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Title:Performance of a multiple stage hot water pretreatment on sugarcane bagasse and its economic analysis
Author(s):Wang, Zhaoqin
Director of Research:Singh, Vijay
Doctoral Committee Chair(s):Singh, Vijay
Doctoral Committee Member(s):Jin, Yong-Su; Rausch, Kent D.; Dien, Bruce S.; Tumbleson, Mike E.
Department / Program:Engineering Administration
Discipline:Agricultural & Biological Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Hot water pretreatment Sugarcane bagasse Cellulosic ethanol
Abstract:Cellulosic ethanol production has and continues to be widely investigated for commercial operation using corn stover and sugarcane bagasse. The lack of an effective and scalable pretreatment operation remains a major technical obstacle to wide spread commercialization. Combining multiple mild pretreatment methods might overcome the drawbacks of each one and achieve desirable product yields. However, combining pretreatment operations increases both process complexity and fixed capital investment. In this thesis, a two-stage hot water and disk milling pretreatment combined with use of a commercial xylose-glucose cofermenting Saccharomyces yeast strain is evaluated for advanced ethanol production. Fermentation of 10% solids resulted in a final ethanol titer of 36.4 g/L from 180°C hot water pretreated and disk milled sugarcane bagasse, which equates to a conversion efficiency of 93.8% of theoretical. Applying disk milling increased both sugar release and ethanol production from hot water pretreated bagasse, but 3 g/L xylose remained after 96 hr of cofermentation. The process was modified to ensure all the monosaccharides extracted from the biomass were fermented to ethanol. The biomass was deacetylated by soaking in a mild alkaline solution prior to pretreatment with hot water and by fermenting with a mixture of two commercial Saccharomyces yeast strains. The original glucose-xylose cofermenting yeast strain was combined with a standard glucose-fermenting strain. The modified three-stage pretreatment process (deacetylation, hot water pretreatment and disk milling) was evaluated for corn stover and sugarcane bagasse. Two thirds of the acetyl groups present in the biomass were removed by deacetylation and acetic acid released during hot water pretreatment was subsequently decreased by 73% with either feedstock. Inclusion of a deacetylation step decreased residual xylose to 1.9 g/L for corn stover and 1.2 g/L for sugarcane bagasse fermentations. Deacetylating corn stover increased the final ethanol titer by 22.7% and had no effect on the sugarcane bagasse fermentation. Residual xylose was successfully eliminated (<0.5 g/L) during fermentation of either feedstock by blending the conventional and glucose-xylose engineered Saccharomyces cerevisiae strains. The economics of the three stage pretreatment using engineered yeast were analyzed for industrial application. The cellulosic ethanol plant was designed to process 2000 M.T. dry sugarcane bagasse per day. Total fixed capital investment was estimated to be $300.38 million, of which 38.94% was contributed by hot water pretreatment. Economics were analyzed assuming either 10% or 16% solids in the fermentation tank. The minimum ethanol selling prices at 10% and 16% solids were $4.71 /gal and $4.62/gal respectively. Using sensitivity cost analysis, we determined that engineered cofermentation yeast medium price was the most important factor.
Issue Date:2019-04-17
Rights Information:Copyright 2019 Zhaoqin Wang
Date Available in IDEALS:2019-08-23
Date Deposited:2019-05

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