Perstraction sweep stream for a membrane reactor

A method for separating a noble metal catalyst from a crude reaction product of a noble metal-catalyzed hydroformylation reaction which comprises: (a) contacting the crude reaction product under perstraction conditions with a membrane capable of allowing a substantial portion of unreacted olefin feed and hydroformylation reaction product to pass therethrough as permeate while retaining a substantial portion of the catalyst as retentate; (b) removing the permeate by sweeping it away from the membrane by means of a sweep stream which is the same as the olefin feed used in the hydroformylation reaction; and (c) retaining the catalyst as retentate.

The present invention relates generally to the use of reactor feed as the 
sweep stream during membrane separation of the reaction products under 
perstraction conditions. This is particularly effective in the separation 
of noble metal catalysts from the resultant aldehydes formed by 
hydroformylation, whereby the olefinic feed used to form the aldehydes is 
also used as the sweep stream or solvent. 
BACKGROUND OF THE INVENTION 
Hydroformylation reactions involve the preparation of oxygenated organic 
compounds by the reaction of carbon monoxide and hydrogen (synthesis gas) 
with carbon compounds containing olefinic unsaturation. The reaction is 
typically performed in the presence of a carbonylation catalyst and 
results in the formation of compounds, for example, aldehydes, which have 
one or more carbon atoms in their molecular structure than the starting 
olefinic feedstock. By way of example, higher alcohols may be produced by 
hydroformylation of commercial C.sub.6 -C.sub.12 olefin fractions to an 
aldehyde-containing oxonation product, which on hydrogenation yields the 
corresponding C.sub.7 -C.sub.13 saturated alcohols. The crude product of 
the hydroformylation reaction will contain catalyst, aldehydes, alcohols, 
unreacted olefin feed, synthesis gas and by-products. 
A variety of transition metals catalyze the hydroformylation reaction, but 
only cobalt and rhodium carbonyl complexes are used in commercial oxo 
plants. The reaction is highly exothermic; the heat release is ca 125 
kJ/mol (30 kcal/mol) The position of the formyl group in the aldehyde 
product depends upon the olefin type, the catalyst, the solvent, and the 
reaction conditions. Reaction conditions have some effect and, with an 
unmodified cobalt catalyst, the yield of straight chain product from a 
linear olefin is favored by higher carbon monoxide (CO) partial pressure. 
In the hydroformylation of terminal olefinic hydrocarbons, the use of a 
catalyst containing selected complexing ligands, e.g., tertiary 
phosphines, results in the predominant formation of the normal isomer. 
In commercial operation, the aldehyde product used as an intermediate is 
converted by hydrogenation to an alcohol or by aldolization and 
hydrogenation to a higher alcohol. The aldol-hydrogenation route is used 
primarily for the manufacture of 2-ethylhexanol from propylene via 
n-butyraldehyde. 
The hydroformylation reaction is catalyzed homogeneously by carbonyls of 
Group VIII metals but there are significant differences in their relative 
activities. Roelen, using a cobalt catalyst, discovered hydroformylation 
in 1938. Dicobalt octacarbonyl, Co.sub.2 (CO).sub.8, which is introduced 
either directly or formed in situ, is the primary conventional 
hydroformylation catalyst precursor. Using an unmodified cobalt catalyst, 
the ratio of linear to branched aldehyde is relatively low. 
Introduction of an organophosphine ligand to form a complex, e.g., Co.sub.2 
(CO).sub.6 [P(n--C.sub.4 H.sub.9).sub.3 ].sub.2, significantly improves 
the selectivity to the straight-chain alcohol. 
Recent developments of low pressure rhodium catalyst systems have been the 
subject of a considerable body of patent art and literature, and 
rhodium-triphenyl phosphine systems have been widely, and successfully, 
used commercially for the hydroformylation of propylene feedstocks to 
produce butyraldehyde. 
The first commercial process to employ a rhodium-modified catalyst was 
developed by Union Carbide, Davy Powergas, and Johnson Matthey. In this 
application, the complexed rhodium catalyst is dissolved in excess ligand 
and the reaction is run at relatively low pressures and temperatures as 
compared to other processes. 
A recent process commercialization has been that of Rhone-Poulenc and 
Ruhrchemie which produces butyraldehyde from propylene but the ligand is a 
sulfonated triphenylphosphine and is utilized as a water-soluble sodium 
salt. Turnover rates are less than in an all-organic system, but the 
normal to iso ratios are high and the catalyst may be separated easily 
from the reaction product by separation of the aqueous layer containing 
the catalyst and the organic layer which constitutes the product. 
In the formation of linear aldehydes using a ligand-modified 
rhodium-catalyzed homogenous process, the reactor comprises the rhodium 
complex catalyst, excess triphenylphosphine and a mixture of product 
aldehydes and condensation by-products. The product aldehyde may be 
recovered from the mixture by volatilization directly from the reactor or 
by distillation in a subsequent step. The catalyst either remains in or is 
recycled to the reactor. However, the complex catalyst and 
triphenylphosphine ligand are slowly deactivated and eventually the spent 
catalyst is removed for recovery of rhodium and reconversion to the active 
catalyst. This process, although effective for lower molecular weight 
aldehyde production, is not favored for higher molecular weight aldehydes. 
Higher molecular weight aldehydes have higher boiling points (i.e., 
distillation temperatures) and catalyst deactivation is accelerated. 
In some cases, such as where the products of the reaction have relatively 
high boiling points or where the olefin feed is not sufficiently soluble 
in water to permit satisfactory reaction rates, neither the process where 
the products are removed from the catalyst by distillation or stripping 
nor where the products are decanted from an aqueous catalyst solution may 
be utilized successfully. In such cases, it may be advantageous to utilize 
an aqueous medium to contain the catalyst and add a surfactant to enhance 
phase contacting so as to improve rate and selectivity to the desired 
products. This type of process is called "Phase Transfer Catalysis." 
However, when a surfactant is added, some carry-over of the noble metal 
into the organic phase at the conclusion of the process often results. 
The present inventors have discovered that when olefins are satisfactorily 
hydroformylated in the presence of water-soluble Group VIII noble 
metal-ligand complex catalysts, the catalyst can be recovered 
quantitatively from a crude reaction product which includes the olefinic 
feed, aldehydes and alcohols by employing membrane separation either 
internal or external to the hydroformylation reactor. 
A variety of membrane separation processes have also been tested for 
separating high boiling point products from an oil soluble catalyst 
complex. Attempts have been made to create large catalyst complexes which 
could be separated by ultrafiltration. In one case, high molecular weight 
phosphine ligands were used to form a homogeneous catalyst complex. High 
molecular weight polymeric phosphine ligands are synthesized by reacting 
polyvinylchloride, polychloroprene or brominated polystyrene with lithium 
diphenylphosphide at 20.degree. C to 25.degree. C. These homogeneous 
catalysts containing bulky ligands are thought to be more easily separated 
from the reaction products by ultrafiltration. See Imyanitov et al., 
All-Union Scientific Research Institute of Petrochemical Processes, 
Neftekhimiva, 32, No. 3:200-7 (May-June 1992). The process described 
herein uses a smaller catalyst complex which is not attached to a 
polymeric backbone. 
It has been known to use membranes to separate catalysts from an aqueous 
solution. An example is set forth in European Patent No. 0 263 953, 
published on Aug. 29, 1986 (assigned to Ruhrchemie Aktiengesellschaft), 
which discloses a process for separating rhodium complex compounds, which 
contain water-soluble organic phosphines as ligands, from aqueous 
solutions in which excess phosphine ligand and, if necessary, other 
components are also dissolved, is characterized by the fact that the 
aqueous solution is subjected to a membrane separation process. According 
to this process, volatile organic substances are separated from the 
solution prior to conducting the membrane separation process. A typical 
membrane for use in this process is a cellulose acetate membrane. This 
process only involves the separation of water-soluble ligands and noble 
metal catalyst from an aqueous solution. As such, this separation process 
does not pertain to the separation of a water-soluble noble metal catalyst 
and a water-soluble ligand from an organic-aqueous emulsion, dispersion or 
suspension produced from a hydroformylation process. 
Another patent which utilizes cellulose acetate, silicone rubber, 
polyolefin or polyamide membranes in the separation of catalysts from high 
boiling by-products of the hydroformylation reaction is Great Britain 
Patent No. 1312076, granted on May 15, 1970. According to this patent the 
aldehydes produced during the hydroformylation process are continuously 
withdrawn as an overhead vapor stream. The liquid stream containing the 
heavy by-products with the catalyst is passed over a membrane wherein 
approximately 78-94.3% of the catalyst is retained and the heavy 
by-products permeated. This is an unacceptably low level of catalyst 
retention which is overcome by the process of the present invention. 
In like manner, Great Britain Patent No. 1432561, granted on Mar. 27, 1972, 
(assigned to Imperial Chemical Industries Ltd.) discloses a process for 
the hydroformylation of olefins which comprises reacting an olefin at 
elevated temperature and pressure with CO and H.sub.2 in the presence of a 
compound of a group VIII metal and a biphyllic ligand of a trivalent P, As 
or Sb to give a crude liquid hydroformylation product containing an 
aldehyde and/or an alcohol, separating the aldehyde and/or alcohol from 
the crude product and leaving a liquid, bringing the liquid after 
separation of the Group VIII metal compound and free from aldehyde and 
alcohol under reverse osmosis conditions into contact with one side of a 
silicone rubber semi-permeable membrane in which the polymer chains have 
been at least partly crosslinked by gamma radiation, whereby the liquid 
retained by the membrane contains a higher concentration of Group VIII 
metal compounds and/or biphyllic ligand than the original liquid. 
In an article by Gosser et al., entitled "Reverse Osmosis in Homogeneous 
Catalysis," Journal of Molecular Catalysis, Vol. 2 (1977), pp. 253-263, a 
selectively permeable polyimide membrane was used to separate soluble 
transition metal complexes from reaction mixtures by reverse osmosis. For 
example, separation of cobalt and rhodium complexes from hydroformylation 
products of 1-pentene. That is, a solution of 0.50 grams of 
RhH(CO)(PPh.sub.3).sub.3 in 40 ml of benzene and 10 ml of 1-pentene was 
stirred at 50.degree. C. with a CO/H.sub.2 mixture at ca. 4 atm pressure 
until no further pressure drop occurred. The pentene was completely 
converted to aldehydes according to proton nuclear magnetic resonance 
(nmr) analysis. The solution was permeated through a polyimide membrane 
under 68 atm nitrogen pressure. The permeate (4.5 grams passed in 2 min.) 
showed only 9% of the original rhodium concentration by X-ray 
fluorescence. 
The permeation rate of rhodium as set forth above, i.e., 9%, is considered 
unacceptable. The rhodium catalyst should be retained in an amount of 
greater than 99% to be a commercially feasible process. 
Another example of the use of membranes to separate metal catalysts from 
hydroformylation products is set forth in Dutch Patent No. 8700881, 
published on Nov. 1, 1988. The method disclosed therein relates to one 
which improves the efficiency of membrane separation of hydroformylation 
products from expensive organometallic catalyst containing reaction 
mixtures. In Dutch Patent No. 8700881 a polydimethylsiloxane membrane 
having a thickness of 7 microns applied to a Teflon.RTM. support was used 
in the separation of a reaction mixture containing C.sub.9-C.sub.15 
alcohols, a homogeneous catalyst system comprising an organometallic 
complex of a transition metal from Group VIII or VIIa or Va of the 
Periodic Table, e.g., a tricarbonyl (triphenyl-phosphine) cobalt catalyst, 
and 40% low-viscosity lubricating oil (an antiswelling or de-swelling 
agent). At a flow of 133 kg/m.sup.2 -day, the cobalt contents in the feed, 
retentate, and permeate were 600, 910, and 18 ppm, verses 840, 1930, and 
160 ppm, respectively, for a mixture without the de-swelling agent. This 
process is directed to the separation of product from a reaction mixture 
containing a homogeneous catalyst system by means of a membrane. The 
ligands disclosed in Dutch Patent No. 8700881 are all organic soluble 
ligands, e.g., triphenylphosphine, tri-n-alkylphosphine or acetyl 
acetonate. Critical to the process of Dutch Patent No. 8700881 is the 
addition of a de-swelling agent to the reaction mixture which assists in 
the separation of the products from the reaction mixture. 
Each of the aforementioned processes for removing metal catalysts from 
crude hydroformylation reaction products are both costly in terms of 
unrecovered catalyst and, as such, would require further expensive 
treatment of the streams to recover catalyst. 
The present inventors have been examining whether rhodium separation from 
hydroformylation products can be performed with a membrane when the 
catalyst complexes are formed using hydrocarbon or oil soluble phosphine 
ligands in the presence of an atmospheric mixture of CO and H.sub.2 and 
also whether such a separation can be effected using water-soluble 
phosphine ligands at higher than atmospheric pressures of CO and H.sub.2. 
For the organic-soluble system, they have discovered that alkylated 
phosphine ligands together with dense nonpolar polymeric membranes are 
capable of substantially retarding the rhodium loss during the separation 
of the rhodium catalyst from the hydroformylation reaction products. It 
was also discovered that triphenylphosphine ligands used in conjunction 
with a dense polymeric, nonpolar membrane also substantially retards 
rhodium catalyst loss, although not as well as alkylated phosphines. 
Optimum operating conditions for the organic-soluble system involve 
performing the separations in an atmosphere of CO and H.sub.2 each with 
partial pressures less than one atmosphere. 
For the water-soluble system the present inventors have discovered that 
rhodium catalysts may be separated from the reaction products using a 
variety of ligands and a variety of hydrophobic membranes. 
In processes which produce high molecular weight products, it may not be 
possible to provide the driving force needed to drive the products through 
the membrane by pervaporation due to the need for high temperatures and 
high vacuum and thus perstraction would be desirable. 
Perstraction typically involves the selective dissolution of particular 
components contained in a mixture into the membrane, the diffusion of 
those components through the membrane and the removal of the diffused 
components from the downstream side of the membrane by use of a liquid 
sweep stream. 
For example, in perstractive separations of aromatics from saturates in 
petroleum or chemical streams (particularly heavy cat naphtha streams) the 
aromatic molecules present in the feedstream dissolve into the membrane 
film due to similarities between the membrane solubility parameter and 
those of the aromatic species in the feed. The aromatics then permeate 
(diffuse) through the membrane and are swept away by a sweep liquid which 
is low in aromatic content. This keeps the concentration of aromatics at 
the permeate side of the membrane film low and maintains the concentration 
gradient which is responsible for the permeation of the aromatics through 
the membrane. 
The sweep liquid should be low in aromatic content so as not to itself 
decrease the concentration gradient. The sweep liquid is preferably a 
saturated hydrocarbon liquid with a boiling point much lower or much 
higher than that of the permeated aromatics. This is to facilitate 
separation, as by simple distillation. Suitable sweep liquids are C.sub.3 
to C.sub.6 saturated hydrocarbons and lube basestocks (C.sub.15 
-C.sub.20). 
The perstraction process is run at any convenient temperature, preferably 
as low as possible. 
The choice of pressure is not critical since the perstraction process is 
not dependent on pressure, but on the ability of the aromatic components 
in the feed to dissolve into and migrate through the membrane under a 
concentration driving force. Consequently, any convenient pressure may be 
employed, the lower the better to avoid undesirable compaction, if the 
membrane is supported on a porous backing, or rupture of the membrane, if 
it is not. 
If C.sub.3 or C.sub.4 sweep liquids are used at 25.degree. C. or above in 
liquid state, the pressure must be increased to keep them in the liquid 
phase. 
A disadvantage of conventional perstraction methods, however, is the need 
to provide a step to remove the perstraction sweep stream that has 
permeated (diffused) to the reaction side from the permeate side of the 
membrane. 
The present inventors have developed a method which overcomes the problems 
associated with diffusion of the sweep stream and contamination of the 
reactants and products located on the reactor side of the membrane. This 
method uses the hydroformylation feedstock, e.g., olefins, as the sweep 
stream. Thus, it is also possible that the hydroformylation feed may be 
supplied to the reactor, in addition to the conventional feed method, by 
diffusion of the sweep stream through the membrane such that it is 
delivered to the hydroformylation reactor together with the retentate 
recycled to the reactor after contacting the membrane separator. 
The present invention also provides many additional advantages which shall 
become apparent as described below. 
SUMMARY OF THE INVENTION 
A method for separating products from reactants in a membrane reactor which 
comprises a retentate compartment and a permeate compartment divided by a 
membrane, wherein the separation occurs under perstraction conditions and 
the sweep stream which passes through the permeate compartment is the same 
as the reactant feedstock. 
This method is particularly suitable for separating a noble metal catalyst 
from a crude reaction product of a noble metal-catalyzed hydroformylation 
reaction under perstraction conditions. The method includes the steps of 
(a) contacting a crude reaction product under perstraction conditions with 
a membrane capable of allowing a substantial portion of unreacted olefin 
feed and hydroformylation reaction product to pass therethrough as 
permeate while retaining a substantial portion of the catalyst as 
retentate; (b) removing the permeate by sweeping it away from the membrane 
by means of an olefinic sweep stream which is the same as the olefinic 
feed used in the hydroformylation reaction; and (c) retaining the catalyst 
as retentate. 
In accordance with another embodiment, the sweep stream permeates through 
the membrane so as to have the dual function of acting as both the 
perstraction sweep stream and a supplemental olefinic feed to the 
hydroformylation reactor. 
Additionally, the present invention pertains to a method for producing 
higher aldehydes and higher alcohols which comprises: (a) hydroformylating 
an olefin feed with synthesis gas in the presence of a Group VIII noble 
metal-ligand complex catalyst to form a crude reaction product comprised 
of unreacted olefin feed, hydroformylation reaction product and a 
catalyst; (b) removing the catalyst from the crude reaction product by 
feeding the crude reaction product under perstraction conditions to a 
membrane separator which comprises a membrane capable of allowing a 
substantial portion of the hydroformylation reaction product and olefin 
feed to pass therethrough as permeate while retaining a substantial 
portion of the catalyst as permeate; (c) recovering the permeate by 
sweeping it away from the membrane by means of an olefinic sweep stream 
which is the same as the olefinic feed used in the hydroformylation 
reaction; (d) retaining the catalyst as retentate; and (e) recycling the 
catalyst to hydroformylation step (a). 
This invention is useful in the separation of a rhodium-ligand complex 
catalyst from both organic and aqueous feed mediums. The ligands and 
membranes must be modified depending which medium is being delivered to 
the membrane reactor unit. The processes for treating an organic reaction 
medium are described above; whereas the processes for treating an aqueous 
reaction medium is described below. 
A method for separating a water-soluble noble metal catalyst from a crude 
reaction product of a noble metal-catalyzed hydroformylation reaction run 
in aqueous solution, in an aqueous emulsion or as an aqueous suspension, 
the crude reaction product including an aqueous phase containing a 
water-soluble Group VIII noble metal-ligand complex catalyst and an 
organic phase containing unreacted olefin feed and an organic 
hydroformylation reaction product, which comprises: (a) contacting the 
crude reaction product under perstraction conditions with a hydrophobic 
membrane capable of allowing a substantial portion of the unreacted olefin 
feed and the organic hydroformylation reaction product to pass 
therethrough as permeate while retaining a substantial portion of the 
water-soluble Group VIII noble metal-ligand complex catalyst as retentate; 
(b) removing the permeate by sweeping it away from the membrane by means 
of a sweep stream which is the same as the olefin feed used in the 
hydroformylation reaction; and (c) retaining the water-soluble Group VIII 
noble metal-ligand complex catalyst as retentate. 
Other and further objects, advantages and features of the present invention 
will be understood by reference to the following specification in 
conjunction with the annexed drawings, wherein like parts have been given 
like numbers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hydroformylation is a process for converting olefins to a product of one or 
more additional carbon numbers by the addition of carbon monoxide and 
hydrogen to the double bond(s) of the olefin in the presence of a catalyst 
at elevated temperatures and pressures. A typical hydroformylation process 
is demonstrated below: 
##STR1## 
At a temperature of 100.degree. C. and a pressure of 1.03.times.10.sup.6 
N/m.sup.2 (150 psi) the normal to iso ratio using rhodium as the catalyst 
may be below 1 or even as high as 100, depending on the ligand, ratio of 
ligand to rhodium, etc. When cobalt is used as the catalyst and is not 
modified by a ligand, the normal to iso ratio is at most below 3. 
Another method for catalytic hydroformylation of olefins, using a 
conventional approach is set forth in U.S. Pat. No. 4,399,312 (Russell et 
al.), which issued on Aug. 16, 1983. The hydroformylation method discussed 
in the above-mentioned patent involves the reacting together, at elevated 
temperature and pressure, of an olefin, H.sub.2 and CO in the presence of 
a catalyst comprising a water-soluble complex of a noble metal and an 
amphiphilic reactant in a reaction medium comprising an aqueous phase and 
an organic phase. The organic phase includes a highly reactive olefin, 
e.g., C.sub.3 -C.sub.20, and a solvent. The noble metal catalyst is 
typically Pt, Rh, Ru or Pd. The aqueous phase preferably contains a 
water-soluble phosphine in complex combination with a complex or catalytic 
precursor of the noble metal, e.g., sulfonated or carboxylated triaryl 
phosphines. The amphiphilic reagent is typically an anionic, nonionic or 
cationic surfactant or phase transfer agent such as a complex ammonium 
salt or a polyoxyethylene nonionic surfactant. The preferred ratio of 
aqueous phase to organic phase is 0.33:1 to 5:1, the ratio of H.sub.2 to 
CO is 1:1 to 5:1, the content of precious metal in the aqueous phase is 
100-500 ppm and the ratio of amphiphilic reagent to precious metal is up 
to 100:1 on a molar basis. It is preferable that the reaction be carried 
out at 300-10,000 kPa, especially 300-3,000 kPa and at a temperature in 
the range between about 40.degree.-150.degree. C. 
The novel method according to the present invention used for producing 
higher aldehydes and higher alcohols by means of hydroformylation using an 
organic-soluble ligand and catalyst can best be described by referring to 
FIG. 1. This method includes the hydroformylating of an olefin feed 
supplied via stream 1 and/or stream 6 together with synthesis gas which is 
supplied via stream 2 in the presence of a Group VIII noble metal-ligand 
complex catalyst within reactors 30 and 32 to form a crude reaction 
product comprised of unreacted olefin feed, hydroformylation reaction 
product and a Group VIII noble metal-ligand complex catalyst. The crude 
reaction product is delivered from reactors 30 and 32 via stream 5 to 
membrane separator 34 wherein the Group VIII noble metal-ligand complex 
catalyst is separated from the crude reaction product by contacting the 
crude reaction product under perstraction conditions against membrane 36 
which is capable of allowing a substantial portion of the hydroformylation 
reaction product and unreacted olefin feed disposed in retentate 
compartment 8 to diffuse through membrane 36 into permeate compartment 9 
as permeate while retaining a substantial portion of the Group VIII noble 
metal-ligand complex catalyst in retentate compartment 8 as retentate. The 
permeate in permeate compartment 9 is sweep away from membrane 36 by means 
of a perstraction sweep stream of olefin feed which is supplied via fresh 
olefin feed stream 7 and/or recycled olefin feed stream 13. Thereafter, 
the retentate, e.g., Group VIII noble metal-ligand complex catalyst, is 
recycled via stream 6 to hydroformylation reactors 30 and 32. 
The permeate swept away by the sweep streams supplied by stream 7 and/or 
stream 13 is delivered to a secondary catalyst recovery unit 38 via stream 
10. The bottoms from secondary catalyst recovery unit 38 are then passed 
on to a series of fractionation columns (40, 42 and 44). Fractionation 
column 40 takes overhead unreacted olefin which can be recycled as a 
perstraction sweep stream via stream 13 or purged via stream 12. The 
bottoms of fractionation column 40 are sent to fractionation column 42 
which takes light aldehydes out overhead via stream 14. The bottoms of 
fractionation column 42 are sent to fractionation column 44 which takes 
heavy aldehydes out overhead via stream 15. The bottoms from fractionation 
column 44 are sent to a phosphine recovery unit 46 via streams 16 and 23 
wherein heavies are removed via stream 25 and phosphines are recovered and 
returned to hydroformylation reactors 30 and 32 via stream 24 and stream 
6. The reactor purge from hydroformylation reactor 32 is delivered via 
stream 21 to a secondary-type catalyst recovery unit 50 and the recovery 
unit effluent is sent to the phosphine recovery unit 46 via streams 22 and 
23. 
The noble metal-catalyzed hydroformylation reaction includes the steps of: 
reacting an olefin feed with hydrogen and carbon monoxide in the presence 
of a Group VIII noble metal-ligand complex catalyst, at a temperature in 
the range between about 80.degree. to 125.degree. C. to produce an 
aldehyde having a normal to iso ratio in the range between about 0.5:1 to 
about 80:1. 
When an organic reaction medium is treated as discussed in FIG. 1, it is 
preferable that the ligand be an alkylated or arylated ligand, such as a 
C.sub.2 to C.sub.8 phosphine ligand with at least one alkyl group bonded 
to the para position. The ligand is preferably selected from the group 
consisting of: triphenylphosphine, para alkylated triphenylphosphines such 
as tri-4-tolyl phosphine, tri-4-propylphenyl phosphine and 
tri-4-octylphenyl phosphine, and trioctylphosphine. 
The membrane which is most suitable for separating organic reaction medium 
is a nonpolar dense polymeric membrane such as that selected from the 
group consisting of: high density polyethylene radiation-crosslinked 
membranes, low density polyethylene radiation-crosslinked membranes, and 
polypropylene membranes. 
The membrane is one which is capable of retaining at least about 99% of the 
Group VII noble metal-ligand complex catalyst. 
The olefin feed is typically a C.sub.4 -C.sub.20 olefin. The sweep stream 
can diffuse through the membrane into the retentate compartment. When the 
sweep stream diffuses through the membrane it can act in a dual capacity, 
i.e., as a perstraction sweep stream and as a reactant feedstock in the 
hydroformylation reaction process. 
FIG. 2 demonstrates the preferred process for separating water-soluble 
noble metal catalyst from an aqueous reaction medium. This system is 
similar to that described above in FIG. 1 for organic reaction mediums, 
except that the reactor purge from hydroformylation reactor 32 is 
delivered via stream 17 to a settler 51 where the aqueous stream 24 of 
settled reactor purge is recycled via streams 24 and 6 to hydroformylation 
reactors 30 and 32, or may alternately be purged or reconstituted via 
stream 26. The organic layer from settler 51 is sent via stream 21 to a 
secondary-type catalyst recovery unit 50 and the recovery unit effluent is 
sent via streams 22 and 23 to purge. 
When treating an aqueous reaction medium it is preferable to use a ligand 
selected from the group consisting of Na-p-(diphenylphosphino) benzoate, 
Na-p-(diphenylphosphino) benzenesulfonate, Na-m-(diphenylphosphino) 
benzenesulfonate, and tris-(sodium m-sulfophenyl)-phosphine. In most 
instances it is desirable to add a surfactant to the noble metal-catalyzed 
hydroformylation reaction. The surfactant is preferably one compound 
selected from the group consisting of: cetyltrimethylammonium bromide, 
sodium laurate, sodium stearate, sodium p-toluenesulfonate and 
dodecylbenzene sulfonate. 
The preferred membranes are high density polyethylene crosslinked 
membranes, natural latex rubber membranes, polychlorotrifluoroethylene 
membranes, crosslinked bromobutyl rubber membranes, and crosslinked 
copolymer membranes of isobutylene and p-bromomethyl styrene. One 
preferred membrane is a copolymer of isobutylene and p-bromomethyl styrene 
crosslinked with hexamethylene diamine. 
The comparative examples below and in FIG. 2 demonstrate the effectiveness 
of using the hydroformylation reaction feed as the perstraction sweep 
stream during the separation of the catalyst from the aldehyde products of 
the hydroformylation process. 
Example 1 
For this example, the present inventors have conducted two comparative 
demonstration runs to illustrate that the olefinic feedstock can be 
successfully used as the perstraction sweep solvent during membrane 
separation of hydroformylation reaction products and unreacted olefins 
from a noble metal catalyst without substantially reducing the rate of 
permeation of the hydroformylation reaction products through the membrane. 
It also shows that the diffusion of the sweep solvent through the membrane 
to the retentate side of the membrane does not result in the contamination 
of the crude reaction products but does provide an effective source of 
feed for reaction with the catalyst to desired reaction products. These 
runs were conducted in an aqueous emulsion using a water-soluble phosphine 
ligand, e.g., sodium p-diphenylphosphino benzoic acid. The decene-1 was 
hydroformylated in a stirred autoclave before transfer to the membrane 
separator. 
2 grams of lauric acid, as surfactant, were added to an aqueous solution of 
sodium p-diphenyl phosphino benzoate (Ph.sub.2 P(p-C.sub.6 H.sub.4 
COO.sub.3 Na)), dissolved at approximately 70.degree. C. with stirring 
under nitrogen in 70 grams of 1N NaHCO.sub.3 solution. The resulting clear 
solution was then introduced through a Hoke bomb to a 1 liter autoclave. 
To this solution, a mixture of 179.23 grams of 1-decene, 9.93 grams of 
hexadecane as an internal standard, 1.24E-01 grams of rhodium acetate 
dimer (i.e., RhII.sub.2 (OOCCH.sub.3).sub.4 dimer) and 10 grams of i-PrOH 
as co-solvent were introduced through the Hoke bomb under a carbon 
monoxide/hydrogen pressure. 
The autoclave was pressurized with a mixture of CO/H.sub.2 in a ratio of 
1:1 and at a pressure of 6.89.times.10.sup.5 N/m.sup.2 (100 psig) at room 
temperature. The contents were then heated to 80.degree. C. while the 
pressure was maintained at 1.03.times.10.sup.6 N/m.sup.2 (150 psig). The 
reaction was monitored by periodic gas chromatographic (GC) analysis of 
the organic layer. At the conclusion of the run the mixture was cooled and 
removed from the autoclave. After settling, the layers were separated and 
the substantially organic layer transferred to the membrane separator. 
A crosslinked copolymer of isobutylene and p-bromomethyl styrene was chosen 
as the membrane for this experiment since it was hydrocarbon, hydrophobic, 
easily crosslinked and capable of meeting our stability criteria. The 
membrane for evaluation in the membrane separator was prepared as follows. 
Into a 250 ml wide mouth jar equipped with a magnetic stirring bar were 
added 34.17 grams of a copolymer of isobutylene and p-bromomethyl styrene 
plus 104.13 grams of toluene. The 25% solution was stirred magnetically 
until all the polymer dissolved. After stirring two days, with occasional 
warming to about 50.degree. C., the polymer dissolved completely resulting 
in a clear yellow viscous liquid. An aliquot or 49.2 grams of the 25% 
polymer solution containing 12.3 grams of polymer which contained 2.2% 
bromine was transferred to a 100 ml wide mouth jar. To this solution was 
added 0.49 grams (0.0042297 m) of 1,6-hexane diamine dissolved in about 
0.6 grams of toluene. After thorough hand mixing, the clear viscous yellow 
liquid was transferred to a centrifuge tube and centrifuged for 20 minutes 
at 10,000 rpm. Thereafter, three membranes were cast on Teflon.RTM. sheets 
(22.86.times.22.86 cm) having a thickness of about 2.2 ml, a pore size of 
about 0.2 microns and a porosity of about 80%. The cast membranes were 
allowed to weather overnight in a nitrogen purge box then heated for 2 
hours at 125.degree. C. The cast membranes were examined for weight loss 
by extraction with refluxing cyclohexane. 
The cast membrane was then mounted in the membrane reactor unit between two 
100 mesh stainless steel screens. The polymer thickness was 48.5 microns, 
with two 53.3 micron sheets of Teflon.RTM. on the outer surface. To the 
evacuated catalyst side of the membrane reactor unit was added the organic 
reactor product which comprised 216.4 grams (1.271 mole) of undecyl 
aldehdes, 16.68 grams (0.12 mole) of decenes and 14.3 grams of hexadecane 
as an internal standard. To the evacuated sweep side of the membrane 
reactor unit was added the following deaerated solution: 306.0 grams (3.64 
moles) of hexene-1 and 23.0 grams of hexadecane. A mixture of 
hydrogen/carbon monoxide gas (51/49) was pressured to the reactor unit to 
approximately 7.58.times.10.sup.5 N/m.sup.2 (110 psi) and the contents 
were heated at 80.degree.-85.degree. C. for 69 hours. The catalyst side 
and sweep side were circulated at 400 cc/minute during this heating 
period. 
Samples were withdrawn from both sides of the membrane separator 
periodically and the compositions analyzed by gas chromatography. The 
results are displayed in FIG. 3. At the conclusion of the run, the sweep 
side of the reactor was calculated to contain 52.17 grams of undecyl 
aldehyde which represents an overall permeation rate of the aldehyde of 
17.8 kg/m.sup.2 /day or 863 kg/.mu./m.sup.2 /day. The sweep side also 
contained 3.92 grams of heptyl aldehydes formed by the permeation of 
hexene-1 to the catalyst side of the separator. The final hexene-1 and 
undecyl aldehyde mixture on the sweep side was analyzed for rhodium and 
found to contain 0.23 ppm. This indicates that about 99.5% of the rhodium 
would be retained if all the undecyl aldehyde had permeated. 
In a comparison run, decene-1 was hydroformylated as above and decene-1 was 
used as the sweep solvent. A crosslinked copolymer of isobutylene and 
p-bromomethyl styrene membrane was cast on Teflon.RTM. and thereafter 
mounted in the membrane reactor unit between two 100 mesh stainless steel 
screens. The polymer thickness was 69.6 microns, with two 53.3 micron 
sheets of Teflon.RTM. on the outer surface. To the evacuated catalyst side 
of the membrane reactor unit was added the organic reactor product which 
comprised 213 grams (1.24 mole) of undecyl aldehydes 14.54 grams of 
decene-1 (0.10 mole) and 14.42 grams of hexadecane as an internal 
standard. To the evacuated sweep side of the membrane reactor unit was 
added the following deaerated solution: 293.84 grams (2.10 moles) of 
decene-1 and 24.8 grams of hexadecane. A mixture of hydrogen/carbon 
monoxide gas (51/49) was pressured to the reactor unit to approximately 
7.58.times.10.sup.5 N/m.sup.2 (110 psi) and the contents were heated at 
80.degree.- 85.degree. C. for 76 hours. The catalyst side and sweep side 
were circulated at 400 cc/minute during this heating period. Samples were 
withdrawn from both sides of the membrane separator periodically and the 
compositions analyzed by gas chromatography. 
The results are displayed in FIG. 4. At the conclusion of the run, the 
sweep side of the reactor was calculated to contain 94.35 grams of undecyl 
aldehyde which represents an overall permeation rate of the aldehyde of 
29.2 kg/m.sup.2 /day or 2030 kg/.mu./m.sup.2 /day. The sweep side also 
contained 188 grams of decene-1. The catalyst side at the conclusion of 
the run contained, by analysis, 242 grams of undecyl aldehyde and 23 grams 
of decene-1. Thus, approximately 123.4 grams (0.72 mole) of undecyl 
aldehyde was produced during the separation experiment and 97.5 grams 
(0.70 mole) of decene-1 consumed. This result also demonstrates that the 
decene-1 that permeated the membrane to the side containing catalyst could 
be reacted and that the catalyst was still active. The final decene-1 and 
undecyl aldehyde mixture on the sweep side was analyzed for rhodium and 
found to contain 0.31 ppm. This indicated that about 99.6% of the rhodium 
would be retained if all the aldehyde initially charged had permeated. 
EXAMPLE 2 
In this experiment, the inventors demonstrated that feed olefin, e.g., 
decene-1, may be introduced into the sweep side of a membrane reactor, 
that the decene-1 permeates the membrane and is reacted on the catalyst 
side of the reactor, and that the product aldehyde permeates to the sweep 
side where it may be recovered from the original feed (i.e., decene-1) 
which is also the perstraction solvent. Further, the inventors have shown 
that the noble metal catalyst, in this case the rhodium, is substantially 
retained on the catalyst side by the membrane. 
The aqueous catalyst solution was prepared in a nitrogen dry box. Into a 
500 ml Erlenmeyer flask were weighed 210 grams of a 1N sodium bicarbonate 
solution, 3.78 grams (0.04494 mole) of sodium bicarbonate, and 4.8 grams 
(1.567.times.10.sup.-2 moles) of diphenyl phosphinobenzoic acid. The 
mixture was heated to about 75.degree. C. with magnetic stirring to 
dissolve the diphenylphosphinobenzoic acid. Next, 6.0 grams 
(2.995.times.10.sup.-2 moles) of lauric acid were added to the mixture in 
the flask. The addition of the lauric acid should occur slowly to prevent 
foaming caused by the release of carbon dioxide. Once all the lauric acid 
dissolved, the mixture was cooled to about 50.degree. C. and 0.45 grams 
(1.744.times.10.sup.-3 moles) of dicarbonyl acetyl acetonate rhodium were 
then added to the mixture. A hazy orange liquid resulted on stirring for 
approximately twenty minutes. The Erlenmeyer flask was stoppered and the 
catalyst solution removed from the nitrogen dry box for addition to the 
membrane reactor unit. 
The crosslinked copolymer membrane was then mounted in the membrane reactor 
unit between two 100 mesh stainless steel screens. The polymer thickness 
was 48.5 microns, with two 53.3 micron sheets of Teflon.RTM. on the outer 
surface. To the preheated evacuated catalyst side of the membrane reactor 
unit was added the entire 225 grams of the hazy orange liquid catalyst 
solution. To the evacuated sweep side of the membrane reactor unit was 
added the following deaerated solution: 300.0 grams (2.14 moles) of 
decene-1 and 23.0 grams of hexadecane. A mixture of hydrogen/carbon 
monoxide gas (51/49) was pressured to the reactor unit to approximately 
7.58.times.10.sup.5 N/m.sup.2 (110 psi) and the contents were heated at 
80.degree.-85.degree. C. for 145 hours. The catalyst side and sweep side 
were circulated at 400 cc/minute during this heating period. At 113 hours 
a sample was withdrawn from both sides of the membrane reactor and the 
compositions analyzed by gas chromatography. 
The catalyst side of the reactor was calculated to contain 57.4 grams 
(0.338 moles) of aldehyde and 17.6 grams (0.114 moles) of decene-1. The 
sweep side of the reactor was calculated to contain 49.6 grams (0.292 
moles) of aldehyde and 184.6 grams (1.191 moles) of decene-1. Thus, 
approximately 33% of the decene-1 was converted to undecyl aldehyde. The 
combined reaction and permeation rate of the aldehyde was 10.3 kg/m.sup.2 
/day. The final decene-1 and undecyl aldehyde mixture on the sweep side 
was analyzed for rhodium and found to contain 1.33 ppm. The original 
starting rhodium concentration was 798 ppm on the catalyst side. 
EXAMPLE 3 
The present inventors have also conducted two comparative demonstration 
runs to illustrate that the olefinic feedstock can be successfully used as 
the perstraction sweep solvent during membrane separation of 
hydroformylation reaction products and unreacted olefins from a noble 
metal catalyst without substantially reducing the rate of permeation of 
the hydroformylation reaction products through the membrane. These 
examples also demonstrate that the diffusion of the sweep solvent through 
the membrane to the retentate side of the membrane does not result in the 
contamination of the crude reaction products but does provide an effective 
source of feed for reaction with the catalyst to desired reaction 
products. In these comparative runs, the ligand is completely soluble in 
the organic reaction medium. 
As illustrated in FIG. 5, decene-1 was hydroformylated using a rhodium 
catalyst and trioctylphosphine as a ligand on the retentate side of a 
polyethylene succinate membrane. Decene-1 was also used as a sweep solvent 
on the permeate side of the membrane and the product aldehyde (i.e., a 
C.sub.11 aldehyde) was allowed to permeate in a perstraction mode under 
the same pressure and temperature as the retentate side of the membrane. 
The rate of aldehyde permeation when the feed olefin was used as the 
perstraction sweep stream was approximately 3.0 kg/m.sup.2 /day. 
This rate of permeation was only slightly less than the rate demonstrated 
when the hydroformylation feed was octene-1, the sweep stream was decene-1 
and the membrane was a polyureaurethane membrane. The octene-1/decene-1 
experiment resulted in a rate of permeation of C.sub.9 aldehydes in the 
amount of 4.6 kg/m.sup.2 /day. When octene-1 was used as the 
hydroformylation feed and decene-1 as the sweep stream for perstraction no 
significant reaction took place on the permeate side of the membrane, 
indicating that no rhodium permeated together with the aldehydes. The fact 
that some of the sweep diffuses through to the retentate side of the 
membrane and reacts with the rhodium catalyst is demonstrated by the small 
amount of C.sub.11 aldehydes detected in the permeate. 
The similarity in aldehyde permeation rates between the two feed/sweep 
systems, i.e., (decene-1/decene-1) and (octene-1/decene-1), illustrates 
that the reaction of the decene-1 to undecanals occurred substantially on 
the retentate side of the membrane and not by reaction of the decene-1 
with rhodium that may have permeated to the permeate side of the membrane. 
Likewise, since it has been demonstrated that virtually no rhodium passed 
through the membrane, it can be concluded that the undecanal permeated 
through the membrane and did not pass due to mechanical or other failure. 
Accordingly, when decene-1 is used as both the reaction feed and 
perstraction sweep solvent, it was able to effectively perstract the 
hydroformylation product, i.e., the undecanals, from the reaction mixture. 
While we have shown and described several embodiments in accordance with 
our invention, it is to be clearly understood that the same are 
susceptible to numerous changes apparent to one skilled in the art. 
Therefore, we do not wish to be limited to the details shown and described 
but intend to show all changes and modifications which come within the 
scope of the appended claims.