Effects of graphene oxide membrane thickness reduction on microstructure and crossflow separation performance in kraft black liquor dewatering

Abstract

Reduced graphene oxide (rGO) membranes are emerging as viable candidates for energy-efficient fractionation of multicomponent biomass streams, such as kraft black liquor (BL). Increased fluxes in rGO membranes under crossflow conditions – while maintaining high solute rejections – are highly desirable for improving the economics of such processes. We have conducted a detailed experimental study of a series of rGO membranes with progressively lower thicknesses (from 130 nm to 40 nm). The influence of the membrane thickness and the membrane microstructure is analyzed in terms of its effects on water permeation flux, divalent salt rejection, and molecular weight cutoff (MWCO) measurements using dye molecules. A selected rGO membrane (70 nm) showing both high fluxes and rejections was scaled up to a 650 cm2 sheet and used for extended crossflow operation under real BL streams for more than 22 days. Techno-economic calculations reveal significant positive effects of membrane thickness reduction on the economics of BL dewatering.