Effect of activated carbon nanoparticles on the performance of PES nanofiltration membranes to separate kraft lignin from black liquor

Abstract

In this work, activated carbon nanoparticles (AC) at concentrations ranging from 0 to 1 wt% were used to prepare polyethersulfone nanofiltration membranes. The effectiveness of these membranes in separating lignin from black liquor (BL) was evaluated under various operating conditions. The addition of AC improved all desirable properties. For instance, water permeability was increased by 57.50 % with the addition of 1 % AC and surface hydrophilicity was improved by reducing the contact angle from 66.8° to 55.2° for 0.5 % AC-based membranes compared to simple polymeric membranes. For BL filtration, 0.1 % AC-based membranes offered the highest flux with an improvement of 120 % at 24 bar and high lignin rejection compared to simple polymeric membranes. In addition, these membranes exhibited the highest water permeability recovery of 98.02 % when used for BL filtration followed by cleaning. During optimization tests of the main operating variables (temperature, pressure and pH) using 0.1 % AC-based membranes, it was found that extremely high conditions for each variable resulted in decreased performance in terms of fouling and lignin rejection. The best performance of these membranes in terms of flux, lignin rejection and fouling resistance was observed around 40 °C, 20 bar and 11.5 pH within the studied range. In this study, a new application for AC-based NF membranes was established for the separation of lignin from BL. The results of this study also showed that under optimal conditions, the performance of AC-based (0.1 %) membranes was improved for the efficient separation of lignin from BL with lower membrane fouling.