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Background: Dilute oxalic acid pretreatment has drawn much attention because it could selectively hydrolyse the hemicellulose fraction during lignocellulose pretreatment. However, there are few studies focusing on the recovery of oxalic acid. Here, we reported a new approach to recycle oxalic acid used in pretreatment via ethanol extraction. Results: The highest xylose content in hydrolysate was 266.70 mg xylose per 1 g corncob (85.0% yield), which was achieved using 150 mmol/L oxalic acid under the optimized treatment condition (140 °C, 2.5 h). These pretreatment conditions were employed to the subsequent pretreatment using recycled oxalic acid. Oxalic acid in the hydrolysate could be recycled according to the following steps: (1) water was removed via evaporation and vacuum drying, (2) ethanol was used to extract oxalic acid in the remaining mixture, and (3) oxalic acid and ethanol were separated by reduced pressure evaporation. The total xylose yields could be stabilized by intermittent adding oxalic acid, and the yields were in range of 46.7–64.3% in this experiment. Conclusions: This sustainable approach of recycling and reuse of oxalic acid has a significant potential application for replacing traditional dilute mineral acid pretreatment of lignocellulose, which could contribute to reduce CO2 emissions and the cost of the pretreatment. [ABSTRACT FROM AUTHOR]

Abstract: During the past few decades, much effort has been devoted to increasing the utilization of lignocellulosic biomass to create biofuels, biochemicals, biocomposites, and a host of other bioproducts to replace fossil-based products. Recently, the utilization of lignocellulosic biomass received much more attention in ionic liquids with strong hydrogen-bond-destroying ability to produce lignocellulosic derivatives containing new functionality. In present study, carboxyl groups were attached onto sugarcane bagasse (SCB) by the homogenous modification of SCB with maleic anhydride in ionic liquid 1-butyl-3-methylimidazolium chloride (BMIMCl) without any catalysts. The parameters optimized included maleic anhydride concentration, reaction temperature and reaction time required in the process. The extent of maleation of SCB was measured by the weight percent gain (WPG), which increased with an increment of maleic anhydride concentration between 1:1 and 5:1 (g/g, maleic anhydride/SCB). It should be noted that WPG decreased at wild conditions, including long reaction duration (>60min) and high temperature (>110°C). The results from FT-IR and solid-state CP/MAS 13C NMR spectroscopies indicated that the maleation of hydroxyl groups in lignin, cellulose and hemicelluloses all occurred. XRD, SEM and TGA/DTG analyses of the native and modified SCB showed that the cellulose crystalline structure of SCB was significantly destroyed after dissolution, maleation, and regeneration in IL. However, the remained cellulose crystalline structure did not change except remarkable decrystallization. The thermal stability of the maleated SCB decreased at low temperature (lower than 300°C), and increased at high temperature (above 300°C) compared with that of native ball-milled SCB. [Copyright &y& Elsevier]