Abstract: SO.sub.2 -containing, hot gases are catalytically converted in part in a first contacting stage. The water and the SO.sub.3 formed is removed from the reaction gas. The remaining gas is heated and then supplied to the second contacting stage. The water vapor content in the reaction gas delivered by a first contacting stage corresponds to an H.sub.2 O/SO.sub.3 mole ratio below 1. The reaction gas delivered by the first contacting stage is precooled by an indirect heat exchange to such a temperature that the wall temperatures of the heat exchanger are above the dew point temperature of the reaction gas. The precooled reaction gas entering a condensing stage is contacted in a venturi with cocurrent sulfuric acid of 98.0 to 100% concentration and a temperature of at least 95.degree. C. The exit temperature of the gas from the condensing stage is maintained at least at 120.degree. C.

Abstract: Concentrated sulfuric acid and/or oleum is prepared by the catalytic oxidation of sulfur dioxide to sulfur trioxide using a gas containing water vapor, SO.sub.2 and oxygen. The catalytic oxidation is carried out in two stages. After the first stage an intermediate cooling of the reaction gas, and absorption of the water vapor content and an intermediate absorption of the sulfur trioxide formed in the first stage are performed. In the second stage the unreacted SO.sub.2 is catalytically oxidized to SO.sub.3 in the absence of water vapor, this SO.sub.3 being absorbed in sulfuric acid. An apparatus for carrying out the process is disclosed including a primary catalysis stage, means for the intermediate cooling of the reaction gas, means for the removal of the water vapor content, means for the intermediate absorption of the SO.sub.2 of the first stage, a secondary stage for the catalytic oxidation of the unreacted sulfur dioxide in the absence of water and an end absorption unit for SO.sub.

Abstract: Sulfur compounds oxidizable to form sulfuric acid and organic compounds oxidizable to CO.sub.2 and H.sub.2 O are removed from an exhaust gas of a contact-process plant for producing sulfuric acid by treating the exhaust gas with a scrubbing solution consisting of dilute sulfuric acid and peroxydisulfuric acid. The peroxydisulfuric acid is produced electrolytically from fresh dilute sulfuric acid and the resulting electrolyte is continuously introduced into the scrubbing acid cycle. The exhaust gas is treated in a vertical venturi with uniflow, i.e. codirectional flow of the gas and the scrubbing solution, and the gas is then passed through a horizontal venturi and subsequently upwardly through a packing layer.CROSS-REFERENCE TO RELATED APPLICATIONThe present Application is related to the commonly assigned copending application Ser. No. 308,849 filed Nov. 22, 1972 and entitled METHOD OF REMOVING GASEOUS IMPURITIES FROM WASTE GASES now abandoned.