The isolation of vanillate from kraft lignin oxidation media by ultrafiltration (UF) has been investigated by Zabkova et al. [135]. The higher molecular weight com­pounds can be easily retained using membranes technology. During the UF process vanillin is collected in the permeate stream, whilst the lignin as a macromolecule stays in the retentate. The appropriate size of membrane cut off can significantly reduce the high molecular weight components from the lignin/vanillin mixture. Due to high physical and chemical resistance the ceramic membranes can be applied under strong pH conditions and high temperature. They observed a high flux decline at higher pH of the filtrated solution and ascribed it to the hydrophobicity membrane surface and solute. To obtain higher flux with acceptable rejection values, a scheme of staging UF membranes starting from larger cut off has been proposed. Formerly, UF was reported as process for fractionation of waste sulfite liquor to obtain a concentrated lignin-rich fraction in order to increase yields of vanillin and reduction of crust formation on reactors in the production of vanillin [169].