Benzene → Nitrobenzene

Participants

Reaction Steps

A stream of sulfuric acid into which first a stream of nitric acid and then a combined stream of fresh benzene and recycled benzene were metered is fed to a reactor. The residence time between the addition of nitric acid to the sulfuric acid and the entry of the nitrating solution into the reactor is less than 10 seconds. 6% of recycled benzene are used as excess benzene. After complete reaction of the nitric acid with the benzene to give nitrobenzene under an adiabatic reaction procedure, the now approx. 130° C. hot reaction product is fed to a phase separation apparatus in which the reaction product breaks down into an organic phase (=crude nitrobenzene, also comprising benzene in addition to nitrobenzene) and an aqueous phase (=waste acid, also comprising small contents of nitrobenzene and benzene in addition to sulfuric acid). The aqueous phase mainly encompassing sulfuric acid is subjected to a flash evaporation of water in an evaporator by sudden pressure reduction and is concentrated in this manner. The concentrated sulfuric acid is temporarily stored in a sulfuric acid reservoir tank to be used again in the nitration. After the crude nitrobenzene has been separated off in the phase separation apparatus, it is cooled to approx. 40° C. to 50° C. in a crude nitrobenzene cooler and fed to a wash for work-up. The purified nitrobenzene stream thus obtained, which has been largely freed from nitrophenols and salts is reheated and freed from water and benzene, which are separated off overhead, in a rectification column, as a result of which dried pure nitrobenzene is obtained in the bottom of the column. The condensed head product of the rectification column is fed to a phase separation apparatus in which the head product breaks down into an organic phase (comprising benzene) and an aqueous phase. The benzene is stored temporarily in a buffer tank and from there is returned as recycle benzene into the inlet of the reactor for reaction, as already described above.

Provenance & Evidence