1,1,1,3,3-五氯丙烷气相氟化合成1,3,3,3-四氟丙烯过程的热力学研究

Thermodynamic analysis on the synthesis of 1,3,3,3-tetrafluoropropene via gas-phase fluorination of 1,1,1,3,3-pentachloropropane

采用密度泛函理论,使用Materials Studio的DMol3模块,计算了1,1,1,3,3-五氯丙烷(HCC-240fa)气相氟化生成1,3,3,3-四氟丙烯(HFO-1234ze)反应体系中各反应的反应焓变和Gibbs自由能变;并通过比较不同温度下各反应的反应焓变和Gibbs自由能变,对反应过程进行了热力学分析.结果表明:HCC-240fa经过氟氯交换和脱HCl反应合成中间体1-氯-3,3,3-三氟丙烯(HCFC-1233zd)的反应为热力学上可自发进行的反应,且产物以HCFC-1233zd(E)为主;低温有利于HCFC-1233zd与HF进行加成反应生成1-氯-1,3,3,3-四氟丙烷(HFC-244fa),HFC-244fa可与HF进行氟氯交换反应合成1,1,1,3,3-五氟丙烷(HFC-245fa);高温有利于HCFC-1233zd进行氟氯交换反应合成HFO-1234ze;HFC-244fa脱HCl反应和HFC-245fa脱HF反应均需要较高的反应温度,主产物为HFO-1234ze(E).

The changes of the enthalpy and Gibbs free energy during the synthesis of 1,3,3,3-tetrafluoropro- pene （ HFO-1234ze） via gas-phase fluorination of 1,1,1,3,3-pentachloropropane （ HCC-240fa ） were esti- mated based on density functional theory （DFT） by using Materials Studio DMol3 calculations. By comparing the changes of the enthalpy and Gibbs free energy as a function of reaction temperature for each independent reaction, thermodynamics of the reaction process were analyzed. The results showed that the synthesis of inter- mediate 1-ehloro-3,3,3-trifluoropropene （ HCFC-1233zd} by fluorination of HCC-240fa was a spontaneous re- action in chemical thermodynamics, with HCFC-1233zd（E） as the main product. The formation of l-chloro-1, 3,3,3-tetrafluoropropane （HFC-244fa） by addition reaction between HCFC-1233zd and HF was favored at lower reaction temperature; while the formation of HFO-1234ze by C1/F exchange reaction between HCFC-1233zd and HF was favored at higher temperature. Moreover, both dehydrochlorination of HFC-244fa and de- hydro fluorination of 1,1,1,3,3-pentafluoropropane （HFC-245 fa） required higher reaction temperature, which resulted in the formation of HFO-1234ze（E）.