Research Of Catalytic Reaction Engineering For Methanol-to-Olefin Process

Focusing on the hot topic named Methanol-to-Olefin (MTO) process in coal chemical region, the dissertation gives some research results about the intrinsic kinetics obtained in an integral isothermal fixed-bed reactor in terms of the preparation of a high active SAPO-34 molecular sieve catalyst. The coking behavior of the catalyst as well as the deactivation kinetic study is investigated in a special thermo gravimetric analysis (TGA) instrument. The mathematical simulations of multi-bed adiabatic and tubular reactors are performed and compared.Several types of highly active SAPO-34 molecular sieves are synthesized, and different methods are introduced to improve the catalytic behavior. A catalyst with the highest reaction activity is prepared, by adopting TEAOH template with 20%concentration and adding Cr3+ metal salt. The distribution of MTO products has a distinct relationship with reaction time and process conditions.3 reaction stages can be detected with reaction time, namely induction period, selective deactivation period and fast deactivation period. The generation of dimethyl ether can be viewed as a signal of catalyst deactivation.The intrinsic kinetic study is conducted by using of an integral isothermal fixed-bed reactor. With the help of lumping kinetics theory, the intrinsic reaction kinetics for MTO reaction is obtained in the integral fixed-bed reactor with the range of 653.15-753.15K temperature and 3-27 h-1 space velocity, taking the elimination of mass transfer phenomenon into consideration. The acquisition of kinetic data is dedicated designed, by considering both induction and fast deactivation reaction stages. A simplified kinetic model including 5 products lumping species for MTO process is established. The equations are solved based on the distribution law of the products.A special thermo gravimetric analysis (TGA) instrument is utilized for the investigation of the coking behavior of SAPO-34 catalyst during MTO process. It is proved that the reaction results from TGA instrument are almost identical with fixed-bed reactor. Both increasing methanol space velocity and methanol partial pressure accelerate the coking rate, while either higher or lower temperature favors coke generation. Water addition in methanol feed would lead to deactivation alleviation to a very limited extent. The type of coke formed in lower temperature could be partly regenerated by raising temperature, with color interchanging phenomenon occurs. The severity of hydrothermal atmosphere could be partly responsible for the coke type in different temperature. An empirical correlation formula is deduced, while the average coke content is related with initial reaction conditions and reaction time. The model is applicable in both coke prediction and deactivation kinetic study.The reaction and deactivation kinetic study for MTO process are carried out in the TGA reactor, through changing reaction temperature and space velocity. MTO results are related with the average catalyst coke content, which proves the selective deactivation is caused by coking. The effect of reaction conditions are studied under almost identical coke content. By the use of the separation kinetic study method, both reaction and deactivation kinetic models are established simultaneously. The established model gives a high correlation coefficient, which gives a valuable fundamental data for commercial use.The one-dimensional pseudo-homogenous mathematical models are set up for 2 types of fixed-bed reactors for MTO plant in commercial scale, namely multi-bed adiabatic and tubular reactors. The operation results for MTO results are simulated, while considering the activity of SAPO-34 catalyst is under a stable state. Reaction temperature is the most important factor governing simulation results than other factors do, while altering temperature could change the ratio between ethylene and propylene (0.78-1.30). Heat release procedure is much smoother in tubular reactor, and the melted salts are chosen as coolant. The circulation mass of melted salts and methanol space velocity have a more distinct influence than inlet reaction temperature, while nitrogen addition has little relationship with simulation results, which embodied the well heat transfer effect in such reactor. However, more identical scale of commercial plants is required simultaneously because of the fast coking rate needing frequent regeneration process for SAPO-34 catalyst.