CS257400B1 - Process for preparing N-phenyl-N-isopropyl-p-phenylenediamine with high processing safety - Google Patents

Abstract

The solution relates to a method for preparing N-phenyl-N'-isopropyl-p-phenylenediamine with high processing safety, from the reaction product of pressure alkylation hydrogenation of p-amino-diphenylamine with acetone. The reaction product containing min. 92 wt. % N-phenyl-N'-isopropyl-p-phenylenediamine, max. 4 wt. % high-molecular substances and thermooxidation products, max. 4 wt. % other impurities, or by-products and with a relative processing safety t(R) of 60 to 90% is vacuum rectified at a pressure of 0.25 to 2.5 kPa and a temperature of 175 to 230 degrees Celsius with a rectification efficiency of 3 to 10 theoretical stages. Vacuum rectification is carried out so that the content of N-phenyl-N'-isopropyl-p-phenylenediamine in the distillation residue is at least 20 and at most 50% by weight.

Description

The invention relates to a process for the preparation of N-phenyl-N‘-isopropyl-p-phenylenediamine (hereinafter IPPD) with high processing safety, IPPD is one of the most widely used rubber chemicals and is used as an antidegradant especially for dynamically stressed rubber products.

IPPD is produced e.g. from p-aminodiphenylamine by pressure alkylation hydrogenation with acetone using a copper chromium catalyst (CS AO 209 731). After the alkylation hydrogenation, a fraction containing mainly acetone, water and 2-propanol is distilled off from the reaction mixture at atmospheric pressure and the technical product of the following composition is obtained after vacuum distillation of the front fractions: min. 92 wt. IPPD, max. 4 wt. high-molecular substances and thermo-oxidation products, max. 4 wt. other impurities, resp. By-products (diphenylamine, p-aminodiphenylamine, N, N-diisopropyl-N-phenyl-p-phenylenediamine). While such a product spins the normed quality parameters, it has been found in practice to have lower and uneven processing safety values in some cases. The processing safety t ₂ is the time to increase the plasticity of the rubber compound during its processing by 2 units above the minimum at the vulcanization temperature. For a mixture without addition of IPPD, this is t ₂ o, for a mixture with addition of t ₂₁ . The relative processing safety t (R) is defined by t (R) = (t ₁₂ / t ₂₀ ). 100%

The addition of IPPD to the rubber compound generally shortens processing safety values and the relative processing safety t (R) falls below 100%. The t (R) values of 50 to 70% result in a significant reduction in the time t ₂₎ , which negatively affects the technological process of processing rubber compounds. Similarly, the fluctuations and imbalances in the processing safety values of the IPPD technical product also have a negative effect. From this point of view, it is obvious that the processing plants of rubber mixtures - due to the smoothness of the technological process - require a certain minimum and mainly balanced level of this parameter (min. 80%). However, in the industrial preparation of an IPPD technical product, processing safety values are in the range of 60-90 ° / o, which is too wide an interval. Furthermore, research has found that significant improvements in processing safety values, even for good IPPD products, occur by exposure to higher temperatures (above 100 ° C); under these conditions, the effect of atmospheric oxygen is particularly adversely affected. In the industrial production of IPPD, these situations may occur due to unfavorable circumstances, respectively. failures of machinery-technological equipment.

Said drawbacks of low and unbalanced process safety are overcome by the process for the preparation of high process safety N-phenyl-N--isopropyl-p-phenylenediamine from the reaction product of the pressure alkylation hydrogenation of p-aminodiphenylamine with acetone according to the invention.

The essence of the invention is that the reaction product containing min. 92 wt. N-phenyl-N‘-isopropyl-p-phenylenediamine, max. 4 wt. high-molecular substances and thermo-oxidation products, max. 4 wt. other admixtures, respectively. by-products and with a relative processing safety t (R) of 60-90% is rectified in vacuo at a pressure of 0.25-2.5 kPa and a temperature of 175-230 degrees Celsius with a rectification efficiency of 3-10 theoretical plates. Vacuum rectification is carried out so that the content of N-phenyl-N-isopropyl-p-phenylenediamine in the distillation residue is at least 20 and at most 50 washes. wt.

In the rectification, pitch-like residues having a content of 20 to 50% by weight are separated. of the active substance N-phenyl-N‘-isopropyl-p-phenylenediamine - (IPPD). It has been found that high molecular weight pitch substances reduce processing safety. It is advantageous to keep the IPPD content at the lower limit, since at higher IPPD content in pitch residues, product losses increase. With an IPPD content below 20% by weight. however, problems arise with the transport and processing of the pitch residue, as its transport properties deteriorate sharply.

An advantage of the process according to the invention is that from technical products with relatively low and unbalanced values of relative processing safety (60 to 90%), rectification on a rectification column with a certain minimum efficiency yields products with high and balanced values of relative processing safety (above 95%). , which is a prerequisite for their full application in processing rubber mixtures. In this way, the value of process safety can also be increased even for products whose low process safety is caused by prolonged thermal exposure, possibly in the presence of air.

A further advantage of the process according to the invention is that it is possible to prepare the final product with a predetermined relative processing safety value by mixing the rectified high t (R) product with a low processing safety product usually not distilled or low in value. t (R) value due to thermooxidation. It has been found that when mixing products, it is possible to follow the formula m ^ ma = [SB — SB (2)] / [SB (1) - SB] (1) in which ni] is the product weight with higher relative processing safety in kg , m ₂ is the weight in kg of the product with lower relative processing safety, SB is the value of the required relative processing safety, SB (1) is the value of higher relative processing safety, SB (2) is the value of lower relative processing safety. SB (1) - SB (1).

The advantage of such a process is that by mixing, the final product is prepared with a sufficiently high and balanced value of relative processing safety, without the need to rectify the entire volume of IPPD produced, thereby saving a significant amount of energy, which is usually organic. heat exchangers with temperatures above 300 ° C.

Relation (1) can be modified to (2) to allow the determination of the relative processing safety value when mixing two or more products with different processing safety values

SB = [mi SB (1) + m ₂ (2) + ... + + m (N j (N)) / [m _t + m ₂ + ... + m (N)] (2)

SB is the resulting value of relative processing safety after mixing N-products, SB (1), SB (2), SB (N] are relative processing safety values of products 1 * 2 ... N, m ,, m ₂ , m _N are product weights 1.2 ... N in kg.

These examples illustrate but do not limit the scope of the invention.

Example 1

A 1000 liter autoclave was charged with 350 kg of p-aminodiphenylminine, 400 L of acetone and 10 kg of copper-chromium catalyst. The reaction mixture was stirred and heated to a reaction temperature of 150 degrees Celsius. Hydrogen was pressurized into the autoclave and maintained at 6 MP for 5 L. The reaction mixture was separated at atmospheric pressure. The light fraction (acetone, isopropyl alcohol, water, methyl isobutyl ketone and the like) was distilled off and then 1% by weight was distilled off under a pressure of 2.4 kPa. called. front fractions. The distillation residue consisted of a technical IPPD of the following composition (GLC)

IPPD - 97.5 wt.

diphenylamine - 0.2 wt.

p-Aminodiphenylamine - 0.8 wt.

N, N-diisopropyl-N-phenyl-p-phenylenediamine - 1.2 wt.

moreover — 0.3 wt.

In addition, the technical IPPD contained about 1.5 wt. high molecular weight substances.

The melting point was 77.2 ° C, relative process safety - · 72%. A 100 kg sample of this product was rectified on a pilot run rectification batch column with an efficiency of 5 theoretical trays at a reflux ratio of 1: 1 and 3.5 kg of distillation residue and 96 kg of distilled product were obtained with a relative process safety value of 99%. The digest residue contained 30% IPPD and was well transportable.

Example 2

The distilled product of Example 1 in an amount of 600 g was charged into an open flask and heated to 130 ° C for 50 hours. At the end of this time, the measured value of relative processing safety was 65%. A sample of this product (500 grams) was distilled under an absolute pressure of 1 kPa to give 469 g of IPPD product with a relative process safety value of 98%.

Example 3

Samples of the non-distilled and distilled product of Example 1 were mixed and the processing safety of these products was measured. Mixing ratios and processing safety values are given in the following table.

obsah nedest. IPPD in mixture [wt. ]

T and b and the content of dest. IPPD in mixture [wt%] processing safety (%)

100

100 99 75 92 50 86 25 78 0 72

The results show a linear dependence of processing safety on the final product composition. .....

Claims (1)

Process for the preparation of N-phenyl-N iz-isopropyl-p-phenylenediamine with high process safety from the reaction product of pressure alkylation hydrogenation of p-aminodithenylamine with acetone, characterized in that the reaction product containing min. 92 wt. N-phenyl-N‘-isopropyl-p-phenylenediamine, max. 4 wt. high-molecular substances and thermo-oxidation products, max. 4 wt. other admixtures, respectively. of secondary product ducts with a relative processing safety t (R) of 60 to 90% is vacuum-rectified at a pressure of 0.25 to 2.5 kPa and a temperature of 175 to 230 ° C with a rectification efficiency of 3 to 10 theoretical levels; the content of N-phenyl-N'-isropropyl-p-phenylenediamine in the distillation residue is at least 20 and at most 50% by weight.