The invention provides a process for the carbonylation of an olefinically or acetylenically unsaturated compound which comprises: PA0 (a) reacting the unsaturated compound with carbon monoxide and a co-reactant in the presence of a carbonylation catalyst, obtainable by combining a source of platinum group metal cations, a phosphine ligand and an anion, to produce a reaction mixture comprising a carbonylation product, the carbonylation catalyst, and excess of the olefinically or acetylenically unsaturated compound and/or the co-reactant, and PA0 (b) recovering the carbonylation product by distillation of the reaction mixture wherein a catalytically active concentrate is removed from the reaction mixture prior to step (b).

The invention relates to carbonylation reactions. More in particular, the 
invention relates to a process for the carbonylation of an olefinically or 
acetylenically unsaturated compound, which comprises reacting the 
unsaturated compound with carbon monoxide and a co-reactant in the 
presence of a carbonylation catalyst, obtainable by combining a source of 
platinum group metal cations, a phosphine ligand and an anion. 
As is known from SRI International PEP Report 11D, Shell has developed a 
route for preparing amongst others methyl methacrylate (MMA) from propyne 
using a homogeneous palladium-phosphine carbonylation catalyst. Although 
this route is already more attractive from an economic point of view than 
the competing routes discussed in this Report, there is still the 
incentive to further lower the cost, in particular the cost related to the 
relatively expensive carbonylation catalyst. It would hence be desirable 
to lower the catalyst cost. This could either be effected through use of 
even lower concentrations of catalyst, or through catalyst recovery and 
recycle. 
It is known (page 9-13 of the Report) that homogeneous catalysts, 
especially those with ligands, are susceptible to slow deactivation and 
poisoning due to accumulation of impurities. Decreasing the content of the 
carbonylation catalyst in the reaction mixture and increasing the 
residence time, therefore, is not only cumbersome because of the already 
very low concentrations, but also suffers from increased sensitivity to 
poisons. Moreover, at longer residence times the catalyst may suffer from 
deactivation as the result of ligand degradation. 
According to the Report and the literature cited therein, the activity of a 
recirculating carbonylation catalyst, collected as bottom stream of the 
MMA distillation column, is believed to be maintained by withdrawing a 
small purge to control the build-up of impurities (cf. page E-25 of the 
Report). The purge stream is then to be treated as discussed below, to 
separate the valuable components for reuse. Alternatively, the purge could 
be packaged and shipped to the palladium supplier or to a custom 
processor. 
As set out in the Report, the purge stream may be treated similar to purge 
streams containing rhodium/triphenylphosphine catalysts. Purge streams 
containing rhodium/triphenylphosphine catalysts are concentrated under 
vacuum in a wiped-film evaporator (WFE) to remove some of the ligand and 
light impurities. Batches of the condensed stream are extracted to leave a 
residue that is mostly ligand for reuse. Rhodium metal residue from the 
WFE is treated with air to oxidise the remaining ligand, then washed with 
acid and solvent. The rhodium is converted to the active species and mixed 
with fresh and recovered ligand. 
Although the process as envisaged by the authors of the Report may be 
operable, one has to realise that this bottom stream has a significantly 
reduced catalytic activity and hence needs to be treated almost in full. 
Naturally this elaborate treatment is preferably avoided. 
In EP-A-0,571,044 (cf. page 4, lines 33-36) a process for the recovery of a 
carboxylate ester reaction product is described which may involve a step 
of separating a stream comprising heavy ends having a volatility lower 
than the volatilities of the reaction product and the azeotrope-forming 
alcohol precursor. This tailing of heavy ends can be effected using common 
chemical technology, for example distillation. The product of such 
distillation step, however, has again significantly reduced catalytic 
activity. 
Surprisingly, the inventors have found that when a carbonylation catalyst, 
obtainable by combining a source of platinum group metal cations, a 
phosphine ligand and an anion is concentrated before distillation of the 
carbonylation product, the concentrate may still retain sufficient 
activity to be reused as carbonylation catalyst without the proposed 
oxidative treatment step. 
Accordingly, the invention provides a process for the carbonylation of an 
olefinically or acetylenically unsaturated compound which comprises: 
(a) reacting the unsaturated compound with carbon monoxide and a 
co-reactant in the presence of a carbonylation catalyst, obtainable by 
combining a source of platinum group metal cations, a phosphine ligand and 
an anion, to produce a reaction mixture comprising a carbonylation 
product, the carbonylation catalyst, and excess of the olefinically or 
acetylenically unsaturated compound and/or the co-reactant, and 
(b) recovering the carbonylation product by distillation of the reaction 
mixture 
wherein a catalytically active concentrate is removed from the reaction 
mixture prior to step (b). 
Preferably, the catalytically active concentrate is removed by 
separating-out the remaining components of the reaction mixture at ambient 
or elevated temperature up to about 150.degree. C., preferably no more 
than 100.degree. C., and normal or subatmospheric pressure, provided that 
the residence time at elevated temperatures is less than 20 minutes. 
In a preferred embodiment, the catalytically active concentrate is removed 
by concentration in an evaporator, whereby an at least a three-fold 
concentration of the carbonylation catalyst is achieved within a residence 
time of the reaction mixture that is less than 20 minutes. 
Typically, the evaporator is a film evaporator such as described in Perry's 
Chemical Engineer's Handbook (6th ed., 11.31-11.38). Film evaporators that 
may be applied very successfully are falling film evaporators and wiped 
film evaporators. The evaporator may be a single evaporator, or a train of 
evaporators, operating in parallel or serial. Preferably, the 
carbonylation catalyst is concentrated at least three-fold, more 
preferably at least six-fold, within a time span of 20 minutes. 
The reactants of the process, i.e., the olefinically or acetylenically 
unsaturated compound as well as the co-reactant may be any of those 
mentioned in EP-A-0,495,547. 
The unsaturated compound may be an olefinically unsaturated compound up to 
30 carbon atoms including compounds having a plurality of unsaturated 
carbon-carbon bonds and/or compounds having one or more functional groups, 
or an acetylenically unsaturated compound up to 30 carbon atoms including 
compounds having a plurality of unsaturated carbon-carbon bonds and/or 
compounds having one or more functional groups. Preferably, the 
unsaturated compound is an acetylene, suitably ethyne or propyne. 
Suitable co-reactants in case of the olefin include molecular hydrogen to 
prepare oxo-aldehydes and oxo-alcohols and nucleophilic compounds, such as 
lower alcohols having 1 to 6 carbon atoms, having one or more active 
hydrogen atoms. An example of the latter includes butanol, to prepare 
solvents like butylproprionate. Suitable co-reactants in case of the 
acetylene include water or a lower alcohol such as methanol (MeOH) to 
prepare for instance acrylic acid, methacrylic acid, methyl acrylate or 
methyl methacrylate (MMA). The invention is particularly useful in the 
production of MMA. 
The reactants are preferably fed to the process in substantial accordance 
with the reaction stoichiometry, i.e., in substantially equimolar amounts 
apart from any recycle streams, although the ratio in the carbonylation 
section may differ from stoichiometry to expedite the reaction. For 
instance, the ratio in the carbonylation section of propyne/carbon 
monoxide/methanol, to produce MMA, is in the range of 1:1-4:1-4, typically 
in the range of a:1-2:1-2, preferably about 1:1.5:1.5-1.9. 
In the present specification the metals of the platinum group are defined 
as the metals with the atomic numbers 28, 46 and 78, i.e. nickel, 
palladium and platinum. Of these, palladium and platinum are preferred. 
Best results have been achieved with carbonylation catalysts based on 
palladium cations and they are therefore most preferred. 
Examples of suitable metal sources are nickel, platinum or palladium 
compounds such as salts of nickel, platinum or palladium and nitric acid, 
sulphuric acid, sulphonic acids or carboxylic acids with up to 12 carbon 
atoms, nickel-, palladium- or platinum complexes, e.g. with carbon 
monoxide or acetylacetonate, or the metal combined with a solid material 
such as an ion exchanger or carbon. Palladium(II) acetate and platinum(II) 
acetylacetonate are examples of preferred metal sources. 
As anion source, any compound generating anions may be used. Suitably, 
acids, or salts thereof, are used as source of anions, for example any of 
the acids mentioned above, which may also participate in the salts of the 
metals of the platinum group. 
In the carbonylation catalysts of the invention, preferably strong acids 
are used as anion source, i.e. acids having a pKa value of less than 3, 
preferably less than 2, measured in aqueous solution at 18.degree. C. The 
anions derived from these acids are non-coordinating or weakly 
coordinating with the metals of the platinum group. 
Typical examples of suitable anions are anions of phosphoric acid, 
sulphuric acid, sulphonic acids and halogenated carboxylic acids such as 
trifluoroacetic acid. 
Sulphonic acids are in particular preferred, for example methanesulphonic 
acid, trifluoromethanesulphonic acid, tert-butanesulphonic acid, 
p-toluenesulphonic acid and 2,4,6-trimethylbenzenesulphonic acid. 
Also, complex anions are suitable, such as the anions generated by a 
combination of a Lewis acid such as BF.sub.3, AlCl.sub.3, Sn(CF.sub.3 
SO.sub.3).sub.2, SnF.sub.2, SnCl.sub.2, GeCl.sub.2 or PF.sub.5, with a 
protic acid, such as a sulphonic acid, e.g. CF.sub.3 SO.sub.3 H or 
CH.sub.3 SO.sub.3 H or a hydrohalogenic acid such as HF of HCl, or a 
combination of a Lewis acid with an alcohol. Examples of suitable complex 
anions are BF.sub.4.sup.-, SnCl.sub.2.CF.sub.3 SO.sub.3 !.sup.-, 
SnCl.sub.3.sup.- and PF.sub.6.sup.-. 
As ligand both monodentate phosphines and bidentate diphosphines may be 
used. Specific examples include triphenylphosphine, 
diphenyl(2-pyridyl)phosphine, 1,2-P,P'-bis(9-phosphabicyclo3,3,1 or 
4,2,1!nonyl)ethane, etc. In the carbonylation of acetylenes preferably 
diphenyl(2-pyridyl)phosphine is used. 
Carbonylation catalysts suitably used are disclosed, for instance, in 
EP-A-0,271,144; EP-A-0,271,145; EP-A-0,274,795; EP-A-386,833; 
EP-A-0,386,834; EP-A-0,495,547; WO 94/21585; WO 95/05357 and 
EP-A-0,499,329. 
The most preferred carbonylation catalyst in the carbonylation of 
acetylenes is thus formed by combining (a) palladium(II) acetate, (b) 
diphenyl(2-pyridyl)phosphine, and (c) methanesulphonic acid. 
The carbonylation catalyst may contain further components such as 
polymerisation inhibitors and the like. Suitably, a polymerisation 
inhibitor such as hydroquinone is included. 
The quantity in which the carbonylation catalyst is used, is not critical 
and may vary within wide limits. Usually amounts in the range of 10.sup.-8 
to 10.sup.-1, preferably in the range of 10.sup.-7 to 10.sup.-2 mole atom 
of platinum group metal per mole of unsaturated compound are used. The 
amounts of the participants in the carbonylation catalyst are conveniently 
selected such that per mole atom of platinum group metal from 0.5 to 100, 
preferably from 1 to 50 moles of ligand are used, from 0.5 to 100, 
preferably from 1 to 50 moles of anion source or a complex anion source. 
The carbon monoxide reacted in the carbonylation step of the present 
process, can be derived from any source. It is preferably used in 
substantially pure form. 
The carbonylation can be suitably carried out at moderate reaction 
conditions. Hence temperatures in the range of 20.degree. to 200.degree. 
C. are recommended, preferred temperatures being in the range of 
30.degree. to 120.degree. C. Reaction pressures in the range of 5 to 100 
bar absolute are preferred, lower or higher pressures may be selected, but 
are not considered particularly advantageous. Moreover, higher pressures 
require special equipment provisions. 
Preferably, the process is carried out in a continuous manner, e.g., as 
described in EP-A-0,521,578. 
The invention will be further illustrated by the drawings. Herein, FIG. 1 
shows a flow scheme of a preferred embodiment of the invention. In this 
figure, the olefinically or acetylenically unsaturated compound is fed 
through line 1, to a carbonylation unit 2, which may be constituted by a 
plurality of individual reactors. In this unit 2 further reactants such as 
carbon monoxide, alcohol and catalyst are introduced either jointly with 
the unsaturated compound through line 1 or separately through a single or 
multitude of lines 3 (only one line shown). The reaction mixture is 
forwarded through line 4 to evaporator 5, e.g., an FFE. The evaporated 
reaction mixture is forwarded to a distillation zone 9, which again may be 
constituted of a plurality of distillation units. The carbonylation 
product is mainly collected as overhead stream 10, whereas the bottom 
stream 11 contains among others methyl crotonate. A catalytically active 
concentrate is collected from the evaporator 5 through line 6. Part 
thereof is purged through line 7. Together with ligand and/or anion to 
make-up for losses, if any, the remainder of the concentrate is recycled 
to unit 2. 
In FIG. 2, part of a more preferred embodiment is shown, similar to FIG. 1, 
but wherein the purge is passed through line 7 to a subsequent evaporator 
8, for instance a WFE, to provide an evaporated stream that is combined 
with the evaporated reaction mixture, and a concentrated purge. 
The design and operation of the carbonylation unit and further work-up 
equipment are within the skills of a chemical technologist, and does not 
require further explanation.

The invention will be illustrated by the non-limiting examples, as 
described hereinafter. 
EXAMPLES 
A fresh carbonylation feed consisting of a mixture of 32 mL/h propyne, 46 
mL/h catalyst solution, and 15 NL/h CO was continuously fed to a 
continuously stirred tank reactor operating at a constant temperature of 
45.degree. C. A liquid level of 220 mL was maintained and the pressure was 
kept at 11 bar abs by means of a constant pressure valve. The catalyst 
solution contained MeOH, palladium-acetate (Pd(OAc).sub.2), 
diphenyl(2-pyridyl)phosphine (PN), methanesulphonic acid (MSA), and 
hydroquinone (HQ). The catalyst molar ratio Pd/PN/MSA was 1/20/20, the 
molar HQ/Pd ratio was 40 and the Pd-concentration amounted to 18 ppmw. The 
reaction mixture, i.e., the liquid reactor effluent containing MMA, 
unreacted feedstocks, and the catalyst components, was collected. After 16 
h the steady-state conversion of propyne was found to be 89% mol, whereas 
the selectivity to MMA was found to be 99.2% mol. Next, the feed flows 
were increased to 77 mL/h catalyst solution, 64 mL/h propyne, and 30 NL/h 
CO. Again the liquid reactor effluent was collected. After 5 h a 
steady-state conversion of 83% mol was measured with a selectivity to MMA 
of 99.2% mol. 
In total, 1827 g of liquid reactor effluent (containing 9.5 ppmw Pd) was 
thus collected and submitted to a WFE, applying a wall temperature of 
85.degree. C. and a pressure of 800 mbar abs. Two product streams were 
obtained; the evaporated product, consisting mainly of MeOH and MMA, and a 
bottom fraction, weighing 285 g and containing the catalyst components 
(60.9 ppmw Pd). The concentration factor in this example was 6.4, at a 
calculated residence time on the `hot wall` of the WFE of less than 6 
minutes. 
To this fraction 625 g of MeOH was added together with 0.45 g of PN, 0.08 g 
of MSA, and 0.68 g of HQ. No Pd-component was added. The thus obtained 
mixture, which contained 18 ppmw of Pd as above, was used as a catalyst 
solution in a following carbonylation run. 
Thus, to the CSTR 28 mL/h of this solution was fed together with 22 mL/h 
propyne and 10 NL/h CO applying similar conditions as set out above. After 
16 h the steady-state conversion of propyne was measured to be 78% mol 
with a selectivity of 98.8 mol %. Next, the feed flows were increased to 
76 mL/h, 65 mL/h and 30 NL/h, respectively. After 5 h the steady-state 
conversion was measured to be 64% mol with a selectivity to MMA of 98.8% 
mol. 
It can be seen that in the second run the Pd-catalyst still exhibits a 
significant activity. 
COMATIVE EXAMPLES 
15 mL of a bottom stream from a MMA distillation column as described in the 
SRI International PEP Report 11D, containing 124 ppmw Pd and other 
catalyst residues in 90% w MMA and 10% w methyl crotonate, was diluted 
with 30 mL of MeOH containing 0.7 mmol of PN, MSA, and HQ. The mixture was 
transferred to a 250 mL batch autoclave which was subsequently closed, 
filled with 60 bar abs of CO, and brought to 60.degree. C. after which 175 
mmol of propyne was added. After 5 h the reaction was completed as 
indicated by a leveling-off of the pressure drop. Turn-over in 5 h was 
12,500 mol propyne per mol Pd or 2500 mol/mol/h. 
The above procedure was followed but fresh MMA (p.a.) was used without any 
Pd-catalyst residues. In the MeOH 0.7 mmol of PN-ligand, MSA, and HQ were 
dissolved plus 0.014 mmol of Pd(OAc).sub.2. After less than 0.5 h the 
pressure drop has leveled-off and the turn-over was found to be more than 
25,000 mol/mol/h. 
The first example proofs that the bottom stream of the MMA distillation 
column has a significantly reduced activity, i.e., an activity which is 
only 10% of that of a fresh catalyst. On the other hand, in the example 
according to the invention about 50% of the activity has been retained.