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.

methane ethane ethylene acetylene propane propylene isobutane n-butane 1-butene pentane isobutylene 1,3-butadiene 1-pentene trans-2-pentene cis-2-pentene 2-methyl butene-2 n-octane 80/100 Res-Sil™ C 20', 1/8" OD x 2mm ID, SilcoSmooth™ tubing (cat. # 80436) Oven temp.: 60°C Inj. temp.: 150°C Det. temp: 150°C FID Flow rate: 30mL/min. He Sample: refinery gas C1-C5 Sample size: 20µL Reference standard courtesy of DCG Partnerships Ltd. Pearland, TX.

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.

100 methane 200 ethane/ethylene 260 acetylene 300 propane 321 propylene 345 propadiene 386 isobutane 400 butane 422 1-butene 434 isobutylene/ trans- 2-butene 443 cis-2-butene 454 1,3-butadiene 488 isopentane 503 pentane/3- methyl- 1-butene 522 1-pentene 533 trans-2-pentene 540 cis-2-pentene 549 2-methyl- 2-butene OPN on Res-Sil™ C, 80/100 mesh, 12' x 2mm ID x 1/8" OD in SilcoSmooth™ tubing (cat.# 80437). 20µL on-column injection of refinery gas. Concentration: 0.1-6 absolute mole % Oven temp.: 50°C Inj. & det. temp.: 200°C Carrier gas: helium Flow rate: 30mL/min Reference standard courtesy of DCG Partnerships Ltd. Pearland, TX.

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.