Preparation Of Silicon Nitride-Based Ceramic Membranes And Their Applications In Membrane Distillation Process

With the growth of the world’s population and the improvement of industrialization, the freshwater resources, which is one of human life necessities, will be sought after by all countries. Under the influence of natural disasters and man-made factors, reserves of few fresh water resources become scarcer, especially in Africa and the Middle East. Some provinces and cities in our country are in a long period of drought conditions, and in serious areas it has affected people’s daily-drinking water problems. Water problem is extremely urgent.Seawater desalination technology is an effective way to obtain fresh water. Vast seawater resources provides enough raw materials for desalination process. Since it began to be used In the middle of the twentieth century, this technology has got vigorous development. The desalination plant, which Built in 1954 by the United States, is still running and continuously providing daily-drinking water. Seawater desalination industry is developing rapidly in the Middle East. Booming oil deals supplied the study with a lot of money and extreme scarcity forced local people to spend a lot of manpower and material resources to develop desalination, the freshwater source incremental project.Membrane distillation is an effective desalination process. It was found since 1963, now is still in the stage of laboratory research and has not been fully implemented in the industry. During the last six years, paper on membrane distillation membranes project (such as the design, preparation of membrane and membrane distillation performance test) has seen a sharp growth in quantity, is developing rapidly.The key point is the study of the separation membrane materials. Development of an effective, efficient and long-acting separation membrane is top priority in the development of Membrane distillation.The aim of this article is to find a membrane material with high stability and potential applicationsin membrane distillation.Based on previous studies, organic membranes lack stability when operating in high temperature sea-water, so our research focused on the non-oxide ceramic membrane with high stabilities, in terms of the preparation, structural optimization and surface modification of ceramic membrane.The first chapter mainly introduced the current status of water resources and the urgency of the fresh water demand; desalination technology industrialization situation and defects of the present desalination; the work principle and classification of membrane distillation technology, the obstacle of realizing the industrialization of membrane distillation process, etc; the preparation methods, characterization process and performance index of ceramic membrane; the current existing methods of surface modification of ceramic membrane. Finally the whole research ideas are expounded.The second chapter introduced the equipment and raw materials used in the experiment.The third chapter could be devided into two parts:First, the preparation and characterization of silicon nitride and β-Sialon flat ceramic membrane through the phase inversion tape castingand sintering method. Silicon nitride and β-Sialon ceramic flat membrane with high strength and high porosity could be achieved through optimizing the composition of slurry of precusor powders, sintering temperature and other conditions. Second, the β-Sialon fiber tube membrane was achieved throughthe phase inversion of extrusion molding with sintering methods. Stable and uniform slurry was obtained by selecting suitable dispersant, and composition of the suspension. And then β-Sialon fiber tube membrane was obtained and the properties were characterized and optimized.The fourth chapter focused on the surface modification of ceramic membrane and the membrane distillation process test of the modified ceramic membranes. Ceramic membrane’s natural hydrophilicity makes it unsuitable for membrane distillation process, so the surface modification process is a key step which enhances its work life and entrusts it potential for the industrial production of fresh water. Three modification methods have been studied to achieve the hydrophobocity of the membrane:(1) FAS modification (2) SiNCO nanoparticles modification (3) PDMS pyrolysis modification. The obtained hydrophobic membranes were used in membrane distillation to obtain pure water as well. The long-term stability is our primary concern. The stability of FAS grafting was much worse than pyrolysis modification.The fifth chapter fouced on the improvement of efficiency of the membrane for practical applications. By improving the forming process of ceramic membrane, using graphite sacrificial layer double layer tape casting and hot pressing technology, we effectively increased the mass transport of the ceramic membrane and the water flux of the membrane distillation process could be enhanced by more than 50%, which improved the efficiency of membrane distillation process and made it more close to industrial application.At chapter six, we introduced another application of the ceramic membrane as the supporting material. We successfully synthesized a compact ZIF-8 membrane at the outer surface of Si3N4 hollow fiber membrane. We confirmed its application in CO2 adsorption and gas separation. The separation of hydrogen and carbon dioxide mixture factor was 11.67.Chapter seven is the conclusion of the work. We pointed out the shortcomings and the further improvements of the work.