Method for extracting high-purity lignin after enzymolysis of corn cob residues

Abstract

The invention relates to the technical field of biomass resource utilization, in particular to a method for extracting high-purity lignin after enzymolysis of corn cob residues. According to the method, waste residues generated in the xylose production process are used for lignin production; according to the method, sediment in the saccharified liquid is removed through sedimentation, separation is conducted through a horizontal screw centrifuge, high-molecular compounds in syrup can be effectively prevented from being intercepted in lignin filter cakes, further dehydration is conducted through a plate-and-frame filter press, syrup residues in lignin are removed as much as possible through washing, and the content of the lignin in the saccharified liquid is reduced. Solid-liquid separation is carried out by adopting a diaphragm plate-and-frame filter press after washing, so that more energy is saved; according to the method disclosed by the invention, a traditional plate-frame separation mode of saccharification liquid is avoided, and the impurity content in the lignin is greatly reduced through sedimentation, horizontal screw centrifuge separation and washing, so that the high-purity lignin is obtained, and an effective technical way is provided for preparing the high-purity lignin from the straws.

Description

Technical Field

[0001] The invention relates to the technical field of biomass resource utilization, and in particular to a method for extracting high-purity lignin after enzymatic hydrolysis of xylose residue. Background Art

[0002] Lignin is a natural organic compound, one of the main components of plant cell walls, and the second most abundant organic matter in the world. In recent years, with the improvement of environmental awareness and the popularization of the concept of sustainable development, lignin, as a green and sustainable resource, has received more and more attention in the international market.

[0003] Since lignin is cross-linked with cellulose, hemicellulose, etc. in space structure in nature, it is difficult to separate lignin. The existing raw material for lignin production is mainly straw. The xylose residue after hemicellulose is extracted from the straw is enzymatically hydrolyzed, and the residue is lignin. However, the obtained lignin and the syrup after cellulose enzymatic hydrolysis are mixed together. Since the raw material is straw, mud and sand are inevitably introduced in actual production. The traditional separation method is plate and frame filtration. When plate and frame filtration is used, part of the mud and sand and the high molecular compounds in the syrup will be retained in the lignin filter cake, resulting in low purity of the obtained lignin product, affecting the product quality.

[0004] Therefore, a process route that can obtain high-purity lignin from the saccharification liquid after enzymatic hydrolysis of xylose residue, thereby effectively improving product quality, is a problem that needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to provide a method for extracting high-purity lignin after enzymatic hydrolysis of xylose residue, so as to solve the problem that the existing lignin production method has low purity of the obtained lignin, which seriously affects the product quality.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a method for extracting high-purity lignin after enzymatic hydrolysis of xylose residue, comprising the following steps:

[0007] S1, drying and crushing the xylose residue, and then performing enzymolysis with cellulase to obtain saccharification liquid;

[0008] The saccharification liquid is a mixture of syrup and lignin;

[0009] S2, separating the syrup and lignin obtained in S1;

[0010] The separation steps are sequentially sedimentation, decanter centrifuge separation and plate-frame separation;

[0011] S3, washing, primary crushing, drying, secondary crushing and magnetic separation of the lignin separated in S2 can obtain the high-purity lignin of the present invention.

[0012] Furthermore, in the above-mentioned S1-S2, the saccharified liquid obtained by enzymatic hydrolysis is transported to a buffer tank, and the sedimentation step is carried out in the buffer tank.

[0013] Furthermore, in the sedimentation step, after the saccharified liquid is transported to the buffer tank, it is first stirred in the buffer tank for 10 to 30 minutes at a stirring intensity of 60 to 120 rpm, and then allowed to stand for 20 to 60 minutes after the stirring is completed.

[0014] Furthermore, after the saccharification liquid has been allowed to stand, the liquid is discharged from a certain height at the bottom of the buffer tank to remove the sediment in the bottom material.

[0015] Furthermore, in S2, separation by a horizontal screw centrifuge can avoid the retention of high molecular weight compounds in the syrup in the lignin filter cake.

[0016] Furthermore, in the above S3, the washing step is performed with salt-free water, the washing is performed at least once, and after washing, a diaphragm plate and frame filter press is used for solid-liquid separation.

[0017] Furthermore, after the diaphragm plate and frame filter press performs solid-liquid separation, the water content in the lignin filter cake is controlled at 40-60%.

[0018] Furthermore, the lignin filter cake is first crushed by a crusher, dried by a fuel dryer, second crushed by an ultrafine grinder, and magnetically separated and impurities removed by a permanent magnetic iron remover.

[0019] Furthermore, the drying temperature is 70-80° C., the moisture content of the lignin after drying is controlled below 1%, and the particle size of the lignin powder after secondary crushing is 1000-5000 meshes.

[0020] Furthermore, the purity of the high-purity lignin can reach more than 90%, and the ash content is less than 1.5%.

[0021] Beneficial effects of the present invention:

[0022] 1. The method of the present invention avoids the method of directly pressing the xylose residue enzymatic saccharification liquid with a plate and frame filter. When separating lignin, the method of stirring and standing is first adopted, so that the sediment in the saccharification liquid can be effectively removed, and the sediment is prevented from mixing into the lignin product to affect the purity of the product, thereby effectively improving the quality of the product;

[0023] 2. The method of the present invention uses a horizontal screw centrifuge for solid-liquid separation. The working principle of the horizontal screw centrifuge makes the filtrate not pass through the filter cake, so that the high molecular compounds in the syrup can be prevented from being trapped in the lignin filter cake, thereby further improving the quality of the product;

[0024] 3. The method of the present invention also adopts a salt-free water washing method to remove the syrup mixed in the lignin as much as possible, thereby ensuring the purity of the obtained product. The purity of the final product lignin can reach more than 90%, and the ash content is less than 1.5%, which is high-quality and highly active lignin on the market. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0026] Example 1

[0027] A batch of xylose residue in the factory was taken and dried for later use. After testing, its moisture content was 9.2%, the cellulose content in the dry matter was 68.3%, the lignin content was 21.4%, and the hemicellulose content was 3.6%.

[0028] Add 1000 L of water to the reactor, take 100 kg of the xylose residue from this batch and add it to the reactor, stir continuously, control the temperature in the reactor at 53 °C, adjust the pH to 5±0.3, then add 8 kg of cellulase to the reactor, continue enzymolysis for 72 hours, and obtain saccharification liquid.

[0029] The obtained saccharification liquid was pumped into a buffer tank, the stirring intensity in the buffer tank was controlled to be 80 rpm, and the stirring was continued for 20 minutes. After the stirring was completed, it was allowed to stand for 30 minutes, and the sediment containing a lot of mud and sand at the bottom was discarded. The obtained saccharification liquid was filtered using a horizontal screw centrifuge. After the filtration was completed, it was dehydrated using a plate and frame to obtain a lignin filter cake.

[0030] The obtained lignin filter cake is washed with salt-free water twice during the process. The first time, 5 volumes of salt-free water are used. After washing, a diaphragm plate and frame filter press is used for solid-liquid separation. The second time, 2 volumes of salt-free water are used for further washing. After washing, a diaphragm plate and frame filter press is used for solid-liquid separation. The water content in the lignin filter residue can be controlled at about 50%.

[0031] The obtained lignin is crushed once, dried, crushed twice, and then magnetically separated to remove impurities, so as to obtain the high-purity lignin of the present invention. After testing, the purity of the lignin in this embodiment is 93.7%, of which the ash content is 1.2%, which is high-quality and high-activity lignin on the market.

[0032] Comparative Example 1

[0033] In this comparative example, the same batch of xylose residues as in Example 1 was taken and subjected to enzymatic hydrolysis to obtain saccharified liquid, and the enzymatic hydrolysis steps were the same as in Example 1.

[0034] In this comparative example, the saccharified liquid obtained by enzymatic hydrolysis was directly filtered using a plate and frame filter press to obtain a lignin filter cake. The filter cake was dried and tested, and the purity of the obtained lignin was only 84.1%, of which the ash content was as high as 5.8%.

[0035] It can be seen that the purity and impurity content of the lignin obtained by the conventional method are significantly higher than those of the lignin obtained by the method of the present invention.

[0036] Comparative Example 2

[0037] In this comparative example, the same batch of xylose residues as in Example 1 was taken and subjected to enzymatic hydrolysis to obtain saccharified liquid, and the enzymatic hydrolysis steps were the same as in Example 1.

[0038] In this comparative example, the saccharified liquid obtained by enzymatic hydrolysis was separated by sedimentation and a horizontal screw centrifuge and then by plate and frame filtration. The operating conditions during the process were the same as those in Example 1.

[0039] The lignin filter cake obtained by the plate-and-frame filtration was directly dried. After testing, the purity of the obtained lignin was 89.3%, wherein the ash content was 2.2%.

[0040] Comparative Example 3

[0041] In this comparative example, the same batch of xylose residues as in Example 1 was taken and subjected to enzymatic hydrolysis to obtain saccharified liquid, and the enzymatic hydrolysis steps were the same as in Example 1.

[0042] In this comparative example, the saccharified liquid obtained by enzymatic hydrolysis is directly filtered using a plate and frame. The lignin obtained by filtration is washed twice, crushed once, dried, crushed twice, and magnetically separated. The operating conditions during the process are the same as those in Example 1. Finally, a lignin product is obtained. The purity of the lignin in the obtained product is 85.7%, and the ash content is 5.6%.

[0043] It can be seen from Comparative Examples 2-3 that the purity of the lignin products obtained by using the technical solutions of S2 or S3 of the present invention alone is not as good as that of the method of the present invention, which shows that the method of the present invention can effectively improve the quality of the lignin products. In addition, it can be seen that when the technical solution of S3 of the present invention is used for treatment in Comparative Example 3, the improvement of the purity of lignin is not obvious. When the technical solution of S3 is used alone, the impurities in the product are difficult to wash out, and S2 needs to be used in combination to achieve better results.

[0044] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for extracting high-purity lignin after enzymatic hydrolysis of xylose residue, characterized in that: The following steps are involved: S1, drying and crushing the xylose residue, and then performing enzymolysis with cellulase to obtain saccharification liquid; The saccharification liquid is a mixture of syrup and lignin; S2, separating the syrup and lignin obtained in S1; The separation steps are sequentially sedimentation, decanter centrifuge separation and plate-frame separation; S3, washing, primary crushing, drying, secondary crushing and magnetic separation of the lignin separated in S2 can obtain the high-purity lignin of the present invention.

2. The method for extracting high-purity lignin from xylose residue after enzymatic hydrolysis according to claim 1, characterized in that: In the above-mentioned S1-S2, the saccharified liquid obtained by enzymatic hydrolysis is transported to a buffer tank, and the sedimentation step is carried out in the buffer tank.

3. The method for extracting high-purity lignin from xylose residue after enzymatic hydrolysis according to claim 2, characterized in that: In the sedimentation step, after the saccharified liquid is transported to the buffer tank, it is first stirred in the buffer tank for 10 to 30 minutes at a stirring intensity of 60 to 120 rpm, and then allowed to stand for 20 to 60 minutes after the stirring is completed.

4. The method for extracting high-purity lignin from xylose residue after enzymatic hydrolysis according to claim 3, characterized in that: After the saccharification liquid has been allowed to stand, it is discharged from a certain height at the bottom of the buffer tank to remove the mud and sand in the bottom material.

5. The method for extracting high-purity lignin from xylose residue after enzymatic hydrolysis according to claim 1, characterized in that: In the above-mentioned S2, the use of a horizontal screw centrifuge for separation can avoid the retention of high molecular weight compounds in the syrup in the lignin filter cake.

6. The method for extracting high-purity lignin after enzymatic hydrolysis of xylose residue according to claim 1, characterized in that: In the above S3, the washing step is performed with salt-free water, the washing is performed at least once, and after washing, a diaphragm plate and frame filter press is used to separate the solid and liquid.

7. The method for extracting high-purity lignin from xylose residue after enzymatic hydrolysis according to claim 6, characterized in that: After the diaphragm plate-frame filter press performs solid-liquid separation, the water content in the lignin filter cake is controlled at 40-60%.

8. The method for extracting high-purity lignin after enzymatic hydrolysis of xylose residue according to claim 7, characterized in that: The lignin filter cake is crushed once by a crusher, dried by a fuel dryer, crushed twice by an ultrafine crusher, and magnetically separated and impurities removed by a permanent magnetic iron remover.

9. The method for extracting high-purity lignin from xylose residue after enzymatic hydrolysis according to claim 8, characterized in that: The drying temperature is 70-80° C., the moisture content of the lignin after drying is controlled below 1%, and the particle size of the lignin powder after secondary crushing is 1000-5000 meshes.

10. The method for extracting high-purity lignin from xylose residue after enzymatic hydrolysis according to any one of claims 1 to 9, characterized in that: The purity of the high-purity lignin can reach more than 90%, and the ash content is less than 1.5%.