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.

Determination of adsorption characteristics of synthetic NaX nanoparticles

Zeolite nanoparticles were synthesized by means of a hydrothermal method and the sorption performances were tested in batch experiments using single and binary components of Pb²⁺, Ni²⁺and Cu²⁺ synthetic solutions. Fast adsorption was observed and the majority of sorption occurred within the first 5 min for each case of metal cations. Percentage metal removal increased with the adsorbent dosage and it was adversely affected by the initial metal concentrations. XRD, FTIR-ATR and XPS analyses revealed that the removal of metal ions occurred mainly on the basis of ion-exchange. Equilibrium sorption data were best described by Sips isotherm model and the maximum attainable metal amount on the NaX were estimated as 1.23, 1.76 and 2.20 mmol/g for the Pb²⁺, Ni²⁺, and Cu²⁺ cations, respectively. A single step desorption process conducted in NaCl solution seemed to be practically applicable for regeneration and after three adsorption/desorption cycles, 79, 76 and 48% of initial sorption capacity of NaX were preserved for lead, nickel and copper ions, respectively. Single isotherm parameters used for the prediction of binary equilibrium data were satisfactory. Binary sorption experiments for Pb²⁺-Ni²⁺, Pb²⁺-Cu²⁺ and Ni²⁺-Cu²⁺ couples reflected that the presence of secondary ions decreased the uptake of the primary one. Lead exhibited greater inhibition of the sorption of nickel and copper, demonstrating the stronger affinity of NaX for Pb²⁺. Extended Freundlich model best described all the three binary metal systems. Adsorption experiments carried out in real wastewater demonstrated that NaX nanoparticle has a high affinity for all the cations except copper.