| Because of the excellent thermal, chemical and structural stability as well as the small pore size, in microporous materials, the small pore size zeolites like SAPO-34, AlPO-34and DD3R have been widely recognized as ideal building blocks for construction of zeolite membranes for gas separation. Although some progress has been made in those zeolite membranes development and application, most of them are hard to form, therefore, they are usually prepared on some small pore size supports to make the nucleation site uniform and obtain a high separation performance. However, the cost is increased and the gas permeances are limited which are adverse to the advancement of industrialization. In the present study, we aim to develop routes for the preparation of high-performance SAPO-34, AlPO-34and Si-DD3R zeolite membranes on low-cost macroporous tublar α-Al2O3supports for gas separation, and the main work of this thesis can be found as follows:(1) A steam-assisted seeding method was proposed to modify the large pores of the supports, enhance adhesion between seed layers and supports and then prepare high-quality SAPO-34zeolite membranes on low-cost macroporous supports. The seeds-containing pastes were coated on the surface of macroporous supports which would be transformed into seed layers after the steam-assisted conversion process. The optimal conditions, such as seed sizes and coating times, for the SAPO-34membranes formation were investigated. A thin and continuous seed layer was formed by the conversion of the500nm SAPO-34seeds-containing paste, coating twice. SAPO-34membrane prepared by this method under optimal conditions showed the H2permeance of6.96×10-6mol·m-2s-1Pa-1, with H2ideal selectivities over CH4, C3H8and i-C4H10of14.8,26.5and53.0, respectively.(2) To simplify the technology, effectively use the template and prepare a high-quality SAPO-34membrane, a seeded dry gel conversion synthesis method was proposed. The effects of synthesis gel concentrations, seed sizes and vapor compositions on the membranes formation were investigated. This membrane synthesized under optimal conditions exhibited a H2permeance of7.04×10-6mol·m-2s-1Pa-1with H2/C3H8and H2/i-C4H10ideal selectivities of25.4and50.6, respectively. The mechanism of SAPO-34membranes forming by this method was explored which could effectively reduce the inter-zeolitic defects through the formation of lots of new nuclei in dry gel, resulting in a good inter-growth SAPO-34membrane.(3) The green and recyclable ionic liquid was used as solvent to synthesize the high-performance AlPO-34molecular sieving membranes by the secondary growth method with template N-MIm free. To increase the nucleation sites on macroporous supports, the effect of HF contents, seed layers and water contents were studied during the membranes preparation. By the cooperation of water and seed layer, the AlPO-34membrane showed H2 permeance of9.74×10-8mol·m-2s-1Pa-1, with high H2selectivities over CO2, CH4, C3H8and i-C4H10of7.49,14.6,39.3and65.8, respectively. These values are higher than the other reported zeolite membranes by ionothermal synthesis.(4) Si-DD3R molecular sieves with an average particle size of30nm were synthesized in the presence of F-and EDA. Compared with the conventional method, the synthesis time was reduced from25days to4days attributing to the assist of microwave heating which could also produce crystal nuclei-containing precursor expecting to helpful for the development of an effective process forits membrane formation. A ball-milling seeds seeded dry gel conversion method was applied to the synthesis of Si-DD3R zeolite membranes, as a result of favors in the support roughness modification and Si-DD3R crystal nucleation sites. The preparation condition of conversion time was investigated. The continuous and high crystalline Si-DD3R membrane was prepared by the induction of three-day conversion seed layer with H2/i-C4H10ideal selectivites of43.8. To further improve the membrane performance, the as-prepared membrane was subjected to polishing treatement to increase the nuclei density following by membrane deposition again. The membrane performance was obviously improved by this secondary repair method under a high concentration of the synthesis gel, showing an improved H2permeance of7.35×10-8mol·m-2s-1Pa-1and the H2/CH4, H2/C3H8, H2/i-C4H10ideal selectivities of8.77,29.2and57.4, respectively. Compared with SAPO-34and AlPO-34membranes, the Si-DD3R membrane could maintain high separation performance even at high temperature which is particularly promising for industial applicitons under hash conditions. |
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