Engineering Technology Of Preparation Of Alumina Ceramic Membrane By Dip-coating Method

Ceramic membranes have wide application in food processing,bio-pharmaceutical,chemical industry and environmental treatment due to its acid resistance,alkali resistance,corrosion resistance,high temperature resistance and long service life.The preparation methods of ceramic membranes include dip-coating method,spray coating method,sol-gel method,chemical vapor deposition method,etc.The dip-coating method is widely used in the industrial production of ceramic membranes because of its simple equipment and convenient operation.However,for a long tubular membrane,there are problems such as uneven coating membrane and high manufacturing cost.In view of these problems,the design of ceramic membrane coating equipment and test fixture,the optimization of ceramic membrane formulation and process,and the preparation of alumina microfiltration membranes by electrostatically coated boehmite sol were studied.A set of coating slurry stirring device was designed and manufactured,which combined the process of raw material stirring and vacuuming to improve the vacuum defoaming efficiency.A set of inclined dip coating device was designed,by controlling each parameter in the coating process,it can achieve precise control of the thickness of the ceramic membrane,and overcome the problem of different dipping time at both ends of the membrane tube,making the thickness of the prepared ceramic membrane more uniform.A set of ceramic membrane test fixtures was designed and manufactured,and the parameters such as average pore size,pore size distribution,pure water flux,and rejection rate of the ceramic membrane were tested.There are many factors influencing the retention performance and permeation flux of ceramic membranes,but the most important ones are the membrane thickness and membrane filtration pore size.The effects of alumina content,organic content,coating time on the thickness of the ceramic membrane and the effects of the particle size of the membrane-forming powder and the sintering temperature on the pore size of the ceramic membrane were studied by the controlled variable method.Finally,by adjusting the thickness and pore size of the membrane,a suitable formulation and process are obtained.The experiment proves that it is a more suitable formula and process parameters when the alumina content is 10 wt%,the organic content is 4.4 wt%,the coating time is 25 s,the particle size of the membrane-forming powder is 0.5?m,and the sintering temperature is 1300?.By electrostatic encapsulation,the boehmite sol particles were wrapped on the surface of the alumina particles,so that the alumina microfiltration membrane was prepared at a sintering temperature of 1250°C.The membrane thickness is 18?m,the average pore size is200 nm,the pure water flux is 4155 Lh^-1m^-2bar^-1.and the average pore size of the membrane does not change much after backwashing for 120 min at a pressure of 2 bar,therefore the bonding strength is high.The rejection rate of carbon ink at 285 nm reachs 98.0%.