Hollow fiber membranes have wide applications in bioprocessing such as in separation of proteins, bioreactors, aeration and sterilization of media. This thesis focuses attention on the application of hollow fiber extraction to penicillin recovery and ethanol fermentation.
In Chapter 1, the relations among membranes, separation and biotechnology are summarized through literature searches and also expected developments are introduced briefly.
In Chapter 2, the transport phenomenon in a single hollow fiber is dealt with. The efficiency of a single fiber is numerically calculated and the effect of flow distribution on the module efficiency is discussed. In the case of countercurrent flow where both the tube-side and shell-side velocities were considered conjugated problem was solved numerically by using finite difference method. Extraction efficiencies were calculated by considering membrane resistance, Graetz numbers on the both sides of the membrane and distribution coefficients of a solute between water and extraction solvent. The efficiency of module becomes lower with the lower head height, the larger fiber diameter, the shorter fiber length, the larger packing density, and the higher Reynolds number of tube-side.
In Chapter 3, the separation of penicillin by membrane extraction was attempted. Solvent extraction in commercial practice was simulated numerically by using two membrane modules and experimentally tested. Extraction module with hydrophilic membrane was used; where solvent flow was in tube-side and penicillin was in shell-side. The flow rates of the two solutions affected the extraction efficiencies as expected. Mass transfer problem did not exist in the reextraction module, where KLa was $306h^{-1}$, 17 times higher than that of perforated plate column. The numerical simulation study was made by assuming the membrane was hydrophobic. The maximum overall extraction efficiency was obtained when the efficiencies of the two modules are similar.
Finally in Chapter 4, experimental and numerical results of hollow fiber membrane reactor for ethanol production are introduced. Productivity enhancement was attempted by using solvent extraction. The toxicity of solvent was alleviated by adapting microorganisms prior to the extractive fermentation. Ethanol producing yeasts were immobilized in the shell side of hollow fiber modules to yield a cell density of 266 g/L and ethanol productivity of 205 g/L.h. Optimum operating condition was calculated based on the continuous fermentation, membrane recycle fermentation, extractive fermentation. Membrane recycle fermentation with extraction gave an ethanol productivity of 51 g/L.h when 83% of 600 g/L glucose was converted and cell concentration was 62 g/L. When the cell concentration was higher than 100 g/L, stable operation was difficult due to bubble formation.
In summary, efficiency of membrane devices was enhanced by adding extraction function to the simple separation function of membranes. This will broaden novel applications of membranes to bioprocessing.
