Sulfur dioxide (SO2) may be converted to sulfur trioxide (SO3) by oxidation SO2 +1/2 O2 ---> SO3.
SO3 has many uses including the production of sulfuric acid (H2SO4). A gas stream having the (molar) composition shown in the figure below is to be passed through a two-stage converter. The fractional conversion of SO2 to SO3 (per single pass) in the first stage is 0.75 and in the second state is 0.65. To boost the overall conversion to 0.95, some of the gas exiting stage 2 is recycled to the inlet of stage 2. How much gas R must be recycled per 100 moles of fresh feed F?