Theoretical and experimental analysis of a soluble enzyme membrane reactor

Recently enzyme immobilization techniques have been proposed that are mainly founded on the formation of an enzyme-gel layer onto the active surface of an ultrafiltration membrane within an unstirred ultrafiltration cell. If the membrane molecular-weight cutoff is less than the enzyme molecular weight and hence such as to completely prevent enzyme permeation (once the enzyme solution has been charged into the test cell and pressure applied to the system), a time progressive increase in enzyme concentration takes place at the upstream membrane surface that can eventually lead to gelation and hence to enzyme immobilization. However, depending on the total enzyme amount fed, the maximum enzyme concentration achieved in the unsteady state could be less than the gelation level. In this situation, no immobilization occurs and the enzyme still remains in the soluble form although it is practically confined within a limited region immediately upstream the membrane and at fairly high concentrations. In this paper, the experimental conditions that allow gelling to occur are discussed together with a theoretical analysis of the soluble enzyme membrane reactor which is obtained when no gelling takes place. Such a system could be usefully employed in performing kinetic analyses at high enzyme concentration levels that are still in the soluble form.