CN112322677A - Efficient pretreatment process for full-component utilization of corn straws - Google Patents

Efficient pretreatment process for full-component utilization of corn straws Download PDF

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CN112322677A
CN112322677A CN202010629893.1A CN202010629893A CN112322677A CN 112322677 A CN112322677 A CN 112322677A CN 202010629893 A CN202010629893 A CN 202010629893A CN 112322677 A CN112322677 A CN 112322677A
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于海龙
侯静静
徐玉芹
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Qingdao University of Science and Technology
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Abstract

The invention discloses an efficient pretreatment process for full-component utilization of corn straws, which comprises the following steps: the method comprises the steps of pretreating corn straws by adopting an organic strong acid solvent, recycling pretreatment liquid for 4 times, hydrolyzing and saccharifying pretreated solid residues by using cellulase with high substrate concentration, diluting and settling the pretreatment liquid recycled for 4 times, mechanically stirring while diluting and settling, obtaining high-performance lignin nano microspheres as solid precipitates, enriching monosaccharide for degrading hemicellulose in supernatant liquid after precipitation, and directly heating to convert the monosaccharide into a platform compound levulinic acid. The invention can fully utilize cellulose, hemicellulose and lignin in the corn straws, the cellulose can be used for preparing fermentable glucose, lignin degradation products can be used for preparing lignin nano microspheres, monosaccharide degraded by the hemicellulose can be converted into an important platform compound levulinic acid after being heated, the yield of the levulinic acid is 57 percent, and the waste p-toluenesulfonic acid solvent can be recovered after extraction, thereby realizing zero emission of waste.

Description

Efficient pretreatment process for full-component utilization of corn straws
Technical Field
The invention belongs to the field of biomass refining, and particularly relates to a pretreatment process for full-component utilization of corn straws.
Background
At present, raw materials in the chemical industry are mainly derived from fossil resources, and the problems of excessive emission of greenhouse gases, difficult degradation and recovery of wastes, environmental pollution, limited resources and the like caused by the raw materials are solved, so that people urgently need a new resource to replace the fossil resources. The biomass resource has the advantages of rich yield, wide source, environmental protection, sustainability and the like, the corn straw is one of the biomass resources and is a byproduct of the main grain crop corn in China, the corn straw is developed as a new resource to replace fossil resources, various problems caused by excessive consumption of the fossil resources are solved, and the current situation of waste of the rice straw resources is changed.
The main components of corn stalks are cellulose, hemicellulose and lignin. Cellulose can be converted into glucose, and then liquid fuels such as ethanol, butanol and the like and other biomass chemicals are produced through fermentation, so that the method is an important way for solving the current energy environment problem, does not influence the food safety of human beings, and becomes an inevitable trend for the development of energy industry. The state explicitly proposes: the popularization and the application of fuel ethanol are promoted, and the cellulosic ethanol is vigorously developed. The conversion of cellulose in the straw into fermentable glucose is a key step in the production of cellulosic ethanol. The enzymatic hydrolysis method is considered to be the cellulose saccharification process with the most application prospect due to the characteristics of mild reaction conditions, few hydrolysis byproducts, high saccharification yield, greenness, no pollution and the like. However, in plant cell walls, lignin and hemicellulose are covalently bound to form lignin-carbohydrate complexes (LCCs) that entrap cellulose molecules, and hemicellulose and cellulose microfibrils are tightly bound together by hydrogen bonds and van der waals forces, thereby forming a natural barrier that prevents effective contact between the enzyme preparation and cellulose. The pretreatment of the wood fiber raw material can destroy the stubborn structure of plant cell walls, remove lignin and hemicellulose, reduce the crystallinity and polymerization degree of cellulose, and increase the porosity of a substrate, thereby improving the accessibility of the material and achieving the aim of improving the enzymolysis saccharification efficiency.
However, the traditional pretreatment technology has the defects of high energy consumption, large pollution, low utilization rate of all components and the like, and is not suitable for large-scale industrial production. Based on the concept of biomass refining, the optimal biomass pretreatment technology not only needs to efficiently separate lignin and hemicellulose, but also realizes high-value utilization of lignin and hemicellulose degradation products. Although there are many patents for improving the efficiency of cellulase hydrolysis of biomass, most of them do not realize the full component utilization of raw materials. For example: patents publication nos. CN109609573A, CN109295111A, CN105063132B, and CN104278065A improve the efficiency of cellulase hydrolysis, but hemicellulose and lignin in the raw material are not fully utilized. Patent publication No. CN109486878A, although it realizes comprehensive utilization of cellulose, lignin and hemicellulose, the pretreatment temperature is high (150-170 ℃).
Disclosure of Invention
In order to realize pretreatment, improve the hydrolysis efficiency of corn straw cellulase and simultaneously utilize degraded lignin and hemicellulose in a high-valued manner, the invention adopts the following technical scheme:
1. pretreatment of corn straws: adopting 30-90% (w/v) p-toluenesulfonic acid solution to pretreat the corn straws at 80-100 ℃, wherein the solid-liquid ratio is 1: 10-1: 20, and the pretreatment time is 60-90 min. And after the pretreatment is finished, filtering and separating the solid substrate and pretreating the hydrolysate. Adding a proper amount of fresh p-toluenesulfonic acid solution into the pretreated hydrolysate, continuing to pretreat the corn straws under the same treatment conditions as the pretreatment conditions, repeating the step of treating the corn straws by the pretreated hydrolysate for 0-4 times, and filtering and separating to obtain a solid substrate rich in cellulose and a pretreated hydrolysate rich in monosaccharide and lignin.
2. Solid substrate cellulase hydrolysis: and (3) washing the solid substrate which is repeatedly pretreated by the hydrolysis solution for 0 time, 1 time, 2 times, 3 times and 4 times by using tap water until the washed liquid is neutral. The washed solid substrate was subjected to cellulase hydrolysis in acetic acid-sodium acetate buffer solution of pH4.8 at a substrate concentration of 15% for 72 hours.
3. Preparing lignin nano microspheres: and after the pretreated hydrolysate is recycled for 4 times, adding the pretreated hydrolysate into deionized water at the speed of 0.5mL/min, mechanically stirring while adding the hydrolysate at the stirring speed of 500-2500r/min until the mass concentration of the p-toluenesulfonic acid is 10%, and performing centrifugal separation to obtain a supernatant and a solid precipitate. And washing the solid precipitate for 5 times to obtain the lignin nano-microspheres.
4. Preparation of levulinic acid: directly heating the supernatant obtained by centrifugal separation in the step 3 to 150 ℃ and 200 ℃, reacting for 0.5-2h, extracting by adopting methyl isobutyl ketone after the reaction is finished, dissolving the prepared levulinic acid in the methyl isobutyl ketone, and obtaining the levulinic acid and the waste p-toluenesulfonic acid solvent after liquid separation treatment, wherein the waste p-toluenesulfonic acid solvent can be recycled.
The invention has the beneficial effects that: the organic solvent p-toluenesulfonic acid is used for pretreating the corn straws. The p-toluenesulfonic acid is a water-soluble auxiliary agent, has strong acidity and surface activity at high concentration, can almost completely degrade hemicellulose in plant cell walls into monosaccharide at lower temperature (80-100 ℃) and shorter reaction time (60-90min), and can dissolve out most lignin. Moreover, the p-toluenesulfonic acid is easy to recycle, and the efficiency is far higher than that of most separation technologies at present. The pretreatment condition is mild, and the operation is simple; the pretreatment solvent can be recycled, the production cost is low, and the pollution is small; the pretreatment efficiency is high, and 83% of lignin and 85% of hemicellulose can be removed; the pretreatment reagent can be used as a good solvent for lignin and hemicellulose degradation products and can also be used as a catalyst for catalyzing degraded monosaccharide to prepare levulinic acid; the prepared lignin nano microspheres have small particle size (100-150nm), uniform shape (spherical shape) and uniform distribution (normal distribution); belongs to an environment-friendly process route.
Drawings
FIG. 1 is a technical scheme of the present invention.
Fig. 2 is an SEM image of lignin nanospheres.
Fig. 3 is a TEM image of lignin nanospheres.
FIG. 4 is a particle size distribution diagram of lignin nanospheres.
The specific implementation mode is as follows:
the process of the present invention is further illustrated by the following examples, which are not intended to limit the invention thereto.
1. Removal of lignin and hemicellulose
Example 1: adopting 30% (w/v) of p-toluenesulfonic acid solution to pretreat the corn straws, wherein the solid-liquid ratio is 1: 10, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, and performing component analysis on the pretreated corn straws according to a American renewable energy laboratory method (NREL), wherein the result shows that: 42% of the lignin and 74% of the hemicellulose were removed while retaining 95% of the cellulose.
Example 2: adopting 50% (w/v) p-toluenesulfonic acid solution to pretreat the corn straws, wherein the solid-liquid ratio is 1: 10, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, and performing component analysis on the pretreated corn straws according to the American renewable energy laboratory method (NREL), wherein the result shows that: 58% of the lignin and 78% of the hemicellulose were removed while retaining 95% of the cellulose.
Example 3: adopting 70% (w/v) p-toluenesulfonic acid solution to pretreat the corn straws, wherein the solid-liquid ratio is 1: 10, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, and performing component analysis on the pretreated corn straws according to the American renewable energy laboratory method (NREL), wherein the result shows that: 78% of the lignin and 82% of the hemicellulose were removed, while 95% of the cellulose was retained.
Example 4: adopting 90% (w/v) p-toluenesulfonic acid solution to pretreat the corn straws, wherein the solid-liquid ratio is 1: 10, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, and performing component analysis on the pretreated corn straws according to the American renewable energy laboratory method (NREL), wherein the result shows that: 83% of the lignin and 85% of the hemicellulose were removed while retaining 95% of the cellulose.
2. Solid substrate cellulase hydrolysis saccharification
Example 5: adopting 90% (w/v) p-toluenesulfonic acid solution to pretreat the corn straws, wherein the solid-liquid ratio is 1: 10, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, filtering and separating a solid substrate and pretreating a hydrolysate after the reaction is finished, and washing the solid substrate and then carrying out cellulase hydrolysis and saccharification. The cellulase hydrolysis conditions are as follows: pH4.8, temperature 50 ℃, substrate concentration 15% (w/v), hydrolysis time 72 h. After the hydrolysis is finished, the yield of the glucose is 93.1 percent, the concentration of the glucose is 110g/L, and the most economical sugar concentration (80g/L) in the industrial production process of the ethanol is achieved. The pretreatment hydrolysate was circulated 0 times.
Example 6: the pretreatment hydrolysate obtained in the example 5 is added with a proper amount of fresh 90% (w/v) p-toluenesulfonic acid solution (the solid-liquid ratio is 1: 10), then the corn straws are pretreated, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, after the reaction is finished, a solid substrate and the pretreatment hydrolysate are filtered and separated, and the solid substrate is washed and then hydrolyzed and saccharified by cellulase. The cellulase hydrolysis conditions are as follows: pH4.8, temperature 50 ℃, substrate concentration 15% (w/v), hydrolysis time 72 h. After the hydrolysis is finished, the glucose yield is 96.8 percent, the glucose concentration is 118g/L, and the most economical sugar concentration (80g/L) in the industrial production process of the ethanol is achieved. The pretreatment hydrolysate was circulated 1 time.
Example 7: the pretreatment hydrolysate obtained in the example 6 is added with a proper amount of fresh 90% (w/v) p-toluenesulfonic acid solution (the solid-to-liquid ratio is 1: 10), then the corn straws are pretreated, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, after the reaction is finished, a solid substrate and the pretreatment hydrolysate are filtered and separated, and the solid substrate is washed and then hydrolyzed and saccharified by cellulase. The cellulase hydrolysis conditions are as follows: pH4.8, temperature 50 ℃, substrate concentration 15% (w/v), hydrolysis time 72 h. After the hydrolysis is finished, the glucose yield is 94.7 percent, the glucose concentration is 115g/L, and the most economical sugar concentration (80g/L) in the industrial production process of the ethanol is achieved. The pretreatment hydrolysate was circulated 2 times.
Example 8: the pretreated hydrolysate obtained in the example 7 is added with a proper amount of fresh 90% (w/v) p-toluenesulfonic acid solution (the solid-to-liquid ratio is 1: 10), then the corn straws are pretreated, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, after the reaction is finished, a solid substrate and the pretreated hydrolysate are filtered and separated, and the solid substrate is washed and then hydrolyzed and saccharified by cellulase. The cellulase hydrolysis conditions are as follows: pH4.8, temperature 50 ℃, substrate concentration 15% (w/v), hydrolysis time 72 h. After the hydrolysis is finished, the glucose yield is 81.5 percent, the glucose concentration is 96g/L, and the most economical sugar concentration (80g/L) in the industrial production process of the ethanol is achieved. The pretreatment hydrolysate was circulated 3 times.
Example 9: the pretreatment hydrolysate obtained in the example 8 is added with a proper amount of fresh 90% (w/v) p-toluenesulfonic acid solution (the solid-to-liquid ratio is 1: 10), then the corn straws are pretreated, the pretreatment temperature is 100 ℃, the pretreatment time is 90min, after the reaction is finished, a solid substrate and the pretreatment hydrolysate are filtered and separated, and the solid substrate is washed and then hydrolyzed and saccharified by cellulase. The cellulase hydrolysis conditions are as follows: pH4.8, temperature 50 ℃, substrate concentration 15% (w/v), hydrolysis time 72 h. After the hydrolysis is finished, the glucose yield is 81.2 percent, the glucose concentration is 96g/L, and the most economical sugar concentration (80g/L) in the industrial production process of the ethanol is achieved. The pretreatment hydrolysate was circulated 4 times.
Comparative example: directly carrying out cellulase hydrolysis saccharification on untreated corn straws, wherein the cellulase hydrolysis conditions are as follows: pH4.8, temperature 50 ℃, substrate concentration 15% (w/v), hydrolysis time 72 h. After the hydrolysis is finished, the glucose yield is 52.1 percent, the glucose concentration is 30g/L, and the most economic sugar concentration (80g/L) in the industrial production process of ethanol is not reached.
3. Preparation of lignin nano-microspheres
Example 10: and after the pretreatment of the hydrolysis solution is recycled for 4 times, adding the hydrolysis solution into deionized water at the speed of 0.5mL/min, stirring at the speed of 500r/min until the concentration of the p-toluenesulfonic acid is 10%, and performing centrifugal separation to obtain solid precipitate, namely the lignin nano microspheres, wherein the particle size of the lignin nano microspheres is 226 nm.
Example 11: and after the pretreatment of the hydrolysis solution is recycled for 4 times, adding the hydrolysis solution into deionized water at the speed of 0.5mL/min, stirring at the speed of 1000r/min until the concentration of the p-toluenesulfonic acid is 10%, and performing centrifugal separation to obtain solid precipitate, namely the lignin nano microspheres, wherein the particle size of the lignin nano microspheres is 177 nm.
Example 12: and after the pretreated hydrolysate is recycled for 4 times, adding the pretreated hydrolysate into deionized water at the speed of 0.5mL/min, stirring at the speed of 1500r/min until the concentration of the p-toluenesulfonic acid is 10%, and performing centrifugal separation to obtain solid precipitate, namely the lignin nano microspheres, wherein the particle size of the lignin nano microspheres is 122 nm.
Example 13: and after the pretreatment of the hydrolysis solution is recycled for 4 times, adding the hydrolysis solution into deionized water at the speed of 0.5mL/min, stirring at the speed of 2000r/min until the concentration of the p-toluenesulfonic acid is 10%, and performing centrifugal separation to obtain solid precipitate, namely the lignin nano microspheres, wherein the particle size of the lignin nano microspheres is 102 nm.
Comparative example: and after the pretreated hydrolysate is recycled for 4 times, adding the pretreated hydrolysate into deionized water at the speed of 0.5mL/min, stirring at the speed of 0 until the concentration of the p-toluenesulfonic acid is 10%, and performing centrifugal separation to obtain solid precipitate, namely the lignin nano microspheres, wherein the particle size of the lignin nano microspheres is 425 nm.
4. Production of levulinic acid
Example 14: and after the pretreatment of the hydrolysate is recycled for 4 times, adding the hydrolysate into deionized water at the speed of 0.5mL/min, stirring at the speed of 2000r/min until the concentration of the p-toluenesulfonic acid is 10%, centrifugally separating to obtain a supernatant, heating the supernatant in a reaction kettle to 150 ℃, reacting for 1h, wherein the concentration of the levulinic acid in the liquid after the reaction is finished is 1.91g/L, and the yield of the levulinic acid is 43.8%.
Example 15: and after the pretreatment of the hydrolysate is recycled for 4 times, adding the hydrolysate into deionized water at the speed of 0.5mL/min, stirring at the speed of 2000r/min until the concentration of the p-toluenesulfonic acid is 10%, centrifugally separating to obtain a supernatant, heating the supernatant to 160 ℃ in a reaction kettle, and reacting for 1h, wherein the concentration of the levulinic acid in the liquid after the reaction is finished is 1.98g/L, and the yield of the levulinic acid is 46.6%.
Example 16: and after the pretreatment of the hydrolysate is recycled for 4 times, adding the hydrolysate into deionized water at the speed of 0.5mL/min, stirring at the speed of 2000r/min until the concentration of the p-toluenesulfonic acid is 10%, centrifugally separating to obtain a supernatant, heating the supernatant to 170 ℃ in a reaction kettle, and reacting for 1h, wherein the concentration of the levulinic acid in the liquid after the reaction is finished is 2.2g/L, and the yield of the levulinic acid is 52.9%.
Example 17: and after the pretreatment of the hydrolysate is recycled for 4 times, adding the hydrolysate into deionized water at the speed of 0.5mL/min, stirring at the speed of 2000r/min until the concentration of the p-toluenesulfonic acid is 10%, centrifugally separating to obtain a supernatant, heating the supernatant in a reaction kettle to 180 ℃, reacting for 1h, wherein the concentration of the levulinic acid in the liquid after the reaction is finished is 2.3g/L, and the yield of the levulinic acid is 57.1%.
Example 18: and after the pretreatment of the hydrolysate is recycled for 4 times, adding the hydrolysate into deionized water at the speed of 0.5mL/min, stirring at the speed of 2000r/min until the concentration of the p-toluenesulfonic acid is 10%, centrifugally separating to obtain a supernatant, heating the supernatant to 190 ℃ in a reaction kettle, and reacting for 1h, wherein the concentration of the levulinic acid in the liquid after the reaction is finished is 2.2g/L, and the yield of the levulinic acid is 51.9%.
Comparative example: and after the pretreated hydrolysate is recycled for 4 times, adding the pretreated hydrolysate into deionized water at the speed of 0.5mL/min, stirring at the speed of 2000r/min until the concentration of the p-toluenesulfonic acid is 10%, and performing centrifugal separation to obtain a supernatant, wherein the concentration of the levulinic acid in the liquid is 0.584 g/L.
The p-toluenesulfonic acid can effectively remove lignin and hemicellulose in the corn straws, the removal rate of the lignin reaches 83 percent, the removal rate of the hemicellulose reaches 85 percent, and simultaneously 95 percent of cellulose can be reserved, thereby creating good conditions for subsequent cellulose hydrolysis and saccharification of solid substrates. After the pretreatment is finished, the cellulase hydrolysis efficiency of the solid residue with high substrate concentration (15%) is greatly improved, and the glucose yield after 72h hydrolysis reaches 93%. The pretreated hydrolysate can be recycled, after 4 times of recycling, the yield of glucose made by solid residues still reaches more than 80%, the glucose concentration is 96g/L, and the most economical sugar concentration (80g/L) in the industrial production process of ethanol is achieved. The reuse of the pretreated hydrolysate can improve the use times of the solvent, reduce the production cost and reduce the environmental pollution. The lignin dissolved in the pretreated hydrolysate can be used for preparing the lignin nanoparticles by dilution and sedimentation, the particle size of the lignin nanoparticles can be regulated and controlled by a simple mechanical stirring mode, the particle size of the lignin nanoparticles can be controlled to be 100-150nm, and the prepared lignin nanoparticles are uniform and spherical and have uniform particle size distribution (as shown in figure 4). The liquid after the lignin nano-microspheres are prepared is rich in hemicellulose degraded monosaccharide, the monosaccharide can be catalyzed and converted into an important platform compound levulinic acid in a direct heating mode due to the strong acidity of the p-toluenesulfonic acid, the yield of the levulinic acid can reach 57%, and the waste p-toluenesulfonic acid solvent can be recovered after extraction, so that zero emission of waste is realized.

Claims (3)

1. A pretreatment process for full-component utilization of corn straws is characterized by comprising the following steps:
1) pretreatment of corn straws: adopting 30-90% (w/v) p-toluenesulfonic acid solution to pretreat the corn straws at 80-100 ℃, wherein the solid-liquid ratio is 1: 10-1: 20, the pretreatment time is 60-90min, filtering and separating a solid substrate and pretreatment hydrolysate after the pretreatment is finished, adding a proper amount of fresh p-toluenesulfonic acid solution into the pretreatment hydrolysate, continuing to pretreat the corn straws, repeating the step of treating the corn straws with the pretreatment hydrolysate for 0-4 times, and filtering and separating to obtain a solid substrate rich in cellulose and a pretreatment hydrolysate rich in monosaccharide and lignin;
2) solid substrate cellulase hydrolysis: respectively washing the solid substrate which is repeatedly pretreated by 0-4 times of hydrolysis liquid by using tap water until the washed liquid is neutral, and carrying out cellulase hydrolysis on the washed solid substrate in an acetic acid-sodium acetate buffer solution with the pH value of 4.8, wherein the concentration of the substrate subjected to the enzymatic hydrolysis is 15 percent, and the time is 72 hours;
3) preparing lignin nano microspheres: after the pretreatment of the hydrolysis solution is recycled for 4 times, adding the pretreated hydrolysis solution into deionized water at the speed of 0.5mL/min, mechanically stirring while adding the hydrolysis solution at the stirring speed of 500-2500r/min until the mass concentration of the p-toluenesulfonic acid is 10%, centrifugally separating to obtain a supernatant and a solid precipitate, and washing the solid precipitate for 5 times to obtain the lignin nano microspheres;
4) preparation of levulinic acid: directly heating the supernatant obtained by centrifugal separation in the step 3 to 150 ℃ and 200 ℃, reacting for 0.5-2h, extracting by adopting methyl isobutyl ketone after the reaction is finished, dissolving the prepared levulinic acid in the methyl isobutyl ketone, and obtaining the levulinic acid and the waste p-toluenesulfonic acid solvent after liquid separation treatment, wherein the waste p-toluenesulfonic acid solvent can be recycled.
2. The pretreatment process for full-component utilization of corn stalks according to claim 1, wherein the mass concentration of the added fresh p-toluenesulfonic acid solution to the pretreated hydrolysate is 30-90%.
3. The pretreatment process of full-component utilization of corn stalks according to claim 2, wherein the reaction conditions for continuing the pretreatment of the corn stalks after adding the fresh p-toluenesulfonic acid solution into the pretreated hydrolysate are as follows: the corn straws are pretreated at the temperature of 80-100 ℃, the solid-liquid ratio is 1: 10-1: 20, and the pretreatment time is 60-90 min.
CN202010629893.1A 2020-07-01 2020-07-01 Efficient pretreatment process for full-component utilization of corn straws Pending CN112322677A (en)

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CN117143364A (en) * 2023-07-13 2023-12-01 中国林业科学研究院林产化学工业研究所 Method for preparing lignin microsphere with controllable size and good bioactivity

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CN116284459A (en) * 2021-12-08 2023-06-23 中国科学院大连化学物理研究所 Preparation method and application of nanocellulose
CN117143364A (en) * 2023-07-13 2023-12-01 中国林业科学研究院林产化学工业研究所 Method for preparing lignin microsphere with controllable size and good bioactivity

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