GB2548976A

GB2548976A - Apparatus and process

Info

Publication number: GB2548976A
Application number: GB1703149.3A
Authority: GB
Inventors: Lord Adrian; John Heaton Christopher; Shah Atul; Welch David; Smidt Martin; L Biedenstein Victoria
Original assignee: Johnson Matthey Davy Technologies Ltd
Current assignee: Johnson Matthey Davy Technologies Ltd
Priority date: 2016-03-01
Filing date: 2017-02-27
Publication date: 2017-10-04
Anticipated expiration: 2037-02-27
Also published as: CN107138182A; CN107138182B; GB2548976B; GB201703149D0; GB201603558D0

Abstract

An apparatus for separating a homogeneous catalyst from a feed stream comprising the homogeneous catalyst and a separation composition which can be separated therefrom by vaporisation. The apparatus comprises a vaporisation zone 111 and means 104 for supplying the feed stream to the vaporisation zone, such that in use the separation composition will be vaporised. The vaporisation zone is configured such that the feed stream has a first residence time in the vaporisation zone. The apparatus also comprises means for removing the vaporised separation composition from the vaporisation zone and a vapour-liquid separator 112, located in direct communication with the vaporisation zone to collect a liquid comprising the homogeneous catalyst. The vapour-liquid separator is configured to allow a residence time of from about 10 secs to about 60 mins. A cooling means is located within the vapour-liquid separator and a means 107 for removing the liquid comprising the homogeneous catalyst from the vapour-liquid separator is provided. The apparatus is configured such that the volume of the liquid comprising the homogeneous catalyst is maintained at a level that the cooling means is substantially submerged within the liquid comprising the homogeneous catalyst. The apparatus may form part of a hydroformylation reaction process.

Description

Apparatus and Process

The present invention relates to an apparatus and process for recovering a homogeneous catalyst for recycle to a reactor. More particularly, the present invention relates to an apparatus and process for recovering a homogeneous catalyst from a stream comprising an aldehyde. Still more particularly, the present invention relates to an apparatus and process for recovering a homogeneous rhodium catalyst from a stream recovered from a hydroformylation reactor.

In a hydroformylation reaction, an olefin is reacted with synthesis gas, i.e. with a gas mixture comprising carbon monoxide and hydrogen, to form an aldehyde. The reaction is generally carried out in the presence of a homogeneous catalyst. Suitable catalysts include rhodium-based catalysts which are generally provided as a complex with one or more phosphorous ligands. Examples of suitable ligands include organophosphite and organophosphine ligands.

As these catalysts are expensive they are generally recovered from streams containing the product aldehyde and recycled to the reactor. As these catalysts can be temperature sensitive, such that their rate of deactivation is increased if they are exposed to high temperatures, the hydroformylation reaction is generally conducted at moderate conditions to protect the catalyst. Even with these mild conditions, the activity of the catalyst decreases at a slow but appreciable rate as the catalyst is continuously separated from the product stream and recycled to the reactor.

The separation of the catalyst from the aldehyde containing stream generally requires vaporising the aldehyde such that it can be separated from the catalyst in a gas/liquid separator. The liquid stream, which will contain the catalyst, is then recycled to the hydroformylation reactor. One example of a process of this type can be found in US 4148830. A similar arrangement is described in US 6100432,

However, in processes of this type, a high temperature is required to vaporise the aldehyde. Indeed, generally, the temperature is such that the environment in the vaporiser is harsher than that employed in the hydroformylation reactor vi^hich can result in an accelerated rate of deactivation of the catalyst. Without wishing to be bound by any theory it is believed that this deactivation is due to the formation of an inactive or less active rhodium species which is susceptible to precipitation under prolonged exposure to the conditions in the vaporiser.

Various proposals have been made to address this problem. For example, the vaporisation may be carried out in more than one stage with the conditions chosen so that successive fractions of progressively lower volatility are removed from the reactor stream. In this arrangement, the successive vaporisation stages are operated at decreased pressure. However, generally this will result In successive stages having increased temperatures, which will increase the rate of deactivation of the catalyst.

In US 4166773 a process is described in which a falling film evaporator is used to vaporise the aldehyde in order to reduce the time the catalyst is exposed to the increased temperature. In this process, vaporised aldehyde and the heated liquid are fed to a separation column where the vaporised products are removed as overheads from the column. The liquid stream is collected at the bottom of the column from where it is circulated through a cooling system which is external to the column. Whilst the period of time for which the catalyst is in the vaporiser is reduced, it is still retained at a high temperature for some time. In addition, this system does increase the capital and operating costs of the system. Further, this system can require complex controls since it is important to maintain a cooling cycle between the bottoms of the separation column and the cooling system even when recycle to the reactor has been suspended.

The relationship between the temperature used for vaporisation and the decomposition of a phosphite ligand of the catalyst is considered in US 5672766 where the need to limit the exposure of the cataiyst to high temperatures is noted and a means of calculating the acceptable combinations of temperature and residence time to minimise the risk of deactivation is proposed. A further arrangement is discussed in US 6500991. Here the liquid fraction recovered from the bottom of the gas/liquid separator is cooled to below reactor temperature and stored at this temperature until it is required to be recycled to the reactor. CN12030622 describes a system in which a cooling means is provided within a vapour liquid separation. However there is no discussion as to the purpose of the bundles or how they are operated.

In CN 203464572 an alternative arrangement is described in which two cooling bundles are located within the vapour liquid separator after the vaporiser such that the liquid portion passes over the cooling bundles. The details of the utility model relate to the closed loop system for providing the cooling water and there is little disclosure of the operation within the vaporiser or the separator.

There is still a need for a simple and effective apparatus and process for recovering a homogeneous catalyst in which the rate of deactivation of the catalyst is minimised but without the need for complex cooling systems. It has been found that this can be achieved by minimising the exposure of the catalyst to high temperature and then rapidly cooling the catalyst. In particular it has been found that this can be achieved by locating the cooling means in direct contact with the vaporisation zone and where the process is operated such that the liquid level of the catalyst containing stream is maintained such that the cooling means is submerged in the catalyst containing stream It has been found that by providing cooling in the vapour liquid separator there is no large hold-up of catalyst at high temperatures.

Thus according to a first aspect of the present invention there is provided an apparatus for separating a homogeneous catalyst from a feed stream comprising the homogeneous catalyst and a separation composition which can be separated therefrom by vaporisation, said apparatus comprising: a vaporisation zone; means for supplying the feed stream to the vaporisation zone, such that in use the separation composition will be vaporised, said vaporisation zone being configured such that the feed stream has a first residence time in the vaporisation zone; means for removing the vaporised separation composition from the vaporisation zone; a vapour-liquid separator, located in direct communication with the vaporisation zone to collect a liquid comprising the homogeneous catalyst, said vapour-liquid separator being configured to allow a residence time of from about 10 sec to about 60 mins; cooling means located within the vapour-liquid separator; means for removing the liquid comprising the homogeneous catalyst from the vapour-liquid separator; wherein said apparatus is configured such that the volume of the liquid comprising the homogeneous catalyst is maintained at a level that the cooling means is substantially submerged within the liquid comprising the homogeneous catalyst.

The structure of the apparatus of the present invention is such that the time for which the homogeneous catalyst is exposed to the high temperature required to vaporise the separation composition in the vaporisation zone can be kept to a minimum. In addition as the vapour-liquid separator in which the cooling means is located is in direct communication with the vaporisation zone, the homogeneous catalyst comes into contact with the cooling means very quickly after vaporisation.

In one arrangement, the residence time in the vapour-liquid separator may be longer than the time period for which the stream is in the vaporisation zone. By the use of this apparatus catalyst deactivation is substantially reduced, such that the catalyst can be recycled more times than has been achievable heretofore before it is deactivated and needs to be replaced.

The vaporisation zone may be of any suitable configuration provided that it comprises a vaporiser. Any suitable vaporiser may be used provided that it will enable the separation composition to be vaporised from the liquid comprising the homogeneous catalyst preferably with minimum residence time-. Suitable vaporisers include a falling film evaporator, a thin-film vaporiser, a wiped film evaporator, a kettle vaporiser, or the like.

The vapour-liquid separator is in direct communication with the vaporisation zone. By ‘direct communication’ it will be understood that vapour/liquld is able to pass between the vaporisation zone and the vapour-liquid separator and without being passed through a cooling means. In one arrangement, the vapour-liquid separator may be integral with the vaporisation zone such that it is located in, or forms, a bottom portion thereof. However, in one arrangement, it may be a separate vessel connected to the vaporisation zone. In this arrangement, the separate vessel will be in close proximity to the vaporiser so that the liquid comprising the homogeneous catalyst may be contacted with the cooling means as soon as possible after vaporisation.

In one arrangement in which the vapour-liquid separator is located in the bottom of the vaporisation zone or forms the bottom thereof, it may have a smaller cross-section than the cross-section of the vaporisation zone. By this means, the volume of liquid comprising the homogeneous catalyst required to maintain the liquid level such that the cooling means is substantially submerged is minimised. The smaller cross-section may be achieved by the configuration of the outer shell or in one arrangement, the cross-section of the outer shell may be kept constant and the vapour-liquid separator may be located in a housing within the shell such that the housing provides the smaller diameter.

Where a housing is present, it may be configured to surround the cooling means.

The vaporiser may include means to direct the liquid comprising the homogeneous catalyst to the cooling means. Such means include one or more plates or baffles.

Any suitable cooling means may be used. Suitable means include cooling tubes, coils or plates having suitable coolant flowing therethrough such that as the liquid comprising the homogeneous catalyst comes into contact with the cooling means, cooling occurs by heat exchange with the coolant. In one arrangement, the cooling means may be a bundle of tubes of the kind known as a 'stab-in bundle’ heat exchanger. A ‘stab-in bundle’ is a term used to describe a series of tubes which generally may be installed and remove from the vessel into which it is inserted via a flange. In use, the tubes will generally sit in a pool of liquid. Generally the series of tubes are provided as a single unit so that the inlet and outlet to each tube is connected to a single tubesheet, such that the coolant is supplied to the tubes from the same head separated by one or several baffles. The tubes are generally U-shaped but any shape tubes may be used provided that the resultant bundle has a bundle which may be introduced through the flange.

Two or more cooling means may be used to increase the cooling of the liquid. The cooling means present where there are two or more cooling means may be the same or different. The cooling means may be selected from cooling tubes, coils, plates, or combinations thereof. Thus for example, two or more tube bundles may be used, in another example, a central tube bundle may be used with a cooling coil located therearound.

In order to Increase the surface available for contact with the liquid, the cooling means may include fins, dimples or the like. Mixtures of means to increase the surface available may be used. Thus, for example, a mixture of fins and dimples may be used.

Means may be located in the vapour-liquid separator to agitate the liquid such that enhanced contact with the cooling means is achieved.

The, or each, cooling means may be removable.

In one arrangement, means may be provided to separate the vapour-liquid separator into an area where the liquid is in contact with the cooling means and a volume where cooled liquid is stored. Where a housing is present, this may additionally provide the means to separate the contact area for the storage area.

The volume of liquid held in the vapour-liquid separator either in a single volume or in a separate storage area acts as an integrated cooled surge tank.

The integration of the storage of the cooled liquid with the vapour-liquid separator offers various advantages, in particular, it will minimise the requirement for transfer lines, decrease the footprint of the unit and reduce capital costs. In addition, the presence of the volume of cooled liquid in the vapour-liquid separator provides a stable suction pressure for a pump which will be used to return the cooled liquid containing the homogeneous catalyst to the reactor. Since the pump used for the return require constant liquid feed, and thus the presence of the vapour-iiquid separator which will act as a surge pot, acts as a surge tank, the presence of which will assist in maximising pump life. In general, the pump used for the return may be operated such that the volume of liquid comprising the homogeneous catalyst is maintained at a level such that it provides stable suction for the pump and avoids gas being pumped.

According to a second aspect of the present invention there is provided a process for separating a homogeneous catalyst from a feed stream comprising the homogeneous catalyst and a separation composition which is separated therefrom by vaporisation; said process comprising the steps of: providing the feed stream to the apparatus of the above first aspect; operating the vaporisation zone such that said separation composition is vaporised and such that the feed stream has a first residence time in the vaporisation zone; removing the vaporised composition from the vaporisation zone; passing a liquid comprising the homogeneous catalyst from the vaporisation zone to the vapour-liquid separator: cooling the liquid in the vapour-liquid separator by means of cooling means located within the vapour-liquid separator; the residence time of the liquid comprising the homogeneous catalyst in the vapour-liquid separator being from about 10 secs to about 60 mins; and recovering the liquid comprising the homogeneous catalyst.

In one arrangement, the residence time in the vapour-liquid separator may be longer than that in the vaporisation zone.

The process of the present invention may be used to separate any composition by vaporisation from a stream comprising a homogeneous cataiysi. In one arrangement, the feed stream may be a stream recovered from a hydroformylation reaction. Thus the homogeneous catalyst may be any suitable catalyst for use in a hydroformylation reaction. The catalyst may be a rhodium catalyst which may be used in combination with one or more ligands. The ligand may be a phosphine or a phosphite, in one arrangement, it may be triphenyiphosphine.

The vaporisation of the separation composition may be carried out at any suitable temperature and pressure and the apparatus of the above first aspect will be configured accordingiy. The temperature and pressure selected will depend on the composition to be vaporised. In one arrangement, the vaporisation may be carried out at a temperature of from about 90°C to about 160°C, or from about 120°C to about 140°C, Any suitable pressure may be used provided that it is below the pressure of the reactor. The pressure may be from about 1 mmHg to about 7600mmHg. The pressure selected will depend on the components comprised in the stream fed to the vaporisation zone. For example, where the stream comprises an aldehyde, in general a lower pressure will be selected where a heavier aldehyde is present than where a lighter aldehyde is present. Thus, for example, where the aldehyde has from 2 to 5 carbon atoms, the pressure may be selected to be from about 1 bara to about 8 bara while for aldehydes having more than 5 carbon atoms, a pressure of up to about 1 bara, may be suitable with pressures being generally in the range from about 0.5 to about 0.7 bara.

The residence time of the feed stream in the vaporisation zone will generally be selected to be as short as possible. Residence times of the order of a few seconds to a few minutes may be used. Suitable times include 2 to 60 seconds and may be 10, 20, 30, 40 or 50 seconds although it may be longer.

Any suitable residence time may be used in the vapour-liquid separator. In one arrangement, the residence time will be longer than that used int eh vaporisation zone. The residence time in the vapour-liquid separator will generally be of the order of a few minutes. Suitable times include 1 to 60 minutes and may be 2, 5, 10, 20 or 30 minutes. Longer times may be used.

After vaporisation, the concentration of the catalyst in the liquid may be from about 50 to about 1000 ppmwt. The conrentraiion of the catalyst may be from about 100 to about 500 ppmwt, or from about 250 to about 400 ppmwt. The concentration of the ligand may be from about 1 to about 500 moles per mole of catalyst.

Any suitable temperature may be used in the vaporisation zone, in one arrangement it may be from about 60“C to about 90°C, from about 70°C to about 85°C, from about 65°C to about 80°C.

Whilst it is important to cool the liquid stream to minimise the risk of damage to the catalyst, it is generally important to prevent the temperature dropping too low as this may result in the catalyst precipitating. If the catalyst precipitates out of the liquid fraction, it is difficult to re-dissolve the catalyst under the process conditions. Thus, precipitation may result in the permanent loss of the catalyst, it will be understood that the reference to ‘catalyst’ includes the catalyst system in total including any ligands which may be present.

The temperature at which the catalyst precipitates out of the liquid fraction will depend on the catalyst used and its concentration in the liquid in the vapour-liquid separator. In order to reduce the Hkeiihood of catalyst precipitation, it is preferable for the cooling means to be maintained at a temperature at least 5“C above the temperature at which precipitation of the catalyst occurs.

Where the cooling means is removable, this offers advantages if any catalyst precipitates on the surface of the cooling means. By removing the cooling means, any catalyst which does precipitate can be mechanically, chemically or otherwise recovered and preferably be reused.

According to a third aspect of the present invention there is provided a hydroformylation reaction comprising: reacting an olefin with synthesis gas in a reactor in the presence of a homogeneous catalyst to form an aldehyde; recovering a stream comprising the aldehyde and the homogeneous catalyst and treating it in accordance with the process of the above second aspect of the present invention such that the separation composition is the aldehyde; and returning the recovered stream comprising the homogeneous catalyst to the reactor.

Any suitable olefin may be used in the hydroformylation reaction. The olefin may be selected from alpha-olefins having from 2 to 20 carbon atoms, or from 3 to 14 carbon atoms. Whilst alpha-olefins will generally be used, it will be understood that commercially available olefins having four or more carbons may contain minor amounts of corresponding internal olefins. In addition, irrespective of the number of carbon atoms, the commercial olefin may include some of the corresponding saturated hydrocarbon. Whilst the olefin may be purified before being subjected to hydroformylation, purification is not generally required.

The hydroformylation reaction is carried out under suitable reaction conditions. For example, the hydroformylation reaction may be carried out at a temperature of from about 45°C to about 200"C, preferably from about 60°C to about 140°C.

The hydroformylation reaction may be carried out at a total gas pressure of from about 1 psia to about 10,000 psia. Preferably, the hydroformylation reaction is carried out at a pressure of less than about 1500 psia, more preferably at a pressure of less than about 500 psia.

The feed stream to the vaporiser may be some or all of a stream recovered from the hydroformylation reaction. In another arrangement, the feed stream to the vaporiser may be a stream after which a portion of the aldehyde product has been removed.

Where the feed stream is a stream recovered from a hydroformylation reaction, the amount of aldehyde present may be up to 90 percent by weight and may be even higher In one arrangement, the amount of aldehyde present will be from about 10 to about 80 percent by weight, or from about 30 to about 70 percent by weight. The amounts present will depend on the particular reaction conditions and efficiency of the hydroformylation reaction,

As the feed stream to the vaporiser is recovered from the hydroformylation reaction, it may generally additionally include unreacted olefin. The amount of olefin present will depend on the efficiency of the hydroformylation reaction. Amounts of unreacted olefin present may be up to about 20 percent by weight of the feed stream. Impurities from the feed olefin such as the corresponding alkane may also be present.

In addition, minor amounts of by-products of the hydroformylation reaction may be present. These may include one or more of unreacted isomerised olefin, hydrogenated olefin, high boiling aldehyde condensation by-products and aiky! substituted phosphorous ligand by-products. In addition any solvent or additive used in the hydroformylation reaction may be present.

The totai gas pressure of hydrogen, carbon monoxide and the olefin in the hydroformylation reaction may be from about 1 to about 10,000 psia but it is more usual to operate it at a pressure of less than about 1500 psia and optionally at about 500 psia or less. The partial pressure used will generally depend on the amount and nature of the reactants employed. Thus, for example, the carbon monoxide partial pressure may be from about 1 psia to about 120 psia, such as from about 3 psia to about 90 psia, the hydrogen partial pressure may be from about 10 psia to about 200 psia, such as from about 20 psia to about 160 psia. In general the molar ratio of hydrogen to carbon monoxide may be from about 1;10 to 100:1 or higher. Molar ratios of from about 1:1 to about 10:1.

The hydroformylation reaction may be a continuous, semi-continuous or batch reaction. The recovered stream comprising the homogeneous catalyst may be returned to the reactor continuously or incrementally.

In order to assist heat control of the hydroformylation reaction, the liquid in the vapour-liquid separator may be cooled by the cooling means to a temperature less than that of the hydroformylation reaction, in some arrangements, the liquid in the vapour liquid separator may be cooled by the cooling means to a temperature of about 30°C less than that of the hydroformylation reaction, or a temperature of about 25X less than that of the hydroformylation reaction, or a temperature of about 20“C less than that of the hydroformylation reaction, or a temperature of about 15°C less than that of the hydroformylation reaction.

The present invention will now be described, by way of example, with reference to the accompanying figures in which:

Figure 1 is a schematic diagram of the process of the third aspect of the present invention:

Figure 2 is a schematic diagram of an apparatus according to a first aspect of the present invention;

Figure 3 is a schematic diagram of an alternative apparatus according to a first aspect of the present invention; and

Figure 4 is a schematic diagram of an alternative apparatus according to a first aspect of the present invention.

For the avoidance of doubt, these figures are intended only as an aid to understanding the invention and are not intended to be construed as limiting the scope of the invention with regard to the precise arrangement of the components illustrated or the positioning thereof, the shape of the vessels or any of the ancillary features. It will be understood by those skilled in the art that the drawings are diagrammatic and that further items of equipment such as feedstock drums, pumps, vacuum pumps, compressors, gas recycling compressors, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks and the like may be required in a commercial plant. Provision of such ancillary equipment forms no part of the present invention and is in accordance with conventionai chemical engineering practice.

As illustrated in Figure 1, a stream comprising hydrogen and carbon monoxide is fed though line 1 and a stream comprising olefin is fed though line 2 to a reaction zone 9 where the hydroformylation reaction occurs in the presence of a rhodium catalyst and a phosphine ligand such as triphenylphosphine. The hydroformylation reaction is carried out in the reaction zone 9 under conditions of elevated temperature and pressure. The reaction zone 9 may comprise one or more hydroformylation reactors, and each reactor may be located in the same or separate vessels. Unwanted gases are removed from the reaction zone 9 in line 3. A feed stream is recovered from the reaction zone 9 in line 4. The feed stream is passed to a product recovery zone 11, which comprises a vaporisation zone and a vapour-liquid separator, not shown. The vaporisaiion zone includes a heat exchanger, not shown, where the feed stream is heated and where some of the aldehyde product may be vaporised. The stream is then passed to the vapour-liquid separator which includes cooling means, not shown. The aldehyde is moved from the product recovery zone in line 6. A liquid stream including the catalyst is recovered from the product recovery zone 11 in line 7 before being pumped using the pump 12 to be returned in line 8 to the reaction zone 9.

One example of the product recovery zone is illustrated in Figure 2. In this arrangement, the feed stream is fed to the vaporisation zone 111 in line 104 where a heat exchanger, which is shown as a falling film vaporiser, heats the feed stream and where some of the aldehyde product is evaporated. The output stream from the vaporisation zone is then passed to the vapour-liquid separator 112, which comprises entrainment prevention internals and a liquid cooling device, not shown, via 105. The aldehyde is removed from the product recovery zone in line 106, A liquid stream including the catalyst is recovered from the product recovery zone in line 107.

One example of the vapour-liquid separator 211 of the product recovery zone is illustrated in Figure 3. In this arrangement, an output stream from the vaporisation zone is fed to the vapour-liquid separator in line 205 where the separation composition, such as the aldehyde, is removed in line 206. The unvaporised liquid flows downwardly to the bottom portion of the vapour-liquid separator 211 in which is located a stab-in bundle heat exchanger 215. The stab-in bundle heat exchanger is supplied with coolant in line 213. The warmed coolant is removed in line 214. A liquid stream which includes the homogeneous catalyst is recovered in line 207. A second example of the vapour-liquid separator 311 of the product recovery zone is illustrated in Figure 4. !n this arrangemeni, an output stream from the vaporisation zone is fed to the vapour-liquid separator in line 305 where the separation composition, such as the aldehyde, is removed in line 306. The unvaporised liquid flows downwardly to the bottom portion of the vapour-liquid separator 311 in which is located a coil heat exchanger 315. The coil heat exchanger is supplied with coolant in line 313. The warmed coolant is removed in line 314. A liquid stream which includes the homogeneous catalyst is recovered in line 307.

Claims

1. An apparatus for separating a homogeneous catalyst from a feed stream comprising the homogeneous catalyst and a separation composition which can be separated therefrom by vaporisation, said apparatus comprising; a vaporisation zone; means for supplying the feed stream to the vaporisation zone, such that in use the separation composition will be vaporised, said vaporisation zone being configured such that the feed stream has a first residence time in the vaporisation zone; means for removing the vaporised separation composition from the vaporisation zone; a vapour-liquid separator, located in direct communication with the vaporisation zone to collect a liquid comprising the homogeneous catalyst, said vapour-liquid separator being configured to allow a residence time of from about 10 secs to about 60 mins; cooling means located within the vapour-liquid separator; means for removing the liquid comprising the homogeneous catalyst from the vapour-liquid separator; wherein said apparatus is configured such that the volume of the liquid comprising the homogeneous catalyst is maintained at a level that the cooling means is substantially submerged within the liquid comprising the homogeneous catalyst, said apparatus being further configured such that liquid comprising the homogeneous catalyst is held in the vapour-liquid separator for a second residence time which is longer than the first residence time.

2. Apparatus according to Claim 1 wherein the residence time in the vapour-liquid separator is longer than the first residence time.

3. Apparatus according to Claim 1 wherein the vaporisation zone comprises a falling film evaporator, a thin-film vaporiser, a wiped film evaporator, or a kettle vaporiser.

4. Apparatus according to any one of Claims 1 to 3 wherein the vapour-liquid separator is integral with the vaporisation-zone.

5. Apparatus according to any one of Claims 1 to 4 wherein the cooling means is selected from cooling tubes, coils, plates, or combinations thereof.

6. Apparatus according to Claim 5 wherein the cooling means is one or more stab-in bundle heat exchangers.

7. Apparatus according to Claim 4 or 5 wherein the cooling means includes means to increase the surface area thereof.

8. Apparatus according to Claim 7 wherein the means to increase the surface are fins, dimples or mixtures thereof.

9. Apparatus according to any one of Claims 1 to 8 wherein the cooling means is removable.

10. Apparatus according to any one of Claims 1 to 9 further comprising a pump for recovering the liquid comprising the homogeneous catalyst.

11. A process for separating a homogeneous catalyst from a feed stream comprising the homogeneous catalyst and a separation composition which is separated therefrom by vaporisation; said process comprising the steps of: providing the feed stream to the apparatus according to any one of Claims 1 to 10; operating the vaporisation zone such that said separation composition is vaporised and such that the feed stream has a first residence time in the vaporisation zone; removing the vaporised composition from the vaporisation zone; passing a liquid comprising the homogeneous catalyst from the vaporisation zone to the vapour-liquid separator; cooling the liquid in the vapour-liquid separator by means of cooling means located within the vapour-liquid separator; the residence time of the liquid comprising the homogeneous catalyst in the vapour-liquid separator being from about 10 secs to about 60 mins; and recovering the liquid comprising the homogeneous catalyst.

12. The process according to Claim 11 wherein the feed stream is a stream recovered from a hydroformyiation reaction.

13. The process according to any one of Claims 11 and 12 wherein the catalyst is a rhodium catalyst which is used in combination with one or more phosphorous based ligands.

14. The process according to any one of Claims 11 to 13 wherein the vaporisation of the separation composition is carried out at a temperature of from about 90°C to about 160°C, or from about 120X to about 140°C

15. The process according to any one of Ciaim 11 to 14 wherein the vaporisation of the separation composition is carried out at a pressure of from about ImmHg to about 7600mmHg.

16. The process according to any one of Claims 11 to 15 wherein the residence time of the feed stream in the vaporisation zone is from about 2 to about 60 seconds.

17. The process accpording to any one of Claims 11 to 16 wherein the residence time in the vapour-liquid separator is longer than in the vaporisation zone.

18. The process according -to any one of Claims 11 to 17 wherein the residence time in the vapour-liquid separator will be from about 1 to about 10 minutes, or from about 2 minutes to about 5 minutes.

19. The process according to any one of Claims 10 to 16 wherein the cooling means is maintained at a temperature at least 5°C above the temperature at which precipitation of the catalyst occurs.

20. A hydroformylation reaction comprising: reacting an olefin with synthesis gas in a reactor in the presence of a homogeneous catalyst to form an aldehyde; recovering a stream comprising the aldehyde and the homogeneous catalyst and treating it in accordance with the process according to any one of Claims 11 to 19 such that the separation composition is the aldehyde; and returning the recovered stream comprising the homogeneous catalyst to the reactor.

21. A hydroformylation reaction according to Claim 20 wherein the stream recovered from the hydroformylation reaction is treated to remove a portion of the aldehyde product before it is fed to the vaporiser.

22. A hydroformylation reaction according to Claim 20 or 21 and wherein the liquid in the vapour-liquid separator is cooled by the cooling means to a temperature that is less than that of the hydroformylation reaction.