CA1142963A - Hydroformylation process - Google Patents

Abstract

PROCESS

ABSTRACT

A rhodium-catalysed hydroformylation process is disclosed in which an overhead vapour stream is recovered from the hydroformylation zone containing reactant alkene, hydrogen, carbon monoxide, alkene hydrogenation product(s), aldehyde product and aldehyde condensation products, This vapour stream is subjected to condensation conditions in one or two stages to condense therefrom condensible components comprising unreacted alkene, aldehyde product, and aldehyde condensation products. Non-condensed components of the vapour stream (e.g. H2 and CO) are recycled to the hydroformylation zone. Unreacted alkene is also recycled in liquid form to the hydroformylation zone.

Description

PROCESS
This invention relates to a hydroformylation process, more par-ticularly a process for the hydroformyla-tion of an alkene-l -to a corresponding aldehyde product containing 5. one more carbon atom than the starting olefin.
Hydroformylation is a well-known ~rocess involving reaction of a mixture of hydrogen and carbon monoxide with the olefinic group of a terminal olefin, Depending on the choice of catalyst, the resulting product may be aldehydic 10. or alcoholic in nature. Although -the catalysts originally proposed were based on cobalt~ more recently there have been proposed catalysts based on rhodium. Such rhodium based catalysts have the advantage that the pressure of operation is much lower -than the pressures necessary when 15. using cobalt catalysts and that produc-t recovery is much - simpler than is the case when using a cobal-t catalys-t. In addition~ when utilising propylene or a higher -terminal olefin to produce butyraldehyde or the correspondlng higher aldehyde, the rhodium catalysts generally permit,-the attain-20. ment of higher n~/iso-product ratios than can be achieved using cobalt catalysts. Since the n-aldehyde usually has a higher value -than the iso-aldehyde, this adds to the economic attractions of the rhodium-catalysed processes.
Commercial plants have been built to manufacture 25. propionaldehyde from ethylene and butyraldehyde from propylene utilising a low pressure process involving a rhodium catalyst. An outline of the process is given in "Chemical Engineering", December 5, 1977, pages 110 to 115.
The process is also described in West German Offenleg~gs-30. schrift 2715685. Further details can be fo~d, for ~L2~:;32.
example, in United States Patent Speciflcation No. 3527809 and in British Patent Speciflcation No. 1338237.
As described in the afore-mentioned "Chemical Engineerlng~l artlcle the gas~recycle system adopted in the 5. original two plants built for propionaldehyde and butyralde-hyde production respectively at Texas City, Texas, U.S.A.
and at Ponce, Puerto Rico, involves removal of the product as vapour in an overhead strea~ taken from the hydro-formylation reactor. After air cooling -to condense lO. aldehyde product the unreacted gases, including unreacted olefinJ are separated from the condensate,compressed and recycled to the hydroformylation reactor. In the butyralde-hyde plant the liquid condensate stream con-tains appreciable amounts of dissolved gases, mainly propylene and propane;
15. these are distilled out in a product s-tripping column and are recycled as gas to the hydroformylation reactor.
Whilst this gas recycle process is eminently suitable for use in the production of propionaldehyde from ethylene or of butyraldehyde from propylene by hydro~ormyla-tion, the 20. lesser volatility of the alclehyde product in -the case of higher olefins, such as butene-l, requires that a corres-pondingly higher gas recycle rate must be used in order to remove the aldehyde from the reactor at essentially the same rate as that at which it is formed in order to 25~ prevent an increase in volume of the liquid phase in the reactor and an undesirable increase in the proportion of polymeric aldehyde condensation products therein. This in turn requires the use of large recycle gas compressors which are extremely expensive items of equipment and 3.
!~ contr~bute significantly to the cost~ o~ in~talllng and operating the plant.
It would be desirable to provide a process ~or the hydroformylation of alkenes, particularly butene-l and 5. higher alkenes, whereby the convenient method of product recovery afforded by gas recycle is coupled with use o~ a relatively small gas recycle compressor.
It is accordingly an object of the invention to provide a process ~hereby aldehydes can be efficiently and 10. economically produced by hydroformylation of a terminal olefin in the presence of a rhodium complex catalyst utilising a gas recycle method and a gas recycle compressor that is as s~all as practicable.
According to the present invention there is described 15. a process for the production of an aldehyde by hydroformy-lation of an alkene in the presence of a rhodium complex catalyst comprising: . .
providing a hydroformylation zone containing a liquid charge comprising (aj a rhodium complex catalyst;wherein 20. rhodium is in complex combination with carbon monoxide and a triorganophosphine, (b) excess triorganophosphine, (c) liquid aldehyde product, and (d) polymerlc aldehyde condensation products;
feeding liquid reactant alkene to the hydroformylation 25. zone;
supplying make up hydrogen and carbon monoxide to the hydroformylation zone;
maintaining in the hydroformylation zone temperature and pressure conditions effective for the hydroformylation

2~63 of the reactant alkene;
recovering from the hydroformylation zo~e an overhead vapour stream containing reactant alkene, hydrogen, carbon monoxide, alkene hydrogenation product(s), aldehyde product and higher boiling aldehyde condensation producks containing hydroxyl group~;
subjecting the vapour stream to condensation conditions to condense therefrom condensible components comprising unreacted alkene, aldehyde product, and higher boiling aldehyde condensation products containing hydroxyl ~roups;
recycling non-condensed componen-~s of the vapour stream comprising hydrogen and carbon monoxide to the hydro~ormylation zone;
recovering aldehyde product; and - 1, recycling unreacted alkene in liquid form to the hydroformylation zone.
The inven-tion is applicable to any alkene capable of undergoing hydroformylation -to gi~e an aldehyde that is relatively volatile~ There is, however, little advantage 2~ in utilising the process in the hydroformylation of ethylene since e~pensive refrigeration is required in order to liquefy the reactant ethylene and to condense unreacted ; ethylene ~rom the overhead vapour stream. The process can be applied in the hydroformylation of propylene but experience has shown that the gas recycle process of West German Offenlegungsschrift 2715685 is commercially satis~actory. It is thus preferred to uti3ise C~ or higher alkenes in the process of the invention. For practical . .~
~'' 2~
- 5 ~

purposes octene-l is probably the highes-t olefin -that can be utilised satisfactorily in the process of the invention. Preferably the olefin comprises butene-l, pentene-l, hexene-l, 2-methyl-butene-1, 3-methyl-bu-tene-1, 2-methyl-pentene-1, 3-methyl-pentene-1, 4-methyl--pentene-l or 2-ethyl-butene-1.
Although the process of the inven-tion can be practised with an essentially pure alkene-l feedstock, mixed hydrocarbon fractions containing, in addition to terminal olefins, internal olefins and/or alkanes can also be utillsed. The proportion of alkene-l in such a rnixed hydrocarbon fraction may vary within wide limits, for example from about 10 mole /0 or up to about 90 mole % alkene-l or more. Typically~ however, such a mixed hydrocarbon frac-tion comprises from about 20 mole %
up to about 80 mole % of alkene-l.
The alkene-l containing feedstock is desirably substantially free from inhibi-tors, such as dienes (e.g. butadiene), and from catalys-t poisons, such as sulphurous cornpounds and chlorine compounds.
A satisfac-tory procedure for removal of dienes, such as butadiene, comprises hydrofining. Higher sulphurous impurities can be removed to an acceptable level by contact of the feedstock with alurnina followed by zinc oxide. Copper-impregnated carbon can be used to reduce -the level of chlorinated impurities to a sufficiently low level.

119~Z~G3 The ratio of hydrogen to carbon monoxide in the make up stream preferably lies in the region of l:l by volume. As i6 well known such H2/C0 mix-tures can be produced by conventional syn-thesis gas plants using hydrocarbon reforming -techniques or partial oxidation of hydrocarbons. Experience has shown -that metal carbonyls, sulphur compounds and chlorine-con-tain-ing compounds are undesirable components of the H2/C0 make up stream. Hence it is desirable to submit the make up synthesis gas to purifica-tion for the removal of these impurities.
Hydroformylation is effected in -the liquid reaction medium in the presence of a ca-talytically effective amount of the rhodium complex catalyst.
Typically the rhodium complex catalyst concentra-tion ranges from about 20 parts per million~ calculated as rhodium metal, up to about 1000 par-ts per million or more. There is no advantage general~y in using concentrations of rhodium in excess of abou-t 500 parts per million and usually, on the grounds of expense alone, it will be preferred to opera-te at a rhodium complex catalyst concentration of not more than about ~00 parts per million, calculated as rhodium metal.
Typical operating conditions utilise rhodium complex catalyst concentrations of from about 50 par-ts per million up to about 150 parts per million, calcula-ted as rhodium metal.

~l~lZS~63 The triorganophosphine ligand may be an aliphatic phosphine, such as -tributyl phosphine, but is preferably an aromatic phosphine, such as triphenylphosphine, tri~ methoxyphenyl) phosphine, trinaph-thylphosphine, tri-tolylphosphine, ~-N,N~
dimethylaminophenyl diphenylphosphine, and the likeO
The preferred ligand is triphenylphosphine. During the course of hydroformylation utilising a rhodium com-plex catalyst small quantities of alkyl diphenylphos-phines may be formed by interaction between the triphenylphosphine ligand and the reactant alkene in the presence of the rhodium cornplex catalyst. Thus, when hydroformylating propylene, for example, small amounts of propyl diphenyl phosphine may be formed as by-product.
The liquid reaction medium contains excess triorganophosphine ligand. Preferably there are a-t least about 2 moles o-~ free ligand for every gram atom of rhodium present. Usually i-t will be preferred to operate in the presence of at least 10 moles of free ligand, typically in the presence of at least 75 moles, for example at least 100 moles, of free triorganophosphine ligand per gram atom of rhodium.
The upper limit of the amount of free triorganophosphine ligand is not particularly critical and is dictated by the solubility thereof in the liquid reaction medium3 as well as by economic and commercial consideratlons.

h~J~3 Although not so expensive as the rhodium inventory, the capi-tal cost of the triphenylphosphine inventory is no-t an insignificant factor. Under typical operating conditions the free triorganophosphine ligand constitutes from about 2% to about 25% by weight of the liquid reaction medium.
The rhodium complex catalyst may be formed by methods known in the art. For example, hydridocar-bonyl tris(triphenylphosphine) rhodium (I) is a crystalline solid and may be introduced into the hydroformylation reactor as such. Alternatively a catalyst precursor, such as rhodium carbonyl triphenyl-phosphine acetylacetonate or rhodium dicarbonyl acetylacetonate may be introduced into the reac-tor and the active catalytic species, which has been postulated to be hydridocarbonyl tris(triphenylphosphine) rhodium (I), generated in situ under hydroformylation conditions in the presence o~ excess triphenylphosphine. Other suitable precursors include Rh203~ Rh~(C0)12 and Rh6(CO)16.
The liquid reaction medium fur.ther includes aldehyde product and polymeric aldehyde condensation products. The nature of such polymeric condensation products (e.g. dimers, trimers, and te-tramers) and a postula-ted mechanism for their formation are discussed in British Patent Specification No. 1338237 ~s, '~

3~3 .. ~.
g The ratio of aldehyde to pol~neric aldehyde condensation products in the liquid reac-tion mixture may vary within wide limits. Typically this ratio lies in the range of from about 1:4 to about 4:1 by weight, e.g. about 1:1 by weight.
In the hydroformylation zone conditions are maintained which are effective for hydroformylation of the reactant alkene. Typically the tempera-ture lies in the range o~ from about 50C up to about 160C or 10 more. The temperature should be at least as high as that required to effect hydroformylation but not so high as to destroy the catalyst or to cause undesirable isomerization of terminal olefins to non-terminal olefins. Usually the temperature will lie in the 15 range of from about 70C to about 140C, e.g. in -the range of from abou-t 90~C to about 130C.
The total pressure in the hydroformylation zone will usually be about 50 kg/cm2 ab,solu-te or less and is preferably less -than about 20 kg/cm absolute.
Typically the partial pressure at-tributable to the olefin is less than abou' 4.0 kg/cm2 absolute and is preferably less than about 1.5 kg/cm2 absolute. The total partial pressure attrlbutable to hydrogen and carbon monoxide is typically less than about 10 kg/cm2 absolute. Usually the carbon monoxide partial pressure ranges from about 0.1 kg/cm2 absolute to about 1.5 kg/cm2 absolu-te whilst the hydrogen partlal pressure preferably ~2~3 ~,~b -- L O
lies in the range of from about 1.5 kg/cm2 absolute to about 7.5 kg/cm~ absolute.
The overhead vapour stream from the hydroformylation zone is subjected to condensa-tion conditions to condense therefrom condensible components comprising unreacted alkene, aldehyde product, and aldehyde condensation products. In one procedure condensation is effected in a single stage so that there is obtained a mixture of condensed alkene, 10 aldehyde product and aldehyde condensation products.
Condensation is generally effected by cooling the vapour stream. Depending on the pressure of the vapour stream cooling may be achieved by air cooling, by external cooling agalnst cooling water, or by 15 refrigeration. The resulting condensed mixture may then be distilled to separate unreacted alkene, which appears overhead, from aldehyde product and aldehyde condensation products, which appear as a bot-toms produc-t. The resulting aldehyde product-rich bot-toms 20 product may then be further purified, e.g. by re-distillation in order -to separate aldehydes from aldehyde condensation products, and possibly also to separate n-aldehyde from iso-aldehyde. The overhead product from the first-mentioned distillation step is cooled by air cooling, by external water cooling or by refrigeration as appropriate, in order to condense unreacted alkene for return to the hydroformylation zone.
/

l~Z~63 In an alternative procedure the vap~ur stream . . , from the hydroformylation zone is subjected -to a two stage condensation procedure by cooling in two stages.
In the first stage an aldehyde-rich condensate is - 5 obtained, containing also aldehyde condensation products, whilst unreacted alkene(s) pass(es) on still in vapour form to be condensed in the second stage. In this case the aldehyde-rich condensate can be further worked up, for example as described above by distillation and re-distillation, whilst second stage condensate containing most of the unreacted alkene is cycled to the hydroformylation zone.
In the process of the invention non-condensed components of the vapour stream from -the hydroformylation zone are recycled to the hydroformy-lation zone. It will usually be preferred to conduct the process so -that the rate of recycle of such non-condensed components -to the hydroformylation'zone is at least sufficient to remove aldehyde produc-t in -the vapour s-tream as fast as it is formed. Preferably a gas cycle rate is chosen that is at least sufficient to remove also aldehyde condensation products in the vapour s-tream as fast as they are produced~ In this way build up o~ uid in the hydroformylation zone can be prevented. In operation, control of the volume of liquid in the hydroformylation zone can be achieved by appropriate choice of temperature, pressure ~Z~63 and gas recycle ra-te, and by recycle of one or more of the condensed components o the vapour s-tream (e,g. unreacted alkene, aldehyde product and/or aldehyde condensation products) to the hydroformylation zone.
To prevent build up in the system of inert materials introduced with the reac-tan-ts or formed as by-products in the process (e.g. alkene hydrogenation product(sj)purge streams may be taken. Thus a purge stream may be taken of -the non-condensed components of the vapour stream in order to limit the quantity of, for example, nitrogen in the reaction system.
In the process of the invention the hydroformylation conditions may be chosen so that essentially only terminal olefins are hydroformyla-ted whilst non-terminal olefins pass unchanged through the hydroformy-lation zone and hence behave as inert materials. Hence it wiLl usually be desirable to purge also a part of -the unreacted alkene-containing stream :in order to limit the amount of non-terminal olefins, as well as paraffin(s) formed as hydrogenation by-product(s), in the system. If the alkene feed stream to the plant is a mixed olefin feedstock, e.g. a mlxed 'ou-tenes feedstock, a preenrichment column can be used in order to separate by distillation an alkene-l rich overhead fraction from a bottoms product containing olefins that are lnert towards the rhodium complex hydroformy-lation catalyst employed. In this case a par-t of the unreacted alkene-containing stream can be returned to this preenrichment column so that non-terminal olefins and hydrogena-tion product(s) are purged as part o~ -the bottoms product therefrom.
~ In order -that the invention may be clearly understood and readily carried into effect a preferred hydroformylation process according to the invention will now be descrlbed by way of example only, with reference to the accompanying drawing which is a diagramma-tic flow sheet of a plant for the production of _-valeraldehyde from a butene-l containing feed stream and of a modi-fication -thereof~
Referring to the drawing a mixed C4 hydrocarbon liquid feed stream is passed-by line 1 to a pretreatment zone 2 in which it is ~reed from light sulphurous impurities such as H2S, COS and me-thyl mercaptan by passage in -turn through beds of ac-tive A1203 and ZnO and also from chlorine- -containing impurities by subsequent passage through a bed of copper-impregnated carbon (Girdler G32J
catalyst, obtainable from Girdler Chemicals Inc., of Louisville, Kentucky, United States of America). In passing through -the bed of active A1~03 any COS
present is hydrolysed to H2S due to the presence o .

2~3~3 traces of water in the feed stream; -the active A1203 bed also serves partially -to remove H2S and rne-thyl mercaptan (CH~SH). The ZnO bed then removes any remaining H2S and CH~SH. Particularly if the feed stream con-tains traces of molecular oxygen (for example by reason of a previous metal carbonyl removal step) some conversion of methyl mercaptan to dimethyl sulphide (CH3SCH3) may also occur.
The C4 hydrocarbon liquid feed stream passes on through lines 3 and 4 to a hydroforrnylation reactor 5~
Hydroformylation reactor 5 contains a - catalytic a~ount of a rhodium-containing hydroformy-lation catalyst comprising rhodiurn complexed with carbon monoxide and triphenylphosphine dissolved in a liquid phase containing, in addition to product n-valeraldehyde, polyrneric aldehyde condensa-tion products such as -krimers, The ca-talytic species has been postulated -to be hydridocarbonyl -tris (triphenylphosphine) rhodium (I), which has -the ~ormula HRh(CO)(PPh3)3, and can be generated in situ during the hydroformylation reaction from a suitable catalyst precursor, such as (2,4-pentandionato) dicarbonyl rhodium (I), i e. the rhodium dicarbonyl complex formed with acetylacetone, or rhodiurn carbonyl triphenylphosphine acetylacetonate. A
description of such a hydroforrnylation catalyst can be found, for example, in United Sta-tes Patent Specification No. 3527809. The use of aldehyde condensation products as a solvent for the rhodium complex catalyst is described in British Patent Specification No. 1338327J In addi-tion to the rhodium complex catalyst the liquid phase in the hydroformylation reactor 5 also con-tains an excess of triphenyl phosphine. The mole ra-tio of triphenyl phosphine:rhodium is approximately ~75:1.
The temperature in reactor 5 is maintained at 110C by circulating cooling water or steam, as appropriate through coil 6. An impeller 7 rotated by a suitable motor (not shown) is provided in order to mix thoroughly the contents of the hydroformylation reactor 5.
A hydrocarbon feedstock, such as natural - gas, naphtha or a gas oil, is supplied through line 8 to a syn-thesis gas plant 9 (for example a partial oxidation plant or a s-tearn reforming plant). An approxirnately 1:1 H2:C0 mixture passes on from plant 9 through line 10 to a purification section 11 in which the synthesis gas is freed from impurities such as carbonyls, sulphurous compounds and chlorinated compounds. The purified synthesis gas is then fed through lines 12 and 13 to a sparger 14 in hydroformy-lation reactor 5.

Z~ 3 A vaporous stream is removed from hydroformy-lation reactor 5 overhead through line 15. After passage through a demis-ter 16 which is provided with a return line 17 -to reactor 5 for condensed liquid, this stream passes on through line 18 to condenser 19 and is cooled therein to 660C by means of cooling water supplied through line 20. The resulting gas/
condensate mixture is supplied through line 21 to a product separator 22 from which a gaseous mixture is removed via line 23. The gaseous mixture flows on through line 24. A part thereof is purged through line 2.5, whilst the remaînder is recycled via lines 26, 27 and 13 to hydroformylation reactor 5 by means of recycle compressor 28. The rate of gas recycle through line 27 is suffici.ently high, in relation to the tempera-ture and pressure conditions prevailing in reactor 5, to remove product _-valeraldehyde in the vapour stream in line 18 at the rate at ~hich it is formed in reactor 5.
The liquid condensate is removed from product separator 22 through line 29 and fed to a distillation column 30 which contains 20 trays; its working tempera-ture is 193C.
A gas stream, consisting essentially of unreacted butene-l, CiS- and trans-butene-2 and saturated C4 alkànes~ is removed overhead via line 31 and is cooled to a temperature of 85~6~C in condenser 2~3 32 whlch is supplied with coollng water through line 33. The resulting li~uid hydrocarbons are -then fed via line 34 to reflux drum 35. A gas purge is with-drawn through line 36.
The liquid butenes-containing stream is pumped from reflux drum 35 through line 37 by means of pump ~8; of this stream a part is returned to column ~0 through line ~9, whilst the remainder is supplied to line 40. A major part of the liquid butenes-containing stream in line 40 is returned to hydroformylation reactor 5 through lines 41~ ~r2 7 43 and 4,.whilst a purge stream is removed from the system through line 44.
A bottoms product, consisting essentially of n-valeraldehyde product and containing a minor proportion of iso-valeraldehyde is withdrawn from column 30 through line 45. Part of this bottoms product is passed to line 46 fo:r puri.fica-tio.n (e.g.
redis-tillation) and/or further processing and/or storage. The remainder of this bottoms produc-t is recycled -through line 47, reboiler 48 and line 49 -to column 30. Reboiler 48 is heated by means of steam supplied through line 50.
In order to prevent build-up of "heavies"
in the solution in the hydroformylation reactor 5 a bleed stream is removed via line 51 and passed to a ~L9tZ'3~3 regeneration section 52. "Heavies", eOg. valeraldehyde tetramers of a formula analogous to ~ormulae (VI) and (VII3 of British Patent Specification No. 1338237, and -triphenylphosphine oxide are removed through llne 53. (Triphenylphosphine oxide may be formed due to -the presence of traces of oxygen in one of the feed streams to the hydroformylation reactor 5). Regenerated solution is recycled to hydroformylation reactor 5 through line 54.
If desired "heavies" removal zone 52 can be dispensed with. Instead spent reactor solution can be withdrawn from the reactor 5 via line 51 and passed to storage, the rate of withdrawal being sufficien-t to prevent build-up of "heavies" in the reactor 5. At the same tirne fresh catalys-t or catalyst precursor is added via line 54 a-t a rate sufficient to main-tain the rhodium concen-tration at approxima-tely the chosen level.
Such fresh catalyst can be dissolved in an approprlate volume of liquid aldehyde product toge-ther wi-th a corresponding amount of free triphenylphosphine. The s-tored spent catalyst solution can be treated for the recovery of triphenyl phosphine and rhodium from which fresh catalyst or catalyst precursor can be manufactured.
A typical method of "heavies" removal in zone 52 involves extraction of the bleed s-tream in line 51 in a conventional mixer-settler, after cooling ~J ~ 3 ~ 19 --to ambient temperature and depressurising, wi-th phosphoric acid or with an aqueous solution of phosphoric acid containing at least about 40~o by weight~ and preferably at least about 600/o by weight, of orthophosphoric acid. This phosphoric acid ex-tract, which contains essentially all the active rhodium catalyst and free triphenylphosphine, is then neutralised in the presence of a suitable organic hydrophobic solvent, e.g. n-valeraldehyde trimer, and the resulting organic phase recycled to reactor 5 through line 54 after drying. The organic residue from the phosphoric acid extraction step, on the other hand, is passed to storage via line 53; this - organic residue contains catalytically inactive rhodium and triphenylphosphine oxide, as well as high boiling n-valeraldehyde condensation products. Such catalytically inactive rhodium may be present due -to traces of ca-talyst poisons in -the feed s-treams to the reactor 5.
As thus described condensation is effected from the vapour stream from reactor 5 in a single stage, i.e. condenser 19. It is alternatively possi~le to effect condensation in two stages~ In this case condenser 19 is operated at a somewhat higher temperature so that unreacted alkene passes on uncondensed in line 21 to produc-t separator 22. Non-condensed components of the vapour stream pass on via line 23 are taken via ~' ~ - 20 -line 55 to a second s-tage condensation zone 56 in which unreacted alkene is condensed~ Cooling wa-ter is supplied to second stage condensation ~one 56 through line 57. A gas/liquid mixture passes on through line 58 to a further product separator 59 from which a liquid butenes-rich fraction is withdrawn through line 60 for recycling to the hydroformylation reactor 5 through lines ~2, 43 and 4. Uncondensed gases pass on through line 61 to line 26 for recycle to the reactor 5. There is no flow in line 24 in this modi~ication of the plant.
If desired the C~ hydrocarbon feed stream can be subjected to a pre-enrichment step so as to boost the proportion of butene-l in the feed strearn to the reactor 5. This purified C4 hydrocarbons can be passed -through line 62 to a~spli-tter column 63 instead of passing on direc-tly via liné 3 to reac-tor 5. Column 63 contains 108 -trays. A bu-tene-l rich stream is rernoved overhead -through line 64, whilst a bo-ttoms product rich in butene-2 is removed through line 65 and is recirculated through line 66 to reboiler 67 before being returned to splitter column 6~ through line 68. Reboiler 67 i5 heated with steam supplied through line 69. A liquid purge, which is rich in cis-and trans-butene-2 and also contains any high boiling sulphurous irnpurities such as dimethyl sulphide, is removed -through line 70.

- The butene-l rich stream in line 64 is passed through condenser 71 which is supplied with cooling water through line 72. The resul-ting liquid condensa-te passes on through line 73 to re~lux drum 74O Drum 74 is provided with a vent line 75. The liquid butene-l rich liquid stream is pumped from drum 74 through line 76 by means of pump 77 and on through line 78. Part of this stream is returned to split-ter column 63 -through line 79, whilst the remainder passes on ~Tia lines 80 and 4 -to hydroformy-lation reactor 5.
When a pre-enrichment step is incorporated in the process of the invention, line 44 can be dispensed wi-th. Instead a part of thé bu-tene-1 containing liquid stream in line 42 can be passed to column 63 via line 81. In this case the purged materials, which would otherwise have been removed from the system in line 44, are removed in line 70.
The invention is-further illus-trated with reference to the following Example.
Example Utilising the plant illustrated in full lines in the drawing, a mixed C4 hydrocarbon liquid feed stream is supplied via line 1 to the pretrea-tment zone 2.
The compositions ~in mole %), flow rates, temperatures, and pressures in various of the important lines in -the plant are set out below in Table 1.

~L4Z~3 ~' ~D
I
~î o. O o~ ~ ~ ~ ~ ~D O
~ ~ ~ ~O ~ ~ ~ ~ O O
.. ~ ' ' O N 1~ ` ri ~i 0 0 0 0 E I

~ O ~ ~ ~ O C~
~1 ~ O O O tD O o GO ~ C~l ~ ~ ~ C\l ~D
a~ ~ 0~ ~
~ O ~ -1 ~1 0C~:) o ~ 1 ~ O 1~ 0 O .1~ ~ 15~ t\l O O ~ ~ ~1 ~ I O
~ C~i ~ ~ r~ O C~ O O ' O ~

H ¦ O

a) o ~D ~ ~ ~ ~D O ~, a~ ~ ~ O ~ILO ~ O O
( ~ O O O
~1 ~D ~I r I

C\l ~ C) ~i a) rd I h ~ h rd ~ ~1 c~ Iv O rd h o ~ ~ ~
/

'3 - 2~ -r~
~ ~ I
a). .
~U~ ~ o .~, ~ o~ ~
,~~ ~ .
.
~ 0 ~
a~
~ ,.~ o~
~ ~1 a~

C~ r~l .

U~ . - .
. ~ ~ ~D
Q) ~ U~ ~D
~ ~ o o o rd ~ ~ ~D ~
.~
o '`Jl ~

~ ~1 ~
~i ' , C~ L~ U~
U~ ~
. . . .
o . oo h +, ~ h~
h c~
oO ~ V U~ C~
~L~: ~ ~,o U:~
~o or ! hO a) h V h.~

1~ 63 ~, O-ther ~signiican-t flow rates are set out below ln Table 2:-, I

2~63 ~ ~ , `. , ~

. ~1-o_, . ~ ~
C~

o ., ,_ .
,_ ~
I'~D

~ I-o~

~Z~3 The overall conversion of butene-l to n- and i_ , ~ ~ valeraldehydes is 8404%~ The n-/iso-aldehyde ratio is .
25.6:1. The resulting aldehyde product can be subjected without further purification to conventional aldolization, dehydration and reduction to yield an acceptable C10-plasticiser alcohol consisting predominantly of 2-propylheptanol.
The stream in line 44 is rich in butene-2 and can be used, for example, in the production of - 10 butylate petroleum or methyl ethyl ketone.
~ It will be appreciated by those skilled in the art that, since the butenes are recycled in the liquid phase to ~he hydroformylation reactor in the form of plant illustrated in the drawing, the gas recycle compressor can be considerably smaller than would be the case if the unreacted butenes were recycled in the gas phase.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the production of an aldehyde by hydroformylation of an alkene in the presence of a rhodium complex catalyst comprising:
providing a hydroformylation zone containing a liquid charge comprising (a) a rhodium complex catalyst wherein rhodium is in complex combination with carbon monoxide and a triorganophosphine, (b) excess triorganophosphine, (c) liquid aldehyde product, and (d) polymeric aldehyde condensation products;
feeding liquid reactant alkene to the hydroformylation zone;
supplying make up hydrogen and carbon monoxide to the hydroformylation zone;
maintaining in the hydroformylation zone temperature and pressure conditions effective for the hydroformylation of the reactant alkene;
recovering from the hydroformylation zone an overhead vapour stream containing reactant alkene, hydrogen, carbon monoxide, alkene hydrogenation product(s), aldehyde product and higher boiling aldehyde condensation products containing hydroxyl groups;
subjecting the vapour stream to condensation comditions to condense therefrom condensible components comprising unreacted alkene, aldehyde product, and higher boiling aldehyde condensation products containing hydroxyl groups;
recycling non-condensed components of the vapour stream comprising hydrogen and carbon monoxide to the hydroformylation zone;
recovering aldehyde product; and recycling unreacted alkene in liquid form to the hydroformylation zone.

2. A process according to claim 1, in which the vapour stream from the hydroformylation zone is cooled to effect condensation of a mixture of the condensible components which is then distilled in a distillation zone to separate an overhead product comprising unreacted alkene from a bottoms product comprising aldehyde product and aldehyde.

3. A process according to claim 2, in which the overhead product from the distillation zone is cooled by air cooling, by external water cooling, or by refrigeration in order to condense unreacted alkene for return to the hydroformylation zone.

4. A process according to claim 19 in which the vapour stream from the hydroformylation zone is cooled to produce an aldehyde-rich condensate containing also aldehyde condensation products, whereupon the uncondensed components comprising unreacted alkene(s) are further cooled to condense unreacted alkene(s) therefrom for recycle to the hydroformylation zone.

5. A process according to claim 4 in which the rate of recycle of non-condensed components of the vapour stream to the hydroformylation zone is at least sufficient to remove aldehyde product in the vapour stream as fast as it is formed.

6. A process according to claim 5, in which the gas cycle rate is at least sufficient to remove aldehyde condensation products in the vapour strearn as fast as they are produced.

7. A process according to claim 1, claim 2 or claim 3, in which the triorganophosphine is triphenylphosphine.

8. A process according to claim 1, claim 2 or claim 3, in which the ternperature in the hydroformylation zone ranges from about 70°C to about 140°C.

9. A process according to claim 1, claim 2 or claim 3, in which the total pressure in the hydroformylation zone is less than about 20 kg/cm2 absolute, the partial pressure attributable to the olefin is less than about 1.5 kg/cm2 absolute, the total partial pressure attributable to hydrogen and carbon monoxide is less than about 10 kg/cm2 absolute, the partial pressure attributable to carbon monoxide ranges from about 0.1 kg/cm2 absolute to about 1.5 kg/cm2 absolute and the partial pressure attributable to hydrogen ranges from about 1.5 kg/cm2 absolute to about 7.5 kg/cm2 absolute.

10. A process according to claim 1, claim 2 or claim 3, in which the alkene comprises butene-1.