The selective absorption of hydrogen sulphide in carbonate solutions

A study of both a wetted-disc and a wetted-wall column has indicated that the latter is the more suitable for obtaining mass-transfer data in spite of the tendency to ripple formation. A study has been made of the absorption of hydrogen sulphide and carbon dioxide from a gas mixture with a CO2 H2S ratio of 30: 1 in solutions of sodium and potassium carbonates. Selectivity for the absorption of hydrogen sulphide has been found to decrease with increase in wetting rate and with increase in temperature. It increases with increase in gas rate and increases slightly with increase in concentration of sodium carbonate in the solution above about 1·1–1·3-N. The concentration of hydrogen sulphide in the gas has no effect on the selectivity provided it is more than 1·3% but below this concentration, the selectivity decreases as the concentration decreases. The gas film conditions are more important than those in the liquid film for hydrogen sulphide concentrations in the gas of about 1%. The absorption of carbon dioxide is independent of gas film conditions and is controlled by the rate of a slow reaction in the liquid film. The practical absorption conditions required to secure maximum removal of hydrogen sulphide and minimum removal of carbon dioxide are listed.