The Use of Lewis Acids During Rapid Steam Hydrolysis

Abstract

Abstract Mixed hardwood chips were treated with various concentrations of aluminum chloride hexahydrate, aluminum sulfate hydrate, and ferric chloride and were subjected to rapid steam hydrolysis pretreatment (RASH). The three levels included 0.01, 0.03, and 0.05 moles of catalyst per 1000 grams of wood. Rapid steam hydrolysis (RASH) was done from 180° to 260°C at 20°C intervals for one minute. The Lewis acid catalyst affected the overall recovery yield of solids, the recovery values of the individual components, the enzymatic rates, and the methanol and water solubility. Overall recovery of pretreated solids generally decreased with the increase in levels of the catalyst. The one exception was AlCl3 ·6H2O where the minimum recovery levels were reached at 0.03 moles per 1000 grams of wood and increased at the higher level of catalyst. Cellulose degradation occurred in the temperature range of 250° to 260°C for the control and at the two lower concentrations of the catalyst. At the higher levels of catalyst, appreciable amounts of cellulose degradation occurred at lower temperatures. Hemicellulose solubilization and degradation were extremely sensitive to the RASH temperature and to the levels of catalyst. Almost all hemicellulose was lost at high temperatures or at high levels of catalyst. Losses of lignin appeared to be affected mainly by the RASH temperature and not by the changes in the levels of catalyst. In contrast, both the temperature and the level of catalyst strongly affected the rates of enzymatic hydrolysis. Generally, the intermediate level of catalyst seemed to give the highest rates of enzymatic hydrolysis at the lowest temperature. Methanol and water solubles increased in the presence of the catalyst and reached a maximum at levels of 0.03 moles between 230° to 250°C.