Process for producing aromatic amines
View Patent ↗Aromatic amines are produced by adiabatic hydrogenation of nitroaromatic compounds in the gas phase on one or more fixed catalysts. The nitroaromatic reactant is passed over the catalyst under pressure and at elevated temperature with hydrogen, water, optionally nitrogen and substantially in the absence of the aromatic amine produced from the nitroaromatic.
1. A process for producing aromatic amines represented by the formula
in which
R 1 represents hydrogen, a methyl group, an ethyl group or an amino group, and
R 2 represents hydrogen, a methyl group, or an ethyl group comprising hydrogenating a nitroaromatic compound represented by the formula
in which
R 2 represents hydrogen, a methyl group, or an ethyl group, and
R 3 represents hydrogen, a methyl group, an ethyl group, or a nitro group,
with hydrogen on a fixed catalyst,
in which:
(1) hydrogenation is performed at
(a) an absolute pressure of from 1 to 50 bar,
(b) a gas mixture inlet temperature of from 150 to 400° C., and
(c) a maximum catalyst temperature of 600° C. under adiabatic conditions, and
(2) a gas mixture comprising:
(i) from 3 to 150 moles of hydrogen per mole of nitro groups and
(ii) from 1 to 100 moles of water per mole of nitro groups is passed through the fixed catalyst at the start of hydrogenation, and
(3) hydrogen which is substantially free from aromatic amine which is separated from the reaction mixture during hydrogenation is returned to the hydrogenation reaction.
2. The process of claim 1 in which the nitroaromatic compound is represented by the formula
in which R 3 represents hydrogen, a methyl group, an ethyl group or a nitro group.
3. The process of claim 1 in which the hydrogenation is performed in 1 to 10 reactors connected in series.
4. The process of claim 3 in which one or more of the reactors connected in series is replaced by up to 5 reactors connected in parallel.
5. The process of claim 1 in which the hydrogenated reaction mixture is cooled and dissipated heat therefrom is used to generate steam.
6. The process of claim 3 in which nitroaromatic compound and hydrogen are fed into the gas mixture before that gas mixture is introduced into each reactor.
7. The process of claim 1 in which the fixed catalyst is in the form of a catalyst bed having a thickness of between 1 cm and 5 m.
8. The process of claim 1 in which the catalyst comprises:
(I) 1-100 g/l catalyst of one or more metals from Groups 8 to 12 of the Periodic Table of Elements,
(II) 1-100 g/l catalyst of one or more transition metals from Groups 4 to 6 and 12 of the Periodic Table of Elements, and
(III) 1-100 g/l catalyst of one or more main group elements from Groups 14 and 15 of the Periodic Table of Elements
on a support with a BET surface area of less than 20 m 2 /g.
9. The process of claim 8 in which the catalyst comprises: (I) from 5 to 40 g of Pd, (II) from 1 to 40 g of Ti, V, Nb, Ta, Cr, Mo and/or W and (III) from 2 to 20 g of Pb and/or Bi per liter of catalyst on α-Al 2 O 3 .
10. The process of claim 1 in which the catalyst comprises palladium on a carbon support having a BET surface area of 0.2 to 10 m 2 /g and a palladium content of from 0.001 to 1.5 mass %, based on the total mass of the catalyst.