KINETIC AND MODELING INVESTIGATION ON 2-STAGE REVERSE-FLOW REACTOR ASAPPLIED TO DILUTE-ACID PRETREATMENT OF AGRICULTURAL RESIDUES

The kinetics of dilute-acid pretreatment/hydrolysis of the hemicellulo se in a mixture of corn cobs and corn stover was investigated. The kin etic data confirmed that the hemicellulose in this feedstock is of a b iphasic nature. The kinetic model recognizes the presence of soluble x ylose oligomers, xylose monomer, and the decomposition of xylose. The kinetic parameters were determined over the conditions of 120-150 degr ees C, and sulfuric acid concentration of 0.44-1.90%. The biphasic nat ure of the kinetics brings about an additional flexibility in the reac tor design and the operation strategy, since different reaction condit ions can be applied to each of the two different fractions of hemicell ulose in the feedstock. With incorporation of the kinetic data, a perc olation reactor operated under various modes, uniform temperature, tem perature step change (along with or without flow rate step change), an d two-stage reverse-flow operation, was modeled and investigated for i ts performance. The modeling results affirmed that a step-change/rever se-flow operation is advantageous for biphasic substrates, including a gricultural residues. The optimum temperature difference in the step-c hange operation was determined to be 30 degrees C over a wide range of reaction temperature. Temperature step change alone (without use of r everse-flow mode) increased the product yield by 3-11% (depending on t he reaction conditions) over that of uniform temperature operation. Th e most significant improvement, however, was seen with application of a two-stage reverse-flow reactor arrangement with temperature step cha nge employing different conditions at each stage. This operation essen tially doubled the sugar concentration over that of the temperature st ep change operation.