The effect of Si/Al ratio of ZSM-12 zeolite on its morphology, acidity and crystal size for the catalytic performance in the HTO process.

In this research, ZSM-12 zeolite with six Si/Al ratios (20 to 320) was synthesized by a hydrothermal method and systematically investigated. The physicochemical properties of the synthesized nano zeolites were evaluated and compared by XRD, FE-SEM,ICP-AES, NH3-TPD, BET, FT-IR, and TGA analyses. The results show that when the Si/Al ratio increases, the amount of microcrystals increases with the dominant competitive phase of cristobalite by decreasing the MTW phase. The catalytic assessment of synthesized zeolites in the (n-hexane to olefins) HTO process in a fixed bed reactor under atmospheric pressure and WHSV equal to 4 h-1 at 550 °C was evaluated and various parameters such as selectivity towards light olefins, P/E ratio, production of light alkanes, and aromatic compounds (BTX) were investigated. The result of the n-hexane to olefins process indicated that the presence of cristobalite as an impurity phase strongly affects the activity of the catalysts. The Z80 zeolite, with a Si/Al ratio of 80, corresponds to the pure form of ZSM-12 and exhibits the highest light olefin yield at 52.5%. This zeolite demonstrates superior propylene selectivity (P/E = 1.75) owing to its well-suited pore structure, wide channels, and optimal acidity derived from the MTW zeolite. On the other hand, zeolite Z320 has a lower light olefin yield (19.4%) and a lower P/E (1.1) ratio. In addition, according to the results of the TGA analysis, the content of coke on the Z80 catalyst after the catalytic reaction is much less than other catalysts after the catalytic reactor test.

Application of cupric or ferric ions as environmentally benign oxidants to the chloride leaching of platinum from spent reforming catalysts.

Recovery of precious metals has been considered due to their limited availability and resources, and the reduction of environmental hazards. In this study, the environmentally friendly chloride leaching method was used to recover platinum (Pt) from a spent reforming catalyst. Hydrochloric acid and sodium chloride were applied as the complexing agent and ferric or cupric chloride (FeCl3, CuCl2) was used as oxidants. Response surface methodology was implemented to investigate the influences of acid concentration (1-3 M), oxidant concentration (0.5-1.3 M), and temperature (70-90 °C) on the Pt extraction at a fixed duration of 3 h using two separate Box-Behnken experimental designs. Increasing temperature and acid concentration improved the Pt recovery from ∼52% to ∼89% in the presence of 1 M FeCl3, and from ∼29% to 94% in the presence of 0.75 M CuCl2. Generally, at low acid concentrations, ferric chloride was more efficient in Pt dissolution, while, at high acid concentrations, cupric chloride performed better. Finally, the platinum content of the pregnant leach solution was precipitated by adding a saturated ammonium chloride solution. According to the results of the X-ray diffraction analysis, the obtained precipitate was mainly composed of ammonium hexachloroplatinate, sodium chloride, and ammonium chloride. Also, the Pt assay of the powder was determined as 21%.