Intermediate versus final H2SO4 making

The final step in sulfuric acid manufacture is the productirai of H2S04(f) from SO3-bearing gas. 

The H2SO4 is made by sending strong sulfuric acid down around ceramic saddles in a packed bed while blowing SO3 gas up through the bed. 

SO3 in the ascending gas reacts with H20(f) in the descending acid to produce strengthened sulfuric acid, i.e.  

The strengthened acid is mostly diluted and sold. Some is recycled to the dehydration and absorption towers. 

Most sulfuric acid plants are double contact plants (Fig. 9.6). They efficiently oxidize their feed SO2 to SO3 and efficiently make the resulting SO3 into H2S04(f). Single contact plants (Fig. 9.1) are simpler and cheaper, but their exit gases contain more SO2. 

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