DE4323680A1 - Process for the preparation of dimethyl carbonate - Google Patents

Abstract

Dimethyl carbonate can be obtained by reaction of carbon monoxide with methyl nitrite in a continuous gas-phase reaction in the presence of a heterogeneous catalyst which has been prepared by application of one or more palladium compounds of the formulae Pd(NH3)2X2, Pd(NH3)3X2 and/or Pd(NH3)4X2, where X stands for halogen, to a suitable support material. In this process, dimethyl carbonate is formed in high selectivity and great temporal stability.

Description

The present invention relates to a process for the continuous production of dime thyl carbonate by reacting carbon monoxide with methyl nitrite in the presence of a he terogenic catalyst, by the application of one or more palladium compounds of the general formulas Pd (NH₃) ₂X₂, Pd (NH₃) ₃X₂ and / or Pd (NH₃) ₄X₂, where X is Halogen stands, was made on a suitable carrier material.

Dialkyl carbonates are of general chemical and technical importance. So is with for example, diethyl carbonate is an excellent solvent in the medium boiling range. Of dialkyl carbonates are also excellent carbonylation and acylation reagents zien. They are of great importance in the production of other carbonates such as for example diphenyl carbonate, urethanes and ureas. After all, they are suitable because of their high oxygen content as fuel additives to improve the Knock resistance of petrol.

It is known that dialkyl carbonates by reacting phosgene or chloramei alkyl acid esters can be prepared with alcohols.

However, there is an increasing interest in the use of the toxic phosgene or derived intermediates such as chloroformate from other processes to solve. Processes in which carbon monoxide is in the gas phase are particularly important here is reacted with alkyl nitrites on catalysts containing heterogeneous platinum metals.

So in the Journal for Catalytic Research (China) Vol.10 (1) p.75-78 (March 1989) the implementation of carbon monoxide with methyl nitrite on a PdCl₂-containing activated carbon Supported catalyst described, in addition to dimethyl oxalate predominantly dimethyl carbonate arises.

In DE-OS 41 23 603 is by using a palladium chloride catalyst with γ-Al₂O₃ as a carrier material, a high selectivity, both based on carbon monoxide and Methyl nitrite, achieved at the same time high sales. However, to maintain the catalytic activity of the educt mixture of hydrogen chloride gas in amounts up to 1000 ppm (Volume) can be added.

EP 503 618 similarly uses dialkyl carbonates described a catalyst that is a platinum metal, at least one element from the Series Fe, Cu, Bi, Co, Ni or Sn, at least one further addition from the series V, Mo or  W and contains at least one halide. The disadvantage of this method is the fact that only low sales of methyl nitrite are achieved. Furthermore, one becomes part considerable deactivation of the catalysts described after just a few hours observed.

This means a considerable additional effort for a technical implementation of the method, which must be operated for catalyst regeneration or catalyst replacement.

In the present invention, these disadvantages could be overcome by using the invention Catalyst can be overcome in a surprising way.

There has been a process for the production of dimethyl carbonate by reacting coal monoxide with methyl nitrite in the presence of an inert gas, in the presence of methanol as well in the presence or absence of nitrogen monoxide on a platinum metal support Talysator found at elevated temperature in a continuous gas phase reaction is characterized in that at a volume ratio of methyl nitrite: carbon monoxide of 0.1: 1 to 10: 1, a pressure of 0.5 to 6 bar and a temperature of 50-150 ° C gear is processed, the catalyst being impregnated with a suitable carrier material one or more palladium compounds of the general formulas Pd (NH₃) ₂X₂, Pd (NH₃) ₃X₂ and / or Pd (NH₃) ₄X₂, in which X represents halogen, was produced.

All carrier materials known to the person skilled in the art are suitable for the process according to the invention rialien such as activated carbons, zeolites, aluminosilicates, metal phosphates, oxides, Hy droxides and hydrated oxides of aluminum and silicon, diatomaceous earth and silicas, dia earthen earth, montmorillonite, layered silicates, oxides of titanium, zinc, iron and manganese or heteropolyacids.

The catalysts of the invention can be prepared, for example, by that first palladium halides, preferably with alkali or alkaline earth metal halides, in a suitable solvent such as water, methanol or acetone in solution and then with ammonia in the sense of one of the reaction equations below be implemented.

M₂PdX₄ +2 NH₃ → Pd (NH₃) ₂X₂ + 2 MX
M₂PdX₄ + 3 NH₃ → Pd (NH₃) ₃X₂ + 2 MX
M₂PdX₄ + 4 NH₃ → Pd (NH₃) ₄X₂ + 2 MX

The direct reaction of palladium halides with ammonia is also possible.

The solutions obtained are then applied to the respective catalyst support in of a type known to the person skilled in the art, for example by impregnation, by adsorption or by spraying.

Another possibility for producing the catalysts according to the invention is at for example, soaking the catalyst with a palladium halide solution and so obtained product either with an ammonia solution or with gaseous ammonia to treat.

The reaction on which the method according to the invention is based runs in the sense of following reaction equation:

CO + 2 MeONO → O = C (OMe) ₂ + 2 NO

While it is basically possible, carbon monoxide with methyl nitrite in the absence of others to implement gaseous reaction components or reaction auxiliaries, for example then when working with mixture compositions outside the explosion limits tet, an inert gas is often used to dilute the reactants. When Inert gases, for example noble gases, nitrogen and carbon dioxide, are preferred Argon, nitrogen or carbon dioxide, particularly preferably nitrogen and carbon dioxide Question.

The amount of inert gas is 20 to 85 vol .-%, based on the total in the reactor volume of gas to be introduced. The inert gas and any unconverted contained therein Residual amounts of the reactants can be recycled in a cycle.

The volume ratio of the reactants methyl nitrite and carbon monoxide to each other is 0.1: 1 to 10: 1, preferably 0.2: 1 to 4: 1, particularly preferably 0.3: 1 to 3: 1.

The gas mixture to be reacted can also contain small amounts of methanol, for example in an amount of 0 to 10 vol .-%, and small amounts of nitrogen monoxide, for example in an amount of 0 to 10 vol .-%, both based on the total volume of the gas mixture to be used. Such additions of methanol or nitrogen monoxide can come from the production of the methyl nitrite and, for example, with this in the reaction gas mixture are carried in.  

A small amount of an activator can also be added to the gas mixture to be reacted be set. These are halogens or hydrogen halides such as chlorine, bromine, Hydrogen chloride and hydrogen bromide in an amount of 0-2000 ppm, preferably 0- 1000 ppm, particularly preferably 0-750 ppm (each volume) are metered in.

Examples Definitions

The space time yield (STY) in [g / l _* h] for dimethyl carbonate in the example given is calculated according to:

where m _{DMC is} the amount of dimethyl carbonate (DMC), V _{cat is} the catalyst volume and t is time.

The selectivity S [%] of the formation of the dimethyl carbonate is calculated according to

in which
n _DMC = amount of dimethyl carbonate
n _ODME = amount of dimethyl oxalate
n _AME = amount of methyl formate
n _FDA = amount of formaldehyde dimethyl acetal
mean.

Catalyst production

0.835 g of PdCl₂ are dissolved in 4 ml of water with the addition of 2 g of sodium chloride. With space temperature, 25 ml of a 25% ammonia solution are added with stirring.  100 ml of activated carbon Norit ROX 0.8 are soaked in this solution and then in Nitrogen stream dried.

Process description

In a vertical tube reactor (glass, length 50 cm, diameter 4 cm) were introduced 0.6 ml of the catalyst described between a filling of Raschig rings.

The glass tube was heated to 120 ° C. and a gas mixture of 50% by volume nitrogen, 30% by volume Methyl nitrite, 15 vol .-% carbon monoxide and 5 vol .-% methanol, corresponding to a Ge total gas load of 5000 l / h was passed through.

The gas flowing out of the reactor was cooled to 5 ° C and the obtained condensed Phase examined by gas chromatography.

The uncondensed products were analyzed by IR spectroscopy and mass spectroscopy detected.

Dimethyl carbonate was formed after 4 h with a space-time yield of STY = 180.5 g / l _* h and a selectivity of S = 97.2%.

After 30 h, the space-time yield was STY = 217.8 g / l _* h and the selectivity S = 89.5%.

Claims (7)

1. A process for the continuous production of dimethyl carbonate by reacting carbon monoxide with methyl nitrite in the gas phase on a heterogeneous catalyst, characterized in that the said catalyst has one or more supported palladium compounds of the general formulas (I), (II) and / or (III) Pd (NH₃) ₂X₂ IPd (NH₃) ₃X₂ IIPd (NH₃) ₄X₂ III in which X represents halogen,
contains
the carrier mentioned from the series of activated carbons, zeolites, aluminosilicates, metal phosphates, oxides, hydroxides and oxide hydrates of aluminum and silicon, diatomaceous earth and silicas, diatomaceous earth, montmorillonites, layered silicates and molecular sieves, oxides of titanium, zinc, iron and from manganese or from heteropolyacids,
the further reaction auxiliaries mentioned comprise at least one inert gas and, if appropriate, moreover an activator of the catalyst and are carried out at a reaction temperature between 60 and 200 ° C. and at a reaction pressure between 0.5 and 10 bar. 2. The method according to claim 1, wherein the carrier material of the series of activated carbons, Zeolites, aluminosilicates, metal phosphates, aluminum oxides and manganese or of heteropolyacids. 3. The method according to claim 1, wherein as a carrier material is an activated carbon or an aluminum minium oxide is used. 4. The method according to any one of claims 1 to 3, characterized in that as a reacti onshilfsstoff an inert gas from the group of noble gases, nitrogen and Koh Lendioxids, preferably nitrogen or carbon dioxide, are used.   5. The method according to any one of claims 1 to 4, characterized in that as a further optionally added reaction agent and acting as activator chlorine, bromine, Hydrogen chloride or hydrogen bromide, preferably chlorine or hydrogen chloride, ver is applied. 6. The method according to any one of claims 1 to 5, characterized in that in one Range from 70 to 150 ° C, preferably from 75 to 145 ° C, for the reaction temperature and from 1 to 6 bar, preferably from 1.5 to 4.5 bar, worked for the reaction pressure becomes. 7. The method according to any one of claims 1 to 6, characterized in that the Volume fractions in the reactant gas mixture for methyl nitrite 5% to 50%, preferably 15% up to 45%, particularly preferably 30% to 35%, for carbon monoxide 10% to 30%, preferably 10% to 25%, particularly preferably 10% to 20%, for the added Inert gas 20% to 85%, preferably 45% to 60%, particularly preferably 50% to 55% and for the added activator 0-2000 ppm, preferably 0-1000 ppm, particularly preferably be 0-750 ppm.