Membranes are a key part of pervaporation processes, which is generally a more
efficient process for selective removal of alcohol from water than distillation. It is
necessary that the membranes have high alcohol permeabilities and selectivities.
Polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) have
demonstrated very promising results. Zeolitic imidazolate framework-71 (ZIF-71)
demonstrated promising alcohol separation abilities. In this dissertation, we present
fundamental studies on the synthesis of ZIF-71/PDMS MMMs.
Free-standing ZIF-71/ PDMS membranes with 0, 5, 25 and 40 wt % ZIF-71
loadings were prepared and the pervaporation separation for ethanol and 1-butanol from
water was measured. ZIF-71/PDMS MMMs were formed through addition cure and
condensation cure methods. Addition cure method was not compatible with ZIF-71
resulting in membranes with poor mechanical properties, while the condensation cure
method resulted in membranes with good mechanical properties. The 40 wt % ZIF-71
loading PDMS nanocomposite membranes achieved a maximum ethanol/water selectivity
of 0.81 ± 0.04 selectivity and maximum 1-butnaol/water selectivity of 5.64 ± 0.15.
The effects of synthesis time, temperature, and reactant ratio on ZIF-71 particle
size and the effect of particle size on membrane performance were studied. Temperature
had the greatest effect on ZIF-71 particle size as the synthesis temperature varied from -
20 to 35 ºC. The ZIF-71 synthesized had particle diameters ranging from 150 nm to 1
μm. ZIF-71 particle size is critical in ZIF-71/PDMS composite membrane performance
for alcohol removal from water through pervaporation. The membranes made with
micron sized ZIF-71 particles showed higher alcohol/water selectivity than those with
smaller particles. Both alcohol and water permeability increased when larger sized ZIF-
71 particles were incorporated.
ZIF-71 particles were modified with four ligands through solvent assisted linker
exchange (SALE) method: benzimidazole (BIM), 5-methylbenzimidazole (MBIM), 5,6-
dimethylbenzimidazole (DMBIM) and 4-Phenylimidazole (PI). The morphology of ZIF-
71 were maintained after the modification. ZIF-71/PDMS composite membranes with 25
wt% loading modified ZIF-71 particles were made for alcohol/water separation. Better
particle dispersion in PDMS polymer matrix was observed with the ligand modified ZIFs.
For both ethanol/water and 1-butanol/water separations, the alcohol permeability and
alcohol/water selectivity were lowered after the ZIF-71 ligand exchange reaction.