A subcritical pretreatment improved by self-produced organic acids to increase xylose yield

Abstract Pretreatment is a crucial step to utilize biomass in the cellulosic ethanol industry, high xylose yield and green pretreatment methods are of concern recently. This study used the self-produced organic acids present in the pretreated liquid to enhance the hydrothermal pretreatment of sweet sorghum bagasse. By comparing pretreatments with acetic acid, lactic acid and self-produced organic acids, it was found that the self-produced organic acids could effectively promote the formation of xylose and inhibit its degradation to furfural. The pretreatments with lactic-acetic acid confirmed that the copresence of acetic acid and lactic acid contributed to the promotion of pretreatment during using self-produced organic acids. The suitable ratio of lactic to acetic was 6:4. Through multi-factor optimization experiments, the suitable conditions were determined as 178–182 °C for 40–45 min with 1.00–1.10 wt% self-produced organics, and the xylose yield was 83–85%. The effect of reused times of pretreated liquid was explored. The results showed that the number of reuse process should not exceed two, otherwise the accumulated by-products may affect the subsequent fermentation. The proposed method could reduce the consumption of water and organic acids, indicating its potentiality in cleaner utilization of biomass.