| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 92 === ABSTRACT
The separation of proteins from microbial cell suspension is generally an essential operation in the bio-product processes. Centrifugal sedimentation has been widely used for the separation, however, the difficulty in scale-up for its continuous operation is not yet overcomed. Although the crossflow filtration can improve the drawback and has fairly extensive application, but in the membrane filtration process there are some disadvantages like the occurrence of membrane fouling and the difficulty in maintaining high recovery of protein. A combination of crossflow shearing action and electric field has been developed and recognized as an effective means for reducing both concentration polarization and membrane deposition in crossflow filtration. But so far, the understanding of the principles of such process is still very limited, especially for the application in the biomaterial suspension separations. The objective of this study is to investigate the effects of electric field strength, electric field mode and other operation parameters such as pH and membrane pore size etc. on the filtration performance of BSA/yeast suspensions.
Experimental results from yeast (1000ppm)/BSA(1000ppm) suspensions in the pH range from 4 to 7 showed that its filtration rate increased almost linearly with the electric field strength. Based on the comparison of the measured steady-state filtration rates with that predicted from theoretical model, it was indicated that the electrophoretic mobility of yeast in pure yeast suspensions can be used in the prediction for the mixture.
Since the charge polarity and zeta potential of BSA will be varied with the pH, therefore both the electric field strength and the pH will give significant influences on its transmission. At pH=4 its electrophoretic mobility is directed toward to the septum and a 120% high transmission was obtained under the electric field strength of 2000V/m.
Filtration performance from two different pore size membranes, 0.2 and 0.45 μm, were also compared. Both gave similar results in steady-state filtration rate, but the larger pore membrane can maintain a BSA transmission over 100% , even to 123%, under the addition of electric field.
The average filtration rate of pulsed electric field mode with on(30)/off(30) is nearly the mean value between that of constant electric field and that without electric field. Both constant and pulsed electric field modes have similar BSA transmission under low electric field strengths, however the later will give higher transmission as higher electric field is applied. Although the energy consumption per unit mass of protein recoveried from the lab-scale electrofiltration is much larger than that from conventional crossflow filtration, but it can be expected that the energy consumption will be reduced significantly for the operation in a large scale process.
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