Synthesis of nanocrystalline ZSM-5 catalyst for production of gasoline from polyolefin waste

Abstract

ZSM-5 was synthesized using two different methods: hydrothermal and xerogel methods. The hydrothermal synthesis method was carried out by mixing sodium metasilicate pentahydrate solution, a sodium aluminate solution and a solution of tetrapropylammonium bromide, followed by crystallization at 170°C for various periods. The xerogel method was studied by synthesizing ZSM-5 from freshly prepared silica. Influences of type of the templates, pH of gel and template/SiO2 ratio on the synthesis of ZSM-5, MFI structure zeolite, were investigated. Tetrapropylammonium bromide and tetrapropylammonium hydroxide were used as templates. The values of pH from 9.0 to 11.0 and template/SiO2 mole ratios from 0.1 to 0.5 were varied. Furthermore, the influence of sonication during the gel formation step was also studied in comparison with zeolite ZSM-5 prepared without sonication. The organic template was removed from the ZSM-5 samples by calcination in a muffle furnace at 550°C. The ZSM-5 catalysts were characterized by X-ray power diffraction, scanning electron microscope, ICP-AES, 27Al-MAS-NMR, nitrogen adsorption, X-ray fluorescence and ammonia-temperature programmed desorption techniques. The obtained ZSM-5 were tested for their catalytic activity in the cracking of HDPE waste in a batch reactor under different conditions. The conversions and the yields of gas fraction and liquid fraction depend on the reaction temperature and the Si/Al ratios in catalyst. The product selectivity is affected by those factors only slightly. The gas products obtained by HDPE cracking are mainly propene, n-butane, i-butene and C5+. The liquid fraction obtained by cracking of HDPE waste composes mainly in the range of C6 to C9. The used ZSM-5 catalyst can be regenerated by simple calcination and its activity still does not change significantly.