CN102399826A - Comprehensive utilization method of sweet sorghum stalks - Google Patents

Abstract

The invention discloses a method for comprehensive utilization of sweet sorghum stalks, which belongs to the field of biomass energy and chemical technology. The method comprises the following steps: 1) solid-state fermentation of sweet sorghum stalks, distillation to obtain ethanol solution and distiller's grains; 2) hydrolysis of the distiller's grains under acidic conditions, solid-liquid separation to obtain xylose solution and acid hydrolysis residue; 3) washing the acid hydrolysis residue, using it as an enzymatic substrate, adding an enzymatic buffer, adding enzymes for enzymatic hydrolysis, and solid-liquid separation to obtain an enzymatic mixed solution and enzymatic lignin; 4) inoculating the enzymatic mixed solution with yeast for fermentation to produce an ethanol solution. The invention not only finds a new way to utilize distiller's grains, but also obtains xylose with high added value, while increasing the cellulose content and cellulase accessibility in the acid hydrolysis residue, and achieving a high conversion rate of cellulose enzymatic hydrolysis saccharification. The method improves the utilization rate of high-sugar-content lignocellulose raw materials, increases the unit crop ethanol yield, and reduces the production cost of cellulosic ethanol.

Description

Comprehensive utilization method of sweet sorghum stalk

technical field

The invention belongs to the technical field of biomass energy and chemical industry, and in particular relates to a method for comprehensive utilization of sweet sorghum stalks after solid fermentation to produce ethanol.

technical background

As an energy crop, sweet sorghum has impressive advantages. Sweet sorghum has a high rate of photosynthesis and a very high biological yield. The stalks of sweet sorghum are rich in sugar, and each hectare of sweet sorghum stalks can be fermented to produce 3000-5000L of ethanol, which varies from variety to variety.

The water requirement for planting sweet sorghum is only 1/3-1/5 of that of sugarcane, and it has wide adaptability to soil conditions, especially its remarkable drought resistance and salinity resistance. Sweet sorghum can be planted on marginal lands such as wasteland, arid land and saline-alkali land, and three crops a year. Planting sweet sorghum to produce fuel ethanol has realized "not competing with others for food and not competing with food for land".

If the sweet sorghum with both grain and stalks is planted, both grains and stems and leaves can be harvested. The grains of sweet sorghum are not only edible, but also used as feed and industrial raw materials; the sugar in the stalk can be converted into ethanol with high efficiency by applying the Advanced Solid State Fermentation Technology (ASSF) developed by Tsinghua University. While producing fuel ethanol, the by-product Lots of distillers grains.

The output of the above distiller's grains is far greater than that of ethanol. At present, the main use of distiller's grains is to provide livestock such as cattle and sheep as feed. However, with the expansion of sweet sorghum ethanol production scale and the shortage of petroleum resources, it is more necessary to use distiller's grains as raw materials for transportation fuel and chemical products to create greater economic value.

Contents of the invention

The object of the present invention is to provide a method for comprehensive utilization of sweet sorghum stalks in view of the current low utilization rate of distiller's grains and low added value of products.

The main components of distiller's grains are hemicellulose, cellulose and lignin. Among them, the hemicellulose content is about 25%, and the cellulose content is about 35.00%. Its hemicellulose component can be acid-hydrolyzed to produce xylose, xylitol, furfural and other important chemical products; Enzymatic hydrolysis and saccharification to generate glucose, and further fermentation to produce fuel ethanol. The residue left by enzymatic hydrolysis, that is, enzymatic lignin, can be used as a fuel with high calorific value, and can also be further processed to produce lignin products. Therefore, the comprehensive utilization of distiller's grains can significantly improve the economics of sweet sorghum planting, improve the economic benefits of fuel ethanol production, alleviate my country's energy crisis and environmental crisis, and have significant social benefits.

Based on above-mentioned principle, technical scheme of the present invention is:

A method for comprehensive utilization of sweet sorghum stalks, comprising the steps of:

(1) crushing sweet sorghum stalks, adjusting water content, solid-state fermentation, and distillation to obtain ethanol solution and distiller's grains;

(2) hydrolyzing the distiller's grains under acidic conditions, and separating the solid and liquid to obtain xylose solution and acid hydrolysis residue;

(3) washing the acid hydrolysis slag as a substrate, adding an enzymatic hydrolysis buffer, then adding an enzyme for enzymolysis, and separating the solid and liquid to obtain an enzymatic hydrolysis mixture and enzymatic lignin;

(4) The above-mentioned enzymatic hydrolysis mixture is inoculated with yeast and fermented to produce an ethanol solution.

The comprehensive utilization of sugar, cellulose, hemicellulose and lignin in straw components is realized through the above steps. Wherein, step (1) is the utilization step of soluble sugar in sweet sorghum stalk; step (2) is the utilization of hemicellulose in sweet sorghum stalk and the acid pretreatment process of cellulosic ethanol; step (3) is the sweet sorghum stalk The process of enzymatic hydrolysis of cellulose to produce enzymatic hydrolysis mixed liquor and enzymatic hydrolysis of lignin; step (4) is the process of fermenting enzymatic hydrolysis mixed liquor to produce ethanol.

The crushing in step (1) is usually crushing the sweet sorghum stalks into filaments with a diameter of 1-2 mm and a length of less than 30 mm;

The preferred method for adjusting the water content is to use deionized water to adjust the water content of sweet sorghum stalks to 70%;

The conditions of the solid-state fermentation are that the inoculum amount of yeast is 10% to 20% (that is, the volume of yeast liquid used per kg of material is 100 to 200mL), the temperature in the tank is 25 to 35°C, and the rotation speed of the fermenter is 0.2 to 0.5rpm Conditions, fermentation 20 ~ 42h. The optimal conditions are: the inoculum amount of yeast is 15% (that is, the volume of yeast liquid used per kg of material is 150mL, and each mL of yeast liquid contains about 1× ¹⁰⁷ yeast cells), the temperature in the tank is 30-32°C, and the fermenter rotates The speed is 0.25rpm, and the fermentation time is 30h;

The distillation is to add 150 to 250 mL of distilled water per 50 g of the fermented material obtained after solid-state fermentation, heat and distill, collect condensate, and stop when the collected condensate reaches half of the amount of distilled water added. The optimal condition is: add 200mL of distilled water to every 50g of fermented material obtained after solid-state fermentation, heat and distill, collect condensate, and stop when the collected condensate reaches half of the amount of distilled water added.

The conditions of acidolysis in step (2) are: the concentration (weight percentage) of acid is 0.5～5%, and temperature is 100～150 ℃, and the weight percentage of acidolysis substrate namely distiller's grains (dry basis) is 5%～20 %, acid hydrolysis 0.1 ~ 4h. The acid used may be one or more of sulfuric acid, phosphoric acid, formic acid, acetic acid, and oxalic acid.

The preferred conditions are: under the condition that the concentration of sulfuric acid (percentage by weight) is 1.5%, the temperature is 120-125° C., and the weight percent of the acidolysis substrate, distiller's grains (on a dry basis), is 10-15 percent, the acid hydrolysis is 0.5 percent. h; or under the condition that the concentration of oxalic acid (percentage by weight) is 3%, the temperature is 120-125° C., and the weight percent of distiller's grains (dry basis) is 10%-15% as the substrate for acidolysis, acidolysis is carried out for 1.5 h.

The enzyme described in step (3) is cellulase or a combination of cellulase and β-glucosidase.

The enzymolysis is to add the enzyme to the enzymolysis solution under the condition that the pH value of the enzymolysis solution is 4.5-5.5, and the weight percentage of the enzymolysis substrate, that is, the acid hydrolysis residue (dry basis) is 5%-20%. In the method, the addition amount is 1-10 FPU/g substrate, and the enzymatic hydrolysis and saccharification is performed for 24-120 hours at a temperature of 45-55°C.

The preferred conditions are: the pH value of the enzymolysis solution is 5.0-5.1, the weight percentage of the enzymolysis substrate (acid hydrolysis residue) (dry basis) is 12.5%, the enzymolysis temperature is 50° C., and the enzymolysis and saccharification is 72 hours.

The solid-liquid separation method may be one or more of suction filtration, centrifugation, sedimentation or hydrocyclone separation.

The yeast used for fermentation in steps (1) and (4) is Angelica or TSH-Sc-001 strain.

The TSH-Sc-001 bacterial classification described in the present invention is the same as the TSH-Sc-001 bacterial classification in the patent CN101033476A (preservation unit: China Microbiological Culture Preservation Management Committee General Microbiology Center, preservation date: March 6, 2007, registration Accession number: 1949).

In step (4), the enzymolysis mixture should be sterilized at 115-121° C. for 10-20 minutes before inoculating the yeast for fermentation. The fermentation conditions are: the inoculum amount of yeast is 5% to 20% (that is, the volume ratio of yeast liquid to enzymolysis mixture is 5% to 20%, and each mL of yeast liquid contains about 1× ¹⁰⁷ yeast cells), the fermenter The internal temperature is 25-35°C, and the fermentation time is 20-42 hours.

The preferred conditions are: the yeast is TSH-Sc-001 strain, the inoculum amount of TSH-Sc-001 is 15%, the temperature in the tank is 28-32° C., and the fermentation time is 30 hours.

The method for the comprehensive utilization of sweet sorghum of the present invention has the advantages of:

1) Sweet sorghum stalks contain 13% to 14% sugar, and the utilization rate of sugar in ethanol produced by solid-state fermentation is higher than 90%. Sweet sorghum-based ethanol realizes "not competing with others for food, not competing with food for land".

2) The solid-state fermentation process makes the structure of distiller's grains looser, which is beneficial to the acid hydrolysis/enzyme hydrolysis reaction.

3) Distiller's grains contain about 25% hemicellulose. After dilute acid treatment, the acid solution can be used to prepare xylose, which can further produce high value-added products such as xylitol or furfural. The acid hydrolysis process is not only the production process of xylose, but also the pretreatment process of cellulosic ethanol production, which effectively reduces the pretreatment cost of cellulosic ethanol production.

4) The cellulose content of distiller's grain acid hydrolysis residue is high, the accessibility of cellulase is high, and the enzymolysis inhibitors are few, so the enzymolysis efficiency is high. The enzyme cost of cellulosic ethanol production is effectively reduced, and the equipment utilization rate of the enzymatic hydrolysis process is improved.

In a word, the comprehensive utilization method of the present invention fully realizes the full utilization of soluble sugar, hemicellulose and cellulose in sweet sorghum stalks. It not only finds a new way for the utilization of distiller's grains, but also obtains high value-added xylose, improves the cellulose content and cellulase accessibility in the acid hydrolysis residue, and realizes a high conversion rate of cellulose enzymatic hydrolysis and saccharification. The method improves the utilization rate of lignocellulosic raw materials with high sugar content, increases the yield of ethanol per unit crop, and reduces the production cost of cellulosic ethanol.

Detailed ways

The following examples can enable those skilled in the art to understand the present invention more comprehensively, but do not limit the present invention in any way. (Note: the percentages in the following examples are percentages by weight unless otherwise specified)

Example 1

Harvest mature sweet sorghum, use sweet sorghum stalks with a total sugar content of 11% and a reducing sugar content of 7% as raw materials, crush them into filaments with a diameter of 1-2 mm and a length of less than 30 mm, and use deionized water to adjust the water content of the crushed sweet sorghum stalks 70%. Add TSH-Sc-001 strains into the closed silo, mix with crushed materials, and then carry out continuous fermentation in a continuous solid-state fermenter. The amount of yeast inoculum is 10% (that is, the ratio of crushed material to yeast liquid is 1kg:100mL, and each mL of yeast liquid contains about 1× ¹⁰⁷ yeast cells), adjust each operating parameter, and keep the temperature in the tank at 30-35°C , the rotation speed of the fermenter is 0.25rpm, and the fermentation time is 30h. Add 200mL of distilled water to every 50g of fermented material, heat and distill, collect the condensate, and stop when the collected condensate reaches half of the amount of distilled water added.

After fermentation, the yield of ethanol is 92.2%, and the conversion rate of total sugar is 98.6%. The composition of distiller's grains is: 38.43% cellulose, 22.63% hemicellulose, 20.07% lignin, and 0.25% ash.

Take 3 g of distiller's grains (dry weight) and put them into a microwave digestion tank, then add 27 mL of 3% sulfuric acid, and carry out acid hydrolysis at 130° C. for 0.5 h. Suction filtration after completion of the reaction to obtain xylose solution and acid hydrolysis residue.

The yield of xylose was 17.05%. The components of the acid hydrolysis residue are: 45.38% cellulose, 9.85% hemicellulose, 22.16% lignin, and 0.68% ash.

Take 0.5g (dry weight) of the acid hydrolysis residue and wash it with water and add it to the Erlenmeyer flask as an enzymolysis substrate, add sodium citrate buffer solution, and adjust the pH value of the enzymolysis solution under the condition that the weight percentage of the enzymolysis substrate is 5%. For 5.1, cellulase was added to the enzymolysis solution in an amount of 10 FPU/g substrate, and the enzymolysis was carried out at a temperature of 50° C. at a speed of 150 rpm.

After the enzymolysis is finished, solid-liquid separation is carried out to obtain the enzymolysis mixture and enzymolysis lignin. The conversion rate of cellulose after enzymatic hydrolysis and saccharification for 72 hours was 82.70%, and the concentration of glucose in the enzymatic hydrolysis mixture was 20.35g/L.

Sterilize the enzymolysis mixture at 115°C for 20 minutes, and then inoculate 15% of the TSH-Sc-001 (that is, the volume ratio of the yeast liquid to the enzymolysis mixture is 15%, and each mL of yeast liquid contains about 1×10 ⁷ yeast cells), fermented for 30 h under the condition that the temperature in the tank was 30°C. The yield of ethanol is up to 90%.

The amount of xylose in the acid hydrolysis liquid and the amount of glucose in the enzymatic hydrolysis mixture were measured by high performance liquid chromatography. The amount of ethanol was determined by gas chromatography. The composition of the materials in the examples is all measured by the NREL method.

Example 2

The solid-state fermentation method of sweet sorghum stalks is the same as in Example 1.

Take 3 g of distiller's grains (dry weight) and put them into a microwave digestion apparatus, add 27 mL of 3% oxalic acid, and carry out acid hydrolysis at 130° C. for 1.5 h. Suction filtration after completion of the reaction to obtain xylose solution and acid hydrolysis residue.

The yield of xylose was 21.48%. The components of the acid hydrolysis residue are: 52.63% cellulose, 11.67% hemicellulose, 20.60% lignin, and 0.70% ash.

The enzymatic hydrolysis method of the acid hydrolysis residue is the same as in Example 1. The conversion rate of cellulose in enzymatic saccharification for 72 hours was 85.56%, and the concentration of glucose was 24.30g/L.

The fermentation conditions of the enzymolysis mixed solution are the same as in Example 1. The yield of ethanol is up to 90%.

The amount of xylose in the acid hydrolysis liquid and the amount of glucose in the enzymatic hydrolysis mixture were measured by high performance liquid chromatography. The amount of ethanol was determined by gas chromatography. The composition of the materials in the examples is all measured by the NREL method.

Example 3

The solid-state fermentation method of sweet sorghum stalks is the same as in Example 1.

Take 3g of distiller's grains (dry weight) and put them into a high-temperature sterilization pot, and use 27mL of 3% oxalic acid for acid hydrolysis at 125°C for 0.5h. Suction filtration after completion of the reaction to obtain xylose solution and acid hydrolysis residue.

The yield of xylose was 21.37%. The components of the acid hydrolysis residue are: 51.03% cellulose, 6.99% hemicellulose, 19.25% lignin, and 0.73% ash.

The enzymatic hydrolysis method of the acid hydrolysis residue is the same as in Example 1. After 48 hours of enzymatic saccharification, the conversion rate of cellulose was 65.22%, and the concentration of glucose was 18.19g/L.

The fermentation conditions of the enzymolysis mixed solution are the same as in Example 1. The yield of ethanol is up to 90%.

The amount of xylose in the acid hydrolysis liquid and the amount of glucose in the enzymatic hydrolysis mixture were measured by high performance liquid chromatography. The amount of ethanol was determined by gas chromatography. The composition of the materials in the examples is all measured by the NREL method.

Example 4

The solid-state fermentation method of sweet sorghum stalks is the same as in Example 1.

Take 3g of distiller's grains (dry weight) and put them into a high-temperature sterilization pot, and use 27mL of 3% sulfuric acid to acidolyze for 0.5h under the condition of 125°C. Suction filtration after completion of the reaction to obtain xylose solution and acid hydrolysis residue.

The yield of xylose was 20.18%. The components of the acid hydrolysis residue are: 51.95% cellulose, 2.84% hemicellulose, 21.26% lignin, and 0.77% ash.

The enzymatic hydrolysis method of the acid hydrolysis residue is the same as in Example 1. The conversion rate of cellulose after enzymatic saccharification for 48 hours was 66.05%, and the concentration of glucose was 18.47g/L.

The fermentation conditions of the enzymolysis mixed solution are the same as in Example 1. The yield of ethanol is up to 90%.

The amount of xylose in the acid hydrolysis liquid and the amount of glucose in the enzymatic hydrolysis mixture were measured by high performance liquid chromatography. The amount of ethanol was determined by gas chromatography. The composition of the materials in the examples is all measured by the NREL method.

Example 5

The sweet sorghum stalks are crushed into filaments with a diameter of 1-2mm and a length less than 30mm, and deionized water is used to adjust the water content of the crushed sweet sorghum stalks to 70%. Then, the sweet sorghum stalks are continuously fermented in a continuous solid-state fermenter, and the inoculum amount of yeast is 15% (that is, the ratio of sweet sorghum stalks to yeast liquid is 1kg:150mL, and each mL of yeast liquid contains about 1× ¹⁰⁷ cells) , adjust various operating parameters, keep the temperature in the tank at 25-27°C, the rotation speed of the fermenter is 0.5rpm, and the fermentation time is 40h. Add 250 mL of distilled water to 50 g of fermented material, heat and distill, collect condensate, stop when the collected condensate reaches 125 mL, and obtain ethanol and distiller's grains.

After fermentation, the yield of ethanol is 89.2%, and the conversion rate of total sugar is 98.6%. The components of distiller's grains are: 37.43% cellulose, 21.63% hemicellulose, 22.07% lignin, and 0.25% ash.

Take 4.5g of distiller's grains (dry weight) into a microwave digestion tank, and then add 27mL of 1.5% sulfuric acid at 120°C for acid hydrolysis for 0.5h. Suction filtration after completion of the reaction to obtain xylose solution and acid hydrolysis residue.

The yield of xylose was 15.78%. The components of the acid hydrolysis residue are: 45.03% cellulose, 12.99% hemicellulose, 15.25% lignin, and 0.73% ash.

Take 0.5g (dry weight) of the acid hydrolysis residue and wash it with water and add it to the Erlenmeyer flask as an enzymolysis substrate, add sodium citrate buffer solution, and adjust the pH value of the enzymolysis solution under the condition that the weight percentage of the enzymolysis substrate is 15%. For 5.1, add the compound enzyme of cellulase and β-glucosidase into the enzymolysis solution, the addition amount is 2 FPU/g substrate, and enzymolyze at a temperature of 50°C at a speed of 150rpm. Enzymatic hydrolysis and saccharification for 48 hours. After the reaction is finished, filter with suction to obtain the enzymolysis mixture and enzymolysis lignin. The conversion rate of cellulose after enzymatic saccharification for 48 hours was 49.05%, and the concentration of glucose was 25.47g/L.

Sterilize the enzymolysis mixture at 121°C for 10 minutes, and then inoculate Angel yeast at 20% (that is, the volume ratio of yeast liquid to enzymolysis mixture is 20%, and each mL of yeast liquid contains about 1× ¹⁰⁷ cells), and the temperature in the tank was 30° C. to ferment for 30 h to obtain an ethanol solution. The yield of ethanol is up to 90%.

The amount of xylose in the acid hydrolysis liquid and the amount of glucose in the enzymatic hydrolysis mixture were measured by high performance liquid chromatography. The amount of ethanol was determined by gas chromatography. The composition of the materials in the examples is all measured by the NREL method.

Claims (10)

1. A method for comprehensive utilization of sweet sorghum stalks, characterized in that: the method may further comprise the steps: (1) crushing sweet sorghum stalks, adjusting the water content, solid-state fermentation, and distilling to obtain ethanol solution and distiller's grains; (2) hydrolyzing the distiller's grains under acidic conditions, and separating the solid and liquid to obtain xylose solution and acid hydrolysis residue; (3) washing the acid hydrolysis slag as a substrate, adding an enzymatic hydrolysis buffer, then adding an enzyme for enzymatic hydrolysis and saccharification, and separating the solid and liquid to obtain an enzymatic hydrolysis mixture and enzymatic lignin; (4) The above-mentioned enzymatic hydrolysis mixture is inoculated with yeast and fermented to produce ethanol solution. 2. The comprehensive utilization method according to claim 1, characterized in that, the conditions of the solid-state fermentation in step (1) are: the inoculum amount of yeast is 10% to 20%, the temperature in the tank is 25 to 35°C, and the fermentation tank The rotation speed is 0.2~0.5rpm, and the fermentation time is 20~42h; the distillation process is: add 150~250mL distilled water to each 50g fermentation material, heat and distill, and collect the condensate, when the collected condensate reaches half of the amount of distilled water added stop after. 3. The comprehensive utilization method according to claim 1, characterized in that, the conditions for hydrolysis under acidic conditions described in step (2) are: at an acid concentration of 0.5% to 5%, the acid hydrolysis substrate is distiller's grains The weight percentage is 5%-20%, and the temperature is 100-150 DEG C, and the acid hydrolysis is carried out for 0.1-4 hours, wherein the weight of the acid hydrolysis substrate is calculated on a dry basis. 4. The comprehensive utilization method according to claim 1, characterized in that, the enzymolysis conditions in step (3) are: the pH value of the enzymolysis solution is 4.5 to 5.5, and the enzymolysis substrate is the acid hydrolysis slag. Under the condition of 5-20% by weight, the enzyme is added to the enzymatic hydrolysis substrate in an amount of 1-10 FPU/g substrate, and the enzymatic hydrolysis and saccharification is carried out at a temperature of 45-55°C for 24-120 hours. 5. The comprehensive utilization method according to claim 1, characterized in that: the conditions of fermentation described in step (4) are: the inoculum amount of yeast is 5% to 20%, the temperature in the fermenter is 25 to 35°C, and the fermented Time 20 ~ 42h. 6. The comprehensive utilization method according to claim 1, characterized in that: xylose described in step (2) is used to produce xylitol or furfural. 7. The comprehensive utilization method according to claim 1, characterized in that: the crushing in step (1) is crushing sweet sorghum stalks into filaments with a diameter of 1-2 mm and a length of less than 30 mm. 8. The comprehensive utilization method according to claim 3, characterized in that: the acid used in step (2) is one or more of sulfuric acid, phosphoric acid, formic acid, acetic acid, and oxalic acid. 9. The comprehensive utilization method according to claim 1, characterized in that: the enzyme described in the step (3) is cellulase, or a combination of cellulase and β-glucosidase. 10. The comprehensive utilization method according to claim 1, characterized in that: the yeast used for fermentation in steps (1) and (4) is Angelica or TSH-Sc-001 strain.