Abstract
Mono- and oligo-galacturonic acids were produced from hydrothermal degradation of pectic acid in a semi-batch reactor with/without a tubular reactor installed downstream over the temperature range from 160 to 260°C at a constant pressure of 10 MPa. In the absence of the second reactor at reaction temperatures below 200°C the yields of galacturonic acid monomer were lower than 5 % on carbon basis of initial sample and the yields of total water soluble (WS) saccharides were higher than 90 %. Although the monomer yields increased at higher temperatures, the yields of total WS saccharides considerably decreased because of the further decomposition of produced saccharides. When the second reactor was installed to increase the residence time of the solution containing dissolved pectic acids, the monomer yield increased and the further decomposition of WS saccharides was suppressed: for instance, at 180°C and a residence time in the second reactor of 120 s, the yields of monomer and total WS saccharides were 22.1 and 67.0 %, respectively. The yields of monomer and the total WS saccharides were correlated with a severity parameter that combines reaction temperature and residence time. Both the increase in monomer yield and the decrease in total WS saccharide yields were proportional to the severity.
