| The lignocellulose was usually used to produce biobased chemicals such as ethanol, lactic acid and so on by anaerobic fermentation at present. Metabolic pathways of microorganism for these products were easily influenced by inhibitors which could lead to the reduction of productivity and yield. In this thesis, sugars from lignocellulosic hydrolysate were directly oxidized to produce saccharic acid procucts with high productivity and yield by aerobic fermentation. This production process is simple and hard to be influenced by inhibitors, shows some obviously advantages. Gluconic and xylonic acids were both two kinds of multifunction and multipurpose bulk biobased platform chemicals, could be applied widely in food, pharmaceutical, construction industry and so on. Industrial production of gluconic and xylonic acids were mostly depend on microbial fermentation from grain crop at present. With the increasing demand of these products, the contradiction between expansion of industrialization and production of grain intensifies day by day. Lignocellulose biomass as an abundant and cheap renewable resource could be used to replace grain crop for bulk biobased chemicals production. In this thesis, a typical lignocellulose, corn stover, was selected as feedstock to produce gluconic and xylonic acids by dry mill biorefinery strategy, which could reduce the generation of wastewater obviously.Firstly, a most widely applied in gluconic acid industrial production stain, Aspergillus niger, was selected to produce gluconic acid using corn stover feedstock, the glucose oxidase of A. niger could directly oxidized glucose into gluconic acid. A. niger SⅡM M276 as an gluconic acid producer showed good gluconic acid fermentability, inhibitors tolerance for 9 kinds of typical lignocellulose derived inhibitors and could convert most of these inhibitors. A. niger SUM M276 could utilize 15% solids loading freshly pretreated corn stover hydrolysate to produce gluconic acid directly, but in the stress of high titer inhibitors from 25% (w/w) solids loading hydrolysate, the dry cell weight and gluconic acid productivity of A. niger SⅡM M276 were decreased 51.4% and 28.9%, respectively. After the pretreated corn stover was detoxified, the cell growth and gluconic acid productivity of A. niger SⅡM M276 were improved about 1 time and 3 times, gluconic acid titer achieved to 105.36 g/L. But, A. niger SⅡM M276 showed some drawbacks in cellulosic gluconic acid production process. A. niger SⅡM M276 was sensitive in corn stover hydrolysate system, a 24-96 h lag phase occurred in fermentation process, the mycelial morphology became unstable after transfer several generations, which reduced the gluconic acid productivity harshly. In addition, A. niger SUM M276 mostly could not utilize xylose in the corn stover hydrolysate which lead to more than 80% of xylose was retained in fermentation broth.Secondly, aim to solve these drawbacks of A. niger SIIM M276 in cellulosic gluconic acid production process such as unstable mycelial morphology, low gluconic acid productivity and poor xylose utilization, a gram-negative bacterium, Gluconobacter oxydans, which had stable bacterial morphology, high gluconic acid productivity and could produce gluconic and xylonic acids together by oxidizing glucose and xylose, was selected as new producer in this study. G. oxydans DSM 2003 showed stronger inhibitors tolerance and inhibitors conversion performance, the gluconic acid productivity could reach to 1.72 g/L/h even in high solids loading (20%, w/w) freshly pretreated corn stover hydrolysate. The gluconic and xylonic acids productivity of G. oxydans DSM 2003 were further improved to 5.59 and 2.16 g/L/h using detoxified corn stover hydrolysate.119.10 g/L gluconic acid and 14.04 g/L xylonic acid were obtained in 50 L fermentor large scale experiment using detoxified corn stover hydrolysate after 32 h fermentation, the gluconic acid productivity reached to 3.68 g/L/h, was more than twice the highest gluconic acid productivity of A. niger SIIM M276. The obtained fermentation broth was test as cement retarder and showed similar excellent retarding performance. Low pH could inhibit the future conversion of gluconic acid into keto-gluconic acid, both high concentration of gluconic acid (111.59 g/L) and xylonic acid (36.56 g/L) were obtained at pH 3.0. This gluconic and xylonic acids production process from corn stover was carried out a techno-economic analysis based on Aspen Plus modeling, the minimum sodium gluconate/xylonate product selling price (MGSP) was only $0.404/kg, which was not only lower than commercial sodium gluconate from starch, showed a very strong economic competitiveness.Finally, in order to effectively utilize the xylose existed in wastewater from cellulosic ethanol production process, a novel xylonic acid production by microbial fermentation or direct catalysis using the xylose in stillage after ethanol distillation of cellulosic ethanol fermentation slurry was investigated. Corn stover as the feedstock though dry dilute acid pretreatment, solid biodetoxification, high solids loading SSF for ethanol production, then 59.80 g/L ethanol fermentation slurry was distilled and the ethanol was collected from column top,65.39 g/L xylose was retained in column bottom stillage. Xylonic acid production using xylose of ethanol distillation stillage by microbial fermentation or whole cell catalysis of G. oxydans DSM 2003 was carried out and higest 66.42 g/L xylonic acid was obtained. Compared with previous xylonic acid fermentation technology from the xylose in pretreatment liquid, this study reduced the energy consumption and waste water generation significantly based on Aspen Plus model analysis.In conclusion, dry mill biorefinery process was the basis, come true the green industrial production of gluconic and xylonic acids was the goal, a whole process flowsheet from lignocellulose biomass to gluconic and xylonic acids products was established in this thesis, and the obtained high titer products showed excellent application as cement retarder. In addition, in order to solve the residual xylose from cellulosic ethanol industry, a novel integrated ethanol and xylonic acid production process flowsheet using corn stover was designed, which generated less wastewater and consumed less energy obviously compared with previous process flowsheet. This new flowsheet reduced the whole production cost of cellulosic ethanol, and improved the development of cellulosic xylonic acid industry. The gluconic and xylonic acids production by aerobic fermentation showed obvious advantages, the glucose and xylose were dicretly converted into gluconic and xylonic acids by the catalysis of glucose dehydrogenase located on the membrane of G. oxydans, it showed strong adaptability in hydrolysate system, high productivity and yield. The tech-economic analysis demonstrated strong practicability and competitiveness of gluconic and xylonic acid production from lignocellulose biomass, this thesis provided a theoretical foundation for large scale industrial cellulosic gluconic and xylonic acids production in future. |
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