Recycling of Dilute Deacetylation Black Liquor to Enable Efficient Recovery and Reuse of Spent Chemicals and Biomass Pretreatment Waste

Our previous publications showed deacetylation/dilute alkaline pretreatment followed by mechanical refining (DMR) is an effective process for overcoming biomass recalcitrance. To successfully commercialize alkaline-based pretreatments, we pioneered a new process modification and strategy to recycle and reuse the weak black liquor in order to reduce water, chemical and energy usage while increasing the solids, sodium, acetate, sugars, and lignin contents in the weak black liquor. Our results suggest that the accumulation of both chemicals and organic matter did not reduce acetyl and lignin removal in alkaline pretreatment, resulting in comparable sugar yields in enzymatic hydrolysis. Sodium and potassium were found the two most important inorganic substances in the recycled weak black liquor. Moreover,   the accumulated sodium and phenolic compounds did not inhibit the downstream fermentation and catalytic upgrading processes.  Finally, techno-economic analysis (TEA) showed the recycling of weak black liquor could save the Minimum Ethanol Selling Price (MESP) by approximately $5-15 cents per gallon of ethanol when compared to conventional non-recycling process.