Preparation Of Yttrium Silicate Ceramic Based Membranes And Applications In Membrane Separation

With the increasing population of the world and the rapid development of industry,each country has a great demand for freshwater resources.More than 70%of the earth’s surface is made up of water,but the freshwater resources that people can use are only less than 0.3%,and the distribution of this rare freshwater resource is also very uneven.Due to the development of industry and the pollution in life,the climate has gradually deteriorated,and the scarce fresh water resources have become more scarcer.In order to solve the problem of lack of fresh water resources,we carry out two aspects,namely,open source and throttling:open source is to obtain fresh water resources from seawater,that is,seawater desalination;throttling is to purify the discharged sewage,so that sewage can be reused.As a technology to solve the shortage of fresh water resources,seawater desalination was proposed to the 16th century and received extensive attention and development in the 1950s.In the Middle East,where freshwater resources are scarce,desalination technology has been developed and applied,where more than 70%of freshwater is obtained from desalination.There are two types of conventional methods of seawater desalination:thermal and membrane methods.Among them,the thermal method mainly has multi-stage flashing and multi-stage evaporation;the membrane method mainly includes electrodialysis and reverse osmosis.Later,a membrane distillation method combining membrane and thermal methods was proposed.In the 1980s,the process of applying some excellent organic membranes to membrane distillation experiments was explored.In this thesis,the y-Y2Si2O7 ceramic material with low thermal conductivity(facilitating the membrane distillation process)was explored.The y-Y2Si2O7 ceramic flat membrane was prepared by tape casting and pressureless sintering.The ceramic membrane was hydrophobically modified and applied to membrane distillation.In experiment.The a-Si3N4 nanowire/y-Y2Si2O7 composite ceramic membrane was prepared by direct nitridation of silicon powder,and the superhydrophobic membrane was obtained by hydrophobic modification and subjected to membrane distillation experiments.The y-Y2Si2O7 ceramic flat membrane was modified with SiO2 nanospheres and subjected to oil-water separation experiments.The specific experimental content is as follows:The first chapter mainly introduces the current situation of freshwater resources;the types,advantages and disadvantages of desalination technology;focuses on the membrane distillation technology(development,membrane material requirements and classification)in seawater desalination technology;the harm and treatment of oily wastewater Preparation of porous ceramic membranes and pore size distribution testing.The second chapter mainly introduces the reagents used in the experiment;the characterization instrument and test instrument used in the experiment,the simple introduction of the instrument;the membrane distillation device and the oil-water separation device are briefly introduced.The third chapter mainly introduces the preparation of γ-Y2Si2O7 ceramic flat membrane.The γ-Y2Si2O7 material with the best comprehensive performance was selected among the low thermal conductivity yttrium silicate ceramic materials.Firstly,pure phase γ-Y2Si2O7 was obtained by sintering SiO2 and Y2O3 powders.Then,the appropriate dispersant was selected by sedimentation test to adjust the optimal dispersant content,and a uniform and stable γ-Y2Si2O7 ceramic slurry was prepared.The slurry is formed by a tape casting process,and a suitable heating rate,reaction temperature,and sintering are performed to obtain a γ-Y2Si2O7 ceramic flat film having the best performance(strength,average pore diameter,porosity,etc.).In the fourth chapter,the γ-Y2Si2O7 ceramic flat membrane obtained in the previous chapter was subjected to hydrophobic modification and membrane distillation experiments.The surface of the ceramic membrane is subjected to a chlorosilane aminolysis pyrolysis reaction,and an inorganic nano-SiCNO structure is grown on the surface of the membrane to make the ceramic membrane hydrophobic.The modified γ-Y2Si2O7 ceramic flat membrane was subjected to a sweep gas membrane distillation experiment and a direct contact membrane distillation experiment,high flux(14.01 L m-2 h-1 at 90 ℃)and high rejection(over 99.9%)were obtained,and the total membrane distillation run time exceeded 400 hours.The fifth chapter mainly introduces the preparation of a-Si3N4 nanowire/γ-Y2Si2O7 composite superhydrophobic ceramic membrane and its application in membrane distillation.In the third chapter,the γ-Y2Si2O7 ceramic slurry was added with silicon powder and catalyst,and the a-Si3N4 nanowire/γ-Y2Si2O7 composite ceramic membrane was prepared by direct nitridation of silicon powder,and the pyrolysis of chlorosilane was carried out.The composite membrane was modified to obtain a superhydrophobic membrane.The modified membrane was subjected to a sweep gas membrane distillation experiment,high rejection(over 99.9%)were obtained,and the total membrane distillation run time exceeded 500 hours.In the sixth chapter,the y-Y2Si2O7 ceramic flat plate prepared in the third chapter was modified by SiO2 nanospheres,and the oil-water separation experiment was carried out.The SiO2 nanospheres were prepared by Stober method,and the y-Y2Si2O7 ceramic flat membranes were modified by SiO2 nanospheres to reduce the pore size of the ceramic membranes.The oil-water separation experiment was carried out on the modified γ-Y2Si2O7 ceramic flat membrane,high flux(594 L m-2 h-1)and high rejection(90.1%)were obtainedThe seventh chapter summarizes the research work of all the papers,discusses some shortcomings in the research work,and forecasts the future research.