Method for improving enzymatic hydrolysis performance of pretreated lignocellulose raw material and application

Abstract

The invention belongs to the technical field of renewable energy sources, and particularly relates to a method for improving the enzyme hydrolysis performance of a pretreated lignocellulose raw material by utilizing a plasma modification technology and increasing the enzyme hydrolysis conversion rate and reducing sugar yield of the lignocellulose raw material and application. The method comprises the following steps: 1) pretreating a lignocellulose raw material by taking oxalic acid as a catalyst and combining an organic solvent method to obtain a lignocellulose wet solid rich in cellulose; 2) spreading the pretreated lignocellulose wet solid in a culture dish, placing the culture dish in a vacuum cavity of plasma equipment, introducing corresponding gas, and performing bombardment under different radio frequency powers, vacuum degrees and treatment time; the method can effectively improve the enzymatic hydrolysis performance of lignocellulose so as to improve the conversion rate and yield of glucose obtained by hydrolysis of cellulose, and has the advantages of greenness, environmental protection and rapidness, simplicity and convenience in operation compared with a conventional pretreatment method.

Description

Technical Field

[0001] The invention belongs to the technical field of renewable energy, and in particular relates to a method for improving the enzymatic hydrolysis performance of pretreated lignocellulose raw materials and an application thereof. Background Art

[0002] With the increasing energy crisis and environmental problems, the recycling of waste biomass resources has become one of the effective ways for the sustainable development of society. Lignocellulose is the most abundant renewable biomass on earth and the most suitable raw material for producing sustainable energy or bio-based chemicals. Lignocellulose is mainly composed of cellulose, hemicellulose and lignin. Its structure is complex and dense, and it is difficult to be degraded by microorganisms or chemicals in its natural state. Therefore, in the process of utilizing lignocellulose raw materials, effective pretreatment technology is usually required to open its structure to improve the utilization rate of lignocellulose components.

[0003] At present, the effective pretreatment methods mainly include: physical method (mechanical crushing, high temperature decomposition, steam explosion, liquid hot water treatment, etc.), chemical method (alkali treatment, acid treatment, organic solvent method, etc.), physical and chemical method, biological method and combined treatment method. Among them, the mechanism of acid pretreatment is to cut the glycosidic bond through hydrogen protons, dissolve hemicellulose and reduce the crystallinity of cellulose. Compared with methods such as alkali pretreatment or solvent pretreatment, this method has less effect on removing lignin. Therefore, the lignin remaining in the wood cellulose is easy to cause ineffective adsorption of cellulase in the subsequent enzymatic hydrolysis process and reduce the enzymatic hydrolysis conversion rate.

[0004] Therefore, it is very necessary to provide a method for improving the enzymatic hydrolysis of pretreated lignocellulosic raw materials. Summary of the invention

[0005] In order to solve the problems of poor pretreatment effect of lignocellulose, low lignin removal rate, low cellulose enzyme hydrolysis conversion rate, high energy consumption, etc. in the prior art, the present invention provides a method and application of improving the enzymatic hydrolysis performance of pretreated lignocellulose raw materials by using plasma modification technology.

[0006] Specifically, the present invention provides a method for improving the enzymatic hydrolysis performance of a pretreated lignocellulose raw material, the method comprising the following steps: 1) adding the crushed lignocellulose raw material and an oxalic acid-tetrahydrofuran / water solvent system to a reactor under high temperature and high pressure conditions for pretreatment; 2) after the pretreatment reaction is completed, cooling the reactor, filtering the reacted material, washing the solid residue with deionized water and setting it aside to obtain wet lignocellulose solid collected after pretreatment; 3) flattening the wet lignocellulose solid collected after pretreatment, and placing it in a plasma device for modification treatment to obtain a modified lignocellulose raw material.

[0007] Furthermore, the solid-liquid mass ratio of the pulverized lignocellulose raw material to the oxalic acid-tetrahydrofuran / water solvent system is 1:20 to 1:10.

[0008] Furthermore, the high temperature and high pressure conditions specifically include: a temperature of 140° C. and a pressure of 1.2 MPa; and a pretreatment time of 30 minutes.

[0009] Furthermore, the cooling treatment is specifically to place the reactor in ice water for an ice bath to quickly cool it to room temperature.

[0010] Furthermore, the radio frequency power of the plasma device is 30-180W, preferably 100W; the vacuum degree of the cavity of the plasma device is 10-200Pa, preferably 100Pa.

[0011] Furthermore, the modification treatment time is 30 to 300 seconds, preferably 120 seconds.

[0012] Furthermore, the plasma gas introduced into the plasma equipment is one or more of air, oxygen, nitrogen, helium, and carbon dioxide, preferably air.

[0013] Furthermore, the lignocellulosic raw material includes one or more of corn stalks, rice straw, wheat straw, spring bamboo shoot peels, and sugarcane bagasse.

[0014] The present invention also provides the use of the above method for improving the enzymatic hydrolysis performance of pretreated lignocellulose raw materials in the production of ethanol and / or sugars.

[0015] The present invention also provides a method for enzymatic hydrolysis of lignocellulose raw materials, comprising treating the lignocellulose raw materials according to the method for improving the enzymatic hydrolysis performance of the pretreated lignocellulose raw materials as described above to obtain modified lignocellulose raw materials; and further comprising mixing the modified lignocellulose raw materials with cellulase and water for enzymatic hydrolysis to obtain a hydrolyzate; wherein the reducing sugar yield in the hydrolyzate is 85% to 95%.

[0016] The beneficial effects of the present invention are:

[0017] The present invention provides a method for improving the enzymatic hydrolysis performance of pretreated lignocellulose raw materials by using plasma modification technology, which changes the aggregation structure and molecular structure of cellulose at a relatively low temperature and in a short time, thereby improving the enzymatic hydrolysis performance of lignocellulose solids, and increasing the enzymatic saccharification efficiency and reducing sugar yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of a method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials provided by the present invention;

[0019] Figure 2 This is a scanning electron microscope comparison diagram of corn stalks before and after plasma modification according to an embodiment of the present invention;

[0020] Figure 3 This is a Fourier infrared spectrum of the corn stover before and after plasma modification according to the embodiment of the invention. DETAILED DESCRIPTION

[0021] The inventors have found that non-thermal plasma (NTP) technology, as an efficient, pollution-free and environmentally friendly non-thermal treatment technology, has been widely used in many fields due to its low operating temperature, strong reactivity and good controllability. In recent years, research on NTP technology in the modification of lignocellulosic biomass has gradually increased. Studies have shown that the hydrogen bond structure of cellulose is destroyed during the NTP technology treatment process, resulting in a decrease in crystallinity, thereby significantly improving its solubility, degradability and other functional properties.

[0022] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0023] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. All reagents or instruments without manufacturer specified are conventional products that can be purchased through regular channels.

[0024] The present invention provides a method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials, such as Figure 1 As shown. The method comprises the following steps: 1) adding the crushed lignocellulose raw material and the oxalic acid-tetrahydrofuran / water solvent system to a reactor under high temperature and high pressure conditions for pretreatment; 2) after the pretreatment reaction is completed, the reactor is cooled, the reacted material is filtered, and the solid residue is washed with deionized water for standby use to obtain the wet lignocellulose solid collected after pretreatment; 3) the wet lignocellulose solid collected after pretreatment is spread flat and placed in a plasma device for modification treatment to obtain a modified lignocellulose raw material. The present invention finds that by treating the pretreated lignocellulose solid with plasma modification technology, the aggregate structure and molecular structure of cellulose can be changed at a relatively low operating temperature and in a short time, thereby improving the enzymatic hydrolysis saccharification efficiency and reducing sugar yield of the modified substrate.

[0025] The yields of reducing sugar and glucose obtained by enzymatic hydrolysis were calculated according to the following formula:

[0026] Reducing sugar yield (%) = reducing sugar concentration × 0.9 × 100 / enzyme hydrolysis substrate concentration;

[0027] Glucose yield (%) = glucose concentration × 0.9 × 100 / enzyme hydrolysis substrate concentration.

[0028] Example 1: Pretreatment and enzymatic hydrolysis method using corn stalks as raw materials

[0029] The corn stalks were crushed into 1-1.5 cm particles, soaked, washed, dried and set aside. 9 g was weighed and placed in a 300 mL high temperature and high pressure reactor, 180 g of tetrahydrofuran / water (mass ratio 3:2) mixed solution and 1.8 g of oxalic acid were added to make the final acid concentration in the mixed solution 1.0 wt%, the reactor was sealed and heated to 140 ° C, and the reaction was kept warm for 30 min. After the reaction was completed, the reactor was placed in an ice water bath to cool for 15 min. The reacted material was filtered, and the solid residue was washed with deionized water and set aside. Under these conditions, the recovered lignocellulose solids had a cellulose content of 81.3%, a hemicellulose content of 6.2%, and a lignin content of 9.6%.

[0030] The pretreated corn stalk samples were further subjected to enzymatic hydrolysis and saccharification, that is, 30 FPU / g substrate cellulase was directly used for hydrolysis at 50°C and pH 4.8 acetic acid-sodium acetate buffer for 96 hours. After enzymatic hydrolysis, the yield of reducing sugar in the hydrolyzate was 81.9%.

[0031] Embodiment 2:

[0032] The cellulose-rich wet solid obtained under the conditions described in Example 1 was spread on a culture dish and placed in the vacuum chamber of a plasma device. The RF power of the plasma device was set to 100 W, the vacuum degree was 100 Pa, the treatment time was 120 s, and air was introduced. After the reaction was completed, the sample was taken out and stirred evenly, and the above steps were repeated twice.

[0033] The corn straw sample obtained by the above steps was further subjected to enzymatic hydrolysis, i.e., 30 FPU / g substrate cellulase was used for hydrolysis at 50°C, pH 4.8 acetic acid-sodium acetate buffer for 96 hours. After enzymatic hydrolysis, the reducing sugar yield in the hydrolyzate was measured to be 92.6%, which was 10.7% higher than that of the unmodified corn straw raw material.

[0034] Comparative Example 1:

[0035] The gas introduced in the conditions described in Example 2 was changed to oxygen, while other conditions remained unchanged.

[0036] The corn stalk sample obtained by the above steps was further subjected to enzymatic hydrolysis, and the hydrolysis conditions were the same as those in Example 2. After enzymatic hydrolysis, the yield of reducing sugar in the hydrolyzate was 84.8%, which was 2.9% higher than that of the unmodified corn stalk raw material.

[0037] Comparative Example 2:

[0038] The gas introduced in the conditions described in Example 2 was changed to nitrogen, and the other conditions remained unchanged.

[0039] The corn stalk sample obtained by the above steps was further subjected to enzymatic hydrolysis, and the hydrolysis conditions were the same as those in Example 2. After enzymatic hydrolysis, the yield of reducing sugar in the hydrolyzate was 87.9%, which was 6.0% higher than that of the unmodified corn stalk raw material.

[0040] Comparative Example 3:

[0041] The gas introduced in the conditions described in Example 2 was changed to helium, while other conditions remained unchanged.

[0042] The corn stalk sample obtained by the above steps was further subjected to enzymatic hydrolysis, and the hydrolysis conditions were the same as those in Example 2. After enzymatic hydrolysis, the yield of reducing sugar in the hydrolyzate was 88.8%, which was 6.9% higher than that of the unmodified corn stalk raw material.

[0043] Embodiment 3:

[0044] After soaking, the untreated corn stalks were placed in a flat dish and placed in the vacuum chamber of the plasma equipment. The RF power of the plasma equipment was set to 200W, the vacuum degree was 120Pa, the treatment time was 90s, and air was introduced. After the reaction was completed, the sample was taken out and stirred evenly, and the above steps were repeated twice.

[0045] The corn straw raw material and the corn straw sample bombarded by plasma were subjected to enzymatic hydrolysis, that is, the cellulase with 30 FPU / g substrate was directly used for hydrolysis at 50°C and pH 4.8 acetic acid-sodium acetate buffer for 96 hours. After enzymatic hydrolysis, the reducing sugar yield in the hydrolyzate of the corn straw raw material was 24.1%, and the reducing sugar yield in the hydrolyzate of the corn straw sample bombarded by plasma was 30.2%.

[0046] Embodiment 4:

[0047] The cellulose-rich wet solid obtained under the conditions described in Example 1 was placed in a vacuum chamber of a plasma device, and the RF power of the plasma device was set to 100 W, the vacuum degree was set to 20 Pa, the treatment time was set to 180 s, and air was introduced. After the reaction was completed, the sample was taken out and stirred evenly, and the above steps were repeated twice.

[0048] The pretreated corn straw samples were further subjected to enzymatic hydrolysis, i.e., cellulase with 30 FPU / g substrate was directly used for hydrolysis at 50°C, pH 4.8, acetic acid-sodium acetate buffer for 96 hours. After enzymatic hydrolysis, the yield of reducing sugar in the hydrolyzate was 87.2%, which was 5.3% higher than that of the unmodified corn straw raw material.

[0049] Embodiment 5:

[0050] The cellulose-rich wet solid obtained under the conditions described in Example 1 was placed in a vacuum chamber of a plasma device, and the RF power of the plasma device was set to 150 W, the vacuum degree was set to 20 Pa, the treatment time was set to 120 s, and air was introduced. After the reaction was completed, the sample was taken out and stirred evenly, and the above steps were repeated twice.

[0051] The pretreated corn straw samples were further subjected to enzymatic hydrolysis, that is, cellulase with 30 FPU / g substrate was directly used for hydrolysis at 50°C and pH 4.8 acetic acid-sodium acetate buffer for 96 hours. After enzymatic hydrolysis, the yield of reducing sugar in the hydrolyzate was 87.5%, which was 5.6% higher than that of the unmodified corn straw raw material.

[0052] Embodiment 6:

[0053] The cellulose-rich wet solid obtained under the conditions described in Example 1 was placed in a vacuum chamber of a plasma device, and the RF power of the plasma device was set to 150 W, the vacuum degree was 180 Pa, the treatment time was 120 s, and air was introduced. After the reaction was completed, the sample was taken out and stirred evenly, and the above reaction steps were repeated twice.

[0054] The pretreated corn straw samples were further subjected to enzymatic hydrolysis and saccharification, that is, 30 FPU / g substrate cellulase was directly used for hydrolysis at 50°C, pH 4.8 acetic acid-sodium acetate buffer for 96 hours. After enzymatic hydrolysis, the yield of reducing sugar in the hydrolyzate was 88.8%, which was 6.9% higher than that of unmodified corn straw.

[0055] Embodiment 7:

[0056] The cellulose-rich wet solid obtained under the conditions described in Example 1 was placed in a vacuum chamber of a plasma device, and the RF power of the plasma device was set to 100 W, the vacuum degree was 180 Pa, the treatment time was 180 s, and air was introduced. After the reaction was completed, the sample was taken out and stirred evenly, and the above steps were repeated twice.

[0057] The pretreated corn straw samples were further subjected to enzymatic hydrolysis, that is, cellulase with 30 FPU / g substrate was directly used for hydrolysis at 50°C and pH 4.8 acetic acid-sodium acetate buffer for 96 hours. After enzymatic hydrolysis, the yield of reducing sugar in the hydrolyzate was 86.8%, which was 4.9% higher than that of unmodified corn straw.

[0058] Figure 2 The morphology and structure of cellulose-rich solids before and after plasma modification. Figure 2 It can be seen that compared with unmodified cellulose, the modified cellulose surface has obvious holes, which may be due to the destruction of the cellulose structure by high-energy particle bombardment. At the same time, the surface roughness of the modified cellulose has also increased, which is one of the reasons for the improvement of its enzymatic hydrolysis performance.

[0059] Figure 3 Fourier infrared images of cellulose-rich solids before and after plasma modification. Figure 3 a is located at 3000-3700cm -1 The broad peaks in the wavenumber range are attributed to the absorption of hydroxyl (-OH), corresponding to the three peaks related to hydrogen bonding ( Figure 3 b) Cellulose modified by plasma at 3450cm -1 and 3538cm -1 The absorption peaks at 3329 cm-1 belonging to O3H≡O5 and O2H≡O6 are blue-shifted, indicating that the intermolecular hydrogen bonds are extended. -1 The absorption peak (O6H—O3) associated with the intramolecular hydrogen bond red-shifts from 3329 cm -1 Shift to 3267cm -1 , which is attributed to the weakening of the bond force caused by the extension of hydrogen bonds. Studies have shown that low-temperature plasma technology can lead to the breaking of hydrogen bonds and the destruction of cellulose chains. Hydrogen bonds are the weakest bonds in cellulose, and nitrogen and oxygen atoms in the air help promote the oxidation of cellulose, thereby reducing the crystallinity of cellulose and enhancing its accessibility to enzymatic hydrolysis.

[0060] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials, characterized in that: The method comprises the following steps: 1) adding the crushed lignocellulose raw material and the oxalic acid-tetrahydrofuran / water solvent system into a reactor under high temperature and high pressure conditions for pretreatment; 2) After the pretreatment reaction is completed, the reactor is cooled, the reacted material is filtered, and the solid residue is washed with deionized water for later use, thereby obtaining wet solids of lignocellulose collected after the pretreatment; 3) The wet solid lignocellulose collected after the pretreatment is spread out and placed in a plasma device for modification to obtain a modified lignocellulose raw material.

2. The method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials according to claim 1, characterized in that: The solid-liquid mass ratio of the pulverized lignocellulose raw material to the oxalic acid-tetrahydrofuran / water solvent system is 1:20 to 1:

10.

3. The method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials according to claim 1, characterized in that: The high temperature and high pressure conditions specifically include: a temperature of 140° C. and a pressure of 1.2 MPa; and a pretreatment time of 30 minutes.

4. The method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials according to claim 1, characterized in that: The cooling treatment specifically includes placing the reactor in ice water for an ice bath to quickly cool it to room temperature.

5. The method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials according to claim 1, characterized in that: The radio frequency power of the plasma equipment is 30-180W, preferably 100W; the vacuum degree of the cavity of the plasma equipment is 10-200Pa, preferably 100Pa.

6. The method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials according to claim 1, characterized in that: The modification treatment time is 30 to 300 seconds, preferably 120 seconds.

7. The method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic biomass according to claim 1, characterized in that: The plasma gas introduced into the plasma equipment is one or more of air, oxygen, nitrogen, helium, and carbon dioxide, preferably air.

8. The method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials according to claim 1, characterized in that: The lignocellulose raw material includes one or more of corn stalks, rice straw, wheat straw, spring bamboo shoot peels, and sugarcane bagasse.

9. Use of the method for improving the enzymatic hydrolysis performance of pretreated lignocellulosic raw materials according to any one of claims 1 to 8 in the production of ethanol and / or sugars.

10. A method for enzymatic hydrolysis of lignocellulose raw materials, characterized in that: The method comprises treating the lignocellulosic raw material according to the method for improving the enzymatic hydrolysis performance of the pretreated lignocellulosic raw material as described in any one of claims 1 to 8 to obtain a modified lignocellulosic raw material; and further comprises mixing the modified lignocellulosic raw material with cellulase and water for enzymatic hydrolysis to obtain a hydrolyzate; wherein the reducing sugar yield in the hydrolyzate is 85% to 95%.

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