CA1204723A - Molded iron catalyst and its preparation - Google Patents

Abstract

Abstract of the Disclosure: Molded iron catalysts which contain metallic iron particles, obtained from anisometric iron oxide particles by contact with hydrogen at ? 500°C, and a lubricant, are prepared.

Description

lZ~7Z~3 O.Z 0050/3611Z

Molded iron catalyst and its preparation The present invention relates to a molded iron catalyst containing metallic iron particles and a lubri-cant, and to its preparation.
In the preparation of amines by hydrogenating nitriles, eg. the preparation of hexamethylened-iamine from adiponitrile, cobalt-containing catalysts are pre-ferably used owing to their high selectiv;ty. Such pro-cesses are d;sclosed in, for example, German Patents 1,072,972 and 1,259,899. However, the life of the cobalt catalysts used no longer meets the technical requirements.
Moreover~ it has been found that, for reasons of indus-tr;al hyg;ene, it is advisable to avoid dusts of metallic cobalt and of ;ts sparingly soluble compounds. Iron-conta;n;ng catalysts have also been employed for the hydrogenat;on of nitriles to amines, but relatively high temperatures are requ;red when these catalysts are used~
This leads to increased formation of by-products, eg.
azacycloheptane and the diam;nes, such as 2-am;nomethyl-ZO cyclopentylamine and 1,2-diaminocyclohexane, which are difficult to separate from the hexamethylenediamine, as well as to the formation of b;shexamethylenetr;amine and oligomers. For example, German Laid-Open Application DOS

2,429,Z93 discloses that magnetite can be melted and then reduced with hydrogen to give a catalyst which exhibits a selectivity with respect to hexamethylenediamine of from 9~ to 99% at hot-spot temperatures of from 150 to 170C. The contents of 1,2-diaminocyclohexane are, however, 0.2% by weight. The process which is described in German Published Application DAS 2,034,380, and in which the catalyst used is a granula~ed iron compound which is converted to metallic iron by reduct;on with hydrogen, also gives selectivities of only 97 - 98.8% by weight. Such iron catalysts do not yet satisfy all industrial requirements and therefore need to be improved.
It is an object of the invention to provide iron catalysts which, when used in the hydrogenation of 7~

~ 2 - O.Z. 0050/36112 n;tr;les to am;nes, have a long l;fe, permit low hydro-genation tempera~ures, produce a smal.l amount of by-; products and have a h;gh selectivity We have found tha~ this object is achieved by molded iron catalysts which contain Metallic iron par-ticles, obta;ned from an;sometr;c iron ox;des by contact with hydrogen at = 500C, and a lubricant.
The present invention furthermore relates to a process for the preparat;on of molded iron catalysts, 10 wherein anisometric iron oxide particles are reduced with hydrogen, at from 250 to 500C, to metallic iron par-ticlesf these are stabilized by treatment with a mixture of n;trogen and a;r, the stab;l;zed iron part;cles are pressed together w;th a lubricant to form moldings and the latter are act~vated by treatment w;th hydrogen at ~ 500C.
The present ;nvention furthermore relates to the use of the molded iron catalysts for the hydrogena-tion of organ;c n;tr;les to the corresponding amines. I
The novel iron catalysts have the advantages of a long l;fe, super;or mechan;cal properties even after prolonged use and high select;vity at low temperatures.
Moreover~ the novel catalysts give fewer by-products wh;ch are d;ff;cult to separate from the des;red products.
The novel catalytic mater;al conta;ns metall;c ;ron part1cles obta;ned from an;sometr;c, eg. ac;cular, ;ron oxide particles by contact with hydrogen at ~ 5ûOC.
Advantageously, the metallic iron particles exhibit a degree of reduction of = 95%. The degree of reduction is the amount of available iron, in %, which ;s present ;n metall;c form.
An;sometr;c 1~-;ron ox;des, ;n part;cular ~-iron (III) oxides and ~-iron(III) oxide hydrate, are prefer-ably used. ~-iron(III) ox;de hydrate, wh;ch ;s known under the name lepidocrocite, ;s particularly preferred, and can be obta;ned, for example, by the method descr;bed ;n German Publ;shed Appl;cat;on DAS 1,061,760. The an;sometr;c ;ron ox;des have a mean particle length of ~2(~723 ~ 3 - O.Z. 0050/3611Z
from 0.1 to 2 ~m, preferably from 0.2 to 1.2 ~m, a length/
width ratio of from 5:1 to 40:1 and a BET specific sur-face area of from 25 to 80 m2tg. The products obtained by heating the stated iron(III) oxides may also be used, heating advantageously being carried out at from 250 to 700C. The iron oxides used advantageously have an alkali content of less than 0.1% by weight, calculated as Na20 The novel iron catalyst furthermore contains a lubricant, for example an inorganic substance with a lattice structure, such as talc or graphite. Advantage-ously, the catalysts contain from 1 to 5% by weight, based on the total catalytic material comprising iron particles and lubricant, of a lubricant. Graph;te has proved a particularly useful lubricant. The novel iron catalyst therefore essentially consists of metallic iron part;cles obtained from an acicular iron oxide, small amounts of iron oxide, depending on the degree of reduc-tion, and a lubricant.
The iron catalyst according to the invention is molded to g;ve, for example, spheres, tablets or extru-dates, and advantageously has an indentation hardness of = 300 kp/cm2.
The novel catalytic material is advantageously prepared from, for example, a ~iron(III) oxide, in par-ticular ~-iron(III) oxide hydrate (lepidocrocite). The products obtained by heating the stated iron(lII) oxides may also be used, heating advantageously being carried out at from 250 to 700C. ~-iron(III) oxide hydrate ;s obtained, for example, from an aqueous solution of an ;ron salt w;th sodium hydroxide solut;on by a process as described in German Published Application DAS 1,061,760.
Advantageously, the ~-iron Gxide hydrate particles are washed until the alkali content is less than 0.1% by weight, calculated as Na20.
The acicular iron(III) oxide particles are re-duced with hydrogen in a fluidized bed, a rotary furnace or, preferably, in a stirred fixed bed at from 260 to 500C, in particular from 300 to 450C, in the course of

3~7~3

- 4 - O.Z. 0050/36112 from 3 to 36 hours. It is advantageous to use a stream of dry hydrogen~ a relatively high flow velocity being maintained. It has proved useful to use not less than a 60~fold excess of hydrogen. Advantageously, reduction is carr;ed out until the degree of reduction is - 95%. The result;ng ac;cular metal particles, which essentially consist of ;ron, substantially retain the shape of the starting materials, and are homogeneous in spite of hav;ng been sub~ected to a convers;on react;on.
The metal particles are then stabilized. This ;s the procedure in wh;ch the metal particles are coated with an oxide layer, by means of controlled oxidation, in order to eliminate ~he pyrophorocity result;ng from the large free surface area of the small part;cles.
This is achieved by passing an air/nitrogen m;xture over the metal powder while exactly ma;nta;n;ng a temperature wh;ch is preferably not more than 100C, in particular not more than 80C. After stab;lization, the degree of reduction should be no less than 80%, preferably no less than 90%. The stabilized iron particles have a BET sur-face area of from 4 to Z5, preferably from 8 to 12, m2/g, lengths of from 0.05 to 2.0 ~m and pore volumes of less than 0.4 cm3/g, and the ratio of micropores to macropores is from 1:6 to 1:1û, macropores therefore predominating.
The stab;lized particles are an;sotropic.
The stabilized iron particles obtained in this manner are mixed with an inert lubricant, preferably graphite. It is advantageous to use from 2 to 5% by weight of lubricantr The mixture of stabilized iron par-ticles and lubricant is advantageously converted to mold-ings, eg. tabletted, under a nitrogen atmosphere. The indentation hardness of the moldings should be - 300 kp/cm2.
The resulting moldings are activated by treatment with a relatively large (egO 60-fold) excess of hydrogen at ~ 5ûOC, preferably from 300 to 360C, under at-mospheric pressure or superatmospheric pressure, eg. from 100 to 150 bar. In this procedure, the degree of reduc-tion achieved is advantageously ~ 95%. The activation

- 5 - O.Z. 0050/36112 increases the indentation hardness of the moldings, for example from 300 to 600-800 kp~cm2~
The molded iron catalysts according to the ;n-vention have a h;gh activity which permits hydrogenation to be carried out at below 120C, whereas prior art procedures require hot-spot temperatures as high as 150C
and above. A striking feature is their low tendency to form undesirable cyclic by-products; for example, in the preparat;on of hexamethylenediamine, the concentrations of 1,2-diaminocyclohexane and azacycloheptane are sub-stantially less than 0.2% and the concentration of 2-aminomethylcyclopentylamine is less than 0.002~. The novel catalyst also has high mechanical stability; this can be achieved by carrying out the molding procedure not at the stage of the anisometric iron(III) oxide but only after the latter has been reduced to metallic iron particles ar,d subsequently stabilized. If moldings are prepared from anisometric irontIII~ oxide and a lubricant and the moldings are then reduced, their indentation ~0 hardness decreases, for e~ample from 300 kp/cm2 to 25 kp/cm2 when the degree of reduction reaches 95~. The t;me-on-stream of the resulting catalyst is less than 100 days. Both the reduction temperature and the hydro-genation temperature are higher than in the case of the process according to the invention, while the selectivity is substantially lowerO
The novel catalysts can be advantageously used for hydrogenating organic nitriles to the corresponding amines.
The catalyst according to the invent;on is par-ticularly useful for the preparation of alkylamines and alkylenediamines by reacting an alkanenitrile or an al-kanedinitrile of 3 to 18 carbon atoms with hydrogen in the presence of ammonia. The novel catalysts are par-3~ ticularly important for the preparation of hexamethylene-diamine by reacting adiponitrile with hydrogen in the presence of ammonia. This process is carried out at from 80 to 140C, preferably from 110 to 120C, and under a ~.2~7~3

- 6 - 0.Z. 0050/36112 pressure of from 100 to 400, preferably from 200 to 300, bar~ The hydrogenation is advantageously carried out in the presence of ammonia, but some of this may be replaced by recycled crude hydrogenation m;xture, which essentially consists of hexamethylenediamine and ammonia. It has proved useful for the volume ratio of adiponitrile to ammonia to be from 1:2 to 1:20, preferably from 1:6 to 1:1Z.
The Examples which follow illustrate the inven-tion~

Preparation of the catalyst 600 kg of acicular lepidocrocite t~-FeOOH), pre-pared as described ;n German Published Appl;cation DAS
1,061,760 and having a chlorine content of ~0.1%, an Na20 content of c0.1%, a specific surface area of 32 m2/g, a mean needle length of 0.8 ~m, a length/width ratio of the needles of 22:1, a bulk density of 0.37 g/cm3 and a pH
of 7.2, are reduced to metallic iron ~Fe - 95%~ with 400 m3tS~T.P.)/hour of hydrogen for 38 hours at ~00C in a stirred fixed bed ~stoichiometric hydrogen excess: 64).
The pyrophoric acicular metallic pigment is then pro-v;ded w;th a stabil;zing ox;de layer at 60C in a nitro-gen/a;r mixture, and the degree of reduction should not fall below 90%. The yield is 400 kg~ The saturation magnet;zation of the iron particles is 153 nT m3/g in a magnet;c f;eld of 160 kA/M. The ;ron part;cles have a specific surface area of 7.2 m2/g (measured by the ~ET
method), and electron microscope photographs show that they possess an an;sotropic geometrical shape (ac;cular or rod-l;ke).
To prepare molded materials having a diameter of 5 mm and a height of 4 mm, the stab;lized pulverulent metallic pigment is ,ixed with 2% by weight of graphite and the mixture is tabletted under a nitrogen atmosphere.
The ;ndentat;on hardness of the tablets should not be less than 300 kp/cm2.

~.Z~7~3 ~ 7 ~ O.Z~ 0050/36112 350 l;ters of the moldings prepared as described in Example 1 are introduced into a reactor having a length of 1,800 mm and an internal diameter of 160 mm, and the moldings are treated with a large excess of hydro-gen at 360C and under 150 bar for 24 hours ;n order to activate them. The hydrogen is circulated via a condenser in order to separate off water formed during the reduc-tion.
After the catalyst has been cooled, the reactor is charged, using a trickling procedure and -under a hydro-gen pressure of 270 bar, with a mixture of 85 liters/hour of adiponitrile and 510 liters/hour of liquid ammonia~
the hydrogen being circulated at a rate of 400 m3(S.T.P.)/
hour. The temperature of the feed mixture is 78C and that at the reactor exit is 110C; the maximum hot-spot temperature is 119C.
After ammonia has been evaporated off from the hydrogenation mixture, gas chromatographic analysis shows that the crude hexamethylenediamine comprises 0.02% by weight of hexylamine, 0.09% by weight of azacycloheptane, 0.11% by weight of 1,2-diaminocyclohexane and 99.78% by we;ght of hexamethylenediamine, as well as ~0.01% of aminocapronitrile. The distillation residue, which pre~
dominantly consists of bishexamethylenetriam;ne, corres-ponds to 0.36%. The selectivity with respect to hexa-methylenediamine is 99.4%. The activity and selectivity of the catalyst was unchanged after a time-on-stream of 400 days and without any regeneration.

In the reactor described in Example 2, 70 liters/
hour of adiponitrile in 430 liters/hour of liquid ammonia and 490 liters/hour of recycled hydrogenation mixture are converted to hexamethylenediamine over the catalyst prepared as described in Example 1. Hydrogen is circulated at the rate of 350 m3(S.T.P.)/hour~ and its pressure is maintained at 250 bar. Complete conversion of the adipo-~.2~47Z3 - 8 - O.Z. 0050/3611Z
nitriLe is achievedO at a feed temperature of 77C; the temperature at the reactor exit is 104C and the maximum temperature in the reactor is 109C.
Gas chromatographic analysis of the crude hexa-methylenediamine after the ammonia has been evaporatedoff gives the following result: 0.01% of hexylamine, 0.05~ of azacycloheptane, 0~11% of 1,2-diaminocyclohexane, û.002% of 2-aminomethylcyclopentylam;ne, 99,8û% of hexa-methylenediam;ne and 0.01% of aminocapron;trile. The distillation residue corresponds to 0.40%, and the selec-tivity with respect to hexamethylenediamine ;s 99.44%.

3 l;ters of the catalyst prepared as described in Example 1 are introduced ;nto a high-pressure reactor having a length of 2,000 mm and an internal diameter of 45 mm, and the catalyst is activated as described in Example 2. 100 ml/hour of adiponitrile and 1,200 ml/hour of liquid ammonia are metered into the reactor. At a hydrogenation temperature of 109C and under a pressure of 260 bar, the selectivity with respect to hexamethylene-diamine is 99.3%. The crude hexamethylenediamine con-tains only 0.04% of azacycloheptane and 0.09% of 1,2-diaminocyclohexane. The dist;llat;on res;due corresponds to 0.23%.

In a 2 liter shaken autoclave, 80 9 of 2-methyl-glutarodinitriLe and 1,000 ml of liquid ammonia are hydrogenated under 260 bar and at 100C in the pre-sence o~ 80 g of catalyst tablets prepared as described in Example 1, hydrogenat;on being continued until hydro-gen ;s no longer absorbed. For complete conversion of the d;n;trile employed, the selectivity with respect to 2-methylpentame.hylened;am;ne is 98.8%.
Using a similar procedur~ and under the above hydrogenation conditions, propionitrile in liquid ammonia is hydrogenated to n-propylamine with a select;vity of L7;~3 - 9 - O.Z. 0050/3$112 97.5~.

The procedure described in Example 4 is followed, except that 3 liters of a catalyst prepared by tablett;ng a mixture of 98% of ~FeOOH and 2% of graphite are used.
The catalyst is reduced with hydrogen at 450C and under atmospheric pressure for 72 hours~ The degree of reduc-tion achieved is 95%. For complete conversion of 400 g/hour of adiponitrile in 1~460 g/hour of NH3, a hydrogenation temperature of 155C and a pressure of 260 bar are required (trickling procedure).
The select;vity of the catalyst is 97.15~ with respect to hexamethylenediamine. The crude hexamethylene-diamine contains 1,56% of products from conversion reac-tions which have proceeded beyond the desired stage, and1l29% of cyclic products t1,2~diaminocyclohexane and aza-cycloheptane)~

The procedure described in Example 4 is followed, 20 except that 3 liters of a catalyst are used which is ob-tained by reducing ~-FeOOH, passivating the surface of the resulting metallic iron pigment, mixing the product with 2% of graphite and tabletting the mixture. The ~-FeOOH is precipitated in an alkaline medium, so that 25 the catalyst contains 0~18~ of sodium hydroxide.
In the reactor, the catalyst is activated by treat;ng it with hydrogen for Z4 hours at 360C and under atmospheric pressure. 400 g/hour of adipodinitrile and 1,460 g/h~ur of NH3 are then metered in by a trickling procedure.
Complete conversion of the adiponitrile is achieved at 172C. The selectivity with respect to hexamethylenediam;ne is 97.8%, and 1.3% of cyclic by-products and 0.8% of products from conversion reactions which have gone beyond the desired stage (predominantly bishexamethylenetriamine) are obtained.

Claims (9)

We claim:-

1. A molded iron catalyst which contains metallic iron particles, obtained from anisometric iron oxide particles by contact with hydrogen at ? 500°C, and a lubricant.

2. A catalytic material as claimed in claim 1, wherein the iron oxide used contains less than 0.1% by weight, calculated as sodium oxide, of alkali.

3. A catalytic material as claimed in claim 1, wherein the molded iron catalyst contains from 1 to 5% by weight of a lubricant.

4. A catalytic material as claimed in claim 1, wherein the molded iron catalyst contains graphite.

5. A catalytic material as claimed in claim 1, wherein the starting material used is anisometric .gamma.-iron(III) oxide hydrate.

6. A catalytic material as claimed in claim 1, wherein the molded iron catalyst has an indentation hardness greater than 300 kp/cm2.

7. A process for the preparation of a molded iron catalyst as claimed in claim 1, wherein anisometric .gamma.-iron oxide particles are reduced with hydrogen, at from 250 to 500°C, to metallic iron particles, these are stabilized by treatment with a mixture of nitrogen and air, the stabilized iron particles are pressed together with a lubricant to form moldings and the latter are activated by treatment with hydrogen at ?500°C.

8. A process as claimed in claim 7, wherein the anisometric .gamma.-iron oxide particles are reduced until the degree of reduction is ? 95%.

9. A process as claimed in claim 7, wherein, when the metallic iron pigment particles are stabilized by treatment with a mixture of nitrogen and air, the degree of reduction does not fall below 80%.