Petroleum gas sampling

Simple evaporation tests in conjunction with vapor pressure measurement give a further guide to composition. In these tests a liquefied petroleum gas sample is allowed to evaporate naturally from an open graduated vessel. Results are recorded on the basis of volume and temperature changes, such as the temperature recorded when 95% has evaporated or the volume left at a particular temperature (ASTM D1837). 

Since dew point can be calculated from composition, direct determination of dew point for a particular hquefied petroleum gas sample is a measure of composition. It is, of course, of more direct practical value, and if small quantities of higher-molecular-weight material are present, it is preferable to use a direct... 

Total sulfur in gas can be determined by combustion (ASTM D-1072), by the lamp method (ASTM D-1266), or by hydrogenation (ASTM D-3031, ASTM D-4468). Trace total organic and bound nitrogen is determined (ASTM D-4629). The current test method for heavy residues in liquefied petroleum gas (ASTM D-2158) involves evaporation of a liquefied petroleum gas sample, measuring the volume of residue and observing the residue for oil stain on a piece of filter paper. 

Figure 10.387 Combustion 1C of a liquefied conductivity injection volume 100 (iL sample petroleum gas sample. Separator column Ion- LPG peaks 15 mg/L fluoride (1), 0.02 mg/L Pac AS11 -HC column dimensions 250 mm x chloride (2), 3 mg/L S as sulfate (3), and 2 mg/L...

Although gas chromatography can give the concentration of each component in a petroleum gas or gasoline sample, the same cannot be said for heavier cuts and one has to be satisfied with analyses by chemical family, by carbon atom distribution, or by representing the sample as a whole by an average molecule. 

Petroleum group analyses are conducted to determine amounts of the petroleum compound classes (e.g., saturates, aromatics, and polars/resins) present in petroleum-contaminated samples. This type of measurement is sometimes used to identify fuel type or to track plumes. It may be particularly useful for higher-boiling products such as asphalt. Group-type test methods include multidimensional gas chromatography (not often used for environmental samples), high-performance... 

Currently, the preferred method for the analysis of liquefied petroleum gas, and indeed for most petroleum-related gases, is gas chromatography (ASTM D2163 IP 264). This technique can be used for the identification and measurement of both primary and trace constituents. However, there may be some accuracy issues that arise in the measurement of the higher-boiling constituents due to relative volatility under the conditions in which the sample is held. 

A general classification of oil eg crude oil, petroleum, gas oil, is often satisfactorily achieved by gas chromatographic techniques possibly coupled with mass spectrometry or infrared spectroscopy applied to a sample of the oil pollutant. The true identification invariably requires samples from potential sources for comparison with the pollutant. 

Place a test sample 3cm 1 in size on an inorganic heat-insulating sheet f which is standardized to more than 10mm thickness and 12-15cm width. A small liquid petroleum gas flame 11 is brought in contact with the sample for 10 seconds 3 and is removed from the sample. Observe whether the test sample combusts with a flame or without a flame (combustion without a flame means the test sample is heated to red heat with out flame) G. If combustion is not observed, repeat this test 10 times. 

Many sulfur-containing organic compounds can be isolated from natural sources such as crude oil, petroleum, gas condensates, and coals <2004MI1>. By chromatographic methods <1999MI58> various polycyclic aromatic sulfur heterocycles (PASHs) (1-7) have been identified from standard samples of coal tar, petroleum crude oil and decant oil. 

I ig. 5-29. Relation between fracture intensity and gas leakage (A) plan showing lineament, fractures and gas sample sites (B) distribution of fracture intersections with distance from lineament (C) distribution of anomalous gas sample sites with distance from lineament (reproduced with permission of the American Association of Petroleum Geologists, whose permission is required for future use, from Richers et al 1986, AAPG Bull., vol. 70, no. 7, Fig. 13, p. 885, AAPG 1986). 

One of the more critical aspects for the analysis of low-boiling hydrocarbons is the question of volumetric measurement (ASTM D-1071) and sampling (ASTM D-1145, ASTM D-1247, ASTM D-1265). However, sampling liquefied petroleum gas from a liquid storage system is complicated by existence of two phases (gas and liquid), and the composition of the supernatant vapor phase will, most probably, differ from the composition of the liquid phase. Furthermore, the compositions of both phases will vary as a sample (or sample) is removed from one or both phases. An accurate check of composition can only be made if samples are taken during filling of the tank or from a fuUy charged tank. 

This test method (ASTM D-2784, IP 243) is valid for sulfur levels of >1 pg/g of sulfur in liquefied petroleum gas, but the samples should not contain more than 100 pg/g of chlorine. In the test, the sample is burned in an oxy-hydrogen burner or in a lamp in a closed system in a carbon dioxide-oxygen atmosphere. The latter is not recommended for trace quantities of sulfur... 

On the other hand, distorted data on gas composition may result when gases are sampled periodically from temporarily shut-in observation wells. It is known that carbon dioxide readily dissolves in petroleum. After the shut-down of observation wells and the formation of a depression on the well bottom, the gas that filters through the bed to the observation well may pick up part of the carbon dioxide that escaped from the oil. Due to this phenomenon, gas samples periodically taken from the observation wells contained up to 25%, and sometimes even more, of carbon dioxide, whereas the gases sampled continuously in the production wells had no more than 21%. 

The test is designed such that individual samples could be tested separately, or combined into assembly. A constant heat flux level is used to ignite the fabric sample. The liquid petroleum gas is used as fuel for the flame to bum the test specimen. 

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