Date of Award

Spring 2004

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering - (Ph.D.)

Department

Chemical Engineering

First Advisor

Kamalesh K. Sirkar

Second Advisor

Piero M. Armenante

Third Advisor

Gordon Lewandowski

Fourth Advisor

Dana E. Knox

Fifth Advisor

Barbara B. Kebbekus

Abstract

A new ultrafiltration technique based on a multimembrane stack has been developed to fractionate proteins closer in molecular weight than conventionally possible. The technique is illustrated here by obtaining a pure protein product from a binary protein mixture. By employing membranes in series using the same membrane without any gaskets or spacers in-between, ultrafiltration is carried out to separate two proteins relatively close in molecular weight. Flat membranes, of the same molecular weight cutoff (MWCO) 30,000 or 100,000, are stacked together in the desired number, and ultrafiltration takes place. The membrane rejection of a protein is amplified with each additional membrane, ultimately resulting in a completely rejected species. Complete purification of the more permeable protein may be achieved by operating under a physicochemical condition that is optimal for selective separation by a single membrane. Three systems; myoglobin and f3-lactoglobulin (molecular weight ratio 2.05), myoglobin, and β-lactalbumin (molecular weight ratio 1.22), and hemoglobin and bovine serum albumin (molecular weight ratio 1.03) were studied under various operating conditions. Complete rejection was achieved using three membranes one on top of the other for all three systems. To achieve complete rejection in a multimembrane stack, the single membrane rejection must be considerable. Cleaning in situ was achieved with reproducible experimental results before and after on-line cleaning. Flux decreased by a factor equal to the number of membranes when a multimembrane composite was used. However, the lost flux may be recovered by increasing the pressure by the same factor. The results clearly demonstrate that multimembrane stacks can be used for effective fractionation of proteins that are quite close in molecular weight. Internally-staged ultrafiltration (ISUF) with one flat membrane on top of the other may therefore overcome some of the limitations of conventional ultrafiltration (UF). Two types of models have been explored, one based on a lumped model, the other based on a convection-diffusion model with concentration polarization to explain the potential amplification of retention with each added membrane.

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