Study On Fluidization Of Vapor-phase Beckmann Rearrangement Reactor

Caprolactam(CPL),an important organic chemical intermediate,is mainly used to produce nylon-6 fiber and nylon-6 engineering plastics.It is mainly produced by cyclohexanone oxime liquid-phase Beckmann rearrangement process in industrial plants.Because of using fuming sulfuric acid and ammonia to assist the reaction,the atomic economy of liquid-phase Beckmann rearrangement process is poor,and the treatment of by-product ammonium sulfate greatly increases the production cost of caprolactam.It also has a greater impact on the ecological environment.The vapor-phase Beckmann rearrangement process is an advanced caprolactam production method.The vapor-phase cyclohexanone oxime is directly converted to caprolactam at T>300℃under the action of catalysts.The process is avoiding the use of fuming sulfuric acid and ammonia,so the theoretical atomic economy of the process can reach 100%,and the technology has no by-product of ammonium sulfate.Therefore,the production cost of caprolactam is greatly reduced,and it has greater market competitiveness.It is a new process in line with green chemistry and sustainable development.At present,only Sumitomo Chemical Co.,Ltd.of Japan has realized the industrialization of vapor-phase rearrangement in the world.In order to develop the vapor-phase rearrangement process,this study focuses on the fluid dynamics research of the vapor-phase rearrangement fluidized bed reactor,and provides basic research data for the industrialization of the technology.The specific contents included the following aspects:(1)A Φ800mm×5000mm turbulent fluidized bed cold model device is built in the laboratory to carry out experimental research according to the characteristics of the vapor-phase rearrangement catalyst.The key parameters such as gas viscosity,gas density,particle density,particle size,static bed height and operating superficial gas velocity under cold mold conditions are basically consistent with those under actual industrial operating conditions.The high-speed differential pressure sensor is used to perform detailed measurement of the axial solid content distribution in the bed,which provides basic experimental data for the design of the vapor-phase rearrangement reactor and the verification of the CFD model.The results show that the solid particles above the gas distributor are mainly distributed in the transition section and the dilute section,and less in the dense section.(2)A CFD model of a turbulent fluidized bed is established based on the MP-PIC method coupled with the filtered drag force model.The Φ800mm full-loop turbulent fluidized bed in this study is modeled and simulated.Four turbulent fluidized bed cooling systems with diameters of Φ152mm,Φ474mm,Φ890mm and Φ1560mm in the literature are selected as supplementary cases to fully verify the established CFD model,which covering the laboratory scale to the industrial scale.The simulation results are compared with the experimental results and the comparison results show that the established CFD model has a good predictive ability for the axial solid hold-up distribution in the turbulent fluidized bed.(3)The hot state CFD model is established by coupling the cold state CFD model with the vapor-phase rearrangement reaction kinetic model and the heat transfer model.A CFD simulation study is carried out on a 3000 tons/year pilot-scale vapor-phase rearrangement reactor,and the characteristics of the chemical reaction,temperature and pressure distribution,solid flux,and vapor-phase back-mixing in the reactor are analyzed.