Comparison of Polypeptide Functionalized Cellulose, Silica, and Other Polymeric Microfiltration Membranes for High Capacity Metal Sequestration
J. Hestekin (1), D. Bhattacharyya (1), S. Ritchie (1), L. G. Bachas (2), and S. K. Sikdar (3)
(1) Dept.of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506-0046 (2) Dept. of Chemistry, University of Kentucky (3) U.S. EPA, NRMRL, Cincinnati, OH 45268
The use of microfiltration (MF) membranes traditionally deals with the separation of particles from solution. However, as membrane applications are used more and more in process streams, new "smart" MF membranes are necessary to achieve the desired separations. One of these new class of MF membranes is polypeptide functionalized MF membranes which allow for the removal of dissolved metals from process streams by sorption onto exchange sites on polypeptides which have been chemically attached to membrane pores convectively. This allows for much higher heavy metal sorption capacity than if chelation was taking place just on the membrane surface. The development of MF-based sorbents containing polymeric chelating (such as polypeptides) agents is a novel technique to achieve very high metal sorption under convective flow conditions [1].
With polypeptides (i.e., polyglutamic acid and polyarginine), a terminal primary amine results from polymerization which is easily reacted with aldhehydes or epoxides derivatized on the membrane surface. We have shown that a variety of membrane materials (i.e., cellulose, silica, cellulose acetate, etc.) can be used for heavy metal sorption. With cellulose, sorption capacities as high as 1.4 g Pb/g membrane have been established with cellulose acetate (CA) starting materials. Since CA is relatively inexpensive, this would be excellent for an application where a low-cost sorbent is required. When it is desired to remove heavy metals from corrosive process streams, a silica based membrane may provide the stability necessary for the desired separation. Even though the sorption per unit weight is lower for silica-based membranes (0.4 g Pb/g membrane), it's sorption per unit surface area is much superior to cellulose (4.9 mg/cm2 for silica compared to 2.2 mg/cm2 for cellulose). Although various different membrane materials were used, the metal sorption results were found to be similar. This project was funded by the US EPA and DoD.
References:
[1] D. Bhattacharyya,J.A. Hestekin, P. Brushaber, L.G. Bachas, and S.K. Sikdar, "Novel poly- glutamic acid functionalized microfiltration membranes for sorption of heavy metals at high capacity". J. Memb. Sci., IN PRESS (1998).