Cryoscopic Analysis of the Shale Oil

Abstract

Some problems of the cryoscopic method of the average molecular mass determination of shale oils were studied and a modification of the method is proposed. Diphenyl ether, diphenylmethane, dioxane, and benzene were compared as cryoscopic solvents. The presence of molecular complexes in the shale oil hampers an accurate determination of its molecular mass by cryoscopic methods.Diphenyl ether is recommended as a solvent for the cryoscopic determination of the molecular mass of the shale oils and their components. It yields more accurate results, as compared to other suitable solvents; besides, it is not hygroscopic, less toxicant, has a low vapor pressure and makes measurements at ambient temperature possible.Diphenylmethane is suitable for the determination of the molecular mass of the hydrocarbons, but cannot be applied to polar compounds.Cryoscopic methods are usually used for the determination of the molecular mass of the shale oils. All the modifications of the cryoscopic methods are based on the measurement of the depression of the solvent freezing point that arises as a result of the sample addition to the solvent. The application of cryoscopic methods is advantageous ifthe samples tobe measured are mixtures of volatile and nonvolatile components, or are unstable, or reactive. These methods are well developed and are applied to shale oils for many years. Nevertheless, some methodical problems may occur. Shale oils are complicated mixtures of compounds having a different chemical naturehydrocarbons of the various types, compounds of oxygen, nitrogen, sulfur, etc. The molecular mass of these compounds may not always be determined by means of the same solvent with the required accuracy.In most cases benzene, and sometimes dioxane, are used as solvents for the molecular mass determination of shale oil products. However, these solvents, especially benzene, have serious disadvantages. -Benzene forms so called solid solutions with phenols, thiophenes, pyridine, some naphthenes, and paraffins [l-3].This results ш ап increase of molecular mass during the measurements. Polar compounds, such as phenols, carboxylic acids, nitrogen compounds, when measured in benzene, also show molecular masses that are too high due to the molecular selfassociation. Benzene and dioxane are toxicant and have a high vapors pressure at ambient temperature. As dioxane gives solutions with water, this solvent must be dried carefully. Freezing points of benzene and dioxane are not convenient for the measurement at the ambient temperatures. |For these reasons we propose that solvents such as diphenylmethane and diphenyl ether will be much more suitable for measuring the molecular mass of the shale oils. These solvents have higher freezing points, as compared to benzene and dioxane, which makes measurements at ambient temperature possible. The cryoscopic constants of these solvents are high enough; this provides for a high