High-Performance Graphene Oxide Nanofiltration Membranes for Black Liquor Concentration

Black liquor (BL) concentration by multi-effect evaporation is an extremely energy-intensive operation in the kraft pulping cycle. Membranes can significantly save energy in this process, but conventional membranes are strongly challenged by low solute rejections and poor stability in BL, which is a complex mixture containing dissolved lignin, other non-lignin organics, multiple inorganic salts at highly alkaline pH and process temperatures of 70-85°C. Here we describe in detail the fabrication, modification, and characterization of robust and high-performance graphene oxide (GO) nanofiltration membranes for BL concentration. We show that polyethersulfone (PES)-supported GO membranes prepared from chemically reduced GO, and then subjected to high-pressure hydraulic compaction, show excellent chemical and mechanical stability under real BL conditions in comparison to conventional GO membranes. These membranes (referred to as ‘GO-3’ in this work) show near-perfect (>99%) lignin rejection, high total organic...