Effect of ultrafiltration swing on the performan-ce of a hollow fiber enzyme reactor

Abstract

A new application of hollow fiber membranes to a membrane/enzyme reactor is suggested by introducing ultrafiltration swing. In the first half of the thesis, mathematical models for hollow fiber artificial kidney and pulsatile flow in a hollow fiber were derived as a first step toward understanding the new operation method of hollow fiber enzyme reactor. A one-dimensional model for diafiltration leads to understanding the role of ultrafiltration in increasing the mass transferrate of "middle molecules". Velocity field in a porous tube under the unrestricted pulsatile flow condition gives us the magnitude of radial velocity component which is so small that ultrafiltration swing induced by the unrestricted pulsatile flow cannot largely contribute to the transfer of solute. It is therefore concluded that pulsatile flow restricted at the outlet of hollow fiber should be used to induce significant ultrafiltration swing. When the ultrafiltration swing is used to enhance the transfer rate of substrate in a membrane/enzyme reactor a mathematical model for predicting conversion enhancement is necessary to understand the superiority of the reactor to the conventional diffusion-moderated membrane/enzyme reactor. Hence a new membrane/enzyme reactor system is proposed and its performance is analytically and numerically examined by operational modes. This membrane separated two compartmental reactor is operated in a cyclic manner such that ultrafiltration swing is induced either by a pulsatile flow or by an alternating pressure difference. Substrate and product solutions are permeable to the membrane while enzyme is impermeable. In one reservoir enzyme solution is stored into which substrate is supplied by diffusion coupled ultrafiltration and product is removed by the same mechanism into the substrate compartment, which is similar to CSTR in view of fluid mixing and continuous inlet-outlet flows, however, differs from CSTR in a sense that reaction takes place only in the enz...