Studies of the Methanol to-hydrocarbon (MTH) reaction over new 8- and 10-ring acidic zeolites

Abstract

Abstract

Developing a process in which natural gas, coal and biomass can be converted to valuable petrochemical products is becoming increasingly important. The methanolto-hydrocarbon (MTH) reactions constitute the final step in one such route. The MTH reaction is catalyzed by acidic zeolites. ZSM-22 zeolite is a less studied catalyst for the MTH reaction and has unidirectional non-interacting channels of 4.6 x 5.7 Å dimensions.

In this work, ZSM-22 zeolite previously believed to be inactive catalyst in the methanol-to-hydrocarbon reaction is investigated as an active catalyst. Several ZSM-22 catalysts were synthesized, and all were found to be active catalysts for the MTH reaction. Low feed rates between 2.05 and 4.05 gg-1h-1 and temperatures 350-500 °C were used for the investigation. The methanol conversion capacity of ZSM-22 was found to be comparable to that of SAPO-34. The C5+ fraction was rich in branched alkenes (~70 %), very little C2 and negligible amounts of aromatic hydrocarbons (~1%) were formed. This product blend meets the requirements for a cleaner gasoline and might be used for the production of environmentally friendly gasoline by hydrogenation. Alternatively, the alkene rich product might be used as alkylation feedstock. The product spectrum of the ZSM-22 catalyzed MTH reaction is intermediate to those found in MTO and MTG, and this might provide product flexibility in an MTH application. Isotopic labeling studies revealed that the alkene methylation-cracking mechanism is the main reaction mechanism for the MTH reaction over ZSM-22 catalys. Alkali treatment of the material is found to be promising for improving its catalytic activity.

SUZ-4 zeolite that has 10-membered ring straight channels interconnected by zigzag 8-ring channels is synthesized. The 10-ring straight channels have dimensions 4.6 x 5.2 Å