Method for preparing ethanol through cellulose enzymolysis and fermentation and catalyst thereof

Abstract

The invention provides a method for preparing ethanol through cellulose enzymolysis and fermentation and a catalyst thereof, and belongs to the technical field of ethanol fuel preparation, the preparation method comprises the following steps: taking straw and starch waste as raw materials, carrying out step-by-step enzymolysis through an activated carbon-enzyme mixed solution, a resin-enzyme mixed solution and a cellulase solution, then fermenting through saccharomyces cerevisiae, and adding a special catalyst, so that the ethanol is prepared. And high-yield ethanol is obtained. The catalyst is prepared from the following raw materials: molybdenum oxide, silicon dioxide, citric acid, sucrose fatty acid ester, cetearyl alcohol polyether, rhamnolipid, magnesium sulfate, calcium pantothenate, 5-nitroguaiacol sodium salt and the like through a special method. According to the method disclosed by the invention, enzymolysis pretreatment of the activated carbon-enzyme mixed solution and the resin-enzyme mixed solution and adsorption of the inhibiting substance are combined with the action of the catalyst and the auxiliary materials, so that enzymolysis fermentation of the cellulase and the saccharomyces cerevisiae can be promoted, the biological activity is improved, and high-yield ethanol can be obtained and the fermentation time is shortened under the condition of reducing the dosage of the cellulase; the fermentation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ethanol fuel preparation, and specifically relates to a method for preparing ethanol by enzymatic fermentation of cellulose and a catalyst thereof. Background Art

[0002] Cellulose is one of the most abundant organic substances on earth and is widely found in plant cell walls. However, due to its complex structure and high degree of crystallization, cellulose is difficult to be directly used to produce ethanol. Traditional fuel ethanol mainly uses food crops such as corn and wheat as raw materials, but this method is not conducive to sustainable development.

[0003] The technology of preparing ethanol by enzymatic hydrolysis and fermentation of cellulose provides a feasible way to solve these problems. First of all, the cellulose resources on the earth are extremely abundant, including agricultural waste (such as straw, rice husk, etc.), forestry waste (such as branches, sawdust, etc.) and energy crops. If these resources can be effectively utilized, it will greatly alleviate the energy pressure and reduce the pollution to the environment. Many countries and regions are actively carrying out research and development work on preparing ethanol by enzymatic hydrolysis and fermentation of cellulose.

[0004] There are many methods for preparing ethanol by enzymatic fermentation of cellulose, and the efficiency and yield vary. At present, the existing preparation methods generally have the following problems:

[0005] (1) The production and storage of cellulase are difficult and costly, which restricts the large-scale application of cellulose enzymatic fermentation to produce ethanol.

[0006] (2) In the actual production process, the activity and stability of the enzyme are easily affected by environmental factors, such as temperature, pH value, inhibitors, etc. In order to maintain the activity of the enzyme, the reaction conditions need to be strictly controlled during the production process, which increases the difficulty and cost of production.

[0007] (3) In terms of raw material pretreatment, although there are many pretreatment methods, such as dilute acid pretreatment and steam explosion pretreatment, the pretreatment effect is still not ideal for some complex lignocellulosic raw materials. It is difficult to completely remove substances such as lignin that have inhibitory effects on enzymatic hydrolysis and fermentation during the pretreatment process, which affects the subsequent enzymatic hydrolysis efficiency and fermentation effect.

[0008] (4) During the pretreatment and enzymatic hydrolysis of cellulose raw materials, some substances that have inhibitory effects on fermentation microorganisms are produced, such as furfural, hydroxymethylfurfural, organic acids, etc. These inhibitors will reduce the fermentation activity of microorganisms and affect the production and yield of ethanol. Removing these inhibitors requires additional processing steps, which increases production costs.

[0009] Therefore, the technology for preparing ethanol by enzymatic fermentation of cellulose needs to be improved. It is necessary to continuously develop and improve the technology in terms of raw materials, pretreatment, enzymes, bacteria, catalysts, etc. to achieve high efficiency of ethanol preparation, increase ethanol yield, and control costs. Summary of the invention

[0010] The existing technology for preparing ethanol by enzymatic hydrolysis and fermentation of cellulose still has the problems of low production efficiency, low ethanol yield and high production cost. The present invention provides a method for preparing ethanol by enzymatic hydrolysis and fermentation of cellulose and a catalyst thereof. The preparation method uses straw and starch waste as raw materials, and gradually hydrolyzes them through activated carbon-enzyme mixture, resin-enzyme mixture and cellulase solution, and then ferments them through brewer's yeast to obtain high-yield ethanol; during the fermentation process, a special catalyst is added. The present invention utilizes the enzymatic hydrolysis pretreatment of activated carbon-enzyme mixture and resin-enzyme mixture and the adsorption of inhibitory substances, combined with the effects of catalysts and auxiliary materials, to promote the enzymatic hydrolysis and fermentation of cellulase and brewer's yeast, improve biological activity, and obtain high-yield ethanol under the condition of reducing the amount of cellulase used, shorten the fermentation time, and improve the fermentation efficiency. The specific technical scheme is as follows:

[0011] A method for preparing ethanol by enzymatic fermentation of cellulose, comprising the following steps:

[0012] S1, raw material pretreatment:

[0013] According to the mass ratio of straw: starch waste = (90-100): (20-30), the straw and starch waste are mixed and crushed to obtain a crushed material; according to the mass ratio of water: crushed material: potassium acetate = (100-150): (20-30): (1-3), the crushed material, potassium acetate and water are homogenized to prepare a raw material slurry;

[0014] S2, enzyme solution preparation:

[0015] S2.1: Take 0.5% to 2% of α-amylase by weight of the crushed material, 0.5% to 2% of saccharifying enzyme by weight of the crushed material, 0.5% to 2% of pectinase by weight of the crushed material, 0.5% to 2% of papain by weight of the crushed material, and 1.5% to 3% of activated carbon by weight of the crushed material, add them into water and mix well to obtain an activated carbon-enzyme mixture;

[0016] S2.2: Take 0.5% to 2% of the mass of the crushed material hemicellulase and 1.5% to 3% of the mass of the crushed material macroporous adsorption resin, add them into water and mix them evenly to obtain a resin-enzyme mixed solution;

[0017] S2.3: Take 0.1% to 0.3% of the mass of the crushed material, 1% to 3% of the mass of hydroxypropyl-β-cyclodextrin, add to water and mix well to obtain a cellulase solution;

[0018] S3, enzymatic hydrolysis:

[0019] The pH value of the raw material slurry is adjusted to 4.5-5.0, the temperature is 45°C-55°C, and the activated carbon-enzyme mixture is added to perform enzymolysis for 3h-5h; then the resin-enzyme mixture is added to continue enzymolysis for 3h-5h; then the cellulase solution is added to continue enzymolysis for 10h-20h; after cooling to room temperature, an enzymolysis solution is obtained;

[0020] S4, Fermentation:

[0021] The pH value of the enzymatic hydrolysate is adjusted to 4-6, the temperature is 28-33°C, 0.5%-1.5% of brewer's yeast by weight of the enzymatic hydrolysate is added, and the solution is stored in an open state for 8-15 hours; then, a catalyst and auxiliary materials are added, mixed evenly, sealed and stored, and anaerobically fermented at 18-28°C for 45-50 days to obtain a fermentation solution;

[0022] S5, post-processing:

[0023] The fermentation liquid is filtered to remove the residue to obtain a filtrate containing ethanol; the filtrate is distilled to obtain high-purity ethanol, which is used for fuel.

[0024] In S1 of the above method, the straw is a combination of one or more of corn straw, wheat straw, and rice straw; the starch waste is waste residue produced after preparing starch from at least one of sweet potato, cassava, potato, and yams.

[0025] In S2.1 of the above method, the mass ratio of the components of the activated carbon-enzyme mixture is: water: (α-amylase + saccharifying enzyme + activated carbon) = (10-15): (1-3); the activated carbon includes powdered activated carbon and granular activated carbon, and the mass ratio of the components of the activated carbon is: powdered activated carbon: granular activated carbon = (1-3): 10; the particle size range of the powdered activated carbon is 100 mesh to 300 mesh, and the particle size range of the granular activated carbon is 1 mm to 3 mm.

[0026] In S2.2 of the above method, the mass ratio of the components of the resin-enzyme mixture is: water: (hemicellulase + macroporous adsorption resin) = (10-15): (1-3); the macroporous adsorption resin is XAD-4 non-ionic macroporous adsorption resin.

[0027] In S2.3 of the above method, the mass ratio of the components of the cellulase solution is: water: (cellulase + hydroxypropyl-β-cyclodextrin) = (15-30): (1-3).

[0028] In S4 of the above method, the added amount of the catalyst is 0.2% to 0.5% of the mass of the enzymatic solution; the excipients include vitamin E, potassium dihydrogen phosphate and peptone, the added amount of vitamin E is 0.05% to 0.15% of the mass of the enzymatic solution, the added amount of potassium dihydrogen phosphate is 0.2% to 0.6% of the mass of the enzymatic solution, and the added amount of peptone is 0.5% to 1% of the mass of the enzymatic solution.

[0029] In S5 of the above method, the distillation temperature is 78°C to 80°C.

[0030] A catalyst for use in the above-mentioned method for preparing ethanol by enzymatic fermentation of cellulose, the catalyst comprising the following raw materials in parts by mass: 0.1 to 0.5 parts of molybdenum oxide, 1 to 3 parts of silicon dioxide, 0.5 to 1 parts of citric acid, 0.1 to 0.5 parts of sucrose fatty acid ester, 0.1 to 0.5 parts of cetearyl alcohol polyether, 1 to 3 parts of rhamnolipid, 0.5 to 1 parts of magnesium sulfate, 0.1 to 0.5 parts of calcium pantothenate, 0.1 to 0.5 parts of sodium 5-nitroguaiacol, and 8 to 12 parts of purified water.

[0031] In the above catalyst, the particle size range of the solid raw materials in the raw materials is all below 250 mesh sieve.

[0032] The preparation method of the above catalyst comprises the following steps:

[0033] N1: Mix citric acid, sodium 5-nitroguaiacol, magnesium sulfate, calcium pantothenate, molybdenum oxide and silicon dioxide according to their mass fractions to obtain a mixture, add deionized water 3 to 5 times the mass of the mixture, mix and disperse evenly, evaporate to remove water at 100° C. to 120° C., and then heat treat at 150° C. to 160° C. for 2 h to 3 h, and obtain a semi-finished catalyst after cooling;

[0034] N2: Add the semi-finished catalyst, sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid into purified water according to their mass proportions, mix well at 45°C to 55°C to obtain the catalyst.

[0035] The method for preparing ethanol by enzymatic fermentation of cellulose and the catalyst thereof provided by the present invention have the following beneficial effects compared with the prior art:

[0036] 1. Using straw and starch waste as raw materials to increase the diversity of raw materials will help improve the richness of fermentation substrates, provide a more comprehensive source of nutrients for subsequent enzymatic hydrolysis and fermentation processes, and improve the utilization rate of agricultural starch waste. Potassium acetate plays a role in regulating the pH and ionic strength of the system during the homogenization process, which helps to maintain the activity and stability of the enzyme and promote subsequent enzymatic hydrolysis reactions. α-Amylase can hydrolyze the α-1,4-glycosidic bonds in starch molecules, decompose starch into smaller molecules, dextrins and oligosaccharides, etc., and provide available carbohydrates for subsequent fermentation. Glucoamylase further converts the hydrolysis products of starch into monosaccharides such as glucose, providing a carbon source for microorganisms in the fermentation process. Pectinase decomposes pectin substances in the raw materials, reduces the viscosity of the raw materials, and improves the permeability of the substrate, which is conducive to the full contact between the subsequent enzymes and microorganisms and the substrate, and promotes the enzymatic hydrolysis and fermentation process. Papain helps to decompose the protein components in the raw materials and convert them into small molecule peptides and amino acids, etc., providing nutrients such as nitrogen sources for microbial growth. Powdered activated carbon has a large specific surface area and can adsorb impurities, pigments and some harmful substances that inhibit enzyme activity and fermentation process in the raw materials, which plays a role in purifying the raw materials and promoting the stability of the enzymatic hydrolysis and fermentation system. Granular activated carbon also has an adsorption effect, which is different from powdered activated carbon in adsorption performance. The combination of the two can more comprehensively adsorb different types of impurities. Hemicellulase hydrolyzes the hemicellulose components in the raw materials in advance and decomposes them into sugar substances for fermentation, such as xylose, arabinose, etc., increasing the types and quantities of carbon sources for fermentation. In addition, the hemicellulose hydrolysis products can also promote the growth and metabolism of fermentation bacteria and enhance their fermentation ability. XAD-4 non-ionic macroporous adsorption resin can adsorb some inhibitory substances and by-products produced during enzymatic hydrolysis and fermentation, such as furfural, hydroxymethylfurfural, organic acids, etc., thereby improving fermentation efficiency and product purity. Cellulase decomposes cellulose in the raw materials and converts it into sugar substances such as glucose for fermentation, improving the utilization rate of raw materials and providing more carbon sources for the fermentation process. Hydroxypropyl-β-cyclodextrin can stabilize cellulase and prevent its inactivation; it can also form a complex with the substrate and the enzyme to improve the efficiency of the enzymatic reaction.

[0037] 2. Design the activated carbon-enzyme mixture to hydrolyze for 3h to 5h. In this stage, α-amylase, saccharifying enzyme, pectinase, papain and activated carbon are mainly used. α-amylase and saccharifying enzyme can initially decompose starchy substances into sugars for fermentation, providing substrates for subsequent fermentation. Pectinase can reduce the viscosity of the raw materials and increase the contact area between subsequent enzymes and microorganisms and substrates. Papain decomposes proteins to provide nitrogen sources. Activated carbon can adsorb some impurities and substances that inhibit subsequent reactions at this stage, creating good conditions for subsequent reactions. 3h to 5h can enable these enzymes to fully play their role, ensure that starchy substances are decomposed to a certain extent, and impurities are effectively adsorbed, laying the foundation for subsequent reactions.

[0038] 3. Design the resin-enzyme mixture to hydrolyze for 3h to 5h. Hemicellulase acts on hemicellulose and decomposes it into sugars for fermentation, increasing the types and quantity of carbon sources. Macroporous adsorption resin can adsorb some inhibitory substances and by-products produced during the enzymatic hydrolysis process, improving the subsequent fermentation efficiency and product purity. After the reaction in the previous stage, 3h to 5h can allow hemicellulase to fully decompose hemicellulose, and the macroporous adsorption resin can give full play to the adsorption effect, further optimizing the composition and environment of the enzymatic hydrolysis products.

[0039] 4. Design the enzymatic hydrolysis of cellulose liquid for 10h to 20h. Cellulose is one of the main components of raw materials such as straw, and it is also a substance that is difficult to decompose. Cellulase specifically acts on cellulose and decomposes it into sugars such as glucose. Since the structure of cellulose is relatively complex and it is difficult to decompose, it takes a long time. The enzymatic hydrolysis time of 10h to 20h can ensure that cellulose is initially decomposed and further decomposed during the fermentation process, maximizing the utilization rate of raw materials and providing sufficient fermentable sugar substances for the early, middle and late fermentation processes, thereby increasing the yield and quality of ethanol.

[0040] 5. After adding brewer's yeast, the open storage is designed for 8h to 15h. In the initial stage of open storage, brewer's yeast can gradually adapt to the environment of the enzymatic solution, including pH value, temperature and nutrients. This process helps yeast cells adjust their own metabolic state and prepare for subsequent fermentation. During open storage, yeast can perform aerobic respiration to a certain extent. Aerobic respiration can provide more energy for yeast cells, allowing them to reproduce and grow rapidly and increase the number of yeast. This will provide sufficient fermentation power for subsequent anaerobic fermentation and improve fermentation efficiency. During open storage, yeast and other possible microorganisms can consume oxygen in the enzymatic solution. In this way, when the subsequent sealed storage is performed for anaerobic fermentation, an anaerobic environment can be better created, which is conducive to anaerobic fermentation of yeast to produce ethanol. In short, open storage can promote the early reproduction of brewer's yeast, discharge bad gases, release fermentation heat, and facilitate material conversion.

[0041] 6. Design sealed storage, and perform anaerobic fermentation at 18℃~28℃ for 45 to 50 days to obtain fermentation liquid; sealed storage can maintain the stability of the fermentation system and prevent interference from external factors such as oxygen and bacteria. The temperature of 18℃~28℃ is relatively low and stable, which is conducive to the continuous fermentation process of yeast in a relatively constant environment and avoids the adverse effects of temperature fluctuations on yeast fermentation. The fermentation time of 45 to 50 days can ensure that the yeast fully utilizes various sugars and other nutrients in the enzymatic hydrolyzate for fermentation. For some complex substrates, the fermentation process may be slow, and it takes enough time to completely convert the substrate into products such as ethanol, thereby increasing the yield and purity of ethanol. During the long fermentation process, yeast can make more sophisticated metabolic adjustments. Yeast also has enough time to carry out various biochemical reactions and optimize the composition of fermentation products.

[0042] VII. The present invention designs a catalyst component, wherein molybdenum oxide can promote chemical reactions during the catalytic process, help to increase the rate of ethanol production and improve key reaction steps during the fermentation process. An appropriate amount of silicon dioxide is used as a carrier to provide attachment points for other active ingredients and increase the stability and dispersibility of the catalyst. Citric acid can adjust the pH of the catalyst, provide a suitable acid-base environment for the catalytic reaction, and can also synergize with other ingredients to promote the reaction. Sucrose fatty acid esters can improve the dispersibility of the catalyst in the reaction system and improve the catalytic efficiency. Cetearyl alcohol polyether helps to improve the dispersibility and stability of the catalyst and promote the catalytic reaction. Rhamnolipid has surface activity and biological activity, can regulate the growth and metabolism of microorganisms during the fermentation process, and promote the production of ethanol. Magnesium sulfate provides necessary nutrients for microorganisms in the fermentation process, maintains the normal growth and metabolism of microorganisms, and indirectly promotes the production of ethanol. Calcium pantothenate, as a form of vitamin B5, provides nutritional support for microorganisms, participates in the metabolic process of microorganisms, and helps to improve fermentation efficiency. Sodium 5-nitroguaiacol has the effect of promoting cell growth and metabolism, stimulates the activity of microorganisms during the fermentation process, and increases the yield of ethanol. The combination of sucrose fatty acid esters, cetearyl alcohol polyethers and rhamnolipids can effectively improve the dispersibility of the catalyst in the reaction system, increase the contact area between the catalyst and the substrate, and improve the catalytic efficiency. At the same time, rhamnolipids can also promote the production of ethanol by regulating the growth and metabolism of microorganisms.

[0043] 8. The semi-finished product catalyst prepared by the present invention can undergo physical and chemical changes in the components of the catalyst by heat treatment at 150°C to 160°C for 2h to 3h, forming a more stable structure and obtaining a metal-acid bifunctional catalyst. This stable structure can improve the heat resistance, mechanical strength and chemical stability of the catalyst, so that it can better play a catalytic role in the fermentation process. Components such as molybdenum oxide and silicon dioxide can provide active sites required for catalytic reactions, promote the progress of key chemical reactions, and promote the conversion of substrates. Components such as citric acid, magnesium sulfate, and calcium pantothenate can adjust the pH, ionic strength and nutritional environment of the reaction system, and provide suitable conditions for the growth and metabolism of microorganisms. A suitable reaction environment can improve the activity of microorganisms and the stability of enzymes, thereby promoting the production of ethanol. Sodium 5-nitroguaiacol has the auxiliary effect of promoting the growth of brewer's yeast and improving fermentation efficiency, and has the effect of improving the dispersibility and bioaffinity of the semi-finished product catalyst itself, thereby promoting catalytic efficiency.

[0044] 9. The present invention utilizes the enzymatic pretreatment of activated carbon-enzyme mixture and resin-enzyme mixture and the adsorption of inhibitory substances, combined with the effects of catalysts and auxiliary materials, which can effectively promote the enzymatic fermentation of cellulase and brewer's yeast and improve biological activity. Under the condition of reducing the dosage of cellulase, high-yield ethanol can be obtained, effectively shortening the fermentation time and improving the fermentation efficiency. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with specific implementation cases, but the present invention is not limited to these embodiments.

[0046] Example 1

[0047] A method for preparing ethanol by enzymatic fermentation of cellulose, comprising the following steps:

[0048] S1, raw material pretreatment:

[0049] The straw and the starch waste are mixed and crushed in a mass ratio of 95:25 to obtain a crushed product; the crushed product, potassium acetate and water are homogenized in a mass ratio of 120:25:2 to obtain a raw material slurry;

[0050] Among them, the straw is corn straw; and the starch waste is the waste residue produced after preparing starch from sweet potatoes.

[0051] S2, enzyme solution preparation:

[0052] S2.1: Take 1% of α-amylase by weight of the crushed material, 1% of saccharifying enzyme by weight of the crushed material, 1% of pectinase by weight of the crushed material, 1% of papain by weight of the crushed material, and 2% of activated carbon by weight of the crushed material; according to the mass ratio of water: (α-amylase + saccharifying enzyme + activated carbon) = 13:2, add α-amylase, saccharifying enzyme, and activated carbon into water and mix evenly to obtain an activated carbon-enzyme mixed solution;

[0053] Among them, the activated carbon includes powdered activated carbon and granular activated carbon, and the mass ratio of the components of the activated carbon is: powdered activated carbon: granular activated carbon = 2.5:10.

[0054] S2.2: Take 1% of the mass of hemicellulase and 2% of the mass of macroporous adsorption resin, wherein the macroporous adsorption resin is XAD-4 non-ionic macroporous adsorption resin; according to the mass ratio of water: (hemicellulase + macroporous adsorption resin) = 13:2, add the hemicellulase and macroporous adsorption resin into water and mix evenly to obtain a resin-enzyme mixed solution.

[0055] S2.3: Take 0.2% of the mass of the crushed material, and 2% of the mass of the crushed material, hydroxypropyl-β-cyclodextrin; according to the mass ratio of water: (cellulase + hydroxypropyl-β-cyclodextrin) = 23:2, add cellulase and hydroxypropyl-β-cyclodextrin into water and mix well to obtain a cellulase solution.

[0056] S3, enzymatic hydrolysis:

[0057] The pH value of the raw material slurry was adjusted to 4.8 and the temperature to 50°C, and an activated carbon-enzyme mixture was added to carry out enzymatic hydrolysis for 4 hours; then a resin-enzyme mixture was added and enzymatic hydrolysis was continued for 4 hours; then a cellulase solution was added and enzymatic hydrolysis was continued for 15 hours; after cooling to room temperature, an enzymatic hydrolyzate was obtained.

[0058] S4, Fermentation:

[0059] The pH value of the enzymatic hydrolysate was adjusted to 5 and the temperature to 30°C, and 1% of brewer's yeast by weight of the enzymatic hydrolysate was added, and the product was stored in an open container for 12 hours. Then, 0.3% of a catalyst by weight of the enzymatic hydrolysate, 0.1% of vitamin E by weight of the enzymatic hydrolysate, 0.4% of potassium dihydrogen phosphate by weight of the enzymatic hydrolysate, and 0.8% of peptone by weight of the enzymatic hydrolysate were added, the product was mixed evenly, and the product was sealed for storage. The product was anaerobically fermented at 20°C for 47 days to obtain a fermentation liquid.

[0060] S5, post-processing:

[0061] The fermentation liquid is filtered using a 200-mesh sieve, a 400-mesh sieve, and an 800-mesh sieve in sequence to remove the residue and obtain a filtrate containing ethanol; the filtrate is distilled at normal pressure and 79° C., and all distillates are collected to obtain high-purity ethanol, which is used for fuel.

[0062] A catalyst for use in the above-mentioned method for preparing ethanol by enzymatic fermentation of cellulose, the catalyst comprising the following raw materials in parts by mass: 0.3 parts of molybdenum oxide, 2 parts of silicon dioxide, 0.8 parts of citric acid, 0.3 parts of sucrose fatty acid ester, 0.3 parts of cetearyl alcohol polyether, 2 parts of rhamnolipid, 0.8 parts of magnesium sulfate, 0.3 parts of calcium pantothenate, 0.3 parts of sodium 5-nitroguaiacol, and 10 parts of purified water; the particle size range of the solid raw materials in the raw materials is all below 250 mesh sieve.

[0063] The preparation method of the above catalyst comprises the following steps:

[0064] N1: Mix citric acid, sodium 5-nitroguaiacol, magnesium sulfate, calcium pantothenate, molybdenum oxide and silicon dioxide in parts by mass to obtain a mixture, add deionized water 4 times the mass of the mixture, mix and disperse evenly, evaporate to remove water at 110°C, then heat treat at 155°C for 2.5h, and cool to obtain a semi-finished catalyst;

[0065] N2: Add the semi-finished catalyst, sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid into purified water according to their mass proportions, stir evenly at 50°C to obtain the catalyst.

[0066] Example 2

[0067] A method for preparing ethanol by enzymatic fermentation of cellulose, comprising the following steps:

[0068] S1, raw material pretreatment:

[0069] The straw and the starch waste are mixed and crushed in a mass ratio of 90:20 to obtain a crushed product; the crushed product, potassium acetate and water are homogenized in a mass ratio of 100:20:1 to obtain a raw material slurry;

[0070] Among them, the straw is wheat straw; and the starch waste is the waste residue produced after preparing starch from potatoes.

[0071] S2, enzyme solution preparation:

[0072] S2.1: Take 0.5% of α-amylase by weight of the crushed material, 0.5% of saccharifying enzyme by weight of the crushed material, 0.5% of pectinase by weight of the crushed material, 0.5% of papain by weight of the crushed material, and 1.5% of activated carbon by weight of the crushed material; according to the mass ratio of water: (α-amylase + saccharifying enzyme + activated carbon) = 10:1, add α-amylase, saccharifying enzyme, and activated carbon into water and mix evenly to obtain an activated carbon-enzyme mixture;

[0073] Among them, activated carbon includes powdered activated carbon and granular activated carbon, and the mass ratio of the activated carbon components is: powdered activated carbon: granular activated carbon = 1:10.

[0074] S2.2: Take 0.5% hemicellulase by weight of the crushed material and 1.5% macroporous adsorption resin by weight of the crushed material, wherein the macroporous adsorption resin is XAD-4 non-ionic macroporous adsorption resin; according to the mass ratio, water: (hemicellulase + macroporous adsorption resin)

[0075] =10:1, add hemicellulase and macroporous adsorption resin into water and mix evenly to obtain a resin-enzyme mixed solution.

[0076] S2.3: Take 0.1% of the mass of the crushed material, and 1% of the mass of the crushed material, hydroxypropyl-β-cyclodextrin; according to the mass ratio of water: (cellulase + hydroxypropyl-β-cyclodextrin) = 15:1, add cellulase and hydroxypropyl-β-cyclodextrin into water and mix evenly to obtain a cellulase solution.

[0077] S3, enzymatic hydrolysis:

[0078] The pH value of the raw material slurry was adjusted to 4.5 and the temperature to 45°C, and an activated carbon-enzyme mixture was added to carry out enzymatic hydrolysis for 3 hours; then a resin-enzyme mixture was added and enzymatic hydrolysis was continued for 3 hours; then a cellulase solution was added and enzymatic hydrolysis was continued for 10 hours; after cooling to room temperature, an enzymatic hydrolyzate was obtained.

[0079] S4, Fermentation:

[0080] The pH value of the enzymatic hydrolysate was adjusted to 4 and the temperature to 28°C, and 0.5% of brewer's yeast by weight of the enzymatic hydrolysate was added, and the product was stored openly for 8 hours; then 0.2% of a catalyst by weight of the enzymatic hydrolysate, 0.05% of vitamin E by weight of the enzymatic hydrolysate, 0.2% of potassium dihydrogen phosphate by weight of the enzymatic hydrolysate, and 0.5% of peptone by weight of the enzymatic hydrolysate were added, the product was mixed evenly, the product was sealed and stored, and anaerobically fermented at 18°C ​​for 50 days to obtain a fermentation liquid.

[0081] S5, post-processing:

[0082] The fermentation liquid is filtered through a 200-mesh sieve, a 400-mesh sieve, and an 800-mesh sieve in sequence to remove the residue and obtain a filtrate containing ethanol; the filtrate is distilled at normal pressure and 78° C., and all the distillates are collected to obtain high-purity ethanol, which is used for fuel.

[0083] A catalyst for use in the above-mentioned method for preparing ethanol by enzymatic fermentation of cellulose, the catalyst comprising the following raw materials in parts by mass: 0.1 part of molybdenum oxide, 1 part of silicon dioxide, 0.5 part of citric acid, 0.1 part of sucrose fatty acid ester, 0.1 part of cetearyl alcohol polyether, 1 part of rhamnolipid, 0.5 part of magnesium sulfate, 0.1 part of calcium pantothenate, 0.1 part of sodium 5-nitroguaiacol, and 8 parts of purified water; the particle size range of the solid raw materials in the raw materials is all below 250 mesh sieve.

[0084] The preparation method of the above catalyst comprises the following steps:

[0085] N1: Mix citric acid, sodium 5-nitroguaiacol, magnesium sulfate, calcium pantothenate, molybdenum oxide and silicon dioxide in parts by mass to obtain a mixture, add deionized water 3 times the mass of the mixture, mix and disperse evenly, evaporate to remove water at 100°C, then heat treat at 150°C for 2h, and cool to obtain a semi-finished catalyst;

[0086] N2: Add the semi-finished catalyst, sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid into purified water according to their mass proportions, stir evenly at 45°C to obtain the catalyst.

[0087] Example 3

[0088] A method for preparing ethanol by enzymatic fermentation of cellulose, comprising the following steps:

[0089] S1, raw material pretreatment:

[0090] The straw and the starch waste are mixed and crushed in a mass ratio of 90:28 to obtain a crushed product; the crushed product, potassium acetate and water are homogenized in a mass ratio of 100:30:1 to obtain a raw material slurry;

[0091] Among them, the straw is rice straw; and the starch waste is the waste residue produced after starch is prepared from cassava.

[0092] S2, enzyme solution preparation:

[0093] S2.1: Take 2% of α-amylase by weight of the crushed material, 0.5% of saccharifying enzyme by weight of the crushed material, 2% of pectinase by weight of the crushed material, 0.5% of papain by weight of the crushed material, and 3% of activated carbon by weight of the crushed material; according to the mass ratio of water: (α-amylase + saccharifying enzyme + activated carbon) = 10:3, add α-amylase, saccharifying enzyme, and activated carbon into water and mix evenly to obtain an activated carbon-enzyme mixed solution;

[0094] Among them, activated carbon includes powdered activated carbon and granular activated carbon, and the mass ratio of the activated carbon components is: powdered activated carbon: granular activated carbon = 1:10.

[0095] S2.2: Take 2% of the mass of hemicellulase and 1.5% of the mass of macroporous adsorption resin, wherein the macroporous adsorption resin is XAD-4 non-ionic macroporous adsorption resin; according to the mass ratio of water: (hemicellulase + macroporous adsorption resin) = 15:1, add hemicellulase and macroporous adsorption resin into water and mix evenly to obtain a resin-enzyme mixed solution.

[0096] S2.3: Take 0.3% of the mass of the crushed material, and 1% of the mass of the crushed material, hydroxypropyl-β-cyclodextrin; according to the mass ratio of water: (cellulase + hydroxypropyl-β-cyclodextrin) = 30:1, add cellulase and hydroxypropyl-β-cyclodextrin into water and mix well to obtain a cellulase solution.

[0097] S3, enzymatic hydrolysis:

[0098] The pH value of the raw material slurry was adjusted to 5.0 and the temperature to 45°C, and an activated carbon-enzyme mixture was added to carry out enzymatic hydrolysis for 5 hours; then a resin-enzyme mixture was added and enzymatic hydrolysis was continued for 3 hours; then a cellulase solution was added and enzymatic hydrolysis was continued for 20 hours; after cooling to room temperature, an enzymatic hydrolyzate was obtained.

[0099] S4, Fermentation:

[0100] The pH value of the enzymatic hydrolysate was adjusted to 4 and the temperature to 33°C, and 0.5% of brewer's yeast by weight of the enzymatic hydrolysate was added, and the product was stored openly for 15 hours; then 0.2% of a catalyst by weight of the enzymatic hydrolysate, 0.15% of vitamin E by weight of the enzymatic hydrolysate, 0.2% of potassium dihydrogen phosphate by weight of the enzymatic hydrolysate, and 1% of peptone by weight of the enzymatic hydrolysate were added, the product was mixed evenly, the product was sealed for storage, and anaerobically fermented at 18°C ​​for 48 days to obtain a fermentation liquid.

[0101] S5, post-processing:

[0102] The fermentation liquid is filtered through a 200-mesh sieve, a 400-mesh sieve, and an 800-mesh sieve in sequence to remove the residue and obtain a filtrate containing ethanol; the filtrate is distilled at normal pressure and 78° C., and all the distillates are collected to obtain high-purity ethanol, which is used for fuel.

[0103] A catalyst for use in the above-mentioned method for preparing ethanol by enzymatic fermentation of cellulose, the catalyst comprising the following raw materials in parts by mass: 0.5 parts of molybdenum oxide, 1 part of silicon dioxide, 1 part of citric acid, 0.1 parts of sucrose fatty acid ester, 0.5 parts of cetearyl alcohol polyether, 1 part of rhamnolipid, 1 part of magnesium sulfate, 0.1 parts of calcium pantothenate, 0.5 parts of sodium 5-nitroguaiacol, and 8 parts of purified water; the particle size range of the solid raw materials in the raw materials is all below 250 mesh sieve.

[0104] The preparation method of the above catalyst comprises the following steps:

[0105] N1: Mix citric acid, sodium 5-nitroguaiacol, magnesium sulfate, calcium pantothenate, molybdenum oxide and silicon dioxide in parts by mass to obtain a mixture, add deionized water 3.5 times the mass of the mixture, mix and disperse evenly, evaporate to remove water at 120°C, then heat treat at 150°C for 3h, and cool to obtain a semi-finished catalyst;

[0106] N2: Add the semi-finished catalyst, sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid into purified water according to their mass proportions, stir evenly at 45°C to obtain the catalyst.

[0107] Example 4

[0108] A method for preparing ethanol by enzymatic fermentation of cellulose, comprising the following steps:

[0109] S1, raw material pretreatment:

[0110] The straw and the starch waste are mixed and crushed in a mass ratio of 100:25 to obtain a crushed product; the crushed product, potassium acetate and water are homogenized in a mass ratio of 150:30:3 to obtain a raw material slurry;

[0111] Among them, the straw refers to corn straw, rice straw and other straws with higher mass ratio; the starch waste refers to the waste residue produced after preparing starch from sweet potatoes.

[0112] S2, enzyme solution preparation:

[0113] S2.1: Take 2% of the mass of α-amylase, 2% of the mass of saccharifying enzyme, 2% of the mass of pectinase, 2% of the mass of papain, and 3% of the mass of activated carbon; according to the mass ratio of water: (α-amylase + saccharifying enzyme + activated carbon) = 15:3, add α-amylase, saccharifying enzyme, and activated carbon into water and mix well to obtain an activated carbon-enzyme mixture;

[0114] Among them, activated carbon includes powdered activated carbon and granular activated carbon, and the mass ratio of the activated carbon components is: powdered activated carbon: granular activated carbon = 3:10.

[0115] S2.2: Take 2% of the mass of hemicellulase and 3% of the mass of macroporous adsorption resin, wherein the macroporous adsorption resin is XAD-4 non-ionic macroporous adsorption resin; according to the mass ratio of water: (hemicellulase + macroporous adsorption resin) = 15:3, add the hemicellulase and macroporous adsorption resin into water and mix evenly to obtain a resin-enzyme mixture.

[0116] S2.3: Take 0.3% of the mass of the crushed material, and 3% of the mass of the crushed material, hydroxypropyl-β-cyclodextrin; according to the mass ratio of water: (cellulase + hydroxypropyl-β-cyclodextrin) = 30:2.5, add cellulase and hydroxypropyl-β-cyclodextrin into water and mix evenly to obtain a cellulase solution.

[0117] S3, enzymatic hydrolysis:

[0118] The pH value of the raw material slurry was adjusted to 5.0 and the temperature to 55°C, and an activated carbon-enzyme mixture was added to perform enzymolysis for 5 hours; then a resin-enzyme mixture was added and the enzymolysis was continued for 5 hours; then a cellulase solution was added and the enzymolysis was continued for 20 hours; after cooling to room temperature, an enzymolysis solution was obtained.

[0119] S4, Fermentation:

[0120] The pH value of the enzymatic hydrolysate was adjusted to 6 and the temperature to 33°C, and 1.5% of brewer's yeast by weight of the enzymatic hydrolysate was added, and the product was stored in an open container for 15 hours. Then, 0.5% of a catalyst by weight of the enzymatic hydrolysate, 0.15% of vitamin E by weight of the enzymatic hydrolysate, 0.6% of potassium dihydrogen phosphate by weight of the enzymatic hydrolysate, and 1% of peptone by weight of the enzymatic hydrolysate were added, the product was mixed evenly, sealed and stored, and anaerobically fermented at 28°C for 45 days to obtain a fermentation liquid.

[0121] S5, post-processing:

[0122] The fermentation liquid is filtered through a 200-mesh sieve, a 400-mesh sieve, and an 800-mesh sieve in sequence to remove the residue and obtain a filtrate containing ethanol; the filtrate is distilled at normal pressure and 80° C., and all the distillates are collected to obtain high-purity ethanol, which is used for fuel.

[0123] A catalyst for use in the above-mentioned method for preparing ethanol by enzymatic fermentation of cellulose, the catalyst comprising the following raw materials in parts by mass: 0.5 parts of molybdenum oxide, 3 parts of silicon dioxide, 1 part of citric acid, 0.5 parts of sucrose fatty acid ester, 0.5 parts of cetearyl alcohol polyether, 3 parts of rhamnolipid, 1 part of magnesium sulfate, 0.5 parts of calcium pantothenate, 0.5 parts of sodium 5-nitroguaiacol, and 12 parts of purified water; the particle size range of the solid raw materials in the raw materials is all below 250 mesh sieve.

[0124] The preparation method of the above catalyst comprises the following steps:

[0125] N1: Mix citric acid, sodium 5-nitroguaiacol, magnesium sulfate, calcium pantothenate, molybdenum oxide and silicon dioxide in parts by mass to obtain a mixture, add deionized water 5 times the mass of the mixture, mix and disperse evenly, evaporate to remove water at 120°C, then heat treat at 160°C for 3h, and cool to obtain a semi-finished catalyst;

[0126] N2: Add the semi-finished catalyst, sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid into purified water according to their mass proportions, stir evenly at 55°C to obtain the catalyst.

[0127] Example 5

[0128] A method for preparing ethanol by enzymatic fermentation of cellulose, comprising the following steps:

[0129] S1, raw material pretreatment:

[0130] The straw and the starch waste are mixed and crushed in a mass ratio of 100:30 to obtain a crushed product; the crushed product, potassium acetate and water are homogenized in a mass ratio of 150:20:3 to obtain a raw material slurry;

[0131] The straw includes corn straw, wheat straw and rice straw of equal mass ratio; the starch waste includes waste residue produced after preparing starch from potato and sweet potato, which is a mixture of waste residues of equal mass ratio.

[0132] S2, enzyme solution preparation:

[0133] S2.1: Take 0.5% of α-amylase by weight of the crushed material, 2% of saccharifying enzyme by weight of the crushed material, 0.5% of pectinase by weight of the crushed material, 2% of papain by weight of the crushed material, and 1.5% of activated carbon by weight of the crushed material; according to the mass ratio of water: (α-amylase + saccharifying enzyme + activated carbon) = 15:1, add α-amylase, saccharifying enzyme, and activated carbon into water and mix evenly to obtain an activated carbon-enzyme mixed solution;

[0134] Among them, activated carbon includes powdered activated carbon and granular activated carbon, and the mass ratio of the activated carbon components is: powdered activated carbon: granular activated carbon = 3:10.

[0135] S2.2: Take 0.5% of the mass of hemicellulase and 3% of the mass of macroporous adsorption resin, wherein the macroporous adsorption resin is XAD-4 non-ionic macroporous adsorption resin; according to the mass ratio of water: (hemicellulase + macroporous adsorption resin) = 10:3, add the hemicellulase and macroporous adsorption resin into water and mix evenly to obtain a resin-enzyme mixture.

[0136] S2.3: Take 0.1% of the mass of the crushed material, and 3% of the mass of the crushed material, hydroxypropyl-β-cyclodextrin; according to the mass ratio of water: (cellulase + hydroxypropyl-β-cyclodextrin) = 20:3, add cellulase and hydroxypropyl-β-cyclodextrin into water and mix evenly to obtain a cellulase solution.

[0137] S3, enzymatic hydrolysis:

[0138] The pH value of the raw material slurry was adjusted to 4.5 and the temperature to 55°C, and an activated carbon-enzyme mixture was added to carry out enzymatic hydrolysis for 3 hours; then a resin-enzyme mixture was added and the enzymatic hydrolysis was continued for 5 hours; then a cellulase solution was added and the enzymatic hydrolysis was continued for 10 hours; after cooling to room temperature, an enzymatic hydrolyzate was obtained.

[0139] S4, Fermentation:

[0140] The pH value of the enzymatic hydrolysate was adjusted to 6 and the temperature to 28°C, and 1.5% of brewer's yeast by weight of the enzymatic hydrolysate was added, and the product was stored openly for 8 hours; then, 0.5% of a catalyst by weight of the enzymatic hydrolysate, 0.05% of vitamin E by weight of the enzymatic hydrolysate, 0.6% of potassium dihydrogen phosphate by weight of the enzymatic hydrolysate, and 0.5% of peptone by weight of the enzymatic hydrolysate were added, the product was mixed evenly, the product was sealed for storage, and anaerobically fermented at 28°C for 46 days to obtain a fermentation liquid.

[0141] S5, post-processing:

[0142] The fermentation liquid is filtered through a 200-mesh sieve, a 400-mesh sieve, and an 800-mesh sieve in sequence to remove the residue and obtain a filtrate containing ethanol; the filtrate is distilled at normal pressure and 80° C., and all the distillates are collected to obtain high-purity ethanol, which is used for fuel.

[0143] A catalyst for use in the above-mentioned method for preparing ethanol by enzymatic fermentation of cellulose, the catalyst comprising the following raw materials in parts by mass: 0.1 parts of molybdenum oxide, 3 parts of silicon dioxide, 0.5 parts of citric acid, 0.5 parts of sucrose fatty acid ester, 0.1 parts of cetearyl alcohol polyether, 3 parts of rhamnolipid, 0.5 parts of magnesium sulfate, 0.5 parts of calcium pantothenate, 0.1 parts of sodium 5-nitroguaiacol, and 12 parts of purified water; the particle size range of the solid raw materials in the raw materials is all below 250 mesh sieve.

[0144] The preparation method of the above catalyst comprises the following steps:

[0145] N1: Citric acid, sodium 5-nitroguaiacol, magnesium sulfate, calcium pantothenate, molybdenum oxide, and silicon dioxide are mixed according to mass fractions to obtain a mixture, and deionized water of 4.5 times the mass of the mixture is added, mixed and dispersed evenly, and water is evaporated at 100° C., and then heat-treated at 160° C. for 2 h, and a semi-finished catalyst is obtained after cooling;

[0146] N2: Add the semi-finished catalyst, sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid into purified water according to their mass proportions, stir evenly at 55°C to obtain the catalyst.

[0147] In the above embodiments, the enzyme activity of α-amylase is 1000U / g, which is derived from Wuhan Bingde Biotechnology Co., Ltd., the enzyme activity of saccharifying enzyme is 50,000 U / g, which is derived from Shandong Yuzhixing Biotechnology Co., Ltd., the enzyme activity of pectinase is 30,000 U / g, which is derived from Shandong Jishuo Biotechnology Co., Ltd., the enzyme activity of papain is 400,000 U / g, which is derived from Shaanxi Wensheng Biotechnology Co., Ltd., the enzyme activity of hemicellulase is 100,000 U / g, which is derived from Jiangsu Yuanshengtong Bioengineering Co., Ltd., the enzyme activity of cellulase is 20,000 U / g, which is derived from Nanning Shanwan Biotechnology Co., Ltd., and the bacterial activity of brewer's yeast is 20 billion CFU / g, which is derived from Jinan Jinyuyuan Biotechnology Co., Ltd. The particle size range of the powdered activated carbon used is 100 mesh to 300 mesh, and the particle size range of the granular activated carbon is 1mm to 3mm.

[0148] The ceteareth used in the catalysts of the above embodiments is ceteareth-20, and the rhamnolipid is L-rhamnolipid.

[0149] Comparative Example 1

[0150] In S2.1, no activated carbon is added to the activated carbon-enzyme mixture, and the content of activated carbon is replaced by water; other methods and parameters are the same as in Example 1.

[0151] Comparative Example 2

[0152] S2.1 is omitted, and the activated carbon-enzyme mixture is not prepared; the activated carbon-enzyme mixture is not used for enzymatic hydrolysis in S3; other methods and parameters are the same as those in Example 1.

[0153] Comparative Example 3

[0154] In S2.2, no macroporous adsorption resin is added to the resin-enzyme mixture, and the content of the macroporous adsorption resin is replaced by water; other methods and parameters are the same as in Example 1.

[0155] Comparative Example 4

[0156] S2.2 was omitted, and the resin-enzyme mixture was not prepared; the resin-enzyme mixture was not used for enzymatic hydrolysis in S3; and the other methods and parameters were the same as those in Example 1.

[0157] Comparative Example 5

[0158] In S4, after adding the brewer's yeast, the mixture is not stored in an open container, but the catalyst adjuvant is directly added and mixed, and then sealed and stored. Other methods and parameters are the same as those in Example 1.

[0159] Comparative Example 6

[0160] In S4, no catalyst is added during fermentation; other methods and parameters are the same as those in Example 1.

[0161] Comparative Example 7

[0162] In S4, 2% of the mass of the enzymatic hydrolyzate is added as catalyst, that is, the catalyst content is too high; other methods and parameters are the same as in Example 1.

[0163] Comparative Example 8

[0164] No sodium 5-nitroguaiacol was added to the catalyst, and other methods and parameters were the same as in Example 1.

[0165] Comparative Example 9

[0166] No sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid are added to the catalyst; other methods and parameters are the same as in Example 1.

[0167] Comparative Example 10

[0168] In the preparation method of the catalyst, no semi-finished catalyst is prepared; that is, all raw materials are directly mixed evenly to obtain the catalyst; other methods and parameters are the same as in Example 1.

[0169] The yield and purity of ethanol prepared in the above embodiments and comparative examples were statistically analyzed, and the results are shown in Table 1 below.

[0170] Table 1 Ethanol yield and purity results

[0171]

[0172]

[0173] It can be seen from the above results that the preparation methods of Examples 1 to 5 can effectively improve the ethanol yield, the distillation crude ethanol has a high purity, and can effectively reduce the amount of cellulase. From the results of Comparative Example 1, it can be seen that activated carbon can absorb some of the components that are harmful to the activity of hemicellulase, cellulase and saccharomyces cerevisiae, improve the efficiency and yield of cellulose enzymatic fermentation to prepare ethanol, and activated carbon can stabilize the fermentation system; the ethanol yield obtained without adding activated carbon is reduced. From the results of Comparative Example 1, it can be seen that no activated carbon-enzyme mixture is prepared, that is, the straw is not pre-treated with α-amylase, saccharifying enzyme, pectinase, and papain, which affects the subsequent enzymatic fermentation conversion efficiency and yield. From the results of Comparative Example 1, it can be seen that the macroporous adsorption resin can adsorb components that are harmful to the activity of cellulase and saccharomyces cerevisiae, and improve the efficiency and yield of cellulose enzymatic fermentation to prepare ethanol. From the results of Comparative Example 4, it can be seen that no resin-enzyme mixture is prepared, that is, the straw is not pre-treated with hemicellulase, which affects the enzymatic efficiency of low-content cellulase, and then affects the fermentation yield. From the results of comparative example 5, it can be seen that open storage can promote the early reproduction of brewer's yeast, discharge bad gases, release fermentation heat, and facilitate material conversion, thereby helping to improve the ethanol yield; without open storage, the ethanol yield decreases. From the results of comparative examples 6 and 7, it can be seen that appropriate catalysts can effectively promote sealed enzymolysis and fermentation, promote the activity of brewer's yeast, promote product conversion, improve product conversion efficiency and yield, and shorten fermentation time; adding excessive catalysts will have slight toxic side effects, affect biological activity, and reduce product yield. From the results of comparative example 8, it can be seen that sodium 5-nitroguaiacol is not added to the catalyst, which affects the effect of the semi-finished product catalyst component. Sodium 5-nitroguaiacol has an auxiliary effect of promoting the growth of brewer's yeast and improving fermentation efficiency, and has the effect of improving the dispersibility and bioaffinity of the semi-finished product catalyst itself, and promoting catalytic efficiency. As shown in the results of Comparative Example 9, sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid are not added to the catalyst, which affects the fermentation yield. Sucrose fatty acid ester has the effect of stabilizing the fermentation system and protecting the saccharomyces cerevisiae cells, cetearyl alcohol polyether has the effect of improving the properties of the fermentation liquid, promoting dispersion, and enhancing the tolerance of saccharomyces cerevisiae, and rhamnolipid has the effect of promoting enzymolysis and fermentation. As shown in the results of Comparative Example 10, citric acid, sodium 5-nitroguaiacol, magnesium sulfate, calcium pantothenate, molybdenum oxide, and silicon dioxide are not mixed and heat-treated to prepare semi-finished catalysts, which will affect the catalytic effect. Among them, the semi-finished catalyst can form a metal-acid bifunctional catalyst to improve the catalytic efficiency.

Claims

1. A method for preparing ethanol by enzymatic fermentation of cellulose, characterized in that: The method comprises the following steps: S1, raw material pretreatment: According to the mass ratio of straw: starch waste = (90-100): (20-30), the straw and starch waste are mixed and crushed to obtain a crushed material; according to the mass ratio of water: crushed material: potassium acetate = (100-150): (20-30): (1-3), the crushed material, potassium acetate and water are homogenized to prepare a raw material slurry; S2, enzyme solution preparation: S2.1: Take 0.5% to 2% of α-amylase by weight of the crushed material, 0.5% to 2% of saccharifying enzyme by weight of the crushed material, 0.5% to 2% of pectinase by weight of the crushed material, 0.5% to 2% of papain by weight of the crushed material, and 1.5% to 3% of activated carbon by weight of the crushed material, add them into water and mix well to obtain an activated carbon-enzyme mixture; S2.2: Take 0.5% to 2% of the mass of the crushed material hemicellulase and 1.5% to 3% of the mass of the crushed material macroporous adsorption resin, add them into water and mix them evenly to obtain a resin-enzyme mixed solution; S2.3: Take 0.1% to 0.3% of the mass of the crushed material, 1% to 3% of the mass of the crushed material, hydroxypropyl-β-cyclodextrin, add to water and mix well to obtain a cellulase solution; S3, enzymatic hydrolysis: The pH value of the raw material slurry is adjusted to 4.5-5.0, the temperature is 45°C-55°C, and the activated carbon-enzyme mixture is added to perform enzymolysis for 3h-5h; then the resin-enzyme mixture is added to continue enzymolysis for 3h-5h; then the cellulase solution is added to continue enzymolysis for 10h-20h; after cooling to room temperature, an enzymolysis solution is obtained; S4, Fermentation: The pH value of the enzymatic hydrolysate is adjusted to 4-6, the temperature is 28-33°C, 0.5%-1.5% of brewer's yeast by weight of the enzymatic hydrolysate is added, and the solution is stored in an open state for 8-15 hours; then, a catalyst and auxiliary materials are added, mixed evenly, sealed and stored, and anaerobically fermented at 18-28°C for 45-50 days to obtain a fermentation solution; S5, post-processing: The fermentation liquid is filtered to remove the residue to obtain a filtrate containing ethanol; the filtrate is distilled to obtain high-purity ethanol, which is used for fuel.

2. The method for preparing ethanol by enzymatic hydrolysis and fermentation of cellulose according to claim 1, characterized in that: In S1, the straw is a combination of one or more of corn straw, wheat straw, and rice straw; the starch waste is waste residue generated after preparing starch from at least one of sweet potato, cassava, potato, and sweet potato.

3. The method for preparing ethanol by enzymatic hydrolysis and fermentation of cellulose according to claim 1, characterized in that: In S2.1, the mass ratio of the components of the activated carbon-enzyme mixture is: water: (α-amylase + saccharifying enzyme + activated carbon) = (10-15): (1-3); the activated carbon includes powdered activated carbon and granular activated carbon, and the mass ratio of the components of the activated carbon is: powdered activated carbon: granular activated carbon = (1-3): 10; the particle size range of the powdered activated carbon is 100 mesh to 300 mesh, and the particle size range of the granular activated carbon is 1 mm to 3 mm.

4. The method for preparing ethanol by enzymatic hydrolysis and fermentation of cellulose according to claim 1, characterized in that: In S2.2, the mass ratio of the components of the resin-enzyme mixture is: water: (hemicellulase + macroporous adsorption resin) = (10-15): (1-3); the macroporous adsorption resin is XAD-4 non-ionic macroporous adsorption resin.

5. The method for preparing ethanol by enzymatic hydrolysis and fermentation of cellulose according to claim 1, characterized in that: In S2.3, the mass ratio of the components of the cellulase solution is: water: (cellulase + hydroxypropyl-β-cyclodextrin) = (15-30): (1-3).

6. The method for preparing ethanol by enzymatic hydrolysis and fermentation of cellulose according to claim 1, characterized in that: In S4, the added amount of the catalyst is 0.2% to 0.5% of the mass of the enzymatic solution; the auxiliary materials include vitamin E, potassium dihydrogen phosphate and peptone, the added amount of the vitamin E is 0.05% to 0.15% of the mass of the enzymatic solution, the added amount of potassium dihydrogen phosphate is 0.2% to 0.6% of the mass of the enzymatic solution, and the added amount of the peptone is 0.5% to 1% of the mass of the enzymatic solution.

7. The method for preparing ethanol by enzymatic hydrolysis and fermentation of cellulose according to claim 1, characterized in that: In S5, the distillation temperature is 78°C to 80°C.

8. A catalyst for use in the above-mentioned method for preparing ethanol by enzymatic fermentation of cellulose, characterized in that: The catalyst comprises the following raw materials in parts by mass: 0.1 to 0.5 parts of molybdenum oxide, 1 to 3 parts of silicon dioxide, 0.5 to 1 parts of citric acid, 0.1 to 0.5 parts of sucrose fatty acid ester, 0.1 to 0.5 parts of cetearyl alcohol polyether, 1 to 3 parts of rhamnolipid, 0.5 to 1 parts of magnesium sulfate, 0.1 to 0.5 parts of calcium pantothenate, 0.1 to 0.5 parts of sodium 5-nitroguaiacol, and 8 to 12 parts of purified water.

9. A catalyst according to claim 8, characterized in that The particle size range of the solid raw materials in the raw materials is all below 250 mesh sieve.

10. A catalyst according to claim 8, characterized in that The preparation method of the catalyst comprises the following steps: N1: Mix citric acid, sodium 5-nitroguaiacol, magnesium sulfate, calcium pantothenate, molybdenum oxide and silicon dioxide according to their mass fractions to obtain a mixture, add deionized water 3 to 5 times the mass of the mixture, mix and disperse evenly, evaporate to remove water at 100° C. to 120° C., and then heat treat at 150° C. to 160° C. for 2 h to 3 h, and obtain a semi-finished catalyst after cooling; N2: Add the semi-finished catalyst, sucrose fatty acid ester, cetearyl alcohol polyether and rhamnolipid into purified water according to their mass proportions, mix well at 45°C to 55°C to obtain the catalyst.

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