Synthesis, Characterization And Evaluation Of Novel Catalytic Materials Containing ZSM-5 Zeolite

Propylene is an important industrial chemical; however, the supply of propylene is not keeping pace with its demand, as a result, research on increasing propylene production has become a topic of interest. ZSM-5 zeolite with three-dimensional sinusoidal and straight channels of molecular dimension was first used by Mobil in 1990s to increase the yield of propylene. This zeolite selectively cracks C7-C13 straight and short branched chain hydrocarbons to C3-C5 olefins. Thus, it increases the yield of light olefins and has become the preferred catalyst or additive for enhancing the yield of propylene in the field of petrochemical processing.The method for in-situ synthesis of ZSM-5 has significant advantages compared to the additive's traditional preparation. In the traditional method of ZSM-5 additive preparation, the active component ZSM-5 is embedded in a binder or matrix which greatly reduces the contact between the feedstock and the active component. Consequently, the efficiency of ZSM-5 zeolite is decreased. This paper focuses on using the method of in-situ synthesis, in this paper ZSM-5 zeolite is synthesized on the surfaces of kaolin microspheres or silica gel microspheres, thus allowing the feed oil easier access to the active component. Furthermore, because the active component and matrix were obtained together during the synthesis of ZSM-5 zeolite, this ZSM-5 crystallization product can be directly used as an additive in industry.The in-situ synthesis of ZSM-5 zeolite on kaolin microspheres calcined at different temperatures was studied first. The results indicate that the synthesis of ZSM-5 is related to the calcination temperature of kaolin. When the kaolin microspheres were calcined at different temperatures, the amounts of chemically active SiO2 and active Al2O3 in the kaolin microspheres were different. However, the chemically active SiO2 and active Al2O3 are the"nutrients"for the zeolite synthesis; therefore the calcination temperature has an important effect on the synthesis of ZSM-5 zeolite. Some variables, including crystallization time, crystallization temperature, silica to alumina ratio of the initial gel and the pH of the initial gel, were investigated. The results showed that, compare to other variables, crystallization time and crystallization temperature played the most important roles of synthesizing pure, high crystallinity ZSM-5 zeolite. Under our experimental conditions, within a certain hour, increasing crystallization temperature can obtain pure and high crystallinity ZSM-5 zeolite. Using this ZSM-5 zeolite as an additive to an FCC catalyst, catalytic cracking reactions were carried out on a heavy oil micro fixed-bed reactor unit. The results show that by adding 10% of ZSM-5 to the base ZC7300 FCC catalyst, the yields of light olefins such as propylene and butylene increased by approximately four percent. This shows that novel ZSM-5 zeolite has a good selectivity for the light olefins.Based on the above research about the in-situ synthesis of ZSM-5 zeolite on the kaolin microspheres, the hydrothermal synthesis of ZSM-5 zeolite was investigated using acid treated kaolin as a raw material. The objective of this study is to convert cheap kaolin to high value ZSM-5 zeolite completely. The XRD, FT-IR, N2 adsorption-desorption, SEM and Pyridine adsorption techniques were used to characterize the obtained ZSM-5 zeolite. The results show that the ZSM-5 zeolite is pure and has high crystallinity, good micropore structure and more B acid site which favors FCC reactions. The cracking catalytic activity of this ZSM-5 zeolite was studied on a heavy oil micro fixed-bed reactor unit using Daqing VGO as a feedstock. The results indicated that by adding 5% of ZSM-5 to the base ZC7300 FCC catalyst, the yields of propylene and LPG increased by approximately three percent and 6.91 percent, respectively. These results demonstrate that this ZSM-5 zeolite obtained from kaoliin has a good selectivity for propylene and can improve the propylene production effectively.In addition, the in-situ synthesis of ZSM-5 zeolite was studied using n-Butylamine as a structure directing agent. Some characterization techniques, including XRD, FT-IR, N2 adsorption-desorption, SEM and pyridine adsorption, were used to measure the properties of ZSM-5 zeolite. Results show that ZSM-5 zeolite was in-situ synthesized on the silica gel microspheres uniformly, and the shape of the silica gel microspheres was retained, and composite materials with micropore structure and macropore structure were formed. The crystal size of ZSM-5 can be tuned by the method of"two-stage temperature crystallization"within the range of 0.5-20 um. Some synthesis variables, such as crystallization time, crystallization temperature, sodium concentration, alkalinity, have been shown to affect the crystallization and morphologies of ZSM-5 zeolite. Using this novel ZSM-5 zeolite with different silica to alumina ratios as an additive of FCC catalyst, heavy oil catalytic cracking reaction was carried out on a micro fixed-bed reactor. The reaction results indicate that by adding 3% of ZSM-5 to the base ZC7300 FCC catalyst, the yields of propylene increased by 3.74% on average. When silica to alumina ratio was increased, the yields of gasoline and diesel were increased gradually and the yields of light olefins including propylene and butylenes were decreased, showing that the ZSM-5 zeolite with lower silica to alumina ratio is much more suitable for improving the yield of light olefins.Extending the research on in-situ synthesis of ZSM-5 zeolite on the surface of silica gel microspheres, the in-situ synthesis of hierarchical ZSM-5 zeoite was investigated. Results showed that ZSM-5 zeolites with hierarchical porosity were successfully synthesized in-situ on the surface of silica gel microspheres under hydrothermal conditions through cetyltrimethylamnonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH) dual templates method. SEM pictures show that the silica gel microspheres were wrapped by a layer of ZSM-5 crystals and the shape of silica gel microspheres was retained very well. TEM pictures and N2 adsorption-desorption data indicate that the ZSM-5 zeolite has intracrystal mesopores with average pore size of 3nm and pore size distribution is only 0.8nm width at half maximum of distribution peak which is very narrow. The pore size can be tuned between 3nm to 20nm by adding the 1, 3, 5-trimethybezene. Catalytic test show that the hierarchical ZSM-5 zeolite catalyst exhibits higher catalytic activity for propylene oligomerization than microporous ZSM-5 zeolite. The high proplylene conversion and aromatic and cycloalkane products selectivity are mainly attributed to the presence of the hierarchical porosity.