Preparation Of Inorganic Microfiltration And Ultrafiltration Composite Membranes By Controlling NaA Zeolite Growth On Macroporous Substrates And Their Applications

The inorganic membranes possess extensive application prospects in the fields of microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF) because of its high chemical and thermal stability, mechanical strength and long working life. The conventional preparation methods such as particles sintering and sol-gel methods need complex and tedious process with rigorous condition, which lead to much higher energy consumption and cost. Besides, it is difficult to prepare membranes with small pore size using the conventional methods, as well as the controlling preparation. Thus, it is of great significance to develop novel and simple method to prepare MF, UF and even NF membrane with tunable pore size and their application.In this thesis, zeolite NaA/a-Al₂O₃ MF and UF membranes with tuneable pore sizes were prepared on the internal surfaces of macoporousα-alumina tubular substrates by controlling NaA zeolite growth with in-situ hydrothermal synthesis method at the simple and mild synthesis conditions. And the as-synthesized MF and UF membranes were applied in the treatment of emulsified oily water, bovine serum albumin (BSA) solution and trace iron wastewater, respectively. The novel, cheap and feasible route can overcome effectively the disadvantages such as high energy consumption and cost of the conventional method. The as-synthesized composite MF and UF membranes were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), single gas permeation and pore size distribution (PSD) testing.The influence of intrinsic factors of synthetic chemistry and external factors of crystallization condition were discussed. The control of molar ratio of synthesis solution, synthesis time and synthesis stages were the key factors of the preparation of the NaA/α-Al₂O₃ MF and UF membranes, so as to obtain ideal method and synthesis condition for controlling preparation NaA/α-Al₂O₃ MF and UF membranes. To study various synthesis factors and condition, to optimize the technological process, the degree of dispersion and intergrowth between the NaA crystals on the surface of macroporousα-Al₂O₃ substrate was controlled well. Thus, the degree of the modification to the support was tuned effectively. NaA/α-Al₂O₃ MF membranes with the main pore size about 0.2 to 1.2um were obtained successfully. And the NaA/α-Al₂O₃ UF membrane with the main pore size about 50 to100nm was prepared after one time synthesis.The as-synthesized NaA/α-Al₂O₃ MF and UF membranes were applied in the treatment of the emulsified oily water and BSA wastewater. The NaA/α-Al₂O₃ MF membrane showed high permeance and good oil rejection up to 99%. The NaA/α-Al₂O₃ UF membrane exhibited high BSA rejection above 98%. The NaA/α-Al₂O₃ MF and UF membranes all showed superior removal performance.The treatment of trace iron wastewater through the tubular ceramic membranes with different pore structure was discussed. The results revealed that ceramic membranes with pore size of 5nm, 50nm and the as-synthesized NaA/α-Al₂O₃ UF membrane all showed good iron-removal performance and the iron rejection was above 95%.The fouling performances of the NaA/α-Al₂O₃ MF, UF and 50nm alumina membranes by emulsified oily water, BSA solution and trace iron wastewater were investigated, respectively. According to the property of the fouled membranes, proper cleaning process was adopted for the regeneration of the membranes. The separation performance of all the membranes could recover to over 97% of the original performance after regeneration, which indicated the effect of cleaning process and the stability and repeated properties of the membranes.