We
report a detailed study of graphene oxide (GO) membranes for
concentration of Kraft black liquor (BL), which is a caustic (pH ∼
12), hot (80–95 °C), and high-volume (∼500 gal/min
in a typical pulp mill) byproduct of the papermaking process. Membrane-based
concentration of BL is attractive as an energy-efficient alternative
to thermally driven evaporation processes but challenging due to the
harsh operating conditions and high fouling potential of BL (15–18
wt % solids). We fabricate thin (<300 nm) GO membranes supported
on macroporous poly(ethersulfone) (PES) supports by vacuum filtration
techniques and discuss in detail their morphology, structure, thermomechanical
stability, and chemical stability as characterized by several techniques.
Furthermore, detailed permeation measurements at transmembrane pressures
(TMPs) up to 50 bar and temperatures up to 85 °C show that the
membranes have high performance in concentrating BL feeds containing
high and low TS (total solids): high flux (in the range of 5–50
kg m–2 h–1), high lignin rejection
(up to 98%), low fouling, and high stability throughout extended exposure
(30 days) to BL at realistic operation conditions. The molecular weight
cutoff (MWCO) of the membranes was determined to be ∼625 Da
by means of dye rejection experiments. The present membranes are also
expected to have low cost due to the use of relatively inexpensive
functional membrane and substrate materials (GO and PES).
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