Hydrocarbon types, ASTM test method

Satisfactory combustion of hydrocarbon gases depends on the matching of burner and appliance design with certain gas characteristics. Various types of test methods are available for the direct determination of calorific value (ASTM D900,... 

In 1948, a procedure was described by A. L. Conrad and later refined by D. W. Ciidle and R. L. LeToumeau for determining olefins, aromatics, and saturates in cracked gasoline. This procedure evolved into ASTM Test Method D1319, Hydrocarbon Types in Liquid Petroleum Products by Fluorescent Indicator Adsorption, often abbreviated as "FIA. ... 

A titration procedure, ASTM Test Method D1159, Bromine Number of Petroleum Distillates and Commercial Aliphatic Olefins by Electrometric Titration, provides an approximation of olefin content within a sample, while ASTM Test Method D2710, Bromine Index of Petroleum Hydrocarbons by Electrometric Titration, can be valuable for determining trace olefin levels. These methods do not directly measure total olefins, and the results are affected by the type of olefinic compound present. 

The first level of compositional information is group-type totals. ASTM Test Method D1319, Hydrocarbon Types in Liquid Petroleum Products by Fluorescent Indicator Adsorption, gives volume percent saturates, olefins, and aromatics in materials that boil below 315 C (600 F). This covers jet fuels but not all diesel fuels, most of which have an end point above 315°C. Despite this limitation, the method has been used widely for diesel fuel due to the lack of a suitable alternative. 

Mass spectrometry has been a powerful technique for hydrocarbon-type analysis of middle distillates. It can provide more compositional detail than chromatographic analysis. Hydrocarbon types are classified in terms of a Z-seiies. Z in the empirical formula C H2 +z is a measure of the hydrogen deficiency of the comp>ound. ASTM Test Method D2425, Hydrocarbon Types in Middle Distillates by Mass Spectrometry, determines eleven hydrocarbon types ranging from Z = -t- 2 (paraffins) to Z = —18 (tricyclic aromatics). 

Density or specific gravity, total sulfur, aniline point, total nitrogen, viscosity, cloud point, pour point, trace metals (Fe, Ni, V), and carbon residue would normally be determined on this fraction. If the fraction is to be used as catalytic cracker feedstock, asphaltenes would also be determined by precipitation with normal-heptane (ASTM Test Method D3279, Heptane Insolubles). Wax content determination by solvent reflux [24] might be included in a lube stock evaluation. Hydrocarbon-type analysis by mass spectrometry or other means is an important part of lube stock evaluation, but this is beyond the scope of this chapter. 

It is important to note that simulated distillation does not always separate hydrocarbons in the order of their boiling point. For example, high-boihng multiple-ring-type compounds may be eluted earher than normal paraffins (used as the calibration standard) of the same boiling point. Gas chromatography is also used in the ASTM D 2427 test method to determine quantitatively ethane through pentane hydrocarbons. 

Separations and Analyses. After removal of trace amounts of acids and bases from the <200° C distillates by extraction methods (16), a chromatographic separation with silica gel provided a check for the presence of olefins. No olefins were detected thus, the acid- and base-free distillates were analyzed by ASTM D2789-71, Standard Method of Test for Hydrocarbon Types in Low Olefinic Gasoline by Mass Spectrometry. The separation and analysis scheme for this distillate is shown in Figure 2. 

Other test methods are available. Content of benzene and other aromatics may be estimated by spectrophotometric analysis (ASTM D-1017) and also by gas-liquid chromatography (ASTM D-2267, ASTM D-2600, IP 262). However, two test methods based on the adsorption concept (ASTM D-2007, ASTM D-2549) are used for classifying oil samples of initial boiling point of at least 200°C (392°F) into the hydrocarbon types of polar compounds, aromatics, and saturates and recovery of representative fractions of these types. Such methods are unsuitable for the majority of naphtha samples because of volatility constraints. 

Coal liquids consist of hundreds of individual components and therefore, it is very difficult to identify all the individual components in a sample. The components can be classified as different types such as paraffins, naph-thenics, and aromatics. Because of an MS ability to identify compound-type unique molecular ion fragment patterns, hydrocarbon-type analysis by MS has been practiced for over four decades. ASTM D-2425 specifies a standard test method for hydrocarbon types in middle distillates by MS, with a boiling range of 20 343°C. This is within the boiling range of many CTL process products, so GC-MS has been used for hydrocarbon-type analysis in coal liquids. Initial product separations are conventionally needed for GC-MS-type analysis, such as distillation (ASTM D-86), elution chromatography. 

Cooperative studies are underway in ASTM D02.04 to find a better test method for total olefins. Cooperative work has been done to validate new gas chromatographic methods that trap the olefins on silver nitrate impregnated traps. These include a gas chromatographic multi-dimensional procedure for oxygenates and paraffin, olefin, naphthene, aromatic (O-PONA) hydrocarbon types in petroleum distillates and a GC fast total olefins analyzer (FTO) method. The FTO method has the advantage that the analysis time is quicker. The O-PONA method is an expanded version of ASTM D5443 and... 

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