Production method of plant-derived useful component

Abstract

To provide a method for producing a useful substance such as cellulose from vegetable biomass of herb or algae, to provide, in particular, a method for producing cellulose with a lower crystallization index suitable for a cellulose nanofiber production, and to provide a production method with little modification by heat with regard to protein or a high ratio of solubilization to a water phase facilitating a later utilization.SOLUTION: Cellulose with a low crystallization index or protein can be recovered through treating with a mixed solvent of water and aliphatic alcohol having 4 to 10 carbon atoms at a comparatively low temperature from a room temperature to 150°C, the solvent that separates at 0°C to 50°C in two phases.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing useful components, particularly cellulose having a low crystallization index, from plants. [Background technology]

[0002] Utilization of biomass contributes to solving problems such as preventing global warming and forming a recycling-based society. For this reason, various methods for producing energy and products from biomass have been developed. The main use of biomass is energy production such as biomass power generation, but development of methods for recovering useful substances from biomass and manufacturing products is also underway. One of these is a method for recovering and manufacturing useful substances using the organosolv method. A method has been developed for separating and using cellulose, hemicellulose, and lignin, which are components of plant biomass such as wood chips (Patent Documents 1 and 2). The organosolv method is considered to be a preferable method for utilizing the entire amount of biomass because it causes less denaturation of lignin compared to treatment with acid or alkali.

[0003] Patent Documents 1 and 2 specifically disclose a method for producing a cellulose-containing solid by heat-treating plant biomass such as bagasse, cedar, and bamboo at a reaction temperature of 100°C or higher and 350°C or lower using an organosolv method. It is known that the higher the crystallization index (cellulose crystallinity index, also called degree of crystallinity) of cellulose, the higher its chemical resistance and heat resistance. Cellulose with a high crystallization index is also required for the production of CNF-reinforced thermoplastic resin produced by compounding cellulose nanofibers (CNF) with engineering plastics. This is because it is considered that the crystallization index of cellulose needs to be high because the crystallization index of plastics is high.

[0004] Since cellulose with a high crystallization index can be obtained by heating at high temperatures, it has been common to heat cellulose at high temperatures of 180°C or higher in the organosolv process to recover the cellulose. However, since the process of producing CNF-reinforced thermoplastic resin includes a heating step, a method has been developed to produce resin by using cellulose with a low crystallization index and adjusting the crystallization index to the desired value by heating in the production process. Therefore, cellulose with a low crystallization index is beginning to attract attention. However, there have been no reports so far on a method of producing cellulose with a low crystallization index. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-000093 A [Patent Document 2] JP 2017-002206 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the methods described in Patent Documents 1 and 2, the reaction temperature, which is thought to have the greatest effect on the cellulose crystallization index, is described as 100°C or higher and 350°C or lower, but in the Examples, cellulose is obtained by heat treatment at 200°C. Although there is no mention of the crystallization index of cellulose, it is presumed that the crystallization index of the obtained cellulose is high because the treatment is performed within a conventional temperature range. An object of the present invention is to provide a method for producing cellulose with a low crystallization index. [Means for solving the problem]

[0007] The present invention relates to the following production method. (1) A method for producing a useful component, comprising treating herbaceous plants or algae in a mixed solvent of water and an aliphatic alcohol having 4 to 10 carbon atoms, the solvent being separated into two phases at a temperature between 0°C and 50°C, at a temperature between room temperature and 150°C to recover the useful component, the useful component containing cellulose, and the cellulose recovered does not exceed a crystallization index of the cellulose inherent to the plant plus 20%. This method makes it possible to recover cellulose with a low crystallization index. Compared to woody biomass, biomass obtained from herbaceous plants and algae has a lower crystallization index for the cellulose contained in the plant before processing. Therefore, by setting the processing conditions appropriately, it is possible to recover cellulose with a low crystallization index. The crystallization index of cellulose differs from plant to plant, but by using this method, it is possible to recover cellulose without exceeding the value obtained by adding 20% ​​to the plant's inherent crystallization index. Cellulose with a low crystallization index is extremely valuable as a raw material for cellulose nanofiber.

[0008] (2) The method according to (1), wherein the solubilized herbaceous or algae-derived useful components further contain protein. This method recovers various useful components such as cellulose, ash, pectin, and alginic acid. Among them, proteins are solubilized in the aqueous phase, making the subsequent purification process simple and suitable for use in livestock feed. Another advantage is that proteins are solubilized at a relatively low temperature, so the degree of denaturation is low.

[0009] (3) The method according to (1) or (2), wherein the aliphatic alcohol is a monohydric aliphatic alcohol having 4 to 6 carbon atoms. Monohydric aliphatic alcohols with 4 to 6 carbon atoms are suitable for recovering cellulose, lignin, etc. [Brief description of the drawings]

[0010] [Figure 1] A graph showing the component ratios of useful ingredients obtained by processing cabbage at various temperatures based on the raw material. [Diagram 2] Crystallization index of cellulose obtained by treating cabbage at various temperatures. (A) shows the analysis results by X-ray diffraction, and (B) shows the crystallization index at each temperature. [Diagram 3] A diagram showing the component ratio of useful components obtained by processing wakame seaweed at various temperatures based on the raw material. [Figure 4] Figure showing the crystallization index of cellulose obtained by treating wakame seaweed at various temperatures. (A) shows the analysis results by X-ray diffraction, and (B) shows the crystallization index at each temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present inventors have investigated the biomass used as a raw material in producing cellulose with a low crystallization index. The crystallization index of cellulose contained in plants before processing varies depending on the type of plant. However, in general, herbaceous biomass has a lower value than woody biomass. Woody biomass has high production stability and storage stability, and is therefore more widely used than herbaceous biomass. On the other hand, there have been very few efforts to use herbaceous biomass such as herbaceous plants and algae as biomass, and its use is also limited. However, as described above, herbaceous biomass has a low crystallization index of cellulose contained in the plant body, so there is a possibility that cellulose with a low crystallization index can be produced. If useful substances can be produced from agricultural residues such as the outer leaves and cores of cabbage, or from abundant algae, among herbaceous plants, not only will it contribute to the achievement of a recycling-based society, but the useful value of the useful substances produced, including cellulose, will be very high. Therefore, a method for producing cellulose from herbaceous plants and algae, which have not been used much until now, was investigated, and the present invention was completed.

[0012] In addition, the present inventors have found, in the course of examining the process for recovering cellulose, that useful substances such as proteins can also be produced in a form that is easy to use later. An object of the present invention is to provide a method for recovering useful substances such as cellulose and proteins having a low crystallization index.

[0013] Hereinafter, the present invention will be described by way of examples, but is not limited to the following embodiments. Herbaceous plants that are the subject of biomass are those whose above-ground parts usually flower, fruit, and die within a year, and whose stems do not become woody or thicken. Herbaceous plants to be used as biomass are preferably agricultural crop residues that are expected to produce a certain amount of biomass. Specifically, these are parts that are not usually sold on the market and are disposed of as waste, such as the outer leaves and cores of leafy vegetables such as cabbage, leaves of fruit vegetables such as tomatoes, leaves of root vegetables such as burdock, rice husks and straw of rice and wheat, and corn stover. In addition, there are microalgae such as chlorella and macroalgae such as wakame and tengusa, and macroalgae are preferably used in terms of the time and cost required for cultivation. Examples of macroalgae include tengusa, gracilaria, wakame, celadon, and ulva.

[0014] The herbaceous plants and algae used to produce useful components can be dried and crushed, and then relatively large pieces are removed, for example, pieces of 300 μm or less can be sieved and used. By crushing into small pieces, the surface area becomes relatively large, and the efficiency of recovering useful substances improves. In addition, after crushing, delipidation and depigmentation can be performed by Soxhlet extraction using an ether solvent such as diethyl ether. Delipidation and depigmentation make it easier to understand the distribution behavior of proteins and stabilize the quality.

[0015] Here, useful substances, although the content varies depending on the plant species used as the raw material, include cellulose, polysaccharides such as hemicellulose, polymeric phenolic compounds such as lignin, proteins, ash, etc. In addition, various other substances are also contained.

[0016] The production of useful components using herbs or algae in this embodiment involves treating pulverized herbs or algae in a mixed solvent of water and aliphatic alcohol at a temperature between room temperature and 150° C. As will be explained below with reference to data, a treatment temperature of 200° C. or higher increases the amount of solubilized useful components, but is not preferable from the viewpoint of separating cellulose with a low crystallization index. The optimal treatment temperature differs depending on the substance to be produced, but it is preferable to carry out treatment suitable for producing the target substance at a temperature range between room temperature and 150° C.

[0017] The water contained in the mixed solvent is not particularly limited, and tap water, industrial water, ion-exchanged water, distilled water, etc. can be used. The aliphatic alcohol contained in the mixed solvent may be any of saturated linear alcohol, unsaturated linear alcohol, saturated branched alcohol, and unsaturated branched alcohol, so long as it has 4 to 10 carbon atoms and separates into two phases from water at 0°C or higher and 50°C or lower. Among these, saturated linear alcohol is preferred. The aliphatic alcohol may be a monohydric alcohol having one hydroxyl group or a polyhydric alcohol having multiple hydroxyl groups, but is preferably a monohydric alcohol. The aliphatic alcohol having 4 to 10 carbon atoms is preferably a monohydric aliphatic alcohol having 4 to 10 carbon atoms, more preferably a monohydric aliphatic alcohol having 4 to 6 carbon atoms, and even more preferably a monohydric saturated linear alcohol having 4 to 6 carbon atoms. Specific examples of the monohydric aliphatic alcohol having 4 to 10 carbon atoms include 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 2-butanol, and 2-methyl-1-propanol. Among these, 1-butanol, 1-pentanol, or 1-hexanol is preferred, and 1-butanol is more preferred. The aliphatic alcohol having 4 to 10 carbon atoms may be used alone or in combination of two or more.

[0018] The mixing ratio (molar ratio) of water to aliphatic alcohol in the mixed solvent is not particularly limited, but may be, for example, 0.5:1 to 45:1. The mixing ratio (molar ratio) is preferably 0.7:1 to 30:1, more preferably 0.9:1 to 20:1, and further preferably 1.8:1 to 10:1.

[0019] The weight ratio of herbaceous plants or algae as the raw material to be subjected to the above treatment to the mixed solvent is not particularly limited, but may be, for example, 1:2 to 1:200. The weight ratio is preferably 1:3 to 1:100, more preferably 1:5 to 1:75, and even more preferably 1:10 to 1:50.

[0020] The above treatment may be carried out in the presence of a catalyst such as a mineral acid, but even without a catalyst, solubilized useful components can be obtained at a sufficiently high extraction rate.

[0021] The lower limit of the temperature in the above treatment is room temperature or higher, preferably 50°C or higher, more preferably 70°C or higher. The upper limit of the temperature in the treatment is 150°C or lower, preferably 120°C or lower, more preferably 100°C or lower, and even more preferably 90°C or lower. The room temperature refers to a temperature that is not particularly cooled or heated. A specific temperature is 20°C ± 15°C, that is, a temperature in the range of 5°C to 35°C, as specified by the Japanese Industrial Standards. Here, the treatment temperature is defined as room temperature or higher, so that the treatment may be performed at a temperature of 5°C or higher, although it naturally varies depending on the season. The treatment temperature depends on the type of plant that is the raw material and the substance to be produced, but an appropriate temperature can be selected within the above range.

[0022] The treatment time can be, for example, 0.1 hours or more, preferably 0.2 hours or more, more preferably 1 hour or more, and the upper limit can be 10 hours or less, preferably 8 hours or less, more preferably 6 hours or less. The treatment time can also be appropriately selected depending on the type of plant material and the substance to be produced.

[0023] The pressure of the reaction system during the above treatment is not particularly limited and can be, for example, 0.5 MPa to 30 MPa. The treatment may be performed in an air atmosphere, or in a nitrogen atmosphere to avoid side reactions.

[0024] The reaction method of the above treatment is not particularly limited, and for example, a general batch reactor, semi-batch reactor, continuous reactor, etc. can be used. Furthermore, a stationary reaction is also possible.

[0025] After the above treatment, the solubilized herbaceous or algae-derived useful components are distributed between the aqueous phase and the aliphatic alcohol phase. The distributed useful components may be used in either phase or both phases may be used together depending on the application. Components remaining in the solid phase may be recovered. Depending on the recovered components and the subsequent use, for example, proteins solubilized in the aqueous phase simplify the subsequent purification process. The solubilized herbaceous or algae-derived useful components may be those that are dissolved in water and / or aliphatic alcohol as the useful components contained in the raw material are intact, or may be those that are decomposed by hydrolysis or the like during the treatment and become soluble in water and / or aliphatic alcohol.

[0026] The solubilized useful components include cellulose, which can be used as a raw material for cellulose nanofibers, hemicellulose and lignin, which can be used as raw materials for plastics, and protein, which can be used as feed for livestock. The components shown as unknown in the examples below include various substances that differ depending on the plant used as the raw material, but since they contain a lot of organic matter, they can also be used as a raw material for fertilizer. EXAMPLES

[0027] The present invention will be described in more detail below with reference to examples in which cabbage was used as the herbaceous plant and wakame was used as the algae, and treatment was carried out under various temperature conditions.

[0028] 1. Production of useful ingredients derived from cabbage <Pretreatment / reaction process> Cabbage cores were crushed, sieved out to remove particles of 300 μm or less, and pretreated with diethyl ether in a Soxhlet extractor at 55°C for 8 hours to remove pigments and lipids. The pretreated cabbage (pretreated raw material) and a mixed solvent of water and 1-butanol (BuOH) were placed in a 150 mL SUS batch reactor. The pretreated raw material / solvent ratio was 1 / 30 (weight ratio), and water / 1-butanol was 4 / 1 (molar ratio).

[0029] After purging the inside of the reactor of the SUS batch reactor with nitrogen, the temperature was raised to each treatment temperature, i.e., room temperature, 50°C, 70°C, 80°C, 100°C, 150°C, and 200°C, and the reaction was carried out for 2 hours. The reaction time was the elapsed time after each temperature was reached. The temperature inside the reactor was measured by a thermocouple.

[0030] <Post-processing and analysis process> After the reaction was completed, the batch reactor was immersed in ice water to cool it, and after the temperature inside the reactor had dropped to around room temperature, the entire contents of the reactor were removed. The solid and liquid contents were separated by filtration, and the filtrate was separated into liquid and liquid using a separatory funnel to obtain a water phase (hereinafter referred to as "water-soluble fraction") and a 1-butanol phase (hereinafter referred to as "BuOH-soluble fraction").

[0031] The collected solids were dried at 60° C. for 3 hours in a vacuum dryer and then subjected to the following analysis. The water-soluble matter was freeze-dried to powderize it into a water-soluble concentrate and subjected to the following analysis.

[0032] In the following analysis, the pretreated raw material, solids, and water-soluble concentrate were analyzed (hereinafter, these analysis targets are also referred to as "samples"). The components contained in each sample were calculated based on the weight of the pretreated raw material excluding water, using the method described below. The BuOH-soluble content in each component was calculated by subtracting the amount of each component contained in the water-soluble content and solids from the amount of each component in the pretreated raw material.

[0033] The moisture and ash content were quantified using a thermogravimetric analyzer. The moisture content was quantified by measuring the weight difference before and after holding the sample at 113°C for 1 hour in an air stream. The ash content was quantified by measuring the amount of ash remaining after heating the sample from room temperature to 591°C at 20°C / min in an air stream.

[0034] Cellulose and hemicellulose were quantified by treating the alcohol-insoluble fraction of each sample with alkali. Specifically, the alcohol-insoluble fraction was obtained by washing each sample three times, first with ethanol and then with tert-butyl alcohol, and the remaining fraction was obtained as the insoluble fraction. Then, the sample was dissolved in a 0.5% aqueous ammonium oxalate solution at 100°C for 5 hours, impurities were removed, and cellulose and hemicellulose were recovered as residues. After this operation was repeated, the residue was dried in a vacuum dryer at 60°C for 3 hours. The residue was dissolved in a 4% aqueous sodium hydroxide solution at room temperature for 24 hours, and cellulose was recovered as a solid fraction by filtration, and hemicellulose was recovered as a soluble fraction. The solid fraction was dried in a vacuum dryer at 60°C for 3 hours, and the amount of cellulose was quantified. The amount of hemicellulose was calculated by subtracting the amount of cellulose from the residue after the above-mentioned impurity removal.

[0035] The crystallization index (Cr.I.) of cellulose was calculated by the following formula using crystallization information obtained by analysis using an X-ray diffractometer (Ultima IV, Rigaku Corporation).

[0036]

number

[0037] Protein was calculated by measuring the nitrogen content with an elemental analyzer and using the nitrogen-protein conversion factor. Water-soluble dietary fiber and other components were calculated by subtracting the sum of the above components from the total.

[0038] The useful components of cabbage were divided into unknown components including cellulose, hemicellulose, protein, ash, pectin, etc., and the proportions recovered as water-soluble or BuOH-soluble components and solids were calculated and shown as the component proportions based on the raw material (Figure 1). It was revealed that the unknown components including hemicellulose, protein, and pectin and ash were solubilized even at room temperature. It was previously thought that useful components needed to be solubilized at high temperatures, but the present inventors' analysis revealed that these components were solubilized even at room temperature. In addition, about half of the protein was solubilized in the aqueous phase at 70°C to 100°C. Proteins solubilized in the aqueous phase have high commercial value, for example, when commercialized as feed, etc., since it is very easy to process and there is no need to remove the organic solvent. In addition, considering that proteins denature, solubilization in the BuOH phase at room temperature to 50°C is considered to be possible to extract undenatured proteins, which is a great advantage.

[0039] As shown in Figure 1, the solubilization of useful components does not change uniformly depending on the treatment temperature. For example, cellulose is partially solubilized in the BuOH phase at 50°C and 200°C, but is hardly solubilized at other temperatures. Proteins are also solubilized in the BuOH phase at room temperature and 50°C, but are not solubilized in the BuOH phase at 70°C and 80°C, and are solubilized in the BuOH phase again at temperatures above 100°C. Although detailed analysis is required, the components that are solubilized in different temperature ranges are still substances classified as cellulose or protein, but we believe that qualitatively different substances are solubilized in different fractions in different temperature ranges due to modifications, molecular structures, changes due to heating, etc.

[0040] The crystallization index of the cellulose obtained by the treatment was analyzed by X-ray diffraction (Figure 2(A)). The lower the crystallization index of cellulose, the easier it is to defibrate, making it easier to handle and more useful as CNF. When treatment was performed at 200°C, the cellulose was dissolved in the BuOH phase, but the crystallization index was high at 45%. Although it is inevitable that the crystallization index will increase to some extent in the useful substance recovery process, it is preferable to treat the raw material itself, i.e., the cellulose inherent in the plant, at a reaction temperature that does not significantly increase the crystallization index. Specifically, it is preferable to treat the plant so that the crystallization index does not exceed the value obtained by adding 20%, more preferably 15%, to the crystallization index of the plant before processing. In this example, the crystallization index of the raw material, the cabbage core, is 11%, so it is preferable to treat the plant so that the crystallization index does not exceed 31%. The cellulose crystallization index of the plant is defined as the crystallization index of the cellulose contained in the plant before processing, i.e., the raw material.

[0041] When cabbage is used as the raw material, cellulose is partially solubilized in the BuOH phase at treatment temperatures of 50°C and 200°C, but is only slightly solubilized at room temperature and in the temperature range of 70°C to 150°C. However, in order to obtain cellulose with a crystallization index suitable for cellulose nanofiber production, it is preferable to treat it at a temperature above room temperature and below 150°C, preferably below 120°C, and more preferably below 100°C (Figure 2(B)).

[0042] 2. Production of useful ingredients derived from wakame seaweed Except for using wakame, the process was the same as for the production of useful components derived from cabbage, and the useful components were treated at various temperatures, divided into unknown fractions including cellulose, hemicellulose, protein, ash, and alginic acid, and the percentages recovered as water-soluble fraction, BuOH-soluble fraction, and solid fraction were calculated and shown as the component percentages based on the raw material (Figure 3). Note that wakame, being an algae, contains a large amount of alginic acid, not pectin, among its unknown fractions.

[0043] It was revealed that when wakame is used as a raw material, hemicellulose, protein, unidentified matter, and ash are solubilized, even at room temperature, just like with cabbage. In addition, protein is more solubilized in the BuOH phase in the entire temperature range analyzed. Considering that protein denatures, the fact that it is solubilized in the BuOH phase at room temperature to 50°C is thought to make it possible to extract undenatured protein, which is a major advantage.

[0044] The crystallization index of the cellulose obtained by the treatment was analyzed by X-ray diffraction (Figure 4(A)). As mentioned above, the lower the crystallization index of cellulose, the easier it is to defibrate, making it easier to handle and more useful as CNF. When treatment was performed at 200°C, the cellulose was dissolved in the BuOH phase, but the crystallization index was high at 43%. As mentioned above, it is inevitable that the crystallization index will increase to some extent in the extraction process, so it is preferable to produce cellulose so that the cellulose index does not exceed the value obtained by adding 20%, more preferably 15%, to the cellulose index of the plant before processing. Since the crystallization index of the raw material wakame seaweed is 17%, it is preferable to treat it at a reaction temperature that does not exceed 37%. When wakame seaweed is used as the raw material, cellulose is solubilized in the BuOH phase at a treatment temperature of 200°C, but is only slightly solubilized at temperatures ranging from room temperature to 150°C. However, in order to produce cellulose with a crystallization index suitable for cellulose nanofiber production, it is preferable to treat it at a temperature above room temperature and below 150°C, preferably below 120°C, and more preferably below 100°C, as in the case of using cabbage as the raw material (Figure 4(B)).

[0045] From the above results, in order to obtain cellulose with a low crystallization index from herbs and algae, it is preferable to treat at a temperature between room temperature and 150°C. Also, in order to obtain proteins that are less likely to be denatured by heat, it is preferable to treat at a temperature between room temperature and 50°C. Although it differs depending on the plant used as the raw material, by treating at a temperature range between room temperature and 150°C, it is possible not only to solubilize but also to separate and produce useful components suitable for subsequent product processing.

[0046] As discussed above in the Examples, in order to recover cellulose with a low crystallization index, it is necessary to treat herbaceous plants or algae in a low temperature range, specifically, at a temperature between room temperature and 150°C. As shown in the Examples above, treatment in this temperature range makes it possible to recover cellulose with a crystallization index of 35% or less. Cellulose with a crystallization index of 35% or less has not been obtained by conventional treatments, and is considered to be useful for use in CNF-reinforced thermoplastic resins, etc.

Claims

1. A method for producing a useful ingredient, comprising the steps of: Herbaceous plants or algae, In a mixed solvent of water and an aliphatic alcohol having 4 to 10 carbon atoms, which separates into two phases at a temperature of 0° C. or higher and 50° C. or lower, Useful components are recovered by treating at a temperature between room temperature and 150°C. The useful components include cellulose, A method for producing a useful ingredient derived from herbaceous plants or algae, characterized in that the cellulose recovered does not exceed a crystallization index of the cellulose inherent to the plant plus 20%.

2. Solubilized herbaceous or algae-derived useful ingredients, The method according to claim 1, further comprising the step of:

3. The method according to claim 1 or 2, wherein the aliphatic alcohol is a monohydric aliphatic alcohol having 4 to 6 carbon atoms.

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