Changes in oxygen functionality of soluble portions and residues from bagasse sub- and supercritical alkanolyses: Identification of complex structural fragments

Abstract

The changes in oxygen functionality of soluble portions and residues from the bagasse methanolysis (BM) and bagasse ethanolysis (BE) at 220, 240, 260, 280, and 300 °C were investigated. The highest yields of soluble portions, 40.8 wt% from BM and 48.1 wt% from BE, can be obtained at 280 °C for 0.5 h. The organic oxygen species evolution of the bagasse and residues were analyzed with Fourier transform infrared spectrometer, thermogravimetric analyzer, and X-ray photoelectron spectrometer. The results show that the contents of oxygen functional moieties between bagasse and residues are significantly different. The cleavage of >Cal-X bonds (X denotes Cal<, O-, N<, and/or S-), especially > Cal-Cal< and >Cal-O- bonds, should be the major reactions during the bagasse alkanolyses. In addition, based on the analysis with a gas chromatograph/mass spectrometer, oxygen-containing organic compounds produced from BM and BE can be divided into alkanols, alkenols, furans & tetrahydrofurans, alkyl-substituted phenols & benzenepolyols, methoxy-substituted benzenes, alkoxy-substituted phenols, benzaldehydes, ketones, esters, carboxylic acids, and other oxygenates. The depolymerization of cellulose and/or hemicellulose to pentose/hexose and/or other small-molecule products could facilitate the formation of cyclopentanones and cyclopent-2-enones. The comparison of the specific methyl and ethyl esters obtained from BM and BE, respectively, confirmed that the 4-hydroxyphenyl, 4-methoxyphenyl, guaiacyl, and/or syringyl units are likely present in the bagasse skeleton. Comparing the organic oxygen transformation during the bagasse alkanolyses will facilitate the utilization of oxygenated chemicals in the biomass-derived oils.