Kinetic study of detoxification of dilute-acid hydrolyzates by Ca(OH)2.

Detoxification of dilute-acid hydrolyzates by addition of Ca(OH)(2) (overliming) and cultivation of the detoxified hydrolyzates by Saccharomyces cerevisiae were examined. The examined overliming involves increasing the pH of the hydrolyzates to 9, 10, 11 or 12, keeping up to 90 min at different temperatures of 30, 45 and 60 degrees C, followed by readjustment of the pH to 5. Increasing the pH, time and/or temperature resulted in more effective degradation of furans and resulted in better fermentability for both of the tested hydrolyzates, but higher loss of the sugars was observed as well. Overliming of glucose and furfural solution at pH 12 showed a rapid decrease in concentration of these chemicals followed by a slow degradation process. Therefore, a kinetic model was proposed for the detoxification, where the sugars or furans make transient complexes with calcium ions and this complex will then be converted to the degradation product. The ANOVA analysis of the model resulted in an average R(2) of 0.99 for the model fitted to all the experimental data points.