This column is based on “Nitrobenzene Production from Benzene – Cost Analysis,” a report published by Intratec. It can be found at: www.intratec.us/analysis/nitrobenzene-production-cost.
Nitrobenzene is an important chemical intermediate. More than 95% of nitrobenzene is used in the production of aniline, which is largely used to manufacture isocyanates for polyurethane foams, plastics and dyes. The relative ease of aromatic nitration has contributed to the varied industrial applications of nitrobenzene derivatives.
The process examined here (Figure 1) is similar to Noram’s adiabatic benzene-nitration process, and consists of three major sections: benzene nitration, purification and vent treatment.
Benzene nitration. Benzene is preheated and fed to a plug-flow nitrator. Nitric acid (65 wt.% solution in water) is also preheated and mixed with fresh and recycled (re-concentrated) sulfuric acid before being fed into the reactor. In the nitrator, benzene reacts with nitric acid, producing nitrobenzene. The process operates with a stoichiometric excess of benzene to ensure complete nitric acid conversion in the nitrator. The reaction product is sent to a decanter, where crude nitrobenzene is separated from the spent sulfuric acid. Spent sulfuric acid recovered from separator is flash-concentrated under vacuum.
Purification. Water removed from spent acid is sent to a vacuum decanter. The organic condensate from the decanter is routed with crude nitrobenzene to a three-step washing train, where most of impurities are removed. The water generated in the wash step is treated with the aqueous condensate from the decanter in a column and discharged as waste. Product material exiting the washing train is sent to a steam stripper to recover the excess benzene, which remains in solution with the nitrobenzene up to this point in the process. Benzene is separated from water and recycled. Finally, the nitrobenzene product is separated from water and sent to an aniline plant.
Vent treatment. Vents generated along the process, after being combined, are sent to a scrubber. The scrubber uses a nitrobenzene slipstream to recover any benzene present in the vent stream. The bottom product is recycled to the washing train, while the overhead stream is sent to a packed bed unit to remove nitrogen oxides, forming a dilute nitric acid solution that is sent back to the nitrator.
Nitrobenzene is commercially manufactured by direct nitration of benzene using a mixture of nitric and sulfuric acids. The nitration plant can also be integrated upstream with a nitric acid production plant. In this case, the main raw materials are benzene and ammonia (which is converted to nitric acid via oxidation and then used in the nitration of benzene). Nitrobenzene production pathways are presented in Figure 2.
The total operating cost (including raw materials, utilities, fixed costs and depreciation costs) estimated to produce nitrobenzene was about $600 per ton of nitrobenzene in the first quarter of 2016. The analysis was based on a plant constructed in the U.S. with the capacity to produce 530,000 metric tons per year of nitrobenzene.
Edited by Scott Jenkins
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