Analysis Of The Products From Alkanolysis Of The Rice-Stalk Powder And Related Mechanistic Study

Rice-stalk powder was alkanolyzed with sub- and supercritical methanol or ethanol in a magnetically stirred, stainless-steel autoclave under different conditions. The reaction mixtures were sequentially extracted with methanol (or ethanol), acetone, carbon disulfide and an acetone/carbon disulfide mixed solvent. The extracts were analyzed with a Hewlett-Packard 6890/5973 gas chromatograph/mass spectrometry system. The effects of reaction temperature, time and hydrogen pressure on the RSP alkanolysis of were examined. The experimental results show that RSP was significantly alkanolyzed under supercritical conditions and the total yield of the alkanolyzed products increased with prolonging reaction time. More than 100 organic compounds were detected from products, most of which are oxygen-containing ones, especially methoxy- and/or ethoxy-containing ones. The relative content of methoxy-containing organic compounds is more than 40% in the products from supercritical methanolysis of RSP, whereas that of ethoxy-containing ones is near 20% and methoxyphenyl-containing ones were also detected with 17.6% of relative content in the products from supercritical ethanolysis of RSP, indicating that the methoxyphenyl-containing moieties is originated from lignin in RSP. A number of phenol derivatives, which can be used as fine chemicals, were detected. In addition, a lot of fatty acid esters were also detected. They can be used to produce advanced lubricants and high quality diesel. According to the analysis of the possible reaction of guaiacyl propane, the mechanism of the RSP's alkanolysis under supercritical conditions has been proposed, which involved pyrolysis and induced breaking of oxygen-containing bridge bond in organic macromolecule. And the inducing groups are the free alkyl and hydroxyl coming from the decomposition of alkanols.The above results show that the organic macromolecules in RSP can be selectively deploymerized under relatively mild conditions (≤300 oC) by using supercritical alcoholysis. The related techniques provides an important approach to the understanding of information on molecular structures of crop stalks and establishes theoretical basis of developing new technology for the effective utilization of crop stalks.