A study on synthesis of ZSM-5 zeolite with enhanced hydrothermal stability for naphtha catalytic cracking

Abstract

ZSM-5 was synthesized by template-free method usi/ng nano-sized crystalline ZSM-5 as a seed and sodium silicate as a silica source. The uniform ZSM-5 crystals with relative crystallinity higher than 100 % could be obtained successfully by the seeding method. To guaranty uniform and crystalline ZSM-5, the nano-sized crystalline seed in the range of 100 nm should be used. The crystal size of ZSM-5 could be controlled easily by the content of seed in mother slurry. The windows of $Na_2O/SiO_2$ and $Al_2O_3/SiO_2$ of mother slurry could be expanded by the introduction of crystalline seed even in template-fee synthesis of ZSM-5 with sodium silicate. The ZSM-5 prepared in the presence of nano-sized crystalline seed also revealed higher hydrothermal stability than those prepared without seed. To compare the catalytic activity of synthesized and commercial ZSM-5, a series of P modified ZSM-5 was prepared using $H_3PO_4$ solution and was evaluated after steaming in a severe condition. The synthesized ZSM-5 shows higher activity than commercial one in naphtha cracking. Finally, enhanced catalytic performance of synthesized ZSM-5 using crystalline seed was confirmed in fluidized bed re-actor. The catalysts were characterized by XRD, Ar adsorption, $^{27} Al$ and $^{31} P MAS NMR$ , $NH_3-TPD$ . Results showed that to obtain the higher hydrothermal stable acid sites, it is important to have the structural stability of framework in ZSM-5 zeolites.