According to the concept of molecular management, selective adsorption of 5A molecular sieve in naphtha can optimize the yield of ethylene aromatics, significantly improve the utilization of petroleum. In order to further improve the efficiency of naphtha adsorption separation process, based on the traditional microporous 5A molecular sieve, a multi-stage porous 5A molecular sieve with composite structure of micropore mesopore was synthesized its adsorption performance was studied. Firstly, molecular dynamics method is used to simulate the diffusion process of simple molecules in one-dimensional molecular sieves. The diffusion coefficient increases with the increase of pore size. The diffusion coefficients of different n-alkanes in 5A zeolite were calculated by using the transition state theory. At 450 K, the diffusion coefficients of c3-c8 n-alkanes in 5A zeolite are 4.22 × 10-10cm2 / s to 4.68 × 10-14cm2. /S, the diffusion process is very slow, multi-stage channel 5A molecular sieves need to be synthesized to improve the adsorption rate. A multi-stage porous 5A molecular sieve was synthesized by hydrothermal method using dimethyl octadecyl [3 - (trimethoxysilyl) propyl] ammonium chloride (tpoac) as soft template. The pore size is about 0.5nm, the mesopore concentration is 7-13nm. The number of mesopores in multistage 5A molecular sieve can be adjusted by changing the number of templates. The optimized synthesis conditions are as follows: molar ratio of raw materials n (SiO2): n (Na2O): n (Al2O3): n (H2O): n (tpoac) = 100:333:67:20000:0.1, crystallization time crystallization temperature 100 ℃, washing methanol to pH = 8, removing the template, obtaining multichannel 5A molecular sieve by calcium ion exchange. The mesoporous volume is 0.0674cm3/g, which is equivalent to 26.7% of the total pore volume. At 288 K, the adsorption capacity of n-hexane is 0.1183g/g molecular sieve. The adsorption kinetics of n-alkanes in multichannel 5A zeolite was studied. The liquid diffusion coefficients of n-pentane, n-hexane n-heptane in 0.1% multistage channel 5A molecular sieve at 288k are about micron. It is 2.02-3.94 times of that in the zeolite with pore size of 5A. The diffusion coefficient of n-alkanes in multi-channel 5A molecular sieve increases with the amount of template. With the increase of carbon number of n-alkanes, the diffusion activation energy increases. The optimized extrusion formula is as follows: 8% additive Tianjin powder 10% nitric acid. The adsorption capacity of n-hexane on 5A molecular sieve with a diameter of 1 mm is 0.1048 g / g, the liquid diffusion coefficient is 2.01 times of the micropore of band 5A molecular sieve.
Small batch can be dried in muffle furnace at 150 ℃ for 2-3 hours, which is now widely used. When used in large-scale equipment such as air separation, 5A molecular sieve needs to be pretreated during driving. As molecular sieves are very hygroscopic, they should be directly exposed to the air during storage, but should be placed in a dry place.