| Itaconic acid and ethanol production using starch or sugars based on materials has been realized in industry scales,but the expensive raw materials(like corn starch,sugar,and nutrients)significantly affect the product costs of itaconic acid and ethanol.Lignocellulosic biomass is cheap,renewable,and rich in fermentable sugars,which is promising to produce liquid biofuels and biochemical.Dry biorefining processing technology including dry acid pretreatment,solid state biodetoxification,and simultaneous saccharification and fermentation at high solids loading has demonstrated to be effective in producing ethanol,lactic acid and other biochemicals with the advantages of high pretreatment efficiency,complete inhibitors removal,low energy consumption and no wastewater discharge.However,itaconic acid production based on this technology has not been investigated yet.In addition,the supplementation of expensive nutrients like yeast extract or corn steep liquor during cellulosic ethanol fermentation is indispensable to ensure the high fermentation performance,which would increase the ethanol production costs.Based on the above analysis,the second chapter of this thesis studied the feasibility of itoconic acid production using dry biorefining processing technology.We found that A.spergillus terreus M69 was sensitive to almost all the inhibitors by the study of seven typical lignocellulose-derived inhibitors.Therefore,it is necessary to remove all the inhibitors from the pretreated corn stover to produce higher concentration of itoconic acid.The hydrolysate prepared using dry acid pretreated and biodetoxified corn stover severely inhibited the organic acid production due to existence of acetic acid(>0.8 g/L)during enzymatic hydrolysis.The treatment on the hydrolysate with activated carbon to remove partial acetic acid help to produce 33.6 g/L itaconic acid at a yield of 0.56 g itaconic acid/g glucose.Most acetic acid released during enzymatic hydrolysis other than pretreatment was responsible for the inhibition of itaconic acid production.The techno-economic analysis based on Aspen plus model showed that the minimum itaconic acid selling price(MIASP)was $1.647 per kg,which was lower than its market price(1.8 $/kg).Improving acetic acid tolerance of A.terreus M69 by evolutionary adaptation or enabling the co-fermentation of glucose and xylose could further decrease the production cost of cellulosic itaconic acid.The third chapter of this thesis explores the feasibility of replacing expensive corn steep liquor during cellulosic ethanol fermentation using the cheap corn ethanol byproduct-Distillers' Dried Grains with Solubles(DDGS).Yeast extract,corn steep liquor,DDGS produced by an American company,and DDGS produced by a local company were compared in terms of ethanol fermentation performance using dry acid pretreated and biodetoxified wheat straw.The results showed that the ethanol fermentation using DDGS could compete with that using corn steep liquor(66.2 g/L vs 63.9 g/L).And the DDGS produed by Chinese local company showed greater advantages than that produced by the American company in terms of purchasing price($179 per kg vs $343 per kg)and ethanol production(66.2 g/L vs 65.4 g/L).The highest ethanol concentration of 74.6 g/L was obtained with 20 g/L DDGS addition after simultaneous saccharification and co-fermentation(SSCF)of wheat straw for 108 hours.In summary,this study showed a great potential of itaconic acid production using lignocellulose biomass to replace the corn starch,and uncovered that acetic acid released during enzymatic hydrolysis was the main inhibitor using the advanced dry biorefining processing technology.Further inproving the acetic acid tolerance or enabling the fermenting strain to co-ferment glucose and xylose could decrease the minimum itaconic acid selling price.In addition,the cheap corn ethanol byproduct-DDGS showed promising to substitute for the expensive corn steep liquor as the nutrient supplementation to produce cellulosic ethanol economically. |
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