The Synthesis And Adsorption Performance Of Hierarchical 5A Zeolites

Based on the molecular scale management, double object optimization of ethylene and aromatics yield can be achieved through separating normal paraffins from naphtha using shape-selective absorption 5A zeolites. In order to improve the adsorption separation efficiency, the micro/mesopore structure hierarchical 5A zeolites was synthesized, and the performance was studied.Firstly, the diffusion of noble gas molecules in one-dimensional zeolite channels was simulated by molecular dynamics method. The diffusion coefficient increased with the zeolite channel diameter. The diffusions of different normal paraffins in 5 A zeolites were calculated using Transition State Theory. The diffusion coefficients of C3-C8 normal paraffins in 5A zeolites were 4.22×10-10 cm2/s to 4.68×10-14 cm2/s at 450K. The diffusion processes carried out very slowly, so it is necessary to synthesize hierarchical 5A zeolites to improve the adsorption rate.The hierarchical 5A zeolites was synthesized by hydrothermal method with the dimethyl octadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (TPOAC) as the soft template. Micropores with the diameter of 0.5 nm were connected with 7-13nm mesopores. The amount of mesopores could be controlled by the template dosage. The optimal synthesis conditions weren(SiO2):n(Na2O):n(Al2O3):n(H2O):n(TPOAC)= 100:333:67:20000:0.1(mol), crystallization at 100℃ for 6h, washed by methanol to pH=8, exchanged by calcium ion. The mesopore volume was 0.0674 cm3/g, which was 26.7% of total pore volume. The adsorption capacity for normal hexane was 0.1183 g/g at 288K.Thirdly, the liquid phase adsorption kinetics of normal paraffins in the hierarchical 5A zeolites was investigated. When the template dosage is 0.1%, the liquid phase diffusion coefficients of n-paraffins in the hierarchical 5A zeolites were larger than those in the micropore 5A zeolites by 2.02-3.94 times at 288K. Diffusion coefficients of n-paraffins in the hierarchical 5A zeolites increased with the template dosage. The diffusion activation energies of n-pentane, n-hexane and n-heptane increased with carbon numbers in the chains.Finally, the molding of hierarchical 5A zeolites was studied. The optimal molding formula was 10% sesbania powder and nitric acid concentration 10%. The adsorption capacity of 1mm bar-type hierarchical 5A zeolites for n-hexane was 0.1048 g/g, and diffusion coefficient was 2.01 times larger than 5A micropore zeolites.