Effect of CO2 Concentration on Improving Yield and Antioxidant Activity of Lignin from Corn Cobs

The efficient conversion of biomass resources has become one of the important topics of current research as the current chemical economy is shifting towards the increasing utilization of renewable feedstocks. In this work, a newly integrated strategy was developed as supercritical CO2/ethanol/water ternary green system for simultaneous production of high antioxidant activity lignin and furfural (FF) from corn cobs. The effect of CO2 concentration on the yields of carbohydrates and lignin was discussed in detail. It showed that the use of high CO2 concentration could effectively increase the permeability of ethanol solvent to corn cobs and promote the degradation of lignin, thereby enhancing the yield of lignin and FF. When the concentration of CO2 was increased to 36%, the yields of lignin and FF and the total conversion rate were 86.17%, 10.28%, and 89.83%, respectively. In addition, the chemical structure of the prepared lignin fractions was characterized, including phenolic hydroxyl content and thermal stability. At last, the antioxidant properties of the prepared lignin fractions were identified. The results showed that this system promoted the beta-O-4 bonds breaking of lignin, thereby leading to the formation of the prepared lignin fraction with higher hydroxyl content and better antioxidant performance. Especially, numbers of -OH and -COOH in L36 were significantly increased with 1.57 mmol/g and 0.96 mmol/g, respectively. Overall, the supercritical CO2/ethanol/water ternary green system is an efficient method for pretreatment of corn cobs lignocellulosic, which shows enormous potential for biomass refining.