Selective Production of Gasoline Fuel Blendstock from Methanol using a Metal-doped HZSM-5 Zeolite Catalyst

¹ School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg 2050, South Africa
² Department of Chemical Engineering Technology, University of Johannesburg, Johannesburg, South Africa

^* Corresponding author: yusuf.isa@wits.ac.za

Abstract

The increasing demand for substitutes for petroleum has become a global concern due to the looming petroleum crisis and the need to reduce carbon dioxide emissions. This study seeks a viable approach for converting methanol into petrochemicals and fuel-range hydrocarbons. A ZSM-5 zeolite catalyst was synthesised and modified with 0.5 wt% transition metals (Co and Ni) to improve selectivity towards the desired liquid product (gasoline) in the methanol-to-hydrocarbon (MTH) conversion. The synthesised catalyst was characterised using various techniques. The catalysts were further evaluated for methanol conversion into fuels and petrochemicals (BTX) under varying weight hourly space velocity (WHSV) (7 and 12 h^-1) at 350 ^oC. Results showed that the synthesised catalyst exhibited characteristic features of a typical MFI framework of a zeolite catalyst. The catalyst evaluation results revealed that changes in operating conditions affected product distribution. A WHSV of 12 h-¹ favoured the production of gasoline range hydrocarbons (C₅-C₁₂) with a yield of over 80 % for all catalysts. In addition, C₁₂+ hydrocarbons were produced with a selectivity of 12.6 %, 0.7 % and 7.5 % for Ni-doped, Co-doped and HZSM-5 catalysts, respectively. In particular, the Co-doped catalyst showed a 7.1 % higher BTX yield under these specific operating conditions (12 h^-1 and 350 ^oC). Compared to 7 h^-1, increasing the WHSV to 12 h^-1 favoured the production of liquid hydrocarbons. Incorporating a small amount of transition metal into the parent catalyst improved the selectivity of the target products and overall liquid hydrocarbon yield. The results concluded that the synthesised catalyst is promising for the MTH process, and catalytic performance can be enhanced by metal modification and optimising reaction conditions to improve biofuel production.