RAPID

Black liquor (BL), also known as “spent pulping liquor”, is a high-volume byproduct of lignocellulosic biomass pretreatment (i.e., wood pulping by the kraft process). BL is a corrosive, toxic, and complex mixture. About 500 million tons/yr of BL are produced in more than 200 kraft process units worldwide (including 99 in the US, with about 0.2 quads/yr energy spent for BL concentration by multi-effect evaporation). Currently, BL concentration is performed by multi-effect evaporators and is one of the most energy-intensive industrial separation processes. Development of a more efficient BL concentration technology is a high priority for the forest products industry, with membrane technology being a particularly feasible alternative. However, membrane technology has been elusive because of the lack of a long-lived/stable, low-cost, high-performance membrane. This project will develop and demonstrate a bench-scale modular graphene oxide (GO)-based membrane system that substantially improves the energy efficiency of concentrating kraft black liquor (BL) from 15 wt% solids (lignin, organic molecules, and inorganic salts) to 30 wt% solids by removing water (maximum 0.1 wt% solids). The key innovation is the development of BL-stable, scaled-up, GO-based NF and RO membranes supported on macroporous polymeric (polyethersulfone, PES) supports for dewatering black liquor. The challenge is in developing and scaling up low-cost membranes that are long-lived in the corrosive conditions. The recent work on this project promises successful development and scale-up of BL-stable graphene oxide (GO) membranes. It would allow this technology to be quickly integrated into existing Kraft processing facilities to leverage existing assets.