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Res-Sil C Bonded GC Packings for Analyses of Light Hydrocarbons

by Barry Burger, Petroleum Innovations Chemist

Bonded silica packings are the petrochemical industry’s number one choice for analyses of C1 to C5 hydrocarbons. These phases are prepared by covalently attaching an n-octane or cyanopropyl (OPN) functional group to the silicon atom. In the past, bonded silica packing materials — the Durapak materials (® Waters Associates, Inc) — were not reproducible and were limited in availability. Our synthesis chemist developed a material to replace the Durapak materials, and Restek has been making high quality, consistent Res-Sil C material for almost 10 years.

Our n-Octane on Res-Sil C packing is a direct replacement for n-Octane on Porasil C (® Waters Associates, Inc), and provides excellent separations of volatile hydrocarbons in petroleum and petrochemical products. Bonding n-octane to a specific silica gel surface produces a unique stationary phase for gas chromatography. Although this phase most commonly is used for process GC, many applications are suitable for laboratory analysis, such as C1 to C5 light hydrocarbons (Figure 1). The most prominent use for this column is the resolution of the C4 hydrocarbons. Separation of saturated and unsaturated C4 hydrocarbons is difficult, regardless of the packing material used. The most difficult compound pair, isobutylene and butane-1, is well resolved on n-Octane on Res-Sil C packing. Other packings exhibit poor reproducibility, or cannot tolerate temperatures above 100°C, which are needed to effect the separation.


Figure 1  n-Octane on Res-Sil C packing has unique selectivity for unsaturated light hydrocarbons.

Peaks
1.Methane
2.Ethane
3.Ethylene
4.Acetylene
5.Propane
6.Propylene
7.Isobutane
8.n-Butane
Peaks
9.1-Butene
10.Pentane
11.Isobutylene
12.1,3-Butadiene
13.1-Pentene
14.trans-2-Pentene
15.cis-2-Pentene
16.2-methylbutene-2
Refinery Gas C1 to C5 Using n-Octane on Res-Sil C Packing
GC_PC00372
Columnn-Octane, 80/100 mesh on Res-Sil C, SilcoSmooth Tubing, 20 ft., 1/8 in. OD, 2 mm ID (cat.# 80436-800)
SampleRefinery gas C1-C5
Injection
Inj. Vol.:20 µL packed not on-column
Inj. Temp.:150 °C
Oven
Oven Temp.:60 °C
Carrier GasHe, constant flow
Flow Rate:30 mL/min
DetectorFID @ 150 °C

C1 to C5 hydrocarbons can be determined rapidly by using an OPN on Res-Sil C packed column (Figure 2). Other column configurations, and the conditions they require, can take up to two times longer to elute 2-methyl-2-butene. Figure 2 demonstrates the baseline separation of the most difficult compound pair in this analysis, cis-2-butene and 1,3-butadiene. When combined in series with other columns, the unique selectivity of the OPN on Res-Sil C column provides petroleum and petrochemical method developers with a powerful tool for fast determination of light hydrocarbons.

Figure 2  OPN on Res-Sil C packing resolves cis-2-butene and 1,3-butadiene to baseline.

PeaksRetention Indices
1.Methane100
2.Ethane/ethylene200
3.Acetylene260
4.Propane300
5.Propylene321
6.Propadiene345
7.Isobutane386
8.Butane400
9.1-Butene422
PeaksRetention Indices
10.Isobutylene/trans-2-butene434
11.cis-2-Butene443
12.1,3-Butadiene454
13.Isopentane488
14.Pentane/3-methyl-1-butene503
15.1-Pentene522
16.trans-2-Pentene533
17.cis-2-Pentene540
18.2-Methyl-2-butene549
Refinery Gas Using OPN on Res-Sil C Packing
GC_PC00373
ColumnOPN, 80/100 mesh on Res-Sil C packing, SilcoSmooth tubing, 12 ft., 1/8 in. OD, 2 mm ID (cat.# 80437-800)
SampleRefinery gas
Conc.:0.1-6 absolute mole %
Injection
Inj. Vol.:20 µL packed on-column
Inj. Temp.:200 °C
Oven
Oven Temp.:50 °C
Carrier GasHe, constant flow
Flow Rate:30 mL/min
DetectorFID @ 200 °C
AcknowledgementStandard courtesy of AC Analytical Controls

Because our Res-Sil C based packings are bonded, they need only minimal conditioning time, and offer lower bleed and longer lifetimes, compared to non-bonded phases used for these analyses. These performance characteristics are especially important for process GC, in which reliability and maintenance-free operation are critical. Laboratory GC systems using multiple columns with valve switching also benefit from the stability of our bonded phases.

In addition to n-octane and OPN on Res-Sil C, Restek offers a wide variety of other bonded packings for packed and micropacked GC columns, including Rtx-1, Stabilwax phases, and Carbowax phases. Each of these low-bleed, long-lifetime packings has a conditioning time of less than 30 minutes, and assures consistent batch-to-batch reproducibility. Every lot of Restek bonded phase packings is tested for bleed and efficiency, and for retention index and retention time reproducibility. In addition, we offer a full range of packed and micropacked columns, available in specially deactivated Silcosteel tubing, for improved inertness and efficiency.

If you are performing light hydrocarbon analyses, and are concerned about column bleed, column lifetime, and reproducibility of your data, we highly recommend these columns to you.

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