AU615093B2 - Process and apparatus for the devolatization of polymer solutions - Google Patents

Description

i i I-~I COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 Form COMPLETE SPECIFICATION FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged:

'S

Complete Specific ation-Lodged: Accepted: Lapsed: Published: Priority: Related Art:

I

a o o i,? t, TO BE COMPLETED BY APPLICANT

G

Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: MONTEDIPE S.r.l.

31 Foro Buonaparte, MILAN, ITALY Andrea Mattiussi; claudio Buonerba; Franco Balestri; Dino Dall'Acqua; Savino Matarrese and Italo Borghi GRIFFITH HACK CO.

71 YORK STREET SYDNEY NSW 2000

AUSTRALIA

Complete Specification for the invention entitled: PROCESS ND APPARATUS FOR THE DEVOLATIZATION OF POLYMER SOLUTIONS The following statement is a full description of this invention, including the best method of performing it known to me/us:- 4450A:rk -2- The present invention relates to a method and to the respective apparatus for removing the volatile components from polymer solutions.

More particularly the present invention relates to a method and to the respective apparatus for removing the volatile components from polymeric solutions having a high viscosity by indirect heating.

The removal of the volatile components from very viscous polymeric solutions is an operation which often recurs in the production of a great many polymers. In particular, in the mass or solution polymerization of ethylenically unsaturated monomers and in the polymerization by polycondensation, the removal of the remaining monomers, of the solvent and of other volatile materials from the solution containing the polymer is a necessary operation.

As known, the separation of the polymer from the volatile components is generally achieved by evaporation, consisting in heating the polymer solution at a temperature higher than the boiling temperature of the volatile 0:20 components. The methods and apparatuses used to this 000 purpose can be subdivided as a function of the viscosity of 0 4 the polymer solution. When the polymer solution is fluid, its viscosity is below 10 centipoises, a thin layer 0 I evaporator can be used, in which the solution is heated o. 25 while flowing along the inner surface of the evaporator.

o A blade rotor provides to spread and move the solution to be treated forward along the devolatizator walls.

However, by using these types of devolatizator, we cannot achieve a very high removal of the volatile 30 substances, unless use is made of apparatuses having a large 0 oo0 volume which need a very expensive operation owing to the required energy.

0° Moreover, these thin layer evaporators impart considerable shearing strengths to the polymer and sometimes they may cause a deterioration of the physical properties.

00 For more viscous solutions, such as for instance the solutions having a viscosity over 106 centipoises, the 7316S:LG r i i I -3devolatilization can be achieved by using ventilated extruders. These extruders, however, require a high operating cost besides having a high starting cost.

Moreover, also by using these apparatuses the thermode-gradation of the polymer cannot be avoided completely.

This is due chiefly to the fact that degradation phenomena of the materials arise owing to the high viscous dissipation and/or to the high stay time of the fluid to be treated in the evaporator.

The different attempts of the Applicant to overcome this drawback, by increasing or by lowering the treatment temperature did not lead to any satisfactory result, as a temperature increase in the treatment chamber involves a more sensible thermal degradation of the material whereas a lowering of the temperature leads to an increase in the fluid viscosity and as consequence causes a more sensible mechanical degradation.

In fact, as known, the degradation of the materials endowed with thermosensitive characteristics depends on the stay time in the treatment chamber, on the viscous dissipations and on the treatment temperature, as described S in Polymer Engineering and Science, August 1978, Vol 18, No pages 812-816.

j 25 Methods and apparatuses are also known, for the devolatilization of polymer solutions by indirect heating.

These methods are often independent on the polymer viscosity but they are not free from drawbacks and limitations as well.

The polymer solutions are very often subjected to high S 0 '30 temperatures for long periods of time, which cause indesired degradations of the polymer chiefly if the latter is very tots sensitive to the heat, such as for instance polystyrene or copolymers or mixtures thereof. This degradation involves a discolouring and/or a degradation of physical-chemical properties of the polymer such as for instance the D toughness. To overcome these drawbacks it was proposed to subject the solution to intermediate temperatures, protracting the stay time in the zone of indirect heating.

7316S:LG -4- Where this is possible, the drawbacks are either a low productivity due to the low flow speed through the zone of thermal exchange or the use of very large and therefore very expensive apparatuses.

S U.S. patent 4,153,501 describes a method and the respective apparatus for removing the vaporizable components from the melt of thermoplastic materials by heating gently in a tubular heat exchanger. This method requires a large zone of indirect thermal exchange, which is added to the starting cost and to the operating cost.

Published European patent application No 226204 describes a method to remove the volatile components from a polymeric solution containing at least 25% by weight of pol-ymers, comprising: a) passing the polymer solution through a zone of indirect thermal exchange comprising a plurality of channels having a substantially uniform ratio surface/volume in the range from 4 to 50, being from about 0.05 to o 0 20 inches high and from about 0.5 to 12 inches long, wherein the polymer solution is heated under pressure at a temperature which is over the temperature of vaporization of the volatile components and is below the boiling point of the polymer in the solution: Sb) evaporating at least 25% of the volatile components of the polymer solution after it has left the zone of indirect thermal exchange, and 30 c) separating the volatile components evaporated from the Oi osolution of the devolatilized polymer.

000o o o The pressure generally ranges from 2 to 200 atmospheres and the temperature is about 160-3300C.

35 This process avoids the thermal degradation of the

U,

o polymer, as it lowers the exposure time of the polymer in the solution at the devolatilization temperature, however it 7316S:LG is not quite satisfactory, as it does not allow to achieve a complete devolatilization of the volatile components from the solution, and therefore it requires more than one devolatilization step.

Moreover, the high difference of temperature between the wall of the heat exchanger and the polymer solution causes both an imperfect distribution of the solution in the single channels arranged in parallel, with consequent dishomogeneity in the distribution of the temperature and an ununiform treatment of the polymer in each channel, as reported by Scott Lynn and Charles F Oldershaw Analysis and Design for Viscous Flow Cooler Heat Transfer Engineering Vol. 5 No 1-2-1984.

Therefore an object of the present invention is to provide a process and a device allowing a nearly complete removal of the volatile components from polymer solutions without the above reported drawbacks take place.

More particularly, an object of the present invention is to provide a more efficient process and device for °20 removing in a nearly complete way the volatile components from polymer solutions without causing a significant decay of the properties of the polymer.

I°o 'The Applicant has now found that the above reported :22 objects can be achieved by carrying out the process of devolatilization under conditions which allow to achieve a 2 difference of temperature below 10 0 C between the temperature of the heating medium and the temperature of the polymer solution leaving the channels and a pressure of the polymer solution in the zone of devolatilization at the inlet of the 30 channels ranging from 2 to 5. 10 Pascal.

Therefore object of the present invention is a process i' for the devolatilization of polymer solutions comprising: a) feeding the polymer solution through a zone of indirect thermal exchange comprising a plurality of channels arranged in parallel among one another, heated to a temperature higher than the temperature of vaporization 7316S:LG -6of the volatile components and up to the boiling temperature of the solution, wherein the ratio between the whole surface of thermal exchange, expressed in 2 m and the flow per hour of the fed polymer solution, expressed in m3 /h is over 80 m 2/m3/h: b) moving the polymer solution forward into each channel at a speed below c) keeping the polymer solution in each channel for a period of time ranging from 120 to 200 seconds, in order to evaporate at least 90% of the volatile components from said polymeric solution; d) separating the volatile components from the devolatilized polymer solution.

Moreover, it has been found that this process can be carried out profitably by using an apparatus comprising a container 20 equiped with an inlet pipe of the polymer solution, with a drain pipe of the volatile components, with an ,itlet pipe S of the devolatilized polymer solution and with a heat exchanger fastened inside the container.

The heat exchanger comprises a central zone connected to the inlet pipe of the polymeric solution to be devolatilized, a plurality of channels surronding the central zone and extending from said central zone, at which the polymeric solution arrives, to the periphery of che heat exchanger and a plurality of pipes perpendicular to said channels, into which one lets a fluid heating medium flow 0. having a temperature higher than the temperature of vaporization of the volatile components of the polymeric solution.

These channels are heated by the pipes in order to form the surface of thermal exchange and are dimensioned in such S0 2 a way that the ratio surface, expressed in m and flow of the fed polymeric solution, expressed in m3/h, is over and the stay time of the polymeric solution in each 7216S:LG -7channel ranges from 120 to 200 seconds and the flow speed of the solution through each channel is below 0.5 mm/second.

The vessel is wrapped in a heating jacket keeping the temperature inside higher than the evaporation temperature of the volatile components.

A gear pump provides to the unload of the devolatilized polymer from the vessel.

Any viscous polymer solution can be used in the process of the present invention. These polymer solutions have generally a viscosity in the melted state over 10,000 centipoises and preferably ranging from 100,000 to 1,000,000 centipoises.

The process of the present invention can be used for the devolatilization of thermoplastic polymers, siliconic polymers, elastomers, lubricants having a high molecular weight and the like.

The term thermoplastic polymers, as used in the present disclosure and claims, comprises the polymers getting plastic and flowing because of heat and prussure. Examples of such thermoplastic polymers include: polystyrene, impact resistant polystyrene, poly-phenylene ethers, polycarbonates, polyvinyl chloride, polyurethanes, polyetherimides, polyamides, polyesters, polyacrylates and polymethacrylates, linear polyethylene, their copolymers such as copolymers styrene-acrylonitrile (ASA or SAN), styrene methyl-methacrylate, stryene maleic anhydride, styrene-acrylonitrile-rubber like ABS or AES, styrene-methyl-methacrylate-rubber and the like, as well a the mixes of such polymers and copolymers, such as for j 30 instance polyphenyl ether-polystyrene and the like.

SThe highly viscous polymer solutions containing at Sleast 25% by weight and preferably 40% by weight of i polystyrene or of a copolymer of styrene either alone or in mixture with other polymers, are particularly preferred in the process of the present invention.

0" Examples of siliconic polymers are the ones corresponding to general formula: 7316S:LG I.' -8- HO--SiD--H wherein R1 and R 2 are monovalent radicals, such as methyl, ethyl, propyl, vinyl, allyl, cyclohexyl, cyclopentyl, phenyl, methyl-pbenyl and the like and n is a whole number over 100.

Examples of elastomers 4nclude dienic rubbers, such as polybutadiene, polyisoprene, butylenic rubbers, polyisobutylene, ethylene-propylene rubbers and ethylene-propylene-diene (EPDM) rubbers; the homonpolymers of vinyl ethers, cyclic esters, methacrylic esters, acrylonitrile and the like.

As lubricants having a high molecular weight, the hydrocarbons are meant having a boiling point ranging from 370 to 550°C and comprise n-paraffins, isoparaffins, cycloparaffins and the like.

°o0 The polymeric solutions to be subjected to the process of devolatization of the present invention are the polymeric solutions obtained directly by the synthesis process of the S. o polymers and contain, besides the polymer, starting monomers 0 or mixtures of monomers and solvents, particularly where the polymerization has been carried out in solution. Moreover, S° said solutions may contain mixtures of polymers and/or o o additives and/or fillers dissolved or dispersed in the solution.

r According to the process of the present invention, the polymeric solution is passed through a zone of indirect thermal exchange, wherein the polymeric solution is heated by a source of heat through a transfer medium, which is generally a metal.

The source of heat is generally a fluid kept at high temperature and the heat is transferred from the fluid to the polymeric solution, that is thus heated.

The polymeric solution is heated to a temperature higher than the temperature of evaporation of the volatile iI -9components and preferably over the temperature of glass transition (Tg) of the polymer in solution. The border-line temperature is the boiling temperature of the polymer solution. One prefers to keep the temperature of the polymeric solution at least 50 0 C over the temperature of glass transition (Tg) of the polymer. We may generally use temperatures of devolatilization ranging from 100 to 400 0

C

and preferably ranging from 150 to 350 0 C; although temperatures over 300 0 C can cause a degradation of the polymer. In the case of polystyrene or of mixtures containing polystyrene, the utilizable temperatures range from 160 to 300 0 C and preferably from 180 to 280 0

C.

In the zone of indirect thermal exchange, the polymer solution is kept under a pressure ranging from 2 to 5.105 Pascal, at the inlet of each channel and at a pressure below the pressure of saturation of the volatile components 1 towards the outlet from the channel.

The stay time of the polymeric solution in the zone of indirect heating ranges from 120 to 200 seconds, so that at least 90% of the volatile components is eliminated in such a 0 zone. Stay times over 200 seconds are not recommended as they should cause an undesired degradation of the polymer.

In order to ensure a quick and efficient transfer of heat and a substantially complete removal of the volatile components from the polymeric solution, the ratio surface of 2 the exchanger (expressed in m2)/flow of the polymer solution (expressed in m 3 is kept at values over 80 and up to 150; values ranging from 100 to 110 are preffered.

0Another parameter which allows to obtain the desired results concerning a high removal of the volatile components is the flow speed of the solution in the indirect heating o zone.

The polymeric solution is let flow through this zone very slowly and in particular at a speed below mm/second; preferably from 0.3 to 0.4 mm/second.

The zone of indirect thermal exchange comprises a pluarlity of channels, each of them being preFerably from and 150 mm long, from 1 to 3 mm high, from 10 to 30 mm wide.

7316S:LG The size and shape of the channels are substantially uniform, in order to ensure a regular and uniform flow of the polymeric solution.

In order to ensure a quick thermal exchange in each channel and a complete removal of the volatile components, the difference of temperature between the heating medium and the polymeric solution at outlet from the channels is kept within values not over 10 OC. Any heating medium, such as diathermic oil, electric resistance and the like, can be used to heat the surface of the channels.

At outlet from the channels, the polymer solution is substantially free from volatile components, as such components evaporate in the zone of indirect heating.

Under the conditions of the process of the present invention the evaporation is quick and complete already inside the channels and the polymeric solution flows substantially free from volatile components at outlet of the channels.

The polymer solution is collected on the bottom of the vessel, whereas the volatile components are collected from the top of the same vessel.

oThese two components can be removed by suitable means O such as pumps, suction, gear pumps and the like.

In figure 1-7 a few kinds of a heat exchanger apparatus are illustrated, suitable to carry out the process of the present invention.

In particular: figure 1 is the schematic longitudinal side-view of a devolatilizator according to the present invention: figure 2 is the schematic view from the top of a plate, the heat exchanger contained in the devolatilizator of figure 1 consists of: figures 3 and 4 represent the schematic prospective and side views respectively of the arrangement of the plates of figure 2: figure 5 represents the view from the top of a second kind of plate, the heat exchanger contained in the devolatilizator of figure 1 may consist of: and 7316S:LG -11figures 6 and 7 represent the schematic prospectic and side views respectively of the arrangement of the plates of figure With reference to figure 1 the devolatilizator according to the present invention comprises double-walled or lined vessel 16 equipped, in the upper part, with inlet pipe 1 of the polymer solution: in the side part, with outlet pipe 3 of the volatile components; and, in the lower part, with outlet duct 2 of the devolatilized polymeric solution.

Inside vessel 16 a heat exchanger is fastened coiprising central chamber 21 for receiving the polymer solution to be devolatilized, fed from inlet pipe 1. Round said central chamber 21 a series of channels 14 is arranged, extending from central chamber 21 to the periphery of the Sheat exchanger. The number ci channels can vary within a Owide range. It generally ranges from 1000 to 100,000.

Channels 14 have a rectangular section and are from 50 to 150 mm long, from 1 to 3 mm high and from 10 to 30 mm wide.

Channels 14 are delimited by superimposed and spaced plates 19.

A pump, which is not illustrated in the figure, provides to feed the polymeric solution to channels 14 through pipe 1 and chamber 21. In order to better subdivide the polymeric solution and to convey it uniformly to channels 14, spacer 10 is arranged in the middle of chamber 21. Spacer 10 can have a cylindrical, conic or frustum-conic shape.

Moreover the heat exchanger comprises the means to heat the surfaces of thermal exchange at a temperature of vaporization of the volatile components. Said heating means comprises a first series of pipes 13 arranged at the periphery of the heat exchanger and through which the heated fluid is let flow, such as a diathermic oil coming from duct 4 through annular chamber 11. A second series of pipes 13 is arranged in the inner part of the exchanger, which pipes communicate with the first pipes in the lower part through 7316S:LG -12annular chamber 17. Said pipes 13 and 13 pass through openings 22 and 22 made in plates 19 and are arranged perpendicularly to the flow of the polymeric solution.

Said pipes 13 and 13 are supported at their ends by two plates 12 and 12.

In the upper part pipes, 13 arranged in the peripheric part of the exchangei, are connected, through annular chamber 11, to pipe 4 for the feed of the heating fluid: whereas pipes 13, arranged in the innerest part, are connected through annular chamber 15 to pipe 5 for the discharge of the heating fluid.

Vessel 16 is double-walled or lined and is kept at the desired temperature by means of a heating fluid coming from pipe 8 and going out of pipe 9.

Feeding pipe 1 is lined and kept at the desired temperature by means of 3 heating fluid coming from pipe 6 and going out of pipe 7.

Pipes 13 and 13 pass through holes 22 and 22 of a plurality of plates 19 superimposed and spaced from one another by a plurality of spacers 20. In order to ensure a perfect seal and resistance of pipes 13 and 13, spacers are provided with holes, said pipes 13 and 13 are inserted into. Thus among various superimposed plates 19 channels 14 form, which extend from the centre to the periphery of the exchanger and represent the channels for the flow of the polymeric solution.

In figures 5-7 an alternative embodiment is illustrated concerning the channels for the passing of the polymeri.z o solution. In this case the plates are replaced with a plurality of blocks 23 having a retangular or isosceles trapezium shape, drilled for the passing of two rows of o adjacent pipes.

By arranging blocks 23 in a spaced way on a first layer and in a spaced or staggered way on a subsequent second layer, so that holes 22 of the superimposed blocks coincide, an annular even plate forms extending round the heat exchanger. The subsequent layers are arranged in a 7316S:LG -13staggered way with respect to the lower layer, in order to form channels 14 extending from the centre to the periphery of the heat exchanger, as illustrated in figures 6 and 7.

The even plate thermal exchanger according to the present invention can be constructed according to known techniques as to the molding and welding. As far as the ducts of the heating fluid are concerned, one prefers to assemble the plates or the blocks and the pipes and subsequently to fasten the whole either by hydraulic or by pneumatic expansion of the pipes. In such a way a perfect contact metal-metal is obtained.

The running of the devolatizator illustrated in figure 1 is the following: the polymeric solution to be treated is fed to pipe 1 through a dosage pump and comes into central chamber 21.

From this chamber the solution passes through channels 14, comes out at the end of these channels, falls into inside 18 of vessel 16 and is discharged at the end of said vessel I o from duct 2 by means of gear pump 24. The heating fluid at 20 a suitable temperature is fed from duct 4, goes through v annular chamber 11, pipes 13, annular chamber 17 and pipes o" 13 and chamber 15 and comes out of duct 5. Vessel 16 is heating by passing a heating fluid coming in from duct 8 and coming out of duct 9. The volatile components are r-moved from duct 3.

The following examples will be given to bitter illustrate the present inventicn, without presenting any limitative characteristic of the same.

EXAMPLE

S° In this example the devolatizator of figure 1 was used. The exchanger comprised 1700 channels, each of them being on the average 16 mm wide, 55 mm long and 1 mmm high.

The channels were obtained by using blocks having an isosceles trapezium shape superimposed in more layers, spaced on each layer.

The oil was heated to 250-300 0 °C and let flow through the pipes.

7316S:LG -14- A vacuum pump was used to remove the volatile components and a gear pump was fastened at the end of the vessel to collect the devolatilized polymeric solution.

A polymeric solution containing 50% by weight of polystyrene, 10% of ethyl-benzene and 40% of monomer styrene was fed at a flow of 30 1/h to the devolatilizator at a temperature of about 120°C and at a pressure at inlet of about 2.105 Pascal.

The devolatilizator was kept at a residual pressure of 3 2.10 Pascal and was heated by circulation of a diathermic oil kept at the temperature of 2500C.

The temperature of the polymer leaving the devolatilizator was about 2450C.

The ratio surface of thermal exchange of the channels/fed polymeric solution was 106 m 2 /m 3 /h.

The speed of the solution in each channel was 0.3 mm/second. The stay time was about 181 seconds.

The polymer leaving the devolatilizator had the following characteristic: residual monomer styrene: 400 ppm total volatile components: 500 ppm EXAMPLE 2 o A polymeric solution consisting of about 50% by weight of a copolymer styrene-acrylonitrile (75-25% by weight), by weight of ethyl-benzene, 22.5% by weight of monomer styrene and 7.5% by weight of acrylonitrile was fed, at a flow of about 30 1/h, to the devolatilizator of example 1.

o0 The temperature at inlet was about 120°C and the .o 30 pressure was about 2.10 Pascal.

S" The devolatilizator was kept at a residual pressure of 2.103 Pascal and was heated by circulation of a diathermic oil kept at the temperature of about 230 0

C.

The temperature of the polymer at outlet was about 2250C. The ratio surface of thermal exchange/fed polymeric solution and the flow speed in the channel were equal to the ones of example 1.

7316S:LG The polymeric solution leaving the devolatilizator had the following characteristics: residual monomer styrene: 500 ppm residual monomer acrylonitrile: 20 ppm total volatile components: 600 ppm EXAMPLE 3 A polymeric solcion consisting of 60% by weight, of a copolymer styrene-methyl methacrylate (55-45% by weight).

by weight o- ethyl-benzene and 20% by weight of a mixture of monomers styrene-methyl methacrylate in a ratio by weight 55/45, was fed at a flow of about 30 1/h to the devolatilizator of example 1. The temperature of the solution at inlet was about 120 0 C and the pressure was about 5 2.10 Pascal.

The devolatilizator was kept at a residual pressure of 2.10 Pascal and heated by circulation of a diathermic oil kept at the temperature of 230 0

C.

S2( The temperature of the polymer at outlet was about 225 0

C.

The polymer leaving the devolatilizator had the following characteristics: residual monomer styrene: 400 ppm residual monomer methyl methacrylate: 20 ppm total volatile components: 500 ppm SEXAMPLE 4 o° 0 A polymeric solution consisting of 65% by weight of polymethylmethacrylate, 20% by weight of butyl acetate and by weight of monomer methyl methacrylate was fed at a flow of about 30 1/h to the devolatilizator of example 1.

The temperature of the solution at inlet was 120 0 C and its 5 pressure was 4.10 Pascal.

The devolatilizator was kept at a residual pressure of 13.10 Pascal and was heated by circulation of a diathermic oil kept at a temperature of 230 0

C.

7316S:LG -16- The temperature of the polymer leaving the devolatilizator was about 225 0

C.

The polymer leaving the apparatus, had the following characteristics: residual monomer methyl-methacrylate: 1000 ppm total volatile components: 2000 ppm EXAMPLE A polymeric solution consisting of 50% by weight of copolymer styrene-maleic anhydride (85-15% by weight), by weight of cyclohexane and 30% by weight of monomer styrene was fed at a flow of 30 1/h to the drvolatilizator of example 1. The temperature of the solution at inlet was 110°C and its pressure was about 2.105 Pascal.

The devolatilizator was kept at a residual pressure of 2.103 Pascal and heated by flow of a diathermic oil kept at a temperature of about 2300C.

o The temperature of the polymer leaving the devolatilizator was about 225 0

C.

The polymer leaving the apparatus had the following characteristics: residual monomer styrene: 500 ppm total volatile components: 600 ppm 0 S 25 EXAMPLE 6 A polymeric solution consisting of 70% by weight of copolymer styrene-acrylonitrile-polybutadiene (87.5-22.5-10% by weight), 20% by weight of ethyl-benzene and 10% by weight o of a mixture of monomers styrene and acrylonitrile in the 30 ratio by weight 75/25, was fed at a flow of about 30 1/h to o the devolatilizator of example 1. The temperature of the solution at inlet was 150 0 C and its pressure was about 3.105 Pascal.

0 S0 o' The devolatilizator was kept at a residual pressure of about 2.103 Pascal and heated by flow of a diathermic oil kept at a temperature of about 250 0

C.

The temperature of the polymer leaving the devolatilizator was about 245 0

C.

7316S:LG -17- The polymer leaving the apparatus had the following characteristics: residual monomer styrene: 500 ppm residual monomer acrylonitrile: 20 ppm total volatile components: 600 ppm EXAMPLE 7 A polymeric solution consisting of about 40% by weight of polycarbonate and about 60% by weight of chloropenzene, was fed at a flow of about 30 1/h to the devolatilizator of example 1. The temperature of the solution at inlet was 120 0 C and its pressure was about 3.105 Pascal.

The devolatilizator was kept at a residual pressure of about 2.103 Pascal and heated by flow of a diathermic oil kept at the temperature of about 295 0

C.

The temperature of the polymer leaving the devolatilizator was about 290 0

C.

I o The content in residual solvent in the solution at outlet was below 500 ppm.

o 20 EXAMPLE 8 SA polymeric solution consisting of about 40% by weight of an alloy polyphenylene oxide-polystyrene 50/50 by weight and of 60% by weight of toluene was fed at a flow of 30 1/h to the devolatilizator of example 1. The temperature of the solution at inlet was 120 0 C and its pressure was about 3.105 Pascal.

The devolatilizator was kept at a residual pressure of about 13.10 Pascal and heated by flow of a diathermic oil ao kept at the temperature of 295 0

C.

30 The temperature of the polymer leaving the S, j devolatilizator was about 295 0

C.

The content in residual solvent in the polymer at outlet was below 1000 ppm.

7316S:LG -i -18- EXAMPLE 9 A solution consisting of 65% by weight of linear low density polyethylene (LLDPE) and 35% by weight of cyclohexanone was fed at a flow of 30 1/h, to the devolatilizator of example 1. The temperature of the solution at inlet was 170 0 C and the pressure was about 3.10 5 Pascal.

The devolatilizator was kept at a residual pressure of 3 about 2.10 Pascal and was heated by flow of a diathermic oil kept at the temperature of 250 0

C.

The temperature of the polymer leaving the devolatilizator was 245 0

C.

The content in residual solvent in the polymer leaving the devolatilizator was below 10 ppm.

EXAMPLE A solution consisting of 65% by weight of high density polyethylene (HDPE) and 35% by weight of cyclohexanone was fed, at a flow of 30 1/h, to the devolatilizator of example 0 1. The temperature of the solution at inlet was 170 0 C and the pressure was about 3.105 Pascal.

The devolatilizator was kept at a residual pressure of about 2.10 Pascal and was heated by flow of a diathermic oil kept at the temperature of about 250 0

C.

°The temperature of the polymer leaving the devolatilizator was 245 0

C.

The content in residual solvent in the polymer leaving the devolatilizator was below 10 ppm.

7316S:LG

Claims (11)

1. A process for the devolatilization of polymer solutions comprising: a) feeding the polymeric solution through a zone of indirect thermal exchange comprising a plurality of channels arranged in parallel among one another, heated to a temperature higher than the temperature of vaporization of the volatile components and up to the boiling temperature of the solution, wherein the ratio between the whole surface of 2 thermal exchange, expressed in m and the flow per hour of the fed polymeric solution, expressed in m3/h is ovr 80 m2 /m3/h; b) moving the polymer solution forward into each o 20 channel at a speed below 0.5 mm/second; c) keeping the polymer solution in each channel for a period of time ranging from 120 to 200 ooo seconds, in order to evaporate at least of the volatile components from said S'polymeric solution; d) separating the volatile components from the devolatilized polymer solution. S S2. A process according to claim 1, wherein the o."o solution of polymers has a viscosity in the melted state over 10,000 centipoises and preferably ranging from 100,000 to 1,000,000 centipoises. 0 -0

3. A process according to claims 1 or 2, wherein the polymer is selected from thermoplastic polymers, siliconic polymers, elastomers and lubricants having a high molecular weight. 7316S:LG

4. A process according to claim 3, wherein the thermoplastic polymer is selected from polystyrene, impact resistant polystyrene, polyphenylene ethers, polycarbonates, polyvinyl chloride, polyurethanes, polyetherimides, polyamides, polyesters, polyacrylates and polymethacrylates, linear polyethylene, their copolymers and the mixes of such polymers and copolymers. A process according to claims 3 or 4, wherein the thermoplastic polymer is selected from the copolymers styrene-acrylonitrile, styrene methyl-methacrylate, styrene-maleic anhydride and styrene-acrylonitrile-rubber.

6. A process according to claims 3 or 4, wherein the polymer is a mixture of polyphenyl ether-polystyrene. So o a oa 7. A process according to any one of the preceding claims, wherein the polymer solution contains at least 25% by weight and preferably at least 40% by weight of polystyrene either alone or in mixture 25 with other polymers. 0 0

8. A process according to any one of the preceding o claims, wherein the polymer solution is heated to a temperature higher than the temperature of glass i"Ai 30 transition (Tg) of the polymer in solution and up to the boiling temperature of the polymeric solution. S9. A process according to claim 8, wherein the 35 temperature of the polymeric solution is at least 0 C over the temperature of glass transition (Tg) of the polymer. 7316S:LG -21- A process according to claims 8 or 9, wherein the temperature of the polymer solution ranges from 100 to 400 0 C, preferably from 150 to 350 0 C. 11 A process according to any one of the preceding claims, wherein the difference between the temperature of the heating medium and the one of the polymer solution leaving the channels is below 0 C.

12. A process according to any one of the preceding claims, wherein the pressure of the polymeric solution at inlet of the channels ranges from 2 to 5.105 Pascal.

13. A process according to claim 12, wherein the pressure of the polymeric solution is lower than the pressure of saturation of the volatile O components towards the outlet from each channel. 'oo

14. A process according to any one of the preceding o claims, wherein the ratio surface of the exchanger 2 (expressed in m2)/flow of the polymeric solution 0 3 (expressed in m ranges from 80 to 150, preferably from 100 to 110. 0o° 0 15. A process according to any one of the preceding claims,' wherein the flow speed of the polymeric 00 solution in each channel ranges from 0.3 to 0.4 mm/second.

16. A process according to any one of the preceding claims, wherein the zone of thermal exchange comprises from 1,000 to 100,000 channels and each channel is from 50 to 150 mm long, from 1 to 3 mm high and from 10 to 30 mm wide. 73,6S:MS -22-

17. A process for the devolatilization of polymer solutions as claimed in claim 1 substantially as herein described with reference to any one of the Examples.

18. An apparatus for the dGvolatilization of polymer solutions substantially as herein described with reference to the drawings. Dated this 24th day of July 1989 00 0001 0 0 0 00 0 0~o 0 0 0 0 0 0~ 4 00 00 I 0 MONTEDIPE S.r.l. By their Patent Attorney GRIFFITH HACK CO. 0 0 *0 01 00 7 316 S LG