NAMS 2002 Workshop - ICOM 2008

Facilitated Transport Membranes – 5
Friday July 18, 11:45 AM-12:15 PM, Wai’anae
Novel Olefin Carrier for Facilitated Transport Membranes: Partially
Polarized Surface of Silver Nanoparticles by Electron Acceptor
Y. Kang (Speaker), Hanyang University, Korea - kangys@hanyang.ac.kr
S. Kang, Seoul National University, Korea
A new application of metallic silver nanoparticles as a novel olefin carrier for
facilitated olefin transport membranes was explored. The surfaces of silver
nanoparticles were chemically activated using electron acceptor such as pbenzoquinone.
The chemically activated surface is expected to form complexes
with olefin molecules resulting in olefin carrier for facilitated transport. Such
facilitated transport membranes were applied for separation of olefin/paraffin
mixtures such as propylene/propane mixtures. The separation performance for
the 50/50 (v/v) propylene/propane mixture through the 1/1/0.85 EPR/AgO/ pbenzoquinone
membrane showed the selectivity of 10 and the mixed gas
permeance of 0.5 GPU for up to 105 hrs. The change in the chemical
environment around the silver nanoparticles in EPR/Ago composite membranes
upon the incorporation of p-benzoquinone was investigated by XPS. The binding
energy of the d5/2 orbital of the silver particle in the EPR/Ago/p-benzoquinone
system increased gradually with increasing p-benzoquinone content. This
indicates that the binding energy of the valence electrons in the silver atoms
increased due to the interactions between the silver atoms and p-benzoquinone,
and that the surface of the silver nanoparticles was partially positively charged.
Quantum mechanical ab-initio calculations were conducted to confirm the
possible theoretical interactions between the surface of the silver nanoparticles
and olefin molecules. Ethylene molecules can interact with the upper edge, the
side, or the palm side of the silver nanoparticle with corresponding complexation
enthalpies (”H) of -4.48, -3.65 and -1.42 kcal/mol, respectively. These ab-initio
calculations suggest the presence of the interactions between the silver
nanoparticle and olefin molecules, with the most probable interaction of ethylene
with the upper edge of the silver nanoparticle. The complexation of propylene
with the surface of the silver nanoparticles was investigated using FT-IR
spectroscopy. The EPR/Ago composite without p-benzoquinone showed two
peaks at 1664 and 1640 cm -1 representing the C=C stretching vibration of
propylene (Å1 and Å2 of C=C in free propylene are 1664 and 1640 cm -1 ,
respectively), upon exposure to propylene. The positions of the peaks remained
unchanged as the exposure time was increased up to 30 minutes. The two
propylene peaks disappeared in the spectra following desorption of propylene for
5 minutes. These results suggest no interaction of propylene with the surface of
the silver nanoparticles in the EPR/Ago composite without p-benzoquinone as
the propylene absorption occurs only in the EPR matrix. On the other hand, the