Aromatic mono-nitro cpds. are prepd. by nitrating aromatic cpds. with 70-100 wt.% conc. HNO3. In nitration mixt wt. ratio (HNO3 + H2O): organic components depends on concn. of HNO3 present and is =3 in presence of 70% HNO3 and =8 in presence of 100% HNO3. Nitration mixt. is worked up in a rectifying column. In the rectifying column wt. ratio (HNO3 + H2O): organic components is =3 (in presence of either 70% HNO3 and mono-nuclear aromatic cpds. or of 78; HNO3 and polynuclear aromatic cpds.) to =8 (in presence of 100% HNO3 and mono- or poly-nuclear aromatic cpds. The nitration mixt. is charged to a rectifying zone. Conc. HNO3 is removed overhead as present in nitration mixt. In sump, in working up nitration mixts. from nitration of reactive aromatic cpds., HNO3 concn. is 66-70 wt.% and in working up nitration mixts. from nitration of less reactive aromatic cpds. HNO3 concn. is 60-85 wt.%, but always lower than concn. in nitration mixt. Aromatic mono-nitro cpds. are sepd. from the sump outlet of rectifying column. Prods. are used as intermediates in dyestuff prodn. Process requires no specific safety measures, despite the use of conc. HNO3. Nitration mixt. can be worked up in a simple rectifying column. Energy consumption is reduced, as HNO3 for nitration can be recovered direction from nitration mixt. without dilution. Small HNO3 vols. are used.
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