Method for producing ethanol by fermenting acid-process corn fiber hydrolysate

Abstract

The invention relates to the technical field of ethanol fermentation, in particular to a method for producing ethanol through fermentation of acid-process corn fiber hydrolysate. The method comprises the following steps: step 1, dilute acid pretreatment of corn fibers; step 2, a raw material size mixing process; step 3, liquefying powder slurry raw materials; step 4, a dry yeast activation process; and 5, fermenting the mixed raw materials with ethanol. According to the method, sugar in the acid-method corn fiber hydrolysate is used for replacing corn raw materials, effective degradation and conversion of corn fibers are achieved, the purpose of increasing the yield of ethanol is achieved, the production process is simple, energy is saved, environment friendliness is achieved, raw materials are saved, detoxification treatment of the corn fiber diluted acid hydrolysate and efficient utilization of the corn fiber raw materials are achieved, and the method has good application prospects. Good industrialization prospects are realized.

Description

Technical field:

[0001] The invention relates to the technical field of ethanol fermentation, and in particular to a method for producing ethanol by fermenting acid-process corn fiber hydrolyzate. Background technology:

[0002] Corn fiber refers to the seed coat of corn kernels, which accounts for about 6% to 8% of the weight of the kernels. The main components include cellulose, hemicellulose, lignin, starch, protein, oil and ash. Among them, cellulose and hemicellulose account for about 60% of the weight of corn fiber, and their mass ratio is 1:2. Corn husk is the seed coat sieved out of corn after wet processing, which contains 17% to 20% cellulose, 30% to 40% hemicellulose, 1.5% to 2.5% lignin, 10% to 12% starch, 9% to 14% protein, 2% to 8% crude fat, 1% to 6% ash, and 6% to 8% other substances.

[0003] The technology of producing ethanol from corn fiber mainly relies on cellulase to hydrolyze cellulose and hemicellulose into yeast fermentable monosaccharides, thereby increasing the ethanol yield. The structure of corn fiber (corn husk) is complex and it is difficult to hydrolyze it directly by enzymatic means. Pretreatment of corn fiber can improve the hydrolysis rate. Corn fiber has a high hemicellulose content and contains a large number of branches and connecting bonds. It is difficult to achieve a good enzymatic hydrolysis effect when the pretreatment intensity is low; however, when the intensity is too high, the monosaccharides produced during the pretreatment process are easily further degraded to generate inhibitors such as furfural and carboxymethylfurfural (HMF).

[0004] Cellulose is a high molecular polymer formed by the polymerization of glucose through β-1,4-glycosidic bonds. It has crystalline and non-crystalline regions. The non-crystalline regions are easily hydrolyzed into glucose molecules by cellulase. The degree of crystallinity of the crystalline region is represented by the crystallinity, which affects the enzymatic hydrolysis effect of cellulase to a certain extent. Hemicellulose has a high content of pentose components, so the probability of further degradation into inhibitors such as furfural after pretreatment is greater. Hemicellulose is mainly composed of pentose (xylose, arabinose, galactose, etc.) and hexose (mannose, glucose, etc.) monosaccharides. It has a disordered and loose structure and is easy to remove by pretreatment. However, the wood cellulose material composed of hydrogen bonds between hemicellulose and lignin has a dense structure, which increases the difficulty of hemicellulose removal.

[0005] The dilute acid hydrolysis pretreatment process can directly degrade starch and hemicellulose into soluble oligosaccharides. When the pretreatment conditions are enhanced, cellulose can also be degraded into soluble oligosaccharides. Monosaccharides hydrolyzed by dilute acid pretreatment will further generate inhibitors such as furfural and 5-hydroxymethylfurfural under a strong pretreatment intensity, affecting the activity of brewer's yeast during ethanol fermentation. The acetyl and uronic acid groups in hemicellulose are hydrolyzed under acidic conditions to form acidic substances such as acetic acid and uronic acid, which will also affect yeast fermentation.

[0006] Due to the dilute acid pretreatment process, the inhibitor content in the hydrolyzed corn fiber (corn husk) is extremely high, and yeast cannot directly use the sugar in the hydrolyzate to ferment and produce ethanol. At present, in order to comprehensively utilize the sugar in the hydrolyzate, physical, chemical, and biological methods are often used to detoxify the inhibitors in the hydrolyzate to reduce the concentration of inhibitors such as furfural, 5-hydroxymethylfurfural, acetic acid, and uronic acid in the hydrolyzate.

[0007] Physical methods include evaporation, organic solvent extraction and adsorption. Evaporation can remove some low-boiling organic matter in fermentation inhibitors; organic solvent extraction can remove most inhibitors, but it is difficult to recover organic solvents; activated carbon adsorption is simple to operate, but it is affected by the nature of the inhibitor, the pH of the hydrolyzate, the temperature, time, type and concentration of the activated carbon pretreatment, and the degree of inhibitor removal is limited; ion exchange resin adsorption has a significant effect on the removal of weak acidic inhibitors, but has a limited effect on the removal of furfural inhibition.

[0008] The chemical method mainly achieves the detoxification effect by adding chemical reagents to precipitate the inhibitors in the hydrolyzate or by adjusting the pH value to change the ionization of the inhibitors. The commonly used chemical method is the calcium hydroxide neutralization method, that is, using calcium hydroxide to adjust the pH to 9-10, and then using sulfuric acid to adjust the pH to about 5.5. This method is simple to operate, low in cost, and has a significant inhibitor removal effect, but due to the precipitation of calcium ions, it is not conducive to various equipment for subsequent operations.

[0009] Biological method refers to the use of some specific enzymes or microorganisms to treat inhibitors to change their structure and reduce their toxicity. Since enzyme catalysis is specific and specific, enzyme treatment can only remove certain inhibitors. Although microbial pretreatment can have a certain detoxification effect on inhibitors in the prehydrolysate, microorganisms can also utilize the sugars in the prehydrolysate. Summary of the invention:

[0010] The technical problem to be solved by the present invention is to provide a method for producing ethanol by fermenting acid-process corn fiber hydrolysate. The method utilizes sugar in the acid-process corn fiber hydrolysate to replace corn raw materials, realizes effective degradation and conversion of corn fiber, and achieves the purpose of increasing ethanol production. The production process is simple, energy-saving and environmentally friendly, and saves raw materials. The method solves the problems of detoxification treatment of corn fiber dilute acid hydrolysate and efficient utilization of corn fiber raw materials, and has good industrialization prospects.

[0011] The technical solution adopted by the present invention is: a method for producing ethanol by fermenting acid-process corn fiber hydrolyzate, the method comprising the following steps:

[0012] Step 1, corn fiber dilute acid pretreatment process: corn husk and dilute acid treatment liquid are mixed and hydrolyzed according to a material-liquid mass ratio of 1:5 to 1:7.5, the treatment temperature is 140° C. to 145° C., and the hydrolysis time is 40 min to 60 min; the material obtained after the corn husk is treated with dilute acid is treated by a horizontal centrifuge to obtain solid acid-processed corn fiber and liquid acid-processed corn fiber hydrolyzate respectively;

[0013] Step 2, raw material slurry preparation process: corn is first-stage crushed, the particle size of corn flour is controlled to be ≤0.5% of the 2mm sieve, and corn flour slurry with a suitable dry matter concentration is prepared; the acid corn fiber hydrolyzate prepared in step 1 and corn flour slurry are mixed and prepared into slurry raw materials in a suitable mass ratio;

[0014] Step 3, liquefaction process of the slurry raw material: pre-add liquefaction enzyme of 1 / 4 to 1 / 3 of the total amount of liquefaction enzyme to the slurry raw material, the liquefaction enzyme activity is ≥ 200,000 U / mL, then heat to 89°C to 94°C, add liquefaction enzyme of 3 / 4 to 2 / 3 of the total amount of the remaining liquefaction enzyme, after liquefaction for a certain period of time, the DE value ranges from 19% to 22%, and a liquefied mash is obtained;

[0015] Step 4, dry yeast activation process: weigh super brewing dry yeast, the number of which is ≥ 20 billion / g, put it into sterile water, and activate it for 20min to 30min at 32°C to 33°C and a rotation speed of 180r / min to 200r / min. The number of live yeast cells in the dry yeast activation solution is ≥ 60 million / mL;

[0016] Step 5, mixed raw material ethanol fermentation process: the liquefied mash is reduced to 32°C-33°C, saccharifying enzyme, urea, acid protease, and cellulase are added, and dry yeast activation liquid is inoculated at 1% of the total volume of the liquefied mash. After fermentation for 72 hours, a mature mash of the mixed raw material fermentation is obtained.

[0017] Furthermore, the main component indicators and hydrolyzate recovery rates of the solid acid-processed corn fiber and liquid acid-processed corn fiber hydrolyzate obtained in step one are as follows: the mass fraction of crude fiber content in the solid sample is 51% to 57%, the glucose content in the liquid sample is 17.6 g / L to 24.8 g / L, the xylose content is 30.9 g / L to 39.6 g / L, and the hydrolyzate recovery rate is ≥89%.

[0018] Furthermore, in the step 2, the particle size control index of the corn flour is 2 mm sieve material ≤ 0.5%, D90 particle size ≤ 1611 μm, and D50 particle size ≤ 405 μm.

[0019] Furthermore, in the step 2, the dry matter concentration of the prepared corn flour slurry is 30% to 33.5% by mass.

[0020] Furthermore, in the step 2, the mixing ratio of the acid-process corn fiber hydrolyzate and the corn flour slurry is 1:9 to 1:9.5 by mass.

[0021] Furthermore, in the step five, the amount of saccharifying enzyme added is 170 mL / t to 200 mL / t of liquefied mash, and the saccharifying enzyme activity is ≥ 180,000 U / mL.

[0022] Furthermore, in the step five, the amount of urea added is 0.4kg / t to 0.45kg / t of liquefied mash.

[0023] Furthermore, in the step five, the amount of acidic protease added is 15 mL / t to 20 mL / t of liquefied mash, and the activity of the acidic protease is ≥ 100,000 U / mL.

[0024] Furthermore, in the step five, the amount of cellulase added is 16000FPU / t to 56000FPU / t of liquefied mash, and the filter paper enzyme activity of the crude cellulase solution is ≥8FPU / mL.

[0025] The beneficial effects of the present invention are:

[0026] The present invention adopts the technology of producing ethanol by fermenting acid-processed corn fiber hydrolysate, mainly using the sugar in the acid-processed corn fiber hydrolysate to replace corn raw materials. The acid-processed corn fiber produced by this process can be used to produce fiber ethanol or other high value-added cellulose products.

[0027] The method for producing ethanol by fermenting acid-process corn fiber hydrolyzate provided by the present invention has a high ethanol-glycerol ratio in the fermented mature mash. The process of the present invention can reduce the output of by-product glycerol and at the same time reduce the viscosity of the fermented mash to facilitate material transportation.

[0028] The method for producing ethanol by fermenting acid-process corn fiber hydrolyzate proposed in the present invention can be combined with a corn starch ethanol process. Not only is the production process simple, energy-saving and environmentally friendly, and raw material-saving, but it also solves the problems of detoxification of corn fiber dilute acid hydrolyzate and efficient utilization of corn fiber raw materials, and has good industrial prospects. Specific implementation method:

[0029] Example 1

[0030] A method for producing ethanol by fermenting acid-process corn fiber hydrolyzate, the method comprising the following steps:

[0031] Step 1: Corn fiber (corn husk) dilute acid pretreatment process:

[0032] Corn husk is used as raw material; a dilute acid treatment liquid is prepared at a concentration of 0.75% (mass fraction) of dilute sulfuric acid; the dilute acid pretreatment conditions are: the mass ratio of corn husk to dilute acid treatment liquid is 1:5, the treatment temperature is 145°C, and the hydrolysis time is 60 minutes; the material obtained after the corn fiber is treated with dilute acid is treated by a horizontal centrifuge to obtain solid acid-processed corn fiber (dry matter content ≥30%) and liquid acid-processed corn fiber hydrolyzate, wherein the crude fiber content in the solid sample is 51% (mass fraction), the glucose content in the liquid sample is 24.8g / L, the xylose content is 39.6g / L, and the liquid recovery rate is ≥89%.

[0033] Step 2: Raw material slurry preparation process:

[0034] After primary crushing, the average starch content of the corn is 73% (mass fraction), which is prepared into corn flour slurry with a dry matter content of 30% (mass fraction). The acid corn fiber hydrolyzate prepared in step 1 and the corn flour slurry are mixed in a mass ratio of 1:9 to prepare the slurry raw material.

[0035] Step 3: liquefaction process of slurry raw materials:

[0036] Add 10 mL / t of liquefaction enzyme (liquefaction enzyme activity ≥ 200,000 U / mL) to the slurry raw material in advance, then raise the temperature to 89°C ~ 92°C, add 30 mL / t of liquefaction enzyme, liquefy for 60 minutes, control the DE value at 22%, and obtain liquefied mash.

[0037] Step 4, dry yeast activation process:

[0038] Weigh 3g of super brewing dry yeast (yeast count ≥ 20 billion / g), put it into 1L of sterile water, activate it for 30min at 32°C and 180r / min, and the number of live yeast cells in the seed activation solution should be ≥ 60 million / mL.

[0039] Step 5, mixed raw material ethanol fermentation process:

[0040] The liquefied mash was cooled to 32°C, and 170 mL / t of saccharifying enzyme (saccharifying enzyme activity ≥ 180,000 U / mL), 0.4 kg / t of urea, 20 mL / t of acidic protease (protease activity ≥ 100,000 U / mL), and 56,000 FPU / t (mash) of cellulase were added. Dry yeast activation solution (live yeast count ≥ 60 million / mL) was inoculated at 1% (volume fraction) of the total volume of the fermented mash. After 72 hours of fermentation, the ethanol concentration reached 110.5 g / L, the glycerol concentration was 7.73 g / L, the residual polysaccharide concentration was 0.53 g / L, the residual glucose concentration was 1.06 g / L, the residual fructose concentration was 4.83 g / L, the residual total sugar concentration was 30.4 g / L, and the ethanol-glycerol ratio was 14.29.

[0041] Example 2

[0042] The method of producing ethanol by fermentation of acid corn fiber hydrolyzate comprises the following steps:

[0043] Step 1: Corn fiber (corn husk) dilute acid pretreatment process:

[0044] Corn husk is used as raw material; a dilute acid treatment liquid is prepared at a concentration of 0.75% (mass fraction) of dilute sulfuric acid; the dilute acid pretreatment conditions are: the mass ratio of corn husk to dilute acid treatment liquid is 1:7.5, the treatment temperature is 140°C, and the hydrolysis time is 40 minutes; the material obtained after the corn fiber is treated with dilute acid is treated by a horizontal centrifuge to obtain solid acid-processed corn fiber (dry matter content ≥30%) and liquid acid-processed corn fiber hydrolyzate, wherein the crude fiber content in the solid sample is 57% (mass fraction), the glucose content in the liquid sample is 17.6 g / L, the xylose content is 30.9 g / L, and the liquid recovery rate is ≥89%.

[0045] Step 2: Raw material slurry preparation process:

[0046] After primary crushing, the average starch content of the corn is 73% (mass fraction), and the corn flour slurry with a dry matter content of 33.5% (mass fraction) is prepared. The acid corn fiber hydrolyzate prepared in step 1 and the corn flour slurry are mixed in a mass ratio of 1:9 to prepare the slurry raw material.

[0047] Step 3: liquefaction process of slurry raw materials:

[0048] Add 10 mL / t of liquefaction enzyme (liquefaction enzyme activity ≥ 200,000 U / mL) to the slurry raw material in advance, then raise the temperature to 90°C ~ 94°C, add 25 mL / t of liquefaction enzyme, liquefy for 50 minutes, control the DE value at 19%, and obtain liquefied mash.

[0049] Step 4, dry yeast activation process:

[0050] Weigh 3g of super brewing dry yeast (yeast count ≥ 20 billion / g), put it into 1L of sterile water, activate it for 20min at 33°C and 200r / min, and the number of live yeast cells in the seed activation solution should be ≥ 60 million / mL.

[0051] Step 5, mixed raw material ethanol fermentation process:

[0052] The liquefied mash was cooled to 33°C, and 200mL / t of saccharifying enzyme (saccharifying enzyme activity ≥ 180,000 U / mL), 0.45kg / t of urea, 15mL / t of acidic protease (protease activity ≥ 100,000 U / mL), and 16,000FPU / t (mash) of cellulase were added. Dry yeast activation solution (live yeast count ≥ 60 million / mL) was inoculated at 1% (volume fraction) of the total volume of the fermented mash. After 72 hours of fermentation, the ethanol concentration reached 122.8g / L, the glycerol concentration was 8.59g / L, the residual polysaccharide concentration was 0.59g / L, the residual glucose concentration was 1.18g / L, the residual fructose concentration was 5.37g / L, the residual total sugar concentration was 33.8g / L, and the ethanol-glycerol ratio was 14.30.

[0053] Comparative Example 1

[0054] The method for producing ethanol by fermenting corn starch comprises the following steps:

[0055] Step 1: Corn flour slurry mixing process:

[0056] The corn is first crushed to an average starch content of 73% (mass fraction); the particle size control index of the corn flour is 2mm sieve material ≤0.5% (D90 particle size ≤1611μm, D50 particle size ≤405μm), and it is prepared into a corn flour slurry with a dry matter content of 30% (mass fraction), and 10mL / t of liquefaction enzyme (liquefaction enzyme activity ≥200,000U / mL) is added.

[0057] Step 2: Starch slurrying process:

[0058] The corn flour slurry is heated to 90°C-94°C, 30 mL / t of liquefaction enzyme (liquefaction enzyme activity ≥ 200,000 U / mL) is added, liquefied for 60 minutes, and the DE value is controlled at 20%.

[0059] Step 3, dry yeast activation process:

[0060] In a biological safety cabinet, weigh 3 g of super brewer's dry yeast (yeast count ≥ 20 billion / g), put it into 1 L of sterile water, activate it at 32°C, 180 r / min for 30 min, and the number of live yeast cells should be ≥ 60 million / mL.

[0061] Step 4, ethanol fermentation process:

[0062] The liquefied mash was cooled to 32°C, 170 mL / t of saccharifying enzyme (saccharifying enzyme activity ≥ 180,000 U / mL), 0.4 kg / t of urea, 20 mL / t of acidic protease (protease activity ≥ 100,000 U / mL), and 1% (volume fraction) of dry yeast activation solution (live yeast count ≥ 60 million / mL) were inoculated. After 72 hours of fermentation, the ethanol concentration reached 118.0 g / L, the glycerol concentration was 11.81 g / L, the residual polysaccharide concentration was 3.87 g / L, the residual glucose concentration was 1.30 g / L, the residual fructose concentration was 0.60 g / L, the residual total sugar concentration was 21.9 g / L, and the ethanol-glycerol ratio was 9.99.

[0063] As shown in Examples 1-2 and Comparative Example 1, the method for producing ethanol by fermenting acid-process corn fiber hydrolyzate provided by the present invention can achieve an ethanol-glycerol ratio of 14.3 in the fermented mature mash, while the ethanol-glycerol ratio of the mash in the control test was 10.0. The process of the present invention can reduce the output of by-product glycerol by 27%. At the same time, the process can reduce the viscosity of the fermented mash, which is beneficial to material transportation.

[0064] It can be understood that the above specific description of the present invention is only used to illustrate the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents to achieve the same technical effects; as long as the use requirements are met, they are within the protection scope of the present invention.

Claims

1. A method for producing ethanol by fermenting acid-process corn fiber hydrolyzate, characterized in that: The steps of this method are as follows: Step 1, corn fiber dilute acid pretreatment process: corn husk and dilute acid treatment liquid are mixed and hydrolyzed according to a material-liquid mass ratio of 1:5 to 1:7.5, the treatment temperature is 140° C. to 145° C., and the hydrolysis time is 40 min to 60 min; the material obtained after the corn husk is treated with dilute acid is treated by a horizontal centrifuge to obtain solid acid-processed corn fiber and liquid acid-processed corn fiber hydrolyzate respectively; Step 2, raw material slurry preparation process: corn is first-stage crushed, the particle size of corn flour is controlled to be ≤0.5% of the 2mm sieve, and corn flour slurry with a suitable dry matter concentration is prepared; the acid corn fiber hydrolyzate prepared in step 1 and corn flour slurry are mixed and prepared into slurry raw materials in a suitable mass ratio; Step 3, liquefaction process of the slurry raw material: pre-add liquefaction enzyme of 1 / 4 to 1 / 3 of the total amount of liquefaction enzyme to the slurry raw material, the liquefaction enzyme activity is ≥ 200,000 U / mL, then heat to 89°C to 94°C, add liquefaction enzyme of 3 / 4 to 2 / 3 of the total amount of the remaining liquefaction enzyme, after liquefaction for a certain period of time, the DE value ranges from 19% to 22%, and a liquefied mash is obtained; Step 4, dry yeast activation process: weigh super brewing dry yeast, the number of which is ≥ 20 billion / g, put it into sterile water, and activate it for 20min to 30min at 32°C to 33°C and a rotation speed of 180r / min to 200r / min. The number of live yeast cells in the dry yeast activation solution is ≥ 60 million / mL; Step 5, mixed raw material ethanol fermentation process: the liquefied mash is reduced to 32°C-33°C, saccharifying enzyme, urea, acid protease, and cellulase are added, and dry yeast activation liquid is inoculated at 1% of the total volume of the liquefied mash. After fermentation for 72 hours, a mature mash of the mixed raw material fermentation is obtained.

2. The method for producing ethanol by fermentation of acid corn fiber hydrolyzate according to claim 1, characterized in that: The main component indicators and hydrolyzate recovery rate of the solid acid-processed corn fiber and liquid acid-processed corn fiber hydrolyzate obtained in the step 1 are as follows: the mass fraction of crude fiber content in the solid sample is 51% to 57%, the glucose content in the liquid sample is 17.6 g / L to 24.8 g / L, the xylose content is 30.9 g / L to 39.6 g / L, and the hydrolyzate recovery rate is ≥89%.

3. The method for producing ethanol by fermentation of acid corn fiber hydrolyzate according to claim 1, characterized in that: In the step 2, the particle size control index of the corn flour is 2 mm sieve material ≤ 0.5%, D90 particle size ≤ 1611 μm, and D50 particle size ≤ 405 μm.

4. The method for producing ethanol by fermentation of acid corn fiber hydrolyzate according to claim 1, characterized in that: In the step 2, the dry matter concentration of the prepared corn flour slurry is 30% to 33.5% by mass.

5. The method for producing ethanol by fermentation of acid corn fiber hydrolyzate according to claim 1, characterized in that: In the step 2, the mixing ratio of the acid corn fiber hydrolyzate and the corn flour slurry is 1:9 to 1:9.5 by mass.

6. The method for producing ethanol by fermentation of acid corn fiber hydrolyzate according to claim 1, characterized in that: In the step 5, the amount of saccharifying enzyme added is 170 mL / t to 200 mL / t of liquefied mash, and the saccharifying enzyme activity is ≥ 180,000 U / mL.

7. The method for producing ethanol by fermentation of acid corn fiber hydrolyzate according to claim 1, characterized in that: In the step 5, the amount of urea added is 0.4kg / t to 0.45kg / t of liquefied mash.

8. The method for producing ethanol by fermentation of acid corn fiber hydrolyzate according to claim 1, characterized in that: In the step 5, the amount of acidic protease added is 15 mL / t to 20 mL / t of liquefied mash, and the activity of the acidic protease is ≥ 100,000 U / mL.

9. The method for producing ethanol by fermentation of acid corn fiber hydrolyzate according to claim 1, characterized in that: In the step 5, the amount of cellulase added is 16000FPU / t to 56000FPU / t of liquefied mash, and the filter paper enzyme activity of the crude cellulase solution is ≥8FPU / mL.