Recovery of vanillin from lignin/vanillin mixture by using tubular ceramic ultrafiltration membranes

The aim of this work is to evaluate the membrane ultrafiltration process for the recovery of vanillin from Kraft lignin oxidation media. Tubular ceramic membranes with molecular weight (M,,) cut-off of 1, 5 and 15 kDa are investigated. The influence of lignin and vanillin concentration and pH of the mixture on the performance of ultrafiltration is studied in batch mode. Permeate flux, lignin and vanillin content in retentate and permeate streams were measured. A theoretical model is used to calculate the variation of the concentration profile within the polarization concentration layer and to estimate the membrane surface concentration during the ultrafiltration operation. The values obtained for the lignin concentration at membrane surface suggests that there is a growth of a gel layer in the ceramic membranes of higher M, cut-off for the operating conditions used. By filtrating the lignin/vanillin mixture at the concentration 60/6 g L-1 and pH 12.5 using I kDa cut-off membrane, the observed rejection of lignin was 0.972. On the other hand, using the membranes with small cut-off leads to significant decline of permeate flux compared with the membranes with larger cut-off. It was observed that very high cleaning efficiency can be obtained using sodium hydroxide solution. (c) 2007 Elsevier B.V. All rights reserved.