CA2031699C - Process for reducing polymer build-up in heat exchangers during polymerization of alpha-olefins - Google Patents
Process for reducing polymer build-up in heat exchangers during polymerization of alpha-olefinsInfo
- Publication number
- CA2031699C CA2031699C CA002031699A CA2031699A CA2031699C CA 2031699 C CA2031699 C CA 2031699C CA 002031699 A CA002031699 A CA 002031699A CA 2031699 A CA2031699 A CA 2031699A CA 2031699 C CA2031699 C CA 2031699C
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- CA
- Canada
- Prior art keywords
- heat exchanger
- reactor
- compressor
- heat
- olefins
- 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.)
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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
- C08F2/00—Processes of polymerisation
- C08F2/34—Polymerisation in gaseous state
-
- 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
- C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
- B01J8/24—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique
- B01J8/26—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique with two or more fluidised beds, e.g. reactor and regeneration installations
-
- 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
- C08F2/00—Processes of polymerisation
- C08F2/002—Scale prevention in a polymerisation reactor or its auxiliary parts
- C08F2/007—Scale prevention in the auxiliary parts
-
- 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
- C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F110/04—Monomers containing three or four carbon atoms
- C08F110/06—Propene
-
- 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
- C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F210/16—Copolymers of ethene with alpha-alkenes, e.g. EP rubbers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S526/00—Synthetic resins or natural rubbers -- part of the class 520 series
- Y10S526/901—Monomer polymerized in vapor state in presence of transition metal containing catalyst
Abstract
A method for inhibiting polymer build-up in a heat exchanger during the gas phase polymerization of alpha-olefins which comprises introducing upstream of the heat exchanger para ethyl ethoxybenzoate in an amount sufficient to inhibit polymer build-up.
Description
' 2031S99 ~ -- 1 PROCESS FOR REDUCING POLYMER
~3UILD-UP IN HEAT ~Y(~~
D~T~TNG poT~vMTpT~T~ATI~)N OF AT P~A--nT T~T~ I
TT~CTINT r AT. FTT;~T n The invention relates to copolymerizing propylene and other alpha-olefins such as ethylene.
More particularly, the present invention relate~ to a process for reducing the amount of heat e~changer fouling during copolymerization of propylene with alpha-olef ins such as ethylene, BAt R(~RnUNn 0~ Tli~ INYFNTION
Although the invention is herein described with reference to systems for copolymerization of propylene and ethylene, it will be understood that the invention can be readily applied to the copolymerization of other alpha-olefin monomer combinations such as propylene-butene, propylene-he~ene and also terpolymer systems produced from three or more olefinic monomers.
nPropylene impact copolymers" are polymers which are composed of a polypropylene homopolymer phase which is intimately mi~ed with one or more ethylene-propylene copolymer phases. This mi~ture results in a product which has good impact resistance and good stiffness.
Impact copolymers are typically produced by two or more reactors in series. The first reactor typically produces polypropylene homopolymer which is then fed to a second reactor. Alternatively, the f irst reactor can be used to produce random copolymer which would then be fed to the second reactor. In the second reactor (and subsequent reactors, if any) the reactant composition is varied such that copolymers with varying f ractions of ethylene and propylene are produced in each reactor and intimately mi~ed with the polymer f rom the previous reactors.
Typically, the reaction in the reactors, which can be gas phase reactors, is cataly~ed by a transition metal catalyst. In most cases the transition metal is titanium.
In general, the equipment for producing propylene impact copolymers is conventional equipment such as two or more reactors, heat e~changers, compressors, discharge systems and piping connected to the various equipment.
11nfortunately, however, during normal operations, the surfaces of the tubes of the heat exchanger or cooler tend to foul with undesirable polymer deposits. These deposits tend to reduce the heat e~changer capability in cooling the recycled gas which removes the heat of reaction, and also it increases the pressure arop across the heat e~changer, which adds to the load on the cycle gas compressor. Because of increasing pressure drop and/or decreased heat e~changer capability the reactor must be shut down within a short time for cleaning .
According to BPA publication No. 0282929 there is disclosed a method for producing a propylene-alpha-olefin block copolymer without 2~3~99 polymer agglomeration in the reactor, by supplying at least one compound selected from the group consisting of an aromatic carbo~ylic acid ester, a phosphorous ester, an unsaturated dicarbo~ylic acid diester, amine compound and an amide compound, to the reactor or recycle line. Tbe preferred carbo~ylic acid ester can be ethyl benzoate and ethyl etho~ybenzoate. Unfortunately however polymer build up in heat exchangers i8 still a problem when using the method disclosed in the EPA publication 0282929 .
S~TMMARY OF rHF INVT;~NTIQN
It has been found that by adding para ethyletho~y-benzoate (PEEB) upstream of the heat eschanger, that the formation of polymer deposits in the heat exchanger can be reduced substantially.
Broadly contemplated therefore the present invention proviaes a method for inhibiting polymer build-up in a heat exchanger during the gas phase polymerization of alpha-olefins which comprises intrQducing upstream of the heat e~changer para ethyl etho~cybenzoate in an amount sufficient to inhibit polymer build-up.
RRTT~T~ nT;~ rRTPTIQN OF THF DRAT~IN(~.C
Figure 1 illustrates a two-reactor polymerization system for producing polypropylene impact copolymers.
D~ tPTION OF THTi ~R~ R~ T~MROpIMT~NTS
It is critical to the instant invention that the para ethyletho~cybenzoate (PEEB, a commercially available material) be added to the recycle line upstream of the heat e~changer i.e., to the recycle line leaving the reactor. It is preferred however to introduce the para ethyl etho ~ybenzoate either upstream of the compressor disposed in the upstream portions of the recycle line or into the compressor or between the compressor and the heat e~changer.
The amount of the para ethyl etho~ybenzoate usea can vary oYer a range of about 5 to about 20 pounds of PEEB per million pounds o polymerized alpha olefins copolymer polypropylene produced. Use of lower amounts will be less effective in preventing polymer growth while use of larger amounts will adversely affect the operation of the reactor. Preferred amounts are within the range of about 6 to about 8 pounas per million pounds.
The preferred alpha olefins produced are polypropylene impact copolymers.
Referring to Pig. 1, two reactor systems of the type illustrated in Fi!~. 1 typically provide a catalyzed e~othermic reaction (e.Q, a fluidized bed 14) within a first reactor RX-l for converting gaseous raw materials into solid product. Raw materials (such as propylene, ethylene, nitrogen, hyarogen, catalyst, cocatalyst and a selectivity control agent) are fed through an input stream 2 to the rsaction system (RX-l). The heat of reaction is removed from the reactor RX-l by circulating a stream of gaseous raw materials 12 through a cooler 10. Reaction temperature may be controlled by adjusting water flow in cooler 10 which removes heat 2~31699 from the circulating gas stream 12. Solid product, in the form of polypropylene homopolymer or random copolymer containing active catalyst, is removed from reactor (RX-l) by perioaically discharging a small portion of the fluidized bed 14 into a product discharge system 4.
The second reactor (R~-2) of the two reactor system o~ Fig. 1 is designed to produce a copolymer of propylene ànd ethylene in intimate mi~ture with the solid homopolymer or random copolymer material produced by the first reactor (RX-l). In this embodiment, the product stream 16 from the first reactor (RX-l) (including e.g., homopolymer and active catalyst) is fed to the second reactor (RX-2). Raw materials (e.g., ethylene and propylene) are fed via input stream 18 to the second reactor (RX-2) to be polymerized by ths still active catalyst in the homopolymer or random copolymer material within the reactor (RX-l) product stream 16.
In the second reactor (RX-2 ), ethylene and propylene are copolymerized in intimate mixture with the propylene homopolymer or random copolymer to produce impact copolymer. The process is maintained by the addition of ingredients from RX-l and input stream 18 and cooling is provided by the circulation of the gaseous stream 8 through a cooler 20.
In the embodiment of Fig. 1, no catalyst is addea to RX-2. The reaction within RX-2 is thus catalyze~ entirely by catalyst contained in the polymer coming f rom RX-l .
D~ ~ ~
Typical objectives for the operstion of a second or subsequent reactor R~-2 in a multi-reactor chain process such as shown in Fig. 1 include maintaining prescribed values for the fraction (hereinafter called "FCn) of the final product (e.g., impact polypropylene) that is created in the second reactor and for the fraction (hereinafter called "ECn) of ethylene contained in the copolymer fraction which is produced in reactor RX-2.
Fc (the fraction of total product that is created in the second reaction (RX-2) depends in general upon the combination of partial pressures of propylene (C3H6, hereinafter "c3n) and ethylene (C2H4), hereinafter "C2n) that e~ist in the reaction system RX-2. With some catalyst systems, however, catalyst or cocatalyst may be added to the second reactor to control Fc. Ec (the fraction of ethylene that is incorporated in the copolymerproducea in reactor RX-2) depends upon the relative partial pressures of ethylene and propylene.
During normal operations the internal surf ace of the tubes of the heat eschanger 20 in the second stage during production of ethylene-propylene copolymer products tend to foul with undesirable polymer deposits.
The benef its of the instant invention are obtained by introducing the para ethyl etho~ybenzoate upstream of the cooler e.g., cooler 20. The para ethyl etho~ybenzoate is thus introduced prior to the compressor through line 22 or to the compressor, or in between the compressor and cooler 20 through line 24. Addition of the para . ~
ethyl etho~ybenzoate in this manner provides dramatic relief f rom fouling .
The following e~amples will further illustr~te the present invention.
~YI~MPL~ 1 This e~ample illustrates the rate of fouling of the heat e~changer when no PEEB is fed to the impact copolymer reactor system.
Impact copolymer polypropylene was produced in powder form in two gas phase fluidized bed reactors operated in series. In the second reaction system, a gas phase consisting of nitrogen was circulated prior to starting the polymerization.
The gas was circulated by a cycle gas compressor through the tube side of a conventional shell and tube heat e~changer where heat was removed f rom the system. The insides of the heat e~changer tubes were cleaned prior to conducting the polymerization by hydroblasting. Reaction was established by transferring homopolymer polypropylene containing active Ziegler-Natta polymerization catalyst from the first reactor to the second reactor; by feeding triethyl aluminum to the second reactor; and by establishing the proper concentration of ethylene, propylene, and hydrogen in the gas phase o~ the second reactor.
The triethyl aluminum feed rate and gas phase composition were adjusted to produce an impact copolymer product having an Ec (ethylene content of the copolymer) of appro~imately 6096 and an ~c (fraction copolymer) of approl~imately 14~6. At the 2~31699 beginning of the run, the heat e~chanqer eressure drop was appro~imately 1 psi.
The reactor was operated for a total of approsimately 5 . 5 days producing impact copolymer with an Fc of approsimately 14 to 17%, after which it was shut down. At the time of shutdown, the cooler pressure drop was approsimately 3.5 psi.
During the run, it had risen at rates of 0.3 to 0.7 psi/day.
Upon inspection, the cooler inlet had a rubbery build up. The inside surfaces of the heat eschanger tubes were coated with thin layers of rubbery polymer. Several tubes were plugqed.
~rAMPL~ 2 This E~ample demonstrates that feeding PEEB
downstream of the heat eschanger does not eliminate polymer build up in the heat eschanger.
Prior to conducting the polymerization, the tube side of the heat e~changer described in Esample 1 was cleaned by hydroblasting. The reactor was started up as in E~cample 1. Operating conditions were regulated to produce an impact copolymer product having an Ec of approsimately 60% and an Fc of appro~imately 15%. After a short period of time, Para ethylethosybenzoate (PEEB) was fed continuously to the cycle gas line down~tre~m of the heat e~changer and upstrean~ of the reactor at a rate of appro~imately 17 lb/million pounds of impact copolymer product. Feeding of PEEB was continued until the end of the run. At the beginining of the run, heat e~changer pressure drop was 1. 3 psi .
.
2~31699 _ 9 _ The run was continued for about 6 days after PEEB
injection was started, producing impact copolymers with an Fc of 14 to 17%. The second reactor was then shut down in order to switch the plant to the production of homopolymer polypropylene. During most of the run, the heat e~changer pressure drop increased steadily at a rate of 1~4 psi/day. At the end of the run, heat eschanger pressure drop had risen to 4.7 psi.
Upon inspection, the inlet tubesheet of the heat eschanger was found to have a heavy buildup of polymer. The inside surfaces of the heat exchanger tubes were coated with thick layers of loosely attached, rubbery polymer. Several tubes were p lugged .
~r~ Pr.~ 3 Impact copolymer polypropylene was produced in powder form in two gas phase fluidized bed reactors operated in series. In the second reaction system, a gas phase consisting of nitrogen was circulated prior to starting the polymerization.
The gas was circulated by a cycle gas compressor through the tube side of a conventional shell and tube heat eschanger where heat was removed f rom the system. The insides of the heat exchanger tubes were cleanell prior to conducting the polymerization by hydroblasting and shell blasting to a smooth bare metal surface. No coating or treatment was applied. Four tubes were left uncleaned for comparison. Reaction was established by transferring homopolymer polypropylene containing - 2031~99 _ 10 --active Ziegler-Natta polymerization catalyst from the first reactor to the second reactor; by feeding triethyl aluminum to the second reactor; and by establishing the proper concentration of ethylene, propylene, and hydrogen in the gas phase of the second reactor.
Triethylaluminum feed rate and gas phase composition were adjusted to produce an impact copolymer product having ~n Ec (ethylene content of the copolymer) of approsimately 60% and an Fc (fraction copolymer) of appro~imately 1896. At the beginning of the run, the heat exchanger pressure drop was S . 7 psi .
The reactor was operated for 9 days producing impact copolymer with an Fc of about 189~, one day with an Fc of about 21~6 and three days with an Fc f about 14 . 5~6 .
After 13 days, the second reactor was shut down in order to switch the plant to the production of homopolymer polypropylene. At this time, the heat exchanger pressure drop had increased to 28 psi. The rate of pressure drop increase was 1. 7 ps i /day .
Upon inspection, the insides of the heat eschanger tubes were found to haYe thin continuous film of rubbery polymer that extended throughout each tube.
~SYD,~PLF~ 4 This E~ample demonstrates polymers growth reduction in the heat eschanger by selective addition of PEEB upstream of the heat eschanger and - 11 203~699 downstream of the compre3sor.
Prior to conducting the polymerization, the tube =~
side of the heat exchanger of Example 3 was cleaned by hydroblasting followed by blasting with walnut shell.
Half of the tubes in the heat exchanger were then treated with UCAR-AFI.-40 a registered trademark (an amino silicone produced by Union Carbide Chemicals and Plastics Co., Inc. ) by blowing a soaked squeegee :~
through each tube first from one end, then from the other end. The I~ ;n1n~ half of the tubes were left untreated .
The reactor was started up as in Example 3 and operating conditions were adjusted to produce initially an impact copolymer product having an Ec of approximately 60~ of an Fc of approximately 21~. From the beginning of the run, paraethylethoxybenzoate (PEEB) was fed continuously to the cycle gas line downstream of the cycle gas compressor and upstream of the heat exchanger at a rate of approximately 7 . 4 lb/million pounds of impact copolymer product.
When the reactor running stabilized, the heat exchanger pressure drop was approximately 11 psi. The overall heat transfer coefficient at this time was approximately 180 BTU/hr. sq. ft. F. The reactor was operated for 8 days producing 2196 Fc impact copolymer, for 5.5 days producing 18~6 Fc impact copolymer, and for 17 days producing 149~ Fc impact copolymer. At this time in the run, the heat exchanger pressure drop had decreased to approximately 6 . 8 p8i and was not changing. The overall heat transfer coefficient had increased to appro~imately 215 ~TU/hr. sq.t.F and was not changing .
Near the end of the run at 141~ Fc, PEEB
flow was stopped. The reactor conditions were than changed to produce a 25~c Fc impact copolymer. About 8 hours after the product change, heat e~changer pressure drop started to rise at A rate o 1.75 psi/day. After about 1-1/2 days, PEEB flow was restarted. Heat e~changer pressure drop stopped rising within 4 hours, and slowly declined for the rest of the run.
Twenty-five percent Fc impact copolymer was produced for about 4 days. The second reactor was then shut down in order to switch the plant to the production of homopolymer polypropylene. At the end of the run, heat exchanger pressure drop was 8 . 6 psi. The overall heat transfer coefficient at this time was appro~imately 230 BTU/hr. sg. ft . ~F. There had been no increase in pressure drop across the heat exchanger e~cept then the PEEB f low upstream of the heat eschanger was stopped as a test, and the heat transfer coefficient actually increased slowly during the entire run.
Upon inspection, the inside surfaces of most o the heat e~changer tubes had a very thin polymer layer. There was no sign of the AFL-40 on the 50% of the tubes which had been treated prior to the run. There was no difference in the appearance o treated tubes and untreated tubes. It was not necessary to clean the heat e~changer prior to the ne~ct planned run.
~3UILD-UP IN HEAT ~Y(~~
D~T~TNG poT~vMTpT~T~ATI~)N OF AT P~A--nT T~T~ I
TT~CTINT r AT. FTT;~T n The invention relates to copolymerizing propylene and other alpha-olefins such as ethylene.
More particularly, the present invention relate~ to a process for reducing the amount of heat e~changer fouling during copolymerization of propylene with alpha-olef ins such as ethylene, BAt R(~RnUNn 0~ Tli~ INYFNTION
Although the invention is herein described with reference to systems for copolymerization of propylene and ethylene, it will be understood that the invention can be readily applied to the copolymerization of other alpha-olefin monomer combinations such as propylene-butene, propylene-he~ene and also terpolymer systems produced from three or more olefinic monomers.
nPropylene impact copolymers" are polymers which are composed of a polypropylene homopolymer phase which is intimately mi~ed with one or more ethylene-propylene copolymer phases. This mi~ture results in a product which has good impact resistance and good stiffness.
Impact copolymers are typically produced by two or more reactors in series. The first reactor typically produces polypropylene homopolymer which is then fed to a second reactor. Alternatively, the f irst reactor can be used to produce random copolymer which would then be fed to the second reactor. In the second reactor (and subsequent reactors, if any) the reactant composition is varied such that copolymers with varying f ractions of ethylene and propylene are produced in each reactor and intimately mi~ed with the polymer f rom the previous reactors.
Typically, the reaction in the reactors, which can be gas phase reactors, is cataly~ed by a transition metal catalyst. In most cases the transition metal is titanium.
In general, the equipment for producing propylene impact copolymers is conventional equipment such as two or more reactors, heat e~changers, compressors, discharge systems and piping connected to the various equipment.
11nfortunately, however, during normal operations, the surfaces of the tubes of the heat exchanger or cooler tend to foul with undesirable polymer deposits. These deposits tend to reduce the heat e~changer capability in cooling the recycled gas which removes the heat of reaction, and also it increases the pressure arop across the heat e~changer, which adds to the load on the cycle gas compressor. Because of increasing pressure drop and/or decreased heat e~changer capability the reactor must be shut down within a short time for cleaning .
According to BPA publication No. 0282929 there is disclosed a method for producing a propylene-alpha-olefin block copolymer without 2~3~99 polymer agglomeration in the reactor, by supplying at least one compound selected from the group consisting of an aromatic carbo~ylic acid ester, a phosphorous ester, an unsaturated dicarbo~ylic acid diester, amine compound and an amide compound, to the reactor or recycle line. Tbe preferred carbo~ylic acid ester can be ethyl benzoate and ethyl etho~ybenzoate. Unfortunately however polymer build up in heat exchangers i8 still a problem when using the method disclosed in the EPA publication 0282929 .
S~TMMARY OF rHF INVT;~NTIQN
It has been found that by adding para ethyletho~y-benzoate (PEEB) upstream of the heat eschanger, that the formation of polymer deposits in the heat exchanger can be reduced substantially.
Broadly contemplated therefore the present invention proviaes a method for inhibiting polymer build-up in a heat exchanger during the gas phase polymerization of alpha-olefins which comprises intrQducing upstream of the heat e~changer para ethyl etho~cybenzoate in an amount sufficient to inhibit polymer build-up.
RRTT~T~ nT;~ rRTPTIQN OF THF DRAT~IN(~.C
Figure 1 illustrates a two-reactor polymerization system for producing polypropylene impact copolymers.
D~ tPTION OF THTi ~R~ R~ T~MROpIMT~NTS
It is critical to the instant invention that the para ethyletho~cybenzoate (PEEB, a commercially available material) be added to the recycle line upstream of the heat e~changer i.e., to the recycle line leaving the reactor. It is preferred however to introduce the para ethyl etho ~ybenzoate either upstream of the compressor disposed in the upstream portions of the recycle line or into the compressor or between the compressor and the heat e~changer.
The amount of the para ethyl etho~ybenzoate usea can vary oYer a range of about 5 to about 20 pounds of PEEB per million pounds o polymerized alpha olefins copolymer polypropylene produced. Use of lower amounts will be less effective in preventing polymer growth while use of larger amounts will adversely affect the operation of the reactor. Preferred amounts are within the range of about 6 to about 8 pounas per million pounds.
The preferred alpha olefins produced are polypropylene impact copolymers.
Referring to Pig. 1, two reactor systems of the type illustrated in Fi!~. 1 typically provide a catalyzed e~othermic reaction (e.Q, a fluidized bed 14) within a first reactor RX-l for converting gaseous raw materials into solid product. Raw materials (such as propylene, ethylene, nitrogen, hyarogen, catalyst, cocatalyst and a selectivity control agent) are fed through an input stream 2 to the rsaction system (RX-l). The heat of reaction is removed from the reactor RX-l by circulating a stream of gaseous raw materials 12 through a cooler 10. Reaction temperature may be controlled by adjusting water flow in cooler 10 which removes heat 2~31699 from the circulating gas stream 12. Solid product, in the form of polypropylene homopolymer or random copolymer containing active catalyst, is removed from reactor (RX-l) by perioaically discharging a small portion of the fluidized bed 14 into a product discharge system 4.
The second reactor (R~-2) of the two reactor system o~ Fig. 1 is designed to produce a copolymer of propylene ànd ethylene in intimate mi~ture with the solid homopolymer or random copolymer material produced by the first reactor (RX-l). In this embodiment, the product stream 16 from the first reactor (RX-l) (including e.g., homopolymer and active catalyst) is fed to the second reactor (RX-2). Raw materials (e.g., ethylene and propylene) are fed via input stream 18 to the second reactor (RX-2) to be polymerized by ths still active catalyst in the homopolymer or random copolymer material within the reactor (RX-l) product stream 16.
In the second reactor (RX-2 ), ethylene and propylene are copolymerized in intimate mixture with the propylene homopolymer or random copolymer to produce impact copolymer. The process is maintained by the addition of ingredients from RX-l and input stream 18 and cooling is provided by the circulation of the gaseous stream 8 through a cooler 20.
In the embodiment of Fig. 1, no catalyst is addea to RX-2. The reaction within RX-2 is thus catalyze~ entirely by catalyst contained in the polymer coming f rom RX-l .
D~ ~ ~
Typical objectives for the operstion of a second or subsequent reactor R~-2 in a multi-reactor chain process such as shown in Fig. 1 include maintaining prescribed values for the fraction (hereinafter called "FCn) of the final product (e.g., impact polypropylene) that is created in the second reactor and for the fraction (hereinafter called "ECn) of ethylene contained in the copolymer fraction which is produced in reactor RX-2.
Fc (the fraction of total product that is created in the second reaction (RX-2) depends in general upon the combination of partial pressures of propylene (C3H6, hereinafter "c3n) and ethylene (C2H4), hereinafter "C2n) that e~ist in the reaction system RX-2. With some catalyst systems, however, catalyst or cocatalyst may be added to the second reactor to control Fc. Ec (the fraction of ethylene that is incorporated in the copolymerproducea in reactor RX-2) depends upon the relative partial pressures of ethylene and propylene.
During normal operations the internal surf ace of the tubes of the heat eschanger 20 in the second stage during production of ethylene-propylene copolymer products tend to foul with undesirable polymer deposits.
The benef its of the instant invention are obtained by introducing the para ethyl etho~ybenzoate upstream of the cooler e.g., cooler 20. The para ethyl etho~ybenzoate is thus introduced prior to the compressor through line 22 or to the compressor, or in between the compressor and cooler 20 through line 24. Addition of the para . ~
ethyl etho~ybenzoate in this manner provides dramatic relief f rom fouling .
The following e~amples will further illustr~te the present invention.
~YI~MPL~ 1 This e~ample illustrates the rate of fouling of the heat e~changer when no PEEB is fed to the impact copolymer reactor system.
Impact copolymer polypropylene was produced in powder form in two gas phase fluidized bed reactors operated in series. In the second reaction system, a gas phase consisting of nitrogen was circulated prior to starting the polymerization.
The gas was circulated by a cycle gas compressor through the tube side of a conventional shell and tube heat e~changer where heat was removed f rom the system. The insides of the heat e~changer tubes were cleaned prior to conducting the polymerization by hydroblasting. Reaction was established by transferring homopolymer polypropylene containing active Ziegler-Natta polymerization catalyst from the first reactor to the second reactor; by feeding triethyl aluminum to the second reactor; and by establishing the proper concentration of ethylene, propylene, and hydrogen in the gas phase o~ the second reactor.
The triethyl aluminum feed rate and gas phase composition were adjusted to produce an impact copolymer product having an Ec (ethylene content of the copolymer) of appro~imately 6096 and an ~c (fraction copolymer) of approl~imately 14~6. At the 2~31699 beginning of the run, the heat e~chanqer eressure drop was appro~imately 1 psi.
The reactor was operated for a total of approsimately 5 . 5 days producing impact copolymer with an Fc of approsimately 14 to 17%, after which it was shut down. At the time of shutdown, the cooler pressure drop was approsimately 3.5 psi.
During the run, it had risen at rates of 0.3 to 0.7 psi/day.
Upon inspection, the cooler inlet had a rubbery build up. The inside surfaces of the heat eschanger tubes were coated with thin layers of rubbery polymer. Several tubes were plugqed.
~rAMPL~ 2 This E~ample demonstrates that feeding PEEB
downstream of the heat eschanger does not eliminate polymer build up in the heat eschanger.
Prior to conducting the polymerization, the tube side of the heat e~changer described in Esample 1 was cleaned by hydroblasting. The reactor was started up as in E~cample 1. Operating conditions were regulated to produce an impact copolymer product having an Ec of approsimately 60% and an Fc of appro~imately 15%. After a short period of time, Para ethylethosybenzoate (PEEB) was fed continuously to the cycle gas line down~tre~m of the heat e~changer and upstrean~ of the reactor at a rate of appro~imately 17 lb/million pounds of impact copolymer product. Feeding of PEEB was continued until the end of the run. At the beginining of the run, heat e~changer pressure drop was 1. 3 psi .
.
2~31699 _ 9 _ The run was continued for about 6 days after PEEB
injection was started, producing impact copolymers with an Fc of 14 to 17%. The second reactor was then shut down in order to switch the plant to the production of homopolymer polypropylene. During most of the run, the heat e~changer pressure drop increased steadily at a rate of 1~4 psi/day. At the end of the run, heat eschanger pressure drop had risen to 4.7 psi.
Upon inspection, the inlet tubesheet of the heat eschanger was found to have a heavy buildup of polymer. The inside surfaces of the heat exchanger tubes were coated with thick layers of loosely attached, rubbery polymer. Several tubes were p lugged .
~r~ Pr.~ 3 Impact copolymer polypropylene was produced in powder form in two gas phase fluidized bed reactors operated in series. In the second reaction system, a gas phase consisting of nitrogen was circulated prior to starting the polymerization.
The gas was circulated by a cycle gas compressor through the tube side of a conventional shell and tube heat eschanger where heat was removed f rom the system. The insides of the heat exchanger tubes were cleanell prior to conducting the polymerization by hydroblasting and shell blasting to a smooth bare metal surface. No coating or treatment was applied. Four tubes were left uncleaned for comparison. Reaction was established by transferring homopolymer polypropylene containing - 2031~99 _ 10 --active Ziegler-Natta polymerization catalyst from the first reactor to the second reactor; by feeding triethyl aluminum to the second reactor; and by establishing the proper concentration of ethylene, propylene, and hydrogen in the gas phase of the second reactor.
Triethylaluminum feed rate and gas phase composition were adjusted to produce an impact copolymer product having ~n Ec (ethylene content of the copolymer) of approsimately 60% and an Fc (fraction copolymer) of appro~imately 1896. At the beginning of the run, the heat exchanger pressure drop was S . 7 psi .
The reactor was operated for 9 days producing impact copolymer with an Fc of about 189~, one day with an Fc of about 21~6 and three days with an Fc f about 14 . 5~6 .
After 13 days, the second reactor was shut down in order to switch the plant to the production of homopolymer polypropylene. At this time, the heat exchanger pressure drop had increased to 28 psi. The rate of pressure drop increase was 1. 7 ps i /day .
Upon inspection, the insides of the heat eschanger tubes were found to haYe thin continuous film of rubbery polymer that extended throughout each tube.
~SYD,~PLF~ 4 This E~ample demonstrates polymers growth reduction in the heat eschanger by selective addition of PEEB upstream of the heat eschanger and - 11 203~699 downstream of the compre3sor.
Prior to conducting the polymerization, the tube =~
side of the heat exchanger of Example 3 was cleaned by hydroblasting followed by blasting with walnut shell.
Half of the tubes in the heat exchanger were then treated with UCAR-AFI.-40 a registered trademark (an amino silicone produced by Union Carbide Chemicals and Plastics Co., Inc. ) by blowing a soaked squeegee :~
through each tube first from one end, then from the other end. The I~ ;n1n~ half of the tubes were left untreated .
The reactor was started up as in Example 3 and operating conditions were adjusted to produce initially an impact copolymer product having an Ec of approximately 60~ of an Fc of approximately 21~. From the beginning of the run, paraethylethoxybenzoate (PEEB) was fed continuously to the cycle gas line downstream of the cycle gas compressor and upstream of the heat exchanger at a rate of approximately 7 . 4 lb/million pounds of impact copolymer product.
When the reactor running stabilized, the heat exchanger pressure drop was approximately 11 psi. The overall heat transfer coefficient at this time was approximately 180 BTU/hr. sq. ft. F. The reactor was operated for 8 days producing 2196 Fc impact copolymer, for 5.5 days producing 18~6 Fc impact copolymer, and for 17 days producing 149~ Fc impact copolymer. At this time in the run, the heat exchanger pressure drop had decreased to approximately 6 . 8 p8i and was not changing. The overall heat transfer coefficient had increased to appro~imately 215 ~TU/hr. sq.t.F and was not changing .
Near the end of the run at 141~ Fc, PEEB
flow was stopped. The reactor conditions were than changed to produce a 25~c Fc impact copolymer. About 8 hours after the product change, heat e~changer pressure drop started to rise at A rate o 1.75 psi/day. After about 1-1/2 days, PEEB flow was restarted. Heat e~changer pressure drop stopped rising within 4 hours, and slowly declined for the rest of the run.
Twenty-five percent Fc impact copolymer was produced for about 4 days. The second reactor was then shut down in order to switch the plant to the production of homopolymer polypropylene. At the end of the run, heat exchanger pressure drop was 8 . 6 psi. The overall heat transfer coefficient at this time was appro~imately 230 BTU/hr. sg. ft . ~F. There had been no increase in pressure drop across the heat exchanger e~cept then the PEEB f low upstream of the heat eschanger was stopped as a test, and the heat transfer coefficient actually increased slowly during the entire run.
Upon inspection, the inside surfaces of most o the heat e~changer tubes had a very thin polymer layer. There was no sign of the AFL-40 on the 50% of the tubes which had been treated prior to the run. There was no difference in the appearance o treated tubes and untreated tubes. It was not necessary to clean the heat e~changer prior to the ne~ct planned run.
Claims (10)
1. A method for inhibiting polymer build-up in a heat exchanger during the gas phase polymerization of alpha-olefins which comprises introducing to the recycle line downstream of the reactor and upstream of the heat exchanger para ethyl ethoxybenzoate in an amount sufficient to inhibit polymer build-up.
2. A method according to Claim 1 wherein said polymerized alpha-olefins are polypropylene impact copolymers.
3. A method according to Claim 1 wherein the amount of ethyl ethoxybenzoate employed is in the range of about 5 to about 20 pounds of ethyl ethoxybenzoate per million pounds of poly-merized alpha-olefins.
4. A method according to Claim 1 wherein the amount of ethyl ethoxybenzoate employed is in the range of about 6 to about 8 pounds of ethyl ethoxybenzoate per million pounds of polymerized alpha-olefins.
5. A method according to Claim 1 wherein a compressor is disposed upstream of said heat exchanger and wherein said ethyl ethoxybenzoate is introduced upstream of said compressor.
6. A method according to Claim 1 wherein a compressor is disposed upstream of said heat exchanger and wherein said ethyl ethoxybenzoate is introduced into said compressor.
7. A method according to Claim 1 wherein a compressor is disposed upstream of said heat exchanger and wherein said ethyl ethoxybenzoate is introduced between said compressor and said heat exchanger.
8. A method for inhibiting polymer build-up in a heat exchanger during the gas phase polymerization of alpha-olefins to form polypropylene impact copolymers which comprises introducing to the recycle line downstream of the reactor and upstream of said heat exchanger para ethyl ethoxybenzoate in an amount of about 5 to about 20 pounds of said ethyl ethoxybenzoate per million pounds of said polypropylene impact copolymers.
9. A method according to claim 8 wherein a compressor is disposed upstream of said heat exchanger and wherein said ethyl ethoxybenzoate is introduced into said compressor.
10. A method according to claim 8 wherein a compressor is disposed upstream of said heat exchangers and wherein said ethyl ethoxybenzoate is introduced between said compressor and said heat exchanger.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/447,049 US5037905A (en) | 1989-12-07 | 1989-12-07 | Process for reducing polymer build-up in heat exchangers during polymerization of alpha-olefins |
| US7/447,049 | 1989-12-07 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2031699A1 CA2031699A1 (en) | 1991-06-08 |
| CA2031699C true CA2031699C (en) | 1996-12-24 |
Family
ID=23774801
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002031699A Expired - Fee Related CA2031699C (en) | 1989-12-07 | 1990-12-06 | Process for reducing polymer build-up in heat exchangers during polymerization of alpha-olefins |
Country Status (19)
| Country | Link |
|---|---|
| US (1) | US5037905A (en) |
| EP (1) | EP0431626B1 (en) |
| JP (1) | JP2512344B2 (en) |
| KR (1) | KR950008719B1 (en) |
| CN (1) | CN1029619C (en) |
| AR (1) | AR244706A1 (en) |
| AT (1) | ATE121425T1 (en) |
| AU (1) | AU625791B2 (en) |
| BR (1) | BR9006060A (en) |
| CA (1) | CA2031699C (en) |
| DE (1) | DE69018785T2 (en) |
| DK (1) | DK0431626T3 (en) |
| ES (1) | ES2070983T3 (en) |
| FI (1) | FI906024A (en) |
| GR (1) | GR3015906T3 (en) |
| HU (1) | HUT57799A (en) |
| MY (1) | MY104558A (en) |
| PT (1) | PT96105A (en) |
| ZA (1) | ZA909812B (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5194526A (en) * | 1992-07-30 | 1993-03-16 | Union Carbide Chemicals & Plastics Technology Corporation | Process for producing sticky polymers |
| US5200502A (en) * | 1992-08-26 | 1993-04-06 | Union Carbide Chemicals & Plastics Technology Corporation | Deactivator reagent for olefin polymerization catalysts |
| US5733988A (en) * | 1994-06-29 | 1998-03-31 | Union Carbide Chemicals & Plastics Technology Corporation | Process for reducing polymer build-up in recycle lines and heat exchangers during polymerizations employing butadiene, isoprene, and/or styrene |
| US5625012A (en) * | 1994-06-29 | 1997-04-29 | Union Carbide Chemicals & Plastics Technology Corporation | Process for reducing polymer build-up in recycle lines and heat exchangers during polymerization of alpha olefins |
| US6124230A (en) * | 1995-07-13 | 2000-09-26 | Exxon Chemical Patents, Inc. | Polymerization catalyst systems, their production and use |
| US6140432A (en) * | 1995-07-13 | 2000-10-31 | Exxon Chemical Patents Inc. | Polymerization catalyst systems, their production and use |
| USH1722H (en) * | 1995-05-05 | 1998-04-07 | Goode; Mark Gregory | Process for producing polypropylene impact block copolymers |
| DE19800020A1 (en) * | 1998-01-05 | 1999-07-08 | Basf Ag | Continuous gas phase polymerization process |
| US6201076B1 (en) | 1999-04-29 | 2001-03-13 | Equistar Chemicals, L.P. | Olefin polymerization process with fatty amine additives for improved activity and reduced fouling |
| FI991015A0 (en) | 1999-05-04 | 1999-05-04 | Borealis As | Process for the preparation of alpha-olefin polymers |
| US6884749B2 (en) | 2002-10-17 | 2005-04-26 | Equistar Chemicals L.P. | Supported catalysts which reduce sheeting in olefin polymerization, process for the preparation and the use thereof |
| US7332070B2 (en) * | 2003-07-15 | 2008-02-19 | Mitsui Chemicals, Inc. | Method of preventing heat exchanger fouling |
| EP1749034A2 (en) * | 2004-05-20 | 2007-02-07 | Univation Technologies, LLC | Gas olefin polymerization process |
| US7754830B2 (en) | 2004-05-20 | 2010-07-13 | Univation Technologies, Llc | Polymerization reaction monitoring with determination of induced condensing agent concentration for preventing discontinuity events |
| US7683140B2 (en) | 2004-05-20 | 2010-03-23 | Univation Technologies, Llc | Method for determining temperature value indicative of resin stickiness from data generated by polymerization reaction monitoring |
| US7253239B2 (en) * | 2004-10-29 | 2007-08-07 | Westlake Longview Corporation | Method for preventing or inhibiting fouling in a gas-phase polyolefin polymerization process |
| RU2448981C2 (en) * | 2006-09-07 | 2012-04-27 | Юнивейшн Текнолоджиз, Ллк | Methods for real-time determination of degree of resin stickiness using model for depression of melt initiation temperature |
| US8273834B2 (en) * | 2006-09-07 | 2012-09-25 | Univation Technologies, Llc | Methods for determining temperature value indicative of resin stickiness from data generated by polymerization reaction monitoring |
| EP2330135B1 (en) * | 2009-12-02 | 2012-11-07 | Borealis AG | Process for producing polyolefins |
| EP3137516B1 (en) | 2015-03-25 | 2018-04-25 | Basell Polyolefine GmbH | Continuous gas-phase polymerization processes |
| EP3592780A1 (en) | 2017-03-09 | 2020-01-15 | ExxonMobil Chemical Patents Inc. | Process for producing polyethylene polymers |
| KR102421977B1 (en) | 2018-12-19 | 2022-07-18 | 주식회사 엘지화학 | Method and apparatus for preparing aromatic vinyl compound-vinylcyan compound copolymer |
| EP3868793A1 (en) * | 2020-02-24 | 2021-08-25 | Borealis AG | Process for producing alpha-olefin polymers in a multistage polymerization process |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5611908A (en) * | 1979-07-11 | 1981-02-05 | Mitsui Petrochem Ind Ltd | Preparation of olefin polymer |
| US4675368A (en) * | 1982-10-04 | 1987-06-23 | Solvay & Cie. | Process for inhibiting crust formation in reactors during alpha-olefin prepolymerization modification of Ziegler catalyst |
| US4520163A (en) * | 1984-01-09 | 1985-05-28 | Shell Oil Company | Process of sequentially copolymerizing propylene-ethylene copolymers and catalyst therefor |
| US4981929A (en) * | 1986-06-23 | 1991-01-01 | Union Carbide Chemicals And Plastics Company, Inc. | Catalyst productivity in the polymerization of olefins |
| EP0282929B2 (en) * | 1987-03-14 | 1997-10-22 | Mitsubishi Kasei Corporation | Method for producing a propylene-alpha-olefin block copolymer |
| CA1312173C (en) * | 1988-05-12 | 1992-12-29 | Fred Chun-Chien Twu | Process for the preparation of random copolymers |
| US4956427A (en) * | 1988-12-23 | 1990-09-11 | Union Carbide Chemicals And Plastics Company Inc. | Process for reducing polymer build-up in polymerization equipment during polymerization of alpha-olefins |
-
1989
- 1989-12-07 US US07/447,049 patent/US5037905A/en not_active Expired - Lifetime
-
1990
- 1990-11-29 BR BR909006060A patent/BR9006060A/en not_active IP Right Cessation
- 1990-12-05 FI FI906024A patent/FI906024A/en not_active IP Right Cessation
- 1990-12-06 CA CA002031699A patent/CA2031699C/en not_active Expired - Fee Related
- 1990-12-06 CN CN90110405A patent/CN1029619C/en not_active Expired - Fee Related
- 1990-12-06 DE DE69018785T patent/DE69018785T2/en not_active Expired - Lifetime
- 1990-12-06 AR AR90318548A patent/AR244706A1/en active
- 1990-12-06 EP EP90123464A patent/EP0431626B1/en not_active Expired - Lifetime
- 1990-12-06 PT PT96105A patent/PT96105A/en not_active Application Discontinuation
- 1990-12-06 KR KR1019900019984A patent/KR950008719B1/en not_active IP Right Cessation
- 1990-12-06 MY MYPI90002147A patent/MY104558A/en unknown
- 1990-12-06 HU HU908100A patent/HUT57799A/en unknown
- 1990-12-06 ZA ZA909812A patent/ZA909812B/en unknown
- 1990-12-06 AU AU67785/90A patent/AU625791B2/en not_active Ceased
- 1990-12-06 ES ES90123464T patent/ES2070983T3/en not_active Expired - Lifetime
- 1990-12-06 DK DK90123464.1T patent/DK0431626T3/en active
- 1990-12-06 AT AT90123464T patent/ATE121425T1/en not_active IP Right Cessation
- 1990-12-06 JP JP2405352A patent/JP2512344B2/en not_active Expired - Lifetime
-
1995
- 1995-04-20 GR GR950400886T patent/GR3015906T3/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU625791B2 (en) | 1992-07-16 |
| CN1054602A (en) | 1991-09-18 |
| EP0431626B1 (en) | 1995-04-19 |
| GR3015906T3 (en) | 1995-07-31 |
| CA2031699A1 (en) | 1991-06-08 |
| DE69018785D1 (en) | 1995-05-24 |
| DE69018785T2 (en) | 1995-08-24 |
| ATE121425T1 (en) | 1995-05-15 |
| JP2512344B2 (en) | 1996-07-03 |
| AR244706A1 (en) | 1993-11-30 |
| HU908100D0 (en) | 1991-06-28 |
| ES2070983T3 (en) | 1995-06-16 |
| JPH0413703A (en) | 1992-01-17 |
| EP0431626A1 (en) | 1991-06-12 |
| KR910011923A (en) | 1991-08-07 |
| MY104558A (en) | 1994-04-30 |
| US5037905A (en) | 1991-08-06 |
| FI906024A0 (en) | 1990-12-05 |
| CN1029619C (en) | 1995-08-30 |
| DK0431626T3 (en) | 1995-05-08 |
| AU6778590A (en) | 1991-06-13 |
| ZA909812B (en) | 1991-10-30 |
| PT96105A (en) | 1991-09-30 |
| BR9006060A (en) | 1991-09-24 |
| FI906024A (en) | 1991-06-08 |
| KR950008719B1 (en) | 1995-08-04 |
| HUT57799A (en) | 1991-12-30 |
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