The determination of miscibility relationships among mixtures consisting of n-butylcarbitol, hydrocarbons, and aqueous sodium salicylate solutions

In the enhanced oil recovery process a cosolvent, for example an alcohol, is used to promote miscibility of the oil and an aqueous solution of a surfactant. In the Chemistry Division at the Oak Ridge National Laboratory a program of fundamental research is underway to investigate phase boundary relationships in model systems related to the enhanced oil recovery process. . In these studies the model surfactants include the sodium salts of substituted aromatic sulfonic and carboxylic acids, while the hydrocarbons include both alkanes and various alkylbenzenes. . For each system the minimum amount of cosolvent, for example, l-butanol or n-butylcarbitol, needed to produce miscibility of the hydrocarbon and the aqueous solution of model surfactant is determined for various weight ratios of hydrocarbon to aqueous solution.

Each system thus contains four components: hydrocarbon, cosolvent, water, and the model surfactant. For convenience, however, the systems may be considered as pseudo-three component systems. For example, the three components may be chosen as hydrocarbon, cosolvent, and the aqueous solution. Alternatively, the components may be considered hydrocarbon, cosolvent, and water. In this latter case the effect of adding various amounts of the model surfactant on the phase boundary relationships in the hydrocarbon, cosolvent, water system is observed. . This representation is referred to as the water basis.

In the present research miscibility relationships in systems containing an aqueous solutionof sodium salicylate, n -butylcarbitol, and a series of hydrocarbons have been investigated. The hydrocarbons included both alkanes and alkylbenzenes. When the aqueous sodium

iv salicylate solution was treated as one component, then increasing the sodium salicylate concentration in the aqueous phase caused salting-in of the hydrocarbon, i.e., less cosolvent was required to produce miscibility of the hydrocarbon and the aqueous solution. On a water basis, however, both salting-in and salting-out effects were observed depending on the hydrocarbon.

At each fixed sodium salicylate concentration the effect of hydrocarbon chain length on the miscibility relationships was observed. It was found that in all cases the weight fraction of n -butylcarbitol required for miscibility gradually increased as the n -alkane chain length increased. For the alkylbenzenes, however, at aqueous sodium salicylate concentrations equal to zero or 1.0 molal, the amount of n-butylbarbitol required for miscibility at first decreased and then increased as the number of carbon atoms in the side chain on the benzene ring increased. At sodium salicylate concentrations of 2.5 molal and above, the amount of n -butylcarbitol required to produce miscibility of the aqueous solution and the hydrocarbon increased in all cases as the number of carbon atoms in the side chain increased. At any fixed sodium salicylate concentration the same amount of n -butylcarbitol was required to produce miscibility with either P-xylene or l-phenylethane. Hence the number of alkyl carbon atoms on the benzene ring and not the arrangement was the important parameter.