CH638477A5 - METHOD FOR PRODUCING TERTIAL ALKYL ETHERS. - Google Patents

Description

The invention relates to a process for the preparation of tertiary alkyl ethers by reacting a tertiary mono-olefin with a primary alcohol in the liquid phase in a reactor and in the presence of a catalyst.

This process is known from NL publications 273 294 and 7505991, the production of methyl tert-butyl ether from isobutene and methanol at a temperature of about 60 ° C. in the presence of acidic cation exchange resins being described as catalysts. It is known that at a lower reaction temperature the equilibrium of the reaction is more favorable for the synthesis of the ether (cf. NL application 7505991, p. 13, lines 13-15). A relatively low temperature is therefore necessary for the synthesis of the ether, the reaction rate having to be increased by a catalyst. However, since the reaction is exothermic, the steadily increasing temperature shifts the reaction equilibrium to the unfavorable side, which in turn results in a considerable loss in yield and conversion.

It has now been found that higher conversions are obtained when part of the reaction mixture is recycled directly.

The invention thus relates to a process for the preparation of tertiary alkyl ethers by reacting a tertiary monoolefin with a primary alcohol in the presence of a liquid phase catalyst in a reactor, which is characterized in that part of the reaction mixture is returned directly from the reactor.

With the process according to the invention, higher conversions are obtained at constant space velocities under otherwise identical conditions than with a process in which no recycle takes place. The advantage of the process according to the invention is that a smaller reactor can be used and that the relatively hot reactor effluent makes preheating the feed stream superfluous during the reaction.

Examples of primary alcohols suitable in the process according to the invention are methanol, ethanol, propanol, butanol and optionally higher alkanols. Methanol is particularly suitable. The molar ratio of alcohol to tertiary monoolefin can vary, a molar ratio of 1: 1 is very suitable.

Tertiary monoolefins with 4 to 7 carbon atoms, in particular isobutene, are particularly important in the process according to the invention.

The process according to the invention is carried out at a temperature of generally 50 to 130 ° C., preferably 60 to 100 ° C., at pressures of 5 to 50 bar or above.

Suitable catalysts in the process according to the invention are cation exchange resins based on vinylaromatic polymers which contain sulfonic acid groups (cf. NL application 273,294), sulfonated resins such as sulfonated carbon obtained by treating bituminous carbon with sulfuric acid, and sulfonated phenol Formaldehyde resins. Products of sulfonated coumarone indene resins with cyclopentadiene or with furfural and of sulfonated cyclopentadiene resins with furfural are also suitable. Preferred catalysts are sulfonated polystyrene resins, e.g. a matrix of divinyl benzene and cross-linked polystyrene with 0.5 to 20% copolymerized divinyl benzene and ionizable sulfonic acid groups. Other suitable catalysts are perfluorinated polymers or copolymers which contain sulfonic acid groups. All of these resins are commercially available. A particularly suitable catalyst is "Duolite C-26", which gives a high reaction rate. In the production of the ether, the reaction rate with “Duolite C-26” as a catalyst is about twice as fast as with “Amberlyst 15 H +”. The exchange capacity of the acidic resin is preferably at least 2.0 mVal H Vg dry resin, in particular 3.0 to 5.5 mVal H + / g dry resin.

In the process according to the invention, the recycle is preferably carried out in such a way that the weight ratio of recycle stream to feed stream of monoolefin and primary alcohol is 0.5: 1 to 6: 1, preferably 1: 1 to 2: 1.

Although a higher conversion is obtained by recycling the reaction mixture, the conversion to methyl tert-butyl ether can be increased even further up to 95% if a second reactor is used. After leaving the first reactor system (with recycle), the reaction mixture is cooled to about 70 ° C. and introduced into the second reactor, where the isobutene and the alcohol can continue to react.

The reaction mixture can be further purified from isobutene and alcohol; but you can also only remove the isobutene and use the methyl tert-butyl ether still containing methanol as such, e.g. to increase the octane number in lead-free or low-lead petrol.

Traces of acid in the reaction mixture originating from the catalyst can e.g. can be removed by treatment with activated alumina. For this purpose, the reaction mixture is passed through a vessel with activated aluminum oxide and neutralized in this way. The aluminum oxide is regularly supplemented or treated with a 2 percent aqueous sodium carbonate solution and reused.

The examples illustrate the invention.

Example 1 (comparison)

A 0.3 liter reactor is filled with an aqueous slurry of 90 g (dry weight) of sulfonated styrene-divinylbenzene resin with an exchange capacity of 4.75 meq H + / g dry weight. The resin is washed with dry methanol to make an anhydrous resin bed.

The reactor is at a pressure of 25 bar and a space velocity of 50 liters. (Liter of catalyst) -1. Std.- 'a stream of methanol and isobutene in a molar ratio of 1.25: 1 continuously passed. The reaction mixture is drawn off continuously. The initial temperature of the feed stream is 70 ° C, the temperature at the reactor outlet 130 ° C. The conversion of methanol and isobutene into methyl tert-butyl ether is determined in the waste stream, it is 73%, based on isobutene.

Example 2

The procedure of Example 1 is repeated, with the difference that the reaction mixture leaving the reactor

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is mixed into two streams. One stream is returned via a line to the inlet of the reactor, the weight ratio of the recycle stream to the fed mixture of methanol and isobutene being 1.5. The space velocity is again 50 liters. (Liter

Catalyst) -1. Hour-1 The feed stream does not have to be passed through a preheater to bring it to 70 ° C. The temperature at the reactor outlet is 104 ° C. The second stream is drawn off. The conversion to 5 methyl tert-butyl ether is 84%, based on isobutene.

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Claims (3)

638477 1. A process for the preparation of tert-alkyl ethers by reacting a tert-monoolefin with a primary alcohol in the presence of a liquid phase catalyst in a reactor, characterized in that part of the reaction mixture is recycled directly from the reactor. 2. The method according to claim 1, characterized in that in a weight ratio of the recycle stream to the feed stream of 0.5: 1 to 6: 1. 2nd PATENT CLAIMS 3. The method according to claim 1 and 2, characterized in that one returns in a weight ratio of recycle stream to feed stream of 1: 1 to 2: 1.