ZSM-5/MAPO Composite Catalyst for Converting Methanol to Olefins in a Two-Stage Unit with a Dimethyl Ether Pre-Reactor

A ZSM-5/MAPO composite catalyst was prepared by adding ZSM-5 zeolite powder to a conventional molecular sieve synthesis system, followed by modification with NH_4H_2PO_4. The samples were characterized by XRD, SEM, IR, NH_3-TPD, and BET analyses. The catalytic property of the samples toward the methanol-to-olefin(MTO) reaction was evaluated in a connected in series two-stage unit equipped with a continuous flow(once-through) fixed-bed tubular reactor similar to an industrial reactor. The first reactor mainly converted methanol into dimethyl ether and water, followed by being subject to continuous reaction in the second reactor, in which DME was converted to hydrocarbons. The composites exhibited the typical framework topology of MFI, AEI and AFI, which represented the ZSM-5 zeolite, the molecular sieves AlPO-18 or SAPO-18, AlPO-5 or SAPO-5, respectively. The composites showed several advantages for optimizing the zeolite acidity, enhancing the mass transfer, and restraining the side reactions. Catalytic reaction results showed that the composites exhibited higher selectivity to light olefins(84.0%) and lower selectivity to C_2―C_4 alkanes and C_5^+ hydrocarbons than pure ZSM-5. Moreover, the composite zeolite loaded with 3% of P demonstrated improved catalytic activity and stability for the conversion of methanol to propylene, because the coking rate was obviously suppressed.

Fast and low-temperature elimination of organic templates from SBA-15 using dielectric barrier discharge plasma

Organic templates P-123 of mesoporous SBA-15 can be effectively removed in a few minutes （4 min） by using the dielectric-barrier discharge （DBD） plasma technique at ambient pressure and low gas temperature （around 130℃）. The mesoporous SBA-15 was characterized by FT-IR, 29Si solid sate NMR, TEM, XRD, TGA and N2 adsorption/desorption isotherms. The as-made SBA-15 treated with DBD plasma exhibited a larger surface area of 790 m2 · g-1 with larger pores and microspore volume than samples prepared by using the conventional thermal calcination method （550 ℃ and 5 h, 660 m2 · g-1）. In addition to less shrinkage of the silica framework, the DBD-prepared SBA-15 showed significantly increased weight loss of 8.3% about 200℃ as compared with that of conventional calcination （5.5%）, which is attributed mainly to the dehydroxylation by condensation of silanol groups.