Process for separating catalysts from organic solutions, by means of semipermeable membranes

Disclosed is a process for separating metal catalysts based on ammonium and phosphonium phosphotungstates from reaction mixtures in which they are dissolved. The process is based on the use of semipermeable membranes and has found an useful application in the separation of the above said catalysts from mixtures obtained from alkenes and soybean oil epoxidation.

The present invention relates to a process for separating catalysts based 
on ammonium and phosphonium phosphotungstates from reaction mixtures in 
which they are dissolved, which process consists in treating said mixtures 
by means of ultrafiltration units equipped with semipermeable membranes. 
It is well known that, in the catalytic processes, the use of homogeneous 
phase catalyst supplies, as compared to the use of heterogeneous phase 
catalysts, several advantages, such as, e.g., milder reaction conditions 
and a greater selectivity. 
However, the use of homogeneous catalysis in organic synthesis processes 
not always can be applied owing to the difficulties which are met in the 
separation and recovery of said catalysts from the reaction mixtures. 
In fact, the use of conventional techniques known in the art of 
separations, supplied often unsatisfactory results, thus limiting the 
development of the processes which take place under homogeneous catalysis 
conditions. 
The problems arising during the separation processes are of several kinds 
and depend on the used techniques. 
The precipitation, for example, requires a large number of processing steps 
and, when as precipitating agents non-solvents are used, it may imply the 
presence of toxic and/or flammable products. 
The distillation makes it possible satisfactory separations of the various 
components of reaction mixtures to be obtained but, on the other hand, 
said components can undergo degradation phenomena owing to their long 
standing at high temperatures. Furthermore, the distillation requires high 
costs for purchasing the distillation facilities and owing to energy 
consumptions. 
The chromatographic techniques such as, e.g., adsorbtion or ionic exchange 
become difficultly applicable when one tries to apply them on a large 
commercial scale. 
The separation by extraction requires, like precipitation, further process 
steps and, generally, the use of toxic and/or flammable products. 
The developement of separation technologies based on ultrafiltration made 
it possible the above drawbacks to be overcome or reduced, in particular 
such technologies display the following advantages: 
they make it possible the addition to the reaction mixture to be avoided of 
other products (including toxic and/or flammable solvents) which, in most 
cases, must be separated during a later step; 
they make it possible submitting heat sensible compounds to an excessive 
heating to be avoided; 
they require a reduced energy consumption, above all as compared to 
distillation; 
they require short operating times; 
they require relatively low facility purchasing and maintenance costs; 
they allow an easy scaling flexibility; 
they make it possible high-molecular weight compounds (pigments, oligomers, 
polymers, degradation products, and so forth) possibly present in the 
reaction mixture, to be removed besides the catalysts. 
On the contrary, the development of such processes requires further that 
investigations are carried out into basic knowledge such as, e.g., the 
catalyst aggregation state in the several organic phases in view of a 
proper selection of membranes to be used. 
In scientific literature, some processes are reported for separating 
catalysts from reaction mixtures by means of the use of semipermeable 
membranes: e.g., E.P. patent 0 263 953 B1 describes the separation by 
membranes, in aqueous media, of metal catalysts complexes, with 
water-soluble phosphines. 
In its turn, U.S. Pat. No. 4,855,491 discloses the separation of metal 
catalysts and possibly present impurities, by means of the use of organic 
membranes, by reverse osmosis. In this case, the mixtures submitted to the 
treatment contain high water levels. 
Also described are systems which allow the selective permeation of metal 
ions to be carried out from an aqueous/organic mixture towards an aqueous 
phase, through a semipermeable membrane which separates said phases (U.S. 
Pat. No. 4,311,521). 
However, the methods known from pertinent technical literature are not 
generally applicable and, in particular, they do not teach to separate 
metal catalysts in homogeneous phase in the case of completely organic 
phases. 
The present Applicant has found now that the above said catalysts can be 
separated in an advantageous way from the organic solutions in which they 
are dissolved. 
In its widest aspect, the present invention relates to a process for 
separating catalysts constituted by an anionic portion based on 
phosphotungstates or arsenotungstates and a counterion with surfactant 
character based on ammonium or phosphonium salts, from the organic 
solutions in which they are dissolved, characterized in that the organic 
solutions are submitted to ultrafiltration in devices equipped with 
semipermeable membranes. 
In the specific case according to the present invention, the dissolution of 
the catalyst is obtained by using counter-ions with surfactant character. 
The results illustrated in the examples confirmed the previously cited 
advantages of this technology and its applicability at a technical level. 
It was furthermore observed that the capability of the membranes, of 
retaining also other high molecular weight impurities, makes it possible 
the quality of the products to be improved, and the inorganic character of 
some of said membranes makes it possible the process to be carried out at 
high temperatures. 
In general, the possibility of selectively separating, by means of 
semipermeable membranes, organic molecules contained in a solution 
strictly depends on both the nature of the membranes and the 
characteristics of the solution. 
The preliminary investigations related to the determination of the suitable 
exclusion molecular weight (=that molecular weight at which the 
fractionation occurs) for the purpose of optimizing the permeate fluxes 
and the type of molecules which can flow through the selected membrane. 
For that purpose, the tests were carried out on a system constituted by 
flat membranes in a static cell which, thanks to the simplicity of the 
equipment, makes it possible the several membranes to be rapidly evaluated 
.

DETAILED DESCRIPTION 
The ultrafiltration system displayed in FIG. 1 consists of a stainless 
steel cell of 0.5 l of capacity, stirred by means of a overhanging 
magnetic bar (3) driven by a driving motor means (7). The necessary 
pressure is supplied by means of nitrogen delivered from the inlet (2) and 
is checked by means of the pressure gauge (1). The ultrafiltration 
membrane (4) is laid on the support (5) connected with the permeate 
manifold (6). 
The filtering surface area is of about 20 cm.sup.2. 
In that way, membranes of FS61PP.RTM. (type membrane manufactured by 
DDS-DOW SEATION SYSTEMS (DK) and constituted by fluorinated polymers); 
and membranes of CARBOSEP.RTM. (type membrane, manufactured by Rhone 
Poulenc, constituted by aluminum oxides and preferably graphite and metal 
oxides) were selected for their capability of retaining (=rejecting) the 
dissolved catalyst in an organic phase. The nominal exclusion limits of 
the selected membranes were comprised within the range of from 5,000 to 
50,000 Da. 
The efficiency of a separation process carried out by means of the use of 
semipermeable membranes can be expressed by the rejection R defined as: 
EQU R=1-Ca/Cp 
wherein: 
Ca=initial concentration of metal to be separated; 
Cp=metal concentration in the permeate stream. 
In general, the systems applied in industry, in order to reach high 
efficiency values, are of tangential ultrafiltration type: in practice, 
the treated fluid is pumped at a high speed, tangentially relatively to 
the filtering surface. 
For this system type, several geometries are available, as: flat membranes, 
membranes in spiral arrangement, hollow fibres, tubular membranes. The 
selection is dictated by the physical-chemical characteristics of the 
fluid to be submitted to the treatment (e.g., amount of suspended solid 
matter, viscosity and chemical composition). 
The process according to the present invention also comprises using a 
tangential ultrafiltration system equipped with tubular membranes of 
CARBOSEP.RTM.. 
Such membranes meet the required conditions for industrial use, which are: 
strength to withstand external physical forces; 
resistance to chemical agents; 
resistance to microorganisms; 
resistance to high temperatures; 
easy of washing, so as to restore the fluxes; 
long useful operating life; 
low costs. 
The tangential ultrafiltration system displayed in FIG. 2 comprises a 
heated tank (1); a metering gear pump model G4 (PULSAFEEDER, Rochester 
N.Y.) (2); a tubular ultrafiltration membrane of CARBOSEP.RTM. 
(RHONE-POULENC ITALIA SpA, Milan) with container (3); pressure gauges for 
checking the module inlet and module outlet pressure (4); a pressure 
control valve (5) and a permeate outlet (6). 
The catalysts which can be separated by means of the process according to 
the present invention are tetra alkyl ammonium or tetra alkyl phosphonium 
tetra (diperoxo tungsto) phosphates (or arsenates) and, in particular, 
* dimethyl[dioctadecyl(76%)+dihexadecyl(24%)]ammonium tetra(diperoxo 
tungsto)phosphate PW.sub.4 O.sub.24 (C.sub.38 H.sub.80 N).sub.3 (76 mol 
%), PW.sub.4 O.sub.24 (C.sub.34 H.sub.72 N).sub.3 (24 mol %); and 
* [tributyl(n-hexadecyl)]phosphonium tetra(diperoxo tungsto)phosphate, 
PW.sub.4 O.sub.24 (C.sub.28 H.sub.60 P).sub.3, prepared as disclosed in 
EP-A-225 990 and generally present in the reaction mixtures at 
concentrations comprised within the range of from 0.01 to 5%. 
In the tangential ultrafiltration system, the recycle flow rate is usually 
so regulated as to keep the linear velocity comprised within the range of 
from 1 to 10 m.seconds.sup.-1 and preferably of from 2 to 5 
m.seconds.sup.-1, respectively corresponding to 170 and 430 L.h.sup.-1 for 
the modules disclosed in the following. 
The operating pressure range is comprised within the range of from 0.1 to 1 
MPa. 
The mixture can be fed at temperatures comprised within the range of from 
0.degree. to 250.degree. C. 
The permeate flow rate is generally comprised within the range of from 1 to 
50 Lm.sup.2 h.sup.-1. 
The analysis of the permeate demonstrates tungsten concentration lower than 
0.03%. 
Some examples follow, which are supplied in order to illustrate the 
invention without limiting it. 
EXAMPLE 1 
The catalyst (0.94 g) composed by a mixture of: 
tri[(di-n-hexadecyl)dimethyl]ammonium tetra(diperoxo tungsto)phosphate 
PW.sub.4 O.sub.24 (C.sub.34 H.sub.72 N).sub.3 (76 mol %) and PW.sub.4 
O.sub.24 (C.sub.38 H.sub.80 N).sub.3 (24 mol %) (0.94 g), separately 
prepared as disclosed in EP-A-225 990, is dissolved in a mixture (0.5 l) 
of internal alkenes (distillation cut C.sub.13 -C.sub.14). The 
concentration of W in this solution is of 5,500 mg.l.sup.-1. The solution 
is submitted to ultrafiltration in the static cell device disclosed in 
FIG. 1, equipped with polymeric membrane FS61PP.RTM. (Dow Separation 
System), having an exclusion molecular weight of 20 kDa. The pressure is 
kept comprised within the range of from 0.5 to 0.6 MPa with nitrogen. 
After causing 0.1 liter of solution to permeate, a concentration of W in 
the permeate of 2,000 mg.l.sup.-1 is obtained, and in the retentate, the 
concentration of W results to be of 6,000 mg.l.sup.-1. 
EXAMPLE 2 
The catalyst (0.94 g) composed by a mixture of: 
tri[(di-n-hexadecyl)dimethyl]ammonium tetra(diperoxo tungsto)phosphate 
PW.sub.4 O.sub.24 (C.sub.34 H.sub.72 N).sub.3 (76 mol %) and PW.sub.4 
O.sub.24 (C.sub.38 H.sub.80 N).sub.3 (24 mol %), separately prepared as 
disclosed in EP-A-225 990, is dissolved in a mixture (0.5 l) of internal 
alkenes (distillation cut C.sub.13 -C.sub.14). The concentration of W in 
this solution is of 5,500 mg.l.sup.-1. The solution is submitted to 
ultrafiltration in the previously disclosed static cell device, equipped 
with polymeric membrane FS81PP.RTM. (Dow Separation System), having an 
exclusion molecular weight of 6 kDa. The pressure is kept comprised within 
the range of from 0.5 to 0.6 MPa with nitrogen. After causing 0.25 liter 
of solution to permeate, a concentration of W in the permeate of 130 
mg.l.sup.-1 is obtained, and in the retentate, the concentration of W 
results to be of 7,000 mg.l.sup.-1. 
EXAMPLE 3 
0.1 liter of organic phase obtained as in the oxidation reaction disclosed 
in Example 6 is filtered on a fast paper filter. The concentration of W in 
this solution is of 190 mg.l.sup.-1. The clear solution is ultrafiltered 
by means of the static cell device disclosed in FIG. 1, equipped with a 
polymeric membrane FS81PP.RTM. (Dow Separation System) having an exclusion 
molecular weight of 6 kDa. The concentration of W in this solution is of 
1,900 mg.l.sup.-1. The pressure is kept at 1.0 MPa with nitrogen. After 
causing 0.09 l of solution to permeate, a concentration of W in the 
permeate of 200 mg.l.sup.-1 is obtained, and in the retentate the 
concentration of W results to be of 18,100 mg.l.sup.-1. 
EXAMPLE 4 
The catalyst dimethyl[dioctadecyl(76%)+dihexadecyl(24%)]ammonium 
tetra(diperoxotungsto)phosphate (2.82 g), separately prepared as disclosed 
in EP-A-225 990 is dissolved in a mixture (1.5 l) of internal alkenes 
(distillation cut C.sub.13 -C.sub.14). The concentration of W in this 
solution is of 545 mg.l.sup.-1. 
The solution is submitted to ultrafiltration in the device schematically 
displayed in FIG. 2, equipped with a tubular membrane CARBOSEP.RTM. M5 
(Rhone-Poulenc) having an exclusion molecular weight of 10 kDA, with an 
inner diameter of 5.5 mm and 600 mm of length. The operating conditions 
are as follows: recycle flow rate 225 l.h.sup.-1 ; pressure at module 
inlet: 0.35 Mpa; temperature 50.degree. C. During the first step of the 
operation, the permeate flow rate results to be of 63 l.m.sup.-2.h.sup.-1. 
After that 1.0 l of mixture has permeated, the permeate flow rate results 
to be of 32 l.m.sup.-2.h.sup.-1. The concentration of W in the permeate is 
lower than 3 mg.l.sup.-1, and the concentration of W in the retentate is 
of 1,600 mg.l.sup.-1, equivalent to a rejection of &gt;99%. 
EXAMPLE 5 
The catalyst (2.82 g) composed by a mixture of: 
tri[(di-n-hexadecyl)dimethyl]ammonium tetra(diperoxotungsto)phosphate 
PW.sub.4 O.sub.24 (C.sub.34 H.sub.72 N).sub.3 (76 mol %) PW.sub.4 O.sub.24 
(C.sub.38 H.sub.80 N).sub.3 (24 mol %), separately prepared as disclosed 
in EP-A-225 990, is dissolved in a mixture (1.5 l) of 1-alkenes 
(distillation cut C.sub.13 -C.sub.14). The concentration of W in this 
solution is of 152 mg.l.sup.-1. The solution is submitted to 
ultrafiltration in the device schematically displayed in FIG. 2, equipped 
with a tubular membrane CARBOSEP.RTM. M2 (Rhone-Poulenc) having an 
exclusion molecular weight of 15 kDA, with an inner diameter of 6 mm and 
600 mm of length. The operating conditions are as follows: recycle flow 
rate 225 l.h.sup.-1 ; pressure at module inlet: 0.35 Mpa; temperature 
50.degree. C. During the first step of the operation, the permeate flow 
rate results to be of 85 l.m.sup.-2.h.sup.-1. After that 1.12 l of mixture 
has permeated, the permeate flow rate results to be of 55 
l.m.sup.-2.h.sup.-1. The concentration of W in the permeate is lower than 
3 mg.l.sup.-1, and the concentration of W in the retentate is of 615 
mg.l.sup.-1. 
EXAMPLE 6 
2,000 g of a mixture of linear internal alkenes (distillation cut C.sub.13 
-C.sub.14), 31 g of catalyst, which is 
tri[(di-n-hexadecyl)dimethyl]ammonium tetra(diperoxotungsto)phosphate 
PW.sub.4 O.sub.24 (C.sub.34 H.sub.72 N).sub.3, and 584 g of distilled 
water are charged to a glass reactor of 5,000 ml, equipped with mechanical 
stirrer, reflux condenser, thermometer and dripping funnel, and provided 
with an external cooling jacket. The temperature of the mixture is 
increased up to 75.degree. C. and then 1,065 ml of H.sub.2 O.sub.2 at 
38.42% (0.6 mol) are added dropwise at such a flow rate that the 
temperature remains comprised within the approximate range of from 
71.degree. to 75.degree. C. 
When addition is ended, the mixture is kept stirred for a further 7 hours. 
The reaction mixture is cooled down to room temperature and is allowed to 
rest until a phase separation is obtained. The aqueous phase is separated 
and then is discarded. 2,182 g of an oily liquid with a content of W of 
3,310 mg.l.sup.-1 is obtained. 
A portion of this solution (1.5 l) is submitted to ultrafiltration in the 
device displayed in FIG. 2, equipped with a tubular micro membrane 
CARBOSEP.RTM. 60 M2 with rated exclusion molecular rate 15,000 Da. The 
operating conditions are as follows: recycle flow rate 280 l.h.sup.-1 ; 
module inlet pressure: 0.35 MPa; temperature 54.degree. C. During the 
first operation step, the flow rate of permeate results to be of 6.0 
m.sup.-2 h.sup.-1. After that 0.5 l of mixture have permeated, the flow 
rate of the permeate results to be of 5.5 l m.sup.-2 h.sup.-1, and the 
concentration of W in the permeate results to be of 110 mg.l.sup.-1, and 
the concentration of W in the retentate is of 4,700 mg.l.sup.-1, 
corresponding to a rejection of 97%. 
EXAMPLE 7 
104.4 g of soybean oil, having an iodine number of 136 (corresponding to a 
maximum epoxy number of 7.9) and 0.9 g of trioctyl methyl ammonium 
tetra(diperoxotungsto)phosphate PW.sub.4 O.sub.24 (C.sub.25 H.sub.54 
N).sub.3 are charged to a 4-necked flask of 250 ml, equipped with 
mechanical stirrer, reflux condenser, thermometer and dripping funnel. The 
temperature of the mixture is increased up to 60.degree. C. and then 53.1 
ml of H.sub.2 O.sub.2 at 38.42% (0.6 mol) is added dropwise with strong 
stirring, at such a flow rate that the internal temperature remains 
approximately constant. 
After the addition, the mixture is kept with stirring for a further 7 
hours. The reaction mixture is cooled down to room temperature, and then 
n-hexane is added, so that a phase separation is obtained. The organic 
phase is separated and the solvent is evaporated under vacuum. 111.8 g is 
obtained of an oil characterized by an iodine number of 2.7 and an epoxy 
number of 7.0. The resulting solution, containing 2,400 mg.ml.sup.-1 of W, 
is submitted to ultrafiltration by means of the device disclosed in FIG. 
2, equipped with a tubular membrane CARBOSEP.RTM. M2. The operating 
conditions are as follows: recycle flow rate 278 l.h.sup.-1 ; module inlet 
pressure: 0.40 MPa; temperature 105.degree. C. 
A permeate with a concentration of W of 123 ppm, equivalent to a rejection 
of 95% is obtained.