Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for the preparation of alde-
hydes by the hydroformylation of olefins. More particularly, it relates to
the catalytic hydroformylation of olefins such as propylene with hydrogen
and carbon monoxide wherein the life of the rhodium complex catalyst is ex-
tended by hydrogenating the impure olefin feed stream to decrease the
activity of unidentified catalyst poisons normally contained therein.
Processes directed to the production of reaction mixtures com-
prising substantial amounts of aldehydes and at eimes lesser amounts of
alcohols by the reaction of olefinic compounds with carbon monoxide and
hydrogen at elevated temperatures and pressures in the presence of conplex
catalysts are well known in the art. The aldehydes and alcohols produced
generally correspond to the compounds obtained by the addition of a carbonyl
or a carbinol group to an olefinically unsaturated carbon atom in the
starting material with simultaneous saturation of the olefin bond. Iso-
merization of the olefin bond may take place to varying degrees under certain
conditions with the consequent variation in the products obtained. These
processes are known in the industry and referred to herein as hydroformyla-
tion.
The use of rhodium complexes as catalysts for the hydroformylation
reaction is also well known in the art. See, for example, United States
Patents3,239,566 and 3,527,809. The rhodium is in complex combination
with carbon monoxide and a ligand containing phosphorus, arsenic, or antimony.
These catalysts are commonly used in solution and the aldehyde product is
produced in the completely homogeneous liquid phase. The catalysts lose
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activity during the course of the reaction, and it is, therefore, necessary
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to add make-up catalyst to the reaction solution to compensate for the
deactivation of the catalyst originally charged to the reactor.
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Summary of Invention
It has been discovered that the co~,mercially available olefin
feedstocks contain impurities that shorten the life of the complex rhodium cat-
alyst used in the hydroformylation reaction. It has also been discovered that
these impurities can be rendered innocuous or less active by hydrogenating the
olefin feedstock. me desired result can be obtained by hydrogenating the
feed under conditions sufficiently mild to avoid saturating a signlficant
amount of the olefin. This practlce substantially reduces the amount of make-
up cat~lyst which must be added to the system, thereby signiflcantly enhancing
the economics of the process.
Accordingly the present invention provides in the process for the
hydroformylation of C2-C25 olefins with hydrogen and carbon monoxlde in a re-
action zone to form aldehydes in which a catalytlc complex ccmprising rhodium,
carbon monoxide and a ligand is utilized, the improvement comprising feeding
to the reaction zone an olefin stream which has been sub~ected to hydrogenation
conditions using from about 0.1 to 1% hydrogen by volume based on the olefin
feed in the presence of a metal hydrogenation catalyst at a temperature of from
about 50 to 150 C and at a pressure of from about 50 to 500 psi.
Detailed Descri~tion of the Invention
This selective hydrogenation process has been demonstrated to be
effective with respect to extending catalyst life in the reaction involv~ng -
the hydroformylation of propylene. It is believed that the technique is bene- --
ficiall~ applicable to the hydroformylation of any branched or straight chain
~ aliphatic or cycloaliphatic compound having at least one ethylenic carbon-to-
-~ carbon bond and which, as ordinarily available commercially, contains a
catalyst poison which is rendered innocuous or less active by hydrogenation.
Thus this selective hydrogenatlon technique can be applied to the hydroformyl-
ation of olefins having, for example, from 2 to 25 carbon atoms3 preferably
from 2 to 10 carbon atoms, to form reaction mix~ures predomi~ating in ali-
phatic aldehydes and alkanols having one more carbon atom than the startin~
olefin. Mono-olefins such as ethylene, propylene, butylene, pentenes,
hexenes, heptenes, octenes, dodecenes etc. and their homologs, are
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a few examples of suitable hydrocarbons.
It has not been determined that each of the above compounds
as ordinarily commercially available contains a poison which will deactiv-
ate the rhodium complex catalyst used in the hydroformylation reaction.
It has been discovered, however, that the rhodium complex cat lyst is
deactivated by a thus far unidentified catalyst poison and that the poi on
is rendered lnnocuous or at least less active when sub~ected to mild hydro-
genatlon condltions. Ihls poison i9 normally associated with propylene
and, therefore,
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may reasonably also be expected to be associated with the other above-
described unsaturated feedstocks.
It has been demonstrated that the life of a catalyst consisting
of a complex of rhodium, carbon monoxide, and triphenylphosphine can be
extended by the use of this selective hydrogenation technique. It is
reasonably expected that the technique can be used to extend the life of
catalysts comprising rhodium in complex com~ination with carbon monoxide
and a wide variety of organic ligands, especially triorgano phosphorus,
arsenic and antimony compounds such as triorgano p ~ phines and phosphites.
Preferably, the ligand is a triarylphosphite, triarylphosphine, trialkyl-
phosphite, or tricycloalkylphosphite. Triphenylphosphine and triphenyl-
phosphite are particularly useful. Specific examples of these ligand are
disclosed in the patents identified hereinabove.
Process operating parameters employed in the present invention
will vary depending upon the nature of the end product desired; the operating
conditions will determine the ratio of aldehydes to alcohols produced as well
as the ratio of normal to branched compounds. In general, the operating
parameters contemplated by the present process are the same as those con-
ventionally employed in prior art hydroformylation processes. For the sake
of convenience, these parameters will be generally described hereinafter; it
being understood, however, that the parameters are not critical to achieving
the improved results of the present invention and do not per se form a part
of the present invention.
In general, the hydroformylation process is conducted under a total
reactlon pressure of hydrogen and carbon monoxide of one at sphere or less
up to a pressure of about 1000 psia or more. For commercial reasons, however,
pressures significantly greater than about 500 psia will not normally be
employed.
The reaction is also normally conducted at a temperature of from
about 50 to about 200 degrees Centigrsde with a temperature within the range
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from about 75 to about 150 degrees Centigrade being most usually employed.
As is appreciated in the prior art, ligand in exces~ of the amount
required to form the metal-carbonyl-ligand complex is preferably employed in
order to achieve optimum reaction conditions. More specifically, it is gen-
erally desirable to employ at least about 2 moles of free ligand per mole of
metal, with from about 5 to about 50 or more moles of free ligand normally
being employed.
The ratio of partial pressures of the hydrogen to carbon monoxide
present in the reaction vessel may be from about 10:1 to 1:10, but will
normally be from about 3:1 to about 1:3, with a hydrogen to carbon monoxide
ratio of at least about 1:1 being preferred.
It has been determined that the use of the selective hydrogenation
process for treatment of commercially available chemical grade propylene
results in extended life for the rhodium complex catalyst. Small amounts of
hydrogen, for example from 0.3 to 0.4 mole percent based upon the propylene
feed, were fed along with the propylene over a promoted (1.0 weight percent
chromium) palladium supported on gamma alumina catalyst at a pressure of
about 195 p.s.i.g. and 175F. Steady state rhodium catalyst makeup rate
was significantly reduced in this and other tests.
It was initially thought that increased catalyst life was due to
the saturation of unsaturated heavy ends associated with the propylene.
Thus far, however, the actual catalyst poison has not been identified.
.
Potential poisons were intentionally fed into the hydroformylation reaction
to determine if the actual poison could be identified. The following com-
~; pounds were tested: 3 hydroxy-3 methyl-butyne, 1,3 butadiene, 1,2 pentadiene,
;~ 1, 3 pentadiene, 1 penten-3-yne, 1 pentyne, dicyclopentadiene, 2,5 dimethyl-
;` 1,5 hexadine, cyclopentadiene, propylene oxide, acrolein, N, N dimethl
formamide, monoethanol amine. No ill effects were observed during these tests
other than severe foaming (approximately 2 ft.) when cyclopentadiene was
j added. These compounds were probably rapidly purged from the system. Because
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1066721
of the means by which the compounds were tested, they cannot be definitely
ruled out as possible poisons. It is presently believed that the poison
is an unsaturated heavy end which is present in the feed in a small, perhaps
non-detectable amount. A poison combining stoichiometrically with rhodium
could cause deactivation when present in such small amounts.
A wide range of hydrogenation conditions can be employed. The
ob~ect is to render the poison innocuous without saturating significant
quantities of propylene. Thus, the hydrogenation may be performed under
strong conditions if very little hydrogen is employed. The temperatures
should vary from 140F to 300F, preferably from 160 to 230F. The amount
of hydrogen that must be employed will vary from feed to feed. It has been
determined that with commercially available chemical grade propylene as
little as 0.2 or 0.3 percent hydrogen, based on the olefin feed, is sufficient
to render innocuous the poison. It is essential to use an amount of hydrogen
sufficient to saturate or render innocuous all of the poison. The amount will
have to be determined experimentally for each feed, but it ls believed that
it will be sufficient to employ hydrogen in an amount from 0.1 to 1.0 percent
based upon the total amount of olefin. The reaction appears to be insensitive
to hydrogen partial pressure, at least over the range of from 1 to 2 p.s.i.a.
Good results have been obtained using a promoted (1.0 weight percent
chromium) palladium supported on gamma alumina catalyst for the hydrogenation
reaction. Other metal hydrogenation catalysts should be suitable including
Raney nickel, Raney cobalt, palladium or platinum. Copper catalysts, parti-
cularly copper catalysts containing the oxides of elements such as chromium,
barium and zinc, can also be used. Other catalysts may be available which will
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effect the hydrogenation of the catalyst poison.
The reaction is relatively insensitive to the quantity of catalyst
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employed. Generally, one should treat from 50 ~o 1000, preferably from 100
to 550 pounds of propylene per hour per cubic foot of catalyst. The tempera-
ture and pressure can vary widely and may be within the range of 50 to 150C
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and 50 to 500 psi.
The propylene feed is preferably vaporized and mixed with hydrogen
in the presence of the hydrogenation catalyst prior to being combined and mixed
with the hydrogen and carbon monoxide required for the hydroformylation reaction.
After the selective prehydrogenation, the treated propylene is mixed with hydro-
gen and carbon monoxide and fed to the hydroformylation process as usual.
The invention is illustrated by the $ollowing Examples:
Example I
The hydroformylation of propylene was conducted in a reaction zone
at 115C under a pressure of 310 p.s.i.g. The reaction zone contained approxi-
mately 2 millimoles of active rhodium and up to twice this amount of inactive
rhodium and approximately 2 moles of triphenylphosphine dissolved in reaction
product. Carbon monoxide, hydrogen and propylene were fed to the reactor in
amounts sufficient to maintain a partial pressure ratio of olefin:carbon monox~de:
hydrogen at 2:1:2.4 p.s.i.a. Rhodium catalyst was added portionwise to maintain
a constant rate of hydroformylation. The steady state catalyst makeup rate in a
550 hour run was 0.013 millimoles per hour.
~ Example II
; A hydroformylation reaction under the conditions specified in Example
-` I was repeated except that the commercially available propylene feed was sub-
~ected to selective hydrogenation prior to being fed to the reactor. The
propylene feed was mixed with small amounts (0.3 - 0.4~) hydrogen and fed
across a promoted (.03 weight percent chromium) palladium supported on gamma
alumina catalyst at 175 p.s.i.g. and 160F. The rates are adjusted to allow
time for all of the hydrogen to react. The hydrogenated stream was then fed
` to the reactor. The test was continued for 500 hours. Steady state catalyst
makeup rate was 0.006 millimoles per hour.
Example III
The selective prehydrogenation technique was tested with propylene
obtained from two commercial sources. The hydroformylation reaction was con-
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ducted in all cases at a temperature of 240F, a pressure of 310 p.s.i.g.,and a triphenylphosphine concentration of about 35 weight percent. Conditions
were otherwise similar to those disclosed in Example I. The hydroformylation
reaction was first performed for 550 hours without selective prehydrogenation
and then the test was continued with the same source of propylene with selective
hydrogenation. The source of propylene was then changed; the test was con-
tinued for 350 hours using selective hydrogenation and then the selective
hydrogenation was discontinued and the test was continued for another 300 hours.
The selective hydrogenation system utilized for these tests involved metering
hydrogen (0.4% of the propylene by volume) into the propylene feed stream. The
hydrogen and propylene were mixed by a static mixer and fed through a one inch
diameter selective hydrogenation reactor. The reactor was packed with five
inches of 3/16" diameter silicon carbide wafers upstream of thè catalyst bed
to distribute flow. The catalyst bed contained 7" of promoted palladium on
alumina catalyst pellets. The hydrogenated propylene was then fed directly
into the hydroformylation reactor. The mixing section and reactor were
immersed in a thermostatic water bath for temperature control. The hydrogena-
tion system was operated at 195 p.s.i.g. and between 155 and 175F. The
results of the test are summarized below:
Propylene Duration Catalyst Usage Selective
Feed Hrs. Rate (relative) Hydrogenation
First Commercial Source 550 l.0 without
" " " 480 0.47 with
Second " " 350 0.45 with
" " " 300~ 1.0 without
This selective hydrogenation technique does not harm the hydroformy-
lation process in any detectable manner. It is believed that reaction effici-
encies and product distribution will not be affected. The only observed
negative aspect of selective hydrogenation is the loss of some propylene to
propane. It may be that 0.3 - 0.4 weight percent propylene will be lost, but
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it may be feasible to reduce this loss by feeding still less hydrogen.
Various modifications and variations can be made to the process
described herein without departing from the spirit and scope of this
discovery.
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