Calorimetric study of reactions occurring between impregnated activated fibres and hydrogen sulphide

Activated carbon fibres, which exhibit high specific area and numerous active surface sites constitute very powerful adsorbents and are widely used in filtration to eliminate pollutants from liquid or gaseous effluents. The fibres studied in this work are devoted to the filtration of gaseous effluents containing very small amounts (few vpm) of hydrogen sulphide. To improve their fixation capacity towards H₂S the activated fibres are impregnated in an aqueous solution of potassium hydroxide and then thermally treated. The treatment leads to the deposition of crystallites of K₂CO₃ showing a great activity for H₂S gas in the presence of water vapour. The H₂S fixation mechanism proposed can be summarised as follow: K₂CO₃ and H₂S dissolve in a liquid aqueous solution formed on the fibre surface. Then carbonate ions and H₂S molecules react together almost completely to yield HS⁻ species. This mechanism has been validated and completed by the study of the thermal effects induced when the treated fibres are in contact with H₂S together with water vapour. The study has been carried out using a calorimetric method. The variations of standard enthalpy of reactions involved in the fixation mechanism are measured and compared to the data given by the thermodynamic tables for bulk solutions.