CA1129888A - Process for the manufacture of methylamines - Google Patents

Abstract

A B S T R A C T o f t h e D I S C L O S U R E
The invention relates to an improved process for the manufacture of methylamines from ammonia and methanol at elevated temperature and optionally under pressure. The new feature of the invention consists in the selection of a cheap catalyst i.e. an acid activated montmorillonite, whereby high conversions of methanol, excellent yields of the amines and a good selectivity to dimethylamine are obtained.

Description

The present invention relates to a process for the manu~acture of methylamines by reacting methanol with ammonia in the gas phase at elevated temperature and op-tionally under ele~ated pressllre in the presence OI a catalyst of the silica-alumina type.
In the catalytic synthesis o~ methylamines starting Pr~m am~onia a~la me-thanol, a vaporized mix-ture oP methanol and excess ammorlia is initially prepared and this mixture is then reacted ;n a reactor at a temper~ture oP
about 200 to 500C. and under a pressure between atmospheric pressure and about 50 bars, by passing it over a catalyst bed.
A large number of catalysts have been proposed Por this synthesis, for example, metal oxides, such as the oxides oP aluminum, zirconiurn, thorium, silicon, tungsten and copper, alone or in the ~orm Or mixtures, which can be used alone or supported on carrier materials. Various salts have also been proposed Por the same purpose, in particular diammonium monohydrogen phosphate, aluminum phosphate, aluminum sulfate and thoriu~ sulPate, or mixtures oP these salts with oxides, such as those mentioned above, these salts being used alone or supported on pumice, actire charcoal, kieselguhr, quartz, asbestos or the like carrier materials.
From the economic point oP vieN, all the a~ove-mentioned catalysts have the common disadvantage that they are based on relatively ex~ensire r~w materials and that they are prepared by manufacturing processes which are also relatively expensive.
A more valuable method from this point of view ~ould be to start directl~ Prom mineral raw materials Nhich are abundant in nature. Thus, for the synthesis of methylamines, U.S. Patent Specification No 1,875,747 proposes the use of naturally occuring aluminum sllicates, such as India~aite, Blue clay, crushed auilding tile, Doucil (natural zeolite~ a Peldspar and Putnam clay. UnPortunately, the results obtained Nit~ -this class oP natural aluminum silicates are rather unfavorable with regard to the production of dimethylamine, thls bein~ the meth~lamine in greatest demand. In P~act, according to this U.S. Patent ISpeciPication, it is partic-uiarl~ desired to produce monomethylamine. However, even if the latter is the desired product, the described process ~s unsatisfactory because oP its low productivity ArtiPicial Qlica-alumina catalysts have also been used for the synthesis of methylamines. Thus, according to German Patent ~pecification No~ 1,543,73i, artiPicial catalysts of the silica-alum;na type are prepared from a silica gel on to which an alumina eel is precipitated. The catalyst is subsequently partially deactivated with steam under pressure and then impre~nated with silver phosphnte, rhenium sulfide, molybdenum sulPide or cobalt sulfide. The resul-ts obtained wi-th these catalysts are superîor to those of U.S. Patent Sneci~ication No. 1,o75,747 mentioned above bu-t the costs of the ra~7 materials and of the manufacture are considerably hi~her. Furthermore, this process also suffers from disad~antages with re~ard to i-ts producti~ti~y. As ~ar as we know, it has never been possible to carry out on an industrial scale the pre~erred production of dimethylamine envisa~ed by this Patent Specification. In Example 1 given hereina~ter, it is shown that these catalysts produce a large amount o~ trimethylamine at the start of the conversion and that they only succeed ~nth difficulty in converting the initially formed trimethylamine to dimethylamine.
The ideal would be to ~ind, amongst naturally occurring mineral substances, catalytic substances which would retain their inherent advantage of low cost, whilst exhibiting a ver~ high and very selective catalytic activity.
~e have now discovered that this objective can be achieved.
Thus, the present invention provides a process for the manufacture of methylamines, wherein a mixture of methanol and excess ammonia is passed in the vapor phase and at e'evated tem~erature over a catalyst comprising an acid activated montmorillonite.
Ideally, montmorillonite has the theoretical for~ula A12(0H)2_Sil~Olo 7 +
n X20. One of its particular characteristics is that its lattice, which is composed of two outer silica tetrahedral layers and a central alumina octahedral layer, ex~ands reversibly by the introduction of water between the layers. lYowever, the silicon ions in the outer layers can be partially replacedby aluminum (beidelitte) and the aluminum ions in the central layer can be replaced by iron (nontronite), magnesium (hector;te) or the like~ Simllarly, some clays, such as bentonite, contain a certain proportion of montmorillonite.
It is to be understood that, a~ter they have been activated by an acid, all these naturally occurrin~ compounds can be used as catalysts for the synthesis of methylamines in accordance with tne process oP the present invention. For further details abou-t montmorillonite and its natural derived forms, re~erence may be made, in part~cu]ar, to Ullmans Encyklopàdie aer technischen Chemie, 3rd edition, volume ~ 53, page 541 et se~., and also to ~.E. Grim, "Clay Mineraho~y", pub. McC7ra~ ook Co., Inc. 1953.

~1~9~

For -the pur~ose o~ ;~s industrial use, mo~tmorillonite and cla~s in ~7hich it is present are act~vated b~ a strong mineral acid, ~or exarnple, hydro-chloric ac~d, sulfuric acid or phosphoric acid. As a result of this treatment, the structure of the ori~inal lat-tice o~ the montmorillonite is more or less pro~oundly modif~ed and it is -this Nhich gives the montmorîllonite lt,s catalytic properties.
The catalytic properties of acid acti~ated montmorillonites have been recognized and used to advantage ~or a lonK time on an industrial scale, i-n particular in the catalytic cracking o~ petrolewrl ~ractions, polymeri~ation, hydrogenation, dehydrogenation, alkylation, de~vdration, isomeri~ation and the like (see German Patent Specifications ~os. 1,051,271; 1,051,864;
1,086,241 and 1,089,168). However, as far as we know, acid activated montmorillonites have never been suggested or used as catalysts for the synthesis of meth~lamines.
Compared with the aluminum silicates pre~iously used, the acid activated montmorillonites used according to the present invention have the following advantages:
1. they are more selective, since they favor the ~ormation of dimethylamine;

2. at the same time, the conversion of the methanol exceeds 96% and the yield of amines, based on converted met~anol exceeds 98%; and

3. they have a longer duration o~ l;fe.
The acid activated montmorillonite used according to the present invention as a catalyst can be in the form of pellets or, alternat~ely, of spheres or cylinders, which can be solid or hollo~ and the size of' which can be f`rom 0.2 to 10 mm. The ap~arent density of the ac;d acti~ated montmorillonite can ~ary from 0.4 to 1.2kg/liter.
The raw materials used in the process according to the present invention are methanol and ammonia.
Tne metnanol and the ammonia used can be pure or, for obvious economlc reasons, of technical grade.
The molar ratio of methanol to ammonia in the gaseous mixture fed into the reactor ma~ vary between 0.3 : 1 and 1 : 1. rt i5 not desirable for this ratio to fall below 0.3 : 1 because it would then be necessary to recycle too large an amount of unreacted ammonia. The operat.ing conditions emplo~ed ln the process of the present ~nvent~on are those whic~ are generall~ used in the manufacture of meth~lamines by the catal~tic react~on of excess ammonia with methanol ~n the gas phase, i.e. at any temperature in the range of f`rom 200 to ~L~2~8~

500C and pre~erably c~ from 350 tc 450~C hnd under a pressure Or from atmospheric pressure to about 100 bars and prefertlbLy in the ranee of ~rom 10 to 50 bars.
The contact time o~ the gasecus methanol/al~nonia rnixture wîth the catalyst used according to the present invention is not critical and c~ntact times in the range Or 1 to 20 seconds may be employed. B~ "contact time" îs meant the ratio o~ the aFparent ~olume o~ the catalyst (in ml) to the ~low rate o~ the gaseous methanol/ammonia mixture, expressed in ml per second, under normal conditions o:~ temperature and pxessure (OGC and 1.013 bar).
There are no restr;ctions with regard to the nature o~ -the apparatus used for carry;ng out -the process of the present invention. The process may be carried out continuously or discontinuously. The catalyst bed may be a fixed or ~luidized bed.
At the outlet o~ the reactor used, the gaseous mi-xture is separated into its various components by known methods, ~or example by ~ract;onal distillation.After se~aration of the various components of the effluent ~rom the reactor, the monomethylamine and/or trimethylamlne Pormed can, i~ desired, be partially or totally recycled through the reactor in order to increase further the yield of dimethylamine whilst, at the same time, reducing the formation of the other methylamines.
In the follow;ng ex~mples, which are given for the purpose of illustra-ting the present invent~on, commerc~ally a~ailable ~roducts, namel~ the "K"
catalysts of the firm Sud Chemie A.G., are used as t~e acti~ated montmorillo-nites, these products beinR described in brochures issued by this company, ~or example "~-~atalysatoren ~ud~Chemie A.G. ~ncnen" 2/77, pages 1 and 4:
Example 1 (Com~arative Example~
In this Exarnple, there is used the artificlal sillca-alumlna catalyst the preparation o~ wh~ch ~s described ln Exarnple 1 of German Patent Specificat~on ~To. 1,543,731: however, in a dry state, t~is catalyst co~tains 0.1~ by weight of metallic s~lver, The reactor used is a "P~rex" glass tube, h&vlng a length of 5 cm and an inner diameter o~ 8 mm which contains from side to side a concentric sheath in which a thermoccuple slides. ("Pyrex" is a R~gistered Trade Ma~k)7 This tube is placed in an oven. The catalyst mass, placed at the ~enter of the tube, consists Or 1 g o~ the above-mentioned catalyst, it~ part;cle si~e being from Oo42 to 0.59 mm. ~hilst keeping the temperatu~e in the reactGr at 423 - O.5C, a gaseous mixture o~ met~anol and ammonia (molar ratio CH30H:~H3 0.54:1), pre-~29~8~

heated to 423C, is passed through. The reaction is carried out atatmospheric pressure.
Analysis ot' the c~mposition of the gaseous mixture leaving the reac-tGf is carried out by gas phase chromatography ;n a sthinless steel colllmn. The stationary phase used ~or this chromatography consist;s o~ potystyrene beads 7 the surface of which has been trea-ted with a silane (Porapak/~ and which ~I~S
been ir~pregnated to an extent o~ 10% with a mixture o-~ tetrae-thylenepen-tamine and potassium hydro~ide.
The results obtained are given 1n the ~ollowing Table 1~ in which:
the "contact time" (in seconds) represents the ratio of the apparent volume (expressed in ml~ o~ the catalyst to the ~lo~ rate expressed in ml per second. These "contact times" make it possible to assess the performance of the catalyst under ;ndustrial conditions. The ~olume which the reactor must have in order to ensure a gi~en production is inaeed easily deduced ~rom the value oP the contact time. The longer is the contact time, the greater must be the volume o~ the reactor ~or a gi~en product;on. Thus, not only will the actual apparatus (reactor~ be more expensi~e but also the mass o~ catalyst will be greater;
MMA = monomethylamine;
DMA = ~methylamine;
TMA = trimethylamine;
DME = dimethyl ether;
the percentages by weig~t o~ MMA~ DMA, TMA, CH30H and DME are expressed relat;~e to the total weight o~ DME+MMA~DMA~TMA ~ CH30H (which compounds require the greatest e~ort ~or their separation); and the weight ratio TMA/DMA represents the ratio o~ the weight o~ TMA to the weight o~ DMA. This ratio makes it possible to assess the selecti~it~ wlth respect to DMA relative to the selectivity with respect to TMA, the lowest TMA/DMA rativ beinK the most pro~itable.

l~g~

TABLE I
% by ~ by % by % by ~ b~ weight contact weight weight welght weight weight ratio time DME _ MMA DMA TMA C~I ~ TMA/D~A
52.22 6.5 20.0 ~.9 42~2 ~.6.3 2.83 I~.00 1~ 5 21.0 18.0 1L6.3 10.0 2.57 5.50 2.6 22 0 20.0 Il6.3 g.o 2.~1 5.73 1.7 22.7 20.6 46.3 8.5 2.25 Example 2.
The procedure of Example 1 is followed but the molar ratio of methanol to ammonia is 0.55:1, the reaction temperature is 424 - 0.5C and the catalyst consists of 1 g o~ activated montmorillon;te according to the present invention (catalyst K 306 ava;lable from Sud-Chemie), ground to a particle size of 0.42 to 0.59 mm.
This catal~st has a speci~ic sur~ace area of 190 to 250 m2/g, a pore volume of 0.19 cm3/g at 14 nm and o~ 0O30 cm3/g at 80 nm, a pressure resistance of 78.4 N and an apparent density of about 650 g~liter.
The following Table 2 gives the results obtained:

% by % by % b~ % by % by weight contact weight weight weight weight weight ratio time DME MMA DMA _ TMAmethanol T~/DMA
1.4 4 17.7 l~.g 33.829.5 2O26 2.34 2 20.9 20.4 3818 4 1.86 255.39 ~ 26.2 25.3 4~.65.3 1.68 5-5 - 26.0 26~o 43 500 1.65 This Table shows the superiority o~ the catalyst used in the present Example, compared w;th the catalyst emplo~ed in Example 1, i.e a) a weight ratio TMA/DMA of 2.26 is reached for a contact time o~ 1.4 seconds whereas, in Example 1, a contact time o~ 5~73 seccnds ;s re~uired ln order to obtain an approximately equal rat;o. Furthermore, this rat;o can drc~ tq 1.65 for a contact time of 5 5 seconds. Consequently, ;n the process of the `
present invention, the selectivi-ty witn respect to DMA relative to the selectivity with respect to TM`A is higher ~or substantiaily shorter contact times;
b~ the amount of DME ~ormed is substantially lower and it ;s even virtuall~
zero for contact times in the range o~ 5 seconds. The y;eld o~ amines, based 88~3 on converted methanol, is therefors very high (small amounts of by-products);
and c) the conversion of the methanol is substantially higher for contact times o~P
the order of 5 seconds. By "conversion o~ methanol" i~ meant the ~ercentage by weig~t o~ Methanol converted during t~e reaction.
Example 3.
The procedure followed is essentially as in ~xample 1. However, the reactor has a larger inner diameter (28 mm), -the molar ratio of methanol to ammonia is 0.58:1 and the rëaction temperature is 440 ~ 0.5C.
The catalyst ;s the same as in Example 2, except that it is in the form of 4 to 5 mm spheres having an apparent density of about 650 g/liter. The amount of catalyst used is greater (5 g) than in the preceding Example.
The ~ollowing Table 3 gives the results as a function of the conversion of methanol:

conversion % by ~ by % by % by % by ~eight of weight weight weight weight weight ratio methanol % Dr~E MMA DMA TMA methanol ~MA/DMA
83.1 1.7 16.3 18.6 40,5 22.7 2.18 o8 0.7 1~.5 22.6 40.8 17 1.80 99~3 - 26.2 28.2 44.5 .9 1.58 This Table shows that the catalyst used according to the present invention makes~t'~bossible to obtain an excellent conversion of the methanol (99.3%), with a very favorable weight ratio TMA/DMA.
Example 4.
This Example is carried out on an industrial scale. The catalyst of Example 3 is charged into an inaustrial reactor having a volume of 10,000 l;ters, the reaction being carried out at a pressure of 20 bars and at a temperature of 420C.
~ith a charge of o.36 kg of methanol/kg of catalyst/hour, the molar yield of amines is 9~%, based on converted methanol, ana the conversion of the methanol is 97.3%. At the outlet of the reactor, the average ~aght ratio TMA/DMA is found to be 1.68, calculated over ian operating period of one month.
~ith a charge of 0.325 kg of methanol/kg of catalyst/hour~ the yield of amines is 98.9% and the conversion of the methanol is 98.4%.
After 11 months of act~ity, the conversion of the methanol with a charge of 0.325 kg of methanol/kg of catalyst/hour is still 96.6% and the yield of amines is 98.3%.

Claims (6)

WE CLAIM :

1. A process for the manufacture of methylamines, which comprises passing in the vapor phase a mixture of methanol and excess ammonia at elevated temperature over a catalyst comprising an acid activated montmorl-lonite.

2. A process according to claim 1, in which the molar ratio of methanol to ammonia is from 0.3:1 to 1:1.

3. A process according to claim 1, in which the temperature is in the range of from 200 to 500°C.

4. A process according to claim 3, in which the temperature is in the range of from 350 to 450°C.

5. A process according to claim 1, in which the reaction is carried out at a pressure of from atmospheric pressure to about 100 bars.

6. A process according to claim 5, in which the pressure is in the range of from 10 to 50 bars,