Abstract
BackgroundDilute 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.ResultsThe 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.ConclusionsThis 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.
Highlights
Dilute oxalic acid pretreatment has drawn much attention because it could selectively hydrolyse the hemicellulose fraction during lignocellulose pretreatment
Dewaxed corncob before pretreatment could obtain 396.69 mg glucose per 1 g corncob, 313.64 mg/g xylose and 39.87 mg/g arabinose, which was determined according to the National Renewable Energy Laboratory (NREL) methodology [33]
In this work, a sustainable approach for the first time was developed to recycle oxalic acid used during the corncob pretreatment, and the recycled oxalic acid subsequently could be reused for corncob pretreatment
Summary
Dilute oxalic acid pretreatment has drawn much attention because it could selectively hydrolyse the hemicellulose fraction during lignocellulose pretreatment. Hemicellulose, as one of the main components in lignocellulosic biomass [9], can be hydrolysed into xylose [10]. Dilute acid pretreatment (DAP) was a conventional technology by which xylan-type hemicellulose in lignocellulose was hydrolysed to xylose-rich hydrolysate [11, 15, 16]. Mineral acids such as H2SO4 [17], HCl [18] and H 3PO4 [19] were used during traditional DAP. Organic acids pretreatment had gradually drawn much attention [21–23]. Among plenty of organic acids, oxalic acid was found to have attractive catalytic performance for pretreatment because it could efficiently and selectively hydrolyse hemicellulose [20, 24–26].
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