BACKGROUND: Barley straw is a potential lignocellulosic biomass for the production of bioethanol because of its high cellulose and hemicelluloses content. Ethanosolv pretreatment catalyzed with inorganic acids has some undesirable effects, and thus, inorganic salts, such as FeCl3, were studied as the catalyst in order to enhance enzymatic digestibility. RESULTS: The addition of 0.1 mol L-1 FeCl3 (Iron(III) chloride) had a particularly strong effect on the enzymatic digestibility, reaching a value as high as 89%, with cellulose recovery as high as 90% after the ethanosolv pretreatment. The enzymatic digestibility was 89% and 55% after the addition of 0.1 mol L-1 FeCl3 and H2SO4 (adjusted to the same pH), respectively. The enzymatic hydrolysis rate was significantly accelerated as the ethanosolv temperature increased, reaching the highest enzymatic digestibility of 89% after 72 h at 170 degrees C. The concentrations of HMF(5-hydroxy-2- methyl furfural) and furfural were 0.011 and 0.148 g L-1 in the hydrolysate during FeCl3-ethanosolv treatment, which were lower than the concentrations quantified during H2SO4-ethanosolv treatment. After the pretreatment, 88.5% of FeCl3 was removed through the filtration process. CONCLUSION: The addition of several inorganic salts significantly accelerated enzymatic digestibility in the ethanosolv. FeCl3 had a particularly strong effect on enzymatic digestibility and cellulose recovery. The formation of HMF and furfural and the remaining amount of FeCl3 were investigated, and FeCl3 had no effect on the subsequent processes after pretreatment. (C) 2010 Society of Chemical Industry