known enzymes can be used, and for example, cellulase is preferable. The above enzyme may be produced in-house or a commercially available one may be used. When produced in-house, for example, an enzyme produced by a continuous culture device is preferably used.

[0029] Cellulose has a polymer structure in which sugars are bonded, but when hydrolyzed, it is saccharified to become a sugar solution. At this time, the addition of an enzyme promotes the above hydrolysis.

[0030] Also, when adding the enzyme, steam may be used to keep the temperature in the saccharification tank T-1 at the enzyme activation temperature. When using cellulase as the enzyme, it is preferably kept in the range of 50°C ± 3°C as the enzyme activation temperature. Steam can be introduced, for example, into the outer jacket of the saccharification tank T-1.

[0031] The saccharification reaction conditions are not particularly limited, and conventionally known conditions can be adopted. For example, when using cellulase as the enzyme, the reaction temperature is preferably 50 ± 3°C.

[0032] In the case of using pulp as the raw material for cellulose in the saccharification reaction, when the solid content concentration of the raw material is 54%, an addition of about 30 FPU / g-pulp of enzyme activity per 1 kg of the raw material is required. Accordingly, the enzyme is introduced into the saccharification tank T-1. Also, when recycling the recovered enzyme, the amount of newly added enzyme is determined according to the amount of the recycled enzyme.

[0033] In the saccharification step of the present embodiment, it is preferable to maintain a saccharification rate of 70% or more, and more preferably 80% or more. In the case of recycling the recovered enzyme, in the production method according to the present embodiment, the recovered enzyme can also be recycled continuously for 5 batches or more. Therefore, when continuing the saccharification step, the amount of newly added enzyme can be as extremely small as about 20% and still be operated without problems, and the effect of reducing the amount of enzyme used in the production method according to the present embodiment is very large.

[0034] In the saccharification step of the present embodiment, for example, a mixed solution in which a sugar solution having a Brix value of about 8 to 9% is about 80% by mass and undegraded cellulose is about 20% by mass is produced. The particle size of the undigested cellulose may be about 4 to 1000 μm, or may be about 100 to 1000 μm.

[0035] 〈Enzyme recovery step〉 The production method according to this embodiment preferably includes an enzyme recovery step after the saccharification step and before concentrating the sugar solution obtained in the saccharification step. Also, solid-liquid separation may be performed before the enzyme recovery step. The sugar solution after solid-liquid separation is supplied to the sugar solution tank T-2.

[0036] The sugar solution in the sugar solution tank T-2 is subjected to microfiltration through the ceramic membrane CM-1, whereby the enzyme is separated from the sugar solution, the enzyme can be recovered, and at the same time, the sugar solution is purified. The above purification means that the undigested cellulose in the sugar solution obtained in the saccharification step is separated from the sugar solution. That is, in the step of recovering the enzyme using the ceramic membrane in this embodiment, it is preferable to recover the undigested cellulose together with the enzyme.

[0037] The enzyme recovered above is preferably returned to the saccharification tank T-1 again as the recovered enzyme and used in the saccharification step (arrow 9 in Fig. 1). At this time, if the undigested cellulose is also returned to the saccharification tank T-1, it will be used again in the saccharification step, and the saccharification rate of cellulose can also be increased.

[0038] Thus, the enzyme recovery step in this embodiment can easily and efficiently recover the enzyme, and if necessary, together with the undigested cellulose, by using the ceramic membrane CM-1. At the same time, it is also possible to continuously perform the purification of the sugar solution, the recovery of the above enzyme and undigested cellulose, and the return to the saccharification tank T-1.

[0039] By repeatedly using the enzyme by recovering and returning the enzyme, the amount of enzyme used can be reduced, leading to a reduction in production costs. Also, reducing the amount of enzyme contained in the waste liquid is advantageous from the perspective of reducing the environmental burden. Note that while repeatedly using the enzyme, a part of the new enzyme may be put into the saccharification tank T-1 and used.

[0040] The ceramic membrane CM-1 in this embodiment preferably has a filtration accuracy of 1.2 to 1.6 μm. Here, the above filtration accuracy is preferably 1.2 μm or more, more preferably 1.25 μm or more, still more preferably 1.3 μm or more, and preferably 1.6 μm or less, more preferably 1.55 μm or less, still more preferably 1.5 μm or less.

[0041] The filtration using the above ceramic membrane CM-1 may be performed, for example, with the temperature of the sugar solution being 40 to 50°C, the filtrate Flux being 70 (±10%) LMH, the circulation flow rate being 30 (±5%) times the Flux, and the circulation pressure being 0.6 to 0.8 MPa (±5%). However, it is not limited to these conditions.

[0042] By using the above ceramic membrane for enzyme recovery, physical friction of highly crystalline undegraded cellulose occurs on the surface of the ceramic membrane, and the particle size of the undegraded cellulose becomes smaller. Then, the saccharification reaction between the recovered enzyme incorporated into the circulating liquid separated by filtration through the ceramic membrane and the fine crystalline undegraded cellulose with a smaller particle size further proceeds. As a result, a sugar solution with a Brix value of about 9 to 10% and a higher concentration can be obtained.

[0043] The ability to stably produce such a high-concentration sugar solution leads to an increase in the amount of water-containing bioethanol obtained in the fermentation process described later. As a result, it also produces effects such as reducing production costs in terms of increasing the yield of the finally obtained bioethanol.

[0044] The enzyme recovery step in this embodiment preferably further includes a step of recovering the enzyme using a UF membrane (ultrafiltration membrane) UF-1 after the step of recovering the enzyme using the ceramic membrane CM-1. In this case, the sugar solution after filtration by the ceramic membrane CM-1 is transferred to the sugar solution tank T-3 and then supplied to the UF membrane UF-1 from there. Specifically, by subjecting the sugar solution transferred to the sugar solution tank T-3 through the step of recovering the enzyme using the ceramic membrane CM-1 to filtration using the UF membrane UF-1, it is possible to separate and recover low-molecular-weight enzymes contained in the sugar solution that could not be completely recovered by filtration using the ceramic membrane CM-1.

[0045] By performing filtration using the UF membrane UF-1, it is also possible to separate and recover low-molecular-weight undegraded cellulose contained in the sugar solution that could not be completely recovered by filtration using the ceramic membrane CM-1.

[0046] By separating low-molecular-weight enzymes and undegraded cellulose through the filtration using the UF membrane UF-1, more precise filtration of the sugar solution is simultaneously carried out.

[0047] Thus, in the step of recovering the enzyme in this embodiment, it is more preferable to perform multi-stage solid-liquid separation using the ceramic membrane CM-1 and the UF membrane UF-1.

[0048] As the UF membrane UF-1, conventionally known ones can be used. For example, it is preferable to use a UF membrane having a fractional molecular weight of MW-3000 to 7000. Here, from the viewpoint of the Flux performance of the ultra-low pressure aquaporin-protein membrane used in the subsequent concentration step, the above fractional molecular weight is preferably MW-3000 or more, more preferably MW-3500 or more, further preferably MW-4000 or more, and even more preferably MW-4500 or more. Also, from the viewpoint of removing low-molecular-weight organic compounds, the above fractional molecular weight is preferably MW-7000 or less, more preferably MW-6500 or less, further preferably Mw-6000 or less, and even more preferably MW-5500 or less.

[0049] Before the enzyme recovery step in this embodiment, that is, before the step of recovering the enzyme using the ceramic membrane, centrifugation or the like may be performed as necessary. Thereby, the recovery efficiency of the sugar solution, undigested cellulose, and enzyme can be increased. Specifically, by dehydrating the sugar solution and recovering the long undigested cellulose and the enzyme contained in its substrate, and then using the ceramic membrane, undigested cellulose and enzyme on the μm order can be separated, recovered, and purified by the ceramic membrane in a short time. As the above centrifugation, for example, a decanter type centrifuge is preferable.

[0050] 〈Step of obtaining concentrated sugar solution〉 The step of obtaining the concentrated sugar solution in this embodiment is a step of concentrating the sugar solution obtained through the saccharification step or the subsequent enzyme recovery step to obtain a concentrated sugar solution. The sugar solution that has passed through the filtration by the ceramic membrane CM-1 and the UF membrane UF-1 is transferred to the sugar solution tank T-4. When concentrating such a sugar solution, it is preferable to use a membrane with high water permeability and good separation of organic and inorganic substances. For example, the RO membrane RO-1 is preferable. Among them, since the sugar solution can be preferably concentrated with lower energy, it is more preferable to concentrate using a protein-supported polyamide RO membrane.

[0051] In addition, when the sugar solution in the sugar solution tank T-2 is not filtered by the ceramic membrane CM-1 and the UF membrane UF-1, the sugar solution tanks T-3 and T-4 become unnecessary, and the sugar solution in the sugar solution tank T-2 is directly subjected to filtration by the RO membrane RO-1. Also, when the sugar solution in the sugar solution tank T-2 is not filtered by the UF membrane UF-1, the sugar solution tank T-4 becomes unnecessary, and the sugar solution in the sugar solution tank T-3 is directly subjected to filtration by the RO membrane RO-1.

[0052] As the protein-supported polyamide RO membrane, for example, a composite polyamide membrane (aquaporin-protein membrane) in which a protein (intrinsic membrane protein) that forms a channel in the cell membrane and controls the water flowing in and out of the cell, called aquaporin (AQP), is arranged on the cell membrane is more preferable, and an ultra-low pressure aquaporin-protein membrane is particularly preferable. Here, the pressure at ultra-low pressure means the pump discharge pressure applied when supplying the sugar solution to the protein-supported polyamide RO membrane. Although the specific pressure varies depending on the composition and concentration of the sugar solution, it can be determined with reference to the osmotic pressure. For example, the osmotic pressure of a 10% sugar solution (glucose) is 222 mOsmol / kg, and based on this value, the operating pressure can be set lower.

[0053] The protein-supported polyamide RO membrane is a membrane that incorporates the theory of the ideal biological membrane. Specifically, it incorporates a layer of natural aquaporin protein into the skin layer of the membrane and is a membrane that utilizes biomimetic technology. That is, aquaporin protein is a water channel existing in nature, present in all living cells, and functions as an ultra-efficient and ultra-selective high-speed channel for water molecules. Therefore, by using the protein-supported polyamide RO membrane, it can function as a reverse osmosis membrane with high water permeability while maintaining the rejection rate, reducing the power consumption required for concentration, and obtaining a CO2 emission reduction effect.

[0054] For example, if the power consumption when concentrating the sugar solution using an evaporation device is set to 100%, it is very advantageous in that the power consumption when concentrating the sugar solution using the protein-supported polyamide RO membrane can be about 40 - 60%.

[0055] The thickness of the protein-supported polyamide RO membrane in this embodiment also varies depending on the membrane configuration. When the protein-supported polyamide RO membrane is a composite membrane composed of three layers in order from the surface: a polyamide thin film, microporous polysulfone, polyester, etc., the thickness of the polyamide thin film is preferably, for example, 0.05 - 0.5 μm, the thickness of the microporous polysulfone is preferably, for example, 20 - 60 μm, and the thickness of the polyester is preferably, for example, 90 - 150 μm.

[0056] Also, a cell membrane may be present between the polyamide thin film and the microporous polysulfone. The thickness of the cell membrane is preferably, for example, 3 to 5 nm, and more preferably 3.5 to 4.5 nm. The protein present in such a cell membrane is called aquaporin. Thereby, water molecules and organic substances can be separated at a high speed and with a high removal rate.

[0057] By using such a protein-supported polyamide RO membrane, it is also possible to separate glucose and water while maintaining a Flux of 8 to 12 LMH and a removal rate of 99.2 to 99.7%.

[0058] In the step of obtaining the concentrated sugar solution in the present embodiment, for example, when the operating pressure is 3.7(+3) MPa and the Flux is 9 LMH, the power consumption required to obtain 1 L of a concentrated sugar solution with a desalination rate of 99.5% or more and a Brix value of about 20% or more is about 0.01 kW, and it can be preferably concentrated with very low energy. This is very low compared to the operating energy required for a conventional evaporation device (MVR type) or a concentration process using a high-pressure reverse osmosis membrane.

[0059] Also, the water separated when obtaining the concentrated sugar solution may be returned to the saccharification tank T-1 as recovered water and reused in the saccharification process (arrow 15, ※1 in Fig. 1).

[0060] 〈Fermentation process〉 The fermentation process in the present embodiment is a process in which yeast is added to the concentrated sugar solution obtained in the step of obtaining the concentrated sugar solution and fermented to obtain hydrous bioethanol.

[0061] The concentrated sugar solution obtained in the step of obtaining the concentrated sugar solution is transferred to the fermentation tank T-5. In addition to the concentrated sugar solution, yeast is also added to the fermentation tank T-5. Optionally, steam, cooling water, a pH adjuster, etc. are also added to the fermentation tank T-5.

[0062] In the fermentation process in the present embodiment, in the fermentation tank T-5, the concentrated sugar solution is decomposed by yeast into ethanol and carbon dioxide (CO2) under anaerobic conditions, and such a reaction is called fermentation.

[0063] The ethanol obtained above, which is called hydrated bioethanol, has a concentration of about several tens of percent, and a purity close to 100% is required for use as fuel. Therefore, the hydrated bioethanol is optionally subjected to a subsequent concentration process after passing through an unreacted yeast recovery process.

[0064] 〈Unreacted Yeast Recovery Process〉 The production method according to this embodiment preferably includes an unreacted yeast recovery process after the fermentation process and before the concentration process.

[0065] In the unreacted yeast recovery process in this embodiment, the hydrated bioethanol in the fermenter T-5 is microfiltered through the ceramic membrane CM-2, so that unreacted yeast, which is yeast that has not been deactivated without reacting, is separated from the hydrated bioethanol and can be recovered, and at the same time, the hydrated bioethanol is purified.

[0066] The unreacted yeast recovered above is preferably returned to the fermenter T-5 as recovered yeast and subjected to the fermentation process again (arrow 21 in FIG. 1).

[0067] By repeatedly using yeast through the recovery and return of the unreacted yeast, the amount of yeast used can be reduced, leading to a reduction in production costs. Also, reducing the amount of yeast contained in the waste liquid is advantageous from the perspective of reducing the environmental burden. Note that while repeatedly using the unreacted yeast, a part of new yeast may be put into the fermenter T-5 and used.

[0068] The ceramic membrane CM-2 in this embodiment can use the same one as the ceramic membrane CM-1 in the enzyme recovery process, and the preferred embodiments are also the same. That is, the ceramic membrane CM-2 preferably has a filtration accuracy of 1.2 to 1.6 μm, for example. In addition, in the manufacturing method according to the present embodiment, the ceramic membrane CM-1 used in the enzyme recovery step and the ceramic membrane CM-2 used in the unreacted yeast recovery step may be the same or different.

[0069] For example, the filtration using the ceramic membrane CM-2 may be performed with the temperature of the hydrous bioethanol being 30 to 40°C, the filtrate Flux being 80 (±5%) LMH, the circulation flow rate Flux being 25 to 30 times the amount (±5%) LMH, and the circulation pressure being 0.6 to 0.8 MPa (±5%). However, it is not limited to these conditions.

[0070] The fact that hydrous bioethanol with a low impurity concentration can be stably produced by such microfiltration leads to an increase in the amount of bioethanol obtained in the subsequent concentration step, and also produces effects such as cost reduction in production from the viewpoint of achieving a high yield.

[0071] In the manufacturing method according to the present embodiment, it is preferable to perform at least one of the above enzyme recovery step and unreacted yeast recovery step, and it is more preferable to perform both. As the enzyme recovery step, it is further preferable to perform a recovery step using a ceramic membrane and a recovery step using a UF membrane.

[0072] 〈Concentration step〉 The concentration step in the present embodiment is a step of concentrating the hydrous bioethanol obtained in the fermentation step to obtain bioethanol. The method for concentrating the hydrous bioethanol transferred to the fermentation liquid tank T-6 is not particularly limited, and a conventionally known method can be adopted. For example, it is preferable to concentrate by distillation, and it is more preferable to concentrate by vacuum distillation using the vacuum distillation apparatus DE-1. The hydrous bioethanol transferred to the fermentation liquid tank T-6 becomes bioethanol through the concentration step and is transferred to the bioethanol tank T-7.

[0073] The concentration (purity) of the finally obtained bioethanol is preferably 99% or more, more preferably 99.3% or more, still more preferably 99.5% or more, and the higher the better.

[0074] By going through the above steps, the production cost can be suitably reduced, and bioethanol can be obtained.

[0075] Also, the water separated during the concentration for obtaining the above bioethanol may be returned to the saccharification tank T-1 as recovered water (recovered warm water) and reused in the saccharification process (※4 in Fig. 1).

[0076] 〈Protein-containing waste liquid recovery step〉 The production method according to the present embodiment may further include a step of recovering waste liquid, and the waste liquid is preferably a protein-containing waste liquid.

[0077] In the production method according to the present embodiment, waste liquid is discharged at least after the saccharification step, fermentation step, and concentration step. The waste liquid after the saccharification step contains at least enzymes and sugars, the waste liquid after the fermentation step contains at least yeast and sugars, and the waste liquid after the concentration step contains enzymes, sugars, and yeast that have not been completely removed until then. That is, the waste liquid after the above steps is all protein-containing waste liquid.

[0078] In addition, in the production method according to the present embodiment, reusing enzymes and unreacted yeast through an enzyme recovery step and an unreacted yeast recovery step is one method for realizing cost reduction. However, if enzymes are repeatedly reused, their activity gradually decreases, and they cannot be reused infinitely, etc., and there is a limit to the number of times enzymes and unreacted yeast can be reused. Therefore, in the saccharification step and the fermentation step, it is necessary to discharge the protein-containing waste liquid at a specific cycle.

[0079] Therefore, the manufacturing method according to this embodiment preferably further includes a step of recovering the protein-containing waste liquid after one or more steps among the saccharification step, the fermentation step, and the concentration step, more preferably further includes a step of recovering the protein-containing waste liquid after two or more steps, and even more preferably further includes a step of recovering the protein-containing waste liquid after all three steps.

[0080] Since the above waste liquid contains protein, gas is generated when a biological reaction is carried out. Specifically, when fermented under anaerobic conditions, biomass gas containing methane gas can be obtained and can be used as renewable energy. The use of the above renewable energy is not particularly limited. For example, if it is used for power drive in the production of bioethanol according to this embodiment, it can also contribute to reducing the production cost of bioethanol.

[0081] Therefore, it is more preferable that the manufacturing method according to this embodiment further includes a step of manufacturing and recovering methane gas using the recovered protein-containing waste liquid. Note that the above does not exclude the generation of other gases together with methane gas. That is, it is only necessary to be able to manufacture and recover biomass gas containing methane gas using the protein-containing waste liquid, and the above biomass gas may contain carbon dioxide and the like in addition to methane gas.

[0082] In the step of manufacturing and recovering methane gas in this embodiment, the protein-containing waste liquid discharged through the saccharification step carried out in the saccharification tank T-1 is transferred into the anaerobic methane gas fermentation device MFE-1 (arrow ※2 in FIG. 1), and the protein-containing waste liquid discharged through the fermentation step carried out in the fermentation tank T-5 is transferred into the anaerobic methane gas fermentation device MFE-1 (arrow ※3 in FIG. 1), and the protein-containing waste liquid discharged when the water-containing bioethanol in the fermentation liquid tank T-6 is concentrated is transferred into the anaerobic methane gas fermentation device MFE-1 (arrow ※5 in FIG. 1). Then, methane gas is manufactured by mixing and reacting with methane-producing bacteria in the anaerobic methane gas fermentation device MFE-1.

[0083] The produced methane gas can be recovered and purified, and then used to generate electricity in a gas turbine. The generated electricity can also be fully reused as the operating energy and power source required for the operation management of the bioethanol production apparatus according to this embodiment.

[0084] 《Bioethanol Production Apparatus》 The bioethanol production apparatus according to this embodiment is used when performing the production method described in the above 《Bioethanol Production Method》.

[0085] One aspect of the bioethanol production apparatus according to this embodiment includes a saccharification tank T-1, a sugar solution tank T-2, a fermentation tank T-5, a bioethanol tank T-7, and a ceramic membrane. Here, the saccharification tank T-1 is a tank in which an enzyme is further added to the input cellulose for saccharification to obtain a sugar solution. The sugar solution tank T-2 is a tank to which a concentrated sugar solution obtained by concentrating the sugar solution generated in the saccharification tank T-1 is supplied. The fermentation tank T-5 is a tank in which yeast is further added to the input concentrated sugar solution for fermentation to obtain hydrous bioethanol. The bioethanol tank T-7 is a tank to which bioethanol obtained by concentrating the hydrous bioethanol generated in the fermentation tank T-5 is supplied.

[0086] The ceramic membrane is preferably provided in at least one of the spaces between the sugar solution tank T-2 and the fermentation tank T-5, and between the fermentation tank T-5 and the bioethanol tank T-7, and more preferably provided in both.

[0087] The enzyme is separated from the sugar solution contained in the sugar solution tank T-2 by the ceramic membrane CM-1 provided between the sugar solution tank T-2 and the fermentation tank T-5. In addition to the enzyme, undigested cellulose can also be separated, and the sugar solution is purified.

[0088] Unreacted yeast is separated from the hydrous bioethanol contained in the fermentation tank T-5 by the ceramic membrane CM-2 provided between the fermentation tank T-5 and the bioethanol tank T-7. Also, the hydrous bioethanol is purified. When having the ceramic membrane CM-2 between the fermentation tank T-5 and the bioethanol tank T-7, the hydrous bioethanol passing through the ceramic membrane CM-2 is transferred to the fermentation broth tank T-6.

[0089] Another aspect of the bioethanol production apparatus according to the present embodiment has a saccharification tank T-1, a sugar solution tank T-2, a fermentation tank T-5, a bioethanol tank T-7, and a protein-supported polyamide RO membrane. Here, the saccharification tank T-1, the sugar solution tank T-2, the fermentation tank T-5, and the bioethanol tank T-7 are the same as those in the above-described aspect, respectively.

[0090] Also, the protein-supported polyamide RO membrane is provided between the sugar solution tank and the fermentation tank T-5. Here, when the production apparatus according to the present embodiment does not have the ceramic membrane CM-1 and the UF membrane UF-1, the sugar solution tanks T-3 and T-4 are unnecessary, and the sugar solution in the sugar solution tank T-2 is subjected to filtration by the protein-supported polyamide RO membrane. Also, when the production apparatus according to the present embodiment does not have the UF membrane UF-1, the sugar solution tank T-4 is unnecessary, and the sugar solution in the sugar solution tank T-3 is subjected to filtration by the protein-supported polyamide RO membrane.

[0091] The bioethanol production apparatus according to the present embodiment may additionally have each of the constituent components described in the above "Method for Producing Bioethanol". For example, an anaerobic methane gas fermentation device MFE-1 for injecting protein-containing waste liquid (enzyme-containing waste liquid) from saccharification tank T-1, protein-containing waste liquid (yeast-containing waste liquid) from fermentation tank T-5, and protein-containing waste liquid (distillation waste liquid) from fermentation liquid tank T-6, a device for purifying and generating electricity from methane gas, a power source for a bioethanol production device that can be driven using the produced methane gas, a system for supplying the recovered enzyme recovered from the sugar solution to liquefaction tank T-1 (arrows 9 and 12 in Fig. 1), a system for supplying unreacted yeast recovered from hydrous bioethanol to fermentation tank T-5 (arrow 21 in Fig. 1), a system for supplying the water obtained when the sugar solution is concentrated into a concentrated sugar solution to saccharification tank T-1 as recovered water (※1 in Fig. 1), a system for supplying the warm water obtained when hydrous bioethanol is distilled to saccharification tank T-1 as recovered warm water (※4 in Fig. 1), etc. can be mentioned. Also, pipes for connecting these respective components and each pump (P-1 to P-7) can be mentioned. In addition to the above, a system for discharging each of the protein-containing waste liquid (enzyme-containing waste liquid) from saccharification tank T-1, the protein-containing waste liquid (yeast-containing waste liquid) from fermentation tank T-5, and the protein-containing waste liquid (distillation waste liquid) from fermentation liquid tank T-6 in a predetermined number of batches may be further provided.

Example

[0092] Hereinafter, the present invention will be described by test examples, but the present invention is not limited thereto.

[0093] Sheet pulp as a raw material pulp containing cellulose, industrial water, an enzyme (cellulase), caustic soda as a pH adjuster, and a fatty acid-based antifoaming agent as an antifoaming agent were introduced into saccharification tank T-1, and the temperature in the tank was maintained at 50 to 55°C to saccharify the above cellulose to obtain a sugar solution. At this time, since the recovered enzyme described later was deposited in saccharification tank T-1 at 80% per 100% addition amount of active FPU, only 20% of the enzyme activity FPU of the insufficient amount of enzyme was supplied for the enzyme (cellulase). In the normal above reaction, since it is necessary to add an enzyme activity of 30 FPU / g-pulp per 1 kg of raw material with a solid content concentration of 54%, it is necessary to add 162 g of a new enzyme for each saccharification step. In contrast, in the saccharification step of the production method according to the present embodiment, since a saccharification rate of 70 to 80% or more is maintained and the recovered enzyme can be reused continuously for 5 batches or more, the amount of enzyme newly added is 20% (33 g), and it is possible to produce a sugar solution (Brix value 8 to 9%) with a significantly small consumption amount. Thereby, a mixed solution of 80% sugar solution and 20% undigested cellulose was obtained. The particle size of the undigested cellulose was included in the mixed solution in a range of 4 to 1000 μm.

[0094] Next, the above mixed solution was transferred to a sugar solution tank T-2, and precision filtration was performed to separate the undigested cellulose and the sugar solution by cross-flow treatment with a ceramic membrane (manufactured by TAMI) having a filtration accuracy of 1.4 μm, and at the same time, the enzyme incorporated into the substrate was recovered. The above cross-flow treatment was performed under the conditions of a liquid temperature of the mixed solution: 40 to 50 °C, a filtrate Flux: 70 (±10%) LMH, a circulation flow rate Flux: 30 (±5%) times the amount, and a circulation pressure: 0.6 MPa (±5%). As a result, a sugar solution with a Brix value of 9 to 10% was obtained in the sugar solution tank T-3. Also, the recovered enzyme was put back into the saccharification tank T-1.

[0095] Subsequently, the sugar solution with a Brix value of 9 to 10% was treated with a UF membrane (manufactured by Kuraray Co., Ltd.) having a fractional molecular weight of MW-5000 to recover the smaller enzyme incorporated into the substrate. The above treatment was performed under the conditions of a liquid temperature of the mixed solution: 30 to 50 °C, a Flux: 80 (±10%) LMH, a circulation flow rate Flux: 10 to 15 (±5%) times the amount, and a circulation pressure: 0.5 MPa (±5%). As a result, a sugar solution with a Brix value of 9.5 to 10.5% was obtained in the sugar solution tank T-4. Also, the recovered enzyme was put back into the saccharification tank T-1.

[0096] The refined sugar solution with a Brix value of 9.5 - 10.5% was separated into demineralized water and a concentrated sugar solution with a Brix value of 20% or more using a protein - supported polyamide RO membrane (manufactured by Aquaporin). The concentrated sugar solution with a Brix value of 20% or more was transferred to fermentation tank T - 5. Here, the above separation was carried out under the conditions of operating pressure: 3.7(+3) MPa, Flux: 9 LMH, and the desalination rate was 99.5% or more. Also, the power consumption required to obtain 1 L of the concentrated sugar solution with a Brix value of 20% or more was 0.01 kW. Compared with the conventionally required power consumption (for reference, the power consumption required when using an evaporation device (MVR type) or a high - pressure reverse osmosis membrane is about 0.04 kW or more), it was confirmed that the concentrated sugar solution could be obtained with low energy. The water separately obtained when obtaining the above concentrated sugar solution was put into saccharification tank T - 1 as recovered water.

[0097] Next, yeast, steam, cooling water, and caustic soda as a pH adjuster were added to fermentation tank T - 5 containing the concentrated sugar solution, the temperature in the tank was maintained at 30 - 35 °C, and the above concentrated sugar solution was fermented to obtain hydrated bioethanol. Here, the amount of yeast added was 70% of the shortage because the recovered yeast described later had accumulated in fermentation tank T - 5 at an activity of about 30% per batch. Thus, in the fermentation process of the manufacturing method according to this embodiment, the amount of newly added yeast can be reduced. Also, since the recovered yeast can be reused multiple times until it is inactivated, the amount of newly added yeast can be reduced.

[0098] The hydrated bioethanol in fermentation tank T - 5 obtained above was subjected to cross - flow treatment with a ceramic membrane (manufactured by TAMI) with a filtration accuracy of 1.4 μm to perform microfiltration and simultaneously recover the unreacted yeast incorporated into the substrate. The above cross - flow treatment was carried out under the conditions of liquid temperature of the hydrated bioethanol: 30 - 40 °C, filtrate Flux: 80 LMH, circulation flow rate Flux: 30 times the amount, and circulation pressure: 0.6 - 0.8 MPa. As a result, 8 - 9 vol% of hydrated bioethanol was obtained in fermentation liquid tank T - 6. In addition, the recovered unreacted yeast was put back into the fermentation tank T-5 again.

[0099] The water-containing bioethanol in the fermentation liquid tank T-6 obtained above was distilled using the vacuum distillation apparatus DE-1 under the condition of a distillation time of 3 hours to produce bioethanol. The distillation was carried out under the condition of a distillation temperature of 78 - 82°C. In addition, the warm water obtained during the above distillation was used as a heat medium for the temperature-raising process of the saccharification tank T-1 as warm water.

[0100] Note that the recovered enzyme and recovered yeast were discarded in 5 batches. However, the protein-containing waste liquid discharged in the saccharification process, fermentation process, and concentration process contained a large amount of protein. The biogas generation amount per wet weight was 174 NL / kg, and the gas generation amount per organic matter was 2,063 NL / kg-VS. Thus, it is possible to recover biogas with a very high value from the protein-containing waste liquid. This is because, among the generally stated upper limit of the ammonia nitrogen concentration in the tank during the medium-temperature fermentation (fermentation temperature around 37°C) of the wet method, which is 3,000 - 4,000 mg / L, when the manufacturing method according to this embodiment is adopted, the ammonia nitrogen concentration is estimated to be about 1,700 mg / L, and it has been confirmed that there is no problem with the operation.

[0101] In addition, the methane concentration in the biogas obtained by fermenting the obtained protein-containing waste liquid was 57%, and methane gas with a high concentration of 98.9 L / kg of methane generation amount per unit was recovered. And when 1 kg of the protein-containing waste liquid was treated, the generated power amount was 0.314 kWh. This amount of renewable energy can cover 65 - 70% of the operating energy of the bioethanol production apparatus according to this embodiment.

[0102] According to the manufacturing method according to the present embodiment described above, the amount of enzymes and yeast used can be reduced, and concentration and the like can be efficiently performed with low energy. In addition to the above, the protein-containing waste liquid discharged from the manufacturing process can be uniquely and effectively utilized for the energy related to the production of bioethanol and the operation of the manufacturing apparatus.

Explanation of Signs

[0103] T-1: Saccharification tank T-2, T-3, T-4: Sugar solution tanks T-5: Fermentation tank T-6: Fermentation broth tank T-7: Bioethanol tank P-1: Saccharification pump P-2: Ceramic membrane pump P-3: UF membrane pump P-4: Concentration pump P-5: Concentrated sugar solution pump P-6: Fermentation pump P-7: Fermentation broth pump CM-1, CM-2: Ceramic membranes UF-1: UF membrane RO-1: RO membrane DE-1: Vacuum distillation apparatus MFE-1: Anaerobic methane gas fermentation apparatus

Claims

1. A method for producing bioethanol from cellulose, comprising: a saccharification step of adding an enzyme to the cellulose to saccharify it to obtain a sugar solution; a step of concentrating the obtained sugar solution to obtain a concentrated sugar solution; a fermentation step of adding yeast to the concentrated sugar solution and fermenting it to obtain hydrous bioethanol; and a concentration step of concentrating the hydrous bioethanol to obtain bioethanol, sequentially including; further including an enzyme recovery step performed after the saccharification step; The enzyme recovery step includes a step of recovering the enzyme using a ceramic membrane, and then a step of recovering the enzyme using a UF membrane. A method for producing bioethanol.

2. The method for producing bioethanol according to claim 1, wherein a UF membrane having a fractional molecular weight of MW-3000 to 7000 is used as the UF membrane.

3. The method for producing bioethanol according to claim 1 or 2, wherein in the enzyme recovery step, undegraded cellulose is also recovered together with the enzyme.

4. further including an unreacted yeast recovery step performed after the fermentation step; The unreacted yeast recovery step uses a ceramic membrane. The method for producing bioethanol according to claim 1 or 2.

5. The method for producing bioethanol according to claim 1 or 2, wherein in the step of obtaining the concentrated sugar solution, the sugar solution is concentrated using an RO membrane.

6. The method for producing bioethanol according to claim 5, wherein a protein-supported polyamide RO membrane is used as the RO membrane.

7. The method for producing bioethanol according to claim 1 or 2, wherein in the enzyme recovery step, a ceramic membrane having a filtration accuracy of 1.2 to 1.6 μm is used as the ceramic membrane.

8. The method for producing bioethanol according to claim 1 or 2, further including a step of recovering a protein-containing waste liquid after one or more of the saccharification step, the fermentation step, and the concentration step.

9. The method for producing bioethanol according to claim 8, further including a step of producing and recovering methane gas using the recovered protein-containing waste liquid.

10. An apparatus for producing bioethanol from cellulose, comprising: a saccharification tank for adding an enzyme to the cellulose to saccharify it to obtain a sugar solution; a sugar solution tank to which the concentrated sugar solution obtained by concentrating the obtained sugar solution is supplied; a fermentation tank for adding yeast to the concentrated sugar solution and fermenting it to obtain hydrous bioethanol; A bioethanol tank to which bioethanol obtained by concentrating the aqueous bioethanol is supplied. At least one of a ceramic membrane for separating the enzyme provided between the sugar solution tank and the fermentation tank, and a ceramic membrane for separating unreacted yeast provided between the fermentation tank and the bioethanol tank. An apparatus for producing bioethanol, further comprising a protein-supported polyamide RO membrane for concentrating the sugar solution between the sugar solution tank and the fermentation tank.

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