NL8001612A - PROCESS FOR THE PREPARATION OF METHYLAMINS - Google Patents

Description

t '- Λ VO 0187

Process for the preparation of methylamines,

The invention relates to a process for the preparation of methylamines by reaction in the vapor phase of methanol with ammonia, at elevated temperature and optionally under elevated pressure, in the presence of a silica-alumina type catalyst.

In the catalytic synthesis of methylamines starting from ammonia and methanol, a vaporous mixture of methanol and excess ammonia is first prepared, which is then reacted in a reactor at temperatures of about 200-500 ° C under a pressure of between atmospheric pressure and about 50 bar, by passing that mixture over a catalyst bed.

A large number of catalysts have been proposed for this synthesis; these are e.g. metal oxides, such as the oxides of aluminum, zirconium, thorium, silicon, tungsten and copper, alone or in the form of mixtures, whether or not supported on supports. For the same purpose, various metal salts have also been proposed, in particular diammonium monohydrogen phosphate, aluminum phosphate, aluminum sulfate, thorium sulfate or mixtures of these salts with oxides, as mentioned above, as such or applied to a support, such as pumice stone, activated carbon, diatomaceous earth, quartz, asbestos, etc.,

Economically, all of the above-mentioned catalysts have the common disadvantage that they require fairly expensive starting materials and that they are prepared by also relatively expensive manufacturing processes.

In this respect it would be a more interesting way to start directly from mineral starting materials, which are abundant in nature. Thus, in U.S. Pat. No. 1,875,747 for the synthesis of methyl amines, natural aluminum silicates such as indananite, blue clay, finely ground tiles, Douciel (natural zeolite), feldspar and Putnam clay have been proposed. Unfortunately, the results obtained with this category of natural aluminum silicates are not very favorable for the production of alpha-1-2-dimethylamine, which is the most desirable methylamine. After all, according to this United States patent, the aim is mainly to prepare mono-methylanine. However, even if this is the desired product, the described process proves to be unsatisfactory because of the low efficiency.

Synthetic catalysts based on silicon oxide and aluminum oxide have also been used for the synthesis of methylamines.

Thus, according to German Patent Specification 10 1 543,731, artificial catalysts of the silicon oxide de-alumina type are prepared starting from a gel of silicon oxide, on which a gel of aluminum oxide is precipitated. The catalyst is then partially deactivated with water vapor under pressure, and then the catalyst is impregnated with silver phosphate or with rhenium, molybdenum or cobalt sulfide. The results obtained with these catalysts are better than those obtained according to the aforementioned U.S. Pat. No. 1,875,747, but the price of the starting materials and the manufacturing costs are considerably higher. Moreover, this method also has disadvantages in terms of efficiency. As far as the applicant is aware of this, the preferred preparation of dimethylamine intended according to the said patent has never found practical industrial application. In Example I below, it is shown that these catalysts produce a lot of trimethylamine at the start of the conversion and lead only with difficulty to the conversion of the initially formed trimethylamine into dimethylamine.

The ideal would be to find catalytic substances among the natural minerals which retain their inherent advantage of a low price and at the same time have a very high and very selective catalytic activity.

The applicant has found that this goal can be achieved.

The invention therefore relates to a process for the preparation of methylamines, which is characterized by passing in the vapor phase and at elevated temperature a mixture of methanol and an excess of ammonia over a catalyst, which Montmorillonite which is acid activated, Montmorillonite ideally has the formula ΑΙ ^ ίΟΗ) ^ / Si ^ O ^ Q ^ + nHgO. Montmorillonite has the peculiarity that its lattice, which is composed of two outer layers of tetrahedra of silicon oxide and one central layer of octahedra of alumina, expands reversibly by incorporating water between the layers. However, the silicon ions of the outer layers can some are replaced by aluminum (beidelite) and the aluminum ions of the central layer by iron (nontronite), magnesium (hectorite), etc. Furthermore, certain clays, such as bentonite, contain a certain amount of montmorillonite. It is noted that all these natural products, after being activated with an acid, are suitable as catalysts for the synthesis of methyl amines according to the method of the present invention. For more information on montmorillonite and its natural derivatives, 20 reference may be made in particular to Ullman

Enoyklopadie der Technischen Chemie, third edition, part A of 1953, page 541 et seq., As well as after the work of H, S. Grim "Clay Mineralogy", Mc.Graw -ill Book Co. Ine., -953

Montmorillonite and the clays containing montmorillonite are subjected to activating treatment with a strong mineral acid, such as hydrochloric, sulfuric or phosphoric acid, for industrial applications thereof. As a result of this treatment, the composition of the initial lattice of montmorillonite is more or less heavily modified, thereby imparting its catalytic properties.

The catalytic properties of montacrillonites activated with acid are known and have been used on an industrial scale for a long time, in particular in the catalytic cracking of petroleum fractions, in polymerization, hydrogenation, dehydrogenation 8001612-4-alkylation, dehydration, isomerization , etc. (see German Pat. Nos. 1,051,271, 1,051,664, 1,086,241 and 1,089,168). To the applicant's knowledge, the acid-activated montmorillonites have hitherto not been proposed or used as catalysts in the synthesis of methylamines.

Compared to the prior art aluminum silicates, the montmorillonites activated according to the invention have the following advantages: they are more selective as they promote the formation of dimethylamine; 2. The conversion of methanol reaches more than 96% and at the same time the yield of amines relative to the converted methanol is more than 9S / 5 5 5. Their service life is longer.

The activated montmorillonite, which is used as a catalyst according to the invention, is in the form of granules or also of balls or cylinders, which are full or hollow, the size of which varies between 0.2 and 10 mm. The apparent density of the activated montmorillonite can range from 0.4-1 / 2 kg / l.

The starting materials used in the process according to the invention are methanol and ammonia.

Methanol and ammonia can be used in pure form or can be of technical quality for obvious economic reasons.

The molar ratio of methanol to ammonia in the gaseous mixture fed to the reactor can vary between 0.5: 1 and 1: 1. It is of no importance that this ratio should fall below 0.5 * 1, since an excessive amount of unused ammonia would then have to be recirculated. The operating conditions used in the process of the invention are those generally used in the preparation of methylamines by catalytic reaction of an excess of ammonia with methanol in the vapor phase, 8001612-5% 9 in a temperature range of 200- 500 ° C, "preferably from 350-450 ° C, and under a pressure from atmospheric pressure to about 100 bar, preferably from about 10-50 bar.

The contact time of the vaporous mixture of methanol 5 and ammonia with the catalyst used according to the invention is not critical and contact times of about 1-20 seconds can be used. Contrast time is understood to mean the ratio of the apparent volume of the catalyst (in cm ^) to the flow rate of the vaporous mixture of methanol and ammonia, expressed in cm ^ / second, under normal conditions of temperature and pressure (0 ° C and 1.013 bar).

There are no restrictions on the nature of the equipment used to perform the present method. The method can be performed continuously or discontinuously. The catalytic bed can be a fixed or a fluidized bed.

At the reactor outlet, the vaporous mixture is separated into its various components by methods known per se, e.g. by fractional distillation.

After the various effluent components have been separated from the reactor, the mono- and / or trimethylamine formed can be recycled, if desired, in part or in whole to the reaction to further increase the yield of dimethylamine, thereby simultaneously increasing their formation. less.

In the examples below, which serve only to illustrate the present invention, commercially available activated montmorillonites are products, namely the catalysts "K" from Süd-Chemie, these products are described in brochures from this company, e.g. in "K-Catalysts Süd-Chemie A.G., Munich", 9/77; pp. 1 and 4.

EXAMPLE 1 (COMPARATIVE EXAMPLE) In this example, the artificial catalyst silica 8001612-6 oxide-alumina, the preparation of which is described in Example 1 of German Patent Specification 1 * 543 »731», used in the dry state, was used. at least 0.1 wt. # of silver metal.

The reactor used was a Pyrex glass tube with a length of 5 cm and an internal diameter of 8 mm, which was passed through a concentric sleeve in which a thermocouple had been inserted. This tube was placed in an oven. The catalytic mass placed in the center of the tube consisted of 10 "of 1 g of said catalyst} its granulometry was between 0.42 and 0.59 mm. While the temperature in the reactor was maintained at 423 + 0.5 ° C , a binary vapor mixture preheated at 423 ° C, consisting of CH 2 OH and (molar ratio CH 2 OH 4 0.54: 1), was passed through and operated at atmospheric pressure.

The analysis of the vaporous mixture leaving the oven was performed by gas chromatography in a stainless steel column. For this chromatography, a stationary phase consisting of polystyrene in the form of 20 granules was used, the surface of which was treated with a silane (Porapak / s) and impregnated, in an amount of 10 #, with a mixture of tetraethylene pentamine and potassium hydroxide.

The results obtained are shown in Table A below, in which the "contact time" (in seconds) represents the quotient of the apparent volume (expressed in cm ^) of the catalyst with the volume flow rate, expressed in cm ^ / second. These "contact times" make it possible to assess the performance of a catalyst in industrial application. After all, it is easy to deduce from the value of the contact time the volume which the reactor must have to ensure a given production. As the contact time is longer, the reactor must have a larger volume to achieve a given production. Thus, not only will the actual equipment 8001612-7 (reactor) be more expensive, but also the amount of catalyst will be greater; - MMA = monomethylamine - DMA * dimethylamine 5 - TMA = trimethylamine DME = dimethyl ether; - the percentages by weight of MMA, DMA, TMA, CH2 OH and DME are given relative to the total weight of DME + MMA + DMA + TMA + CH, 0H (substances requiring the greatest separation difficulty); - the weight ratio TMA / DKA represents the ratio of the weight of TMA to the weight of DMA. This ratio allows to assess the selectivity of DMA relative to that of TMA, the smallest ratio being the most favorable.

TA35L A

contact wt $ wt $ wt $ wt $ wtfo weight ratio time DME MMA DMA TMA CH ^ OH TMA / DKA

2.22 6.5 20.0 14.9 42.2 16.5 2.83 20 4.00 4.5 21.0 18.0 46.5 10.0 2.57 5.50 2.6 22 .0 20.0 46.5 9.0 2.51 5.75 1.7 22.7 20.6 46.3 8.5 2.25

Example II

The procedure was as in Example 1, but the molar ratio of methanol: ammonia was 0.55 * 1, the reaction temperature was 424 + 0.5 ° C, and the catalyst consisted of 1 g of montmoril lonite, which had been activated according to the invention (catalyst K.3O6 from Süd-Chemie) and was ground to a granulometry of 0.42-0.59 nm.

That catalyst had a specific surface area of 190-250 2 m / g, a pore volume of 0.19 cm / g at 14 nm and of 0.30 ca / g at 80 nm, a compressive strength of 78.4 V and an apparent density of about 65Ο g / l.

The results obtained are shown in the table below Ξ.

8001612 - 8 - TABLE B * contact wt ^ wt.fi wt. $ Wt.fi wt.fi weight time DIS MMA DMA T2JA methanol ratio

_ _ _ _ ___ TMA / DMA

5. 1.4 4 H, 7 14.9 33.8 29.5 2.26 2.54 2 20.9 20.4 38 18.4 1.86 5.39 - 26.2 25.3 42.6 5 .3 1.68 5.5 26.0 26.0 43 5.0 1.65

The above tahel shows that the catalyst used in this example is better than the catalyst used in example I, in particular on the following points: a) a weight ratio TMA / DMA of 2.26 was reached at a contact time of 1 .4 seconds, whereas in Example 1 a contact time of 5.73 seconds was required to obtain a substantially equal ratio. In addition, this ratio can decrease to 1.65 with a contact time of 5.5 seconds; consequently, in the method of the invention, the selectivity of DMA over that of TKA is greater for markedly shorter contact times; b) the formation of DME was markedly lower and hardly any DM3 was formed at contact times of about 5 seconds; the yield of amines relative to the converted methanol is thus very high (few by-products); c) the conversion of the methanol wa3 markedly greater at contact times of about 5 seconds.

By "conversion of the methanol" is meant the weight percentage of this alcohol which is converted during its passage through the reactor.

Example III

The procedure was almost as in Example 1; the reactor possibly had a larger inner diameter (28 mm), the molar ratio of methanol: ammonia was 0.58: 1, and the reaction temperature was 1/1 O 1 O 1, f y y uv Tv 9 y-yr 8001612 4 * & - 9 -

The catalyst was the same as in the previous example, except that it was in the form of 4-5 µm spheres with an apparent density of about 650 g / l. The amount of catalyst used was greater (5 g) than in the preceding example.

The results obtained as a function of the conversion of the methanol are shown in Table C below.

TABLE C

conversion wt% wt, wt $ wt ^ wt $ wt 10 of DMS MMA DMA TMA methanol ratio

methanol $ _ _____ ___ _______ T? .TA / DMA

83.1 1.7 16.3 18.6 40.5 22.7 2.18 88 0.7 19.5 22.6 40.8_ 17 1.30 99.5 - 26.2 28.2 44. 0.9 1.58 ♦ This table shows that the catalysts according to the invention make it possible to obtain an excellent conversion of methanol (99.3%) at a very favorable weight ratio tma / dma.

Example IV

This example was performed on an industrial scale. The catalyst of Example III was placed in an industrial reactor, which contained a catalytic charge with a volume of 10,000 liters.

The reaction was carried out at a pressure of 20 bar and a temperature of 420 ° C,

At a charge of 0.36 kg of methanol / kg of catalyst / hour, the molar yield of amines relative to the converted methanol was $ 99 and the conversion of the methanol was $ 97.3. The reactor effluent was found to be averaged and calculated over a 1 month duration of action, the weight ratio TMA / DMA was 1.68.

At a charge of 0.325 kg of methanol / kg of catalyst / hour, the yield of amines was 98.9% and the conversion of the methanol was 98.4%.

After an operating time of 11 months, the conversion 8001612-10 of the methanol with a charge of 0.325 kg methanol / kg catalyst / hour was still 96.6. and the yield of amines was still 98.3 $ 8001612

Claims (4)

1. Process for the preparation of methylamines, characterized in that in the vapor phase and at elevated temperature a mixture of methanol and an excess of ammonia is passed over a catalyst containing a montmorillonite which is activated with acid. 2. Process according to claim 1, characterized in that the molar ratio of the methanol to the ammonia varies between 0.3: 1 and 1: 1, 3. Process according to claim 1 or 2, characterized in that the reaction is carried out at a temperature between 200 and 500 ° C, preferably between 350 and 450 ° C. 4. Process according to claims 1-3, characterized in that the reaction is carried out under a pressure between atmospheric pressure and about 100 bar, preferably between 10 and 50 bar. 3001612