Chapter 6, Problem 6.77P

Acetaldehyde is synthesized by the catalytic dehydrogenation of ethanol:

   ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}\to {\text{CH}}_{\text{3}}{\text{CHO+H}}_{\text{2}}$

Fresh feed (pure ethanol) is blended with a recycle stream (95 mole% ethanol and 5% acetaldehyde), and the combined stream is heated and vaporized, entering the reactor at 280°C. Gases leaving the reactor are cooled to -40°C to condense the acetaldehyde and unreacted ethanol. Off-gas from the condenser is sent to a scrubber, where the uncondensed organic compounds are removed and hydrogen is recovered as a by-product. The condensate from the condenser, which is 45 mole% ethanol, is sent to a distillation column that produces a distillate containing 99 mole% acetaldehyde and a bottoms product that constitutes the recycle blended with fresh feed to the process. The production rate of the distillate is 1000kg/h. The pressure throughout the process may be taken as 1 atm absolute

(a) Calculate the molar ?ow rates (kmol/h) of the fresh feed, the recycle stream, and the hydrogen in the off-gas. Also determine the volumetric ?ow rate (m³/h) of the feed to the reactor. (Suggestion: Use Raoult’s law in the analysis of the condenser.)

(b) Estimate (i) the overall and single—pass conversions of ethanol and (ii) the rates (kmol/h) at which ethanol and acetaldehyde are sent to the scrubber.