Biofuels and chemicals from lignocellulosic biomass are a renewable and sustainable alternative to traditional fossil fuel sources.However, the reality of commercial lignocellulosic biofuels depends on feasibly overcoming the recalcitrance of the biomass plant cell wall, which consists of lignin and the sugar polymers cellulose and hemicellulose, the source of value-added products.“Pretreatment” is the term that describes the chemical, physical or physicochemical process that breaks the structure of biomass prior to further processing, and represents the most expensive step in the production of biofuels.Towards a more economically feasible and green pretreatment process, this dissertation introduces a new pretreatment method using butadiene sulfone (C4H6O2S), a solvent that is inexpensive and recyclable, and effectively pretreats biomass in one step under mild conditions.The production and recovery of butadiene sulfone is available at an industrial scale, thus facilitating a potential transfer of these processes to a large scale lignocellulosic-based operation.Miscanthus x giganteus, a perennial grass and energy crop, was pretreated with butadiene sulfone in a batch reactor at 90 °C-110 °C for 6-30 h.The ability of butadiene sulfone to “switch” in equilibrium to 1,3-butadiene and sulfur dioxide, allowed for the formation of sulfurous acid in the presence of water.The sulfurous acid hydrolyzed xylan (hemicellulose), removing up to 91% of xylan into the liquid phase as a potential source of value-added products.In the pretreated solids, 90-99% of glucan was preserved, the key substrate for enzymatic hydrolysis of glucan to glucose and downstream fermentation to biofuels and chemicals.The butadiene sulfone in equilibrium solubilized up to 58% of lignin, an important aspect of pretreatment, as lignin is known to inhibit the action of enzymes to release glucose from glucan. The kinetics of xylan hydrolysis and solubilization mechanisms of lignin from the butadiene sulfone-water pretreatment of Miscanthus, were also studied.The hydrolysis of xylan, via Brønsted acid catalysis, followed irreversible first-order kinetics with the activation energy determined to be 89 kJ/mol.The solubilization of lignin was attributed to the solvent interactions with the delocalized lignin during or after the hydrolysis of xylan.Butadiene sulfone was also used to pretreat the solids after the production of furfural from sugarcane bagasse.These furfural residues are rich in glucan, but mostly used as boiler fuel at a commercial-scale.Alternatively, a furfural-based biochemical conversion approach was proposed, consisting in the pretreatment of the glucan-rich furfural residues with butadiene sulfone-water, followed by enzymatic hydrolysis of glucan to glucose for potential production of biofuels.Xylan in sugarcane bagasse was converted in a batch reactor to furfural via sulfuric acid catalysis at 170 °C and 180 °C for 10 min.The furfural yields were comparable to industrial batch production, achieving 38% and 50% of theoretical at 170 °C and 180 °C, respectively.The furfural residues were subjected to pretreatment with butadiene sulfone in the presence of water at 110 °C for 3 h, resulting in the solubilization of 22-28% of the solids, corresponding to the removal of 33-39% of the total lignin in the furfural residues.Finally, it was demonstrated via thermogravimetric analysis that butadiene sulfone can be completely decomposed at 130 °C and 70 min for potential recovery and reformation, as the solvent’s decomposition gases are the raw materials for its production.
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Switchable butadiene sulfone pretreatment of lignocellulosic biomass
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