Synthesis of hydrocarbons over ZSM series zeolites catalysts

Abstract

Zeolite ZSM-5, ZSM-8, and ZSM-35 among the ZSM series zeolites were synthesized using tetraproply-ammonium hydroxide, tetraethylammonium hydroxide, and ethylenediamine as organic cation sources. The conversions of methanol, ethanol, ethylene, and propylene into hydrocarbons were studied, and compared with the reactions over faujasites and mordenite catalysts. The conversion products over zeolite HZSM-5 catalyst were olefins, paraffins, cycloparaffins, and aromatics. The catalyst showed especially high selectivity toward the formation of aromatics amounting to 50 mol% of the product. Shapeselective catalysis was observed, which confined the hydrocarbons produced within the size of 1,3,5-trimethylbenzene. Hydrogen form (HZSM-5) of catalysts showed higher activity than NaZSM-5, and the acidity of the catalysts seemed to have controlling effect in the conversion of methanol to hydrocarbons. The reaction products over HZSM-8 catalyst were also confined within about the size of 1,2,4-trimethylbenzene. The largest molecule produced over HZSM-35 catalyst was 1,3,5-trimethylbenzene which was the same as with HZSM-5 catalyst. Selectivity to aliphatics was higher over HZSM-8 than HZSM-5 and HZSM-35 showed higher selectivity to aromatics than HZSM-5. Results on the adsorption of 1,3,5-trimethylbenzene and other hydrocarbons on these ZSM series zeolites also indicated that shape-selective effects played an important role in determining product distribution. Over faujasite catalysts, the formation of aromatics was not observed, but over mordenite catalyst large amount of aromatics was produced. The formation of aromatic compounds seemed to have occurred in the cylindrical pore channel, which faujasite structure does not have. Reaction pathways of methanol conversion to aromatic compounds appeared to be dimethylether was by dehydration of methanol, and $C_2-C_5$ olefins were formed from dimethylether, then olefins were converted into hydrocarbons having higher contents o...