Hydrothermal degradation of polysaccharides in a semi-batch reactor: product distribution as a function of severity parameter

The naturally occurring polysaccharides, starch and pectic acid, were hydrothermally degraded in a semibatch reactor coupled with a plug-flow reactor (PFR) to produce valuable chemicals including mono- and oligosaccharides over a temperature range from 160 to 240 C at 10 MPa. The solid polysaccharide samples were solubilized in a semi-batch reactor, and the water-soluble (WS) components instantly entered the PFR in which further degradation took place. The reaction temperature and/or residence time in the PFR significantly affected the yields of oligosaccharides, monosaccharides and secondary decomposition products, and also the average molecular weight of WS components. The product distributions were expressed with severity, which combines the effects of temperature and time on the progress of the reaction, as a single reaction parameter. Using this parameter, it was found that similar product distributions were obtained at equal levels of severity. The severity parameter enabled easy interpretation of the change in product distribution for these reactions.