Production of reducing sugars from sago waste via sequential ionic liquid dissolution-solid acid saccharification / Lee Kiat Moon

• Main Author: Lee, Kiat Moon
• Format: Thesis
• Published: 2015
• Subjects: TP Chemical technology
• Online Access: http://studentsrepo.um.edu.my/5913/1/Thesis_LKM.pdf; http://studentsrepo.um.edu.my/5913/

Lignocellulosic biomass can be saccharified to produce reducing sugars that can be converted into various valuable products. This research aimed to produce reducing sugars from sago waste via sequential ionic liquid dissolution-solid acid saccharification process. The study included determining the best ionic liquid and solid acid catalyst combination, process optimisation, and kinetic study of the process, as well as product separation and catalyst recyclability. The ionic liquids investigated were 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) and 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM][(EtO)2PO2]), while the solid acid catalysts investigated were Amberlyst 15 (A15), Amberlite IR120 and Nafion NR50. The study has provided a better understanding of the sequential process. [BMIM]Cl and A15 combination was the preferred process as it produced the highest reducing sugars yield and with the lowest dissolution energy of 3.04 kJ/g sago waste. The sequential process was optimised by applying central composite design (CCD) of response surface methodology (RSM) to yield 98% reducing sugars at a dissolution condition of 160oC with 1.5% substrate loading in 1.75 h, and a saccharification condition of 130oC with 4% catalyst loading in 0.5 h. In the kinetic study, the generalised Saeman kinetic model was shown to fit the experimental data and so indicated that saccharification of the prehydrolysates obtained from the ionic liquid dissolution process is first order sugars production-first order sugar degradation reaction. The rate constant for sugars formation (k1) was significantly higher than the rate constant of degradation (k2). Empirical equations for k1 and k2 that accounted for the interactive effects of temperature and catalyst have been developed. Lower activation energies for sugars production (125.1 kJ mol-1) and sugar degradation (60.8 kJ mol-1) of sago waste were obtained compared to sulfuric acid-catalysed saccharification of other biomasses. The lower values are attributed to high starch content sago waste. Reducing sugars formed by the sequential process was successfully separated from the ionic liquid by using an aqueous biphasic system (ABS) containing kosmostropic salt, potassium phosphate (K3PO4). Approximately 100% and 60% recovery of reducing sugars and ionic liquid respectively were obtained after three extraction cycles. The saccharification efficiency of A15 dropped to less than 60% after three cycles. However, regeneration with sulfuric acid after each cycle restored the efficiency back to almost 100%. The research findings demonstrated the feasibility of sequential ionic liquid dissolution-solid acid saccharification in producing reducing sugars from sago waste.