Benzene → Nitrobenzene

Participants

Reaction Steps

A sulfuric acid stream (11), a nitric acid stream (12), a fresh benzene stream (13) and a recycle benzene stream (21) are fed into a reactor (1). The benzene is used in 5 to 10% excess, based on nitric acid. The amount of recycle benzene obtained depends on this excess and the quality of the starting benzene. Once all the nitric acid has reacted with the benzene to give nitrobenzene under adiabatic reaction conditions, the reaction product (14), now at a temperature of approx. 130° C., is fed into a phase separation apparatus (2), in which the reaction product (14) separates into an organic phase ((15)=crude nitrobenzene, comprising benzene and low boilers in addition to nitrobenzene) and an aqueous phase ((16)=waste acid, still comprising small proportions of nitrobenzene and benzene in addition to sulfuric acid). The aqueous phase (16), comprising mainly sulfuric acid, is subjected to a flash evaporation of water in the evaporator (3) by sudden pressure reduction, and is thereby concentrated. The concentrated sulfuric acid (17) is stored in the sulfuric acid tank (4) until it is re-used. After separation in the phase separation apparatus, the crude nitrobenzene (15) is cooled to approx. 50° C. in the crude nitrobenzene cooler (5) and fed into the wash (6). The resulting stream of purified crude nitrobenzene (18), substantially freed of nitrophenols and salts, is heated again and, in a distillation column (7), freed of water, benzene and other low boilers, which are separated off (19) overhead, to give dried pure nitrobenzene (20), which is stored in a tank (8). The condensed head product (19) of the distillation column (7) is fed into a phase separation apparatus (9), in which the head product separates into an organic phase ((21), comprising benzene and low boilers) and an aqueous phase (22). The organic phase (21) is temporarily stored in a buffer tank (10) and from there, as already described above, is returned into the inlet of the reactor (1) for reaction. Nitrobenzene prepared in this way typically has a purity of approx. 99.96% (GC), a residual benzene content of 0.0028% (GC), a 1,3-dinitrobenzene content of 0.0273% (GC) and a nitrophenole content of <5 ppm (HPLC). Furthermore, the nitrobenzene has a water content of 0.0079% (Karl-Fischer).

Provenance & Evidence