The process of thermodialysis and the efficiency increase ofbioreactors operating under non-isothermal conditions

When a catalytic membrane is employed in a non-isothermal bioreactor its activity increases as a direct function of the applied temperature gradient and decreases when both average temperature or substrate concentration increase. To know the physical cause responsible for this behaviour, substrate fluxes have been studied under isothermal conditions diffusion and non-isothermal conditions thermodialysis . Strong analogies between the behaviour of the catalytic membrane and the substrate fluxes produced by the process of thermodialysis have been observed. By introducing diffusive and thermodiffusive substrate fluxes in appropriate mass balance equations the substrate concentration profiles into the catalytic membrane have been deduced by computer simulation. In absence of catalysis and under non-isothermal conditions the profiles are higher than the ones corresponding under comparable isothermal conditions, while the contrary occurs in the presence of catalysis. The percentage increases of enzyme activity, calculated by the curves of the substrate concentration profiles, show the same temperature and concentration dependence than those actually observed with the catalytic membrane. The role of thermodialysis in affecting the enzyme activity in non-isothermal bioreactor has been discussed and demonstrated

Modulation of immobilized enzyme activity by altering the hydrophobicity of nylon-grafted membranes. Part 2: Non-isothermal conditions

Lactose hydrolysis by β-galactosidase immobilized on two nylonmembranes, differently grafted, has been studied in a bioreactor operating under isothermal and non-isothermalconditions. One membrane (M1) was obtained by chemical grafting of methylmethacrylate (MAA); the other one (M2) by a double chemical grafting: styrene (Sty) and MAA. Hexamethylenediamine was used as a spacer between the graftedmembranes and the enzyme. Both membranes have been physically characterized studying their permeabilities in presence of pressure or temperature gradients. Under non-isothermalconditions, the increase in activity of membrane M2 was higher than that of membrane M1. The α and β coefficients, giving the percentage of activity increase when a temperature difference of 1°C is applied across the catalytic membranes, have been calculated. Results have been discussed with reference to the greater hydrophobicity of membrane M2 with respect to membrane M1, the hydrophobicity being a prerequisite for the occurrence of the process of thermodialysis