Cellulose hydrolysis under extremely low sulfuric acid and high-temperature conditions

The kinetics of cellulose hydrolysis under extremely low acid (ELA) conditions (0.07 wt%) and at temperatures >200 degrees C was investigated using batch reactors and bed-shrinking flow-through (BSFT) reactors. The maximum yield of glucose obtained from batch reactor experiments was about 60% for alpha-cellulose, which occurred at 205 and 220 degrees C. The maximum glucose yields from yellow poplar feedstocks were substantially lower, falling in the range of 26-50%. With yellow poplar feedstocks, a large amount of glucose was unaccounted for at the latter phase of the batch reactions. It appears that a substantial amount of released glucose condenses with nonglucosidic substances in liquid. The rate of glucan hydrolysis under ELA was relatively insensitive to temperature in batch experiments for all three substrates. This contradicts the traditional concept of cellulose hydrolysis and implies that additional factors influence the hydrolysis of glucan under ELA. In experiments using BSFT reactors, the glucose yields of 87.5, 90.3, and 90.8% were obtained for yellow poplar feedstocks at 205, 220, and 235 degrees C, respectively. The hydrolysis rate for glucan was about three times higher with the BSFT than with the batch reactors. The difference of observed kinetics and performance data between the BSFT and the batch reactors was far above that predicted by the reactor theory.