Sugar solution manufacturing method

Abstract

Provided is a new method for producing sugar solution that can achieve both a sufficient saccharification rate and economic efficiency. [Solution] A method for producing a sugar solution from pulp containing cellulose as a main component, comprising: a saccharification step in which an enzyme is added to the pulp to perform saccharification treatment and obtain a reaction mixture containing a sugar solution; a solid-liquid separation step in which the reaction mixture is solid-liquid separated and a sugar solution and a saccharification residue are recovered, respectively; an extrusion step in which the saccharification residue is extruded; and a re-saccharification step in which the saccharification residue after the extrusion treatment is subjected to a second saccharification treatment and solid-liquid separation to obtain a sugar solution, wherein the extrusion step involves kneading the saccharification residue in the presence of an enzyme at an optimal temperature for enzyme reaction.

Description

[Technical Field]

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

[0002] In recent years, as paperless society advances and paper consumption decreases, there has been growing interest in technology that utilizes existing pulp manufacturing facilities to produce sugar solutions from cellulosic biomass.

[0003] Patent Document 1 discloses that cellulose, the main component of pulp, is rapidly hydrolyzed by cellulase, resulting in rapid liquefaction and saccharification. However, some cellulose is difficult to hydrolyze with enzymes and tends to remain undecomposed during the process. Therefore, Patent Document 2 proposes a process for recovering such undecomposed cellulose and re-saccharifying it.

[0004] On the other hand, if the majority of the undecomposed material is crystalline cellulose, it is difficult to improve the saccharification rate, which makes it difficult to maintain the reuse cycle. In light of this, Non-Patent Document 1 states that "amorphization treatment," which converts crystalline cellulose into amorphous cellulose, is extremely important for efficient saccharification of cellulose.

[0005] As one specific example of such a means, Non-Patent Documents 2 and 3 use "bioextrusion" to simultaneously perform mechanical and enzymatic treatments on various plant-derived biomass materials, including cellulose. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5562492 [Patent Document 2] Patent No. 7708485 [Non-patent literature]

[0007] [Non-Patent Document 1] The FEBS Journal, (US), 2010, Volume 277(6), p. 1571-1582 [Non-patent document 2] Bioresource Technology, (English), 2021, Volume 327, p. 124819 [Non-patent document 3] Industrial Crops and Products, (Netherlands), 2018, Volume 122, p. 329-339 Summary of the Invention [Problem to be solved by the invention]

[0008] However, as disclosed in Non-Patent Documents 2 and 3, even when extrusion is performed using a conventional extruder, the processing time for each extrusion is short, and sufficient amorphization cannot be achieved in a single process. The same is true for cellulose, which requires multiple extrusion processes. This creates new challenges, such as increased load on the equipment, higher energy costs, and more complicated processing flows. As a result, it is difficult to achieve both a sufficient saccharification rate and economic efficiency with conventional bioextrusion, which is a bottleneck in scaling up for industrial use.

[0009] Therefore, an object of the present invention is to provide a new method for producing sugar solution that can achieve both a sufficient saccharification rate and economic efficiency. [Means for solving the problem]

[0010] In response to the above, the present inventors conducted extensive research and came up with the idea of ​​first carrying out a saccharification step, then subjecting the resulting reaction mixture to solid-liquid separation to extract a saccharification residue, and then amorphizing this residue before subjecting it to a re-saccharification treatment. When amorphizing the entire pulp, which is primarily composed of cellulose, as in the past, even the parts that are easily saccharified are treated, requiring multiple treatments, which ultimately reduces the economic viability.

[0011] In contrast, in the present invention, only the saccharification residue containing a large amount of components that are difficult to saccharify is subjected to amorphization. This is efficient and economical because it avoids excessive treatment of unnecessary parts. Furthermore, by performing this amorphization in the presence of enzymes, saccharification also progresses in situ, improving the saccharification rate. Then, by subjecting the residue to a saccharification treatment again (re-saccharification treatment), a sugar solution can be easily obtained, and ultimately a sufficiently high saccharification rate can be achieved. In this way, the present invention has been completed.

[0012] The gist of one embodiment of the present invention is as follows. [1] A method for producing a sugar solution from pulp containing cellulose as a main component, comprising: a saccharification treatment step in which an enzyme is added to the pulp to perform saccharification treatment, thereby obtaining a reaction mixture containing a sugar solution; a solid-liquid separation step of subjecting the reaction mixture to solid-liquid separation to recover a sugar solution and a saccharification residue, respectively; an extrusion step of extruding the saccharification residue; and a re-saccharification treatment step of subjecting the saccharification residue after the extrusion treatment to a second saccharification treatment and solid-liquid separation to obtain a sugar solution, The method for producing a sugar solution, wherein the extrusion step comprises kneading the saccharification residue in the presence of an enzyme at an optimum temperature for enzyme reaction. [2] The method for producing a sugar solution according to [1], wherein the saccharification treatment step is carried out under the conditions of a pulp concentration of 5 to 30% by mass, a cellulase addition amount of 3 to 30 FPU / g-pulp, and a reaction time of 15 minutes or more at an optimum temperature for the enzyme reaction. [3] The method for producing a sugar solution according to [1] or [2], wherein the extrusion step is carried out using a twin-screw extruder under conditions of a barrel temperature of less than 70°C and a residence time of 10 minutes or less. [4] As the enzyme in the extrusion treatment step, at least one of the enzymes added in the saccharification treatment step that remain in the saccharification residue recovered in the solid-liquid separation step and the enzymes newly added is used, and The method for producing a sugar solution according to any one of [1] to [3] above, wherein the enzyme used in the extrusion treatment step is subjected to the second saccharification treatment step together with the saccharification residue after the extrusion treatment. [5] The method for producing a sugar liquid according to any one of [1] to [4] above, wherein the sugar liquid obtained in the solid-liquid separation step and the re-saccharification treatment step is used as a biorefinery feedstock. [Effects of the Invention]

[0013] According to this embodiment, a sugar solution can be produced by a production method that achieves both a sufficient saccharification rate and economic efficiency. Specifically, only the saccharification residue obtained in the solid-liquid separation process, which is difficult to saccharify, can be amorphized by the extrusion process. The extrusion process can be carried out more efficiently than conventional processes, resulting in excellent economic efficiency. Furthermore, since saccharification can proceed simultaneously with the amorphization, and the amorphized saccharification residue after the extrusion process can be subjected to a second saccharification process and solid-liquid separation to obtain a satisfactory sugar solution, a sufficient saccharification rate can be achieved. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 shows XRD patterns of the saccharification residue in Example 1 before and after the extrusion treatment step. [Figure 2] FIG. 2 shows XRD patterns of the saccharification residue in Example 2 before and after the extrusion process. [Figure 3] FIG. 3 shows the XRD patterns of the saccharification residues of Examples 2 and 3 after the extrusion process. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the embodiments described below. In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0016] <Method for producing sugar solution> One aspect of the method for producing a sugar solution according to this embodiment includes the following steps 1 to 4 in order. Step 1: A saccharification process in which enzymes are added to pulp, which is primarily composed of cellulose, to perform saccharification, thereby obtaining a reaction mixture containing sugar solution. Step 2: A solid-liquid separation step in which the reaction mixture obtained in Step 1 is subjected to solid-liquid separation to recover a sugar solution and a saccharification residue. Step 3: Extrusion treatment step of extruding the saccharification residue obtained in Step 2 Step 4: A re-saccharification step in which the saccharification residue after the extrusion treatment in Step 3 is subjected to a second saccharification treatment and solid-liquid separation to obtain a sugar solution. Here, in the extrusion treatment step of step 3, the saccharification residue obtained in step 2 is subjected to a kneading treatment in the presence of an enzyme at an optimum temperature for the enzyme reaction.

[0017] In the production method according to this embodiment, only materials that are resistant to saccharification, such as undigested pulp, obtained in the solid-liquid separation step (step 2) can be separated and recovered at a high concentration as saccharification residue. Therefore, in the subsequent extrusion step (step 3), the saccharification residue that is resistant to saccharification can be efficiently amorphized, resulting in excellent cost efficiency. Furthermore, in this extrusion step, a kneading treatment is performed in the presence of an enzyme at an optimal temperature for enzymatic reaction. While the enzyme may be added separately, the enzyme added in step 1 typically remains in the saccharification residue, allowing it to be used as is, which is economical. Furthermore, for materials that have become more susceptible to saccharification through amorphization by extrusion due to the presence of this enzyme, the enzymatic reaction proceeds during step 3, resulting in saccharification. Even if saccharification is not performed here, the amorphization proceeds in step 3, making the material more susceptible to enzyme reaction (easily saccharified). Therefore, saccharification can be performed efficiently through the subsequent re-saccharification step (step 4), and a sugar solution can be obtained by solid-liquid separation. This allows for a sufficient saccharification rate to be achieved.

[0018] Each step of the manufacturing method according to this embodiment will be described.

[0019] <Step 1: Saccharification process> The saccharification treatment step in this embodiment is a step in which an enzyme is added to pulp containing cellulose as a main component to perform saccharification treatment, thereby obtaining a reaction mixture containing a sugar solution.

[0020] The pulp is not particularly limited as long as it contains cellulose as a main component. For example, virgin pulp such as wood pulp or non-wood pulp may be used, or recycled paper pulp may be used. Also, mechanical pulp or chemical pulp may be used. Furthermore, two or more types of pulp may be mixed and used.

[0021] The pulp used in this embodiment may be either wood pulp or non-wood pulp. Examples of wood pulp include N-wood (softwood pulp; Nadelholz pulp) and L-wood (hardwood pulp; Laubholz pulp). Examples of non-wood pulp that can be used include straw pulp, bagasse pulp, reed pulp, kenaf pulp, mulberry pulp, and fruit-derived pulp.

[0022] In step 1 of this embodiment, from the viewpoint of effectively utilizing existing pulp manufacturing facilities, kraft pulp (KP), bleached kraft pulp (NBKP, LBKP), sulfite pulp (SP), etc. are preferred, and bleached kraft pulp (particularly LBKP) is more preferred. From the viewpoint of availability of raw materials and low cost, deinked waste paper pulp (DIP) and unbleached kraft pulp (UKP) are preferred, with deinked waste paper pulp being more preferred. Furthermore, from the viewpoint of high cellulose purity and excellent saccharification yield, dissolving pulp is preferred, and dissolving pulp with a high α-cellulose content is more preferred.

[0023] In this embodiment, the pulp contains cellulose as a main component, and the term "main component" means that the component that is contained in the highest proportion among the components that make up the pulp.

[0024] When saccharifying pulp, pretreatment may be carried out as necessary to facilitate the progress of saccharification and fermentation. Examples of pretreatment include steam explosion, hydrothermal treatment, concentrated sulfuric acid method, dilute sulfuric acid method, ammonia freeze explosion method, ammonia permeation method, alkali cooking method, lime method, and methods using organic solvents. One type of pretreatment may be carried out, or two or more types may be combined. From the viewpoint of production costs, it is also preferable not to carry out such pretreatment.

[0025] In step 1, an enzyme is added to the pulp to carry out saccharification treatment, thereby obtaining a reaction mixture containing a sugar solution. Any enzyme may be used as long as it reacts with cellulose to promote saccharification, and any conventionally known enzyme may be used, with cellulase being preferred, for example.

[0026] The enzyme may be prepared or commercially available, but when prepared, it is preferable to use an enzyme produced, for example, in a continuous culture apparatus.

[0027] The cellulose contained in pulp has a polymer structure with sugars bound to it, and is hydrolyzed to saccharify it into a sugar solution. The addition of enzymes to this process accelerates the hydrolysis.

[0028] When adding the enzyme, steam may be used to maintain the temperature inside the saccharification tank at the optimum temperature for the enzyme reaction (enzyme activity temperature). When cellulase is used as the enzyme, it is particularly preferable to maintain the optimum temperature for the enzyme reaction in the range of 50°C ± 3°C.

[0029] When pulp is used as the cellulose raw material, the amount of cellulase added during the saccharification reaction is preferably about 3 to 30 FPU / g-pulp, although this depends on the solids concentration of the pulp. The enzyme is added to the saccharification tank so that the amount of cellulase added falls within the above range. When the recovered enzyme is reused, the amount of new enzyme added is determined based on the amount of enzyme to be reused. From the viewpoints of reaction efficiency and suppression of viscosity increase, the amount of cellulase added is preferably 3 FPU / g-pulp or more, more preferably 5 FPU / g-pulp or more, and even more preferably 7 FPU / g-pulp or more, whereas from the viewpoint of economy, the amount of cellulase added is preferably 30 FPU / g-pulp or less, more preferably 25 FPU / g-pulp or less, and even more preferably 20 FPU / g-pulp or less.

[0030] The pulp concentration in the saccharification treatment is preferably 5 to 30% by mass. From the viewpoint of sugar concentration, the pulp concentration is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. From the viewpoint of saccharification rate, the pulp concentration is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less.

[0031] The temperature at which the saccharification treatment is carried out is not particularly limited as long as it is within the optimal temperature range for the enzyme used, but is usually preferably 40°C or higher and 70°C or lower. From the viewpoint of smoothly progressing the reaction, the temperature is preferably 40°C or higher, more preferably 45°C or higher, and even more preferably 48°C or higher. On the other hand, from the viewpoint of preventing the deactivation of the enzyme, the temperature is preferably 70°C or lower, more preferably less than 70°C, even more preferably 65°C or lower, and even more preferably 60°C or lower. In this specification, the saccharification treatment temperature refers to the temperature set in the saccharification tank.

[0032] The saccharification treatment time is not particularly limited and varies depending on the type and concentration of the pulp added, the activity of the enzyme used, etc. Generally, 15 minutes or more is preferred, and 15 minutes to 60 hours is more preferred. From the viewpoint of allowing the enzymatic reaction to proceed sufficiently, the treatment time is preferably 15 minutes or longer, more preferably 30 minutes or longer, and even more preferably 1 hour or longer, and from the viewpoint of economy, the treatment time is preferably 60 hours or shorter, more preferably 55 hours or shorter, and even more preferably 50 hours or shorter.

[0033] The saccharification treatment step in this embodiment is more preferably carried out under conditions of a pulp concentration of 5 to 30% by mass, a cellulase addition amount of 3 to 30 FPU / g-pulp, and a reaction time of 15 minutes or longer at an optimum temperature for the enzyme reaction. In other words, it is more preferable that the saccharification residue recovered by the subsequent solid-liquid separation step in step 2 is saccharification residue that has not been saccharified under the following conditions: a pulp concentration of 5 to 30% by mass, a cellulase addition amount of 3 to 30 FPU / g-pulp, and a reaction time of 15 minutes or more at the optimal temperature for the enzyme reaction.

[0034] In this embodiment, the Brix value (sugar concentration) of the sugar solution in the reaction mixture obtained in the saccharification treatment step corresponds approximately to the concentration of the pulp added, and is usually about 5 to 30%. From the viewpoints of fermentation efficiency and productivity, the Brix value of the sugar solution is preferably 10 to 20%. From the viewpoint of increasing the concentration of the product obtained by fermentation, the Brix value is preferably 10% or more, while from the viewpoint of suppressing a decrease in fermentation efficiency due to an increase in solution viscosity and the influence of osmotic pressure, the Brix value is preferably 20% or less. In other words, by setting the Brix value to about 10 to 20%, both the product concentration and fermentation efficiency can be achieved.

[0035] In the saccharification treatment of this embodiment, in addition to adding an enzyme to the pulp, any optional components may be further added within a range that does not impair the effects of the present invention. As the optional component, conventionally known components can be used, for example, water (industrial water), pH adjusters, antifoaming agents, surfactants, steam, etc.

[0036] <Step 2: Solid-liquid separation step> The solid-liquid separation step in this embodiment is a step of subjecting the reaction mixture obtained in the saccharification treatment step (step 1) to solid-liquid separation, and recovering a sugar solution and a saccharification residue.

[0037] The method for carrying out solid-liquid separation is not particularly limited, and conventionally known methods can be used, such as filtration and centrifugation. As the filtration method, a drum filter, a disc filter, a belt filter, a screw press, a filter press, etc. can be used. Examples of the centrifugal separation method include decanter-type and disk-type centrifuges. In addition to the above, a thickener, a clarifier, a pressurized flotation separator, or the like may be used as a settling or flotation method. Additionally, membrane separation methods such as microfilters, ultrafilters, nanofilters, and reverse osmosis membranes can be applied as needed. These methods may be used alone or in combination.

[0038] The sugar liquid recovered by the solid-liquid separation is preferably used as a biorefinery feedstock. In this case, for example, the recovered sugar liquid may be subjected to a step of concentrating it to obtain a concentrated sugar liquid, a fermentation step of adding yeast to the concentrated sugar liquid to ferment it to obtain hydrous bioethanol, or a concentration step of concentrating the hydrous bioethanol to obtain bioethanol, as necessary.

[0039] In the production method according to this embodiment, the saccharification residue is subjected to the subsequent step 3, an extrusion treatment step. It is preferable that at least a portion of the enzyme added in step 1 remains in the saccharification residue.

[0040] That is, the saccharification residue contains undecomposed pulp and water, and preferably further contains enzymes.

[0041] The undecomposed pulp in this embodiment is preferably composed mainly of crystalline cellulose, and it is more preferable that the component with the highest content among the components constituting the undecomposed pulp is crystalline cellulose. The presence of crystalline cellulose can be confirmed by observing peaks at 2θ=approximately 16.5° and 22.5° in X-ray diffraction measurement.

[0042] <Step 3: Extrusion Processing Step> The extrusion step in this embodiment is a step of extruding the saccharification residue obtained in the solid-liquid separation step of step 2. In the extrusion treatment, the saccharification residue obtained in step 2 is subjected to a kneading treatment in the presence of an enzyme at an optimum temperature for the enzyme reaction.

[0043] The term "in the presence of an enzyme" refers to the case where the enzyme added in step 1 remains in the saccharification residue, and therefore there is no need to add the enzyme separately. In other words, it is preferable to use, as the enzyme in the extrusion step, the enzyme that was added in the saccharification step and remains in the saccharification residue after the solid-liquid separation step. However, this does not exclude the addition of an enzyme separately in addition to or instead of this. When an enzyme is added separately, although there is no particular limitation, it is preferable to use the same enzyme as that used in the saccharification treatment step in step 1, and the preferred embodiments of the enzyme in this case are also similar. That is, it is preferable to use, as the enzyme in step 3, at least one of the enzymes added in the above saccharification treatment step that remain in the saccharification residue recovered in the solid-liquid separation step and newly added enzymes. Furthermore, it is preferable that the enzyme used in the extrusion process is subjected to a second saccharification process, such as process 1, together with the saccharification residue after the extrusion process. In this case, the same effect as adding the enzyme in process 1 is essentially achieved. Therefore, it is possible to add some or all of the enzymes that are to be added in step 1 in step 3, which can improve the enzyme utilization efficiency and reduce the cost of the entire process.

[0044] In the extrusion process, the kneading process is carried out at the optimum temperature for the enzyme reaction. A preferred method for achieving such a process is a method using an extruder. An extruder is an extruder that can knead the raw material (saccharification residue) while transporting it, and can also adjust the temperature (heating, cooling, etc.) and pressure as needed. Among these, a twin-screw extruder is more preferred from the viewpoints of process uniformity and kneading efficiency.

[0045] When the extrusion step of step 3 is carried out using a twin-screw extruder, the barrel temperature is preferably the optimum temperature for the enzyme reaction, more preferably 70°C or lower, and even more preferably 40°C or higher and 70°C or lower. Here, from the viewpoint of allowing the enzymatic saccharification reaction to proceed favorably, the barrel temperature is, for example, preferably 40°C or higher, more preferably 45°C or higher, and even more preferably 48°C or higher. On the other hand, from the viewpoint of preventing the deactivation of the enzyme, the temperature is preferably 70°C or lower, more preferably less than 70°C, even more preferably 65°C or lower, and even more preferably 60°C or lower. The interior of the barrel may be heated or cooled to adjust the barrel temperature to the optimum temperature for the enzyme reaction. For example, if heat is generated during the kneading treatment of the saccharification residue and the barrel temperature becomes higher than the desired temperature, cooling may be performed. Furthermore, if the barrel temperature has already reached the desired temperature, additional heating or cooling is not necessarily required.

[0046] The residence time in the extrusion process using a twin-screw extruder is preferably 10 minutes or less, more preferably 2.5 to 5 minutes. Here, the residence time is preferably 10 minutes or less, more preferably 8 minutes or less, and even more preferably 5 minutes or less. From the viewpoint of sufficiently amorphizing the undecomposed pulp, the residence time is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 2.5 minutes or more. Furthermore, when the barrel temperature is high, the residence time can be shortened and the kneading frequency can be increased by increasing the screw rotation speed, thereby efficiently amorphizing the saccharification residue while avoiding deactivation of the enzyme.

[0047] If desired, the extrusion treatment may be accompanied by a pressurization treatment. However, as the extrusion treatment of the saccharification residue progresses, the saccharification residue becomes liquefied, making it difficult to apply pressure. Therefore, it is difficult to uniquely determine the pressure inside the barrel during the extrusion treatment.

[0048] When the extrusion process in step 3 is carried out using a twin-screw extruder, it is more preferable to carry out the extrusion process under the following conditions: a barrel temperature of less than 70°C and a residence time of 10 minutes or less.

[0049] Other extrusion processing conditions vary depending on the type of equipment used, the amount and viscosity of the saccharification residue, etc. For example, when using Process 11 manufactured by Thermo Fisher Scientific, the screw rotation speed is preferably 30 to 1000 rpm. From the viewpoint of promoting the amorphization of undecomposed pulp, the rotation speed is preferably 30 rpm or higher, more preferably 40 rpm or higher, and even more preferably 50 rpm or higher. Furthermore, the higher the rotation speed, the higher the local temperature of the saccharification residue in contact with the screw, even if the barrel temperature is kept constant, which raises concerns about enzyme deactivation. From this viewpoint, the rotation speed is preferably 1000 rpm or lower, more preferably 800 rpm or lower, even more preferably 600 rpm or lower, even more preferably 500 rpm or lower, and particularly preferably 400 rpm or lower.

[0050] Here, if the screw rotation speed is increased to, for example, 300 rpm or higher, the amorphization of undecomposed pulp can proceed even if the residence time is shortened to, for example, 3 minutes or less. Therefore, even if the barrel temperature is set to about 70°C, the saccharification reaction by the enzymatic reaction can proceed without deactivating the enzyme. In this way, the screw rotation speed, residence time, and barrel temperature can be adjusted while maintaining a balance.

[0051] <Step 4: Re-saccharification process> The re-saccharification step in this embodiment is a step in which the saccharification residue after the extrusion treatment in the extrusion treatment step 3 is subjected to saccharification treatment and solid-liquid separation again to obtain a sugar solution.

[0052] The second saccharification treatment can be carried out in the same manner as the saccharification treatment in step 1, and the preferred embodiments are also similar. The second solid-liquid separation can be carried out in the same manner as the solid-liquid separation in step 2, and the preferred embodiments are also similar.

[0053] The sugar liquid obtained in the re-saccharification treatment step is preferably used as a biorefinery feedstock, similar to the sugar liquid obtained through steps 1 and 2. In this case, for example, the recovered sugar liquid may be subjected to a step of concentrating it to obtain a concentrated sugar liquid, a fermentation step of adding yeast to the concentrated sugar liquid to ferment it to obtain hydrous bioethanol, or a concentration step of concentrating the hydrous bioethanol to obtain bioethanol, as needed. That is, in the production method according to this embodiment, it is more preferable to use the sugar solution obtained by the solid-liquid separation step in step 2 and the re-saccharification treatment step in step 4 as a biorefinery feedstock.

[0054] <Other processes> The manufacturing method according to this embodiment may include, in addition to the above steps 1 to 4, other steps as long as the effects of the present invention are not impaired. Other steps may include, for example, a step of recovering the enzyme, and the recovered enzyme may be reused. Furthermore, as described above, the method may further include a step of concentrating the sugar solution, a step of adding yeast to the concentrated sugar solution to obtain aqueous bioethanol, a step of concentrating the aqueous bioethanol to obtain bioethanol, etc. Furthermore, the method may further include a step of recovering unreacted yeast when the aqueous bioethanol is obtained, and may further include a step of recovering waste liquid after each step. [Example]

[0055] The present invention will be explained below by way of test examples, but the present invention is not limited thereto. Note that all of the following test examples involve a saccharification process, a solid-liquid separation process, and an extrusion process, but do not involve a subsequent re-saccharification process. However, the re-saccharification process can be carried out by repeating the same operations as the saccharification process and the solid-liquid separation process. Furthermore, if it can be said that the production method according to this embodiment separates and recovers only those substances that are difficult to saccharify in the solid-liquid separation process as a saccharification residue at a high concentration, and that the saccharification residue efficiently undergoes both amorphization and an enzymatic reaction in the extrusion process, then it can be recognized as having achieved an effect and being able to solve the problem. Therefore, the following test examples can be regarded as examples or comparative examples, respectively.

[0056] <Test Example> Example 1 NBKP (bleached softwood kraft pulp) was used as the raw material, and 12 kg of water was added to 3 kg of the raw material on an oven-dry basis to adjust the total weight to 15 kg (pulp concentration 20 w / w%). Enzyme (Meiji Seika Pharma, Acremonium cellulase) was added in an amount of 10 FPU / g pulp, and the mixture was allowed to react at pH 5 and 50°C for 48 hours to carry out saccharification, yielding a reaction mixture containing a sugar solution. The resulting reaction mixture was subjected to solid-liquid separation using a polypropylene filter cloth and a manual press, and a sugar solution (11 kg, Brix 13-14%) and undecomposed pulp (4 kg, moisture content 70%) were recovered as the saccharification residue. The presence of enzymes remaining in the saccharification residue was confirmed by the progress of liquefaction observed when the mixture was re-reacted at 50°C for 48 hours, which is equivalent to a second saccharification treatment after the extrusion treatment described below. The undecomposed pulp, which was the saccharification residue obtained above, was subjected to extrusion treatment using a twin-screw extruder (Thermo Fisher Scientific, Process 11) under the following conditions: barrel temperature 50°C, screw rotation speed 50 rpm, raw material supply rate approximately 240 g / h, and residence time 5 minutes.

[0057] Example 2 The same processing was carried out under the same conditions as in Example 1, except that the undecomposed pulp, which was the saccharification residue, was extruded using a twin-screw extruder (Thermo Fisher Scientific, Process 11) under the following conditions: barrel temperature 70°C, screw rotation speed 50 rpm, raw material supply rate approximately 240 g / h, and residence time 5 minutes.

[0058] Example 3 The same processing was carried out under the same conditions as in Example 1, except that the undecomposed pulp, which was the saccharification residue, was extruded using a twin-screw extruder (Thermo Fisher Scientific, Process 11) under the following conditions: barrel temperature 70°C, screw rotation speed 400 rpm, raw material supply rate approximately 240 g / h, and residence time 2.5 minutes.

[0059] "evaluation" <X-ray diffraction measurement> X-ray diffraction measurements were performed on the saccharification residue before and after the extrusion treatment in each example. The X-ray diffraction apparatus used was an EQUINOX100 manufactured by Thermo Fisher Scientific, and measurements were carried out under the following conditions. Radiation source: CuKα radiation Tube current: 0.9mA Tube voltage: 40kV Slit width: 100 μm x 5 mm Scanning angle: 2θ=0~100°

[0060] The XRD patterns of the saccharification residues before and after the extrusion process in Examples 1 and 2 are shown in Figures 1 and 2, respectively. Also, Figure 3 shows the XRD patterns of the saccharification residues after the extrusion process in Examples 2 and 3.

[0061] In Example 1, only those resistant to saccharification were separated and recovered at high concentrations as saccharification residue, and extrusion treatment was performed. Therefore, amorphization was achieved in just 5 minutes of extrusion treatment. Furthermore, the results of Example 1 shown in Figure 1 show that the extrusion treatment reduced the peak intensity around 2θ = 16.5° and 22.5°, which represent the peaks of crystalline cellulose, and broadened the peaks overall, indicating significant amorphization. Furthermore, in Example 1, the extrusion treatment was performed at a barrel temperature of 50°C, so amorphization by kneading and the enzymatic reaction could be performed simultaneously without deactivating the enzyme.

[0062] In Example 2, the saccharification residue was extruded for 5 minutes at a barrel temperature of 70°C. The XRD results shown in Figure 2 show that the intensity of the crystalline cellulose peak (near 2θ = 22.5°) is actually higher, indicating that the overall progress of amorphization is limited. This is thought to be because the high treatment temperature significantly reduced the enzyme activity, and amorphization by kneading did not proceed sufficiently, while the low-crystallinity regions present in the residue and other partially saccharifiable components were decomposed to a limited extent, resulting in a relatively emphasized peak for crystalline cellulose. In other words, although the degree of amorphization was insufficient compared to Examples 1 and 3, a certain degree of change in the crystalline structure was observed even under these conditions.

[0063] In Example 3, the barrel temperature was the same as in Example 2 (70°C), but the screw rotation speed in the extrusion process was increased from 50 rpm to 400 rpm, and the residence time was shortened from 5 minutes to 2.5 minutes. As a result, as shown in Figure 3, the peak intensities around 2θ = 16.5° and 22.5°, which represent the peaks of crystalline cellulose, both decreased, and the peaks became broad overall, indicating significant amorphization. Thus, even when the extrusion process was performed at a barrel temperature of 70°C, by shortening the processing time while tightening the kneading conditions, it was possible to simultaneously perform amorphization by kneading and the enzymatic reaction while suppressing enzyme deactivation.

[0064] As described above, according to the production method of this embodiment, a sugar solution can be produced with both a sufficient saccharification rate and economic efficiency.

Claims

1. A method for producing a sugar solution from pulp containing cellulose as a main component, comprising: a saccharification treatment step in which cellulase is added as an enzyme to the pulp to perform saccharification treatment, thereby obtaining a reaction mixture containing a sugar solution; a solid-liquid separation step of subjecting the reaction mixture to solid-liquid separation to recover a sugar solution and a saccharification residue, respectively; an extrusion step of extruding the saccharification residue; and a re-saccharification treatment step of subjecting the saccharification residue after the extrusion treatment to a second saccharification treatment and solid-liquid separation to obtain a sugar solution, The extrusion step involves kneading the saccharification residue in the presence of cellulase as an enzyme at an optimum temperature for enzyme reaction using a twin-screw extruder at a barrel temperature of 70°C or less and a residence time of 10 minutes or less, thereby causing amorphization and saccharification of the saccharification residue.

2. 2. The method for producing a sugar solution according to claim 1, wherein the saccharification treatment step is carried out under conditions of a pulp concentration of 5 to 30% by mass, a cellulase addition amount of 3 to 30 FPU / g-pulp, and a reaction time of 15 minutes or longer at an optimum temperature for enzyme reaction.

3. The method for producing a sugar solution according to claim 1 or 2, wherein the extrusion step is carried out under conditions in which the residence time is 5 minutes or less.

4. A method for producing sugar solution as described in claim 1 or 2, wherein the extrusion process is carried out under conditions where the barrel temperature is less than 70°C.

5. As the enzyme in the extrusion treatment step, at least one of the enzyme added in the saccharification treatment step that remains in the saccharification residue recovered in the solid-liquid separation step and the enzyme newly added is used, and The method for producing a sugar solution according to claim 1 or 2, wherein the enzyme used in the extrusion treatment step is subjected to the second saccharification treatment step together with the saccharification residue after the extrusion treatment.

6. The method for producing a sugar liquid according to claim 1 or 2, wherein the sugar liquid obtained by the solid-liquid separation step and the re-saccharification treatment step is used as a biorefinery feedstock.

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