WO2013107902A1

WO2013107902A1 - Process for the separation of a dissolved catalyst system from an alkoxycarbonylation reaction mixture

Info

Publication number: WO2013107902A1
Application number: PCT/EP2013/051020
Authority: WO
Inventors: De Johannes Gerardus Vries; Michèle Catherine Christianne JANSSEN; Rudy Francois Maria Jozef Parton; Hendrik Derk Hoving
Original assignee: DSM IP Assets BV
Current assignee: DSM IP Assets BV
Priority date: 2012-01-20
Filing date: 2013-01-21
Publication date: 2013-07-25
Anticipated expiration: 2014-07-20

Description

PROCESS FOR THE SEPARATION OF A DISSOLVED CATALYST SYSTEM FROM AN ALKOXYCARBONYLATION REACTION MIXTURE

Field of the invention

The present invention relates a process for the separation of a dissolved catalyst system from an alkoxycarbonylation reaction mixture.

Background of the invention

Alkoxycarbonylation reactions are industrially relevant. For example, WO2001/068583 describes the Pd catalyzed methoxycarbonylation of ethylenically unsaturated compounds such as 2-butene, 1 -octene, and methyl-3-pentenoate. Methoxycarbonylation of methylpentenoates yields d imethylad ipate wh ich is an intermediate in the production of adipic acid (1 ,6-hexanedioic acid). Adipic acid is a precursor for the production of polyamides such as polyamide 6,6.

Alkoxycarbonylation reactions are usually carried out in the presence of a dissolved catalyst system comprising a group 8-10 metal, usually Pd, a ligand, and an acid promoter. Exa m p l es of s u i ta b l e l i g a n d s p h os p h i n e l i g a n d s u ch a s triphenylphosphine ligands or bidentate biphosphine ligands such as described in WO/9619434.

As in any industrial chemical reaction, the cost of the catalyst is an important factor in the economy of the process.

However, a problem associated with carbonylation reactions using a Pd catalyst system is that the catalyst system tends to inactivate over time. This is not so much of a problem when the Pd catalyst is used only for a limited period, e.g. in a (single) batch process. However, in processes wherein the catalyst is used repetitively or continuously, as in repetitive batch or in continuous processes, respectively, inactivation of the Pd catalyst system may form a problem. The problem is understood to reside in the reduction of the ionic Pd to metallic Pd. Such process is also referred to as the formation of Pd black.

WO/9619434, WO2009010782, WO01 10551 , WO2005079981 , WO0168583, and WO2007020379 all describe alkoxycarbonylation processes involving a Pd catalyst system. They describe that "dispersed" metal can be removed from the reaction stream using filtration and is then disposed or processed for re-use. Dispersed metal involves inactive, particulate (solid) metal. A common example of inactivation of the metal catalyst in alkoxycarbonylation reactions is caused by the formation of Pd black, which consists of particulate metallic Pd which can be removed from the stream by simple solid-liquid separation such as filtration, e.g. using a sieve. Pd black is inactive and it is useless to feed such Pd back to the alkoxycarbonylation reaction. It must first be processed.

It is desirable to recover any catalyst system which has not been inactivated, e.g. which is still in the dissolved form, from the reaction mixture, such that it can be re-used in a subsequent alkoxycarbonylation reaction. WO01 10551 , WO/9619434, WO2009010782, WO2005079981 , WO0168583, and WO2007020379 all describe alkoxycarbonylation processes using a Pd phosphine catalyst system, but are silent on the separation of the dissolved catalyst system.

In WO201 1073653 is described the methoxycarbonylation of ethene using a dissolved, Pd phosphine catalytic complex. It is described that active, dissolved ("useful") metal catalyst system can be separated from the reaction mixture by distillation, and can then be returned to the reactor vessel.

Likewise, EP0284170 describes the separation of a Pd polydentate catalyst system from an ethoxycarbonylation reaction by distillation, whereby it is fed back to the reactor.

A problem associated with the use of distillation to separate the catalyst system is that it can result in (thermal) inactivation, for example due to oxidation of the catalytic metal.

It is an aim of the invention to provide a process to separate dissolved catalyst system from an alkoxycarbonylation reaction mixture which does not lead to inactivation, which is simple, and/or which is suitable to feed the separated catalyst system back to the alkoxycarbonylation reaction.

Detailed description of the invention

The invention provides a process to separate a dissolved catalyst system from a mixture obtained by an alkoxycarbonylation reaction, the process comprising subjecting said mixture to membrane filtration using a membrane which is impermeable for molecules having a molecular weight of 1 kDa or more to yield a retentate and a permeate, wherein the concentration of the dissolved catalyst system in the retentate is higher than in the permeate.

The mixture may be fed to the membrane filtration at a pressure which is greater than the pressure at which the alkoxycarbonylation reaction is carried out, and wherein the permeate of the membrane filtration is kept at a pressure which is at least equal to said pressure at which the alkoxycarbonylation reaction is carried out. The pressure at which the mixture is fed to the membrane filtration is preferably at least 10% greater than the pressure at which the alkoxycarbonylation reaction is carried, more preferably this pressure is at least 20% greater, more preferably at least 30%, 50% greater, more preferably at least 75% greater, even more preferably it is at least 100% greater than the pressure at which the alkoxycarbonylation reaction is carried out. By way of example, if the alkoxycarbonylation reaction is carried out at 20 bar, and the pressure at which the mixture is fed to the membrane filtration is 40 bar, the pressure at which the mixture is fed to the membrane filtration is understood to be 100% greater than the pressure at which the alkoxycarbonylation reaction is carried out. The pressure at which the mixture is fed to the membrane filtration is preferably at least 5 bar above the pressure at which the alkoxycarbonylation reaction is carried out, more preferably at least 10 bar, more preferably at least 15 bar above the pressure at which the alkoxycarbonylation reaction is carried out. This may advantageously prevent the undesired phenomenon of flashing. Particularly, if the pressure of the permeate drops below the pressure at which the alkoxycarbonylation reaction is carried out, unwanted flashing may occur. This may cause problems in subsequent process steps, and may also pose a safety problem. Heat may be advantageously exchanged between the mixture fed to the membrane filtration and the retentate, saving energy and thus cost.

The pressure at which the mixture is fed to the membrane filtration may range between 10-100 bar, preferably between 20-60 bar, more preferably between 30-50 bar.

Preferably, the pressure between the alkoxycarbonylation reaction step and the membrane filtration step does not drop more than 90% below the pressure at which the alkoxycarbonylation reaction is carried out. This is to say, between the moment the mixture leaves the alkoxycarbonylation reaction and the moment that the mixture is subjected to the membrane filtration, the pressure has not dropped more than 90% as compared to the pressure of the reaction. More preferably the pressure does not drop more than 80%, 60%, more preferably not more than 40%, 20%, even more preferably not more than 10%. Most preferably the pressure between the alkoxycarbonylation reaction step and the membrane filtration step does not drop below the pressure at which the alkoxycarbonylation reaction is carried out. This advantageously may prevent the flashing out of low boilers such as methanol or CO prior to the membrane filtration.

The process of the invention may comprise the step of increasing the pressure of the mixture prior to the membrane filtration step, e.g. by using a pump.

In another embodiment, prior to the membrane filtration step, the mixture is depressurized, preferably the pressure is reduced to at least 90% relative to the pressure at which the alkoxycarbonylation reaction is carried out, more preferably the pressure is reduced to at least 95%. Most preferably the pressure is reduced to atmospheric pressure. If the mixture is not depressurized, any residual CO or alkanol in the permeate may be released. This phenomenon is also referred to as "flashing" and may be detrimental to both safety and process. First reducing the pressure and cooling of the mixture and then increasing the pressure prior to membrane filtration may reduce or remove CO or alkanol from the mixture prior to the membrane filtration. This may advantageously allow the permeate to be fed to distillation without any intermittent flashing.

The process of the invention may comprise (in this order):

- reducing the pressure of the mixture prior to the membrane filtration, preferably to atmospheric pressure, preferably by using a flasher;

- cooling the mixture below the maximum membrane operation temperature;

- increasing the pressure of the mixture, preferably to above atmospheric pressure;

- feeding the mixture to the membrane filtration; and

- subjecting the permeate to distillation to yield a distillate and a distillation residue.

The permeate of the membrane filtration may be subjected to a flasher and then to a distillation to yield a distillate and a distillation residue. In the flasher the pressure of the permeate is reduced, preferably to atmospheric pressure.

The inventors have found out that the process of the invention may have several advantages. Firstly, the process may reduce or even avoid inactivation of the catalyst system, for example through Pd-black formation, since the catalyst is not exposed to high temperature (which is typical for distillation). Furthermore, membrane filtration can be performed under reactive gas (e.g. CO) which prevents catalyst deactivation as well. In the context of the invention "impermeable for molecules having a molecular weight of 1 kDa or more" means that the membrane is permeable to molecules having a molecular weight of up to 1 kDa. The membrane can be easily selected by the skilled person based on the molecular weight cut off (MWCO). The MWCO, Molecular Weight Cut Off, describes the retention performance of a membrane. Cut-off is defined as that molecular weight of a molecule which is 90% rejected by the membrane. The retention R is defined as R=100%(1 -Cp/Cf), wherein Cp is the concentration of the molecule in the permeate and Cf is the concentration of the molecule in the feed to the membrane filtration. In a continuous system, the concentration of the molecule in the feed will be more or less constant, whereas in a batch-system said concentration will increase in time. A suitable handbook for membrane separation is "Basic principles of membrane technology by M. Mulder, 1991 , Kluwer Academic, Dordrecht, The Netherlands.

In the context of the invention "impermeable" does not necessarily mean that all molecules having a molecular weight of 1 kDa are retained by the membrane. In the context of the invention "impermeable for molecules having a molecular weight of 1 kDa or more" is defined such that 90% or more of a 1 kDa solute is retained by the membrane, preferably more than 95%, even more preferably more than 98% (all based on weight).

The membrane is impermeable for molecules having a molecular weight of 1 kDa or more, preferably of 500 Da or more, more preferably of 350 Da or more. Preferably 90wt% or more of the dissolved catalyst system is retained by the membrane, preferably more than 95wt%, even more preferably more than 98wt%.

The process of the invention is particularly suitable for the separation of dissolved, active catalyst system. This advantageously allows for feeding the retentate back to th e a l koxyca rbon yl ati on p rocess . P refe ra b ly 90 % o r m o re of th e alkoxycarbonylation activity is retained by the membrane, preferably more than 95%, even more preferably more than 98%. The activity yield of the membrane filtration can be determined e.g., by using the retentate as catalyst in a subsequent alkoxycarbonylation reaction under identical conditions and comparing the activity.

The membrane filtration may advantageously be carried out in the absence of oxygen. This may reduce or prevent inactivation of the catalyst system.

If part of the catalyst system is inactive, e.g. as Pd black, some of such inactive (and particulate) catalyst system may be present in the retentate and may be removed from the retentate using solid-liquid separation such as filtration, e.g. prior to feeding the retentate back to the alkoxycarbonylation reaction. Alternatively, prior to feeding the mixture to the membrane separation, said mixture may be subjected to solid-liquid separation.

Membrane filtration involves separation from one or more dissolved components from one or more other dissolved components. In the art, "membrane filtration" and "filtration" are not the same. "Filtration" is understood to be, and is herein defined as a form of solid/liquid separation involving particles having a size larger than 5 micron. Membrane separation, or membrane filtration, on the other hand, relates to particles < 5 micron and dissolved particles. From suspended particles of 5 micron down to about 0.1 micron the process is termed microfiltration, while below that the term ultrafiltration applies. Ultrafiltration covers the finest distinct particles (such as colloids), but its lower limits is usually set in molecular weight terms, measured in Daltons. Below ultrafiltration (UF) comes nanofiltration (NF) and reverse osmosis (RO). (Filters and Filtration Handbook, Ken Sutherland, 2008, published by Elsevier, Amsterdam). In membrane separation (membrane filtration) the fraction passing through the membrane is referred to as "permeate" and the fraction that is retained by the membrane is referred to as "retentate". Membranes having a molecular weight cut off of more than 1 kDa are not suitable in the process in the invention because both the catalyst system and the alkoxycarbonylation product may permeate.

The transmembrane pressure in the membrane separation process is preferably 5-60 bar, the crossflow velocity is preferably 0.1 -10 m/s, and the temperature is preferably in the range of 25-100°C. The mixture is fed to the membrane filtration at a temperature which is below the maximum allowable temperature of the membrane. The maximum allowable temperature of the membrane is typically given by the manufacturer of the membrane.

In the process of the invention, the membrane separation may comprise one or more membranes. Depending on the separation efficiency of the membrane and the desired retention, the desired retention can be achieved by connecting a plurality of membranes or membrane modules in series. If the process comprises multiple membranes, said membranes are preferably used in the form of membrane modules. In these modules, the membranes are arranged so that liquid flows over the retentate side of the membranes in such a way that the concentration polarization of the components separated off (the enrichment of the components separated off at the membrane) can be countered and, in addition, the necessary driving force (pressure) can be applied. The permeate can be collected in the permeate collection space on the permeate side of the membranes and discharged from the module. Customary membrane modules for polymer membranes have the membranes in the form of membrane disks, membrane cushions or membrane pockets. Customary membrane modules for membranes based on ceramic supports have these in the form of tubular modules. The membrane modules preferably have open-channel cushion module systems in which the membranes are thermally welded or adhesively bonded to form membrane pockets or cushions or open- channel (wide-spacer) rolled modules in which the membranes are adhesively bonded or welded to form membrane pockets or membrane cushions and rolled up together with spacers to form a permeate collection tube or have the membrane modules in tubular modules. An arrangement in series can be effected so that either the retentate or the permeate, preferably the permeate, of a first membrane separation is passed as feed to a further membrane separation. Any further membrane separation(s) following the first membrane separation according to the invention can be carried out under the same conditions as the first membrane separation or under different conditions, in particular different temperatures or pressures. Also membrane cascade systems comprising ultrafiltration, nanofiltration and reverse osmosis could be used in the invention.

The membrane is preferably a nanofiltration membrane, preferably a solvent- resistant nanofiltration membrane. Nanofiltration membranes are commercially available and well described in Nanofiltration: Principles and Applications by Anthony Gordon Fane et al. 2005, published by Elsevier, Oxford. Solvent-resistant membranes are known in the field and are commercially available. The preparation of solvent-resistant membranes is known and is described e.g. by P. Vandezande et al., Chem. Soc. Rev., 2008, vol 37, 365-405. Peeva et al. [Nanofiltration Operations in Nonaqueous Systems, Comprehensive Membrane Science and Engineering, 2010, Chapter 2.05, Pages 91 - 1 13, L.G. Peeva, M. Sairam, A.G. Livingston] describe the characteristics of a number of solvent-resistant nanofiltration membranes to be used in non-aqueous systems.

Nanofilter membrane separation is preferably conducted as crossflow nanofiltration which may be performed using a nanofiltration material having a cut off for normal alkanes dissolved in toluene giving 90% rejection at 300 Da.

Suitable solvent-resistant nanofiltration membranes are commercially available from e.g. Solsep (The Netherlands), Borsig/GMT (Germany) Bio Pure Technology (Israel), Koch Membrane (USA) and Evonik-MET Duramem, Puramem, UOP-MET, Starmem (United Kingdom). Membrane modules which have the tubular membranes on a ceramic support can be procured from, for example, Inopor (Germany) membranes, a spin-off company of HITK (Germany) / FraunhoferJKTS (Germany). Suitable membranes include polyimide based or polydimethylsiloxane membranes. They may be employed in spiral wound modules. Suitable membranes are stable in alcohols (e.g., butanol, ethanol, and iso-propanol); in alkanes (e.g., hexane and heptane); in aromatics (e.g., toluene and xylene); in ethers (e.g., methyl-tert-butyl-ether); in ketones (e.g., methyl-ethyl-ketone and methyl-isobutyl-ketone); or in esters (e.g., butyl acetate , ethyl acetate, methyl pentenoate and/or dimethyl adipate).

In an embodiment the retentate comprising the dissolved catalyst is fed to an alkoxycarbonylation reaction. The separation process of the invention is preferably a continuous process.

The alkoxycarbonylation reaction comprises reacting an optionally substituted alkene with alkanol and CO in the presence of an acid promoter and a catalyst system comprising a group 8-10 metal and a ligand.

The ligand in the alkoxycarbonylation reaction is preferably a bidentate ligand, preferably a bidentate phosphine ligand of formula I;

R1 R2P - R3 - R - R4 - PR5R6 (I)

wherein P represents a phosphorous atom; R1 , R2, R5 and R6 can independently represent the same or different optionally substituted organic groups containing a tertiary carbon atom through which the group is linked to the phosphorus atom; R3 and R4 independently represent optionally substituted lower alkylene groups and R represents an optionally substituted aromatic group, preferably wherein R1 , R2, R5, and R6 are tert-butyl, R3 and R4 are methylene, and R is ortho-phenylene.

The catalyst system in the process of the invention is dissolved in the mixture, which preferably is a non-aqueous solution. In the context of the invention, "dissolved" is defined as forming a homogeneous phase; a clear solution is formed. "Dissolved" is different from particulate or dispersed. Dispersed particles form a separate phase from the reaction mixture; this is typically a heterogeneous systems. The catalyst system of the invention may be dissolved in a reactant such as an alkanol, e.g. methanol. If the alkoxycarbonylation reaction comprises a solvent, such as an aprotic solvent, the catalyst system may be dissolved in such solvent.

The catalyst system preferably comprises a cationic metal-ligand complex comprising said group 8-10 metal and said ligand. The process of the invention may be particularly suitable for cationic metal-ligand complexes as compared to e.g. neutral or acidic metal-ligand complexes.

The catalyst system or its components thereof may have a molecular weight of 500 Da and more, preferably 1000 Da or more.

The alkoxycarbonylation reaction is typically carried out at elevated pressure, preferably at a pressure between 5 and 100 bar, more preferably between 10 and 50 bar, even more preferably between 15 and 25 bar. A suitable temperature range for alkoxycarbonylation reactions is between 20-160°C, more preferably between 50-120°C.

The group 8-10 metal preferably comprises Pd, preferably from a source selected from the group consisting of palladium halide, palladium carboxylate and Pd2(dba)3.

The optionally substituted alkene preferably has a boiling temperature of 120°C, or higher, measured at atmospheric pressure, and preferably comprises pentenoic acid or a pentenoic acid alkyl ester. A preferred alkanol is methanol. Boiling temperatures can be found in the Handbook of Chemistry and Physics.

I n a n em bod i ment th e d issolved cata lyst system is sepa rated from a carbonylation reaction product, preferably from adipic acid dimethyl ester. Thus, the mixture may comprise a carbonylation reaction product such as adipic acid dimethyl ester.

Depending on the boiling points of the alkoxycarbonylation product and any solutes and solvent, several distillation units (a so-called "train") may be required. If there is more than one distillation unit, the process of the invention may comprise more than one distillate; within the context of the invention "a distillate" may include one, two, or more distillates.

The maximum membrane operation temperature is related to the integrity of the membrane and membrane housing and generally specified in datasheets given by the membrane filtration unit manufacturer.

The invention also provides a continuous alkoxycarbonylation process comprising:

(a) reacting an alkene with CO and an alkanol in an alkoxycarbonylation reaction further comprising an acid promoter and a dissolved catalyst system, said catalyst system comprising a group 8-10 metal and a ligand, to yield a mixture comprising an alkoxycarbonylation reaction product; (b) separating the catalyst system from the mixture obtained in step (a) i n a separation process of the invention to yield a retentate and a permeate, wherein the concentration of the dissolved catalyst system in the retentate is higher than in the permeate;

(c) feeding the retentate obtained in step (b) back to the alkoxycarbonylation reaction; and

(d) repeating step (a).

(a) reacting an alkene with CO and an alkanol in an alkoxycarbonylation reaction comprising a dissolved catalyst system to yield a mixture comprising an alkoxycarbonylation reaction product;

(b) separating the catalyst system from the mixture obtained in step (a) using membrane filtration using a membrane which is impermeable to molecules having a molecular weight of up to 1 kDa or more to yield a retentate and a permeate, wherein the concentration of the dissolved catalyst system in the retentate is higher than in the permeate;

(d) repeating step (a).

Figure 1 : Schematic representation a continuous flow membrane reactor for an alkoxycarbonylation reaction. The reactor R is fed (F) with an alkene, CO, an alkanol, an acid promoter and a catalyst system comprising a group 8-10 metal and a ligand. The reaction mixture is fed to a membrane filtration unit comprising a membrane M by means of a pump. The retentate comprising the catalyst system ("catalyst") is fed back to the alkoxycarbonylation reaction. The permeate (P) comprising the carbonylation product can be subjected to e.g. distillation.

The invention will be further elucidated with reference to the following examples, without however being limited thereto.

EXAMPLES Example 1

In this Example, the suitability of membranes permeable to molecules up to 1 kDa was tested to separate dissolved Pd catalyst systems.

An alkoxycarbonylation reaction mixture was obtained by methoxycarbonylation of methylpentenoates (mixture of isomers, 400 mL) with methanol (600 mL) and carbon monoxide in the presence of a Pd/(1 ,2-Bis(di-tert-Butylphosphinomethyl)benzene/ methanesulfonic acid catalyst (180 mg / 1.6 g / 660 μΙ_) and 200 mL dimethyl adipate as stabilizer in a 2 liter stainless steel reactor. Reaction conditions: PCO = 20 bar, T = 100°C for 4h. Pd, and P were measured using ICP-AES. First flash, 1 bar. CO was removed by flashing removed..

An amount of 200 gram of the flashed reaction mixture was subjected to nanofiltration on a laboratory crossflow membrane test unit, type CM Celfa P28. The transmembrane pressure was set (with nitrogen) on 7-37 bar and temperature was kept at 40°C. The tested flatsheet membranes had an area of 28 cm2. An amount of 20-25 grams permeate was produced and collected at atmospheric level.

Samples were analysed by means of ICP-AES on Pd and P levels. The results are summarized in Table 1.

Table 1

Δ Pressure: refers to the trans membrane pressure difference

CF: concentration factor

For the Borsig GMT-oNF-1 membrane, the yields of methanol and DMA was analyzed before and after filtration. Before the membrane filtration, the amount of methanol was 38 wt% and the amount of was DMA 50 wt% based on the total weight of the carbonylation mixture. After membrane filtration the amount of methanol in the permeate ranged between 35 wt% and 40 wt%, and in the retentate between 37 wt% and 41 wt%; the amount of DMA in the permeate ranged between 48 and 52 wt%, and in the retentate it ranged between 48 and 51 wt%. This shows that both methanol and dimethyl adipate pass the membrane unhindered, i.e. neither MeOH nor DMA is more concentrated at the retentate side than on the permeated side.

Example 2

An alkoxycarbonylation reaction of an alkene with carbon monoxide and methanol in the presence of a transition metal based soluble catalyst is carried out in a continuous flow membrane reactor. The alkoxycarbonylation reaction is carried out at Pco = 20 bar. Before entering the membrane module, the P_Co is boosted to a pressure > 20 bar, typically 40 bar (this pressure can be chosen in such a way that the desired trans membrane pressure is achieved, taking into account that the pressure at the permeate side of the membrane is equal to the reaction pressure in order to prevent flashing of volatile components). The heat of the feed to the membrane filtration unit is transferred via a heat exchanger to the retentate to minimize energy loss and contribute to sustainability.

Claims

1 . Process to separate a dissolved catalyst system from a mixture obtained by an alkoxycarbonylation reaction, the process comprising subjecting said mixture to membrane filtration using a membrane which is impermeable to molecules having a molecular weight of up to 1 kDa or more to yield a retentate and a permeate, wherein the concentration of the dissolved catalyst system in the retentate is higher than in the permeate.

2. Process according to claim 1 wherein the mixture is fed to the membrane filtration at a pressure which is greater than the pressure at which the alkoxycarbonylation reaction is carried out, and wherein the permeate of the membrane filtration is kept at a pressure which is at least equal to said pressure at which the alkoxycarbonylation reaction is carried out.

3. Process according to claim 2 wherein the pressure at which the mixture is fed to the membrane filtration is at least 10% greater than the pressu re at which the alkoxycarbonylation reaction is carried out.

4. Process according to any one of claim 1 -3 wherein the pressure between the alkoxycarbonylation reaction step and the membrane filtration step does not drop more than 90% bar below the pressure at which the alkoxycarbonylation reaction is carried out.

5. Process according to any one of claim 1 -4 further comprising the step of increasing the pressure of the mixture prior to the membrane filtration step.

6. Process according to claim 1 , whereby prior to the membrane filtration, the mixture is depressurized.

7. Process according to any one of claim 1 -6 wherein the membrane is a nanofiltration membrane, preferably a solvent-resistant nanofiltration membrane.

8. Process according to any one of claim 1 -7 which is a continuous process and wherein the retentate comprising said dissolved catalyst system is fed to a n alkoxycarbonylation reaction.

9. Process according to any one of claim 1 -8 wherein the catalyst system comprises Pd and a bidentate phosphine ligand.

10. Process according to any one of claim 1 -9 wherein the dissolved catalyst system is separated from adipic acid dimethyl ester.

1 1 . Continuous alkoxycarbonylation process comprising: (a) reacting an alkene with CO and an alkanol in an alkoxycarbonylation reaction comprising a dissolved catalyst system to yield a mixture comprising an alkoxycarbonylation reaction product;

(d) repeating step (a).