GB2348881A - Polyketone separation - Google Patents

Abstract

A process for separating a mixture of a polyketone polymer and a solvent is characterised in that the polyketone polymer is separated from the solvent using a rotary drum filter. The solvent is e.g the solvent used in the preparation of the polyketone polymer. The separated polyketone polymer can also be washed in the rotary drum filter to remove any soluble impurities contaminating the separated polyketone polymer.

Description

POLYMER SEPARATION The present invention relates to a process for separating a polyketone polymer from a solvent using a rotary drum filter.

For the purposes of this patent, polyketones are defined as linear polymers having an alternating structure of (a) units derived from carbon monoxide and (b) units derived from one or more olefinically unsaturated compounds. Such polyketones have the formula:

where the Ri, R2, R3 and R4 groups are independently hydrogen or hydrocarbyl groups, and m is a large integer; they are disclosed in several patents e. g. US 3694412. Processes for preparing the polyketones are disclosed in US 3694412 and also in EP 18111014A and EP 121965A. Although for the purposes of this patent polyketones correspond to this idealised structure, it is envisaged that materials corresponding to this structure in the main but containing small regimes (i. e. up to 10 wt%) of the corresponding homopolymer or copolymer derived from the olefinically unsaturated compound, also fall within the definition.

To obtain a polyketone having acceptable quality and chemical stability it is often necessary to remove soluble impurities (e. g. polymerisation reaction by-products, catalyst residues and co-catalyst residues) from the polyketone. This may be achieved by contacting the polyketone with a solvent in which the impurities are soluble and the polyketone is insoluble, removing the solvent and dissolved impurities from the polyketone and subsequently drying the polyketone.

A process for washing and drying polyketones in the absence of molecular oxygen is described in EP 0228733. It is stated that the term"drying"is understood to comprise two successive steps, viz. Firstly a liquid-solid phase separation, such as settling, filtration or centrifugation, and secondly the removal of solvent residues from the wet copolymer by heating, preferably to a temperature of at least T-30 C, where T is the boiling point in C of the solvent at the prevailing pressure.

Rotary drum filters have been used for the processing of the following products: aluminium hydroxide, aluminium sulphate, red mud, gypsum, soda and sodium bicarbonate, cryolite, phosphates, flotation concentrates such as coal, ore and potassium slurries, dyestuffs, pigments such as titanium dioxide and white lead, herbicides and insecticides, antibiotics and mycelium, proteins, sugar solutions and industrial and municipal effluents.

It has now been found that a rotary drum filter is particularly suitable for separating a polyketone polymer from a solvent. Rotary drum filters have the advantage that they have very large capacities compared with many other types of filtration apparatus. In addition, it has been found that the separated polyketone polymer can be washed in a rotary drum filter to remove any soluble impurities contaminating the separated polyketone polymer. An advantage of this washing procedure is that there is no requirement to re-suspend the polymer in a wash solvent.

According to the present invention there is provided a process for separating a mixture of a polyketone polymer and a solvent characterised in that the polyketone polymer is separated from the solvent using a rotary drum filter.

The skilled person would know how to operate a rotary drum filter so as to effect separation of the polyketone polymer. However, for avoidance of doubt, a typical rotary drum filter and its mode of operation is discussed below.

Typically, a rotary drum filter has a rotary drum partially submerged in a trough containing the mixture to be filtered and having a filter cloth which substantially enwraps the drum. Preferably, the filter cloth is an endless belt filter cloth. A wide range of filtration fabrics are available for the filter cloth ensuring the desired filtration quality and the person skilled in the art would know how to select a suitable filtration fabric.

Suitable rotary drum filters are sold by Krauss Maffei (Rotary Vacuum Drum Filter TSF).

In rotary drum filters, filtering is only effected in the immersed part of the drum.

In fact for any given point on the drum filtering only usually takes place between the time at which that point dips into the mixture to be filtered and shortly before it emerges from the mixture. Generally, approximately a third of the filter area is submerged in the mixture to be filtered. Preferably, the drum rotates at a rate of between 10 and 60 revolutions per hour.

During the filtering operation a mixture of polyketone polymer and solvent is fed continuously to the trough. Suction or pressure is applied so that the solvent passes through the filter cloth and a filter cake (of polyketone polymer) is formed on the filter cloth on the immersion side of the drum. Preferably, the mixture of the polyketone and solvent is agitated to prevent sedimentation of the polyketone polymer. This may be achieved by using mechanical agitators or by withdrawing a portion of the contents of the trough and subsequently returning it. Conveniently, the unfiltered mixture of polyketone polymer and solvent can be withdrawn to an auxiliary vessel as described in GB 993,169 which is herein incorporated by reference. The separated polyketone polymer (filter cake) may be detached from the filter cloth (for example, using a scraper, roller, belt or string discharge) and is collected. Rotary drum filters having these types of discharge are sold by Krauss Maffei. Preferably, the filter cloth is cleaned before reimmersion in the mixture of polyketone polymer and solvent.

The solvent which is separated from the polyketone polymer comprises reaction solvent, that is the solvent used in the preparation of the polyketone polymer. The reaction solvent is typically an aliphatic alcohol such as methanol or a chlorinated solvent such as dichloromethane. The reaction solvent contains soluble impurities. As discussed above, typical soluble impurities include catalyst residues, co-catalyst residues and polymerisation reaction by-products. Catalyst residues and co-catalyst residues are for the purposes of this patent defined as active catalyst and co-catalyst used in the preparation of the contaminated polyketone polymer as well as inactive species derived from the catalyst and co-catalyst. Polymerisation reaction by-products include low molecular weight polyketones which are soluble in the solvent used in the process of the present invention.

Preferably, the mixture of polyketone polymer and reaction solvent is diluted with a wash solvent prior to being separated using the process of the present invention.

Preferably, the polyketone polymer (filter cake) which is deposited on the filter cloth is washed with a wash solvent as the drum rotates. This may be achieved by feeding wash solvent onto the filter cake either directly via wash devices (for example, weirs or spray nozzles) or via a wash belt lying on top of the filter cake.

Preferably the washing is continued until an acceptable level of soluble impurities is attained in the solvent which is forced through the filter cloth. Typically, the washing is continued until the level of soluble impurities in the solvent which passes through the filter cloth falls below 10%, preferably below 5%, more preferably below 2.5%, most preferably below 1% of their original level in the reaction solvent. Preferably, the washing is continued until the level of soluble impurities falls below the limits of detection for the impurities.

The wash solvent which is used in the process of the present invention is one in which the polyketone polymer is insoluble or virtually insoluble and in which the soluble impurities are soluble. Since polyketones tend to be insoluble in most solvents a wide choice of wash solvents is available. Typical examples of preferred wash solvents are aliphatic alcohols (e. g. isopropanol, methanol or butanol), ketones (e. g. methyl isobutyl ketone, methyl ether ketone or acetone), ethers (e. g. diethyl ether or dimethyl ether), saturated hydrocarbons (e. g. pentane, hexane, heptane) and water. Any soluble impurities which are present in the reaction solvent and optional wash solvent are separated from the polyketone polymer in the process of the present invention.

The solvent (reaction solvent and any wash solvent) which passes through the filter cloth of the rotary drum filter is collected and removed from the rotary drum filter.

Purified solvent may be separated from the soluble impurities (for example, by distillation). Where the reaction solvent and wash solvent are different, the reaction solvent and wash solvent may be separated by distillation. The separated wash solvent may then be recycled to the process of the present invention.

Preferably, the filter cake is suction dried after washing.

Preferably, the process of the present invention is carried out in the absence of molecular oxygen. The absence of molecular oxygen can suitably be effected by maintaining an atmosphere of inert gas, preferably nitrogen, in the rotary drum filter during the filling and discharging operations. Preferably, the process of the present invention is carried out in the absence of water.

Where it is desired that the separated polyketone polymer should be essentially free of any volatile contaminants, the polyketone polymer removed from the rotary drum filter is dried, for example, using a rotary drier or plate drier.

In a further aspect of the present invention there is provided a process for separating and drying a polyketone polymer which process comprises the steps of : (a) diluting a mixture of a polyketone polymer and reaction solvent with a wash solvent ; (b) separating the polyketone polymer from the solvent using a rotary drum filter ; (c) optionally spraying the separated polyketone polymer with a wash solvent in the rotary drum filter (e) discharging the polyketone polymer from the rotary drum filter; and (f) removing solvent residues from the separated polyketone polymer by heating the polyketone polymer to a temperature of at least T-30 C, where T is the boiling point in C of the solvent at the prevailing pressure.

As noted above, for the purposes of this patent, polyketone polymers are defined as linear polymers having an alternating structure of (a) units derived from carbon monoxide and (b) units derived from one or more olefinically unsaturated compounds.

Suitable olefinic units are those derived from C2 to ~12 alpha-olefins or substituted derivatives thereof or styrene or alkyl substituted derivatives of styrene. It is preferred that such olefin or olefins are selected from C2 to C6 normal (straight chain) alpha-olefins and it is particularly preferred that the olefin units are either derived from ethylene or most preferred of all from a mixture of ethylene and one or more C3 to C6 normal alphaolefin (s) especially propylene or butylene. In these most preferable materials it is further preferred that the molar ratio of ethylene units to C3 to C6 normal alpha-olefin units is greater than or equal to 1 most preferably between 2 and 30. Typically, the polyketone polymer will be a copolymer of ethylene/propylene/CO or ethylene/butylene/CO where the units derived from propylene or butylene are present in an amount in the range 5-8 % e. g. 6 % by weight of the polymer.

The polyketone polymer will suitably have a number average molecular weight of between 20,000 and 1,000,000 relative to a polymethyl methacrylate standard, preferably between 40,000 and 500,000, more preferably between 50,000 and 250,000, for example, 60,000 to 150,000. A preferred polyketone polymer is an ethylene/propylene/CO terpolymer or an ethylene/butylene/CO terpolymer having a number average molecular weight in the range 60,000 to 150,000.

The polyketone polymer will suitably have a particle size in the range 1 lum to 2000 m preferably 10 pm to 10001lm and most preferably 50 m to 750 Zm.

The polyketone polymer will suitably have a density in the range 1.10 kg/litre to 1.30 kg/litre, preferably 1.23 kg/litre to 1.25 kg/litre.

Claims (1)

1. Claims: 1. A process for separating a mixture of a polyketone polymer and a solvent characterised in that the polyketone polymer is separated from the solvent using a rotary drum filter.