Fouling and regeneration of ceramic membranes used in recovering titanium silicalite-1 catalysts

Ceramic ultrafiltration (UF) membranes were used to separate titanium silicalite-1 (TS-1) catalysts from slurry in catalytic ammoximation of cyclohexanone to the oxime. Both the fouling mechanisms and the regeneration of fouled membranes were studied. The fouling was mainly caused by TS-1 particles deposition, silica additive adsorption and iron precipitation. The interaction between the two solutes in the system, silica additive and TS-1 catalysts, played a significant role in the formation of dense cake layers at the membrane surface, leading to a greater flux decline during ultrafiltration of TS-1 particles. Estimation of hydrodynamic forces acting on a single particle shows crossflow velocity (CFV) has an important effect on the deposition of TS-1 particles. However, after particles have deposited, increasing CFV will not resuspend them due to the strong and dense cake layer formation. The cleaning of a fouled membrane can be achieved by sequential use of strongly basic and acidic solutions. In addition, a particle-cleaning method was applied. Micro-sized alumina particles were used for their scouring effect to remove the cake layer from the membrane surface effectively. The particle cleaning combined with acid cleaning was effective to fully restore membrane flux.