| abstract |
Variations of this invention reduce or avoid lignin precipitation during acidic hydrolysis of biomass hydrolysates (such as hemicellulose-containing liquid extracts). Net acid usage and byproduct salt formation are significantly reduced. In some embodiments, hemicellulosic oligomers are hydrolyzed, in the presence of sulfur dioxide, to produce fermentable hemicellulosic sugars; the process comprising recovering and recycling at least a portion of the sulfur dioxide, wherein at least a portion of the sulfur dioxide reacts with the lignin to produce hydrophilic sulfonated lignin that has less tendency to precipitate or stick. In other embodiments, hemicellulosic oligomers are hydrolyzed, in the presence of a catalyst selected from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and combinations thereof, and an additive selected from metal sulfites, metal bisulfites, and combinations thereof, to produce fermentable hemicellulosic sugars, wherein at least a portion of the additive reacts with the lignin to produce sulfonated lignin. |