PREPARATION OF SULPHUR TRIOXIDE

of the Disclosure Preparation of sulphur trioxide In the production of sulphur trioxide by passing a mixture of sulphur dioxide and oxygen through a fluidized bed of catalyst, the improvement wherein the gas mixture at a temperature of about 200.degree.C to 700.degree.C and containing up to 66.7% sulphur dioxide is reacted with the oxygen in a single stage fluidized bed of catalyst material to convert over 90% of the sulphur dioxide to sulphur trioxide, the reaction gases containing SO3 are transferred to a stage of intermediate absorption and, when freed from sulphur trioxide, the gased are further reacted within a single stage or two stage catalyst, the height of the single stage fluidized bed being about from 0.1 to 2 m in the fluidized state, the average particle size of the catalyst mass being about from 0.4 to 2mm, the gas velocity in the empty fluidized bed chamber being about from 0.1 to 0.6 mn/sec. and the velocity of the gas after reaching the bottom of the inlet chamber and before making contact with the catalyst particles being up to 9 mn/sec., and the temperature of the catalyst mass being controlled by heat exchange. The process is almost isothermic. Le A 20 080