Haldor Topsoe and Comprimo has developed the TopClaus® process, which combines the well-known Claus and WSA technologies into a process, ensuring very low emissions, high energy efficiency and elemental sulfur as the only product. The WSA process treat the Claus tail gas by converting all sulfur species into concentrated sulfuric acid, which is then recycled to the thermal stage of the Claus plant. This paper examines the faith of the sulfuric acid in the Claus thermal stage, both theoretically and experimentally, and answers the questions on how fast sulfuric acid is destroyed in the thermal stage and if the sulfuric acid somehow interacts with the commonly present Claus feed gas "contaminants" such as CH4, BTX and NH3. The theoretical work was carried out in collaboration with the CHEC group at the Technical University of Denmark and the experimental work was carried out in collaboration with Alberta Sulfur Research Ltd., Canada.