GB2187741A - Producing tertiary ether/tertiary alcohol mixtures - Google Patents

Abstract

Methyl t-butyl ether and/or t-amyl methyl ether is produced by reaction of methanol with a C4 and/or C5 tertiary olefin in the presence of deliberately added water, thereby co-producing the corresponding C4 and/or C5 tertiary alcohol. The product mixture is suitable for blending with hydrocarbon fuels.

Description

SPECIFICATION Gasoline blending components The present invention relates to a process for the preparation of motor spirit blending components.

Motor spirit is a blend of several components which can be selected from, for example, catalytically cracked gasoline, steam cracked gasoline, alkylate, catalytic reformate and isomerate.

In recent years attempts have been made to cut the costs of running motor vehicles, for example by better design of vehicle bodies, by improvements to engines and by improvements to fuels. At the same time, governments have become more and more concerned about vehicle exhaust pollution and increasingly the laws of many countries have set limits on the type and amount of pollution which will be tolerated. For example, lead alkyls have been added for many years to motor spirit at anti-knock additives but these -compounds have the disadvantages that they are poisonous to man and deactivate the catalysts which are used in the exhaust gas converters used to reduce polluting emissions. As a result, governments have legislated to severely limit or ban the use of lead compounds in motor spirit.

The absence of lead compounds from motor spirit poses problems for the motor vehicle and oil industries in finding alternative, acceptable substitutes. One possibility would be to design vehicle engines with lower compression ratios which would run on fuels having lower octane values. However, this would reduce engine efficiency and increase fuel consumption and is not regarded as an acceptable solution.

Another approach is to use alternative fuel additives and a number of additives have been proposed. Some of these have also been rejected because of their adverse environmental effects but certain other compounds have been found to be effective and environmentally acceptable. In particular, certain oxygenated compounds such as alcohols and ether have been used. There have been many proposals dating back to the earliest days of motoring, for the use of- alcohols, especially methanol, in fuels. The use of methanol itself as an additive however poses considerable problems. It has a high latent heat of vaporisation, it is toxic and it has a great affinity for water. Even the presence of a small amount of water in motor spirit which contains methanol causes phase separation.

As a result of these difficulties, methanol per se has not been greatly favoured as a fuel additive. Instead, it is usually added in the- form of an ether derivative or in combination with a higher alcohol such as tertiary butanol. In this respect the use of methyl tertiary butyl ether (MTBE) has grown considerably in recent years. There- are a number of processes for making MTBE but most of them use-the reaction between isobutene and methanol to produce MTBE.

The isobutene is usually obtained as one component of the C4 hydrocarbon fraction produced in other hydrocarbon conversion processes, especially cracking to produce olefins.

Some hydrocarbon conversion processes, for example olefin plants and fluidised catalytic cracking plants, also produce C5 hydrocarbon streams which contain, inter alia, isoamylenes. It has been proposed to react these isoamylenes with methanol to produce the corresponding ether tertiary amyl methyl ether (TAME) and to use this ether as an additive for motor spirit.

In producing MTBE it is necessary to include a post-reaction stage to remove any unreacted methanol from the product before the latter is used for blending with motor spirit. A similar methanol-removal stage is necessary in the production of TAME which also forms an azeotrope with methanol.

We have now found that it is possible to produce MTBE and TAME in a process which does not require a methanol-removal stage and which produces a product suitable for blending directly into motor spirit.

According to the present invention a process for the production of MTBE and/or TAME comprises reacting methanol with a feedstock comprising a C4 and/or C5 tertiary olefin in known manner characterised in that the reaction is carried out in the presence of deliberately added water whereby to co-produce the corresponding C4 and/or C5 tertiary alcohol.

In the case of a process for the production of MTBE, the c-o-produced alcohol is tertiary butanol. In the case of a TAME process, the alcohol is tertiary amyl alcohol.

Preferably, the etherification reaction and the reaction to co-produce alcohol are carried out simultaneously and over a common catalyst, for example an acid ion-exchange resin. The water may be added to the etherification process at any convenient point in the process provided that thereby the aim of the present invention is fulfilled viz to enable unreacted methanol to be incorporated into motor spirit formulations without difficulties arising. This aim is achieved by coproducing sufficient higher alcohol, for example tertiary butanol or tertiary amyl alcohol, to counteract the unreacted methanol present in the crude reaction product. In practice, this means that the product should contain at least about the same amount of higher alcohol as methanol.

As an example, one type of etherification process comprises two reaction stages. In the first reactor a relatively high temperature is used thereby to carry out most of the reaction. Substan tially all of the product of the first reactor is conveyed to a second similar reactor operating at a lower temperature and in which the etherification reaction is completed. When applying the present invention to this process, the water may be deliberately added tóieither one or both of the two reactors.

In another example of a two-stage etherification process, ether product is removed after the first stage and unreacted tertiary olefin is fed forward to the second stage where it is reacted with further alcohol to form more ether. In operating the present invention in process of this type, the water may- once again- be deliberately added to either one or both of the two reactors.

The process of this invention has the advantage that any water that is present in the etherification process is largely, if not entirely convertd to either tertiary butanol or tertiary amylalcohol and is no longer able to induce phase separation of lie methanol in à motor spirit blend.

Moreover, should the motor spirit blend containing these components encounter water during subsequent handling -or use, the tertiary butanol and/or tertiary amyl alcohol act as co-solvent(s) for the methanol, thereby inhibiting phase separation.

The present invention therefore provides the blender of motor spirits with a convenient way of avoiding the difficulties posed by the presence of methanol and also - lowers the cost of the octane additive. Whereas prior art processes have sought to produce ethers such as MTBE containing as little methanol (and other alcohols) as possible, the present invention enables the blender to tolerate the presence- of methanol provided that the blend also contains TBA or TAA.

In a further-aspect the present invention- also comprises a motor spirit blend containing, as additives, a- component comprising co-produced MTBE and t-butanol-ahd/or a componentcom- prising co-producedTTAME and t-amyl alcohol.

EXAMPLE A C5 hydrotreated- steam cracker cut contaning 17% by weight isoamylenes and possessing RON92, MOWN78 clear, is etherified with methanol in the- presence a controlled amount of added water. The etherified product contains by weight 16% TAME, 1% TAA and 1% methanol and exhibits an enhanced octane rating of RON95, MON83 clear The product is an acceptable blending. stream in gasoline blending operations.

Claims (7)

1. A process for the production of MTBE and/or TAME which comprises reacting methanol with a feedstock comprising a C4 and/or C5 tertiary olefin in known manner-characterised in that the reaction is carried out in the presence of deliberately added water whereby to co-produce the corresponding C4 and/or C5 tertiary alcohol.

2. A process as claimed in claim 1 wherein the etherification reaction and the reaction to coproduce alcohol are carried out simultaneously and over a common catalyst.

3. A process as claimed in claim 2 wherein the common catalyst is an acid ion-exchange resin.

4. A process as claimed in claim 1 wherein the etherification process comprises two reaction- stages comprising a first stage operated at a relatively-high temperature to-effect most of the etherification and -a second stage operated at a relatively lower temperature than said first stage whereby to substantially complete the etherification.

5. A process as -ciaimed in claim 4 wherein the water is deliberately added to either one or both of the reaction stages.

6. A process as claimed in claim 4 or 5 wherein ether product is removed after the first reaction stage, unreacted tertiary olefin is- fed forward to the second reaction stage and reacted therein with-further alcohol.

7. A motor spirit blend comprising a motor spirit and, as additives, a component-comprising co-produced MTBE and t-butanol and/or a component comprising co-produced TAME and t-amyl alcohol.