Method and system for efficient pretreatment of lignocellulose

Abstract

The present application relates to a kind of lignocellulose efficient pretreatment method, lignocellulose is loaded into stirred tank, after adding calcium bisulfite stirring uniformly, it is sent to reactor by feeder.Low-pressure steam is introduced to carry out steam explosion, and material is separated by cyclone separator and is sent to hydrolysis kettle for hydrolysis.After steam is sprayed, it is recycled by steam return air duct, and is used for the heating of pipeline and hydrolysis kettle.The present application can significantly improve the pretreatment effect of lignocellulose using calcium bisulfite as accelerator: reaction temperature is low, energy is saved, and the generation of enzymatic hydrolysis and fermentation inhibitor is reduced;The solid content of pretreatment liquid is high, more conducive to large-scale production;And calcium bisulfite is converted into calcium sulfate precipitate after pretreatment, and additional detoxification treatment is not needed.Lignocellulose raw material pretreated using the method is used for simultaneous saccharification and fermentation to produce lactic acid, and the lactic acid concentration in fermentation broth can reach 98 g / L, and the lactic acid yield can reach 42.4 g / 100g lignocellulose.

Description

TECHNICAL FIELD

[0001] The present application relates to a method and system for efficient pretreatment of lignocellulose, belonging to the field of bio-chemical engineering. BACKGROUND

[0002] With the depletion of fossil energy such as oil and natural gas, the production of chemicals using refinery products as raw materials also faces problems such as high price and unsustainable development. Bio-fermentation has attracted great attention due to its mild production process, low greenhouse gas emissions and sustainability. Traditional bio-fermentation mainly uses food such as sugarcane, corn and potato as raw materials for production, which is costly and can lead to the problem of "competing with people for food". Using crop straw, forestry waste and sawdust as lignocellulosic raw materials to produce chemicals is one of the ideal solutions to the above problems.

[0003] Lignocellulose is composed of cellulose, hemicellulose and lignin, which are connected by complex chemical bonds to form a firm network structure, providing rigid support for plants. In nature, there are a large number of hydrogen bonds and van der Waals forces between cellulose molecules, which form cross-linked structures, and further cause the cellulose molecules to be very close and difficult to be biodegraded. Therefore, pretreatment of lignocellulosic raw materials is required for diversified applications. The pretreatment methods of lignocellulose include physical pretreatment, chemical pretreatment, physical-chemical pretreatment and biological pretreatment. Among these pretreatment methods, acid pretreatment and steam explosion are more mature.

[0004] Acid pretreatment method usually requires high acid concentration and reaction temperature, which not only increases the cost of the reactor, but also makes it difficult to separate the residual chemical additives from the raw materials, and is less environmentally friendly; toxic by-products are easily produced during pretreatment, which inhibits the subsequent fermentation (Zhang YG et al. [J]. Southwestern Agricultural Sciences, 2016, 29(12): 2982-2987.). CA 108252144 discloses a solid acid pretreatment method, which requires the addition of 10-25 times the volume of sulfamic acid to achieve good enzymatic hydrolysis effect. CA 108690859 discloses a low-pressure steam heating dilute sulfuric acid pretreatment method, with a heating temperature as high as 130-220℃. CA 108060189 discloses a method of mixing dilute acid with straw under low liquid-solid ratio to achieve the absence of free-state dilute acid to reduce the corrosion degree of the reactor. However, this method requires a high temperature of 175℃ for 5 minutes. 117187308 discloses a method of pretreating rice straw with dilute sulfuric acid, but active carbon and Ca(OH)2 are needed for detoxification in the subsequent use.

[0005] Steam explosion is a pretreatment method of lignocellulose based on the combination of thermal, chemical and mechanical effects. The high-pressure steam is introduced and rapidly released in the steam explosion process, which can promote the degradation of hemicellulose into monosaccharides, the swelling and breaking of cellulose, the change of cellulose crystallinity and the conversion of part of lignin, resulting in the destruction of the dense three-dimensional network structure of lignocellulose, providing more enzyme contact sites and thus improving the saccharification rate of cellulose. CN 103224966 discloses a method for improving the enzymatic hydrolysis and saccharification efficiency of straw by dry storage coupled steam explosion pretreatment, and the steam explosion temperature is 160-220℃. CN 115418376 discloses a method for reducing the energy consumption of steam explosion pretreatment of agricultural biomass, and the steam explosion temperature is reduced to 150-190℃; however, the solid loading is low because the material-to-liquid ratio of the agricultural biomass raw material to acid is 1:1. CN 105780565 discloses a method for steam explosion pretreatment of lignocellulose with dilute acid, which can be operated at a temperature of 140-200℃; however, the method requires the use of sulfuric acid, sodium chloride, sodium dodecyl sulfonate or ammonium oxalate solution for pretreatment of lignocellulose at 105-145℃ for 5-20 minutes. The steam explosion pretreatment method has high reaction temperature and high energy consumption, and a large amount of inhibitors such as acetic acid, furfural and hydroxymethyl furfural are generated, which often requires an additional detoxification step.

[0006] The current developed dilute acid pretreatment and steam explosion pretreatment technologies generally have high pretreatment temperature, many inhibitors, and the need for detoxification. Most existing technologies generally require the addition of an acid or an aqueous solution of a promoter to improve the pretreatment effect; in order to ensure the solid content of the pretreated lignocellulose, the raw material needs to be dried to eliminate the dilution effect of its own moisture; in addition, the traditional pretreatment method also has the problems of incomplete and insufficient treatment, resulting in a high cellulase usage of more than 20 FPU / g of lignocellulose raw material in the subsequent enzymatic hydrolysis step. Therefore, there is an urgent need for a new method that can reduce energy consumption, cellulase usage and fermentation inhibitors without the need for an additional detoxification step to solve this contradiction. SUMMARY

[0007] In view of the deficiencies of the prior art, the technical problem to be solved by the present application is to provide a method and system for efficient pretreatment of lignocellulose.

[0008] To solve the above technical problems, the technical scheme of the present application is as follows: a method for efficient pretreatment of lignocellulose, comprising the following steps:

[0009] S1: loading the lignocellulose into a stirred tank and adding a promoter and stirring uniformly;

[0010] S2: opening the feed valve and conveying the material into the reactor;

[0011] S3: heating to a certain temperature with low pressure steam and keeping for a rated time;

[0012] S4: opening the spray valve, separating the material after steam explosion by cyclone separator, and recycling the steam after spraying through steam return pipeline;

[0013] S5: transferring the material after steam explosion to the hydrolysis kettle;

[0014] S6: recycling the steam into new low pressure steam and heating the material in the hydrolysis kettle, keeping for a rated time;

[0015] S7: after the reaction, storing the pretreatment liquid in the storage tank and directly using it in the next step;

[0016] S8: carrying out simultaneous saccharification and fermentation of the pretreated lignocellulose in the fermentation tank to produce lactic acid.

[0017] Preferably, the raw material of the lignocellulose is corn straw, rice straw, sugarcane residue, sugarcane leaf, tobacco straw and bamboo shoot shell.

[0018] Preferably, the accelerator is calcium hydrogen sulfate, and the weight ratio of calcium hydrogen sulfate to lignocellulose is 3% to 10%.

[0019] Preferably, the temperature in the reactor before steam explosion is 130°C to 150°C, and the pressure is 600 to 700 kpa.

[0020] Preferably, after the temperature in the reactor before steam explosion reaches the rated temperature, the keeping time is 3 to 5 minutes.

[0021] Preferably, the temperature in the hydrolysis kettle is 80°C to 100°C, and the keeping time is 30 to 60 minutes.

[0022] A treatment system of a method for efficient pretreatment of lignocellulose, comprising a stirring kettle, a feeder, a reactor, a spray valve, an explosion cylinder, a hydrolysis kettle, a storage tank.

[0023] Preferably, the bottom outlet of the stirring kettle and the inlet of the feeder are communicated, the outlet of the feeder and the inlet of the reactor are communicated, the outlet of the reactor is connected to the material inlet of the explosion cylinder through the spray valve, the bottom of the explosion cylinder is connected to the cyclone separator, the cyclone separator is directly connected to the hydrolysis kettle, and the outlet of the hydrolysis kettle and the inlet of the storage tank are communicated.

[0024] Preferably, the stirring paddle inside the stirring kettle is driven to rotate by a motor, and the stirring paddle is composed of a folding scraper, an oblique blade and a gear, wherein the folding scraper is located at the bottom of the stirring shaft, the gear is coaxially located at the top of the stirring shaft, and the oblique blade is spiral and distributed on the stirring shaft between the folding scraper and the gear.

[0025] Preferably, the processing system further comprises a first low-pressure steam pipe, a second low-pressure steam pipe, and a steam return pipe, the first low-pressure steam pipe is connected to the reactor and provided with a first one-way valve, the second low-pressure steam pipe is connected to the hydrolysis kettle and provided with a second one-way valve, and the steam return pipe is connected between the explosion cylinder and the second low-pressure steam pipe.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] 1. The solid calcium bisulfite is used as the accelerator, and no water is needed to prepare a solution, thus saving water resources and increasing the solid content of the pretreatment liquid;

[0028] 2. The lignocellulose raw material does not need to be dried to eliminate the dilution effect of its own moisture, thus saving energy consumption;

[0029] 3. The calcium bisulfite is a strong acid salt, which can reduce the crystallinity of cellulose and hemicellulose by breaking the hydrogen bond within and between molecules; in the steam explosion process, the required reaction temperature is low, the holding time is short, and the generation of inhibitors such as furfural is also reduced;

[0030] 4. The calcium bisulfite is used as the accelerator, and part of the hydrogen ions are consumed in the pretreatment process, and the calcium bisulfite is converted into calcium sulfate precipitate which is slightly soluble in water; this reduces the salt concentration of the pretreatment liquid, and no additional removal of sulfate operation is needed in the subsequent fermentation step, thus simplifying the process flow;

[0031] 5. The residual heat energy of the steam explosion is recycled through the steam return pipe and used for heating the hydrolysis kettle, thus saving energy consumption;

[0032] 6. The low-temperature hydrolysis further degrades the lignocellulose raw material which is not fully and completely exploded in the steam explosion, thus reducing the crystallinity of the cellulose raw material and being more beneficial to the subsequent enzymatic saccharification step;

[0033] 7. The hydrolysis reaction temperature is lower than 100℃, and no pressure vessel is needed, thus reducing the equipment requirements;

[0034] 8. The pretreatment liquid does not need an additional detoxification operation and can be used in the subsequent simultaneous saccharification and fermentation step;

[0035] 9. Compared with other acid-accelerated lignocellulose pretreatment methods, the present technical solution has mild conditions and good pretreatment effect; the system is simple and has low energy consumption.

[0036] The present application will be further described in detail below in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The figure is a schematic diagram of the pretreatment system of the present embodiment.

[0038] Figure 2 A schematic diagram of the stirring paddle inside the stirred tank.

[0039] Figure 3 A schematic diagram of the folding blade from above.

[0040] Figure 4 A diagram of the lactic acid concentration in the fermentation liquid of the example and the comparative example.

[0041] In the diagram: stirred tank 1, feeder 2, reactor 3, blow-off valve 4, cylinder 5, hydrolysis tank 6, storage tank 7, stirring paddle 8, folding blade 9, bevel blade 10, gear 11, first low-pressure steam pipeline 12, second low-pressure steam pipeline 13, steam return pipeline 14, first one-way valve 15, second one-way valve 16, cyclone separator 17. DETAILED DESCRIPTION

[0042] The application will be further described below in conjunction with the drawings and examples.

[0043] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0044] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0045] As shown in Figures 1-4 The embodiment provides a method for efficient pretreatment of lignocellulose, which comprises the following steps:

[0046] S1: loading the lignocellulose into a stirred tank, and adding a promoter to stir uniformly;

[0047] S2: opening the feeding valve to transfer the material into the reactor;

[0048] S3: heating to a certain temperature with low-pressure steam, and maintaining the temperature for a rated time;

[0049] S4: opening the blow-off valve, and separating the material after steam explosion by a cyclone separator; and recycling the steam after blow-off by a steam return pipeline;

[0050] S5: transferring the material after steam explosion into a hydrolysis tank;

[0051] S6: The recovered steam is merged with new low-pressure steam, and the material in the hydrolysis kettle is heated for a rated time;

[0052] S7: After the reaction is completed, the pretreatment liquid is stored in a storage tank and directly used in the next step.

[0053] S8: The pretreated lignocellulose is subjected to simultaneous saccharification and fermentation in a fermentation tank to produce lactic acid.

[0054] In the embodiment of the present application, the lignocellulose raw material in step S1 is corn straw, rice straw, sugarcane residue, sugarcane leaf, tobacco straw and bamboo shell.

[0055] The lignocellulose raw material does not need to be dried, and the amount of dry matter can be calculated by measuring the moisture content.

[0056] In the embodiment of the present application, the promoter in step S1 is calcium bisulfite, and the weight ratio of calcium bisulfite to lignocellulose is 3% to 10%.

[0057] In the embodiment of the present application, the temperature in the reactor before steam explosion in step S3 is 130°C to 150°C, and the pressure is 600 to 700 kpa.

[0058] In the embodiment of the present application, after the rated temperature is reached in the reactor before steam explosion in step S3, the holding time is 3 to 5 minutes.

[0059] In the embodiment of the present application, the temperature in the hydrolysis kettle in step S6 is 80°C to 100°C, and the holding time is 30 to 60 minutes.

[0060] In the embodiment of the present application, the simultaneous saccharification and fermentation step in step S8 does not need to be detoxified.

[0061] A processing system for a method of efficient pretreatment of lignocellulose, comprising a stirred tank 1, a feeder 2, a reactor 3, a spray valve 4, an explosion cylinder 5, a hydrolysis kettle 6, a storage tank 7.

[0062] In the embodiment of the present application, the bottom outlet of the stirred tank is communicated with the inlet of the feeder, the outlet of the feeder is communicated with the inlet of the reactor, the outlet of the reactor is connected to the material inlet of the explosion cylinder through the spray valve, the bottom of the explosion cylinder is connected to a cyclone separator, and the cyclone separator 17 is directly connected to the hydrolysis kettle, and the outlet of the hydrolysis kettle is communicated with the inlet of the storage tank.

[0063] In the embodiment of the present application, the inside of the stirred tank is provided with a stirring paddle 8 rotating driven by a motor, and the stirring paddle is composed of a folding scraper 9, an oblique cutting blade 10 and a stainless steel gear 11, wherein the folding scraper is located at the bottom of the stirring shaft of the stirring paddle, the gear is coaxially located at the top of the stirring shaft, and the oblique cutting blade is helical and distributed on the stirring shaft between the folding scraper and the gear.

[0064] The folding blade scraper is beneficial to scrape the lignocellulose raw material from the bottom or edge of the container; the bevel blade can provide high shear force, and the design of the bevel blade makes the load on the mechanical seal smaller, thereby ensuring the stability of the equipment; the stainless steel gear can well disperse the material and is beneficial to the mixing of the accelerant and the lignocellulose raw material.

[0065] In the embodiment of the present application, the treatment system further comprises a first low-pressure steam pipeline 12, a second low-pressure steam pipeline 13 and a steam return pipeline 14, the first low-pressure steam pipeline is connected to the reactor and is provided with a first one-way valve 15, the second low-pressure steam pipeline is connected to the hydrolysis kettle and is provided with a second one-way valve 16, and the steam return pipeline is connected between the explosion cylinder and the second low-pressure steam pipeline and is used for steam recovery after steam explosion.

[0066] The present application can significantly reduce the reaction temperature of steam explosion and hydrolysis pretreatment in the way of combination of steam explosion and dilute acid pretreatment, ensure the pretreatment effect and reduce the generation of inhibitors.

[0067] Specific implementation process: Example 1

[0068] 1 kg of corn straw with dry weight is loaded into a stirred tank, 50 g of calcium bisulfite powder is added, and stirring is performed for 10 minutes. The feeding valve is opened, and the material is conveyed to the reactor through the feeder. The electric heating steam generator is opened, the first one-way valve is opened, the material is heated to 145 DEG C, and the temperature is maintained for 5 minutes. The spray valve is opened, and the material is instantaneously released into the explosion cylinder; the pretreated lignocellulose mixture is introduced into the hydrolysis kettle through the cyclone separator; the sprayed steam is collected into new low-pressure steam through the steam return pipeline, the lignocellulose raw material in the hydrolysis kettle is heated to 95 DEG C, and the temperature is maintained for 30 minutes, and then transferred to a storage tank. The pretreated lignocellulose raw material is cooled to room temperature, 10 FPU / g of cellulase is added, and Bacillus coagulans is inoculated, and simultaneous saccharification and fermentation is performed. When the lactic acid concentration no longer increases (72 hours), the lactic acid concentration in the solution is measured to be 88 g / L, and the lactic acid yield is 38.1 g / 100 g of corn straw. Example 2

[0069] Example 1 Example 2

[0070] Example 3

[0071] Comparative Example 1

[0072] Comparative Example 2

[0073] Comparative Example 3

[0074] Put 1 kg dried bagasse into a pre-impregnation tank, add 2 kg of 5% by mass sulfuric acid solution, and impregnate for 2 hours. Heat the material to 195 °C in a reactor, and maintain for 10 minutes. Open the release valve to instantaneously release the material into a burst cylinder; cool the pretreated lignocellulosic feedstock to room temperature, add 10 FPU / g cellulase and inoculate with Bacillus coagulans, and perform simultaneous saccharification and fermentation. Ferment until the lactic acid concentration no longer increases (72 hours), and measure the lactic acid concentration in the solution to be 56 g / L, and the lactic acid yield to be 24.2 g / 100 g bagasse.

[0075] Comparative Example 3

[0076] Put 1 kg dried corn stalks into a hydrolysis kettle, add 10 kg of 2% by mass sulfuric acid solution, heat the material to 130 °C, and maintain for 120 minutes. Cool the pretreated lignocellulosic feedstock to room temperature, add 10 FPU / g cellulase and inoculate with Bacillus coagulans, and perform simultaneous saccharification and fermentation. Ferment until the lactic acid concentration no longer increases (72 hours), and measure the lactic acid concentration in the solution to be 47 g / L, and the lactic acid yield to be 20.3 g / 100 g corn stalks.

[0077] Traditional steam explosion methods have high acidity and high temperatures of above 190 °C, and the pretreatment solution contains a large amount of inhibitors such as furfural and 2-methyl furfural for enzymatic hydrolysis and fermentation, and thus needs to be detoxified before fermentation, otherwise the fermentation product yield is low. Although traditional acid pretreatment methods have a lower temperature, a large amount of acid solution is used, which greatly affects the subsequent microbial fermentation process; and because the pretreatment temperature is low, the reaction time needs to be extended to ensure the pretreatment effect, which leads to an increase in fermentation and enzymatic hydrolysis inhibitors, and thus a detoxification step is still needed to improve the fermentation product yield.

[0078] The lactic acid yield of the present application is much higher than that of traditional steam explosion and acid pretreatment methods when the lignocellulose is pretreated by the method of the present application and then subjected to simultaneous saccharification and fermentation. The steam explosion temperature of the present application is relatively low and the steam recovery system is used, which on the one hand effectively avoids the generation of inhibitors for cellulose saccharification and fermentation, and improves the lactic acid yield; and on the other hand, the steam is recycled, which reduces the energy consumption. The accelerator of the present application is calcium bisulfite, which is not prone to dehydration and polymerization and other side reactions at a relatively low steam explosion temperature, and the hydrolysis step further makes the pretreatment more complete. The consumption of hydrogen ions during low-temperature steam explosion and hydrolysis converts calcium bisulfite into calcium sulfate precipitate, and thus the pretreatment solution does not need additional desulfation treatment and can be subjected to subsequent saccharification and fermentation steps.

[0079] The above merely describes preferred embodiments of the present application, but is not intended to limit the present application to other forms, and any person skilled in the art can make changes or modifications to the above disclosed technical contents into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments without departing from the technical solution content of the present application and according to the technical essence of the present application still belongs to the protection scope of the technical solution of the present application.

Claims

1. A method for high efficiency pretreatment of lignocellulose, characterized by: The method comprises the following steps: S1: loading lignocellulose into a stirred tank, adding a promoter and stirring uniformly to obtain a material; S2: opening a feeding valve to transfer the material in S1 into a reactor; S3: heating to a certain temperature with low-pressure steam and maintaining for a rated time; S4: opening a blow-off valve, separating the material after steam explosion by a cyclone separator and transferring into a hydrolysis kettle; and recycling the steam after blow-off through a steam return pipeline; S5: recycling the steam into new low-pressure steam to heat the material in the hydrolysis kettle and maintaining for a rated time; S6: obtaining pretreated lignocellulose after reaction, storing in a storage tank and directly using in the next step; S7: performing simultaneous saccharification and fermentation of the pretreated lignocellulose in a fermentation tank to produce lactic acid. The promoter is calcium bisulfite, and the weight ratio of calcium bisulfite to lignocellulose is 3% to 10%.

2. The method of high efficiency pretreatment of lignocellulose according to claim 1, characterized by: The raw material of the lignocellulose is corn stalk, rice straw, sugarcane residue, sugarcane leaf, tobacco stalk and bamboo shoot shell.

3. The method of high efficiency pretreatment of lignocellulosic biomass according to claim 1, wherein: The temperature in the reactor before steam explosion is 130°C to 150°C, and the pressure is 600 to 700 kpa.

4. The method of high efficiency pretreatment of lignocellulosic biomass according to claim 1, wherein: After the reactor reaches the rated temperature before steam explosion, the maintaining time is 3 to 5 minutes.

5. The method of high efficiency pretreatment of lignocellulosic biomass according to claim 1, wherein: The temperature in the hydrolysis kettle is 80°C to 100°C, and the maintaining time is 30 to 60 minutes.

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