Adsorption of fatty acids from solutions in organic solvents on the surface of finely dispersed magnetite: 1. Isotherms of adsorption of oleic, linoleic, and linolenic acid from carbon tetrachloride and hexane

Abstract

Isotherms of adsorption of oleic, linoleic, and linolenic acids on magnetite from solutions in carbon tetrachloride and hexane are measured. When CCl 4 is used as a solvent, the adsorption values increase in the following order: oleic, linoleic, and linolenic acid. In the case of hexane, the order is opposite. Adsorption isotherms of the fatty acids on aggregated magnetite are described in terms of the theory of volume filling of micropores. It is disclosed that, in the case of CCl 4 , the limiting adsorption values and characteristic energies of the process increase in a series: oleic, linoleic, and linolenic acid, but in the case of hexane, they decrease in the same sequence. Upon the adsorption of fatty acids from solutions in CCl 4 and hexane on finely dispersed magnetite, molecules of the acids and solvents compete for the active sites on the adsorbent surface. The number of double bonds in the molecules of unsaturated fatty acids and the desolvation of both the adsorbent surface and adsorbate molecules substantially affect the adsorption of these acids. The effect of the solvents is most pronounced for the adsorption of oleic acid, decreasing with a rise in the number of double bonds in a fatty acid molecule.

Adsorption of fatty acids from solutions in organic solvents on the surface of finely dispersed magnetite: 2. Heats of oleic, linoleic, and linolenic acid adsorption from carbon tetrachloride and hexane

“…As was shown earlier [14], the dissolution of studied fatty acids in CCl 4 and hexane is accompanied by their solvation; hence, it should be expected that, in these…”

“…Finely dispersed magnetite was prepared according to [14]. A highly sensitive automatic differential titration calorimeter designed for detecting the low heat effects of endo-and exothermic processes [15] was used to measure the heats of fatty acid adsorption on magnetite surface.…”

“…The amount of adsorbate adsorbed after the addition of each calorimetric dose was measured in a thermostated adsorption cell, which allowed us to reliably model the calorimetric experiment [14]; i.e., the same amounts of the adsorbent and solvent were placed into the cell, the same volumes of an adsorbate were added, and the corresponding regime of stirring was used. Particles of the adsorbent (magnetite) were sedimented using a permanent magnet.…”

Volume properties of solutions of oleic, linoleic, and linolenic acids in n-hexane and n-heptane at 298.15 K

“…The two last compounds are classified as essential acids of the vitamin F group, which are also used as ad sorbates to provide aggregative and sedimentation stabil ity of magnetic liquids. [4][5][6][7][8] These UFA are interesting, first of all, due to the fact that their "long chain" molecules contain the same num ber of carbon atoms (C 18:n ) but differ in the number of double bonds n C=C in the cis 3 , cis 6 , and cis 9 posi tions with respect to the terminal methyl group. 1,2 There fore, each of the compared UFA has specific features governing solvation in solutions.…”

“…[6][7][8][9] Previously, 7 we studied the heats of solvation of oleic and linoleic acids in n hexane to establish the solvating power of nonpolar solvents with respect to UFA. It is shown that the solvation process becomes less endother mic with an increase in n C=C in an acid molecule.…”