A Study On Moving Bed Methanol To Propylene Reaction Process

Methanol to propylene (MTP) process is an important way to both guarantee source of propylene and to develop clean coal chemical industry. Compared with fixed-bed and fluidized-bed MTP processes, moving-bed MTP process is more advanced in technology and economy, with less investment, higher propylene selectivity, easier operation and greater development potential.The key and difficulty of moving-bed methanol to propylene (MMTP) process lie in two aspects. One is the preparation of spherical ZSM-5 catalysts with high propylene selectivity; the other is the design of moving-bed reactor and process which agrees quite well with reaction performance of ZSM-5 catalysts. So far, the scientific problems in the development of MMTP process haven't been reported or solved. They are summarized as the relationship between the structure of ZSM-5 molecular sieve and MTP reaction performance, the dynamic behavior of spherical ZSM-5 catalyst in MTP reaction, and the distribution of fluids and particles in moving-bed reactor. Therefore, it is significant to both industrial application and theoretical research to study the key scientific problems, to prepare spherical ZSM-5 catalysts with high propylene selectivity, to clarify dynamic behavior of MTP reaction, and to design moving-bed reactor and MMTP process to match reaction performance of ZSM-5 catalysts.The scientific problems mentioned above were studied to guide the development of MMTP process as follows, based on the principle that reaction performance of the catalysts should match the structure of the reactor. Firstly, structure-activity relationship between ZSM-5 structure and MTP reaction performance, structural modification of ZSM-5, MTP reaction performance of phosphorus modified spherical ZSM-5 catalysts and coking performance of ZSM-5 were identified. Secondly, MTP reaction process, effect of process variables and reaction materials on MTP reaction, and global kinetics were also investigated. Thirdly, on the basis of the designed moving-bed reactor and MMTP process, MMTP process and its heat exchanger net were simulated using Aspen Plus software and pinch technology. Finally, we presented gas distribution and particles moving in two-dimensional moving-bed reactor, when acoustic emission technology was applied to monitor particles moving. The main achievements of this research are as follows. 1. Based on the study of ZSM-5 structure and its MTP reaction performance, their structure-activity relationship was clarified, and ZSM-5 catalysts with high propylene selectivity and stability were prepared. Firstly, we studied the effect of Si/Al molar ratio, crystal size and hierarchical structure on MTP reaction, as well as the structure-activity relationship between the structure of ZSM-5 molecular sieve and the MTP reaction. Secondly, by adding metal compounds to ZSM-5 crystallization, we prepared ZSM-5 molecular sieve with different metal heteroatoms, and studied their MTP reaction performances. Meanwhile, the feasibility, advantage and disadvantage of the modification method above were discussed, compared with impregnation. Thirdly, we prepared phosphorus modified spherical ZSM-5 catalysts by incipient impregnation, and studied their MTP reaction stability and products distribution. Finally, we investigated the coking behavior of ZSM-5 catalysts using diffuse reflectance infrared and micro-reactor.2. With experiments in micro-reactor, we studied MTP reaction and global kinetics on spherical ZSM-5 catalyst. Firstly, we investigated the effect of temperature, space velocity and water/methanol ratio on MTP reaction of spherical ZSM-5 catalysts. Secondly, we also discussed the effect of different reaction materials on MTP reaction of spherical ZSM-5 catalysts. Finally, we modeled global kinetics using lumping method.3. By process simulation and cold-model experiments, we studied moving-bed reactor and MMTP process. Firstly, we proposed several designs of moving-bed reactor and MMTP process, and discussed the advantage and disadvantage. Secondly, we researched MMTP process simulation and its heat exchanger net by the use of Aspen Plus software and pinch technology. Finally, we investigated gas distribution and particles moving in two-dimensional moving-bed reactor by pressure drop measurements, tracing particles experiments and acoustic emission detecting.