Clay gel

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). 

Chromatography A technique for separating a sample material into constituent components and then measuring or identifying the compounds by other methods. As an example separation, especially of closely related compounds, is caused by allowing a solution or mixture to seep through an absorbent such as clay, gel, or paper. Result is that each compound becomes adsorbed in a separate, often colored layer. 

Determination of hydrocarbon groups in rubber extender oils by clay-gel adsorption (ASTM D2007)... 

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. 

Thixotropic Time-dependent pseudoplastic flow. At constant applied shear rate, viscosity decreases. In a flow curve, hysteresis occurs. Paint, quicksand. In bentonite clay gels which liquefy on shaking and solidify on standing, there is a time-dependent aligning to match the induced flow. After the shear rate is reduced it takes some time for the original alignments to be restored. 

Figure 6.14 Bingham yield stress of clay gels as a function ofthe amount of NaCI added. From van Olphen [1], Copyright 1977, Wiley-lnterscience.

Rheopexy refers to dilatant flow which is time dependent. At a constant applied shear rate viscosity increases, as shown in Figure 6.15. In a flow curve, hysteresis occurs (but opposite to the thixotropic case). An example of a rheopectic system is a bentonite clay gel system which sets slowly on standing, but sets quickly when gently agitated. 

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. 

More extensive separations (21,22) provide further detail in some cases, but in our work we prefer to rely mainly on high-resolution MS and keep separations to a minimum. In fact, we will forego even the clay-gel separation in most routine analyses and restrict its use to calibrations and in-depth investigations. 

There are four obvious possibilities for the state of a polymer molecule in and around a clay gel ... 

The average number of polymer chains per unit volume of solution Nv (pm3) can be obtained from the density p= 1.13 g/cm3 of PEO and the polymer volume fraction Vj inside the clay gel through the relation... 

A definite prediction of DLVO theory is that charge-stabilized colloids can only be kinetically, as opposed to thermodynamically, stable. The theory does not mean anything at all if we cannot identify the crystalline clay state (d 20 A) with the primary minimum and the clay gel state (d 100 to 1000 A) with the secondary minimum in a well-defined model experimental system. We were therefore amazed to discover a reversible phase transition of clear thermodynamic character in the n-butylammonium vermiculite system, both with respect to temperature T and pressure P. These results rock the foundations of colloid science to their roots and... 

Separations. The asphaltene fractions were obtained by solvent extraction with benzene and subsequent precipitation with cyclohexane. The cyclo-hexane-soluble fractions were separated into saturate, aromatic, and polar aromatic fractions by the clay-gel technique, ASTM D-2007 (modified). This separation is also applicable to asphaltenes. 

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)...

Using wt % polars as determined by clay-gel separation. Using factor Ks = 52.0 mL-ct/mg. 

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