Note: Descriptions are shown in the official language in which they were submitted.
10816-1
This invention relates to the preparation of
aldehydes by the "Hydroformylation" process in which an
alpha-olefin i9 hydroformylated with carbon monoxide ~nd
hydrogen in the presence of a rhodium catalyst.
J. Falbe, "Carbon Monoxide in Organic Synthesis",
Springer-Verlag, New York (1970)~ at page 3, has stated:
"Hydroformylation is the reaction of an unsaturated
compound (or a saturated compound which may generate an
unsaturated compound) with carbon monoxide and hydrogen
to yield an aldehyde". The process has also been called
the Oxo process. Until recently, all commercial hydro-
formylation reactio~s were catalyzed by cobalt carbonyl
catalysts. According to Falbe (at page 70), ~upra, with
the ~ingle exception of the process developed by Shell,
"all industriaLly applied oxo processes more or less follow
the technique which was developed by Ruhrchemie AG in
Oberhausen/Germany in co-operation with BA5F." He states
that the existing oxo plants operate continuously and, in
general, "they consi~t of the following sections:
1. Hydroformylation reactor. 20 Catalyst removal section.
3. Catalyst: work-up and make-up section. 4. Aldehyde
distillation. 5. Aldehyde hydrogenation reactor.
6 . Alcohol dis tillation" .
The Shell process differs by employing a modified
cobalt catalyst made by combining in the hydroformylation
2.
,
10816-1
~ ~ 9 0 ~ 2 3
reactor a cobalt salt of organic acids, trialkyl phos-
phines (e.g. tributyl phosphine) and alkali, such as KOH.
The in situ formed HCo(CO)3PR3 ca~alyst "is thermally
more stable than HCo(CO)4" thus allowing lower reactor
pressure of "around 100 atm, versus 200-300 atm in the
other processes" (Falbe, ~ , page 73)~
Though the earliest Oxo plants were intended to
be a heterogenous reaction patterned after Fisçher Tropsch
catalysis) it was eventually found that the catalysis ~as
homogeneous (Falbe, supra, page 14). The separation and
recovery of the catalyst was therefore an essential step
in the Oxo process. This is significantly the case when
the catalys~ comprises the precious metal rhodium. As
s ated by Cornils et al., "Hydrocarbon Yrocessing", June
1975, at page 86: '~hile Rh compounds are more active
than cobalt, they are much more expensive. Cobalt costs
approximately 20DM/kg and rhodium between 44,000 and
72yOOODM/kg (S~ptember 1974 and February 197S). This
shows the speculative character of the rhodium price.
Cost would be o~ no importance if rhodium could be lOO
percent recovered and used at low metal concentration
levels. Impossible economic rhodium recycle has avoided
appl~cation o~ unmodiied Rh compounds so far, even when
branched chain aldehydes are desired or when only Rh
salts can ~nable the oxo reaction. This is because the
low Rh concentratlons desired from several ppm* up to
(*"ppm" means parts per million)
3.
10816-1
Z;~
se~eral hundred ppm, related to olefin feed (cobalt 0.1
up to 1 percent, depending Oll the process applied)
make even more difficult a chemical, thermal or extractive
treatment of the metal carbollyl containing oxo products.
mereore there are a number o~ spe~ial processes for the
removal of rhodium traces from oxo products (e.g.
adsorption on solids with large surface, distillative
concentration with the heavy ends of oxo synthesis, the
treatment with steam, halogens or carbo-~ylic acids os
others). Often these methods require an expensive
recovery step for concentration o~tside of the oxo unit.
A rhodium loss of only one ppm per ~ilogr2m of oxo
product produced causes material costs o~ approximately
0.04 up to 0.07 DM/kg (compared to 0.02 DM/kg with Co
catalys ts ) . "
Gornils et al., pages87, B8 and 90, depict in
Figure 9 ~ proposed commercial plant design based upon
a modified rhodium catalyzed Oxo process. They
characterize that the catalyst has to be recycled to the
20 reactor from the distillation column. Owing to the
formstion o heavy ends, Cornils et al., at page 8~,
~tate that "a complete recycling of rhodium only via the
'primary' recycle 9 would cause enrichment of higher boil-
ing components". According to Cornils et al., page 88,
"to avoid ~his, part of the bottom of.column 3 is with-
drawn continuousLy as a slipstream and distilled in
~9~823 10816-1
column 6 to give a 'light aldols' overhead". They
continue with the following:
"Provided there is suficient activity,
the bottoms which are thermally treated
twice at this point are recycled to the
reactor as a 'secondary' Rh cycle 10. The
distilLation in column 6 does not remove the
medium and high boiling byproducts of oxo
synthesis, the latter because hey can not be
separated from the e~ces~ ligand. The separa-
tion of the Rh complexe~ from the medium
boiling components ls done in column 7 which
i9 fed a slipstream of the bottoms of 6. The
bottoms of 7 are treated thermally so often
that their rhodium content is oxo inactive and
must be wor~ed-up in an external make-up
~tep 8. This rhodlum is recycled to the
reactor as a 'tertlary' Rh recycle 11, losing
however the comple~ bonded ligand and the
~scess of complexing ligands. me amount per
year of rhodium passing the tertiary recycle is
about t~ce the first Rh filling of the whole
oxo system."
Cornils et al~ state at page 89:
"Rhodium concentrations of 0~1 percent
together with the amounts of rhodium belng
1081~-l
~ 8 ~ 3
present in the diffl3rent steps of recycle and
recovery a~ each moment require high cost for
the firs~ catalyst :in~estment. The relation
of the first cataly~ t inves tment in cobalt and
in Rh modified oxo units is 1:5 (1:3, depend-
ing on Rh price).- More important than
the ~irst eataLyst investment are the rhodium
leakage and working losses. In comparison to
other commercial processes using noble metal
catalysts, a rhodium loss of one milligram per
kilogram of oxo products is regarded t~ be
realis~ic. This results in material costs of
approximately 0.04-0.07 DM/kg, depending on
the Rh price. To equal the material cos~ of
the conventional oxo process catalyst the
rhodium losses have to decrease to less than
0.3 pp~."
A similar process to that described by Cornils
et al. is set forth i~ British Patent 1,228,201. In the
proceqses described in that patent, the catalyst recycle
is a critical facet of the proces~ e~cept in those cases
where the s:atalyst i9 on a solid support in a ixed bed
system. Howe~er, as was pointed out previously by
J. Falbe, the reaction is in reality a homogeneous
reaction and one would have to pres~me subs~antial
catalyst losses by putting the rhodium on a inert support.
In British Patent Speci~ication 1,312,076, there
10816-1
~ 3
is employed a different technique for separation of the
catalyst from the product of the reaction. This invoLves
removing a ~ product stream overhead from which the
aldehyde product is separated by ~ractional distillation,
continuously withdrawing from the reactor a Liquid stream
comprising the complex catalyst, aldehyde and high boiling
residues, passing the liquid stream under reaction
pressure over the surace of a membrane such that a pro-
portion of the high boiling residues and aLdehydes permeate
through the membrane and are removed, with recycling o
the remainder of the liquid stream conta;ning the
catalyst to the reactor 8 88J
In Briti~h
there is noted the fact that in homogeneous catalysis of
the type described herein, the r~moval of cataLyst ~rom
~he reaction products for recycle is a diffic~lt operation.
It is stated in the Specification that the catalyst can be
recycled in the heavy residue obtained after dlstilla~ion
o the main reaction products at the expense of catalyst
loss.
To further demonstrate the di~iculties as~oci-
ated wlth recovering catalyst from the oxo reaction,
reference is made to Olivier and Snyde~ U.S. 3,539,634,
patented ~ovember L0, 1970, which describes passing the
heavy and/or bottoms of the separated pr~ducts of the re-
act~on containing the catalyst through an inert bed from
which is e~tracted the catalyst with reaction solvent.
10816 -
lO~&lZ3
Such a process demands that the solvent be a type which
has extraction capabilities while at thP same time requires
infinite extraction capabilities to insure no catalyst loss.
m ere is described herein a process for the manu-
facture of such Oxo products by hydro~ormylation of alpha-
olefins with a modified rhodium catalyst which avoids ~or
all p~ctical purposes rhodium catalyst losses over extended
periods o time.
The process of this invention is a continuwus one
for producing aldehydes by the hydroformylation of alpha-
ole ins containing two to about five carbon atoms. It
involves establishing a liquid body of a homogeneous mix-
ture containing the olefin, carbon monoxide and hydrogen
being supplied thereto, a~dehyde products and higher boiling
, aldehyde condensation products being continuously formed
therein, a soluble r'nodium catalyst complexed with carbon
monoxide and a triaryl phosphine. The amount Q~ triaryl
phosphine provided in ~he liquid body is equal to at
least 10-mols for each mol of rhodium metal provided in
the liquid body. There is suppLied to the liquid body a
gaseous recycle stream comprising hydrogen and ole in
and there is supplied ma~e-up quantities of carbon monoxide,
hydrogen and olefin to the liquid body, The temperature
of the liqu~d body is maintained at about 50 C. to about
130C., and the total pressure is maintained at less
tha~ about 400 pounds per square inch absolute. The
carbon monoxide partial pressure in the reaction is
less than about 50 pounds per square inch absolute and
the hydrogen partial pressure is less than about 200
8.
10816-1
~9 0 ~ Z 3
psunds per square inch absolute. There is removed from
the liquid body a vaporous mixture comprising olefin,
hydrogen, ~aporized aldehyde products and an amount o
vapDrized aldehyde condensation prod~ct~ essentially
cqual to the rate of their formation in the body whereby
the size of the liquid body is maintained at a predeter-
mined value. Aldehyde products and aldehyde condensation
products are recovered rom the vaporQus mixture and this
forms the gaseous recycled stream which is supplied to
the liquid body as mentioned above.
United States Patent 39527,809, entitled
ydro~ormylation Process" by R. L. Pruett and J. A.
Smith, issued September 8, 1970, discloses a significant
development in hydroformylation of alpha-olefins to
produce aldehydes at high yields, low te~peratures and
pressures, excellent catalyst stability and wh~ch when
the alpha-olefin contains 3 or more carbon atoms, pro-
duces aldehyde mixtures containing a high normal to
iso- (or branched-chain) isomer ratio. The process
2Q employs certain rhodium complex compounds to effectively
catalyze ~mder a de~ined set of variables, in the
presence o~ se7ect triorganophosphorus ligands, the
hydroformylation of olefins wi~h hydrogen aQd carbon
monoxide. The variables include (1) the rhodium complex
catalyst, (2) the olefin ~eed, (3) the triorganophosphorus
ligand and its concentration, (4) a relatively low
1081~1
Z;~
temperature range, (5) a relatively low total hydrogen
and carbon monoxide pressure, and (6) a l~itation on
the partial pressure exerted by carbon monoxide. The
process of this invention adc~pts the variables of the
invention of U.S. 3,5~7,809, and by experiences from
operations herein dPscribed establishes the tremendous
ad~ance that invention represents in the Oxo a.rt.
Among the catalysts described in the aforesaid
U.S. patent, are compounds containing rhodium in complex
combination with carbon monoxide and triarylphosphorus
ligands in particular triarylphosphine ligands exempli-
fied by triphenylphosphine (TPP). A typical active
catalytlc species is rhodium hydridocarbonyltris (tri~
phenylphosphine) which has the for~ula RhH(CO)[P(C6H5)3]3.
e process uses an excess of the triorganophosphorus
ligand.
The active rhodium catalyst, as is known in
recent literature, can be preformed and then introduced
into the reaction mixture media, or the acti~e catalyst
species can be prepared in situ during the hydro~ormyla-
tion reaction. As an example of the latter, (2,4-pentane-
dionato) dicarbonylrhodium(I) can be introduced into the
~eaction medium where, under the operative condi~ions
therein, it reacts with the triorganophosphorus ligand,
e.g., triphenyLphosphine, to thus form acti~e catalyst
~uch as rhodium hydridocarbonyl-tris(triphenylphosphine).
10 ~
1081~1
~9 ~ 8 Z 3
When the process of U.S. Patent 3,527,809
employs normally-liquid inert organic solvents which are
not products of the reaction or reac~ants ln the process
the product mixture e~entually becomes, either at room
tempcrature or at the chosen operating temperature o~, for
example, 80C., slightly cloudy in nature or it possesses
a noticeable precipitatio~. Elemental analyses indicates
that 3uch solids ~cloudiness or precipitate) contain
rhodium. In some in tances, it appears that "polymeric"
rhodlum ~omplex solids have fonmed and in other instances,
the solids are similar to an active form of the rhodium
complex species. Such solids can become lost in the
system, e.g~, deposit in small crevices or plug valves.
As noted above, a truly efficient commercial Oxo opera-
tion cannot tolerate the loss of even small ~uantities of
rhodium. A further disadvantage of introducing the
rhodium species as a solution in such an extraneous orgsnic
liquid is the obvious requirement of separating the oxy-
gsnated products formed in the reaction ~rom such organic
liquid. Since Oxo reactions produce aldehydes and high
boiling aldehyde condensation products which are removed
to mainta:Ln the solvent concen~rations, as noted above,
the removal of the condensation products by distillation
affect the solvent, some being distilled (if not all
distilled), and the Rh values it contains. The initial
introduction into the Oxo reaction zone of a catalytic
11.
10816 -1
~o 9 ~'~3
solution in extraneous organic Liquids is effe~tive,
However, ~uch a commercially based Oxo operat~on demands
csnt~nuous~or intermittent catalyst introduction which
can be fresh catalyst, regenerated catalyst9 or catalyst
contained in a recycle stre2m. Catalyst losses are the
result of such practices.
Copending U.S. Patent Application S.N. 556,270,
~iled March 7, 1975, a continuation o S.N, 887,370,
iled December 22, 1969, rom which British Patent Speci-
fication 1,338,237 is derived, ~mploys the high boiling
liquid aldehyde condensation products as a primary solvent
for the catalyst. As a result, no removal of the solvent
~rom the catalyst is necessary except for a small purOe
stream to keep down the concentration of condensation
products and poisons to the reactio~. As a result, the
hydroformylation of 3 carbon olefins~ or higher,maintains
the high ratio of normal/iso isomer distribution of alde-
hydic product over extended periods of time and the
co~tinuous recycling of the rhodium species in substantial
quantitie~ of such condensation products does not result
in extensive precipitation of the rhodium i~ one orm or
another, No discernible lo s in th~ life of the catalyst
wa~ detect:ed over extended periods of operation. The use
of such condensation products as the media to solubilize
the rhodium-containing catalyst was advantageous from the
standpoint that extraneous organic liquids could be
12.
- 10 9~ ~ ~ 3
1081~1
excluded entirely from the hydroformylation zone, i~
desired. The use of excess, ~ree triorganophosphorus
ligand in the reaction medium containing the dissimilar
high boiling condens~tion products to provide the advantages
cited in U.S. 3,527,809 did not inhibit the activity or
solub~l~ty of the rhodiu~ complex catalyst even over long
perlods of continuous operatlon. Since these condensation
products are formed in situ, She economics of the afore-
mentioned process are extremely favorable.
After substantial repeated use it was found that
co~tinuous recycle o rhodium species dissolved in the high
boiling liquid condensation products presented disadvantages.
The constant movement of ca alyst led to some catalyst loss,
considerable catalyst volume was required because in th
liquid ~ecycle a portion of the catalyst is outside of the
reactor; rate of residue formatîon remained at significant
levels and had to be removed, ~hus affecting catalyst
stability on such occasions; control of carbon monoxide
gas pressure was difficult; the nature o the recycle
brought about heat,losses because of the constant movement
of hot liquids through the system; and there developed a
tendency to have small oxygen leak~ge which proved dele-
terious to the process.
It has been determined that a hydroformylation
reaction using a non-volatile catalyst, such as hydrido-
car~onyltris (triphenylphosphine)rhodium(I), in the liquid
13.
10816 -1
~ 0 ~ 0 8 Z 3
phase can be carried out in a more convenient manner and
with simpler equipment by allowing the aldehyde reaction
product and their higher boiling condensation products to
distil out of the catalyst containing liquid body (or solu-
tion) at the reaction t~mperature and pres~ure, by condens-
ing the aldehyde reaction product and the condensation
products out of the off gas from the reaction vessel in a
product recovery ~one and by recycling the unreacted start-
~g materials (e.g., carbon monoxide, hydrogen and/or
alpha-olefin) in the vapor p~ase from the product recovery
zone to ~he reaction zone. Furthermore, by recycling gas
, from the product recovery zone coupled ~ith make-up start-
ing material~ to the reaction zone in sufficient amounts,
it is po~sible, using a C2 to C5 olefin as the alpha-
' olefin starting material, to achieve a mass balance in theliquid body in the reactor and thereby remo~e from the
reaction zone at a rate at least as great as their rate of
formation essentially all the higher boiling condensation
products resulting from self condensation of the aldehyde
product. If the gas recycle is not sufficient, such con-
densation products would otherwise build up in the react`ion
vessel.
According to the present invention a process for
the production of an aliphatic aldehyde containing from
3 to 6 carbon atoms comprises passing an aliphatic alpha-
olefin containing from 2 to 5 carbon atoms together with
hydrogen and carbon monoxide at a pre~cribed temperature
1~, .
08
~09~8~3
- and pressure through a reaction zone containing the
catalyst dissolved in the liquid body, the catalyst being
esqentially non-volatile and being effective for hydro-
formylation of the alpha-olefin, continuously removing a
vapor pha~e from the reaction zone, passing the vapor phase
to a product separation zone, separating a liquid aldehyde
containing product in the product separation zone by con-
densation from the gaseous unreacted starting materials,
a~d recycling the gaseous unreacted starting materials from
the product separation zone to the reaction zone. Prefer-
ably the gaseous unreacted starting materials plus make-up
starting materials are recycled at a rate at least as great
as that required to maintain a mass balance i~ the reaction
zone.
In the process of the invention there is con-
temFlated the use of alpha-olefins o 2 to 5 carbon atoms,
preferably 2, 3 or 4 carbon atoms. Such alpha~oleins are
characterized by a terminal ethylenic carbon-to-carbon bond
which may be a viny~idene group, i.e., CH2 ~ C <, or a
vinyl group, ~.e., CH2 ~ CH-. They may be straight-chain
or branched-chain and may contain groups or substituents
which do not essentially interfere with the course of
thls process. Illustrative alpha-olefins include ethylene,
propylene, l-butene, iso-butylene, 2-methyl-1-butene,
l-pentene, and the like.
TSe reaction is advantageously conducted at a
15.
~.5~ ~ 8 Z 3 10816-1
temperature of from about 50(' to about 140C. A
temperature in the range of from about 60C to about
120C is preferred and it will usually be convenien~
to operate at a temperature oi. from about 90 to about
115C
A feature of the invention is the low total
pressures which are required to effect a commercial
process. Total pressures less than about 400 psia and
as low as one atmosphere, an~ lower, can be employed with
effective results. Total pressures of less than 350
psia are preferred. The rèaction can be effected at
pressures ranging between about 100 to about 300 psia.
The partial pressure of the carbon monoxide is
an important factor in the process of the invention. It
has been observed that when using the complex rhodium
catalysts a noticeable decrease in the normal/iso alde-
hydric product isomer ratio occurs as the partial pressure
attributable ~o carbon monoxide approaches a value of
about 75 per cent of the total gas pressure (CO + H2).
In general, a partial pressure attributable to hydrogen
of from 25 to 95 per cent and more, based on the total
gas pressure (CO + H2) is suitable. It is generally
advantageous to employ a total gas pressure in which the
partial pressure attributable to hydrogen is significan~ly
greater than the partial pressure attributable to carbon
monoxide, e.g., the hydrogen to carbon monoxide ratio
being between 3 : 2 and 100: 1. Routinely, this ratio
can be at about 62.5 : 1 to about 12.5 : 1.
16.
~ Z 3 10816_~
The partial pressure of the C~-olefin in the
reaction zone may be up to about 35 per cent of the
total pressure, preferably in the region of 10 to 20
per cent of the total pressure.
In a preferred operation the C0 partial pressure
is typically not in excess of about 50 p.s.i.a., most
desirably not in excess of about 35 p.s.i.a. The pre-
ferred hydrogen partial pressure should be less than
about 200 p.s.i.a. For example, the H2 partial pressure
may be 125 p.s.i.a. and the C0 partial pressure may
ra~ge fro~ 2 to 10 p.s.i.a.
The catalyst may be any non-volatile catalyst
that is effective for hydroformylation of alpha-olefins
but in view of the known advantages as taught in U.S.
3,527,809 of catalysts based on rhodium, it constitutes
in modified form the catalyst of choice. When a C3 or
higher olefin is used as a starting material it is
preferred to choose a catalyst that gives a high
n-/iso-ratio in the aldehyde product mixture. The
~0 general class of rhodium catalysts depicted in U.S.
3,527,809 may be used in the practice of this invention.
The preferred catalyst of this invention
comprises rhodium complexed with carbon monoxide and a
triarylphosphine ligand. The most desirable catalyst
is free of halogen such as chlorine, and contains
hydrogen, carbon monoxide and triaryl phosphine com-
plexed with rhodium metal to produce a catalyst soluble
in the aforementioned liquid body and stable under the
conditions of the reaction. Illustrative triaryl-
~ 7.
10816-1
1 ~ ~ 0 ~ ~ 3
phosphine li~ands are triphenylphosphine, trinaphthyl-
phine, tritolylphosphine, tri(p biphenyl)phosphine,
tri(p-methoxyphenyl)phosphine, tri(m-chlorophenyl)-
phosphine, p-N,N-dimethylaminophenyl bis-phenyl
phosphine, and the like. Triphenylphosphine is the
preferred ligand. As pointed out previously, the
reaction is effected in a liquid body containing excess,
~ree triarylphosphine.
Rhodium is preferably introduced into the liquid
body as a preformed catalyst, e.g., a stable crystalline
solid, rhodium hydridocarbonyl-tris(triphenyl phosphine),
RhH(CO)(PPh3)3. The rhodium can be introduced to the
liquid body as a precursor form which is converted in situ
into the catalyst. Examples of such precursor form are
rhodium carbonyl triphenylphosphine acetylacetonate, Rh203,
Rh4(CO)l~, Rh6(CO)16, and rhodium dicarbonyl acetylace~onateO
Both the catalyst compounds which will provide active
species in the reaction medium and their preparation are
known by the art, see Brown et al., Journal_of the Chemical
Society, 1970, pp. 2753-2764.
In ultimate terms the rhodium concentration in
the li~uid body can range from about 25 ppm to about
1200 ppm of rhodium calculated as free metal, and the
triarylphosphine is present in the range of about 0.5
~ percent to about 30 percent by weight, based on the weight
of the total reaction mixture, and in an amount sufficient
to provide at least 10 moles of free triarylphosphine per
mole of rhodium.
18.
10816-1
10~30~23
The significance of free ligand is taught in
U.S. 3,527,~09, ~e~, British Patent Specification 1,338,225,
and Br~wn et al., supra, pages 2759 and 2761.
In general the optimum catalyst concentration
depends on the concentration of the alpha-olefin, such as
propylene. Fur example, the higher the propylene concentration
the lower usually will be the catalyst concentration that
can be used to achieve a given co~version rate to aldehyde
products in a given size of reactor. Recognizing that
partial pressures and concentration are related, the use of
higher propylene partial pressure leads to an increased
proportion of propylene in the "off gas" from the liquid
~ody. Since it may be necessary to purge part of the gas
stream from the product recovery zone before recycle to
the liquid body in order to remove a portion of the propane
which may be present, the higher the propylene content of
the "off gas" is, the more propylene that will be lost in
the propane purge stream. Thus it is necessary to balance
the economic value of the propylene lost in the propane
~0 purge stream against the capital savings associated with
lower catalyst concentration.
An unforeseen advantage of this modified Rh
catalyzed process is that in the hydroformylation of ethylene
no diethyl ketone is formed in measurable quantities whereas
all of the Co catalyzed processes produce significant amounts
of diethyl ketone.
It is preferred to effect the process of the
invention using a liquid phase in the reaction zone which
19 .
. 10816-1
~ ~ 9 ~ ~ ~ 3
con~ains one of the aforement:ioned rhodium complex
cataLysts and9 as a solvent t:herefor, higher boiLing liquid
aldehyde condensation produc~:s (as hereinafter defined
which are rich in hydroxylic compounds).
By the term "higher boiling liquid aldehyde
cond~nsation products" as used herein is meant the com-
plex mixture of high boiling liquid products which result
from the condensation reactions of the C3 to C6 alkanal
product of the process of the in~ention, as ilLustrated
below in the series of equations involving n-buty~aldehyde
a~ the model. Such condensation products can be pre~ormed
or produeed in situ in the Oxo process. The rhodium com-
plex species is soluble in these relatively high boiling
liquid aldehyde condensation products while exhibitin~
high catalyst li$e over extended periods of continuous
hydroformylation.
Inltially, the hydroformylation reaction can be
e~$ected in the absence or in the presence of small amounts
of higher boiling liquid aldehyde condensation products as
a solvent for the rhodium complex, or the reaction can be
condu~ted with up to about 70 weight per cent, and even
as much as about 90 weight per cent, and more, of such
condensation products, based on the weight of the liquid
body. A small amount of the higher boiling liquid alde-
hyde condensation products can be as little as 5 weight
per cent, preferably more than 15 weight per cen , based
on the weight of the liquid body.
20.
. loal6-
~090823
In ~he hydroformylation of, for example,
propylene, two products are possible, namely normal and
iso-butyraLdehydes. Since normal butyraldehyde is the
more attractive product commercially, high normal/iso
ratios of butyraldehydes are desirable. However, the
aldehydic products being reacti~e compounds themselves
slowly undergo condensation reactions, even in the
absence o~ catalysts and at comparat~veLy low tempera-
tures, to form high boiling liquid conden~ation productq.
Some aldehyde product, therefore, is involved in ~arious
reactions as depicted below using n-butyraldehyde as an
illustration:
OH
I ~H~O
2CH3CH2CH2CHO ~ CH3CH2CEI2CHCHGH2cH3 > CH3CH2CH2~H ~
CHO CH3 CH2
al~ol (I) substituted acrolein(II)
CH3CH2CH2CH
IH \ / ICCH2c~2cH3
20CH3CH2CH2~1CHcH2cH3 '~ ~ CH3CH2CH2 2 3
l ll CH20
C~20CCH2C 2CH3
(trimer III) (trlmer IV)
21.
10816-1
~ 0 ~ 0 ~ 2 3
(trimer III) (trimer IV)
heat
IH l l CH3CH2CE2C~O
CH3CH2CH2cHI CH2CH3 CH3CH2C~2cHcHcH2cH3
CH20H \' O
\ ll
CHzOCC~I2CH2 CH 3
(dimer V) ttetramer VI)
In addition, aldol I can undergo the fo~lowing
reaction:
. ~H
2 aldol I - > CH3CH2CH2CHCHCH2CH3
¦ OH
COOCH2CH~HCH2CH2C~3
CH3
~tetramer VII)
The names in parentheses in the afore-illustrated
equations, aLdol I, substituted acrolein II, trimer III,
trimer IV, dimer V, tetramer VI, and tetramer VII, are for
convenience only. Aldol I is formed by an aldol condensa-
~ion; trlmer III and te~ramer ~II are ormed via Tischenko
reactions; trimer IV by a transesterification reaction;
dimer V and tetramer VI by a dismutation reaction. Prin-
~ipal condensation products are trimer III, trimer IV,
and tetrc~mer VII, with lesser amounts o the other prod-
ucts being present. Such condensa~lon products, therefore,
contain substantial quantities of hydroxylic compounds as
witnessed, for example, by trimers III and IV and tetramer
VII .
10816-1
Similar condensation products are produced by
self condensation of iso-butyraldehyde a~d a further range
of compounds is formed by condensation of one molecule of
normal butyraldehyde with one molecule of iso-butyraldehyde.
Since a molecule of normal butyraldehyde can aldolize by
reaction with a molecule of iso~butyraldehyde in two dif-
ferent ways to form two different aldols VIII and IX, a
total of four possible aldols can be produced by conden-
sation reactions of a normal/iso mixture of butyraldehydes.
IH CH3
~3cH2~2~o ~ ~3CHcH3 ~3 ~H3cEI2cH2cH-fcEI3
~ O CHO
Aldol (VIII)
CH3 OX
i -CHi CH2CH3
CH3 CH0
Aldol (IX)
Aldol I can undergo further condensation wlth
isobutyraldehyde to form a trimer isomeric with trimer III
and aldols VIII and IX and the corre~ponding aldol X pro-
duced by self condensation of two molecules o~ isobuty-
raldehyde can undergo further react~ons with either normal
or isobutyraldehyde to fonm corresponding lsomeric trimers~
These trimers can react ~urther a~alogously to trimer III
so tha~ a complex mixture o~ conden9ation products is
~ormed.
It is highly desirable to maintain the sub-
stituted acrolein II and its i~omers at low concentrations,
10816-1
~ ~ O ~ Z 3
e.g. below about 5 weight per cent. The substituted
acrolein II, specifically termed 2-ethyl, 3-propyl-
acrolein (~'EPA"), is formed in situ along with other
condensation products and has been found to inhibit
catalyst activity. The ultimate effect of EPA or like
products is to reduce hydroformylation rates to such an
exent ~hat any process where the EPA is present in
amounts greater tha~ about 5 weight percent, even greater
than about one percent by weight based on the weight of
the liquid body, will suffer an economic penalty.
In a preferred form of the process of the inven-
tion the higher boiling liquid eondensation products to be
used as solvents are preformed prior to introduction into
the reaction zone and the start-up of the process.
Alternatively, it is possible to add, for example, Aldol I
at process start-up and to allow the other products to
build up as the reaction proceeds.
In certain instances, it may also be desirable
to use minor amounts of an organic co-solvent which is
normally liquid and inert during the hydro~ormylation
process, e.g. toluene or cyclohexanone, particularly at
start up of the process. They can be allowed to be replaced
in the liquid phase in the reaction zone by the higher
boiling liquid aldehyde condensation products as the
reaction proceeds.
The liquid body will contain, in addition to
the catalyst and any added diluent such as free ligand
triphenylphosphine, an aldehyde or a mixture of aldehydes
24.
10816-1
1~ 9 ~ ~ ~ 3
and the aldols, trimers, diesters, etc. derived ~rom them.
The relative proportion of each product in solution
is controlled by the (amount of gas) passing through the
solution. Increasing this amount decreases the equilibrium
aldehyde concentration and increases the rate of by-product
removal from solution. The by-products include the higher
boiling liquid aldehyde condensation products. The decreased
aldehyde c~ncentration leads to a reduction in the rate o
formation of the by-products.
' The dual effect of increased removaL rate and
decreased formation rate means that the mass balanee in
~y-products in the reactor is very sensitive to the amount
of gas passing through the liquid body. The gas cycle
typically includes make-up quantities of hydrogen, carbon
monoxide and alpha-olefin. However, the most meaning~ul
factor is the amount of recycle gas returned to the liquid
body since this determines the degree of reaction, the
amou~t of product formed and the amount of by product
(as a consPquence) removed.
Operation of the hydroormylation reaction with
a given flow rate of olefin and synthesis gas and with a
total low amount ~f gas recycle less than a critical
threshold rate results in a high equilibrium aldehyde
concentration i~ solution and h~nce, in high by-product
formation rates.
10816-1
~ 8 ~ 3
The rate ofremoval of by-products in the vapor phase
effluent from the reactio~ zone (liquid body) under such
conditions will be low because the low vapor phase
effluent flow rate from the reaction zone can only result
in a relatively low rate of carry-over of by-products.
The net effect is a build-up of by-products in the liquid
body solution causing an increase in the soluti~n volume
with a consequent lcss of catalyst productivity. A purge
must therefore be taken from the solution when the
hydroformylation process is operated under such low gas
flow rate conditions in order to remove by~products and
hence maintain a mass balance over the reaction zone.
If however, the gas flow rate through the reac-
tion zone is increased by increasing the gas recycle rate
the solution aldehyde content falls, the by-product
for~ation rate is decreased and by-product removal rate in
the vapor phase effluent from the reaction zone is in-
creased. The net effect of this change is to increase the
proportion of the by-products removed with vapor phase
effluent from the reaction zone. Increasing the gas flow
rate through the reaction zone still further by a further
increase in the gas recycle rate leads to a situation in
which by-products are removed in the vapor phase effluent
from the reaction zone at the same rate as they are
formed, thus establishing a mass balance over the reaction
26.
10816-1
~ 3
zone. This is the critical threshold gas recycle rate
which is the preferred min~m~m gas recycle rate used in
the process of the invention. If the process is operated
with a gas recycle rate higher than this threshold gas
recycle rate the volume o~ the liquid body in the reaction
zone will tend to decrease and so, at gas recycle rates
above the threshold rate, some of the crude aldehyde by-
product mixture should be returned to the reaction zone
from the product separation zone in order to keep constant
the ~ol~me of the liquid phase i~ the reaction zone.
me critical threshold gas recycle flow rate can
be found by a process of trial and error for a given olefin
and ~ynthesis gas ~the mlxture of CO and hydrogen) feed
rate. Operating a~ recycle rates below the critical thres-
hold rates will increase the volume of the liquid phase
with time. Operating the threshold rate keeps the volu~e
constant. Operating above the threshold rate decreases
the volume. The critical threshold gas recycle rate can
be calculated from the vapor pressures at the reac~ion
temperature of the aldehyde or aldehydes and of each of
the by-products present.
With the process operating at a gas recycle rate
at or greater than the threshold rate, by-produc~s are
removed i~ ~he gaseous vapors removed from the reaction
zone containing the liquid body at the same ra~e as or
faster than they are formed, and thus do no~ accumulate
10816 -1
~ Z 3
in the liquid phase in the reac~ion zone. Under such
circumstances, it is unnecessary to purge the liquid body
containing the catalyst from ~he reaction zone in order to
remove by-products. This has the advantage of obviating
removaL of catalyst rom the reaction zone, except at
- extended intervals when renovation of the ca~aLyst is
necessary, and thus the chance of losses of expensive
catalyst by accldental spillage or leakage iq reduced.
Furthermore there is no need for high temperature treat-
ment of the catalyst-containlng purge solution or by-
product removal and thus catalyst life is extended.
Experience to date suggests that catalyst renovation of
any kind is not required for at least one (1) year's
op2ration.
The residence period of aldehyde ln the reaction
zone can ~ary from about a couple of minutes to several
hours in duration and, as is well appreciated, this vari-
able wil~ be inluenced, to a certain extent, by the
reaction tem~erature, the choice of the alpha-olefin of
the catalyst, and of the ligand, the concentration of the
ligand, the total synthesis gas pressure and the partial
pressure e~erted by its components, and other factors.
As a practical matter the reaction i~ effected ~or a period
o time wh:ich is sufficient to hydroformylate the alpha or
terminal ethylenic bond of the alpha-olein.
- 28.
10816 l
~0 ~'~3
~ by-product of the hydroformylation process is
the alkane formed by hydrogenation of the alpha olefin.
Thus, for example, in the hydroformylation of propylene a
by~product is propane. Preferably, therefore, a purge
8tream is taken from the gas recycle stream from the product
recovery zone in order to remo~e propane and prevent its
build-up within the reaction system. This purge stream will
contain, in addition to unwanted propane, unreacted
propy1ene, some inert gases introduced in the feedstock
and a mixture of carbon monoxide and hydrogen. The purge
stream can, if desired, be su~mitted to conventional ga
separation techniques, e.g. cryogenic techniques, in order
to recover the propylene. However, i~ w~ll usually be
uneconomical to do this and the purge stream is ypically
used a~ a fuel. The principal romposition of the recycle
gas are hydrogen and propylene. However, if the G0 is not
consumed in the reaction, the excess CO will also be part
of the recycle gas. Usual1y the recycle gas will contain
a-kane even with purging beore recycLe.
It will be appreciated that the process of the
invention can be operated continuously for long periods of
tlme w~thout remo~ing any of the catalyst containing liquid
body from the reaction zone. However, rom time to time it
may be necessary to regenerate the rhodium catalyst, in which
case a purge stream can be taken from the reactor through
a normally locked valve, frash catalyst being added to
29.
~ ~ z 3 1081~1
maintain the catalyst concentration in the liquid body
or the removed catalyst can be regenerated. After
removal from the liquid body in a reactor, the vapor
effluent is fed to a product separation zone where the m~x-
ture of the aldehyde or aldehydes and the dimers, trimers
and other higher boiling liquid condensation products are
worked up by conventional techniques, e.g. distillation,
in order to remove the aldehyde or aldehydes and, if
appropriate, to separate the aldehydes one from another
and recover the h;gher boiling liquid aldehyde condensa-
tion products.
The alpha-olefin used as starting ma~erial in
the process must be rigorously purified in order to remove
~he typical potential Oxo catalyst poisons, see Falbe,
supra, pages 18-22. The carbon monoxide and hydrogen
required for the process can be produced by partial oxida-
tion of a suitable hydrocarbon ~eedstock, e.g. naphtha,
and mNSt also be purified rigorously to exclude potential
ca~alyst poisoning impurities.
The inventi~n is further illustrated with
reference to the accompanying drawing which sche~atically
shows a diagramat~c flowsheet suitable in practising
the process of the in~ention.
Referring to the drawing, a stainless steel
reactor 1 is provided with one or more disc impeller 6 con-
taining perpendicularly mounted blades and rotated by means
30.
~9~8Z3 10816 -1
of shaft 7, by a suitable motor (not shown). Located below
the impeller 6 is a circular tubular sparger 5 for feeding
the ~ -olefin? and synthesis gas plus the recycle gas.
The sparger 5 contains a plurality of holes of sufficient
size to provide sufficient gas flow in ~ the liquid body at
about the impeller 6 to provide the desired amount of the
reacta~ts in the liquid body. The reactor is also provided
with a steam jacket (not shown) by means of which the
contentsof the vessel can be brought up to reaction
temperature at start-up and internal cooling coils (not shown)
Vaporous product effluent from the reactor 1
are removed via line lO to separator 11 where they are passed
through a demisting pad lla therein to return some aldehyde
and condensation product and to prevent potential carry-over
of catalyst. The reactor effluent is passed by line 13 to
a condenser 14 and then through line 15 to catchpot 16 in
which the aldehyde product and any by-product can be condensed
out of the off gases (effluent). Condensed aldehyde and
by-products are removed from the catchpot 16 by line 17.
Gaseous materials are passed via line 18 to separator 19
containing a demisting pad and recycle line 20. Recycle
gases are removed by line 21 to line 8 from which a purge
through line 22 is pulled to control saturated hydro
carbon content. The remaining and major porportion
of the gases can be recycled via line 8 to line
4 into which is fed make-up reactant feeds through
lines 2 a~d 3. The combined total of reactants are fed
~0 90 8 ~ ~ 10816 -1
to the reactor L. Compressor 26 aids in transporting the
recycle gases.
Fresh catalyst solution can be added to the
reactor 1 b~ line 9. The single reactor 1 can o co~rse,
be replaced by a plurality of reactors in parallel.
The crude aldehyd~ product of line 17 can be
treated by conventional aistillation to ~eparate the
various aldehydes and the condensation products. A por-
tion of the crude can be recycled to reactor 1 through
line 23 and fed as indica~ed by broken-line 25 to a point
above impeller 6 for ~he purpose of maintaining the liquid
le~el in reactor 1 if such is required.
.The following example serves to illustrate the
practice of this invention and not lim~t it.
EXAMPLE
~ The reactor employed is a stainless steel cylin-
drical vessel as characterized in tha drawing, having dimensio
of ~3 feet inside diameter and 24 feet height containing a
4 feet diP~eter, 8 ~nches inside diameter tubular sparger
located immediately below the impeller. The sparger con-
tains a plurality of holes to allow feed of reactants.
The c~nditions of the reaction using the process
de~ign of the drawi~g are set forth in Tables 1 and 2.
32.
10816 -1
~ ~ ~ O ~ ~,3
TABLE 1
Contents of Reactor 1
Com~ nent Characterization Amount
Liquid Volume 42,000 liters
Rh, determined as metal* 275 ppm
Triphenyl Phosphine 7.5 weight %
Total butyraldehydes 35 weight %
Trimer 50 weight %
Other higher boiling 7.5 weigh~ %
condensation products
*The rhodium is supplied as hydridocarbonyltris-
(triphe~ylphosphine)rhodium(I~.
~ ~ ~3 3 10816-1
o ~ ~ ~ aR
V3 ~ ~ O ~1 ~1
w ~ ~ ~ ~ 8 1~
~ ~ o U~
C~ o
Z ~n o u~ .
~ ~1 ~ ~ In
.
C~l
. . . ...... _ .
o ~ ~
,, _,
~o ~ 8
o o
~ ~ o ,
P~ ~o
~ ~ ,
_ , _ _ _
o ~ ~ ~ ~ ~ ~ ~ ~
~ ~ _I ,1 ~ ~ ~ ,1 ,1
P4 0 0 0 0 0 0 0 0 u~ o o
~3 ~ E~ E E3 li 8 e 8 E i`
c~ ~3 o ~ u~ ~ oo c~ ~ ~ r~
~-o
O C`~ ~1 ~ ~ ~D
~ ~ o . ,1 ~ ~
~on
c~. E~ ~-
æ
o o o o o o o o Q ~`I o
e E; E3
~D ~ I~
~: ~~ o~ 9 o
~ ~ .
o
~ ~ ~ 8 ~ 3 E E3 E
P~ ~ O ~1 ~ ~ ~ G~ 0
~D _I C`l
C`~ .
~ . ,
CJ
~a
~ ~ Z ~ ~ ~ o
~:1 O 1~ l O O ~ U ~C) ~ E~
~ ~ ~, o ~ ~ o ~J ~1 ¢ ~ ~ I o
O ¢
pc ~ ~c~
, ~ H
34.
2 3 10816 -1
The make-up of product frsm line 17 is as
- ollows:
COMPONENT CONIENTS OF
CHARACTERIZATION~RUDE PRODUCT
_
Composition(wt.%~
CO 0.06
H2 O . 01
C3H6 4.82
C3H8 4.40
C2 O.39
CH4~ 0.08
Normal Butyraldehyde 82.59
Iso Butyraldehyde7.14
Aldols 0.01
EPA 0.16
H20 0.13
Trimers 0.20
Diester 0.01
Diol 0.01
TPP Trace
E;ssentially the same procedure has been
proven to be a most effective technique to produce
propionaldehyde from ethylene.
35.
