(528e) Depressed Deactivation of SAPO-34 during Methanol-to-Olefins Procee By MgO

Authors: 
Chen, S. L., China University of Petroleum-Beijing
Wang, Y., China University of Petroleum-Beijing
Gao, Y. L., China University of Petroleum-Beijing
Zhang, Q., China University of Petroleum-Beijing
Cao, Y. Q., China University of Petroleum-Beijing
Benziger, J., Princeton University
Chang, W. K., China University of Petroleum-Beijing
SAPO-34 molecular sieve is the best catalyst for methanol to olefins (MTO) reaction owing to its high ethene and propene selectivity. However, the SAPO-34 molecular sieve is deactivated rapidly due to coke deposition in its small pores, and has relatively short working-life time when used as the MTO catalyst. In order to prolong the working lifetime of the catalyst in MTO reaction, a great deal of efforts, such as optimizing the crystallite size and modifying the pores of zeolite to create hierarchical structure, have been done to enhance mass transfer and to reduce coke formation rate. What’s more, modification of SAPO-34 catalyst with different cations by various methods, such as direct hydrothermal synthesis, incipient wet impregnation and ion exchange, can also improve the catalyst working lifetime. However, little attention is paid to prolong SAPO-34 lifetime through physically mixing SAPO-34 with another component.

Reported here in this paper, the rate of SAPO-34 coking was reduced by physical mixing SAPO-34 with MgO, and even the MgO, separated from the SAPO-34 by inert quartz sand layer, was also able to significantly reduce the rate of SAPO-34 coking, and therefore increase the working life time. That is to say, the catalytic performance of SAPO-34 can be significantly affected by MgO which stands “far away” from the SAPO-34. The coke content and coking deposition rate of SAPO-34 were measured, and it was shown that once the SAPO-34 was deactivated, content of coke deposited on the SAPO-34 was the same, regardless with or without the MgO as catalyst promoter. The MgO decreased the rate of SAPO-34 coking and hence increase the working life time. The CO and CO2 were formed when SAPO-34 was promoted with MgO, while no CO and CO2 were detected when pure SAPO-34 was used as the catalyst. MgO by itself shows almost no catalytic reactivity for methanol conversion. But when MgO is sandwiched between layers of SAPO-34 the catalytic activity and production distribution from methanol is significantly altered to favor carbon oxides compared to SAPO-34 by itself. MgO is only catalytically active when sandwiched between layers of SAPO-34, indicating that reaction intermediates are transported from SAPO-34 to MgO and back again. A mechanism for MgO to reduce the coking rate of SAP-34 and the formation of CO, CO2 and H2 was proposed. This research work provides not only a new route for the modification of SAPO-34, but also provided a simple, and convenient way for improving catalytic performance of SAPO-34 used for commercial MTO.

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