Performance Features for Urea Hydrolysis in A Cstr with Microencapsulated Urease

Abstract

The factors which influence the steady state performance of a CSTR operation with microencapasulated urease for the regeneration of a dialysated solution have been studied at various enzyme activities. The theoretical model considered the effect of microcapsule diameter, pH-dependent kinetics, and product inhibition and substrate depletion, in relation to urea conversion and the capsule effectiveness factor. The limiting effects of pH, product inhibition and substrate depletion were also studied individually and in combination under eight case studies. The base case which included these three limiting factors in the reaction process, predicted the lowest urea conversion values at the enzyme activities considered. However, the effectiveness factor for each case at a fixed microcapsule diameter depended on the enzyme activity. This behaviour was studied for two different microcapsule diameters, 5 μm and 500 μm. At enzyme activities lower than 1 mM/s, a model considering Michaelis-Menten kinetics alone, predicted the highest effectiveness factors. On the other hand, beyond 1 mM/s enzyme activity, the lowest effectiveness factors were predicted, although higher conversions than that of the base case were achieved. This might be due to the rapid depletion of substrate at high activities when Michaelis-Menten kinetics were considered, leads to residual substrate concentrations (S_p) lower than the Michaelis-Menten constant K_m,o a condition for a dramatic drop in the intraparticle reaction rate. The limiting factors in the base case held S_r at a relatively higher value than K_m,o.

Key Words:

• urea hydrolysis
• microencapsulated urease
• dialysate solution
• effectiveness factor