Hydrogen peroxide-ester solution for lignin removal and method for removing lignin in lignocellulose raw material

Abstract

The invention provides a hydrogen peroxide-ester 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 hydrogen peroxide-ester solution for lignin removal. The hydrogen peroxide-ester solution comprises a hydrogen peroxide solution and a mixture containing an acid catalyst and liquid ester, the liquid ester is one or more of propyl acetate, butyl acetate, diethyl oxalate and glyceryl triacetate; the acid catalyst comprises one or more of aluminum chloride, sulfuric acid and p-toluenesulfonic acid. The boiling point of the ester is above 100 DEG C, the ester is not easy to volatilize in the removal process of the lignin, and the ester can be decomposed and peracetic acid can be synthesized at the same time by adjusting the type of the catalyst, so that the efficient removal of the lignin is improved. The result of the embodiment shows that 85% or above of the lignin component of the untreated raw material can be removed when the removal time is 1 h.

Description

Technical Field

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

[0002] As an important component of the plant cell wall, lignin not only provides the necessary mechanical strength for plants but also plays a key protective role. However, due to its complex chemical structure and poor degradability, lignin seriously hinders the process of biomass conversion into high-value chemicals and reduces the overall utilization efficiency of biomass. Therefore, in the field of biomass refining, the removal of lignin has become an urgent problem to be solved.

[0003] Currently, the hydrogen peroxide-ethyl acetate pretreatment system is widely used for lignin removal. This system can relatively retain more carbohydrate components in biomass at room temperature, thus achieving effective separation of lignin. However, this method also has significant limitations: it takes up to 3 days of reaction time at room temperature to complete lignin removal. Even when the temperature is raised to 60 °C, it still takes 8 h to reach a lignin removal rate of over 90%. But further increasing the temperature will cause solvent volatilization due to the low boiling point of ethyl acetate (77.1 °C), thereby reducing the reaction efficiency. The low boiling point has become a key factor restricting the reaction rate and lignin removal efficiency of this method. At the same time, in the pretreatment of biomass raw materials with high ash content, the loss of xylan is more serious, and the lignin removal effect is weakened. Therefore, developing a hydrogen peroxide-ester pretreatment with high-boiling esters to achieve efficient removal of lignin components from biomass raw materials (especially high-ash raw materials) is the core problem to be solved in this field.

[0004] In the hydrogen peroxide-ethyl acetate system, sulfuric acid simultaneously acts as a catalyst for ester decomposition and peracetic acid synthesis. However, in the hydrogen peroxide-high-boiling ester system, it is still unknown whether sulfuric acid can simultaneously have a catalytic effect on ester decomposition and peroxyacid synthesis. There are few reports on the research of catalysts to enhance peroxyacid synthesis in the hydrogen peroxide-high-boiling ester system and their influence on the removal of biomass lignin components. Therefore, developing a corresponding efficient catalyst is the key problem to be solved in this system. Summary of the Invention

[0005] The present invention provides a hydrogen peroxide-ester solution for lignin removal and a method for removing lignin from lignocellulosic raw materials. The hydrogen peroxide-ester solution of the present invention can achieve efficient removal of lignin.

[0006] The present invention provides a hydrogen peroxide-ester solution for lignin removal, comprising a hydrogen peroxide solution and a mixture containing an acid catalyst and a liquid ester;

[0007] The liquid ester is one or more of propyl acetate, butyl acetate, diethyl oxalate, and glyceryl triacetate;

[0008] The acid catalyst includes one or more of aluminum chloride, sulfuric acid, and p-toluenesulfonic acid.

[0009] Preferably, when the liquid ester includes glyceryl triacetate, the acid catalyst includes one or more of aluminum chloride, sulfuric acid, and p-toluenesulfonic acid;

[0010] When the liquid ester includes diethyl oxalate, the acid catalyst includes sulfuric acid and / or p-toluenesulfonic acid;

[0011] When the liquid ester includes propyl acetate or butyl acetate, the acid catalyst includes aluminum chloride.

[0012] Preferably, the volume ratio of the hydrogen peroxide solution to the liquid ester is 1:0.8 - 1.2; the mass concentration of the hydrogen peroxide solution is 10 - 30%.

[0013] Preferably, the concentration of aluminum chloride in the mixture is 100 - 300 mM;

[0014] The concentration of sulfuric acid in the mixture is 50 - 200 mM;

[0015] The concentration of p-toluenesulfonic acid in the mixture is 50 - 200 mM.

[0016] The present invention also provides a method for removing lignin from lignocellulosic raw materials, comprising the following steps:

[0017] Mix the hydrogen peroxide-ester solution described in the above technical solution with the lignocellulosic raw material, and then remove lignin.

[0018] Preferably, the mixing includes the following steps:

[0019] Mix the mixture containing the acid catalyst and the liquid ester with the lignocellulosic raw material for the first time to obtain a first mixture;

[0020] Mix the first mixture with the hydrogen peroxide solution for the second time.

[0021] Preferably, the lignocellulosic raw material includes one or more of poplar, pennisetum, miscanthus, and corn stover.

[0022] Preferably, the ash content of the lignocellulosic raw material is 1 - 10%.

[0023] Preferably, the mass ratio of the mixture containing the acid catalyst and the liquid ester to the lignocellulosic raw material is 1:4 - 6.

[0024] Preferably, the temperature for removal is 60 - 80°C and the time is 1 h.

[0025] The esters of the present invention all have boiling points above 100°C and are not easily volatilized during the removal of lignin. By adjusting the type of catalyst, the ester can be decomposed and peracetic acid can be synthesized simultaneously, thereby improving the efficient removal of lignin. The results of the examples show that the present invention can remove more than 85% of the lignin components in the untreated raw materials when the removal time is 1 h.

[0026] In addition, the ash of the biomass raw material contains some transition metal ions, which can undergo advanced oxidation reactions with hydrogen peroxide or peracetic acid, not only intensifying the ineffective decomposition of hydrogen peroxide but also causing a large loss of xylan. Therefore, in the traditional hydrogen peroxide - acetic acid pretreatment, the effect of selectively removing lignin from high - ash raw materials is not very ideal. However, in the hydrogen peroxide - ester system of the present invention, the alcohol generated by the decomposition of the ester has a quenching effect on free radicals, weakening the advanced oxidation reaction and alleviating the loss caused to xylan. This characteristic expands the universality of the pretreatment for raw materials. Specific embodiments

[0027] The present invention provides a hydrogen peroxide - ester solution for lignin removal, comprising a hydrogen peroxide solution, and a mixture containing an acid catalyst and a liquid ester;

[0028] The liquid ester is one or more of propyl acetate, butyl acetate, diethyl oxalate, and glycerol triacetate;

[0029] The acid catalyst includes one or more of aluminum chloride, sulfuric acid, and p - toluenesulfonic acid.

[0030] In the present invention, the volume ratio of the hydrogen peroxide solution to the liquid ester is preferably 1:0.8 - 1.2. In specific examples of the present invention, the volume ratio can be 1:1; the mass concentration of the hydrogen peroxide solution is preferably 30%.

[0031] In the present invention, when the liquid ester includes glycerol triacetate, the acid catalyst preferably includes one or more of aluminum chloride, sulfuric acid, and p - toluenesulfonic acid;

[0032] When the liquid ester includes diethyl oxalate, the acid catalyst preferably includes sulfuric acid and / or p - toluenesulfonic acid;

[0033] When the liquid ester includes propyl acetate or butyl acetate, the acid catalyst preferably includes aluminum chloride.

[0034] The acidity of the aluminum chloride catalyst is weaker than that of sulfuric acid, which can reduce the acidic corrosion of the reagent to the equipment.

[0035] In the present invention, the concentration of aluminum chloride in the mixture is 100 - 300 mM. In specific embodiments, the concentration of aluminum chloride in the mixture can be 100 mM, 150 mM, 200 mM, 250 mM, or 300 mM; the concentration of sulfuric acid in the mixture is 50 - 200 mM. In specific embodiments, the concentration of sulfuric acid in the mixture can be 50 mM, 100 mM, 150 mM, or 200 mM; the concentration of p-toluenesulfonic acid in the mixture is 50 - 200 mM. In specific embodiments, the concentration of p-toluenesulfonic acid in the mixture can be 50 mM, 100 mM, 150 mM, or 200 mM.

[0036] The present invention also provides a method for removing lignin from lignocellulosic raw materials, comprising the following steps:

[0037] Mix the hydrogen peroxide - ester solution described in the above solution with the lignocellulosic raw material, and then remove the lignin.

[0038] In the present invention, the mixing preferably comprises the following steps:

[0039] Perform a first mixing of the mixture containing an acid catalyst and a liquid ester with the lignocellulosic raw material to obtain a first mixture;

[0040] Perform a second mixing of the first mixture with a hydrogen peroxide solution.

[0041] In the present invention, the mass ratio of the mixture containing an acid catalyst and a liquid ester to the lignocellulosic raw material is preferably 1:4 - 6. In specific embodiments of the present invention, the mass ratio of the mixture containing an acid catalyst and a liquid ester to the lignocellulosic raw material can be 1:4, 1:5, or 1:6; the lignocellulosic raw material includes one or more of poplar, miscanthus, and corn stover; the ash content of the lignocellulosic raw material is preferably 1 - 10%.

[0042] In the present invention, the temperature for the removal is preferably 60 - 80 °C, and the time is preferably 1 h. In specific embodiments of the present invention, the temperature for the removal can be 60 °C, 65 °C, 70 °C, 75 °C, or 80 °C.

[0043] After the removal, the present invention preferably further comprises: performing solid - liquid separation on the product obtained from the removal, and then washing the obtained solid with water.

[0044] 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.

[0045] The following is a detailed description of the hydrogen peroxide - ester solution for lignin removal and the method for removing lignin from lignocellulosic raw materials provided by the present invention in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0046] Example 1

[0047] Measure 50 mL of propyl acetate and add aluminum chloride to mix evenly (the concentration of aluminum chloride in the mixture is 100 mM). Then add 10 g of poplar wood powder (ash content 1.8%) and mix well. Finally, add 50 mL of hydrogen peroxide solution with a mass concentration of 30% and mix evenly. React for 1 h at a temperature of 80 °C, and the pretreatment is completed. Then use vacuum filtration for solid - liquid separation, and the solid residue is poplar wood with lignin removed. At this time, the lignin removal rate of poplar wood is 88%, and the xylan loss rate is 15%.

[0048] Example 2

[0049] The pretreatment method and reaction conditions are the same as those in Example 1, except that the concentration of aluminum chloride in the mixture is 200 mM aluminum chloride. At this time, the lignin removal rate of poplar wood is 94%, and the xylan loss rate is 19%.

[0050] Example 3

[0051] The pretreatment method and reaction conditions are the same as those in Example 1, except that the concentration of aluminum chloride in the mixture is 300 mM. At this time, the lignin removal rate of poplar wood is 96%, and the xylan loss rate is 22%.

[0052] Example 4

[0053] The pretreatment method and reaction conditions are the same as those in Example 1, except that the catalyst is sulfuric acid and the concentration of sulfuric acid in the mixture is 100 mM. At this time, the lignin removal rate of poplar wood is 46%, and the xylan loss rate is 24%.

[0054] Example 5

[0055] The pretreatment method and reaction conditions are the same as those in Example 1, except that the catalyst is p - toluenesulfonic acid and the concentration of p - toluenesulfonic acid in the mixture is 100 mM. At this time, the lignin removal rate of poplar wood is 45%, and the xylan loss rate is 22%.

[0056] Example 6

[0057] The pretreatment method and reaction conditions are the same as those in Example 1, except that both propyl acetate and hydrogen peroxide are 60 mL. At this time, the lignin removal rate of poplar wood is 97%, and the xylan loss rate is 22%.

[0058] Example 7

[0059] The pretreatment method and reaction conditions were the same as those in Example 1, except that the ester was butyl acetate. At this time, the removal rate of poplar lignin was 91%, and the loss rate of xylan was 17%.

[0060] Example 8

[0061] The pretreatment method and reaction conditions were the same as those in Example 4, except that the ester was butyl acetate. At this time, the removal rate of poplar lignin was 46%, and the loss rate of xylan was 20%.

[0062] Example 9

[0063] The pretreatment method and reaction conditions were the same as those in Example 5, except that the ester was butyl acetate. At this time, the removal rate of poplar lignin was 43%, and the loss rate of xylan was 21%.

[0064] Example 10

[0065] The pretreatment method and reaction conditions were the same as those in Example 3, except that the ester was diethyl oxalate. At this time, the removal rate of poplar lignin was 87%, and the loss rate of xylan was 18%.

[0066] Example 11

[0067] The pretreatment method and reaction conditions were the same as those in Example 4, except that the ester was diethyl oxalate. At this time, the removal rate of poplar lignin was 98%, and the loss rate of xylan was 24%.

[0068] Example 12

[0069] The pretreatment method and reaction conditions were the same as those in Example 5, except that the ester was diethyl oxalate. At this time, the removal rate of poplar lignin was 97%, and the loss rate of xylan was 22%.

[0070] Example 13

[0071] The pretreatment method and reaction conditions were the same as those in Example 1, except that the ester was glycerol triacetate. At this time, the removal rate of poplar lignin was 95%, and the loss rate of xylan was 16%.

[0072] Example 14

[0073] The pretreatment method and reaction conditions were the same as those in Example 4, except that the ester was glycerol triacetate. At this time, the removal rate of poplar lignin was 98%, and the loss rate of xylan was 23%.

[0074] Example 15

[0075] The pretreatment method and reaction conditions were the same as those in Example 5, except that the ester was glycerol triacetate. At this time, the removal rate of poplar lignin was 96%, and the loss rate of xylan was 20%.

[0076] Example 16

[0077] The pretreatment method and reaction conditions are the same as those in Example 7, except that the raw material is Pennisetum alopecuroides with an ash content of 6.9%. At this time, the lignin removal rate of Pennisetum alopecuroides is 87%, and the xylan loss rate is 20%.

[0078] Example 17

[0079] The pretreatment method and reaction conditions are the same as those in Example 7, except that the raw material is Miscanthus sinensis with an ash content of 7.2%. At this time, the lignin removal rate of Miscanthus sinensis is 90%, and the xylan loss rate is 21%.

[0080] Example 18

[0081] The pretreatment method and reaction conditions are the same as those in Example 7, except that the raw material is corn straw with an ash content of 5.4%. At this time, the lignin removal rate of corn straw is 91%, and the xylan loss rate is 20%.

[0082] Comparative Example 1

[0083] Weigh 50 mL of propyl acetate and 10 grams of poplar wood powder, mix them evenly, then add 50 mL of hydrogen peroxide solution with a mass concentration of 30% and mix evenly. React at a temperature of 80 °C for 1 h, and the pretreatment is completed. Then use vacuum filtration for solid-liquid separation, and the solid residue is poplar wood with lignin removed. At this time, the lignin removal rate of poplar wood is 15%, and the xylan loss rate is 5%.

[0084] Comparative Example 2

[0085] The pretreatment method and reaction conditions are the same as those in Comparative Example 1, except that the ester is butyl acetate. At this time, the lignin removal rate of poplar wood is 13%, and the xylan loss rate is 5%.

[0086] Comparative Example 3

[0087] The pretreatment method and reaction conditions are the same as those in Comparative Example 1, except that the ester is diethyl oxalate. At this time, the lignin removal rate of poplar wood is 20%, and the xylan loss rate is 7%.

[0088] Comparative Example 4

[0089] The pretreatment method and reaction conditions are the same as those in Comparative Example 1, except that the ester is glycerol triacetate. At this time, the lignin removal rate of Miscanthus sinensis is 14%, and the xylan loss rate is 5%.

[0090] Comparative Example 5

[0091] The pretreatment method and reaction conditions were the same as those in Comparative Example 1, except that the ester was ethyl lactate, and after mixing ethyl lactate with aluminum chloride (the concentration of aluminum chloride in the mixture of ethyl lactate and aluminum chloride was 300 mM), it was then mixed with poplar powder. At this time, the lignin removal rate of poplar was 33%, and the xylan loss rate was 10%.

[0092] Comparative Example 6

[0093] The pretreatment method and reaction conditions were the same as those in Comparative Example 5, except that the catalyst was sulfuric acid; the concentration of sulfuric acid in the mixture of ethyl lactate and sulfuric acid was 100 mM. At this time, the lignin removal rate of poplar was 41%, and the xylan loss rate was 15%.

[0094] Comparative Example 7

[0095] The pretreatment method and reaction conditions were the same as those in Comparative Example 5, except that the catalyst was p-toluenesulfonic acid; the concentration of sulfuric acid in the mixture of ethyl lactate and p-toluenesulfonic acid was 100 mM. At this time, the lignin removal rate of poplar was 38%, and the xylan loss rate was 11%.

[0096] Comparative Example 8

[0097] The pretreatment method and reaction conditions were the same as those in Comparative Example 5, except that the ester was 50 g of ethyl p-toluenesulfonate. At this time, the lignin removal rate of poplar was 10%, and the xylan loss rate was 5%.

[0098] Comparative Example 9

[0099] The pretreatment method and reaction conditions were the same as those in Comparative Example 6, except that the ester was 50 g of ethyl p-toluenesulfonate. At this time, the lignin removal rate of poplar was 7%, and the xylan loss rate was 5%.

[0100] Comparative Example 10

[0101] The pretreatment method and reaction conditions were the same as those in Comparative Example 7, except that the ester was 50 g of ethyl p-toluenesulfonate. At this time, the lignin removal rate of poplar was 8%, and the xylan loss rate was 5%.

[0102] The lignin removal rates of poplar in Comparative Examples 1-4 were all lower than 30%, indicating that a catalyst was required to achieve the selective removal of lignin.

[0103] The lignin removal rates of poplar in Comparative Examples 5-10 were low: indicating that different pretreatment systems constructed with different esters required different catalysts to achieve the selective removal of lignin.

[0104] 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 hydrogen peroxide-ester solution for lignin removal, characterized in that: A mixture comprising a hydrogen peroxide solution, an acid catalyst and a liquid ester; The liquid ester is one or more of propyl acetate, butyl acetate, diethyl oxalate and triacetin; The acid catalyst includes one or more of aluminum chloride, sulfuric acid and p-toluenesulfonic acid.

2. The hydrogen peroxide-ester solution according to claim 1, characterized in that When the liquid ester comprises triacetin, the acid catalyst comprises one or more of aluminum chloride, sulfuric acid and p-toluenesulfonic acid; When the liquid ester comprises diethyl oxalate, the acid catalyst comprises sulfuric acid and / or p-toluenesulfonic acid; When the liquid ester comprises propyl acetate or butyl acetate, the acid catalyst comprises aluminum chloride.

3. The hydrogen peroxide-ester solution according to claim 1 or 2, characterized in that The volume ratio of the hydrogen peroxide solution to the liquid ester is 1:0.8-1.2; the mass concentration of the hydrogen peroxide solution is 10-30%.

4. The hydrogen peroxide-ester solution according to claim 1 or 2, characterized in that The concentration of aluminum chloride in the mixture is 100-300 mM; The concentration of sulfuric acid in the mixture is 50-200 mM; The concentration of p-toluenesulfonic acid in the mixture is 50-200 mM.

5. A method for removing lignin from a lignocellulose raw material, characterized in that: The following steps are involved: The hydrogen peroxide-ester solution according to any one of claims 1 to 4 is mixed with a lignocellulose raw material to remove lignin.

6. The method according to claim 5, characterized in that The mixing comprises the following steps: A mixture containing an acid catalyst and a liquid ester is first mixed with a lignocellulosic raw material to obtain a first mixture; The first mixture is secondarily mixed with a hydrogen peroxide solution.

7. The method according to claim 5, characterized in that The lignocellulosic raw material includes one or more of poplar, pennisetum, miscanthus and corn stalks.

8. The method according to claim 5, 6 or 7, characterized in that: The ash content of the lignocellulose raw material is 1-10%.

9. The method according to claim 6, characterized in that The mass ratio of the mixture containing the acid catalyst and the liquid ester to the lignocellulose raw material is 1:4-6.

10. The method according to claim 5, characterized in that The removal temperature is 60-80°C and the time is 1 hour.