CA1090823A - Cyclic hydroformylation process - Google Patents

Abstract

CYCLIC HYDROFORMYLATION PROCESS

ABSTRACT

Hydroformylating alpha-olefins in a cyclic homogeneous liquid phase process utilizing a modified rhodium catalyst, the improvement which involves uti-lizing a gas recycle to maintain the liquid level in the reaction and control build-up of high molecular weight components.
This application is a continuation-in-part of copending U.S. Application Serial No. 674,823, filed April 8, 1976.

Description

This invention relates to the preparation of aldehydes by the "Hydroformylation" process in which an alpha-olefin i9 hydroformylated with carbon monoxide ~nd hydrogen in the presence of a rhodium catalyst.
J. Falbe, "Carbon Monoxide in Organic Synthesis", Springer-Verlag, New York (1970)~ at page 3, has stated:
"Hydroformylation is the reaction of an unsaturated compound (or a saturated compound which may generate an unsaturated compound) with carbon monoxide and hydrogen to yield an aldehyde". The process has also been called the Oxo process. Until recently, all commercial hydro-formylation reactio~s were catalyzed by cobalt carbonyl catalysts. According to Falbe (at page 70), ~upra, with the ~ingle exception of the process developed by Shell, "all industriaLly applied oxo processes more or less follow the technique which was developed by Ruhrchemie AG in Oberhausen/Germany in co-operation with BA5F." He states that the existing oxo plants operate continuously and, in general, "they consi~t of the following sections:
1. Hydroformylation reactor. 20 Catalyst removal section.
3. Catalyst: work-up and make-up section. 4. Aldehyde distillation. 5. Aldehyde hydrogenation reactor.
6 . Alcohol dis tillation" .
The Shell process differs by employing a modified cobalt catalyst made by combining in the hydroformylation

2.

, ~ ~ 9 0 ~ 2 3 reactor a cobalt salt of organic acids, trialkyl phos-phines (e.g. tributyl phosphine) and alkali, such as KOH.
The in situ formed HCo(CO)3PR3 ca~alyst "is thermally more stable than HCo(CO)4" thus allowing lower reactor pressure of "around 100 atm, versus 200-300 atm in the other processes" (Falbe, ~ , page 73)~
Though the earliest Oxo plants were intended to be a heterogenous reaction patterned after Fisçher Tropsch catalysis) it was eventually found that the catalysis ~as homogeneous (Falbe, supra, page 14). The separation and recovery of the catalyst was therefore an essential step in the Oxo process. This is significantly the case when the catalys~ comprises the precious metal rhodium. As s ated by Cornils et al., "Hydrocarbon Yrocessing", June 1975, at page 86: '~hile Rh compounds are more active than cobalt, they are much more expensive. Cobalt costs approximately 20DM/kg and rhodium between 44,000 and 72yOOODM/kg (S~ptember 1974 and February 197S). This shows the speculative character of the rhodium price.
Cost would be o~ no importance if rhodium could be lOO
percent recovered and used at low metal concentration levels. Impossible economic rhodium recycle has avoided appl~cation o~ unmodiied Rh compounds so far, even when branched chain aldehydes are desired or when only Rh salts can ~nable the oxo reaction. This is because the low Rh concentratlons desired from several ppm* up to (*"ppm" means parts per million)

3.

Z;~

se~eral hundred ppm, related to olefin feed (cobalt 0.1 up to 1 percent, depending Oll the process applied) make even more difficult a chemical, thermal or extractive treatment of the metal carbollyl containing oxo products.
mereore there are a number o~ spe~ial processes for the removal of rhodium traces from oxo products (e.g.
adsorption on solids with large surface, distillative concentration with the heavy ends of oxo synthesis, the treatment with steam, halogens or carbo-~ylic acids os others). Often these methods require an expensive recovery step for concentration o~tside of the oxo unit.
A rhodium loss of only one ppm per ~ilogr2m of oxo product produced causes material costs o~ approximately 0.04 up to 0.07 DM/kg (compared to 0.02 DM/kg with Co catalys ts ) . "
Gornils et al., pages87, B8 and 90, depict in Figure 9 ~ proposed commercial plant design based upon a modified rhodium catalyzed Oxo process. They characterize that the catalyst has to be recycled to the 20 reactor from the distillation column. Owing to the formstion o heavy ends, Cornils et al., at page 8~, ~tate that "a complete recycling of rhodium only via the 'primary' recycle 9 would cause enrichment of higher boil-ing components". According to Cornils et al., page 88, "to avoid ~his, part of the bottom of.column 3 is with-drawn continuousLy as a slipstream and distilled in ~9~823 10816-1 column 6 to give a 'light aldols' overhead". They continue with the following:
"Provided there is suficient activity, the bottoms which are thermally treated twice at this point are recycled to the reactor as a 'secondary' Rh cycle 10. The distilLation in column 6 does not remove the medium and high boiling byproducts of oxo synthesis, the latter because hey can not be separated from the e~ces~ ligand. The separa-tion of the Rh complexe~ from the medium boiling components ls done in column 7 which i9 fed a slipstream of the bottoms of 6. The bottoms of 7 are treated thermally so often that their rhodium content is oxo inactive and must be wor~ed-up in an external make-up ~tep 8. This rhodlum is recycled to the reactor as a 'tertlary' Rh recycle 11, losing however the comple~ bonded ligand and the ~scess of complexing ligands. me amount per year of rhodium passing the tertiary recycle is about t~ce the first Rh filling of the whole oxo system."
Cornils et al~ state at page 89:
"Rhodium concentrations of 0~1 percent together with the amounts of rhodium belng 1081~-l ~ 8 ~ 3 present in the diffl3rent steps of recycle and recovery a~ each moment require high cost for the firs~ catalyst :in~estment. The relation of the first cataly~ t inves tment in cobalt and in Rh modified oxo units is 1:5 (1:3, depend-ing on Rh price).- More important than the ~irst eataLyst investment are the rhodium leakage and working losses. In comparison to other commercial processes using noble metal catalysts, a rhodium loss of one milligram per kilogram of oxo products is regarded t~ be realis~ic. This results in material costs of approximately 0.04-0.07 DM/kg, depending on the Rh price. To equal the material cos~ of the conventional oxo process catalyst the rhodium losses have to decrease to less than 0.3 pp~."
A similar process to that described by Cornils et al. is set forth i~ British Patent 1,228,201. In the proceqses described in that patent, the catalyst recycle is a critical facet of the proces~ e~cept in those cases where the s:atalyst i9 on a solid support in a ixed bed system. Howe~er, as was pointed out previously by J. Falbe, the reaction is in reality a homogeneous reaction and one would have to pres~me subs~antial catalyst losses by putting the rhodium on a inert support.
In British Patent Speci~ication 1,312,076, there ~ 3 is employed a different technique for separation of the catalyst from the product of the reaction. This invoLves removing a ~ product stream overhead from which the aldehyde product is separated by ~ractional distillation, continuously withdrawing from the reactor a Liquid stream comprising the complex catalyst, aldehyde and high boiling residues, passing the liquid stream under reaction pressure over the surace of a membrane such that a pro-portion of the high boiling residues and aLdehydes permeate through the membrane and are removed, with recycling o the remainder of the liquid stream conta;ning the catalyst to the reactor 8 88J
In Briti~h there is noted the fact that in homogeneous catalysis of the type described herein, the r~moval of cataLyst ~rom ~he reaction products for recycle is a diffic~lt operation.
It is stated in the Specification that the catalyst can be recycled in the heavy residue obtained after dlstilla~ion o the main reaction products at the expense of catalyst loss.
To further demonstrate the di~iculties as~oci-ated wlth recovering catalyst from the oxo reaction, reference is made to Olivier and Snyde~ U.S. 3,539,634, patented ~ovember L0, 1970, which describes passing the heavy and/or bottoms of the separated pr~ducts of the re-act~on containing the catalyst through an inert bed from which is e~tracted the catalyst with reaction solvent.

lO~&lZ3 Such a process demands that the solvent be a type which has extraction capabilities while at thP same time requires infinite extraction capabilities to insure no catalyst loss.
m ere is described herein a process for the manu-facture of such Oxo products by hydro~ormylation of alpha-olefins with a modified rhodium catalyst which avoids ~or all p~ctical purposes rhodium catalyst losses over extended periods o time.
The process of this invention is a continuwus one for producing aldehydes by the hydroformylation of alpha-ole ins containing two to about five carbon atoms. It involves establishing a liquid body of a homogeneous mix-ture containing the olefin, carbon monoxide and hydrogen being supplied thereto, a~dehyde products and higher boiling , aldehyde condensation products being continuously formed therein, a soluble r'nodium catalyst complexed with carbon monoxide and a triaryl phosphine. The amount Q~ triaryl phosphine provided in ~he liquid body is equal to at least 10-mols for each mol of rhodium metal provided in the liquid body. There is suppLied to the liquid body a gaseous recycle stream comprising hydrogen and ole in and there is supplied ma~e-up quantities of carbon monoxide, hydrogen and olefin to the liquid body, The temperature of the liqu~d body is maintained at about 50 C. to about 130C., and the total pressure is maintained at less tha~ about 400 pounds per square inch absolute. The carbon monoxide partial pressure in the reaction is less than about 50 pounds per square inch absolute and the hydrogen partial pressure is less than about 200 8.

~9 0 ~ Z 3 psunds per square inch absolute. There is removed from the liquid body a vaporous mixture comprising olefin, hydrogen, ~aporized aldehyde products and an amount o vapDrized aldehyde condensation prod~ct~ essentially cqual to the rate of their formation in the body whereby the size of the liquid body is maintained at a predeter-mined value. Aldehyde products and aldehyde condensation products are recovered rom the vaporQus mixture and this forms the gaseous recycled stream which is supplied to the liquid body as mentioned above.
United States Patent 39527,809, entitled ydro~ormylation Process" by R. L. Pruett and J. A.
Smith, issued September 8, 1970, discloses a significant development in hydroformylation of alpha-olefins to produce aldehydes at high yields, low te~peratures and pressures, excellent catalyst stability and wh~ch when the alpha-olefin contains 3 or more carbon atoms, pro-duces aldehyde mixtures containing a high normal to iso- (or branched-chain) isomer ratio. The process 2Q employs certain rhodium complex compounds to effectively catalyze ~mder a de~ined set of variables, in the presence o~ se7ect triorganophosphorus ligands, the hydroformylation of olefins wi~h hydrogen aQd carbon monoxide. The variables include (1) the rhodium complex catalyst, (2) the olefin ~eed, (3) the triorganophosphorus ligand and its concentration, (4) a relatively low 1081~1 Z;~

temperature range, (5) a relatively low total hydrogen and carbon monoxide pressure, and (6) a l~itation on the partial pressure exerted by carbon monoxide. The process of this invention adc~pts the variables of the invention of U.S. 3,5~7,809, and by experiences from operations herein dPscribed establishes the tremendous ad~ance that invention represents in the Oxo a.rt.
Among the catalysts described in the aforesaid U.S. patent, are compounds containing rhodium in complex combination with carbon monoxide and triarylphosphorus ligands in particular triarylphosphine ligands exempli-fied by triphenylphosphine (TPP). A typical active catalytlc species is rhodium hydridocarbonyltris (tri~
phenylphosphine) which has the for~ula RhH(CO)[P(C6H5)3]3.
e process uses an excess of the triorganophosphorus ligand.
The active rhodium catalyst, as is known in recent literature, can be preformed and then introduced into the reaction mixture media, or the acti~e catalyst species can be prepared in situ during the hydro~ormyla-tion reaction. As an example of the latter, (2,4-pentane-dionato) dicarbonylrhodium(I) can be introduced into the ~eaction medium where, under the operative condi~ions therein, it reacts with the triorganophosphorus ligand, e.g., triphenyLphosphine, to thus form acti~e catalyst ~uch as rhodium hydridocarbonyl-tris(triphenylphosphine).

10 ~

1081~1 ~9 ~ 8 Z 3 When the process of U.S. Patent 3,527,809 employs normally-liquid inert organic solvents which are not products of the reaction or reac~ants ln the process the product mixture e~entually becomes, either at room tempcrature or at the chosen operating temperature o~, for example, 80C., slightly cloudy in nature or it possesses a noticeable precipitatio~. Elemental analyses indicates that 3uch solids ~cloudiness or precipitate) contain rhodium. In some in tances, it appears that "polymeric"
rhodlum ~omplex solids have fonmed and in other instances, the solids are similar to an active form of the rhodium complex species. Such solids can become lost in the system, e.g~, deposit in small crevices or plug valves.
As noted above, a truly efficient commercial Oxo opera-tion cannot tolerate the loss of even small ~uantities of rhodium. A further disadvantage of introducing the rhodium species as a solution in such an extraneous orgsnic liquid is the obvious requirement of separating the oxy-gsnated products formed in the reaction ~rom such organic liquid. Since Oxo reactions produce aldehydes and high boiling aldehyde condensation products which are removed to mainta:Ln the solvent concen~rations, as noted above, the removal of the condensation products by distillation affect the solvent, some being distilled (if not all distilled), and the Rh values it contains. The initial introduction into the Oxo reaction zone of a catalytic 11.

~o 9 ~'~3 solution in extraneous organic Liquids is effe~tive, However, ~uch a commercially based Oxo operat~on demands csnt~nuous~or intermittent catalyst introduction which can be fresh catalyst, regenerated catalyst9 or catalyst contained in a recycle stre2m. Catalyst losses are the result of such practices.
Copending U.S. Patent Application S.N. 556,270, ~iled March 7, 1975, a continuation o S.N, 887,370, iled December 22, 1969, rom which British Patent Speci-fication 1,338,237 is derived, ~mploys the high boiling liquid aldehyde condensation products as a primary solvent for the catalyst. As a result, no removal of the solvent ~rom the catalyst is necessary except for a small purOe stream to keep down the concentration of condensation products and poisons to the reactio~. As a result, the hydroformylation of 3 carbon olefins~ or higher,maintains the high ratio of normal/iso isomer distribution of alde-hydic product over extended periods of time and the co~tinuous recycling of the rhodium species in substantial quantitie~ of such condensation products does not result in extensive precipitation of the rhodium i~ one orm or another, No discernible lo s in th~ life of the catalyst wa~ detect:ed over extended periods of operation. The use of such condensation products as the media to solubilize the rhodium-containing catalyst was advantageous from the standpoint that extraneous organic liquids could be 12.

- 10 9~ ~ ~ 3 1081~1 excluded entirely from the hydroformylation zone, i~
desired. The use of excess, ~ree triorganophosphorus ligand in the reaction medium containing the dissimilar high boiling condens~tion products to provide the advantages cited in U.S. 3,527,809 did not inhibit the activity or solub~l~ty of the rhodiu~ complex catalyst even over long perlods of continuous operatlon. Since these condensation products are formed in situ, She economics of the afore-mentioned process are extremely favorable.
After substantial repeated use it was found that co~tinuous recycle o rhodium species dissolved in the high boiling liquid condensation products presented disadvantages.
The constant movement of ca alyst led to some catalyst loss, considerable catalyst volume was required because in th liquid ~ecycle a portion of the catalyst is outside of the reactor; rate of residue formatîon remained at significant levels and had to be removed, ~hus affecting catalyst stability on such occasions; control of carbon monoxide gas pressure was difficult; the nature o the recycle brought about heat,losses because of the constant movement of hot liquids through the system; and there developed a tendency to have small oxygen leak~ge which proved dele-terious to the process.
It has been determined that a hydroformylation reaction using a non-volatile catalyst, such as hydrido-car~onyltris (triphenylphosphine)rhodium(I), in the liquid 13.

~ 0 ~ 0 8 Z 3 phase can be carried out in a more convenient manner and with simpler equipment by allowing the aldehyde reaction product and their higher boiling condensation products to distil out of the catalyst containing liquid body (or solu-tion) at the reaction t~mperature and pres~ure, by condens-ing the aldehyde reaction product and the condensation products out of the off gas from the reaction vessel in a product recovery ~one and by recycling the unreacted start-~g materials (e.g., carbon monoxide, hydrogen and/or alpha-olefin) in the vapor p~ase from the product recovery zone to ~he reaction zone. Furthermore, by recycling gas , from the product recovery zone coupled ~ith make-up start-ing material~ to the reaction zone in sufficient amounts, it is po~sible, using a C2 to C5 olefin as the alpha-' olefin starting material, to achieve a mass balance in theliquid body in the reactor and thereby remo~e from the reaction zone at a rate at least as great as their rate of formation essentially all the higher boiling condensation products resulting from self condensation of the aldehyde product. If the gas recycle is not sufficient, such con-densation products would otherwise build up in the react`ion vessel.
According to the present invention a process for the production of an aliphatic aldehyde containing from 3 to 6 carbon atoms comprises passing an aliphatic alpha-olefin containing from 2 to 5 carbon atoms together with hydrogen and carbon monoxide at a pre~cribed temperature 1~, .

~09~8~3 - and pressure through a reaction zone containing the catalyst dissolved in the liquid body, the catalyst being esqentially non-volatile and being effective for hydro-formylation of the alpha-olefin, continuously removing a vapor pha~e from the reaction zone, passing the vapor phase to a product separation zone, separating a liquid aldehyde containing product in the product separation zone by con-densation from the gaseous unreacted starting materials, a~d recycling the gaseous unreacted starting materials from the product separation zone to the reaction zone. Prefer-ably the gaseous unreacted starting materials plus make-up starting materials are recycled at a rate at least as great as that required to maintain a mass balance i~ the reaction zone.
In the process of the invention there is con-temFlated the use of alpha-olefins o 2 to 5 carbon atoms, preferably 2, 3 or 4 carbon atoms. Such alpha~oleins are characterized by a terminal ethylenic carbon-to-carbon bond which may be a viny~idene group, i.e., CH2 ~ C <, or a vinyl group, ~.e., CH2 ~ CH-. They may be straight-chain or branched-chain and may contain groups or substituents which do not essentially interfere with the course of thls process. Illustrative alpha-olefins include ethylene, propylene, l-butene, iso-butylene, 2-methyl-1-butene, l-pentene, and the like.
TSe reaction is advantageously conducted at a 15.

~.5~ ~ 8 Z 3 10816-1 temperature of from about 50(' to about 140C. A
temperature in the range of from about 60C to about 120C is preferred and it will usually be convenien~
to operate at a temperature oi. from about 90 to about A feature of the invention is the low total pressures which are required to effect a commercial process. Total pressures less than about 400 psia and as low as one atmosphere, an~ lower, can be employed with effective results. Total pressures of less than 350 psia are preferred. The rèaction can be effected at pressures ranging between about 100 to about 300 psia.
The partial pressure of the carbon monoxide is an important factor in the process of the invention. It has been observed that when using the complex rhodium catalysts a noticeable decrease in the normal/iso alde-hydric product isomer ratio occurs as the partial pressure attributable ~o carbon monoxide approaches a value of about 75 per cent of the total gas pressure (CO + H2).
In general, a partial pressure attributable to hydrogen of from 25 to 95 per cent and more, based on the total gas pressure (CO + H2) is suitable. It is generally advantageous to employ a total gas pressure in which the partial pressure attributable to hydrogen is significan~ly greater than the partial pressure attributable to carbon monoxide, e.g., the hydrogen to carbon monoxide ratio being between 3 : 2 and 100: 1. Routinely, this ratio can be at about 62.5 : 1 to about 12.5 : 1.

16.

~ Z 3 10816_~

The partial pressure of the C~-olefin in the reaction zone may be up to about 35 per cent of the total pressure, preferably in the region of 10 to 20 per cent of the total pressure.
In a preferred operation the C0 partial pressure is typically not in excess of about 50 p.s.i.a., most desirably not in excess of about 35 p.s.i.a. The pre-ferred hydrogen partial pressure should be less than about 200 p.s.i.a. For example, the H2 partial pressure may be 125 p.s.i.a. and the C0 partial pressure may ra~ge fro~ 2 to 10 p.s.i.a.
The catalyst may be any non-volatile catalyst that is effective for hydroformylation of alpha-olefins but in view of the known advantages as taught in U.S.
3,527,809 of catalysts based on rhodium, it constitutes in modified form the catalyst of choice. When a C3 or higher olefin is used as a starting material it is preferred to choose a catalyst that gives a high n-/iso-ratio in the aldehyde product mixture. The ~0 general class of rhodium catalysts depicted in U.S.
3,527,809 may be used in the practice of this invention.
The preferred catalyst of this invention comprises rhodium complexed with carbon monoxide and a triarylphosphine ligand. The most desirable catalyst is free of halogen such as chlorine, and contains hydrogen, carbon monoxide and triaryl phosphine com-plexed with rhodium metal to produce a catalyst soluble in the aforementioned liquid body and stable under the conditions of the reaction. Illustrative triaryl-~ 7.

1 ~ ~ 0 ~ ~ 3 phosphine li~ands are triphenylphosphine, trinaphthyl-phine, tritolylphosphine, tri(p biphenyl)phosphine, tri(p-methoxyphenyl)phosphine, tri(m-chlorophenyl)-phosphine, p-N,N-dimethylaminophenyl bis-phenyl phosphine, and the like. Triphenylphosphine is the preferred ligand. As pointed out previously, the reaction is effected in a liquid body containing excess, ~ree triarylphosphine.
Rhodium is preferably introduced into the liquid body as a preformed catalyst, e.g., a stable crystalline solid, rhodium hydridocarbonyl-tris(triphenyl phosphine), RhH(CO)(PPh3)3. The rhodium can be introduced to the liquid body as a precursor form which is converted in situ into the catalyst. Examples of such precursor form are rhodium carbonyl triphenylphosphine acetylacetonate, Rh203, Rh4(CO)l~, Rh6(CO)16, and rhodium dicarbonyl acetylace~onateO
Both the catalyst compounds which will provide active species in the reaction medium and their preparation are known by the art, see Brown et al., Journal_of the Chemical Society, 1970, pp. 2753-2764.
In ultimate terms the rhodium concentration in the li~uid body can range from about 25 ppm to about 1200 ppm of rhodium calculated as free metal, and the triarylphosphine is present in the range of about 0.5 ~ percent to about 30 percent by weight, based on the weight of the total reaction mixture, and in an amount sufficient to provide at least 10 moles of free triarylphosphine per mole of rhodium.
18.

10~30~23 The significance of free ligand is taught in U.S. 3,527,~09, ~e~, British Patent Specification 1,338,225, and Br~wn et al., supra, pages 2759 and 2761.
In general the optimum catalyst concentration depends on the concentration of the alpha-olefin, such as propylene. Fur example, the higher the propylene concentration the lower usually will be the catalyst concentration that can be used to achieve a given co~version rate to aldehyde products in a given size of reactor. Recognizing that partial pressures and concentration are related, the use of higher propylene partial pressure leads to an increased proportion of propylene in the "off gas" from the liquid ~ody. Since it may be necessary to purge part of the gas stream from the product recovery zone before recycle to the liquid body in order to remove a portion of the propane which may be present, the higher the propylene content of the "off gas" is, the more propylene that will be lost in the propane purge stream. Thus it is necessary to balance the economic value of the propylene lost in the propane ~0 purge stream against the capital savings associated with lower catalyst concentration.
An unforeseen advantage of this modified Rh catalyzed process is that in the hydroformylation of ethylene no diethyl ketone is formed in measurable quantities whereas all of the Co catalyzed processes produce significant amounts of diethyl ketone.
It is preferred to effect the process of the invention using a liquid phase in the reaction zone which 19 .

. 10816-1 ~ ~ 9 ~ ~ ~ 3 con~ains one of the aforement:ioned rhodium complex cataLysts and9 as a solvent t:herefor, higher boiLing liquid aldehyde condensation produc~:s (as hereinafter defined which are rich in hydroxylic compounds).
By the term "higher boiling liquid aldehyde cond~nsation products" as used herein is meant the com-plex mixture of high boiling liquid products which result from the condensation reactions of the C3 to C6 alkanal product of the process of the in~ention, as ilLustrated below in the series of equations involving n-buty~aldehyde a~ the model. Such condensation products can be pre~ormed or produeed in situ in the Oxo process. The rhodium com-plex species is soluble in these relatively high boiling liquid aldehyde condensation products while exhibitin~
high catalyst li$e over extended periods of continuous hydroformylation.
Inltially, the hydroformylation reaction can be e~$ected in the absence or in the presence of small amounts of higher boiling liquid aldehyde condensation products as a solvent for the rhodium complex, or the reaction can be condu~ted with up to about 70 weight per cent, and even as much as about 90 weight per cent, and more, of such condensation products, based on the weight of the liquid body. A small amount of the higher boiling liquid alde-hyde condensation products can be as little as 5 weight per cent, preferably more than 15 weight per cen , based on the weight of the liquid body.

20.

. loal6-~090823 In ~he hydroformylation of, for example, propylene, two products are possible, namely normal and iso-butyraLdehydes. Since normal butyraldehyde is the more attractive product commercially, high normal/iso ratios of butyraldehydes are desirable. However, the aldehydic products being reacti~e compounds themselves slowly undergo condensation reactions, even in the absence o~ catalysts and at comparat~veLy low tempera-tures, to form high boiling liquid conden~ation productq.
Some aldehyde product, therefore, is involved in ~arious reactions as depicted below using n-butyraldehyde as an illustration:

OH
I ~H~O
2CH3CH2CH2CHO ~ CH3CH2CEI2CHCHGH2cH3 > CH3CH2CH2~H ~

al~ol (I) substituted acrolein(II) IH \ / ICCH2c~2cH3 20CH3CH2CH2~1CHcH2cH3 '~ ~ CH3CH2CH2 2 3 l ll CH20 C~20CCH2C 2CH3 (trimer III) (trlmer IV) 21.

~ 0 ~ 0 ~ 2 3 (trimer III) (trimer IV) heat IH l l CH3CH2CE2C~O

CH3CH2CH2cHI CH2CH3 CH3CH2C~2cHcHcH2cH3 CH20H \' O
\ ll CHzOCC~I2CH2 CH 3 (dimer V) ttetramer VI) In addition, aldol I can undergo the fo~lowing reaction:
. ~H

2 aldol I - > CH3CH2CH2CHCHCH2CH3 ¦ OH
COOCH2CH~HCH2CH2C~3 ~tetramer VII) The names in parentheses in the afore-illustrated equations, aLdol I, substituted acrolein II, trimer III, trimer IV, dimer V, tetramer VI, and tetramer VII, are for convenience only. Aldol I is formed by an aldol condensa-~ion; trlmer III and te~ramer ~II are ormed via Tischenko reactions; trimer IV by a transesterification reaction;
dimer V and tetramer VI by a dismutation reaction. Prin-~ipal condensation products are trimer III, trimer IV, and tetrc~mer VII, with lesser amounts o the other prod-ucts being present. Such condensa~lon products, therefore, contain substantial quantities of hydroxylic compounds as witnessed, for example, by trimers III and IV and tetramer VII .

Similar condensation products are produced by self condensation of iso-butyraldehyde a~d a further range of compounds is formed by condensation of one molecule of normal butyraldehyde with one molecule of iso-butyraldehyde.
Since a molecule of normal butyraldehyde can aldolize by reaction with a molecule of iso~butyraldehyde in two dif-ferent ways to form two different aldols VIII and IX, a total of four possible aldols can be produced by conden-sation reactions of a normal/iso mixture of butyraldehydes.

~3cH2~2~o ~ ~3CHcH3 ~3 ~H3cEI2cH2cH-fcEI3 ~ O CHO
Aldol (VIII) i -CHi CH2CH3 Aldol (IX) Aldol I can undergo further condensation wlth isobutyraldehyde to form a trimer isomeric with trimer III
and aldols VIII and IX and the corre~ponding aldol X pro-duced by self condensation of two molecules o~ isobuty-raldehyde can undergo further react~ons with either normal or isobutyraldehyde to fonm corresponding lsomeric trimers~
These trimers can react ~urther a~alogously to trimer III

so tha~ a complex mixture o~ conden9ation products is ~ormed.
It is highly desirable to maintain the sub-stituted acrolein II and its i~omers at low concentrations, ~ ~ O ~ Z 3 e.g. below about 5 weight per cent. The substituted acrolein II, specifically termed 2-ethyl, 3-propyl-acrolein (~'EPA"), is formed in situ along with other condensation products and has been found to inhibit catalyst activity. The ultimate effect of EPA or like products is to reduce hydroformylation rates to such an exent ~hat any process where the EPA is present in amounts greater tha~ about 5 weight percent, even greater than about one percent by weight based on the weight of the liquid body, will suffer an economic penalty.
In a preferred form of the process of the inven-tion the higher boiling liquid eondensation products to be used as solvents are preformed prior to introduction into the reaction zone and the start-up of the process.
Alternatively, it is possible to add, for example, Aldol I
at process start-up and to allow the other products to build up as the reaction proceeds.
In certain instances, it may also be desirable to use minor amounts of an organic co-solvent which is normally liquid and inert during the hydro~ormylation process, e.g. toluene or cyclohexanone, particularly at start up of the process. They can be allowed to be replaced in the liquid phase in the reaction zone by the higher boiling liquid aldehyde condensation products as the reaction proceeds.
The liquid body will contain, in addition to the catalyst and any added diluent such as free ligand triphenylphosphine, an aldehyde or a mixture of aldehydes 24.

1~ 9 ~ ~ ~ 3 and the aldols, trimers, diesters, etc. derived ~rom them.
The relative proportion of each product in solution is controlled by the (amount of gas) passing through the solution. Increasing this amount decreases the equilibrium aldehyde concentration and increases the rate of by-product removal from solution. The by-products include the higher boiling liquid aldehyde condensation products. The decreased aldehyde c~ncentration leads to a reduction in the rate o formation of the by-products.
' The dual effect of increased removaL rate and decreased formation rate means that the mass balanee in ~y-products in the reactor is very sensitive to the amount of gas passing through the liquid body. The gas cycle typically includes make-up quantities of hydrogen, carbon monoxide and alpha-olefin. However, the most meaning~ul factor is the amount of recycle gas returned to the liquid body since this determines the degree of reaction, the amou~t of product formed and the amount of by product (as a consPquence) removed.
Operation of the hydroormylation reaction with a given flow rate of olefin and synthesis gas and with a total low amount ~f gas recycle less than a critical threshold rate results in a high equilibrium aldehyde concentration i~ solution and h~nce, in high by-product formation rates.

~ 8 ~ 3 The rate ofremoval of by-products in the vapor phase effluent from the reactio~ zone (liquid body) under such conditions will be low because the low vapor phase effluent flow rate from the reaction zone can only result in a relatively low rate of carry-over of by-products.
The net effect is a build-up of by-products in the liquid body solution causing an increase in the soluti~n volume with a consequent lcss of catalyst productivity. A purge must therefore be taken from the solution when the hydroformylation process is operated under such low gas flow rate conditions in order to remove by~products and hence maintain a mass balance over the reaction zone.
If however, the gas flow rate through the reac-tion zone is increased by increasing the gas recycle rate the solution aldehyde content falls, the by-product for~ation rate is decreased and by-product removal rate in the vapor phase effluent from the reaction zone is in-creased. The net effect of this change is to increase the proportion of the by-products removed with vapor phase effluent from the reaction zone. Increasing the gas flow rate through the reaction zone still further by a further increase in the gas recycle rate leads to a situation in which by-products are removed in the vapor phase effluent from the reaction zone at the same rate as they are formed, thus establishing a mass balance over the reaction 26.

~ 3 zone. This is the critical threshold gas recycle rate which is the preferred min~m~m gas recycle rate used in the process of the invention. If the process is operated with a gas recycle rate higher than this threshold gas recycle rate the volume o~ the liquid body in the reaction zone will tend to decrease and so, at gas recycle rates above the threshold rate, some of the crude aldehyde by-product mixture should be returned to the reaction zone from the product separation zone in order to keep constant the ~ol~me of the liquid phase i~ the reaction zone.
me critical threshold gas recycle flow rate can be found by a process of trial and error for a given olefin and ~ynthesis gas ~the mlxture of CO and hydrogen) feed rate. Operating a~ recycle rates below the critical thres-hold rates will increase the volume of the liquid phase with time. Operating the threshold rate keeps the volu~e constant. Operating above the threshold rate decreases the volume. The critical threshold gas recycle rate can be calculated from the vapor pressures at the reac~ion temperature of the aldehyde or aldehydes and of each of the by-products present.
With the process operating at a gas recycle rate at or greater than the threshold rate, by-produc~s are removed i~ ~he gaseous vapors removed from the reaction zone containing the liquid body at the same ra~e as or faster than they are formed, and thus do no~ accumulate ~ Z 3 in the liquid phase in the reac~ion zone. Under such circumstances, it is unnecessary to purge the liquid body containing the catalyst from ~he reaction zone in order to remove by-products. This has the advantage of obviating removaL of catalyst rom the reaction zone, except at - extended intervals when renovation of the ca~aLyst is necessary, and thus the chance of losses of expensive catalyst by accldental spillage or leakage iq reduced.
Furthermore there is no need for high temperature treat-ment of the catalyst-containlng purge solution or by-product removal and thus catalyst life is extended.
Experience to date suggests that catalyst renovation of any kind is not required for at least one (1) year's op2ration.
The residence period of aldehyde ln the reaction zone can ~ary from about a couple of minutes to several hours in duration and, as is well appreciated, this vari-able wil~ be inluenced, to a certain extent, by the reaction tem~erature, the choice of the alpha-olefin of the catalyst, and of the ligand, the concentration of the ligand, the total synthesis gas pressure and the partial pressure e~erted by its components, and other factors.
As a practical matter the reaction i~ effected ~or a period o time wh:ich is sufficient to hydroformylate the alpha or terminal ethylenic bond of the alpha-olein.

- 28.

10816 l ~0 ~'~3 ~ by-product of the hydroformylation process is the alkane formed by hydrogenation of the alpha olefin.
Thus, for example, in the hydroformylation of propylene a by~product is propane. Preferably, therefore, a purge 8tream is taken from the gas recycle stream from the product recovery zone in order to remo~e propane and prevent its build-up within the reaction system. This purge stream will contain, in addition to unwanted propane, unreacted propy1ene, some inert gases introduced in the feedstock and a mixture of carbon monoxide and hydrogen. The purge stream can, if desired, be su~mitted to conventional ga separation techniques, e.g. cryogenic techniques, in order to recover the propylene. However, i~ w~ll usually be uneconomical to do this and the purge stream is ypically used a~ a fuel. The principal romposition of the recycle gas are hydrogen and propylene. However, if the G0 is not consumed in the reaction, the excess CO will also be part of the recycle gas. Usual1y the recycle gas will contain a-kane even with purging beore recycLe.
It will be appreciated that the process of the invention can be operated continuously for long periods of tlme w~thout remo~ing any of the catalyst containing liquid body from the reaction zone. However, rom time to time it may be necessary to regenerate the rhodium catalyst, in which case a purge stream can be taken from the reactor through a normally locked valve, frash catalyst being added to 29.

~ ~ z 3 1081~1 maintain the catalyst concentration in the liquid body or the removed catalyst can be regenerated. After removal from the liquid body in a reactor, the vapor effluent is fed to a product separation zone where the m~x-ture of the aldehyde or aldehydes and the dimers, trimers and other higher boiling liquid condensation products are worked up by conventional techniques, e.g. distillation, in order to remove the aldehyde or aldehydes and, if appropriate, to separate the aldehydes one from another and recover the h;gher boiling liquid aldehyde condensa-tion products.
The alpha-olefin used as starting ma~erial in the process must be rigorously purified in order to remove ~he typical potential Oxo catalyst poisons, see Falbe, supra, pages 18-22. The carbon monoxide and hydrogen required for the process can be produced by partial oxida-tion of a suitable hydrocarbon ~eedstock, e.g. naphtha, and mNSt also be purified rigorously to exclude potential ca~alyst poisoning impurities.
The inventi~n is further illustrated with reference to the accompanying drawing which sche~atically shows a diagramat~c flowsheet suitable in practising the process of the in~ention.
Referring to the drawing, a stainless steel reactor 1 is provided with one or more disc impeller 6 con-taining perpendicularly mounted blades and rotated by means 30.

~9~8Z3 10816 -1 of shaft 7, by a suitable motor (not shown). Located below the impeller 6 is a circular tubular sparger 5 for feeding the ~ -olefin? and synthesis gas plus the recycle gas.
The sparger 5 contains a plurality of holes of sufficient size to provide sufficient gas flow in ~ the liquid body at about the impeller 6 to provide the desired amount of the reacta~ts in the liquid body. The reactor is also provided with a steam jacket (not shown) by means of which the contentsof the vessel can be brought up to reaction temperature at start-up and internal cooling coils (not shown) Vaporous product effluent from the reactor 1 are removed via line lO to separator 11 where they are passed through a demisting pad lla therein to return some aldehyde and condensation product and to prevent potential carry-over of catalyst. The reactor effluent is passed by line 13 to a condenser 14 and then through line 15 to catchpot 16 in which the aldehyde product and any by-product can be condensed out of the off gases (effluent). Condensed aldehyde and by-products are removed from the catchpot 16 by line 17.
Gaseous materials are passed via line 18 to separator 19 containing a demisting pad and recycle line 20. Recycle gases are removed by line 21 to line 8 from which a purge through line 22 is pulled to control saturated hydro carbon content. The remaining and major porportion of the gases can be recycled via line 8 to line

4 into which is fed make-up reactant feeds through lines 2 a~d 3. The combined total of reactants are fed ~0 90 8 ~ ~ 10816 -1 to the reactor L. Compressor 26 aids in transporting the recycle gases.
Fresh catalyst solution can be added to the reactor 1 b~ line 9. The single reactor 1 can o co~rse, be replaced by a plurality of reactors in parallel.
The crude aldehyd~ product of line 17 can be treated by conventional aistillation to ~eparate the various aldehydes and the condensation products. A por-tion of the crude can be recycled to reactor 1 through line 23 and fed as indica~ed by broken-line 25 to a point above impeller 6 for ~he purpose of maintaining the liquid le~el in reactor 1 if such is required.
.The following example serves to illustrate the practice of this invention and not lim~t it.

EXAMPLE
~ The reactor employed is a stainless steel cylin-drical vessel as characterized in tha drawing, having dimensio of ~3 feet inside diameter and 24 feet height containing a 4 feet diP~eter, 8 ~nches inside diameter tubular sparger located immediately below the impeller. The sparger con-tains a plurality of holes to allow feed of reactants.
The c~nditions of the reaction using the process de~ign of the drawi~g are set forth in Tables 1 and 2.

32.

~ ~ ~ O ~ ~,3 Contents of Reactor 1 Com~ nent Characterization Amount Liquid Volume 42,000 liters Rh, determined as metal* 275 ppm Triphenyl Phosphine 7.5 weight %
Total butyraldehydes 35 weight %
Trimer 50 weight %
Other higher boiling 7.5 weigh~ %
condensation products *The rhodium is supplied as hydridocarbonyltris-(triphe~ylphosphine)rhodium(I~.

~ ~ ~3 3 10816-1 o ~ ~ ~ aR
V3 ~ ~ O ~1 ~1 w ~ ~ ~ ~ 8 1~
~ ~ o U~
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C~l . . . ...... _ .
o ~ ~
,, _, ~o ~ 8 o o ~ ~ o , P~ ~o ~ ~ , _ , _ _ _ o ~ ~ ~ ~ ~ ~ ~ ~
~ ~ _I ,1 ~ ~ ~ ,1 ,1 P4 0 0 0 0 0 0 0 0 u~ o o ~3 ~ E~ E E3 li 8 e 8 E i`
c~ ~3 o ~ u~ ~ oo c~ ~ ~ r~
~-o O C`~ ~1 ~ ~ ~D
~ ~ o . ,1 ~ ~

~on c~. E~ ~-æ
o o o o o o o o Q ~`I o e E; E3 ~D ~ I~
~: ~~ o~ 9 o ~ ~ .
o ~ ~ ~ 8 ~ 3 E E3 E
P~ ~ O ~1 ~ ~ ~ G~ 0 ~D _I C`l C`~ .

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~a ~ ~ Z ~ ~ ~ o ~:1 O 1~ l O O ~ U ~C) ~ E~
~ ~ ~, o ~ ~ o ~J ~1 ¢ ~ ~ I o O ¢
pc ~ ~c~
, ~ H

34.

The make-up of product frsm line 17 is as - ollows:
COMPONENT CONIENTS OF
CHARACTERIZATION~RUDE PRODUCT
_ Composition(wt.%~
CO 0.06 H2 O . 01 C3H6 4.82 C3H8 4.40 C2 O.39 CH4~ 0.08 Normal Butyraldehyde 82.59 Iso Butyraldehyde7.14 Aldols 0.01 EPA 0.16 H20 0.13 Trimers 0.20 Diester 0.01 Diol 0.01 TPP Trace E;ssentially the same procedure has been proven to be a most effective technique to produce propionaldehyde from ethylene.

35.

Claims (10)

WHAT IS CLAIMED IS:

1. The continuous process of producing alde-hydes by the hydroformylation of alpha-olefins containing 2 to about 5 carbon atoms comprising:
establishing a liquid body of a homogeneous mixture containing olefin, aldehyde products and higher boiling aldehyde condensation products continuously formed therein, a soluble rhodium catalyst complexed with carbon monoxide and a triarylphosphine, and at least ten moles of free triarylphosphine for each mole of rhodium metal, supplying to the liquid body a gaseous recycle stream comprising hydrogen and the olefin;
supplying make-up quantities of carbon monoxide, hydrogen and olefin to the liquid body;
maintaining the temperature of the liquid body at about 50°C. to about 140°C. , the total pressure at less than about 400 psia, the carbon monoxide partial pressure at less than about 50 psia and the hydrogen partial pressure at less than about 200 psia;
removing from said liquid body an amount of vaporous mixture comprising said olefin, hydrogen, vapor-ized aldehyde product, and an amount of vaporized aldehyde condensation products essentially equal to the rate of their formation in said body whereby the size of said body is maintained at a predetermined value; and recovering aldehyde product and aldehyde con-densation product from said vaporous mixture and forming said gaseous recycle stream.

36.

2. The process of claim 1 wherein the alpha-olefin is propylene.

3. The process of claim 1 wherein the gaseous recycle stream comprises hydrogen, the alpha-olefin and carbon monoxide.

4. The process of claim 2 wherein the gaseous recycle stream comprises hydrogen, the alpha-olefin and carbon monoxide.

5. The process of claim 2 wherein the triarylphosphine is triphenylphosphine.

6. The process of claim 1 wherein the total pressure is less than 350 pounds psia.

7. The process of claim 2 wherein the hydrogen to carbon monoxide is at a mole ratio between 3 to 2 and 20 to 1.

8. The process of claim 2 wherein the temperature is from about 60°C. to about 120°C.

9. The process of claim 1 wherein the alpha-olefin is ethylene.

10. The process of claim 1 wherein the alpha-olefin is l-butene.

37.