This thesis studies a latest innovation biorefinery process, which utilizes sulfur dioxide (SO2) -ethanol-water (AVAP®) mixture as the solvent to fractionate sugarcane (SC) straw and further to produce value-added bioproducts. The effects of liquor composition, liquor-to-solid ratio, and temperature on the kinetics of delignification, hemicelluloses removal, and cellulose hydrolysis were investigated. The interpretation was given in terms of major fractionation reactions, removal of non-carbohydrate components and xylan, as well as acid hydrolysis of cellulose, and was compared to other lignocellulosic substrates. Material balances of AVAP® fractionation of SC straw were investigated at various conditions in terms of lignin, ash, glucan, xylan, SO2, and ethanol. Most of the lignin and ash dissolved in the liquor and 40-80% was precipitated after ethanol removal as pure (~98%) and sulfur-lean (<2%) fractions. Straw lignin behavior exhibited differences compared to wood lignin including high apparent content in fiber, higher degree of sulfonation, and dense char-like precipitate formation upon ethanol removal. Glucan was mostly retained in the fiber product, while xylan dissolved in the liquor in the form of xylose and xylosides (mostly ethyl xylosides), which could then be converted to xylose and ethanol in aqueous solution. Furfural and HMF formation was dependent on the severity of the AVAP® cook but remained small as compared to that in acid sulfite cooking. Sulfur dioxide was primarily bound to lignosulfonic acids, while considerably lower amounts were bound to the pulp and precipitated lignin. A higher degree of sulfonation was observed for dissolved straw lignin compared to wood lignin (0.8-0.9 vs. 0.25 S/C9). Therefore, SC straw required higher SO2 make-up in AVAP® process compared to wood. Besides the amount of SO2 bound to dissolved lignin, the residual SO2 and nearly all charged ethanol were recovered by distillation from the spent fractionation liquors. Overall, the AVAP® process efficiently fractionates SC straw by separating cellulose from both non-carbohydrate components and xylan while reducing the cellulose degree of polymerization. The purified and hydrolyzed AVAP® cellulose is a suitable feedstock for cellulose products as well as high-purity glucose for biochemicals and biofuels. Variation in fractionation conditions did not have a significant effect on lignin properties, while post-sulfonation was capable of changing its form from char-like to colloidal precipitate. Carbohydrate mass balance indicated no major sugar losses. Moreover, the AVAP® process was characterized by high recovery rates of SO2 and ethanol.
|Translated title of the contribution||Kinetics studies and mass balances of sulfur dioxide-ethanol-water fractionation of sugarcane straw|
- , Supervisor
- Adriaan van Heiningen, Supervisor
- Mikhail Iakovlev, Advisor
|Publication status||Published - 2018|
|MoE publication type||G5 Doctoral dissertation (article)|
- biorefinery, AVAP® process, sugarcane straw, SO2-ethanol-water fractionation, mass balance, lignin, sugars, SO2 and ethanol recovery