Supporting Information
An advanced gas/vapor permeation system for barrier materials;
design and applications to poly(ethylene terephthalate)
Jong Suk Leea, Preeti Chandraa,b, Steven K. Burgessa, Robert Kriegelc, William J. Korosa,*
a
School of Chemical and Biomolecular Engineering
Georgia Institute of Technology, Atlanta, GA-30332, USA
b
c
Praxair Inc, Tonawanda, NY-14150, USA
The Coca-Cola Company, Atlanta, G-30313, USA
Determination of the methanol activity for gas/vapor permeation
The total number of moles for O2/CO2/CH3OH in the upstream can be estimated by
converting the mass flow rate in the upstream bypass to the number of moles. Let the molar flow
rate in the upstream bypass line be BTOT. Then, the total number of moles per minute in the feed
stream is estimated as:
1  mol 
 ccSTP 
nTOT  BTOT 


 min  22, 414  ccSTP 
(S.1)
On the other hand, the number of moles for CH3OH vapor is estimated by using the
volumetric flow rate of CH3OH from the syringe pump based on the assumption that all CH3OH
molecules are evaporated prior to reaching the permeation cell. Let the volumetric flow rate of
CH3OH be VCH3OH , then:
 cc 
1  mol 
 l 
g
nCH3OH  VCH3OH 
 CH3OH   103   



 min 
 cc 
 l  M CH3OH  g 
(S.2)
where, CH3OH is the density of CH3OH (i.e. 0.792 (g/cc)) at 35ºC and M CH3OH is the molecular
weight of CH3OH (i.e. 32 (g/mol)), so the respective partial pressure of CH3OH is obtained as:
1
pCH3OH 
nCH3OH
nTOT
 pTOT
(S.3)
where, pTOT is the total pressure of the feed stream. As long as the partial pressure of the CH3OH
*
vapor component is less than the corresponding vapor pressure at 35ºC (i.e. pCH
 35o C  = 202.3
3OH
mmHg), condensation can be avoided. By adjusting the volumetric flow rate of CH3OH and the
mass flow rate of retentate flow, the desirable CH3OH activity level can be easily achieved.
Gas Chromatography for a multicomponent permeation
Gas Chromatography (GC) has been used to analyze the composition of the permeate in the
case of mixed gas/vapor feeds. The feed composition of custom prepared gas/vapor mixtures has
also been analyzed similarly. The instrument is a 6890N from Agilent Technologies (Palo Alto,
CA). The valve diagram of the GC is shown below:
Figure S. 1. Valve configuration for gas sampling
A 2 cc sample loop has been used. The ‘sample in’ port is connected to the permeate and the
feed side, whereas the ‘sample out’ port is connected to a 100 Torr MKS BaratronTM transducer
and vacuum pump in series. The following are the operating conditions at the time of a GC run.
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Table S. 1. GC operation conditions
Parameter
Oven Temperature
Total Run Time
Back Inlet
Split Ratio
Column
Column Flow
Carrier Gas
Detector Reference Gas
Detector Make-up Gas Flow
Heated Valve Box
Sample with methanol
120 ºC
4.00 min
150 ºC
10:1
HP Plot Q, 30m long, 0.32 mm diameter, 0.20
coating width
3.4 mL/min at 20 psi
Helium
20.0 mil/min
7.0 mL/min
130 ºC
The GC was calibrated using pure gases and vapor. Pure CO2 and O2 was expanded into the
sample loop from the downstream of the permeation box and allowed to equilibrate for 3
minutes. Different pressures in the range of 0-10 Torr for the gases were injected. Methanol
vapor was expanded into the GC from a vapor source volume that was kept outside the
permeation box. The vapor was prepared by taking liquid methanol in a vial. Dissolved and
headspace air was removed by at least five freeze-pump-thaw cycles. The vapor in the headspace
of the liquid vial was then allowed to expand into a 1000 cc colume that was connected to the
vial. This volume had been evacuated previously. Vapor from this volume was expanded into the
GC sample loop. Methanol vapor in the range of 0-0.5 Torr was used. These pressures were
chosen because this was the expected range of partial pressures in the permeate. All the transfer
lines were heated to least 70 ºC to ensure that methanol did not adsorb on the transfer lines
which would results in smaller peaks.
Upon expansion into the sample loop, the sample (either a gas or vapor) was allowed an
equilibration time of 3 minutes if the pressure was higher than 5 Torr and 5 minutes of the
pressure was less than 5 Torr. Care had been taken to ensure that the leak rate of atmospheric air
into the transfer lines was minimal and that no leak peak for air was observed during blank runs.
The calibration factors obtained are shown below:
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Table S. 2. Calibration factors for CO2, O2, and CH3OH
Parameter
Carbon dioxide
Oxygen
Methanol
Sample with methanol (Area/Torr)
67.748
46.136
46.465
During a permeation run, the mixed gas/vapor feed was analyzed by expanding the feed
mixture into the sample loop. Nearly 20-30 Torr of the mixture was injected. This ensured that
methanol partial pressures lay in the calibration range. The mole fraction of methanol in the feed
was calculated using equation S.1:
YMeOH =
AMeOH
MeOHpinjected
(S.4)
pinjected is the pressure read off by the transducer in the GC transfer line. AMeOH is the measured
area, and βMeOH is the calibration factor.
When sufficient permeate was accumulated, which was in the range of 3-6 Torr, it was
expanded into the sample loop (the sample loop is made of 1/16” tubing). Care was also taken to
ensure that methanol partial pressures did not exceed 0.5 Torr in the downstream in most cases.
This is because control tests of methanol adsorption were carried out only up till 0.5 Torr. The
permeate was allowed to expand into the sample loop for 5 mins after which the run was started.
Areas of the species were obtained and their mole fraction was calculated using the following
expression:
YA 
AA  A
AA  A  AB B  AC C
(S.5)
Ai is the area of the species and is the calibration factor. The permeability of the species was then
calculated using the following equation:
4
dp
dpA
 YA  TOT
dt
dt
(S.6)
dpA dt 101325  V 106  22414  L 14696
PA 
1010  Barrers 
60  760  8.314  T  A  p  76
(S.7)
PA is the permeability; dpA/dt is the rate of pressure rise for a given species in Torr/min. For
oxygen, the actual dp/dt is evaluated by subtracting out the measured leak rate. This was because
it is air that leaks in, and contributes only to the oxygen peak, not the other gases. V is the
downstream volume in cc. R = 8.314 J/mol/K, L is the film thickness in cm, ∆p, in psia, is the
pressure differential across the film which is the upstream pressure in this case. A is the film area
in cm2.
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