(534h) Process Simulation and Technoeconomic Analysis of Black Liquor Concentration with Graphene Oxide Membranes

Black liquor (BL) dewatering by multi-effect evaporation in the conventional kraft paper making process is extremely energy-intensive. In our previous work, we have shown that graphene oxide (GO) nanofiltration membranes can remove lignin, other organics, and inorganic salts from BL while exhibiting stability in caustic BL conditions. In this work, we design and simulate several candidate processes for GO nanofiltration membrane-based BL dewatering and evaluate their technoeconomic characteristics. All the processes concentrate BL from 15 wt% to more than 30 wt% solutes, while producing a permeate water product, which were simulated in custom-built ASPEN Plus flowsheets interfaced with Microsoft Excel and MATLAB. All processes deliver large (>40%) energy savings over conventional multi-effect evaporation. Detailed technoeconomic analysis showed that option A processes will be profitable in those kraft mills that are equipped with condensing turbines, but not profitable if only purchased fuel savings are considered. Option B processes are profitable with both electricity generation and also with purchased fuel savings, but require the caustic permeate stream to be utilized in other kraft process units. They are also profitable with electricity generation when operated at a smaller scale with a permeate flow rate matched with the requirements of other kraft process units. Monte Carlo sensitivity analysis shows that Option A processes can yield median 20-year NPVs up to ~$10MM and Option B process up to ~$25MM. Overall, this study indicates that GO membrane-based BL dewatering is economically promising, assuming successful slipstream piloting and scale-up campaigns. This technology has immediate sustainability benefits resulting from significant energy savings, as well a number of broader implications for biorefinery processes due to the ability to fractionate biomass feedstock components under harsh conditions.