However, for an efficient desulfurization the lower pH of the experimental pH operating window using the Fe(II)SO
4 or ZnSO4 solution was higher than indicated by thermodynamics.
The reason for this must probably be attributed to a reduced precipitation rate at decreasing pH. When a CuSO4
solution is used as washing liquor the solution can efficiently remove H2S over the entire pH range studied (as low as pH = 1.4). In this case only the upper pH boundary of the operating window (that indicates the possible formation of copper hydroxide or copper carbonates) seems to be a relevant limit in practice.The laboratory experiments indicate that the absorption of H2S in a CuSO4 solution, at the experimental conditions tested, is a gas phase mass
transfer limited process.