Synthesis Of SAPO-34 Zeolite Membrane By Secondary Growth Method For CH₄/CO₂ Gas Separation

Natural gas contains 6%-12% of carbon dioxide,generally ioxide not only reduces the heat of natural gas,but also corrodes the transport pipeline and storage equipment.Methane is the main component of natural gas,so the separation of CH₄/CO₂ is an indispensable unit before natural gas transport.At present,the separation methods of CH₄/CO₂ mixture include absorption method,pressure swing adsorption method,cold separation method,membrane separation method and so on.Compared with other separation processes,membrane separation method have some advantages such as simple operation,low energy consumption,high efficiency,easy industrial amplification Advantage.Zeolite membranes have great research value and application prospect for the separation of CH₄/CO₂ mixture by high mechanical stability,corrosion resistance and high thermal stability.SAPO-34?0.38 nm?is one of the representatives of microporous molecular sieves which has the pore size similar to that of CH4?0.38nm?and larger than that of CO2?0.33nm?.According to the literature,the adsorption capacity of CO2 on SAPO-34 is greater than that of CH4.Therefore,SAPO-34 zeolite membrane has a good separation performance on CH₄/CO₂ mixture under the synergistic effect of molecular s ieving and competitive adsorption.In this paper,continuous dense SAPO-34 zeolite membranes were prepared by secondary growth method using ?-A12O3 as carrier.The zeolite,seed layer and SAPO-34 zeolite membrane were characterized by XRD,SEM and N2 single-element permeation.The separation performance of CH₄/CO₂ mixed system was studied on SAPO-34 zeolite membranes.The results are as follows:1,Preparation of SAPO-34 molecular sieves which size is matching with carrier pore size.The size of SAPO-34 molecular sieves were investigated by changing the crystallization temperature and crystallization time by in situ hydrothermal synthesis.When the molar ratio of Al₂O₃: 2.0 P2O5: 0.6 SiO2: 4.0TEAOH: 150H2 O,aging time is 24 h,crystallization temperature is 200?C and crystallization time is 8h,SAPO-34 molecular sieve seeds are uniform with the size of 600-700 nm.2,The effects of secondary crystallization conditions such as aging time and crystallization time on the structure and properties of zeolite membranes were investigated.The results show that SAPO-34 zeolite membranes are continuous dense when the molar ratio of secondary synthetic solution is 1.0 Al₂O₃: 1.0 P2O5: 0.6 SiO2: 1.0 TEAOH: 1.6DPA: 150 H2 O,the aging time is 3 days,the crystallization time is 15 h,the crystallization temperature is 220 °C.3,The effect of the quality of seed layer on the structure and properties of zeolite membrane.The effects of the surface properties of the carrier,loading the seeds and the concentration of seed crystals on the structure and properties of SAPO-34 zeolite membranes were investigated.The results show that the carrier was treated with cationic polymer?PDDA?,the seed dispersion medium was deionized water and the seed crystal concentration was 1%,A high quality seed layer could be prepared by dip spin coating method And then can be prepared more dense flattened SAPO-34 zeolite membrane,The separation selectivity of CO₂/CH₄ can reach 12.76,and the permeation rate of CO2 is 4.64 × 10-7mol/?m2·s·Pa?.