RU2164222C1 - Method of catalytic liquid-phase reduction of aromatic nitro compounds - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: described is method of catalytic liquid phase reduction of aromatic nitrocompounds with hydrogen into amines; in order to reduce wear of catalyst under conditions of great flow rates (more than 1m/s), active metal includes VIII group elements (e.g. nickel, palladium) applied onto granular aluminium oxide with particle size of 20-200 mcm and bulk density of 0.6-0.3 g/cubic cm. Reduction is carried out at pressure of 0.1- 5.0 Mpa and temperature by at least 10 C lower than solvent boiling temperature. Process is carried out in closed system consisting of reaction, separation and recirculation zones. Hydrogen is fed into lower portion of reaction zone into which nitrocompound solution and catalyst recirculating in reaction products are weighted simultaneously. Recirculation is made possible due to difference of densitier of ascending gas-filled flow in reaction zone, and reaction products, in recirculation zone. EFFECT: smaller amount of catalyst and longer service life thereof. 1 tbl

Description

 The present invention relates to chemical technology, more specifically to processes for producing aromatic amines used in the manufacture of polyurethanes and other polymeric materials, as well as dyes and medicinal compounds.

 The method of catalytic reduction of aromatic hydrocarbons with hydrogen has been known for over 50 years and is widely used in industry for the production of aniline and other aromatic amines, gradually replacing other reduction methods.

 In known processes, the reduction is carried out in the vapor or liquid phase using catalysts mainly related to Group VIII metals.

 Recovery in the vapor phase is used for boiling nitro compounds, for example nitrobenzene. To restore dinitro compounds, the vapor-phase reduction method is practically not used because of the increased danger of these processes. However, in the patent of Germany N 3734344 proposed to restore dinitrotoluene (DNT) in the vapor phase, using a very large excess of hydrogen.

 The liquid phase catalytic reduction of nitrobenzene and other aromatic nitro compounds is the subject of numerous patents and copyright certificates. It is carried out in many versions, differing in the composition of the reaction masses, the nature of the metal catalyst and carrier, the hardware design of the processes and other conditions.

 The process can be carried out in the presence of inert solvents, of which aliphatic alcohols are most often used (England patent N 852144, Germany patent N 1044099, US patent N 2233129, USSR copyright certificate N 215226), water or mixtures of water with amines (US patent N 4185036 , German patent DE N 4323687 A1) and other compounds.

 The most common catalysts for the liquid phase reduction process of nitro compounds are Group VIII metals, including noble metals, primarily platinum and palladium (US Pat. Nos. 4,400,538 and 4,118,536), and nickel in various forms: Raney nickel, metallic nickel, and nickel deposited on the surface media (US patent N 3032586 and N 3213141, Germany patent N 348784). Activated carbon, zeolites, aluminum and its oxide are most often used as a carrier.

 The differences in the hardware design of the recovery process are very large. Batch and continuous processes are used with a stationary (US Pat. No. 4,400,538) or liquid-suspended catalyst (US Pat. No. 3,761,521).

 As a prototype, US Pat. No. 3,546,296 was selected. According to the patent, the catalytic reduction process is conducted in a closed system consisting of a reaction zone, a separation zone and a recirculation zone. The reduction is carried out in an organic solvent medium in which the nitro compound and reaction products are soluble. A vertical cylindrical pipe with a coil located inside it is used as the main element of the reactor.

A three-phase flow moves up the pipe:
1) liquid phase - a solution of the nitro compound and reaction products (amines and water) in a high boiling solvent (for example, 2-ethylbutanol);
2) the gas phase is hydrogen;
3) solid phase — catalyst — nickel or copper on the support.

 Due to the excess of hydrogen (3-6 times against the necessary), the reaction mass is intensively mixed, which ensures a high speed of the recovery process. In addition, the density of the reaction mass sharply decreases in the rising stream. This allows for its recirculation without the use of mechanical devices - due to the difference in the densities of the rising and falling flows (after separation from the gas, part of the liquid goes to isolate the reaction product, and the catalyst suspension in the rest of the liquid returns to the bottom of the column through a parallel pipe).

 The prototype has a significant drawback due to the high flow rate in the vertical pipe (more than 1 m / s) - significant grinding of the catalyst particles as a result of intense friction between themselves and against the walls of the reactor. This reduces the activity of the catalyst and deteriorates its separation from the liquid in the separator, which leads to the breakthrough of part of the catalyst to the stage of separation of the amine. It should be noted that technical alumina is a fine crystalline powder with a particle size of less than 20 microns and therefore is not completely separated from the reaction mass in the separator.

The invention is aimed at improving the abrasion resistance of the catalyst, increasing the life of the catalyst and reducing its losses as a result of unsatisfactory separation of the catalyst from the reaction mass. The essence of the invention lies in a method for continuous catalytic liquid-phase reduction of aromatic nitro compounds with hydrogen to aromatic amines, in which hydrogen is dispersed in a liquid phase consisting of an organic solvent, nitro compounds and reaction products dissolved in it, and a catalyst suspended in it; in which the process is carried out in a closed reaction system with a continuous recycle stream of the reaction mass, created without using a pump due to the difference in densities in the rising three-phase (gas - liquid - solid) stream (reaction zone) and in the falling (catalyst suspension in the solution of reaction products) flow (recirculation zone), taking part of the finished product in the form of a solution from the separation zone and returning the catalyst with most of the reaction mass from the separation zone through the recirculation zone to the bottom a second part of the reaction tower into which is simultaneously fed nitro solution, characterized in that the catalyst is a Group VII metal supported on a granular alumina having a particle size of 20-200 microns and a bulk density of 0.6 - 0.9 g / cm ³ and the recovery is carried out at a pressure of 0.1-5 MPa and a temperature which should be at least 10 ^° C. lower than the boiling point of the solvent at the process pressure.

 The process is carried out in the presence of an organic solvent that satisfactorily dissolves both the starting nitro compound and the resulting amine. The most convenient solvents of this type for a wide range of nitro compounds are lower alcohols, in particular isopropyl alcohol, in some cases toluene, ethyl acetate and other solvents can be used. The use of a solvent not only reduces the explosiveness of the process associated with the use of nitro compounds, but also significantly reduces the concentration of nitro compounds in the reaction zone, which prevents catalyst poisoning.

 It is proposed to use metallic nickel or palladium deposited on the surface of aluminum oxide granules as a catalyst. To obtain a catalyst, the granules are saturated with a solution of the corresponding salts, then they are subsequently subjected to heat treatment and reduction with hydrogen. The nickel content in the catalyst is 15-35%, optimally 20-32%. The advantage of such a catalyst compared to Raney nickel is less pyrophoricity without reducing the catalytic effect and more complete separation of the catalyst in the separator. The palladium content in the catalyst is 0.5 to 5.0%, mainly 3-4%.

To ensure high catalyst efficiency, it is necessary to use granules with a size of 20-200 microns, optimally 50-100 microns, and with a bulk density of 0.6 -0.9 g / cm ³ . The process is carried out at a pressure of 0.1-5.0 MPa, optimally 0.1-1.0 MPa.

Example 1
Into a reactor consisting of a reaction zone (a vertical pipe with a diameter of 0.02 m and a height of 5 m, equipped with a heated jacket, through which a three-phase flow having a density of 0.3 g / cm ³ rises at a speed of 1 m / s), a separation zone and recirculation zones (a similar pipe through which a suspension of catalyst in the reaction mass moves downward, having a density of 0.9 g / cm ³ ), a 20% solution of DNT in isopropyl alcohol (1000 ml / h) and hydrogen at the rate of 15 moles of H ₂ are continuously fed per 1 mol of DNT. Before starting continuous operation, 3.5 l of isopropyl alcohol and 500 g of catalyst (20% Ni on aluminum oxide granules with an average particle size of 50 μm and bulk density of 0.75 g / cm ³ ) are loaded into the apparatus, the suspension is slowly heated to 110 ^° C with a constant supply of hydrogen, the pressure of which at the end of the preparatory period reaches 0.5 MPa. The experiment lasted 400 hours without a significant decrease in catalyst activity. Despite the large number of cycles, the average duration of which was about 30 s, the ablation of the catalyst due to its grinding was not more than 10%. The yield of technical diaminotoluene 99.5%, the content of DNT in the product is less than 0.01%.

Example 2
Into a reactor consisting of a reaction zone (a vertical pipe with a diameter of 0.02 m and a height of 5 m, equipped with a heated jacket, through which a three-phase flow having a density of 0.3 g / cm ³ rises at a speed of 1 m / s), a separation zone and recirculation zones (a similar pipe through which a suspension of catalyst in the reaction mass moves with a density of 0.9 g / cm ³ ) continuously feeds a 20% solution of DNT in isopropyl alcohol (1000 ml / h) and hydrogen at the rate of 15 moles of H ₂ per 1 mol of DNT. Before starting continuous operation, 3.5 l of isopropyl alcohol and 500 g of catalyst (3% Pd on aluminum oxide granules with an average particle size of 90 μm and bulk density of 0.83 g / cm ³ ) are loaded into the apparatus, the suspension is slowly heated to 70 ^° C with a constant supply of hydrogen, the pressure of which at the end of the preparatory period reaches 1.6 MPa (absolute). The experiment lasted 200 hours without a significant decrease in catalyst activity. Despite the large number of cycles, the average duration of which was about 30 s, the grinding of the catalyst was negligible and its ablation did not exceed 8%. The yield of technical diaminotoluene exceeded 99%, the content of DNT was less than 0.01%.

 Under similar conditions, when using a Pd / C catalyst, almost the entire catalyst is abraded after 3 days of operation (with an initial size> 120 μm it completely passes through a 70 μm sieve).

 To assess the effect of the particle size of the catalyst on the process of separating it from the reaction mass in the separator, experiments were carried out, the results of which are shown in the table. They determined the deposition rate of the catalyst depending on the particle size. The total deposition time was determined in a glass tube with a diameter of 40 mm and a length of 740 mm for a 0.5 g sample; average values from 5 measurements are given.

 Already with a particle size of 30 or more micrometers, the residence time in the separation unit is sufficient for almost complete separation of the catalyst from the liquid sent to the separation stage. When the particle size is more than 200 microns in a falling flow, conditions are created that lead to a violation of the uniformity of the system.

Claims (1)

A method of continuous catalytic liquid-phase reduction of aromatic nitro compounds with hydrogen to aromatic amines, in which hydrogen is dispersed in a liquid phase consisting of an organic solvent, nitro compounds and reaction products dissolved in it, and a catalyst suspended in it, in which the process is carried out in a closed reaction system with continuous recycle the flow of the reaction mass created without using a pump due to the difference in densities in the rising three-phase (gas - liquid - solid body) in the flow (reaction zone) and in the flow (suspension of the catalyst in the reaction product solution) (recirculation zone), taking part of the finished product in the form of a solution from the separation zone and returning the catalyst with most of the reaction mass from the separation zone through the recirculation zone in the lower part of the reaction zone, into which a solution of nitro compounds is simultaneously supplied, characterized in that a group VIII metal supported on granular alumina with a particle size of 20-200 is used as a catalyst km and a bulk density of 0.6 - 0.9 g / cm ^3, and the reduction is performed at a pressure of 0.1-5 MPa and at a temperature, which should be not less than 10 ° C below the boiling point of the solvent at the process pressure.

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