Recovery of thiophene and its derivatives from light benzene

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Technological Progress in Recovering Thiophene and Its Derivatives from Coked Light Benzene Zhou Xiaping and Qin Songbo (East China University of Science and Technology, Shanghai 200237) Thiophene and its derivatives are harmful impurities that must be removed but are difficult to remove in the purification of coked light benzene (the boiling point difference with benzene is 3.8°C). They are also important raw materials for developing and utilizing medicines and catalysts. The output of coking light benzene in my country is about 600,000 t/a (in 2005). If the thiophene content is calculated from 0.2% to 1.6%, about 6,000 tons of thiophene can be recovered. According to literature statistics, currently there are broad-spectrum antibacterial drugs prepared from thiophene and its derivatives.: Ticarcillin-clavulanic acid, prothiolate and tioconazole, etc. Thiophenes are used to treat cardiovascular disease: Azosemide, titanic acid and hyteronium bromide, etc. ； Taida-thiophenyl porphyrin, a new anti-cancer drug based on thiophene core, has entered the clinical testing stage in the United States, Spain and my country due to its unique efficacy in treating tumors and blood diseases. Thiophene derivatives and thiophene polymers are also new photosensitive and superconducting materials that can be used to develop organic conductors and prepare smectic liquid crystal compounds. In the development of vapor-phase grown carbon fibers and carbon nanotubes, adding thiophene cocatalyst can increase the conversion rate. 2-Thienformyltrifluoropropane made from thiophene is a catalyst for extracting rare earth metals zirconium and hafnium, and can be used to separate uranium, thorium and nuclear reaction products. In view of the differences in dipole moments and molecular polarities between benzene, toluene, thiophene, and methylthiophene, as well as the experimental results of poor extraction efficiency of methylthiophene in toluene fractions, this article focuses on a review of various new extractive distillation combination processes that are practical, environmentally friendly, and economically feasible. It has certain reference value for exploring the multiple catalytic mechanisms of new catalysts such as heteropoly acids and ionic liquids, and for small and medium-sized enterprises in the technological transformation of light benzene processing technology. 1. Thiophene recovery process combining extractive distillation and molecular sieve adsorption. The extractive distillation method is based on adding an extractant to change the relative volatility between light benzene components. The advantages and disadvantages of the extractant can be described and screened by the activity coefficient formula under infinite dilution. Except for the Makeebck Coking Plant in the former Soviet Union, which used diethylene glycol to extract benzene containing 1.44% thiophene, with an annual output of 1,200 tons of thiophene. Domestically, following Ruan Xiangquan and Liu Jiaqi of Tianjin University, Zheng Ying'e and Zhao Weipeng of Nanjing University of Chemical Technology conducted a large amount of gas-liquid equilibrium basic data and experimental research on the separation of benzene and thiophene by extractive distillation. Liu Bing et al. used large-scale computer software to simulate the gas-liquid phase flow rate distribution of the extraction separation tower. Usually, commercial thiophene and high-quality coked benzene can be obtained from coked light benzene with a thiophene content of 1% through secondary extraction and distillation. The method of adsorbing and separating thiophene from coked light benzene is based on the structural properties and adsorption performance of the adsorbent and the difference in molecular size and dipole moment between benzene and thiophene. Gu Zhenhua and others from Qiqihar University based on the minor property differences between non-polar benzene and polar thiophene, through strengthened and improved 5A, 10x, 10y, 13x molecular sieves and natural zeolites, activated clay, diatomaceous earth and kaolin, etc. , the No. 100 adsorbent with an adsorption capacity of 3.15mg/L and a separation factor of about 10 was screened out. It can show strong adsorption capacity regardless of the thiophene mass concentration (1780~4505mg/L). The raw materials of No. 100 adsorbent are easy to obtain and the cost is low. It can be regenerated more than 10 times at 400°C and still has good adsorption effect. If four columns of Ф10mm×1000mm are used in series for adsorption, the thiophene content in light benzene can be reduced from 1000mg/L to 15mg/L. Luo Guohua of Beijing Petroleum Institute and others used a combined process of extractive distillation and selective adsorption of zeolite molecules. Through extractive distillation, the thiophene content in coked benzene can be reduced from 4063mg/L to 22.5mg/L, and the thiophene removal rate is 99.51%. The thiophene content of coked benzene distilled from the top of the extractive distillation tower can be reduced to 22.5mg/L. Using this coked benzene as raw material, using adsorption method to desulfurize, and modifying CuZSM-5 and RECuZSM-5 by silanization, the SiO2-CuZSM-5 and SiO2-REZSM-5 adsorbents are adsorbed at normal pressure, a temperature of 50°C and a space velocity of 1.0h-1, so that there is no thiophene in the adsorbed coked benzene, and the penetration time of the adsorption bed can be as long as 79 h. The saturated adsorbent can be regenerated under hot nitrogen purging at 350°C. Silanization can effectively improve the mechanism of action of adsorbents B acid and L acid, and can also slow down adsorbent deactivation and other deficiencies. 2 Thiophene recovery process combining extractive distillation and reactive distillation (extraction) Reactive distillation is a chemical process that couples chemical reaction and distillation. Reactive distillation has the advantages of high selectivity, high conversion rate, enhanced equipment production capacity, low energy consumption and operating costs, and low investment. This research group of East China University of Science and Technology uses the fluorosulfonic acid resin provided by Shanghai Organic Chemistry as a catalyst. The efficiency of single-time removal of thiophene is better than that of HD-8 and other cationic resins (solid acid) provided by the school's Huazhen Company. However, the fluorosulfonic acid catalyst has shortcomings such as being expensive, prone to carbon deposition on the catalyst surface, and difficult to regenerate online. The unsaturated compounds contained in coked light benzene are used to collaboratively separate benzene and thiophene using HD-8 catalyst. Due to the presence of unsaturated compounds in the raw material light benzene, the alkylation reaction can proceed smoothly. And because the HD-8 catalyst mainly uses sulfonic acid groups to provide protic acid for catalysis, the activity of the catalyst is directly related to the acid function value. The experiment was based on the definition of super acid and the scale of whether m-nitrotoluene can significantly change color. In the study, the Hammett indicator method was used to distinguish strong acid and super acid catalysts. For strong acid catalysts that cannot be determined according to Hammett indicator, the PK value is determined using potentiometric titration. Experiments show that when the acid function of the ion exchange resin catalyst is between -8.5 and 9.0, the kinetics of the alkylation reaction of thiophene is approximately a zero-order reaction, and the removal rate of thiophene in benzene is high. When the acid function drops to -2.1, the thiophene removal rate decreases rapidly. The HD-8 catalyst can be regenerated online in the tower by lower alcohol or co-swelling, and the thiophene derivatives can be recovered. When the temperature is ≤140°C, this operation can be cycled 6 to 8 times, but its service life is far from industrial application. When catalyzed by external doped polyacid (a polybasic acid formed by the condensation of two or more inorganic oxygen-containing acids) and non-coking auxiliary agents, the reactive distillation method can achieve a removal rate of 95% of thiophene, and can obtain special-grade benzene, toluene and 10°C xylene, with a triphenyl yield of ≥88%. The temperature and pressure controlled by the reactive distillation method for synergistic separation of coked benzene-thiophene are similar to the traditional distillation method of benzene processing. The solid agent plays both a catalytic role and a filler role in the process. It is more suitable to be in the form of a catalyst firmware in the distillation tower. Combined with computer application software such as ASPEN PLUS, the technical parameters of the extractive distillation tower can be effectively calculated according to the strict method. This was verified in the thiophene recovery test conducted by East China University of Science and Technology for Henan Kaisun Chemical Company. By adding liquid heteropoly acid, since heteropoly acid can generate a passivation layer on the surface of stainless steel, the corrosion problem can be solved well by using stainless steel. This combined process can ensure the activity of the solid acid catalyst and extend the life of the solid acid catalyst, so it is more likely to be industrialized. 3. Thiophene recovery process combining extractive distillation and ionic liquid method. Ionic liquid is also called room temperature ionic liquid. It refers to a salt composed of ions that is liquid at room temperature or low temperature. Compared with solid substances, it is liquid. ； It is ionic compared to traditional liquid substances. Therefore, ionic liquids present advantages that conventional solid and liquid catalysts do not have, and are a new type of "green" media and catalysts. Due to their good thermal stability, strong solubility and almost no vapor pressure, ionic liquids are used in Friedel-Crafts, Diels-Alder and other reactions, involving chemical engineering, energy, environment, materials, drug synthesis and other disciplines or interdisciplinary subjects. In recent years, ionic liquid catalysts have been used abroad to remove organic sulfur (thiophenes) from fuel. The ionic liquid of organic sulfur in the absorption plant can destroy the original chemical and physical balance through distillation and other methods, so that the ionic liquid catalyst can be regenerated and thiophene can be recovered. In China, Gu Yanlong, Deng Youquan and others from the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, used methylimidazole fluoroborate ionic liquid to treat n-octane simulated fuel oil at room temperature. The thiophene content in it can be reduced from 1500mg/kg to about 500mg/kg, and the best can reach about 150mg/kg. Wang Yuxin, Li Dandong, and Yuan Qiuju of Liaoning University of Petrochemical Technology used fluorophosphorus-imidazole ionic liquid complex to adsorb thiophene compounds in diesel. Within the range of agent-oil ratio 0.05-0.20, temperature 20-60°C, and reaction time 60 minutes, the thiophene removal rate can reach 69.1%, and the diesel yield is about 95%-99%. After repeated 6 times, the ionic liquid catalyst can still effectively remove more than 67% of thiophene. Compared with chloroaluminic acid ionic liquids, hexafluorophosphoric acid-imidazole ionic liquids are stable when exposed to water and air and are not easy to decompose. In addition to the high cost of treatment, the principles are the same if they are used to depyrophenylate coking light benzene. This method, combined with the extractive distillation process of coked hydroxybenzene-thiophene, can significantly reduce the sulfur treatment capacity of ionic liquids, making it a good environmental and economical industrial application prospect.