Gas-lift reactor for hydrogen sulfide removal

Hydrogen sulfide (H2S) removal by the Lo-Cat process [reaction with iron(3+) chelates] consists of two steps: the removal reaction and catalyst regeneration. The internal loop gas lift or the autocirculation reactor is an appropriate reactor for the Lo-Cat process because it combines the reaction and regeneration steps in a single device. The removal reaction takes place in the riser, and the used catalyst solution is regenerated in the downcomer. This research involved the study of the performance of the Lo-Cat air-lift reactor on H2S removal under various operating conditions. H2S could be removed completely (> 99.9%) when the superficial H2S velocity in the riser was 0.03 m/s and the superficial air velocity in the downcomer was 0.01 m/s. Iron(2+) ethylenediaminetetraacetic acid [Fe (2+)EDTA] was regenerated to Fe 3EDTA in the downcomer with a conversion of up to 79%. The conversions of H2S, Fe(3+)EDTA, and Fe(2+)EDTA decreased with increasing superficial gas velocity in the riser for a fixed gas velocity in the downcomer. This was due to the decrease in the liquid-phase circulation time in the riser and downcomer with an increase in the superficial gas velocity in the riser at a constant downcomer velocity. A mixing cell model for gas and liquid phases was also developed to describe the H2S degradation behavior of the reactor, and the model was found to be consistent with the measured data.