Kinetics of hemicellulose autohydrolysis for wheat straw
Hemicellulose and nonstructural carbohydrates, such as fructosans, can be removed from the fiber complex of wheat straw during a pretreatment process called autohydrolysis. The autohydrolysis process for wheat straw was modeled as a series of first order reactions from polymer to oligomer, to monomer and finally to degradation products. The rate equations derived from mass balances for this series of first order reactions were integrated to obtain time and temperature dependent expressions for the concentrations of the several species involved in the process. The rate limiting step in xylose monomer production was found to be the conversion of oligomer to monomer. The addition of Al/sub 2/(SO/sub 4/)/sub 3/ was found to increase this rate of conversion. Several isothermal autohydrolysis runs were conducted on fructosan-free wheat straw over the temperature range of 140 to 170/sup 0/C to obtain xylose oligomer and monomer profiles as a function of time in distilled water and in a 0.2 wt % Al/sub 2/(SO/sub 4/)/sub 3/ solution. The 0.2 wt % Al/sub 2/(SO/sub 4/)/sub 3/ solution was determined to be an approximation of the optimum dosage for maximum sugar recovery. The values of the rate constants associated with the formation of xylose were estimated by a simplex search of an objective function. Activation energies and frequency factors were estimated for each rate constant from Arrhenius-type plots of ln K vs 1/T. From these studies, the optimum process for sugar recovery during wheat straw autohydrolysis is envisioned as occurring in two steps. First, fructosan is extracted at 120/sup 0/C for 35 minutes. Next, the fructosan-free straw is autohydrolyzed at a higher temperature. The two operating options for the autohydrolysis reactor to obtain maximum monomer recovery are: (a) 155/sup 0/C for 50 minutes in 0.2 wt % Al/sub 2/(SO/sub 4/)/sub 3/; and (b) 170/sup 0/C for 120 minutes in distilled water for the temperature range tested (155 to 170/sup 0/C). 50 references, 23 figures, 17 tables.
- Research Organization:
- Colorado State Univ., Fort Collins (USA). Dept. of Agricultural and Chemical Engineering
- DOE Contract Number:
- AS07-79ID12051
- OSTI ID:
- 6721713
- Report Number(s):
- DOE/ID/12051-T2; ON: DE84014792
- Resource Relation:
- Other Information: Portions are illegible in microfiche products. Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
15 GEOTHERMAL ENERGY
HEMICELLULOSE
DEPOLYMERIZATION
HYDROLYSIS
CHEMICAL REACTION KINETICS
GEOTHERMAL ENERGY
HEAT TREATMENTS
POLYMERS
PROCESS HEAT
STRAW
XYLOSE
ALDEHYDES
CARBOHYDRATES
CHEMICAL REACTIONS
DECOMPOSITION
ENERGY
ENERGY SOURCES
HEAT
KINETICS
LYSIS
MONOSACCHARIDES
ORGANIC COMPOUNDS
PENTOSES
POLYSACCHARIDES
REACTION KINETICS
RENEWABLE ENERGY SOURCES
SACCHARIDES
SOLVOLYSIS
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