App note-Detailed Hydrocarbon Analysis using ASTM method D6729 & D6729 Appendix X2
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Updated date
11 January 19
Title
App note-Detailed Hydrocarbon Analysis using ASTM method D6729 & D6729 Appendix X2
Keywords
DHA, hydrocarbon, ASTM, method, D6729, D6729, Appendix, X2, Article, Ed, Connor
Product Range
*None
Language
UK English
Company Brand
Peak Scientific
Extracted text
Your local gas generation partner
Detailed hydrocarbon analysis
(DHA) using ASTM method
D6729 & D6729 Appendix X2
www.peakscientific.com
Detailed hydrocarbon
analysis (DHA) using
ASTM method D6729
and D6729 appendix
X2.
Ed Connor Dr. Sc.
& Joaquin Lubkowitz PhD
Introduction
Detailed hydrocarbon analysis (DHA) is a
separation technique used by a variety of
laboratories involved in the petrochemical
industry for analysis and identification of
individual components as well as for bulk
hydrocarbon characterisation of a particular
sample. Bulk analysis looks at gasoline
composition in terms of PONA components
(Paraffins, Olefins, Naphthalenes and Aromatics)
and other fuels in the C1-C13 range since this gives
an indication of overall quality of the sample.
The analysis of gasoline for spark ignition
components is essential for quality control.
Owing to the complex nature of gasoline samples,
good resolution between eluents is required and
therefore a long column is used (typically 100m).
Several methods are routinely
used for DHA which differ in their oven
temperature ramp rates or in the length of
column used. Each method has its advantages
and disadvantages since some improve peak
resolution of low boiling compounds whereas
others provide better resolution of heavier
compounds at the end of the chromatogram.
The complex nature of the methodology coupled
with the use of such a long column
means that run times can easily exceed 120
minutes when using helium carrier gas. However,
the use of hydrogen can vastly increase run rates
because of its efficiency
at higher linear velocities. This is a particularly
attractive prospect for oil analysis laboratories
since faster throughput of sample means
increased profitability. The benefits of using
hydrogen in terms of improved chromatography
combined with the increasing cost of helium
along with supply issues means that laboratories
switching from helium to hydrogen can become
much more profitable whilst maintaining
standards of analysis that conform to industry
standards.
This application note demonstrates a comparison
of gasoline analysis using helium carrier gas
following ASTM method D67291 and the use of
unfiltered hydrogen carrier
gas produced by a Peak Scientific Precision Trace
hydrogen generator in DHA following ASTM
method D6729 appendix X22 and demonstrates
the improvement in run time whilst maintaining
crucial separations between certain components.
Results & Discussion
Detailed hydrocarbon analysis of gasoline showed
that the elution time of the last compound in the
mixture, n-Pentadecane, could be reduced from
125 minutes to less than 74 minutes by switching
carrier gas from helium to hydrogen (figure 1).
Despite the difference in analysis times, the PONA
analysis showed that quantitative differences
were not significantly different when using either
carrier gas (table 1).
Despite the much higher carrier gas flow
rates when using hydrogen carrier gas, critical
separations were still achieved in most cases and
in certain cases were even improved. Separation
of 1-methylcyclopentene and benzene, which
is highly regulated analysis because of the
importance of the benzene fraction, was actually
improved when using hydrogen carrier gas despite
the quicker elution times of the compounds with
hydrogen as a carrier gas (figure 2). Separation
of Toluene and 2,3,3-Trimethylpentane was
achieved using helium whereas with hydrogen
the two compounds co-eluted (figure 3). To
separate these two compounds using hydrogen
carrier gas some improvements to the method
would
need to be made. Separation of Tridecane and
1-methylnaphthalene was achieved equally well
using both carrier gases (figure 4).
The results of the DHA show that the use of
hydrogen as a carrier gas, following ASTM
D6729 appendix 2 methodology can vastly
reduce analysis times for gasoline analysis whilst
providing the necessary resolution required for
separations of critical components.
References
1.
Designation D 6729-01 Standard Test Method for
Determination of Individual Components in Spark Ignition
Engine Fuels by 100 Meter Capillary High Resolution Gas
Chromatography. ASTM International 2002.
2.
Designation D6729 – 01 Appendix X2. Hydrocarbon
data using hydrogen carrier. ASTM International 2004.
Carrier Gas
Hydrogen
Helium
Carrier gas
Peak Scientific
Precision 500
hydrogen generator
Cylinder helium from
Airgas (99.999%).
Eluent
Gasoline
Gasoline
Injector Temperature
280
280
Injection volume
0.2
0.2
Split Ratio
250:1
250:1
Column
100%
imethylpolysolixane,
100 m, 0.25 mm,
0.5 μm film
thickness (J&W)
100%
imethylpolysolixane,
100 m, 0.25 mm,
0.5 μm film
thickness (J&W)
Column flow
2.5 mL/min
1.8 mL/min
Oven Initial
Temperature
35 °C (7.70 min hold)
35 °C (13 min hold)
Oven ramp 1
17 °C/min to 45 °C
(8.80 min hold)
10 °C/min to 45 °C
(15 min hold)
Oven ramp 2
1.7 °C/min to 60 °C
(8.80 min hold)
1 °C/min to 60 °C
Oven ramp 3
3.39 °C/min to 220
°C (2.92 min hold)
Gas chromatograph
Agilent 7890A
Agilent 7890A
Detector
FID
FID
Method
ASTM D6729
Appendix 2
ASTM D6729
Analysis software
Hydrocarbon Expert
5.10 (Separation
systems)
Hydrocarbon Expert
5.10 (Separation
systems)
Figure 1. Comparison of DHA of total gasoline sample using
hydrogen and helium.
(15 min hold)
2 °C/min to 220 °C
(5 min hold)
Group %
Weight %
Weight
Difference
Paraffin
10.990
10.749
Figure 2. Comparison of separation of 1-methylcyclopentene and
benzene when using hydrogen and helium as carrier gas.
0.241
I-Paraffins
31.846
31.795
0.051
Aromatics
42.605
42.953
-0.348
Mono-Aromatics
40.211
40.466
-0.255
Naphthalenes
1.090
1.133
-0.043
Indanes
0.731
0.755
-0.024
Indenes
0.573
0.600
-0.027
Naphthenes
4.676
4.926
-0.249
Mono-Naphthenes
4.676
4.926
-0.249
Di/Bicyclo-Naphthenes
0.000
0.000
Figure 3. Comparison of separation of Toluene and
2,3,3-Trimethylpentane when using hydrogen and helium as carrier gas.
0.000
Olefins
9.835
9.455
0.381
n-Olefins
3.258
2.947
0.311
Iso-Olefins
5.683
5.676
0.007
Naphtheno-Olefins
0.869
0.784
0.085
Di-Olefins
0.026
0.047
-0.021
Oxygenates
0.000
0.000
0.000
Unidentified
0.047
0.122
-0.075
Plus
0.000
0.000
0.000
Total
100.000
100.000
Figure 4. Comparison of separation of Tridecane and
1-methylnaphthalene when using hydrogen and helium as carrier gas.
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