Simulation And Optimization For Fixed Bed MTP Reaction And Regeneration Process

Propylene is an important basic organic chemical raw material in China.In recent years,both the supply and demand of propylene keep steady growth in China.Currently,the petroleum route represented by FCC process is an important source of propylene production.However,the non-petroleum route,represented by Methanol-to-Olefin(MTO),Methanol-to-Propylene(MTP)and Propane-Dehydrogenation(PDH),is increasing rapidly,which has become an important supplement of propylene.Because the non-petroleum route like MTO/MTP process matches the "deficient oil,lean gas,rich coal" energy structure,China has vigorously developed the projects of coal chemical industry during the "12th Five-Year Plan" period,and gradually improved the proportion of non-petroleum route to produce ethylene and propylene.Compared with the FCC process,the MTO/MTP process has the inherent disadvantages of high investment and energy consumption.During the period of low oil price,MTO/MTP prpcess lacks competitive advantages of the economy.Therefore,how to reduce energy consumption and increase the yield of propylene has become the key to improve the competitiveness of MTO/MTP process.For the reaction process,the effect of changing the proportion of recycled olefins and the proportion of feed composition on the yield of propylene is investigated,and the optimal range of feed composition is given.The maximum yield of propylene in this range can reach 72.4%,which is 7%points higher than the industrial design value.For the regeneration process,the effect of different conditions on the regeneration effect is investigated,an optimal regeneration scheme with a target of "minimum nitrogen consumption" is proposed,which can effectively reduce the nitrogen consumption by 30%.The simulation can provide guidance for the operation and technical transformation of the fixed bed MTP device.As the medium for the reaction and regeneration process,coke plugging is the main reason for the deactivation of ZSM-5 catalyst.Therefore,a discrete model is used to study the coke plugging behavior of MTP reaction,and the coke plugging effect on the performance of catalyst is investigated.The detailed contents of this paper are as follows:(1)A one-dimensional heterogeneous steady-state model has been established to simulate the fixed-bed MTP reaction process as well as investigating the effect of changing proportion of recycled olefins and the proportion of feed composition on the yield of propylene.The results show that the ratio of C4～C6 olefins has little effect on the yield of propylene when the total amount of recycled olefins is constant.There is an optimal range for feed composition,under this range,the yield of propylene is high and the highest can reach 72.4%,which is 7%higher than the industrial design value.(2)A one-dimensional heterogeneous dynamic model has been established to simulate the fixed-bed MTP reaction process.The results show that under the existing conditions,the proportion of butane increases while the yield of propylene decreases with C4 recycled olefin flowrate increased.(3)A one-dimensional pseudo homogeneous dynamic model has been established to simulate the fixed-bed MTP regeneration process,and a preliminary understanding of MTP regeneration process is obtained.Furthermore,the effects of oxygen content,inlet temperature and the regeneration gas flowrate on regeneration result have been investigated.The results show that the oxygen concentration had the greatest effect on the regeneration result,followed by the inlet temperature and regeneration gas flowrate.An optimal regeneration scheme for "Raising the amount of regeneration gas flowrate"is proposed,which can reduce the consumption of fresh nitrogen by 30%.(4)A discrete model has been established to study the coke plugging effect of MTP reaction,a two-dimensional square pore network is established to investigate the coke plugging effect on the performance of catalyst.The results show that due to the severe diffusion limitation of the ZSM-5 catalyst,the MTP reaction mainly occurs on the outer surface of the catalyst where the coke is preferentially formed.After the coke deposition,it will prevent the reactants diffusing into the central region of the catalyst,which leads to the decrease of the effectiveness factor of the catalyst.The spatial distribution of the pore network has a great effect on the performance of the catalyst.When the large size pores are close to the outer surface of the catalyst,the overall performance of the catalyst will be greatly improved.