Catalytic and environmentally friendly removal of hydrogen sulfide from Claus-derived molten sulfur by nanosilica

Removal of hydrogen sulfide as one of the most dangerous pollutants in molten sulfur has been studied here. In fact, catalytic degassing of Claus-derived molten sulfur containing about 150–200 ppmw of dissolved hydrogen sulfide and hydrogen polysulfide was performed over silica and nanosilica catalytic extrudates to reduce the hydrogen sulfide content up to environmental standard levels. In this regard, small extrude cylinders of silica and nanosilica particles were placed in a basket (mesh size of 4 mm) inside a batch reactor. Outlet of the degassing system was monitored by a hydrogen sulfide analyzer and also analyzed by IBT method. The results showed that residual content of hydrogen sulfide in molten sulfur during 4 h of degassing at 150 °C was as low as 6, 20, 60 ppmw for degassing by nanosilica, bulk silica, and nitrogen, respectively. This revealed the positive effect of accessible surface area in the decomposition of polysulfide bonds in molten sulfur. Degassing catalysts were then subjected to characterization by analytical methods including Brunauer, Emmett, and Teller analysis, field-emission scanning electron microscope, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and mechanical strength test. The spent catalysts were also regenerated by using Piranha solution for increasing the density of the lost silanol groups, which decreased the residual hydrogen sulfide in molten sulfur until 12 ppmw. This reflected the effect of surface silanol groups in improvement of proton abstraction, as the main reason for decomposition of hydrogen polysulfide in system.