CA1203348A - Separation of polymer from hydrocarbon solvent in a process for the manufacture of polymers of ethylene - Google Patents
Separation of polymer from hydrocarbon solvent in a process for the manufacture of polymers of ethyleneInfo
- Publication number
- CA1203348A CA1203348A CA000422287A CA422287A CA1203348A CA 1203348 A CA1203348 A CA 1203348A CA 000422287 A CA000422287 A CA 000422287A CA 422287 A CA422287 A CA 422287A CA 1203348 A CA1203348 A CA 1203348A
- Authority
- CA
- Canada
- Prior art keywords
- polymer
- vessel
- solution
- temperature
- ethylene
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F6/00—Post-polymerisation treatments
- C08F6/06—Treatment of polymer solutions
- C08F6/12—Separation of polymers from solutions
Abstract
ABSTRACT OF THE DISCLOSURE
An improved method for the separation of polymer from hydrocarbon solvent in a process for the manufacture of poly- -olefins is disclosed. A solution of polymer and solvent at a temperature above 130°C and a pressure above atmospheric pressure is passed through pressure reduction means into a vessel. Solvent is flashed off and the polymer forms a pool of molten polymer. The temperature of the walls of the vessel above the pressure reduction means is maintained at least 10°C, and especially at least 30°C, above the temperature of the walls of the remainder of the vessel.
The improved method is less susceptible to the formation of gel in the polymer.
An improved method for the separation of polymer from hydrocarbon solvent in a process for the manufacture of poly- -olefins is disclosed. A solution of polymer and solvent at a temperature above 130°C and a pressure above atmospheric pressure is passed through pressure reduction means into a vessel. Solvent is flashed off and the polymer forms a pool of molten polymer. The temperature of the walls of the vessel above the pressure reduction means is maintained at least 10°C, and especially at least 30°C, above the temperature of the walls of the remainder of the vessel.
The improved method is less susceptible to the formation of gel in the polymer.
Description
12~33~
SEP~RATION OF POLYMER FROM HYDROCARBON SOLVE~T
IN A PROCESS FOR THE MANUFACTURE OF POLYMERS OF ETHYLENE
The present invention relates to a method for ~he separation of polymer from hydrocarbon solvent in a process for -the manufacture of po:Ly-~-olefins, and especially to an improved method for such separation -that is less susceptib]e to the formation of gel in the polymer.
Polymers of ethylene, for example, homopolymers o:E
ethylene and copolymers of ethylene and higher ~-olefins, are used in lar~é volumes for a wide variety of end uses, for example, in the form o film, fibres, moulded or thermoformed articLes, pipe, coatings and the like. In many of these end-uses it is important that the level of gel in the polymer be at a low level and moreover be consistently at a low level.
As used herein, gel refers to that matter which remains after Soxhlet extraction of polyethylene using xylene as solvent and a 200 Tyler~ mesh wire screen in the extraction apparatus.
Processes Eor the preparation of homopolymers of ethylene and copo:Lymers of ethylene and higher ~-olefins are known. Such proces~es include processes in which the mono-mer.s are polymeri~ed in the presence of a co-ordination catalyst, eor exarnple, a catalyst comprising a compound of a transition metal belonging to Groups IVB-VI~ of the Periodic Table and an organometallic compound of a meta:L belonging to Groups I-IIIA of the Periodic Table.
There are two types of processes for the manufac-ture of polyethylene that involve the polymerization of mono-mers in the presence of a co-ordination catalyst viz. those processes which operate at temperatures below the mel-ting or solubilization temperature of the polymer and those processes which operate at temperatures above the melting or solubili-zation temperature of the polymer. The latter are referred to as "solution" process.
A preferred process for the polymerization of ..~
33~Ei ~-olelns is the high temperature or "solution" polymeri~a-tion process, an exarnple of which is described in Canadian Patent 660 869 o~ A.W. Anderson, E.L. Fallwell and J.M.
Bruce, which issued 1963 April 09. ~n a solution process, the process is operated so that both the monomer and polymer are soluble in the reaction medium.
Solution polymerization processes are operated at pressures above atmospheric pressure. It is necessary, in order to recover polymer, to reduce the pressure to atmos-pheric pressure and to separate the hydrocarbon solvent fromthe polymer. One method of accompLishiny the pressure reduc-tion and polymer separation is to pass a solution of polymer and hydrocarbon solvent, at a temperature above the melting point of the polymer and a pressure above atmospheric pres-sure, through a pressure reduction valve to reduce the pres-sure to substantially atmospheric pressure. As the solution is passed through the pressure reduction valve, solvent is flashed off from the polymer to yive a pol~mer containing relatively minor amounts of solvent, such polymer being in the Eorm of molten polymer. Hc)wever, in such a method some polymer may become entrained in the hydrocarbon solvent being E;Lashed off and may become deposited on the walls of the ve~el being used for separation oE solvent from polymer.
Such deposited polymer is at a temperature abave the melting point o~ the polymer. There is a tendency ~or the deposited polymer to degrade, and hence form gel particles, over a period oE time. The molten polymer in the vessel may become contaminated with such gel pa~rticles especially when degraded polymer separates from the walls of the vessel and becomes admixed with the molten polymer.
An intermediate separator in which the pressure is reduced from the pressure of the polymerization reaction to a lower pressure that is greater than atmospheric pressure may be employed between the reactor and the method used to separ-ate polymer from solvent, as is disclosed in Canadian Patent568 721 of ~.D. Johnson, which issued 1959 January 6.
A method of reducing the tendency for the formation of gel in the separation of polymer from solvent in a so]u-' .:
?33~
tion polymerization process has now been found.
Accordingly, the present invention provides in aprocess Eor the separation, in a solution process for -the manufacture of polymers oE ethylene selected from ~he group consi.sting of homopolymers of ethylene and copolymers of ethylene an~ higher ~-olefins, of a ~olution comprising said pol~ner and inert hydrocarbon sol~ent into fractions compris-ing said polymer and said solvent, said solution being at a tsmperature above 130C and at a pressure above atmospheric pressure, wherein the pressure of said solution is reduced by passing said solution through pressure reduction means and into a substantially vertical elongated vessel, such that the solution passes into the vessel in a downward direction, said polymer forming a pool of moLten polymer below said pressure reduction means and said solvent passing in the form of a vapour ~rom -the top of said vessel, the walls of said vessel being maintained at a tempera-ture above the melting point of the polymer, the improvement comprising maintaining the ~alls oE the vessel in the region above sa.id pressure reduction means at a temperature that is at least 10C higher than the temperature of the remainder of the walls o-f the vessel.
In a preferred embocliment of the process of the present i~vention, khe temperature of the walls above the valve is at least 30C higher than the temperature of the remaincler of the walls.
The present invention is directed to a solution polymerization process for the preparation of high molecular weight polymers of ethylene. ln particular, the polymers are homopolymers of ethylene and copolymers of e-thylene and higher ~-olefins, especially such higher ~-olefins having 3 to 12 carbon atoms, i.e., C3- C12 ~-olefins, including bicyclic ~-olefins, examples of which ~-olefins are butene-l, hexene-l, octene-l, and bicyclo-(2,2,1)-2-heptene. In addi-tion, cyclic endomethylenic dienes may be fed to the process with the e~hylene or mixtures of ethylene and C3- C12 olefin.
In a solution polymerization process monomer(s), a ~33~3 co-ordination catalyst and inert hydrocarbon solvent are fed to a reactor. Co-ordination catalysts Eor solution polymer-ization processes are known, for example, -those described in the a~orementioned Canadian Paten-t 660 869. The monomer may be solely ethy]ene or a mixture or ethylene and one or more of the higher ~-olefins and is dissolved in the reaction solvent.
Solution polymerization processes may be operated at temperatures in the range of about 10~-320C and especial-ly in the range 105-310C. The pressures used in the process of the present invention are those known for solution poly-merization processes, especially in the range of about 4-25MPa. The pressure and temperature are controlled so that both the unreac-ted monomers and the polymer formed remain in solution, a requirement of a solution polymerization process.
The hydrocarbon solven~ used in the polymerization process is a hydrocarbon solvent that is inert with respect to the co-ordination catalyst. Such solvents are known and inc:Lude hexane, heptane, octane, cyclohexane, methylcyclohe~-ane and hydrogenated naphtha. The solvent used in the poly-merization process is preferably used in the preparation of the co-ordination catalyst. The hydrocarbon solvent is the rnajor component of the polymerization rnixture fed to the reactor, usually comprisin~ at least 75% of the reaction mixture.
The mixture that exits from the polymerization reactor comprises polymer, unreacted monomer, co-ordination catalyst, some of which remains in an active state, and hydrocarbon solvent. The polymerization reac-tion in a solu-tion polymerization process is normally terminated by addi-tion o~ a so-callad "deactivator", for example, a fatty acid, an alcohol or an al~aline earth metal/carboxylic acid salt.
The deactivator is admixed with hydrocarbon solvent, normally the solvent of the polymerization process, and fed into the polymerization mixture, usually shortly after that mixture passes from the reactor. The polymerization mixture tha-t has been treated with deactivator contains catalyst residues which may be removed by contacting the mixture with an adsor-.~
~33~
bent, for e~ample, alumina. Such a deactivation and catalyst removal process is described in Canadian Pa-tent 732 279 of B.B. Baker, K.M. Brauner and A.N. Oemler, which issued 1966 April 12.
Subsequently, the polymerization mixture is sub-jec-ted to one or more steps to reduce the temperature and pressure o the polymerization mixture to atmospheric pres-sure and temperature. In a solution polymerization process this is normally done by first reducing the pressure to atmospheric pressure in one or more steps and subsequently cooling the molten polymer until it solidifies, usually in the form of pellets. A method for reducing the pressure in the process that may be used, in part, is that described in the aforementioned Patent 568 721.
The present invention will be further exemplified with reference to the following drawings:
Fig. 1 is a schematic representa-tion of apparatus for the separation of polymer from solvent, and ~ig. 2 is a cross-section of the apparatus o Fig. 1.
Referring to Fig. 1, the apparatus used in conjunc-tion with a process of the present invention comprises an upper vessel 1 and a lower vessel 2. Both upper vessel 1 and lower vessel 2 are elongated vessels with upper vessel 1 be-ing located above lower vessel 2. Upper vessel 1 and lower vessel 2 are joined at sieve plate 3, sieve plate 3 being adapted to pass molten polymer. Upper vessel 1 has heating coils 4, 5, and 6 passing around the vessel. Heating coil 4 spirals around the upper portion of upper vessel 1 a plurali-ty of times in order that that portion of upper vessel 1 may be heated in a controlled manner. Similarly heating coils 5 and 6 spiral around the middle and lower portions, respec-tively, of upper vessel 1. In addition heating coil 7 spirals around lower vessel 2 a plurality of times in order that that vessel may be heated in a controlled and uniform manner. Upper vessel 1 and lower vessel 2, together with heating coils 4-7, are insulated by means not shown. Each of heating coils ~, 5, 6, and 7 is connected to a source oE
)33~
6~eam through s-team pipes 9, 10, 11 and 12 respec-tively.
Solution inlet 15 is located in upper vessel 1.
~s is shown in Figure 1, heating coils 4 and 5 are located at and above solution inle-t 15. Heating coils 4 and 5 are both located above melt pool 16 (see Fig. 2). Each of heat-ing coils 4, 5, 6 and 7 has an outlet (not shown) for removal of condensate from the steam-heated coils.
Vapour outlet 13 is located in -the upper portion oE
upper vessel 1 and polymer outlet 14 is :Located at the bottom of lower vessel 2.
Referring to Fig. 2, solution inlet 15 passes into upper vessel 1 to a position that is axiall~ located within upper vessel 1. The outLe-t of solution inlet 15 i.e. nozzle 20 of a pressure reduction valve ~not shown), is adapted to axially discharge solution passing therethrough in a downward direction into upper vessel 1. A melt pool 16 is located below the outlet oE solution inlet 15 and above sieve plate 3, melt pool 16 being spaced apart from said outlet.
The pressure reduction means may comprise a pres-~0 sure reduction valve Located within upper ve~sel 1 or, pref-erably, a pressure reduction valve located outside upper ves~el 1 in fluid-flow relationship with nozzle 20 which is located within upper vessel 1 and adopted to discharge so:Lution in a downward direction.
~lthough the present invention has been particular-ly described with reference to ~he use of heating coils to heat and control the temperature o~ the vessels, it will be understood by those skilled in the art -that other heating and control means may be used e.g. heating jackets, electric coils and the like.
In operation a solution of polymer in solvent passes through solution inlet 15 and is discharged from noz-zle 20 into upper vessel 1. The solvent is flashed off and the vapour thereof passed through vapour outlet 13 to a con denser (not shown). The polymer forms melt pool 16. The polymer of melt pool 16 flows through sieve plate 3, forming polymer s-trands 17 which fall into mel-t pool 18 in the bottom of lower vessel 2. ~he polymer o~ melt pool 18 passes through . .
~2~33~3 pol~mer outlet 1~ to, for e~ample, an extruder (not shown) adapked to forrn sald polymer into solid pellets of polymer.
As -the solvent i5 flashed of~ from the solution oE
polymer in solvent, polymer may becom~ entrained in the sol-vent vapour. Such entrained polymer may in turn become deposited on the walls of upper vessel 1, especially said walls located a'oove solution inlet 15. Such deposited poly-mer 19 is shown in Fig. 2.
In the process of the present invention the walls o~ upper vessel 1, located above solution inlet 15 i.e. the walls heated by heating coils 4 and 5, are maintained at a temperature that is at least 10C, and especially at least 30C, higher than the temperature o:E the remainder of said walls o~ upper vessel 1. ~ven though it is known that homo-polymers of ethylene and copolymers of ethylene and higher ~-olefins degrade at a faster rate as the temperature of the polymer is increased, the example hereinafter shows -that the use of the higher wall temperatures actually results in a decrease in degraded polymer as measured by -the length oE the periods during which polymer of acceptable gel content is manufactured.
The present invention is illustrated by the follow-ing example.
E~am~le 1 A commercial-scale process for the manufacture of homopolymers of ethy:Lene and copolymers of ethylene and high-er ~-olefins was operated using a pressure reduction system of the type shown in the drawings. When the process was operated with the walls oE upper vessel 1 at the same temper-ature i.e. heating coils 4, 5 and 6 operating at the same temperature, it was found -that the gel content of the polymer obtained normally remained at accep-table levels for abou-t 3 to 4 months, it being necessary to manually clean the vessel ~7hen the gel content of the polymer became unaccept-able. However when the temperature of heating coils 4 and 5 was increased by 50C it was found that the gel content of the polymer obtained normally remained at acceptable levels for about 7 to 10 months. Thus the use of the present inven-;?3~
tion re~ulted in a significant increase in the length o~ the averaye period during which the gel content of the polymer was acceptable.
: 25 . .
SEP~RATION OF POLYMER FROM HYDROCARBON SOLVE~T
IN A PROCESS FOR THE MANUFACTURE OF POLYMERS OF ETHYLENE
The present invention relates to a method for ~he separation of polymer from hydrocarbon solvent in a process for -the manufacture of po:Ly-~-olefins, and especially to an improved method for such separation -that is less susceptib]e to the formation of gel in the polymer.
Polymers of ethylene, for example, homopolymers o:E
ethylene and copolymers of ethylene and higher ~-olefins, are used in lar~é volumes for a wide variety of end uses, for example, in the form o film, fibres, moulded or thermoformed articLes, pipe, coatings and the like. In many of these end-uses it is important that the level of gel in the polymer be at a low level and moreover be consistently at a low level.
As used herein, gel refers to that matter which remains after Soxhlet extraction of polyethylene using xylene as solvent and a 200 Tyler~ mesh wire screen in the extraction apparatus.
Processes Eor the preparation of homopolymers of ethylene and copo:Lymers of ethylene and higher ~-olefins are known. Such proces~es include processes in which the mono-mer.s are polymeri~ed in the presence of a co-ordination catalyst, eor exarnple, a catalyst comprising a compound of a transition metal belonging to Groups IVB-VI~ of the Periodic Table and an organometallic compound of a meta:L belonging to Groups I-IIIA of the Periodic Table.
There are two types of processes for the manufac-ture of polyethylene that involve the polymerization of mono-mers in the presence of a co-ordination catalyst viz. those processes which operate at temperatures below the mel-ting or solubilization temperature of the polymer and those processes which operate at temperatures above the melting or solubili-zation temperature of the polymer. The latter are referred to as "solution" process.
A preferred process for the polymerization of ..~
33~Ei ~-olelns is the high temperature or "solution" polymeri~a-tion process, an exarnple of which is described in Canadian Patent 660 869 o~ A.W. Anderson, E.L. Fallwell and J.M.
Bruce, which issued 1963 April 09. ~n a solution process, the process is operated so that both the monomer and polymer are soluble in the reaction medium.
Solution polymerization processes are operated at pressures above atmospheric pressure. It is necessary, in order to recover polymer, to reduce the pressure to atmos-pheric pressure and to separate the hydrocarbon solvent fromthe polymer. One method of accompLishiny the pressure reduc-tion and polymer separation is to pass a solution of polymer and hydrocarbon solvent, at a temperature above the melting point of the polymer and a pressure above atmospheric pres-sure, through a pressure reduction valve to reduce the pres-sure to substantially atmospheric pressure. As the solution is passed through the pressure reduction valve, solvent is flashed off from the polymer to yive a pol~mer containing relatively minor amounts of solvent, such polymer being in the Eorm of molten polymer. Hc)wever, in such a method some polymer may become entrained in the hydrocarbon solvent being E;Lashed off and may become deposited on the walls of the ve~el being used for separation oE solvent from polymer.
Such deposited polymer is at a temperature abave the melting point o~ the polymer. There is a tendency ~or the deposited polymer to degrade, and hence form gel particles, over a period oE time. The molten polymer in the vessel may become contaminated with such gel pa~rticles especially when degraded polymer separates from the walls of the vessel and becomes admixed with the molten polymer.
An intermediate separator in which the pressure is reduced from the pressure of the polymerization reaction to a lower pressure that is greater than atmospheric pressure may be employed between the reactor and the method used to separ-ate polymer from solvent, as is disclosed in Canadian Patent568 721 of ~.D. Johnson, which issued 1959 January 6.
A method of reducing the tendency for the formation of gel in the separation of polymer from solvent in a so]u-' .:
?33~
tion polymerization process has now been found.
Accordingly, the present invention provides in aprocess Eor the separation, in a solution process for -the manufacture of polymers oE ethylene selected from ~he group consi.sting of homopolymers of ethylene and copolymers of ethylene an~ higher ~-olefins, of a ~olution comprising said pol~ner and inert hydrocarbon sol~ent into fractions compris-ing said polymer and said solvent, said solution being at a tsmperature above 130C and at a pressure above atmospheric pressure, wherein the pressure of said solution is reduced by passing said solution through pressure reduction means and into a substantially vertical elongated vessel, such that the solution passes into the vessel in a downward direction, said polymer forming a pool of moLten polymer below said pressure reduction means and said solvent passing in the form of a vapour ~rom -the top of said vessel, the walls of said vessel being maintained at a tempera-ture above the melting point of the polymer, the improvement comprising maintaining the ~alls oE the vessel in the region above sa.id pressure reduction means at a temperature that is at least 10C higher than the temperature of the remainder of the walls o-f the vessel.
In a preferred embocliment of the process of the present i~vention, khe temperature of the walls above the valve is at least 30C higher than the temperature of the remaincler of the walls.
The present invention is directed to a solution polymerization process for the preparation of high molecular weight polymers of ethylene. ln particular, the polymers are homopolymers of ethylene and copolymers of e-thylene and higher ~-olefins, especially such higher ~-olefins having 3 to 12 carbon atoms, i.e., C3- C12 ~-olefins, including bicyclic ~-olefins, examples of which ~-olefins are butene-l, hexene-l, octene-l, and bicyclo-(2,2,1)-2-heptene. In addi-tion, cyclic endomethylenic dienes may be fed to the process with the e~hylene or mixtures of ethylene and C3- C12 olefin.
In a solution polymerization process monomer(s), a ~33~3 co-ordination catalyst and inert hydrocarbon solvent are fed to a reactor. Co-ordination catalysts Eor solution polymer-ization processes are known, for example, -those described in the a~orementioned Canadian Paten-t 660 869. The monomer may be solely ethy]ene or a mixture or ethylene and one or more of the higher ~-olefins and is dissolved in the reaction solvent.
Solution polymerization processes may be operated at temperatures in the range of about 10~-320C and especial-ly in the range 105-310C. The pressures used in the process of the present invention are those known for solution poly-merization processes, especially in the range of about 4-25MPa. The pressure and temperature are controlled so that both the unreac-ted monomers and the polymer formed remain in solution, a requirement of a solution polymerization process.
The hydrocarbon solven~ used in the polymerization process is a hydrocarbon solvent that is inert with respect to the co-ordination catalyst. Such solvents are known and inc:Lude hexane, heptane, octane, cyclohexane, methylcyclohe~-ane and hydrogenated naphtha. The solvent used in the poly-merization process is preferably used in the preparation of the co-ordination catalyst. The hydrocarbon solvent is the rnajor component of the polymerization rnixture fed to the reactor, usually comprisin~ at least 75% of the reaction mixture.
The mixture that exits from the polymerization reactor comprises polymer, unreacted monomer, co-ordination catalyst, some of which remains in an active state, and hydrocarbon solvent. The polymerization reac-tion in a solu-tion polymerization process is normally terminated by addi-tion o~ a so-callad "deactivator", for example, a fatty acid, an alcohol or an al~aline earth metal/carboxylic acid salt.
The deactivator is admixed with hydrocarbon solvent, normally the solvent of the polymerization process, and fed into the polymerization mixture, usually shortly after that mixture passes from the reactor. The polymerization mixture tha-t has been treated with deactivator contains catalyst residues which may be removed by contacting the mixture with an adsor-.~
~33~
bent, for e~ample, alumina. Such a deactivation and catalyst removal process is described in Canadian Pa-tent 732 279 of B.B. Baker, K.M. Brauner and A.N. Oemler, which issued 1966 April 12.
Subsequently, the polymerization mixture is sub-jec-ted to one or more steps to reduce the temperature and pressure o the polymerization mixture to atmospheric pres-sure and temperature. In a solution polymerization process this is normally done by first reducing the pressure to atmospheric pressure in one or more steps and subsequently cooling the molten polymer until it solidifies, usually in the form of pellets. A method for reducing the pressure in the process that may be used, in part, is that described in the aforementioned Patent 568 721.
The present invention will be further exemplified with reference to the following drawings:
Fig. 1 is a schematic representa-tion of apparatus for the separation of polymer from solvent, and ~ig. 2 is a cross-section of the apparatus o Fig. 1.
Referring to Fig. 1, the apparatus used in conjunc-tion with a process of the present invention comprises an upper vessel 1 and a lower vessel 2. Both upper vessel 1 and lower vessel 2 are elongated vessels with upper vessel 1 be-ing located above lower vessel 2. Upper vessel 1 and lower vessel 2 are joined at sieve plate 3, sieve plate 3 being adapted to pass molten polymer. Upper vessel 1 has heating coils 4, 5, and 6 passing around the vessel. Heating coil 4 spirals around the upper portion of upper vessel 1 a plurali-ty of times in order that that portion of upper vessel 1 may be heated in a controlled manner. Similarly heating coils 5 and 6 spiral around the middle and lower portions, respec-tively, of upper vessel 1. In addition heating coil 7 spirals around lower vessel 2 a plurality of times in order that that vessel may be heated in a controlled and uniform manner. Upper vessel 1 and lower vessel 2, together with heating coils 4-7, are insulated by means not shown. Each of heating coils ~, 5, 6, and 7 is connected to a source oE
)33~
6~eam through s-team pipes 9, 10, 11 and 12 respec-tively.
Solution inlet 15 is located in upper vessel 1.
~s is shown in Figure 1, heating coils 4 and 5 are located at and above solution inle-t 15. Heating coils 4 and 5 are both located above melt pool 16 (see Fig. 2). Each of heat-ing coils 4, 5, 6 and 7 has an outlet (not shown) for removal of condensate from the steam-heated coils.
Vapour outlet 13 is located in -the upper portion oE
upper vessel 1 and polymer outlet 14 is :Located at the bottom of lower vessel 2.
Referring to Fig. 2, solution inlet 15 passes into upper vessel 1 to a position that is axiall~ located within upper vessel 1. The outLe-t of solution inlet 15 i.e. nozzle 20 of a pressure reduction valve ~not shown), is adapted to axially discharge solution passing therethrough in a downward direction into upper vessel 1. A melt pool 16 is located below the outlet oE solution inlet 15 and above sieve plate 3, melt pool 16 being spaced apart from said outlet.
The pressure reduction means may comprise a pres-~0 sure reduction valve Located within upper ve~sel 1 or, pref-erably, a pressure reduction valve located outside upper ves~el 1 in fluid-flow relationship with nozzle 20 which is located within upper vessel 1 and adopted to discharge so:Lution in a downward direction.
~lthough the present invention has been particular-ly described with reference to ~he use of heating coils to heat and control the temperature o~ the vessels, it will be understood by those skilled in the art -that other heating and control means may be used e.g. heating jackets, electric coils and the like.
In operation a solution of polymer in solvent passes through solution inlet 15 and is discharged from noz-zle 20 into upper vessel 1. The solvent is flashed off and the vapour thereof passed through vapour outlet 13 to a con denser (not shown). The polymer forms melt pool 16. The polymer of melt pool 16 flows through sieve plate 3, forming polymer s-trands 17 which fall into mel-t pool 18 in the bottom of lower vessel 2. ~he polymer o~ melt pool 18 passes through . .
~2~33~3 pol~mer outlet 1~ to, for e~ample, an extruder (not shown) adapked to forrn sald polymer into solid pellets of polymer.
As -the solvent i5 flashed of~ from the solution oE
polymer in solvent, polymer may becom~ entrained in the sol-vent vapour. Such entrained polymer may in turn become deposited on the walls of upper vessel 1, especially said walls located a'oove solution inlet 15. Such deposited poly-mer 19 is shown in Fig. 2.
In the process of the present invention the walls o~ upper vessel 1, located above solution inlet 15 i.e. the walls heated by heating coils 4 and 5, are maintained at a temperature that is at least 10C, and especially at least 30C, higher than the temperature o:E the remainder of said walls o~ upper vessel 1. ~ven though it is known that homo-polymers of ethylene and copolymers of ethylene and higher ~-olefins degrade at a faster rate as the temperature of the polymer is increased, the example hereinafter shows -that the use of the higher wall temperatures actually results in a decrease in degraded polymer as measured by -the length oE the periods during which polymer of acceptable gel content is manufactured.
The present invention is illustrated by the follow-ing example.
E~am~le 1 A commercial-scale process for the manufacture of homopolymers of ethy:Lene and copolymers of ethylene and high-er ~-olefins was operated using a pressure reduction system of the type shown in the drawings. When the process was operated with the walls oE upper vessel 1 at the same temper-ature i.e. heating coils 4, 5 and 6 operating at the same temperature, it was found -that the gel content of the polymer obtained normally remained at accep-table levels for abou-t 3 to 4 months, it being necessary to manually clean the vessel ~7hen the gel content of the polymer became unaccept-able. However when the temperature of heating coils 4 and 5 was increased by 50C it was found that the gel content of the polymer obtained normally remained at acceptable levels for about 7 to 10 months. Thus the use of the present inven-;?3~
tion re~ulted in a significant increase in the length o~ the averaye period during which the gel content of the polymer was acceptable.
: 25 . .
Claims (6)
1. In a process for the separation, in a solution process for the manufacture of polymers of ethylene selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and higher .alpha.-olefins, of a solution comprising .alpha.-olefin polymer and inert hydrocarbon solvent into fractions comprising said polymer and said solvent, said solution being at a temperature above 130°C and at a pressure above atmospheric pressure, wherein the pressure of said solution is reduced by passing said solution through pressure reduction means and into a substantially vertical elongated vessel, such that the solution passes into the vessel in a downward direction, said polymer forming a pool of molten polymer below said pressure reduction means and said solvent passing in a form of a vapour from the top of said vessel, the walls of said vessel being maintained at a temperature above the melting point of the polymer, the improvement comprising maintaining the walls of the vessel in the region above said pressure reduction means at a temperature that is at least 10°C higher than the temperature of the remainder of the walls of the vessel.
2. The process of Claim 1 in which the temperature of the walls above the valve is at least 30°C higher than the temperature of the remainder of the walls.
3. The process of Claim 3 in which the polymer is a homopolymer of ethylene.
4. The process of Claim 3 in which the polymer is a copolymer of ethylene and higher .alpha.-olefin.
5. The process of Claim 1 or Claim 2 in which the hydrocarbon solvent is hexane or cyclohexane.
6. The process of Claim 3 or Claim 4 in which the hydrocarbon solvent is hexane or cyclohexane.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000422287A CA1203348A (en) | 1983-02-24 | 1983-02-24 | Separation of polymer from hydrocarbon solvent in a process for the manufacture of polymers of ethylene |
| US06/837,162 US4673768A (en) | 1983-02-24 | 1986-03-07 | Separation of polymer from hydrocarbon solvent in the manufacture of polymers of ethylene |
| AU54479/86A AU577182B2 (en) | 1983-02-24 | 1986-03-07 | Solvent separation from ethylene polymers |
| JP61051575A JPH0674289B2 (en) | 1983-02-24 | 1986-03-11 | Separation of polymer from hydrocarbon solvent in a method for producing ethylene polymer |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000422287A CA1203348A (en) | 1983-02-24 | 1983-02-24 | Separation of polymer from hydrocarbon solvent in a process for the manufacture of polymers of ethylene |
| EP86301542A EP0235421A1 (en) | 1986-03-05 | 1986-03-05 | Separation of polymer from hydrocarbon solvent in a process for the manufacture of polymers of ethylene |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1203348A true CA1203348A (en) | 1986-04-15 |
Family
ID=25669950
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000422287A Expired CA1203348A (en) | 1983-02-24 | 1983-02-24 | Separation of polymer from hydrocarbon solvent in a process for the manufacture of polymers of ethylene |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1203348A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011008955A1 (en) | 2009-07-16 | 2011-01-20 | Dow Global Technologies Inc. | Polymerization process for olefin-based polymers |
| WO2012088235A2 (en) | 2010-12-21 | 2012-06-28 | Dow Global Technologies Llc | Olefin-based polymers and dispersion polymerizations |
-
1983
- 1983-02-24 CA CA000422287A patent/CA1203348A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011008955A1 (en) | 2009-07-16 | 2011-01-20 | Dow Global Technologies Inc. | Polymerization process for olefin-based polymers |
| EP2738182A1 (en) | 2009-07-16 | 2014-06-04 | Dow Global Technologies LLC | Polymerization process for olefin-based polymers |
| WO2012088235A2 (en) | 2010-12-21 | 2012-06-28 | Dow Global Technologies Llc | Olefin-based polymers and dispersion polymerizations |
| US9388254B2 (en) | 2010-12-21 | 2016-07-12 | Dow Global Technologies Llc | Olefin-based polymers and dispersion polymerizations |
| EP3091038A1 (en) | 2010-12-21 | 2016-11-09 | Dow Global Technologies LLC | Olefin-based polymers and dispersion polymerizations |
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