petroleum& petrochemicals
Applications
note
Restek Corporation • (800) 356-1688 • (814) 353-1300 •
petroleum&petrochemicals
AHigh-TemperaturePolydimethylsiloxane-PhaseColumn for
ASTMD-6352-98SimulatedDistillationAnalyses:MXT
®
1HTSimDist
#59479
Stable to 430ºC.
Low bleed.
Long lifetime at high temperatures.
Symmetrical hydrocarbon peaks.
Consistent resolution and retention times.
Boiling point elution of hydrocarbons.
Polarity equivalent to existing liquid phases.
Simulated distillation perASTMD-6352-98 is used for determin-
ing the boiling point range distribution of petroleum distillate frac-
tionswith initial boiling points (BP) > 174ºC and final boiling
points < 700ºC at atmospheric pressure. High temperature SimDist
presentsmany challenges. The stationary phasemust meet rigid
resolution and retention time requirements, yet be stable at high
temperatures. Further, the polyimide protective coating on the
outer surface ofmost capillary columns has amaximumworking
temperature of about 380ºC.Above this temperature the polyimide
rapidly deteriorates.When repeatedly programmed to temperatures
above 400ºC, or allowed to cool below 50ºC, the aluminum sheath
onmost aluminum-clad fused silica columns separates from the
underlying fused silica surface. The tubing becomes extremely
brittle, and column lifetime is significantly shortened.
To conform to the critical criteria set forth byASTM, Restek
chemists have developed theMXT
®
1HTSimDist simulated distil-
lation column. TheMXT
®
1HTpolymer is a 100% polydimethyl-
siloxane (PDMS)material that is thermally stable to 430ºC,
requiresminimal conditioning, and is 100% crosslinked. The
MXT
®
1HTphase is coated onto highly deactivated stainless steel
tubing that has the inertness of fused silicawithout the temperature
limitations. TheMXT
®
1HTSimDist column has a lifetime of at
least 400 injections under typical SimDist conditions.
To demonstrate the robustness ofMXT
®
1HTSimDist columns,
wemade a series of 400 injections of Polywax
®
1000 (cold on-col-
umn, CS2 solvent, 1µLeach) onto a randomly chosen column, and
monitored critical performance characteristics over the course of
these injections: resolution, retention times, stationary phase bleed.
Figure 1 illustrates the Polywax
®
1000 analysis after 400 injec-
tions. The hydrocarbon components still arewell resolved and are
easily quantified. Figure 2 plots the reproducibility of C50/C52
resolution and Figure 3 shows retention time reproducibility.After
400 injections, both of these critical characteristics still meet simu-
lated distillation specifications. Figure 4 plots the consistently low
bleed at 430ºC over the series of 400 injections.
The stainless steel tubing used tomakeMXT
®
1HTSimDist
columns incorporates state-of-the-art Sulfinert™ deactivation. The
deactivation layer is incorporated into the framework of atoms on
the tubing surface, and thereforewill not fracture or flake off, even
if the column is flexed or bent.MXT
®
1HTSimDist columns do
not exhibit higher selectivity toward aromatics than toward normal
hydrocarbons, thus they provide true boiling point values.
Figure 1
Polywax
®
1000 hydrocarbonswell resolved on an
MXT
®
1HT SimDist column after 400 injections.
Figure 2
C50/C52 resolution is stable over a series of 400
injections on anMXT
®
1HT SimDist column.
5
10
15
20
25
30
35
40
C50
C100
4
3
2
1
0
400
350
300
250
200
150
100
50
0
ColumnResolution
5
Cycle #
C52RetentionTime (minutes)
30
29
28
27
26
25
24
23
22
21
20
200
150
100
50
0
250 300 350 400
Cycle #
Figure 3
C52 retention shows little change after 400 injections
on anMXT
®
1HT SimDist column.
