Principle of ceramic membrane
The ceramic membrane separation process is a "cross-flow filtration" type of fluid separation process: the feed liquid is flowing at high speed in the membrane tube, and the pressure-driven clarified permeate containing small molecular components passes through the membrane in a direction perpendicular thereto. The turbid concentrated liquid containing macromolecular components is trapped by the membrane, so that the fluid can be separated, concentrated, and purified. The ceramic membrane is an asymmetric composite membrane made of a ceramic carrier with a porosity of 30% to 50% and a pore size of 50 nm to 15 μm using a sol-gel method or other processes. The structure of the ceramic membrane used for the separation is generally sandwich-type: a support layer (also referred to as a carrier layer), a transition layer (also referred to as an intermediate layer), and a membrane layer (also referred to as a separation layer). The pore size of the support layer is generally 1 to 20 μm and the porosity is 30% to 65%. Its role is to increase the mechanical strength of the membrane; the pore size of the intermediate layer is smaller than the pore size of the support layer, and its role is to prevent the particles during the preparation of the membrane layer. The porous support layer has a thickness of approximately 20 to 60 μm and a porosity of 30% to 40%. The membrane layer has a separation function, and the pore diameter ranges from 0.8 nm to 1 μm, the thickness is approximately 3 to 10 μm, and the porosity is 40%. ~55%. The pore size distribution of the entire membrane gradually decreases from the support layer to the membrane layer, forming an asymmetrical structural distribution. Ceramic membranes can be classified into microfiltration (pore diameter greater than 50 nm), ultrafiltration (pore diameter 2 to 50 nm), and nanofiltration (pore diameter less than 2 nm) depending on the pore size. During the separation, under the action of external forces, small molecules pass through the membrane and macromolecules are trapped by the membrane, thereby achieving separation, concentration, purification, removal of impurities, and sterilization.