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

Kinetics of the reaction of hydrogen sulfide with ferric chelates of e thylenediaminetetraacetic 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 fr om 40 to 150 mol/m3 and the pH was varied from 4 to 10. Only the hydro xy 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. Un certainty in this constant is due to the characteristics of the EDTA c omplex at pH values above 7. For the HEDTA complex, the activation ene rgy of the reaction of hydrogen sulfide with the monohydroxy ferric ch elate 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.