It is known to produce polyketones which are linear alternating polymers of (a) one or more olefins and (b) carbon monoxide, by a liquid phase (slurry) process in which the olefins and carbon monoxide are polymerised together in methanol, ethanol or propanol solvent in the presence of a palladium catalyst. Such a process, which is disclosed in more detail in, for example, EP 121965 and EP 314309, typically employs a catalyst derived from (a) a palladium compound (b) a source of an anion which is either non-coordinating or only weakly coordinating to palladium and (c) a bisphosphine of formula RIR2P-R-PR3R4 (I) where R'to R4are independently aryl groups which can optionally be polar substituted and R is a divalent organic bridging group such as- (CH2) n- (n = 2-6). A source of the anion is typically its conjugate acid.

EP 0516239 relates to a process for the preparation of polyketones in a system comprising at least one reactor and at least one mechanical contact zone wherein the volume of suspension present in the mechanical contact zone is substantially less than the volume of the suspension present in the reactor, the suspension is passed through the mechanical contact zone and high shearing forces of at least 0.25 kW/m3, relative to the total volume of the polymer suspension present in the reactor are exerted on the polymer particles dispersed in the suspension present in the mechanical contact zone. In particular EP 0516239 relates to a loop system where the polymer suspension is recycled from the bottom of the reactor by means of a pump to the top of an injector-mixing

nozzle.

However, a problem with carrying out the process of the prior art, particularly in an alcohol based slurry phase, is that fouling of the reactor occurs and, in particular, fouling of the loop. Without wishing to be bound by any theory, it is believed that fouling takes the form of a thin layer of paper-like material upon which particulate product is subsequently deposited. This fouling would severely restrict the operation of the process particularly if the process was operated in continuous mode. Fouling of mechanical parts such as the pump and the eductor of an injector-mixing nozzle is particularly serious since this may lead to the process being shut-down.

A number of approaches to overcoming the fouling problem have been tried.

Soluble additives can be used. However, these are not very successful at reducing the fouling and in addition increase the complexity of the catalyst system or even deactivate it. Seeding the reactor at the start of the process has the effect of decreasing the level of fouling. In particular, the seed material can itself be a polyketone. However, the fouling is decreased, but not eliminated by such an approach. Further approaches have included polishing the reactor surfaces or applying Nylon or Teflon coatings to them, in order to reduce or prevent adhesion of the fouling layer. However, these also have not proved totally effective, and add to the cost of the procedure. It would therefore be desirable to effect circulation of the polymer suspension around a loop reactor system without using a mechanical device such as a pump.

It has also been found that the stability of the catalyst used in a polyketone polymerisation process may be dependent upon the concentration of the gaseous reagents in the liquid reagents (such as the diluent) and, in particular, the concentration of carbon monoxide in the diluent. It is therefore desirable to ensure that there is good mixing (good mass transfer) between the gaseous reagents and the liquid reagents.

Thus, according to the present invention, there is provided a process for the preparation of a linear alternating polymer of (a) one or more olefins and (b) carbon monoxide in a reactor system comprising a reactor vessel and a loop conduit having a riser section, which process comprises: A) contacting a mixture of carbon monoxide and one or more olefins in the reactor vessel at an elevated temperature and pressure with a catalyst in a liquid diluent in which diluent the catalyst is dissolved and the polymer forms a suspension;

B) withdrawing polymer suspension from the reactor vessel ; C) recycling the polymer suspension to the reactor vessel through the loop conduit ; wherein the polymer suspension is circulated though the loop conduit by introducing a gaseous stream comprising a gaseous reagent into the loop conduit.

An avantage of using a gaseous stream comprising a gaseous reagent to circulate the polymer suspension through the loop conduit is that there is good mass transfer between the gaseous reagent and the liquid reagents.

Preferably, the polymer suspension is withdrawn from the lower part of the reactor vessel and is recycled to the upper part of the reactor vessel.

When it is desired to prepare a carbon monoxide/ethylene copolymer using the process of the present invention, the gaseous stream which is introduced to the loop conduit preferably comprises carbon monoxide and optionally ethylene. When it is desired to prepare a carbon monoxide/ethylene/propene or a carbon monoxide/ethylene/butylene terpolymer, the gaseous stream preferably comprises carbon monoxide and optionally the gaseous olefinic reagents.

In a further aspect of the present invention there is provided a reactor system comprising: (A) a reactor vessel having an outlet for withdrawing polymer suspension and an inlet for recycling the withdrawn polymer suspension to the reactor vessel, the inlet being at a greater height in the reactor vessel than the outlet; (B) a loop conduit having a first end which is in communication with the outlet and a second end which is in communication with the inlet so that the loop conduit has a riser section; and (C) a facility for introducing a gaseous stream into the loop conduit.

The facility for introduction of the gaseous stream into the loop conduit may be multi-functional, for example, for the introduction of a liquid stream as well as a gaseous stream or may be dedicated to the introduction of a gaseous stream. Where the facility introduces both a liquid stream and a gaseous stream, the liquid stream may comprise a liquid reagent selected from the group consisting of liquid olefins, catalyst/co-catalyst solutions, and solvents. Preferably, the facility is dedicated to the introduction of a gaseous stream into the loop conduit. Preferably, the facility for introducing the gaseous stream is a gas nozzle.

Preferably, the gaseous stream is introduced to the lower part of the riser section of the loop conduit, most preferably, at the bottom of the riser section of the loop conduit. Preferably, there is a gaseous headspace in the upper part of the riser section of the loop conduit. Suitably, the upper part of the riser section of the loop conduit is of increased diameter (so as to provide a bulb). Where the riser section of the loop conduit has a headspace, the level of polymer suspension in the riser section of the loop conduit is higher than the level of polymer suspension in the reactor vessel. Preferably, polymer suspension is returned to the reactor vessel under gravity via a downwardly orientated section of the loop conduit. Typically, this downwardly orientated section of the loop conduit is fed with polymer suspension from a region below the bulb. This type of pump is generally known as a gas lift pump.

It is envisaged that a gaseous stream comprising a gaseous reagent can also be introduced into the reactor vessel to assist in mixing the contents of the reactor vessel, provided that sufficient gaseous reagent is introduced into the loop conduit to effect circulation of the polymer suspension through the loop conduit. Optionally, a mechanical agitato such as a stirring device (for example, a paddle, propeller or turbine) may be positioned in the reactor vessel so as to provide an additional means of mixing the contents of the reactor vessel. Preferably, the power transmitted by the optional mechanical agitator to the polymer suspension is at least 1.5 kW/m', more preferably in the range 2 to 15 kW/m3, based on the volume of polymer suspension present in the reactor vessel.

The pressure of the gaseous stream which is introduced into the loop conduit is higher than the pressure to which the gas expands. The pressure of the gaseous stream is at least sufficient to lift the polymer suspension through the loop conduit and to overcome frictional losses in the loop conduit. It is known how to determine the pressure of the gaseous stream required to achieve this duty.

The minimum volumetric flow rate, V, of the gaseous stream introduced into the loop conduit is defined herein as the minimum volumetric flow rate required to lift the polymer suspension through the loop conduit. It is known how to calculate the minimum volumetric flow rate, V, for a gas-lift pump (see"Chemical Engineering", Volume One, Revised Second Edition, Coulsen and Richardson, pages 156-158;"Flow Characteristics of Gas Lift in Oil Production", S F Shaw, Texas Eng. Experimental Station, Bulletin No.

113 (1949), and"An Analytical and Experimental Study of Air Lift Pump Performance", A H Stenning and C B Martin, Journal of Engineering for Power 90,106-110). Without wishing to be bound by any theory, the minimum volumetric flow rate, V, will be dependent upon the pressure of the gaseous stream introduced into the loop conduit, PI, the pressure to which the gaseous stream expands, P2, and the work, W, done in lifting the polymer suspension through the loop conduit. Thus, the minimum volumetric flow rate, V, of the gaseous stream introduced into the loop conduit can be calculated from the following equation: V= W P2. 1s1 (P,/P2) Preferably, the contents of the loop conduit are maintained above a minimum flow velocity. Typically, the flow velocity of the polymer suspension through the loop conduit is in the range 5 to 15 m/s, preferably 6 to 12 m/s. It is known how to adjust the flow rate of the polymer suspension through the loop conduit. This is achieved by adjusting the volumetric flow rate of the gaseous stream introduced to the loop conduit (provided that the volumetric flow rate is maintained above the minimum level defined above). The flow of the polymer suspension through the loop conduit may be laminar, turbulent or plug flow, preferably laminar.

The loop conduit should also be designed so as to avoid any settling of the polymer particles and/or deposition of polymer particles on the walls of the loop conduit.

This may be accomplished by adopting one or more of the following measures: minimising the number of bends in the loop conduit, avoiding any sharp bends, ensuring the loop conduit has smooth surfaces, positioning the loop vertically and designing the loop so as to provide maximum flow in the vertical direction and a minimum flow in the horizontal direction, for example, by providing a loop conduit having a short horizontal length and a long vertical length. Usually, the loop conduit is sized to provide a vertical length which is between about 3 and about 20 times the horizontal length. Typically, the diameter of the loop conduit is at least 1 mch preferably at least 5 inches, more preferably at least 10 inches. The diameter of the loop conduit is typically in the range 1 to 24 inches, preferably 10 to 18 inches.

Preferably, the volume of polymer suspension present in the loop conduit is greater than 10%, more preferably greater than 20%, most preferably greater than 25%

of the total volume of the suspension present in the reactor system.

There will usually be associated with the reactor system other ancillary equipment ; for example, where the process is operated in the continuous mode, a means for discharging polymer continuously from the reactor system will typically be fitted, together with a heat exchanger and optionally an overhead condenser. The overhead condenser is fitted to the reactor vessel. Preferably, the heat exchanger is fitted to the loop conduit. Preferably, the heat exchanger is operated in counter-current mode. In the absence of a condenser the loop conduit should be of sufficient length to provide a sufficient heat transfer area. Typically, the heat exchanger is operated using a temperate coolant. An advantage of operating the heat exchanger in counter-current mode and of using a temperate coolant is that this reduces fouling in the loop conduit in the region of the heat exchanger. Without wishing to be bound by any theory, it is believed that fouling is increased in regions where the circulating slurry comes into contact with cold surfaces.

Preferably, the upper part of the riser section of the loop conduit is fitted with a gas vent. Where, the upper part of the riser section of the loop conduit is of increased diameter, the gas vent is fitted to the bulb. An avantage of a gas vent is that this provides flexibility with respect to the rate of addition of gaseous reagents to the reactor system. Thus, at high addition rates any excess gaseous reagents can be vented from the reactor system. The provision of a vent also allows excess gaseous reagents to be present in the reactor system. A gas vent may also be fitted to the overhead condenser (if used). Preferably, any vented gas is re-pressurised and is recycled to the facility for introducing gaseous reagents. Preferably, any entrained liquid is stripped from the vented gas before the gas is re-pressurised.

By the term polyketone is meant a linear polymer comprised of alternating-CO- and-X-units derived from one or more olefins. Typically X is either-CH2CH2-, in the case where carbon monoxide and ethylene are copolymerised, or a statistical mixture of- CH2CH2-and-CH2CH (R)- (R = Cl-C8 alkyl, phenyl or methyl or ethyl substituted phenyl), in the case where carbon monoxide, ethylene and at least one C3-CIo alpha olefin are polymerised. It is preferred that the process of the present invention is used to prepare polyketones of the latter composition and in particular that the polyketones are those prepared from carbon monoxide and mixtures of ethylene and C3-C6 alpha olefins.

Most preferred of all are those materials prepared from carbon monoxide and mixtures of ethylene and propylene or ethylene and butylene. For the preferred polyketones, it is preferred that at least 70 mol% of the-X-units are-CH2CH2-, most preferably at least 80 mol%. The exact composition of the polyketone can be adjusted by making appropriate changes to the relative proportions of the reactants employed.

The polyketone prepared using the method of the present invention may have a number average molecular weight of between 20,000 and 1,000,000 preferably between 40,000 and 500,000, more preferably between 50,000 and 250,000, for example 60,000 to 150,000.

The polyketone prepared using the method of the present invention will suitably have a particle size in the range 1 u. m to 2000 u. m, preferably 10 u. m to lOOOjlm and most preferably 50 urn to 750 Rm As regards the catalyst, any catalyst which is suitable for the polymerisation of carbon monoxide and one or more olefins to give polyketones can be used. In particular, Group VIII metal catalysts are preferred and in particular those based on palladium. A typical catalyst composition would be that described in EP 121965 and EP 314309, as set out herein above.

Alternatively, a catalyst composition which is based on: (a) a Group VIII metal compound, (b) a Lewis acid of the general formula MFn, in which M represents an element that can form a Lewis acid with fluorine, F represents fluorine and n has the value 3 or 5 and (c) a dentate tigand containing at teast two phosphorus-, nitrogen-or sulphur-containing dentate groups through which the dentate ligand can complex with the group VIII metal.

These catalyst compositions are set out in EP 508502.

Also suitable are catalyst compositions as detailed in EP 619335 which comprise (a) a Group VIII metal compound, containing at least one ligand capable of coordinating to the Group VIII metal and (b) a boron hydrocarbyl compound preferably a Lewis acid of the formula BXYZ where at least one of X, Y and Z is a monovalent hydrocarbyl group.

Typically the boron hydrocarbyl compound is a compound of the formula BR-,

where R is a Cl-C6 alkyl, or an aryl-group for example, a substituted or unsubstituted phenyl group, for example C6H5, CIC6H4, or C6F5.

The ligand capable of coordinating to the Group VIII metal may be a bidentate phosphine ligand having at least two phosphorus atoms joined by a bridging group of the formula-(N) X-(P) y~N~ where(N) X-(P) y~N~ where x is 0 or 1 and y is 0 or 1, in particular, a bridging group of the formula- (NR2) x-(PR3) y~NR2~ where each R is the same or different and R2 and R3 represent a monovalent organic group. A preferred ligand has the formula (II) Rl2P- (NR2) X-(PR3) y-NR2-PRI2 where each R'is independently an aryl, alkyl, alkoxy, amido or substituted derivative thereof, R2 is a hydrogen, a hydrocarbyl or hetero group, R3 is a hydrocarbyl or hetero group. For any of the catalyst systems described herein above preferred bidentate ligands are (o-anisyl) 2P-X-P (o-anisyl) 2 or Ph2P-X-PPh2 (Ph = phenyl, X =- (CH2)"-where n = 2-4, or X = N (R) where R = Cl-C6 alkyl or aryl).

Suitable solvents for the process include alcohols, (e. g. methanol or ethanol), ketones (e. g. acetone), ethers, halogenated solvents (e. g. chloroform or dichloromethane), saturated or unsaturated hydrocarbons (e. g. toluene, pentane, hexane, heptane, or cyclohexane) and mixtures thereof. Alternatively, the process can be solvent-free if one of the reactant olefins is a liquid under reaction conditions.

The process is suitably carried out under super-atmospheric pressure e. g. 1-300 barg, preferably 1-150 barg, more preferably 10-100 barg, most preferably 20-70 barg, for example, 40-70 barg. Suitably, the process is carried out at a temperature in the range 25-130°C for example 50-95°C.

The molar ratio of olefinic compounds to carbon monoxide is preferably 10: 1- 1: 10 in particular 5: 1-1: 5.

The process of the invention may of course be carried out in conjunction with other known methods for reducing fouling, such as the use of polished or coated reactor surfaces, additives and seeding as previously mentioned.

Preferred embodiments of the reactor system for operating the process of the invention is shown in the accompanying drawings. Figure 1 shows a reactor system comprising a reactor vessel 1, a circulation loop conduit 2 comprising a lower horizontal section 3, a vertical section 4 and a downwardly orientated section 5. The circulation loop conduit 2 is fitted with a facility 6 for introducing gaseous reagents (for example, a gas nozzle), a bulb 7 having a vent 8, a heat exchanger 9, and a set of actuated dump

valves (not shown). A portion of the reactor slurry is transferred to a flash vessel (not shown) through the dump valves, and then transferred to a storage vessel (not shown) prior to polymer isolation. The remainder of the reactor slurry is returned to the reactor vessel 1 via downwardly oriented section 5.

Figure 2 shows a reactor system comprising a reactor vessel 11, a circulation loop conduit 12 comprising a lower horizontal section 13, and a riser section 14. The circulation loop conduit 12 is fitted with a facility 15 for introducing gaseous reagents (for example, a gas nozzle), a heat exchanger 16, and a set of actuated dump valves (not shown). A portion of the reactor slurry is transferred to a flash vessel (not shown) through the dump valves, and then transferred to a storage vessel (not shown) prior to polymer isolation. A gaseous stream may be removed from the reactor vessel via a gas vent which is fitted to an overhead condenser (not shown).

The calculation of the volumetric flow rate for a small scale plant is given in the following Example.

Example 1 This Example models the flow of liquid diluent through a loop conduit using a gas lift pump. It has been found that the density of gas saturated dichloromethane (liquid diluent) at a temperature of 70°C is approximately 1000 kg/m3.

The minimum amount of work required to circulate the diluent through a loop conduit at a flow velocity of 30 m3/hr and to lift the diluent through a height of 3 metres is: = 30/3600 m3/s x 1000 kg/m3 x 3m x 9.81 m/s2 = 245.25 Watts.

If it is assumed that the efficiency of the gas-lift pump is 30% then the work done, W, is 817.5 Watts.

As discussed above, the minimum volumetric flow rate, V, can be calculated using the following formula: V= W P2. ln (P, lP

Assuming that Pi is 60 barg (61.01325x105 Pa) and P2 is 50 barg (51.01325x105 Pa): V =817.5 51.01325x105.ln(61.01325x105/51.01325x105) 8.95x10-4 m³/s.