Europâisches Patentamt European Patent Office (îj) Publication number: 0 026 071 Office européen des brevets Bl 12 EUROPEAN PATENT SPECIFICATION @ Dateof publication of patent spécification: 27.07.83 © Int. Cl.3: C 07 C 85/02, C 07 C 87/08 @ Application number: 80303181.4 (g) Date of filing: 10.09.80 (54) Process for disproportionating monomethylamine using zeolitic catalystto produce dimethylamine. (30) Priority: 1 1 .09.79 US 74419 (73) Proprietor: E.l. DU PONT DE NEMOURS AND 06.06.80 US 154482 COMPANY Légal Department 1 007 Market Street Wilmington Delaware 19898 (US) (43) Date of publication of application: 01.04.81 Bulletin 81/13 (72) Inventor: Weigert, Frank Julian Stratford Apts., Apt. J-1 0 Shipley & Naamans (45) Publication of the grantof the patent: Roads 27.07.83 Bulletin 83/30 Wilmington Delaware 1 981 0 (US) (84) Designated Contracting States: (74) Représentative: Woodcraft, David Charles et al, BE DE FR GB IT NL BROOKES & MARTIN High Holborn House 52/54 High Holborn London.WC1V6SE (GB) (56) Références cited: US - A - 1 926 691 Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have beenfiled until the opposition fee has been paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. This invention relates to an improved preparation of dimethylamine by a catalytic dispropor- tionation of monomethylamine. It is well known in the art that the catalyzed reaction of methanol and ammonia can be employed to produce mono-, di- and/or trimethylamine. To facilitate the formation of any one of the methylamines various expedients can be used. For example, it is known that the use of dimethyl ether in conjunction with or in place of methanol, recycling unwanted methylamines, the use of varying molar ratios of the reactants and the use of specific dehydrating or aminating catalysts can be employed to alter the relative amounts of the various amines in the product. Exemplary, but not intended to be all inclusive, of such art, U.S. 3,278,598 discloses an improved, Raney nickel-catalyzed, liquid phase process of reacting primary and secondary alcohols and ammonia, the improvement comprising the use of a rhodium, palladium or ruthenium cocatalyst, to provide increased formation of secondary amine. Similarly, U.S. 3,387,032 discloses a catalytic process for providing increased amounts of dimethylamine from methanol and/or dimethyl ether and ammonia, using as the catalyst a silica gel-based alumina which has been partially steam deactivated and then impregnated with silver phosphate, rhenium heptasulfide, molybdenum sulfide or cobalt sulfide. U.S. 2,394,515 and 2,394,516 disclose catalytic processes for preparing polyalkylamines, with lesser quantities of the monoalkylamine, from an alcohol and/or ether of 1-5 carbon atoms and ammonia, using as the catalyst an aluminum oxide or salt which has been coated, first with silica and then with a vanadium salt or molybdenum oxide. The related U.S. 2,349,222 utilizes as the catalyst a granular alumina which has been coated with a nickel, cobalt or chromium oxide hydrogenation/dehydro- genation catalyst. U.S. 2,456,599 discloses that higher amounts of mono- and dimethylamine, and a reduced amount of trimethylamine, can be achieved in the catalyzed process wherein water is introduced along with the methanol and ammonia. U.S. 1,799,722 and U.S. Reissue 19,632 disclose catalytic processes wherein trimethylamine is introduced with the methanol and ammonia to suppress the formation of trimethylamine and provide increased amounts of dimethylamine. U.S. 1,992,935 discloses a catalytic process for preparing a mixture of primary, secondary and tertiary methylamines, principally dimethylamine, from methanol and ammonia, using as the catalyst a dehydrating oxide supported on a porous rigid gel such as silica gel. British 422,563 discloses a catalytic process for producing secondary amine by employing the primary amine as starting material in addition to ammonia and alcohol. Restelli et al. in A.I.Ch.E. Journal, Vol. 12, No. 2, 292-296, March, 1966, describe studies of transmethylation reactions of monomethylamine and dimethylamine over montmorillonite, a hydrated magnesium/calcium oxide, containing aluminosilicate. With the reactions being carried out at about 320-371 °C, at low conversions the monomethylamine is converted to dimethylamine, the rate being directly proportional to the amine partial pressure, thus indicating that adsorption of monomethylamine on the catalyst surface is rate-determining. U.S. 1,926,691 discloses the disproportionation of monomethylamine over oxide catalysts, including aluminum silicate (silica-alumina) and partially dehydrated alumina. In the only example given, the disproportionation of monomethylamine over anhydrous alumina is highly selective for the production of dimethylamine. All the oxide catalysts disclosed are suggested to be equivalent in this regard, being broadly classified as amination catalysts. U.S. 3,384,667 discloses a process for producing monosubstituted and disubstituted amines, in preference to trisubstituted amines, by reacting an alcohol and ammonia over a dehydrated crystalline aluminosilicate catalyst having pores of a diameter that pass the monosubstituted and disubstituted amine products but not the trisubstituted amine products. The related U.S. 4,082,805 discloses a process for producing primary aliphatic amines, in preference to secondary and tertiary amines, from a C,-Cs alcohol or ether and ammonia over a natural or synthetic dehydrated crystalline aluminosilicate having the structure of ZSM-5, ZSM-11 or ZSM-21, at 300-5000C at one atmosphere to 1000 psig pressure, the feeds of alcohol or ether and ammonia being within the ratio 1:1 to 5:1. Methylamines presently are generally produced commercially by a continuous process from methanol and ammonis, using an amorphous silica-alumina catalyst. At moderate methanol conversions such processes generally produce more trimethylamine than mono- and dimethylamine (at very low conversions monomethylamine is the major product). Because of its greater usage industrially as a chemical intermediate dimethylamine is the most desirable methylamine product, with monomethylamine being next most preferred. Production of the maximum amounts of monomethylamine and dimethylamine is achieved when equilibrium is reached, at about 100% methanol conversion. However, the relative amounts of the three amines produced at equilibrium depend, to a large extent, on the carbon/nitrogen (C/N) ratio, that is, the methanol/ammonia ratio in the reactants. At carbon/nitrogen ratios of about one the product mixture contains, on a mole basis, about 55% ammonia, 22% trimethylamine (TMA), 12% monomethylamine (MMA) and 12% dimethylamine (DMA). The product mixture can be separated and the less desirable methylamines can be recycled. However, recycling monomethylamine provides only about 10% dimethylamine per pass, at renewed equilibrium, with most of the monomethylamine being converted to trimethylamine and ammonia. At no C/N ratio, at equilibrium, is dimethylamine the favored product. The synthesis of methylamines is distinguishable from the synthesis of ethylamines. For example, the thermodynamics of the ethylamine reactions corresponding to those discussed above are such that the formation of diethylamine is favored at an ethyl/nitrogen ratio of about 2. This, the production of dimethylamine is substantially more complex and difficult than is the production of diethylamine, using similar processes. An object of this invention, therefore, is to provide an improved process for converting monomethylamine directly to dimethylamine and ammonia, to the substantial exclusion of trimethylamine, thus obviating production of the least desirable methylamine and the concomitant recovery and recycling processes associated therewith. Another object is to provide a process which uses a catalyst which can accomplish this objective in the presence of water, such as water which may be present along with the monomethylamine. Other objects will become apparent hereinafter. The accompanying drawings forming a material part of this disclosure provide plots showing the selectivity of the catalyst of the invention process (Figure 3), as compared to the use of a conventional amorphous silica-alumina catalyst (Figure 1) and a conventional alumina catalyst (Figure 2), both of which are outside the invention, in converting monomethylamine to dimethylamine. More specifically, the drawings provide plots showing the percentages of dimethylamine in the dimethylamine/trimethylamine products obtained at varying conversions of monomethylamine. The drawings are based on data provided in the examples and experiments. The silica-alumina catalyst represented in Figure 1 may be seen to be non-selective whether the system is dry or contains water. The alumina catalyst represented in Figure 2 may be seen to be selective when dry but non-selective when water is present in the system. The natural ferrierite catalyst represented in Figure 3 may be seen to be selective whether the system is dry or contains water. For further comprehension of the invention, and of the objects and advantages thereof, reference may be made to the following description and accompanying drawings and to the appended claims