A multidimensional gas chromatography method for the analysis of dissolved hydrogen sulfide in liquid crude oil samples is presented. A Deans switch is used to heart-cut light sulfur gases for separation on a secondary column and detection on a sulfur chemiluminescence detector.
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Method Article
Measurement of H2S in Crude Oil and Crude Oil Headspace Using Multidimensional Gas Chromatography, Deans Switching and Sulfur-selective Detection
In This Article
Summary
Abstract
A method for the analysis of dissolved hydrogen sulfide in crude oil samples is demonstrated using gas chromatography. In order to effectively eliminate interferences, a two dimensional column configuration is used, with a Deans switch employed to transfer hydrogen sulfide from the first to the second column (heart-cutting). Liquid crude samples are first separated on a dimethylpolysiloxane column, and light gases are heart-cut and further separated on a bonded porous layer open tubular (PLOT) column that is able to separate hydrogen sulfide from other light sulfur species. Hydrogen sulfide is then detected with a sulfur chemiluminescence detector, adding an additional layer of selectivity. Following separation and detection of hydrogen sulfide, the system is backflushed to remove the high-boiling hydrocarbons present in the crude samples and to preserve chromatographic integrity. Dissolved hydrogen sulfide has been quantified in liquid samples from 1.1 to 500 ppm, demonstrating wide applicability to a range of samples. The method has also been successfully applied for the analysis of gas samples from crude oil headspace and process gas bags, with measurement from 0.7 to 9,700 ppm hydrogen sulfide.
Introduction
Accurate analysis of crude oil is essential for the oil and gas industry, as health and safety regulations and economics are functions of oil quality. In order to protect transporters of crude samples, it is necessary to determine the properties of crude samples to develop safety regulations to be implemented in the event of a release or spill. In particular, quantification of hydrogen sulfide (H2S) is important, due to its high toxicity in the gas phase; exposures as low as 100 ppm can be fatal (http://www.cdc.gov/niosh/idlh/7783064.html)1,2. Dissolved H2S in crude samples is generally considered to be corrosive3,4, and can....
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Protocol
Caution: Please consult all relevant material safety data sheets (MSDS) for materials before using. In particular, CS2 is highly flammable and should be stored and handled appropriately. H2S gas is highly toxic, and any containers or gas bags containing H2S should not be opened or handled outside of a properly vented fumehood. Work with crude oil samples should only be done with full personal protective equipment (gloves, safety glasses, lab coat, pants and closed-toe shoes), and all crude samples should be opened, transferred and handled in a fumehood. Certified gas standards will be delivered from the manufacturer with an expiry date....
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Results
In order to obtain reliable quantification of H2S for both liquid and gas samples, proper calibration is necessary. For calibration injections and sample injections, the H2S peak should not be overlapping with neighboring peaks and should have a reproducible peak area. Figure 3 shows an injection of a gas sample where the gas is too concentrated for this method. It was found that gas concentrations of greater than 500 ppm using a 250 µl syringe overloaded the detector. This issue wa.......
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Discussion
In order to achieve optimum measurement of H2S, this method employs a Deans switch, backflushing and a sulfur chemiluminescence detector (SCD). A dimethylpolysiloxane column is used as the first dimension GC column, and serves to retard the movement of heavier hydrocarbons present in the sample so that they do not contaminate the PLOT column. This effect is enhanced by a cool (50 °C) initial separation. Light gases pass through the first dimension column and are captured by the PLOT column during the hear.......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
The authors would like to acknowledge support from the Government of Canada's interdepartmental Program of Energy Research and Development, PERD 113, Petroleum Conversion for Cleaner Air. N.E.H would like to acknowledge her Natural Sciences and Engineering Research Council of Canada Visiting Fellowship.
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Deans switch | Agilent | G2855A | Or equivalent flow switching device |
| Restrictor tubing | Agilent | 160-2615-10 | Fused silica, deactivated, 180 µm |
| HP-PONA column | Agilent | 19091S-001 | |
| GasPro column | Agilent | 113-4332 | |
| Sulfur chemiluminescence detector, 355 | Agilent/Sievers | G6603A | |
| H2S calibration standard, in He | Air Liquide | Custom order | 211 ppm H2S |
| CS2 | Fisher Scientific | C184-500 | |
| Toluene, HPLC grade | Fisher Scientific | T290-4 | |
| Gas bag, 2 L | Calibrated Instruments, Inc. | GSB-P/2 | Twist on/off nozzle |
| 250 µl gas tight syringe | Hamilton | 81130 | |
| 500 ml amber glass bottle | Scientific Specialties | N73616 | |
| Open top screw caps | Scientific Specialties | 169628 | |
| Tegrabond disc for screw caps | Chromatographic Specialties | C889125C | 25 mm, 10/90 MIL |
| 1 ml gas tight syringe | Hamilton | 81330 | |
| 2.5% H2S in He gas standard | Air Liquide | Custom order |
References
- Guidotti, T. L. Hydrogen sulphide. Occ. Med. 46, 367-371 (1996).
- Reiffenstein, R. J., Hulbert, W. C., Roth, S. H. Toxicology of Hydrogen Sulfide. Annu. Rev. Pharmacol. Toxicol. , 109-134 (1992).
- Qi, Y., et al.
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