**Production technology of thiophene

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**Tetrahydrothiophene is an important sulfur-containing saturated heterocyclic compound, abbreviated as THT； Product name: Alerton88 ； Molecular formula: C4H8S ； Molecular weight: 88.1 ； Flash point: >18℃ ； Specific gravity: 4/20°C 0.9987 ； Boiling point: 760 mmHg 120.9℃ ； Freezing point: -96.16 ； Autoignition point: 200℃ ； It is practically insoluble in water at 20°C, but soluble in ethanol, ether, and propane; it is a colorless, transparent oily liquid with a foul odor. Due to its stable chemical properties, unique taste, and safety and efficiency, **thiophene is primarily used as a odorant in gas and natural gas. Furthermore, **thiophene can also be used to synthesize a variety of intermediates for new pharmaceuticals, pesticides, and additives for polymer synthesis; it serves as a solvent, chain transfer inhibitor, modifier, catalyst, petroleum model compound, and dielectric material for lithium batteries. It can also be used in the formulation of dental and pharmaceutical primers, hence there is a high demand for it in China. 1 Production technology **The industrial production methods for thiophene mainly fall into two categories based on the raw material route: catalytic hydrogenation of thiophene and** the furan synthesis method. 1.1 Thiophene catalytic hydrogenation method 1.1.1 **Production process of thiophene** The thiophene catalytic hydrogenation method is a traditional synthesis technique for thiophene; it uses thiophene as the raw material, and in a fixed-bed reactor, molybdenum disulfide or palladium supported on activated carbon is employed as a catalyst. By introducing circulating hydrogen gas, thiophene is hydrogenated and reduced to almost entirely convert into **thiophene**. This process technology is mature and has concise steps, but the source of the raw material thiophene is difficult to find and its price is high; therefore, when using this process, it should be integrated with thiophene production facilities. 1.1.2 Production process of thiophene Thiophene, also known as thiofuran, is a stable five-membered heterocyclic compound with the properties of aromatic compounds. The production methods of thiophene include extraction and synthesis. Thiophene is present in the crude benzene fraction obtained during coking process and is considered an impurity in tar. The boiling points of thiophene and benzene differ by only 4°C, making separation extremely difficult. Therefore, the main extraction methods include hydrorefining, sulfuric acid refining, and solvent extraction. Hydrorefining is costly and requires significant investment, making it difficult to implement on an industrial scale ； The sulfuric acid purification method is highly polluting, has a low yield, and presents difficulties in post-treatment; it belongs to an outdated process ； Solvent extraction is a production process that requires low investment, offers high yields, and produces products of high purity; it is widely used at present. Methods for synthesizing thiophene include the gas-phase catalytic method using butane and sulfur, the heteropolyacid-catalyzed method using furan and carbon disulfide, and the synthesis method using acetylene and pyrite. Among them, the gas-phase catalytic method using butane and sulfur was the first thiophene production technique to be industrialized, but it was phased out due to low yields, severe equipment corrosion, and environmental pollution. **The heteropolyacid-catalyzed method for furan and carbon disulfide involves the formation of thiophene from furan and carbon disulfide in a fixed-bed reactor at 400°C, under the action of a heteropolyacid catalyst. The reaction yield reaches 93%, the catalyst has a long lifespan and does not require periodic regeneration, making it a process suitable for industrial application. However, overall, the synthesis processes for thiophene are quite complex, require high technical expertise, and are not suitable for large-scale production. Therefore, the production of thiophene still relies primarily on extraction methods, with most facilities being built in locations where thiophene resources are available. Due to the limited availability of thiophene and its high price, coupled with the rapid increase in demand for thiophene in the pharmaceutical and pesticide industries in recent years, this has affected the development of processes for producing **thiophene via catalytic hydrogenation. 1.2 **Furan synthesis method 1.2.1 **Thiophene production process **The furan synthesis method is a thiophene production process that has been developed in recent years; it uses furan as a raw material, and in a tubular fixed-bed reactor, it undergoes catalytic thioformation to produce thiophene at high temperature and normal pressure, in the presence of refined hydrogen sulfide and a heteropolyacid catalyst supported on γ-Al2O3. At present, several domestic research institutions, such as Shenyang Institute of Chemical Technology, Heilongjiang Research Institute of Petrochemistry, and Sichuan Natural Gas Chemical Industry Research Institute, have successfully developed this technology. The entire process consists of four parts: the raw material and recovery system, the synthesis reaction, product distillation, and the treatment of waste materials. It has advantages such as a simple production process, high product yield, low investment, and easy treatment of waste materials. Using **furan and hydrogen sulfide as raw materials, they are relatively cheaper than thiophene; however, hydrogen sulfide is difficult to store and transport. Therefore, this process should be used in conjunction with hydrogen sulfide handling facilities. 1.2.2 Production processes of hydrogen sulfide Hydrogen sulfide is a colorless, flammable, and highly toxic gas or liquid that causes severe environmental pollution; its production methods can be classified into metal sulfide methods, direct synthesis methods, and recovery and purification methods, depending on the source of raw materials. The metal sulfide method is a traditional approach for producing hydrogen sulfide, with the barium salt method and the sodium salt method being the main types. The barium salt method involves first reacting barium sulfate with coal powder at high temperatures to produce barium sulfide, and then reacting barium sulfide with hydrochloric acid to generate hydrogen sulfide; refined hydrogen sulfide can be obtained after purification. This processing equipment is large in size and causes severe pollution; although its cost is low, it does not meet environmental protection requirements, and it is now hardly used. The sodium salt method replaces barium sulfide with sodium sulfide; it is a simple and easy-to-operate process. However, the hydrogen sulfide produced contains a high amount of water, which causes severe corrosion to the equipment. The direct synthesis method is a process in which highly pure sublimed sulfur is reacted directly with an excess of highly pure hydrogen to produce hydrogen sulfide. This process has no side reactions and high product yield, but it requires significant equipment investment and is complex; therefore, it is only suitable for the large-scale production of high-purity hydrogen sulfide. The recovery and purification method involves extracting hydrogen sulfide from the waste gases generated in industries such as fertilizers, chemicals, pesticides, rubber, and petroleum, where hydrogen sulfide concentrations are high. Common techniques used include selective absorption, vacuum distillation, and pressure liquefaction. Domestic natural gas, refining, and coal chemical enterprises possess large amounts of hydrogen sulfide recovery resources, which can be used to produce high-purity hydrogen sulfide through this process. Although this process is relatively complex, it recovers harmful industrial exhaust gases, eliminating the need for their purification; therefore, it is suitable for enterprises with hydrogen sulfide resources to produce refined hydrogen sulfide, develop downstream products based on hydrogen sulfide, and enhance the competitiveness of their original facilities. Comparing the various processes, no matter which one is used, it is inevitable to ultimately employ methods such as liquefaction, gas-liquid separation, and distillation in order to obtain refined hydrogen sulfide. Therefore, when there is a need for hydrogen sulfide but no requirement for large-scale production of it, and hydrogen sulfide resources are available, the recovery and purification method should be a good option.