22.2.4 Process Technology (Figure 22.1)

Figure 22.1 Flow sheet of Phenol production from Cumene

• • Fresh cumene is mixed with hydrogenated unreacted cumene, cumene + alpha methyl styrene (recycle streams).

• The pre-purification step involves converting unsaturates such as alpha methyl styrene and others to saturates. This is done by using nickel catalyst at 100°C and feeding hydrogen to the pre-purification reactor. The product from this unit then mixes with the fresh cumene.

• The fresh cumene and processed cumene and alpha methyl styrene are fed to the oxidation reactor. The oxidation reactor refers to a gas liquid reaction between air (Oxygen) and the cumene.

• An emulsion of cumene is prepared in the oxidation reactor by adding alkali to it.

• pH is maintained in the range of 8.5 – 10.5 to suit good emulsification conditions.

• After reaction, vent gases are condensed and recycled back and the product is sent to a cleavage unit.

• The cleavage unit consists of a stirrer and is fed with fresh and recycled H₂SO₄ aqueous solution to enable the hydrolysis of cumene hydroperoxide.

• The product streams from the cleavage unit enter a settler (phase separator) which upon gravity settling yields two streams namely the acid rich aqueous stream and the phenol rich organic stream.

• The aqueous stream consists of the sulphuric acid and is sent back to the cleavage unit as a recycle stream.

• The organic stream consists of cumene (unreacted), phenol (product), acetone (side product), alpha methyl styrene (side product) and acetophenone (side product).

• The organic stream from the gravity settler unit then enters a scrubber fed with water. In this operation, water extracts the remaining acids in the organic stream and produces crude phenol stream. Water leaving the unit consists of acidified wash water.

• The crude phenol then enters a distillation unit that separates acetone from the other components.

• The bottom product from this distillation column enters a vacuum distillation column that produces cumene as a top product.

• The bottom product from the distillation column enters another vacuum distillation unit to produce alpha methyl styrene.

• The bottom product of this distillation column enters the final vacuum distillation unit to produce phenol as top product and acetophenone as the bottom product.