MXPA98000124A - Process for the manufacturing of methylamine - Google Patents

Abstract

The present invention relates to a process for the preparation of a modified ammonium mordenite, characterized in that it comprises the steps of: 1) drying an ammonium mordenite under conditions such that the mordenite is maintained in the form of ammonium and 2) treating the mordenite of dry ammonium adsorbed with tetrachlorosilane in gas phase at a temperature between 300 and 600

Description

PROCESS FOR MANUFACTURING OF METHYLAMINS SPECIFICATION The present invention relates to a process for the preparation of a modified ammonium mordenite, and in particular to a catalyst comprising this modified ammonium mordenite prepared by such a process, as well as to a process for the manufacture of methylamines by the reaction of methanol with gas phase ammonia at elevated temperature, and optionally at elevated pressure, in which catalyst is used. In the catalytic synthesis of methylamines from ammonia and methanol, a vaporized mixture of methanol and ammonia is first prepared, which is then reacted in a reactor at temperatures from about 220 to about 500 ° C at pressures between the pressure atmospheric and approximately 50 bars, passing over a catalyst bed. The product of the reaction between ammonia and methanol consists of a mixture of three amines, onomethylamine (abbreviated MMA), dimethylamine (abbreviated DMA), trimethylamine (abbreviated TMA), water, ammonia and unreacted methanol.

In addition, dimethyl ether (abbreviated DME) can be formed as a by-product. Among these products, dimethylamine is the REF: 26460 most wanted amine as far as the industry is concerned; it is currently used as raw material for the manufacture of many commercial products such as solvents, pharmaceuticals, vulcanization accelerators, surfactants, fungicides (for example tetramethylthiuram disulfide) and the like. The production of dimethylamine from ammonia and methanol necessarily involves a separation step of the products obtained after the reaction. However, the isolation of dimethylamine by distillation of the methylamines mixture is considerably complicated by the fact that in the residual ammonia and the methylamines produced form azeotropic mixtures. Until now, methylamines are manufactured on an industrial scale from methanol and ammonia, using in most cases amorphous silica-alumina catalysts, because these catalysts have outstanding catalytic properties. However, the methylamines mixture obtained in the presence of these catalysts contains a larger portion of trimethylamine and, consequently, the production of the desired dimethylamine is insufficient. This is why many investigations have been carried out to find catalysts that allow dimethylamine to be obtained selectively while suppressing the production of trimethylamine, as much as possible. The amounts of the different methylamines in the reaction product are determined by the thermodynamic equilibrium of the reaction; these quantities depend, among other parameters, on the reaction temperature and the molar ratio of the reactants. For example, in the case of a reaction temperature of 300 ° C, a feed of ammonia and methanol corresponding to an atomic ratio of N / C of 2: 1 and a feed rate of methanol of 0.3 kg / h / kg of catalyst, the composition, in% by weight, of the mixture of methylamines at equilibrium is 20% MMA, 22.5% DMA and 57.5% MA for an active but non-selective catalyst, when a total conversion of methanol is achieved . This composition of the product corresponds to the composition of the thermodynamic equilibrium. Trimethylamine is thus predominantly produced under these conditions. On the other hand, if the production of trimethylamine were suppressed, the composition in% by weight of the mixture of MMA and DMA at equilibrium could be 31.5% of MMA and 68.5% of DMA under the same conditions and when a total conversion was achieved of methanol. The interest in the development of selective catalysts that almost completely prevent the production of trimethylamine can be seen immediately.

A large number of catalysts have been proposed to achieve this goal. Literature mentions, in particular, similar synthetic or natural zeolites, for example, zeolites X, Y, ZK-5, ZSM-5, ZSM-12, FU-1, SK, erionite, ferrierite, faujasite, cabasite, clinoptilolite and more particularly mordenite. These zeolites have been used either as such or after having been subjected to various treatments to modify their characteristics, such as the number of acid sites, the pore size or the silicon / aluminum ratio. The proposed treatments include, inter alia, the modification of the nature and proportion of the cations, treatments with acids, calcination with or without the presence of steam, or silylation by means of various silylating agents. The different treatments proposed can result in some improvements in the catalytic activity and / or in the selectivity for the production of monomethylamine or dimethylamine. However, when these zeolites are used as catalysts, the selectivity for the production of dimethylamine generally remains relatively low. Very often, the values obtained are very close to the values that can be obtained when the thermodynamic equilibrium between the three methylamines is obtained. For example, in an article related to the selective synthesis of dimethylamine from methanol and ammonia in the presence of several zeolites (I. Mochida et al., J. Catal., 82_, (1983), 313-321), authors report that methanol conversions and selectivities for dimethylamine are obtained with mordenites (Zeolon from the company Norton Co. Ltd) in protonic form or in a form in which the cations are exchanged with sodium, magnesium or lanthanum-hydrogen cations . In this last form and for a reaction temperature of 400 ° C, the conversion of methanol is up to 94.5 mol% and a selectivity for the DMA of 51.5 mol% is obtained. The amount of trimethylamine formed is, however, very negligible, since the selectivity for the TMA reaches 11.9 mol%. In U.S. Patents 5,137,854 and 5,210,308, this disadvantage is overcome by using the protonated mordenite which is subjected to a specific treatment. This treatment consists in subjecting a sodium mordenite to a treatment with tetrachlorosilane in the gas phase, at an elevated temperature (approximately 700 ° C in the example) and converting the sodium mordenite thus treated to a protonated mordenite by ion exchange. For this exchange, the sodium ions of the treated mordenite are exchanged with ammonium ions and the ammonium mordenite thus obtained is subjected to calcination for several hours at 450 ° C. According to these patents, this treatment of mordenite does not appreciably modify its atomic ratio of Si / Al, in other words, mordenite does not undergo dealumination. This modified mordenite makes it possible to obtain a methanol conversion of 98.9 mol% and a selectivity for dimethylamine of 61.2 mol%. The process described in those patents therefore provides a good conversion of methanol and a good selectivity for dimethylamine. However, trimethylamine production remains high (see Example 4 below). An attempt was made to solve this problem in European Patent Application 593,086, which proposes a. process for the preparation of methylamines that allows to produce monomethylamine and dimethylamines selectively and reduce the production of trimethylamines to a low%. For this purpose, the synthesis of the methylamines was carried out in the presence of a specific catalyst. This catalyst is first formed by subjecting a protonated mordenite to one or more silylation treatments with a silylating agent in the liquid phase and then performing a heat treatment at a temperature of 300 to 600 ° C in the presence of air or oxygen. The silylation treatment was carried out by dispersing the mordenite in a solution of silylating agent in a solvent. However, prior to silylation treatment, the water content of the mordenite was adjusted to a predetermined value. In this way, when the solvent used is soluble in water (for example in alcohol) the mordenite was calcined at a temperature of 350 to 600 ° C until the water content is 4% by weight or less. When the solvent used is not miscible in water (benzene and the like) the mordenite must contain from 3 to 40% by weight of water before being treated with the silylating agent; This water content is obtained either by controlled drying of mordenite or by calcination and conditioning in a humid atmosphere. This process allows to achieve a very good selectivity for dimethylamine (approximately 64%). However, the conversion of methanol is only about 90%, which means that, on an industrial scale, the application of this process will require recycling a significant amount of unconverted methanol. In addition, these results obtain the price of an elaborate and delicate technology. In fact, after several calcinations at high temperature in the presence of air for the preparation of the catalyst; furthermore, before the silylation treatment, the water content of the mordenite has to be scrupulously controlled, otherwise it is not possible to keep the production of trimethylamine at a low level (see, in particular, Examples 3, 6, and 8). of this patent application). Therefore, despite the availability of many catalysts for the catalytic synthesis of methylamine from ammonia and methanol, there is a need to find a catalyst which is, at the same time, (a) highly selective for the production of monometry. laminate and the desired dimethylamine (which allows, for example, to achieve dimethylamine selectivities of 70% by mol or more), while at the same time practically not producing trimethylamine or by-products, especially dimethyl ether; (b) highly active, to carry out the reaction at very high methanol conversions, preferably close to 100% mol (to avoid recycling of methanol); (c) capable of being prepared by a process that can be carried easily and economically on an industrial scale. It has now been found, quite surprisingly, that it is possible to prepare a highly active and highly selective catalyst from an ammonium mordenite, when this mordenite is subjected to a specific silylation treatment with tetrachlorosilane in the gas phase under specific conditions. In fact it has been found that by using this specific catalyst based on ammonium mordenite in the synthesis of methylamines, remarkable selectivities are obtained for dimethylamine which exceed 70 mol%, and can still reach 81.6 mol%, virtually without formation of trimethylamine and dimethyl ether, and with conversions of methanol close to 100% mol. Accordingly, an object of the present invention is a process for the preparation of a modified ammonium mordenite, characterized in that it comprises the steps of (1) drying an ammonium mordenite under conditions such that the mordenite is maintained in the form of ammonium and ( 2) treats the dry ammonium mordenite thus obtained with tetrachlorosilane in the gas phase at a temperature between 300 and 600 ° C. Another object of the present invention is a catalyst, more particularly, a catalyst for the preparation of methylamines from ammonia and methanol, comprising a modified ammonium mordenite obtained by the aforementioned process. Finally, another object of the present invention is a process for the manufacture of methylamines, characterized in that a mixture of methanol and ammonia gas phase is passed at elevated temperature on a catalyst comprising a modified ammonium mordenite prepared by the process mentioned previously. The catalyst used according to the invention in the catalytic synthesis of methylamines from methanol and ammonia is prepared from an ammonium mordenite.

A mordenite is a crystalline aluminosilicate which can be found directly in nature or can be prepared by chemical synthesis. The total composition of natural mordenites can generally be expressed by the formula Na8 [(A102) 8 (SiO2) 0] .24H2O. The natural mordenites therefore have the atomic ratio of Si / Al of 5: 1. However, synthetic mordenites are also known in which the Si / Al ratio is greater than 5: 1 (see pages 321-332 of PA Jacobs and JA Martens, "Synthesis of High-Silica Aluminosilicate Zeolites", volume 33 of "Studies in Surface Science and Catalysis", Elsevier, 1987) or in which the sodium ions have been replaced with hydrogen, alkaline earth ions or ammonium, or also with other alkali ions. The mordenite used as starting material for the preparation of the catalyst according to the present invention is an ammonium mordenite in which the atomic ratio of Si / Al is between 5: 1 and 20: 1, preferably 5: 1 and 12: 1. Its sodium content must be very low, preferably less than 0.1% by weight in relation to the weight of the mordenite. Ammonium mordenites are commercially available or can be prepared from a mordenite containing alkali metal or alkaline earth metal ions, exchanging those ions with ammonium ions. This ion exchange can be carried out by methods which are known per se, for example, by treatment with an aqueous solution of ammonium nitrate. The ammonium mordenite which is suitable as a catalyst according to the present invention is prepared by a process which essentially comprises a drying step followed by a silylation step. With respect to the drying step, this must be carried out under conditions such that the mordenite remains in the form of ammonium. In fact, it has been found that above a temperature of 400 ° C, the ammonium mordenite is. easily converts to a protonated mordenite. This is for that reason that the drying step of the process according to the present invention is generally carried out at a temperature which is lower than 400 ° C, and preferably, at a temperature in the range of 230 ° C. at 350 ° C, in a stream of dry inert gas (nitrogen). The temperature and duration of drying should be sufficient to remove all the water absorbed on the mordenite, but this temperature should not be too high or the period of drying very long, to avoid volatilizing the chemically bound ammonia (chemoabsorbed). The drying period is generally 180 to 540 minutes, preferably 360 to 480 minutes. Any process for drying the mordenite can be used according to the present invention. In this way, for example, the mordenite can be dried under vacuum at room temperature. The drying can therefore be carried out at a pressure that is lower or higher than the atmospheric pressure. The drying is preferably carried out at a pressure that is less than or equal to 3 bars. During this drying step, the amount of water released can be verified, for example by condensing this at the outlet of the reactor or by mass spectrometry analysis. Drying stops when the water release has finished. In addition, the analysis of the gases released, by bubbling in water and the determination by titration of the ammonia present in the aqueous solutions obtained, has shown that the amount of ammonia that is released by the drying process is less than 0.01% in relation to the weight of the mordenite used. The amount of ammonia released during drying is therefore negligible with respect to the amount of ammonia present in the initial mordenite. At the end of this drying step, the dry product is allowed to cool under a stream of inert gas (nitrogen), to bring it back to room temperature. The silylation of dry ammonium mordenite is carried out with tetrachlorosilane in the gas phase, by heating to room temperature, and gradually increasing the temperature starting from 1 to 5 ° C per minute, preferably from 2.5 to 4 ° C per minute, to a temperature of 300 to 600 ° C, preferably from 450 to 500 ° C. 550 ° C, and then maintaining this temperature for a period of 60 to 180 minutes, preferably 120 to 160 minutes. Preferably, a gas mixture containing an inert gas and tetrachlorosilane is used, in which the partial pressure of the tetrachlorosilane is between 0.05 and 1.0 bar, in particular between 0.2 and 0.6 bar. During this step of silylation a slight dealumination of the mordenite takes place: the atomic ratio of Si / Al changes from an initial value of between 5: 1 and 20: 1 to a value of between 10: 1 and 30: 1. According to the present invention, it is essential to use tetrachlorosilane as a silylating agent. In fact, it has been found that silylation with other silylating agents (dichloromethylsilane or polydimethylsiloxane) does not make it possible to obtain a catalyst which is selective for the formation of dimethylamine in the catalytic synthesis of methylamines from ammonia and methanol. After cooling under a stream of inert gas at room temperature, the treated mordenite was thoroughly rinsed with distilled water to remove the aluminum chlorides and residual aluminum salts. The washing is repeated several times until the pH of the supernatant solution is neutral. The modified ammonium mordenite thus obtained is then dried at 60 ° C at constant pH.

Modified ammonium mordenites used as catalysts according to the present invention generally have an Si / Al atomic ratio of 10: 1 to 30: 1, preferably 15: 1 to 25: 1. The process for the preparation of the modified ammonium mordenite according to the present invention is simple and less expensive than the process of the state of the art. Indeed, contrary to the processes for the preparation of the modified mordenite described in U.S. Patents 5,137,854 and 5,210,308, which comprise four essential steps, including two steps of calcination, the process for the preparation of modified ammonium mordenite according to US Pat. the present invention takes place in two steps (drying and silylation), without involving a calcination step. In addition, the process according to the present invention is easier to carry out than the process according to European Patent Application 593,086, in which scrupulous care must be taken to adjust the water content in the mordenite to a predetermined value before the silylation step, and in which several calcinations are also carried out. Accordingly, the process for the preparation of modified ammonium mordenite according to the present invention is easier and economically applicable on an industrial scale, as opposed to processes of the prior art. In the process for the synthesis of methylamines according to the present invention, the methanol and ammonia used as starting materials must be pure or, for obvious economic reasons, be of technical grade. The raw materials are used in the process according to the invention in amounts such that the atomic ratio of nitrogen / carbon (N / C) is from 0.5: 1 to 5: 1, preferably from 0.8: 1 to 2: 1. . When the atomic ratio of N / C increases, the selectivity for methylamine production tends to decrease, whereas when the atomic ratio of N / C decreases, the production of trimethylamine increases. For this reason it is not recommended to work with an atomic ratio of N / C outside the range of 0.5: 1 to 5: 1. The methanol feed rate is advantageously between 0.1 and 2 kg / h / kg of catalyst. The operating conditions used in the process of the invention are those generally used for the manufacture of methylamine by the gas phase catalytic reaction of ammonia with methanol. The process is generally carried out at a temperature in the range of 220-350 ° C, preferably between 280 and 320 ° C, a pressure that fluctuates from atmospheric pressure to about 100 bar, preferably ranges from about 1 to 50. Pub. No restrictions are placed on the nature of the apparatus used to carry out the process of the invention. The process can be conducted continuously or not continuously. The catalyst bed can be a stationary or fluidized bed. At the outlet of the reactor, the gaseous mixture is separated into its various constituents by methods that are known per se, for example, by fractional distillation. After separation of the different constituents of the reactor effluent, the ammonia, monomethylamine and / or dimethylamine can, if desired, be partially or completely recycled. In the process according to the invention, which uses a modified ammonium mordenite prepared as described above as catalyst, very high selectivities for the production of dimethylamine are obtained very easily, which can reach from 72 to 82 mol%, with Methanol conversions close to 100% mol. In addition, trimethylamine is practically not formed, products such as dimethyl ether. In addition, the same good results are obtained when the gaseous mixture of methanol and ammonia contains monomethylamine and / or dimethylamine and / or trimethylamine. The methylamines formed can therefore be recycled with the ammonia in the gas mixture which is fed into the reactor without affecting the selective production of the dimethylamine. This constitutes a considerable industrial advantage. Finally, as shown in the examples below, the catalyst retains its activity and selectivity for a prolonged period. The following examples illustrate the present invention without limiting it. In those examples the atomic ratios of Si / Al mentioned were determined by Resonance Magnetic Nuclear by Rotation of the Magic Angle of 29A1 (abbreviated MAS NMR) using as reference, a mordenite containing exclusively aluminum atoms in tetrahedral sites, the aluminum content of which was determined by the coupled inductive plasma technique as described by D. R. Corbin et al. in Anal. Chem. 59 (1987), 2722-2728.

Example 1. Preparation of the catalyst according to the invention.

In this example, the mordenite used is Zeolite CBV 20A of PQ (From PQ Corporation, Valley Forge, United States), which is a synthetic aluminum mordenite, with a low Na content (0.01% by weight in relation to the weight of the mordenite). This mordenite has a Si / Al atomic ratio of 10: 1 and a nitrogen content in the form of ammonia of 1.95% by weight. The ammonia content was determined by displacement of the NH4 + ions from the mordenite with concentrated aqueous sodium hydroxide solution, followed by steam distillation of the ammonia formed, condensation of the vapor and determination of the ammonia in the aqueous solution thus obtained. (1) Drying.

About 25g of mordenite were formed and samples were taken to give 10g of granules which have a particle size between 250 and 500 μm. The mordenite fraction having this particle size was introduced into a quartz tube of 25 mm in diameter, equipped with a thermal well. The portion of the tube used was heated externally by means of an electric coil placed in such a way as to ensure a uniform temperature in the catalyst bed. The mordenite was heated to 300 ° C at atmospheric pressure at 2.5 ° C / minute in a stream of nitrogen at a flow rate of 40 ml / min and the mordenite was maintained at a temperature of 300 ° C for 5 hours. It was then allowed to cool to room temperature under a stream of dry nitrogen. The analysis showed that the amount of ammonia released during this drying step is negligible with respect to the weight of the mordenite used. (2) Treatment with tetrachlorosilane.

A stream of nitrogen was passed through a bubbler containing tetrachlorosilane, maintained at a temperature that ensured a partial tetrachlorosilane pressure of about 0.24 bar. The gaseous mixture of nitrogen and tetrachlorosilane was then added to the catalyst bed (dry mordenite) at a flow rate of 40 ml / min, the catalyst bed being gradually heated to 550 ° C at 3.5 ° C / min. The mordenite was maintained at 550 ° C for an additional 2 hours under the gas stream and then allowed to cool to room temperature under nitrogen. The mordenite thus treated was suspended in 2 liters of distilled water, the water was decanted and this operation was repeated until the pH of the supernatant solution was neutral. The mordenite thus obtained was dried at 60 ° C at constant weight. The modified ammonium mordenite thus obtained has an atomic ratio of Si / Al of 25: 1. Its nitrogen content in the form of ammonia is 0.7% by weight. The ammonia content was determined by a displacement of the NH 4 + ions with a concentrated aqueous solution of sodium hydroxide, followed by steam distillation of the ammonia formed, condensation of the vapor and determination of the ammonia in the aqueous solution thus obtained. In the case of a mordenite having an atomic radius of Si / Al of 25: 1, this nitrogen content means that the mordenite obtained after the silylation is still in the form of ammonium. Indeed, the theoretical general formula of such a mordenite should be (NH4)? .85 [(A102)? .85 (Si02) 46.15] -24H20, and its theoretical molecular weight could therefore be 3550. The theoretical content of nitrogen expressed in percent by weight in relation to the total weight of the mordenite is therefore [(14 x 1.85) / 3550] x 100 = 0.73% by weight. Since the experimental nitrogen content is 0.7% by weight relative to the weight of the mordenite, it is clear that the mordenite is still in the form of ammonium after performing the silylation treatment according to the invention.

Example 2 (comparative). Preparation of the catalyst based on several zeolites.

In this example the process used is the same as in Example 1, except that it is applied to several commercial or synthetic zeolites. The purpose of the preparation of these catalysts based on several zeolites is to compare their operation in the synthesis of methylamines from ammonia and methanol with the operation of the modified ammonium mordenite prepared according to the process of the invention (see Example 4 ahead) . 2. 1. Silylation of Beta H + zeolite.

The preparation was carried out exactly as in the preparation of the catalyst of Example 1, but the starting mordenite was replaced with zeolite Beta H + CP 811-25 (PQ Zeolites BV, Leiden, The Netherlands), which is a synthetic protonated zeolite with a radius atomic of Si / Al of 13: 1. The modified Beta H + zeolite thus obtained has a Si / Al ratio of 150: 1. 2. 2. Silylation of the Beta Na + zeolite. a) The zeolite Beta H + CP 811-25 used in Example 2.1 above was converted to a Beta zeolite in sodium form by stirring in an aqueous solution of NH3 at room temperature, followed by stirring in an aqueous solution of sodium chloride at room temperature. reflux for 4 hours. This was then washed with distilled water until no more chloride ions were detected, then dried at 60 ° C. b) The beta zeolite in the sodium form prepared in 2.2.a) was then dried and treated exactly as in Example 1 to give a modified Beta Na1 zeolite with an atomic ratio of Si / Al of 40: 1. 2. 3. Silylation of a sodium mordenite, a) The ammonium mordenite CBV 20A PQ Zeolite used in Example 1 was converted to its sodium form by stirring in an aqueous sodium chloride solution at reflux temperature for 4 hours. It was then washed with distilled water until no more chloride ions were detected and then dried at 60 ° C. A sodium mordenite having an atomic ratio of Si / Al of 10.1 was obtained. b) The sodium mordenite prepared in 2.3.a) was then dried and treated exactly as described in Example 1 to give a modified sodium mordenite having an atomic ratio of Si / Al of 17: 1.

Example 3 (comparative). Preparation of the catalyst described in U.S. Patent 5,137,854.

By way of comparison, a modified protonated mordenite was also prepared according to the process described in U.S. Patent 5,137,854. 3. 1. PQ Zeolite CBV 20A ammonium mordenite used in Example 1 was converted to its sodium form by stirring in an aqueous sodium chloride solution at reflux temperature for 4 hours. It was then washed with distilled water until no more chloride ions were detected and then dried at 60 ° C.

A sodium mordenite was obtained which has an atomic ratio of Si / Al of 10: 1.

Next, the catalyst preparation method described in the example of US Pat. No. 5,137,854 (column 6, line 50 to column 7, line 34) was reproduced exactly using the sodium mordenite prepared from 3.1 above. In this process, the sodium mordenite was heated in a stream of nitrogen at 700 ° for 30 minutes and then subjected to this temperature to a gas stream of tetrachlorosilane and nitrogen for about 3 hours; the mordenite thus treated was washed with distilled water until no more chloride ions were detected, this was subjected to calcination at 450 ° C, the sodium ions on the mordenite were exchanged with ammonium ions by treatment with a solution of NH4N03, and the mordenite of ammonium thus obtained was finally subjected to another calcination for 2 hours at 450 ° C. A protonated mordenite was obtained which has an atomic ratio of Si / Al of 10: 1.

Example 4. Synthesis of methylamines.

In this example, the catalytic operations of a modified ammonium mordenite prepared according to the process of the invention (see Example 1) were compared with those of several other zeolites treated or not treated with tetrachlorosil'an. 4. 1. Apparatus and operating conditions.

The reactor used is a Pyrex glass tube with a height of 50 cm and an internal diameter of approximately 22 mm. A thermal well in which a thermocouple can run running through the center of this tube, to allow close verification of the catalyst temperature. This tube was placed in a sand bath fluidized externally by an electrical resistance to ensure a uniform distribution of temperature. In the tube, the catalyst layer under test is preceded by a layer of inert material (α-alumina) which was used to preheat the gaseous reactants before passing them over the catalyst bed. 7 grams of catalyst in the form of ground granules having a particle size of between 300 and 400 μm were used for the tests; the catalyst was further diluted with an inert material. The mixture of ammonia and methanol in the gas phase was fed to the reactor in the upper part downwards. The reaction was carried out at a temperature of 300 ° C, at atmospheric pressure and with a methanol feed rate of 0.3 kg / h / kg of catalyst. The feed rate of the ammonia is such that an atomic ratio of N / C of 2: 1 was produced. Experience shows that these tests, carried out at atmospheric pressure with a gaseous mixture of methanol, ammonia and possibly recycled methylamines, constitute a good method of comparing the catalyst, as well as a reliable basis for extrapolation at higher pressure conditions. At the outlet of the reactor, a known flow rate of nitrogen dilutes the outgoing gaseous products and prevents their condensation. The analysis of the composition of the gas mixture was carried out by chromatography in gas phase ration of the operations of the «catalyst.

The results obtained for each catalyst tested in the synthesis of methylamines under the conditions described in Example 4.1. they are given in Table I below. In this table the terms used have the following meanings: zeolite Beta H +: Zeolite Beta H + CP 811-25 sold by PQ Zeolites B.V., Leiden, The Netherlands; zeolite Beta H + 'SiCl 4: silylated zeolite prepared in Example 2.1; zeolite Beta Na + 'SiCl 4: silylated zeolite prepared in Example 2.2; - zeolite ZSM-12 calcined NH4 +: sodium zeolite, obtained according to the method described on page 13 (Example 6a) of the book by PA Jacobs and JA Martens Synthesis of High Silica Aluminosilicate Zeolites ", volume 33 of" Studies in Surface Science and Catalysis ", Elsevier, 1987, which was then exchanged with an aqueous NH 3 solution at room temperature and calcined at 500 ° C for 4 hours in the presence of air.

Calcined NH4 + mordenite: PQ CBV 20A zeolite mordenite (The PQ Corporation, Valley Forge, United States). Calcined at 500 ° C for 4 hours in the presence of air. - 100 H + mordenite: commercial highly dealuminated protonated mordenite, which has a Si / Al ratio of 100: 1 (sold by Zeocat 44500, Montoir de Bretagne, France); - Na + 'SiCl 4 mordenite: silylated mordenite prepared in Example 2.3; SiCl4'H + mordenite: the silylated mordenite prepared in Example 3 according to the process described in US Pat. No. 5,137,854. mordenite NH4 + "SiCl4:: modified ammonium mordenite prepared in Example 1 (according to the invention); Si / Al: the Si / Al atomic ratio of the used catalyst; CMeoH: the conversion of methanol (in% in mol) calculated by the formula moles of unconverted methanol, n? 100 -. 100 - mol = is d-2e methanol. to r ~ i-menrt-ad.o x 100 '' SDME- the selectivity for dimethyl ether (in% mol), calculated by the formula 2x moles of DME? I Q Q DME 2 x moles of DME + I x moles of MMA + 2 x moles of DMA + 3 x moles of TMA SMA selectivity for monomethylamine (in% mol), calculated by the formula I moles of MMA. ? \ QQ - MMA 2 x moles of DME + 1 x moles of MMA + 2 x moles of DMA + 3 x moles of TMA SDMA. "The selectivity for dimethylamine (in% mol), calculated by the formula 2x moles of DMA 1 00 * - DMA 2 x moles of DME + l x moles of MMA + 2 x moles of DMA + 3 x moles of TMA STMA- the selectivity for trimethylamine (in% mol), calculated by the formula 3x moles of TMA? i go - TMA 2 x mol-ss d DME + 1 x mol «3S of MMA + 2 x moles of DMA + 3 x moles of TMA In those formulas, MeOH * methanol DME = dimethyl ether MMA = monomethylamine - DMA = • dimethylamine TMA = trimethylamine TABLE I - DME MA Table I clearly shows that zeolites Beta and ZSM-12 promote the production of trimethylamine to the detriment of the production of dimethylamine. In fact, the methylamine compositions obtained with those zeolites are very close to the values that can theoretically be reached when the thermodynamic equilibrium between the three methylamines is reached. These zeolites are therefore not very selective for the production of dimethylamine. In addition, Table I shows that mordenites generally exhibit very good activity with high methanol conversions. Non-silylated protonated mordenites (calcined NH4 + mordenite and 100 H + mordenite) also promote the formation of trimethylamine in place of dimethylamine. Silylated sodium mordenite (Na'SiCl4 mordenite) is more selective for the production of dimethylamine (38 mol%). However, the selectivity for trimethylamine remains high (22 mol%). The sodium mordenite treated with SiCl and converted to a protonated mordenite, prepared according to the process described in US Patents 5,137,854 and 5,210,308, is highly selective for the production of dimethylamine (51 mol%). However, the production of trimethylamine remains high, since the selectivity for trimethylamine is 27 mol%. Table I clearly shows the superiority of the mordenite-based catalyst prepared according to the process of the invention when compared to catalysts based on other zeolites, whether or not treated with SiCl 4. In fact, the ammonium mordenite treated according to the invention with tetrachlorosilane in the gas phase at elevated temperature constitutes the most effective catalyst for the production of dimethylamine, with a DMA selectivity of 72.1 mol%; furthermore, with this catalyst, the production of trimethylamine and dimethyl ether is extremely low (0.7 mol% for the combined total of these two products) and the conversion of methanol is almost complete (97 mol%).

Ej «ampio 5. Influence of the atomic ratio of N / C In this example, the conditions for the synthesis of the methylamines were varied to determine the optimum conditions of use of the catalyst according to the invention. The same operating conditions as in Example 4 were used, using the modified ammonium mordenite prepared in Example 1 as a catalyst, at 300 ° C, but varying the atomic ratio N / C and the methanol feed rate (number of kilograms of methanol per hour per kilogram of catalyst). The results obtained are given in Table II, in which CMeoH SOME SMMA, SDMA and STMA have the same meanings as in Example 4.

TABLE II Table II shows that at 300 ° C and with a methanol feed rate of 0.3 kg / h / kg of catalyst, the production of trimethylamine is practically zero and that of dimethyl ether is very low, close to 0.5%, regardless of the atomic ratio of N / C in the feed gases. The selectivity for dimethylamine can reach 81.6 mol% in the case of an atomic ratio of N / C of 1.3. It also shows that the selectivity of dimethylamine decreases when the atomic ratio of N / C increases.

Example 6. Influence of the reaction temperature The reaction was carried out under the same conditions as in Example 4, using the modified ammonium mordenite prepared in Example 1 as a catalyst, except that the reaction temperature was decreased. The results obtained are given in Table III, in which CMeoH SDME SMMA SMA and STMA have the same meanings as in Example 4.

TABLE III Table III shows that at lower temperatures, in other words, at an incomplete methanol conversion, the operations of the catalyst according to the invention are still very good; the formation of trimethylamine and dimethyl ether remains very low.

Example 7. Stability of the catalyst The synthesis of methylamines was carried out as described in Example 4, using the modified ammonium mordenite prepared in Example 1 as a catalyst. This catalyst was maintained for 70 days at 300 ° C, at atmospheric pressure, with an atomic ratio of N / C in the feed gases of 2: 2 and a methanol feed rate of 0.2 kg / h / kg of catalyst. During this period the catalyst retains its activity with a methanol conversion greater than 99 mol% and a selectivity for dimethylamine which remains constant at 73 mol%.

Example ?. Conversion of monomethylamine.

In this example, the operation of the catalyst according to the invention was studied in the synthesis of methylamines from a gaseous mixture of ammonia and methanol containing monomethylamine. The reaction was carried out under the same conditions as in Example 4, using the modified ammonium mordenite prepared in Example 1 as a catalyst, at a reaction temperature of 300 ° C, except that a gaseous ammonia mixture was fed, methanol and monomethylamine to the reactor in amounts such that the atomic ratio of N / C is 2: 1, with a methanol flow rate of 0.1 kg / h / kg of catalyst and a flow rate of monomethylamine of 0.2 kg / h / kg of catalyst. Under these conditions the conversion of methanol is greater than 99 mol% and the selectivity for dimethylamine is 73 mol%. From this, it is concluded that the formed monomethylamine can be easily recycled to the gas mixture fed to the reactor and can itself be converted to dimethylamine.

Example 9 In this example, the operation of the catalyst according to the invention was studied in the synthesis of methylamines from a gaseous mixture of ammonia and methanol containing trimethylamine. The reaction was carried out under the same conditions as in Example 4, using the modified ammonium mordenite prepared in Example 1 as a catalyst, at a reaction temperature of 300 ° C, except that a gaseous ammonia mixture was fed, methanol and trimethylamine to the reactor in amounts such that the atomic ratio of N / C is 2: 1, with a methanol flow rate of 0.1 kg / h / kg of catalyst and a flow rate of trimethylamine of 0.067 kg / h / kg of catalyst. Under these conditions the conversion of methanol is 100 mol%, with a selectivity for dimethylamine of 73 mol%. In addition, the amount of trimethylamine found at the outlet of the reactor is the same as at the reactor inlet.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (13)

1. A process for the preparation of a modified ammonium mordenite, characterized 5 because it comprises the steps of: (1) drying an ammonium mordenite under conditions such that the mordenite is maintained in the form of ammonium and (2) treating the dried ammonium mordenite thus obtained with tetrachlorosilane in the gas phase at a temperature between 300 and 600 ° C.

2. The process according to claim 1, characterized in that the drying step (1) was carried out at a temperature which is lower than 400 ° C, preferably at a temperature in the range of 230 to 350 ° C, during a period of 180 to 540 20 minutes, preferably 360 to 480 minutes.

3. The process according to any of claims 1 and 3, characterized in that the drying step (1) is carried out at a pressure q? E that is less than or equal to 3 bars.

The process according to any of claims 1 to 3, characterized in that the step of silylation (2) is carried out at atmospheric pressure at a temperature of 450 to 550 ° C for a period of 60 to 180 minutes, preferably 120 160 minutes.

5. The process according to claim 1, characterized in that the mordenite in modified ammonium form has an atomic ratio of Si / Al of 10: 1 to 30: 1, 15 preferably from 15: 1 to 25: 1.

6. A catalyst, characterized in that it comprises a modified ammonium mordenite obtained by the process in accordance with any 20 of claims 1 to 5.

7. A catalyst for the preparation of methylamines from methanol and ammonia, characterized in that it comprises a mordenite 25 of modified ammonium obtained by the process according to any of claims 1 to 5.

8. A process for the manufacture of methylamines, characterized in that a mixture of methanol and ammonia is passed in the gas phase at elevated temperature on a catalyst comprising a modified ammonium mordenite prepared by the process according to any of claims 1 to 5.

9. The process according to claim 8, characterized in that the mixture of methanol and ammonia is used in 15 amounts so that the nitrogen / carbon atomic ratio is from 0.5: 1 to 5: 1, preferably from 0.8: 1 to 2: 1.

10. The process according to any of claims 8 and 9, characterized in that the feed rate of the methanol is between 0.1 and 2 kg / h / kg of catalyst.

11. The process according to any of claims 8 to 10, characterized in that the reaction is carried out at a temperature between 220 ° C and 350 ° C, preferably 5 between 280 ° C and 320 ° C.

12. The process according to any of claims 8 to 11, characterized in that the reaction is carried out at a 10 pressure between the atmospheric pressure and 100 bars, preferably 1 and 50 bars.

13. The process according to any of claims 8 to 12, characterized 15 because the mixture of methanol and ammonia contains a monomethylamine and / or dimethylamine and / or trimethylamine.