A continuous process for the preparation of 2,2,5,5-tetramethyltetrahydrofuran and catalysts used therein

Abstract

This application relates to the field of chemical synthesis, specifically to a continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran and the catalyst used therein. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran involves the dehydration of 2,5-dimethyl-2,5-hexanediol in a reactor at 50°C to 200°C in the presence of a catalyst. The catalyst provided in this application for the synthesis of 2,2,5,5-tetramethyltetrahydrofuran can catalyze the reaction of 2,5-dimethyl-2,5-hexanediol with a high conversion rate and very high selectivity, exceeding 99%. The catalyst used has good stability and a long lifespan, thereby further reducing production energy consumption and costs, and facilitating industrial-scale production.

Description

Technical Field

[0001] This application relates to the field of chemical synthesis, and more specifically, to a method for the continuous preparation of 2,2,5,5-tetramethyltetrahydrofuran from the dehydration of 2,5-dimethyl-2,5-hexanediol, as well as the catalyst used in this method and its preparation method. Background Technology

[0002]

[0003] 2,2,5,5-Tetramethyltetrahydrofuran (TMTHF), CAS No. 15045-43-9, is a colorless liquid with a freezing point of -92℃, a boiling point of 112℃, a relative density of 0.811 (25℃), a refractive index of 1.409 (19℃), and a flash point of 3.9℃. 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 is widely used in industrial production as a novel solvent, potentially replacing traditional hydrocarbon solvents such as toluene and hexane. Although TMTHF is defined as an ether because it contains RO-R' groups (where R and R' are alkyl groups), it does not possess the peroxide formation potential of other ethers (such as THF or 2-MeTHF). This is because, unlike ether oxygen, there is no proton at the α-position. The α-proton in traditional ethers is easily removed by low-energy light, forming a free radical. Oxygen from the air can react with this free radical to form an explosive peroxide. The rate of peroxide formation potential in ethers increases with increasing radical stability: primary α-carbon << secondary α-carbon < tertiary α-carbon. Since TMTHF contains two quaternary ether carbons and no α-protons, the peroxide formation potential is eliminated. This combination of highly favorable properties makes TMTHF a rare low-boiling, low-polarity molecule that lacks a peroxide formation potential and can be readily produced from biomass.

[0004]

[0005] Current literature reports on the dehydration synthesis of TMTHF from 2,5-dimethyl-2,5-hexanediol (as shown above) include: Denney et al. in J. Org. Chem. 1984, 49, p2831, who disclosed a method for preparing TMTHF, comprising contacting 2,5-dimethyl-2,5-hexanediol with pentaethoxyphosphine as a catalyst in DCM as a solvent; Vlad and Ungur in Synthesis 1983, p216, who disclosed a method for preparing TMTHF, comprising contacting 2,5-dimethyl-2,5-hexanediol with trimethylchlorosilane as a catalyst in benzene as a solvent; and Gillis & Beck in J. Org. Chem. 1963, 28, p1388, who disclosed a method for preparing TMTHF, comprising contacting 2,5-dimethyl-2,5-hexanediol with DMSO as both a solvent and a catalyst. Yamaguchi et al. disclosed a method for preparing TMTHF in Catal. Today 2012, 185, p302, which involves contacting 2,5-dimethyl-2,5-hexanediol with hydrothermal liquid water in high-pressure carbon dioxide, which serves as both catalyst and solvent. In fact, in all the methods described above, the TMTHF yield does not exceed 80% in the presence of a solvent. Higher yields were achieved in solvent-free methods. DE700036C discloses a method for preparing TMTHF that 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 have already used Nafion-H as a catalyst in the synthesis of TMTHF from 2,5-dimethyl-2,5-hexanediol as a precursor. The advantage of solid catalysts like Nafion-H is that it can be easily separated from the reaction mixture, and this synthesis achieved a yield of 94%. CN 109790134 A discloses the synthesis of TMTHF by the dehydration reaction of H-Beta with 2,5-dimethyl-2,5-hexanediol under various molecular sieve catalysts, and compares the reaction results. It is found that H-Beta has higher reactivity and product selectivity under the same conditions compared with other molecular sieves (HY, H-ZSM5).

[0006] Currently, existing technologies often employ batch reactions, which are simple to operate but prone to low yields and high production costs due to carbon buildup caused by difficulty in controlling residence time. Another approach is continuous reactions, represented by fixed-bed / fluidized-bed reactors, using solid acid catalysts. These reactions are characterized by continuous operation and precise control of residence time, achieving high yields and ensuring safety. Molecular sieves such as H-Beta, HY, and H-ZSM5 can be used as catalysts. However, the acidity / alkalinity of these catalysts is generally controlled by adjusting the content of various oxide components and synthesis conditions such as crystallization temperature, crystallization time, and aging temperature. These methods struggle to precisely control the acidity / alkalinity of the catalyst surface. The catalyst synthesis process typically requires highly toxic template agents, and the carbon buildup generated during the reaction can easily clog the active sites on the catalyst surface, causing deactivation. Furthermore, continuous operation places certain demands on catalyst stability, and frequent catalyst regeneration increases the operational complexity.

[0007] Therefore, improving the stability of solid acid catalysts while maintaining high selectivity for TMTHF in the product is a challenge. Biomass carbon materials, due to their abundant surface pore structure and easily tunable surface groups, often exhibit catalytic activity and product selectivity different from traditional metal oxides. Furthermore, the surface properties of carbon materials can be controlled by doping with heterogeneous elements. Through this approach, catalysts can be rationally designed and controlled according to the active sites required for different reactions, enabling the targeted synthesis of highly efficient catalysts with high selectivity for specific reactions. These catalysts have advantages such as wide availability and renewability of raw materials, easy control of catalyst surface properties, and no use of metal components, and are gradually attracting attention. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention aims to provide a continuous preparation method for 2,2,5,5-tetramethyltetrahydrofuran. This method uses 2,5-dimethyl-2,5-hexanediol as a raw material for a continuous dehydration reaction to prepare 2,2,5,5-tetramethyltetrahydrofuran. The invention also includes a catalyst used in this method and a method for preparing the catalyst, which can operate stably for a long time.

[0009] To achieve the above objectives, according to one aspect of the present invention, one object of the present invention is to provide a continuous method for preparing 2,2,5,5-tetramethyltetrahydrofuran, wherein the method involves dehydrating 2,5-dimethyl-2,5-hexanediol in a reactor at 50°C to 200°C in the presence of a catalyst.

[0010] According to one embodiment of this 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 it can be a mixed reactor of two or more of these reactors connected together; preferably, it is a fixed bed reactor.

[0011] According to one embodiment of this application, the catalyst may be in the form of strips, columns, or flakes;

[0012] According to one embodiment of this application, the dehydration reaction temperature can preferably be 80°C to 150°C;

[0013] According to one embodiment of this application, the dehydration reaction can be carried out under one or more of a nitrogen atmosphere, a helium atmosphere, or an argon atmosphere;

[0014] According to one embodiment of this 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 atmospheric pressure to 4 MPa, preferably atmospheric pressure to 2 MPa.

[0015] According to one embodiment of this application, the 2,5-dimethyl-2,5-hexanediol can be reacted in the presence 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;

[0016] According to one embodiment of this application, the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran can be completed in 0.05 hours. -1 ~5h -1 Preferably 0.1h -1 ~3h -1 The reaction proceeds at a reaction space velocity of [value missing].

[0017] According to one embodiment of this application, the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran further includes activating the catalyst before the reaction. Specifically, before 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.

[0018] According to one embodiment of this application, the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran further includes post-reaction processing. Specifically, the reaction product is subjected to condensation and gas-liquid separation, followed by distillation. The condensation, gas-liquid separation, and distillation are conventional methods and conditions in the art for separating 2,2,5,5-tetramethyltetrahydrofuran and byproducts, and will not be described in detail here.

[0019] According to another aspect of the invention, another object of the invention is to provide a catalyst used in the continuous preparation method of said 2,2,5,5-tetramethyltetrahydrofuran, said catalyst being prepared by a method comprising the following steps:

[0020] (1) After the biomass raw material is crushed by a pulverizer, it is added to a ball mill along with a solid acid catalyst and ball milled into fine powder. The powder is then added to a reaction vessel, distilled water is added, the reaction vessel is sealed and heated to carry out hydrolysis reaction. After the reaction is completed, the temperature is lowered, the pressure is released, and the filtrate is filtered under reduced pressure. The filtrate is then distilled and concentrated into a concentrated solution.

[0021] (2) Add the acid solution to the concentrated solution in step (1) under vigorous stirring. After mixing evenly, add chitosan, transfer to a hydrothermal reactor, perform hydrothermal treatment, cool down, depressurize, and then wash and dry the obtained product with anhydrous ethanol and deionized water respectively to obtain the doped carbon material.

[0022] (3) Add alkali to the doped carbon material obtained in step (2), stir and mix evenly, place it in a tube furnace, heat it under an inert gas atmosphere for carbonization treatment, cool it down after carbonization, wash the obtained material with distilled water until the filtrate is neutral, and dry it.

[0023] (4) Mix the doped carbon material obtained in step (3) with acid or oxidant, heat it, cool it down and filter it after the treatment is completed. Wash the material with distilled water until the filtrate is neutral and dry it.

[0024] Further, 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.

[0025] Furthermore, the solid acid catalyst is selected from one or more of the following: silicon dioxide, γ-alumina, zirconium dioxide, cerium dioxide, tungsten trioxide, niobium pentoxide, zeolite molecular sieve, and ion exchange resin.

[0026] Further, the solid acid catalyst is preferably one or more of silica, 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.

[0027] Furthermore, the zeolite molecules are selected from one or more of HZSM5, HZSM11, HY, Hβ, HMOR, and SAPO-34.

[0028] Furthermore, in step (1):

[0029] After the dried biomass raw material is crushed by a pulverizer, it is added together with the solid acid catalyst and ball-milled into a fine powder of 200-400 mesh. After sealing the reaction vessel, the heating temperature is 150-250℃.

[0030] Furthermore, the mass ratio of distilled water to biomass raw material is 50:1-2:1; preferably 20:1-5:1.

[0031] Furthermore, the hydrolysis reaction temperature is 120-250℃; preferably 150-220℃; more preferably 160-210℃;

[0032] Furthermore, the hydrolysis reaction time is 4-10 hours; preferably 4-6 hours.

[0033] Furthermore, the mass concentration of the concentrated solution is 10%-30%; preferably 10%-20%.

[0034] Furthermore, in step (2):

[0035] The acid is selected from one or more of formic acid, acetic acid, propionic acid, and hydrochloric acid;

[0036] The acid solution has a mass concentration of 1%-30%; preferably 3%-10%.

[0037] The mass ratio of the acid solution to the concentrated solution is 1:1-10:1; preferably 1:1-5:1.

[0038] The mass ratio of chitosan to concentrated solution is 1:10-1:100;

[0039] The hydrothermal treatment temperature is 160-220℃; preferably 180-210℃.

[0040] The hydrothermal treatment time is 4-20 hours; preferably 5-10 hours.

[0041] The product was washed three times with anhydrous ethanol and deionized water, and then dried at 110°C for 12 hours.

[0042] Furthermore, in step (3):

[0043] The alkali is selected from one or more of sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, and potassium ethoxide.

[0044] The mass ratio of the alkali to the doped carbon material is 1:1-10:1; preferably 1:1-5:1; more preferably 1:1-3:1.

[0045] 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.

[0046] The carbonization temperature is 300-700℃ and the treatment time is 4-20h; after carbon washing, it is dried at 110℃ for 12h.

[0047] Furthermore, in step (4):

[0048] The acid is one or more of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, and phosphoric acid;

[0049] The oxidant is one or more of hydrogen peroxide with a mass concentration of 30 wt% and sodium hypochlorite with an available chlorine concentration of 6%.

[0050] The mass ratio of the acid to the doped carbon material is 1:1 to 10:1;

[0051] The mass ratio of the oxidant to the doped carbon material is 1:1 to 10:1.

[0052] The heat treatment temperature is 60-90℃;

[0053] The heat treatment time is 4-10 hours;

[0054] After washing, dry at 110℃ for 12 hours.

[0055] Furthermore, after the reaction in step (1) is completed, the filter cake obtained by filtration contains the solid acid catalyst. The filter cake is calcined in air at 350-550°C for 3-6 hours to remove organic matter and obtain the solid acid catalyst. The obtained solid acid catalyst can be recycled.

[0056] According to another aspect of the invention, another object of the invention is to provide the use of the catalyst in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to the invention.

[0057] Beneficial effects

[0058] The catalyst provided in this application for the synthesis of 2,2,5,5-tetramethyltetrahydrofuran can catalyze the reaction of 2,5-dimethyl-2,5-hexanediol with a high conversion rate and a very high selectivity (up to 99% or more). The catalyst used has good stability and long lifespan, thereby further reducing production energy consumption, reducing production costs, and facilitating industrial production. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of a synthesis apparatus for 2,2,5,5-tetramethyltetrahydrofuran according to one embodiment of this application.

[0060] Figure 2 The adsorption performance of the catalyst products in Example 6, compared with those in Comparative Example 1 and Comparative Example 2, was tested using ammonia temperature-programmed desorption.

[0061] Figure 3 The graph shows the results of the reaction stability test in Example 2.

[0062] Figure 4 The graph shows the results of the reaction stability test in Example 3.

[0063] Figure 5 The graph shows the results of the reaction stability test in Example 6.

[0064] Figure 6 The graph shows the reaction stability test results in Comparative Example 1.

[0065] Figure 7 The graph shows the reaction stability test results in Comparative Example 2. Detailed Implementation

[0066] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Before description, it should be understood that the terminology used in the specification and appended claims should not be construed as limited to its general and dictionary meaning, but rather should be interpreted based on the principle of allowing the inventors to appropriately define the terminology for the best interpretation, and based on its meaning and concept corresponding to the technical level of the invention. Therefore, the description herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention; thus, it should be understood that other equivalent implementations and modifications can be made without departing from the spirit and scope of the invention.

[0067] The following embodiments are merely examples of implementation schemes of this application and do not constitute any limitation on this application. Those skilled in the art will understand that any modifications that do not depart from the essence and concept of this application fall within the protection scope of this application.

[0068] Preparation of 2,2,5,5-Tetramethyltetrahydrofuran

[0069] In the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to this application, 2,5-dimethyl-2,5-hexanediol is used as a starting material, and a cyclic ether is obtained through a dehydration reaction. The product obtained after post-processing is filtered through a 0.22 μm filter membrane and analyzed by gas chromatography (GC). Qualitative analysis of the low-boiling-point product is performed by GC-MS and comparison with the GC retention time of the standard, confirming that the main reaction product is 2,2,5,5-tetramethyltetrahydrofuran. Quantitative determination of the low-boiling-point substance is performed using a Shimadzu-GC 2020 gas chromatograph, and quantitative analysis is performed by comparing the retention time with the standard and the peak area. The relevant calculation formulas are as follows:

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] The flow rate of 2,5-dimethyl-2,5-hexanediol is expressed in g / min, and the amount of catalyst is expressed in g.

[0076] like Figure 1 The diagram shows a schematic of a synthesis apparatus for 2,2,5,5-tetramethyltetrahydrofuran according to one embodiment of this application. The reaction tube is filled with a catalyst according to this application for the continuous preparation of 2,2,5,5-tetramethyltetrahydrofuran. First, a carrier gas is introduced into the reaction tube at a controlled flow rate using a mass flow meter to create a carrier gas atmosphere. Then, a furnace can be used to heat the reactor to activate the catalyst. Next, while maintaining the temperature of the reaction tube, 2,5-dimethyl-2,5-hexanediol is fed into the reaction tube via a feed pump. Under the carrier gas atmosphere and with the catalyst catalyzing, the reaction produces a product containing 2,2,5,5-tetramethyltetrahydrofuran. After condensation and gas-liquid separation, 2,2,5,5-tetramethyltetrahydrofuran can be collected.

[0077] According to this application, the catalyst is applied to the process of preparing 2,2,5,5-tetramethyltetrahydrofuran from 2,5-dimethyl-2,5-hexanediol. By reducing the formation of byproducts, the selectivity of 2,2,5,5-tetramethyltetrahydrofuran is improved, and the separation difficulty is reduced. The method for preparing 2,2,5,5-tetramethyltetrahydrofuran provided in this application uses readily available raw materials, has a more environmentally friendly route, a simple process, high efficiency, and can be used for continuous production.

[0078] Unless otherwise specified, all raw materials used in this application are commercially available, and all methods and equipment used are conventional methods and equipment in the field.

[0079] 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.

[0080] Catalyst preparation

[0081] Preparation Example 1

[0082] A catalyst for the preparation of 2,2,5,5-tetramethyltetrahydrofuran is prepared by a method including the following steps:

[0083] 1. After crushing 150g of dried corn cob in a pulverizer, add it together with 15g of HZSM5 catalyst to a ball mill and ball mill it into a fine powder of 200-400 mesh. Add the powder to a reaction vessel, add 800ml of distilled water, seal the reaction vessel, heat to 200℃, and carry out the hydrolysis reaction for 6 hours. After the reaction is completed, cool down, depressurize, filter under reduced pressure, and distill and concentrate the filtrate to obtain 143ml of concentrated solution.

[0084] 2. Add 200 ml of a 10% formic acid solution to the concentrated solution described in step 1 under vigorous stirring. Add 5 g of chitosan, mix well, and then add the mixture to a hydrothermal reactor. Hydrothermally treat the mixture at 180°C for 10 h. After cooling and depressurization, wash the resulting product three times with anhydrous ethanol and deionized water, respectively, and then dry it at 110°C for 12 h to obtain the doped carbon material.

[0085] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide, stir and mix evenly, place in a tube furnace, heat to 500℃ under an inert gas 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.

[0086] 4. Add 100 ml of 20 wt% nitric acid aqueous solution to 10 g of the doped carbon material obtained in step 3, heat to 60 °C for 6 h, cool and filter, wash the material with distilled water until the filtrate is neutral, and dry at 110 °C for 12 h. After cooling, take it out to obtain catalyst 1.

[0087] Preparation Example 2

[0088] 1. After pulverizing 150g of dried bamboo shoots with a pulverizer, add them together with 15g of HY catalyst to a ball mill and grind them into a fine powder of 200-400 mesh. Add the powder to a reaction vessel, add 800ml of distilled water, seal the reaction vessel, and heat to 200℃ for hydrolysis reaction for 6h. After the reaction is completed, cool down, depressurize, filter under reduced pressure, and distill and concentrate the filtrate to obtain 140ml of concentrated solution.

[0089] 2. Add 200 ml of 10% acetic acid solution to the concentrated solution described in step 1 under vigorous stirring, then add 5 g of chitosan and mix well. Add the mixture to a hydrothermal reactor and hydrothermally treat at 180°C for 10 h. After cooling and depressurization, wash the obtained product three times with anhydrous ethanol and deionized water respectively, and then dry at 110°C for 12 h to obtain the doped carbon material.

[0090] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide, stir and mix evenly, place in a tube furnace, heat to 600℃ under an inert gas 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.

[0091] 4. Add 100 ml of 30 wt% hydrochloric acid to 10 g of the doped carbon material obtained in step 3, heat to 70 °C for 6 h, cool and filter, wash the material with distilled water until the filtrate is neutral, and dry at 110 °C for 12 h. After cooling, take it out to obtain catalyst 2.

[0092] Preparation Example 3

[0093] 1. After crushing 300g of dried peanut shells with a pulverizer, add them together with 30g of Hβ catalyst to a ball mill and ball mill them into a fine powder of 200-400 mesh. Add the powder to a reaction vessel, add 1500ml of distilled water, seal the reaction vessel, heat to 200℃, and carry out the hydrolysis reaction for 6 hours. After the reaction is completed, cool down, depressurize, filter under reduced pressure, and distill and concentrate the filtrate to obtain 380ml of concentrated solution.

[0094] 2. Add 400 ml of 10% hydrochloric acid solution to the concentrated solution described in step 1 under vigorous stirring, add 10 g of chitosan, mix well, and then add to a hydrothermal reactor. Treat the mixture at 180°C for 10 h. After cooling and depressurization, wash the resulting product three times with anhydrous ethanol and deionized water, and then dry it at 110°C for 12 h to obtain the doped carbon material.

[0095] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide, stir and mix evenly, place in a tube furnace, heat to 600℃ under an inert gas 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.

[0096] 4. Add 100 ml of sodium hypochlorite aqueous solution (6% available chlorine) to 15 g of the doped carbon material obtained in step 3, heat to 60 °C for 6 h, cool and filter, wash the material with distilled water until the filtrate is neutral, and dry at 110 °C for 12 h. After cooling, take it out to obtain catalyst 3.

[0097] Preparation Example 4

[0098] 1. After crushing 300g of dried peanut shells with a pulverizer, add them together with 30g of Hβ catalyst to a ball mill and ball mill them into a fine powder of 200-400 mesh. Add the powder to a reaction vessel, add 1500ml of distilled water, seal the reaction vessel, heat to 200℃, and carry out the hydrolysis reaction for 6 hours. After the reaction is completed, cool down, release the pressure, filter under reduced pressure, and distill and concentrate the filtrate to obtain 369ml of concentrated solution.

[0099] 2. Add 400 ml of a 10% formic acid solution to the concentrated solution described in step 1 under vigorous stirring. Add 6 g of chitosan and mix well. Then, add the mixture to a hydrothermal reactor and hydrothermally treat it at 180°C for 10 h. After cooling and depressurization, wash the resulting product three times with anhydrous ethanol and deionized water, respectively. Then, dry it at 110°C for 12 h to obtain the doped carbon material.

[0100] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide, stir and mix evenly, place in a tube furnace, heat to 600℃ under an inert gas 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.

[0101] 4. Add 100 ml of 20 wt% sulfuric acid aqueous solution to 18 g of the doped carbon material obtained in step 3, heat to 80 °C for 6 h, cool and filter, wash the material with distilled water until the filtrate is neutral, and dry at 110 °C for 12 h. After cooling, take it out to obtain catalyst 4.

[0102] Preparation Example 5

[0103] 1. After crushing 300g of dried corn stalks in a pulverizer, add them together with 30g of γ-Al2O3 catalyst to a ball mill and grind them into a fine powder of 200-400 mesh. Add the powder to a reaction vessel, add 1500ml of distilled water, seal the reaction vessel, and heat to 200℃ for hydrolysis reaction for 6h. After the reaction is completed, cool down, depressurize, filter under reduced pressure, and distill and concentrate the filtrate to obtain 369ml of concentrated solution.

[0104] 2. Add 400 ml of 10% acetic acid solution to the concentrated solution described in step 1 under vigorous stirring. Add 4 g of chitosan and mix well. Then, add the mixture to a hydrothermal reactor and hydrothermally treat it at 180°C for 10 h. After cooling and depressurization, wash the obtained product three times with anhydrous ethanol and deionized water, respectively. Then, dry it at 110°C for 12 h to obtain the doped carbon material.

[0105] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of potassium hydroxide, stir and mix evenly, place in a tube furnace, heat to 600℃ under 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.

[0106] 4. Add 100 ml of 20 wt% nitric acid aqueous solution to 15 g of the doped carbon material obtained in step 3, heat to 60 °C for 6 h, cool and filter, wash the material with distilled water until the filtrate is neutral, and dry at 110 °C for 12 h. After cooling, take out to obtain catalyst 5.

[0107] Preparation Example 6

[0108] 1. Crush 300g of dried corn cobs using a pulverizer, and then add them together with 30g of Nb2O5 to a ball mill to grind them into a fine powder of 200-400 mesh. Add the powder to a reaction vessel, add 1500ml of distilled water, seal the reaction vessel, and heat to 200℃ for hydrolysis reaction for 6 hours. After the reaction is completed, cool down, release the pressure, filter under reduced pressure, and distill and concentrate the filtrate to obtain 341ml of concentrated solution.

[0109] 2. Add 400 ml of 10% acetic acid solution to the concentrated solution described in step 1 under vigorous stirring, add 5 g of chitosan, mix well, and then add to a hydrothermal reactor. Hydrothermally treat at 180°C for 10 h. After cooling and depressurization, wash the obtained product three times with anhydrous ethanol and deionized water respectively, and then dry at 110°C for 12 h to obtain the doped carbon material.

[0110] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of sodium hydroxide, stir and mix evenly, place in a tube furnace, heat to 600℃ under 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.

[0111] 4. Add 100 ml of 40 wt% sulfuric acid aqueous solution to 15 g of the doped carbon material obtained in step 3, heat to 60 °C for 6 h, cool and filter, wash the material with distilled water until the filtrate is neutral, and dry at 110 °C for 12 h. After cooling, take it out to obtain catalyst 6.

[0112] Comparative Example 1

[0113] 1. Crush 300g of dried corn cobs using a pulverizer, and then add them together with 30g of Nb2O5 to a ball mill to grind them into a fine powder of 200-400 mesh. Add the powder to a reaction vessel, add 1500ml of distilled water, seal the reaction vessel, and heat to 200℃ for hydrolysis reaction for 6 hours. After the reaction is completed, cool down, release the pressure, filter under reduced pressure, and distill and concentrate the filtrate to obtain 341ml of concentrated solution.

[0114] 2. Add 400 ml of acetic acid solution with a mass percentage concentration of 10% to the concentrated solution in step 1 under vigorous stirring. After mixing evenly, add the solution to a hydrothermal reactor and hydrothermally treat it at 180°C for 10 h. After cooling and depressurization, wash the obtained product three times with anhydrous ethanol and deionized water respectively, and then dry it at 110°C for 12 h to obtain the doped carbon material.

[0115] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of sodium hydroxide, stir and mix evenly, place in a tube furnace, heat to 600℃ under 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.

[0116] 4. Add 100 ml of 40 wt% sulfuric acid aqueous solution to 15 g of the doped carbon material obtained in step 3, heat to 60 °C for 6 h, cool and filter, wash the material with distilled water until the filtrate is neutral, and dry at 110 °C for 12 h. After cooling, take it out to obtain comparative catalyst 1.

[0117] Comparative Example 2

[0118] 1. Crush 300g of dried corn cobs using a pulverizer, and then add them together with 30g of Nb2O5 to a ball mill to grind them into a fine powder of 200-400 mesh. Add the powder to a reaction vessel, add 1500ml of distilled water, seal the reaction vessel, and heat to 200℃ for hydrolysis reaction for 6 hours. After the reaction is completed, cool down, release the pressure, filter under reduced pressure, and distill and concentrate the filtrate to obtain 341ml of concentrated solution.

[0119] 2. Add 400 ml of acetic acid solution with a mass percentage concentration of 10% to the concentrated solution in step 1 under vigorous stirring. After mixing evenly, add the solution to a hydrothermal reactor and hydrothermally treat it at 180°C for 10 h. After cooling and depressurization, wash the obtained product three times with anhydrous ethanol and deionized water respectively, and then dry it at 110°C for 12 h to obtain the doped carbon material.

[0120] 3. Take 20g of the doped carbon material obtained in step 2, add 60g of sodium hydroxide, stir and mix evenly, place in a tube furnace, heat to 600℃ under 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.

[0121] Characterization of catalyst products

[0122] 1. Catalyst elemental analysis

[0123] Table 1 below shows the elemental analysis results of the catalyst products prepared in Examples 1-6 and Comparative Examples 1-2.

[0124] Table 1: Elemental Analysis of Catalysts

[0125] Carbon (wt%) Nitrogen (wt%) Oxygen (wt%) Hydrogen (wt%) Preparation Example 1 79.3 10.6 3.7 1.9 Preparation Example 2 78.2 10.0 4.3 1.1 Preparation Example 3 78.5 9.2 3.3 1.3 Preparation Example 4 77.3 10.1 3.2 1.9 Preparation Example 5 79.1 8.3 3.3 1.8 Preparation Example 6 80.6 9.3 3.2 1.4 Comparative Example 1 84.6 1.7 5.2 1.9 Comparative Example 2 81.6 9.0 2.9 1.1

[0126] Elemental analysis results show that nitrogen from chitosan can be effectively incorporated into carbon materials during the synthesis of carbon-based catalysts, with the synthesized doped carbon material containing approximately 10 wt% nitrogen. In Comparative Example 1, which did not include chitosan, the resulting carbon material had a lower nitrogen content, indicating that the above synthesis method can effectively incorporate nitrogen from chitosan into carbon materials.

[0127] 2. Quantitative detection of surface functional groups on catalysts

[0128] The surface groups of the prepared catalyst were quantitatively detected using the Boehm titration method, as follows:

[0129] Preparation:

[0130] 1) Boil the deionized water in an oil bath at 160°C for a few minutes, then seal and store it.

[0131] 2) Prepare standard titration solutions of NaOH, HCl, Na2CO3, and NaHCO3, and determine the concentration of the standard titration solutions.

[0132] Boehm titration:

[0133] 1) Weigh out three samples of approximately 1.0g each and place them in three stoppered conical flasks (made of plastic and thoroughly dried). Add 50mL of 0.05mol / L NaOH, Na2CO3, and NaHCO3 solutions to each flask.

[0134] 2) Place the conical flask on a shaker and shake for 4 hours, then let it stand at room temperature for 24 hours (generally, the longer the better).

[0135] 3) Filter the activated carbon slurry once and take 20 mL of the filtrate.

[0136] 4) Add 20 mL of 0.05 mol / L hydrochloric acid to 20 mL of filtrate (add 40 mL of hydrochloric acid to the filtrate containing Na2CO3, and boil again to remove CO2 from the filtrate containing Na2CO3 or NaHCO3 after adding hydrochloric acid).

[0137] 5) Using phenolphthalein as an indicator, back-titrate excess acid with 0.05 mol / L standard NaOH solution until the solution turns slightly red.

[0138] Alkali consumption:

[0139] a=(V*C NaOH +20*C0-20*C HCl )*2.5 / M(Calculation formula for NaOH, NaHCO3)

[0140] a=(V*C NaOH +20*C0-40*C HCl )*2.5 / M (Na2CO3 calculation formula)

[0141] Explanation of the calculation formula:

[0142] The concentration C0 in the formula is based on the equivalent concentration. Since Na2CO3 is a diprotic base, when calculating Na2CO3, C0 should be the molar concentration of Na2CO3 multiplied by 2.

[0143] V is the volume of NaOH consumed, C0 is the concentration of the added alkali solution, and C HCl M represents the concentration of the hydrochloric acid solution used, and M represents the mass of activated carbon.

[0144] calculate:

[0145] The number of carboxyl groups is represented by the amount of NaHCO3 consumed, aNaHCO3; the number of lactone groups is represented by the difference between the amounts of Na2CO3 and NaHCO3 consumed, aNa2CO3 - aNaHCO3; the number of phenolic hydroxyl groups is represented by the difference between the amounts of NaOH and Na2CO3 consumed, aNaOH - aNa2CO3.

[0146] Table 2 below shows the surface group number analysis results of the catalyst products prepared in Preparation Examples 1-6 and Comparative Examples 1-2.

[0147] Table 2: Number of functional groups on catalyst surface

[0148]

[0149] As shown in Table 2 above, the doped carbon catalysts synthesized in this application all possess abundant surface groups. The amounts of carboxyl groups, lactone groups, and phenolic hydroxyl groups on the catalyst surface are approximately 0.5-0.6 mmol / g, 0.6-0.7 mmol / g, and 0.1 mmol / g, respectively. In Comparative Example 2, which did not use acid or / and oxidizing agents, the amounts of carboxyl groups, lactone groups, and phenolic hydroxyl groups in the obtained carbon material were 0.33 mmol / g, 0.21 mmol / g, and 0.06 mmol / g, respectively, which are significantly lower than the contents of other carbon materials described in this patent application. This indicates that acid / oxidizing agent treatment can greatly enrich the number of groups on the surface of carbon materials.

[0150] 3. Detection of catalyst ammonia desorption by temperature programmed rise

[0151] The NH3 characterization of the catalyst product was performed using a Micromeritics AutoChem 2920 chemisorption analyzer. The specific experimental procedure was as follows: 0.1 g of sample was placed in a U-shaped quartz tube and purged at 150 °C for 2 h in an Ar atmosphere. The temperature was then lowered to 100 °C, and 5 wt% NH3 / Ar mixture was adsorbed at 100 °C for 2 h. Then, the physicoadsorbed ammonia was purged under an Ar atmosphere for 1 h. After leveling the baseline, the temperature was increased to 800 °C at a rate of 10 °C / min. The NH3 signal was recorded using a TCD detector. The results are as follows: Figure 2 As shown.

[0152] from Figure 2 As can be seen from the comparison results of NH3-TPD between catalyst 6 and comparative catalysts 1-2, the results are as follows: Figure 2As shown, catalyst 1 exhibits a distinct NH3 desorption peak at 200℃, indicating certain weakly acidic sites. Catalyst 2, in addition to the NH3- desorption peak near 200℃, also shows desorption peaks at higher temperatures (around 440℃), indicating stronger acidity. Catalyst 6 shows an even stronger NH3 desorption peak at 230℃. This demonstrates that acid or / and oxidant treatment significantly enhances the acidity of the catalyst surface, and the significantly increased NH3 desorption temperature indicates stronger acidity and higher acid content. This result is consistent with the catalyst surface group content obtained from the Boehm titration test, showing that acid / oxidant treatment can significantly increase the number of groups on the catalyst surface, thereby enhancing the surface acidity.

[0153] Reaction Examples

[0154] 2,2,5,5-Tetramethyltetrahydrofuran is prepared by the following steps:

[0155] 2g of the catalyst prepared above was added to a fixed-bed reactor, and the reactor was heated to 400℃ and held for 3h under a N2 atmosphere for activation. The temperature was then lowered to 95-110℃. At a reaction temperature of 110℃ and atmospheric pressure, 2,5-dimethyl-2,5-hexanediol was added at a rate of 0.2-0.3h. -1 The gas was introduced into the reactor at a space velocity to carry out the reaction. The reaction products were condensed and separated from the gas, and then analyzed by GC. The results for each catalyst are shown in Table 3 below:

[0156] Table 3. Reaction results using different catalysts

[0157]

[0158]

[0159] Based on the reaction results of the above examples, it can be seen that the conversion rate of comparative catalyst 2 is significantly enhanced compared to comparative catalyst 1, but its stability time is relatively short. This result is consistent with the above catalyst characterization results showing that comparative catalyst 2 has stronger acidity, indicating that acid / oxidant treatment can significantly increase the number of functional groups on the catalyst surface, thereby enhancing the acidity of the catalyst surface. When using molecular sieves as catalysts, higher conversion rates and selectivity can be achieved, but the catalyst stability is poor. However, when using the catalysts prepared according to Examples 1-6 of this application, the selectivity of TMTHF increases while the catalyst lifespan is significantly enhanced, making the target product TMTHF production possible and improving efficiency. This further reduces production energy consumption, lowers production costs, and facilitates industrial-scale production.

[0160] The specific embodiments described above are merely preferred embodiments for explaining this application and are not intended to limit this application. Those skilled in the art can make modifications without creative contribution as needed after reading this specification. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A continuous preparation method for 2,2,5,5-tetramethyltetrahydrofuran, characterized in that, The method involves dehydrating 2,5-dimethyl-2,5-hexanediol in a reactor at 50°C to 200°C in the presence of a catalyst. The catalyst used is prepared by a method including the following steps: (1) After the biomass raw material is crushed by a pulverizer, it is added to a ball mill along with a solid acid catalyst and ball milled into fine powder. The powder is then added to a reaction vessel, distilled water is added, the reaction vessel is sealed and heated to carry out hydrolysis reaction. After the reaction is completed, the temperature is lowered, the pressure is released, and the filtrate is filtered under reduced pressure. The filtrate is then distilled and concentrated into a concentrated solution. (2) Add the acid solution to the concentrated solution in step (1) under vigorous stirring. After mixing evenly, add chitosan, transfer to a hydrothermal reactor, perform hydrothermal treatment, cool down, depressurize, and then wash and dry the obtained product with anhydrous ethanol and deionized water respectively to obtain the doped carbon material. (3) Add alkali to the doped carbon material obtained in step (2), stir and mix evenly, place it in a tube furnace, heat it under an inert gas atmosphere for carbonization treatment, cool it down after carbonization, wash the obtained material with distilled water until the filtrate is neutral, and dry it. (4) Mix the doped carbon material obtained in step (3) with acid or oxidant, heat it, cool it down and filter it after the treatment is completed. Wash the material with distilled water until the filtrate is neutral and dry it.

2. The 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 the following reactors: continuous stirred tank reactor, plug flow reactor, stationary phase reactor, and fluidized bed reactor, or a mixed reactor consisting of two or more of these reactors connected together.

3. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 1, characterized in that, The reactor used in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran is a fixed-bed reactor.

4. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 2, characterized in that, Includes at least one of the following features (a) to (g): (a) The catalyst is in the form of strips, columns, or flakes; (b) The dehydration reaction temperature is 80℃~150℃; (c) The dehydration reaction is carried out under one or more of nitrogen, helium and argon atmospheres; (d) The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran is carried out at a reaction pressure of 0.1 MPa to 4 MPa; or at a reaction pressure of atmospheric pressure to 4 MPa. (e) The 2,5-dimethyl-2,5-hexanediol is reacted in the absence of solvent or in the presence of solvent, wherein the solvent is one or more selected from tetrahydrofuran, acetonitrile and 1,4-dioxane; (f) The continuous preparation method of the 2,2,5,5-tetramethyltetrahydrofuran takes 0.05 h. -1 ~5h -1 The reaction proceeds at a reaction space velocity of [value missing].

5. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 4, characterized in that, In feature (d), the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran is carried out at a reaction pressure of 0.1 MPa to 2 MPa; or at a reaction pressure of atmospheric pressure to 2 MPa. In feature (e), the solvent is tetrahydrofuran or 1,4-dioxane; In feature (f), the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran takes 0.1 h. -1 ~3h -1 The reaction proceeds at a reaction space velocity of [value missing].

6. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 4, characterized in that, The method includes at least one of the following features (a) and (b): (a) The preparation method further includes activating the catalyst before the reaction: before the reaction, the catalyst is heated to an activation temperature of 300°C to 500°C and held for 1 to 6 hours; (b) The preparation method further includes post-reaction processing: the reaction product is condensed and separated into gas and liquid phases, and then distilled.

7. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 6, characterized in that, In feature (a), the activation temperature is 300℃~400℃.

8. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 1, characterized in that, In step (1), the biomass material is selected from one or more of corn cobs, corn stalks, sawdust, peanut shells, and bamboo shoots; The solid acid catalyst is selected from one or more of the following: silicon dioxide, γ-alumina, zirconium dioxide, cerium dioxide, tungsten trioxide, niobium pentoxide, 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 step (1): After the dried biomass raw material is crushed by a pulverizer, it is added together with the solid acid catalyst and ball-milled into a fine powder of 200-400 mesh. After sealing the reaction vessel, the heating temperature is 150-250℃. The mass ratio of distilled water to biomass raw material is 50:1-2:1; The hydrolysis reaction temperature is 120-250℃; The hydrolysis reaction time is 4-10 hours; The concentrated solution has a mass concentration of 10%-30%.

9. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 8, characterized in that, In step (1), the biomass material is one or more of corn cobs, corn stalks, and peanut shells; The solid acid catalyst is one or more of the following: silicon dioxide, γ-alumina, tungsten trioxide, niobium pentoxide, zeolite molecular sieve, and ion exchange resin. In step (1): The mass ratio of distilled water to biomass raw material is 20:1-5:1; The hydrolysis reaction temperature is 150-220℃; The hydrolysis reaction time is 4-6 hours; The concentrated solution has a mass concentration of 10%-20%.

10. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 9, characterized in that, In step (1), the biomass material is one or more of corn cobs and corn stalks; The solid acid catalyst is one or more of γ-alumina, zeolite molecular sieve, and ion exchange resin. In step (1), the hydrolysis reaction temperature is 160-210℃.

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

12. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 11, characterized in that, In step (2): The mass concentration of the acid solution is 3%-10%; The mass ratio of the acid solution to the concentrated solution is 1:1 to 5:1; The hydrothermal treatment temperature is 180-210℃; The hydrothermal treatment time is 5-10 hours.

13. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 1, characterized in that, In step (3): The alkali 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 alkali to the doped carbon material is 1:1 to 10:1; The inert gas used in the carbonization process is selected from one or more of nitrogen, helium, and argon. The carbonization temperature is 300-700℃ and the treatment time is 4-20h; after carbon washing, it is dried at 110℃ for 12h.

14. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 13, characterized in that, In step (3): The mass ratio of the alkali to the doped carbon material is 1:1 to 5:1; The inert gas used in the carbonization process is one or more of nitrogen and argon.

15. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 14, characterized in that, In step (3): the mass ratio of the alkali to the doped carbon material is 1:1-3:

1.

16. The continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to claim 1, characterized in that, In 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 30 wt% and sodium hypochlorite with an available chlorine concentration of 6%. The mass ratio of the acid to the doped carbon material is 1:1 to 10:1; The mass ratio of the oxidant to the doped carbon material is 1:1 to 10:1; The heat treatment temperature is 60-90℃; The heat treatment time is 4-10 hours; After washing, dry at 110℃ for 12 hours; After the reaction in step (1) is completed, the filter cake obtained by filtration contains the solid acid catalyst. The filter cake is calcined in air at 350-550°C for 3-6 hours to remove organic matter and obtain the solid acid catalyst. The obtained solid acid catalyst can be recycled.

17. Use of the catalyst in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran according to any one of claims 1-16 in the continuous preparation method of 2,2,5,5-tetramethyltetrahydrofuran.

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