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ABSTRACT:Quantitative gas chromatographic analyses supplemented by X-ray diffraction studies of the adsorption of ethanol and acetone (as model polar organic compounds) on homoionic montmorillonite revealed marked variation in the number of molecules associated with each exchange cation. The results show increasing association in the order K + ~Na+~ Ba 2+ ~Ca z+. K + and Na + associate with two and three molecules, respectively, of either ethanol or acetone, and the resulting complexes expand to form a monolayer (,-.~13 A). Ba 2+ and Ca z+ form both monolayer complexes as well as double layer complexes. In the single layer complexes Ba 2+ associates with either four molecules of ethanol or four molecules of acetone, CaZ+ associates with five molecules of ethanol or four molecules of acetone. In the double-layer complexes the observed cation-molecule ratios are 1 : 8 for both Ba2+--ethanol and Ba2+-acetone, I : 10 for Ca2+--ethanol, and 1 : 8 for CaZ+-acetone.The striking dependence of ethanol and acetone adsorption on the nature of the exchangeable cation suggests that cation-dipole interactions play an important role in the adsorption process. Structural models of the organic complexes are presented.

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We present a study of vanadium (V) isotope compositions for 17 crude oils spanning a wide range of concentrations and formation ages. Bulk organic geochemical and biomarker compositions are investigated for 11 co-genetic crude oils from the Barbados oil field. About 2‰ V isotope fractionation was observed and they are primarily correlated with V/Ni ratios and most likely reflect the depositional environment of the petroleum source rocks. Factors such as the lithology of the source rocks, Eh and pH of the depositional environment, and possibly the V isotope composition of seawater could all play a role in the V isotope composition. The Eh and pH conditions determine the speciation and coordination of V ions in fluids, whereas the lithology of the source rock defines the competing phases for available V ions in solution. The V isotopes are significantly modified by maturation and biodegradation. The V isotope fractionation during biodegradation has most probably resulted from the microbial activity-induced changes in the species and coordination geometries of V ions in fluids. The progressive decrease of δ51V with the increase of maturation might suggest a preferential loss of 51V during de-metalation and/or a preferential incorporation of 50V in the newly formed V-organometallic compounds.