Covalently Functionalized Graphene for Black Liquor Concentration Membranes

Graphene oxide (GO)-based membranes with high selectivity and permeability can reduce energy use and address environmental impact in chemical separations. These materials are of particular interest to mitigate the energy-intensive weak black liquor (WBL) concentration in the kraft pulping process. WBL is a high pH (& SIM;12) corrosive fluid that includes polymers, other organic compounds, inorganic salts, and high total solids that is processed at elevated temperature (up to 95 & DEG;C). Herein, we focused on a covalently functionalized graphene synthesized through a Johnson-Claisen rearrangement of GO, providing ethyl ester groups attached to the basal plane via robust carbon- carbon bonds, to endure the harsh separation conditions. Amidation was achieved under mild conditions between the saponified Claisen-rearranged graphene and linear diamines and this functionalization improves the selectivity for separation of the large organics included in WBL, enhances permeability, and produces a robust enlarged interlayer spacing stabilized by cross-linking. We successfully synthesized four types of water-dispersible graphene derivatives with different interlayer spacings (up to 17.67 & ANGS;) and created membranes on hydrophilic poly(ether sulfone) supports. The expanded interlayer spacing and hydrophilic nature enhanced the selectivity for the exclusion of large molecules (& SIM;1 kDa) and gave high permeability. WBL was concentrated with a stable rate and permeance using the graphene derivative functionalized with poly(ethylene glycol) diamine. The versatile amidated graphene demonstrated significant potential in the production of membranes for WBL concentration, and the base methods can be adapted to other chemical separations.

Automated summary

Graphene oxide (GO)-based membranes have great potential in reducing energy consumption and environmental impact in chemical separations. This study focuses on concentration of weak black liquor (WBL) and utilizes functionalized graphene derivatives to improve separation selectivity. Membranes with expanded interlayer spacing and hydrophilic nature were successfully synthesized, showing high selectivity and permeability.