Hydrocarbon Processing - September 2021 - 84

Process Controls, Instrumentation and Automation
method used was ASTM D8098-179
.
Two column sets in the isothermal oven,
each with one packed and one capillary
column, were used to separate the analytes
(10 ppm each, as shown in FIG. 6).
The chromatogram shows two sections
with a rising baseline at 3.7 min resulting
from the switch between the column
sets. The first column set resolved and
and
quantified H2, O2/Ar composite, N2
. The observed baseline shift
is a consequence of switching column
sets during the run. The MDLs for these
analytes were H2
(100 ppb), O2
/Ar and
N2 (500 ppb), CO (20 ppb) and CO2
(30 ppb). Methane was observed on
each column set but analyzed by the FID
(shown below).
While the MSD and PDHID trains
were analyzing their respective compounds,
the FID speciated and quantified
hydrocarbons. The reference method
used was ASTM D6159-1710
. Here, an
ethylene stream was interrogated for hydrocarbons
(200-ppm refinery gas mix),
which were resolved on a 50-m column in
MCO1 and speciated by a flame ionization
detector (FID, shown in FIG. 7). C1
C4 hydrocarbons were speciated while
heavier species were backflushed as C5+
-
.
CO. The second column then set quantified
CO2
The MDL was determined to be 2 ppm
for these components.
The precision of the micro-convection
oven temperature and electronic pressure
controls were also examined in a separate
engineering study (FIG. 8). Retention time
reproducibility is a measure of how tightly
controlled the temperature, pressure and
backpressure in a system are. To examine
the retention time reproducibility, data
taken over two days from eight injections
of a hydrocarbon mixture were obtained.
The relative standard deviation (%RSD)
of the results was calculated and found
to be excellent for all eight compounds
in the blend. Peak area reproducibility
is measure of a system's ability to repeatably
deliver the same amount of a sample
to the analytical column. It is a function
of split inlet performance and mass flow
control. To evaluate these parameters, 5%
methane in argon was injected 12 times.
Again, %RSD results obtained rival those
obtained on laboratory GCs and are unparalleled
in online PGCs.
FIG. 7. Hydrocarbons by FID. Chromatogram
showing results for 1.) C5
+ backflush, 2.)
methane, 3.) ethane, 4.) ethylene*, 5.) propane,
6.) propylene, 7.) acetylene, 8.) propadiene,
9.) isobutane and 10.) n-butane. *Matrix.
Takeaway. The goal of this study was
to design a single PGC capable of ppb
detection of analytes of importance for
ethylene and propylene producers and
their customers. A novel approach using
process GC-MS was developed to
take full advantage of the sensitivity and
specificity of MSDs. Tightly controlled
and temperature-programmable ovens allowed
for the use of fused silica capillary
columns for the greatest resolving power.
Parallel chromatography with the MSD,
PDHID and FID detector trains allowed
for analysis of an extensive range of possible
monomer contaminants at ppb levels
not previously attainable with process
GCs. Together, the data presented here
clearly demonstrate that, when using the
same technologies available to laboratory
GCs, lab-quality performance can be
achieved from a process instrument.
NOTES
a Wasson-ECE Instrumentation's Eclipse Neutrin
b Agilent Technologies' 5977B Mass Spectrometer
c Valco PDHID
d Wasson-ECE FID
REFERENCES
1
Figure modified from the original, online: https://
commons.wikimedia.org/wiki/File:Quadrupole_
ion_trajectory.svg
2
Silverstein, R. M., F. X. Webster and D. J. Kiemle,
Spectrometric identification of organic compounds, 7th
Ed., Wiley, 2005.
3
Wentworth, W. E., S. V. Vasnin, S. D. Stearns and C.
J. Meyer, " Pulsed discharge helium ionization detector, "
Chromatographia, Vol. 34, September/October
1992.
4
UOP Standard 1015-17, " Determination of trace
oxygenates in polymer grade ethylene and propylene
by gas chromatography mass spectrometry, "
Honeywell UOP, Des Plaines, Illinois, 2017, online:
https://www.astm.org/Standards/UOP1015.htm
5
UOP Standard 1021-19, " Determination of trace
methyl mercaptan, ethyl mercaptan, and isopropyl
disulfide in polymer grade ethylene and propylene
by gas chromatography mass spectrometry, "
Honeywell UOP, Des Plaines, Illinois, 2019, online:
https://www.astm.org/Standards/UOP1021.htm
6
UOP Standard 1022-18, " Determination of trace carbonyl
sulfide and hydrogen sulfide in polymer grade
ethylene and propylene by gas chromatography mass
spectrometry, " Honeywell UOP, Des Plaines, Illinois,
2018, online: https://www.astm.org/Standards/
UOP1022.htm
Complete Literature Cited available online at
www.HydrocarbonProcessing.com
JOHN WASSON is the Founder
and President of Wasson-ECE
Instrumentation. Beginning with the
industry's first gas autosampler in
1984 and continuing today with the
industry's first process GC delivering
lab-quality chromatography,
Mr. Wasson is a force for innovation in the field of gas
chromatography. An MS degree in analytical chemistry
from California Polytechnic Institute and early career
training at Carle Instruments and Hach provided a
strong foundation in GC fundamentals. Designing,
building and applicating more than 5,000 customized
instruments has given Mr. Wasson a depth of
expertise unparalleled in the specialty chemical and
hydrocarbon processing industries. He built WassonECE
from a " start-up " in a garage to a multi-national
company with offices in five countries.
A passion for analytical
instrumentation and a wealth of
troubleshooting and business skills
make THERESA RUSSELL a
valuable member of the Eclipse
Process GC team at Wasson-ECE
Instrumentation. Dr. Russell earned
FIG. 8. A screenshot of micro-convection oven performance.
84 SEPTEMBER 2021 | HydrocarbonProcessing.com
a PhD in biochemistry from Colorado State University
and has expertise in biomarker discovery using
tandem mass spectrometry (MS/MS). As a patentholding
research scientist, she has contributed 14
peer-reviewed publications to the body of scientific
knowledge in proteomics, infectious disease, cancer
and diagnostic development. At Wasson-ECE,
Dr. Russell contributes to the business side of science
with technical writing, product management,
business development and marketing.
https://commons.wikimedia.org/wiki/File:Quadrupole_ion_trajectory.svg https://commons.wikimedia.org/wiki/File:Quadrupole_ion_trajectory.svg https://commons.wikimedia.org/wiki/File:Quadrupole_ion_trajectory.svg https://www.astm.org/Standards/UOP1015.htm https://www.astm.org/Standards/UOP1021.htm https://www.astm.org/Standards/UOP1022.htm https://www.astm.org/Standards/UOP1022.htm http://www.HydrocarbonProcessing.com http://www.HydrocarbonProcessing.com
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