Method for continuously preparing 2,2,5,5-tetramethyltetrahydrofuran and catalyst used therefor

Abstract

A method for continuously preparing 2,2,5,5-tetramethyltetrahydrofuran and a catalyst used therefor. In the method for continuously preparing 2,2,5,5-tetramethyltetrahydrofuran, 2,5-dimethyl-2,5-hexanediol is subjected to a dehydration reaction in the presence of the catalyst in a reactor at a temperature of 50-200°C. The catalyst for synthesizing 2,2,5,5-tetramethyltetrahydrofuran can catalyze the reaction of 2,5-dimethyl-2,5-hexanediol at a higher conversion rate, and the reaction has very high selectivity of up to 99% or more. The catalyst used therefor has good stability and a long service life, so that the production energy consumption is further reduced, the production cost is reduced, and industrial production is easy to realize.

Description

A continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran and catalyst used therein Technical Field

[0001] The present application relates to the field of chemical synthesis, and in particular to a method for continuously preparing 2,2,5,5-tetramethyltetrahydrofuran by dehydrating 2,5-dimethyl-2,5-hexanediol, a catalyst used in the method, and a preparation method thereof. Background Art

[0002]

[0003] 2,2,5,5-Tetramethyltetrahydrofuran (CAS number: 15045-43-9, abbreviated as TMTHF) is a colorless liquid with a freezing point of -92°C, a boiling point of 112°C, a relative density of 0.811 at 25°C, a refractive index of 1.409 at 19°C, and a flash point of 3.9°C. It is an important organic intermediate and an excellent solvent. Due to its low density, low boiling point, and low ETN value of 0.111, it has the potential to replace traditional hydrocarbon solvents such as toluene and hexane, and is widely used as a new solvent in industrial production. Although TMTHF is an ether by definition because it contains an RO-R' group (where R and R' are alkyl groups), it does not have the peroxide-forming potential of other ethers such as THF or 2-MeTHF. This is because there is no proton at the α-position relative to the ether oxygen. The α-proton in traditional ethers is easily removed by low-energy light, forming free radicals. Oxygen from the air can react with the free radicals to form explosive peroxides. The rate of peroxide formation potential in ethers increases with increasing radical stability: primary α-carbon << secondary α-carbon < tertiary α-carbon. Because TMTHF contains two quaternary ether carbons and no α-protons, the potential for peroxide formation is eliminated. This combination of highly favorable properties makes TMTHF a rare low-boiling, low-polarity molecule that has no peroxide formation potential and can be readily produced from biomass.

[0004] There are literature reports on the dehydration of 2,5-dimethyl-2,5-hexanediol (as shown above) to synthesize TMTHF, such as Denney et al. in J.Org.Chem.1984,49,p2831, which discloses a method for preparing TMTHF, comprising contacting 2,5-dimethyl-2,5-hexanediol with pentaethoxyphosphorane as a catalyst in DCM as a solvent. Vlad and Ungur disclosed a method for preparing TMTHF in Synthesis 1983,1983,p216, which comprises contacting 2,5-dimethyl-2,5-hexanediol with trimethylchlorosilane as a catalyst in benzene as a solvent. Gillis & Beck disclosed a method for preparing TMTHF in J.Org.Chem.1963,28,p1388, which comprises contacting 2,5-dimethyl-2,5-hexanediol with DMSO as a solvent and a catalyst. Yamaguchi et al., in Catal. Today 2012, 185, p302, disclose a method for preparing TMTHF, which involves contacting 2,5-dimethyl-2,5-hexanediol with hot liquid water in the presence of high-pressure carbon dioxide as both a catalyst and a solvent. In fact, in all of the aforementioned methods, the yield of TMTHF does not exceed 80% in the presence of a solvent. Solvent-free methods, however, achieve higher yields. DE700036C discloses a method for preparing TMTHF, which involves contacting 2,5-dimethyl-2,5-hexanediol with potassium pyrosulfate in the absence of a solvent, achieving a yield of 94.6%. Olah et al., in Synthesis 1981, p474, used Nafion-H as a catalyst in the synthesis of TMTHF from 2,5-dimethyl-2,5-hexanediol as a precursor. The advantage of a solid catalyst such as Nafion-H is that it can be easily separated from the reaction mixture, resulting in a 94% yield. CN 109790134 A discloses the synthesis of TMTHF by the dehydration reaction of 2,5-dimethyl-2,5-hexanediol using H-Beta and various molecular sieve catalysts, and compares the reaction results. It is found that compared with other molecular sieves (HY, H-ZSM5) under the same conditions, H-Beta has higher reaction activity and product selectivity.

[0005] Currently, the existing technology often uses a batch reaction, which is simple to operate but prone to carbon deposition due to difficulty in controlling residence time, resulting in low yields and high production costs. Another method is a continuous reaction, represented by fixed-bed / fluidized-bed reactors, using solid acid catalysts. Its characteristics are that the reaction proceeds continuously and the residence time can be precisely controlled, achieving high yields and ensuring safety. This reaction can be catalyzed by molecular sieves such as H-Beta, HY, and H-ZSM5. However, the surface acidity and alkalinity of the catalyst are generally controlled by controlling the content of the various oxide components and the synthesis process conditions such as crystallization temperature, crystallization time, and aging temperature. These methods make it difficult to precisely control the surface acidity and alkalinity of the catalyst. The catalyst synthesis process generally requires the use of highly toxic templates, and the carbon deposits generated during the reaction process can easily clog the surface of the catalyst active sites, causing catalyst deactivation. Continuous operation also requires certain catalyst stability requirements, and frequent catalyst regeneration increases the operational difficulty to a certain extent.

[0006] Therefore, how to improve the stability of solid acid catalysts while maintaining high selectivity for TMTHF in the product is a difficult problem. Biomass carbon materials, due to their rich surface pore structure and easily regulated surface groups, often exhibit catalytic activity and product selectivity different from traditional metal oxides. In addition, the surface properties of the material can also be regulated by doping the carbon material with heteroelements. Through this method, the catalyst can be rationally designed and regulated according to the active sites required for different reactions, and efficient catalysts that catalyze specific reactions with high selectivity can be synthesized in a targeted manner. This type of catalyst has the advantages of a wide range of raw material sources, renewability, easy regulation of catalyst surface properties, and no use of metal components, and is gradually attracting attention. Summary of the Invention

[0007] In response to the problems existing in the above-mentioned prior art, the object of the present invention is to provide a continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran, which uses 2,5-dimethyl-2,5-hexanediol as a raw material to continuously dehydrate the raw material to prepare 2,2,5,5-tetramethyltetrahydrofuran, as well as a catalyst used in the method and a method for preparing the catalyst, wherein the catalyst can operate stably for a long time.

[0008] To achieve the above objectives, according to one aspect of the present invention, an object of the present invention is to provide a continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran, wherein the method comprises dehydrating 2,5-dimethyl-2,5-hexanediol in a reactor at 50°C to 200°C in the presence of a catalyst.

[0009] According to one embodiment of the present application, the reactor in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran is selected from any one of a continuous stirred tank reactor, a plug flow reactor, a fixed phase reactor and a fluidized bed reactor, or can be a mixed reactor of two or more of these reactors connected; preferably a fixed bed reactor;

[0010] According to one embodiment of the present application, the catalyst may be in the form of strips, columns or sheets;

[0011] According to one embodiment of the present application, the dehydration reaction temperature may preferably be 80°C to 150°C;

[0012] According to one embodiment of the present application, the dehydration reaction can be carried out under one or more of a nitrogen atmosphere, a helium atmosphere or an argon atmosphere;

[0013] According to one embodiment of the present application, the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran can be carried out at a reaction pressure of 0.1 MPa to 4 MPa, preferably 0.1 MPa to 2 MPa; or at a reaction pressure of normal pressure to 4 MPa, preferably normal pressure to 2 MPa;

[0014] According to one embodiment of the present application, the 2,5-dimethyl-2,5-hexanediol can be reacted in the absence of a solvent or in the presence of a solvent, and the solvent is one or more selected from tetrahydrofuran, acetonitrile and 1,4-dioxane, preferably tetrahydrofuran or 1,4-dioxane;

[0015] According to one embodiment of the present application, the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran can be carried out in 0.05h -1 ~5h -1 , preferably 0.1h -1 ~3h -1 The reaction was carried out at a space velocity of .

[0016] According to one embodiment of the present application, the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran further comprises activating the catalyst prior to the reaction. Specifically, prior to the reaction, the catalyst is heated to an activation temperature of 300°C to 500°C and maintained for 1 to 6 hours. Preferably, the activation temperature can be 300°C to 400°C.

[0017] According to one embodiment of the present application, the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran further includes post-reaction treatment. Specifically, the reaction product is condensed and subjected to gas-liquid separation, followed by rectification. The condensation, gas-liquid separation, and rectification are conventional methods and conditions for separating 2,2,5,5-tetramethyltetrahydrofuran and byproducts in the art and are not further described here.

[0018] According to another aspect of the present invention, another object of the present invention is to provide a catalyst used in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran, wherein the catalyst is prepared by a method comprising the following steps:

[0019] (1) The biomass raw material is crushed by a pulverizer, and then added to a ball mill together with a solid acid catalyst to form a fine powder, which is then added to a reactor, distilled water is added, the reactor is sealed, and then heated to perform a hydrolysis reaction. After the reaction is completed, the temperature is lowered, the pressure is released, and the filtrate is filtered under reduced pressure, and the filtrate is distilled and concentrated to obtain a concentrated solution;

[0020] (2) adding the acid solution to the concentrated solution in step (1) under vigorous stirring, mixing uniformly, adding chitosan, transferring the mixture into a hydrothermal kettle, performing hydrothermal treatment, cooling, and releasing the pressure, washing the resulting product with anhydrous ethanol and deionized water, respectively, and drying the product to obtain a doped carbon material;

[0021] (3) adding alkali to the doped carbon material obtained in step (2), stirring and mixing, placing in a tube furnace, heating under an inert gas atmosphere for carbonization treatment, cooling after carbonization, washing the obtained material with distilled water until the filtrate is neutral, and drying;

[0022] (4) The doped carbon material obtained in step (3) is mixed and stirred evenly with an acid or an oxidant, and subjected to heat treatment. After the treatment, the temperature is lowered and filtered, and the material is washed with distilled water until the filtrate is neutral, and then dried.

[0023] Furthermore, in step (1), the biomass material is selected from one or more of corn cobs, corn stalks, sawdust, peanut shells, and bamboo shoots; preferably one or more of corn cobs, corn stalks, and peanut shells, and more preferably one or more of corn cobs and corn stalks;

[0024] Furthermore, the solid acid catalyst is selected from one or more of silicon dioxide, γ-alumina, zirconium dioxide, cerium dioxide, tungsten trioxide, niobium pentoxide, zeolite molecular sieve, and ion exchange resin;

[0025] Furthermore, the solid acid catalyst is preferably one or more of silicon dioxide, γ-alumina, tungsten trioxide, niobium pentoxide, zeolite molecular sieve, and ion exchange resin; more preferably one or more of γ-alumina, zeolite molecular sieve, and ion exchange resin;

[0026] Furthermore, the zeolite molecular sieve is selected from one or more of HZSM5, HZSM11, HY, Hβ, HMOR, and SAPO-34.

[0027] Furthermore, in step (1):

[0028] The dried biomass raw materials were crushed by a pulverizer, and then added to a ball mill together with a solid acid catalyst to form a fine powder of 200-400 mesh. The reactor was sealed and heated to 150-250°C.

[0029] Furthermore, the mass ratio of the distilled water to the biomass raw material is 50:1-2:1; preferably 20:1-5:1;

[0030] Furthermore, the hydrolysis reaction temperature is 120-250°C; preferably 150-220°C; more preferably 160-210°C;

[0031] Furthermore, the hydrolysis reaction time is 4-10 hours; preferably 4-6 hours;

[0032] Furthermore, the mass concentration of the concentrated solution is 10%-30%, preferably 10%-20%.

[0033] Furthermore, in step (2):

[0034] The acid is selected from one or more of formic acid, acetic acid, propionic acid, and hydrochloric acid;

[0035] The mass concentration of the acid solution is 1%-30%, preferably 3%-10%;

[0036] The mass ratio of the acid solution to the concentrated solution is 1:1-10:1; preferably 1:1-5:1;

[0037] The mass ratio of the chitosan to the concentrated solution is 1:10-1:100;

[0038] The hydrothermal treatment temperature is 160-220°C; preferably 180-210°C;

[0039] The hydrothermal treatment time is 4-20 hours; preferably 5-10 hours;

[0040] The obtained product was washed with anhydrous ethanol and deionized water three times respectively, and dried at 110 °C for 12 h.

[0041] Furthermore, in step (3):

[0042] The base is selected from one or more of sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, and potassium ethoxide;

[0043] The mass ratio of the base to the doped carbon material is 1:1-10:1; preferably 1:1-5:1; more preferably 1:1-3:1;

[0044] The inert gas used in the carbonization process is selected from one or more of nitrogen, helium, and argon; preferably one or more of nitrogen and argon.

[0045] The carbonization treatment temperature is 300-700°C, and the treatment time is 4-20 hours; after the carbon is washed, it is dried at 110°C for 12 hours.

[0046] Furthermore, in step (4):

[0047] The acid is one or more of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, and phosphoric acid;

[0048] The oxidant is one or more of hydrogen peroxide with a mass concentration of 30wt% and sodium hypochlorite with an effective chlorine content of 6%;

[0049] The mass ratio of the acid to the doped carbon material is 1:1-10:1;

[0050] The mass ratio of the oxidant to the doped carbon material is 1:1-10:1.

[0051] The heating treatment temperature is 60-90°C;

[0052] The heating treatment time is 4-10h;

[0053] After washing, the mixture was dried at 110°C for 12 h.

[0054] Furthermore, after the reaction in step (1) is completed, the filter cake obtained by suction filtration contains the solid acid catalyst, and the filter cake is calcined at 350-550° C. in an air atmosphere for 3-6 hours to remove organic matter to obtain the solid acid catalyst, and the obtained solid acid catalyst can be repeatedly recycled.

[0055] According to another aspect of the present invention, another object of the present invention is to provide use of the catalyst in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to the present invention. Beneficial effects

[0056] The catalyst provided in the present application for synthesizing 2,2,5,5-tetramethyltetrahydrofuran can catalyze the reaction of 2,5-dimethyl-2,5-hexanediol with a high conversion rate, and the reaction has a very high selectivity (up to 99% or more). The catalyst used has good stability and a long life, thereby further reducing production energy consumption, reducing production costs, and facilitating industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG1 is a schematic diagram of a 2,2,5,5-tetramethyltetrahydrofuran synthesis reaction device according to one embodiment of the present application.

[0058] FIG2 is a temperature-programmed desorption test result of ammonia adsorption performance of the catalyst products of Preparation Example 6, Comparative Example 1 and Comparative Example 2.

[0059] FIG3 is a graph showing the reaction stability test results in Reaction Example 2.

[0060] FIG4 is a graph showing the reaction stability test results in Reaction Example 3.

[0061] FIG5 is a graph showing the reaction stability test results in Reaction Example 6.

[0062] FIG6 is a graph showing the reaction stability test results in Comparative Example 1.

[0063] FIG7 is a graph showing the reaction stability test results in Comparative Example 2. DETAILED DESCRIPTION

[0064] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims are not to be construed as limited to their general and dictionary meanings, but rather should be interpreted based on the meanings and concepts corresponding to the technical aspects of the present invention, based on the principle that allows the inventor to appropriately define the terms for the best interpretation. Therefore, the description herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the present invention. It should be understood that other equivalent implementations and modifications may be made without departing from the spirit and scope of the present invention.

[0065] The following examples are merely listed as examples of implementation schemes of the present application and do not constitute any limitation to the present application. Those skilled in the art will understand that modifications that do not deviate from the essence and concept of the present application fall within the scope of protection of the present application.

[0066] Preparation of 2,2,5,5-tetramethyltetrahydrofuran

[0067] In the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to the present application, 2,5-dimethyl-2,5-hexanediol is used as a raw material, and a cyclic ether is obtained by dehydration reaction. The product obtained after post-treatment is passed through a 0.22 μm filter membrane and analyzed and detected by gas chromatography (GC). The low-boiling point product was qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS) and the GC retention time of the standard, and it was determined that the reaction product was mainly 2,2,5,5-tetramethyltetrahydrofuran. The low-boiling point substance was quantitatively determined by Shimadzu-GC 2020 gas chromatograph, and the quantitative analysis was performed by comparing the retention time and peak area size with the standard. The relevant calculation formula is as follows:

[0068] The unit of the flow rate of 2,5-dimethyl-2,5-hexanediol is g / min, and the unit of the amount of catalyst used is g.

[0069] As shown in Figure 1, it is a schematic diagram of a synthetic reaction device for 2,2,5,5-tetramethyltetrahydrofuran according to an embodiment of the present application. Among them, the reaction tube is filled with a catalyst for continuously preparing 2,2,5,5-tetramethyltetrahydrofuran according to the present application. First, the carrier gas is passed into the reaction tube by controlling the flow rate through a mass flow meter to create a carrier gas atmosphere, and then the heating furnace can be heated to activate the catalyst. Then, the temperature of the reaction tube is maintained, and 2,5-dimethyl-2,5-hexanediol is fed into the reaction tube through a feed pump. Under the catalytic conditions of the carrier gas atmosphere and the catalyst, the reaction generates a product containing 2,2,5,5-tetramethyltetrahydrofuran. After condensation and gas-liquid separation, 2,2,5,5-tetramethyltetrahydrofuran can be collected.

[0070] According to the present application, the catalyst is applied to the process of preparing 2,2,5,5-tetramethyltetrahydrofuran using 2,5-dimethyl-2,5-hexanediol as a raw material. By reducing the formation of byproducts, the selectivity of 2,2,5,5-tetramethyltetrahydrofuran is improved, and the difficulty of separation is reduced. The method for preparing 2,2,5,5-tetramethyltetrahydrofuran provided in the present application has readily available raw materials, a more environmentally friendly route, a simple process, high efficiency, and can be produced continuously.

[0071] Unless otherwise specified, all raw materials used in this application were commercially available, and the methods and equipment used were conventional methods and equipment in the art.

[0072] In the following examples, 2,5-dimethyl-2,5-hexanediol, sodium hydroxide, potassium hydroxide, formic acid, acetic acid, hydrochloric acid, sulfuric acid, and nitric acid were purchased from Sinopharm Chemical Reagent Co., Ltd., high-purity nitrogen, high-purity helium, and air were purchased from Qingdao Dehai Weiye Technology Co., Ltd., and corn cobs, corn stalks, and peanut shells were purchased locally.

[0073] Catalyst preparation

[0074] Preparation Example 1

[0075] A catalyst for preparing 2,2,5,5-tetramethyltetrahydrofuran is prepared by a method comprising the following steps:

[0076] 1. 150g of dried corn cobs were crushed in a grinder and added to a ball mill along with 15g of HZSM5 catalyst to form a 200-400 mesh fine powder. The powder was then added to a reactor and 800ml of distilled water was added. The reactor was sealed and heated to 200°C for a hydrolysis reaction for 6h. After the reaction was completed, the temperature was lowered, the pressure was released, and the filtrate was filtered under reduced pressure. The filtrate was concentrated by distillation to obtain 143ml of concentrated solution.

[0077] 2. Add 200 ml of 10% formic acid solution by mass to the concentrated solution described in step 1 under vigorous stirring, add 5 g of chitosan, mix well, add to a hydrothermal kettle, hydrothermally treat at 180°C for 10 hours, cool, and release the pressure. Wash the resulting product with anhydrous ethanol and deionized water three times respectively, and then dry it at 110°C for 12 hours to obtain the doped carbon material.

[0078] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide thereto, stir and mix evenly, place in a tube furnace, heat to 500℃ under an inert gas atmosphere and carbonize for 5h. After the carbonization is completed, cool down, wash the obtained material with distilled water until the filtrate is neutral, and dry at 110℃ for 12h.

[0079] 4. To 10 g of the doped carbon material obtained in step 3, add 100 ml of a 20 wt% aqueous nitric acid solution. Heat to 60°C for 6 h. After treatment, cool and filter. Wash the material with distilled water until the filtrate is neutral and dry at 110°C for 12 h. After cooling, remove and obtain Catalyst 1.

[0080] Preparation Example 2

[0081] 1. After 150g of dried bamboo shoots were crushed in a grinder, they were added to a ball mill together with 15g of HY catalyst and ball-milled into a fine powder of 200-400 mesh. The powder was added to a reactor and 800ml of distilled water was added. The reactor was sealed and heated to 200°C for hydrolysis for 6h. After the reaction was completed, the temperature was lowered, the pressure was released, and the filtrate was filtered under reduced pressure. The filtrate was distilled and concentrated to obtain 140ml of concentrated solution.

[0082] 2. Add 200 ml of 10% acetic acid solution by mass to the concentrated solution described in step 1 under vigorous stirring, then add 5 g of chitosan and mix evenly, add to the hydrothermal kettle, hydrothermally treat at 180 ° C for 10 h, cool and release the pressure, wash the resulting product with anhydrous ethanol and deionized water three times respectively, and then dry at 110 ° C for 12 h to obtain the doped carbon material.

[0083] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide thereto, stir and mix evenly, place in a tube furnace, heat to 600℃ under an inert gas atmosphere and carbonize for 5h. After the carbonization is completed, cool down, wash the obtained material with distilled water until the filtrate is neutral, and dry at 110℃ for 12h.

[0084] 4. To 10 g of the doped carbon material obtained in step 3, add 100 ml of 30 wt% hydrochloric acid and heat to 70°C for 6 h. After treatment, cool and filter the material. Wash the material with distilled water until the filtrate is neutral and dry at 110°C for 12 h. After cooling, remove the material to obtain Catalyst 2.

[0085] Preparation Example 3

[0086] 1. 300g of dried peanut shells were crushed in a grinder and added to a ball mill along with 30g of Hβ catalyst to form a 200-400 mesh fine powder. The powder was then added to a reactor and 1500ml of distilled water was added. The reactor was sealed and heated to 200°C for a hydrolysis reaction for 6h. After the reaction was completed, the temperature was lowered, the pressure was released, and the filtrate was filtered under reduced pressure. The filtrate was concentrated by distillation to obtain 380ml of concentrated solution.

[0087] 2. Add 400 ml of 10% hydrochloric acid solution by mass to the concentrated solution described in step 1 under vigorous stirring, add 10 g of chitosan, mix well, add to a hydrothermal kettle, hydrothermally treat at 180°C for 10 h, cool, release the pressure, and wash the resulting product with anhydrous ethanol and deionized water three times respectively, and then dry at 110°C for 12 h to obtain the doped carbon material.

[0088] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide thereto, stir and mix evenly, place in a tube furnace, heat to 600℃ under an inert gas atmosphere and carbonize for 5h. After the carbonization is completed, cool down, wash the obtained material with distilled water until the filtrate is neutral, and dry at 110℃ for 12h.

[0089] 4. To 15 g of the doped carbon material obtained in step 3, 100 ml of an aqueous sodium hypochlorite solution (6% available chlorine) was added. The mixture was heated to 60°C for 6 h. After the treatment, the mixture was cooled, filtered, and washed with distilled water until the filtrate was neutral. The mixture was then dried at 110°C for 12 h. After cooling, the mixture was removed to obtain Catalyst 3.

[0090] Preparation Example 4

[0091] 1. 300g of dried peanut shells were crushed in a grinder and added to a ball mill along with 30g of Hβ catalyst to form a 200-400 mesh fine powder. The powder was then added to a reactor and 1500ml of distilled water was added. The reactor was sealed and heated to 200°C for a hydrolysis reaction for 6h. After the reaction was completed, the temperature was lowered, the pressure was released, and the filtrate was filtered under reduced pressure. The filtrate was concentrated by distillation to obtain 369ml of concentrated solution.

[0092] 2. 400 ml of 10% formic acid solution by mass was added to the concentrated solution described in step 1 under vigorous stirring, 6 g of chitosan was added and mixed evenly, and then added to a hydrothermal kettle and hydrothermally treated at 180°C for 10 h. After cooling and pressure relief, the resulting product was washed three times with anhydrous ethanol and deionized water, respectively, and then dried at 110°C for 12 h to obtain a doped carbon material.

[0093] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide thereto, stir and mix evenly, place in a tube furnace, heat to 600℃ under an inert gas atmosphere and carbonize for 5h. After the carbonization is completed, cool down, wash the obtained material with distilled water until the filtrate is neutral, and dry at 110℃ for 12h.

[0094] 4. To 18 g of the doped carbon material obtained in step 3, 100 ml of a 20 wt% aqueous sulfuric acid solution was added. The mixture was heated to 80°C for 6 h. After the treatment, the mixture was cooled, filtered, and washed with distilled water until the filtrate was neutral. The mixture was then dried at 110°C for 12 h. After cooling, the mixture was removed to obtain catalyst 4.

[0095] Preparation Example 5

[0096] 1. 300g of dried corn stalks were crushed in a grinder and added to a ball mill together with 30g of γ-Al2O3 catalyst to form a fine powder of 200-400 mesh. The powder was then added to a reactor and 1500ml of distilled water was added. The reactor was sealed and heated to 200°C for hydrolysis for 6h. After the reaction was completed, the temperature was lowered, the pressure was released, and the filtrate was filtered under reduced pressure. The filtrate was concentrated by distillation to obtain 369ml of concentrated solution.

[0097] 2. 400 ml of 10% acetic acid solution was added to the concentrated solution in step 1 under vigorous stirring, 4 g of chitosan was added and mixed evenly, and then added to a hydrothermal kettle and hydrothermally treated at 180°C for 10 h. After cooling and pressure relief, the resulting product was washed three times with anhydrous ethanol and deionized water, respectively, and then dried at 110°C for 12 h to obtain a doped carbon material.

[0098] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide thereto, stir and mix evenly, place in a tube furnace, heat to 600℃ under a nitrogen atmosphere and carbonize for 5h. After the carbonization is completed, cool down, wash the obtained material with distilled water until the filtrate is neutral, and dry at 110℃ for 12h.

[0099] 4. To 15 g of the doped carbon material obtained in step 3, add 100 ml of a 20 wt% aqueous nitric acid solution. Heat to 60°C for 6 h. After treatment, cool and filter. Wash the material with distilled water until the filtrate is neutral and dry at 110°C for 12 h. After cooling, remove the material to obtain Catalyst 5.

[0100] Preparation Example 6

[0101] 1. 300g of dried corn cobs were crushed in a grinder and then added to a ball mill together with 30g of Nb2O5 to form a 200-400 mesh fine powder. The powder was then added to a reactor and 1500ml of distilled water was added. The reactor was sealed and heated to 200°C for a hydrolysis reaction for 6h. After the reaction was completed, the temperature was lowered, the pressure was released, and the filtrate was filtered under reduced pressure. The filtrate was concentrated by distillation to obtain 341ml of concentrated solution.

[0102] 2. Add 400 ml of 10% acetic acid solution by mass to the concentrated solution described in step 1 under vigorous stirring, add 5 g of chitosan, mix well, add to a hydrothermal kettle, hydrothermally treat at 180 ° C for 10 h, cool, release the pressure, and wash the resulting product with anhydrous ethanol and deionized water three times respectively, and then dry at 110 ° C for 12 h to obtain a doped carbon material.

[0103] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of sodium hydroxide thereto, stir and mix evenly, place in a tube furnace, heat to 600℃ under a nitrogen atmosphere and carbonize for 5h. After carbonization, cool down, wash the obtained material with distilled water until the filtrate is neutral, and dry at 110℃ for 12h.

[0104] 4. To 15 g of the doped carbon material obtained in step 3, 100 ml of a 40 wt% aqueous sulfuric acid solution was added. The mixture was heated to 60°C for 6 h. After the treatment, the mixture was cooled, filtered, and washed with distilled water until the filtrate was neutral. The mixture was then dried at 110°C for 12 h. After cooling, the mixture was removed to obtain Catalyst 6.

[0105] Comparative Example 1

[0106] 1. 300g of dried corn cobs were crushed in a grinder and then added to a ball mill together with 30g of Nb2O5 to form a 200-400 mesh fine powder. The powder was then added to a reactor and 1500ml of distilled water was added. The reactor was sealed and heated to 200°C for a hydrolysis reaction for 6h. After the reaction was completed, the temperature was lowered, the pressure was released, and the filtrate was filtered under reduced pressure. The filtrate was concentrated by distillation to obtain 341ml of concentrated solution.

[0107] 2. 400 ml of 10% acetic acid solution by mass was added to the concentrated solution described in step 1 under vigorous stirring. After mixing evenly, the mixture was added to a hydrothermal kettle and hydrothermally treated at 180°C for 10 h. After cooling and pressure relief, the resulting product was washed three times with anhydrous ethanol and deionized water, respectively, and then dried at 110°C for 12 h to obtain a doped carbon material.

[0108] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of sodium hydroxide thereto, stir and mix evenly, place in a tube furnace, heat to 600℃ under a nitrogen atmosphere and carbonize for 5h. After carbonization, cool down, wash the obtained material with distilled water until the filtrate is neutral, and dry at 110℃ for 12h.

[0109] 4. To 15 g of the doped carbon material obtained in step 3, 100 ml of a 40 wt% aqueous sulfuric acid solution was added. The mixture was heated to 60°C for 6 h. After the treatment, the mixture was cooled, filtered, and washed with distilled water until the filtrate was neutral. The mixture was then dried at 110°C for 12 h. After cooling, the mixture was removed to obtain comparative catalyst 1.

[0110] Comparative Example 2

[0111] 1. 300g of dried corn cobs were crushed in a grinder and then added to a ball mill together with 30g of Nb2O5 to form a 200-400 mesh fine powder. The powder was then added to a reactor and 1500ml of distilled water was added. The reactor was sealed and heated to 200°C for a hydrolysis reaction for 6h. After the reaction was completed, the temperature was lowered, the pressure was released, and the filtrate was filtered under reduced pressure. The filtrate was concentrated by distillation to obtain 341ml of concentrated solution.

[0112] 2. 400 ml of 10% acetic acid solution by mass was added to the concentrated solution described in step 1 under vigorous stirring. After mixing evenly, the mixture was added to a hydrothermal kettle and hydrothermally treated at 180°C for 10 h. After cooling and pressure relief, the resulting product was washed three times with anhydrous ethanol and deionized water, respectively, and then dried at 110°C for 12 h to obtain a doped carbon material.

[0113] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of sodium hydroxide thereto, stir and mix evenly, place in a tube furnace, heat to 600℃ under a nitrogen atmosphere for carbonization treatment for 5h, after carbonization, cool down, wash the obtained material with distilled water until the filtrate is neutral, and dry at 110℃ for 12h to obtain comparative catalyst 2.

[0114] Characterization of catalyst products

[0115] 1. Catalyst element analysis

[0116] Table 1 below shows the elemental analysis results of the catalyst products prepared in Preparation Examples 1-6 and Comparative Examples 1-2.

[0117] Table 1: Elemental analysis of catalysts

[0118] Elemental analysis results indicate that nitrogen from chitosan can be effectively incorporated into the carbon material during the synthesis of the carbon-based catalyst material, resulting in a nitrogen content of approximately 10 wt%. In Comparative Example 1, in which chitosan was not added, the resulting carbon material had a relatively low nitrogen content, demonstrating that the aforementioned synthesis method can incorporate nitrogen from chitosan into the carbon material.

[0119] 2. Quantitative detection of catalyst surface groups

[0120] The surface groups of the prepared catalyst were quantitatively detected by Boehm titration method as follows:

[0121] Preparation:

[0122] 1) Boil deionized water in an oil bath at 160°C for a few minutes and store in a sealed container.

[0123] 2) Prepare standard titration solutions of NaOH, HCl, Na2CO3, and NaHCO3, and determine the concentrations of the standard titration solutions.

[0124] Boehm titration:

[0125] 1) Weigh three 1.0 g portions of sample each and place them into three stoppered conical flasks (made of plastic and thoroughly dried). Add 50 mL of 0.05 mol / L NaOH, Na2CO3, or NaHCO3 solution, respectively.

[0126] 2) Place the conical flask on an oscillator for 4 hours and then let it stand at room temperature for 24 hours (generally, the longer the time, the better).

[0127] 3) Filter the activated carbon slurry once and take 20 mL of the filtrate.

[0128] 4) Add 20 mL of 0.05 mol / L hydrochloric acid to 20 mL of the filtrate (add 40 mL of hydrochloric acid to the filtrate with Na2CO3, and boil the filtrate with Na2CO3 or NaHCO3 again after adding hydrochloric acid to remove CO2).

[0129] 5) Use phenolphthalein as an indicator and back-titrate the excess acid with 0.05 mol / L standard NaOH solution until the solution turns slightly red.

[0130] Alkali consumption:

[0131] a=(V*C NaOH +20*C0-20*C HCl )*2.5 / M(NaOH,NaHCO3 calculation formula)

[0132] a=(V*C NaOH +20*C0-40*C HCl )*2.5 / M(Na2CO3 calculation formula)

[0133] Calculation formula description:

[0134] The concentration C0 in the formula is based on the equivalent concentration. Since Na2CO3 is a diproton base, when calculating Na2CO3, C0 should be the molar concentration of Na2CO3 multiplied by 2.

[0135] V is the volume of NaOH consumed, C0 is the concentration of added alkali solution, C HCl is the concentration of the hydrochloric acid solution used, and M is the mass of the activated carbon.

[0136] calculate:

[0137] The number of carboxyl groups is represented by the consumption of NaHCO3 aNaHCO3; the number of lactone groups is represented by the difference between the consumption of Na2CO3 and NaHCO3 aNa2CO3-aNaHCO3; the number of phenolic hydroxyl groups is represented by the difference between the consumption of NaOH and Na2CO3 aNaOH-aNa2CO3

[0138] Table 2 below shows the results of surface group number analysis of the catalyst products prepared in Preparation Examples 1-6 and Comparative Examples 1-2.

[0139] Table 2: Number of catalyst surface groups

[0140] As can be seen from Table 2 above, the doped carbon material catalysts synthesized in this application all have rich surface groups, and the amounts of carboxyl groups, lactone groups, and phenolic hydroxyl groups on the surface of the catalyst material are respectively 0.5-0.6 mmol / g, 0.6-0.7 mmol / g, and 0.1 mmol / g. In Comparative Example 2, which is not treated with an acid or an oxidant, the amounts of surface groups carboxyl groups, lactone groups, and phenolic hydroxyl groups in the obtained carbon material are respectively 0.33 mmol / g, 0.21 mmol / g, and 0.06 mmol / g, which are significantly lower than the contents of other carbon materials described in this patent application, indicating that acid / oxidant treatment can greatly enrich the number of groups on the surface of the carbon material.

[0141] 3. Detection of temperature-programmed desorption of ammonia on catalyst

[0142] The NH3 characterization of the catalyst product was conducted on a Micromeritics AutoChem 2920 chemical adsorption instrument. The specific experimental steps were as follows: 0.1 g of sample was placed in a U-shaped quartz tube and purged under an Ar atmosphere at 150°C for 2 hours. The sample was then cooled to 100°C and adsorbed with a 5 wt% NH3 / Ar mixture at 100°C for 2 hours. The sample was then switched to an Ar atmosphere to purge the physically adsorbed ammonia for 1 hour. After the baseline leveled, the sample was heated at a rate of 10°C / min to 800°C. The NH3 signal was recorded using a TCD detector. The results are shown in Figure 2.

[0143] As can be seen from Figure 2, the NH3-TPD comparison results of Catalyst 6 and Comparative Catalysts 1-2 are shown in Figure 2. It can be seen that Comparative Catalyst 1 has an obvious NH3 desorption peak at 200°C, indicating a certain weak acidic site. Comparative Catalyst 2 has an NH3-desorption peak near 200°C and a desorption peak at a higher temperature (around 440°C), indicating stronger acidity. Catalyst 6 has a stronger NH3 desorption peak at 230°C. It can be seen that acid or / oxidant treatment can significantly enhance the acidity of the catalyst surface, and the desorption temperature of NH3 is significantly increased, indicating that the acid strength of the catalyst is stronger and the acid amount is higher. This result is consistent with the catalyst surface group content result obtained by the above-mentioned Boehm titration test, indicating that acid / oxidant treatment can significantly increase the number of groups on the catalyst surface, thereby enhancing the catalyst surface acidity.

[0144] Reaction Example

[0145] 2,2,5,5-Tetramethyltetrahydrofuran was prepared by the following steps:

[0146] 2g of the above-prepared catalyst was added to a fixed bed reactor, heated to 400℃ under N2 atmosphere and maintained for 3h for activation, then cooled to 95-110℃; at a reaction temperature of 110℃ and normal pressure, 2,5-dimethyl-2,5-hexanediol was added at a rate of 0.2-0.3h. -1 The reaction product was condensed and separated into gas and liquid, and then GC analysis was performed. The results of each catalyst are shown in Table 3 below:

[0147] Table 3. Reaction results using different catalysts

[0148] According to the reaction results of the above reaction examples, the conversion rate of comparative catalyst 2 is significantly enhanced compared to comparative catalyst 1, but its stabilization time is relatively short. This result is consistent with the above catalyst characterization results that comparative catalyst 2 has strong acidity, indicating that the acid / oxidant treatment can significantly increase the number of groups on the catalyst surface, thereby enhancing the catalyst surface acidity. When molecular sieves are used as catalysts for the reaction, higher conversion rates and selectivity can be achieved, but the stability of the catalyst is poor. When the catalysts prepared according to Preparation Examples 1 to 6 of the present application are used, the selectivity of TMTHF is increased while the service life of the catalyst is significantly enhanced, so that the target product TMTHF can be produced and the efficiency is improved, thereby further reducing production energy consumption, reducing production costs, and facilitating industrial production.

[0149] The above-mentioned specific embodiments of the present application are merely preferred embodiments for explaining the present application, and are not limitations of the present application. After reading this specification, those skilled in the art may make modifications without creative contribution as needed. However, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran, characterized in that: The method is to carry out a dehydration reaction of 2,5-dimethyl-2,5-hexanediol in a reactor at 50° C. to 200° C. in the presence of a catalyst.

2. A continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 1, characterized in that, The reactor in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran is selected from any one of a continuous stirred tank reactor, a plug flow reactor, a fixed phase reactor and a fluidized bed reactor, or a mixed reactor of two or more of these reactors connected; preferably a fixed bed reactor.

3. A continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 2, characterized in that, The invention comprises at least one of the following features (a) to (g): (a) The catalyst may be in the form of strips, columns or sheets; (b) The dehydration reaction temperature may preferably be 80°C to 150°C; (c) the dehydration reaction may be carried out under one or more of a nitrogen atmosphere, a helium atmosphere and an argon atmosphere; (d) The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran can be carried out at a reaction pressure of 0.1 MPa to 4 MPa, preferably 0.1 MPa to 2 MPa; or at a reaction pressure of normal pressure to 4 MPa, preferably normal pressure to 2 MPa; (e) the 2,5-dimethyl-2,5-hexanediol may be reacted in the absence of a solvent or in the presence of a solvent, wherein the solvent is one or more selected from tetrahydrofuran, acetonitrile and 1,4-dioxane, preferably tetrahydrofuran or 1,4-dioxane; (f) The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran can be carried out in 0.05h -1 ~5h -1 , preferably 0.1h -1 ~3h -1 The reaction was carried out at a space velocity of .

4. A continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 3, characterized in that, The method comprises at least one of the following features (a) and (b): (a) The preparation method further comprises activating the catalyst before the reaction: before the reaction, the catalyst is heated to an activation temperature of 300°C to 500°C and maintained for 1h to 6h; preferably, the activation temperature may be 300°C to 400°C; (b) The preparation method further comprises post-reaction treatment: the reaction product is condensed and separated into gas and liquid, and then distilled.

5. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 1, characterized in that: The catalyst used therein is prepared by a method comprising the following steps: (1) The biomass raw material is crushed by a pulverizer, and then added to a ball mill together with a solid acid catalyst to be ball-milled into fine powder, which is then added to a reactor, and distilled water is added. The reactor is sealed and heated to perform a hydrolysis reaction. After the reaction is completed, the temperature is lowered, the pressure is released, and the filtrate is filtered under reduced pressure, and the filtrate is distilled and concentrated into a concentrated solution; (2) adding the acid solution to the concentrated solution in step (1) under vigorous stirring, mixing evenly, adding chitosan, transferring to a hydrothermal kettle, performing hydrothermal treatment, cooling, and relieving pressure, washing the obtained product with anhydrous ethanol and deionized water, respectively, and drying to obtain a doped carbon material; (3) adding alkali to the doped carbon material obtained in step (2), stirring and mixing, placing in a tube furnace, heating in an inert gas atmosphere for carbonization treatment, cooling after carbonization, washing the obtained material with distilled water until the filtrate is neutral, and drying; (4) The doped carbon material obtained in step (3) is mixed and stirred evenly with an acid or an oxidant, and subjected to heat treatment. After the treatment, the temperature is reduced and filtered, and the material is washed with distilled water until the filtrate is neutral, and then dried.

6. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 5, characterized in that: In the step (1), the biomass material is selected from one or more of corn cobs, corn stalks, sawdust, peanut shells, and bamboo shoots; preferably one or more of corn cobs, corn stalks, and peanut shells, and more preferably one or more of corn cobs and corn stalks; The solid acid catalyst is selected from one or more of silicon dioxide, γ-alumina, zirconium dioxide, cerium dioxide, tungsten trioxide, niobium pentoxide, zeolite molecular sieve, and ion exchange resin; The solid acid catalyst is preferably one or more of silicon dioxide, γ-alumina, tungsten trioxide, niobium pentoxide, zeolite molecular sieve, and ion exchange resin; more preferably one or more of γ-alumina, zeolite molecular sieve, and ion exchange resin; The zeolite molecules are selected from one or more of HZSM5, HZSM11, HY, Hβ, HMOR, and SAPO-34; In the step (1): The dried biomass raw material is crushed by a pulverizer, and then added to a ball mill together with a solid acid catalyst to be ball-milled into a fine powder of 200-400 meshes, and the reactor is sealed and heated to a temperature of 150-250°C; The mass ratio of distilled water to biomass raw material is 50:1-2:1; preferably 20:1-5:1; The hydrolysis reaction temperature is 120-250°C; preferably 150-220°C; more preferably 160-210°C; The hydrolysis reaction time is 4-10h; preferably 4-6h; The mass concentration of the concentrated solution is 10%-30%, preferably 10%-20%.

7. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 5, characterized in that: In the step (2): The acid is selected from one or more of formic acid, acetic acid, propionic acid, and hydrochloric acid; The mass concentration of the acid solution is 1%-30%, preferably 3%-10%; The mass ratio of the acid solution to the concentrated solution is 1:1-10:1; preferably 1:1-5:1; The mass ratio of chitosan to concentrated solution is 1:10-1:100; The hydrothermal treatment temperature is 160-220°C; preferably 180-210°C; The hydrothermal treatment time is 4-20 hours; preferably 5-10 hours; The obtained product was washed with anhydrous ethanol and deionized water three times respectively, and dried at 110 °C for 12 h.

8. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 5, characterized in that: In the step (3): The base is selected from one or more of sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, and potassium ethoxide; The mass ratio of the base to the doped carbon material is 1:1-10:1; preferably 1:1-5:1; more preferably 1:1-3:1; The inert gas used in the carbonization process is selected from one or more of nitrogen, helium and argon; preferably one or more of nitrogen and argon; The carbonization treatment temperature is 300-700°C, and the treatment time is 4-20h; after the carbon is washed, it is dried at 110°C for 12h.

9. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 5, characterized in that: In the step (4): The acid is one or more of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, and phosphoric acid; The oxidant is one or more of hydrogen peroxide with a mass concentration of 30wt% and sodium hypochlorite with an effective chlorine content of 6%; The mass ratio of the acid to the doped carbon material is 1:1-10:1; The mass ratio of the oxidant to the doped carbon material is 1:1-10:1; The heating treatment temperature is 60-90°C; The heating treatment time is 4-10h; After washing, dry at 110°C for 12h; After the reaction in step (1) is completed, the filter cake obtained by suction filtration contains the solid acid catalyst. The filter cake is calcined at 350-550° C. in an air atmosphere for 3-6 hours to remove organic matter to obtain the solid acid catalyst. The obtained solid acid catalyst can be repeatedly recycled.

10. Use of the catalyst in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to any one of claims 1 to 9 in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran.

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