DD149213A1 - PREPARATION OF METHYLAMINES - Google Patents

Abstract

Preparation of methylamines by catalytic reaction of methanol and ammonia. The aim of the invention is the technical-economic improvement of the process for the preparation of methylamines from methanol and ammonia. By using dehydrating catalysts containing active alumina, a catalyst of defined structure and composition prepared on the basis of kaolin and pseudoboehmite is used according to the invention and worked at high catalyst loading. The catalyst is highly active and has a longer service life.

Description

- A-

VEB Leuna-Y / erke 'Leuna, 4.2.1980

»Walter Ulbricht« DC Hi / Schu

LP 7986

Title of the Invention Preparation of methylamines

Field of application of the invention

The invention relates to a process for the preparation of methylamines by catalytic reaction of methanol and ammonia on dehydratiaiere.nd acting catalysts containing active alumina.

Characteristic of the known technical solutions

The catalytic reaction of methanol with ammonia to form methylamines has been described many times in the literature (Gerber, G .: Dissertation ETH Zurich, 1963, Issoire, J .: Bull Soc Soc Chim Prance 1960, 2004) "Thereafter, the catalytic reaction predominantly in the vapor phase at temperatures of 200 bia 500 C and at pressures of 1 to 20 MPa on fixed catalysts. In this case, the procedure is usually that the catalytic conversion of methanol and ammonia takes place in the presence of excess monomethylamine and trimethylamine. Monomethylamine and trimethylamine are usually formed in methylamine synthesis with respect to the sales of methylamine in excess and must therefore be recycled to the synthesis stage.

Suitable catalysts are a wide variety of dehydrating variants. They are preferably made of natural aluminosilicates, synthetic aluminas or aluminosilicates or mixtures thereof (DE-PS 621,124, US-PS 1992935, 2017051, 4082805, DD-PS 108275) and can be used z.T. still contain additives (US-PS 3387032).

In practice, the catalyst used to ensure high efficiency of methylamine synthesis should meet the following main requirements: The catalyst must have sufficient mechanical strength and resistance especially to water vapor under reaction conditions, high catalytic activity and selectivity to dimethylamine formation and high resilience and a long life. None of the described catalysts fully meets these main requirements under full scale conditions. Rather, the effectiveness and / or life of the catalysts is mainly limited by the fact that either catalysts with desired high mechanical shear strength contain only limited amounts of active alumina, thus reducing the activity, or at least no high loading - complete iviethanolurase provided that it is possible, or during the use of the catalysts, the catalytic activity decreases as a result of strong coking, which at the same time in most cases entails a serious loss of strength. A loss of strength is also caused by the fact that active alumina dehydrated to boehmite. Natural and synthetic aluminosilicates have better stability, but lower activity · Known technical catalysts are therefore usually compromises, resulting u.a. a limited load capacity under reaction conditions follows. ,

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Object of the invention.

The aim of the invention is therefore to use an active alumina-containing catalyst for the synthesis of methylamines, which has sufficient catalytic activity and at the same time a greatly reduced coking tendency, so that on the one hand high reaction yields or loads are possible and on the other hand a clear extended life is achieved.

Explanation of the essence of the invention

It was therefore an object to develop a catalyst whose content of active alumina is increased, but at the same time in addition to a specific chemical composition has a defined secondary structure to reduce coking tendency or by-product formation, and this catalyst under suitable further reaction conditions for the reaction of methanol with ammonia to use methylamines

The object is achieved by a process for the preparation of methylamines by catalytic reaction of methanol and ammonia in the presence of excess monomethylamine and triethylamine at temperatures of 300 bi3 450 ⁰ C and. Pressing up to 20 MPa of dehydrating catalysts containing active alumina, according to the invention solved by using a catalyst based on kaolin and pseudo-boehmite containing in addition to alumina 12 to 18 Ma ··· silica, wherein the structure of the secondary particles pseudoboehmite is acicular and the particle size is less than 15 nm, the total pore volume of which is greater than 0.5 ml / g, the proportion of pores having a diameter smaller than 4 nm being at least 30 % and larger than 15 nm being at most 10 % , its particle size or wall thickness is less than 4 mm and the hourly throughput of methanol to be converted is greater than 24 kmol / nr catalyst.

A preferred embodiment of the method according to the invention is characterized in that the. Size of the secondary particles of the pseudoboehmite used is 3 to 9 nm, the total pore volume is 0.55 to 0.75 ml / g, the catalyst orforrnlinge have a maximum particle size or wall thickness of 2.5 mm, the hollow strand form is preferably used , and the C / N ratio of the reactants is 0.8 to 1.2 »

By the method according to the invention, the large-scale production of methylamines in various Hineicht is significantly improved.

The new catalyst produced on the basis of kaolin and pseudo-boehmite has a very high content of active alumina compared to comparable known catalysts. "Despite this high content of alumina, the new catalyst is mechanically extremely stable. Even at high catalyst beds occur virtually no strength reductions of the catalyst moldings. This is surprising to those skilled in the art, since a reduction of the mechanical strength, in particular under conditions of reaction at water vapor partial pressures around 3000 kPa, had to be expected. The pseudo-boehmite used in the sense of the invention has a needle-shaped structure of its secondary particles whose size is less than 15 nm, preferably 3 to 9 nm. The proportion of pseudo-boehmite for catalyst preparation hars be sized so that in the catalyst, a content of silica from 12 to 18 Ma. -% results. At lower levels in particular the desired strength is not achieved and at higher levels than 18 Ma. -% decreases the catalyst load capacity at full Methaholumsatz strong. In this area, unexpectedly hitherto unusual space-time yields are achieved without strength changes occurring at maximum activity of the catalyst.

This advantage of erfindungsgeraäßen catalyst is greater, the greater its load. According to the invention, therefore, the hourly throughput of methanol to be reacted is more than 24 kmol / nr catalyst and the C / N ratio of the reactants is between 0.8 and 1.2. If the new catalyst is used in already existing plants, an increase of the throughput by 30 to 50 % is possible, as far as the technical conditions are given ·

In connection with the secondary structure of the catalyst according to the invention, which is characterized by a certain pore structure and a total pore volume preferably between 0.55 and 0.75 * nl / g, the adiabatic mode of operation is characterized by: catalyst charge for the activity or utilization of the catalyst and its selectivity for the formation of the most desirable dimethylarain favorable radial and axial temperature profiles. However, a maximum temperature of 390 to 420 ⁰ C should not be exceeded. The known catalysts have a higher proportion of pores which are greater than 15 nm, and a Gesaratporenvoluraen, which is significantly less than 0.5 ml / g · This is among other factors a cause that in known catalysts by-product formation a disturbing As a result, the carbon formation and deposition on the catalyst, combined with the destruction of the catalyst structure, is so strong that only a limited service life of a few months is achieved with a continuously decreasing activity of the catalyst. The catalysts of the invention, however, are unexpectedly longer than 1 year to use.

Preferably, a catalyst in hollow strand form is used for the process according to the invention. However, any other form of catalyst can in principle be used if a maximum particle size or wall thickness of 2.5 mm is not exceeded.

1 9 1

The other process conditions, such as pressure, proportion of the recycled excess monomethylamine or trimethylamine in the synthesis step or the proportion of diethyl ether in the input mixture, are not within the known limits for the inventive method, crucial.

The pressure may therefore be in the range between about 2 and 20 MPa, the lower limit being substantially determined by the subsequent separation technology of the amine mixture. The proportion of "recirculated monomethyl- and triethylamine in the synthesis step depends on the particular sales structure of the pure methylamines." For the most part, this results in approximately constant conditions over long periods of time, so that the synthesis input mixture also has a constant composition The recirculated amines, methanol and possibly dimethyl ether, ammonia and possibly V / asser and certain proportions of hydrogen, is compressed to the reaction pressure, heated by suitable heat exchangers depending on the proportion of methanol to about 300 to 330 ⁰ C and by the As a result, the inlet temperature is set as a function of the desired maximum temperature, and the catalyst is fixed in the reactor as a bed.

The reaction mixture is cooled and brought to the pressure necessary for the distillation. Conveniently, in the first distillation stage, all excess products are separated together with the ammonia-trimethylamine azeotrope, and then the remaining aqueous ammonia-free mixture is further distilled by distillation. In principle, however, the distillation technology is not decisive for the process according to the invention. "A typical procedure for the process according to the invention, including the characterization of the preparation of the catalyst according to the invention in the exemplary embodiment. given a game.

Exemplary embodiment Preparation of the catalyst:

100 kg of pseudo-boehmite having a needle-shaped structure of the secondary particles, the size of which is about 7 nm, which is accessible in a known manner, are intensively mixed together with 50 kg of kaolin in a kneading machine. This mixture is then kneaded with 10 l of 5% nitric acid and 60 l of distilled water to a plastic mass, the desired plasticity of the mass is set after completion of the kneading process by adding 150 ml of 25% by weight ammonium hydroxide. The resulting plastic Mas3e is deformed by means of a single-screw extruder screw, which is preceded by a hollow-stranded plate at the product outlet, into hollow-strand moldings and cut. The moldings have an outer diameter of 8 mm and an inner diameter of 3j2 mm, resulting in a wall thickness of less than 2.5 mm. Subsequently, the hollow-strand moldings are dried at a maximum of 120 ⁰ C and finally calcined at 600 ⁰ C for 6 hours.,

 The catalyst thus obtained has the following properties:

Bulk density in kg / 1 0.610

SiCSiO content in mass% 15.2

2 surface in m / g 182

Pore volume in ml / g 0.57

of which greater than 15 nm 0.04

and less than 4 nm 0.18

Use of the catalyst:

2.5 m of the catalyst are in a vertically mounted full-space reactor, 7575 kg of a mixture of the following composition are passed over the catalyst per hour:

29.70% by mass of methanol

31.70 "ammonia

8.45 "

0.07% by weight of dimethylamine 30.08 ", trimethylamine

The C / N ratio of the mixture is 1.03. The hourly catalyst load with respect to the methanol throughput is calculated to be 28.1 kmol / m. At a product exit temperature from the reactor of 410 ⁰ C, the inlet temperature into the reactor 315 ⁰ Co The reaction pressure is adjusted to 13.5 MPa. The resulting reaction mixture has the following composition:

24,03 Mass ~% ammonia , 9.19 Il Monomethylamine 17.27 M dimethylamine 32,70 It TriinetbylaBiin 0.12 Il methanol 16.69 Il water

The Methanolurnsatz is therefore 99.6 %. After an operating time of 13 months, the Methanolunsatz has only slightly reduced. The content of by-products in the reaction mixture is less than 0.05 I <tnsse- / S. The average carbon content in the catalyst is 1.2% by mass.

For comparison, a catalyst prepared from kaolin and boehmite was used under otherwise identical reaction conditions. The catalyst had the following properties:

Bulk density in kg / 1 0.690 SiO content in l / lasse-jS 15.9

Surface area in m / g 142 pore volume in ml / g 0.34 thereof greater than 15 nm 0.11 and less than 4 nm 0.07

- 9 The following results were obtained:

The methanol conversion decreased to 86 % and the dimethylamine content in the reaction mixture to 11.2% by mass. The by-product formation was about 0.2% by mass, based on the reaction mixture. After an operating time of 96 days, the catalyst had to be removed. He had a carbon content of 10.8 mass%.

Claims (2)

Influence3ans.pruch 1. Preparation of methylamines by catalytic reaction of methanol and ammonia in the presence of excess monomethylamine and trimethylamine at temperatures of 300 to 450 ⁰ C and pressures to 20 IvIPa of dehydrating catalysts containing active alumina, characterized in that a on the Based on kaolin and pseudo-boehmite containing, in addition to alumina, 12 to 18 mass% of silica, the structure of the secondary particles of the pseudo-boehmite being needle-shaped and the particle size is less than 15 nra, the total pore volume being greater than 0.5.ml / g i3t, wherein the proportion of pores having a diameter smaller than 4 nm at least 30 % ... λ and greater than 15 nm at most 10 % is concerned, its grain size or wall thickness is less than 4 mm, and the hourly throughput of methanol to be reacted greater than 24 kmol / m catalyst, 2. The method according to item 1, characterized in that the size of the secondary particles of the pseudoboehmite used is 3 to 9 nm, the total pore volume is 0.55 to 0.75 ml / g, the catalyst moldings have a maximum particle size or wall thickness of 2.5 mm, the hollow strand form being preferably used, and the C / N ratio of the reactants is 0.8 to 1.2