Intensification of alkaline delignification of sugarcane bagasse using ultrasound assisted approach

Ultrasound-assisted approach has been investigated for delignification so as to develop green and sustainable technology. Combination of NaOH with ultrasound has been applied with detailed study into effect of various parameters such as time (operating range of 15–90 min), alkali concentration (0.25 M−2.5 M), solvent loading (1:15–1:30 w/v), temperature (50–90 ˚C), power (40–140 W) and duty cycle (40–70 %) at fixed frequency of 20 kHz. The optimized operating conditions established for the ultrasonic horn were 1 M as the NaOH concentration, 1 h as treatment time, 70˚C as the operating temperature, 1:20 as the biomass loading ratio, 100 W as the ultrasonic power and 70% duty cycle yielding 67.30% as the delignification extent. Comparative study performed using conventional and ultrasonic bath assisted alkaline treatment revealed lower delignification as 48.09% and 61.55% respectively. The biomass samples were characterized by SEM, XRD, FTIR and BET techniques to establish the role of ultrasound during the treatment. The morphological changes based on the ultrasound treatment demonstrated by SEM were favorable for enhanced delignification and also the crystallinity index was more in the case of ultrasound treated material than that obtained by conventional method. Specific surface area and pore size determinations based on BET analysis also confirmed beneficial role of ultrasound. The overall results clearly demonstrated the intensification obtained due to the use of ultrasonic reactors.     

Intensification of dilute acid hydrolysis of spent tea powder using ultrasound for enhanced production of reducing sugars

Spent tea (ST) powder is one of the potential sustainable sources available abundantly and can be utilized to produce reducing sugars required for production of platform chemicals. The current study aims at intensifying the reducing sugars production based on ultrasound assisted dilute acid hydrolysis (UADAH). The effects of reaction time, solid liquid ratio, acid concentration and temperature on the yield of reducing sugars were investigated initially for UADAH process based on ultrasonic (US) horn. The highest yield of 24.75 g/L for the reducing sugars was obtained at solid liquid ratio of 1:8, acid concentration of 1% w/v and temperature of 60 °C within 120 min. Use of oxidants like hydrogen peroxide (H₂O₂) and Fenton’s reagent to further intensify the production has also been studied. Use of H₂O₂ at optimum loading of 0.75 g/L resulted in reducing sugars yield of 26.2 g/L within 75 min while using same H₂O₂ loading with FeSO₄ at loading of 0.75 g/L along with UADAH reduced the reaction time to 60 min for almost similar yield. Large scale studies performed using US flow cell revealed that yield of reducing sugars as 22.4 g/L is obtained in 120 min in the case of only UADAH, while in the case of UADAH along with H₂O₂ and Fenton’s reagent, similar yield of reducing sugars was obtained in only 90 and 60 min respectively. UADAH in combination with oxidants has been demonstrated as an effective and intensified approach to produce reducing sugars from spent tea powder available as sustainable source.