Chromatographic method for determining organochlorine compounds in oil

Abstract

Chlorine is present in the oil in the form of chloride salts, quite effectively removed at the stage of
oil preparation, and in small quantities in the form of organochlorine compounds (HOS). HOS is practically
not removed from oil at the stage of its preparation, which represents a serious danger to refining processes.
Organic chlorine can form hydrochloric acid, which causes corrosion and destruction of equipment, and also
leads to the formation of ammonium chloride in the form of deposits that disrupt the operation of heat exchange
equipment.
In the 2000s. at a number of refineries in Russia, there were cases of emergency shutdowns of hydrotreating
units for raw materials of the reforming unit, caused by volatile HOS added during the oil production
stage. The use of HOS in the process of extraction, transportation and oil processing is unacceptable, as
the traditional technology of oil treatment at ELOU does not ensure their removal, and the damage from their
presence during oil refining is significant. Therefore, in Russian State standard 51858 “Oil. General technical
conditions "standards were introduced on the content of organic chlorides in the fraction boiling up to 204 °
C.
Standard methods for the determination of organochlorine compounds specified in Russian State
standard 52247-2004 have a few significant drawbacks: the loss of light HOS during distillation, the inability
to determine the qualitative composition of the compounds present, and hence the determination of their
source.
A perspective method for the determination of HOS in oil is the method of gas chromatography with
an electron capture detector (ECD). In developing the method of determination, in order to obtain more reliable results, the test substances were divided into two groups, which should be determined with different modes
of chromatography. The first group includes carbon tetrachloromethane, trichloromethane, dichloromethane,
1,2-dichloroethane, tetrachloroethene, trichloroethene, hexachloroethane, 1,1,1,2- tetrachloroethane.
The second group includes сhloronaphthalene, 1,1,2,2- tetrachloroethane. The detection limit of the method
for HOS 1 group is 0.1 ppm, for HOS 2 groups - 0.3 ppm. When preparing calibration samples, reference
isooctane was chosen as a solvent.
As a result of testing model and real samples of oils containing HOS in various concentrations, indicators
of the precision of the developed method were determined. A comparison was also made of the accuracy
indicators of the developed method with the existing standard methods for the determination of HOS. As
can be seen from the obtained data, the developed method has a lower detection limit and better precision
indicators than existing methods, which makes it possible to determine lower concentrations with high accuracy