Production of organic carboxylic acids by hydrothermal conversion of electron beam irradiation pretreated wheat straw

At present, wheat straw is comprehensively studied to produce chemicals and biofuels, such as bioethanol, biohydrogen, and biogas. In this study, we used wheat straw as raw material to produce organic carboxylic acids in NaIO 4 + H 2 SO 4 , and electron beam irradiation (EBI) pretreatment was used in the process to enhance the efficiency of straw conversion. Scanning electron microscopy (SEM) images of raw and pretreated wheat straw showed that surfaces have been fractured after EBI pretreatment, and there were many micropores distributed in the pretreated straw. Moreover, the experimental results showed that EBI pretreatment can efficiently promote the transformation of wheat straw to organic carboxylic acids. Effects of irradiation dose, temperature, reaction time, the amount of sulfuric acid and sodium periodate on the yield of lactic acid (LA), formic acid (FA), and acetic acid (AA) were investigated. The highest LA yield of 34.37% was obtained at the optimum conditions (EBI 100 kGy, H 2 SO 4 concentration 2 wt%, NaIO 4 concentration 0.6 wt%, reaction time 45 min, reaction temperature 200 °C). And the yields of FA and AA were 29.16% and 10.39%, respectively. FT-IR analysis showed that hemicellulose, compared to cellulose and lignin, was partially removed after irradiation. The reaction pathways and mechanisms were inferred by analyzing the products of hydrothermal conversion of several intermediates. Graphical abstract Synopsis: The agricultural waste (wheat straw) pretreated by electron beam irradiation was subjected to oxidative degradation with the existence of sodium periodate and sulfuric acid. Electron beam irradiation pretreatment can destroy the structure of hemicellulose by ionizing radiation, thereby forming micropores on the surface of wheat straw and improving the hydrothermal degradation efficiency of wheat straw. Sodium periodate generated periodic acid (H 5 IO 6 ) in acidic solutions, which oxidized the ortho-dihydroxy structure and o-dicarbonyl group to break C-C bond to generate carboxyl compounds leading to the enhancement of yields of organic carboxylic acids.