Method for continuous synthesis of 2,2,5,5-tetramethyltetrahydrofuran

Abstract

The present application relates to the field of chemical synthesis, and specifically relates to a method for continuous synthesis of 2,2,5,5-tetramethyltetrahydrofuran. The method comprises reacting 2,5-dimethyl-2,5-hexanediol as a raw material and a catalyst in a continuous reactor, to obtain 2,2,5,5-tetramethyltetrahydrofuran, the catalyst being a solid acid catalyst. By means of adjusting reaction conditions (reaction temperature, air speed, pressure, carrier gas flow speed, etc.), the synthesis method of the present application can enable a product to achieve a very high yield. The synthesis method of the present application can achieve continuous reaction. The reaction temperature is 90°C or higher, which is more suited to the use of a fixed bed reaction, thereby being beneficial for production efficiency.

Description

A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran Technical Field

[0001] The present application relates to the field of chemical synthesis, and in particular to a method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran. Background Art

[0002]

[0003] 2,2,5,5-Tetramethyltetrahydrofuran, CAS number: 15045-43-0, abbreviated as TMTHF, colorless liquid, freezing point -92℃, boiling point 112℃, relative density 0.811 g / mL (25℃), refractive index 1.409, flash point 39℉.

[0004] Toluene is an important solvent in the chemical industry, but due to its odor and toxicity, the pollution and harm caused during use are also obvious. According to research by Fergal P. Byrne et al. (Journal of Cleaner Production, Volume 240, 2019, 118175), 2,2,5,5-tetramethyltetrahydrofuran has similar characteristics to toluene, such as low polarity and low boiling point, and is more environmentally friendly and cleaner than toluene, making it a promising alternative to solvents such as toluene.

[0005] Regarding the synthesis of TMTHF, according to literature records, the method of Denney et al. (J. Org. Chem. 1984, 49, p. 2831) uses DCM as a solvent to react 2,5-dimethyl-2,5-hexanediol with a catalyst, pentaethoxyphosphorane; the method of Vlad et al. (Synthesis 1983, 1983, p. 216) uses benzene as a solvent to react 2,5-dimethyl-2,5-hexanediol with a catalyst, trimethylchlorosilane; and the method of Gillis et al. (J. Org. Chem. 1963, 28, p. 1388) uses DMSO as both a solvent and a catalyst to react with 2,5-dimethyl-2,5-hexanediol.

[0006] Regarding the synthesis of TMTHF using solid acid catalysts, Olah et al.'s method (Synthesis 1981, p. 474) uses Nafion-H as a catalyst in a reaction with 2,5-dimethyl-2,5-hexanediol. Nafion-H, also known as perfluorosulfonic acid resin, is the strongest solid superacid known. However, compared to molecular sieve catalysts, it is too acidic, has poor stability, poor regeneration ability, and low reuse rate, resulting in higher costs. To optimize these issues, researchers have further investigated molecular sieve catalysts for this reaction. Molecular sieve catalysts, also known as zeolite catalysts, are widely used in chemical synthesis due to their unique structure, excellent reproducibility, and low cost. H-type molecular sieves have also become widely used solid acid catalysts.

[0007] The research of Fergal B et al. (Green Chemistry, 2017, 19(15)) shows that in the reaction of synthesizing TMTHF from 2,5-dimethyl-2,5-hexanediol, the use of HBEA in β-zeolite has the best effect; CN 109790134 A also shows that the use of β-zeolites HBEA-25 and HCZB-25 can make the yield of TMTHF reach more than 95%, while the yield of ZSM5-80 is only 28%; the above-mentioned reactions are all batch reactions. The present application aims to use the ZSM5 type molecular sieve, which is more widely used and has lower cost, and adopt a continuous reactor to achieve a higher yield of TMTHF and improve production efficiency. Summary of the Invention Technical issues

[0008] The present application provides a method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran, wherein the method comprises reacting raw materials in a continuous reactor in the presence of a catalyst, wherein the raw material is 2,5-dimethyl-2,5-hexanediol, the catalyst is a solid acid catalyst, preferably a ZSM5 molecular sieve, and the continuous reactor is preferably a fixed bed reactor.

[0009] Technical Solution

[0010] A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran comprises reacting a raw material, 2,5-dimethyl-2,5-hexanediol, in a continuous reactor in the presence of a catalyst to obtain 2,2,5,5-tetramethyltetrahydrofuran, wherein the catalyst is a solid acid catalyst, and the reaction formula is as follows:

[0011] Furthermore, the solid acid catalyst is selected from one or more of activated carbon, ion exchange resin, γ-Al2O3, SiO2, ZrO2, CeO2, WO3, Nb2O5, and zeolite molecular sieve;

[0012] The zeolite molecules are selected from one or more of ZSM5, HY, and β zeolite;

[0013] Preferably, it is a ZSM5 molecular sieve, with a Si / Al ratio of 25:1-500:1, preferably 25:1-100:1.

[0014] Furthermore, the continuous reactor is any one of a continuous stirred tank reactor, a plug flow reactor, a fixed bed reactor and a fluidized bed reactor, or a mixed reactor of two or more of these reactors connected as a continuous reactor, preferably a fixed bed reactor.

[0015] The method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran specifically comprises the following steps:

[0016] (1) adding a solid acid catalyst into a reactor and heating the reactor to a reaction temperature under an inert gas atmosphere;

[0017] (2) After the temperature stabilizes, liquid 2,5-dimethyl-2,5-hexanediol is introduced into the reactor for reaction.

[0018] Furthermore, the reaction temperature in step (1) is in the range of 50-250°C, preferably 100-200°C;

[0019] Furthermore, the inert gas in step (1) is one or more of nitrogen atmosphere, helium atmosphere and argon atmosphere.

[0020] Furthermore, in step (2), the space velocity of 2,5-dimethyl-2,5-hexanediol is in the range of 0.02-3.00h -1 , preferably 0.05-0.80h -1 ;

[0021] Furthermore, the reaction in step (2) is carried out at a reaction pressure of normal pressure to 2 MPa, preferably normal pressure to 0.5 MPa;

[0022] Furthermore, in step (2), the reaction carrier gas flow rate is 5-80 mL / min, preferably 10-50 mL / min.

[0023] Furthermore, in the step (2), the raw material 2,5-dimethyl-2,5-hexanediol is reacted in the absence of a solvent or in the presence of a solvent, wherein the solvent is one or more of tetrahydrofuran, 1,4-dioxane, and acetonitrile, preferably tetrahydrofuran or 1,4-dioxane. Beneficial effects

[0024] 1. The synthesis method of the present application can achieve a very high yield of the product by adjusting the reaction conditions (reaction temperature, space velocity, pressure, carrier gas flow rate, etc.).

[0025] 2. The synthesis method of the present application can realize continuous reaction.

[0026] 3. The reaction temperature is above 90°C, which is more suitable for fixed bed reaction and is beneficial to production efficiency.

[0027] 4. The method described in this application can use ZSM5 molecular sieve, which is more widely used and lower in cost than β zeolite, to achieve a yield equivalent to or even higher than that when using β zeolite in a continuous reaction to synthesize 2,2,5,5-tetramethyltetrahydrofuran (TMTHF), with lower cost, higher production efficiency, higher yield, and better environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 shows the reaction results of continuous reaction for 500 h under the optimal reaction conditions. The optimal reaction conditions are: catalyst 10 g 20-40 mesh ZSM5 molecular sieve, molten 2,5-dimethyl-2,5-hexanediol, normal pressure, nitrogen 20 mL / min, reaction temperature 110 ° C, space velocity 0.120 h -1 Continuous reaction in a fixed-bed reactor. Figure: Con.: 2,5-dimethyl-2,5-hexanediol conversion; Sel.-TMTHF: 2,2,5,5-tetramethyltetrahydrofuran selectivity.

[0029] Figure 2 is a schematic diagram of a continuous reaction fixed bed reactor.

[0030] Figure 3 is a schematic diagram of a batch reactor. DETAILED DESCRIPTION

[0031] In the method for synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to the present application, 2,5-dimethyl-2,5-hexanediol is used as a raw material, and a product is obtained by dehydration reaction. The product is analyzed and detected by gas chromatography (GC), and the low-boiling point product is qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS) and standard GC retention time control to determine that the raw material involved in the reaction is 2,5-dimethyl-2,5-hexanediol. The low-boiling point substance is quantitatively determined by Shimadzu-GC 2020 gas chromatography, and quantitative analysis is performed by comparing the retention time and peak area size with the standard. The relevant calculation formula is as follows: Yield of 2,2,5,5-tetramethyltetrahydrofuran = Conversion of 2,5-dimethyl-2,5-hexanediol * Selectivity of 2,2,5,5-tetramethyltetrahydrofuran

[0032] 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.

[0033] The catalyst used in this method is preferably ZSM5 molecular sieve, which is widely used in chemical synthesis and has low cost. The acidity of ZSM5 molecular sieve varies due to different Si / Al values. The larger the Si / Al value, the weaker the acidity of the catalyst and the slower the deactivation rate. The Si / Al value can be flexibly selected according to production needs to match the appropriate reaction conditions for the reaction. In addition, ZSM5 molecular sieve has strong stability and slow catalyst deactivation. The deactivation problem can be solved by calcining the catalyst for regeneration. It has high reusability and reduces production costs. The following examples demonstrate its excellent stability and reproducibility, and the reaction conversion rate increases with the use time of the catalyst. , it starts to decline at about 350h, the product selectivity does not change significantly, and the conversion rate drops below 90% for calcination regeneration. The calcination conditions are 550℃, air flow rate 200mL / min, and calcination for 5h. After calcination regeneration, the activity of the catalyst can be restored to a level close to that of the fresh catalyst. The experimental results show that not all solid catalysts can catalyze this reaction. It can be seen in the following examples that the reaction does not proceed towards the formation of the target product when using γ-Al2O3. The use of acidic molecular sieves of the same type as ZSM5, such as β zeolite, Y-type molecular sieve, etc., can achieve results comparable to those achieved by ZSM5. The advantage of ZSM5 lies in its wide application and lower cost.

[0034] This method uses a continuous reactor, preferably a fixed bed reactor. During the reaction of a traditional batch reactor, a large amount of raw materials and a small amount of catalyst are in contact. Therefore, the time and area for the raw materials to contact the catalyst are limited, resulting in the inability to improve the conversion rate of the raw materials using a small amount of catalyst; this method uses a fixed bed reactor, which can continuously feed and discharge materials. The time for the raw materials to contact the catalyst can be flexibly changed by adjusting the air velocity of the raw materials entering the fixed bed, so that a small amount of raw materials can contact a large amount of catalyst, thereby improving the conversion rate of the raw materials, and a certain amount of catalyst can be reused for a long time and regenerated in the fixed bed, reducing production costs and labor costs, reducing waste generation, and being more environmentally friendly; the continuous production mode of the continuous reactor improves production efficiency; the results obtained from the test show that the results of this reaction in the continuous reactor are better than those in the batch reactor, as can be seen in the following examples.

[0035] The raw material 2,5-dimethyl-2,5-hexanediol is white crystals at room temperature with a melting point of 86-88°C. A reaction temperature above 90°C allows the reaction to proceed in a liquid-solid phase, making it more suitable for a fixed-bed reaction. The reaction can be carried out with or without a solvent. A solvent can be used to dissolve the raw material before entering the fixed-bed reaction, or the raw material can be directly preheated to 90°C before entering the fixed-bed reaction. Flexible adjustments can be made based on actual production needs.

[0036] CN109790134A clearly states that the use of β zeolite can achieve a TMTHF yield of over 95%, while the yield of ZSM5 is very low, only 28%. Taking into account the above advantages, the method described in this application can use ZSM5 molecular sieve, which is more widely used and less expensive than β zeolite, to achieve a yield equivalent to or even higher than that of β zeolite in a continuous reaction to synthesize 2,2,5,5-tetramethyltetrahydrofuran (TMTHF), lowering costs, improving production efficiency, increasing yield, and being more environmentally friendly.

[0037] Example

[0038] 2,2,5,5-Tetramethyltetrahydrofuran was prepared by the following steps:

[0039] Continuous reaction: Add 10g of 20-40 mesh catalyst to a fixed bed reaction tube, heat to the reaction temperature under N2 atmosphere, and after the temperature stabilizes, under a certain pressure, introduce molten 2,5-dimethyl-2,5-hexanediol or 2,5-dimethyl-2,5-hexanediol dissolved in a solvent into the fixed bed reactor at a certain space velocity for reaction. If a solvent is used for dissolution, the solvent is preferably tetrahydrofuran and 1,4-dioxane, and the mass concentration of 2,5-dimethyl-2,5-hexanediol is (10±5)%.

[0040] Batch reaction: Install a spherical condenser above a three-necked flask with a condensation temperature of 0-5°C. Add a certain amount of solid 2,5-dimethyl-2,5-hexanediol to the flask and heat it to melt it. When all the raw materials become molten, add a certain amount of catalyst powder, heat to the reaction temperature, and stir the reaction for 5 hours.

[0041] The reaction results under different reaction conditions are shown in Table 1.

[0042] Table 1. Reaction results using different catalysts and different reaction conditions

[0043] In Table 1, lines 2 and 3 are comparisons of batch reactions using β zeolite and ZSM5 molecular sieves carried out under the conditions described in CN109790134A; lines 4-9 are comparisons of continuous and batch reactions using ZSM5 molecular sieves under different forms of raw materials, pressures, carrier gas flow rates, reaction temperatures, and space velocities. It can be seen that the yield under the continuous reaction conditions is significantly better than that under the batch reaction conditions.

[0044] Rows 10-13 in Table 1 compare the continuous reaction and batch reaction using β zeolite and HY molecular sieve. It can also be concluded that the yield of the continuous reaction is better than that of the batch reaction. In addition, it can also be concluded that under the same conditions, the yield of the continuous reaction using ZSM5 molecular sieve is better than that of β zeolite and HY.

[0045] Rows 14-16 in Table 1 compare the continuous reactions using γ-Al2O3, A35, and A15. Under the same conditions, the yield of ZSM5 molecular sieves is superior to that of γ-Al2O3, A35, and A15. In summary, the continuous synthesis of 2,2,5,5-tetramethyltetrahydrofuran using the method described in this application is significantly superior to batch reactions.

[0046] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran, characterized in that: The raw material 2,5-dimethyl-2,5-hexanediol and a catalyst are reacted in a continuous reactor to obtain 2,2,5,5-tetramethyltetrahydrofuran, wherein the catalyst is a solid acid catalyst, and the reaction formula is as follows:

2. A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to claim 1, characterized in that: The solid acid catalyst is selected from one or more of activated carbon, ion exchange resin, γ-Al2O3, SiO2, ZrO2, CeO2, WO3, Nb2O5, and zeolite molecular sieve; The zeolite molecules are selected from one or more of ZSM5, HY, and β zeolite; Preferably it is a ZSM5 molecular sieve, with a Si / Al ratio of 25:1-500:1, preferably 25:1-100:

1.

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

4. A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to any one of claims 1 to 3, characterized in that: The method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran specifically comprises the following steps: (1) adding a solid acid catalyst into a reactor and heating the reactor to a reaction temperature under an inert gas atmosphere; (2) After the temperature stabilizes, liquid 2,5-dimethyl-2,5-hexanediol is introduced into the reactor for reaction.

5. A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to claim 4, characterized in that: The reaction temperature in step (1) is in the range of 50-250°C, preferably 100-200°C.

6. A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to claim 4, characterized in that: In the step (1), the inert gas is one or more of a nitrogen atmosphere, a helium atmosphere and an argon atmosphere.

7. A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to claim 4, characterized in that: In step (2), the space velocity of 2,5-dimethyl-2,5-hexanediol is in the range of 0.02-3.00h -1 , preferably 0.05-0.80h -1 .

8. A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to claim 4, characterized in that: The reaction in step (2) is carried out at a reaction pressure of normal pressure to 2 MPa, preferably normal pressure to 0.5 MPa.

9. A method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to claim 4, characterized in that: The reaction carrier gas flow rate in step (2) is 5-80 mL / min, preferably 10-50 mL / min.

10. The method for continuously synthesizing 2,2,5,5-tetramethyltetrahydrofuran according to claim 4, characterized in that: In the step (2), the raw material 2,5-dimethyl-2,5-hexanediol is reacted in the absence of a solvent or in the presence of a solvent, wherein the solvent is one or more of tetrahydrofuran, 1,4-dioxane, and acetonitrile, preferably tetrahydrofuran or 1,4-dioxane.

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