CS275893B6 - Process for producing acrylamide or methacrylamide - Google Patents

Abstract

The solution concerns the method of producing (meth)acrylamide by hydration of (meth)acrylonitrile on a highly active and selective Raney copper type catalyst at elevated pressure. The catalyst is prepared from a special alloy Cu - AI, which is activated or reacts with a 1 to 15% aqueous solution of alkaline hydroxide with the addition of 1 to 5% by weight of glucose or formaldehyde at a temperature below 80°C and washes with demi-water.

Description

The invention relates to a process for the preparation of acrylaniide by hydration of acrylonitrile or methacrylamide from methacrylonitrile. Acrylamide is an attractive monomer that has a wide range of uses, e.g. for the production of flocculants.

The classic process for the production of acrylamide by hydration of acrylonitrile in a sulfuric acid environment is no longer interesting, especially from an ecological point of view. The need to treat large amounts of acid waste, e.g. ammonium sulphate, is the cause of the low economy of this classical process.

The literature, in particular the patent, describes a series of methods for hydrating acrylonitrile to acrylamide and methacrylonitrile to methacrylamide by catalyzing copper-containing substances. Because it is a reaction in the liquid (aqueous) phase, catalysts without a support and various binders which lose their mechanical strength in an aqueous medium are most preferred. Most preferably, the catalysts are obtained by reduction of copper-containing salts and oxides. Raney copper type skeletal catalysts show the best properties. These catalysts have very good mechanical properties, which are one of the conditions suitable for the life of the catalyst. Hydration of acrylonitrile on this type of catalyst is usually carried out with a conversion of 60 to 75% with 90 to 95% selectivity (U.S. Pat. No. 3,894,084, U.S. Pat. No. 4,000,195).

Several ways have been described to increase the activity of Raney media scaffold catalysts used in both batch and continuous processes.

It is known that the activity of the catalyst increases with the reduction of the particles used. However, the fine dust particles have poor mechanical properties and are the cause of unsatisfactory hydraulic properties in the flow reactor.

The authors of U.S. Pat. No. 3,894,962 developed a method for aggregating fine catalyst particles with water-insoluble resins.

Other authors describe the activation of a Raney copper catalyst using carbohydrates and glycosides (U.S. Patent No. 3,953,367, NSR Patent No. 2,448,603). The maximum achieved conversions of acrylonitrile to acrylamide are around 80%.

Activation was also carried out using aluminates (U.S. Pat. No. 3,928,440), which are formed by leaching a Cu-Al alloy (in an approximate 1: 1 weight ratio) with the addition of organic hydroacids such as e.g. gluconic acid. By applying the catalyst thus activated, 71.4% of the initial conversion of acrylonitrile was achieved, which dropped to 50.6% after 142 hours of operation.

Activation of the Cu - AI alloy was performed by the authors of the US patent no. No. 3,928,442 with aqueous solutions of nitrogenous bases in the absence of alkali metal hydroxides. Using alkylamines and quaternary ammonium salts, they achieved 65-73% conversion of acrylonitrile to acrylamide upon hydration. .

Activation of Cu - Al alloy with IIC1 resp. I ^ SO ^. Subsequent is the activation of lyes or. with nitrogenous bases. In hydration, the authors of U.S. Pat. No. 3,928,443 describe a 60% conversion of acrylonitrile.

Further work has shown that the quality of said skeletal catalyst depends not only on the method of its activation, but also on the primary preparation of the Ra - Cu alloy, as can be seen from the phase binary diagram of the Al - Cu alloy in FIG. 1. ·

The present invention relates to a process for the preparation of acrylamide or methacrylamide from acrylonitrile or methacrylonitrile and water at a temperature of 60 to 140 ° C in the presence of a copper-aluminum alloy catalyst activated with an aqueous alkali hydroxide solution at a temperature below 80 ° C. carried out at a pressure of 0.1 to 1.5 MPa and in the presence of a catalyst which can be prepared by activating or reactivating a copper-aluminum alloy which contains 30 to 70% by weight, preferably 50.5 to 54% by weight, and consists of 90 to 98% by weight of copper. % by weight of the compound Al 2 O 3, with a 1 to 15% aqueous solution of an alkali hydroxide with the addition of 1 to 5% by weight of glucose or formaldehyde and washing the catalyst with demi-water.

CS 275893 86 2

The copper skeletal catalyst prepared according to the present invention has several fundamental advantages.

In FIG. 1 is a eutectic diagram of a Cu-Al alloy. The x-axis shows the percentage Cu content and the y-axis the temperature in ° C. the individual lines show the properties of the alloy.

An alloy made so that the Cu: Al ratio is around the region of the phase binary diagram (Fig. 1) can advantageously be processed into a crumb with a defined grain, which can be easily charged to the reactor before activation. Commonly used alloys are characterized by higher toughness, are difficult to crush and do not have many crystalline defects, where the active sites of the catalyst are most concentrated.

The actual activation or reactivation, which can be repeated several times, is carried out directly in the reactor with an aqueous lye solution, e.g. NaOH with the addition of an additive 1 to 5 by weight (calculated on the alloy), preferably 1 to 3% by weight, which may be glucose or another suitable reducing compound, at a temperature of 20 to 70 ° C, preferably 20 to 50 ° C, at a concentration of an aqueous solution e.g. NaOH 1 to 15% by weight, preferably 3 to 7% by weight, the rate of activation being controlled by the rate of dosing of the hydroxide solution being recirculated, depending on the temperature and the amount of hydrogen released, which controls the degree of catalyst activation. After completion of the activation, the catalyst is eluted with demi-water until neutral, this time being insufficient and the washing must be extended to twice the leaching time of the lye. Washing with demi-water should not only be prolonged to remove the hydroxide inside the scaffold catalyst, which causes ethylene cyanohydrin to form selectivity, but also to release some of the catalyst surface from adsorbed hydrogen, which blocks the catalyst surface and prevents chemisorption of acrylonitrile. Furthermore, longer washing allows a documentary washing of residual inorganic fractions, e.g. aluminates, etc.

The actual hydration of acrylonitrile with water in the cannular (iv discontinuous) mode is carried out at a temperature of 60 to 140 ° C, preferably 80 to 110 ° C, at a reactor pressure of 0.1 to 1.5 MPa, preferably 0.3 to 0 ° C. 9 MPa, with catalyst retraction W / F = 0.2 to 2.5, preferably 0.5 to 1.5. The great advantage of this catalyst is its high productivity, the initial concentration of acrylonitrile (calculated on the total feed) is 10 to 45% by weight, preferably 20 to 35% by weight, at 100% selectivity of hydration to acrylamide the conversion of acrylonitrile ranges from 60 to 100%.

Another advantage is the production of an aqueous acrylamide solution with a content of 14 to 60% by weight, preferably 20 to 46% by weight, which leads to energy savings in concentrating the solution or in the production of crystalline acrylamide.

Common problems of Cu-based catalysts include the undesired content of Cu ²⁺ resp. Cu * in an aqueous solution of acrylamide, which is carried off in the form of soluble complexes of copper ions with acryloni2 + + triol or acrylamide. Cu formation resp. Cu is related to the oxidation of the metallic medium by oxygen, which comes to the catalyst with raw materials, especially demi-water.

According to the present invention, the catalyst is protected from access to oxygen by treating the domain by heat treatment, blowing with nitrogen, or by means of redox-ion exchangers, thereby suppressing the oxidation of Cu to Cu by O + 2+, and oj, original 60 ppm to 20 ppm.

One of the greatest advantages of said copper skeletal catalyst is its long service life and excellent regenerability. The service life of this catalyst after the first activation ranges from 1,200 to 2,000 h, with each reactivation increasing the service life by a further 1,500 to 2,500 h, the total number of reactivations being given by the residual aluminum content of the catalyst.

The invention is illustrated by the following non-limiting examples.

CS 275893 B 6

Example 1

200 g (150 .mu.l) of unactivated catalyst with a grain size of 2 to 3 mm are introduced into a continuous steel forum reactor, equipped with a tempering jacket, temperature measurement, condenser, storage tank, pressure control of a diameter of 29 .mu.m and a length of 1 .mu.m. The unactivated catalyst (Al - Cu alloy) contains 50.3% by weight of Cu and its composition corresponds to the left edge of the Al - Cu phase diagram region in FIG. 1. An alloy of this composition contains up to 98% of an aluminum-copper compound. The reactor was flooded with demi-water and heated to 30 ° C. 240 ml / h of a 3% strength by weight aqueous NaOH solution with an additive content of 3% by weight of the original inactivated catalyst are metered into the reactor by means of a metering pump. The reaction is exothermic, evolving at a rate of 0.06 l of hydrogen / wine and therefore the reactor must be cooled vigorously. The degree of catalyst activation (Cu content in the catalyst) is regulated according to the amount of hydrogen released. After the release of 58 l of hydrogen, which represents 960 minutes of activation, the supply of activating solution is stopped, the reactor is cooled to 20 DEG C. and eluted with demi-water at a rate of 200 to 400 ml / h. The wash water ceases to be alkaline after 4 l of demi-water. Next, the catalyst must be washed with another 8 l of demi-water. The catalyst is kept under water without access to oxygen. The medium content of the active catalyst was 68% by weight.

Before the actual hydration, 75 ml / h of water containing 10 ppvi of inhibitor e.g. methylhydroquinone (calculated on the whole feed) and the reactor is heated to 100 ° C. Acrylonitrile is metered in over the course of 2 hours with a second metering pump, the flow rate of which is increased from 0 to 32 .mu.l / h. The spray contains 25% by weight of acrylonitrile. The pressure in the reactor is maintained at 0.6 MPa. After passing through the catalyst bed, the reaction mixture leaves a reservoir from which samples were taken and acrylonitrile, acrylamide, ethylene cyanohydrin and acrylic acid were determined by the gas-liquid method.

The initial activity of the catalyst is very high, the conversion was up to 99%. After 60 h it decreased to 80% with 100% selectivity, after 600 h it decreased to 70% and after 1700 h it stabilized at a conversion of 62%, which represents 20.7% by weight of acrylamide in the reaction mixture. Ethylene cyanohydrin or acrylic acid were not found in the reaction mixture even once during 1,700 hours of operation.

Example 2

75 ml of water containing 10 ppvi of hydroquinone are metered into the continuous reactor described in Example 1, filled with catalyst, the activation of which is also described in Example 1, and 39.2 ml of methacrylonitrile are metered in separately with a second metering pump. The reactor is heated to 120 ° C at a pressure of 0.8 MPa. At steady state after about 600 hours, the conversion of methacrylonitrile was 61% with 100% selectivity to methacrylamide. 24.1% of methacrylamide was determined in the reaction mixture.

Example 3

In the continuous reactor described in Example 1, 200 g / 150 .mu.l of unactivated catalyst with a grain size of 3 to 4 mm, which contains 53.7% by weight of Cu, are introduced. The composition of the alloy falls within the right part of the region 7 of the Al-Cu phase diagram in FIG. 1. The activation procedure is identical to that in Example 1, except that the activation temperature is maintained at 50 ° C and the concentration of the metered solution is 7% by weight NaOH at a content of 2% by weight of formaldehyde in an amount of 200 ml / h. The evolution of hydrogen is intense at about 0.08 1 Hg / viin. Activation is terminated after the release of 60 l of hydrogen. The reactor is cooled to 20 DEG C. and eluted with water at a rate of 300 ml / h. A total of 12 l of demi-water is used to wash the catalyst. The medium content of the activated catalyst was 70.5% by weight.

Prior to the actual hydration, 75 [mu] l / h of demi-water containing 10 ppvi of inhibitor are metered into the reactor and the reactor is heated to 90 [deg.] C. Acrylonitrile is metered in over the course of 2 hours with a second metering pump so that the concentration of acrylonitrile in the spray rises to 33 to 34%

CS 275893 B 6 wt. After 600 hours, the conversion of acrylonitrile stabilized at 70% and the acrylamide content of the product at 31.6% by weight. No by-products were found. The content of unreacted acrylonitrile is around 10%.

Example 4

The catalyst prepared according to Example 3 was partially deactivated after 1600 h (acrylonitrile conversion dropped below 60 °) and was reactivated as follows. The demi-water is eluted for 8 hours at a flow rate of 240 ml / h, thereby eluting the adsorbed acrylamide. It is then reactivated according to the procedure of Example 1 with a 2% strength by weight NaOH solution with a 4% strength by weight additive at a rate of 200 ml / h at a temperature of 25-30 [deg.] C. After the evolution of 30 l of hydrogen, the reactivation is stopped and the catalyst is eluted with 12 l of demi-water at a rate of 240 ml / h.

After the reactivation is complete, the hydration of the acrylonitrile can be continued by injecting 85 ml / h of demi-water containing 10 ppm of hydroquinone as inhibitor and the second pump is metering in enough acrylonitrile so that the concentration of acrylonitrile in the injection is about 20% by weight. It is operated at a temperature of 100 ° C and a pressure of 0.6 to 0.8 MPa. After 456 hours of steady state, the conversion of acrylonitrile is 60% with 100% selectivity to acrylamide. The acrylamide content of the product is 16.1% by weight.

Claims (1)

PATENT CLAIMS Process for the preparation of acrylamide or methacrylamide from acrylonitrile or methacrylonitrile and water at a temperature of 60 to 140 ° C in the presence of a copper-aluminum alloy catalyst activated with an aqueous alkali hydroxide solution at a temperature below 80 ° C, characterized in that the hydration is carried out at pressure of 0.1 to 1.5 MPa and in the presence of a catalyst obtainable by activation or reactivation of a copper-aluminum alloy which contains 30 to 70% by weight, preferably 50.5 to 54% by weight of medium, and consists of 90 to 98% by weight. by weight of an AlgCu compound, with a 1 to 15% aqueous alkali hydroxide solution with the addition of 1 to 5% by weight of glucose or formaldehyde and eluting the catalyst with demi-water.