Vapor-Liquid Equilibrium Ratios of Gases and Light Hydrocarbons in Methyl Cyanoacetate
Authors: Woertz Byron B. 
Published: December 2007

Vapor-liquid equilibrium values (K-values) for nitrogen, CO2, H2S and the paraffin hydrocarbons, methane through n-octane, in methyl cyanoacetate (MCA) were published in 1972. K-values for the hydrocarbons through C4 were based on vapor-liquid equilibrium data obtained using a pressurized cylinder maintained in a bath at constant temperature. K-values for n-hexane and heavier were obtained by extrapolation of low pressure values estimated from liquid-liquid miscibilities. Data on the pentanes were obtained from both sources.

The K-values for the heavier hydrocarbons were based on the small amount of data available at the time. Since the 1972 publication, experimentally determined K-values have been obtained for hydrogen and carbon monoxide, and the liquid-liquid miscibility type of K-value determination bas been extended to higher pressures. Here, improved, revised K-charts are presented. The miscibility method for determining K-values is described in the Appendix.

TESTING THE DATA

Fig. 1 is a representative plot of K's obtained from liquid-liquid miscibility experiments and K-values from direct experimental measurements. The data are plotted using the method of Galimberti and Campbell, plotted using the method of Galimberti and Campbell, which involves plotting log K vs absolute critical temperature squared. The method proposed by these authors was intended for use with hydrocarbon systems. However, Fig. 1 indicates that their method is applicable to other systems also.

Plots similar to Fig. 1 were prepared for pressures of 600 to 1,500 psia and at temperatures in the range of 0 degrees to 100 degrees Fahrenheit to obtain additional measures of the consistency of the data and to aid in crossplotting. In certain cases the fit of the points to a line was somewhat poorer than in Fig. 1; but in all cases the points defined a substantially straight, or slightly curved, line. This finding tends to confirm that the liquid-liquid miscibility method can be used to obtain K-values for nominally liquid hydrocarbons in MCA. Owing to the difficulty of analyzing for, or calculating amounts, of these hydrocarbons in each of the phases in typical vapor-liquid equilibrium experiments, the miscibility method could result in increased accuracy of the K-value. The plot Fig. 1 indicates that in this instance the accuracy was satisfactory in that the miscibility type K's plotted well with experimental K's for the lighter hydrocarbons.

THE K-CHARTS

The plotting method of Galimberti and Campbell and crossplotting techniques were used with previous experimental K-data and the present liquid-liquid miscibility type K-data for liquid hydrocarbons to prepare the charts presented here. prepare the charts presented here.Figs. 2 through 16 are K-charts for hydrogen, nitrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, and methane through n-octane, all at equilibrium conditions in methyl cyanoacetate (MCA). The charts show K-values at pressures up 2,000 psia over the temperature range of 0 degrees to 100 degrees Fahrenheit.

SPEJ

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