The Synthesis Of 2-Acetyl Thiophene And The Deactivation Of C₂₅ Zeolite

As one of the thiophene derivatives, 2-acetyl thiophene has a wide range of applications in medical, chemical and food industries. 2-acetyl thiophene is mainly synthesized through the Friedel-Crafts acylation reaction. The catalyst has been changed from the traditional catalyst such as phosphoric acid and stannic chloride to the new environment friendly solid-acid catalyst such as phosphotungstic acid, Sc?OTf?3, HZSM-5, C₂₅ and so on to avoid the defect like the pollution of the environment, the corrosion of the equipment and the difficulty to recycle the catalyst. However, at present the reaction of 2-acetyl thiophene's synthesis is mostly studied using batch reaction system, in order to realize industrial continuous production, improve production efficiency and economic benefits, there also need to implement the continuous reaction in the reaction device.In this article, with C₂₅ zeolite as catalyst,acetic anhydride as acylating reagent,continuous reaction of thiophene acylation reaction was conducted in a trickle bed reactor to investigate the effects of reaction temperature,feed flow rate,molar ratio of raw materials on the Friedel-Crafts acylation reaction via orthogonal experiment. Besides, the by-product acetic acid is added as solvent for the reaction. The optimum reaction condition was determine through comprehensive analysis of thiophene's initial conversion rate, catalyst's service life and product output.With methylene chloride as extracting agent, soxhlet extraction of the deactivated catalyst was conducted. The deactivated material was measured by mass spectrometry and determined as 2-acetyl thiophene and the by-products of acylation and dehydrated dimer of 2-acetyl thiophene, and their related reaction mechanism was discussed. Different periods of the reaction were studied and the content of the coke was analyzed. It shows that the deactivation is due to the retention of 2-acetyl thiophene and the dehydrated dimer, which trapped in the zeolite micropore.With the theory of quantum chemistry, all the molecules in the reaction system have been calculated through the density functional theory to optimize the molecular structure. The calculation about the size of molecules effectively explain the shape selectivity of molecular sieve, and the mechanism of reaction and deactivation has explained respectively from the aspect of the reactants and products through the calculation of reactive sites and standard molar enthalpy.Finally, three methods can slow down the deactivation by changing the calcination temperature of the zeolite, adding acetic acid solvent and modifying zeolite by various acids. These measures change the surface acidity of the zeolite, increase the liquidity of products, expand the pore diameter of molecular sieves, and the effect is remarkable.