Selectivity Regulation in Methanol Conversion to Hydrocarbons on Zeolites

Abstract

Selectivity regulation in the conversion of methanol to hydrocarbons on several zeolites was studied. The model analysis of reaction gave the following assumptions for the catalysis of H-Y or H-Moldenite in comparison with H-ZSM-5:
( 1 ) The concentration of acid site is very high.
( 2 ) The degree of unsaturation of adsorbed hydrocarbon species is high.
( 3 ) Therefore, the adsorbed hydrocarbon species with 3 or more ca r bon atoms polymerize, without desorbing, to form coke. The hydrogen which evolved during the coking, reacts with C₁- and C₂adsorbed species to form CH₄ and C₂ hydrocarbons.
While the reactions on the zeolites which carried sulfided nickel (Ni (S) ) on them gave results quite similar to those on the unearned ones under nitrogen atmosphere, the reactions under pressurized hydrogen gave markedly different results. On a Ni(S ) /H-ZSM-5 catalyst the selectivity of CH, increased by about 100 times to around 90% with an unchanged conversion (Table 3). On a Ni ( S )/H-Moldentite catalyst the rate of deactivation decreased to one tenth or less, compared to that in the reaction of nitrogen atmosphere, accompanied by the decrease in the selectivity of coke formation to about one tenth. At the same time, the selectivities of Ca₃∼C₇ aliphatic hydrocarbons and aromatic hydrocarbons increased from 2.4%and 0% to 26.6% and 15.4%, respectively (Table 4).