Page 76 - Coulson Richardson's Chemical Engineering Vol.6 Chemical Engineering Design 4th Edition

FUNDAMENTALS OF MATERIAL BALANCES
recycle stream below 5 per cent. The fresh hydrogen feed is 99.5 per cent pure,
the remainder being inerts. All percentages are molar. 59
For a feed rate of 100 kmol/h of nitrobenzene, calculate:
(a) the fresh hydrogen feed,
(b) the purge rate required,
(c) the composition of the reactor outlet stream.
2.6. In the manufacture of aniline by the hydrogenation of nitrobenzene, the off-
gases from the reactor are cooled and the products and unreacted nitrobenzene
condensed. The hydrogen and inerts, containing only traces of the condensed
materials, are recycled.
Using the typical composition of the reactor off-gas given below, estimate the
stream compositions leaving the condenser.
Composition, kmol/h: aniline 950, cyclo-hexylamine 10, water 1920, hydrogen
5640, nitrobenzene 40, inerts 300.
2.7. In the manufacture of aniline, the condensed reactor products are separated in a
decanter. The decanter separates the feed into an organic phase and an aqueous
phase. Most of the aniline in the feed is contained in the organic phase and most of
the water in the aqueous phase. Using the data given below, calculate the stream
compositions.
Data:
Typical feed composition, including impurities and by-products, weight per cent:
water 23.8, aniline 72.2, nitrobenzene 3.2, cyclo-hexylamine 0.8.
Density of aqueous layer 0.995, density of organic layer 1.006. Therefore, the
organic layer will be at the bottom.
Solubility of aniline in water 3.2 per cent w/w, and water in aniline 5.15 per cent
w/w.
Partition coefficient of nitrobenzene between the aqueous and organic phases:
C organic /C water D 300
Solubility of cyclo-hexylamine in the water phase 0.12 per cent w/w and in the
organic phase 1.0 per cent w/w.
2.8. In the manufacture of aniline from nitrobenzene the reactor products are condensed
and separated into an aqueous and organic phases in a decanter. The organic
phase is fed to a striping column to recover the aniline. Aniline and water form
an azeotrope, composition 0.96 mol fraction aniline. For the feed composition
given below, make a mass balance round the column and determine the stream
compositions and flow-rates. Take as the basis for the balance 100 kg/h feed and
a 99.9 percentage recovery of the aniline in the overhead product. Assume that
the nitrobenzene leaves with the water stream from the base of the column.
Feed composition, weight percentage: water 2.4, aniline 73.0, nitrobenzene 3.2,
cyclo-hexylamine trace.

Note: Problems 2.5 to 2.8 can be taken together as an exercise in the calculation of a preliminary material
balance for the manufacture of aniline by the process described in detail in Appendix F, Problem F.8.