Abstract
Deacetylation/dilute alkaline pretreatment followed by mechanical refining (DMR) has been proven as an effective process for biomass sugar liberation without severe chemical modification to lignin. Previous research has been focused on optimizing deacetylation conditions, reducing energy consumptions in mechanical refining, and improving sugar yields and titers in enzymatic hydrolysis. To successfully commercialize this process, another critical challenge is to develop a robust process to balance water usage, recover spent chemicals and utilize waste carbons from the dilute deacetylation waste liquor. In this work, a new process modification and strategy is pioneered to recycle and reuse the weak black liquor (WBL) in order to reduce water, chemical, and energy usage while increasing both inorganic and organic contents in the WBLto facilitate downstream processing. Results suggest that the accumulation did not lower acetyl and lignin removal in alkaline pretreatment, resulting in comparable sugar yields in enzymatic hydrolysis. Sodium and potassium were found to be the two most important inorganic compounds in the recycled weak black liquor. Moreover, the accumulated sodium and phenolic compounds did not inhibit the downstream ethanol fermentation processes. Finally, techno-economic analysis (TEA) showed a decrease in the minimum ethanol selling price (MESP) by approximately 5 to 15 cents per gallon of ethanol resulting from the inclusion of the recycling of weak black liquor when compared to a conventional non-recycling process.
Highlights
The Deacetylation and Mechanical Refining (DMR) process deconstructs and fractionates biomass into low toxicity, high concentration sugar syrups that have been demonstrated to be highly fermentable to ethanol with high ethanol yields, titers, and productivities (Chen et al, 2016), as well as highly reactive, tractable lignin streams that have been demonstrated to be upgradable to biojet fuel blendstocks and other bioproducts (Laskar et al, 2014; Jeon et al, 2015; Wang et al, 2015, 2017)
Deacetylation Water for deacetylation Wash water after deacetylation Steam for A200 Total water used for A200 minimum ethanol selling price (MESP) ($/gal)
The recycling of the weak black liquor (WBL) in the DMR process increases the concentrations of extracted components from corn stover biomass, making the black liquor from deacetylation a more valuable stream with upgradable lignin, acetate, and sugars
Summary
The Deacetylation and Mechanical Refining (DMR) process deconstructs and fractionates biomass into low toxicity, high concentration sugar syrups that have been demonstrated to be highly fermentable to ethanol with high ethanol yields, titers, and productivities (Chen et al, 2016), as well as highly reactive, tractable lignin streams that have been demonstrated to be upgradable to biojet fuel blendstocks and other bioproducts (Laskar et al, 2014; Jeon et al, 2015; Wang et al, 2015, 2017). The major role of alkali, primarily sodium hydroxide (NaOH), in deacetylation/dilute alkaline pretreatments is to catalyze the saponification of acetyl groups from hemicellulose and partially delignify the biomass (Chen et al, 2012). In the deacetylation of corn stover feedstocks, ∼10–30% of the solids in the biomass were found solubilized, including 70–80% of the acetate, 2–10% of the xylan, 1% of the glucan, and 20–40% of the lignin, which forms a weak black liquor (WBL) along with spent chemicals (Chen et al, 2012). The WBL is separated from the biomass by draining and washing potentially recovering the spent chemicals, especially the sodium, to reduce environmental impacts, capitial, operational, and disposal costs
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