Pretreatment solution for lignin removal and method for removing lignin in lignocellulose raw material

Abstract

The invention provides a pretreatment solution for lignin removal and a method for removing lignin from a lignocellulose raw material, and belongs to the field of biodegradation and conversion of forestry biomass. The invention provides a pretreatment solution for lignin removal. The pretreatment solution comprises a hydrogen peroxide solution and an acidic substance, the acidic substance comprises one or more of inorganic acid, acidic inorganic salt, sulfonic acid and liquid carboxylic acid; the liquid carboxylic acid comprises one or more of formic acid, acetic acid and propionic acid; when the acidic material comprises liquid carboxylic acid and the liquid carboxylic acid does not comprise formic acid, the pretreatment solution further comprises a catalyst; the catalyst comprises one or more of aluminum sulfate, gallium sulfate, activated aluminum oxide, a tungsten simple substance, a tungsten-containing inorganic compound, a molybdenum simple substance and a molybdenum-containing inorganic compound; when the acidic species includes a liquid carboxylic acid and when the liquid carboxylic acid includes formic acid, the pretreatment solution includes or does not include the catalyst.

Description

Technical Field

[0001] The present invention relates to the field of forestry biomass biodegradation and transformation, and specifically relates to a pretreatment solution for lignin removal and a method for removing lignin from lignocellulosic raw materials. Background Art

[0002] As one of the most abundant renewable biomass resources on the earth, lignocellulosic raw materials have great application potential in the fields of bioenergy, bio-based chemicals and materials. However, the high anti-degradability of lignocellulosic raw materials limits their effective utilization. Pretreatment, as a key step to improve the accessibility and fermentability of lignocellulosic raw materials, is crucial for subsequent bioconversion to prepare biomass fuels and biomass materials.

[0003] The hydrogen peroxide-acetic acid pretreatment method has received wide attention because it can effectively remove lignin, thereby improving the accessibility of cellulose and hemicellulose. This pretreatment method uses sulfuric acid to catalyze the synthesis of peracetic acid from hydrogen peroxide and acetic acid, promoting the oxidative degradation of lignin structure. However, this pretreatment method has a significant problem of xylan loss, which is mainly due to the strong acidity of the sulfuric acid catalyst during the pretreatment process, resulting in the degradation of hemicellulose (especially xylan).

[0004] To improve the xylan retention rate, researchers have tried to reduce the acidity of the pretreatment system by adjusting the pretreatment conditions, such as reducing the amount of sulfuric acid catalyst or using other catalysts with weaker acidity. Although reducing the amount of sulfuric acid alleviates the xylan loss to a certain extent, it also reduces the lignin removal efficiency, limiting the improvement of the pretreatment effect.

[0005] In addition, although sulfuric acid can catalyze the synthesis of peracetic acid in hydrogen peroxide-acetic acid, it cannot activate peracetic acid and hydrogen peroxide to generate free radicals. Although transition metal ions such as iron, manganese, and cobalt can catalyze peracetic acid and hydrogen peroxide to generate free radicals, they cannot catalyze the synthesis of peracetic acid, and the lignin removal efficiency still needs to be improved. Summary of the Invention

[0006] The present invention provides a pretreatment solution for lignin removal and a method for removing lignin from lignocellulosic raw materials. The pretreatment solution provided by the present invention can efficiently remove lignin.

[0007] The present invention provides a pretreatment solution for lignin removal, comprising the following raw materials: a solution of hydrogen peroxide and an acidic substance;

[0008] The acidic substance includes one or more of inorganic acids, acidic inorganic salts, sulfonic acids, and liquid carboxylic acids;

[0009] The liquid carboxylic acid includes one or more of formic acid, acetic acid, and propionic acid;

[0010] When the acidic substance includes a liquid carboxylic acid and when the liquid carboxylic acid includes formic acid, the pretreatment solution includes the catalyst or does not include the catalyst;

[0011] The catalyst includes one or more of aluminum sulfate, gallium sulfate, activated alumina, tungsten, tungsten-containing inorganic compounds, molybdenum, and molybdenum-containing inorganic compounds.

[0012] Preferably, the liquid carboxylic acid and sulfonic acid do not contain branched chains and reducing functional groups.

[0013] Preferably, the inorganic acid includes sulfuric acid;

[0014] The acidic inorganic salt includes sodium bisulfate and / or sodium bisulfite;

[0015] The sulfonic acid includes one or more of benzenesulfonic acid, p-toluenesulfonic acid, ethylsulfonic acid, and sulfamic acid;

[0016] Preferably, the mass concentration of hydrogen peroxide in the pretreatment solution is 6-15%; the mass concentration of the hydrogen peroxide solution is 10-30%;

[0017] When the acidic substance includes a liquid carboxylic acid, the mass concentration of the liquid carboxylic acid in the pretreatment solution is 40-60%;

[0018] When the acidic substance includes an inorganic acid and / or an acidic inorganic salt, the raw materials of the pretreatment solution further include: water, and the concentration of the inorganic acid and the concentration of the acidic inorganic salt in the pretreatment solution are independently 250-500 mM;

[0019] When the acidic substance includes a sulfonic acid, the raw materials of the pretreatment solution further include: water, and the concentration of the sulfonic acid in the pretreatment solution is 70-500 mM.

[0020] Preferably, the tungsten-containing inorganic compound includes one or more of tungstate, tungstic acid, tungsten sulfide, and tungsten carbide;

[0021] The molybdenum-containing inorganic compound includes one or more of molybdate, molybdic acid, molybdenum sulfide, and molybdenum carbide.

[0022] Preferably, the tungstate includes sodium tungstate and / or ammonium tungstate;

[0023] The molybdate includes sodium molybdate and / or ammonium molybdate.

[0024] Preferably, when the catalyst comprises aluminum sulfate and / or gallium sulfate and the pretreatment solution further comprises a promoter, the concentration of aluminum sulfate and gallium sulfate in the pretreatment solution is independently 50-100 mM, and the concentration of the promoter in the pretreatment solution is 10-30 mM; the promoter comprises sulfonic acid and / or sulfuric acid;

[0025] When the catalyst comprises aluminum sulfate and / or gallium sulfate and the pretreatment solution does not contain a promoter, the concentration of aluminum sulfate and gallium sulfate in the pretreatment solution is independently 100-200 mM;

[0026] When the catalyst comprises activated alumina, the concentration of activated alumina in the pretreatment solution is 50-80 g / L;

[0027] When the catalyst comprises a tungsten-containing inorganic compound and / or a molybdenum-containing inorganic compound, the concentration of tungsten element of the tungsten-containing inorganic compound and molybdenum element of the molybdenum-containing inorganic compound in the pretreatment solution is independently 5-20 mM;

[0028] When the catalyst comprises tungsten metal and / or molybdenum metal, the concentration of tungsten metal and molybdenum metal in the pretreatment solution is independently 0.9-3.6 g / L.

[0029] The present invention also provides a method for removing lignin from lignocellulosic raw materials, comprising the following steps:

[0030] Mix the pretreatment solution according to any one of claims 1-7 with the lignocellulosic raw material, and then remove lignin.

[0031] Preferably, the lignocellulosic raw material comprises one or more of poplar, pennisetum, miscanthus and corn stover.

[0032] Preferably, the temperature for the removal is 60-80 °C and the time is 5-60 min; the removal is carried out under closed conditions;

[0033] When the acid is formic acid and the initial pressure of the reaction system during the removal ≥ 0.8 bar, the pretreatment solution does not contain a catalyst, and the mass ratio of the lignocellulosic raw material to the pretreatment solution is 1:3-10;

[0034] When the acid is formic acid and the initial pressure of the reaction system during the removal < 0.8 bar, the pretreatment solution contains a catalyst, and the mass ratio of the lignocellulosic raw material to the pretreatment solution is 1:8-12;

[0035] When the acid is one or more of sulfuric acid, acetic acid, propionic acid, benzenesulfonic acid, p-toluenesulfonic acid, ethylsulfonic acid, and sulfamic acid, the mass ratio of the lignocellulosic raw material to the pretreatment solution is 1:8 to 12, and the initial pressure of the reaction system during removal is ≤0.8 bar.

[0036] The catalyst selected in the present invention can activate peroxyacid to generate free radicals and can catalyze the in-situ synthesis of peroxyacid, enabling efficient removal of lignin. The pretreatment solution of the present invention can achieve more than 90% lignin removal from lignocellulosic raw materials within 5 to 60 minutes.

[0037] Moreover, the metal ion salt catalysts of the present invention can all be recovered, and alumina can be directly recovered and reused.

[0038] Furthermore, tungsten sulfide, tungsten carbide, molybdenum sulfide, molybdenum carbide, sodium tungstate, ammonium tungstate, sodium molybdate, ammonium molybdate, aluminum sulfate, gallium sulfate, activated alumina, tungsten metal, and molybdenum metal are all non-acid catalysts, which can reduce the corrosion of equipment and lower costs. Detailed Embodiments

[0039] The present invention provides a pretreatment solution for lignin removal, comprising the following raw materials: a solution of hydrogen peroxide and an acidic substance;

[0040] The acidic substance includes one or more of inorganic acids, acidic inorganic salts, sulfonic acids, and liquid carboxylic acids;

[0041] The liquid carboxylic acid includes one or more of formic acid, acetic acid, and propionic acid;

[0042] When the acidic substance includes a liquid carboxylic acid and the liquid carboxylic acid does not include formic acid, the pretreatment solution further includes a catalyst;

[0043] The catalyst includes one or more of aluminum sulfate, gallium sulfate, activated alumina, tungsten metal, tungsten-containing inorganic compounds, molybdenum metal, and molybdenum-containing inorganic compounds;

[0044] When the acidic substance includes a liquid carboxylic acid and when the liquid carboxylic acid includes formic acid, the pretreatment solution includes the catalyst or does not include the catalyst.

[0045] The pretreatment solution provided by the present invention includes a solution of hydrogen peroxide. The mass fraction of hydrogen peroxide in the pretreatment solution is preferably 6 to 15%, and the mass fraction of the hydrogen peroxide solution is preferably 10 to 30%. In specific embodiments of the present invention, the mass fraction of the hydrogen peroxide solution in the pretreatment solution can be 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, and the mass fraction of the hydrogen peroxide solution can be 10%, 15%, 20%, 25%, or 30%.

[0046] The pretreatment solution provided by the present invention comprises an acidic compound; the acidic compound comprises one or more of inorganic acids, acidic inorganic salts, sulfonic acids, and liquid carboxylic acids; in the present invention, the liquid carboxylic acids and sulfonic acids preferably do not contain branched chains and reducing functional groups; the reducing functional groups preferably comprise one or more of hydroxyl groups, halogen substituents, keto groups, carbon-carbon double bonds, and carbon-carbon triple bonds; the above-mentioned reducing functional groups are liable to undergo oxidative decomposition with hydrogen peroxide.

[0047] When the acidic substance comprises an inorganic acid and / or an acidic inorganic salt, the raw materials of the pretreatment solution further comprise: water, and the concentration of the inorganic acid and the concentration of the acidic inorganic salt in the pretreatment solution are preferably independently 250 - 500 mM. In specific embodiments of the present invention, the concentration of the inorganic acid and the concentration of the acidic inorganic salt in the pretreatment solution can independently be 250 mM, 300 mM, 350 mM, 400 mM, 450 mM, or 500 mM.

[0048] In the present invention, the inorganic acid preferably comprises sulfuric acid; the acidic inorganic salt preferably comprises sodium bisulfate and / or sodium bisulfite.

[0049] In the present invention, when the acidic substance comprises a sulfonic acid, the raw materials of the pretreatment solution further comprise: water, and the concentration of the sulfonic acid in the pretreatment solution is preferably 70 - 500 mM. In specific embodiments of the present invention, the concentration of the sulfonic acid in the pretreatment solution can be 70 mM, 100 mM, 200 mM, 300 mM, 400 mM, or 500 mM.

[0050] In the present invention, the sulfonic acid preferably comprises one or more of benzenesulfonic acid, p-toluenesulfonic acid, ethylsulfonic acid, and aminosulfonic acid.

[0051] When the acidic substance is one or more of inorganic salts, inorganic acids, sulfonic acids, and liquid carboxylic acids, the pretreatment solution does not contain a catalyst.

[0052] In the present invention, when the acidic substance comprises a liquid carboxylic acid, the mass concentration of the liquid carboxylic acid in the pretreatment solution is preferably 40 - 60%. In specific embodiments of the present invention, the mass concentration of the liquid carboxylic acid in the pretreatment solution can be 40%, 45%, 50%, 55%, or 60%.

[0053] In the present invention, the liquid carboxylic acid preferably comprises one or more of formic acid, acetic acid, and propionic acid.

[0054] In the present invention, when the acidic substance comprises a liquid carboxylic acid and the liquid carboxylic acid does not comprise formic acid, the pretreatment solution further comprises a catalyst;

[0055] The catalyst includes one or more of aluminum sulfate, gallium sulfate, activated alumina, tungsten metal, tungsten-containing inorganic compounds, molybdenum metal, and molybdenum-containing inorganic compounds. The tungsten-containing inorganic compounds preferably include one or more of tungstates, tungstic acid, tungsten sulfide, and tungsten carbide; the tungstates preferably include sodium tungstate and / or ammonium tungstate; the molybdenum-containing inorganic compounds preferably include one or more of molybdates, molybdic acid, molybdenum sulfide, and molybdenum carbide; the molybdates preferably include sodium molybdate and / or ammonium molybdate.

[0056] In the present invention, when the catalyst includes aluminum sulfate and / or gallium sulfate and the pretreatment liquid does not contain a cocatalyst, the concentration of aluminum sulfate and gallium sulfate in the pretreatment solution is preferably independently 100 - 200 mM. In specific embodiments of the present invention, the concentration of aluminum sulfate and gallium sulfate can independently be 100 mM, 120 mM, 140 mM, 160 mM, 180 mM, or 200 mM;

[0057] When the catalyst includes aluminum sulfate and / or gallium sulfate and the pretreatment solution further includes a cocatalyst, the concentration of the cocatalyst in the pretreatment solution is preferably 10 - 30 mM. In specific embodiments of the present invention, the concentration of the cocatalyst in the pretreatment solution can be 10 mM, 15 mM, 20 mM, 25 mM, or 30 mM. In the present invention, the cocatalyst preferably includes sulfonic acid and / or sulfuric acid. When the cocatalyst is contained, the concentration of aluminum sulfate and gallium sulfate in the pretreatment solution is preferably independently 50 - 100 mM. In specific embodiments of the present invention, the concentration of aluminum sulfate and gallium sulfate in the pretreatment solution can independently be 50 mM, 60 mM, 70 mM, 80 mM, 90 mM, or 100 mM.

[0058] In the present invention, when the catalyst includes activated alumina, the concentration of activated alumina in the pretreatment solution is preferably 50 - 80 g / L. In specific embodiments of the present invention, the concentration of activated alumina can be 50 g / L, 60 g / L, 70 g / L, or 80 g / L. The activated alumina can be recovered in the form of solid particles and reused 3 - 4 times.

[0059] In the present invention, when the catalyst includes tungsten-containing inorganic compounds and / or molybdenum-containing inorganic compounds, the concentration of tungsten in the tungsten-containing inorganic compounds and molybdenum in the molybdenum-containing inorganic compounds in the pretreatment solution is preferably independently 5 - 20 mM. In specific embodiments of the present invention, the concentration of tungsten in the tungsten-containing inorganic compounds and molybdenum in the molybdenum-containing inorganic compounds can independently be 5 mM, 8 mM, 10 mM, 12 mM, 15 mM, 18 mM, or 20 mM.

[0060] In the present invention, when the catalyst includes tungsten and / or molybdenum in elemental form, the concentration of tungsten and molybdenum in elemental form in the pretreatment solution is preferably independently 0.9 - 3.6 g / L. In specific embodiments of the present invention, the concentration of tungsten and molybdenum in elemental form in the pretreatment solution can independently be 0.9 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L or 3.6 g / L.

[0061] The present invention also provides a method for removing lignin from lignocellulosic raw materials, comprising the following steps:

[0062] Mix the pretreatment solution described in the above technical solution with the lignocellulosic raw material, and then remove lignin.

[0063] In the present invention, when the acidic substance includes one or more of inorganic acids, acidic inorganic salts and sulfonic acids, the pretreatment solution further includes: water. The mixing preferably includes:

[0064] Perform a first mixing of the acidic substance and water to obtain a first mixture (i.e., a solution of the acidic substance);

[0065] Perform a second mixing of the solution of the acidic substance and the lignocellulosic raw material to obtain a second mixture;

[0066] Perform a third mixing of the second mixture and a solution of hydrogen peroxide;

[0067] When the acidic substance includes a liquid carboxylic acid and the liquid carboxylic acid does not include formic acid, and the pretreatment solution further includes a catalyst, the mixing preferably includes:

[0068] Perform a first mixing of the acidic substance and the catalyst to obtain a first mixture;

[0069] Perform a second mixing of the mixture containing the acidic substance and the catalyst and the lignocellulosic raw material to obtain a second mixture;

[0070] Perform a third mixing of the second mixture and a solution of hydrogen peroxide.

[0071] In the present invention, the temperature of the reaction system during the removal is preferably 60 - 80 °C, and the time is preferably 5 - 60 min. In specific embodiments of the present invention, the temperature of the reaction system during the removal can be 60 °C, 70 °C, 75 °C or 80 °C, and the time can be 5 min, 10 min, 20 min, 30 min, 40 min, 50 min or 60 min. In the present invention, the removal is preferably carried out under closed conditions; the removal is preferably carried out under water bath conditions.

[0072] In the present invention, when the acid is formic acid and the initial pressure of the reaction system during the removal is ≥ 0.8 bar, the pretreatment solution does not include a catalyst, and the mass ratio of the lignocellulosic raw material to the pretreatment solution is preferably 1:3 to 10. In specific embodiments of the present invention, the mass ratio of the lignocellulosic raw material to the pretreatment solution can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10;

[0073] When the acid is formic acid and the initial pressure of the reaction system during the removal is < 0.8 bar, the pretreatment solution includes a catalyst, and the mass ratio of the lignocellulosic raw material to the pretreatment solution is preferably 1:8 to 12. In specific embodiments of the present invention, the mass ratio of the pretreatment solution to the lignocellulosic raw material can be 1:8, 1:10, or 1:12.

[0074] When the acid is one or more of sulfuric acid, acetic acid, propionic acid, benzenesulfonic acid, p-toluenesulfonic acid, ethylsulfonic acid, and sulfamic acid, the mass ratio of the lignocellulosic raw material to the pretreatment solution is 1:8 to 12, and the initial pressure of the reaction system during the removal is ≤ 0.8 bar. In specific embodiments of the present invention, the mass ratio of the pretreatment solution to the lignocellulosic raw material can be 1:8, 1:10, or 1:12.

[0075] In the present invention, the lignocellulosic raw material includes one or more of poplar, miscanthus, and corn stover.

[0076] After the removal, the present invention preferably further includes: performing solid-liquid separation on the product obtained by the removal, and then washing the obtained solid with water.

[0077] The present invention has no special limitation on the water washing, and it can be washed to neutral using a method well-known to those skilled in the art.

[0078] The following combines examples to detail the pretreatment solution for lignin removal and the method for removing lignin from lignocellulosic raw materials provided by the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0079] Example 1

[0080] Measure 50 mL of a sulfuric acid solution with a concentration of 500 mM, mix it evenly with 10 grams of absolute dry poplar, acidify the raw material, and then measure 50 mL of a hydrogen peroxide solution with a mass concentration of 30% and mix well (at this time, the concentration of sulfuric acid in the total system is 250 mM). React statically for 1 h under closed conditions at 80 °C and an initial pressure of atmospheric pressure. After the pretreatment is completed, use vacuum filtration for solid-liquid separation, and the solid residue is poplar with lignin removed. At this time, the lignin removal rate of poplar is 92%, and the xylan loss rate is 35%.

[0081] Example 2

[0082] The pretreatment method and reaction conditions are the same as those in Example 1, except that: the acidic substance is sodium bisulfate; the concentration of the acidic substance solution is 600 mM (the concentration of sodium bisulfate in the total system is 300 mM). At this time, the lignin removal rate of poplar is 97%, and the xylan loss rate is 32%.

[0083] Example 3

[0084] The pretreatment method and reaction conditions are the same as those in Example 1, except that: the acidic substance is sodium bisulfite; the concentration of the acidic substance solution is 600 mM (the concentration of sodium bisulfite in the total system is 300 mM). At this time, the lignin removal rate of poplar is 93%, and the xylan loss rate is 33%.

[0085] Example 4

[0086] The pretreatment method and reaction conditions are the same as those in Example 1, except that: the acidic substance is p-toluenesulfonic acid; the concentration of the acidic substance solution is 200 mM (the concentration of p-toluenesulfonic acid in the total system is 100 mM). At this time, the lignin removal rate of poplar is 97%, and the xylan loss rate is 36%.

[0087] Example 5

[0088] Measure 80 mL of p-toluenesulfonic acid solution with a concentration of 375 mM, mix it evenly with 10 g of absolute dry poplar, acidify the raw material, and then measure 20 mL of hydrogen peroxide solution with a mass concentration of 30% and mix well (at this time, the concentration of p-toluenesulfonic acid in the total system is 300 mM). React statically for 1 h under closed conditions at 80 °C and an initial pressure of normal pressure. After the pretreatment is completed, vacuum filtration is used for solid-liquid separation, and the solid residue is poplar with lignin removed. At this time, the lignin removal rate of poplar is 91%, and the xylan loss rate is 39%.

[0089] Example 6

[0090] The pretreatment method and reaction conditions are the same as those in Example 1, except that: the acidic substance is benzenesulfonic acid; the concentration of the acidic substance solution is 200 mM (the concentration of benzenesulfonic acid in the total system is 100 mM). At this time, the lignin removal rate of poplar is 97%, and the xylan loss rate is 30%.

[0091] Example 7

[0092] The pretreatment method and reaction conditions were the same as those in Example 1, except that the acidic substance was ethylsulfonic acid and the concentration of the acidic substance solution was 200 mM (the concentration of ethylsulfonic acid in the total system was 100 mM). At this time, the lignin removal rate of poplar was 96%, and the xylan loss rate was 32%.

[0093] Example 8

[0094] The pretreatment method and reaction conditions were the same as those in Example 1, except that the acidic substance was sulfamic acid and the concentration of the acidic substance solution was 200 mM (the concentration of sulfamic acid in the total system was 100 mM). At this time, the lignin removal rate of poplar was 96%, and the xylan loss rate was 33%.

[0095] Example 9

[0096] Measure 15 mL of formic acid and mix it evenly with 10 g of absolute dry poplar to acidify the raw material. Then measure 15 mL of hydrogen peroxide solution with a mass concentration of 30% and mix it evenly. The reaction conditions were 80 °C, and the system was closed and pressurized to make the initial pressure of the system 0.8 bar. React for 5 min, release the pressure after the pretreatment is completed, and then use vacuum filtration for solid-liquid separation. The solid residue is poplar with lignin removed. At this time, the lignin removal rate of poplar was 97%, and the xylan loss rate was 56%.

[0097] Example 10

[0098] Measure 50 mL of formic acid and mix it evenly with 10 g of absolute dry poplar to acidify the raw material. Then measure 50 mL of hydrogen peroxide solution with a mass concentration of 30% and mix it evenly. The reaction conditions were 60 °C, and the system was closed and pressurized to make the initial pressure of the system 0.8 bar. React for 60 min, release the pressure after the pretreatment is completed, and then use vacuum filtration for solid-liquid separation. The solid residue is poplar with lignin removed. At this time, the lignin removal rate of poplar was 98%, and the xylan loss rate was 78%.

[0099] Example 11

[0100] Measure 50 mL of a mixture of formic acid and sodium tungstate (the concentration of sodium tungstate in the mixture was 10 mM) and mix it evenly with 10 g of absolute dry poplar to acidify the raw material. Then measure 50 mL of hydrogen peroxide solution with a mass concentration of 30% and mix it evenly (at this time, the concentration of sodium tungstate in the total system was 5 mM). The reaction conditions were 60 °C, and the system was closed and pressurized to make the initial pressure of the system 0.8 bar. React for 30 min, release the pressure after the pretreatment is completed, and then use vacuum filtration for solid-liquid separation. The solid residue is poplar with lignin removed. At this time, the lignin removal rate of poplar was 92%, and the xylan loss rate was 43%.

[0101] Example 12

[0102] The pretreatment method and reaction conditions were the same as those in Example 11, except that formic acid was replaced with acetic acid. At this time, the removal rate of poplar lignin was 92%, and the loss rate of xylan was 23%.

[0103] Example 13

[0104] The pretreatment method and reaction conditions were the same as those in Example 11, except that formic acid was replaced with propionic acid. At this time, the removal rate of poplar lignin was 93%, and the loss rate of xylan was 20%.

[0105] Example 14

[0106] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was sodium molybdate and the concentration of sodium molybdate in the total system was 10 mM. At this time, the removal rate of poplar lignin was 91%, and the loss rate of xylan was 18%.

[0107] Example 15

[0108] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was ammonium molybdate and the concentration of ammonium molybdate in the total system was 10 mM. At this time, the removal rate of poplar lignin was 92%, and the loss rate of xylan was 19%.

[0109] Example 16

[0110] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was ammonium tungstate and the concentration of ammonium tungstate in the total system was 5 mM. At this time, the removal rate of poplar lignin was 92%, and the loss rate of xylan was 20%.

[0111] Example 17

[0112] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was molybdenum sulfide and the concentration of molybdenum sulfide in the total system was 10 mM. At this time, the removal rate of poplar lignin was 93%, and the loss rate of xylan was 23%.

[0113] Example 18

[0114] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was tungsten sulfide and the concentration of tungsten sulfide in the total system was 5 mM. At this time, the removal rate of poplar lignin was 92%, and the loss rate of xylan was 22%.

[0115] Example 19

[0116] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was molybdenum carbide and the concentration of molybdenum carbide in the total system was 10 mM. At this time, the removal rate of poplar lignin was 92%, and the loss rate of xylan was 23%.

[0117] Example 20

[0118] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was tungsten carbide and the concentration of tungsten carbide in the total system was 10 mM. At this time, the removal rate of poplar lignin was 93%, and the loss rate of xylan was 20%.

[0119] Example 21

[0120] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was aluminum sulfate and the concentration of aluminum sulfate in the total system was 150 mM. At this time, the removal rate of poplar lignin was 90%, and the loss rate of xylan was 21%.

[0121] Example 22

[0122] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was gallium sulfate and the concentration of gallium sulfate in the total system was 150 mM. At this time, the removal rate of poplar lignin was 92%, and the loss rate of xylan was 22%.

[0123] Example 23

[0124] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was activated alumina and the mass of activated alumina in the total system was 6 g. At this time, the removal rate of poplar lignin was 94%, and the loss rate of xylan was 15%.

[0125] Example 24

[0126] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was the recovered activated alumina in Example 23 (the recovery method was: after depressurization, the spherical alumina particles in Example 23 were directly fished out, washed with distilled water and dried). At this time, the removal rate of poplar lignin was 91%, and the loss rate of xylan was 14%.

[0127] Example 25

[0128] Measure 15 mL of formic acid and mix it evenly with 10 g of absolute dry poplar to acidify the raw material. Then measure 15 mL of hydrogen peroxide solution with a mass concentration of 30% and mix it evenly. The reaction conditions were 90 °C, and the initial pressure of the system was 0.8 bar under closed pressure. After reacting at 90 °C for 90 s, it was cooled for 10 min. After the pretreatment, the pressure was released, and then vacuum filtration was used for solid-liquid separation. The solid residue was poplar with lignin removed. At this time, the removal rate of poplar lignin was 95%, and the loss rate of xylan was 32%.

[0129] Example 26

[0130] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was elemental tungsten and the mass of elemental tungsten in the total system was 0.09 g. At this time, the removal rate of poplar lignin was 95%, and the loss rate of xylan was 13%.

[0131] Example 27

[0132] The pretreatment method and reaction conditions were the same as those in Example 12, except that the catalyst was elemental molybdenum and the mass of elemental molybdenum in the total system was 0.1 g. At this time, the removal rate of poplar lignin was 92%, and the loss rate of xylan was 12%.

[0133] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A pretreatment solution for lignin removal, characterized in that: The material comprises the following: a solution of hydrogen peroxide and an acidic substance; The acidic substance includes one or more of an inorganic acid, an acidic inorganic salt, a sulfonic acid and a liquid carboxylic acid; The liquid carboxylic acid comprises one or more of formic acid, acetic acid and propionic acid; When the acidic substance includes liquid carboxylic acid and the liquid carboxylic acid does not include formic acid, the pretreatment solution further includes a catalyst; The catalyst includes one or more of aluminum sulfate, gallium sulfate, activated alumina, tungsten, an inorganic compound containing tungsten, molybdenum, and an inorganic compound containing molybdenum; When the acidic substance includes a liquid carboxylic acid and when the liquid carboxylic acid includes formic acid, the pretreatment solution includes the catalyst or does not include the catalyst.

2. The pretreatment solution according to claim 1, characterized in that The liquid carboxylic acid and sulfonic acid contain no branched chain and no reducing functional group.

3. The pretreatment solution according to claim 1 or 2, characterized in that: The inorganic acid includes sulfuric acid; The acidic inorganic salt includes sodium bisulfate and / or sodium bisulfite; The sulfonic acid includes one or more of benzenesulfonic acid, p-toluenesulfonic acid, ethylsulfonic acid and aminosulfonic acid.

4. The pretreatment solution according to claim 1, characterized in that The mass concentration of hydrogen peroxide in the pretreatment solution is 6-15%; the mass concentration of the hydrogen peroxide solution is 10-30%; When the acidic substance includes liquid carboxylic acid, the mass concentration of the liquid carboxylic acid in the pretreatment solution is 40 to 60%; When the acidic substance includes an inorganic acid and / or an acidic inorganic salt, the raw materials of the pretreatment solution further include: water, and the concentration of the inorganic acid and the concentration of the acidic inorganic salt in the pretreatment solution are independently 250 to 500 mM; When the acidic substance includes sulfonic acid, the raw material of the pretreatment solution further includes: water, and the concentration of the sulfonic acid in the pretreatment solution is 70-500 mM.

5. The pretreatment solution according to claim 1, characterized in that The tungsten-containing inorganic compound includes one or more of tungstate, tungstic acid, tungsten sulfide and tungsten carbide; The inorganic compound containing molybdenum includes one or more of molybdate, molybdic acid, molybdenum sulfide and molybdenum carbide.

6. The pretreatment solution according to claim 5, characterized in that The tungstate includes sodium tungstate and / or ammonium tungstate; The molybdate includes sodium molybdate and / or ammonium molybdate.

7. The pretreatment solution according to claim 1, characterized in that When the catalyst comprises aluminum sulfate and / or gallium sulfate and the pretreatment solution further comprises a promoter, the concentrations of aluminum sulfate and gallium sulfate in the pretreatment solution are independently 50 to 100 mM, and the concentration of the promoter in the pretreatment solution is 10 to 30 mM; the promoter comprises sulfonic acid and / or sulfuric acid; When the catalyst comprises aluminum sulfate and / or gallium sulfate and the pretreatment solution does not contain a promoter, the concentrations of aluminum sulfate and gallium sulfate in the pretreatment solution are independently 100 to 200 mM; When the catalyst comprises activated alumina, the concentration of activated alumina in the pretreatment solution is 50 to 80 g / L; When the catalyst comprises an inorganic compound containing tungsten and / or an inorganic compound containing molybdenum, the concentrations of the tungsten element of the inorganic compound containing tungsten and the molybdenum element of the inorganic compound containing molybdenum in the pretreatment solution are independently 5 to 20 mM; When the catalyst includes tungsten and / or molybdenum, the concentrations of tungsten and molybdenum in the pretreatment solution are independently 0.9 to 3.6 g / L.

8. A method for removing lignin from a lignocellulose raw material, characterized in that: The following steps are involved: The pretreatment solution according to any one of claims 1 to 7 is mixed with a lignocellulose raw material to remove lignin.

9. The method according to claim 8, characterized in that The lignocellulosic raw material includes one or more of poplar, pennisetum, miscanthus and corn stalks.

10. The method according to claim 8, characterized in that The removal temperature is 60-80°C and the time is 5-60 minutes; the removal is carried out under closed conditions; When the acid is formic acid and the initial pressure of the reaction system during the removal is ≥0.8 bar, the pretreatment liquid does not include a catalyst, and the mass ratio of the lignocellulosic raw material to the pretreatment liquid is 1:3-10; When the acid is formic acid and the initial pressure of the reaction system during the removal is less than 0.8 bar, the pretreatment liquid includes a catalyst, and the mass ratio of the lignocellulosic raw material to the pretreatment liquid is 1:8-12; When the acid is one or more of sulfuric acid, acetic acid, propionic acid, benzenesulfonic acid, p-toluenesulfonic acid, ethylsulfonic acid and aminosulfonic acid, the mass ratio of the lignocellulosic raw material to the pretreatment liquid is 1:8-12, and the initial pressure of the reaction system during the removal is ≤0.8 bar.