A lignocellulosic pretreatment system for fermentative production of lactic acid and a method thereof

Abstract

The present application relates to a kind of lignocellulose pretreatment system and its method for fermenting production lactic acid, lignocellulose is loaded into pre-impregnation tank, and lactic acid solution is added and impregnated;Material in pre-impregnation tank is transferred to first reactor, heated with low pressure steam, and keeps temperature for rated time;First blow valve is opened, and first steam explosion is carried out in first explosion cylinder, and the material after explosion is only separated by first cyclone separator, and is transferred to second reactor;The steam recovered after spraying is merged into new low pressure steam and sent into second reactor, heats second reactor for rated time;Second blow valve is opened, and second steam explosion is carried out in second explosion cylinder, and the material after explosion is separated by second cyclone separator, and is collected by storage tank again.The present application can significantly improve the hydrolysis rate of hemicellulose, reduce the crystallinity of cellulose, reduce the generation of enzymatic hydrolysis and fermentation inhibitor;Without additional post-treatment, simultaneous saccharification and fermentation can be carried out to produce lactic acid;Energy is saved, and environmental pollution is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a lignocellulose pretreatment system for fermentative production of lactic acid and a method thereof. BACKGROUND

[0002] Lignocellulose is composed of lignin, hemicellulose and cellulose, and the cellulose microfibril has alternating amorphous cellulose chains, which are deeply associated with hemicellulose, so that pretreatment is required for saccharification and degradation and other development and utilization. The pretreatment methods of lignocellulose include physical pretreatment, chemical pretreatment, physical-chemical pretreatment and biological pretreatment methods. Many pretreatment methods are only at the laboratory research and development stage due to low yield, high cost and serious pollution, and only the dilute acid warm roasting method and the steam explosion method are relatively mature.

[0003] The dilute acid warm roasting method (Tsao et al. 1982) is a relatively mature method, which generally uses 1% to 2% dilute sulfuric acid to pretreat lignocellulose at 90°C to 95°C for 8 to 24 hours. This method hydrolyzes hemicellulose, reduces the crystallinity of cellulose, increases its surface area, and increases the accessibility of cellulase in the subsequent enzymatic hydrolysis process. The dilute acid warm roasting method has low acid concentration, low hemicellulose hydrolysis efficiency (70% to 80%), and long reaction time. The long heating process not only increases the power cost, but also leads to the further conversion of sugar monomers into inhibitors such as acetic acid, furfural and hydroxymethyl furfural, affecting the subsequent enzymatic hydrolysis and fermentation. While increasing the acid concentration can improve the catalytic efficiency and shorten the reaction time, the resulting pollution problem is difficult to solve.

[0004] The steam explosion method (Brownell and Saddler, 1984) initially uses high-pressure steam (generally greater than 200°C) to rapidly heat without adding any catalyst, and the hydrogen ions dissociated at high temperature catalyze the hydrolysis of most of the hemicellulose in lignocellulose, and the cellulose is transformed from a highly crystalline state to an amorphous structure to facilitate subsequent enzymatic hydrolysis. Due to the low concentration of hydrogen ions, the catalytic efficiency is low, and the hemicellulose hydrolysis rate is only about 65% to 70%. Due to the high reaction temperature, this method has huge energy consumption, and a large amount of inhibitors such as acetic acid, furfural and hydroxymethyl furfural are generated. The addition of sulfuric acid, hydrochloric acid, p-toluenesulfonic acid and other pre-impregnated acids can reduce the reaction temperature and increase the hemicellulose hydrolysis rate. The addition of pre-impregnated acid often requires additional post-treatment (commonly known as detoxification) of the lignocellulose solution after pretreatment, in order to carry out subsequent development and utilization, and the acidic wastewater will also cause serious pollution problems. Therefore, there is an urgent need for a new method that can reduce energy consumption and reduce fermentation inhibitors and environmental pollution to solve this contradiction. SUMMARY

[0005] The present application improves the prior art, and aims at providing a lignocellulose pretreatment system and method for fermentative production of lactic acid, which is reasonable in design, increases cellulase accessibility, and reduces fermentation inhibitors and environmental pollution.

[0006] To achieve the above object, the present application adopts the technical scheme of a lignocellulose pretreatment system for fermentative production of lactic acid, comprising a pre-impregnation tank, a first feeder, a first reactor, a first blow-off valve, a first explosion cylinder, a first cyclone separator, a second feeder, a second reactor, a second blow-off valve, a second explosion cylinder, a second cyclone separator, and a storage tank, the bottom of the pre-impregnation tank is connected with the feeding end of the first reactor through the first feeder, the discharging end of the first reactor is connected with the feeding end of the first explosion cylinder through the first blow-off valve, the discharging end of the first explosion cylinder is provided with the first cyclone separator, the discharging end of the first cyclone separator is connected with the feeding end of the second reactor through the second feeder, the discharging end of the second reactor is connected with the feeding end of the second explosion cylinder through the second blow-off valve, and the discharging end of the second explosion cylinder is connected with the storage tank through the second cyclone separator; the first reactor and the second reactor are both heated by low-pressure steam.

[0007] Further, the first low-pressure steam conveying pipe and the second low-pressure steam conveying pipe are respectively connected with the output end of the steam generator, the first low-pressure steam conveying pipe is connected with the first reactor, and the first low-pressure steam conveying pipe is provided with the first one-way valve; the second low-pressure steam conveying pipe is connected with the second reactor, and the second low-pressure steam conveying pipe is provided with the second one-way valve.

[0008] Further, the top of the first explosion cylinder is connected with a steam return air pipe, the steam return air pipe is connected with the second low-pressure steam conveying pipe, and the connection position of the steam return air pipe and the second low-pressure steam conveying pipe is located on the output side of the second one-way valve.

[0009] Further, the top of the second explosion cylinder is connected with a tail gas output pipe.

[0010] Another technical scheme adopted by the present application is a lignocellulose pretreatment method for fermentative production of lactic acid, comprising the following steps:

[0011] Step S1: loading lignocellulose into the pre-impregnation tank, and adding lactic acid solution into the pre-impregnation tank for impregnation for 2 hours;

[0012] Step S2: opening the pre-impregnation tank, conveying the materials in the pre-impregnation tank into the first reactor through the first feeder, conveying low-pressure steam into the first reactor, heating the materials in the first reactor by the low-pressure steam, and keeping the temperature for a rated time;

[0013] Step S3: opening the first blow valve, carrying out first steam explosion in the first explosion cylinder, separating the exploded material through the first cyclone separator, and conveying the separated material into the second reactor through the second feeder, and recycling the exploded steam through the steam recycling pipeline;

[0014] Step S4: collecting the recycled steam in step S3 into new low-pressure steam and conveying the low-pressure steam to the second reactor to heat the material in the second reactor and keeping the temperature for a rated time;

[0015] Step S5: opening the second blow valve, carrying out second steam explosion in the second explosion cylinder, separating the exploded material through the second cyclone separator, and collecting the separated material through the storage tank.

[0016] Further, in step S1, lactic acid solution is used in the wood cellulose pre-impregnation, the lactic acid solution is lactic acid with a mass fraction of 2%-8%; and the mass ratio of the wood cellulose and the lactic acid solution is 1:1-8.

[0017] Further, in step S3, the temperature in the first reactor before the first steam explosion is 150-170 DEG C, and the pressure is 800-900 kpa.

[0018] Further, in step S3, after the first reactor reaches the rated temperature before the first steam explosion, the temperature keeping time is 5-10 minutes.

[0019] Further, in step S5, the temperature in the second reactor before the second steam explosion is 140-160 DEG C, and the pressure is 750-850 kpa.

[0020] Further, in step S5, after the second reactor reaches the rated temperature before the second steam explosion, the temperature keeping time is 5-10 minutes.

[0021] Compared with the prior art, the present application has the following effects: the present application has reasonable design, adopts the way of twice steam explosion, ensures the pretreatment effect, reduces the reaction temperature, reduces the generation of inhibiting substances, can significantly improve the hydrolysis rate of hemicellulose, reduce the crystallinity of cellulose, and reduce the generation of enzymatic hydrolysis and fermentation inhibiting substances; no additional post-treatment is needed to carry out simultaneous saccharification and fermentation to produce lactic acid; energy is saved, and environmental pollution is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a structure schematic diagram of an embodiment of the present application.

[0023] In the drawings:

[0024] 1 - pre-dip tank; 2 - first feeder; 3 - first reactor; 4 - first blow-down valve; 5 - first flash tank; 6 - first cyclone; 7 - second feeder; 8 - second reactor; 9 - second blow-down valve; 10 - second flash tank; 11 - storage tank; 12 - first low pressure steam line; 13 - second low pressure steam line; 14 - first check valve; 15 - second check valve; 16 - steam return line; 17 - off-gas line; 18 - second cyclone. DETAILED DESCRIPTION:

[0025] The application will be further described below in conjunction with the drawings and specific embodiments.

[0026] In the description of the application, it is to be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like are terms of convenience indicating orientation or position relationships based on the orientation or position relationships shown in the drawings and are not to be construed as indicating or implying specific orientations or configurations of the devices or elements shown and described herein, and are not intended to limit the scope of the application, unless otherwise indicated.

[0027] As Figure 1As shown, the wood fiber pretreatment system for fermenting production of lactic acid comprises a pre-impregnation tank 1, a first feeder 2, a first reactor 3, a first blow valve 4, a first explosion cylinder 5, a first cyclone separator 6, a second feeder 7, a second reactor 8, a second blow valve 9, a second explosion cylinder 10, a second cyclone separator 18 and a storage tank 11. The pre-impregnation tank 1 is used for impregnating wood fiber, and the bottom of the pre-impregnation tank 1 is connected with the feeding end of the first reactor 3 through the first feeder 2, and the first feeder 2 is used for conveying the material in the pre-impregnation tank 1 into the first reactor 3. The discharging end of the first reactor 3 is connected with the feeding end of the first explosion cylinder 5 through the first blow valve 4, the discharging end of the first explosion cylinder 5 is provided with the first cyclone separator 6, the discharging end of the first cyclone separator 6 is connected with the feeding end of the second reactor 8 through the second feeder 7, the discharging end of the second reactor 8 is connected with the feeding end of the second explosion cylinder 10 through the second blow valve 9, and the discharging end of the second explosion cylinder 10 is connected with the storage tank 12 through the second cyclone separator 11. The first reactor 3 and the second reactor 8 are both heated by low-pressure steam. In operation, wood fiber is loaded into the pre-impregnation tank 1, and lactic acid solution is added for impregnation for 2 hours. Then, the feeding valve is opened, the material in the pre-impregnation tank 1 is conveyed into the first reactor 3 through the first feeder 2, heated by low-pressure steam, and kept for a rated time. Then, the first blow valve 4 is opened, and the first explosion cylinder 5 is subjected to steam explosion. The exploded material is separated by the first cyclone separator 6, and conveyed into the second reactor 8 through the second feeder 7. The recovered steam after the explosion is collected as new low-pressure steam and sent into the second reactor 8 for heating and keeping for a rated time. Then, the second blow valve 9 is opened, the second explosion cylinder 10 is subjected to secondary steam explosion, the exploded material is separated by the second cyclone separator 18, and collected by the storage tank 11.

[0028] In the embodiment, the first low-pressure steam conveying pipe 12 and the second low-pressure steam conveying pipe 13 are connected with the output end of the steam generator respectively. The first low-pressure steam conveying pipe 12 is connected with the first reactor 3, and used for conveying low-pressure steam to the first reactor. The first one-way valve 14 is installed on the first low-pressure steam conveying pipe 12, so as to avoid the low-pressure steam in the first reactor flowing back to the first low-pressure steam conveying pipe. The second low-pressure steam conveying pipe 13 is connected with the second reactor 8, and used for conveying low-pressure steam to the second reactor. The second one-way valve 15 is installed on the second low-pressure steam conveying pipe 13, so as to avoid the low-pressure steam in the second reactor flowing back to the second low-pressure steam conveying pipe.

[0029] In the embodiment, the top of the first explosion cylinder 5 is connected with a steam return air pipeline 16, the steam return air pipeline 16 is connected with the second low-pressure steam conveying pipeline 13, and the connection position of the steam return air pipeline 16 and the second low-pressure steam conveying pipeline 13 is located at the output side of the second one-way valve 15, so that the steam recovered after the first steam explosion is merged into the new low-pressure steam.

[0030] In the embodiment, the top of the second explosion cylinder 10 is connected with a tail gas output pipeline 17, so as to facilitate the output of the tail gas after the second steam explosion.

[0031] Another technical solution adopted by the present application is a lignocellulose pretreatment method for fermenting and producing lactic acid, comprising the following steps:

[0032] Step S1: lignocellulose is loaded into a pre-impregnation tank 1, and a lactic acid solution is added into the pre-impregnation tank 1 for impregnation for 2 hours;

[0033] Step S2: the feed valve at the bottom of the pre-impregnation tank 1 is opened, the material in the pre-impregnation tank 1 is conveyed into a first reactor 3 through a first feeder 2, low-pressure steam is conveyed into the first reactor 3, the material in the first reactor 3 is heated by the low-pressure steam, and the temperature is kept at 150-170 DEG C for 5-10 minutes;

[0034] Step S3: a first blow-off valve 4 is opened, the first steam explosion is carried out in a first explosion cylinder 5, the exploded material is separated through a first cyclone separator 6, the separated material is conveyed into a second reactor 8 through a second feeder 7, and the exploded steam is recovered through a steam return air pipeline 16;

[0035] Step S4: the recovered steam in step S3 is merged into new low-pressure steam and conveyed into the second reactor 8, the material in the second reactor 8 is heated by the low-pressure steam, and the temperature is kept at 140-160 DEG C for 5-10 minutes;

[0036] Step S5: a second blow-off valve 9 is opened, the second steam explosion is carried out in a second explosion cylinder 10, the exploded material is separated through a second cyclone separator 18, and the separated material is collected through a storage tank 11.

[0037] In the embodiment, the lignocellulose is corn stalk, corn leaf, corn cob, rice straw, sugarcane residue, miscanthus, reed, wheat straw, etc.

[0038] In the embodiment, in step S1, a lactic acid solution is used for pre-impregnation of the lignocellulose, the lactic acid solution is lactic acid with a mass fraction of 2-8%, and the mass ratio of the lignocellulose and the lactic acid solution is 1:1-8.

[0039] In this embodiment, the temperature in the first reactor 3 before the first steam explosion in step S3 is 150-170°C, and the pressure is 800-900 kPa.

[0040] In this embodiment, the temperature in the second reactor 8 before the second steam explosion in step S5 is 140-160°C, and the pressure is 750-850 kPa.

[0041] In this embodiment, the steam explosion is carried out at a lower temperature, acidity and pressure, so that the lactic acid is less likely to dehydrate to generate by-products such as acrylic acid, and is less likely to polymerize to generate polymers such as lactide; after the reaction is completed, the collected steam-exploded lignocellulose and its aqueous solution are directly used for the simultaneous saccharification and fermentation of lactic acid, without the need for detoxification and other post-treatments.

[0042] In this embodiment, the pre-impregnation with the lactic acid solution can also:

[0043] 1. The reaction is carried out with a smaller amount of water, saving water and reducing energy consumption;

[0044] 2. The concentration of lactic acid can be adjusted according to the concentration required during fermentation;

[0045] 3. The second low-temperature steam explosion is carried out by using the recovered steam, saving energy and reducing costs;

[0046] 4. Compared with pre-impregnation with inorganic strong acids, it is more gentle and produces less inhibitors;

[0047] 5. Compared with pre-impregnation with other organic acids, the introduction of impurities is reduced, and saccharification and fermentation can be carried out without additional post-treatment processes; after the fermentation is completed, there is no need for additional steps to remove the organic acid used during pre-impregnation.

[0048] Example 1

[0049] 1 kg of dry corn stalks were placed in a pre-impregnation tank, and 2 kg of a 5% (w / w) lactic acid solution was added. The mixture was impregnated for 2 hours. The feed valve was opened, allowing the material to be conveyed to the first reactor via the first feeder. The electric heating steam generator was turned on, and the first one-way valve was opened to heat the material to 165°C and maintain this temperature for 8 minutes. The first vent valve was opened, allowing the material to be instantly released into the first explosion tank. The pretreated lignocellulose mixture was fed into the second feeder via the first cyclone separator and conveyed to the second reactor. The released steam was channeled through the steam return pipe to new low-pressure steam, heating the lignocellulose raw material in the second reactor to 150°C and maintaining this temperature for 6 minutes. The second vent valve was opened, allowing the material to be instantly released into the second explosion tank. The pretreated lignocellulose mixture was collected via the second cyclone separator. The pretreated lignocellulose raw material was cooled to room temperature, and cellulase was added and Bacillus coagulans was inoculated for simultaneous saccharification and fermentation. Fermentation continued until the lactic acid concentration no longer increased (72 hours). The lactic acid concentration in the solution was measured to be 108 g / L, and the lactic acid yield was 47.0 g / 100 g corn straw. (The mass of lactic acid added during pretreatment has been deducted from the lactic acid yield calculation.)

[0050] Example 2

[0051] 1 kg of dried sugarcane bagasse was placed in a pre-impregnation tank, and 2 kg of a 3.5% lactic acid solution was added. The mixture was impregnated for 2 hours. Feed valve 1 was opened, allowing the material to be conveyed to the first reactor via the first feeder. The electric heating steam generator was turned on, and the first one-way valve was opened to heat the material to 165°C and maintain this temperature for 8 minutes. The first vent valve was opened, allowing the material to be instantly released into the first explosion tank. The pretreated lignocellulose mixture entered the second feeder through the first cyclone separator and was conveyed to the second reactor. The released steam was channeled through the steam return pipe to new low-pressure steam, heating the lignocellulose raw material in the second reactor to 150°C and maintaining this temperature for 6 minutes. The second vent valve was opened, allowing the material to be instantly released into the second explosion tank. The pretreated lignocellulose mixture was collected through the second cyclone separator. The pretreated lignocellulose raw material was cooled to room temperature, and cellulase was added and Bacillus coagulans was inoculated for simultaneous saccharification and fermentation. Fermentation continued until the lactic acid concentration no longer increased (72 hours). The lactic acid concentration in the solution was measured to be 112 g / L, and the lactic acid yield was 48.7 g / 100 g sugarcane bagasse. (The mass of lactic acid added during pretreatment has been deducted from the lactic acid yield calculation.)

[0052] Example 3

[0053] Put 1 kg of dry water rice straw into the pre-soaking tank, add 2 kg of 5% mass fraction of lactic acid solution, and soak for 2 hours. Open the feeding valve 1, and make the material pass through the first feeder to the first reactor. Open the electric heating steam generator, and open the first one-way valve to heat the material to 165°C for 8 minutes. Open the first blow valve to make the material instantaneously release into the first explosion cylinder; the pretreated lignocellulosic mixture passes through the first cyclone separator to the second feeder, and is transferred to the second reactor; the sprayed steam is collected through the steam return pipeline to form new low-pressure steam, and the lignocellulose raw material in the second reactor is heated to 150°C for 6 minutes. Open the second blow valve to make the material instantaneously release into the second explosion cylinder; the pretreated lignocellulosic mixture is collected through the second cyclone separator. The pretreated lignocellulosic raw material is cooled to room temperature, and cellulase is added and inoculated with Bacillus coagulans for simultaneous saccharification and fermentation. When the lactic acid concentration no longer increases (72 hours), the lactic acid concentration in the solution is measured to be 103 g / L, and the lactic acid yield is 44.8 g / 100 g of water rice straw. (The mass of lactic acid added during pretreatment is deducted when calculating the lactic acid yield)

[0054] Comparative Example 1

[0055] Put 1 kg of dry water rice straw into the pre-soaking tank, add 2 kg of 5% mass fraction of lactic acid solution, and soak for 2 hours. Open the feeding valve, and make the material pass through the first feeder to the first reactor. Open the electric heating steam generator, and open the first one-way valve to heat the material to 165°C for 8 minutes. Open the first blow valve to make the material instantaneously release into the first explosion cylinder; the pretreated lignocellulosic mixture passes through the first cyclone separator to the second feeder, and is transferred to the second reactor; the sprayed steam is collected through the steam return pipeline to form new low-pressure steam, and the lignocellulose raw material in the second reactor is heated to 150°C for 6 minutes. Open the second blow valve to make the material instantaneously release into the second explosion cylinder; the pretreated lignocellulosic mixture is collected through the second cyclone separator. The pretreated lignocellulosic raw material is cooled to room temperature, and cellulase is added and inoculated with Bacillus coagulans for simultaneous saccharification and fermentation. When the lactic acid concentration no longer increases (72 hours), the lactic acid concentration in the solution is measured to be 103 g / L, and the lactic acid yield is 44.8 g / 100 g of water rice straw. (The mass of lactic acid added during pretreatment is deducted when calculating the lactic acid yield)

[0056] Comparative Example 2

[0057] Put 1 kg of dry water rice straw into the pre-soaking tank, add 2 kg of 5% mass fraction of lactic acid solution, and soak for 2 hours. Open the feeding valve, and make the material pass through the first feeder to the first reactor. Open the electric heating steam generator, and open the first one-way valve to heat the material to 165°C for 8 minutes. Open the first blow valve to make the material instantaneously release into the first explosion cylinder; the pretreated lignocellulosic mixture passes through the first cyclone separator to the second feeder, and is transferred to the second reactor; the sprayed steam is collected through the steam return pipeline to form new low-pressure steam, and the lignocellulose raw material in the second reactor is heated to 150°C for 6 minutes. Open the second blow valve to make the material instantaneously release into the second explosion cylinder; the pretreated lignocellulosic mixture is collected through the second cyclone separator. The pretreated lignocellulosic raw material is cooled to room temperature, and cellulase is added and inoculated with Bacillus coagulans for simultaneous saccharification and fermentation. When the lactic acid concentration no longer increases (72 hours), the lactic acid concentration in the solution is measured to be 103 g / L, and the lactic acid yield is 44.8 g / 100 g of water rice straw. (The mass of lactic acid added during pretreatment is deducted when calculating the lactic acid yield)

[0058] Comparative Example 3

[0059] Put 1 kg of dry rice straw into a pre-soaking tank, add 2 kg of 5% sulfuric acid solution, and soak for 2 hours. Open the feed valve and transfer the material to the first reactor through the first feeder. Open the electric heating steam generator, open the first one-way valve, and heat the material to 185°C for 10 minutes. Open the first blow valve and release the material to the first explosion cylinder; the pretreated lignocellulosic mixture is collected by the cyclone separator. After pretreatment, the lignocellulosic raw material is cooled to room temperature, cellulase is added, and Bacillus coagulans is inoculated for simultaneous saccharification and fermentation. When the lactic acid concentration no longer increases (72 hours), the lactic acid concentration in the solution is measured to be 70 g / L, and the lactic acid yield is 30.5 g / 100 g of rice straw.

[0060] The traditional sulfuric acid pre-soaking method has high acidity and a temperature of up to 185°C or higher during steam explosion. Using this method, inhibitors such as furfural and 2-methyl furfural are easily generated during enzymatic hydrolysis and fermentation; the sulfate ions added during pre-soaking affect the osmotic pressure of Bacillus coagulans, and desulfation treatment (detoxification) is required before fermentation. Using the method of the present application to pretreat lignocellulose (corn straw, sugarcane residue, and rice straw, etc.), the lactic acid yield during simultaneous saccharification and fermentation is much higher than that of the traditional sulfuric acid pre-soaking method. The method of the present application has a lower temperature during steam explosion and contains a steam recovery system, which on the one hand effectively avoids the generation of inhibitors for cellulose saccharification and fermentation, improving the lactic acid yield; on the other hand, the steam is recycled, reducing energy consumption. The pre-soaking acid of the method of the present application is lactic acid, which is less likely to undergo side reactions such as dehydration and polymerization at a lower steam explosion temperature, and no additional treatment is required for the subsequent saccharification and fermentation steps, and the lactic acid added during pre-soaking can be recovered during the separation and extraction step, achieving zero discharge of pre-soaking acid.

[0061] The advantages of the present application are: (1) it can significantly improve the hydrolysis rate of hemicellulose, reduce the crystallinity of cellulose, and reduce the generation of enzymatic and fermentation inhibitors; no additional post-treatment is required for simultaneous saccharification and fermentation to produce lactic acid; energy is saved, and environmental pollution is reduced. Using this method to pretreat lignocellulosic raw materials for simultaneous saccharification and fermentation to produce lactic acid, the lactic acid concentration in the fermentation broth can reach 112 g / L, and the lactic acid yield can reach 48.7 g / 100 g of lignocellulose. (2) The secondary steam explosion method ensures the pretreatment effect, reduces the reaction temperature, and reduces the generation of inhibitors. (3) The use of steam recovery from the first steam explosion in the system reduces the energy consumption of the pretreatment process.

[0062] If the present application discloses or relates to mutually fixedly connected parts or structural members, unless otherwise stated, the fixed connection can be understood as: detachably fixedly connected (for example, connected using bolts or screws), and can also be understood as: non-detachable fixed connection (for example, riveting, welding), of course, the mutually fixed connection can also be replaced by an integral structure (for example, manufactured by integral forming using a casting process) (obviously, integral forming process cannot be used).

[0063] In addition, the terms used to represent the positional relationship or shape in any of the technical solutions disclosed in the present application include states or shapes similar, similar or close to them, unless otherwise stated.

[0064] Any component provided by the present application can be assembled from multiple individual components, or can be a single component manufactured by integral forming process.

[0065] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application and not to limit them; although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or some technical features can be replaced by equivalents; without departing from the spirit of the technical solutions of the present application, they should be covered in the technical solution range of the present application claimed.

Claims

1. A lignocellulosic pretreatment system for the fermentative production of lactic acid, characterized in that: The system comprises a pre-dipping tank, a first feeder, a first reactor, a first blow valve, a first explosion cylinder, a first cyclone separator, a second feeder, a second reactor, a second blow valve, a second explosion cylinder, a second cyclone separator and a storage tank, the bottom of the pre-dipping tank is connected with the feeding end of the first reactor through the first feeder, the discharging end of the first reactor is connected with the feeding end of the first explosion cylinder through the first blow valve, the discharging end of the first explosion cylinder is provided with the first cyclone separator, the discharging end of the first cyclone separator is connected with the feeding end of the second reactor through the second feeder, the discharging end of the second reactor is connected with the feeding end of the second explosion cylinder through the second blow valve, and the discharging end of the second explosion cylinder is connected with the storage tank through the second cyclone separator; the first reactor and the second reactor are both heated by low-pressure steam.

2. A lignocellulosic pretreatment system for the fermentative production of lactic acid according to claim 1, characterized in that: The system further comprises a first low-pressure steam conveying pipe and a second low-pressure steam conveying pipe which are respectively connected with the output end of the steam generator, the first low-pressure steam conveying pipe is connected with the first reactor, and a first one-way valve is arranged on the first low-pressure steam conveying pipe; the second low-pressure steam conveying pipe is connected with the second reactor, and a second one-way valve is arranged on the second low-pressure steam conveying pipe.

3. A lignocellulosic pretreatment system for the fermentative production of lactic acid according to claim 2, characterized in that: The top of the first explosion cylinder is connected with a steam return air pipe, the steam return air pipe is connected with the second low-pressure steam conveying pipe, and the connection position of the steam return air pipe and the second low-pressure steam conveying pipe is located on the output side of the second one-way valve.

4. The lignocellulosic pretreatment system for fermentative production of lactic acid according to claim 1, characterized in that: The top of the second explosion cylinder is connected with a tail gas output pipe.

5. A lignocellulosic pretreatment method for the fermentative production of lactic acid, characterized by: The system comprises a wood fiber pretreatment system for fermenting and producing lactic acid, and comprises the following steps: Step S1: loading wood fiber into a pre-dipping tank, and dipping the wood fiber in the pre-dipping tank in a lactic acid solution for 2 hours; Step S2: opening the pre-dipping tank, conveying the material in the pre-dipping tank into the first reactor through the first feeder, conveying low-pressure steam into the first reactor, heating the material in the first reactor by the low-pressure steam, and keeping the temperature for a rated time; Step S3: opening the first blow valve, performing a first steam explosion in the first explosion cylinder, separating the exploded material by the first cyclone separator, conveying the separated material into the second reactor through the second feeder, and recycling the steam by the steam return air pipe; Step S4: recycling the steam in step S3 into new low-pressure steam, conveying the new low-pressure steam into the second reactor, heating the material in the second reactor by the low-pressure steam, and keeping the temperature for a rated time; Step S5: opening the second blow valve, performing a second steam explosion in the second explosion cylinder, separating the exploded material by the second cyclone separator, and collecting the separated material by the storage tank.

6. A lignocellulosic pretreatment method for fermentative lactic acid production according to claim 5, characterized in that: In step S1, a lactic acid solution is used for pre-dipping the wood fiber, the lactic acid solution has a mass fraction of 2% to 8% of lactic acid, and the mass ratio of the wood fiber to the lactic acid solution is 1:1 to 8.

7. A lignocellulosic pretreatment method for fermentative lactic acid production according to claim 5, characterized in that: In step S3, the temperature in the first reactor before the first steam explosion is 150°C to 170°C, and the pressure is 800-900kpa.

8. The lignocellulosic pretreatment method for fermentative production of lactic acid according to claim 5, characterized in that: In step S3, after the temperature in the first reactor reaches the rated temperature, the temperature is kept for 5 to 10 minutes. In step S3, after the temperature in the first reactor reaches the rated temperature, the temperature is kept for 5 to 10 minutes.

9. The lignocellulosic pretreatment method for fermentative production of lactic acid according to claim 5, characterized in that: In step S5, the temperature in the second reactor before the secondary steam explosion is 140-160℃, and the pressure is 750-850kpa.

10. The lignocellulosic pretreatment method for fermentative lactic acid production according to claim 5, characterized in that: In step S5, the temperature in the second reactor reaches the rated temperature, and the holding time is 5-10 minutes.

Images