Note: Descriptions are shown in the official language in which they were submitted.
.7`~
3~59
Backgroul,d of the Invention
Processes for hydroformylating aD olefin to prep~re a carbonyl
derivative containing one carbon atom more than the parent olefin by
reacting the olefin with synthesis gas in the presence of a Group VIII
metal, e. g. rhodium, in complex combination with an organic ligand,
carbon monoxide also being a component of the catalyst complex, are
well known in the art and of growing industrial importance. This
technology is summarized, for example, in U. S. Patent No. 3, 527, 809
to Pruett et al. The olefin reactant is contacted with the catalyst and
the synthesis gas (a mixture of carbon monoxida and hydrogen~ in the
presence of a liquid reaction medium, which may or may not cornprise
a separate inert liquid solvent species. A gas comprising the carbon
monoxide and hydrogen is typically bubbled through the liquid reaction
medium which is contained in a hydroformylation reactor which can be
mechanically stirred or which may be agitated solely by the action of
reactant gas being bubbled therethrough. The gas, in addition to
hydrogen and carbon monoxide, may also contain vapors of the reactant
olefin, in a proportion which will depend upon such factors as reaction
conversion rate and the volatility of the olefin.
Z0 The aldehyde hydroformylation product can be recovered from the
liquid hydroformylation reaction medium in various ways, but, especi~lly
when the aldehyde i8 of comparatively low molecular weight, e. g., when
it contains from three to about seven carbon atoms and especially when it
contains from three to about five carbon atoms, it is conveniently stripped
Z5 out in vapor form by distillation, e~Taporation, or, especially, by being
stripped out of the hydroformylation reaction zone in the gases which are
being bubbled through the liquid contained therein. ~lershn~an et al. have
described this technology in "I &EC Product Research and Development"
1~ ~3~59
8, pp 372-375 (1969) in a discu9sion of the hydroformylation of propylene
in a gas-sparged reactor.
In more recent years varioùs patents and other publications have
appeared directed to the use of special reaction solvents and/or special
5 techniques for stripping the aldehyde product out of the liquid reaction
medium. For example, U. S. Patent 4,148, 830 (Pruett et al. ) recom-
mends using high-boiling reaction by-products as the reaction solvent,
with the aldehyde product being subsequently recovered from the reaction
medium in a separate vaporization operation.
The employment of intensive stripping of the liquid reaction mi~ture
not only to recover the aldehyde product but also to reduce the formation
of high-boiling reaction by-products is taught in U. S. '1,151,209 to
Paul et al., such intensive stripping serving not only to recover the
product but also to reduce catalyst deactivation. The stripping can be
15 accomplished by distillation, simple evaporation, or, especially, by the
stripping action of the reaction gases being sparged through the liquid
contained in the hydroformylation reactor. Any of a number of inert
reaction solvent~ can be employed if desired, including in particular
polyalkylene glycols of molecular weight of at least about 500, although
20 the invention itself lies fundamentally in the degree of stripping which
is employed and not in choice of the solvent. As the primary control
for the degree of stripping, Paul et al. employ the ratio of phosphorus
contained in high-boiling reaction by-products to the phosphorus contained
in the ligand which is present (the reaction system with which the patentees
25 are concerned being one which employs triorganophosphine ligand~.
Paul et al. supply no teachings regarding control of stripping when the
ligand employed is other than a triorganophosphine, and, so long as the
specified high stripping rate is employed, they are not concerned wi h
--2--
12385~ ~3
the identity of any separatel~-added solvent species which may be added
to the reaction system so long as ik is che~nically Lnert in the system,
compatible with the reactants and catalyst9, and sufficiently non-volatile
that it will not be removed overhead to any great extent dur~ng the
5 stripping operation.
There are additional factors affecting the maintenance of optimum
conditions in the stripping operation. Specifically and for example overly-
intensive stripping can lead to a condltion in which, depending in part upon
the proportions of the hydroformylation reaction vessel, the contained
10 liquid reaction medium becomes so expanded with gas bubbles that it
begins to be entrained out the top of the reactor with the exiting gases.
There is also continuing need for reliable means for reducing where
possible the energy requirements and the gas-handling apparatus re~uire-
ments of the reaction systems as taught in the prior art and as exemplified
15 by Paul et al.
It will also be seen that the control system of Paul et al. is essentially
directed to reaction systems where phosphorus-containing ligands are
employed, That i8, Paul et al. teach a process control system which relies
on monitoring the relative concentrations of certain phosphorus derivatives
20 in the liquid reaction medium with the result that in nonphosphorus l;gand
systems it would be necessary to seek other control parameters or, at best,
rely on analogies between the chemistry of organic compounds of phosphorus
and those of I for example, antimony.
It is, accordingly, an object of the present invention to provide a more
2~ precise and efficient reaction control method for hydroformylation reaction
systems aR discussed hereinàbove. It is a further object to provide a
method whereby the degree of reaction product stripping can be reliably
controlled without suffering the cost drawbacks of possible over-stripping
--3--
~.23~3S~
and the occasional difficulties with reaction liquid entrainInent sometimes
experienced in the prior art processes. Other objects will be apparent
from the following detailed dcscription.
Summary of the Invention
In accordance with the present invention the stripping employed in
recovering the aldehyde product from the liquid reaction mixture formed
by the hydroformylation of an alpha-ethylenically unsaturated compoun~
with a Group VIII metal catalyst in complex combination with an organic
ligand dissolved in a liquid reaction medium is facilitated, while main-
lo taining minimal formation of undesired high-boiling reaction by-products,
by incorporating into the reaction medium~an inert solvent which is of
relatively high molecular weight as will be further explained below. The
molecular weight of the added inert liquid, and the proportion of said inert
liquid which is employed, are so chosen that, when the stripping rate is
set at such a level that the liquid reaction product mixture being stripped
contains about 1 to 2 gram moles of hydroformylation product aldehyde per
liter, the mole fraction of product aldehyde in the reaction product mixture
will be about 0,4 to 0. 7 . The crux of the invention lies to a great extent
in using a high molecular weight inert liquid in substantial proportions
whereby, at a given (and relatively low) molar concentration of product
aldehyde in the mixture, its mole fraction in the mixture will, at the same
time, be relatively high because of the fact that even a large weight pro-
portion of the high molecular weight solvent will contribute to the mixture
only a very few moles. That is, addition of the high molecular weight
solvent has reduced the molar density of the mixture, i. e. the to~al moles
oi all components contained in a unit volume of the liquid. Thus, the case
of stripping out product aldehyde is greater from a mixture of low n~olar
den~ity comprising substantial quantities of the high molecular weight
--4--
~Z3~5~
solvent than would be the case if ~he solvent were a lower
molecular weight ma-terial present in the same weight proportion
and therefore causing a rela-tively high molar density in the
mixture. Hydroformylation reaction by-products such as conclen-
sation derivatives of the aldehyde are also stripped out more
easily by reason of the same considerations of enhanced mole
fraction obtaining in the presence of the low molar density
mixtures as compared with the higher molar density mixtures.
While a very low volatility is also desired in the added inert
solvent, as already known in the prior art, a high molecular
weight is also required in the present invention, and solvents
having low volatility but at the same time relatively low mole-
cular weight are not sufficient for the present purposes.
The net result of operating in this manner is that at, for
example, a given fixed rate of stripping gas or a given rate of
boilup in a stripping-type distillation, it is easier to maintain
a specified low molar concentration of aldehyde product in the
reaction medium than when the reaction medium is of a relatively
low molecular weight. The relatively low molar concentration of
product aldehyde which is easily maintained by the present method
also results in reduced formation of undesired condensation pro-
ducts formed from the aldehyde in the reaction medium.
Thus, in accordance with the present invention; there is
provided in a process for hydroformylating an olefin of 2 to about
20 carbon atoms having an ethylenic double bond in the alpha
position by reacting said olefin at about 80C to 150C and
superatmospheric pressure with carbon monoxide and hydrogen in
admixture with a liquid reaction medium comprising a high-boiling
inert reaction solvent containing an effective amount of a hydro-
formylation catalyst comprising a Group VIII metal in complexcon~ination with a monodentate or polydentate ligand comprising
-- 5 --
.~1
~38sg
triorganophosphine, triorganophospllite, triorganoarsine, or
triorganostibine moiety to form a liquid reac-tion product
mixture comprising said ligand, an aldehyde derivative of said
olefin, and said high-boiling inert reaction solvent while
continuously stripping said liquid reaction product mixture by
dis-tillation, evaporation, or gas stripping to recover vapors
comprising said aldehyde therefrom, the improvement which
comprises:
a) employing said high-boiling inert reaction solvent a
liquid which has a molecular weight of at least about 700 and
which is a solvent for said catalyst and said olefin, said
solvent being incorporated into said liquid rèaction medium in a
proportion of about 40% to 95~ by weight, and
b) controlling the rate of stripping at a level such
that, when the olefin is ethylene, the concentration of propion-
aldehyde maintained in the liquid reaction product mixture is
about 1 to 2 gram moles per liter or, when the olefin is propylene
or a higher alkene, the maintained concentration of the sum of
the corresponding normal and iso-aldehyde hydroformylation
derivatives is about 1 to 2 gram moles per liter.
Detailed Description and Preferred Embodiments
The present process improvement is directed to liquid-
phase catalytic hydroformylation processes broadly, and it will
be seen that the details of the particular reaction system being
dealt with are secondary. That is, the controlling parameters
comprise predominantly vapor pressure, solubility, and molecular
weight of the several system components rather than their chemi-
cal composition. The method is broadly applicable to any hydro-
formylation system in which the aldehyde product is to be separat
ed as a vapor from the liquid reaction medium in which it has
been formed.
- 5a -
i~;,
23859
The invention does not lie in the discovery of any new hydroformylation
reaction system insofar as the chemistry of such systems is concerned,
but only in an improved method for removing volatile reaction products
rapidly and efficiently from the reaction product mixture while inhibiting
5 by-product forma-tion. However, the following is a summary of the hydro-
formylation technology the operability of which is enhanced by application
of the present process improvement-
Group VIII metals broadly, particularly rhodium and ruthenium andespecially rhodium, are employed in organometallic comple~ces as cata-
10 lysts for the reaction of a synthesis gas (i.e., a mixture of hydrogen andcarbon monoxide) with alpha-olefins to form aldehyde derivatives of the
olefins which have one more carbon atom than the parent olefin. While
a wide range of olefinic feedstocks can be employed in such procssses,
including substituted olefins and especially olefins having no heteroatoms
15 other than oxygen, olefinic feedstocks of industrial importance comprise
predominantly alpha-olefinic hydrocarbons of 2 to about 20 carbon atoms,
especially 2 to about 8 carbon atoms. While the present process improve-
ment is broadly applicable to the hydroformylation of olefins of 2 to about
20 carbon atoms, considerations of vapor pressure at the temperatures
20 normally employed in hydroformylation reaction systems mean that, as
will be explained hereinbelow, its most useful applications are with olefins,
and especially olefinic hydrocarbons, of 2 to about 6 carbon atoms, Par
ticular utility obtains in processes for hydroformylating ethylene and
propylene. These known hydroformylation processes are carried out at
25 superatmospheric pressure, typically under a partial pressure of about
4 to 20 atmospheres of hydrogen and carbon monoxide combined and with
the molar ratio of hydrogen to carbon monoxide being about 0. 5 1 to 10:1.
The hydroformylation reaction temperature is normally within the range of
_6--
359
80C to 150C. It will be understood that the hydroformylation reaction
para~neters are explained here by way of general background and not as
limitations on the present process improvement, which does not have to
do directly with the hydroformylation reaction itself.
The liquid reaction medium or catalyst solution which is employed
comprises, as is already known in the art, (a~ the catalyst complex, (b?
typically, an excess of the organic ligand employed in forming the com-
plex over and above the amount required to complex the metallic com-
ponent of the catalyst, (c) the hydroformylation reaction product along
lO with by-products typically resulting from ~mdesired condensation o the
hydroformylation product aldehyde with itself, (d) a quantity of the olefin
being hydroformylated, in an amount varying with the molecular weight of
said olefin (the proportion of liquid olefin in the reaction medium usually
being greater with high molecular weight olefins than with lower alkenes
15 such as ethylene), and (e) in most systems involving the processing of
olefins of low to moderate molecular weight, an inert reaction solvent
With higher weight olefins such as, for example, octene, the olefin itsel~
in liquid phase can function as reaction solvent.
The catalyst contained in the reaction mixture can be, as known in
20 the art, any Group VIII metal complexed with an organi~ ligand. It will
be understood that, while the complex is characterized as comprising the
metal and the organic ligand, the active catalyst as it actually functions in
the reaction is a hydridocarbonyl. That is, the catalytic me~al is complexed
with hydrogen and carbon monoxide as well as with an organic ligand.
25 While other organic ligands can be employed, those of particular significance
comprise either monodentate or polydentate triorganophosphines, triorgano-
phosphites, triorganoarsines, or triorganostibines, with the phosphines and
phosphites being of particular industrial importance. Simple monodentate
--7--
~23~
phosphines and ~hosphites, as exemplified by triphenylphosphine
and triphenylphosphite, are commonly employed industrially. How-
ever, polydentate ligands have advantages in that large excesses
of ligand which are often used with the monodentate ligands are
not needed. For example, the phosphine-modified ferrocene-based
ligands as taught in U.S. 4,138,420 to Unruh et al., are applic~
able as well as the sterically restricted bidentate phosphorus-
containing ligands described in U.S. 4,139,565. Ligands modified
by the incorporation of electronegative substituents into the
molecule also have advantages, as set forth in U.S. 4,152,344 to
Unruh. The catalytic complex can be formed in situ in the hydro-
formylation reactor, or it can be performed, the exact nature and
origin of the hydroformylation catalyst being outside the scope of
the present invention. It should be mentioned, as prior art which
is slightly relevant to the present invention, that one mode of
introducing catalyst into the reaction system can, if desired,
entail the employment, as a solvent in which the catalyst is
introduced into the reaction system, of relatively low molecular
weight polyalkylene glycols, as disclosed in U.S. patent number
4,158,020 issued on June 12, 1979, by Stautzenberger et al. The
relevance of these low weight polyalkylene glycols to the present
invention is that they are similar chemically to the polyalkylene
glycols which, as will be explained hereinbelow, are especially
applicable as reaction solvents in the present process improvement.
The polyglycols of Stautzenberger et al. are extremely compatible
with the polyalkylene glycol reaction solvents of the present
invention, but they are much lower in molecular weight such that
their use as solvent for introducing the catalyst into the reaction
system would not inherently achieve the objects of the present
process improvement which r~quires higher molecular weights.
~r~
~L I Z38S9 s
The concentration of catalyst to be maintained in the hydroformylation
reaction medium is not critical to the successful employment of the present
invention. Typically, however, whèn the catalytic metal is rhodium and
when the ligand i5 triphenylphosphine, the liquid reaction medium will
5 contain about 0. 01 to 1 0% rhodium and up to about Z0% or more triphenyl-
phosphine by weight where suppression of iso-aldehydes is desired, In
hydroformyiating ethylene, the iso-aldehyde problem does not exist, and
very low ligand concentrations can be employed, e. g. 1% or less. In the
absence of the added inert reaction solvent with which the present invention
10 is concerned, the triphenylphosphine content in hydroformylating propylene,
for example, may be as high as about 40%.' Typically, the ligand concen-
tration will not exceed about 45 weight percent,
The identity of the inert solvent which is sometimes used in the
reaction system as taught by the prior art is not critical so long as it
15 be miscible with the catalyst system and with the reactants and reaction
products, low in volatility so as to facilitate stripping reaction product
and by-products from it, and, of course, either chemically inert in the
hydroformylation reaction system or else forming in that system a
derivative which is itself inert while still fulfilling the other named
20 requirements. ~That is, a suitable solvent could be one which might
undergo hydrogenation in the reactor and then in the hydrogenated forrn,
be inert to further reaction. ) Molecular weight is not a significant factor
in the reaction solvents as taught in the prior art except as it relates to
volatility, relatively high molecular weight being desired, of course, to
25 facilitate retention of the inert solvent as a heavy end while the reaction
products are stripped out of it. Thus, in the prior art as exemplified by
U. S. 4,151, 209, it is already known to employ any of a large number of
inert liquids including, for example, alkyl-substituted b~nzenes; pyridine
_9_
1~.2~1~59
and alkyl-s~lbstituted pyridines; tertiary arnines; high-boiling esters such
as dialkyldicarboxylates and triorganophosphates as well as esters of
polyols such as trirnethylolpropane and pentaerythritol; ketones; alcohols
such as the butanols; nitriles such as acetonitriles; and hydrocarbons
5 including both saturated hydrocarbons such as kerosene, mineral oil,
cyclohexane, naphtha, etc. and aromatics such as biphenyl It is further
emphasi~ed in U. S. 4,151, 209 that, in addition to the prior art solvents
as just listed, the high degree of stripping taught by the patentees makes
it desirable to employ solvents which are of extremely low volatility, in
10 particular compounds or mixtures of compounds which are less volatile
than the ligands used in the hydroformylation reaction many of which are
themselves of very low volatility. Thus, it is taught in U. S. 4,151, 209
that particularly useful solvents include triphenylphosphine oxide and
polyglycols, e. g. polyethylene glycol and polypropylene glycol, which
15 have molecular weights of at least about 500. The teachings of the patentees
are that molecular weight of the polyalkylene solvents is important as a
factor relating to volatility, with molecular weight in and of itself not
otherwise being significant.
As mentioned previously it is also known to use as solvent some or
20 all of the high-boiling aldehyde condensation products which are formed as
by-products in the course of the hydroformylation reaction, as taught in
U. S. 4,148,830 to Pruett et al.
In practicing the present inventio~ it is possible to use a solvent of
any of the types just listed, except that molecular weight in and of itself is
25 a significant factor in addition to low volatility. That is, it is desired that
the solvent have a molecular weight of at least about 700 (or higher in son~e
circumstances as will be explained) even though solvent volatility, if this
were the only factor being considered, might be sufficiently low at lower
-10-
3~5g
molecular weights to satisfy the requirements of the prior art as exemplified
by U. S. 4,151, 209. Subject to thi9 requirement regarding solvent molec~l-
lar weight, the solvent can7 insofar as its chemical characteristics are
concerned, be of any of the types already listed hereinabove. Especially
5 useful solvents, however, which fit all the criteria just set forth and which
are also available industrially in a wide range of molecular weights, are
the polyalkylene glycols, especially -- because of their ready availability -
polyethylene glycol and polypropylene glycol. In this context, the term
"polyalkylene glycol" refers both to polyalkylene glycols as such (that is,
10 to polymeric alkylene glycols having a hydroxy group at each end) and also
to those having one or both ends capped Wit~T an alkoxy group such as buto~Yy.
In addition to being readily available in a wide range of molecular weights,
these materials are suitably inert and also compatible with the several
components of the hydroformylation system.
In carrying out the present improved process the hydroformylation
reaction is conducted in the same manner as in any of the several variants
of those prior-art processes which do employ an added inert solvent
Mechanical agitation of the liquid contents of the hydroformylation reactor
can be employed if desired, but it is simple and satisfactory to obtain
20 adequate agitation by sparging the synthesis gas through the liquid reaction
medium. A mixture of gases and vapors withdrawn from the top of the
reaction vessel contains the aldehyde product in vapor form, as well as
unreacted olefin. The aldehyde is recovered from these withdrawn gases
and vapors, which are then recycled to the reaction sparger along with
25 fresh olefin and synthesis gas. The reaction temperature and pressure
are set at known prior-art levels at which the hydroformylation reaction
takes place at commercially satisfactory rates and yields. The rate of
gas recycle can be varied to control the rate at which product is stripped
' ?
~23~5~
out of the li-luid reaction mixture contained in the reaction vessel. It will
be seen, of course, that stripping rate is affected by all three factors
(temperature, pressure, and gas recycle rate) and that it is possible, as
already understood in the prior art, to vary each of these factor9 to some
5 extent to attain a desired product stripping rate.
An alternative mode of operation which can be employed in place of
the above-described method for stripping product out of the reactor with
the recycling gases is to withdraw a slip stream of liquid from the hydro-
formylation reactor and distill it to recover a distillate comprising the
10 aldehyde product while leaving a distillation residue comprising the re-
action solvent and catalyst, this residue theh being returned to the hydro-
formylation reactor. Yet another alternative is to subject the withdrawn
slip stream to simple evaporation, although distillation is preferable
because it facilitates making a sharper separation bet~,veen reaction prod-
15 ucts and high-boiling solvent.
As previously explained, conducting the reaction and the product
recovery operation in accordance with the prior art methods has entailed
the consideration8 of volatility, chemical compatibility, and product
degradation through intermolecular condensation reactions (as emphasized,
20 for example, in U. S. 4,151, ~09). All these factors continue to be signifi-
cant in the present improved process, of course, but it has now been
realized 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
25 volatile products and simultaneously prevent buildup of the heavier reaction
by-products. This additional parameter is the mole fraction of aldehyde in
the liquid reaction medium contained in the hydroformylation reactor and,
associated with the mole fraction, the molar concentration of product
_12-
"~ "
~ 23~359
aldehyde in the liquid. If a low volatility is the only consideration inchoosing the inert reaction solvent which is to be employed, all that would
be required in adjusting the composition of the liquid reaction mixture from
which the aldehyde product is being stripped would be that the solvent be
5 chemically inert, that it be compatible with the other components of the
system, and that it be present in sufficient quantity to maintain fluidity.
With such a system it is possible to maintain operability and achieve, for
example, the purposes of U. S. 4,151, 209 in maintaining catalyst activity.
However, stringent stripping conditions may be required to accomplish
10 these ends with prior-art solvents. Alternatively, with less stringent
stripping while using the prior-art solvents, one may approach the
borderline of conditions under which a buildup of high-boiling reaction by-
products begins to take place.
In accordance with the present process improve~nent, the ease of
15 stripping is improved as compared with the prior art by employing as the
inert solvent a liquid which has a higher molecular weight than previously
contemplated, without necessarily changing, for example, the molar
proportion of the solvent to the other components, Essentially, substitu-
tion of a solvent having a high molecular weight in place of a solvent (or
20 other system component) which has a relatively lower molecular weight
brings about a reduction in the molar density of the mixture, i. e., the
total moles of all components of whatever nature which are present in a
unit volume of the liquid. The result of this modification is that, at a
constant molar concentration of aldehyde in the mixture, the mole fraction
25 of aldehyde is greater in the case of the modified mixture having the
lowered molar density than it is with the unmodified mixture wherein,
lacking the high molecular weight solvent additive, the molar density is
higher. Alternatively and preferably, to maintain a given mole fraction
-13-
~.2~359
of aldehyde in the modified mixture containing the high molecular weightsolvent requires a lower aldehyde concentration (expresed in, for e~cample,
moles per liter) than is required to maintain the same aldehyde mole
fraction in the unmodified mixture. Thus one can, as he wishes, either
5 reduce the rate of stripping gas or else, with the rate of stripping gas being
unchanged, enhance the efficiency of aldehyde stripping per unit quantity of
stripping gas. Since the formation of undesired condensation derivatives of
the product aldehyde is a function of the concentration of that aldehyde in the
reaction product mixture, the present technique facilitates reducing such
o side reactions or almost eliminating them entirely. Particularly satis-
factory results obtain when the mole fractidn of product aldehyde in the
liquid reaction mixture is from about 0,4 to about 0,7.
To effect the desired reduction in molar density, it is recommended
that sufficient high molecular weight diluent be incorporated into the hydro-
15 formylation reaction medium that the resulting liquid mixture contain atleast about 50% of the high molecular weight diluent, computed on the
product aldehyde-free basis. Lesser proportions of the diluent will have
some effect, of course, but a proportion of at least 50% by weight is
desirable, Proportions higher than about 50 weight percent are desirable,
20 up to an upper limit which will be imposed by the fact that in many reaction
systems there will be a substantial excess of ligand, e. g. triphenyl-
phine, which will itself constit~te a substantial fraction of the reaction
medium. For example, the liquid may frequently contain about 30-40 wt %
of excess ligand which is thus unavoidably a substantial component. Broadly
Z5 speaking, then, it is recommended that the diluent be incorporated into the
reaction medium in a proportion of at least about 50% by weight, with
lower proportions of the order of about 40% by weight or even less still
being advantageous, while the upper limit is normally imposed by the fact
_14-
3~5g
that there are present other essential components such as the organicligand which can be reduced in concentration only at the cost of reduced
reactor throughput. In most situations the diluted reaction medi~m will
contain, by weight, about 40% to about 60%, or more broadly about 40%
5 to 95% of the high molecular weight diluent on the product aldehyde-free
basis. Product aldehyde itself will typically amount to roughly 10% to
15% of the total reaction mixture.
- When the olefin being hydroformylated is ethylene, it is recom-
mended that the added diluent have a molecular weight of about 700 to 800.
10 When the reactant olefin is propylene or a higher olefin, it is preferred
that the diluent have a molecular weight of-about 1500 to 2000 With
further reference to the m~tter of the molecular weight of the diluent, it
will be understood that some of the prior-art reaction solvents may them-
selves have a high molècular weight although it may not be appreciated
15 that the hydroformylation system in which they are being used can, with
some additional control in the stripping operation, enjoy some of the
benefits of the present method. Preferably, ho~vever, the inert solvent
should have a molecular weight of at least about 700 in order that a given
quantity of it may have a significant effect in reducing the molar density
20 o the mixture, As the molecular weight of the diluent increases, it of
course becomes more efficacious in the desired reduction of molar density
although with increasing molecular weight of the diluent the chemical rate
of hydroformylation may be lowered and the mass-transfer properties of
the resulting mixture become less satisfactory such that it is desirable in
25 some cases to increase the catalyst concentration and/or increase the
quantity of a liquid reaction medium per unit of desired reactor aldehyde
output. While there is no sharp upper limit of solvent molecular weight
above which the present method is inoperative, it is preferred that the
-15-
~2385~
molecular weight of the diluent liquid not exceed about 3000.
In carrying out the hydroformylation reaction using the prescntdiluted reaction medium it is, as previously explained, easier to maint~in
a relatively low concentration of product aldehyde than when using un
5 diluted reaction medium. Reduction in aldehyde concentration means a
reduction in by-product formation. The aldehyde content (i. e., the content
of the desired hydroformylation product aldehyde as distinguished from
undesired heavy by-products which might also have aldehyde moiety in the
molecule) is controlled by controlling the intensity of the product stripping
lO which is employed to remove the aldehyde from the reaction medium. The
details of how this control is maintained arë, of course, obvious to one
skilled in the art. That is, an elevation of stripping ten~perature or an
increase in the rate of stripping gas throughput serves to reduce the prod-
uct aldehyde content of the reaction product mixture which is being stripped.
15 In practicing the present invention it is recommended that the stripping be
so controlled as to maintain in the liquid reaction medium contained in the
hydroormylation reactor an aldehyde content of about 1 to 2 gram moles
per liter, Very good results obtain when the aldehyde concentration is l to
l . 5 in the case of propionaldehyde and l. 5 to 2, 0 in the case of butyralde-
20 hydes. These relatively low aldehyde contents are recommended if it isdesired to hold to a minimum the formation of undesired aldehyde condensa-
tion reaction by-products. It will be seen, however, that it is also possible
within the scope of the invention to use the present dilution method not for
reducing by-product formation by stripping to this relatively low aldehyde
25 concentration but, rather, to take advantage of the fact that, at a given and
unchanged aldehyde concentration in the reaction mixture, the stripping rate
can be reduced with resultant saving in ~nergy and in, for example, stripping
gas recirculation apparatus. That is, one can use the improved properties
-16-
385~1
of the prescnt diluted mixture (improved as regards the ease of strippingthe aldehyde therefrom) either to strip out the aldehyde more completely
without increasing the rate of, for example, stripping gas recirculation
or, alternatively, he can allow the aldehyde concentration in the liquid to
5 be unchanged but still benefit from the incorporation of the diluent by
economizing through reducing the intensity of the stripping operation,
The following examples are given to illustrate further the applica-
tion o the invention. It will be understood that many variations can be
made therefrom within the scope of the invention.
EXAMPLE 1
Propylene is hydroformylated to produce butyraldehyde by being
sparged, in admixture with synthesis gas, through a liquid reaction
medium, or catalyst solution, which is contained in a hydroformylation
reactor operating at 115C and at a pressure of 2Z.4 atmospheres absolute,
15 and cooled by recirculation of its liquid contents through an external heat
exchanger and back into the top of the vessel, The reactor is agitated by
the buboling action of the gas sprager. The gas mixture being sparged
into the base of the reactor comprises, in mole percent, 32. 68% hydrogen,
13,16% carbonmonoxide, 21,79% propylene, 25.25% propane, 5.12%
20 methane, slightly less than 1% butyraldehydes, and lesser quantities of
various minor components. The propane and methanè are present as a
result of having been allowed to build up in the course of recycling gases
from the reactor through a product recovery operation and back into the
reactor, uncontrolled buildup being prevented by continuously purging a
25 portion of the recycling gas.
The liquid reaction medium, or catalyst solution, contained in the
hysIroformylation reactor has the fol~owing composition.
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BUTYRALDEHYDE PRODUCTION
LIQUID REACTION MEDIUM
gm Mols per Liter
Component Mol ~ Wt ~ of Solution
r
i-Butyraldehyde4.55 1,31 0. l 64
n-Butyraldehyde47.3 B13.69 1.71
Butanols 1.35 0.40 0.046
TPP( ) 33.11 34.79 1.19
TPPO( ) 2.69 3.00 0.097
PDPP(3) 2.19 ~.00 0.079
10 Heavy ends 0.78 0.55 0.033
Rhodiurn 0~ 63 Q 26 0.023
Polyglycol(4)7.32 44.0 0.209
Total 100.0 100.0 3.6
15 (1) Triphenylphosphine
(2) Triphenylphosphine oxide
(3) Propyldiphenylphosphine
(4) Polypropylene glycol capped with butoxy group at one end.
Molecular weight approximately 1500. Sold by Union Carbide
Corp. under trade name "UCON LB625".
The butyraldehydes content in the reaction medium is maintained at
approximately 1.9 gm mols per liter as tabulated above by controlling the
rate at which the gas is sparged into the reaction medium. Under the
conditions of pressure, temperature, and reaction medium as tabulated
25 above, the desired butyraldehydes content is maintained by controlling
the gas sparge rate at approximately 350 gm mols of gas per hour per
liter of liquid reaction medium contained in the hydroformylation reactor
and excluding liquid contained in the recirculated cooling loop.
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The gas evolving from the surface of the liquid reaction medium
passes upwardly through a short section of perforated gas-liquid contacting
trays (5 trays) against a small down flowing stream of crude butyraldehyde
product amounting to approximately 0. 05 to 0. 1 grams of this crude butyr-
aldehyde scrubbing liquid per liter of gas evolving from the surface oL the
liquid reaction medium and entering the perforated tray section. This
liquid comprises, byweight, approxill~ately 88% n-butyraldehyde, 7.5%
isobutyraldehyde, 2% propane, and 1.5% propylene. From the bottom
- tray, the scrubbing liquid flows back into the hydroformylation reactor.
lo The product gas leaving the top of the perforated tray section amounts to
183 gram mols of the total gas per hour per~ liter of liquid contained in tlle
hydroformylation reactor and comprises, in mol %, appro~;imately 30.1%
hydrogen, 9.1% carbon monoxide, 5. 6% methane, 18.8% propylene~ ~8.1%
propane, O. 6% isobutyraldehyde, 6.5% normal butyraldehyde, and lesser
quantities of minor diluents. It also contains approximately 0. 5 gram of
reaction heavy ends per hour per liter of liquid reaction medium contained
in the hydroformylation reactor, or approximately 0. 001 mol % in the
reactor outlet gas. The gas just described is then cooled to approximately
SO~C without appreciable lowering of its pressure, to form a crude aldehyde
ZO product condensate and a recycle gas stream. The bulk of the gas is re-
cycled to the hydroformylation reactor while a portion is vented to control
buildup of inerts. The majority of the condensate liquid is drawn off as
crude aldehyde product, while a small portion is returned to the top of the
perforated tray section as previously explained.
The net make of gases and vapors, i.e. the sum of the crude alde-
hyde product dra~h-off, the gas recycle, and the gas vent stream, amounts
to 179. 5 gram mols per hour per liter of liquid reaction medium of
catalyst solution contained in the hydroformylation reactor and contains
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~lZ3~5~
55. 22 mols of hydrogen, l 6. 63 mols of carbon monoxide, 33 . 59 mols of
propylene, 50.38 mol9 of propane, 10.35 mol9 of normal butyraldehydc,
l .00 mol of isobutyraldehyde, 10. 17 mols of methane, 0.1~ mol of water,
0. 02 mol of butanols, and the ren~ainder minor diluents. The space-time
yield of n-but~rraldehyde i9 12 to 14 gram9 mols per liter of liquid reaction
medium per hour computed, as above, on the basis of liquid contained in
the reactor itself. The concentration of reaction heavy ends does not
build up appreciably in the catalyst solution or liquid reaction medium over
extended periods of time, i.e., over a period of months, and the activity of
the catalyst is also not appreciably decreased over a period of months.
While the process as exemplified here operates at 22,4 atmospheres
pressure, lower pressures can be employed down to about 10 atmospheres,
below which the reaction rate begins to fall off more than is normally
desired. The only upper limit on I7ressure is imposed by economic con-
siderations of apparatus design strength, although it will be understood that,
as pressure increases. ,the mols of stripping gas required per unit of aldehyde
to be stripped out will increase for reasons obvious to those skilled in
chemical engineering. Normally pressures ~vill not exceed 70 atmospheres,
E~AMPLE 2
Ethylene is hydroformylated to produce propionaldehyde by being
sparged, in admixture with synthesis gas and reaction recycle gas as in
Example l, through a liquid reaction medium contained in a hydroformyla-
tion reactor operated at 115DC and 35 atmospheres absolute and, as in
Example l, cooled by recirculation of the contained liquid through an
external heat exchanger and back into the top of the top of the reaction
vessel. As in Example l, the contents of the reactor are agitated by the
action of the gas sparger. The gas sparged into the base of the reactor
comprises, in mol percent, 60. 5% hydrogen, 19. 9% carbon mono~ide,
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3859
10.7% ethyl~De, 3,0% methane, o,6% ethane, o~6% carbon dioxide, 2 0%
propionaldehyde, and the remainder minor contaminants. This gas i9
sparged through the liquid reaction medium, or catalyst solution, at the
rate of 177.1 gram mols per hour per liter of catalyst sollltion in the
5 reactor itself, as in Example 1, and the propionaldehyde stripped out of
the catalyst solution with the exiting gases amounts to 20 5 gram mols of
propionaldehyde per liter of catalyst solution per hour.
The liquid reaction medium, or catalyst solution, contained in the
hydroformylation reactor and through which the gas is sparged as just
10 explained, has the following composition:
PROPIONALDEHYDE PRODUCTION
LIQUID REACTION MEDIUM
gm Mols per I.iter
Component Mol % Wt % of Solution
.. . . .
Propionaldehyde 53. 0 8. 7 1. 37
15 2-Methylpentanal 0. 07 0. 02 0. 0018
Ester MW 174 1.4 0.7 0.0364
Heavy ends 0. 6 0,4 0. 0144
Triphenylphosphine 0. ~ 0. 6 0. û22
Rhodium 0. 04 0. 01 0. 001
20 Polyglycol(l) 44. 1 89. 6 1 . 14
(1) Polypropylene glycol capped with butoxy group at one end. Molecular
weight approximately 725. Sold by Union Carbide Corporation under
trade name "UCON LB165".
The gase~ evolved from the surface of the catalyst- solution are drawn
out from the top of the hydroformylation reactor and are cooled to 50C at
3i. 67 atmospheres absolute pressure. The condensate i3 drawn off as crude
alde'nyde product, and the uncondensed gas is recycled to the hydroformylation
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~t'~ ~I fr~ e ~I~!a~"k
~23~359
reactor. The gases drawn out from the top of the hydroformylation reactor
comprise, in mol percent, 63.4% hydrogen, 12.7% carbon monoxide,
14. 1% propionaldehyde, 3. 7 % methane, 3 . 0% nitrogen, l . 3 % ethylene,
0.8% ethane, 2.1 x 10 4 % methylpentanal, and 2.1 x lO ~ ester.
With the reaction system operating in this manner, the space-time
yield of propionaldehyde amounts to approximately 16. 9 gm mols of propion-
aldehyde per hour per liter of catalyst solution. The molar density of the
catalyst solution including the poly~lkylene glycol diluent is 2. 6 gm mols per
liter. The concentration of reaction heavy ends does not build up appreciably
lo over an extended period of time, and the activity of the catalyst is also stable
for extended periods.
While the process as exemplified here operates at 35 atmospberes
pressure, lower pressures can be employed down to about 15 atmospheres,
below which the reaction rate begins to fall off more than is normally
desired. The only upper limit on pressure is imposed by economic consid-
erations of apparatus design strength, although it will also be understood
that, as pressure increases, the moles of stripping gaQ required per unit
of aldehyde to be stripped out will increase for reasons obvious to those
9killed in chemical engineering. Normally pressures will not exceed 70
atmospheres.
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