Clay-gel analysis

Molecular type analysis separates an oil into different molecular species. A molecular type analysis is the so-called clay-gel analysis. In this method, group separation is achieved by adsorption in a percolation column with selected grades of clay and silica gel as the adsorption media (ASTM D-2007). 

ASTM D2226 classifies petroleum process oils used in rubber compounding. This system of classification is based on the test results from ASTM D2007, a column chromatographic method called "clay-gel analysis." This procedure classifies an oil on its content of saturates, aromatics, and polar compounds, as well as asphaltene content. Under this classification system, very aromatic oil is designated Type 101 while aromatic oil is designated Type 102. 

Total aromatics (by clay-gel analysis) of 30% minimum are the general boundary although not hard and fast. Generally, naphthenic process oils are not recommended for polar elastomers but can be used to good advantage in semipolar elastomers. Naphthenic oils do not need to be labeled as carcinogenic if they have been adequately hydro-treated or extracted to meet industry and OSHA standards. 

D. Tinet, A. M. Faugere, and R. Prost, Cd NMR chemical shift tensor analysis of cadmium-exchanged clays and clay gels, J. Phys. Chem. 95 8804 (1991). 

However, fractional separation has been the basis for most asphalt composition analysis (Fig. 15.5). The separation methods that have been used divide asphalt into operationally defined fractions. Three types of asphalt separation procedures are now in use (a) chemical precipitation in which n-pentane separation of asphaltenes is followed by chemical precipitation of other fractions with sulfuric acid of increasing concentration (ASTM D-2006) (b) adsorption chromatography with a clay-gel procedure in which, after removal of the asphaltenes, the remaining constituents are separated by selective adsorption/desorption on an adsorbent (ASTM D-2007 and ASTM D-4124) and (c) size exclusion chromatography in which gel permeation chromatographic (GPC) separation of asphalt constituents occurs based on their associated sizes in dilute solutions (ASTM D-3593). 

Barman, B.N. Hydrocarbon-type analysis of base oils and other heavy distillates by thin-layer chromatography with flame-ionization detection and hy the clay-gel method. J. Chromatogr. Sci. 1996, 34 (5), 219-225. 

Asphaltenes seem to be relatively constant in composition in residual asphalts, despite the source, as deterrnined by elemental analysis (6). Deterrnination of asphaltenes is relatively standard, and the fractions are termed / -pentane, / -hexane, / -heptane, or naphtha-insoluble, depending upon the precipitant used (5,6,49). After the asphaltenes are removed, resinous fractions are removed from the maltenes-petrolenes usually by adsorption on activated gels or clays. Recovery of the resin fraction by desorbtion is usually nearly quantitative. 

The technique of differential thermal analysis (D.T.A.) has been extensively employed in the study of clay and other minerals for elucidating their structures for more than three decades. The application of D.T.A. as a tool has not been widely made to the systematic study of solid catalysts. Only a few references on the subject could be foimd 1-6). In the present article, differential thermal studies of a number of solid catalysts like chromic oxide gels, ferric oxide gels, and chromic oxide-ferric oxide are reported. An attempt has also been made to correlate the data with x-ray... 

The most commonly used separation technique is open column separation using clay followed by silica gel, e.g., ASTM D2007 [52]. Polar components in the mixture are retained on clay, and saturate and aromatic compounds are allowed to flow through the column. The polar components can be recovered later using a polar solvent for analysis or further separations [78]. The mixture of saturates and aromatics is then separated on a silica gel column using proper solvents. High-performance liquid chromatography (HPLC) with both normal phase and reversed phase procedures can also be used for the same purposes [58]. 

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