Method

Gas Chromatograph

Chromatec-Kristall 5000/9000

Detector

Electron Capture Detector (ECD) or micro-ECD
Alternatively, a combination of a Mass Selective Detector (MSD) and an ECD

Column

BPX-90, 60 m × 0.25 mm × 0.25 µm, Cat. No. 054590

Column Backflushing

Partial column-backflush system

Additional Equipment

Gas fittings kit, Part No. 4.078.000
Filter 20.0 for catalytic removal of oxygen impurities from nitrogen

Method Description

Organochlorine compounds (OCCs) found in crude oil can be divided into three groups:

Chloride salts: Inorganic metal chlorides that are always present in formation fluids extracted together with crude oil during production.
Native organochlorine compounds: Naturally occurring OCCs concentrated mainly in the asphaltene and resin fractions of crude oil.
Volatile organochlorine compounds: Compounds such as chloroform, carbon tetrachloride, dichloroethane, trichloroethane, tetrachloroethane, benzyl chloride, and others.

Gas chromatography can specifically be used to monitor volatile organochlorine compounds. This group of compounds is not naturally present in crude oil. These chemicals may be added to enhance oil recovery or remove paraffin deposits.

Some OCCs may also form when particular components used in chemical reagents decompose at the high temperatures encountered during crude-oil distillation. One example is the formation of benzyl chloride through the decomposition of quaternary ammonium salts.

In their pure form, these compounds are highly stable, have low reactivity, and present no significant risk during pipeline transportation. However, they can cause serious problems during crude-oil processing. During distillation, hydrogen chloride may form through hydrolysis under high-temperature conditions or during catalytic hydrogen treatment. At significant OCC concentrations, processing equipment can be severely damaged within only a few days.

The harmful effects of OCC contamination first became a major issue in Russia in 2001, when their use in oil production was prohibited. The ban was lifted by an order of the Russian Ministry of Energy in 2012. In the spring of 2019, the well-known contamination incident involving the Druzhba pipeline and refineries in the Republic of Belarus resulted in catastrophic losses.

Organochlorine Compounds in Crude Oil and Chemical Reagents

GOST 33342-2015 is currently used in Russia for the analysis of organochlorine compounds in crude oil. This standard is essentially comparable to the international ASTM D4929 standard.

The GOST standard includes three analytical procedures:

Method A: Sodium biphenyl treatment followed by potentiometry
Method B: Combustion followed by coulometry
Method C: Wavelength-dispersive X-ray fluorescence (WDXRF) and monochromatic wavelength-dispersive X-ray fluorescence (MWDXRF)

The chromatographic method is not currently included in the GOST standard. Nevertheless, it offers several advantages over the other methods:

All the specified non-chromatographic methods require preliminary distillation. In addition to being time-consuming, this procedure may result in OCC losses because not all organochlorine compounds are transferred completely into the naphtha fraction. In practice, these methods determine the OCC content of the naphtha rather than that of the original crude oil.
If bromine or iodine is present in the naphtha, it may also be measured as chlorine, producing errors in Methods A and B—sodium biphenyl with potentiometry and combustion with coulometry.
Sulfur present in the sample interferes with Method B, which uses combustion and coulometry.
X-ray methods measure all forms of chlorine, including naturally occurring inorganic chloride salts.
All these non-chromatographic methods report only the total OCC concentration and cannot identify the individual compounds responsible for contaminating the crude oil.

The chromatographic method offers high sensitivity, starting from 0.1 ppm. It also determines the concentrations of individual OCCs and does not require preliminary sample distillation.

Two main analytical applications are currently relevant:

Analysis of OCCs in crude oil
Analysis of OCCs in chemical reagents

Both applications are complex and involve specific analytical challenges.

When analyzing crude oil, the method must cover the entire possible range of volatile organochlorine compounds while overcoming interference from the hydrocarbon matrix.

Reagent analysis presents different challenges. Solid reagents require appropriate extraction conditions, and the analysis must account for the possible formation of OCCs under the high-temperature and high-pressure conditions encountered during petroleum processing. Liquid reagents generally do not require extraction and can be injected directly into the vaporizing injector.

Both applications can be performed using the same chromatograph configuration. The ideal solution combines MSD and ECD detectors in a single system with an automatic sampler capable of serving both analytical channels.

The ECD is selective for organochlorine compounds, although its sensitivity varies significantly among individual compounds. Its sensitivity to unsaturated hydrocarbons is lower than its sensitivity to saturated hydrocarbons, with differences reaching several orders of magnitude. Sensitivity to chlorobenzene and chlorotoluene is approximately 100–1,000 times lower than sensitivity to carbon tetrachloride or chloroform.

A second analytical channel equipped with an MSD is therefore recommended for analyzing these compounds and for reliable qualitative identification. The MSD is particularly effective when analyzing reagents whose matrices consist of only a limited number of compounds. It provides high sensitivity to all organochlorine compounds.

Using ECD and MSD detectors together provides the greatest amount of analytical information, improved sensitivity, and faster analysis. A system equipped with a DAZh-2M 3D automatic sampler can be configured to inject the sample into both vaporizing injectors, producing results from two analytical channels in a single run.

When a validated analytical procedure is required, laboratories may contact the pioneers in this field—TomskNIPIneft, which developed MVI 223.0087/01.00258/2013—or use the method described by VNIINP researchers:

Podlesnova, E. V., Botin, A. A., Dmitrieva, A. A., Vartapetyan, A. R., & Leonteva, S. A. (2019). Chromatographic Determination of Organochlorine Compounds in Crude Oil. Sorption and Chromatographic Processes, 19(5), 581–587.

SvNIINP is also working on the development of analytical methods in this field.

Chromatec actively collaborates on chromatographic method development with specialized Russian research institutes and organizations that possess extensive experience in OCC analysis, including TomskNIPIneft, VNIINP, and the Neftepromkhim State Center for Standard Samples.

This cooperation ensures that results obtained using Chromatec-Kristall systems are scientifically justified and reliable.

References

Novikov, E. A. Determination of Chlorine in Crude Oil: A Review of Analytical Methods. The World of Petroleum Products, No. 1, 2020.

Sinyov, A. V., Devyashin, T. V., Kunakova, A. M., Saifutdinova, L. R., Usmanova, F. G., Krikun, A. N., & Lestev, A. E. Formation of Highly Volatile Organochlorine Compounds During Primary Crude-Oil Distillation as a Result of the Decomposition of Chemical Reagents Containing Quaternary Ammonium Salts. PROneft: Professional Insights into Oil, 2019, No. 4(14), pp. 63–69.

MVI 223.0087/01.00258/2013 — Crude Oil and Petroleum Products: Procedure for Measuring the Mass Fractions of Volatile Organochlorine Compounds—Carbon Tetrachloride, Tetrachloroethylene, and Benzyl Chloride—in Crude Oil and Petroleum Products by Gas–Liquid Chromatography. Certificate of Validation No. 223.0087/01.00258/2013, dated May 14, 2013. Rights holder: TomskNIPIneft.