RU2226187C1 - Liquid-phase catalytic aromatics' nitration process - Google Patents

Abstract

FIELD: industrial organic synthesis. SUBSTANCE: invention relates to improved process of liquid-phase catalytic nitration of aromatics, which can be used as intermediates in production of polyurethanes and other polymer materials, dyes, drugs, and explosives. In particular, liquid-phase catalytic nitration with only nitric acid (50-80%) at 20 to 120 C is described. Process is carried out in circulation reactor comprising two vertical cylindrical zones (reaction and recycling) interconnected by overflows in top and bottom sections, wherein reaction zone is filled with cellular high-porous catalyst consisting of aluminabased carrier and properly catalyst consisted of IVB and VIB metal oxides or their sulfurized forms. EFFECT: eliminated filtration of reaction mass and rectification of nitrated products mixed with starting aromatics. 4 cl, 3 ex

Description

The invention relates to chemical technology, more specifically, to processes for producing aromatic nitro compounds used as intermediates in the production of polyurethanes and other polymeric materials, dyes, pharmaceutical compounds and explosives.

Currently, the volume of production of aromatic nitro compounds in the world is measured in several million tons per year. Throughout the 20th century, sulfuric-nitric acid mixtures were used to obtain these substances, primarily nitrobenzene, nitrotoluene and nitrochlorobenzene, and, as a result, there was a need for regeneration or elimination of waste acids. The latter processes are accompanied by significant emissions into the environment (Berkman B.E. Industrial synthesis of aromatic nitro compounds and amines. - M.: Chemistry, 1964).

In the second half of the 20th century, processes devoid of this drawback began to be developed.

One of the directions is based on adiabatic nitration of aromatic hydrocarbons with sulfuric-nitric acid mixtures under conditions when the water released during the reaction is removed from the reaction mass in the form of steam (US Patent US 3981935, German Patent DE 4410417 A1). This path leads to a sharp reduction in the consumption of sulfuric acid.

The second direction is based on the complete rejection of the use of sulfuric acid in the process. Attempts to nitrate hydrocarbons (in conditions of their large excess) with one nitric acid were undertaken by Otmer in 1942-1944. (Othmer DP, Jacobs JJ, Levy JF // Ind. Eng.Chem., 1942. V.34. No. 3. P.286-291, Othmer DF, Kleinhans HL // Ind. Eng.Chem., 1944. V .36. No. 5. P.447-451).

The disadvantages of the method were the relatively low speed of the process and its potential explosiveness.

Since the 1980s, catalytic heterophasic processes for nitration of aromatic hydrocarbons with nitric acid or nitrogen oxides have been developed. Mainly considered processes occurring in the gas phase. As the nitrating agent, nitrogen oxides (NO ₂ , N ₂ O ₄ , mixtures of NO ₂ and NO) are used in pure form or in a mixture with oxidizing agents (oxygen, ozone) (Suzuki N. // Chem. Lett., 1993. P. 1421-1424, Suzuki H., Yonezawa S., Nonoyama N., Mori T. // J. Chem. Soc., Perkin Trans. 1, 1996. P. 2385-2389) or nitric acid (Milczak T., Jacniacki J., Zawadski, J. et al // Synth. Commun., V. 31. No. 2. P.173-188).

Silica gel (US Pat. US 2,109,873), phosphates on an inorganic support (US Pat. England 586732), mixed oxides (MoO ₃ —WO ₃ , MoO ₃ —NiO ₂ , TiO ₂ —SiO ₂ ) (Pat. CIUAUS) were proposed as catalysts. 4551568, US Pat. US 5004846) and others.

The nitration process is carried out at a temperature of 120-300 ° C. The catalysts used are prepared in the form of fine particles (for example, a 24-48 mesh fraction) from which tablets are pressed or the product is poured between the restrictors located on the flow paths of the hydrocarbon vapor and nitrating agent.

There are only a few reports of liquid phase nitration of aromatic hydrocarbons in the presence of solid catalysts.

Nitration is carried out, as a rule, in an organic solvent medium with nitrogen oxides or nitric acid with catalysts of different acidity based on zeolite or ZrO ₂ (Nagi Sh.M., Zubkov E.A., Shubin V.G. // Izv. AN SSSR, ser.chem., 1989, No. 8. S.1933-1934, Nagi Sh.M., Zubkov E.A., Shubin V.G. // Izv. AN SSSR, ser.chem., 1990, No. 7. S.1650-1652).

The disadvantage of this method is the necessity of using and separating an organic solvent.

As a prototype selected US patent No. 6376726. According to the patent, nitration of benzene and other aromatic hydrocarbons is carried out by fuming nitric acid, which usually contains 95-100% HNO ₃ , in the presence of catalysts based on metal-modified montmorillonite clays. The powder catalyst is distributed in an organic compound to which concentrated nitric acid is pinned. After completion of the process, the catalyst is filtered off and the nitro product is isolated from the original by distillation or by some other method.

You can highlight a number of disadvantages of the process proposed in the prototype.

1) The patent does not contain data on the content of dinitro compounds in the reaction products, although for industrial products there are strict restrictions on the content of these impurities;

2) The degree of conversion of benzene is much lower than theoretically calculated for a given amount of nitric acid and, therefore, there is spent acid, for the regeneration of which sulfuric acid must be used;

3) The stages of filtering the catalyst and rectification of mixtures of the starting aromatic compound and nitration products are necessary.

The invention is aimed at eliminating the stages of filtering the reaction mixture from the catalyst and rectification of the products obtained by nitration - a mixture of the original aromatic hydrocarbons and nitro compounds. This is achieved by using a stationary catalyst and producing mononitro compounds in the process, the content of which of the initial aromatic hydrocarbons and dinitro compounds is within the requirements for technical products.

The invention consists in a method of liquid-phase catalytic nitration of aromatic compounds with one nitric acid, characterized in that the nitration is carried out with 50-80% nitric acid at a temperature of 20-120 ° C in a circulation reactor, which consists of two vertical cylindrical zones (reaction and recirculation ), connected by flows in the upper and lower parts, in which the reaction zone is filled with a highly porous cellular catalyst based on metal oxides or their sulfated forms. As follows from the essence of the invention, we propose to replace fuming nitric acid with 50-80% and use, instead of a powder metal-modified catalyst based on montmorillonite clay, a stationary catalyst, the support for which is based on high-strength cellular alumina with a porosity of 45 - 90% and the active agent are oxides of metals of variable valency (for example, Mo, Ti or Zr) or their sulfated forms, while maintaining the main advantage of the prototype, the creation of a process without the use of sulfur oh acid.

The use of 50-80% nitric acid makes it possible to completely eliminate the formation of dinitro compounds, the content of which in technical products, as a rule, should not exceed 0.1%. The decrease in the reaction rate observed during the transition from 95-100% HNO ₃ to 50-80% HNO ₃ can be compensated for by using high acid catalysts, which include, in particular, molybdenum oxide, sulfated forms of titanium and zirconium.

The use of a stationary catalyst instead of a powder makes the filtration step unnecessary, which not only simplifies the process, but also eliminates the attrition of the catalyst and, consequently, its loss.

The use of a circulating reactor in the process makes it possible to obtain a nitro product with a low content of the initial aromatic hydrocarbon, which makes it possible to abandon the rectification stage. The reactor consists of two vertical cylindrical zones (reaction and recirculation), connected by overflows in the upper and lower parts. The reaction zone is filled with a highly porous cellular catalyst based on metal oxides or their sulfated forms.

The circulation in the reactor can be carried out under the action of a mechanical pump (a high-speed mixer can play its role) or when gas is supplied to the lower part of the reaction zone due to the difference in densities of the rising gas-liquid flow in the reaction zone and the descending liquid flow in the recirculation zone.

The nitration process catalyst used in the proposed method consists of a carrier and a catalyst deposited on its surface. The carrier is a highly porous material with a mesh-cellular structure, which is obtained by reproducing the structure of foamed polyurethane foam, after application to the last charge (including dispersed alumina powder (40-50%), an inert carrier, including coarse Al ₂ O ₃ , ( 50-60%) and additives of metal oxides of groups II and IV of the periodic table) and heat treatment, during which the organic base burns out. Compounds capable of forming acid sites on the surface are used as catalysts for nitration processes (as well as many other electrophilic processes). This requirement is met by a large group of metal oxides IVB and VIB - groups of the periodic table and their sulfated forms.

Example 1

Used a batch glass reactor, which is a closed loop consisting of two vertical tubes (inner diameter 12 mm), equipped with shirts, and connecting them flows; the working volume of the reactor is 150 ml. A high speed centrifugal pump type agitator was used. A catalyst — a carrier based on cellular alumina coated with MoO ₃ — was placed in the reaction zone — catalyst volume — 15 ml, catalyst porosity 78%. 127 ml of 70.5% HNO _{3 were} poured into the reactor, it was heated to 70 ° C and 23 ml of benzene was added. After 9 minutes of the reaction, the content of nitrobenzene in the reaction product is more than 99.5%, the content of DNB is less than 0.01%.

Example 2

In a similar reactor with a catalyst based on sulfated titanium (catalyst porosity 82%). 100 ml of 70.5% nitric acid were charged into the reactor, heated to 110 ° C and 19 ml of chlorobenzene were added. About 40% of chlorobenzene reacted in the first 3 minutes. After 60 minutes of reaction, a product was obtained containing 99% of a mixture of nitrochlorobenzenes.

Example 3

Installation of continuous operation without mechanical stirring with circulation due to the difference in densities in the reaction and recirculation zones (due to the supply of nitrogen to the lower part of the reaction zone). The design of the installation is similar to the previous one, but supplemented by a gas separator, the total volume is 3 l, the catalyst is sulfated titanium on cellular alumina, the volume of the catalyst is 1 l. 70% HNO ₃ and benzene were continuously dosed into the unit, temperature 70 ° C. The amount of NB obtained was 0.5 kg / h, the benzene content was 0.1-1%, the dinitrobenzene content was less than 0.02%.

Claims (4)

1. The method of liquid-phase catalytic nitration of aromatic compounds with one nitric acid, characterized in that the nitration is carried out with 50-80% nitric acid at a temperature of 20-120 ° C in a circulation reactor, the reactor consists of two vertical cylindrical zones (reaction and recirculation), connected by flows in the upper and lower parts, in which the reaction zone is filled with a highly porous cellular catalyst, consisting of a support based on aluminum oxide and the catalyst itself, consisting of metal oxides IV B and VI In groups of the periodic table or their sulfated forms. 2. The method according to claim 1, characterized in that the circulation of the stream in the reactor is created using a mechanical pump. 3. The method according to claim 1, characterized in that the circulation of the flow is ensured by the supply of gas (nitrogen) to the lower part of the recirculation zone behind the set of the difference in liquid densities in the reaction and recirculation zones. 4. The method according to claim 1, characterized in that the catalyst is used oxides and their sulfated forms of molybdenum, titanium, zirconium, and as a carrier for it is a cellular frame based on aluminum oxide with a porosity of 45-90%.