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

A new set of vapor-liquid equilibrium ratios (K-charts) is presented for methane through n-octane, nitrogen, CO2 and H2S, all in methyl cyanoacetate (MCA). The K-values for the hydrocarbons show a temperature inversion at pressures of 1,000 psia and above in that solubility in MCA increases with temperature. Nitrogen appears to exhibit temperature inversion at all pressures studied.

Nitrogen, CO2 and methane were the only components in which the K-values did not increase at high pressure in the pressure ranges studied. At some temperatures K-values of ethane and propane also did not increase with pressure at high pressures. pressures

Introduction

Additional pilot plant data have recently been published on the use of methyl cyanoacetate (MCA) to published on the use of methyl cyanoacetate (MCA) to remove acid gases (CO2 and H2S) from high-pressure natural gas. In that publication, K-values for the dissolved components, which had originally been published by the author in 1965, were omitted. Since published by the author in 1965, were omitted. Since 1965 additional equilibrium experiments have been made, resulting in some changes and in extension of the pressure range covered. Determinations of hydrocarbon K-values in hydrocarbon systems have been made elsewhere from time to time over a period of about 40 years, and information is still being developed. Thus, it seems appropriate that K-values of hydrocarbon-solvent systems be extended and modified as new data are obtained. The original K-value data were obtained from equilibrium experiments with MCA and a multicomponent mixture of CO2, methane, ethane, propane and n-butane. Some of the mixtures also propane and n-butane. Some of the mixtures also contained H2S. Compositions of the phases, resulting from flashing rich solvent in the pilot plant, were used with the previous data to estimate plant, were used with the previous data to estimate K-charts for nitrogen, i-butane, the pentanes, and all the K-values at low pressure. Thus, from the original equilibrium experiments (150 or 600 psia; and 0 degrees, 40 degrees or 70 degrees F) and the pilot plant flashing data, the original K-charts pilot plant flashing data, the original K-charts (Figs. 6 through 15, inclusive, in Ref. 2) were obtained.

New K-Value Experiments

The new data consist of the following:1. K-values calculated from atmospheric pressure solubility at either ambient temperature or 33 degrees F (Bunsen solubility).2. K-values determined at about 1,000 to 1,500 psia on multicomponent gas mixtures containing psia on multicomponent gas mixtures containing i-butane and n-pentane in addition to previously mentioned components. Also, measurements were made of the solubility of pure nitrogen or methane in MCA at these pressures.3. K-values at 2,000 psia for CO2, H2S and methane at 0 degrees or 100 degrees F.4. K-values calculated from chromatographic analysis of air in equilibrium with known mixture of MCA with benzene, toluene, or -xylene at atmospheric pressure and either ambient temperature or 33 degrees F.5. K-values for i-pentane, n-pentane, n-hexane, n-heptane and water calculated from liquid-liquid miscibility experiments at either ambient temperature or 33 degrees F. The method of (Galimberti and Campbell was used in smoothing and extrapolating the data. In this method, at constant system pressure and temperature, the log of the K-value of hydrocarbons is a linear function of (absolute critical temperature). This method was originally proposed for hydrocarbon systems, but also seems to work well on hydrocarbon-solvent systems.