A Study on the characteristics and reaction parameters of dewaxing catalysts for upgrading heavy hydrocarbon

Abstract

Various zeolites supported platinum catalysts were prepared by an impregnation method and were applied to the hydroisomerization of n-hexadecane. Among the catalysts, Pt/ZSM-23 catalysts with a one-dimensional channel structure showed better isomerization selectivity. Effort has been made to improve the selectivity to iso-hexadecane by introducing the magnesium promoter. The catalytic performances between Pt/ZSM-23 and magnesium promoted Pt/ZSM-23 were compared in terms of the correlation between conversion and selectivity. Magnesium promoter resulted in the changes of acidity and the dispersion of Pt metal; the acid amount decreased and the Lewis acid sites increased. The dispersion of Pt metal was also improved. Magnesium-promoted Pt/ZSM-23 showed a higher yield of iso-hexadcanes due to its Lewis type acidic properties and higher Pt dispersion. In addition, hydroisomerization and hydrocracking of n-hexadecane in the presence of sulfur and nitrogen compound were investigated over four different platinum loaded (Pt, Pt-Pd, Pt-Mg and Pt-Pd-Mg) ZSM-23 catalysts, for n-paraffin dewaxing as a model reaction. Sulfur and nitrogen compounds poisoned metal and acid sites of bifunctional catalysts, respectively. Effort has been made to improve the sulfur and nitrogen tolerance in the conversion of n-hexadecane by introducing palladium and magnesium as additives. Pt-Pd bimetallic catalyst could increase the amount of electron-deficient metal sites, resulting in improvement of sulfur tolerance. Also, the addition of magnesium could improve the resistance against poisoning of nitrogen compound due to the increase in the concentration of Lewis acid sites. The potential to apply Pt-Pd-Mg/ZSM-23 catalyst for commercial dewaxing process was further examined using diesel feed in a high pressure pilot plant. Ni/ZSM-5 which is widely used in the commercial dewaxing process also was tested in the same reactor for comparison. It was found that Pt-Pd-Mg/ZSM-23 exhibited better perf...