(400b) Tunable and Robust Graphene Oxide Membranes for Fractionation and Recycle of Kraft Black Liquor Components

A new generation of nanofiltration membranes is essential to address the rapidly increasing difficulties in sustainable production and recycle of water and organic components from complex biorefinery streams. An important example of such energy-intensive water treatment processes is the concentration of kraft black liquor (BL), which is a caustic (pH ~ 13), high temperature (>70^oC) and high-concentration byproduct stream generated at very high volumes (~ 1 billion tons/yr globally) from lignocellulosic biomass depolymerization. BL dewatering is currently performed with multi-effect evaporation. Recently we developed graphene oxide membranes [1] that are able to concentrate BL by lignin separation with excellent (>99%) rejection, are robust in a BL environment (> 1,500 hours of continuous operation), and are easily scaled up into membrane sheets. In this talk, we discuss the structural tuning of GO membranes for further fractionation of the clarified (lignin-free) BL stream, with the objectives of separating low-molecular weight organic components and inorganic salts while producing water with low solids content. We show that a series of non-covalently functionalized GO membranes display dramatically enhanced rejections for salts and organic solutes over a wide concentration range. Furthermore, we find that the counter-intuitive solute rejection behaviors observed in these functionalized GO membranes can be explained by a complex mechanism that will be discussed in detail. These membranes show high chemical and mechanical robustness in fractionation of clarified BL at elevated pH, temperature, stream velocity, and solids content, and are scalable by minimal modification of the same techniques reported earlier for GO membrane fabrication [1].

References:

[1] Z. Wang, C. Ma, S. A. Sinquefield, M. L. Shofner, S. Nair, High-Performance Graphene Oxide Nanofiltration Membranes for Black Liquor Concentration, ACS Sustainable Chemistry & Engineering 7 (17), 14915-14923 (2019).