Vapor-Liquid Equilibrium Ratios of Gases and Light Hydrocarbons in Methyl Cyanoacetate
- Byron B. Woertz (Union Oil Co. of California)
- Document ID
- Society of Petroleum Engineers
- Society of Petroleum Engineers Journal
- Publication Date
- February 1975
- Document Type
- Journal Paper
- 7 - 12
- 1975. Society of Petroleum Engineers
- 4.3.4 Scale, 4.6 Natural Gas
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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 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.
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