CA1066721A - Hydroformylation process - Google Patents

Abstract

HYDROFORMYLATION PROCESS
Abstract of Disclosure The Invention relates to a process for the preparation of aldehydes by the hydroformylation of olefins using a catalyst solution containing a rhodium coordination complex. The catalyst life is extended by selectively prehydrogenating the commercially available olefin feed to decrease the effect of unidentified catalyst poisons ordinarily contained therein.
Prehydrogenation is performed under sufficiently mild conditions to avoid hydrogenating substantial amounts of the olefin.

Description

~ ~066721 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 ~`
activity during the course of the reaction, and it is, therefore, necessary ;~
to add make-up catalyst to the reaction solution to compensate for the deactivation of the catalyst originally charged to the reactor.

`~ ~0667Zl 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 ~ - 2 -1~ ~
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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, ~X, ~ .

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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 106672:~
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.

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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 ' - 4 -; , ' ; '~, ; , ' 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 . .
effect the hydrogenation of the catalyst poison.

The reaction is relatively insensitive to the quantity of catalyst . .
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

. - 5 -10667Zl 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-~ 10667Zl 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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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In the process for the hydroformylation of C2-C25 olefins with hydrogen and carbon monoxide in a reaction zone to form aldehydes in which a catalytic complex comprising rhodium, carbon monoxide and a ligand is util-ized, the improvement comprising feeding to the reaction zone an olefin stream which has been subjected 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.

2. A process according to claim 1 wherein the olefin has from 2 to 10 carbon atoms.

3. A process according to claim 1 wherein the olefin is selected from the group ethylene, propylene, butylene, pentenes, hexenes, heptenes, octenes and dodecenes.

4. A process according to claim 3 wherein the metal hydrogenation catalyst is selected from the group palladium promoted by 0.1 weight %
chromium, Raney nickel, Raney cobalt, palladium or platinum, and copper catalysts containing oxides of the elements chromium, barium and zinc.

5. A process according to claim 4 wherein the hydrogenation is con-ducted at a temperaure of from 140 to 300°F.

6. A process according to claim 5 wherein the hydrogenation is con-ducted at a temperature of from 160 to 230°F.

7. A process according to claim 1, 3 or 5 wherein the olefin feed is propylene and is treated with from 0.1 to 1% hydrogen by volume based on the propylene at a temperature of from 140 to 250°F in the presence of a palladium hydrogenation catalyst.