Synthesis of Chainlike ZSM-5 with a Polyelectrolyte as a Second Template for Oleic Acid and Ethanol Cracking into Light Olefins.

Chainlike ZSM-5 was synthesized in a tetrapropylammonium hydroxide (TPAOH) and poly(diallydimethylammonium chloride) (PDDA) dual-template system. The synthesis parameters and formation mechanism of chainlike zeolites were investigated. The optimized composition of the synthesis mixture was as follows: the PDDA/SiO2, TPAOH/SiO2, SiO2/Al2O3, and H2O/SiO2 molar ratios are, respectively, 0.16, 0.4, 50, and 40, with tetraethyl orthosilicate and aluminum nitrate as silicon/aluminum sources. The resultant ZSM-5 showed a cross-linked chainlike morphology, mesopore-dominated pore structure, and mild acidity. The formation of the chainlike zeolite was attributed to synergistic actions between PDDA and TPAOH. TPAOH acted as an alkali source and helped to induce nucleation and control the crystal size. PDDA acted as a soft template to promote crystal nucleation, and a hard template to form a three-dimensional mesoporous structure. Light olefin (C2-4 =) selectivities from cracking of ethanol and oleic acid over the present chainlike ZSM-5 at 400 °C reached 90 and 75.7%, respectively, which were much higher than those from commercial ZSM-5 (75 and 52.3%, respectively), demonstrating the excellent hydrothermal stability and catalytic performance of the synthesized chainlike zeolite.

Preparation of sodium silicate/red mud-based ZSM-5 with glucose as a second template for catalytic cracking of waste plastics into useful chemicals.

ZSM-5 was economically synthesized with red mud (RM) and industrial sodium silicate (ISS) in a tetrapropylammonium bromide (TPABr)-glucose dual-template system. The roles of glucose, Fe and Ca in RM on the formation of ZSM-5 were investigated. The catalytic performances of the resultant ZSM-5 were tested by cracking waste plastics. It was found that the formation of ZSM-5 was attributed to a synergistic effect between TPABr and glucose. The addition of glucose decreased the pH value in the crystallization solution and thus promoted the crystallization effect. Glucose acted as a hard template to generate mesopores. Fe atoms were partly distributed in the framework and partly adsorbed in the pores of ZSM-5, and helped to generate more Lewis acid sites. Ca atoms were mainly adsorbed in the pores of ZSM-5, and showed an inhibitory effect on the formation of zeolites. The synthesized ZSM-5 showed a weakly acidic and mesoporous structure and achieved an enhanced effect on producing gaseous products (gas yield: 85.3%), especially light olefins (C[double bond, length as m-dash] 2-4) (selectivity: 77.1%) from cracking of low density polyethylene at 500 °C. The long-term cracking experiment showed that the synthesized ZSM-5 is superior in converting waste plastics to light olefins (ethylene and propene) than the commercial ZSM-5.