Transformation of Methanol to Hydrocarbons (MTH): Comparison Between MeAPO-36 (Me = Zn, Co, Mg) and Modified ZSM-5 Catalysts

Abstract

This paper presents a study of the use of zeolitic catalysts and modified zeotypes for the reaction of transformation of methanol to hydrocarbons (MTH). Materials of the aluminophosphate type MeAPO-36 where Me is Zn, Mg and Co were prepared, in addition to modifying an acidic commercial zeolite with zinc ions by ion exchange. The physicochemical properties of the zeotypes were studied using XRD (X-ray diffraction), N2 adsorption–desorption, temperature programmed desorption of NH3 and SEM (Scanning Electron Microscopy). The catalytic performance of these catalysts was studied in the MTO reaction at 400 °C and atmospheric pressure using a WHSV of 4.24 h−1 in a fixed bed reactor. The incorporation of Zn in the ZSM-5 zeolite induced a relevant effect on acidity, generating a higher density of acid sites. In this sense, Zn-modified ZSM-5 showed higher selectivity to the BTX fraction (benzene, toluene and xylenes). The commercial zeolite modified with Zn ions presented a complete conversion of methanol with a higher selectivity of aromatics compounds totals (34.9% mol) at 400 °C. On the other hand, the incorporation of metals (Zn, Co, Mg) in MeAPO-36 materials had an important effect on acidity and therefore on selectivity in the MTH process. The olefins and paraffins selectivity decreased in the order Zn < Co ≈ Mg, being the selectivity to olefins close to 71–73% mol with these two latter catalysts, probably due to their low acidity. On the other hand, the ZnAPO-36 material was selective for the formation of aromatic compounds, due to the presence of zinc, which is an aromatizing agent. Graphical Abstract: [Figure not available: see fulltext.]