Investigation of the effect of HZSM-5 over HDS and reforming processes for clean gasoline production

HZSM-5 catalysts with different SiO₂/Al₂O₃ ratios were synthesized, and the effect of acidity over the octane enhancement alongside with desulfurization of heavy naphtha was investigated. In this way, the catalysts with the SiO₂/Al₂O₃ ratios of 20, 40, 60, 80 and 200 were experimentally synthesized and their physical characteristics besides their acidities were measured through X-ray diffraction, the Brunauer–Emmett–Teller and temperature-programmed desorption of ammonia (NH₃-TPD) tests. All of them were examined under a specific condition of 5 barg pressure, 450 °C temperature, H₂/Oil = 150 ml/Nml, and weight hourly space velocity = 1 h⁻¹ inside a fixed bed reactor. To measure liquid hydrocarbon compositions, analyses of the off-gases, the value of research octane number and the amount of total sulfur of the feed and products were done by means of some tests, including the standard of detailed hydrocarbon analysis, gas chromatography, ASTM D-2699 and ASTM-D5453 utilized, respectively. At SiO₂/Al₂O₃ = 40, the amount of total sulfur went down by 74 wt% and the amount of the Research Octane Number hopefully increased from 51.9 to 93. However, analysis of off-gases stated that despite decreasing the amount of sulfur and increasing the value of octane number in the outlet yields, the ratio of 40 ratio led to by-production of light hydrocarbons, besides 76% liquid yield inevitably. Depending on the results, by using the proposed parallel aromatization–desulfurization process, engineers could bring together the HDS and CRU processes and could diminish the capital and operating costs.