Heptane combinations, solubilities

Briefly, the asphaltene fraction of crude oil is that fraction which is precipitated by the addition of a large excess of a low-boiling liquid hydrocarbon (usually n-heptane) (Chapter 3). On the other hand, resins are those materials which remain soluble in the pentane but will be adsorbed by a surface-active material such as fuller s earth, while the oils fraction is soluble in pentane but is not adsorbed from the pentane solution by any surface-active material. The asphaltic fraction of any petroleum, heavy oil, or residuum is usually a combination of the asphaltene and resin fraction and, in many instances, may constitute a large portion of a heavy oil or, especially, of a residuum. 

Ultrasound in combination with an organic solvent facilitates the formation of binary systems with an aqueous electrolyte, thereby increasing the current intensity Figure 8.14B shows this effect on the sono-voltammogram of A/,A/,A/, /V -tetramethyl-p-phenylenediamine (TMPD) in 0.1 M aqueous KCI with and without the addition of 40% v/v heptane [156]. The increased current in the acoustically emulsified media was ascribed to enhanced transport of electroactive material in heptane droplets towards the electrode surface, and related to the analyte solubility in the organic phase. The ratio of the current increase to the volume fraction of organic solvent ([Pg.286]

Asphaltenes are generally defined as those components in petroleum and coal liquids that under certain conditions are soluble in benzene but insoluble in aliphatic solvents, such as n-pentane, n-heptane, or cyclohexane. This definition obviously includes a broad variety of components, as insolubility in the above solvents can be caused by high molecular weight, high polarity, hydrogen bonding, acid-base complexing, or combinations of these parameters. 

Lake Fork, outcrop (244 g) heptane-soluble fraction benzene-soluble fraction combined heptane- and benzene-soluble fractions... 

Normal phase systems consist of a polar adsorbent and a less polar mobile phase. Because these were the first available chromatographic systems they were named normal phase systems. They are for instance silica gels or other oxides in conjunction with a non-polar solvent such as heptane, hexane or some slightly polar solvents like dioxane. Semi-polar adsorbents such as cyano or diol phases can be operated in the normal phase mode as well. The combination of water and silica is not recommended due to the strong interaction between water and adsorbent. Furthermore silica is slightly soluble in water, which results in a shortened lifetime of the adsorbent. Normal phase systems are limited to organic solvents and thus the solutes have to be soluble in these solvents. 

In a saturator, gas should principally be combined only with those liquids in which this gas is hardly soluble (e.g., not propane with hexane/heptane, not carbon dioxide with water). In the case of soluted gas this may lead to a drop in vapor pressure (Raoul s law) in relation to the tabeled values for the pure liquid. 

The solubility of asphaltenes is highly dependent on the medium in which they are placed (81). The presence of dissolved asphaltenes in crude oil is mediated by a combination of crude aromaticity and petroleum resins that act to solvate asphaltene aggregates. Adding an excess of aliphatic solvent, namely n-hep-tane, sufficiently reduces the solubility of asphaltenes in crude oil and causes precipitation. To perform subsequent film experiments these precipitated asphaltenes were then redissolved in toluene. As n-heptane was added to the asphaltene—toluene solutions. 

Three component systems are found to exist with various arrangements of phases. The three components may be essentially immiscible and exist as three distinct phases. Consider combining benzene, mercury, and water, which are all immisdble. They will form three layers in order of their inverse density benzene < water < mercury. If the three components are all totally miscible, they will exist as a single miscible phase. This is the case with aliphatic hydrocarbon mixtures (e.g., hexane, heptane, and octane) under most conditions. Intermediate situations are possible where varying levels of solubility between components widely exist. These often give rise to two phase configurations. One example is when two of the components are fully miscible and both are immiscible with a third component (e.g., benzene and toluene with water as a third component). If the three components have a limited mutual solubility, there will be composition ranges where one, two, or three phases exist and each contains some of each of the components. The classical solution thermodynamics of ternary solutions is implicit in most treatments of chemical thermodynamics (1,2,3]. 

---