Kinetics of Diluted Acid Hydrolysis of Pentosan in Different Cellulose Materials
1985 Volume 59 Issue 2 Pages 123-128
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1985 Volume 59 Issue 2 Pages 123-128
The kinetics of diluted (0.1_??_1.82 mol/liter) sulfuric acid hydrolysis of pentosan of buna wood and nemagari-dake (bamboo) was studied at elevated temperatures (74_??_146°C). The reaction consisted of four first-order reactions with different rate constants ki (i=A'1, A 1, A 2, and B 2). Native pentosan A' was hydrolyzed to yield the insoluble linear segment A with constant kA'1 and A was by parallel reaction transformed into the least accessible crystalline pentosan B with kA1 and hydrolyzed to soluble sugars (mono- and oligosaccharides) S with kA2, and finally B was hydrolyzed to S with kB2. The four rate constants were determined and expressed for acidity function and for acid molarity at the stated temperature range. The results were compared with those of corncobs and isolated xylan.
The values of kB2 were approximately the same for the four kinds of pentosan but those of the other rate constants were distinctly different. According to the Zucker-Hammett criterion, the three hydrolytic reactions of pentosan of buna wood and nemagari-dake followed the bimolecular mechanism (A-2) in contrast to the unimolecular mechanism (A-1) for isolated xylan. The activation energy at each step of hydrolysis reaction of pentosan in cellulose materials was about one-half that of cellulose.
