Various processes for the production of olefins are known. A well known process is the steam cracking of paraffinic hydrocarbons containing two or more carbon atoms.

Such processes, involve the pyrolysis of the hydrocarbon at high temperature. The heat required for the pyrolysis is provided by indirect heat transfer from a radiant furnace.

An alternative process is the production of olefins from an oxygenated feed such as methanol. In this process, the oxygenate feed is contacte with a suitable catalyst which is typically a molecular sieve. This process is disclosed in US 5744680, US 4912281 and US 5028400. This process has the avantage that the olefin can be obtained from a feed containing one carbon atom, the selectivity to ethylene and propylene is greater than the conventional steam cracking process and the operating temperature is significantly less.

A problem associated with the process, however, is that whilst the product stream is rich in C2/C3 olefins, also present are methane, other paraffins higher olefins and small amounts Of C2/C3 acetylenic compound, hydrogen and carbon monoxide. Ethylene and propylene are the most desired products and there is therefore a need to separate these from the product stream. Conventionally, such separation has been accomplished through the use of cryogenic distillation which is a multi-stage process comprising (1) a first step of separating and removing methane, carbon monoxide, and hydrogen via a demethaniser; (2) a second step of separating C2/C3 hydrocarbons from the heavier hydrocarbons; (3) a third step of hydrogenating the C2/C3 acetylenic compound to

ethylene and propylene; and (4) a fourth step of separating ethylene from ethane and of separating propylene from propane.

Whilst the above mentioned process is efficient, it is expensive. We have developed a means of separating and isolating the C2/C3 olefins from the product stream which is integral with the oxygenate conversion process and which avoids the use of the most expensive and energy intensive cryogenic stages as required in the conventional art.

Accordingly, the present invention provides a process for the production and recovery of light olefins, said process comprising the steps of (a) contacting an oxygenated feedstock with a catalyst selective for the conversion of the feedstock into light olefins under conditions to produce a product stream comprising light olefins; (b) contacting said product stream with a solution of a metallic salt, said metallic salt being capable of selectively chemically absorbing the light olefins to produce a chemically absorbe olefin rich liquid stream; and (c) recovering said light olefins from the metallic salt.

The present invention provides an effective, efficient and inexpensive means of producing and isolating the highly desirable light olefins.

For the purpose of the present invention, by light olefins is meant ethylene and propylene.

The feedstock of the present process is an oxygenated feedstock. Suitable examples of an oxygenated feedstock include alcools, ethers, aldehydes, ketones and mixtures thereof. Typically, the oxygenate feed may comprise 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms. The preferred oxygenate feed is methanol.

The feedstock may be diluted with a diluent such as steam, hydrogen, nitrogen, carbon monoxide, carbon dioxide, methane and other light paraffinic hydrocarbons.

The feedstock and optional diluent is contacte with a catalyst capable of converting the oxygenate feed to olefins. The catalyst is a molecular sieve. Suitable catalysts include silico alumino phosphates, for example SAPO 34 and SAPO 17, zeolites for example ZSM-5 and ZSM-11.

The conversion process is carried out under conditions suitable for the production of olefins. Suitably, the process is carried out in the liquid or vapour phase. It is preferred to carry out the process in the vapour phase. Suitably the process is carried

out at a temperature of from 200 to 700°C, preferably from 300 to 500°C and under a pressure of from 0.001 to 1000 atmospheres, preferably from 0.01 to 100 atmospheres.

The conversion process may be carried out in any suitable reactor, for example a fixed bed, fluid bed or spouted bed reactor.

The products of the process comprise light olefins, e. g. ethylene and propylene in addition to butylenes and small amounts of hydrogen, carbon osides, methane, acetylenes, ethane, propane, butanes and higher hydrocarbons. The products may also comprise water, which should be removed, preferably, prior to the olefin recovery step b).

The products of the conversion process are contacte with a solution of a metallic salt. Optionally, but preferably, the product stream is pre-treated prior to contact with the metallic salt. The pre-treatment step may comprise one or more of amine scrubbing, catalytic oxidation and/or reduction and other steps, known to those skilled in the art, to remove components such as carbon dioxide, oxygen, hydrogen, oxygenates and the like <BR> <BR> which may be present in small amonts. Optionally, C4 and heavier hydrocarbons may also be removed in a like manner.

The product stream is contacte with a solution of a metallic salt which is capable of chemically absorbing the light olefinic products. Suitable metallic salts include salts of chromium, copper (1), manganese, nickel, iron, mercury, silver, gold, palladium, rhodium, ruthenium, osmium, molybdenum, tungsten and rhenium. The preferred metallic salt is a copper (1) salt or a silver salt. The salt may be an acetate, nitrate, sulphate, carboxylate and borates. The preferred salt is a nitrate e. g. copper (1) nitrate, silver nitrate. Equally preferred is silver fluoroborate.

The solution of metallic salt is suitably an aqueous solution and may comprise an organic nitrogen-containing compound such as pyridine, piperidene, hydroxy- propionitrile, diethylene triamine, acetonitrile, formamide, acetamide and derivatives thereof.

Suitably the concentration of metal salt to nitrogen-containing compound in the aqueous solution is in the range from 1: 1 to 1: 6, preferably 1: 2. The concentration of metal salt in the solution is suitably at least 0.5 moles of salt per litre of solvent, preferably at least 2 moles of salt per litre of solvent.

The process for isolating the ethylene and propylene comprises contacting the

product stream obtained from the oxygenate conversion process with a metal complex which is capable of complexing or absorbing ethylene and/or propylene. The separation process may be carried out by any suitable means known to the person skilled in the art.

For example, the first stage of the separation process can be carried out in an absorber column designed to provide efficient contacting between the gas mixture and the complexing solution. Optionally, the absorption stage of the process can utilise a hydrophobic hollow fibre membrane. Suitably the complexing rection is carried out at a temperature of from-10 to 300°C, preferably from 5 to 70°C. Suitably, the rection is carried out under a pressure of from 1 to 70 barg preferably 3 to 20 barg.

A second step in the separation process is the removal of dissolve gases from the complex solution. This may be carried out by degassing at a temperature of from 0 to 80°C, preferably 15 to 35°C above the temperature of formation of the complex.

Alternatively this step may be carried out under pressure of 2 to 98% of the absolut pressure used to form the complex, preferably 10 to 80% of the absolut pressure used to form the complex. Alternatively, a combination of reduced pressure and increased temperature may be used.

The third step is recovery of ethylene and/or propylene by dissociation of these gases from the metal complex. Typically this dissociation may be carried out at a temperature of from 0 to 80°C, preferably 15 to 35°C above the temperature used to remove dissolve gases. Alternatively, this step may be carried out under pressure at 2 to 98% of the absolut pressure used to remove the dissolve gases, preferably 10 to 80% of the absolut pressure used to remove the dissolve gases. Alternatively, a combination of reduced pressure and increased temperature may be used.

The regenerated olefin-free solution is then returned to the absorber column to complex more olefins.