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(1) Production of Formaldehyde

Formaldehyde results from the oxidation of methanol according to the

equation:

CH3OH + 1/2 O2 HCHO + H2O

The oxidation is achieved through passing air stream into a converter to

react with the vaporized methanol. Fresh and recycle methanol is withdrawn

from a charge tank, evaporized and superheated then it is passed into the

methanol air mixture.

Atmospheric air is purified in an air-scrubber using dilute caustic as a

scrubbing solution. The purified air is filtered, compressed and then

preheated to about 55oc in a heat exchanger.

The product leaves the converter at about 620 oc. The converter is a water-

jacketed vessel containing silver catalyst. About 65% of methanol is

converted into formaldehyde. The reactor outlet contains about 25%

formaldehyde which is absorbed in water together with the unreacted

methanol and sent to a holding tank. This tank feeds a distillation column to

separate the formaldehyde product as bottom and the recycle methanol as the

as a top product.

Formaldehyde is marketed as 37% solution known as FORMALIN.

(2) Production of Acetic Acid

Acetic acid is produced by the vapor phase oxidation according to the

following reaction:

CH3COCH3 + 2O2 CH3COOH + CO2 + H2O

Ag- catalyst

Flowsheeting

Sheet (1)

21/2/2015

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The reaction is being carried out continuously in a fixed bed catalytic reactor

with acetone vapor and air. The liquid acetone is being continuously fed

from its reservoir into a horizontal vaporizer made of steel tube (L = 2 m, ID

= 50 mm), outside which superheated steam is condensing in countercurrent

flow pattern. Air and acetone vapor are mixed before passing through

preheater before feeding to the reactor. The reaction is conducted at 304 kPa

and the temperature is maintained at 250oC by circulating cooling water

through a cooling coil fitted in the fixed bed. The air used is 30% excess of

the theoretical amount. The conversion factor is only 70% based on both

reactants. The gases outlets the reactor are fed to cooler condenser where

non condensable gases are disposed off while the unreacted acetone-acetic

acid mixture is fed to a distillation tower to obtain pure acetic acid at a rate

of 300 ton/day. Unreacted acetone is withdrawn at its boiling point from the

tower and recycled to the process while the produced water from the

distillation tower is directed to water treatment unit.

Compound Boiling point, oC

Acetone 58

Acetic acid 120

O2 -183

CO2 -78.5

H2O 100

(3) Production of Trichlorobenzene

In the process of producing trichlorobenzene (TCB) by direct chlorination of

benzene dissolved in ethyl alcohol (1:1 by weight) in the presence of

a catalyst (10% by weight of starting benzene), other chlorobenzene isomers

(mono & di isomers: MCB & DCB) are produced as side products. In order

to maximize the yield of TCB, a 20% excess of Cl2 gas (by weight, based on

the theoretical amount of Cl2 required to produce TCB) should be used. The

Cl2 gas is fed at 35oC and 20 atm to a jacketed batch reactor, to which the

benzene-alcohol solution and the catalyst are charged. The chlorination

reaction is endothermic and 1290 kJ are absorbed for each kg mole of the

chlorobenzene isomer produced. Heat of the reaction is supplied by a steam

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condensation in the reactor jacket (latent heat of steam condensation is 200

kJ/ Kg). the mixture if the isomers is discharged from the reactor and fed to

a distillation column operating continuously to recover the unreacted Cl2 gas,

which is disposed off and not recycled back to the reactor. The bottom

product from the distillation column is fed to a 3 stages crystallizer.

Hint: the melting points of the chloro isomers are: MCB +15 oC, DCB -40

oC & TCB -12

oC

(4) Production of Nitro toluene

The nitration of toluene to produce the 3 isomers: mono – di - & tri-nitro

toluene can be carried out as follows:-

Toluene is fed to a batch reactor where the required amount of mixed acid

(nitric & sulfuric) has been previously added. After mixture is damped into a

settler where the nitro isomers and unreacted toluene are separated from the

unconsumed mixed acid, the nitro isomers & unreacted toluene are then fed

to a tank with a mixer to be washed by a dilute solution of sodium carbonate.

After washing, the resulting mixture is dumped into a second settler to

separate the washed isomers and unreacted toluene from the spent alkali

solution.

The isomers and unreacted toluene mixture is finally washed with water in a

similar way as for the washing with the dilute alkali solution. The finally

washed isomers & unreacted toluene mixture is fed to a continuous

distillation column, where unreacted toluene is separated as an overhead

product and recycled to the reactor. The bottom product from the first

distillation column is fed to a second distillation column, where the 3

isomers are produced as pure products in the order of increasing boiling

point (mono- > di- > tri).

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(5) The production of Aniline

Aniline is an important starting material for the production of intermediates

that are used in the synthesis of dyes stuffs.

Aniline is being produced by the vapor phase reduction of nitrobenzene

according to the following reaction:-

C6H5NO2 + 3H2 C6H5NH2 + 2H2O

The reaction is being carried out continuously in a fluidized bed catalytic

reactor fed with nitrobenzene vapor and hydrogen gas. The crude

nitrobenzene is being fed continuously from its reservoir into a vaporizer

made of vertical brass tubes (L = 2m, ID = 50mm), outside which

superheated steam is condensing. Hydrogen gas is introduced into the

nitrobenzene vaporizer outlet pipe. The nitrobenzene vapor – hydrogen

mixture is passed through a preheater before feeding to the reactor. The

reaction is conducted at 188 kN/m2 and the temperature is maintained at

270oC by circulating cooling water through a jacket around the reactor. The

hydrogen used is 200% excess of the theoretical amount. Catalyst employed

copper on silica. Degree of reaction completion is 95 % based on

nitrobenzene fed.

The reaction products are fed to a condenser, where aniline and water

condense, while excess hydrogen leaves the condenser to be compressed and

recycled into the process. The aniline – water mixture is to be separated by

means of settling and decantation.

The water layer still contains some aniline (solubility of aniline at 25oC is

3.5 parts per 100 parts of water). This water layer is fed to a distillation unit

to recover the dissolved aniline. The decanted aniline layer containing crude

aniline and unreacted nitrobenzene is fed into a steam distillation unit to

obtain the final pure aniline product.

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(6) The production of Xylene

The 3 isomers of xylene (o, m, and p) are being produced according to the

equation:-

C6H6 + 2C3H6 C6H4 (CH3)2 + 2C2H4

The reaction is being carried out in the gaseous phase in a tubular continuous

flow reactor. The reactants are fed from their storage tanks, from where pure

benzene is passed through a vaporizer followed by a mixing feed blower. In

this blower both benzene vapor and propylene gas are mixed in the required

ratio and then the gaseous mixture is delivered to a preheater. After the

preheater, the mixture is fed to the reactor by another blower. The mixture

enters the reactor at 500 K and 2 atm. The reaction is only 70% complete so

that 60% of the moles of xylene isomers produced are p-xylene, while the

rest is equally divided between the other 2 isomers. The effluent exits from

the reactor is fed to a cooler condenser, where all the components (products

& unreacted materials), except the produced ethylene and unreacted

propylene are condensed. The liquid mixture from the cooler condenser is

fed to a continuous distillation column operating at a reflux ratio of 2:1

where all the unreacted benzene is separated. The mixture of isomers is fed

to a fractional crystallized out.

The remaining liquid is fed to a preheater followed by a distillation column

that separate 90% of the second isomer as pure overhead product.

The following information is available:-

Compound Benzene o-xylene m-xylene p-xylene

Melting

point, oC

-5 +5 -40 -60

Boiling

point, oC

80 170 120 160