A process for the preparation of 1,4-cyclohexanediol from lignocellulose

Abstract

The present application mainly aims to provide a method for preparing 1,4-cyclohexanediol from lignocellulose, which comprises the following steps: lignocellulose raw materials and a first solvent are mixed and added into a high-pressure reaction kettle to perform a first reaction, and a first product is obtained through separation and purification; the first product is placed in a second solvent, hydrogen peroxide and sodium hydroxide solution are added and stirred to perform a second reaction; a second product is mixed with a third solvent and a first catalyst to perform a third reaction under the condition of no external hydrogen to obtain 1,4-cyclohexanediol. The yield of lignin monomers in the first step can reach 9.2-21.1 wt%, the conversion rate of the oxidation reaction of hydroxybenzaldehyde compounds in the second step reaches 90%, and the yield of 1,4-cyclohexanediol in the third step can reach 80%. In the catalytic system used in the present application, a commercially available base metal catalyst is used, and no external hydrogen source is required during the reaction process, the product yield is high, and a green and sustainable method for producing 1,4-cyclohexanediol is provided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high-value utilization of biomass, and particularly relates to a method for preparing 1,4-cyclohexanediol from lignocellulose. BACKGROUND

[0002] 1,4-cyclohexanediol is a high-value-added compound with unique cis / trans isomerism, and has great potential for application in chemical synthesis, medical treatment and materials. In the aspect of materials, it can be used for synthesizing polycarbonate, polyether and polyester materials; and it can also be used as a precursor for synthesizing drugs, such as phenylcyclohexylcarboxamide and dihydroartemisinin, by functionalization of the two hydroxyl groups.

[0003] Current methods for synthesizing 1,4-cyclohexanediol mainly rely on using benzene from fossil resources, modifying and oxidizing benzene to obtain hydroquinone, and then preparing 1,4-cyclohexanediol by hydrogenation of hydroquinone. Existing reports all use fossil resources as raw materials, and there are problems such as complex synthesis steps, many harmful waste in the reaction, and harsh reaction conditions. Therefore, it is of great significance to seek a green and sustainable method for preparing 1,4-cyclohexanediol.

[0004] Lignocellulose, which is the most abundant renewable biomass resource on earth, is mainly composed of cellulose, lignin and hemicellulose, and has the characteristics of renewability and "carbon neutrality". Its components can be converted into energy, chemicals and materials complementary to petroleum after separation. Among them, lignin, as the only renewable aromatic polymer in nature, has a unique phenylpropane structural unit, and therefore can be used to prepare monomolecular phenol compounds, which can be used to synthesize various chemicals. SUMMARY

[0005] The main purpose of the present application is to provide a method for preparing 1,4-cyclohexanediol from renewable lignocellulose raw materials, and to solve the technical problem of providing a green and sustainable reaction system using catalytic conversion from lignocellulose raw materials. The present application overcomes the defects in the prior art that a large amount of fossil resources are used as raw materials, a multi-step synthesis method is used to synthesize the precursor hydroquinone, and the product can only be successfully prepared in a high-temperature and high-pressure hydrogen atmosphere. The reaction conditions of the present application are mild, green and renewable lignocellulose is used as raw material, lignin is preferentially oxidized and degraded to obtain high-yield lignin monomers, and then the lignin monomers are converted to obtain high-yield cyclohexanediol. No external hydrogen is needed in the reaction, the process is green and environmentally friendly, the product separation and purification are convenient, and the production process of 1,4-cyclohexanediol is more suitable for green and sustainable production.

[0006] The technical scheme of the present application is as follows: a method for preparing 1,4-cyclohexanediol from lignocellulose comprises the following steps:

[0007] (1) wood fiber raw material and first solvent are mixed and added into a high-pressure reaction kettle to perform a first reaction, and a first product is obtained through separation and purification; the first solvent is sodium hydroxide solution, and the mass concentration of the sodium hydroxide solution ranges from 3% to 10%;

[0008] (2) the first product is placed in a second solvent, hydrogen peroxide and sodium hydroxide solution are added, and a second reaction is performed through stirring, and a second product is obtained through separation and purification; the second solvent is deionized water;

[0009] (3) the second product is mixed with a third solvent and a first catalyst and added into a reaction kettle, and a third reaction is performed without introducing external hydrogen, and a hydrogen deoxidation reaction is completed to obtain 1,4-cyclohexanediol.

[0010] The technical scheme of the present application is as follows: a method for preparing 1,4-cyclohexanediol from lignocellulose comprises the following steps:

[0011] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose comprises the following steps:

[0012] (1) synthetic air is used for blowing for 3 to 5 times, synthetic air or oxygen is filled to a pressure of 1 to 3 MPa, and lignin monomers are obtained through stirring reaction at a temperature of 140 to 180 ℃ for 1 to 12 h to degrade lignin;

[0013] (2) the separation and purification comprises: the product after degradation of the raw material is filtered to perform solid-liquid separation, liquid components are extracted using ethyl acetate to obtain an ethyl acetate solution rich in lignin, the ethyl acetate is evaporated to obtain an oily lignin component, and then the first product is obtained through column chromatography.

[0014] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose comprises the following steps:

[0015] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose comprises the following steps:

[0016] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose, the mass ratio of the lignocellulose raw material to the first solvent is 1:25-1:50.

[0017] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose, the molar ratio of the first product to hydrogen peroxide is 1:1.2.

[0018] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose, the ratio of the second product to the first catalyst is 1:0.5-1:1.

[0019] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose, the structure of the first product is as follows:

[0020]

[0021] wherein R1 is at least one of -H or -OCH3;

[0022] The structure of the second product is as follows:

[0023]

[0024] wherein R1 is at least one of -H or -OCH3.

[0025] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose, wherein, in the third reaction, only Raney nickel is used as a hydrogen donor to provide hydrogen and complete the benzene ring hydrogenation of the second product.

[0026] Preferably, the method for preparing 1,4-cyclohexanediol from lignocellulose, the lignocellulose raw material is at least one of poplar, pine or eucalyptus.

[0027] By the above technical solution, the method for preparing 1,4-cyclohexanediol from lignocellulose has at least the following advantages:

[0028] (1) The catalyst used in the application is a commercially available base metal catalyst, which is cheap, easy to obtain and has high activity. The raw material used in the application is derived from green renewable biomass, and the reaction catalytic system has mild conditions, avoiding the use of high-pressure hydrogen, and is easy to expand production.

[0029] (2) The three-step method for preparing 1,4-cyclohexanediol from lignocellulose has the following advantages: in the first step, the yield of lignin monomer can reach 8-21wt%; in the second step, the yield of 2-methoxyhydroquinone can reach 80-90wt%; and in the third step, the yield of 1,4-cyclohexanediol can reach 55-82wt%.

[0030] In summary, compared with the traditional process of preparing 1,4-cyclohexanediol from benzene in fossil fuel through alkylation and oxidation, the present application uses lignin in lignocellulose as raw material, the reaction condition is relatively mild, the yield and selectivity of the product are better, and the separation and purification method is relatively simple. Therefore, the method of the present application is more in line with the actual needs of chemical production, and has broad production prospects.

[0031] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application and can be implemented according to the content of the specification, the following will be described in detail as follows. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 For Example 1, the technical route of preparing 1,4-cyclohexanediol from pine wood.

[0033] Figure 2 For Example 1, the gas chromatogram analysis spectrum of the lignin component obtained by degradation of pine wood.

[0034] Figure 3 For Example 2, the mass spectrum of the compound analyzed by gas chromatography of the second product component obtained by the second reaction.

[0035] Figure 4 For Example 2, the gas chromatogram analysis spectrum of the second product component obtained by the second reaction.

[0036] Figure 5 For Example 3, the gas chromatogram analysis spectrum of 1,4-cyclohexanediol obtained by the third reaction.

[0037] Figure 6 For Example 3, the mass spectrum of the compound analyzed by gas chromatography of the obtained 1,4-cyclohexanediol. DETAILED DESCRIPTION

[0038] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined object of the application, the following will be described in detail as follows in combination with the drawings and the preferred embodiments, the method for preparing 1,4-cyclohexanediol from lignocellulose and its specific implementation, structure, characteristics and effects according to the present application.

[0039] The present application provides a method for preparing 1,4-cyclohexanediol from lignocellulose, which comprises the following steps:

[0040] (1) In-situ degradation of lignin in lignocellulose raw materials under high pressure air or oxygen atmosphere: The lignin raw material is mixed with a first solvent to carry out a first reaction, and the first product is obtained after separation and purification. The first solvent is a sodium hydroxide solution with a mass concentration ranging from 3% to 10%.

[0041] Specifically, lignocellulose raw materials and a first solvent are added to a reaction vessel to carry out a first reaction. The first reaction conditions are: synthesis air or oxygen at a pressure of 1–3 MPa, a reaction temperature of 140–180°C, and stirring for 1–12 hours to allow lignin to fully degrade. The lignin monomer is then obtained through separation and purification. The obtained lignin monomer is dissolved in an organic solvent and analyzed by gas chromatography.

[0042] Qualitative analysis by GC-MS followed by quantitative analysis by FID yields the component composition and content of the obtained lignin monomers. The lignin monomers obtained by gas chromatography include, but are not limited to, 3-methoxy-4-hydroxybenzaldehyde and 3,5-dimethoxy-4-hydroxybenzaldehyde.

[0043] The separation and purification in this step refers to: adjusting the pH of the lignin degradation product to acidic by adding hydrochloric acid, filtering to achieve solid-liquid separation, extracting the liquid phase component with ethyl acetate to obtain a lignin-rich ethyl acetate solution, distilling off the ethyl acetate to obtain an oily lignin component, and then separating it by column chromatography to obtain the first product. The first product includes 3-methoxy-4-hydroxybenzaldehyde and 3,5-dimethoxy-4-hydroxybenzaldehyde. The composition of the first product will vary depending on the lignin raw material used in the reaction; the composition of the first product is determined based on the actual lignin raw material used.

[0044]

[0045] In this step, the mass ratio of the wood fiber raw material to the first solvent is 1:25 to 1:50.

[0046] The lignocellulose raw material mentioned above is lignocellulose containing lignin. Lignocellulose raw materials in this article include, but are not limited to, pine, poplar, eucalyptus, and other raw materials rich in cellulose, hemicellulose, and lignin.

[0047] (2) The first product is placed in a second solvent, and hydrogen peroxide and sodium hydroxide solution are added. The mixture is stirred to carry out a second reaction. The second product is obtained by separation and purification. The second solvent is deionized water.

[0048] Specifically, the lignin monomer obtained in step 1 is added to water, and 10% NaOH solution is added dropwise to adjust the pH to 8-10. Then, 3% H2O2 solution and 10% NaOH solution are added dropwise, keeping the reaction pH at 8-10 throughout the process, and the reaction is stirred for 0.5-2 hours. The separation and purification process includes: extracting the mixed solution after the reaction with ethyl acetate to obtain the second product.

[0049] In this step, the second reaction involves one or a mixture of two of the lignin derivatives 3-methoxy-4-hydroxybenzaldehyde and 3,5-dimethoxy-4-hydroxybenzaldehyde. After the reaction, the corresponding products are 2-methoxyhydroquinone and 2,6-dimethoxyhydroquinone.

[0050] The molar ratio of the first product to hydrogen peroxide is 1:1.2.

[0051] The main chemical reaction formula for this reaction is:

[0052]

[0053] Where R is either -H or -OCH3.

[0054] (3) The second product is mixed with the third solvent and the first catalyst and added to the reactor. No external hydrogen gas is required to carry out the third reaction and complete the hydrogenation reaction to obtain 1,4-cyclohexanediol.

[0055] Specifically, the second product obtained from reaction 2 is placed in a reaction vessel, mixed with the first catalyst and the third solvent, and stirred at a temperature of 160℃~220℃ for 1-12 hours to obtain the product.

[0056] The ratio of the second product to the first catalyst is 1:0.5 to 1:1.

[0057]

[0058] The specific embodiments of the present invention will be described in further detail below with reference to examples, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention still fall within the scope of protection of the present invention.

[0059] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0060] Example 1

[0061] (1) Using Pinus tabuliformis as the wood fiber raw material, lignin depolymerization was carried out. The specific steps are as follows:

[0062] Weigh 0.5g of pine wood powder (40-60 mesh), 1.62g of sodium hydroxide, and 20ml of water, add them to a 50ml stainless steel reactor, purge with 1MPa of synthetic air, heat the hydrothermal reactor to the required temperature (160℃ in this embodiment), and after the reaction is complete (the reaction time in this embodiment is 2h), cool the reaction to room temperature.

[0063] The product after the reaction was adjusted to acidic pH with hydrochloric acid, and then transferred to a vacuum filtration flask for solid-liquid separation. The resulting liquid phase was extracted with ethyl acetate (3×10 ml), and 20 μl of n-decane was added to the extracted solution as an internal standard. The solution was then analyzed by gas chromatography.

[0064] Gas chromatography conditions: GC7890A gas chromatograph, FID detector, capillary column (HP-5), temperature programmed, starting column temperature 40℃, hold for 3 min, then ramp to 300℃ at a rate of 10℃ / min and hold for 2 min.

[0065] Table 1: Analysis results of pine wood degradation products at different reaction times

[0066]

[0067] The yields described in Table 1 refer to the percentage of a single compound in the lignin contained in the feedstock.

[0068] As can be seen from the results in Table 1, the technical solution of Example 1 under the reaction conditions yields a relatively simple monomer structure and a highly selective first product.

[0069] Example 2:

[0070] The Dakin reaction is based on the first product (3-methoxy-4-hydroxybenzaldehyde). The specific steps are as follows:

[0071] Weigh 0.15g of 3-methoxy-4-hydroxybenzaldehyde into a round-bottom flask, add 5ml of deionized water, add 10% wt NaOH solution in small amounts several times to adjust the pH to 8-9, add 1.4ml of 3% H2O2 solution in 10-20 portions, adjusting the pH with NaOH solution during the dropwise addition to keep the pH at 8-9, and stir the reaction for 40min.

[0072] After the reaction was complete, the reaction solution was extracted with ethyl acetate (3 × 10 ml). The extracted ethyl acetate phase was analyzed by gas chromatography.

[0073] Gas chromatography conditions: GC7890A gas chromatograph, FID detector, capillary column (HP-5), temperature programmed, starting column temperature 40℃, hold for 3 min, then ramp to 300℃ at a rate of 10℃ / min and hold for 2 min.

[0074] As can be seen from the gas chromatogram of the reaction, 3-methoxy-4-hydroxybenzaldehyde was completely converted to 2-methoxyhydroquinone after the Dakin oxidation reaction. Calculations show that the yield of 2-methoxyhydroquinone in this example reached 90%, proving that this step can achieve the conversion of 3-methoxy-4-hydroxybenzaldehyde in high yield.

[0075] Example 3:

[0076] Results of the preparation of 1,4-cyclohexanediol from the hydrogenation and deoxygenation of 2-methoxyhydroquinone at different reaction times

[0077] Weigh 0.1g of 2-methoxyhydroquinone, 0.1g of Raney nickel catalyst, and 3ml of isopropanol, add them to the reaction vessel, heat the reaction vessel to the required temperature (the reaction temperature in this example is 200℃), wait for the reaction to finish (the reaction time in this example is 2h), and cool the reaction vessel to room temperature.

[0078] The catalyst was attracted by a magnet, and the resulting solution was transferred to a volumetric flask, diluted to 10 ml with ethanol, and analyzed by gas chromatography.

[0079] Gas chromatography conditions: GC7890A gas chromatograph, FID detector, capillary column (HP-5), temperature programmed, starting column temperature 40℃, hold for 3 min, then ramp to 300℃ at a rate of 10℃ / min and hold for 2 min.

[0080] Table 2: Results of the preparation of 1,4-cyclohexanediol from the hydrogenation-deoxygenation reaction of 2-methoxyhydroquinone at different reaction times

[0081]

[0082] The conversion rate calculation method described in the table is as follows: The selective calculation method is: mass of single compound / mass of all products × 100%.

[0083] As shown in Table 2, the conversion rate of 2-methoxyhydroquinone increased with time. After 3 hours, complete conversion of 2-methoxyhydroquinone was achieved. However, the yield of 1,4-cyclohexanediol could be further increased. This is because the intermediate generated in the reaction was not completely converted. With increasing time, the intermediate gradually converted to 1,4-cyclohexanediol, achieving a high yield of 1,4-cyclohexanediol. The reaction mechanism is explained below:

[0084]

[0085] As can be seen from the above reaction mechanism, the reaction proceeds in two steps. The first step is reaction one, in which isopropanol undergoes dehydrogenation using Raney nickel as a catalyst, and the secondary alcohol in isopropanol is dehydrogenated to produce ketone and active hydrogen. The second step is the hydrogenation and deoxygenation reaction of 2-methoxyhydroquinone. The active hydrogen obtained from reaction one serves as the hydrogen source and directly participates in the hydrogenation reaction using Raney nickel as a catalyst. 2-methoxyhydroquinone undergoes demethoxylation and benzene ring hydrogenation reactions in sequence, and the final product 1,4-cyclohexanediol is obtained through two pathways.

[0086] Example 4:

[0087] Results of the preparation of 1,4-cyclohexanediol from the hydrogenation and deoxygenation of 2,6-dimethoxyhydroquinone at different reaction times

[0088] Weigh 0.1g of 2,6-dimethoxyhydroquinone, 0.1g of Raney nickel catalyst, and 3ml of isopropanol, add them to the reaction vessel, heat the reaction vessel to the required temperature (the reaction temperature in this example is 200℃), and after the reaction is completed (the reaction time in this example is 2h), cool the reaction vessel to room temperature.

[0089] The catalyst was attracted by a magnet, and the resulting solution was transferred to a volumetric flask, diluted to 10 ml with ethanol, and analyzed by gas chromatography.

[0090] Gas chromatography conditions: GC7890A gas chromatograph, FID detector, capillary column (HP-5), temperature programmed, starting column temperature 40℃, hold for 3 min, then ramp to 300℃ at a rate of 10℃ / min and hold for 2 min.

[0091] Table 3: Results of the preparation of 1,4-cyclohexanediol from the hydrogenation-deoxygenation reaction of 2,6-dimethoxyhydroquinone at different reaction times

[0092]

[0093] The above three-step method for preparing 1,4-cyclohexanediol from lignocellulose, using 0.5g of pine wood (30% lignin content) as raw material, achieves the following yields: 9.2-21.1 wt% lignin monomer in the first step, 90% conversion rate of hydroxybenzaldehyde compounds in the second step, and 80% yield of 1,4-cyclohexanediol in the third step. Using pine wood as raw material, this method can produce approximately 21mg of 1,4-cyclohexanediol.

[0094] The technical features in the claims and / or specification of this invention can be combined, and the combination is not limited to the combinations obtained through reference in the claims. Technical solutions obtained by combining the technical features in the claims and / or specification are also within the scope of protection of this invention.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing 1,4-cyclohexanediol from lignocellulose, characterized in that, Includes the following steps: (1) The wood fiber raw material and the first solvent are mixed and added to a high-pressure reactor for a first reaction. The first product is obtained by separation and purification. The first solvent is a sodium hydroxide solution with a mass concentration range of 3% to 10%. The first reaction conditions are: synthesis air or oxygen at a pressure of 1 to 3 MPa, a reaction temperature of 140 to 180°C, and stirring for 1 to 12 hours. The structural formula of the first product is as follows: Wherein, R1 is at least one of -H or -OCH3; (2) The first product is placed in a second solvent, and hydrogen peroxide and sodium hydroxide solution are added. The mixture is stirred to carry out a second reaction. The second product is obtained by separation and purification. The second solvent is deionized water. The structural formula of the second product is as follows: Wherein, R1 is at least one of -H or -OCH3; (3) The second product is mixed with the third solvent and the first catalyst and added to the reactor. No external hydrogen gas is required to carry out the third reaction and complete the hydrogenation reaction to obtain 1,4-cyclohexanediol. During the third reaction, only the Raney nickel / isopropanol system is used as the hydrogen source to provide hydrogen gas and complete the benzene ring hydrogenation reaction of the second product.

2. The method for preparing 1,4-cyclohexanediol from lignocellulose according to claim 1, characterized in that, The first reaction includes the following steps: (1) Purge with synthetic air 3 to 5 times, fill with synthetic air or oxygen to a pressure of 1 to 3 MPa, and then stir at a temperature of 120 to 200°C for 1 to 12 hours to degrade lignin and obtain lignin monomers. (2) The separation and purification process includes: filtering the product after the raw material degradation for solid-liquid separation, extracting the liquid phase component with ethyl acetate to obtain an ethyl acetate solution rich in lignin, distilling off the ethyl acetate to obtain an oily lignin component, and then separating the first product by column chromatography.

3. The method for preparing 1,4-cyclohexanediol from lignocellulose according to claim 1, characterized in that, The reaction conditions for the second reaction are as follows: first, add 10% NaOH solution dropwise to adjust the pH to 8-10, then add 3% H2O2 solution and 10% NaOH solution dropwise, keeping the reaction pH at 8-10 throughout, and stirring the reaction for 0.5-2 hours. The separation and purification process includes: extracting the mixed solution after the reaction with ethyl acetate.

4. The method for preparing 1,4-cyclohexanediol from lignocellulose according to claim 1, characterized in that, The third reaction conditions are: temperature 160℃~220℃, reaction time 1-12h, to obtain 1,4-cyclohexanediol.

5. The method for preparing 1,4-cyclohexanediol from lignocellulose according to claim 1, characterized in that, The mass ratio of the wood fiber raw material to the first solvent is 1:25 to 1:

50.

6. The method for preparing 1,4-cyclohexanediol from lignocellulose according to claim 1, characterized in that, The molar ratio of the first product to hydrogen peroxide is 1:1.

2.

7. The method for preparing 1,4-cyclohexanediol from lignocellulose according to claim 1, characterized in that, The ratio of the second product to the first catalyst is 1:0.5 to 1:

1.

8. The method for preparing 1,4-cyclohexanediol from lignocellulose according to claim 1, characterized in that, The lignocellulose raw material is at least one of poplar, pine, or eucalyptus.

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