GB1560940A

GB1560940A - Treating polymers

Info

Publication number: GB1560940A
Application number: GB4204475A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1975-10-14
Filing date: 1975-10-14
Publication date: 1980-02-13
Also published as: AU507841B2; NZ182229A; AU1837776A; NL7611257A

Description

(54) TREATING POLYMERS ('it) ) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SW1P 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to the processing of olefine polymers obtained using halogen-containing catalyst systems, residues of which remain in the polymer.

According to the present invention an olefine polymer which is in the form of discrete particles and which contains residues of a halogen-containing catalyst system is introduced into a first stage of a packed bed system having at least two stages, is treated in the said first stage with an agent which is effective to react with those hologen-containing materials which can give rise to hydrogen halide or ionic halide, and then passed to a second stage of the packed bed system in which a stream of an inert gas is passed through the polymer particles.

The halogen-containing materials which are present in the polymer and which can give rise to hydrogen halide or ionic halide, will hereafter be referred to as "active halides." The reactive agent which is effective to react with the active halides will, for convenience, hereafter be referred to simply as "the reactive agent." The treatment with the reactive agent is conveniently effected in the presence of water. The reactive agent, together with the water if used, is conveniently passed into the polymer particles in the vapour form, for example admixed with an inert gas, at a rate sufficient to uniformly disperse the reactive agent, and any water. throughout the polymer particles in the packed bed. In the first stage of the packed bed, the polymer particles are contacted with the reactive agent for a time sufficient for reaction to occur between the reactive agent and at least part of the active halides present in the polymer.

The stream of inert gas which is subsequently passed through the polymer particles in the second stage, removes at least some volatile materials from the polymer, particularly any excess unreacted quantities of the reactive agent and water, and also any volatile halogen-containing reaction products resulting from the treatment of the polymer with the reactive agent.

The process of the present invention can be applied to the treatment of polymer particles which have been subjected to no previous treatment to remove catalyst residues from the product.

It is desirable that the polymers treated by the process of the present invention have a relatively low level of active halide, for example when the halogen is chlorine, the level of active chlorine is preferably less than 1000 parts per million by weight (ppm), especially not more than about 600 ppm.

Such levels of halogen can be obtained by polymerising olefine monomers to give a high yield of polymer relative to the catalyst used whereby the polymer obtained contains a relatively low level of residual catalyst even without subjecting the polymer to any catalyst removal treatment.

Polymers of the above type, which contain residual active chlorine levels of 500 ppm are corrosive, even when containing conventional levels, for example 0.10 up to 0.20% by weight, of an anti-acid material such as calcium stearate. However, if such a polymer is subjected to the process of the present invention, the product thereby obtained is of low corrosivity and we have obtained polymers which are non-corrosive even in the absence of any added anti-acid material.

The treatment of the present invention is effected at a temperature below that at which the polymer particles agglomerate. It is preferred to effect the treatment at an elevated temperature, for example at least 60 C, and for the treatment of propylene polymers the temperature preferably does not exceed about 110 C. The treatment is conveniently effected at a temperature in the range from 80 up to 100cm.

The reactive agent may be an alkylene oxide, particularly an alkylene oxide containing from 2 to 6 carbon atoms such as propylene oxide. Alternatively the reactive agent may be an organic carbonate compound, for example a compound of the formula RR'CO3 where R and R' are both hydrocarbyl groups which may together form a bivalent hydrocarbyl group as in ethylene carbonate.

The amount of the reactive agent used will be dependent on the nature of the reactive agent and also on the proportion of active halide which is present in the polymer. We have obtained a non-corrosive product by treating a polymer containing 500 ppm of chlorine-containing materials with as little as 0.5% by weight of a reactive agent together with 0.5'my by weight of water. In general the amount of reactive agent is in the range from 0.2 up to 2.0% by weight relative to the polymer. If water is also present, this is conveniently used in the same proportions as the reactive agent.

The time for the treatment with the reactive agent is conveniently at least 5 minutes and preferably is at least 30 minutes. The subsequent treatment with the stream of an inert gas is conveniently effected for a period of at least 5 minutes and preferably for at least 30 minutes.

By effecting the procedure of the present invention in a packed bed system, the gas flow rate through the bed of polymer particles can be low and still provide effective removal of the undesirable active halides.

The procedure of the present invention is effected in a packed bed system having at least two stages.

More specifically there is provided apparatus for the treatment of an olefine polymer, said apparatus comprising a packed bed apparatus and a source of a solid particulate olefine polymer to be treated, the packed bed apparatus having at least two distinct zones wherein the first zone is provided with at least one supply conduit said at least one supply conduit, entering the first zone at or near the tope thereof means connecting said supply conduit to the source of the solid particulate olefine polymer at least one inlet orifice for the introduction into said first zone of a gaseous mixture containing a reactive agent, said at least one inlet orifice being located at or near the bottom of the first zone, at least one outlet orifice for the removal of gaseous materials from said first zone, said at least one outlet orifice being located at or near the top of the first zone, at least one polymer transfer means from a point, or points, at or near the bottom of the first zone to a point, or points, at or near the top of the second zone, at least one inlet orifice for the introduction of a stream of an inert gas into said second zone, said at least one inlet orifice being located at or near the bottom of the second zone, at least one outlet orifice for the removal of gaseous materials from said second zone, said at least one outlet orifice being located at or near the top of the second zone and at least one polymer removal conduit which is located at or near the bottom of the second zone.

The apparatus conveniently comprises a single tower which is divided internally into at least two zones by one or more divider plates, each of said divider plates being provided with at least one opening which acts as a polymer transfer means between two adjacent zones. Conveniently the tower is divided into two zones by a single divider plate. The divider plate may be in the form of one or more frusto conical sections provided with a central cylindrical section.

Such an arrangement provides a gas space at the top of the second zone in which gas space may be located the outlet orifice, or orifices, for removal of gaseous materials from the second zone.

A two stage packed bed tower suitable for effecting the treatment of the present invention is illustrated diagrammatically in the drawing accompanying the provisional specification.

A tower 1 is divided internally into two sections by a divider plate 2. The divider plate 2 is formed of an outer frusto conical section 3 and a central cylindrical section 4. The outer perimeter of section 3 is secured to the inner surface of the tower 1.

The divider plate 2 divides the tower 1 into an upper zone 5 and a lower zone 6. An inlet conduit 7 enters the upper zone 5 at the top of the zone. An outlet pipe 8 is located at the side of the tower 1 near the top of zone 5. A further outlet pipe 9 is located at the side of the tower 1, just below the point at which the divider plate 2 is secured to the tower 1. The outlet pipes 8 and 9 join together to form an outlet conduit 10.

An outlet conduit 11, provided with a valve 12 is located at the bottom of the tower 1. An inlet pipe 13 is located near the bottom of the tower 1 and an inlet pipe 14 is located just above the divider plate 2.

In operation, polymer powder, which may be transferred directly from a polymerisation reactor through a separation device such as a cyclone, is passed into the tower 1 through the conduit 7. A gaseous mixture of nitrogen, propylene oxide and water vapour at a temperature in the range 80--1000C is introduced through inlet pipe 14. The rate of flow of the gaseous mixture is dependent on the rate at which the polymer is introduced into the tower, and is preferably such that the amount of propylene oxide and the amount of water vapour are each from 0.2 up to 2.0% by weight. The gases are withdrawn from zone 5 through the outlet pipe 8.

A stream of nitrogen is introduced through the inlet pipe 13 at a temperature in the range 80--1000C and at a rate such that most of the volatile reactants and reaction products are removed by the nitrogen stream, which is withdrawn through the outlet pipe 9. The treated polymer is removed through the outlet conduit 11, the valve 12 being adjusted so that the rate of polymer removal is the same as the rate of polymer addition.

The following examples are illustrative of the present invention.

EXAMPLE 1 Polypropylene was obtained by polymerisation in the gas phase and contained 440 parts per million, by weight of chlorine. This polymer at 80"C was introduced continuously, at a rate of 30 g/hour, into a tower as illustrated in the drawing. The tower has a diameter of 1.5 cm and each zone was 30 cm in length.

A stream of nitrogen at 80 C containing propylene oxide (0.333 ml/100 ml nitrogen) and water vapour (0.333 g/100 ml nitrogen) was introduced into the tower through the inlet pipe 14 at a rate of 180 ml/hour (equivalent to 600 ml nitrogen, 2 ml propylene oxide and 2 g water per 100 g of polymer).

The residence time of the polymer in each of zones 5 and 6 was one hour. Through inlet pipe 13 a stream of nitrogen at 80 C was introduced at a rate of six litres/hour (equivalent to 20 litres nitrogen per 100 g of polymer.

EXAMPLE 2 The polypropylene used in this example has. been obtained by gas phase polymerisation and contained 350 parts per million, by weight, of chlorine.

The polymer was introduced, at a temperature of 80 C, into an apparatus having an internal diameter of 7.6 cm. The apparatus was divided into two zones. The polymer was introduced at a rate of 50 g every five minutes into the first zone of the apparatus, and correspondingly 50 g of polymer were transferred, every five minutes, from the first zone to the second zone and 50 g of polymer were withdrawn, every five minutes, from the second zone.

Each zone contained 600 g of polymer, thus giving an average residence time of one hour in each zone. Water at 95 C was circulated through a water jacket surrounding each zone.

Nitrogen gas at 80 C was introduced into the first zone at a rate of 4.8 litres per hour.

Into this nitrogen stream an injection of 0.25 ml of propylene oxide and 0.125 ml of water was made every five minutes.

Nitrogen gas at 80 C was introduced into the second zone at a rate of 120 litres per hour.

The treated polymers of Examples 1 and 2 were subjected to a corrosivity test both with and without the addition of 0.1 7O by weight of calcium stearate. The test was carried out as follows: A mild steel sheet of thickness 0.005 inches was degreased by washing with liquid alkane and drying. Approximately 0.5 g of polymer powder was placed on the sheet and this was sandwiched between two sheets of aluminium foil. The sandwich was then placed between two steel plattens of thickness about 0.125 inches. The whole assembly was then pressed at 280 C for 7 minutes in a hydraulic press using a light load (about 2 tonnes/square foot).

After pressing, the assembly was cooled, removed from the press and opened. The polymer film formed in the pressing stage was stripped off the mild steel and the sheet was placed in a humidity cabinet at ambient temperature and a relative humidity of 100% for three hours. The appearance of the sheet was then assessed visually.

In the experiments, in which calcium stearate was used, this was mixed with the polymer powder by shaking together the appropriate quantities of polymer and calcium stearate in a glass tube and then pressing a sample of the mixture.

The results are set out in the Table, which also includes some analytical results obtained with the polymer products.

Corrosion test result (a) Analysis (ppm by weight) Polymer Example No additive 0.1% Ca. St. Chlorine Chioropropanol 1 A A 80 20 2 - | A 60 5

(a) A means non-corrosive (there was no sign of corrosion).

The untreated polymers, from which the products of Examples 1 and 2 were obtained were also subjected to a corrosion test.

These untreated polymers resulted in considerable amounts of visible corrosion over the test area.

WHAT WE CLAIM IS: 1. A process for the treatment of an olefin polymer wherein an olefine polymer in the form of discrete particles which contains residues of a halogen-containing catalyst system is introduced into a first stage of a packed bed system having at least two stages, the polymer is treated in the said first stage with a reactive agent which is effective to react with those halogen-containing materials which can give rise to hydrogen halide or ionic halide, and then passed to a second stage of the packed bed system in which a stream of an inert gas is passed through the polymer particles.

2. A process as claimed in Claim 1 wherein in the first stage a mixture of the reactive agent, water vapour and an inert gas is passed through the polymer.

3. A process as claimed in Claim 1 or Claim 2 wherein the reactive agent is an alkylene oxide or an organic carbonate compound.

4. A process as claimed in any one of Claims 1 to 3 wherein the amount of reactive agent is in the range from 0.2 up to 2.0 70 by weight relative to the polymer.

5. A process for the treatment of an olefine polymer as claimed in Claim 1 which is substantially as hereinbefore described with reference to either Example 1 or Example 2.

6. Apparatus for the treatment of an olefine polymer, said apparatus comprising a packed bed apparatus and a source of a solid particulate olefine polymer to be treated, the packed bed apparatus having at least two distinct zones wherein the first zone is provided with at least one supply conduit, said at least one supply conduit entering the first zone at or near the top thereof means connecting said supply conduit to the source of the solid particulate olefine polymer, at least one inlet orifice for the introduction into said first zone of a gaseous mixure containing a reactive agent, said at least one inlet orifice being located at or near the bottom of the first zone, at least one outlet orifice for the removal of gaseous materials from said first zone, said at least one outlet orifice being located at or near the top of the first zone, at least one polymer transfer means from a point, or points, at or near the bottom of the first zone, to a point, or points, at or near the top of the second zone, at least one inlet orifice for the introduction of a stream of an inert gas into said second zone, said at least one inlet orifice being located at or near the bottom of the second zone, at least one outlet orifice for the removal of gaseous materials from said second zone, said at least one outlet orifice being located at or near the top of the second zone and at least one polymer removal conduit which is located at or near the bottom of the second zone.

7. Apparatus as claimed in Claim 6 which comprises a single tower which is divided internally into at least two zones by one or more divider plates, each of said divider plates being provided with at least one opening which acts as a polymer transfer means between two adjacent zones.

8. Apparatus as claimed in Claim 7 wherein the tower is divided into two zones by a single divider plate.

9. Apparatus as claimed in Claim 8 wherein the divider plate is in the form of one or more frusto conical sections provided with a central cylindrical section.

10. A packed bed apparatus as claimed in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Corrosion test result (a) Analysis (ppm by weight) Polymer Example No additive 0.1% Ca. St. Chlorine Chioropropanol 1 A A 80 20 2 - | A 60 5 (a) A means non-corrosive (there was no sign of corrosion). The untreated polymers, from which the products of Examples 1 and 2 were obtained were also subjected to a corrosion test. These untreated polymers resulted in considerable amounts of visible corrosion over the test area. WHAT WE CLAIM IS:

1. A process for the treatment of an olefin polymer wherein an olefine polymer in the form of discrete particles which contains residues of a halogen-containing catalyst system is introduced into a first stage of a packed bed system having at least two stages, the polymer is treated in the said first stage with a reactive agent which is effective to react with those halogen-containing materials which can give rise to hydrogen halide or ionic halide, and then passed to a second stage of the packed bed system in which a stream of an inert gas is passed through the polymer particles.

10. A packed bed apparatus as claimed in

Claim 6 which is substantially as hereinbefore described with reference to the accompanying drawings.