KINETICS OF H2S ABSORPTION INTO AQUEOUS FERRIC SOLUTIONS OF EDTA AND HEDTA

Kinetics of the reaction of hydrogen sulfide with ferric chelates of ethylenediaminetetraacetic acid (EDTA) at 22-degrees-C and with ferric chelates of hydroxyethylethylenediaminetriacetic acid (HEDTA) from 21-degrees-C to 60-degrees-C were studied in a stirred cell reactor under industrial conditions. Concentration of the ferric chelates ranged from 40 to 150 mol/m3 and the pH was varied from 4 to 10. Only the hydroxy forms of the ferric chelates appear to react with hydrogen sulfide. Under the conditions applied, the reaction appeared to be first-order in hydrogen sulfide and first-order in hydroxy ferric chelate. At 22-degrees-C the rate constant for the EDTA complex is 14-21 m3/mol.s. Uncertainty in this constant is due to the characteristics of the EDTA complex at pH values above 7. For the HEDTA complex, the activation energy of the reaction of hydrogen sulfide with the monohydroxy ferric chelate is (26.4 +/- 0.6) kJ/mol with k11m = 1.8 m3/mol.s at 25-degrees-C. The rate constant for the reaction with the dihydroxyferric chelate is (300 +/- 150) m3/mol.s in the temperature range investigated.