Recovery of sulfur from sour acid gas: A review of the technology

The modified Claus process is the major technology for the recovery of elemental sulfur from H2S and SO2. A number of commercial technologies for the recovery of sulfur from acid gases are also highlighted here. A Claus tail-gas clean-up treatment is essential to give high sulfur recovery efficiency from sour acid gases. Generally, the existing tail-gas clean-up technologies can be classified into two groups: those that attain 99% overall sulfur recovery efficiency, and those that achieve 99.9% efficiency, including the sulfur recovered in the Claus unit. These processes are the Amoco's Cold Bed Adsorption (CBA), the SNPA/Lurgi Sulfreen, the IFP, the SCOT, the Beavon, and the Wellman-Lord processes. The SCOT process is generally the most reliable and flexible technology. Process comparisons are also summarized in terms of the sulfur recovery efficiency, hazards and disadvantages, reliability and advantages, plant capacity and ecological impacts. Several changes and new trends are also highlighted here, such as the introduction of non-permselective catalytic membrane reactors for the Claus reaction, and the in situ adsorption of water inside the Claus catalytic reactor. The successful utilization of H2S by converting it to sulfur and H-2 attains the triple objectives of waste minimization, resource utilization, and environmental pollution reduction. Photochemical and plasmochemical methods are still in the development stage. Application of electrochemical technology to H2S requires further development. Research for an optimum porous catalyst structure is ongoing for obtaining a relation of micropores and macropores which would provide effective conversion of H2S and SO2.