Naphtha test methods

Table 7.9 Specifications and test methods for naphthas. These products are industrial intermediates and are not subject to ...

The data from the density (specific gravity) test method (ASTM D1298 IP 160) provides a means of identification of a grade of naphtha but is not a guarantee of composition and can only be used to indicate evaluate product composition or quality when used in conjunction with the data from other test methods. Density data are used primarily to convert naphtha volume to a weight basis, a requirement in many of the industries concerned. For the necessary temperature corrections and also for volume corrections, the appropriate sections of the petroleum measurement tables (ASTM D1250 IP 200) are used. 

Tests should also be carried out for sediment if the naphtha has been subjected to events (such as oxidation) that could lead to sediment formation and instability of the naphtha and resulting products. Test methods are available for the determination of sediment by extraction (ASTM D473, IP 285) or by membrane filtration (ASTM D4807 IP 286) and the determination of simultaneously sediment with water by centrifugation (ASTM D96, D1796, D2709, D4007 IP 373, 374). 

Table 1.6 Typical naphtha specifications and testing methods [18]...

The test method for the determination of aniline point and mixed aniline point of hydrocarbon solvents (ASTM D-611, IP 2) is a means for determining the solvent power of naphtha by estimating of the relative amounts of the various hydrocarbon constituents. It is a more precise technique than the method for kauri-butanol number (ASTM D-1133). 

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. 

An indication of naphtha composition may also be obtained from the determination of aniline point (ASTM D-1012, IP 2), freezing point (ASTM D-852, ASTM D-1015, ASTM D-1493) (Fig. 4.2), cloud point (ASTM D-2500) (Fig. 4.3), and solidification point (ASTM D-1493). And, although refinery treatment should ensure no alkalinity and acidity (ASTM D-847, ASTM D-1093, ASTM D-1613, ASTM D-2896, IP 1) and no olefins present, the relevant tests using bromine number (ASTM D-875, ASTM D-1159, IP 130), bromine index (ASTM D-2710), and flame ionization absorption (ASTM D-1319, IP 156) are necessary to ensure low levels (at the maximum) of hydrogen sulfide (ASTM D-853) as well as the sulfur compounds in general (ASTM D-130, ASTM D-849, ASTM D-1266, ASTM D-2324, ASTM D-3120, ASTM D-4045, ASTM D-6212, IP 107, IP 154) and especially corrosive sulfur compounds such as are determined by the Doctor test method (ASTM D-4952, IP 30). 

The various test methods dedicated to the determination of the amounts of carbon, hydrogen, and nitrogen (ASTM D-5291) as well as the determination of oxygen, sulfur, metals, and chlorine (ASTM D-808) are not included in this discussion. Although necessary, the various tests available for composition (Chapter 2) are left to the discretion of the analyst. In addition, test methods recommended for naphtha (Chapter 4) may also be applied, in many circumstances, to gasoline. 

The test protocols used for gasoline are similar to the protocols used for naphtha. The similarity of the two liquids requires the application of similar test methods. However, knocking properties are emphasized for gasoline and there are several other differences that must be recognized. But, all in aU, consultation of the test methods used for the analysis of naphtha (Chapter 4) can assist in developing protocols for gasoline. 

Standard Test Method for Aromatics in Light Naphthas and Aviation Gaso-... 

ASTM D 847-96. Standard test method for acidity of benzene, toluene, xylenes, solvent naphthas, and... 

D5134 Standard Test Method for Detailed Analysis of Petroleum Naphthas Through n-Nonane by Capillary GC... 

This test method covers the distillation of natural gasolines, motor gasolines, aviation gasolines, aviation turbine fuels, special boiling point spirits, naphthas, white spirit, kerosines, gas oils, distillate fuel oils, and similar petroieum products, utilizing either manual or automated equipment... 

This test method can also be applied to any petroleum mixture except liquified petroleum gases, very light naphthas, and fractions having initial boiling points above 400°C. 

This test method can be used as an analytical tool for examination of other petroleum mixtures with the exception of LPG, very light naphthas, and mixtures with initial boiling points above 400 C. 

ASTM Precipitation Naphtha, (Warning—See Note 4), conforming to the requirements of Test Method D 91. 

This test method covers the measurement of sulfur in hydrocarbons such as naphthas, distillates, fuel oils, residues, lubricating base oils and nonleaded gasoline. The concentration range is from 0.05 to 5 mass %. 

This test method covers the determination of the trace total nitrogen naturally found in liquid hydrocarbons boiling in the range from approximately 50°C to 400 C, with viscosities between approximately 0.2 and 10 cSt (mmVs) at room temperature. This test method is applicable to naphthas, distillates, and oils containing 0.3 to 100 mg/kg total nitrogen. 

These test methods involve the distillation of crude oil test specimens to obtain a naphtha fraction prior to chloride determination. The chloride content of the naphtha fraction of the whole crude oil can thereby be obtained. 

Test Method A covers the determination of organic chloride in the washed naphtha fraction of crude oil by sodium biphenyl reduction followed by potentiometric titration. 

A crude oil distillation is performed to obtain the naphtha cut at 204 C (400 F). The distillation method was adapted from Test Method D86 for the distillation of petroleum products. The naphtha cut is washed successively with caustic and water to remove hydrogen sulfide and inorganic chlorides. 

Test Method B, Combustion and Microcoulometry—The washed naphtha fiaction of a crude oil specimen is injected into a flowing stream of gas containing about 80 % oxygen and 20 % inert gas such as argon, helium, or nitrogen. The gas and sample flow through a combustion tube maintained at about 800 C. The chlorine is converted to chloride and oxychlorides whidi then flow into a titration cell where they react with the silver ions in the titration cell. The silver ions thus consumed are coulometrically replaced. The total current required to replace the silver ions is a measure of the chlorine present in the injected samples. 

Despite the many advances in capillary gas chromatography instrumentation and the remarkable resolution achievable, it has proven difficult to standardize a test method for the analysis of a mixture as complex as petroleum naphtha. Because of the proliferation of numerous, similar columns and the endless choices of phase thickness, column internal diameter, length, etc., as well as instrument operating parameters, many laboratories use similar but not identical methods for the capillary GC analysis of petroleum naphthas. Even minute differences in column polarity or column oven temperature, for example, can change resolution or elution order of components and make their identiflcation an individual interpretive process rather than the desirable, objective application of standard retention data. To avoid this, stringent column specifications and temperature and flow conditions have been adopted in this test method to ensure consistent elution order and resolution and reproducible retention times. Strict adherence to the specified conditions is essential to the successful application of this test method. 

This test method covers the determination of hydrocarbon components of petroleum naphthas as enumerated in Table 1. Components eluting after n-nonane (bp 150.8 C) are determined as a single group. 

This test method is applicable to olefln-free (<2 % olefins by liquid volume) liquid hydrocarbon mixtures including virgin naphthas, reformates, and alkylates. Olefin content can be determined by Test Method D 1319. The hydrocarbon mixture must have a 98 % point of 250 C or less as determined by Test Method D 3710. 

Separation of naphtha components by the procedure described in this test method can result in some peaks that represent coeluting compounds. This test method cannot attribute relative concentrations to the coelutants. In the absence of supporting information, use of the results of this test method for purposes which require such attribution is not recommended. 

The nitrogen test method is not applicable to light materials or those containing < 0.75 mass % nitrogen, or both, such as gasoline, jet fuel, naphtha, diesel fuel, or chemical solvents. 

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