Dilute Sulfuric Acid Prehydrolysis of Southern Red Oak Chips By Direct Steam Heating

Abstract

Design of commercial scale processes for acid prehydrolysis of wood to useful products requires information on expected product yields under practical operating conditions. In this study, 650-gram batches of green southern red oak chips were hydrolyzed at 170°C. Particular attention was directed to conserving acid by low liquor-to-wood ratios, and to uniform acid distribution by vacuum impregnation. Carboxylate groups within the wood caused a significant, but unavoidable, loss of acid strength. As a consequence of this and other losses, satisfactory hydrolyses required 2.0 to 2.5% H₂S0, for 5-minute impregnations. Long impregnations, which provided partial neutralization of the carboxylate groups, were hydrolyzed at equivalent rates by 0.47 to 0.73% H2S04. A 5-minute vacuum impregnation of green chips with 2.5% H₂SO₄, followed by a 6-minute hydrolysis, removed 81% of the wood xylose as xylose and xylose oligomers, and 10% as furfural. Hydrolyses after long acid impregnations produced more xylose and less furfural. From 75 to 85% of the wood acetyl was recovered as acetic acid.