Device and method for treating biomass and separating lignin through electrothermal coupling dilute alkali

Abstract

The invention discloses a device and a method for treating biomass and separating lignin through electrothermal coupling dilute alkali, and belongs to the technical field of biomass resource utilization. The device comprises an electric heating reaction unit, a time-varying magnetic field in a magnetic core in the electric heating reaction unit serves as an excitation source to spontaneously induce an electric effect and a heat effect on reaction feed liquid in a reaction tube, and electric heating coprocessing is completed. The method comprises the following steps: mixing a wood fiber raw material with a dilute alkali solution, and then carrying out electric heating pretreatment by using the device disclosed by the invention; a large amount of lignin and a small amount of hemicellulose in the wood fibers can be removed through electrothermal coupling dilute alkali pretreatment. The energy loss of traditional hydrothermal treatment is reduced, the wood fibers are pretreated by means of the electric effect, the pretreatment temperature is reduced, and the requirement for equipment or devices in the high-temperature and high-pressure environment is avoided.

Description

Technical Field

[0001] The present invention particularly relates to a device and method for treating biomass and separating lignin by electrothermal coupling with diluted alkali, belonging to the technical field of biomass resource utilization. Background Art

[0002] my country is a large agricultural country with abundant wood fiber biomass resources. At the same time, wood cellulose, as a good renewable resource, not only helps to replace traditional fossil resources, but also promotes the realization of "carbon balance". Since the development concept of "green, safe and environmentally friendly", some traditional chemical industries have faced development difficulties, and some industries are in urgent need of transformation. The biochemical and biomanufacturing industries have developed rapidly due to their advantages such as mild production conditions, high selectivity and low environmental pollution. However, the production of biochemical and biomanufacturing industries cannot be separated from glycogen. With the promotion of the policy of "not competing with people for food and not competing with food for land", starch sugar will gradually be replaced or partially replaced by fiber sugar. In addition, the promotion of biochemical products fuel ethanol and the promotion of bio-based degradable materials under the "plastic restriction order" will gradually promote the development of wood cellulose component separation and its high-value utilization through downstream products and market demand.

[0003] Lignocellulose is a complex, non-uniform three-dimensional structure formed by the entanglement of three polymers, namely cellulose, hemicellulose and lignin. It is stubborn and resistant to degradation by enzymes and microorganisms. The presence of hemicellulose, cellulose and lignin and their structural changes may have different effects on cellulose enzymatic hydrolysis, such as the crystallinity index and depolymerization of cellulose, the accessibility of enzymes, the content and structural characteristics of hemicellulose and lignin, etc. In order to destroy or eliminate the compact and complex structure of lignocellulose, separate the three major components in lignocellulosic biomass, and promote the enzymatic saccharification efficiency of cellulose and hemicellulose, various physical / chemical / biological pretreatment processes have been developed. Alkali pretreatment is considered to be one of the more traditional chemical pretreatment methods in the field of biomass resource utilization industry. Alkali pretreatment weakens the intermolecular hydrogen bonds between cellulose, thereby causing swelling and making it easier for the solvent to approach the cellulose structure; in addition, it can also destroy the connection between lignin and hemicellulose, or eliminate lignin by breaking the cross-linking bonds between xylan and lignin; so alkaline pretreatment can effectively dissolve lignin and part of hemicellulose.

[0004] However, most of the alkaline pretreatment processes rely on the use of organic solvents or the addition of related catalysts, and the recovery and environmental problems of organic solvents have not been well solved; secondly, most of the existing alkaline pretreatment processes still need to be carried out in a high temperature environment, which will lead to the degradation of some cellulose and hemicellulose on the one hand, and on the other hand, the process needs to be completed with the assistance of a reactor, which limits the large-scale promotion and application. For example, CN 104232705 A discloses a method for pretreating lignocellulose at low temperature by coupling sodium hydroxide with ethanol, and pretreating lignocellulose with a sodium hydroxide-ethanol mixed solution at a temperature of 30-80°C; CN 102561082A discloses a method for extracting hemicellulose, cellulose and lignin from lignocellulose raw materials, and separating lignin with an alkaline organic solvent (methanol or ethanol); CN 104328225 B discloses a method for extracting lignocellulose using a conjugate acid-base pair as a medium, and pretreating biomass raw materials at 100-200°C using a conjugate acid-base pair buffer solution. The above-mentioned pretreatment technologies and methods are currently the mainstream technologies, but they have the following problems: (1) the problem of recycling organic solvents (methanol or ethanol, etc.) and the environmental pollution caused by them; (2) the pretreatment temperature is too high, which can easily lead to partial degradation of cellulose and hemicellulose; (3) traditional hydrothermal treatment equipment needs to use reactors or reactors to achieve high-temperature environments, which makes it difficult to achieve large-scale treatment. Summary of the invention

[0005] The main purpose of the present invention is to provide a device and method for pretreating wood fiber and separating lignin by electrothermal coupling with dilute alkali, thereby overcoming the shortcomings of the prior art.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0007] On one hand, the present invention provides a device for pretreating wood fiber and separating lignin by electrothermal coupling with dilute alkali, the device comprising an electrothermal reaction unit 100, a pumping device 200, a stirring device 300, a power supply device 400, and a cooling device 500;

[0008] The electrothermal reaction unit 100 is composed of reaction tubes 101-102, a magnetic core 103, a water cooling plate 104 and an excitation coil 105;

[0009] The magnetic core 103 is a ring-shaped plate-shaped magnetic conductive material with a hole in the middle; the water-cooling plate 104 is a ring-shaped plate-shaped metal material with a hole in the middle, which is placed alternately with the magnetic core; the outer edge of the water-cooling plate 104 is embedded with cooling pipes 201-202 for cooling liquid circulation;

[0010] The water cooling plate 104 is connected to the cooling device 500 through the cooling pipes 201-202; the cooling device 500 is used to cool the coolant in the cooling pipes 201-202;

[0011] The reaction tubes 101-102 pass through the middle holes of the magnetic core 103 and the water-cooling plate 104 and are wound around the magnetic core and the water-cooling plate; the reaction tube inlet end 101 is located at the bottom end of the electrothermal reaction unit and is connected to the pumping device 200; the reaction tube outlet end 102 is located at the top end of the electrothermal reaction unit and is connected to the stirring device 300 through a pipeline;

[0012] The excitation coil 105 is wound around the magnetic core 103 and connected to a power supply device 400; the power supply device 400 is used to provide an excitation voltage, so that the magnetic core 103 generates a time-varying magnetic field as an excitation source, and spontaneously induces an induced voltage and an induced current inside the reaction tubes 101-102;

[0013] The stirring device 300 is connected to the pumping device 200 through a pipeline, and the pipeline of the pumping device contacts the bottom of the container in the stirring device to ensure the pumping of the solution.

[0014] Furthermore, the material of the magnetic core 103 is amorphous nanocrystalline soft magnetic material.

[0015] Furthermore, the length L1 of the magnetic core 103 is 30-100 cm, the width W1 is 15-50 cm, the height H is 3-8 cm, the distance l1 from the middle hole to the width is 5-20 cm, and the distance w1 from the middle hole to the length is 5-20 cm.

[0016] Furthermore, the diameter of the reaction tubes 101-102 ranges from 10 mm to 50 mm.

[0017] Furthermore, the reaction tubes 101-102 are acid- and alkali-resistant glass or silicone tubes.

[0018] The device provided by the present invention is used in the field of wood fiber separation.

[0019] Another aspect of the present invention provides a method for pretreating wood fiber and separating lignin by electrothermal coupling with dilute alkali, wherein the method is carried out using the above-mentioned device for separating all components of wood fiber and improving the efficiency of enzymatic saccharification;

[0020] The method specifically comprises the following steps:

[0021] (1) washing the wood fiber raw material, then immersing it in an organic solvent for decolorization, and then drying and crushing it for later use;

[0022] (2) placing the pulverized wood fiber raw material and the dilute alkali solution in the above stirring device, starting stirring to mix, and after the mixture is evenly mixed to obtain a mixed solution, starting a pumping device to send the mixed solution into a reaction tube, and starting a power supply device and a cooling device to react;

[0023] (3) After the reaction in step (2) is completed, solid-liquid separation is performed, the solid is washed to electrical neutrality, and dried to obtain a dry solid residue, and the separated supernatant is pH adjusted, allowed to stand, and filtered to obtain a lignin solid component.

[0024] Furthermore, the wood fiber raw material in step (1) includes straw and sawdust.

[0025] Furthermore, the straw includes wheat straw and corn straw.

[0026] Furthermore, the wood chips include poplar wood chips, eucalyptus wood chips, bagasse and bamboo powder.

[0027] Furthermore, the organic solvent in step (1) includes ethanol.

[0028] Furthermore, the mesh size of the pulverization in step (1) is 30 to 80 meshes.

[0029] Furthermore, the dilute alkaline solution in step (2) includes one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia water.

[0030] Furthermore, the concentration of the dilute alkaline solution in step (2) is 0.5%-3%.

[0031] Furthermore, the mass volume ratio of the dried solid residue to the dilute alkali solution in step (2) is 1 g:10-50 mL.

[0032] Furthermore, in step (2), the reaction temperature is 50-90° C. and the treatment time is 3-7 h.

[0033] Preferably, in step (2), the treatment temperature is 70-80° C. and the treatment time is 4-5 h.

[0034] Furthermore, the parameters of the power supply device in step (2) are set to a voltage of 100-800V, a current of 2-10A, and a power of 0.2-8KW.

[0035] Furthermore, in step (2), the ratio of the voltage set by the power supply device to the diameter of the reaction tubes 101-102 is 200-250V:10mm.

[0036] Furthermore, after the power supply device in step (2) is turned on, the magnetic field strength of the magnetic core is 0.5-2T.

[0037] Furthermore, the acid solution in step (3) is a sulfuric acid solution with a concentration of 65-80%.

[0038] Furthermore, in step (3), the pH is adjusted to 1-3.

[0039] Compared with the prior art, the beneficial effects of the present invention include:

[0040] 1) The present invention provides a new device, in which the electric thermal reaction unit uses induction heat generation, which avoids the energy consumption of medium heat transfer in the traditional hydrothermal treatment process, greatly improves the thermal energy utilization rate, reduces the traditional hydrothermal pretreatment temperature, controls the pretreatment temperature within 100°C, and avoids the requirements for equipment or devices in high temperature and high pressure environments.

[0041] 2) The present invention combines the use of a new device, uses the electrical effect to assist in the pretreatment of wood fibers, reduces the pretreatment temperature of traditional hydrothermal treatment, can remove most of the lignin components, and avoids the use of organic solvents. It is carried out under low temperature and normal pressure, with a simple process, mild conditions, and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 The present invention is a schematic diagram of the overall structure of a device for pretreating wood fibers and separating lignin by electrothermal coupling with dilute alkali, provided in a typical embodiment of the present invention; the diagram includes: an electrothermal reaction unit (100), a pumping device (200), a stirring device (300), a power supply device (400), and a cooling device (500).

[0044] Figure 2 A typical implementation case of the present invention provides an electrothermal reaction unit in a device for electrothermal coupling dilute alkali pretreatment of wood fiber and separation of lignin, and its top view, magnetic core, and water-cooled plate structural schematic diagrams; reaction tubes (101-102), magnetic cores (103), water-cooled plates (104), excitation coils (105), and condensing water pipes (201-202).

[0045] Figure 3 It is a comparison chart of the effects of the electrothermal pretreatment and hydrothermal pretreatment provided in Example 2 of the present invention and Comparative Example 1 on the contents of various components in wood fiber.

[0046] Figure 4It is a comparison chart of the effects of the electrothermal pretreatment and hydrothermal pretreatment provided in Example 3 of the present invention and Comparative Example 2 on the contents of various components in wood fibers.

[0047] Figure 5 It is a comparison chart of the effects of the electrothermal pretreatment and hydrothermal pretreatment provided in Example 4 of the present invention and Comparative Example 3 on the contents of various components in wood fibers. DETAILED DESCRIPTION

[0048] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0049] The technical solution, its implementation process and principles, etc. will be further explained below in conjunction with the accompanying drawings and specific implementation cases. Unless otherwise specified, the power supply device, pumping device, electrothermal reaction unit, stirring device, cooling device, magnetic core, water-cooled plate, etc. used in the present invention are all known to those skilled in the art and can be purchased commercially. The specific product models and structures are not limited here.

[0050] Source of raw materials

[0051] Cellulase (400u / mg), filter paper enzyme activity (250FPU / g), Shanghai Yuanye Biotechnology Co., Ltd.; wheat straw, Donghai County, Lianyungang City, Jiangsu Province.

[0052] Example 1

[0053] This embodiment provides a device for separating all components of wood fiber and improving the efficiency of enzymatic saccharification, as shown in the attached Figure 1 As shown in , its composition includes an electrothermal reaction unit 100, a pumping device 200, a stirring device 300, a power supply device 400, and a cooling device 500.

[0054] In the device, the electrothermal reaction unit 100, as shown in the attached Figure 2As shown in , its composition includes reaction tubes 101-102, magnetic cores 103, water cooling plates 104 and excitation coils 105. The electrothermal reaction unit 100 is used to generate a time-varying magnetic field as an excitation source, and spontaneously induces an induced voltage and an induced current inside the reaction tubes 101-102. The induced voltage acts on the reaction liquid to produce an electrical effect, and the induced current acts on the reaction liquid to produce a thermal effect, completing the electrothermal coordinated reaction; the pumping device 200 is used to transport the liquid from the stirring device 300 into the reaction tubes 101-102 for electrothermal coordinated reaction; the stirring device 300 is used to stir the liquid to maintain the uniformity of the reaction liquid, and the stirring device 300 is connected to the pumping device 200 through a pipeline, and the pipeline of the pumping device contacts the bottom of the container in the stirring device to ensure the pumping of the solution; the power supply device 400 provides an excitation voltage to the magnetic core 103 through the excitation coil 105; the cooling device 500 is used to cool the cooling water in the cooling tubes 201-202.

[0055] In the electrothermal reaction unit 100, the magnetic core 103 is a rectangular annular plate-shaped magnetic conductive material with a hole in the middle; the water-cooled plate 104 is a rectangular annular plate-shaped metal material with a hole in the middle, which is placed alternately with the magnetic core 103, so as to facilitate the heat energy generated by eddy current loss and hysteresis loss in the magnetic core to be dissipated through the water-cooled plate; cooling pipes 201-202 are embedded in the four sides of the water-cooled plate 104 for cooling water circulation; the water-cooled plate 104 is connected to the cooling device 500 through the cooling pipes 201-202; the reaction tubes 101-102 The middle hole passing through the magnetic core 103 and the water-cooling plate 104 is wrapped around the magnetic core 103 and the water-cooling plate 104; the reaction tube inlet end 101 is located at the bottom end of the electrothermal reaction unit 100, and is connected to the pumping device 200 through a pipeline, so that the pipeline is filled with liquid during transportation; the reaction tube outlet end 102 is located at the top end of the electrothermal reaction unit 100, and is connected to the stirring device 300 through a pipeline, and the liquid is circulated to the stirring device 300; the excitation coil 105 is wrapped around the magnetic core 103 and connected to the power supply device 400.

[0056] The method of using the device is as follows: first, the stirring device 300 is turned on to maintain the uniformity of the reaction liquid, and then the pumping device 200 is started to inject the reaction liquid into the reaction tube 101-102. When the liquid begins to flow out of the reaction tube outlet 102, the reaction tube is filled with liquid. At this time, the power supply device 400 is turned on, and an excitation voltage is provided to the magnetic core 103 through the excitation coil 105. The time-varying magnetic field inside the magnetic core 103 is used as an excitation source to spontaneously induce an induced voltage and an induced current inside the reaction tube 101-102, and an electrothermal coordinated reaction begins. Then, the cooling device 500 is started to circulate cooling water to cool the device. The number of water-cooled plates 104 and magnetic cores 103 can be adjusted according to actual applications.

[0057] Example 2

[0058] The present invention provides Figure 1 and Figure 2 The device shown in the figure for pretreating wood fiber and separating lignin by electrothermal coupling with dilute alkali adopts a reaction tube with a diameter of 10 mm, and the material of the reaction tube is silica gel; a magnetic core with L1 of 30 cm, l1 of 6 cm, W1 of 18 cm, w1 of 6 cm, and H of 3 cm is adopted; the size of the water-cooling plate adopted is equivalent to the size of the magnetic core; the number of magnetic cores in the electrothermal reaction unit adopted is 3, the number of water-cooling plates is 2, and the water-cooling plate is placed between the two magnetic cores to dissipate heat.

[0059] Operation process: 25g of crushed wheat straw powder (50 mesh) and 1L of sodium hydroxide solution (solution concentration of 1%) are mixed evenly to obtain a mixed liquid, and then the mixed liquid is placed in a stirring device, and the mixed liquid enters the electrothermal reaction unit through a pumping device for electrothermal cycle treatment (the treatment temperature is 80°C, the treatment time is 5h; the voltage provided by the power supply device is 200V, the current is 5A, and the power is 1KW), and the treated mixed liquid is separated from the solid and liquid, and the solid residue (wood fiber) is washed to electrical neutrality and dried with air to prepare for the analysis of its components. 72% sulfuric acid solution is added to the supernatant until the pH is 2, and it is left overnight to precipitate lignin, and then vacuum filtered, and the retained lignin solid component is washed with acidified warm water, and the water is dried at 50°C to obtain lignin.

[0060] The cellulose content of untreated wheat straw is 33.3%, the hemicellulose content is 22.7%, the lignin content is 20.6%, and the ash content is 2.4%; after electrothermal coupled dilute alkali pretreatment, analysis shows that the cellulose content of wheat straw is 48.3%, the hemicellulose content is 36.8%, the lignin content is 3.7%, and the ash content is 4.1%; the removal rate of lignin in wheat straw after pretreatment is calculated to be 85.6%; the lignin solid component in the supernatant is weighed to be 3.8g.

[0061] Example 3

[0062] The present invention provides Figure 1 and Figure 2 The device shown is for pretreating wood fiber and separating lignin by electrothermal coupling with dilute alkali, adopting a reaction tube with a diameter of 10 mm, the material of the reaction tube being silica gel; adopting a magnetic core with L1 of 30 cm, l1 of 6 cm, W1 of 18 cm, w1 of 6 cm, and H of 3 cm; the size of the water-cooling plate adopted is equivalent to the size of the magnetic core; the number of magnetic cores in the electrothermal reaction unit adopted is 3, the number of water-cooling plates is 2, and the water-cooling plate is placed between the two magnetic cores to dissipate heat.

[0063] Operation process: 25g of crushed wheat straw powder (50 mesh) and 1L of sodium hydroxide solution (solution concentration is 2%) are mixed evenly to obtain a mixed liquid, and then the mixed liquid is placed in a stirring device, and the mixed liquid enters the electrothermal reaction unit through a pumping device for electrothermal cycle treatment (the treatment temperature is 80°C, the treatment time is 3h; the voltage provided by the power supply device is 200V, the current is 5A, and the power is 1KW), and the treated mixed liquid is separated from the solid and liquid, and the solid residue (wood fiber) is washed to electrical neutrality and dried with air to prepare for the analysis of its components. 72% sulfuric acid solution is added to the supernatant until the pH is 2, and it is left overnight to precipitate lignin, and then vacuum filtered, and the retained lignin solid component is washed with acidified warm water, and the water is dried at 50°C to obtain lignin.

[0064] The cellulose content of untreated wheat straw is 33.3%, the hemicellulose content is 22.7%, the lignin content is 20.6%, and the ash content is 2.4%; after electrothermal coupled dilute alkali pretreatment, analysis shows that the cellulose content of wheat straw is 46.9%, the hemicellulose content is 34.2%, the lignin content is 2.6%, and the ash content is 4.7%; the removal rate of lignin in wheat straw after pretreatment is calculated to be 89.3%; the lignin solid component in the supernatant is weighed to be 4.2g.

[0065] Example 4

[0066] The present invention provides Figure 1 and Figure 2 The device shown is for pretreating wood fiber and separating lignin by electrothermal coupling with dilute alkali, adopting a reaction tube with a diameter of 20 mm, the material of the reaction tube being silica gel; adopting a magnetic core with L1 of 60 cm, l1 of 15 cm, W1 of 30 cm, w1 of 10 cm, and H of 5 cm; the size of the water-cooling plate adopted is equivalent to the size of the magnetic core; the number of magnetic cores in the electrothermal reaction unit adopted is 8, the number of water-cooling plates is 7, and the water-cooling plate is placed between the two magnetic cores to dissipate heat.

[0067] Operation process: 500g of crushed wheat straw powder (50 mesh) is mixed with 10L of sodium hydroxide solution (solution concentration is 1%) to obtain a mixed liquid, and then the mixed liquid is placed in a stirring device, and the mixed liquid enters the electrothermal reaction unit through a pumping device for electrothermal cycle treatment (the treatment temperature is 80°C, the treatment time is 5h; the voltage provided by the power supply device is 500V, the current is 10A, and the power is 5KW), and the treated mixed liquid is separated into solid and liquid, and the solid residue (wood fiber) is washed to electrical neutrality and dried with air to prepare for the analysis of its components. 72% sulfuric acid solution is added to the supernatant until the pH is 2, and it is left overnight to precipitate lignin, and then vacuum filtered, and the retained lignin solid component is washed with acidified warm water, and the water is dried at 50°C to obtain lignin.

[0068] The cellulose content of untreated wheat straw is 33.3%, the hemicellulose content is 22.7%, the lignin content is 20.6%, and the ash content is 2.4%; after electrothermal coupled dilute alkali pretreatment, analysis shows that the cellulose content of wheat straw is 47.5%, the hemicellulose content is 36.3%, the lignin content is 3.5%, and the ash content is 4.3%; the removal rate of lignin in wheat straw after pretreatment is calculated to be 87.1%; the lignin solid component in the supernatant is weighed to be 84.6g.

[0069] Comparative Example 1

[0070] The specific implementation method is the same as Example 2, except that: Comparative Example 1 directly uses a hydrothermal treatment device and a laboratory-level circulating water bath for operation. The specific operation steps are as follows:

[0071] 25 g of crushed wheat straw powder (50 mesh) was mixed with 1 L of sodium hydroxide solution (solution concentration was 1%) to obtain a mixed liquid, and then the mixed liquid was placed in a glass bottle and mixed evenly on a magnetic stirring device, and the mixed liquid was pumped into a circulating water bath cavity by a peristaltic pump for hydrothermal circulation treatment (the treatment temperature was 80°C and the treatment time was 5 h), and the treated mixed liquid was subjected to solid-liquid separation, the solid residue (wood fiber) was washed to electrical neutrality, and air-dried for analysis of its components, 72% sulfuric acid solution was added to the supernatant until the pH was 2, and the mixture was left overnight to precipitate lignin, and then vacuum filtered, the retained lignin solid component was washed with acidified warm water, and the water was dried at 50°C to obtain lignin.

[0072] The cellulose content of untreated wheat straw is 33.3%, the hemicellulose content is 22.7%, the lignin content is 20.6%, and the ash content is 2.4%; after hydrothermal pretreatment, analysis shows that the cellulose content of wheat straw is 46.7%, the hemicellulose content is 35.3%, the lignin content is 9.3%, and the ash content is 4.4%; the calculated removal rate of lignin in wheat straw after pretreatment is 56.2%; the lignin solid component in the supernatant is weighed to be 2.5g.

[0073] Comparative Example 2

[0074] The specific implementation method is the same as Example 3, except that: Comparative Example 2 directly uses a hydrothermal treatment device and a laboratory-level circulating water bath for operation. The specific operation steps are as follows:

[0075] 25 g of crushed wheat straw powder (50 mesh) was mixed with 1 L of sodium hydroxide solution (solution concentration was 2%) to obtain a mixed liquid, and then the mixed liquid was placed in a glass bottle and mixed evenly on a magnetic stirring device, and the mixed liquid was pumped into a circulating water bath cavity by a peristaltic pump for hydrothermal circulation treatment (the treatment temperature was 80°C and the treatment time was 3h), and the treated mixed liquid was subjected to solid-liquid separation, the solid residue (wood fiber) was washed to electrical neutrality, and air-dried for analysis of its components, 72% sulfuric acid solution was added to the supernatant until the pH was 2, and it was left overnight to precipitate lignin, and then vacuum filtered, the retained lignin solid component was washed with acidified warm water, and the water was dried at 50°C to obtain lignin.

[0076] The cellulose content of untreated wheat straw is 33.3%, the hemicellulose content is 22.7%, the lignin content is 20.6%, and the ash content is 2.4%; after hydrothermal pretreatment, analysis shows that the cellulose content of wheat straw is 44.6%, the hemicellulose content is 32.8%, the lignin content is 7.5%, and the ash content is 4.3%; the calculation shows that the removal rate of lignin in wheat straw after pretreatment is 66.1%; the lignin solid component in the supernatant is weighed to be 2.8g.

[0077] Comparative Example 3

[0078] The specific implementation method is the same as Example 4, except that: Comparative Example 3 directly uses a hydrothermal treatment device and an industrial-grade reactor for operation. The specific operation steps are as follows:

[0079] 500 g of crushed wheat straw powder (50 mesh) was mixed with 10 L of sodium hydroxide solution (solution concentration was 1%) to obtain a mixed liquid, and then the mixed liquid was placed in a glass bottle and mixed evenly on a magnetic stirring device, and the mixed liquid was pumped into a circulating water bath cavity by a peristaltic pump for hydrothermal circulation treatment (the treatment temperature was 80°C and the treatment time was 5 h), and the treated mixed liquid was subjected to solid-liquid separation, the solid residue (wood fiber) was washed to electrical neutrality, and air-dried for analysis of its components, 72% sulfuric acid solution was added to the supernatant until the pH was 2, and it was left overnight to precipitate pre-lignin, and then vacuum filtered, the retained lignin solid component was washed with acidified warm water, and the water was dried at 50°C to obtain lignin.

[0080] The cellulose content of untreated wheat straw is 33.3%, the hemicellulose content is 22.7%, the lignin content is 20.6%, and the ash content is 2.4%; after hydrothermal pretreatment, analysis shows that the cellulose content of wheat straw is 46.2%, the hemicellulose content is 35.2%, the lignin content is 9.1%, and the ash content is 4.5%; the removal rate of lignin in wheat straw after pretreatment is calculated to be 58.7%; the lignin solid component in the supernatant is weighed to be 54.7g.

[0081]

[0082] Table 1 Test data of Examples 2 to 4 and Comparative Examples 1 to 3

[0083] In summary, compared with Comparative Examples 1, 2, and 3, respectively, the electrothermal pretreatment of Examples 2, 3, and 4 is more effective in removing lignin from wood fibers than the hydrothermal pretreatment, and the lignin solid component in the electrothermal pretreatment hydrolyzate is significantly higher than that in the hydrothermal pretreatment group; taking the lignin removal rate in wood fibers or the obtained lignin solids as the dependent variables, the advantages of the device and method of the present invention for electrothermal coupled dilute alkali pretreatment of wood fibers and separation of lignin are demonstrated; compared with traditional hydrothermal treatment, the device and method of the present invention also improve energy utilization.

[0084] Comparative Example 4

[0085] This comparative example is a comparison with Example 2. The same device as Example 2 is used, and only the voltage in operation is adjusted from 200V to 500V, and other operations and parameters remain unchanged.

[0086] Table 2 Pretreatment results of Example 2 and Comparative Example 4

[0087]

[0088] According to Table 2, it can be found that when the voltage is adjusted to 500 V, although the removal rate of lignin in wheat straw is improved, the content of cellulose and hemicellulose is reduced. This may be because cellulose and hemicellulose are partially degraded under higher thermal and electrical effects. This shows that the voltage selected in the present invention cannot be too high. Therefore, in the device of the present invention, the voltage selection range is between 200 V and 800 V and is adjusted according to the volume of the slurry.

[0089] Comparative Example 5

[0090] This comparative example is a comparison with Example 2. The same device as Example 2 is used, and only the voltage in operation is adjusted from 200V to 100V, and other operations and parameters remain unchanged.

[0091] Table 3 Pretreatment results of Example 2 and Comparative Example 5

[0092]

[0093] According to Table 3, it can be found that when the voltage is adjusted to 100 V, the removal rate of lignin in wheat straw decreases, and the cellulose and hemicellulose contents decrease significantly. This is because the lower thermal effect and weaker electrical effect have a poorer effect on the removal of lignin. This shows that the voltage selected in the present invention cannot be too low and needs to be adjusted according to the volume of the slurry.

[0094] It should be understood that 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. Any equivalent changes or 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 pretreating wood fiber and separating lignin by electrothermal coupling with dilute alkali, characterized in that: The method is carried out using a device for achieving full component separation of wood fiber and improving enzymatic saccharification efficiency; the device is composed of an electric heating reaction unit, a pumping device, a stirring device, a power supply device, and a cooling device; The electrothermal reaction unit is composed of a reaction tube, a magnetic core, a water cooling plate and an excitation coil; The magnetic core is a ring-shaped plate-shaped magnetic conductive material with a hole in the middle; the water-cooling plate is a ring-shaped plate-shaped metal material with a hole in the middle, which is placed alternately with the magnetic core; a cooling pipe is embedded in the outer edge of the water-cooling plate for the circulation of cooling liquid; The water-cooled plate is connected to the cooling device through a cooling pipe; the cooling device is used for cooling the coolant in the cooling pipe; The reaction tube passes through the middle hole of the magnetic core and the water-cooling plate and is wound around the magnetic core and the water-cooling plate; the inlet end of the reaction tube is located at the bottom end of the electrothermal reaction unit and is connected to the pumping device; the outlet end of the reaction tube is located at the top end of the electrothermal reaction unit and is connected to the stirring device through a pipeline; The excitation coil is wound around the magnetic core and connected to a power supply device; the power supply device is used to provide an excitation voltage, so that the magnetic core generates a time-varying magnetic field as an excitation source, and spontaneously induces an induced voltage and an induced current inside the reaction tube; The stirring device is connected to the pumping device through a pipeline, and the pipeline of the pumping device contacts the bottom of the container in the stirring device to ensure the pumping of the solution; The method specifically comprises the following steps: (1) washing the wood fiber raw material, then immersing it in an organic solvent for decolorization, and then drying and crushing it for later use; (2) placing the pulverized wood fiber raw material and the dilute alkali solution in the stirring device, starting the stirring to mix, and after the mixture is evenly mixed to obtain a mixed solution, starting the pumping device to send the mixed solution into the reaction tube, and starting the power supply device and the cooling device to react; (3) After the reaction in step (2) is completed, solid-liquid separation is performed, the solid is washed to electrical neutrality, and dried to obtain a dry solid residue, and the separated supernatant is pH adjusted, allowed to stand, and filtered to obtain a lignin solid component.

2. The method according to claim 1, characterized in that The wood fiber raw materials in step (1) include straw and wood chips; the straw includes wheat straw and corn straw; the wood chips include poplar sawdust, eucalyptus sawdust, bagasse and bamboo powder.

3. The method according to claim 1, characterized in that In step (2), the dilute alkali solution includes one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia water; and the concentration of the dilute alkali solution is 0.5%-3%.

4. The method according to claim 1, characterized in that The mass volume ratio of the dried solid residue to the dilute alkali solution in step (2) is 1 g: 10-50 mL.

5. The method according to claim 1, characterized in that In step (2), the reaction temperature is 50-90° C. and the treatment time is 3-7 h.

6. The method according to claim 1, characterized in that In step (2), the treatment temperature is 70-80° C. and the treatment time is 4-5 h.

7. The method according to claim 1, characterized in that The parameters of the power supply device in step (2) are set as voltage of 100-800V, current of 2-10A, and power of 0.2-8KW.

8. The method according to claim 1, characterized in that In step (2), the ratio of the voltage set by the power supply device to the diameter of the reaction tube is 200-250V:10mm.

9. The method according to claim 1, characterized in that After the power supply device is turned on in step (2), the magnetic field strength of the magnetic core is 0.5-2T.

10. The method according to claim 1, characterized in that In step (3), the acid solution is a sulfuric acid solution with a concentration of 65-80%; and the pH is adjusted to 1-3.

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