چكيده به لاتين
Hydroisomerization of n-alkanes is an effective way to improve the fuel quality of cars and reduce the use of toxic compounds in the fuel. Zeolite catalysts, because of their acidic properties, are suitable option for the hydroisomerization reaction. However, their mass transfer limitations may reduce their performance. Applying post-synthesis operations on zeolites is one of the most important methods to improve their performance to reduce their mass transfer limitations. The purpose of this study was to investigate the effect of post-synthesis treatments on the performance of ZSM-5 zeolite catalyst in the hydroisomerization reaction. In order to increase pore size and surface area of ZSM-5 catalysis, desilication with NaOH solution and synthesizing MCM-41/ZSM-5 with CTAB was performed on the parentzeolite. The synthesized catalysts were charactrized using XRD, FTIR, N2 adsorption-desorption, FE-SEM and NH3-TPD. It was found that post-synthesis operations increased the surface area and pore size of the catalyst and maintained the crystal structure of ZSM-5 as well. Desilication with lower concentrations of NaOH solution led to increase in acidity of parent zeolite and the crystalline structure preserved. In addition, in the composite synthesis method, it was found that pH = 8.5 is suitable and increased the specific surface area from 350 m2/g to 470 m2/g and regular meso-pores were adde to the structure. The performance of the synthesized catalysts in the n-pentane hydroisomerization reaction was investigated by varying the factors such as temperature, WHSV and mode reaction time. It was found that increasing the surface area and pore sizes improved the accessibility of the n-pentane reactive molecules to the active catalytic sites. This effect improves the catalyst performance in converting normal pentane to isopentane. In addition, having high surface area and larger pores probabley improves distribution of active metal sites and the synergy of these two effects increases the conversion rate and selectivity to iso-pentane, 30% and 20% respectively.
