A single-step catalytic process for the conversion of methane to gasoline over tungsten zeolite catalysts

Abstract

The catalytic conversion of methane to higher hydrocarbons in the gasoline range has been performed. The dehydroaromatization of methane (DHAM) over a series of 3 wt% W-based catalysts prepared with different supports, under different preparation conditions and several Si/Al ratios of HZSM-5 was carried out. The DHAM was also investigated over a series of W-supported on ZSM-5 modified with varying degrees of Li+ content. The reaction was conducted with and without the presence of oxygen. It was found that modified Li+ in the 3 % W loaded-HZSM-5 catalyst having 74% of the original HZSM-5 strong acid sites exhibited maximum activity and stability under both conditions: with and without oxygen addition in the feed gas. The improved performance in the catalyst activity and stability is attributed to the suitable amount of Brönsted acid sites in the catalysts and addition of oxygen in the feed. The methane conversion up to 20% was obtained over the most active catalyst. The main products are benzene, naphthalene (80–90% selectivity), and coke (10% and even higher). Furthermore, direct one-step methane cotransformation with other light alkanes as co-feed into heavier hydrocarbons in the gasoline range product was studied on W/HZSM-5 catalysts. Catalysts were characterized by BET surface area and pore size distribution measurements, X-ray diffraction (XRD), Fourier transform infrared (FT-IR), ammonia temperatureprogrammed desorption and oxidation (TPD-NH3 and TPO), UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS), thermogravimetric analysis (TGA). The catalytic conversion of a mixture of methane, ethylene and methanol to gasoline has been studied over W/HZSM-5 catalyst. The effect of process variables such as temperature, % vol. of ethylene in the methane stream, and catalyst loading on the distribution of hydrocarbons was studied. The reaction was conducted in a fixed-bed quartz micro reactor in the temperature range of 300 to 500 oC using % vol. of ethylene in methane stream between 25 – 75 % and catalyst loading of 0.2 – 0.4 gram. The reaction of methane-ethylene feed over W/HZSM-5 catalyst produces gasoline rich hydrocarbons in the C5-C10 non-aromatics and also aromatics range. Kinetic study of the methane conversion in the presence of co-feeding ethylene and methanol to produce higher hydrocarbons in gasoline range has been performed over W/HZSM-5 catalyst. The kinetic model was proposed based on a Langmuir- Hinshelwood-Hougen-Watson reaction mechanism. The correlation between experimental and calculated reaction rate indicates that the model fits the data very well