Preparation And Characterization Of External-pressure Planar-honeycomb Thin-wall Ceramic Microfiltration Membranes

Ceramic membranes are widely applied in biological medicine, chemical engineering and environmental protection, due to their unique advantages, such as high mechanical strength, good acid/alkali corrosion-resistance and regeneration. It has become one of the important separation technologies to be researched and developed. Commercial ceramic membrane has generally the inner-pressure type, because it is easy to seal. The separation layer locates at the surface of membrane channel and the feed flows in the membrane channels. The trans-membrane pressure directs from the inner to the outer. The inner-pressure type membrane has the egg shell-like structure, in which, the force focus on the concave surface. Therefore, this type ceramic membrane is easy to be broken. To avoid this, the thickness of the ceramic membrane support is more than 2 mm, which inevitably increases the permeating resistance of ceramic membrane and decreases the flux. The separation layer of the external pressure type ceramic membrane locates at the surface. The trans-membrane pressure directs from the outside to the inside. This type of the membrane requires the thin support. The key is that the thin wall of the support will certainty put forward to higher technical requirements for the preparation of support and membrane layer.In this paper, the preparation of the external-pressure planar-honeycomb thin-wall ceramic microfiltration membranes was studied. Cordierite support was prepared by extrusion molding method. The planar-honeycomb thin-wall ceramic membrane support with good quality was obtained by controlling the composition of the mud, the dry conditions and the sintering. The defect-free middle layer and the separation layer with the uniform thickness were prepared by improving the solid content of the cordierite suspension. The effects of the solid content, the dip-coating time and the suspension viscosity on the thickness of cordierite membrane layer were researched. The formation mechanism of the wet membrane was analyzed. And the effects of drying and sintering on the membrane pore size distribution were also investigated. The conclusions can be drawn as following:(1) The planar-honeycomb thin-wall ceramic membrane support is prepared by controlling the extrusion, the drying and the sintering process, whose size is 1000mm×95mm×13mm(length* width* height). The thickness of the support is 1 mm with double row seepage channels. The porosity of the support is 49%, the average pore diameter is 4.25?m, and the bending strength is 6.0 MPa when the support is sintering at 1350? for 1.5 h.(2) To avoid the decrease of the wet membrane thickness and the membrane defects caused by the decrease of the support thickness, increasing the solids content of the suspension was adopted. The results show that the wet membrane thickness increases with the increase of the solid content. When the suspension solid content is 30%, the membrane thickness is 30?m and the mean pore diameter is 0.65?m. The membrane surface is smooth and the maximum pore size is only 1.1 p?m. And the contribution of capillary adsorption mechanism on wet membrane thickness increases with the increase of the suspension solids content, but the degree of increase reduces. The contribution of the film coating mechanism to the wet membrane for motion increases with the increase of the suspension viscosity.(3) The separation layer of the microfiltration membrane is good when the suspension solid content of the separation layer is 15% and the dipping time is 25s. The membrane thickness is 10?m, the maximum pore size is 0.35?m and the average pore size is 0.24 ?m.