نفت و گاز

تعیین سولفید هیدروژن و مرکاپتان‌ها در نفت مطابق با استانداردهای GOST R 50802 و GOST 32918

Method

Gas Chromatograph

Kristall 2000M or Chromatec-Kristall 5000/9000

Detector

Flame Photometric Detector (FPD)

Capillary Column

BP-5 column, 30 m × 0.53 mm × 5.0 µm

Sample Inlet

Capillary vaporizing injector

Forward/backflush system for the capillary column

Additional Equipment

  • Ultra-high-purity hydrogen generator

  • Air compressor

  • Gas fittings kit, Part No. 4.078.000

  • Certified mixtures of sulfur-containing compounds (SCCs) for chromatograph calibration

  • Tee fitting with a filter for collecting gas samples from a gas stream using a syringe

  • Gas sample injection syringes for calibration

  • Crude oil sample injection syringes

Sampling Devices

  • PGO-50 aluminum samplers

  • Containers compliant with GOST 24676

Method Description

Gas chromatography is commonly used to determine hydrogen sulfide, methyl mercaptan, and ethyl mercaptan in crude oil. Hydrogen sulfide and mercaptans are highly reactive and can cause severe corrosion of storage tanks, vessels, tank cars, and pipelines.

Hydrogen sulfide is also highly toxic, and exposure to high H₂S concentrations can be fatal. The maximum permissible concentration in air is 10 mg/m³. Determining and monitoring hydrogen sulfide and mercaptans in crude oil and petroleum products is therefore essential.

According to GOST R 50802 and GOST 32918, hydrogen sulfide, methyl mercaptan, and ethyl mercaptan can be determined in crude oil and petroleum products over a concentration range of 1.0–300 ppm. This range can be extended by diluting the sample with a sulfur-free solvent.

GOST R 50802 specifies the use of a packed column; however, producing a column with the required characteristics is extremely difficult in practice. The best results are obtained using an 11 m × 2 mm Sulfinert packed column containing 12% polyphenyl ether and 0.5% H₃PO₄ on 60/80 Chromosorb T, manufactured by Restek. However, its long delivery time and high cost make it an uneconomical option.

Capillary columns provide the required separation, offer good inertness toward the corrosive effects of hydrogen sulfide, and are considerably less expensive than the packed columns used for this application. The revised GOST 32918-2014 standard describes both packed and capillary columns. Chromatec offers the CR-5 column, 30 m × 0.53 mm × 5.0 µm, Cat. No. 6.903.859.

Stable operation of the chromatographic system in this analysis requires regular replacement of the liner packing and the use of column forward/backflushing. Otherwise, heavy components contaminate the system, impair column separation, and reduce detector sensitivity.

PGO-50 aluminum samplers, designed specifically for this application, are recommended for sample collection. Aluminum is more inert toward hydrogen sulfide than untreated stainless steel samplers. Chromatec PGO-50 aluminum samplers feature a side fitting with a septum for syringe sampling, helping prevent the loss of volatile hydrogen sulfide.

GOST R 50802 and GOST 32918 state that the method may also be applied to gas condensates, light hydrocarbon fractions, and natural and petroleum gases intended for automotive, industrial, utility, and domestic applications. Consequently, some laboratories attempt to use these methods to determine hydrogen sulfide, methyl mercaptan, and ethyl mercaptan in liquefied gas samples.

Unfortunately, the method does not describe a procedure for introducing pressurized liquefied gas samples, nor does it provide a calibration procedure. It also fails to account for the specific composition of liquefied gas samples, whose main components are generally propane, n-butane, and isobutane. As a result, the columns recommended by the method do not provide adequate separation of sulfur-containing compounds from hydrocarbons.

Chromatographs configured strictly in accordance with GOST R 50802 and GOST 32918 cannot be used to analyze liquefied gas samples. For monitoring sulfur-containing compounds in liquefied petroleum gases, it is more appropriate to use specially developed methods, such as:

  • GOST R 57038-2016, identical to ASTM D5623-94 (2014)

  • ASTM D5504

Both methods use a sulfur chemiluminescence detector (SCD).

Other applicable methods include:

  • ASTM D6228, using a pulsed flame photometric detector (PFPD)

  • The VNIIUS method for analyzing sulfur-containing compounds in liquefied hydrocarbon gases, using a flame photometric detector (FPD)

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