GB2348430A

GB2348430A - Process for drying polyketones

Info

Publication number: GB2348430A
Application number: GB0002724A
Authority: GB
Inventors: Paul Dornan
Original assignee: BP Chemicals Ltd
Current assignee: BP Chemicals Ltd
Priority date: 1999-03-29
Filing date: 2000-02-08
Publication date: 2000-10-04
Also published as: GB0002724D0; GB9907157D0

Abstract

A process for drying a polyketone polymer is carried out in two successive steps. The first step comprises a solid-liquid phase separation and the second step comprises the removal of solvent residues from the wet polyketone polymer by evaporating the solvent residues by heating. The second step is carried out using a rotary drier.

Description

PROCESS FOR DRYING POLYETONES The present invention relates to a process for drying a polyketone polymer.

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 olefinicafly unsaturated compound.

Such polyketones have the formula : o CR1R2-CR3) Cm where the Rl, 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 envisage 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.

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 OC of the solvent at the prevailing pressure. It has now been found that a rotary drier is particularly suitable for removal of the solvent residues resulting in a very dry product.

Thus, according to the present invention there is provided a process for drying a polyketone polymer which process is carried out in two successive steps, the first of which comprising a solid-liquid phase separation, and the second comprising the removal of solvent residues from the wet polyketone polymer by evaporating the solvent residues by heating, characterised in that the second step is carried out using a rotary drier.

By solid-liquid phase separation is meant separation by settling, filtration or centrifugation. Preferably, the solid-liquid phase separation is carried out using a peeler type centrifuge. Preferably, the solid-liquid phase separation inclues a washing procedure in which the polyketone is contacte with a wash solvent to remove soluble impurities.

By solvent residues is meant residues of the solvent used in the preparation of the polyketone polymer (typically an aliphatic alcohol such as methanol or a chlorinated solvent such as dichloromethane) and residues of any wash solvent used during the solidliquid phase separation. Typical solvent residues include aliphatic alcools (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), chlorinated solvents (e. g. dichloromethane) and water.

By rotary drier is meant a rotary n-ding apparats wherein heat is either directly or indirectly transferred to the wet polyketone polymer to evaporate solvent residues while the polyketone polymer is being mixed.

Suitably, the rotary drier comprises a cylindrical casing having an inlet for charging the cylindrical casing with wet polyketone polymer, an outlet for discharging dry polyketone polymer from said cylindrical casing and a means for mixing the wet polyketone polymer. Preferably, the wet polyketone polymer is mixed by means of mixing blades connecte to a rotatable shaft.

Rotary driers in which heat is indirectly transferred to the wet polyketone polymer are described in US 3, 250, 321, US 3, 285, 330, US 3, 500, 901, US 3, 765, 481, US 4, 824, 257, US 4, 941, 130 and US 5, 121, 992 which are herein incorporated by reference. Generally, the shaft and blades of such rotary driers are hollow and a heat exchange fluid is passed through the internal spaces of the shaft and blades thereby supplying heat to the polyketone polymer. The walls of the cylindrical casing may also be heated. Thus, the cylindrical casing may be surrounded by a heat jacket or by heating channels. Suitably, the cylindrical casing has an outlet (in the upper part of the casing) for extracting vapours comprising the solvent impurities. Where heat is directly transferred to the wet polyketone polymer, a hot gas is passed through the drier.

Preferably, the hot gas is nitrogen. It is also envisage that the process of the present invention may employ a rotary drier in which heat is both directly and indirectly transferred to the wet polyketone polymer.

The polyketone polymer may be processed in the rotary drier as a slurry, paste or a wet solid.

Preferably, the rotary drier is heated to a temperature of at least T-30 C, where T is the boiling point ion'C of the highest boiling solvent residue at the prevailing pressure.

Suitably, a continuous rotary drier is employed. Generally, the polyketone polymer will be fed to one end of the continuous rotary drier and the drying takes place as the polyketone is mixed and conveyed to the discharge end of the rotary drier.

Typically, the polyketone polymer is mixed by means of a shaft extending longitudinally of the cylindrical casing and rotatably supporte therein and having mixing blades connecte to the shaft. Generally, rotation of the mixing blades, preferably in cooperation with a weir means, causes the polyketone polymer to advance from the inlet to the outlet of the cylindrical casing. A continuous rotary drier may be of sufficient length to allow the polyketone to be dried as it is being conveyed from the inlet to the outlet of the apparats. Alternatively, two or more continuous rotary driers can be operated in series.

Preferably, the polyketone po (amer is processed in the absence of oxygen. The absence of molecular oxygen can suitably be effected by maintaining an atmosphere of inert gas, preferably nitrogen, in the rotary drier. Alternatively, where heat is indirectly transferred to the polyketone polymer, the drying can be carried out under reduced pressure, for example, at a pressure of 50 mbar or less.

Preferably, the polyketone polymer is processed in the absence of water.

In a further aspect of the present invention there is provided a process for the removal of solvent residues from a wet polyketone polymer in a rotary drier characterised in that the process comprises the steps : (a) heating the rotary drier to a temperature of T-30 C, where T is the boiling point ion'C of the highest boiling point solvent residue at the prevailing pressure ; (b) feeding wet polyketone polymer to the drier ; and (c) removing dried polyketone polymer from the drier.

Preferably, the dry polyketone polymer contains no more than 1000 ppm, more preferably no more than 100 ppm, most preferably no more than 25 ppm of solvent residues.

As noted above for the purposes of this patent, polyketones are deftned as linear polymers having an alternating structure of (a) units derived from carbon monoxide and (b) units derived from one or more olefinically unsaturated compound. Suitable olefinic units are those derived from C2 to C12 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 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 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 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 will suitably have a particle size in the range I pm to 2000 llm, preferably 10 gm to 10OOgm and most preferably 50 zm to 750 pm.

The present invention will now be illustrated by the following Examples.

Example 1 A sample of polyketoneldichloromethane/isopropanol slurry containing 18% polyketone solids was charged to a Bethlehem Corporation IP 1203JTB single shaft, indirectly heated batch operated rotary dryer. The diameter of the dryer agitato was 0. 305 metres (12 inches) and the length was 0. 91 metres (3 feet). The agitato shaft was fitted with 0 pitched paddles to provide cut and fold mixing of the process bed material inside the dryer without material transportation. Side wall breaker bars with 45'angle blades were used to increase bed agitation. The dryer had a maximum operating volume of 0. 062m3 (2. 2ft3) and a maximum heat transfer surface of 2. 1 su2 (23. 15ft2). The agitato was rotated at 20rpm. A vacuum of 0. 1 bar (70 mmHgA) was applied to the dryer during drying using a vacuum pump. The temperature of the dryer was 124 C and after 90 minutes drying time the product temperature inside the dryer was 123 C. After 90 minutes drying time the product had a residual solvent concentration of less than 10 ppm isopropanol and less than lppm dichloromethane.

Example 2 A sample of polyketone/dichloromethansopropanol slurry used in Example 1 was filtered to a filter cake containing 57. 5% residual dichloromethaneAlsopropanol solvent in a laboratory filter press. This filter cake was charged to the same rotary dryer as used in Example 1. A vacuum of 0. 13 bar (98mmHgA) was applied to the dryer during drying using a vacuum pump. The temperature of the dryer was 126 C and after 80 minutes drying time the product temperature inside the dryer was 124 C.

After 80 minutes drying the product had a residual solvent concentration of less than I Oppm isopropanol and less than I ppm dichloromethane.

Claims

Claims :

1. A process for drying a polyketone polymer which process is carried out in two successive steps, the first of which comprising a solid-liquid phase separation, and the second comprising the removal of solvent residues from the wet polyketone polymer by evaporating the solvent residues by heating, characterised in that the second step is carried out using a rotary drier.