Synthesis And Gas Separation Performance Of Zeolite Membrane

Since zeolite has regular porous structure with uniform pore size distribution, the membrane can realize the separation in molecular level. Therefore, the research and exploring of zeolite membrane are of the potential significance for industrial application.So far,many methods have been reported for the synthesis of zeolite membrane, but only next two method show good effect, i.e. pre-coating seeds combined with a secondary hydrothermal synthesis and microwave synthesis. However, only a few studies have been carried out for this method. There still exist many defects to synthesis of zeolite membrane, such as complicate operation, high cost, few practical types etc. This thesis comprises following studies: (1) NaA zeolite membrane is selected as one object owing to fewer study and the application prospect of separating gases. Microwave heating method and conventional heating method are used to synthesize NaA zeolite membrane. The method of pre-coating nanosized seeds obtained by the vapor phase transformation method followed by a secondary synthesis could produce NaA zeolite membrane with high quality. (2) Nanosized NaY zeolites were synthesized by microwave heating method for the first time. NaY zeolite membrane with high quality was synthesized by pre-coating nanosized seeds prepared above followed by a secondary synthesis. (3) Nanosized ZSM-5 zeolite was synthesized by adding alkali metal salts. Nanosized zeolites were used as seeds to synthesize ZSM-5 zeolite membrane with high quality.The performance of zeolite membrane was obviously affected by substrate quality. The porous substrate with narrower distribution was prepared by calcining nanosized alumina at 1150℃. Two types of primary membrane evaluating methods were compared and analyzed in chapter two the second chapter. The sweeping method can obtain an accurate result as to membrane with lower permeance due to difficult to attain stabilizing state. The pressure difference method has the advantage of easy operation, and also can obtain an accurate result as to membrane with higher permeance. Novel methods to synthesize zeolite membrane were explored as follows.1. NaA zeolite membraneMicrowave heating to synthesize zeolite has many advantages, such as shortening synthesis time, reducing crystal size, obtaining uniform distribution as well as restraining transformation crystal. Zeolite with crystal size of 300nm prepared by microwave heating method in chapter three, and it was used as seeds to the synthesis of NaA zeolite membrane in gel system by microwave heatingmethod. Effects of synthesis conditions, such as seeds, placement manner, alkalinity, Na+ concentration, water amount, stirring synthesis, synthesis time and synthesis times on the integrity of zeolite membrane were investigated in detail. The results showed that the integrity of NaA zeolite membrane was improved by employing the multi-stage synthesis when the pre-coating seeds was in micrometer size. In order to reduce synthesis times and prepare zeolite membrane with high quality. In chapter three, a good seed layer was prepared on the substrate surface by vapor phase transformation method and then subjected to microwave heating. The highly compact NaA membranes obtained above were composed of intergrown crystals. Under the conditions at 25癈 and pressure difference of 0.1 MPa, the H2 permeance of the membrane synthesized with microwave heating for 20min was 1.6 X 10-7 mol/Pa-m2-s, and the ideal H2/N2 selectivity attained 13.4, higher than the corresponding Knudsen diffusion value(3.74), indicating that the gas separation was affected by the pore channel of zeolite. With increasing temperature, the permeance increased whereas the permselectivity decreased.In order to testify the applicability of pre-coating nanosized seeds obtained by the vapor transformation method, it was applied to conventional heating synthesis of NaA zeolite membrane in the fourth chapter of this thesis. When the synthesis time was 36h, the ideal H2/N2 selectivity reached a maximum of 14.10 and the id...