A high-efficiency separation of corn stalks dimer imidazole bromide and its preparation method and application

Abstract

The application provides a gemini imidazole bromide for efficiently separating corn stalks and a preparation method and application thereof, wherein 1, m-alkyl-di(bromination-3-alkyl imidazole) [C n ‑C m ‑C n im]Br2 is prepared through a designed preparation method, the product has a multi-charge and multi-alkyl structure, the preparation method is simple and efficient, raw materials are easy to obtain, and the cost is low. The gemini imidazole bromide [C n ‑C m ‑C n im]Br2 has a multi-charge and multi-alkyl structure, which has a strong interaction with lignin with hydrophilicity and hydrophobicity, most of the lignin can be dissolved in ethylene glycol without adding an additive, and hemicellulose and cellulose are rarely dissolved, the reaction liquid can be recycled, the performance of separating lignin is almost not decreased after being repeatedly used for 5 times, the application is economical and energy-saving, the operation is simple and safe, and the separation efficiency is high. The obtained holocellulose can be applied to the fields of preparing ethanol, lactic acid and the like through biomass fermentation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biomass component separation, and particularly relates to a high-efficiency corn stalk separation dication imidazole bromide and a preparation method and application thereof. BACKGROUND

[0002] Corn stalks, as by-products of grain production, have the advantages of being renewable, environmentally friendly, and having a large supply. However, due to the limitations of pretreatment technology, a large amount of corn stalks cannot be effectively utilized, and are directly discharged into the ecological system without treatment, resulting in waste of agricultural and forestry stalks, farmland pests and diseases, and environmental pollution, which has a negative impact on the soil, atmosphere, and microorganisms. Therefore, how to effectively utilize corn stalks as raw materials to produce high-value-added products is of great significance to resource utilization and environmental protection.

[0003] Corn stalks mainly contain cellulose, hemicellulose, and lignin, which can all be converted into high-value-added products. Existing corn stalk separation and conversion technologies are difficult to achieve efficient separation of cellulose, hemicellulose, and lignin, and thus are difficult to carry out subsequent biomass conversion, such as fermentation to produce ethanol, lactic acid, and other energy and monomer bio-based materials. Traditional lactic acid biosynthesis still uses starchy raw materials as substrates, which has the problem of competing with people for food and land, and currently using renewable lignocellulose as a substrate has become the main direction of monomer synthesis of bio-based materials. In the separation of the three components in corn stalks, most of them are carried out in aqueous systems using strong inorganic acids or strong bases as catalysts, such as sulfuric acid, hydrochloric acid, and sodium hydroxide. However, using inorganic acid as a catalyst has many disadvantages, such as high degree of cellulose decomposition, which makes it difficult to be used in subsequent utilization (such as 5-hydroxymethylfurfural), serious corrosion of inorganic acid to equipment, and significant safety problems. Using strong alkali in water will be accompanied by degradation of hemicellulose during treatment, and there are also problems of alkali recovery, neutralization, washing, and environmental pollution.

[0004] In recent years, ionic liquids (ILs) have shown great potential in the field of biomass pretreatment due to their excellent physicochemical properties, especially strong solubility. For example, [C4mim]Cl can effectively dissolve cellulose, and the solubility of cellulose in it can reach 25wt%, but the cellulose will partially degrade during the dissolution, and then the cellulose is extracted and regenerated, which will increase the energy consumption and reagent consumption, and the economy is not good. It is a good strategy to pretreat biomass by dissolving lignin and retaining holocellulose (the total of hemicellulose and cellulose) in the biomass, but the extraction rate of lignin from sawdust, bagasse and bamboo is not higher than 26% using 1-butyl-3-methyl as the cation, halogen, carboxylate, sulfate, phosphate, tetrafluoroborate as the anion, and ethyl acetate (or methanol, ethanol), water as the mixed solvent at high temperature and high pressure. At the same time, due to the existence of the complex protective layer of lignin-hemicellulose, it is necessary to reduce the particle size of lignocellulose by grinding, and the pretreatment temperature is high (>170℃) and the pretreatment time is long (>8h), which will cause huge energy consumption.

[0005] The above studies show that there is still a lot of room for improvement in the pretreatment of lignocellulose by ionic liquids, and more energy-saving technologies for dissolving and separating lignocellulose need to be developed to realize the efficient utilization of lignocellulose resources. In addition, the high cost and high viscosity of ionic liquids are also important factors limiting their industrial application. SUMMARY

[0006] The purpose of the present application is to provide a kind of high-efficiency separation of corn stalks Gemini imidazolium bromide and its preparation method, by the preparation method designed to prepare 1,m-alkyl-di (bromide-3-alkyl imidazole) [C n -C m -C n Im]Br2, the product has multiple charges and multiple alkyl structures;The preparation method is simple, efficient, and the raw materials are easy to obtain, and the cost is low.

[0007] The present application also has the purpose of providing a kind of high-efficiency separation of corn stalks Gemini imidazolium bromide application, for separating corn stalks, can efficiently remove lignin in the stalk, obtain high-purity holocellulose, the separation method is simple, and can retain a large amount of holocellulose while dissolving and separating lignin in corn stalks.

[0008] The specific technical scheme of the present application is as follows:

[0009] A kind of high-efficiency separation of corn stalks Gemini imidazolium bromide, the high-efficiency separation of corn stalks Gemini imidazolium bromide is 1,m-alkyl-di (bromide-3-alkyl imidazole) [C n -C m -Cn im]Br2, wherein m = 1, 2, 4, 6, n = 1, 2, 4, 8, 12, 16.

[0010] The structure of the dimeric imidazole bromide for efficiently separating corn stalks is as follows:

[0011] wherein m = 1, 2, 4, 6, n = 1, 2, 4, 8, 12, 16.

[0012] The application provides a preparation method of the dimeric imidazole bromide for efficiently separating corn stalks.

[0013] The short-chain alkyl imidazole is dissolved in anhydrous ethanol, dibromoalkane is added, and the reaction is carried out under stirring and heating reflux in a protective atmosphere; after the reaction is completed, separation and purification are performed to obtain the dimeric imidazole bromide for efficiently separating corn stalks.

[0014] The ratio of the short-chain alkyl imidazole to ethanol is 2-5 mol / L.

[0015] The ratio of the short-chain alkyl imidazole to dibromoalkane is 2.4:1-3.0:1.

[0016] The short-chain alkyl imidazole is preferably methyl imidazole, and the dibromoalkane is preferably 1,2-dibromoethane.

[0017] The protective atmosphere is nitrogen.

[0018] The heating reflux reaction has a reaction time of 24-48 h and a reflux reaction temperature of 65-100 DEG C.

[0019] Preferably, the dimeric imidazole bromide for efficiently separating corn stalks is [C1-C2-C1im]Br2.

[0020] The separation and purification refer to that after the reaction is completed, the sample is rotary evaporated, and then recrystallized with petroleum ether for more than three times; and then placed in a dryer to dry until the weight is constant.

[0021] Another preparation method of the dimeric imidazole bromide for efficiently separating corn stalks is provided, which comprises the following steps.

[0022] 1) Sodium alcoholate is dissolved in ethanol, imidazole is added, and bromoalkane is added dropwise; the reaction is carried out under stirring and heating reflux in a protective atmosphere; after the reaction is completed, separation and purification are performed to obtain alkyl imidazole.

[0023] 2) The alkyl imidazole is dissolved in ethanol, dibromoalkane is added, and the reaction is carried out under stirring and heating reflux in a protective atmosphere; after the reaction is completed, separation and purification are performed to obtain the dimeric imidazole bromide for efficiently separating corn stalks.

[0024] In step 1), the usage ratio of the sodium alcoholate and ethanol is 0.04-0.08 g / mL;

[0025] In step 1), the molar ratio of the imidazole and bromoalkane is 1.3:1-1.8:1;

[0026] In step 1), the usage ratio of the imidazole and ethanol is 2-3 mol / L;

[0027] In step 1), the bromoalkane is preferably bromohexadecane;

[0028] In step 1), the sodium alcoholate is preferably sodium ethoxide;

[0029] In step 1), the protective atmosphere is nitrogen;

[0030] In step 1), the stirring and heating reflux reaction is carried out for 24-48 h, and the reflux reaction temperature is 60-75℃.

[0031] In step 1), the separation and purification refers to that after the reaction is completed, the upper clear liquid is taken, ethanol is removed by rotary evaporation, and the crude product is distilled under reduced pressure to obtain the alkyl imidazole;

[0032] In step 2), the usage ratio of the alkyl imidazole and ethanol is 1-1.5 mol / L;

[0033] In step 2), the molar ratio of the alkyl imidazole and dibromoalkane is 2.4:1-3.0:1;

[0034] In step 2), the dibromoalkane is preferably 1,6-dibromohexane;

[0035] In step 2), the protective atmosphere is nitrogen;

[0036] In step 2), the stirring and heating reflux reaction is carried out for 24-48 h, and the reflux reaction temperature is 85-100℃.

[0037] In step 2), the separation and purification refers to that after the ethanol is rotary evaporated, the petroleum ether is used for recrystallization for more than three times, and the drying is carried out until the constant weight.

[0038] The application of the high-efficiency separation corn straw gemini imidazole bromide provided by the application is used for separating corn straw, and the specific application method is as follows:

[0039] The selective lignin dissolving solution formed by mixing the high-efficiency separation corn straw gemini imidazole bromide and high-boiling alcohol is used for treating corn straw.

[0040] Preferably, the high-efficiency corn stalk separating gemini imidazole bromide is dissolved in a high-boiling alcohol, corn stalk is added, temperature is raised, reaction is carried out, and after the reaction is completed, solid-liquid separation is carried out to obtain a solution containing lignin and holocellulose.

[0041] The concentration of the high-efficiency corn stalk separating gemini imidazole bromide in the high-boiling alcohol is 1.0-5.0wt%;

[0042] The solid-liquid ratio of the dissolving solution and corn stalk is 1g:30mL-1g:10mL;

[0043] The high-boiling alcohol is an alcohol with a boiling point of 180℃ or above, and is preferably any one of ethylene glycol, propylene glycol or butylene glycol;

[0044] The corn stalk is dried and crushed into a powder with a mesh size of 20-100, and then treated;

[0045] The corn stalk is treated under nitrogen protection, and the treatment reaction temperature is 100-160℃ and the time is 60-240min;

[0046] The method for treating corn stalk provided by the application has a lignin removal rate of 65% or above and a holocellulose yield of 87% or above; only corn stalk needs to be crushed to realize the treatment, and no complex pretreatment is needed; and the separation can be realized under the conditions of 100-160℃ for 60-240min, the treatment temperature is low, the time is short, the energy consumption is low, and the method is energy-saving and environmentally friendly.

[0047] The high-efficiency corn stalk separating gemini imidazole bromide provided by the application can efficiently dissolve lignin in corn stalk in a high-boiling alcohol without adding an additive, and high-yield and high-quality holocellulose can be obtained, and the active sites of cellulose can be exposed, the crystallinity of cellulose is reduced, and the cellulose becomes a platform material suitable for fermentation to produce sugar, ethanol, lactic acid and the like.

[0048] Compared with the prior art, the present invention is based on the rich charge and strong surface activity of geminimidazole bromide and surfactant, which can effectively destroy the strong hydrogen bonds between cellulose, hemicellulose and lignin in corn straw. Lignin is a complex organic bromide formed by the polymerization of phenylpropane monomers and contains a large number of hydroxyl groups. Therefore, its surface is hydrophilic and can produce strong interactions with geminimidazole bromide and surfactant. The surface of lignin is occupied by a large number of methyl and methylene groups, making it difficult for external non-polar molecules (such as fatty acids) to penetrate, showing hydrophobicity. The use of amphiphilic surfactants can have a strong interaction with them and promote their dissolution. In the treatment of corn straw, using pure high-boiling point alcohol as a solvent can be operated under normal pressure and avoid solvent volatilization. The viscosity of the solution is reduced, the contact between the pretreatment solution and the corn straw is enhanced, and the material transfer capacity is enhanced. It can also reduce the amount of geminimidazole bromide and surfactant used, while avoiding the degradation of cellulose in the corn straw.

[0049] The present invention utilizes gemini imidazole bromide and surfactant [C n -C m -C n The unique multi-charge and polyalkyl structure of im]Br2 strongly interacts with both hydrophilic and hydrophobic lignin, dissolving most of the lignin in ethylene glycol without the need for additives (lignin removal rate exceeding 65%) while dissolving very little hemicellulose and cellulose. Furthermore, the reaction solution is recyclable, with minimal degradation in lignin separation performance after five reuses. This makes the process economical in terms of materials and environmentally friendly, with simple and safe operation and high separation efficiency. High-quality holocellulose can be obtained through solid separation and cleaning, resolving the difficult degradation problem of corn straw. This process is applicable to biomass fermentation for ethanol and lactic acid production, possessing significant scientific and economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 For geminimidazole bromide [C 12 -C2-C 12 im] Br2 H NMR spectrum;

[0051] Figure 2 This is a digital photo of the corn stover sample after [C1-C2-C1im]Br2 pretreatment;

[0052] Figure 3 The raw material is straw and the residue after [C1-C2-C1im]Br2 / ethylene glycol treatment 13 C NMR spectrum. DETAILED DESCRIPTION

[0053] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0054] The test materials and reagents used in the following embodiments, and the like, can be obtained from commercial channels, unless otherwise specified.

[0055] The specific techniques or conditions not specified in the embodiments can be performed according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0056] Embodiment 1

[0057] A preparation method of a high-efficiency corn straw separation gemini imidazole bromide [C1-C2-C1im]Br2, the structural formula of which is as follows.

[0058]

[0059] The specific steps are as follows:

[0060] 55.15 g of methyl imidazole was dissolved in 150 mL of ethanol, then 45.11 g of 1,2-dibromoethane was added, the molar ratio of methyl imidazole to 1,2-dibromoethane was 2.8:1, and the reaction was carried out at 85°C for 36 h under the condition of nitrogen protection. After the reaction was completed, the sample was rotary evaporated, and then recrystallized with petroleum ether for three times; after the product was placed in a desiccator and dried to constant weight, [C1-C2-C1im]Br2 was obtained, and the product yield was 88.1%.

[0061] Embodiment 2

[0062] A preparation method of a high-efficiency corn straw separation gemini imidazole bromide [C 16 -C6-C 16 im]Br2, the structural formula of which is as follows.

[0063]

[0064] The specific steps are as follows:

[0065] 1) Preparation of hexadecyl imidazole: 8.30 g of sodium ethoxide was added to a 500 mL three-necked flask containing 140 mL of ethanol (in a cold water bath); 22.4 g of imidazole was added, followed by the slow dropwise addition of 67.06 g of hexadecyl bromide to achieve a molar ratio of imidazole to hexadecyl bromide of 1.50:1.00. The mixture was reacted at 65° C. under N2 protection for 36 h. After the reaction, the supernatant was removed, the ethanol was removed by rotary evaporation, and the crude product was distilled under reduced pressure to obtain hexadecyl imidazole in a yield of 56.8%.

[0066] 2) Preparation of [C 16 -C6-C 16 im]Br2: 20.8 g of hexadecyl imidazole was dissolved in 60.0 mL of ethanol, and then 7.22 g of 1,6-dibromohexane was added. The ratio of hexadecyl imidazole to 1,6-dibromohexane was controlled to be 2.4:1. The mixture was reacted at 85 °C for 36 h under nitrogen protection. After the reaction was completed, the ethanol was rotary evaporated and the mixture was recrystallized three times with petroleum ether and dried to constant weight to obtain [C 16 -C6-C 16 im]Br2, with a yield of 72.3%.

[0067] Example 3

[0068] An application of geminimidazole bromide for efficient separation of corn stalks, using geminimidazole bromide

[0069] The method for efficiently removing lignin from corn straw using [C1-C2-C1im]Br2 mainly comprises the following steps:

[0070] 1) Grind the dried corn stalks into 60 mesh powder;

[0071] 2) Corn straw and geminimidazole bromide [C1-C2-C1im]Br2 were added to a 250 mL round-bottom flask, and ethylene glycol was added to obtain a [C1-C2-C1im]Br2 concentration of 4.00 wt % and a solid-liquid ratio of 1 g:30 mL to obtain a mixture.

[0072] 3) reacting the mixture at 150° C. for 3 h under nitrogen protection, and obtaining a reaction liquid and a solid residue after separation;

[0073] 4) washing the solid residue twice with anhydrous ethanol, combining the washing solution with the reaction solution, and removing the ethanol by rotary evaporation to obtain a reused reaction solution;

[0074] 5) The solid residue is washed twice with distilled water and dried at 100°C to obtain holocellulose;

[0075] 6) Repeat steps 1) to 5) above 4 times using the reused reaction solution.

[0076] The results of the holocellulose detection show that after 5 treatments with the gemini imidazole bromide [C1-C2-C1im]Br2, the yield of holocellulose is 91.2%, 90.8%, 90.6%, 90.9% and 90.1% respectively, and the lignin removal rate is 76.8%, 76.3%, 75.9%, 75.2% and 75.5% respectively.

[0077] Example 4

[0078] A method for efficiently removing lignin in corn stalks by using a gemini imidazole bromide, which utilizes a gemini imidazole surfactant [C

[0079] The method for efficiently removing lignin in corn stalks by using [C1-C1-C1im]Br2 mainly includes the following steps:

[0080] 1) 18.38 g (0.224 mol) of methyl imidazole was dissolved in 50 mL of ethanol, then 13.90 g (0.080 mol) of 1,2-dibromomethane (MW: 173.84 g / mol) was added, and the reaction was carried out at 65°C for 36 h under nitrogen protection. After the reaction was completed, the sample was rotary evaporated to remove ethanol, then recrystallized with petroleum ether for three times, and finally vacuum dried to obtain [C1-C1-C1im]Br2 with a yield of 68.1%. The structural formula is as follows:

[0081]

[0082] 2) In a 250 mL round-bottom flask, 1.00 g of 60 mesh corn stalks and 1.00 g of gemini imidazole bromide [C1-C1-C1im]Br2 were added, then 25 mL of ethylene glycol was added to obtain a mixture.

[0083] 3) The above mixture was reacted at 120°C for 4 h under nitrogen protection, and then separated to obtain a reaction liquid and a solid residue;

[0084] 4) The solid residue was washed with distilled water for 2 times, and then dried at 100°C to obtain holocellulose;

[0085] The results of the holocellulose detection show that after 5 treatments with the gemini imidazole bromide [C1-C1-C1im]Br2, the yield of holocellulose is 91.2%, 90.8%, 90.6%, 90.9% and 90.1% respectively, and the lignin removal rate is 76.8%, 76.3%, 75.9%, 75.2% and 75.5% respectively.

[0086] Example 5

[0087] A method for efficiently removing lignin in corn stalks by using a gemini imidazole bromide, which utilizes a gemini imidazole surfactant [C 12 -C2-C 12 im]Br2 mainly includes the following steps:

[0088] 1) Dissolve 26.47 g (0.112 mol) of dodecyl imidazole (MW: 236.39 g / mol) in 50 mL of ethanol, then add 7.52 g (0.040 mol) of 1,2-dibromoethane (MW: 187.86 g / mol). Incubate at 85°C under nitrogen for 48 hours. After the reaction, remove the ethanol by rotary evaporation, recrystallize three times from petroleum ether, and dry in vacuo to obtain [C1-C1-C1im]Br2 in an 89.1% yield. Its structural formula is as follows:

[0089]

[0090] 2) Add 60 mesh corn straw and geminimidazole bromide into a 250 mL round bottom flask.

[0091] [C 12 -C2-C 12 im]Br2, then add ethylene glycol to make [C 12 -C2-C 12 im]Br2 concentration is 1.50wt%, and the solid-liquid ratio is 1g:25mL to obtain a mixture.

[0092] 3) reacting the mixture at 130° C. for 3 h under nitrogen protection, and obtaining a reaction liquid and a solid residue after separation;

[0093] 4) The solid residue is washed twice with distilled water and dried at 100°C to obtain holocellulose;

[0094] The test of holocellulose showed that after the treatment with geminimidazole bromide [C 12 -C2-C 12 im]Br2 treatment, the yield of holocellulose was 92.8% and the lignin removal rate was 65.2%.

[0095] Example 6

[0096] An application of geminimidazole bromide for efficient separation of corn stalks, using geminimidazole bromide

[0097] [C 16 -C6-C 16 The method for efficiently removing lignin from corn straw by im]Br2 mainly comprises the following steps:

[0098] 1) Grind the dried corn stalks into 40 mesh powder;

[0099] 2) Add corn straw and geminimidazole bromide [C 16 -C6-C 16 im]Br2, then add ethylene glycol to make [C 16 -C6-C16 The concentration of im]Br2 is 4.00wt%, the solid-liquid ratio is 1g:26mL, and the mixture is obtained.

[0100] 3) The above mixture is reacted at 150℃ for 4h under nitrogen protection, and after separation, the reaction liquid and solid residue are obtained;

[0101] 4) The solid residue is washed with anhydrous ethanol for 2 times, the washing liquid is combined with the reaction liquid, and after the ethanol is removed by rotary evaporation, the reused reaction liquid is obtained;

[0102] 5) The solid residue is washed with distilled water for 2 times, and is dried at 100℃ to obtain the holocellulose;

[0103] 6) The above steps 1)-5) are repeated 4 times by using the reused reaction liquid as the treatment liquid.

[0104] The detection of the holocellulose shows that: after being treated by the gemini imidazole bromide [C 16 -C6-C 16 im]Br2 for 5 times, the yield of the holocellulose is 88.8%, 88.3%, 88.1%, 87.9% and 87.5% respectively, and the lignin removal rate is 69.1%, 68.8%, 68.6%, 68.9% and 68.1% respectively.

[0105] The present application utilizes the multiple charges and multiple alkyl structures of the gemini imidazole bromide [C n -C m -C n im]Br2, which has a strong interaction with the lignin with hydrophilicity and hydrophobicity, can dissolve most of the lignin in ethylene glycol (the lignin removal rate is above 65%) without adding any additive, and can hardly dissolve the hemicellulose and cellulose, and the reaction liquid can be recycled and reused, and after being reused for 5 times, the performance of separating the lignin is almost not decreased, so the present application is relatively economical in material, friendly to the environment, simple and safe to operate, and has high separation efficiency. The holocellulose with high quality can be obtained by solid separation and washing, and the problem that the corn straw is difficult to degrade is solved, and the present application can be applied to the fields of preparing ethanol and lactic acid by biomass fermentation, and has significant scientific significance and economic value.

[0106] The present application provides a kind of system corn straw high-efficiency separation method, by high-efficiency lignin dissolution, to achieve the high-efficiency separation of holocellulose and lignin in corn straw, to obtain high holocellulose yield and quality, and to provide platform material for subsequent biomass preparation of lactic acid.

[0107] The above description of the embodiments is made for the purpose of enabling a person of ordinary skill in the art to understand and use the application. It is obvious that those skilled in the art can easily make various modifications to the embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present application is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present application without departing from the scope of the present application should be within the scope of the present application.

Claims

1. Use of a gemini imidazolium bromide in the separation of corn stover, characterized in that, The specific application method is: The selective lignin dissolving solution formed by mixing the bisimidazole bromide and the high-boiling alcohol is used for treating corn stalks. The bisimidazole bromide is , , , any one of; The high-boiling alcohol is any one of ethylene glycol, propylene glycol and butylene glycol.

2. Use according to claim 1, characterized in that, The concentration of the bisimidazole bromide for separating corn stalks in the high-boiling alcohol is 1.0-5.0wt%; the solid-liquid ratio of the dissolving solution and the corn stalks is 1g:30mL-1g:10mL.

3. Use according to claim 1 or 2, characterized in that, The corn stalks are treated under nitrogen protection, the treatment reaction temperature is 100-160℃, and the time is 60-240min.

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