Micro-and Macro-reaction Kinetics Study Of Ethylene Epoxidation To Ethylene Oxide

Ethylene oxide is the second most important ethylene derivative after polyethylene and polyvinyl chloride.Industrial production of ethylene oxide uses a direct oxidation process of ethylene and oxygen over silver catalysts.However,the ideal selective epoxidation of ethylene to ethylene oxide is accompanied by thermodynamically very favorable side reactions that pose a great challenge to achieve high selectivity and safe production of ethylene oxide.In order to obtain higher economic efficiency and safe production,the industrial production of ethylene epoxidation to ethylene oxide over silver catalysts has been improved in two main directions: 1)developing new silver-based catalysts with high activity,high selectivity and high stability;2)optimizing the production process of ethylene epoxidation to find the optimal operating conditions to maximize the safe production and economic efficiency.Based on the above two improvement directions,this paper investigates the design of new silver-based catalysts and the guided application of reactor simulation through the microscopic and macroscopic reaction kinetics of ethylene epoxidation,respectively.The main studies are as follows.(1)A strategy for predicting catalyst performance on particle models was proposed by first-principles calculations,classical Wulff Construction theory and microscopic reaction kinetics analysis.Applied to the design of new doped silver-based catalysts for ethylene epoxidation to ethylene oxide,the Cu,Cs Re,Cs Cu,Co Cu,Co Cs and Re Cu doped silver particle models were found to be more selective than the Pure silver particle model.Furthermore,Pure,Cu,Re Cu,Cu Cs and Cs Re doped silver-based catalysts tend to generate the primary and secondary reaction products on the oxygen reconstituted Orec Ag(111)surface,while Co Cu and Co Cs doped silver-based catalysts tend to generate the primary and secondary reaction products on the oxygen reconstituted Orec Ag(100)surface.(2)The experimental design of Cu Cs-doped silver-based catalysts was guided by theoretical design.The theoretical part investigated the catalytic performance of the two metal surfaces and at different temperatures,and predicted that the Cu Cs-doped silver-based catalysts outperformed the pure silver catalysts in terms of selectivity and activity on the particle model.And the experimental part verified the theoretical predictions.In addition,the characterization analysis shows that Cu Cs doping promotes the growth and dispersion of silver particles,generating a grain boundary-rich silver particle with beneficial catalytic performance.Moreover,Cu Cs doping promotes the formation of electrophilic oxygen and the desorption of adsorbed ethylene oxide,which is beneficial to the selectivity of ethylene oxide.(3)An industrially applicable macroscopic reaction kinetic model for ethylene epoxidation was optimized by industrial data and optimized correction method.In addition,reactor simulations were performed based on the preferred model and industrial reaction conditions.The simulation analysis results showed that increasing the molar fraction of feed gas inlet components ethylene and oxygen and the temperature of heat transfer medium,the reactor bed temperature increased and the production load increased.The reactor bed temperature decreases as the space velocity increases.The influence of feed gas inlet temperature on the reactor performance is less.