By alkylation mechanism, an alkane (paraffin) is reacted with an aromatic compound to produce a high-quality fuel substitute like cumene. To improve the octane number of gasoline, compounds produced from alkylation process are blended with it. Cumene known as isopropylbenzene is produced by alkylation process to use it as an aviation fuel blend. Catalytic alkylation method uses aluminium chloride and hydrochloric acid as a catalyst to initiate the reaction between benzene and propylene. This technology was proposed by Monsanto and named as Monsanto-Lmmus Crest cumene production process.
Description of cumene production by alkylation:
Aluminum chloride (AlCl3) is a category of Friedel-Crafts type catalyst used to add alkyl group to the aromatic ring of benzene. The chemical reaction takes place at 130-135 oC temperature and 3.4 to 3.5 atm pressure. Due to exothermic nature heat is released during the reaction. With the help of preheater, the feed is heated with the reactor effluent and even used to generate steam. Two reactors are used to carry out the alkylation and transalkylation process. Benzene is vaporised in a vaporizer and mixed with propylene. The feed stream is heated to reactor condition along with catalyst. Alkylation reactor converts benzene and propylene to cumene and diisopropylbenzene. The effluent stream is mixed with recycle stream of polypropylbenzenes and passed into transalkylation reactor where it reacts with excess benzene and converts into cumene.
The catalyst is separated from the organic compounds by a water wash in a separator. The separated organic mixture is treated with caustic to remove the traces of acids. The catalyst is concentrated with steam and recycled to the alkylation reactor. Cumene is distilled out by a series of distillation towers that splits out unreacted raw materials.