Manufacture of Phenol
The vast majority of phenol is made by the cumene process. The process has three stages:
• Production of cumene
• Conversion of cumene to cumene hydroperoxide
• Decomposition of cumene hydroperoxide
Figure 1. The Phenol production by the cumene process
A) Production of cumene
Cumene is the name often given to (1-methylethyl) benzene (isopropylbenzene). It is produced by the reaction of benzene and propene, using an acid catalyst; this is an example of a Friedel-Crafts reaction:
In one process, benzene and propene (3:1) are passed over an acid catalyst, usually a zeolite such as ZSM-5 at ca 600 K and under pressure (ca 10 atm) in a fixed bed reactor. The zeolite is more environmentally friendly than traditional acid catalysts such as aluminium chloride. The effluent is much cleaner and lower temperatures and pressures can be used.
Alternatively, propene gas is liquefied under pressure (ca 30 atm) and mixed with benzene before being passed, still under pressure, through a reactor containing the solid zeolite at ca 435 K. This process is becoming more popular as it uses even lower temperatures and thus saves energy.
In some plants, solid phosphoric acid is used as the catalyst, in place of zeolites.
B) Conversion of cumene to cumene hydroperoxide
Cumene is then oxidized with air to give the hydroperoxide (Figure 3). The reaction is autocatalyzed by cumene hydroperoxide. The overall reaction can be represented as:
The reaction takes place at temperatures between 350-390 K and 1-7 atm pressure, the latter to retain the system in the liquid phase.
At higher temperatures, the hydroperoxide is unstable and could decompose violently. The oxidizers are generally built some distance from the rest of the plant.
C) Decomposition of cumene hydroperoxide
Finally, the hydroperoxide is mixed with sulfuric acid at 313-373 K to give, after neutralisation, phenol and propanone. This reaction when carried out with small amounts of sulfuric acid (500 ppm by mass) is termed homogeneous cleavage:
The products are separated by distillation, in up to six columns. Product yield is 85-87%, based on benzene.
Annual production of phenol including following information:
World:
- 8.9 million tonnes1,2
Asia:
- 3.7 million tonnes1
Europe:
- 2.7 million tonnes1
US:
- 2.3 million tonnes1
Application of phenol
The most important chemical made from phenol is bisphenol A, which is used to make the polycarbonates. Phenol is also catalytically reduced to cyclohexanol, which is used in the manufacture of polyamides. Phenol is also used to make a range of thermosetting polymers (resins).
Figure 2. Application of phenol
Among the other uses of phenol is the production of phenylamine (aniline) needed, for example, for the manufacture of dyes. Antiseptics such as 2,4-and 2,6 dichlorophenols are also made from phenol.