A Comprehensive Review Covering Conventional and Structured Catalysis for Methanol to Propylene Conversion

The conversion of methanol to propylene is a value-added process and has gained extreme significance because of high demand for propylene in the production of petrochemicals. The demand for propylene is increasing due to increasing usage of polypropylene. During the last two decades, propylene demand growth has far overtaken ethylene demand growth and it is predicted to be more than double in the next 20 years. The Dalian Institute of Chemical Physics has been working for the last three decades in the R&D of the methanol to olefins reaction and have developed MTP technology. The catalytic materials used in methanol to propylene conversion include SAPO-34 (small-pore molecular sieves), ZSM-5 (medium-pore zeolites) and its modified forms. Limited research has also been done using large pore zeolites such as mordenite and beta. High-silica EU-1 zeolite has been found as an efficient catalyst for MTP conversion. The use of SAPO-18, ZSM-23 and CON-type zeolite for MTP reaction has also been discussed. Methanol to propylene research has been carried using structured catalysts including ceramic based honeycomb or monolith and silicon carbide foam. The major difference in process design between SAPO-34 and H-ZSM-5 is that the SAPO-34 is used in fluidized bed process while H-ZSM-5 catalyst is used in fixed bed process. SAPO-34 is a selective catalyst for olefins but deactivates fast and thus requires frequent regeneration. The H-ZSM-5 is less selective for olefins but shows less deactivation and thus quite stable. A number of structured supports such as monolith, foam, and mesh have been researched for coating with the active zeolite based catalysts. The structured catalysts have the advantage to reduce the diffusional limitations of pellet catalyst system and have exhibited excellent results in terms of activity and selectivity for olefins as well as in reducing aromatics formation. The results obtained in our research using zeolite coated structured catalysts have shown significant increase in propylene selectivity. The significant findings of our work has been published and patented with US Patent and Trademark Office (USPTO).