GB2201153A

GB2201153A - Chemical processes involving methanol

Info

Publication number: GB2201153A
Application number: GB8801837A
Authority: GB
Inventors: Christopher Leslie Winter
Original assignee: Humphreys and Glasgow Ltd
Current assignee: Humphreys and Glasgow Ltd
Priority date: 1987-01-29
Filing date: 1988-01-27
Publication date: 1988-08-24
Also published as: GB8701806D0; GB8801837D0

Abstract

In a chemical process reaction (the 'main'-process) that uses methanol as a starting material or in which methanol is present in the product mixture, some of the methanol is converted into dimethyl ether, some of the water concurrently formed with the dimethyl ether is removed and the dimethyl ether-containing stream is fed to the 'main' process. The 'main' process may be the production of alcohols by a reaction involving carbon monoxide.

Description

CHEMICAL PROCESS IMPROVEMENT This invention relates to the enhancement of chemical processes which use methanol as a feedstock and/or have methanol coming out of a reactor which is to be reused in the process. Such process is hereafter called the Main process.

This invention is concerned with Main processes in which water is formed as a by-product - particularly those in which the water is detrimental to the formation of the desired product, or inhibits its formation, or causes other problems.

In Main processes water may be undesirable for a number of reasons. Firstly it may be costly to remove from the desired product. Secondly it may react with another compound in an undesirable way, e.g. in the formation of higher alcohols from hydrogen and oxide(s) of carbon with or without methanol, any water formed may react with any carbon monoxide present to form carbon dioxide and hydrogen. This not only results in a waste of carbon monoxide, but the carbon dioxide and hydrogen so formed may have to be removed from the system - often with a further loss of carbon monoxide and other compounds.

This invention comprises converting at least some of the methanol into dimethyl ether (DME), separating it from the water also formed when methanol is so converted, and feeding the DME to the reaction zone, either alone, or with methanol, or with water.

The formation of DME may be represented by the following equation:

The above reaction is reversible. It may easily be seen that DME may be regarded as partially dewatered methanol. Thus by means of this invention the amount of undesirable 'potential' water fed to the Main process reactor may be reduced by up to half.

OME is virtually non-polar, and has the very low boiling point of -25 Deg.

Centigrade. Thus by means of condensing out the water (and if necessary, any unreacted methanol) DME may be readily separated from the water formed with it.

There are a number of ways in which this invention may be employed. The simplest is the conversion of at least part of the methanol to be fed to the Main process reactor, into DME, and feeding this to the Main process reactor.

One embodiment of this invention is described below.

In the production of higher alcohols from stream containing carbon monoxide (the Main process in this example), methanol, separated from the product, is recycled to the Main process reactor together with fresh and recycled gas -- the synthesis loop. During the Main process reaction water is formed. Because the catalyst also promotes the carbon mbnoxide shift reaction, the water reacts with remaining carbon monoxide to form carbon dioxide (the shift reaction), with the problems described above. Additionally, the hydrogen so formed tends to promote the formation of methane, and reduce the formation of higher alcohols. The DME is formed by a second reaction step in the synthesis loop itself. After leaving the higher alcohols catalyst bed, and with a suitable adjustment to the temperature, e.g. a reduction from 280 Deg.Centrigrade to 130 Deg. Centigrade, the Main process reactor catalyst effluent is passed over a catalyst which converts methanol to DME.

The mixture is then further cooled to condense out not only the higher alcohols, but also the water formed by the shift reaction. The gases leaving the condensing section are then recycled to the Main process catalyst - preferably after adjusting their composition by the removal of a purge stream carrying with it unwanted by-products such as methane, hydrogen and carbon dioxide.

In another embodiment, the higher alcohol product, on leaving its catalyst bed, is first condensed (along with any water present), its methanol separated and passed over a methanol to DME catalyst. The DME-containing stream is then cooled to remove by condensation the water formed with the DME. This embodiment has the disadvantage of needing the input of heat to effect to DME formation, and a second condensing section, but has the advantage of separately separating the water formed by the DME formation.

Catalysts for the conversion of methanol to DME are well known but are typically acidic, and/or dehydrating in nature, e.g. acidic ion exchange resins, alumina, and acids.

In order to convert the DME back to methanol it may be necessary to have some DME-to-methanol catalyst present in the Main process reactor. Similarly it may be necessary to feed some methanol and/or water to the Main process reactor to enable the DME to react back to methanol, either by reacting with the water so added, or with water produced when the methanol so added reacts to form water. The necessity for these depend upon the properties of-the catalyst for the Main reaction.

Thus this invention may comprise: In any Main chemical process reaction that uses methanol, or that has methanol coming out of a catalyst bed which is to be reused in the process, the conversion of some of the methanol into dimethyl ether, the removal of some of the water concurrently formed with the dimethyl ether, and feeding the dimethyl ether-containing stream to the Main chemical process reaction.

Claims

1. In any Main chemical process reaction that uses methanol, or that has methanol coming out of a catalyst bed which is to be ~reused in the process, the conversion of some of the methanol into dimethyl ether, the removal of some of the water concurrently formed with the dimethyl ether, and feeding the dimethyl ether-containing stream to the Main chemical process reaction.

2. Products produced by means of the invention claimed in Claim 1.

3. A process substantially as herein described.

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