CS195139B1 - Method for isolating diphenylamine from a reaction mixture containing diphenylamine, aniline, water and higher boilers by continuous rectification - Google Patents

Description

The invention relates to the isolation of diphenylamine from a reaction mixture comprising diphenylamine, aniline, water and high boilers. These mixtures are obtained by condensation of aniline to diphenylamine in the presence of various acid catalysts in the gas or liquid phase. Diphenylamine is the starting material in the manufacture of rubber chemicals and stabilizers.

The condensation of aniline to diphenylamine is carried out in a gaseous or liquid phase at temperatures in the range of 300 to 450 ° C, in a liquid phase at temperatures of 300 to 350 ° C, and in a gas phase at 400 to 450 ° C. In both processes, only 15-40% of the aniline is converted and the reaction mixture contains a considerable amount of the reacted aniline. In the liquid phase condensation of aniline, the mixture also contains an acidic catalyst (AlCl 3, HCl, BF 3 and derivatives thereof, etc.) which is removed in various ways, the remainder of the catalyst being washed with water. The extracted reaction mixture contains 1 to 3% water.

This crude mixture contains diphenylamine, aniline, water and high boiling substances of predominantly pitch-like character. The difference in the boiling points of the individual components is considerable and the rectification separation is not difficult. In large units, where continuous rectification of the reaction mixture is employed, water is initially separated with part of the aniline, on another column, aniline, and on the third column, the diphenylamine is separated from the pitch.

The crude reaction mixture is heated before it enters the first column or only in the first column by steam, which, due to the low concentration of diphenylamine in the mixture, consumes a considerable amount of heat, calculated per unit of production of diphenylamine. Aniline and diphenylamine at normal pressure differ by 118 K at boiling point and their distribution is not in principle difficult. However, with the known rectification on the dine column, the desired high separation sharpness, i.e. a low content of diphenylamine in aniline and at the same time a low content of aniline in diphenylamine (below 0.05%), is difficult to guarantee. In this arrangement, the diphenylamine leaving the bottom of the column, typically about 0.17, contains aniline, with distilled aniline having 1 to 2% diphenylamine. The separated aniline is returned to the reactor and the diphenylamine content of this recycle reduces the plant performance by 5 to 15 Z.

Diphenylamine is separated from nonvolatile pitch by simple distillation or rectification with very low potency. We have found that the diphenylamine thus obtained contains some high-boiling impurities, in particular carbazole, in an amount of several tenths of a percent. Thus, the problem of continuous rectification of the reaction mixture in the production of diphenylamine is the use of heat and the purity of diphenylamine and aniline.

The above drawbacks of the known process for isolating diphenylamine from the reaction mixture by continuous rectification removes the process of the invention. The invention is characterized in that the mixture is rectified on four columns, water is separated in the first column, 80 to 95% of the aniline injected in the second column, and 5 to 20 liters of aniline are fed to the third column. , wherein the aniline residue is distilled off with a portion of the diphenylamine, which is preferably conducted without condensation back to the

9513.9 of the second column, in the fourth column, the diphenylamine is separated from the high-boiling residue, the feed of the reaction mixture into the first column being preheated by the condensation vapors of aniline from the second column.

Most of the heat is consumed to distill off the aniline, whose mixture contains 40 to 80% and this heat is used according to the invention to heat the reaction mixture entering the first column from 20 to 30 ° C to 80 and 110 ° C. and the heat cannot be recovered by the distillate or residue of each column.

By being. on the second column, leaving between 5 and 20% aniline in the digester, on the one hand, the boiling point of the remainder of the column is reduced to such an extent that steam can be used for heating and at the same time aniline can be distilled at a relatively higher pressure of 5 to 10 kPa; on one column requiring lower pressure, it will reduce the required column diameter. Splitting the aniline distillation into two columns will reduce the efficiency requirements of the main aniline column, further reducing its cost. Thus, the two-stage aniline de-distillation is cheaper not only operationally, lower energy consumption and cheaper type of energy is used, but also investment, because the second column is very small and cheaper than the difference in cost of the main aniline column in the two alternatives compared. The purity effect of both obtained products is also significant. The distilled aniline contains less than 0.2% diphenylamine & the crude diphenylamine leaving the bottom of the additional column contains less than 0.05% aniline.

In all processes for the condensation of aniline to diphenylamine, 0.2 to 0.5% carbazole, based on diphenylamine, produces, besides other substances, a higher boiling point than carbazole. According to the invention, these impurities are separated by reactivation on a column with 8 to 15 theoretical plates, with a reflux ratio of 0.5 to 1.

This gives diphenylamine with a carbazole content of less than 0.05%.

Example

A mixture of 1020 kg / h of diphenylamine, 1590 kg / h of aniline, 80 kg / h of water, 5 kg / h of carbazole and 35 kg / h of pitch was heated in the exchanger 8 as shown in the attached drawing. at 100 ° C and injected onto the top of the first column 6. The first column 6 had a diameter of 450 mm and contained 8 m height of 25 mm Pall rings. The first column 6 operated without reflux at normal pressure. The distillate contained 10 wt.

% water and 70 wt. % aniline. The residue, in which less than 0.1% water was present, was fed to the second column 6. From this second column 6, which had 10 cap tray trays of 1500 mm diameter, aniline containing 0.3 wt. % diphenylamine. The vapor condensation was performed in two stages. In the ejector 8, the distillate gave about 400 ML / h of feed onto the first column,, in the condenser oval condensed the rest of the distillate vapors. The distillation residue from the second column 8 contained 8 wt. % aniline. This residue was fed to the top of a third column 6 of the same construction as the first column 6. A distillate containing 70% by weight was discharged from this third column, which was operated at a head pressure of 10 kPa and without reflux. % of aniline without condensation back to the second column 2. The distillation residue from the third column 6 contained 0.03 wt. % of aniline, was fed to a fourth column 8, which had 15 cap tray plates with a diameter of 1500 mm. At a head pressure of 2 kPa, diphenylamine containing less than 0.2 wt.

% carbazole. The remainder of this fourth column 6 contained 25 wt. % diphenylamine. The boilers of the first three columns £, £, £ were heated with steam reduced from a 4 MPa network.

Only the fourth coion was heated by an organic heat exchanger at a temperature of 320 ° C.

Claims (3)

SUBJECT What is claimed is: 1. A process for the isolation of diphenylamine from a reaction mixture comprising diphenylamine, aniline and water and high boilers by continuous rectification, characterized in that the mixture is rectified in four columns, water is separated in the first column and separated in a second column. 80 to 95% of the unsprayed aniline, the product from the bottom of the column containing 5 to 20% aniline is fed to a third column, where the aniline residue is distilled off with a portion of diphenylamine which is preferably returned to the second column without condensation. OF THE INVENTION, the diphenylamine is separated from the high-boiling residue, wherein the feed of the reheat mixture to the first column is preheated by condensation vapors of aniline from the second column. 2. The process according to claim 1, wherein the aniline in the second column is rectified at a pressure of 5 to 10 kPa at the top of the column. 3. The process according to claim 1, wherein the diphenylamine in the fourth column is rectified with 8 to 15 theoretical plates at a reflux ratio of 0.5 to 1.