In a stirred tank reactor, during catalysis with immobilized cephalosporin C acylase (CCA), the microenvironmental pH dropped to 7.2 in a nonbuffered system (with the pH maintained at 8.5 by adding alkali) due to the existence of diffusional resistance. Moreover, the immobilized CCA only catalyzed five batch reactions, suggesting that the sharp pH gradient impaired the enzyme stability. To buffer the protons produced in the hydrolysis of cephalosporin C by CCA, phosphate and bicarbonate buffers were introduced. When CCA was catalyzed with 0.1 M ammonium bicarbonate buffer, no obvious gradient between the bulk solution and intraparticle pH was detected, and the catalysis of 15 batch reactions was achieved. Accordingly, with 0.2 M ammonium bicarbonate buffer in a packed bed reactor, the immobilized CCA exhibited continuous catalysis with high conversion rates (≥95%) for 21 days. Reactions with ammonium bicarbonate buffer showed significant increases in the stability and catalytic efficiency of the immobilized CCA in different reactors compared to those in nonbuffered systems.
Keywords: ammonium bicarbonate; cephalosporin C acylase; immobilized enzyme; microenvironmental pH regulation; packed bed reactor.
© 2019 American Institute of Chemical Engineers.