A biomass pretreatment process is being developed based on contacting lignocellulosic biomass with 70% sulfuric acid and subsequent hydrolysis by adding water. In this process, the hydrolysate can be fermented yielding ethanol, while the sulfuric acid is partly recovered by anion-selective membranes before the fermentation process, and partly via biological sulfate reduction in an anaerobic waste water treatment plant. The sulfide produced is recovered as H2S gas and chemically converted (burned) into SO2 and SO3 (by which heat is recovered as well) and subsequently into sulfuric acid. In this unique approach, the sulfuric acid is recycled to a large extent. This process, the Biosulfurol process, is able to handle a wide variety of lignocellulosic biomass and does not need the addition of enzymes. In the project switch grass and willow wood were tested as model substrates.
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