Process for the production of aldehydes by hydroformylation

Continuous process for hydroformylation of olefins containing, typically, from 6 to 20 carbon atoms to produce the corresponding aldehydes. The rate of formation of high boiling aldehyde condensation products is minimized by use of a high boiling inert solvent whose boiling point, at the pressure prevailing in the product recovery zone, lies intermediate between that of the highest boiling aldehyde product produced in the hydroformylation reaction and that of the ligand, as well as by maintaining the concentration of product aldehyde at or below a predetermined minor amount. In this way the length of a production run can be significantly extended before it becomes necessary to shut down the plant due to accumulation of high boiling aldehyde condensation products.

This invention relates to a continuous process for the production of 
aldehydes by hydroformylation of olefins. 
Hydroformylation is a well known process in which an olefin, often a 
terminal olefin of the formula: 
EQU R.CH:CH.sub.2, 
where R represents a hydrogen atom or an optionally substituted hydrocarbon 
group, is reacted under elevated temperature and pressure conditions in 
the presence of a suitable catalyst with carbon monoxide and hydrogen to 
yield an aldehyde, according to the following equation: 
EQU R.CH:CH.sub.2 +CO+H.sub.2 =R.CH.sub.2.CH.sub.2. CHO. 
Typically R represents a hydrogen atom or an alkyl radical. 
The catalysts initially suggested were based on cobalt but these require 
use of high operating pressures and usually result in production of 
significantly high quantities of the corresponding alcohol of formula 
R.CH.sub.2.CH.sub.2.CH.sub.2 OH, as well as by-products such as acetals, 
esters, and the like. In addition, product recovery is complicated by the 
fact that the cobalt carbonyl catalysts are volatile and toxic, which 
means that the product stream from the hydroformylation zone has to be 
subjected to a decobalting step, a procedure which generally destroys the 
cobalt catalyst, before the decobalted product stream can be subjected to 
distillation or further treatment for recovery of aldehyde product. Hence, 
for economic operation, provision has to be made for recovering cobalt and 
for regenerating the cobalt catalyst therefrom. Ethylene gives rise to a 
single aldehyde hydroformylation product, i.e. propionaldehyde, but when 
propylene or a higher olefin is hydroformylated, the product stream always 
contains, besides the desired n-aldehyde, a proportion of the 
corresponding iso-aldehyde, which is formed according to the equation: 
EQU R.CH:CH.sub.2 +CO+H.sub.2 =R.CH(CHO).CH.sub.3. 
Typically the n-/iso-aldehyde product ratio from propylene and higher 
olefins, when using a cobalt hydroformylation catalyst, is of the order 
4:1 or so. 
A major advance in hydroformylation came with the advent of rhodium complex 
hydroformylation catalysts. These afforded great advantages, notably a 
non-volatile catalyst, a lower operating pressure, much reduced yields of 
alcohols and other by-products, and usually a significantly higher n-/iso- 
product aldehyde ratio. For further details of rhodium complex 
hydroformylation catalysts and conditions of operation therewith, the 
attention of the reader is drawn, for example, to U.S. Pat. No. 3,527,809. 
A description of a typical commercial plant employing such a catalyst will 
be found in the article: "Low-pressure OXO process yields a better product 
mix", Chemical Engineering, Dec. 5, 1977, pages 110 to 115. 
The rhodium catalyst employed commercially in such a process generally 
comprises rhodium in complex combination with carbon monoxide and with a 
ligand, such as triphenylphosphine. 
Usually the desired product of a hydroformylation reaction is the 
n-aldehyde, rather than the iso-aldehyde, for which there may be a limited 
commercial market; hence in many commercially operating hydroformylation 
plants the iso-aldehyde is burnt as a fuel since there is no ready market 
therefor. The use of a phosphine ligand, such as triphenylphosphine, has 
the advantage that high n-aldehyde/iso-aldehyde molar ratios can be 
obtained from terminal olefins. In some cases, however, the iso-aldehyde 
is the preferred product; for example, it has been proposed to produce 
isoprene from but-2-ene by hydroformylation to yield the iso-aldehyde, 
2-methylbutanal, followed by dehydration by passage at elevated 
temperature over a suitable catalyst. When the desired product is the 
iso-aldehyde it has been proposed in EP-A-0096987 to use a rhodium complex 
hydroformylation catalyst and a phosphite ligand, such as 
triphenylphosphite. Alternatively it has been proposed in EP-A-0096988 to 
produce iso-aldehydes by hydroformylation of internal olefins using a 
rhodium complex hydroformylation catalyst and a cyclic phosphite ligand. 
Hydroformylation of alpha-olefins using a similar catalyst system to 
produce aldehyde mixtures whose n-/iso-aldehyde molar ratios approximate 
those obtained by using cobalt catalysts is described in EP-A-0096986. 
Although the use of added solvents has been proposed on many occasions in 
the prior art, including U.S. Pat. No. 3,527,809, most commercially 
operating hydroformylation plants operate in so-called "natural process 
solvent", i.e. a mixture of aldehyde and aldehyde condensation products. 
The nature of such aldehyde condensation products is further discussed in 
U.S. Pat. No. 4,148,830. 
At start up of a commercial plant product aldehyde is often used as the 
reaction solvent, this gradually being displaced by aldehyde condensation 
products until the "natural process solvent" has been generated. 
It has been proposed to operate hydroformylation reaction using high 
boiling solvents, including ethylene glycol, propylene glycol and 
polyalkylene glycols such as diethylene glycol, triethylene glycol, 
dipropylene glycol and tripropylene glycol; the use of such solvents has 
been proposed in U.S. Pat. Nos. 4,158,020 and 4,159,999. Polyglycols, such 
as polyethylene glycol and polypropylene glycol, which have molecular 
weights of at least about 500, have been proposed as a solvent in U.S. 
Pat. No. 4,151,209; according to this last-mentioned proposal progressive 
deactivation of the catalyst, as well as loss of the ligand species 
through by-product formation, are reduced by continuously stripping the 
liquid reaction medium to a degree such that the content of high-boiling 
organophosphorous by-products therein is maintained at a low level such 
that the ratio of phosphorus contained in said high boiling by-products to 
phosphorus contained in the ligand present in the reaction medium does not 
exceed about 0.2. According to column 7, line 38 et seq: 
". . . it is desirable to employ solvent species which are of extremely low 
volatility, in particular compounds (or mixtures of compounds) which are 
less volatile than the ligand species being employed in the 
hydrocarbonylation reaction." 
Besides polyglycols (e.g. polyethylene glycol and polypropylene glycol), 
solvents recommended for use in the process of U.S. Pat. No. 4,151,209 
include triphenylphosphine oxide and high-boiling esters of vapour 
pressure lower than that of the ligand being employed, either alone or in 
admixture with another solvent species, e.g. a polyglycol. A disadvantage 
of the use of glycols and polyglycols is that such materials can react 
with the aldehyde products to form cyclic or acyclic acetals. Hence 
glycols and polyglycols cannot be regarded as inert solvents. 
U.S. Pat. No. 4,329,511 teaches a process in which a liquid which has a 
molecular weight of at least about 700 is used as a solvent for a rhodium 
complex hydroformylation catalyst. This specification teaches that: 
". . . yet another parameter is of industrial significance in carrying out 
the product recovery at minimal cost and at optimal efficiency in, for 
example, the required rate of gas circulation necessary to recover the 
volatile products and simultaneously prevent build-up of the heavier 
reaction by-products. This additional parameter is the mole fraction of 
aldehyde in the liquid reaction medium contained in a hydroformylation 
reactor and, associated with the mole fraction, the molar concentration of 
product aldehyde in the liquid" (column 7, lines 40 to 51). 
U.S. Pat. No. 4,329,511 further teaches that the hydroformylation reaction 
medium should contain at least about 50% of the high molecular weight 
diluent, computed on the product aldehyde-free basis (column 8, lines 38 
to 43), whilst product aldehyde itself typically amounts to roughly 10% to 
15% of the total reaction mixture (column 8, lines 66 to 68). The aldehyde 
content is controlled by controlling the intensity of the product 
stripping which is employed to remove the aldehyde from the reaction 
medium (column 9, line 35 et seq), it being recommended that stripping be 
so controlled as to maintain in the liquid reaction medium contained in 
the hydroformylation reactor an aldehyde content of about 1 to 2 gram 
moles per liter (column 9, lines 47 to 51). 
Amongst methods of product recovery, U.S. Pat. No. 4,329,511 proposes 
withdrawal of a slip stream of liquid from the hydroformylation reactor, 
followed by distillation to recover a distillate comprising the aldehyde 
product, while leaving a distillation residue comprising the high 
molecular weight reaction solvent and catalyst, this residue then being 
returned to the hydroformylation reactor (column 7, lines 21 to 29). 
Alternatively the withdrawn slip stream can be subjected to simple 
evaporation (column 7, line 29 et seq of U.S. Pat. No. 4,329,511). 
Although U.S. Pat. No. 4,329,511 proposes use of an alpha-olefinic 
hydrocarbons of 2 to about 20 carbon atoms, especially 2 to about 8 carbon 
atoms, difficulties arise due to considerations of vapour pressure at 
temperatures normally employed in the hydroformylation reaction systems, 
as discussed at column 4, line 15 et seq of U.S. Pat. No. 4,329,511. Hence 
the process of U.S. Pat. No. 4,329,511 is effectively restricted to use of 
olefinic hydrocarbons of 2 to about 6 carbon atoms, according to column 4, 
lines 21 and 22, ethylene and propylene being preferred. 
It is well recognised in the prior art that, although it is possible to 
control to some extent the formation of aldehyde condensation by-products 
in the hydroformylation reaction medium, yet it is impossible to suppress 
entirely formation of such by-products. In the hydroformylation of low 
molecular weight olefins containing, for example, from 2 to about 5 carbon 
atoms, the resulting dimers and trimers are relatively low molecular 
weight compounds and their vapour pressure represents a minor, but 
significant, contribution to the total vapour pressure of the liquid 
medium. This means that, when operating with C.sub.2 to C.sub.5 olefins, 
the level of aldehyde condensation products in the liquid reaction medium 
can be controlled by using a sufficiently high gas recycle rate, as taught 
by U.S. Pat. No. 4,247,486. However, such measures cannot be used in 
practice when hydroformylating C.sub.6 and higher olefins since the 
volatility of the aldehyde condensation by-products, specifically the 
"trimer III" and "trimer IV" type products (to adopt the nomenclature of 
U.S. Pat. No. 4,148,830) approaches that of triphenylphosphine and any 
attempt to control the level of aldehyde condensation by-products by the 
gas recycle process of U.S. Pat. No. 4,247,486 will tend to result in a 
concomitant loss of ligand from the hydroformylation medium. Moreover, in 
order to obtain a sufficiently high aldehyde condensation by-product 
vapour pressure, it is necessary to raise the reaction temperature to an 
unacceptably high level at which the risk of catalyst deactivation, by 
mechanisms such as rhodium cluster formation, and the rate of by-product 
formation become unacceptably high. If lower reactor temperatures are 
used, then the rate of gas recycle must be correspondingly increased which 
in turn leads to an unacceptably high capital cost for the gas recycle 
compressor and also unacceptably high operating costs, whilst the problem 
of potential ligand loss still remains. 
For these reasons it is in practice necessary when operating with, for 
example, C.sub.6 and higher olefins to recover product aldehyde from the 
hydroformylation reaction by distillation of, or evaporation from, a 
liquid product stream from the hydroformylation reactor. 
Although the process of U.S. Pat. No. 4,329,511 recognises that it is 
beneficial to reduce the aldehyde concentration in the hydroformylation 
reaction medium so as to reduce the rate of aldehyde condensation product 
formation, yet the use of high boiling solvents leads in turn to further 
problems. Thus, for example, the use of high boiling solvents means that 
the temperature to which the hydroformylation medium is exposed in the 
distillation or evaporation step is increased with a consequent increase 
in the risk of catalyst deactivation as well as a corresponding increase 
in the rate of formation of aldehyde condensation by-products. Moreover, 
when operating the process continuously, removal of the inevitably formed 
aldehyde condensation by-products becomes problematic. In order to 
compensate for their formation it is necessary to purge some of the 
recirculating medium, which in turn means loss of rhodium catalyst and of 
ligand from the system. In view of the expense of rhodium and of the 
triphenylphosphine or other ligand, it is impractical to discard the purge 
stream and, as it is also expensive to store it and to replenish the 
reactor with fresh rhodium and ligand, it is accordingly necessary to 
include in the plant a catalyst and ligand recovery system for treatment 
of the purge stream for recovery of these valuable components. 
The present invention seeks to provide an improved hydroformylation process 
for the production of C.sub.7 and higher aldehydes from C.sub.6 and higher 
olefins which can be operated continuously for extended periods of time 
and wherein the rate of formation of by-product aldehyde condensation 
by-products can be minimised. It further seeks to provide an improved 
process for effecting hydroformylation of C.sub.6 and higher olefins in 
which adjustment of the volume of the circulating hydroformylation 
reaction medium, due to the inevitable formation of aldehyde condensation 
by-products, can be effected without loss of rhodium or ligand from the 
system. 
According to the present invention there is provided a continuous process 
for the production of optionally substituted aldehydes containing at least 
7 carbon atoms by hydroformylation of an optionally substituted olefin 
containing from 6 to about 20 carbon atoms, which process comprises: 
providing a hydroformylation zone, a product recovery zone, and means for 
circulating liquid between said hydroformylation zone and said product 
recovery zone; 
providing in said hydroformylation zone a substantially constant 
predetermined volume of a liquid hydroformylation medium containing 
uniformly distributed therein (a) a rhodium complex hydroformylation 
catalyst comprising rhodium in complex combination with carbon monoxide 
and with a ligand, (b) free ligand, (c) not more than a predetermined 
minor amount of at least one said optionally substituted aldehyde, and (d) 
an inert solvent that is less volatile than any optionally substituted 
aldehyde formed by the hydroformylation reaction but is more volatile than 
said ligand; 
continuously supplying carbon monoxide and hydrogen to said 
hydroformylation zone; 
continuously supplying said optionally substituted olefin to said 
hydroformylation zone; 
maintaining said hydroformylation zone under hydroformylation conditions; 
passing liquid hydroformylation medium to said product recovery zone; 
maintaining said product recovery zone under vaporisation conditions 
selected to cause vaporisation of said at least one optionally substituted 
aldehyde and at least a minor amount of said solvent; 
recovering from said product recovery zone (i) a vaporous stream containing 
a major amount of said at least one optionally substituted aldehyde and a 
minor amount of said solvent and (ii) a liquid stream containing said 
catalyst and said ligand; 
continuously recycling said liquid stream to said hydroformylation zone; 
controlling the vaporisation conditions in the product recovery zone so 
that the rate at which said solvent is recovered in said vaporous stream 
is at least equal to the rate of formation of aldehyde condensation 
by-products in said hydroformylation zone; and 
controlling the volume of liquid in said hydroformylation zone by supplying 
solvent thereto, if necessary, at a rate sufficient to maintain said 
substantially constant predetermined volume of liquid hydroformylation 
medium in said hydroformylation zone: 
whereby the amount of said at least one optionally substituted aldehyde in 
said hydroformylation zone is maintained at or below said predetermined 
minor amount so as to minimise the rate of formation of aldehyde 
condensation by-products and whereby said solvent is gradually displaced 
from the hydroformylation zone by high boiling materials including 
aldehyde condensation by-products formed by self-condensation of said at 
least one optionally substituted aldehyde. 
It will be appreciated by the skilled reader that the invention does not 
lie in the discovery of any new hydroformylation reaction system, insofar 
as the chemistry of such systems is concerned, but resides in use of an 
inert solvent having certain specific properties and in controlled 
vaporisation thereof in the product recovery step, and in controlling the 
volume of the hydroformylation reaction medium by supply, if necessary, of 
inert solvent thereto. In this way the concentration of aldehyde or 
aldehydes is kept as low as possible in the hydroformylation zone, which 
in turn results in a correspondingly low rate of formation of high boiling 
aldehyde condensation by-products which gradually displace the inert 
solvent as the reaction proceeds. The formation of high boiling aldehyde 
condensation by-products cannot be prevented entirely and these will 
inevitably accumulate in the liquid hydroformylation medium and will 
eventually cause problems in maintaining a constant volume of liquid 
hydroformylation medium in the hydroformylation zone, if the vaporiser 
temperature is maintained constant, or will eventually necessitate 
adoption of an unacceptable operating temperature and/or pressure of 
operation of the vaporiser simply in order to control the volume of the 
liquid hydroformylation medium. Hence eventually it will be necessary to 
shut down the plant and to recharge it with fresh liquid hydroformylation 
medium for one or other of these reasons. However, by selecting for use in 
the process of the invention a solvent which has a boiling point 
intermediate between that of the aldehyde product, or that of the highest 
boiling aldehyde product, and that of the ligand, the rate of formation of 
high boiling aldehyde condensation products can be minimised. Moreover, 
displacement of such solvent by high boiling aldehyde condensation 
by-products as these are formed can be accomplished without significant 
loss of ligand or catalyst from the circulating liquid and without 
exposing the catalyst to excessively high temperatures in the product 
recovery zone, since the temperature therein is limited by the boiling 
point of the solvent at the relevant operating pressure. By minimising in 
this way the rate of formation of aldehyde condensation by-products, which 
have, in general, boiling points that are similar to, or higher than, that 
of the ligand, it is possible to extend the length of production run, 
compared with conventional techniques in which the initial charge uses 
product aldehyde or aldehyde condensation by-products as solvent. Hence 
less frequent shutdowns of the plant are required when using the process 
of the invention than when using such conventional operating techniques. 
The process can be used with optionally substituted olefins containing from 
about 6 to about 20 carbon atoms, preferably from about 8 to about 16 
carbon atoms. Such compounds include not only olefins but also substituted 
olefins containing one or more substituents whose presence is not harmful 
to the hydroformylation catalyst under the selected hydroformylation 
conditions, for example ester or ether groups. The optionally substituted 
olefins may contain one or more alpha-olefinic groups of the formula 
--CH:CH.sub.2 or &gt;C:CH.sub.2 and/or may contain one or more internal 
olefinic groups of the formula &gt;C:C&lt;. Illustrative optionally substituted 
olefins include 1-hexene, cis- and trans-2- and -3-hexene, 1-heptene, cis- 
and trans-2-, -3-, and -4-heptene, 1-octene, cis- and trans-2-, -3-, and 
-4-octene, 1-nonene, cis- and trans-4-nonene, 1-decene, cis- and 
trans-4-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 
1-hexadecene, 1-octadecene, 2-, 3-, 4- and 5-methyl-1-hexene, 
2-methyl-1-heptene, 2-methyl-2-heptene, 2-, 3-, and 4-methyl-1-pentene, 
2-, methyl-2-pentene, cis- and trans-3-methyl-2-pentene, 2-methyl-1- and 
-2-heptene, allyl t-butyl ether, allyl propionate, allyl n-butyrate, allyl 
caproate, and the like. 
In the hydroformylation of an olefin containing an alpha-olefinic group, 
such as 1-decene, the ligand is preferably a triarylphosphine, such as 
triphenylphosphine. However, when hydroformylating compounds containing 
one or more internal olefinic groups, such as trans-2-heptene, the ligand 
is preferably a triarylphosphite, such as triphenylphosphite, or a cyclic 
phosphite, such as one of the cyclic phosphites recommended in 
EP-A-0096988. 
The liquid reaction medium contains a rhodium complex hydroformylation 
catalyst comprising rhodium in complex combination with carbon monoxide 
and with the ligand. Such catalysts can be preformed and then introduced 
into the reaction medium or the active catalyst species can be prepared in 
situ from a suitable catalyst precursor, such as (2,4-pentane dionato) 
dicarbonyl rhodium (I). Such methods for preparing reactive catalyst 
species are well known in the art. 
The rhodium concentration in the reaction medium preferably ranges from 
about 20 ppm up to about 500 ppm or more, calculated as rhodium metal. 
However, in view of the expense of rhodium, the preferred rhodium 
concentration is from about 120 ppm up to about 300 ppm, calculated as 
rhodium metal. 
The reaction medium contains excess ligand. Usually the ligand:rhodium 
molar ratio is at least about 2:1, preferably 3:1 or higher, up to about 
100:1 or more. Preferably there is at least one mole of free ligand per 
mole of rhodium catalyst. Typically the concentration of ligand in the 
hydroformylation medium ranges from about 0.5% by volume, usually from at 
least about 1% by volume, up to about 50% by volume. For example, the 
ligand concentration may range from about 5% by volume to about 20% by 
volume when the ligand is a triaryl phosphine, such as triphenylphosphine, 
or is an alkyl diarylphosphine, such as hexyl diphenylphosphine, while 
somewhat lower ligand concentrations, for example from about 0.5% by 
volume up to about 10% by volume, may be preferred when a phosphite 
ligand, such as triphenylphosphite, or a cyclic phosphite ligand, such as 
one of those suggested for use in EP-B-0096988, is used. 
The inert solvent can be any inert solvent that has a boiling point that is 
higher than any aldehyde formed by the hydroformylation reaction but lower 
than the boiling point of the ligand. Preferably the boiling point of the 
solvent at the pressure prevailing in the product recovery zone is at 
least about 10.degree. C. higher than that of any aldehyde 
hydroformylation product at that pressure. Desirably it is also at least 
about 10.degree. C. lower than the boiling point of the ligand at the 
pressure prevailing in the product recovery zone. The product recovery 
zone may be operated at atmospheric pressure when a C.sub.6 olefin is used 
in the process of the invention. However, it is preferably operated at a 
sub-atmospheric pressure, particularly when a C.sub.8 or higher olefin is 
used in the process of the invention. 
The solvent is inert, that is to say it does not react with the aldehyde 
product or products or with any other component present in the liquid 
hydroformylation medium. Alcohols and other materials containing alcoholic 
hydroxyl groups, such as alkylene glycols, polyalkylene glycols, and 
mono-ethers and mono-esters thereof, are excluded from consideration since 
these materials may form high boiling cyclic or acyclic acetals with the 
aldehyde hydroformylation products and hence contribute to the problems 
associated with formation of high boiling by-products. As examples of 
suitable solvents there can be mentioned hydrocarbons, including paraffins 
and cycloparaffins, such as decane, dodecane, tetradecane, octadecane, 
(C.sub.1 - to C.sub.8 - alkyl)-decalins, (C.sub.6 -to C.sub.12 - 
alkyl)-cyclohexanes, and the like. Other suitable solvents include 
aromatic hydrocarbons, such as (C.sub.6 - to C.sub.12 - alkyl)-benzenes, 
(C.sub.1 - to C.sub.6 - alkyl)-naphthalenes, (C.sub.1 - to C.sub.6 - 
alkyl)-tetralins, o-terphenyl, m-terphenyl, diphenylmethane, and aryl 
naphthalenes, such as 1- or 2-phenylnaphthalene. Ethers are further 
examples of suitable inert solvents, including mixed aliphatic aromatic 
ethers. Examples are alkyl ethers of aromatic mono-, di- and polyhydroxy 
compounds, such as (C.sub.1 - to C.sub.16 - alkyl)-anisoles (e.g. 
1-methoxy-4-ethylbenzene, 1-methoxy-3-n-decylbenzene, and the like), 
di-(C.sub.1 - to C.sub.6 -alkoxy)-benzenes (e.g. 1,4-dimethoxy- and 
-diethoxybenzene and the like), (C.sub.1 - to C.sub.6 
-alkyl)-dimethoxybenzenes (e.g. toluhydroquinone dimethyl ether and the 
like), (C.sub.6 - to C.sub.12 -alkoxy)-benzenes, and (C.sub.1 - to 
C.sub.12 -alkoxy)-naphthalenes. Aliphatic and cycloaliphatic ethers are 
further examples of ethers which can be used as solvent in the process of 
the present invention. Typical aliphatic ethers include C.sub.12 - to 
C.sub.18 - dialkyl ethers (e.g. di-n-hexyl ether, di-n-octyl ether, 
di-n-nonyl ether, n-butyl n-decyl ether, and the like), and triethylene 
glycol dimethyl ether. As examples of cycloaliphatic ethers there can be 
mentioned (C.sub.6 - to C.sub.14 -alkyl)-tetrahydrofurans, and (C.sub.6 - 
to C.sub.14 -alkyl)-1,4-dioxanes. Also contemplated for use as the inert 
solvent are ketones. Examples of suitable ketones include mono- and 
di-(C.sub.1 - to C.sub.6 -alkyl) aryl ketones (e.g. acetophenone, 
4-t-butylacetophenone, propiophenone, p-methylpropiophenone, n-hexyl 
phenyl ketone, and the like), (C.sub.1 - to C.sub.4 -alkyl) substituted 
diaryl ketones (e.g. 2-methylbenzophenone), C.sub.10 to C.sub.18 dialkyl 
ketones, and the like. As further examples of suitable solvents there can 
be mentioned materials derived from the product aldehydes, including 
dimethyl acetals, diethyl acetals, 2-alkyl-1,3-dioxolanes, and 
2-alkyl-1,3-dioxanes derived from the product aldehyde or aldehydes or 
from an aldehyde of lower molecular weight than the product aldehyde or 
aldehydes. Also contemplated for use as inert solvent in the process of 
the invention are aldehyde condensation products formed in 
hydroformylation of C.sub.2 to C.sub.5 olefins, for example aldehyde 
condensation products of the type discussed in U.S. Pat. No. 4,148,830 
formed by hydroformylation of propylene or of 1-butene. Mixtures of two or 
more solvents can be used. 
It will be appreciated by the skilled reader that not every solvent in the 
above list can be used with every ligand and for hydroformylation of every 
C.sub.6 or higher olefin. Generally speaking it will be necessary to 
select as a solvent a compound having a molecular weight which is, in 
general terms, intermediate between that of the product aldehyde or 
aldehydes and that of the ligand. In addition it will usually be preferred 
to select, if possible, a solvent whose boiling point is closer to that of 
the aldehyde product, or to that of the highest boiling aldehyde product, 
under the conditions prevailing in the product recovery zone than to that 
of the ligand. In this way the maximum temperature to which the 
catalyst-containing medium is exposed in the product recovery zone is kept 
as low as possible. 
Boiling points of some typical aldehydes which can be produced by the 
process of the present invention are listed below: 
______________________________________ 
Aldehyde Boiling point 
______________________________________ 
n-heptanal 59.6.degree. C. 
at 30 mm Hg (0.040 bar) 
-n-octanal 72.degree. C. 
at 20 mm Hg (0.027 bar) 
-n-nonanal 93.5.degree. C. 
at 23 mm Hg (0.031 bar) 
-n-decanal 81.degree. C. 
at 7 mm Hg (0.009 bar) 
-n-undecanal 117.degree. C. 
at 18 mm Hg (0.023 bar) 
-n-dodecanal 100.degree. C. 
at 3.5 mm Hg (0.005 bar) 
-n-tridecanal 
156.degree. C. 
at 17 mm Hg (0.017 bar) 
-n-tetradecanal 
166.degree. C. 
at 24 mm Hg (0.032 bar) 
______________________________________ 
Boiling points of typical ligands are as follows: 
______________________________________ 
Ligand Boiling point 
______________________________________ 
Triphenylphosphine 
188.degree. C. 
at 1 mm Hg (0.001 bar) 
Triphenylphosphite 
200-201.degree. C. 
at 5 mm Hg (0.007 bar) 
Tri- -o-cresylphosphite 
238.degree. C. 
at 11 mm Hg (0.015 bar) 
Tri- -p-cresylphosphite 
250-255.degree. C. 
at 10 mm Hg (0.013 bar) 
______________________________________ 
Boiling points of typical solvents are: 
______________________________________ 
Solvent Boiling point 
______________________________________ 
-n-decane 57.6.degree. C. 
at 10 mm Hg (0.013 bar) 
-n-dodecane 91.5.degree. C. 
at 10 mm Hg (0.013 bar) 
-n-tetradecane 
121.9.degree. C. 
at 10 mm Hg (0.013 bar) 
-n-octadecane 
173.5.degree. C. 
at 20 mm Hg (0.027 bar) 
heptylbenzene 116.degree. C. 
at 12 mm Hg (0.016 bar) 
dodecylbezene 185-188.degree. C. 
at 15 mm Hg (0.020 bar) 
1-methylnaphthalene 
107.4.degree. C. 
at 10 mm Hg (0.013 bar) 
2-methylnaphthalene 
104.7.degree. C. 
at 10 mm Hg (0.013 bar) 
2-methyltetralin 
99-101.degree. C. 
at 13 mm Hg (0.017 bar) 
-o-terphenyl 160-170.degree. C. 
at 2 mm Hg (0.003 bar) 
diphenylmethane 
125.5.degree. C. 
at 10 mm Hg (0.013 bar) 
1-phenylnaphthalene 
190.degree. C. 
at 12 mm Hg (0.016 bar) 
2-phenylnaphthalene 
185-190.degree. C. 
at 5 mm Hg (0.007 bar) 
1-methoxy-4-ethylben- 
83-84.degree. C. 
at 16 mm Hg (0.021 bar) 
zene-di- -n-octyl ether 
286-287.degree. C. 
at 760 mm Hg (1.013 bar) 
triethylene glycol 
224-227.degree. C. 
at 760 mm Hg (1.013 bar) 
dimethyl ether 
1,4-dimethoxybenzene 
109.degree. C. 
at 20 mm Hg (0.027 bar) 
1,4-diethoxybenzene 
246.degree. C. 
at 760 mm Hg (1.013 bar) 
hexyl phenyl ether 
130.degree. C. 
at 22 mm Hg (0.029 bar) 
1-methoxynaphthalene 
135.degree. C. 
at 10 mm Hg (0.013 bar) 
2-methoxynaphthalene 
138.degree. C. 
at 10 mm Hg (0.013 bar) 
1-ethoxynaphthalene 
136-138.degree. C. 
at 14 mm Hg (0.019 bar) 
2-ethoxynaphthalene 
148.degree. C. 
at 10 mm Hg (0.013 bar) 
1-ethoxynaphthalene 
167.degree. C. 
at 18 mm Hg (0.024 bar) 
2-propoxynaphthalene 
144.degree. C. 
at 10 mm Hg (0.013 bar) 
acetophenone 79.degree. C. 
at 10 mm Hg (0.013 bar) 
4- .sub.- t-butylacetophenone 
136-138.degree. C. 
at 20 mm Hg (0.027 bar) 
propiophenone 91.6.degree. C. 
at 10 mm Hg (0.013 bar) 
-p-methylpropiophenone 
120.degree. C. 
at 18 mm Hg (0.024 bar) 
2-methylbenzphenone 
128.degree. C. 
at 12 mm Hg (0.016 bar) 
______________________________________ 
A mixture of aldehyde condensation products produced as by-products in the 
hydroformylation of propylene by the process of U.S. Pat. No. 3,527,809 is 
available from Union Carbide Corporation of Old Ridgebury Road, Danbury, 
Conn. 06817, United States of America, under the trade name "Filmer 351". 
This mixture is suitable for use in the process of the invention. It boils 
at 263.5.degree. C. at 760 mm Hg (1.013 bar). 
Although triphenylphosphine can be used as ligand when hydroformylating 
terminal olefins containing up to about 12 carbon atoms, it may be 
desirable to use a higher molecular weight ligand when hydroformylating 
higher olefins, for example a tri(alkyl- or alkoxyphenyl)-phosphine, such 
as tri-p-tolyl phosphine or tri-p-methoxyphenylphosphine, or a 
tri-halophenylphosphine, such as tri-(p-chlorophenyl)-phosphine, in place 
of triphenylphosphine. Other suitable phosphine ligands are mentioned, for 
example, in U.S. Pat. No. 3,527,809. Similarly, when using a phosphite 
ligand in the process of EP-A-0096987, another of the phosphites mentioned 
therein and having a higher molecular weight than triphenylphosphite may 
be substituted for triphenylphosphite in the process of the present 
invention. Similarly, it is possible to use in the process of the present 
invention any of the cyclic phosphites mentioned in EP-A-0096988 or 
EP-A-0096986 in place of the preferred ligand disclosed therein, i.e. 
4-ethyl-2,6,7-trioxa-bicyclo-[2,2,2]-octane. 
In operation of the process of the invention it will usually be desirable 
to select a ligand which has, at the pressure prevailing in the product 
recovery zone, a boiling point at least 20.degree. C. higher than any 
product aldehyde produced in the hydroformylation zone and to select an 
inert solvent that has, at the same pressure, a boiling point that is at 
least 10.degree. C. higher than that of any product aldehyde but lower 
than that of the chosen ligand. 
In operation of the process of the invention, the liquid hydroformylation 
medium will contain, in addition to the rhodium complex hydroformylation 
catalyst, free ligand and inert solvent, also unreacted olefin and product 
aldehyde or aldehydes, besides by-products, including hydrogenation 
products (e.g. alkanes) and "heavies", including aldehyde condensation 
by-products formed by condensation of the product aldehyde or aldehydes, 
for example "trimer III" and "trimer IV" type products of the kind 
disclosed in U.S. Pat. No. 4,148,830. 
In the process of the invention the vaporous stream recovered from the 
product recovery zone contains, in addition to the desired optionally 
substituted aldehyde or aldehydes and any materials with lower boiling 
points than the product aldehyde or aldehydes, such as unreacted starting 
olefin and minor amounts of any hydrogenation by-product thereof, also a 
minor amount of inert solvent. Such solvent is usually recovered in a 
downstream solvent recovery zone, which may be located either immediately 
downstream from the product recovery zone or downstream from a subsequent 
process step, such as downstream from a hydrogenation step or downstream 
from aldolisation, dehydration, and hydrogenation steps, depending upon 
whether the desired end product is an alcohol having the same number of 
carbon atoms as the product aldehyde or aldehydes or an alcohol having 
twice as many carbon atoms as the product aldehyde or aldehydes. When 
using a ketone solvent it is preferable to locate the solvent recovery 
zone immediately downstream from the product recovery zone since the 
ketone will otherwise undergo at least partial hydrogenation in passage 
through an aldehyde hydrogenation zone and hence yield a secondary 
alcohol; in other words the ketone will be converted into a non-inert 
solvent. 
It is possible so to operate the process that the rate of removal of 
solvent in the vaporous stream from the product recovery zone is 
substantially equal to the rate of formation of aldehyde condensation 
products. In this case no make up solvent is required in order to maintain 
the predetermined volume of liquid hydroformylation medium in the 
hydroformylation zone. 
Alternatively it is possible to operate the process such that the rate of 
removal of inert solvent in the vaporous stream from the product recovery 
zone exceeds the rate of formation of aldehyde condensation by-products. 
In this case the volume of liquid hydroformylation medium can be 
maintained constant in the hydroformylation zone by supplying fresh 
solvent or solvent recovered in the downstream solvent recovery zone as 
make up solvent. 
We have found that, under hydroformylation conditions, the formation of 
aldehyde condensation by-products is approximately second order with 
respect to aldehyde concentration. Hence, in order to maintain the rate of 
formation of aldehyde condensation by-products as low as possible, it will 
usually be preferred to select a rate of recovery of the liquid 
hydroformylation medium from the hydroformylation zone and to adjust the 
rate of recycle of catalyst containing solution and, if necessary, the 
rate of supply of solvent to the hydroformylation zone so as to maintain 
in the hydroformylation zone a product aldehyde concentration of not more 
than about 2 gram moles per liter of reaction medium, typically from about 
1 to about 2 gram moles of aldehyde per liter of reaction medium. 
The hydroformylation zone may comprise a single reactor. Alternatively it 
may comprise two or more reactors connected, for example, in series. 
The hydroformylation zone is operated under hydroformylation conditions, 
such hydroformylation conditions being selected in dependence upon the 
nature of the olefin, the ligand, the rhodium concentration and other 
design factors, as will be immediately apparent to the man skilled in the 
art. For details of typical hydroformylation reaction conditions reference 
should be made to U.S. Pat. No. 3,527,809, 4,148,830, 4,247,486, 
EP-A-0096986, EP-A-0096987, EP-A-0096988 and other patent specifications 
describing rhodium catalysed hydroformylation reactions. Generally 
speaking such conditions include use of a temperature in the range of from 
about 40.degree. C. to about 160.degree. C. and a pressure in the range of 
from about 1 bar absolute to about 100 bar absolute. 
The product recovery zone is preferably operated under reduced pressure as 
a distillation zone or as an evaporation zone. It is preferably operated 
at a sub-atmospheric pressure in order to limit as far as possible the 
exposure of catalyst and of aldehyde to elevated temperatures in excess of 
the temperature in the hydroformylation zone. Typical operating conditions 
in the product recovery zone include use of temperatures in the range of 
from about 60.degree. C. to about 200.degree. C., pressures in the range 
of from about 0.0001 bar to about 0.5 bar, and residence times which are 
as short as possible, preferably in the range of from about 2 seconds to 
about 5 minutes, for example in the range of from about 5 seconds to about 
2 minutes. Preferably the product recovery zone is operated at a 
temperature which is no higher than about 160.degree. C. and even more 
preferably no higher than about 150.degree. C. Due precautions must be 
taken in the product recovery zone to obviate loss of catalyst solution 
components with the hydroformylation product and inert diluent vapours due 
to entrainment of droplets in the vaporous stream. The product recovery 
zone can comprise a distillation column but preferably comprises a wiped 
film or falling film evaporator, since such evaporators enable residence 
times in the product recovery zone to be minimised. 
The solvent recovery zone may follow immediately after the product recovery 
zone. In this case the solvent recovery zone can comprise a fractionation 
zone, from which the product aldehydes are recovered overhead, together 
with unreacted olefin or olefins and hydrogenation by-products, whilst the 
solvent appears as a bottom product therefrom. 
It is also feasible to subject the mixture of aldehyde and solvent to 
further processing steps, for example, to hydrogenation or to 
aldolisation, dehydration and hydrogenation, so as to produce the 
corresponding alcohol. In this case the solvent recovery zone can follow 
such further processing steps. Distillation is a suitable method of 
solvent recovery.

FIG. 1 of the drawings is a flow diagram of a laboratory scale apparatus 
for studying continuous hydroformylation of olefins using a rhodium 
complex hydroformylation catalyst which can be used for operation of the 
process of the invention. This includes a 2-liter stainless autoclave 1 
fitted with an internal cooling coil 2 and with a magnetically coupled 
stirrer 3 which is arranged to be driven by a motor 4. The stirrer 3 has a 
hollow shaft and is designed so as to induce gas down its hollow shaft 
from the head space above the liquid level within autoclave 1 and to 
disperse such gas into the liquid charge within autoclave 1. Autoclave 1 
and its contents can be heated by means of a thermostatically controlled 
oil bath 5, whose temperature is controlled to be approximately 2.degree. 
C. above the temperature desired in autoclave 1. Fine control of the 
temperature of the liquid charge in autoclave 1 is achieved by allowing 
cooling water, supplied in line 6, to flow through cooling coil 2 by 
opening valve 7 which is controlled by a temperature controller 8. 
Liquid 1-decene is supplied to reactor 1 in line 9 and a CO/H.sub.2 mixture 
is fed to the apparatus in line 10. The olefin and the mixture of CO and 
hydrogen supplied to the apparatus is previously subjected to rigorous 
purification for the removal therefrom of sulphurous and halogenated 
impurities which are known to act as catalyst poisons for rhodium complex 
hydroformylation catalysts. The resulting mixture of olefin, CO and 
hydrogen passes on in line 11, is admixed with catalyst recycle solution 
in line 12, and then flows into autoclave 1 by way of line 13. Liquid 
reaction medium is recovered from autoclave 1 in line 14 and is cooled in 
cooler 15, which is supplied with cooling water in line 16. The position 
of the lower end of line 14 within autoclave 1 enables the volume of 
liquid in autoclave 1 to be set at a predetermined level during operation. 
The cooled reaction medium in line 16 then enters vapour/liquid separator 
17 in which some of the dissolved gases flash off and are recovered in 
line 18 to exit the apparatus via pressure control valve 19. The 
substantially degassed liquid phase then passes in line 20 via pressure 
reduction valve 21, which is under the control of level controller 22, to 
line 23 and thence to evaporator 24 which is operated under 
sub-atmospheric pressure. 
Product aldehydes are vaporised in evaporator 24, together with a 
proportion of any other component present whose boiling point is lower 
than that of the ligand, whilst rhodium catalyst, ligand and aldehyde 
condensation by-products, are recovered in line 25 for recycle to line 12 
with the aid of pump 26. If desired the bottom of evaporator 24 can be 
filled with glass beads, or a similar inert filling, so as to reduce the 
volume of liquid therein and hence reduce the residence time of the liquid 
at elevated temperature in evaporator 24. 
Hot oil is supplied in line 27 at 150.degree. C. and is circulated through 
heating coil 28 at a rate such that the level of liquid in the bottom of 
evaporator 24 tends to fall. A vaporous mixture containing product 
C.sub.11 aldehydes and other "light" materials present, such as unreacted 
1-decene, isomerised C.sub.10 internal olefins, such as cis- and 
trans-2-decane, and hydrogenation produce (i.e. n-decane) passes upwards 
through packing 29 and is partially condensed by evaporator reflux 
condenser 30. The reflux stream induced by condenser 30 flowing down over 
packing 29 ensures that substantially all materials with boiling points 
higher than the C.sub.11 aldehyde products, including the ligand, are 
condensed and returned to the bottom of evaporator 24 and that only an 
amount of material with a boiling point higher than the C.sub.11 aldehyde 
products which corresponds to the rate of formation of aldehyde 
condensation by-products passes overhead in the vaporous stream in line 34 
with the C.sub.11 aldehyde products. Condenser 30 is supplied with cooling 
water in line 31 under the control of a valve 32 which is in turn 
controlled by a level controller 33. Uncondensed vapours are recovered 
overhead from evaporator 24 in line 34 and pass through condenser 35 which 
is supplied with cooling water in line 36. The resulting condensate is 
collected in a graduated product vessel 37, from which liquid condensate 
is removed for analysis from time to time in line 38 by means of pump 39. 
Line 40 is connected to a vacuum pump (not shown) by means of which 
evaporator 24 and product vessel 37 are maintained under reduced pressure. 
Condenser 41, which is supplied with chilled cooling water in line 42, 
serves to minimise loss of condensible materials in line 40. 
At start up of the apparatus 1.15 liters of hydroformylation medium 
containing 10% w/w triphenylphosphine and 250 ppm w/w rhodium metal in the 
form of hydridocarbonyl tris-(triphenylphosphine) rhodium (I), i.e. 
HRh(CO)(PPh.sub.3).sub.3, or of a catalyst precursor, such as (2,4-pentane 
dionato) dicarbonyl rhodium (I), is charged to autoclave 1 which is then 
purged of air through vent valve 43 by repeated pressurisation and then 
depressurisation with nitrogen, followed by passage of nitrogen through 
lines 10, 11, 13, 14 and 18, valve 19 being opened for this purpose. 
During this operation approximately 150 ml of liquid is transferred to 
vapour/liquid separator 17. Hence the "dynamic volume" of liquid in the 
autoclave 1 under operational conditions is approximately 1 liter. 
Level controller 22 is then actuated so that liquid begings to accumulate 
in the bottom of evaporator 24. Recycle pump 26 is then started to return 
liquid to the autoclave 1 via lines 25 and 12. At the same time the vacuum 
pump is started so as to evacuate product vessel 37 and evaporator 24 to a 
pressure of 10 mm Hg (0.0133 bar). When the desired operating pressure has 
been achieved in evaporator 24 and product vessel 39, pump 26 is adjusted 
until its flow rate is 400 ml/hour. Liquid is allowed to circulate while 
50 liters hour of nitrogen is supplied by way of line 10 to autoclave 1, 
thereby lifting liquid via line 14 to liquid/vapour separator 17. Next the 
pressure control valve 19 is adjusted to give a reactor pressure of 110 
psig (8.58 bar) and autoclave 1 is heated to 80.degree. C. using the 
external oil bath 5. The gas supply in line 10 is then changed to 50 
liters hour of a mixture of carbon monoxide and hydrogen, whilst 400 
ml/hour of 1-decene is supplied through line 9. 
The gas supply is increased progressively to approximately 84 liters/hour 
so that about 5 to 6 liters/hour of gas is vented through line 18. The 
temperature of oil bath 5 is then held at about 82.degree. C. while water 
is supplied through cooling coil 2 to maintain the temperature in 
autoclave 1, as detected by temperature controller 8, at 80.degree. C. 
Hot oil is circulated at 153.degree. C. through line 27 at a rate such that 
the level in evaporator 24 tends to fall by reason of the material 
boiling. The condensate collecting in product vessel 37 contains the net 
"make" of C.sub.11 "Oxo"-aldehydes, by-product paraffin and internal 
olefin. Packing 29 serves to prevent any triphenylphosphine, entrained 
solution droplets and heavy by-product materials reaching product vessel 
37. 
During the initial start-up period the ratio of hydrogen and carbon 
monoxide in the feed gas supplied in line 10 is adjusted slightly so that 
the H.sub.2 :CO molar ratio in line 18 is 3:1. After about 10 hours 
operation the system is found to operate in a steady manner. 
The invention is further illustrated in the following Examples in which the 
apparatus of FIG. 1 is used. 
COMATIVE EXAMPLE A 
The liquid charged to autoclave 1 is a solution of 10% w/w of 
triphenylphosphine in 1-undecanal containing 250 ppm w/w of dissolved 
rhodium, the rhodium being added in the form of HRh(CO)(PPh.sub.3).sub.3. 
After steady state operation conditions are achieved the reactor is 
operated for 30 days under the following conditions: 
______________________________________ 
Reactor Temperature 
81.degree. C. .+-. 2.degree. C. 
ppm w/w rhodium 248 .+-. 5 
% w/w triphenylphosphine in 
10.1 .+-. 0.6 
reactor 
Hydrogen partial pressure in 
90 psi .+-. 2 (6.21 bar .+-. 0.14) 
reactor 
Carbon monoxide partial 
30 psi .+-. 1.2 (2.07 bar .+-. 0.08) 
pressure 
Residence time in evaporator 24 
30 seconds 
______________________________________ 
Under these conditions the following results are obtained: 
______________________________________ 
% olefin converted 84.0 .+-. 2 
% -n-aldehyde selectivity 
85.5 .+-. 1 
in product 
% iso-aldehyde selectivity 
8.2 .+-. 0.3 
in product 
% (decane + internal decenes) 
6.3 .+-. 0.2 
______________________________________ 
Analysis of the reactor solution by gas chromatography shows that 
"heavies", i.e. aldehyde condensation by-products, accumulate in the 
reactor solution in the manner set out in Table 1 below. The method of 
analysis uses a Pye Unicam PU 4500 capillary column chromatograph fitted 
with a flame ionisation detector and using helium as the carrier gas. The 
column is a 25 meter SE54 capillary column with an inside diameter of 0.32 
mm and a film thickness of 0.23 .mu.m. With an inlet splitter ratio of 
100/1 and an inlet carrier gas pressure of about 2.1 bar absolute 0.5 
.mu.l samples are subjected to temperature programming as follows: 5 
minutes isothermal operation at 150.degree. C., followed by an increase in 
temperature to 300.degree. C. at 20.degree. C./minute, followed by a final 
10 minutes isothermal stage at 300.degree. C. 
TABLE 1 
______________________________________ 
Days of operation 
% w/v "heavies" in reactor solution 
______________________________________ 
5 2.81 
10 5.50 
15 7.91 
20 10.10 
25 12.32 
30 14.42 
______________________________________ 
By extrapolation from this data it is possible to calculate that the 
"heavies" concentration will reach 40% by volume in approximately 133 
days, at which stage it will probably become expedient to shut the reactor 
down because it will have become difficult or impossible to control the 
volume of liquid in the apparatus. 
EXAMPLE 1 
The procedure of Comparative Example A is repeated except that the 
1-undecanal used as solvent in the initial liquid charge is replaced by a 
60:40 undecanal:diphenyl ether v/v mixture. The reaction conditions are as 
set out above in the Comparative Example. In this case a minor amount of 
diphenyl ether passes overhead in line 34, at a rate corresponding to the 
rate of formation of aldehyde condensation by-products, and collected in 
product vessel 37. The build-up of "heavies" in the reaction medium is 
monitored in a similar manner to that used in Comparative Example A with 
the results set out below in Table 2. 
TABLE 2 
______________________________________ 
Days of operation 
% w/v "heavies" in reactor solution 
______________________________________ 
5 0.70 
10 1.45 
15 2.17 
20 2.88 
25 3.61 
30 4.36 
______________________________________ 
From these figures it is possible to calculate by extrapolation that it 
will take approximately 270 days before the "heavies" level reaches 40% 
v/v of the reactor solution and it becomes expedient to shut down the 
reactor because all of the diphenyl ether will have been displaced from 
the reaction system and it will become increasingly difficult to control 
the volume of liquid in the apparatus. In addition, the temperature of the 
liquid in the bottom of evaporator 24 will tend to increase after all the 
diphenyl ether has been displaced, thereby increasing the risk of catalyst 
deactivation and also the rate of formation of aldehyde condensation 
by-products. 
It will be readily apparent to those skilled in the art from these results 
that, by using an inert solvent in accordance with the teachings of the 
invention it is possible to prolong substantially the length of a 
hydroformylation run, thus extending the interval between successive 
shutdowns of the plant and increasing the annual production capacity of 
the plant. 
COMATIVE EXAMPLE B 
The apparatus used in this experiment was constructed as illustrated 
diagrammatically in FIG. 1 except that the volume of autoclave 1 was 300 
cc which was charged at start up with 175 ml of a solution containing 10% 
w/v triphenylphosphine in n-nonanal containing 200 ppm w/w rhodium added 
as HRh(CO)(PPh.sub.3).sub.3. Instead of n-decene, however, the olefin was 
liquid 1-octene; this was fed to autoclave 1 at an initial liquid feed 
rate of 58 ml/hr. The feed gas was a mixture of H.sub.2, CO and N.sub.2. 
Under steady state conditions the reactor temperature was held at 
120.degree. C., with a total pressure of 195 psia (13.44 bar). The 
hydrogen partial pressure was 60 psia (4.13 bar), whilst that of carbon 
monoxide was 15 psia (1.03 bar) and that of nitrogen and the organic 
components was 120 psia (8.27 bar). The liquid recycle rate in line 12 was 
90 ml/hr, whilst the temperature in evaporator 24 was maintained by 
supplying hot oil at a temperature of from about 110.degree. C. to about 
120.degree. C. in line 27. The pressure in evaporator 24 was 10 mm Hg 
(0.0133 bar). Using an analysis technique similar to that described above 
in Comparative Example A, the concentrations of aldehyde (i.e. n-nonanal) 
and of "heavies" (i.e. mainly C.sub.18 -dimers and C.sub.27 -trimers) were 
determined from time to time after steady state operating conditions had 
been achieved. The results are plotted in FIG. 2. After 47 hours it was 
necessary to reduce the 1-octene feed rate to 30 ml/hr in order to 
maintain the temperature in evaporator 24 below 120.degree. C. 
It will be noted from FIG. 2 that, although the rate of "heavies" formation 
was initially quite low, this rate increased quite rapidly after about 24 
hours of operation to a maximum rate. Moreover it appeared that the 
formation of C.sub.18 and higher "heavies" results from an approximately 
second order reaction. 
Due to the rapid increase of the "heavies" concentration, it would soon 
have been necessary, probably no more than about 24 hours later, to shut 
down the reaction system because it would have become necessary to raise 
the temperature of evaporator 24 appreciably above 120.degree. C., with a 
consequent increased risk of thermal deactivation of the rhodium complex 
catalyst, in order to evaporate the C.sub.18 and higher "heavies" and to 
prevent them from flooding the system. 
It will be appreciated by the skilled reader that the operating conditions 
used in Comparative Example B were selected so as to provide an 
accelerated rate of "heavies" formation such that the experiment could be 
completed within a reasonable time. In practice, operating conditions for 
a commercial plant could be somewhat less severe; in particular, an 
operating temperature appreciably lower than 120.degree. C. (e.g. about 
80.degree. C. to about 105.degree. C.) could be used, which would result 
in a correspondingly lower rate of "heavies" formation. 
EXAMPLE 2 
Using the same apparatus as was used in Comparative Example B, autoclave 1 
was charged with a rhodium-free solution containing 10% w/v 
triphenylphosphine dissolved in a 50/50 v/v mixture of Filmer 351 and 
n-nonanal. (Filmer 351 is a mixture of aldehyde condensation products of 
the type discussed in U.S. Pat. No. 4,148,830, obtained as a by-product of 
the hydroformylation of propylene; it is mainly a mixture of C.sub.12 
"trimer III" and "trimer IV" type products and has a boiling point at 10 
mm Hg (0.0133 bar) of approximately 140.degree. C. "Filmer" is a trade 
name of Union Carbide Corporation of Old Ridgebury Road, Danbury, Conn. 
06817, United States of America). 
Pump 26 was switched on in order to circulate liquid through the apparatus 
and autoclave 1 was heated to 88.degree. C. under a total gas pressure of 
195 psia (13.44 bar). The hydrogen partial pressure, the carbon monoxide 
partial pressure, and the nitrogen partial pressure were as in Comparative 
Example B. 
When the apparatus had reached equilibrium; after about 3 hours from the 
start of the experiment, further n-nonanal was introduced into autoclave 1 
by way of line 9 at a rate of 58 ml/hr, thus instigating C.sub.9 -aldehyde 
vaporisation in evaporator 24. 
Approximately 9 hours after the start of the experiment, the n-nonanal feed 
was changed to a solution of approximately 3.0% v/v Filmer 351 in 
n-nonanal. This concentration was sufficient to ensure that the rate of 
removal of Filmer 351 by vaporisation in evaporator 24 balanced its rate 
of introduction, along with n-nonanal, by way of line 9. In this way a 
substantially constant liquid composition was achieved in autoclave 1 such 
that the n-nonanal concentration in the liquid medium was approximately 
30%, corresponding to the aldehyde concentration at the end of Comparative 
Example B. 
About 19 hours after the start of the experiment rhodium, in the form of 
HRh(CO)(PPh.sub.3).sub.3, was charged to autoclave 1 so as to result in a 
rhodium concentration of 200 ppm w/v, calculated as rhodium metal. The 
feed to the reactor was then changed to 58 ml/hr of a 3% v/v solution of 
Filmer 351 in 1-octene. 
The temperature of autoclave 1 was raised to 120.degree. C. and hot oil was 
circulated through evaporator 24, also at 120.degree. C. 
In a manner similar to that described above in Comparative Example A, the 
composition of the reaction solution was determined. The results are 
plotted in FIG. 3. 
It will be seen that the rate of build up of "heavies", which are plotted 
in FIG. 3 as "DIMER+TRIMER" (i.e. a mixture of C.sub.18 and C.sub.29 
aldehyde condensation products), is significantly lower in Example 2 than 
in Comparative Example B. Thus it will be possible to continue to operate 
the process for a considerably longer period of time, under the conditions 
of Example 2, than when using the conditions of Comparative Example B. 
It will be appreciated by those skilled in the art that the conditions 
selected in Example 2 are more severe than the conditions preferred for 
industrial operation of the process, having been selected so as to be 
directly comparable with the conditions of Comparative Example B (which 
were in turn selected with the specific aim of causing a significant rate 
of formation of C.sub.18 and higher "heavies" in the reaction solution 
such that the experiment would be completed within a reasonable time). 
Hence, in operating a commercial reactor, a temperature of, for example, 
about 105.degree. C. could be used, thus resulting in a correspondingly 
lower rate of formation of C.sub.18 and higher "heavies" than is indicated 
in FIG. 3. In this way the period for which a commercial reactor could be 
operated would be extended considerably beyond the length of time that 
could be achieved under conditions of Example 2 before the reaction had to 
be shut down either due to flooding of the reactor with "heavies" or to 
deactivation of the catalyst due to use of excessively high temperatures 
in evaporator 24.