Analysis of Impurities in Ethylene by ASTM D6159-97
Ethylene is one of the highest volume chemicals produced in the world with global production exceeding 100 million metric tons annually. Ethylene is primarily used in the manufacture of polyethylene, ethylene oxide, and ethylene dichloride as well as many other lower volume products. Most of these production processes use various catalysts to improve product quality and process yield. Impurities in ethylene can damage the catalysts, resulting in significant replacement costs, reduced product quality, process downtime, and decreased yield.
Ethylene is typically manufactured through the use of steam cracking. In this process, gaseous or light liquid hydrocarbons are combined with steam and heated to 750–950 °C in a pyrolysis furnace. Numerous free radical reactions are initiated, and larger hydrocarbons are converted (cracked) into smaller hydrocarbons. The high temperatures used in steam cracking promote the formation of unsaturated or olefinic compounds like ethylene. Ethylene feedstocks must be tested to ensure that only high-purity ethylene is delivered for subsequent chemical processing.
Testing typically follows ASTM D6159-97, a GC/FID method that employs a two-column configuration consisting of an alumina PLOT column with KCl deactivation (50 m x 0.53 mm ID) coupled to a methyl silicone column (30 m x 0.53 mm ID x 5.0 μm df).
Figure 1: Methane and ethane are well resolved in high-purity ethylene samples.

Column | See notes. |
---|---|
Standard/Sample | Ethylene gas |
Injection | |
Inj. Vol.: | 1.0 µL split |
Liner: | 2mm Splitless |
Inj. Temp.: | 200 °C |
Split Vent Flow Rate: | 60 mL/min. |
Oven | |
Oven Temp.: | 35 °C (hold 2 min) to 190 °C at 4 °C/min (hold 15 min) |
Carrier Gas | He, constant pressure (8.0 psi, 55.2 kPa) |
Linear Velocity: | 25.4 cm/sec @ 35 °C |
Detector | FID @ 200 °C |
---|---|
Make-up Gas Type: | N2 |
Data Rate: | 20 Hz |
Instrument | HP5890 GC |
Notes | GC liner cat.# 20712 was used to produce this chromatogram, but it has since been discontinued. We recommend GC liner cat.# 20713 as an alternative. Rt-Alumina BOND/KCl, 50 m, 0.53 mm ID, 10.0 µm (cat.# 19760) in series with Rtx-1, 30 m, 0.53 mm ID, 5.0 µm (cat.# 10179), connected with a Universal Press-Tight Connector (cat.# 20401) |
Samples of high-purity ethylene typically contain only two minor impurities, methane and ethane, which can be detected in low ppmv concentrations (Figure 1). However, steam cracking can also produce higher molecular weight hydrocarbons, especially when propane, butane, or light liquid hydrocarbons are used as starting materials. Although fractionation is used in the final production stages to produce a high-purity ethylene product, it is still important to be able to identify and quantify any other hydrocarbons present in an ethylene sample. Achieving sufficient resolution of all of these compounds can be challenging due to their similarities in boiling point and chemical structure. ASTM D6159-97 addresses this issue by combining the separation power of two different types of capillary columns.
The Rt-Alumina BOND/KCl PLOT column has excellent separation capabilities for low molecular weight hydrocarbons ranging from C1 through C12, but complete resolution of all compounds is not always possible depending on the conditions that are employed. Figure 2 shows the analysis of an ethylene sample that has been spiked with the typical hydrocarbons that may be present after ethylene production. When using the temperature conditions supplied in the method, there are coelutions between three different peak pairs. Acetylene and isobutane (peaks 7 and 8) elute at the same retention time; propadiene and n-butane (peaks 9 and 10) are only partially resolved; and there is a complete coelution between methyl acetylene and n-pentane (peaks 16 and 17).
Figure 2: Analyzing ethylene on an alumina column alone results in coelutions that prevent quantification of several impurities.

Peaks | |
---|---|
1. | Methane |
2. | Ethane |
3. | Ethylene |
4. | Propane |
5. | Cyclopropane |
6. | Propylene |
7. | Acetylene |
8. | Isobutane |
9. | Propadiene |
Peaks | |
---|---|
10. | n-Butane |
11. | trans-2-Butene |
12. | 1-Butene |
13. | Isobutylene |
14. | cis-2-Butene |
15. | Isopentane |
16. | Methylacetylene |
17. | n-Pentane |
18. | 1,3-Butadiene |
Column | Rt®-Alumina BOND/KCl, 50 m, 0.53 mm ID, 10 µm (cat.# 19760) |
---|---|
Standard/Sample | ethylene gas plus C1-C5 hydrocarbons |
Injection | |
Inj. Vol.: | 1 µL split |
Liner: | 2mm Splitless |
Inj. Temp.: | 200 °C |
Split Vent Flow Rate: | 60 mL/min. |
Oven | |
Oven Temp.: | 35 °C (hold 2 min) to 190 °C at 4 °C/min (hold 15 min) |
Carrier Gas | He, constant pressure (5.0 psi, 34.5 kPa) |
Linear Velocity: | 25 cm/sec @ 35 °C |
Detector | FID @ 200 °C |
---|---|
Make-up Gas Type: | N2 |
Data Rate: | 20 Hz |
Instrument | HP5890 GC |
Notes | GC liner cat.# 20712 was used to produce this chromatogram, but it has since been discontinued. We recommend GC liner cat.# 20713 as an alternative. |
By combining an Rt-Alumina BOND/KCl column with an Rtx-1 column, complete resolution for all of the compounds of interest can be achieved. The Rtx-1 column supplements the separation achieved on the Rt-Alumina BOND/KCl column by contributing additional selective retention of less polar compounds like isobutane, n-butane, and n-pentane. The extra retention of these compounds allows for the complete separation of the slightly more polar compounds like acetylene, propadiene, and methyl acetylene. Figure 3 shows the analysis of the same ethylene sample spiked with hydrocarbons. All of the compounds that are identified in the method can now be resolved for accurate identification and quantitation.
Figure 3: All impurities are fully resolved and easily quantifiable when using an Rt-Alumina BOND/KCl column coupled to an Rtx-1 column.

Peaks | |
---|---|
1. | Methane |
2. | Ethane |
3. | Ethylene |
4. | Propane |
5. | Cyclopropane |
6. | Propylene |
7. | Acetylene |
8. | Isobutane |
9. | Propadiene |
Peaks | |
---|---|
10. | n-Butane |
11. | trans-2-Butene |
12. | 1-Butene |
13. | Isobutylene |
14. | cis-2-Butene |
15. | iso-Pentane |
16. | Methylacetylene |
17. | n-Pentane |
18. | 1,3-Butadiene |
Column | Rt-Alumina BOND/KCl *, 50 m, 0.53 mm ID, 10 µm (cat.# 19760) |
---|---|
Standard/Sample | Ethylene gas plus C1 through C5 hydrocarbons |
Injection | |
Inj. Vol.: | 1 µL split |
Liner: | 2 mm splitless |
Inj. Temp.: | 200 °C |
Split Vent Flow Rate: | 60 ml/min. |
Oven | |
Oven Temp.: | 35 °C (hold 2 min) to 190 °C at 4 °C/min (hold 15 min) |
Carrier Gas | He, constant pressure (8.0 psi, 55.2 kPa) |
Linear Velocity: | 25.4 cm/sec @ 35 °C |
Detector | FID @ 200 °C |
---|---|
Make-up Gas Type: | N2 |
Data Rate: | 20 Hz |
Instrument | HP5890 GC |
Notes | GC liner cat.# 20712 was used to produce this chromatogram, but it has since been discontinued. We recommend GC liner cat.# 20713 as an alternative. * Rt-Alumina BOND/KCl, 50 m, 0.53 mm ID, 10.0 μm (cat.# 19760) in series with an Rtx-1, 30 m, 0.53 mm ID, 5.0 μm (cat.# 10179) connected using a universal Press-Tight connector (cat. # 20401). (conditions as per ASTM D6159-97) |
When testing for impurities in ethylene using ASTM D6159-97, the combination of an Rt-Alumina BOND/KCl column coupled to an Rtx-1 column provides the best resolution of the most common hydrocarbon contaminants. Restek PLOT columns are manufactured using a new technology that significantly reduces particle release, extending column lifetime and giving highly reproducible retention times. Restek columns provide reliable results that can be used to protect expensive catalysts, make faster process adjustments, and improve product yield.