Clay-gel chromatographic

In many cases we rely on the clay-gel chromatographic technique (17) (modifications related to applications with coal-derived liquids are given in Ref. 18) that separates aromatic furans and thiophenes from polar compounds such as phenols and thiols. Generally, this simple separation enables us to assign reasonable structures to the oxygen compounds. In our experience these are prevalently phenolic, although significant amounts of furans are also present. 

Determination of Response Factors. Speciflc response factors were obtained by injecting known concentrations of saturates and aromatics fractions obtained by clay-gel chromatographic separation of various gas oil fractions as well as residua boiling above 510°C. All of the clay-gel saturates fractions showed the presence of some aromatic impurities (2-20%) by HPLC. This was particularly true of the saturates obtained from the 510°C residue samples. Also, the aromatics fractions showed the presence of some saturates (2-3%) by HPLC. The response factors for these saturates and aromatics fractions are listed in Table II. Based on the values shown in Table II, the response for the aromatics was about 1.7 times that for the saturates. The ratio of the response factors for the gas oil fractions differs from the ratio for the residuum samples by about 6%, relative. 

Comparison of the HPLC Technique with Clay—Gel Chromatographic Separation. A number of vacuum gas oils were analyzed by preparing solutions in n-heptane at a concentration near 100 mg/mL. These samples were injected into the HPLC equipment and the concentration of saturates and aromatics calculated from the response factors shown in Table II. The absolute percentages of saturates and aromatics are shown in Table III along with the polar aromatics obtained by subtracting the sum of these from 100%. 

Table V. Comparison of Moving-Wire Detector with the Refractive Index Detector and Clay—Gel Chromatographic Separation (Vacuum Gas Oil)...

ASTM D-2007. Standard Test Method for Characteristic Groups in Rubber Extender and Processing Oils and Other Petroleum-Derived Oils by the Clay-Gel Absorption Chromatographic Method. 

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). 

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. 

Most of the parallel reactions described in Schemes 4.23 and 4.24 were performed as dry-media reactions, in the absence of any solvent. In many cases, the starting materials and/or reagents were supported on an inorganic solid support, such as silica gel, alumina, or clay, that absorbs microwave energy or acts as a catalyst for the reaction (see also Section 4.1). In this context, an interesting method for the optimization of silica-supported reactions has been described [83], The reagents were co-spotted neat or in solution onto a thin-layer chromatographic (TLC) plate. 

After chromatographing through silica-gel-clay column 260... 

All commercial samples of cumene tested by us contained considerable amounts of cumene hydroperoxide. Furthermore, a simple distillation, even in a thirty-plate column, is not sufficient to remove its effect. The hydroperoxide probably decomposes at the boiling point of cumene into other lower boiling inhibitors. The inhibitors can be effectively removed by chromatographing through silica gel or clay. 

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