Biobutanol production from eucalyptus cellulose fraction by hydrolysis and fermentation within a biorefinery approach
There is growing interest in the production of chemicals and fuels in a way that is more sustainable and beneficial to the environment. Butanol has been shown to have superior fuel properties when compared to ethanol, and has many applications in chemical industries. Its production from renewable li...
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| Format: | masterThesis |
| Language: | English Spanish |
| Published: |
2018
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| Subjects: | |
| Online Access: | https://hdl.handle.net/20.500.12008/48638 |
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| Summary: | There is growing interest in the production of chemicals and fuels in a way that is more sustainable and beneficial to the environment. Butanol has been shown to have superior fuel properties when compared to ethanol, and has many applications in chemical industries. Its production from renewable lignocellulosic biomass by means of fermentation was investigated in the past decades. Eucalyptus wood has gained attention as an alternative biobutanol feedstock because of its high carbohydrate content, as well as its availability and sustainable supply. However, its utilization requires the development of pretreatment technologies necessary to break up lignin structures, to separate the three biopolymers (lignin, cellulose and hemicellulose) and to enhance further enzymatic hydrolysis of cellulose. Although several pretreatments have been proposed and investigated, the selection of an effective one still remains a goal. In this work, eucalyptus wood was evaluated as a raw material for the production of biobutanol using a biorefinery approach. Autohydrolysis, organosolv and steam explosion pretreatments were studied under different operational conditions (temperature, reaction time, solvent concentration) for eucalyptus pretreatment prior to fermentation, attending hemicellulose solubilization and recovery and further cellulose enzymatic hydrolysis. Both autohydrolysis and steam explosion pretreatments resulted good in solubilizing hemicellulose, allowing to recover hemicellulose-derived sugars in a separate stream which can be used for the production of biofuels or other value-added products, while enhancing further enzymatic hydrolysis of the pretreated substrate. However, organosolv pretreatment achieved a partial hemicellulose solubilization but resulted effective for eucalyptus delignification, allowing to achieve pretreated substrates with a lower lignin content which improved cellulose enzymatic hydrolysis. Increasing pretreatment severity enhanced hemicellulose solubilization and further cellulose hydrolysis of the pretreated substrate, but decomposition reactions occurring at harsher conditions became unavoidable and decreased overall carbohydrates recovery. To overcome this, strategies such as the addition of lignosulfonates and acid catalyst during pretreatment were investigated in order to increase hemicellulose solubilization, while allowing to work at lower pretreatment severities. The supplementation of sulfuric acid and lignosulfonates during steam pretreatment effectively enhanced hemicellulose solubilization, which allowed to work at the lowest pretreatment severity and obtain higher overall carbohydrates recoveries, while achieving a high cellulose enzymatic hydrolysis of the resulting pretreated substrate. Moreover, the addition of surfactant during enzymatic hydrolysis was also assessed in order to carry out the pretreatment step at milder conditions and enhance the subsequent enzymatic hydrolysis of the pretreated substrates. In fact, the highest cellulose hydrolysis was obtained in presence of PEG 6000. All the pretreated eucalyptus substrates were effectively hydrolyzed by the commercial cellulase enzymes used in this study. Autohydrolysis-pretreated eucalyptus substrates were effectively fermented by anaerobic bacteria C. beijerinckii DSM 6423 and C. acetobutylicum DSM 792 under the different process configurations studied (SHF, SSF, PSSF). However, better butanol yields and productivities were obtained when the enzymatic hydrolysis and fermentation steps were done separately (SHF). The results obtained in this study demonstrates that eucalyptus wood represents a potential feedstock for biobutanol production. |
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