The LOCAT® process is a liquid phase oxidation process based on a dilute solution of a proprietary, organically chelated iron in water that converts the hydrogen sulfide to water and elemental sulfur. The process is not reactive to CO2. A small portion of the chelating agent degrades in some side reactions and is lost with the precipitated sulfur. Normally, sulfur is separated by gravity, centrifuging, or melting.
Figure 7-8 represents a process flow diagram of the LOCAT® process. The H2S is contacted with the reagent in an absorber; it reacts with the dissolved iron to form elemental sulfur. The reactions involved are the following:
The iron, now in a reduced ferrous form, is not consumed; instead, it is continuously regenerated by bubbling air through the solution. The sulfur precipitates out of the solution and is removed from the reactor with a portion of the reagent. The sulfur slurry is pumped to a melter requiring a small amount of heat and then to a sulfur separator where the reagent in the vapor phase is recovered, condensed, and recycled back to the reactor.
LOCAT® units can be used for tail-gas clean-up from chemical or physical solvent processes. They can also be used directly as a gas sweetening unit by separating the absorber/oxidizer into two vessels. The regenerated solution is pumped to a high-pressure absorber to contact the gas. A light slurry of rich solution comes off the bottom of the absorber and flows to an atmospheric oxidizer tank where it is regenerated. A dense slurry is pumped off the base of the oxidizer to the melter and sulfur separator.