Method for simultaneously preparing iron oxide red pigment and aromatic amine
A method for simultaneously preparing an iron oxide red pigment and an aromatic amine is provided. In the method, an aromatic nitro compound and ferrous iron are first used to prepare an iron oxide red seed crystal under the action of a catalyst, and then iron powder is used to reduce the aromatic nitro compound and generate iron oxide in situ which grows into iron oxide red with pigment performance on the seed crystal. The method provides a clean and economical way for the reduction of an aromatic nitro compound (especially those in which there are other easily-reduced substituents on an aromatic ring) to prepare an aromatic amine.
1. A method for simultaneously preparing an iron oxide red pigment and an aromatic amine, comprising the following steps:
step (1):
adding a specified amount of water to an open reactor provided with a stirrer,
adding a catalyst to the open reactor to obtain a first solution, wherein a mass of the catalyst is 0.1% to 1.0% of a mass of the iron oxide red pigment produced,
heating the first solution to 85° C. to 90° C. and simultaneously adding a solution of a ferrous salt and a solution of an aromatic nitro compound dropwise to the first solution, wherein a dropping rate of the solution of the ferrous salt is larger than a dropping rate of the solution of the aromatic nitro compound so that the solution of the aromatic nitro compound is left when the solution of the ferrous salt is completely consumed;
after finishing adding the solution of the ferrous salt, stopping adding the solution of the aromatic nitro compound to obtain a second solution, and
using a caustic soda solution to tune a pH of the second solution to be 3.8-4.1, wherein the aromatic nitro compound is reduced by ferrous ions to produce an aromatic amine and an α-Fe 2 O 3 crystal nucleus
step (2):
adding a first amount of an iron powder to the second solution when the pH of the second solution decreases to 3.5 to 3.8;
after 10 min, adding dropwise the solution of the aromatic nitro compound left in the step (1) in a duration of 210 min to obtain a third solution, wherein a second amount of the iron powder is added at 70 minutes, and a third amount of the iron powder is added at 140 minutes; a temperature of the duration is kept from 85° C. to 88° C.; and
after finishing adding the solution of the aromatic nitro compound keeping the third solution at the temperature for a period of time to produce a mixture of the iron oxide red pigment and the aromatic amine;
step (3):
filtering the mixture to obtain the iron oxide red pigment and a filtrate; and
acidifying the filtrate to obtain the aromatic amine.
2. The method for simultaneously preparing the iron oxide red pigment and the aromatic amine according to claim 1 , wherein the catalyst used in the step (1) is α-Fe 2 O 3 with a particle size of less than 100 nm or in-situ amorphous δ-FeOOH.
3. The method for simultaneously preparing the iron oxide red pigment and the aromatic amine according to claim 1 , wherein the ferrous salt is any one or a mixture of two from the group consisting of ferrous sulfate and ferrous chloride.
4. The method for simultaneously preparing the iron oxide red pigment and the aromatic amine according to claim 1 , wherein in the step (2), the iron powder has a mesh size of 80 mesh to 100 mesh.
5. The method for simultaneously preparing the iron oxide red pigment and the aromatic amine according to claim 1 , wherein in the step (2), the period of time is from 40 min to 50 min.
6. The method for simultaneously preparing the iron oxide red pigment and the aromatic amine according to claim 1 , the first amount of the iron powder, the second amount of the iron powder, and the third amount of the iron powder are the same.