Lignin as an effective agent for increasing the separation performance of crosslinked polybenzoxazine based membranes in pervaporation dehydration application

Abstract

This work reports the utilization of lignin, a renewable and biomass-based material, as an effective modifying agent for thermally stable and hydrophobic membranes based on crosslinked polybenzoxazine (CRPBz) to significantly enhance their permeation fluxes in pervaporation dehydration tests. Lignin could involve in the crosslinking reaction of polybenzoxazine so as to be chemically embedded in the polymer networks. In addition to the inherent hydrophilicity of lignin, lignin could release the hydrophilic groups (phenol and tertiary amine) of crosslinked polybenzoxazine with formation of hydrogen bonding with crosslinked polybenzoxazine, consequently to significantly enhance the hydrophilicity and water permeation fluxes of the studied membranes. With feeding a 70 wt% tetrahydrofuran aqueous solution at 25 °C, lignin modification increases the permeation flux of the CRPBz based membrane from 237 g m−2 h−1 to 490 g m−2 h−1 and separation factor from 11,920 to 19,440. Lignin modification significantly enhances the water permeation flux of the membrane without scarifying separation ability. A 3.4-folds of pervaporation separation index (PSI, the product of permeation flux and separation factor) has been demonstrated with the lignin modification. Similar performance has also been recorded on the tests on a 70 wt% isopropanol aqueous solution. The effect of lignin has been attributed to increase the membrane hydrophilicity for facilitating water permeation. The results demonstrate the wide application scopes of the lignin-modified CRPBz based membranes in pervaporation dehydration based on their high stability and hydrophilicity.