Question

Maleic anhydride, C4H2O3, is produced by the vapour phase reaction of benzene with air(take as 21% oxygen and 79% nitrogen). The fresh feed of benzene has the following composition: 99% w/w benzene, 1% w/w toluene. \mathrm{C}_{6} \mathrm{H}_{6}+41 / 2 \mathrm{O}_{2} \rightarrow \mathrm{C}_{4} \mathrm{H}_{2} \mathrm{O}_{3}+2 \mathrm{CO}_{2}+2 \mathrm{H}_{2} \mathrm{O} The vapour phase catalysed reaction takes place in a fluidised bed reactor. The"idealised" reactor operates at 78% conversion per pass of benzene. Assume there is no oxygen in the reactor outlet. The reactor efflux is cooled and partly condensed and then(ideally) separated into two streams: a gas stream containing all the nitrogen, carbon dioxide, toluene and the unreacted benzene and a liquid stream containing the crude maleic anhydride and water. Assume the gas stream is cooled and all the nitrogen and carbon dioxide leave the process, leaving the benzene and toluene in the liquid phase.Part of this stream is recycled, but the rest is purged to avoid a build-up of toluene. The purge rate is 2.057% by volume of the liquid outlet from the second partial condenser. Draw a block diagram of the system and annotate it with the components for each of the streams.[3 marks] For a 100 kmol h-1 fresh feed of benzene and toluene mixture, calculate the rate and composition of: (i)the recycle stream. (ii)the outlet streams from the first and second condenser. (ii)the purge. Check the overall mass balance. List three assumptions made in the mass balance.

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