Flux Modulations and Separations with Temperature and pH Responsive Membranes

Flux Modulations and Separations with Temperature and pH Responsive Membranes

K. Waldrop*, L. Xiao, D. Bhattacharyya

Krysta.waldrop@gmail.com, li.xiao@uky.edu, DB@uky.edu

Dept. of Chemical and Materials Engineering

University of Kentucky

Lexington, Kentucky

Temperature responsive materials have proven to be very useful in bioseparation, water treatment, and drug delivery. By functionalizing a membrane with a temperature-responsive polymer, tunable flux can be achieved quickly with minimal energy consumption, making a valuable tool for the aforementioned fields. Poly-N(isopropyl acrylamide) (PNIPAM) is a temperature-responsive polymer which has drawn much attention in recent years.  At temperatures below 32°C (the lower critical solution temperature, or LCST) PNIPAM exists in a hydrophilic state, causing the polymer chains to absorb water and swell, but, above the LCST, the polymer becomes hydrophobic, collapsing the polymer chains. When PNIPAM is functionalized within membrane pores, the temperature responsive behavior allows for control of the effective pore size. The goal of this research was to study the permeation and rejection behavior with changing temperature of PNIPAM functionalized polyvinylidene fluoride (PVDF) membranes. PVDF membranes were functionalized with PNIPAM using free radical in situ polymerization. The flux and dextran rejection (2,000,000 MW) were studied at 2.1 bar and temperatures of 30°C and 34°C. Tests confirmed that below LCST the flux was 1.44 LMH and 95% of dextran was rejected, and above the LCST flux increased to 9.72 LMH and only 30% of the dextran was rejected. PNIPAM functionalized full-scale PAA-PVDF membranes were also developed to observe both temperature and pH effects on flux and sodium sulfate rejection (100ppm). Below LCST, functionalized full-scale membranes rejected 50% of the sodium sulfate with a flux of 13 LMH at a pH of 4 and at a pH of 8, 90% of the sodium sulfate was rejected with a flux of 10 LMH. Above the LCST, sodium rejection was 25% with flux at 81 LMH at a pH of 4 and a flux of 52 LMH with an 82% rejection was observed at a pH of 8.  It could be concluded that an increase in temperature led to an overall increased flux but decreased rejection.

This work was supported by NIEHS-SRP