Synthesis method of ETFE

Abstract

The invention discloses a synthesis method of ETFE, and belongs to the technical field of organic synthesis. The method comprises the following steps: carrying out a dehydration reaction on THFA and alkali metal hydroxide in methylcyclohexane, separating out water generated in the dehydration reaction, and adding halogenated ethane to carry out a condensation reaction, so as to obtain a salt-containing ETFE crude product; and filtering the salt-containing ETFE crude product to remove halide salt, and sequentially separating and recovering methylcyclohexane and ETFE distillate through atmospheric distillation. According to the method, the synthesis process of alkoxide is simplified, side reactions are few, subsequent condensation and distillation separation are facilitated, the yield of the obtained ETFE is higher than 98.0%, and the mass content is gt; the anionic polymerization structure regulator has the advantages of low cost, environmental protection, safety and reliability, and can meet the application requirements of the anionic polymerization structure regulator.

Description

Technical Field

[0001] This invention relates to a method for synthesizing tetrahydrofurfuryl ethyl ether (ETFE), and particularly to an improved Williamson method for synthesizing ETFE, belonging to the field of organic synthesis. Background Technology

[0002] Ethyl tetrahydrofurfuryl alcohol (THFA) is synthesized from ethane chloride using the Williamson process to produce tetrahydrofurfuryl alcohol ethyl ether (ETFE). Because the boiling points of ETFE and THFA differ by only 21°C, separation between the two is difficult. As a structure modifier in the anionic polymerization of conjugated diene polymers, ETFE requires medium-pressure preparation and its high boiling point makes separation and purification challenging. ETFE was first developed by Penner Chemicals in the United States and is primarily used as an activating structure modifier in the production of anionic polymers such as butadiene-styrene polymers like SBS, SSBR, and SEBS. It can improve the vinyl unit content and the uniformity of diene copolymers at lower dosages and higher temperatures. For example, US Patent 4305878A discloses the extraction of THFA and ethanol from a mixture containing tetrahydrofurfuryl alcohol, ethyl tetrahydrofurfuryl alcohol ether, ethanol, and water using an alkaline earth metal chloride, and mentions that it is difficult to separate ETFE from the mixture by distillation. The method involves two or more extractions, mixing 76% ETFE, 23% THFA, and 3% ethanol with a saturated calcium chloride aqueous solution. The aqueous layer is then removed, and the oil phase is dissolved in a saturated calcium chloride aqueous solution before the aqueous phase is removed again. The resulting ETFE has a purity of 96.6%, while water, THFA, and other impurities account for 3.4%. However, this method still does not meet the standards for anionic polymerization grade ETFE. Meanwhile, British patent GB2000771A discloses a method for preparing THFA salts using a large excess of THFA. Although THFA has excellent solubility for THFA salts, and the mixture of THFA and THFA salts still exhibits fluid dynamics at 30°C, which is beneficial for mass and heat transfer in the subsequent condensation reaction to generate ether units, the THFA residue in the ether is difficult to separate and remove. The method used in this paper to synthesize crude ETFE from ethane chloride and THFA is not described in terms of purification.

[0003] The literature (“Synthesis of Tetrahydrofurfuryl Ethyl Ether, a Novel Structure Modifier for Styrene-Butadiene Rubber” Zhang Jianguo et al., Sichuan Chemical Industry, 2010.3(13)) describes the preparation of tetrahydrofurfuryl ethyl ether using tetrahydrofurfuryl alcohol, sodium hydroxide, bromoethane, and maleic anhydride as raw materials. The process involves purifying ETFE from the product of the reaction of THFA with bromoethane, etc., with n(tetrahydrofurfuryl alcohol):n(sodium hydroxide):n(bromoethane) = 1:1:(1~1.2); n(residual tetrahydrofurfuryl alcohol during refining):n(maleic anhydride) = 1:1.2. Because THFA and ETFE (boiling range 156-158℃) have a 20℃ boiling point difference, even with high plate numbers and high reflux ratios during distillation, the collected ETFE still contains 2-3% THFA. In lithium-based anionic polymerization, if the ETFE still contains 2-3% THFA, even a small amount of THFA can kill the active species in the anionic polymerization. Therefore, it is difficult to obtain high-purity ETFE using conventional distillation methods. The authors treated the synthesized ETFE-THFA mixture with maleic anhydride to convert THFA into the addition polymer maleic acid monotetrahydrofurfuryl alcohol ester. However, this conversion method has drawbacks such as long reaction time, low conversion efficiency, and the presence of unreacted THFA in the purified ETFE. To effectively separate ETFE...

[0004] Chinese patent CN113896698A discloses a method for synthesizing tetrahydrofurfuryl ethyl ether. This method involves reacting THFA with an alkali metal hydroxide in an alkoxide solvent system containing a dehydrating agent to undergo a dehydration reaction, simultaneously separating the water produced during the dehydration reaction to obtain the alkoxide product. The alkoxide solvent is C7-C6. 12 The method involves reacting aryl alcohols or furan ethers with alkyl halides after cooling to obtain crude ETFE containing salt. The crude ETFE product is then filtered to remove chloride salts, and the ETFE fraction is collected by distillation. The obtained ETFE fraction has a mass content higher than 98.0% ETFE, and the overall reaction yield is >95%. The distillate solvent can be recycled. This method avoids the use of excessive THFA by using a special alkoxide solvent. However, it requires a dehydrating agent, and the yield is limited to a maximum of 96%. Furthermore, the distillation process still requires a relatively high number of theoretical plates (40-50) and a high reflux ratio (2-3), resulting in high energy consumption. Summary of the Invention

[0005] To address the aforementioned deficiencies in existing ETFE synthesis methods, the present invention aims to provide a method for synthesizing ETFE. This method yields ETFE with a THFA conversion rate of not less than 98.0%, and the ETFE obtained using a simple conventional distillation method has a mass fraction of not less than 98.5% and a polar impurity content of not more than 0.4%. This method meets the requirements for use as a structure modifier in the preparation of conjugated diene elastic materials by anionic polymerization. Furthermore, this method is convenient to operate, has a simple process, and is low-cost, making it suitable for large-scale industrial production.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for synthesizing ETFE. The method involves dehydrating THFA and alkali metal hydroxide in methylcyclohexane, while separating the water produced in the dehydration reaction, and then adding haloethane for a condensation reaction to obtain a crude ETFE product containing salt. After filtering to remove the halosal salt from the crude ETFE product, the methylcyclohexane and ETFE fractions are separated and recovered sequentially by atmospheric distillation.

[0007] Since THFA alkoxides remain solid above 110°C, they negatively impact mass and heat transfer in the condensation reaction environment between THFA alkoxides and haloethanes, and may even hinder reaction stirring. Therefore, the key to this invention is the use of methylcyclohexane, whose boiling point differs from ETFE by 55°C, as the reaction medium. Firstly, it acts as a dehydrating agent; its suitable boiling point allows it to form an azeotrope with water, effectively separating the water formed from the reaction of THFA with alkali metal hydroxides, significantly improving the alkoxide yield. Secondly, methylcyclohexane has a higher solubility for THFA alkoxides than other alkanes (such as cyclohexane), which is beneficial for the reaction between THFA and alkali metal hydroxides. Thirdly, it ensures the low-temperature fluidity of THFA alkoxides, improving the efficiency of subsequent condensation reactions and reducing side reactions. Furthermore, the methylcyclohexane is completely separated and recycled.

[0008] As a preferred embodiment, the molar ratio of THFA to the alkali metal hydroxide is 1:1.10 to 1:1.15. It is worth further clarification that: compared to the alkali metal hydroxide, if THFA is slightly in excess, the crude ETFE containing salt will contain a certain amount of THFA, making it difficult to completely remove THFA from the crude product; if the alkali metal hydroxide is excessively excessive, too much ethane halide will be consumed during the condensation reaction with the addition of ethane halide. Ethane halide will undergo elimination and hydrolysis reactions under alkaline conditions, producing ethylene and ethanol as byproducts, respectively. Furthermore, THFA is weakly acidic and readily reacts with strong bases to form sodium alkoxide and water. However, the generated water must be removed from the reaction environment immediately to maximize the complete conversion of THFA into alkoxide, preventing unconverted THFA from remaining in the sodium alkoxide and affecting subsequent ETFE purification. This is one of the core aspects of this invention. In existing technologies, such as (GB2000771A), the solvent used is THFA, which is the starting material for the reaction. That is, THFA salt is prepared by a method of THFA in large excess. This technology brings difficulties to the subsequent separation of ETFE.

[0009] As a preferred embodiment, the alkali metal hydroxide is solid sodium hydroxide. Among all alkali metal hydroxides, sodium hydroxide is the most economical, and as a solid alkali, its mass fraction ≥96% is sufficient.

[0010] As a preferred embodiment, the amount of methylcyclohexane used is 1.5 to 2.5 times the mass of THFA. Patent GB2000771A uses THFA as the starting material, i.e., a THFA-in-excess method to prepare THFA alkoxides. Although THFA has excellent solubility for THFA salts, and the mixture of THFA and THFA salts still exhibits fluidity at 30°C, which is beneficial for mass and heat transfer in the subsequent condensation reaction to form ether units, THFA residues in the ether are difficult to separate and remove. The methylcyclohexane of this invention enables the THFA alkoxides to maintain high fluidity at around 70°C, which is beneficial for subsequent condensation reactions. Since methylcyclohexane acts as both a dehydrating agent and a solvent, its amount cannot be too low. If the amount is too low, the THFA alkoxides will have poor fluidity; if the amount is too high, it will mainly increase the energy consumption for subsequent recovery.

[0011] As a preferred embodiment, the dehydration reaction conditions are: a temperature of 105–115°C and a time of 7–8 hours. It is worth noting that methylcyclohexane is used as both the solvent and the dehydrating agent. This is to remove the azeotropically generated water from the reaction environment at its boiling point, which is beneficial for shifting the reaction to the right and ensuring the complete formation of alkoxides from THFA within a certain timeframe, achieving a dehydration rate of not less than 99.0%.

[0012] As a preferred embodiment, the molar ratio of the haloethane to the alkali metal hydroxide is 1.05–1.10. The haloethane is preferably chloroethane, which is cheaper than bromoethane. If the proportion of haloethane is too low, efficient conversion of THFA alkoxides is difficult; if the proportion is too high, elimination and substitution byproducts are easily generated. A slight excess of haloethane is beneficial for the complete conversion of THFA alkoxides to ETFE, preventing the incomplete conversion of THFA alkoxides from hydrolyzing back to THFA, thus affecting the purification of ETFE.

[0013] As a preferred embodiment, the condensation reaction conditions are: pressure 4–6 bar, temperature 60–80 °C, and time 3–4 h. It is well known that the condensation reaction of alkoxides with ethane halides can proceed at room temperature. However, for this reaction, appropriately increasing the condensation temperature can lower the activation energy and also facilitate the melting and dissolution of the alkoxide into a liquid phase, improving mass and heat transfer. If the temperature is too high, the saturated vapor pressure of the ethane halide is high, and the hydrolysis and elimination side reactions of the ethane halide will increase; if the temperature is too low, the condensation reaction rate of the THFA alkoxide with the ethane halide decreases, or even fails to occur. A pressure environment of 4–6 bar can effectively reduce the side reactions of the ethane halide.

[0014] It is worth further elaborating that, under the condition of limiting the amount of methylcyclohexane, the THFA alkoxide / methylcyclohexane mixture exhibits a molten state at temperatures above 60°C. When the temperature is below 60°C, the reaction liquid changes from a molten state to a muddy or solid state, which can cause the stirring blades to seize, preventing the condensation reaction from proceeding as scheduled. Furthermore, the condensation reaction of THFA alkoxides with haloethanes is an exothermic reaction. Therefore, during the condensation reaction process, ensuring the THFA alkoxide mixture exhibits a readily flowing dynamic state, haloethanes should be added to the THFA alkoxide slowly. Simultaneously, the heat of reaction must be removed to prevent localized overheating, boiling over, material leakage, and the occurrence of side reactions. Excessive heat removal and a drop in temperature too low can lead to solidification of the reactants. Additionally, the small amount of ethylene produced as a byproduct during the condensation reaction should be periodically vented to avoid overpressure in the reaction environment and unsafe conditions.

[0015] The preferred method for desalting the crude ETFE product of the present invention is to use conventional and well-known methods to remove the crystalline sodium chloride generated in the reaction solution by pressure filtration. The filtrate contains ETFE, methylcyclohexane, and trace amounts of byproducts such as ethanol and ethylene, which are organic impurities.

[0016] As a preferred embodiment, the atmospheric distillation process employs a packed column. Under the conditions of 8 to 10 theoretical plates and a reflux ratio of R = 1, the light components below 78°C are first removed, followed by the collection of the methylcyclohexane fraction at 101°C, and then the collection of the ETFE fraction at 156 to 157°C.

[0017] The ETFE separation described in this invention is obtained by distillation purification from the filtrate. As a preferred embodiment, in the process of distillation purification of ETFE, the distillation column is a packed column with 8 to 10 theoretical plates, intermittent distillation, and a reflux ratio of R=1. First, light components such as water, ethylene, ethanol, and chloroethane are removed before 78°C. Then, the methylcyclohexane fraction at 101°C is collected under atmospheric pressure and a reflux ratio of R=1. Finally, the ETFE fraction at 156 to 158°C is collected under atmospheric pressure and a reflux ratio of R=1.

[0018] The methylcyclohexane fraction collected at 101°C according to the present invention has a content >98.0% and can be recycled as a solvent; the ETFE fraction collected at 156-158°C under normal pressure and reflux ratio R=1 has a mass content >98.5%.

[0019] The ETFE preparation method provided by this invention includes the following specific steps:

[0020] 1) Add a measured amount of methylcyclohexane, THFA, and caustic soda to a steel reactor equipped with a stirrer, condenser, dehydration separator, and thermometer. Stir and heat to 101-115°C to carry out the dehydration reaction. Since the dehydration reaction is reversible, continue until no water generated in the reaction system escapes and precipitates out into the water separator.

[0021] 2) After dehydration, the reactants are cooled to 60-80°C. At this time, a certain amount of chloroethane is slowly added to the reactor to carry out the condensation reaction. The pressure in the reactor is controlled to 4.5-5.0 bar. At the same time, the heat of reaction is removed with cold water until the addition of chloroethane is completed. Then, the reaction is stirred at 70-80°C for another 2 hours to obtain the crude product containing salt.

[0022] 3) The above-mentioned salt-containing crude product is filtered at room temperature to remove sodium chloride, thereby obtaining a salt-free crude ETFE product;

[0023] 4) Under normal pressure, the crude ETFE product without salt is distilled in a distillation column with 8 to 10 theoretical plates to remove low-boiling-point impurities below 80°C. Then, with a reflux ratio R = 1 and 101°C methylcyclohexane recovered by distillation, the kettle temperature is raised to 158 to 160°C, R = 1, and the ETFE fraction at 156 to 158°C is collected by distillation to obtain the target ETFE product with a mass fraction >98.5%.

[0024] The ETFE prepared by this invention has a yield of >98.0% and a mass content of >98.5%. The methylcyclohexane recovered by distillation can be recycled to the sodium tetrahydrofurfuryl alcohol preparation unit for reuse.

[0025] Compared with existing technologies, the beneficial effects of the technical solution of this invention are as follows:

[0026] The present invention provides a process for preparing ETFE from tetrahydrofurfuryl alcohol. The alkoxide synthesis reaction time is short, and the dehydration efficiency is high. The synthesized THFA sodium salt and methylcyclohexane mixture remains a readily flowing melt at around 70°C. The condensation reaction of the THFA alkoxide / methylcyclohexane melt with chloroethane ensures the activation energy of the reaction, allowing the condensation reaction to proceed normally and effectively. Mass and heat transfer are good, and the reaction is easy to control. The yield of ETFE, based on THFA, is >98.0%. Methylcyclohexane can be effectively recovered using conventional simple distillation and can be recycled back to the tetrahydrofurfuryl alcohol sodium preparation unit for reuse. The mass fraction of ETFE obtained by simple distillation and purification is >98.5%. In applications as anionic polymer active structure modifiers, it has the advantages of low dosage, strong regulating ability, and is a highly efficient structure modifier for conjugated diene polymers, meeting the standard requirements for anionic polymerization.

[0027] This invention selects the condensation reaction of THFA alkoxide / methylcyclohexane melt with chloroethane to prepare ETFE. It has the advantages of readily available and inexpensive raw materials, high selectivity, and a conversion rate of less than 3% from chloroethane to by-product ethylene and ethanol. The manufacturing cost of ETFE is only half that of tetrahydrofurfuryl ethyl ether prepared by the bromoethane method. It is environmentally friendly, safe and reliable. Attached Figure Description

[0028] Figure 1 The image shows the gas chromatogram of ETFE prepared in Example 1. Detailed Implementation

[0029] The present invention is illustrated by the following embodiments, which do not constitute a limitation on the scope or implementation of the present invention.

[0030] In the following examples, gas chromatography was used to determine the content of organic raw materials, reactions, purification, and byproducts in each production unit.

[0031] Example 1

[0032] In a 2-liter steel reactor equipped with a stirrer, a dehydrator, and a thermometer, 800g of methylcyclohexane, 420g of THFA (98.6% by mass), and 195g of caustic soda (96.0% by mass) were added sequentially. The mixture was stirred and heated to 105°C to carry out an esterification and dehydration reaction. When no obvious reaction water was generated and escaped from the water separator, the dehydration reaction time was 7 hours.

[0033] The dehydrated reactants were then cooled to 70°C with 25°C water. The alkoxides became yellow, viscous, non-Newtonian fluids. At this point, 305.6g of ethane (greater than 99.5% by mass) was added uniformly to the reactor over 1.5 hours to initiate a condensation reaction. The reactor pressure was controlled at 4.5 bar. If necessary, the heat of reaction was removed with cold water, and the condensation reaction temperature was controlled at 75°C. After the ethane was completely added, the mixture was stirred for another 2 hours. When no exothermic reaction was observed, the crude ETFE product containing salt was obtained.

[0034] The salt-containing crude product was filtered at room temperature and washed with 150g of methylcyclohexane to obtain 238.8g of sodium chloride. 1474g of filtrate containing salt-free crude product was obtained. The mass composition of the filtrate was determined by gas chromatography and is shown in Table 1. The yield of ETFE was 98.3%.

[0035] Table 1

[0036]

[0037] The filtrate was placed in a three-necked flask containing a 25mm inner diameter silver-plated glass column with approximately nine glass spring packing plates for distillation. The reflux ratio R = 1 was controlled. The light fraction up to 101°C was collected, followed by the large amount of methylcyclohexane fraction at 101°C (the methylcyclohexane mass fraction was measured to be 98.3%). A small amount of transition fraction above 101°C and below 156°C was then removed. Finally, the fraction from 156 to 158°C was collected under atmospheric pressure and a reflux ratio R = 1. The ETFE mass fraction was measured to be 98.7%, and the THFA mass fraction was 0.44%. The gas chromatogram of ETFE is shown in [Figure number missing]. Figure 1 .

[0038] Example 2

[0039] The process conditions and parameters in Example 1 were kept unchanged, except for the addition of 450g of THFA. The composition of the resulting desalination filtrate is shown in Table 2, with an ETFE yield of 98.27%.

[0040] Table 2

[0041]

[0042]

[0043] The quality score of collected ETFEs was 98.52%, of which THFA accounted for 0.93%.

[0044] Example 3

[0045] The relevant process conditions and parameters in Example 2 were kept unchanged, except that 170g of caustic soda was added.

[0046] The composition of the desalted filtrate obtained is shown in Table 3, in which the yield of ETFE was 96.22%.

[0047] Table 3

[0048]

[0049] The quality score of collected ETFE was 97.21%, of which THFA accounted for 1.86%.

[0050] Example 4

[0051] The relevant process conditions and parameters in Example 1 were kept unchanged, except that 265.7g of chloroethane was added.

[0052] The composition of the desalted filtrate obtained is shown in Table 4, with an ETFE yield of 94.95%.

[0053] Table 4

[0054]

[0055]

[0056] The quality score of collected ETFE was 96.83%, of which THFA accounted for 2.74%.

[0057] Example 5

[0058] The relevant process conditions and parameters in Example 1 were kept unchanged, except that 650g of methylcyclohexane was added. After the dehydration reaction was carried out for 7 hours, the mixture was then cooled to 75°C.

[0059] The resulting reactant, sodium THFA, exhibited a non-flowing, muddy consistency.

[0060] Example 6

[0061] The relevant process conditions and parameters in Example 1 were kept unchanged, except that methylcyclohexane was replaced with cyclohexane, the dehydration reaction temperature was 90°C, and the dehydration reaction was carried out for 10 hours.

[0062] The actual dehydration rate was 73.8% of the theoretical amount. When the reactants were cooled to 75°C, the sodium THFA salt reactant appeared as a non-flowing solid wax.

[0063] Example 7

[0064] Keeping the relevant process conditions and parameters in Example 1 unchanged, except that the amount of caustic soda added was 215g, and after dehydration reaction at 105°C for 6h, the theoretical dehydration rate was 99.3%, the ethanol content in the condensation reaction product was 0.87%, and the yield of ETFE was 96.6%.

[0065] Example 8

[0066] In a clean 5L polymerization reactor, 3500mL of cyclohexane solvent, 0.45mL of ETFE prepared in Example 1, 100mL of freshly purified styrene monomer, 300mL of butadiene, and 4.50mL of 0.4mol / L lithium n-butadiene initiator were added. The reaction was carried out at 70°C and 4.5bar nitrogen pressure for 60min with stirring. The resulting solution-polymerized styrene-butadiene rubber raw material weighed 282g, with a 1,2-addition unit content of 61.3% in its molecule.

Claims

1. A method for synthesizing ETFE, characterized in that: THFA and alkali metal hydroxide were dehydrated in methylcyclohexane, and the water produced in the dehydration reaction was separated. Then, haloethane was added to carry out a condensation reaction to obtain a crude product containing salt ETFE. After the crude product containing salt ETFE was filtered to remove the halide salt, the methylcyclohexane and ETFE fractions were separated and recovered by atmospheric distillation.

2. The method for synthesizing ETFE according to claim 1, characterized in that: The molar ratio of THFA to the alkali metal hydroxide is 1:1.10 to 1:1.

15.

3. A method for synthesizing ETFE according to claim 1 or 2, characterized in that: The alkali metal hydroxide is solid sodium hydroxide.

4. The method for synthesizing ETFE according to claim 1, characterized in that: The amount of methylcyclohexane used is 1.5 to 2.5 times the mass of THFA.

5. The method for synthesizing ETFE according to claim 1, characterized in that: The conditions for the dehydration reaction are: temperature 105-115℃, time 7-8h.

6. The method for synthesizing ETFE according to claim 1, characterized in that: The molar ratio of the haloethane to the alkali metal hydroxide is 1.05 to 1.

10.

7. The method for synthesizing ETFE according to claim 1, characterized in that: The conditions for the condensation reaction are: pressure of 4-6 bar, temperature of 60-80°C, and time of 3-4 hours.

8. The method for synthesizing ETFE according to claim 1, characterized in that: In the atmospheric distillation process, a packed column is used. Under the conditions of 8 to 10 theoretical plates and a reflux ratio of R=1, the light components before 78°C are removed first, then the methylcyclohexane fraction at 101°C is collected, and finally the ETFE fraction at 156°C to 158°C is collected.

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