Para-xylene production from toluene methylation: Novel catalyst synthesis, fabrication and ANFIS modelling

Background: Toluene methylation to p-xylene is a key reaction in the petrochemical industry, with p-xylene being an important feedstock for the manufacturing of many chemical commodities. Methods: The present contribution reports the synthesise of Al-HMS industrial catalysts with different Si/Al ratios and H-ZSM-11 industrial catalysts with surface modification (SM-H-ZSM-11). The properties of the catalysts were characterized by X-ray crystallography (XRD), scanning electron microscope (SEM), thermogravimetric Analysis (TGA), Fourier-transform infrared spectroscopy (FTIR) of pyridine adsorption, and NH₃ TPD. catalytic performances were evaluated for the toluene methylation with methanol by assessing the effects of temperature, pore size, acidic strength, and residence time of reactants on the shape-selectivity of the product. Significant finding: The results show that whilst an increase in pore size has an unfavorable impact on the shape selectivity of p-xylene, an increase in the strength of the acid site enhances the shape selectivity of p-xylene, hence counterbalancing the effect of pore size. In particular, Al-HMS-5 has a larger pore size than that of H-ZSM-11 but the stronger acidity of Al-HMS-5 is more effective on the shape selectivity of the catalyst. Beside experimental studies, a computational process modelling was carried out to estimate percentage of toluene conversion as a function of the reaction temperature (K), WHSV (h⁻¹), toluene/MeOH molar ratio, acidity of catalyst (mmol/g), and surface area (m²/g) using an adaptive neuro-fuzzy inference system optimized by a particle swarm optimization algorithm. Excellent agreement between measured and predicted toluene conversion confirmed the satisfactory performance of our model. The results show that by suitable tuning of catalyst acidity it is possible to retain high selectivity whilst increasing pore size, hence alleviating potential problems due to diffusion limitation in small pores. The relevancy factor calculated for reaction temperature, WHSV, acidity, and BET surface area of the catalysts were1.35, 0.096, 0.0071, and 10.42, respectively, which shows that highest sensitivity of toluene methylation relates to BET surface area of the catalysts.