Page 212 - Chemical engineering design

FLOW-SHEETING
Using the data given below, calculate the stream flows and draw up a preliminary
flow-sheet for the production of 1.0 tonne monochlorobenzene per day. 189
Hint: start the material balance at the reactor inlet (after the addition of the recycle
streams) and use a basis of 100 kmol/h benzene at this point.
Data
Reactor
Reactions: C 6 H 6 C Cl 2 ! C 6 H 5 C HCl

C 6 H 6 C 2Cl 2 ! C 6 H 4 Cl 2 C 2HCl

mol ratio Cl 2 :C 6 H 6 at inlet to reactor D 0.9
overall conversion of benzene D 55.3 per cent
yield of monochlorobenzene D 73.6 per cent
yield of dichlorobenzene D 27.3 per cent
production of other chlorinated compounds can be neglected.
Condenser
Assume that all the chlorobenzenes and unreacted benzene condenses. Assume
that the vapour pressure of the liquid at the condenser temperature is not signif-
icant; i.e. that no chlorobenzene or benzene are carried over in the gas stream.
Separator
Assume complete separation of the liquid and gas phases.
Absorber
Assume 100 per cent absorption of hydrogen chloride, and that 98 per cent of
the chlorine is recycled, the remainder being dissolved in the water. The water
supply to the absorber is set to produce a 30 per cent w/w strength hydrochloric
acid.
Distillation column
Take the recovery of benzene to be 95 per cent, and complete separation of the
chlorobenzenes.
4.2. Methyl tertiary butyl ether (MTBE) is used as an anti-knock additive in petrol
(gasoline).
It is manufactured by the reaction of isobutene with methanol. The reaction is
highly selective and practically any C 4 stream containing isobutene can be used
as a feedstock

C O
CH 2 C CH 3 2 C CH 3 OH ! CH 3 3 CH 3
A 10 per cent excess of methanol is used to suppress side reactions.
In a typical process, the conversion of isobutene in the reactor stage is 97 per cent.
The product is separated from the unreacted methanol and any C 4 ’s by distillation.
The essentially pure, liquid, MTBE leaves the base of the distillation column and
is sent to storage. The methanol and C 4 ’s leave the top of the column as vapour
and pass to a column where the methanol is separated by absorption in water. The
C 4 ’s leave the top of the absorption column, saturated with water, and are used as
a fuel gas. The methanol is separated from the water solvent by distillation and
recycled to the reactor stage. The water, which leaves the base of the column, is