Diethylamine oriented synthesis of hollow fiber supported SAPO-34 molecular sieve membrane

As a clean and efficient energy source, natural gas has broad application prospects in power generation, heating, and fuel. Since the natural gas feedstock gas contains CO2 gas impurities, it not only reduces the calorific value of natural gas, but also easily precipitates out dry ice during transportation to cause blockage and combine with water vapor to corrode pipelines. Therefore, it is very important to decarbonize natural gas before transportation. Traditional CO2 separation technologies such as pressure swing adsorption and solvent absorption have disadvantages such as high energy consumption, complex processes, and environmental pollution. As a new type of separation technology, membrane separation has the advantages of high efficiency, energy saving, convenient operation, and easy process control, and has attracted wide attention from researchers.

SAPO-34 molecular sieve membrane is a silicoaluminophosphate material with uniform and regular pore structure, unique CO2 adsorption and good thermochemical stability and mechanical properties. SAPO-34 molecular sieve membrane has an effective pore size of 0.38 nm, which is between the molecular dynamics diameter of CO2 (0.33 nm) and CH4 (0.38 nm), and shows excellent separation performance in CO2/CH4 separation.

SAPO-34 molecular sieve membrane usually needs organic template to induce synthesis, currently tetraethylammonium hydroxide (TEAOH) is mainly used. In 1997, Zhang et al. used TEAOH as a template for the first time to prepare a defect-free SAPO-34 molecular sieve membrane through in-situ growth. Later, Li et al. used TEAOH as a template to prepare a high-performance SAPO-34 molecular sieve membrane for CO2/CH4 separation on the surface of the tubular carrier. The CO2 permeability is 1.6×10﹣7 mol·m﹣2·s﹣1·Pa ﹣1, the separation selectivity is 67. Because TEAOH template is expensive, the preparation cost of SAPO-34 molecular sieve membrane is relatively high, and its large-scale production is restricted. The researchers found that the use of mixed templates can not only prepare a thinner SAPO-34 molecular sieve membrane layer, but also reduce the amount of TEAOH and reduce the cost of membrane production. In 2008, Carreon and others used TEAOH single template and TEAOH/CHA (cyclohexylamine), TEAOH/DPA (dipropylamine) and TEAOH/CHA/DPA three mixed templates to prepare SAPO-34 molecular sieve membrane. The membrane prepared by the composite template method has better CO2/CH4 separation performance. In the early stage of our research group, TEAOH/DPA mixed template was also used to prepare hollow fiber-supported SAPO-34 molecular sieve membrane and used for CO2/CH4 separation. Its CO2 permeability was significantly better than most reported results.

Choosing suitable membrane preparation materials to further reduce the preparation cost of SAPO-34 molecular sieve membranes is of great significance to the practical application of this type of membrane materials. Literature [19-21] has reported that low-cost diethylamine (DEA) can induce SAPO-34 molecular sieve crystals. However, there is no literature report on the preparation of SAPO-34 molecular sieve membrane by diethylamine. Based on this, this article attempts to use diethylamine as the template and industrial-grade pseudo-boehmite as the aluminum source to prepare SAPO-34 molecular sieve membranes at low cost for CO2/CH4 gas separation. In order to reduce the resistance of the support and increase the packing density of the membrane, this paper uses a self-made ceramic hollow fiber carrier to systematically investigate the influence of the induced seed size, the diethylamine content in the membrane synthesis solution, the aluminum source content and the crystallization time on the membrane structure. And separation performance.