Interaction parameters hydrocarbon-water

Experimental solubility data are available for some higher alkane - water systems (see, for example, Skripka et al., (38)). However, these data either cover only a very limited temperature range or contain results for one phase only. No attempt has been made to determine the interaction parameters for water - hydrocarbon systems where the hydrocarbon is larger than n-octane. 

Water-Hydrocarbon Systems. The application of the PR equation to two and three-phase equilibrium calculations for systems containing water has recently been Illustrated by Peng and Robinson ( ). As in the case of other hydrocarbon-non-hydrocarbon mixtures, one fitted binary interaction parameter for water with each of the hydrocarbons is required. These parameters were obtained from experimental data available in the literature on each of the water-hydrocarbon binaries. 

For ternary and higher order mixtures, we have usually assumed that the interaction parameters for the non-water binary pairs in the water rich phase are identical to the vapor (hydrocarbon rich liquid phase) interaction parameters. Some work has been done on changing all water phase interaction parameters we concluded that predicted results were not improved enough to warrant the expenditure of time required to develop the additional parameters. A third interaction parameter for the hydrocarbon rich liquid could also be determined. Again, our work indicated that little improvement resulted from using this third parameter. Additional work is being done on both points. 

A similar strategy was used to develop the PFGC-MES equation of state parameters for describing the behavior of methanol hydrocarbon acid gas water systems. Multiple phase binary interaction parameters were used as required. Again, these second phase binary interaction parameters were usually not temperature dependent. 

Other Hydrocarbon - Water Systems. Interaction parameters were generated for the benzene - water system. The data used were those of Scheffer (31 ) > Rebert and Kay 35) > and Connolly... 

J. As with the alkane - water systems, the interaction parameters for the aqueous liquid phase were found to be temperature - dependent. However, the compositions for the benzene - rich phases could not be accurately represented using any single value for the constant interaction parameter. The calculated water mole fractions in the hydrocarbon - rich phases were always greater than the experimental values as reported by Rebert and Kay (35). The final value for the constant interaction parameter was chosen to fit the three phase locus of this system. Nevertheless, the calculated three-phase critical point was about 9°C lower than the experimental value. 

Interaction parameter was also generated for the hydrocarbon -rich phases of the n-octane - water system. The data of Kalafati and Piir (37j were used. There were no data available for the water - rich liquid phase for this binary. 

TABLE 5 Correlation Volumes and Intermolecular Interaction Energy Parameters in Hydrocarbon/Water Systems at Infinite Dilution"... 

Tables 4 and 5 also list the values of the energy interaction parameters Tij for the alcohol/water and hydrocarbon/water systems. For the alcohol/water systems, the parameters were calculated for both dilute solutions of alcohol in water and dilute solutions of water in alcohol. For hydrocarbon/water systems, the calculations were carried out only for dilute solutions of hydrocarbon in water, because no experimental information could be found for the solutions of water in hydrocarbons. Figure 3 presents a plot of F12 versus the number of carbon atoms in molecules for normal alcohols and hydrocarbons.

For the prediction of the mixed-gas solubilities from the solubilities of the pure individual gases, the pressure dependence of the binary parameters ku is needed. The Peng—Robinson EOS was used to determine the binary parameters ku. The binary interaction parameter qi2 in the van der Waals mixing rule was taken from ref 28, where it was evaluated for the water-rich phases of water—hydrocarbon and water—carbon dioxide binary mixtures. The calculated binary parameters ku are listed in Table 1. One should note that, as expected for a liquid phase, the above parameters are almost independent of pressure, in contrast to their dependence on pressure in the gaseous phase near the critical point,... 

Wilson s equation of state is found from Equations (14) and (15). It can be seen that for obtaining the activity coefficient of a component 1 in a pure solvent 2, we need four interaction parameters (A12, A21, An a A22, which are temperature dependent. It is evident that for calculating the value of the binary interaction parameters, additional experimental data, such as molar volume is needed. Other models which belong to the first category have the same limitations as Wilson s method. The Wilson model was used in the prediction of various hydrocarbons in water in pure form and mixed with other solvents by Matsuda et al. [11], In order to estimate the pure properties of the species, the Tassios method [12] with DECHEMA VLE handbook [13] were used. Matsuda et al. also took some assumptions in the estimation of binary interactions (because of the lack of data) that resulted in some deviations from the experimental data. 

Immobilized Artificial Membrane (LAM) packings for HPLC provide a different environment from that of the hydrocarbon-based ODS columns [17,30—32]. In this model, IAMs are purified phospholipids that are covalently bonded to the silicon support. At this time, only IAM columns prepared from phosphatidylcholine are commercially available (Regis Technologies, Inc., Morton Grove, IL). The hypothesis is that the bonded phospholipid layer is akin to the cellular monolayer that represents a barrier to transport. Interaction of the solute with the phospholipid results in a capacity factor ( J that is proportional to the membrane partition coefficient [PCm in Eq. (1)]. In this sense, the IAM approach does not attempt to correlate with literature values of oil water partition coefficients, but seeks to establish a unique membrane interaction parameter. 

With emulsions, nanoemulsions and microemulsions, the surfactant adsorbs at the oil/water (O/W) interface, with the hydrophilic head group immersed in the aqueous phase and leaving the hydrocarbon chain in the oil phase. Again, the mechanism of stabilisation of emulsions, nanoemulsions and microemulsions depends on the adsorption and orientation of the surfactant molecules at the Uquid/liquid (L/L) interface. Surfactants consist of a small number of units and are mostly reversibly adsorbed, which in turn allows some thermodynamic treatments to be applied. In this case, it is possible to describe adsorption in terms of various interaction parameters such as chain/surface, chain solvent and surface solvent. Moreover, the configuration of the surfactant molecule can be simply described in terms of these possible interactions. 

It is clear from Equation (12.10) that when the Flory-Hugging interaction parameter, y, is less than 0.5 - that is, the chains are in good solvent conditions - then will be positive and the interaction repulsive, and wiU increase very rapidly with decreasing h, when the latter is lower than 25. This explains the strong repulsion obtained between water droplets surrounded by PHS chains. The latter are highly soluble in the hydrocarbon medium, and any attempt to overlap the chains results in very strong repulsion as a result of the above-mentioned unfavourable mixing. 

The UNIQUAC equation, based on the name UNlversal QUAsi Chemical, is applicable to liquid solutions of hydrocarbons, alcohols, nitriles, ketones, aldehydes, organic acids, and water. Partially miscible solutions are represented. The two interaction parameters are determined by htting binary-solution data, and the equations are useful for binary as well as multicomponent solutions. 

The variations of the cmc with temperature have been used to estimate the thermodynamic parameters for micellization, and more rigorous direct measurements from heats of solution have also been made [1,2,7-9,34], Tanford [18] estimates a contribution of ca. 700 cal/mole per methylene group to the free energy of micellization, which is consistent with hydrophobic interactions of hydrocarbons in water. 

This correction introduces two additional temperature-independent interaction parameters for each binary mixture, that are and This approach results in a precise representation of the binary (water + hydrocarbon) LEE and VLB. However, when the model was extended to ternary mixtures, it was found unable to adequately represent the measured LEE. 

An explicit account of hydrogen bonding in water by the equation of state results in substantial improvement of the correlation of (water + hydrocarbon) LEE. In Figure 4.6, LEE for (water + hexane) is shown. The CPA equation of state correlates the water solubility with an Absolute Average Deviation of 4.5 % and reasonable agreement is obtained between experiment and calculations for hexane solubility. Unfortunately, the minimum of the solubility of hydrocarbon cannot be captured with a single temperature-independent binary interaction parameter. 

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