ASTM D4045 Test Method for Sulfur in Petroleum Products
ASTM D4045 Standard Test Method for Sulfur in Petroleum Products by Hydrogenolysis and Rateometric Colorimetry
5. Apparatus
5.1 Pyrolysis Furnace - A furnace that can provide an adjustable temperature from 900 to 1400°C in a 5-mm inside diameter or larger tube is required to pyrolyze the sample. The furnace entry temperature shall allow insertion of the hypodermic tip to a depth at which the temperature is 550°C to provide sample vaporization at the injection syringe tip. This temperature shall be above the boiling point of the sample and of the sulfur compounds in the sample (see Fig. 1). The pyrolyzer tube may be of quartz; however, the lifetime is limited above 1250°C. Ceramic may be used at any temperature.
5.2 Rateometric H2S Readout - Hydrogenolysis products contain H2S in proportion to sulfur in the sample. The H2S is measured by measuring rate of change of reflectance caused by darkening when lead sulfide is formed. Rateometric electronics, adapted to provide a first derivative output, allows sufficient sensitivity to measure below 0.1 mg/L (see Fig. 2).
5.3 Hypodermic Syringe - A hypodermic having a needle long enough to reach the 550°C zone is required. A side port is convenient for vacuum filling and for flushing the syringe. A 100-µL syringe is satisfactory for injection rates down to 3 µL/min and a 25-µL syringe for lower rates. (Warning - Exercise caution as hypodermics can cause accidental injury.)
5.4 Syringe Injection Drive - The drive shall provide uniform, continuous sample injections. Variation in drive injection rate caused by mechanical irregularities of gears will cause noise. The adjustable drive shall be capable of injection from 6 µL/min to 0.06 µL/min over a 6-min interval.
5.5 Recorder - A chart recorder with 10-V full scale and 10 000-V input or greater and having a chart speed of 0.2 to 1 in./min (approximately 0.5 to 3 cm/min) is required. An attenuator can be used for more sensitive recorders. Newer instruments that display the results are acceptable in lieu of a chart recorder.
5.6 Thermocouple - A thermocouple suitable for use at 500 to 1400°C, 250-mm long with readout is required. Type K, 1/16-in. (1.6-mm) diameter, Type 316 stainless steel sheath is suitable.
6. Reagents and Materials
6.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
6.2 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean Type II reagent grade water conforming to Specification D1193.
6.3 Sensing Tape - Lead acetate impregnated paper of chromatographic quality shall be used. (Warning - Lead is a cumulative poison.)
6.4 Hydrogen - As no commercial grade of hydrogen has a sulfur specification sufficiently low, each new source of supply must be tested. A change in the zero base line of 5 % of full scale from no flow to full flow indicates impure hydrogen. (Warning - Extremely flammable gas under pressure. Hydrogen is a flammable gas. Test all flow systems for leaks and purge with inert gas before introducing hydrogen and after removing hydrogen. Keep all flow systems as small in volume as practical and provide protective screening for containers other than sample flow lines. Dispose of exhaust gases in a fume hood or by vacuuming to a safe area. If gas cylinders are used handle carefully as rupture of the valve or cylinder is dangerous.)
6.5 Reference Standards:
6.5.1 2,2,4 Trimethyl Pentane (Isooctane) - (Warning - Extremely flammable.)
6.5.1.1 ASTM Knock Test Reference Fuel may be used as the solvent. However, when this material is used, each new lot shall be tested for sulfur by this procedure because the specifications are not rigorous enough for this application.
NOTE 1 - Heptane or equivalent material may also be used but precision data is based on the use of isooctane.
6.6 Acetic Acid Solution - Mix glacial acetic acid 1 part by volume into 19 parts water (see 6.2). (Warning - Corrosive.)
6.7 Di-n-Butyl Sulfide - (CH3CH 2CH2CH2)2S) is used to prepare standards. Equivalent sulfur compound may be used if care is exercised to prevent more volatile compounds from evaporating during preparation or use of standards.
6.8 Helium or Nitrogen Purge Gas. (Warning - Compressed gas under high pressure.)
