Aqueous Alkanolamine Solutions

Effect Of The Presence Of Sour Gases On The Solubility Of Light Hydrocarbons In Aqueous Alkanolamine Solutions

In the current literature the results of the measurement and correlation of systems involving the equilibrium solubility of light hydrocarbons in aqueous alkanolamine solutions have led to two basic generalized conclusions:

  1. The solubility of light hydrocarbons in aqueous amine solutions is greater than they are in pure water.
  2. The presence of sour gases such as H2S and CO2 lowers the hydrocarbon solubility in the aqueous amine solutions.

The rather strong implication or general rule arising from these two opposing effects is that, for all practical purposes, we can simply consider that the solubility of light hydrocarbons in aqueous amine solutions containing significant concentrations of sour gases to be identical to the solubility in pure water.

The quantity of data in the present literature which includes the presence of acid gases in aqueous amine solutions is not plentiful.  In addition, these meager data include only methane and hydrogen as the principal solutes.  Here we have attempted to analyze these data with the prime objective of verifying the more or less general solubility rule assumed above.  The key parameter used in this evaluation was the solubility ratio defined as the solubility of HC solute in the complete aqueous solution containing the alkanolamine and dissolved acid gases divided by the corresponding HC solubility in pure water.

The experimental measurements of Lawson and Garst for CH4 in 25 wt. % DEA with varying loadings of H2S or CO2 in solution strongly support the general solubility rule.

However, the data sets  of Kohl and Riesenfeld for CH4 dissolved in 25.3 wt. % MEA with 0.47 moles of acid gases/ mole MEA and of Dingman for H2 and CH4 in 50 wt.      % DGA  with 0.35 moles H2S/ mole DGA  do not allow us to draw such a clear cut conclusion.  However, considering that the magnitude of the hydrocarbon solubilities reported are of the order of 10-4 mole fraction, it might be expected that the observations made in this study may also have to be assessed more thoroughly in the light of measurement uncertainty.

In any case, within the scope of normal required engineering design accuracy, the general proposed solubility rule here should be a reasonable one to follow.

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