CA2010850C - Process for separating volatile components from reaction mixtures obtained through high-pressure polymerization - Google Patents
Process for separating volatile components from reaction mixtures obtained through high-pressure polymerizationInfo
- Publication number
- CA2010850C CA2010850C CA002010850A CA2010850A CA2010850C CA 2010850 C CA2010850 C CA 2010850C CA 002010850 A CA002010850 A CA 002010850A CA 2010850 A CA2010850 A CA 2010850A CA 2010850 C CA2010850 C CA 2010850C
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- Prior art keywords
- ethylene
- pressure
- melt
- mpa
- polymer
- Prior art date
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Links
- 238000000034 method Methods 0.000 title claims abstract description 42
- 238000006116 polymerization reaction Methods 0.000 title claims description 21
- 239000011541 reaction mixture Substances 0.000 title description 5
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 claims abstract description 57
- 239000005977 Ethylene Substances 0.000 claims abstract description 57
- 229920000642 polymer Polymers 0.000 claims abstract description 38
- 239000000155 melt Substances 0.000 claims abstract description 23
- 150000001875 compounds Chemical class 0.000 claims abstract description 9
- 238000000926 separation method Methods 0.000 claims abstract description 9
- 238000007334 copolymerization reaction Methods 0.000 claims abstract description 7
- 239000000203 mixture Substances 0.000 claims description 4
- 239000007789 gas Substances 0.000 description 13
- XTXRWKRVRITETP-UHFFFAOYSA-N Vinyl acetate Chemical compound CC(=O)OC=C XTXRWKRVRITETP-UHFFFAOYSA-N 0.000 description 12
- 239000000047 product Substances 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 3
- 150000003384 small molecules Chemical class 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 150000001336 alkenes Chemical class 0.000 description 2
- CUZMQPZYCDIHQL-VCTVXEGHSA-L calcium;(2s)-1-[(2s)-3-[(2r)-2-(cyclohexanecarbonylamino)propanoyl]sulfanyl-2-methylpropanoyl]pyrrolidine-2-carboxylate Chemical compound [Ca+2].N([C@H](C)C(=O)SC[C@@H](C)C(=O)N1[C@@H](CCC1)C([O-])=O)C(=O)C1CCCCC1.N([C@H](C)C(=O)SC[C@@H](C)C(=O)N1[C@@H](CCC1)C([O-])=O)C(=O)C1CCCCC1 CUZMQPZYCDIHQL-VCTVXEGHSA-L 0.000 description 2
- 239000003999 initiator Substances 0.000 description 2
- 239000000178 monomer Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 239000004698 Polyethylene Substances 0.000 description 1
- 238000013019 agitation Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001735 carboxylic acids Chemical class 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000007859 condensation product Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000011872 intimate mixture Substances 0.000 description 1
- 239000012263 liquid product Substances 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 235000019645 odor Nutrition 0.000 description 1
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- -1 polyethylenes Polymers 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000005201 scrubbing Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 229920001567 vinyl ester resin Polymers 0.000 description 1
- 125000000391 vinyl group Chemical group [H]C([*])=C([H])[H] 0.000 description 1
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
- C08F6/26—Treatment of polymers prepared in bulk also solid polymers or polymer melts
- C08F6/28—Purification
Landscapes
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
Separation of volatile components from the polymer melts formed during the homopolymerization of ethylene or the copolymerization of ethylene with other copolymerizable compounds at elevated pressures and elevated temperatures by countercurrent treatment with ethylene. Superior separations are obtained by the process.
Description
2~
A Process for Separating Volatile Components from Reaction Mixtures Obtained through High~pressure Polymerization The invention relates to a process for separating volatile components from polymer melts which are obtained from the polymerization of ethylene and the copolymerization of ethylene with other copolymerizable compounds under high pressure.
BAC~GROUND OF THE INVENTION
The radical high~pressure polymerization of ethylene alone or together with comonomers is performed on a commercial scale in tubular reactors or in autoclaves with agitation at pressures of 50 to 400 MPa, in particular 140 to 250 MPa, and temperatures of 100 to 400C.
A diagram of the process is shown in Figure 1.
Fresh ethylene is first fed into low~pressure compressor 8 via line 9, compressed to 10 to 35 MPa and then, together with the unreacted ethylene from the polymerization stage and which is recycled, it is raised to the reaction pressure in a high~pressure compressor 5. With the aid of suitable pumping equipment, e.g, piston pumps, the initiators present in solution are mixed into the compressed ethylene or metered into the reactor directly.
2 20~850 Comonomers such as vinyl esters, olefinically unsaturated carboxylic acids, or alpha~olefins are also fed into the high~pressure compressor 5 via feed line 10.
In reactor 1 between 10 and 45 % by weight of the monomers entering the reactor are reacted in one run. The polymer is precipitated in high-pressure separator 3 by reducing the pressure on the mixture to 5 to 50 MPa, preferably 10 to 35 MPa, after optional cooling in cooler 2. During pressure~relief, the gaseous components released are returned to the high~pressure compressor 5 via high~pressure return gas system 4. The polymer, which contains dissolved unreacted monomers, is pressure~relieved via a system consisting of low~pressure separator 6 and low~pressure cooler 7. The low-molecular weight compounds released are returned via the low~pressure compressor g to the high~pressure compressor 5. The polymer precipitated in the low-pressure separator 6 contains not only residual amounts of ethylene and comonomers but also oligomers.
Even when the polymerization products are separated carefully, it is impossible to avoid volatile admixtures such as comonomers, their decomposition products, and other low~molecular weight compounds being retained in the polymers. During storage and processing of the polymers, these residues lead to undesirable emissions and odors; in addition, the flame point of the polymers is considerably reduced. Therefore, efforts are made to insure that the products are free of volatile compounds by taldng suitable measures during the plessule-relieving process and by subjecting the polymer to an additional tre~tm~-nt Further difficulties are caused by the fact that the ethylene liberated in the low-ple~ulc sepal~or contains comonomers, oligomers, and other compounds which 5 condense out when the sepal~ed ethylene is recycled, forming deposits in the colllplcssors and pumps which can lead to clogging.
According to a process described in DD-PS 131 824, issued July 26, 1978, either the reaction ~ lure is brought into contact intensively with the ethylene downstream of the polymP.ri7~tion reactor or the polymer melt is brought into contact 10 intensively with the ethylene after separation of the majority of the unreacted gas llli~lurc in a pressure stage and the llli~lure is then sep~ t-0A in a stabilizing zone.
According to an al)pr~liate embodiment of this process, the reaction l~ lurc is fed c~unlel-;ullelllly into a widening tube, ethylene also being ~im~llt~n~ously introduced and the Illi~lurc thus formed is separated in the low-pressure sepal~tor.
Another procedure for high-plcs~ulc polymeri7~tion of ethylene is disclosed in the DE-AS 21 31 145, issued January 14, 1982. It mixes the reaction Illi~.lulc coming from the reaction zone with the fresh ethylene feed and the recycled ethylene coming from the low-pres~.lre sep~tor.
JJ: ~l . 3 A~
``_ 20 1 0850 Both processes lead only to a slight reduction in the concentration of low-molecular weight ad~ Lures in the polymer. Moreover, additional appa,~tus is required for their pt;lÇol",al~ce.
It is also known that unreacted gas origin~ting from the low-pres~ure S sep~lor can be recycled to the high-plt;s~u~ cycle with the aid of an injector (cf. DD-PS 202 882, issued October 5, 1983). However, this process does not reduce the concentration of the low-molecular components re~ inillg in the product.
With liquid products, the low-molecular weight compounds can be sepal~led by gas scrubbing with nitrogen or other inert gaseous substances. However, 10 additional appa-~lus is also required for this process and the sep~r~ted co",~onents cannot be returned without çl~ning.
BRIEF DESCRIPIION OF THE INVENTION
Therefore, the problem was to develop a process which avoids the disadvantages described above, guarantees nearly complete removal of the volatile 15 co,.,~nents from the polymer melt, and insures that little or no condensed conll?ollents are contained in the cycle gas of the low-pressure stage.
JJ: 4 The invention consists in a process for separating volatile components from polymer melts formed during the homopolymerization of ethylene or the copolymerization of ethylene with other copolymerizable compounds at elevated pressures and elevated temperatures. It is characterized in that ethylene is passed in countercurrent flow through the melt at pressures of 5 to 70 MPa and a temperature in the melt of at least approximately 120C.
Surprisingly, with the new process it is possible to almost completely remove the volatile components contained in the polymer melt formed during high-pressure polymerization. Further cleaning, e.g. in the extruder or during storage of the product, is not necessary. The concentration of the low~molecular components in the recycled ethylene is reduced until condensation products do not form during the compression of the ethylene and product losses are avoided.
The claimed procedure can be performed with different polymerizations and copolymerizations o~
ethylene using the high-pressure process, in both tubular reactors and autoclaves. It can be used both with solvent and solvent~free processes, and also with processes for the preparation of linear low~density polyethylenes (LLDPE).
Volatile components contained in the polymer melt are understood to be low~molecular weight compounds which are contained in the polymerization products, e.g. as comonomers, decomposition products of comonomers, and oligomers. Thus, for example, in the preparation of copolymers of ethylene and vinyl acetate, acetic acid formed by the decomposition of vinyl acetate is to be found in the products. Furthermore, volatile compounds include solvents which, for example, enter the reaction mixture with initiators and molecular mass regulators.
Lubricants and other auxiliaries, which are required to operate the polymerization plant, also are present in the polymer melt.
According to the claimed process, the polymer melt is treated at elevated pressure, preferably at 5 to 70 ~Pa and in particular at 10 to 40 MPa. It is not necessary to provide a separate reactor for treatment; it can be successfully performed in the polymer separator of a high~pressure polymerization plant. It is expedient to remove most of the unreacted gas mixture by reducing the pressure to the above~mentioned range and then bringing the melt into contact with the ethylene. The high~pressure separator used in the polymerization process is particularly suitable for this purpose.
~ 2010850 To insure that the volatile components are separated either completely or nearly completely from the melt, it is necessary to maintain a temperature of at least 120C therein. It has proved particularly valuable to treat the ethylene at temperatures above approximately 150C. The higher the temperature, the more completely the volatile substances are separated.
The only upper limit for the treatment temperature is the temperature at which the melt from the polymerization enters the chamber where the volatile substances are separated.
In order to guarantee as high a temperature as possible in the melt, it is expedient to pass heated ethylene in countercurrent flow to the melt. It is important to the claimed procedure that the ethylene and melt flow in opposing directions when they meet each other. This insures an extremely intimate mixture of melt and olefin.
The effectiveness of the ethylene stream can be further increased by forcefully diverting it from a straight path in the chamber where the melt is treated.
In this manner, fresh ethylene is passed several times through the precipitated product. The ethylene is diverted by means of suitable installations in the reactor, in the simplest case by plates which are located on opposite sides thereof and in staggered formation.
- 8- 201~850 The amount of ethylene required for treating the polymer melt depends on the temperature, the viscosity, and the comonomer content of the melt. The required amount of ethylene increases with the viscosity and the comonomer content and decreases with increasing temperature. In general, 0.1 to 2 parts by weight of ethylene are used per one part by weight of melt.
Pure ethylene can be used to separate the volatile components from the melt. It is compressed in the low~pressure compressor and fed into the polymer melt in the high~pressure separator. The ethylene charged with the volatile components of the melt is passed through the high~pressure gas system and then, after separation of the volatile components, is fed via a partial stream to the inlet side of the high pressure compressor and on into the polymerization reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, constituting a part hereof and in which like reference characters indicate like parts, Figure l is a flow diagram of a prior art process;
~ 9 _ 20~C~8S0 Figure 2 is a flow diagram of the process of the present invention; and Figure 3 is a schematic view of the high pressure separator of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
A diagram of the claimed process is shown in Figure 2. Fresh ethylene from pipe 19 is compressed in low~pressure compressor 18 to 10 to 35 MPa, heated in heating device 22 to at least 120C and passed through line 21 into high~pressure separator 13. There it meets the polymer flowing in the countercurrent direction.
Charged with volatile, low~molecular weight components of the polymer melt, the ethylene enters a high~pressure gas recycling system. The low molecular components such as solvent, lubrication oil, and oligomers are separated by means of pressure-relieving device 23 and line 24. The ethylene, optionally containing comonomers which can be replenished via line 20, is fed to high~pressure compressor 15 and then to reactor 11. The polymer is separated at a pressure of 5 to 70 MPa in high~pressure separator 13, after it has been cooled in cooler 12, if necessary. The gaseous parts enter high~pressure gas recycling system 14 together with the fresh ethylene passed in the countercurrent direction.
201(~850 The polymer is pressure~relieved via low-pressure separator 16 and low-pressure cooler 17; the liberated low-molecular weight compounds are compressed in the low~pressure compressor together with fresh ethylene from line 19.
Figure 3 shows separator 13 with baffles 25 where the polymer is treated with ethylene. The melt enters into the separator through line 27 and the ethylene through line 21. The melt leaves the separator through line 29 and the ethylene charged with volatile components from the melt through line 30.
The new process is explained in the following examples which are intended to be illustrative, not limitative.
Example 1 A reaction mixture obtained from the polymerization of 720 parts by weight of ethylene and 280 parts by weight of vinyl acetate, and which has a percentage of 32.9 % by weight of polymer, is fed into a high~pressure separator without baffles. The polymer is precipitated and can be drawn off via a bottom valve.
Countercurrent to the polymer, 250 parts of ethylene are introduced and withdrawn from the head together with the low-molecular weight components of the melt. The treated polymer contains 0.62 % by weight of monomeric vinyl acetate, and the vinyl acetate concentration of the low-pressure gas cycle is 12.5 % by volume.
20~0850 Example 2 (Comparison) The same procedure as in Example 1 is carried out, except that the ethylene is not fed into the high~pressure separator but is passed directly to the high-pressure compressor in known manner. The polymer contains 2 % by weight of monomeric vinyl acetate, and the vinyl acetate concentration in the low~pressure gas cycle is more than 40 ~ by volume.
Example 3 A reaction mixture obtained from the polymerization of 720 parts by weight of ethylene and 2~0 parts by weight of vinyl acetate, and which has a percentage of 33 % by weight of polymer, is fed into a high~pressure separator with baffles according to Figure 3. The polymer is precipitated and can be drawn off via the bottom valve.
Countercurrent to the polymer, 260 parts of ethylene are introduced and withdrawn from the head together with low~molecular weight components of the melt. The treated polymer contains 0.33 % by weight of monomeric vinyl acetate, and the vinyl acetate concentration in the low~pressure gas cycle is 4.4 ~ by volume.
~ _ 20iO850 Example 4 (Comparison) The procedure of Example 3 is followed except that the ethylene is not fed into the high-pressure separator, but is passed directly to the high~pressure compressor in known manner. The polymer contains 1.1 % by weight of vinyl acetate, and the vinyl acetate concentration in the low~pressure gas cycle is 33 % by volume.
The viscosity of the polymers prepared according to Examples 1 to 4 is the same and is 250 mPa x sec at 140C.
A Process for Separating Volatile Components from Reaction Mixtures Obtained through High~pressure Polymerization The invention relates to a process for separating volatile components from polymer melts which are obtained from the polymerization of ethylene and the copolymerization of ethylene with other copolymerizable compounds under high pressure.
BAC~GROUND OF THE INVENTION
The radical high~pressure polymerization of ethylene alone or together with comonomers is performed on a commercial scale in tubular reactors or in autoclaves with agitation at pressures of 50 to 400 MPa, in particular 140 to 250 MPa, and temperatures of 100 to 400C.
A diagram of the process is shown in Figure 1.
Fresh ethylene is first fed into low~pressure compressor 8 via line 9, compressed to 10 to 35 MPa and then, together with the unreacted ethylene from the polymerization stage and which is recycled, it is raised to the reaction pressure in a high~pressure compressor 5. With the aid of suitable pumping equipment, e.g, piston pumps, the initiators present in solution are mixed into the compressed ethylene or metered into the reactor directly.
2 20~850 Comonomers such as vinyl esters, olefinically unsaturated carboxylic acids, or alpha~olefins are also fed into the high~pressure compressor 5 via feed line 10.
In reactor 1 between 10 and 45 % by weight of the monomers entering the reactor are reacted in one run. The polymer is precipitated in high-pressure separator 3 by reducing the pressure on the mixture to 5 to 50 MPa, preferably 10 to 35 MPa, after optional cooling in cooler 2. During pressure~relief, the gaseous components released are returned to the high~pressure compressor 5 via high~pressure return gas system 4. The polymer, which contains dissolved unreacted monomers, is pressure~relieved via a system consisting of low~pressure separator 6 and low~pressure cooler 7. The low-molecular weight compounds released are returned via the low~pressure compressor g to the high~pressure compressor 5. The polymer precipitated in the low-pressure separator 6 contains not only residual amounts of ethylene and comonomers but also oligomers.
Even when the polymerization products are separated carefully, it is impossible to avoid volatile admixtures such as comonomers, their decomposition products, and other low~molecular weight compounds being retained in the polymers. During storage and processing of the polymers, these residues lead to undesirable emissions and odors; in addition, the flame point of the polymers is considerably reduced. Therefore, efforts are made to insure that the products are free of volatile compounds by taldng suitable measures during the plessule-relieving process and by subjecting the polymer to an additional tre~tm~-nt Further difficulties are caused by the fact that the ethylene liberated in the low-ple~ulc sepal~or contains comonomers, oligomers, and other compounds which 5 condense out when the sepal~ed ethylene is recycled, forming deposits in the colllplcssors and pumps which can lead to clogging.
According to a process described in DD-PS 131 824, issued July 26, 1978, either the reaction ~ lure is brought into contact intensively with the ethylene downstream of the polymP.ri7~tion reactor or the polymer melt is brought into contact 10 intensively with the ethylene after separation of the majority of the unreacted gas llli~lurc in a pressure stage and the llli~lure is then sep~ t-0A in a stabilizing zone.
According to an al)pr~liate embodiment of this process, the reaction l~ lurc is fed c~unlel-;ullelllly into a widening tube, ethylene also being ~im~llt~n~ously introduced and the Illi~lurc thus formed is separated in the low-pressure sepal~tor.
Another procedure for high-plcs~ulc polymeri7~tion of ethylene is disclosed in the DE-AS 21 31 145, issued January 14, 1982. It mixes the reaction Illi~.lulc coming from the reaction zone with the fresh ethylene feed and the recycled ethylene coming from the low-pres~.lre sep~tor.
JJ: ~l . 3 A~
``_ 20 1 0850 Both processes lead only to a slight reduction in the concentration of low-molecular weight ad~ Lures in the polymer. Moreover, additional appa,~tus is required for their pt;lÇol",al~ce.
It is also known that unreacted gas origin~ting from the low-pres~ure S sep~lor can be recycled to the high-plt;s~u~ cycle with the aid of an injector (cf. DD-PS 202 882, issued October 5, 1983). However, this process does not reduce the concentration of the low-molecular components re~ inillg in the product.
With liquid products, the low-molecular weight compounds can be sepal~led by gas scrubbing with nitrogen or other inert gaseous substances. However, 10 additional appa-~lus is also required for this process and the sep~r~ted co",~onents cannot be returned without çl~ning.
BRIEF DESCRIPIION OF THE INVENTION
Therefore, the problem was to develop a process which avoids the disadvantages described above, guarantees nearly complete removal of the volatile 15 co,.,~nents from the polymer melt, and insures that little or no condensed conll?ollents are contained in the cycle gas of the low-pressure stage.
JJ: 4 The invention consists in a process for separating volatile components from polymer melts formed during the homopolymerization of ethylene or the copolymerization of ethylene with other copolymerizable compounds at elevated pressures and elevated temperatures. It is characterized in that ethylene is passed in countercurrent flow through the melt at pressures of 5 to 70 MPa and a temperature in the melt of at least approximately 120C.
Surprisingly, with the new process it is possible to almost completely remove the volatile components contained in the polymer melt formed during high-pressure polymerization. Further cleaning, e.g. in the extruder or during storage of the product, is not necessary. The concentration of the low~molecular components in the recycled ethylene is reduced until condensation products do not form during the compression of the ethylene and product losses are avoided.
The claimed procedure can be performed with different polymerizations and copolymerizations o~
ethylene using the high-pressure process, in both tubular reactors and autoclaves. It can be used both with solvent and solvent~free processes, and also with processes for the preparation of linear low~density polyethylenes (LLDPE).
Volatile components contained in the polymer melt are understood to be low~molecular weight compounds which are contained in the polymerization products, e.g. as comonomers, decomposition products of comonomers, and oligomers. Thus, for example, in the preparation of copolymers of ethylene and vinyl acetate, acetic acid formed by the decomposition of vinyl acetate is to be found in the products. Furthermore, volatile compounds include solvents which, for example, enter the reaction mixture with initiators and molecular mass regulators.
Lubricants and other auxiliaries, which are required to operate the polymerization plant, also are present in the polymer melt.
According to the claimed process, the polymer melt is treated at elevated pressure, preferably at 5 to 70 ~Pa and in particular at 10 to 40 MPa. It is not necessary to provide a separate reactor for treatment; it can be successfully performed in the polymer separator of a high~pressure polymerization plant. It is expedient to remove most of the unreacted gas mixture by reducing the pressure to the above~mentioned range and then bringing the melt into contact with the ethylene. The high~pressure separator used in the polymerization process is particularly suitable for this purpose.
~ 2010850 To insure that the volatile components are separated either completely or nearly completely from the melt, it is necessary to maintain a temperature of at least 120C therein. It has proved particularly valuable to treat the ethylene at temperatures above approximately 150C. The higher the temperature, the more completely the volatile substances are separated.
The only upper limit for the treatment temperature is the temperature at which the melt from the polymerization enters the chamber where the volatile substances are separated.
In order to guarantee as high a temperature as possible in the melt, it is expedient to pass heated ethylene in countercurrent flow to the melt. It is important to the claimed procedure that the ethylene and melt flow in opposing directions when they meet each other. This insures an extremely intimate mixture of melt and olefin.
The effectiveness of the ethylene stream can be further increased by forcefully diverting it from a straight path in the chamber where the melt is treated.
In this manner, fresh ethylene is passed several times through the precipitated product. The ethylene is diverted by means of suitable installations in the reactor, in the simplest case by plates which are located on opposite sides thereof and in staggered formation.
- 8- 201~850 The amount of ethylene required for treating the polymer melt depends on the temperature, the viscosity, and the comonomer content of the melt. The required amount of ethylene increases with the viscosity and the comonomer content and decreases with increasing temperature. In general, 0.1 to 2 parts by weight of ethylene are used per one part by weight of melt.
Pure ethylene can be used to separate the volatile components from the melt. It is compressed in the low~pressure compressor and fed into the polymer melt in the high~pressure separator. The ethylene charged with the volatile components of the melt is passed through the high~pressure gas system and then, after separation of the volatile components, is fed via a partial stream to the inlet side of the high pressure compressor and on into the polymerization reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, constituting a part hereof and in which like reference characters indicate like parts, Figure l is a flow diagram of a prior art process;
~ 9 _ 20~C~8S0 Figure 2 is a flow diagram of the process of the present invention; and Figure 3 is a schematic view of the high pressure separator of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
A diagram of the claimed process is shown in Figure 2. Fresh ethylene from pipe 19 is compressed in low~pressure compressor 18 to 10 to 35 MPa, heated in heating device 22 to at least 120C and passed through line 21 into high~pressure separator 13. There it meets the polymer flowing in the countercurrent direction.
Charged with volatile, low~molecular weight components of the polymer melt, the ethylene enters a high~pressure gas recycling system. The low molecular components such as solvent, lubrication oil, and oligomers are separated by means of pressure-relieving device 23 and line 24. The ethylene, optionally containing comonomers which can be replenished via line 20, is fed to high~pressure compressor 15 and then to reactor 11. The polymer is separated at a pressure of 5 to 70 MPa in high~pressure separator 13, after it has been cooled in cooler 12, if necessary. The gaseous parts enter high~pressure gas recycling system 14 together with the fresh ethylene passed in the countercurrent direction.
201(~850 The polymer is pressure~relieved via low-pressure separator 16 and low-pressure cooler 17; the liberated low-molecular weight compounds are compressed in the low~pressure compressor together with fresh ethylene from line 19.
Figure 3 shows separator 13 with baffles 25 where the polymer is treated with ethylene. The melt enters into the separator through line 27 and the ethylene through line 21. The melt leaves the separator through line 29 and the ethylene charged with volatile components from the melt through line 30.
The new process is explained in the following examples which are intended to be illustrative, not limitative.
Example 1 A reaction mixture obtained from the polymerization of 720 parts by weight of ethylene and 280 parts by weight of vinyl acetate, and which has a percentage of 32.9 % by weight of polymer, is fed into a high~pressure separator without baffles. The polymer is precipitated and can be drawn off via a bottom valve.
Countercurrent to the polymer, 250 parts of ethylene are introduced and withdrawn from the head together with the low-molecular weight components of the melt. The treated polymer contains 0.62 % by weight of monomeric vinyl acetate, and the vinyl acetate concentration of the low-pressure gas cycle is 12.5 % by volume.
20~0850 Example 2 (Comparison) The same procedure as in Example 1 is carried out, except that the ethylene is not fed into the high~pressure separator but is passed directly to the high-pressure compressor in known manner. The polymer contains 2 % by weight of monomeric vinyl acetate, and the vinyl acetate concentration in the low~pressure gas cycle is more than 40 ~ by volume.
Example 3 A reaction mixture obtained from the polymerization of 720 parts by weight of ethylene and 2~0 parts by weight of vinyl acetate, and which has a percentage of 33 % by weight of polymer, is fed into a high~pressure separator with baffles according to Figure 3. The polymer is precipitated and can be drawn off via the bottom valve.
Countercurrent to the polymer, 260 parts of ethylene are introduced and withdrawn from the head together with low~molecular weight components of the melt. The treated polymer contains 0.33 % by weight of monomeric vinyl acetate, and the vinyl acetate concentration in the low~pressure gas cycle is 4.4 ~ by volume.
~ _ 20iO850 Example 4 (Comparison) The procedure of Example 3 is followed except that the ethylene is not fed into the high-pressure separator, but is passed directly to the high~pressure compressor in known manner. The polymer contains 1.1 % by weight of vinyl acetate, and the vinyl acetate concentration in the low~pressure gas cycle is 33 % by volume.
The viscosity of the polymers prepared according to Examples 1 to 4 is the same and is 250 mPa x sec at 140C.
Claims (15)
1. The process for the separation of volatile components from polymer melts formed during the homopolymerization of ethylene or the copolymerization of ethylene with other copolymerizable compounds at elevated pressures and elevated temperatures, wherein a ratio of ethylene is passed countercurrently to said melts at a separation pressure of about 5 to about 70 MPa and a melt temperature of at least about 120°C.
2. The process of Claim 1 wherein said pressure is about 10 to about 40 MPa.
3. The process of Claim 1 wherein said separation takes place in a polymer separator of a high-pressure polymerization plant.
4. The process of Claim 1 wherein said homopolymerization or said copolymerization is carried out at a polymerization pressure of about 50 to 400 MPa and said polymerization pressure is thereafter reduced to said separation pressure of about 5 to 70 MPa before said ethylene contacts said melt, whereby a portion of unreacted gas mixture present is removed from said melt.
5. The process of Claim 4 wherein said portion is a majority of said mixture.
6. The process of Claim 4 wherein said separation pressure is about 10 to 40 MPa.
7. The process of Claim 1 wherein said melt temperatures are above about 150°C.
8. The process of Claim 4 wherein said polymerization pressure is 140 to 250 MPa.
9. The process of Claim 1 wherein said melts are cooled after said homopolymerization or said copolymerization and before said polymerization pressure is reduced.
10. The process of Claim 1 wherein said ratio is 0.1 to 2.0 parts by weight of said ethylene to 1 part by weight of said melt.
11. The process of Claim 3 wherein flows of said ethylene and said melt are diverted from a direct path.
12. The process of Claim 11 wherein said flows are diverted by means of at least one impediment to direct flow located in said separator.
13. The process of Claim 12 wherein said impediment is at least one baffle.
14. The process of Claim 13 wherein there are a plurality of said baffles located on opposite sides of said separator.
15. The process of Claim 14 wherein said baffles are staggered.
Priority Applications (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3844180A DE3844180A1 (en) | 1988-12-29 | 1988-12-29 | METHOD FOR SEPARATING VOLATILE COMPONENTS FROM REACTION MIXTURES OBTAINED BY HIGH PRESSURE POLYMERIZATION |
| EP90102255A EP0440838B1 (en) | 1988-12-29 | 1990-02-06 | Process for separating volatile materials from reaction mixtures obtained by high-pressure polymerization |
| ES90102255T ES2057200T3 (en) | 1988-12-29 | 1990-02-06 | PROCEDURE FOR THE SEPARATION OF VOLATILE COMPONENTS FROM REACTION MIXTURES OBTAINED BY A HIGH PRESSURE POLYMERIZATION. |
| AU49395/90A AU622278B2 (en) | 1988-12-29 | 1990-02-14 | Process for separating volatile components from reaction mixtures obtained through high-pressure polymerisation |
| JP3642190A JP2904846B2 (en) | 1988-12-29 | 1990-02-19 | Method for separating volatile components from reaction mixture obtained by high pressure polymerization |
| CA002010850A CA2010850C (en) | 1988-12-29 | 1990-02-23 | Process for separating volatile components from reaction mixtures obtained through high-pressure polymerization |
| US07/790,126 US5200486A (en) | 1988-12-29 | 1991-11-06 | Process for separating volatile components from reaction mixtures obtained through high-pressure polymerization |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3844180A DE3844180A1 (en) | 1988-12-29 | 1988-12-29 | METHOD FOR SEPARATING VOLATILE COMPONENTS FROM REACTION MIXTURES OBTAINED BY HIGH PRESSURE POLYMERIZATION |
| CA002010850A CA2010850C (en) | 1988-12-29 | 1990-02-23 | Process for separating volatile components from reaction mixtures obtained through high-pressure polymerization |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2010850A1 CA2010850A1 (en) | 1991-08-23 |
| CA2010850C true CA2010850C (en) | 1995-10-24 |
Family
ID=25673975
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002010850A Expired - Fee Related CA2010850C (en) | 1988-12-29 | 1990-02-23 | Process for separating volatile components from reaction mixtures obtained through high-pressure polymerization |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0440838B1 (en) |
| JP (1) | JP2904846B2 (en) |
| AU (1) | AU622278B2 (en) |
| CA (1) | CA2010850C (en) |
| DE (1) | DE3844180A1 (en) |
| ES (1) | ES2057200T3 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9012577B2 (en) | 2005-07-29 | 2015-04-21 | Saudi Basic Industries Corporation | Method for preparing linear alpha-olefins with improved heat removal |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NZ264288A (en) * | 1993-09-30 | 1996-08-27 | Boc Group Inc | Preparation of ethylene and propylene polymers from mixtures of ethylene/ethane and propylene/propane, respectively, with either pre-polymerisation or post-polmerisation adsorption of the unsaturated component and recycling of at least part of the unreacted monomer |
| DE19922677C1 (en) † | 1999-05-18 | 2001-04-19 | Elenac Gmbh | Process for drying and degassing polyolefins and polyethylene produced by this process |
| EP1749808B1 (en) * | 2005-07-29 | 2010-02-03 | Linde AG | Method for the preparation of linear alpha-olefins and reactor system therefore with improved disposal of high molecular weight oligomers |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BG25100A3 (en) * | 1970-06-23 | 1978-07-12 | Snamprogetti S.P.A. | A method of obtaining of polyethilene at yigh pressure |
| DD131824A3 (en) * | 1975-11-13 | 1978-07-26 | Manfred Raetzsch | METHOD FOR SEPARATING THE REACTION MIXTURE IN HIGH-PRESSURE POLYMERIZATION PLANTS |
| JPS5813563B2 (en) * | 1976-04-03 | 1983-03-14 | 信越化学工業株式会社 | Method and apparatus for removing unreacted monomers from an aqueous dispersion of vinyl chloride |
| DE2746909C3 (en) * | 1977-10-19 | 1982-03-11 | Hoechst Ag, 6000 Frankfurt | Process for the continuous removal of residual hydrocarbons from polyolefins |
| DD202882A1 (en) * | 1981-10-27 | 1983-10-05 | Leuna Werke Veb | METHOD FOR RECYCLING COMONOMER-CONTAINING LOW-PRESSURE RECYCLING GAS IN THE HIGH-PRESSURE POLYMERIZATION PROCESS |
| DE3815487A1 (en) * | 1988-05-06 | 1989-11-16 | Basf Ag | METHOD FOR LOW-PRESSURE COPOLYMERISATION OF ETHYLENE WITH (ALPHA) -OLEFINES AND ETHYLENE COPOLYMERISATE WITH LOW RESIDUAL MONOMER CONTENT |
| IT1226303B (en) * | 1988-07-26 | 1990-12-27 | Montedipe Spa | PROCESS AND APPARATUS FOR DEVOLATILIZATION OF POLYMER SOLUTIONS. |
-
1988
- 1988-12-29 DE DE3844180A patent/DE3844180A1/en not_active Withdrawn
-
1990
- 1990-02-06 EP EP90102255A patent/EP0440838B1/en not_active Expired - Lifetime
- 1990-02-06 ES ES90102255T patent/ES2057200T3/en not_active Expired - Lifetime
- 1990-02-14 AU AU49395/90A patent/AU622278B2/en not_active Ceased
- 1990-02-19 JP JP3642190A patent/JP2904846B2/en not_active Expired - Lifetime
- 1990-02-23 CA CA002010850A patent/CA2010850C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9012577B2 (en) | 2005-07-29 | 2015-04-21 | Saudi Basic Industries Corporation | Method for preparing linear alpha-olefins with improved heat removal |
Also Published As
| Publication number | Publication date |
|---|---|
| ES2057200T3 (en) | 1994-10-16 |
| AU4939590A (en) | 1991-08-15 |
| AU622278B2 (en) | 1992-04-02 |
| DE3844180A1 (en) | 1990-07-05 |
| JPH03239705A (en) | 1991-10-25 |
| CA2010850A1 (en) | 1991-08-23 |
| EP0440838A1 (en) | 1991-08-14 |
| EP0440838B1 (en) | 1993-04-14 |
| JP2904846B2 (en) | 1999-06-14 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |