EP1395618A1 - Method for producing ethylene homopolymers and copolymers by means of radical high pressure polymerization - Google Patents

Method for producing ethylene homopolymers and copolymers by means of radical high pressure polymerization

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Publication number
EP1395618A1
EP1395618A1 EP02743142A EP02743142A EP1395618A1 EP 1395618 A1 EP1395618 A1 EP 1395618A1 EP 02743142 A EP02743142 A EP 02743142A EP 02743142 A EP02743142 A EP 02743142A EP 1395618 A1 EP1395618 A1 EP 1395618A1
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zone
reactor
mfr
tubular reactor
ethylene
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EP02743142A
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German (de)
French (fr)
Inventor
Wilhelm Zoller
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Basell Polyolefine GmbH
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Basell Polyolefine GmbH
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Publication of EP1395618A1 publication Critical patent/EP1395618A1/en
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    • 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
    • C08F10/02—Ethene
    • 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
    • C08F110/02—Ethene

Definitions

  • Polyethylene is produced by polymerizing ethylene using two fundamentally different methods, the high-pressure and the low-pressure / medium-pressure process.
  • the low pressure / medium pressure process can be carried out as solution polymerization, as suspension / emulsion polymerization or as gas phase polymerization.
  • the high pressure process is carried out at pressures higher than 1500 bar (corresponding to 150 to 400 MPa) and takes place according to a radical mechanism.
  • the low-pressure / medium-pressure process is carried out at pressures below 100 bar and as a rule catalyzed.
  • products from the high-pressure process which have a high branching, a lower crystallinity and a low density
  • products from the low-pressure / medium-pressure process are mostly of a linear, little branched structure, and have a high crystallinity (mostly 60 - 90%), a high melting range (typically 120 - 35 ° C) and a high density (usually 0.93 - 0.97 g / cm 3 ).
  • a high density of polyethylene is usually combined with a high glass transition temperature, high hardness, a high melting range, high brittleness and low stickiness. The above properties generally characterize low-pressure / medium-pressure polyethylene.
  • the low-density polyethylene (LDPE) which is produced by the high-pressure process in tubular reactors, is still a standard plastic, for which the highest demand is still registered worldwide because of the material is less brittle and is simply easier to process for numerous applications.
  • the high-pressure polymerization process is still a proven process for the production of low-density polyethylene (LDPE), which is carried out on a large scale in numerous plants worldwide with great success.
  • the start of the polymerization is usually effected by atmospheric oxygen or by peroxides or by other free radical formers or by mixtures of these.
  • the radical chain initiators used to start the polymerization have to be added to the reaction medium in a suitable manner.
  • the high-pressure polymerization of ethylene is therefore to be considered below, in which comonomers such as vinyl acetate, vinyl esters, olefinically unsaturated carboxylic acids or alpha-olefins are also used. It is a copolymerization in which the crystallinity of the product obtained can be controlled in a targeted manner by varying the amount of comonomer in the monomer mixture.
  • the reaction gas is first heated to a temperature in the range from 90 to 200 ° C. in order to start the strongly exothermic polymerization reaction.
  • the heat of reaction released is removed by water cooling, with up to 40% of the monomers used being converted to polymer in one pass through the continuously operated reactor.
  • the resulting polymer is separated in a two-stage process comprising high-pressure and low-pressure separation.
  • the polymer arriving in the low-pressure separation is then freed from the remaining part of the unreacted reaction gases by further depressurization to 1 to 5 bar.
  • the gases are returned while the polymer obtained is fed to a melt extruder, homogenized and then granulated.
  • the polymer so produced tends to speckle to a certain extent.
  • the object of the present invention was therefore to carry out the high-pressure polymerization of ethylene and other comonomers in such a way that a higher throughput is achieved by optimizing the reactor cooling mode, the reaction temperature and the cooling water distribution while maintaining the quality of the polymer produced in this way.
  • This object is achieved by a process for high-pressure polymerization of ethylene in a tubular reactor which is designed as a double-tube heat exchanger, in which fresh ethylene is first subjected to low-pressure compression and then brought to reaction pressure together with recyclate, initiators, moderators and comonomer in a high-pressure compressor,
  • the characteristics of which can be seen in the fact that the polymer is carried out at a pressure in the range from 2000 to 3500 bar and that the reaction mixture runs through a temperature profile in the range from 100 to 350 ° C within the tubular reactor.
  • the reaction mixture of inert gas, molecular weight regulator, ethylene and comonomer is preferably first compressed to a pressure of 2800 bar and then heated to a temperature of 120 ° C.
  • the hot reaction mixture is then fed into the tubular reactor, where the high pressure piston pumps are used at the very beginning Peroxide initiator in an amount of 10 to 400 ppm, based on the weight of the reaction mixture, is added.
  • the immediately occurring exothermic polymerization reaction releases heat of reaction, which must be dissipated quickly by water cooling, because otherwise the reaction mixture would overheat and there would be a risk of uncontrolled decomposition of the ethylene.
  • the cooling is carried out according to the invention in such a way that the entire reactor is divided lengthwise into two zones.
  • the first zone comprises the two front thirds of the total length of the tubular reactor
  • the second zone comprises the rear third of the total length of the tubular reactor.
  • Both zones of the reactor are cooled separately with water of different temperatures, the preferred water temperature for the production of ethylene homopolymer in the two zones being calculated using the following formula:
  • MFR represents the melt index of the product obtained at the end of the reactor in [dg / min], measured according to ASTM D-1238, Condition (E), i.e. at a temperature of 190 ° C and a weight of 2.16 kg.
  • the water temperature preferred according to the invention for the production of ethylene copolymer with vinyl acetate in the two zones is calculated using the following formula:
  • MFR also represents the melt index of the product obtained at the end of the reactor in [dg / min], measured in accordance with ASTM D-1238, Condition (E), ie at a temperature of 190 ° C. and a coating weight of 2.16 kg.
  • E ASTM D-1238, Condition
  • the reaction mixture is cooled and, by reducing the pressure to a value in the range between 10 to 70 MPa, essentially freed of volatile constituents.
  • the polymer melt is freed of the residual adhering reaction gases by further depressurization to 1 to 5 bar, as described above, homogenized in the extruder, granulated and filled.
  • molecular weight regulators Conventional polar or non-polar organic compounds such as ketones, aldehydes, alkanes or alkenes having 3 to 20 carbon atoms can be used as molecular weight regulators.
  • Preferred molecular weight regulators are acetone,
  • peroxides such as aliphatic diacyl (C 3 to C 2 ) peroxides, tertiary-butylperoxypivalate (TBPP), tertiary-butylperoxy-3,5,5-trimethylhexanoate (TBPIN), di-tertiary-butyl peroxide (DTBP), tertiary- Butyl perisononate or mixtures or solutions of these can be used in suitable solvents.
  • the radical chain initiators are fed in amounts in the range from 10 to 1000 g / t of PE produced, preferably from 100 to 600 g / t of PE produced.
  • the flowing flow medium to which the above-mentioned radical chain initiators are fed according to the invention can, in addition to ethylene as a comonomer, additionally 1-olefins having 3 to 20 C atoms, preferably having 3 to 10 C atoms, in an amount in the range from 0 to 10% by weight .-%, Based on the amount of ethylene monomer, preferably in an amount in the range of 1 to 5 wt .-%.
  • the flowing fluid medium according to the invention Contain polyethylene in an amount in the range of 0 to 40 wt .-%, based on the total weight of the monomers, preferably from 1 to 30 wt .-%.
  • the radical chain starters are supplied in a region of the tubular reactor in which the diameter of the tubular reactor is reduced to a value of approximately 0.6 to 0.9 times the diameter D of the reactor in the feed zone, the flow rate of the flowing fluid medium is 1.2 to 2.8 times, preferably 1.8 to 2.5 times, the flow rate within the feed zone of the tubular reactor is increased.
  • Flow velocity of the flowing flow medium in the supply area of the radical chain starters according to the invention in the range from 10 to 40 m / s, preferably from 15 to 30 m / s, particularly preferably from 20 to 25 m / s.
  • the process according to the invention has the advantage that stable reactor operation can be maintained at unusually high maximum temperatures of up to 350 ° C. without a tendency to decompose.
  • Another advantage of the process according to the invention is that the start of the polymerization starts at lower temperatures and that the temperature rise of the reaction mixture then takes place in a controlled manner.
  • the service life of the radical chain starters which usually have only a relatively short half-life, is better utilized for the polymerization and thus for the production of LDPE.
  • the process according to the invention improves sales and above all product properties such as density and MFR.
  • the amount of radical chain starter to be used could be reduced by approximately 15% and the operating constancy of the tubular reactor was increased.
  • the polyethylene worked up at the end of the reactor in a known manner had a density of 0.924 g / cm 3 and an MFR of 0.65 dg / min.

Abstract

The invention relates to a method for producing ethylene homopolymers and copolymers by means of radical polymerization in a tubular reactor at pressures greater than 1000 bar and temperatures ranging from 120 to 400 DEG C. Initially, small quantities of radical chain starters are supplied to a streaming flow medium containing ethylene, molar mass regulators and optionally, polyethylene, whereupon polymerization takes place. According to the invention, polymerization takes place at pressures between 2000 and 3500 bar, and the temperature profile of the reaction mixture inside the tubular reactor ranges from 100 to 350 DEG C.

Description

Verfahren zur Herstellung von Ethylenhomo- und -copolymeren durch radikalische HochdruckpolymerisationProcess for the production of ethylene homo- and copolymers by radical high pressure polymerization
Polyethylen wird durch Polymerisation von Ethylen nach zwei grundsätzlich unterschiedlichen Methoden, dem Hochdruck- und dem Niederdruck-/Mitteldruck- Verfahren hergestellt. Das Niederdruck-/Mitteldruck-Verfahren kann als Lösungspolymerisation, als Suspensions-/Emulsions-Polymerisation oder als Gasphasenpolymerisation durchgeführt werden. Das Hochdruckverfahren wird bei höheren Drücken als 1500 bar (entsprechend 150 bis 400 MPa) durchgeführt und läuft nach einem radikalischen Mechanismus ab.Polyethylene is produced by polymerizing ethylene using two fundamentally different methods, the high-pressure and the low-pressure / medium-pressure process. The low pressure / medium pressure process can be carried out as solution polymerization, as suspension / emulsion polymerization or as gas phase polymerization. The high pressure process is carried out at pressures higher than 1500 bar (corresponding to 150 to 400 MPa) and takes place according to a radical mechanism.
Im allgemeinen wird das Niederdruck-/Mitteldruckverfahren bei Drücken unter 100 bar und dabei in der Regel katalysiert durchgeführt. Im Gegensatz zu den Produkten aus dem Hochdruckverfahren, die eine hohe Verzweigung, eine niedrigere Kristallinität und eine niedrige Dichte aufweisen, sind Produkte aus dem Niederdruck-/Mitteldruck- verfahren meist von linearer, wenig verzweigter Struktur, und besitzen eine hohe Kristallinität (meist 60 - 90 %), einen hohen Schmelzbereich (typisch 120 - 35 °C) und eine hohe Dichte (meist 0,93 - 0,97 g/cm3). Eine hohe Dichte des Polyethylens ist in der Regel gleichzeitig mit einer hohen Glasübergangstemperatur, einer hohen Härte, einem hohen Schmelzbereich, einer hohen Sprödigkeit und einer geringen Klebrigkeit verbunden. Vorstehende Eigenschaften zeichnen das Niederdruck-/Mitteldruck- polyethylen im allgemeinen aus.In general, the low-pressure / medium-pressure process is carried out at pressures below 100 bar and as a rule catalyzed. In contrast to the products from the high-pressure process, which have a high branching, a lower crystallinity and a low density, products from the low-pressure / medium-pressure process are mostly of a linear, little branched structure, and have a high crystallinity (mostly 60 - 90%), a high melting range (typically 120 - 35 ° C) and a high density (usually 0.93 - 0.97 g / cm 3 ). A high density of polyethylene is usually combined with a high glass transition temperature, high hardness, a high melting range, high brittleness and low stickiness. The above properties generally characterize low-pressure / medium-pressure polyethylene.
Da diese Eigenschaften allerdings anwendungstechnisch nicht immer und überall gefragt sind, stellt das niedrig dichte Polyethylen (LDPE) das nach dem Hochdruckverfahren in Rohrreaktoren hergestellt wird, nach wie vor einen Standardkunststoff dar, für den weltweit immer noch die höchste Nachfrage registriert wird, weil das Material weniger spröde ist und sich für zahlreiche Anwendungszwecke einfach leichter verarbeiten lässt. Aus diesem Grund ist das Hochdruckpolymerisationsverfahren nach wie vor ein bewährtes Verfahren zur Herstellung von Polyethylen mit niedriger Dichte (LDPE), das weltweit in zahlreichen Anlagen großtechnisch mit großem Erfolg durchgeführt wird. Der Start der Polymerisation wird bei der Hochdruckpolymerisation üblicherweise durch Luftsauerstoff oder durch Peroxide oder durch andere Radikalbildner oder durch Gemische aus diesen bewirkt. Die zum Start der Polymerisation eingesetzten Radikalkettenstarter müssen hierzu dem Reaktionsmedium in irgendwie geeigneter Weise zugesetzt werden.However, since these properties are not always and everywhere in demand from an application point of view, the low-density polyethylene (LDPE), which is produced by the high-pressure process in tubular reactors, is still a standard plastic, for which the highest demand is still registered worldwide because of the material is less brittle and is simply easier to process for numerous applications. For this reason, the high-pressure polymerization process is still a proven process for the production of low-density polyethylene (LDPE), which is carried out on a large scale in numerous plants worldwide with great success. In high pressure polymerization, the start of the polymerization is usually effected by atmospheric oxygen or by peroxides or by other free radical formers or by mixtures of these. The radical chain initiators used to start the polymerization have to be added to the reaction medium in a suitable manner.
Im folgenden soll daher die Hochdruckpolymerisation von Ethylen betrachtet werden, bei der auch Comonomere wie Vinylacetat, Vinylester, olefinisch ungesättigte Carbonsäuren oder alpha-Olefine eingesetzt werden. Es handelt sich um eine Copoly- merisation, bei der durch Variation der Menge an Comonomer im Monomergemisch die Kristallinität des erhaltenen Produkts gezielt steuerbar ist. In der Firmenschrift "engineering news 4-94" der Uhde GmbH ist unter dem Titel: "The advanced Ruhrchemie Process" schematisch ein Verfahren dargestellt, bei dem Frischethylen zunächst einer Niederdruckkompression unterworfen wird und dann zusammen mit Rezyklat, das bei der eigentlichen Polymerisation nicht verbraucht wurde, mit Initiatoren, Moderatoren und Comonomeren in einem Hochdruckkompressor auf Reaktionsdruck gebracht wird. Die eigentliche Polymerisationsreaktion findet dann in einem Rohrreaktor statt, der als Doppelrohr-Wärmetauscher konstruiert ist.The high-pressure polymerization of ethylene is therefore to be considered below, in which comonomers such as vinyl acetate, vinyl esters, olefinically unsaturated carboxylic acids or alpha-olefins are also used. It is a copolymerization in which the crystallinity of the product obtained can be controlled in a targeted manner by varying the amount of comonomer in the monomer mixture. Uhde GmbH's "engineering news 4-94" company brochure, entitled "The advanced Ruhrchemie Process", schematically shows a process in which fresh ethylene is first subjected to low-pressure compression and then together with recyclate, which is not consumed in the actual polymerization was brought to reaction pressure with initiators, moderators and comonomers in a high pressure compressor. The actual polymerization reaction then takes place in a tubular reactor that is constructed as a double-tube heat exchanger.
Das Reaktionsgas wird zunächst auf eine Temperatur im Bereich von 90 bis 200 °C erhitzt, um die stark exotherme Polymerisationsreaktion zu starten. Die dabei frei werdende Reaktionswärme wird durch Wasserkühlung abgeführt, wobei in einem Durchgang durch den kontinuierlich betriebenen Reaktor bis zu 40 % der eingesetzten Monomeren zu Polymer umgesetzt wird.The reaction gas is first heated to a temperature in the range from 90 to 200 ° C. in order to start the strongly exothermic polymerization reaction. The heat of reaction released is removed by water cooling, with up to 40% of the monomers used being converted to polymer in one pass through the continuously operated reactor.
Die Abscheidung des entstandenen Polymers geschieht in einem Zweistufenverfahren umfassend eine Hochdruck- und eine Niederdrucktrennung. Zunächst wird durch Druckverminderung auf etwa 180 bis 350 bar nicht verbrauchtes Reaktionsgas zum größten Teil von dem entstandenen Polymer abgetrennt und nach Abkühlung und Reinigung wieder als Rezyklat in die Polymerisationsreaktion zurückgeschleust. Dann wird das in der Niederdrucktrennung ankommende Polymer durch weitere Entspannung auf 1 bis 5 bar vom restlichen Teil der nicht umgesetzten Reaktionsgase befreit. Die Gase werden wieder zurückgeführt, während das erhaltene Polymer einem Schmelzeextruder zugeführt, homogenisiert und anschließend granuliert wird.The resulting polymer is separated in a two-stage process comprising high-pressure and low-pressure separation. First, by reducing the pressure to about 180 to 350 bar most of the consumed reaction gas is separated from the polymer formed and, after cooling and purification, is fed back into the polymerization reaction as recyclate. The polymer arriving in the low-pressure separation is then freed from the remaining part of the unreacted reaction gases by further depressurization to 1 to 5 bar. The gases are returned while the polymer obtained is fed to a melt extruder, homogenized and then granulated.
Nachteiligerweise neigt jedoch das so hergestellte Polymer in gewissem Umfang zur Stippenbildung.Disadvantageously, however, the polymer so produced tends to speckle to a certain extent.
Aufgabe der vorliegenden Erfindung war es daher, die Hochdruckpolymerisation von Ethylen und weiteren Comonomeren so durchzuführen, dass durch Optimierung der Reaktorkühlweise, der Reaktionstemperatur und der Kühlwasserverteilung bei gleichbleibender Qualität des so hergestellten Polymers ein höherer Durchsatz erreicht wird.The object of the present invention was therefore to carry out the high-pressure polymerization of ethylene and other comonomers in such a way that a higher throughput is achieved by optimizing the reactor cooling mode, the reaction temperature and the cooling water distribution while maintaining the quality of the polymer produced in this way.
Gelöst wird diese Aufgabe durch ein Verfahren zur Hochdruckpolymerisation von Ethylen in einem Rohrreaktor, der als Doppelrohr-Wärmetauscher ausgebildet ist, bei dem Frischethylen zunächst einer Niederdruckkompression unterworfen wird und dann zusammen mit Rezyklat, Initiatoren, Moderatoren und Comonomer in einem Hochdruckkompressor auf Reaktionsdruck gebracht wird, dessen Kennzeichenmerkmale darin zu sehen sind, dass die Polymeristaion bei einem Druck im Bereich von 2000 bis 3500 bar durchgeführt wird und dass die Reaktionsmischung innerhalb des Rohrreaktors ein Temperaturprofil im Bereich von 100 bis 350 °C durchläuft.This object is achieved by a process for high-pressure polymerization of ethylene in a tubular reactor which is designed as a double-tube heat exchanger, in which fresh ethylene is first subjected to low-pressure compression and then brought to reaction pressure together with recyclate, initiators, moderators and comonomer in a high-pressure compressor, The characteristics of which can be seen in the fact that the polymer is carried out at a pressure in the range from 2000 to 3500 bar and that the reaction mixture runs through a temperature profile in the range from 100 to 350 ° C within the tubular reactor.
Vorzugsweise wird die Reaktionsmischung aus Inertgas, Molmassenregler, Ethylen und Comonomer zunächst auf einen Druck von 2800 bar komprimiert und dann auf eine Temperatur von 120 °C erhitzt. Die heiße Reaktionsmischung wird dann in den Rohrreaktor eingespeist, wo gleich zu Beginn über Hochdruckkolbenpumpen der Peroxidinitiator in einer Menge von 10 bis 400 ppm, bezogen auf das Gewicht der Reaktionsmischung, zugegeben wird. Durch die sofort einsetzende exotherme Polymerisationsreaktion wird Reaktionswärme frei, die durch Wasserkühlung schnell abgeführt werden muss, weil sich das Reaktionsgemisch sonst zu stark überhitzen würde und die Gefahr einer unkontrollierten Zersetzung des Ethylens bestünde. Die Kühlung wird erfindungsgemäß so durchgeführt, dass der gesamte Reaktor der Länge nach in zwei Zonen eingeteilt wird. Die erste Zone umfasst die zwei vorderen Drittel der Gesamtlänge des Rohrreaktors, die zweite Zone umfasst das hintere Drittel der Gesamtlänge des Rohrreaktors. Beide Zonen des Reaktors werden separat mit Wasser von unterschiedlicher Temperatur gekühlt, wobei sich die bevorzugte Wassertemperatur für die Herstellung von Ethylenhomopolymer in den beiden Zonen nach folgender Formel berechnet:The reaction mixture of inert gas, molecular weight regulator, ethylene and comonomer is preferably first compressed to a pressure of 2800 bar and then heated to a temperature of 120 ° C. The hot reaction mixture is then fed into the tubular reactor, where the high pressure piston pumps are used at the very beginning Peroxide initiator in an amount of 10 to 400 ppm, based on the weight of the reaction mixture, is added. The immediately occurring exothermic polymerization reaction releases heat of reaction, which must be dissipated quickly by water cooling, because otherwise the reaction mixture would overheat and there would be a risk of uncontrolled decomposition of the ethylene. The cooling is carried out according to the invention in such a way that the entire reactor is divided lengthwise into two zones. The first zone comprises the two front thirds of the total length of the tubular reactor, the second zone comprises the rear third of the total length of the tubular reactor. Both zones of the reactor are cooled separately with water of different temperatures, the preferred water temperature for the production of ethylene homopolymer in the two zones being calculated using the following formula:
T(H2O) [°C] Zone 1 = 200 - 7,77 • MFR und T(H2O) [°C] Zone 2 = 159 - 7,62 ■ MFR,T (H 2 O) [° C] zone 1 = 200 - 7.77 • MFR and T (H 2 O) [° C] zone 2 = 159 - 7.62 ■ MFR,
wobei MFR den Schmelzindex des am Ende des Reaktors erhaltenen Produktes in [dg/min] darstellt, gemessen nach ASTM D-1238, Condition (E), d.h. bei einer Temperatur von 190 °C und einem Auflagegewicht von 2,16 kg.where MFR represents the melt index of the product obtained at the end of the reactor in [dg / min], measured according to ASTM D-1238, Condition (E), i.e. at a temperature of 190 ° C and a weight of 2.16 kg.
Die erfindungsgemäß bevorzugte Wassertemperatur für die Herstellung von Ethylencopolymer mit Vinylacetat in den beiden Zonen berechnet sich nach folgender Formel:The water temperature preferred according to the invention for the production of ethylene copolymer with vinyl acetate in the two zones is calculated using the following formula:
T(H2O) [°C] Zone 1 = 130 - 1 ,77 • MFR und T(H2O) [°C] Zone 2 = 120 - 3,0 MFR,T (H 2 O) [° C] zone 1 = 130 - 1, 77 • MFR and T (H 2 O) [° C] zone 2 = 120 - 3.0 MFR,
wobei MFR ebenfalls den Schmelzindex des am Ende des Reaktors erhaltenen Produktes darstellt in [dg/min], gemessen nach ASTM D-1238, Condition (E), d.h. bei einer Temperatur von 190 °C und einem Auflagegewicht von 2, 16 kg. Am Ende des Rohrreaktors wird die Reaktionsmischung abgekühlt und durch Herabsetzen des Druckes auf einen Wert im Bereich zwischen 10 bis 70 MPa im Wesentlichen von flüchtigen Bestandteilen befreit. Danach wird die Polymerschmelze wie vorstehend beschrieben durch weiteres Entspannen auf 1 bis 5 bar von den rest- liehen anhaftenden Reaktionsgasen befreit, im Extruder homogenisiert, granuliert und abgefüllt.where MFR also represents the melt index of the product obtained at the end of the reactor in [dg / min], measured in accordance with ASTM D-1238, Condition (E), ie at a temperature of 190 ° C. and a coating weight of 2.16 kg. At the end of the tubular reactor, the reaction mixture is cooled and, by reducing the pressure to a value in the range between 10 to 70 MPa, essentially freed of volatile constituents. Thereafter, the polymer melt is freed of the residual adhering reaction gases by further depressurization to 1 to 5 bar, as described above, homogenized in the extruder, granulated and filled.
Überraschend hat sich gezeigt, dass sich durch die Einhaltung des erfindungsgemäß vorgeschriebenen Temperaturprofils bei der Polymerisation die Wärmeübertragung verbessert und dass die Reaktorausbeute damit gesteigert werden kann.Surprisingly, it has been shown that the heat transfer is improved during the polymerization by adhering to the temperature profile prescribed according to the invention, and that the reactor yield can thus be increased.
Als Molmassenregler können erfindungsgemäß gängige polare oder unpolare organische Verbindungen wie Ketone, Aldehyde, Alkane oder Alkene mit 3 bis 20 C- Atomen eingesetzt werden. Bevorzugte Molmassenregler sind Aceton,Conventional polar or non-polar organic compounds such as ketones, aldehydes, alkanes or alkenes having 3 to 20 carbon atoms can be used as molecular weight regulators. Preferred molecular weight regulators are acetone,
Methylethylketon, Propionaldehyd, Propan, Propen, Butan, Buten oder Hexen.Methyl ethyl ketone, propionaldehyde, propane, propene, butane, butene or hexene.
Als Radikalkettenstarter können erfindungsgemäß Peroxide wie aliphatische Diacyl(C3 bis C-ι2)peroxide, tertiär-Butylperoxypivalat (TBPP), tertiär-Butylperoxy- 3,5,5-trimethylhexanoat (TBPIN), Di-tertiärbutylperoxid (DTBP), tertiär- Butylperisononat oder Gemische oder Lösungen von diesen in geeigneten Lösemitteln verwendet werden. Die Radikalkettenstarter werden erfindungsgemäß in Mengen im Bereich von 10 bis 1000 g/t erzeugtes PE, vorzugsweise von 100 bis 600 g/t erzeugtes PE, zugeleitet.According to the invention, peroxides such as aliphatic diacyl (C 3 to C 2 ) peroxides, tertiary-butylperoxypivalate (TBPP), tertiary-butylperoxy-3,5,5-trimethylhexanoate (TBPIN), di-tertiary-butyl peroxide (DTBP), tertiary- Butyl perisononate or mixtures or solutions of these can be used in suitable solvents. According to the invention, the radical chain initiators are fed in amounts in the range from 10 to 1000 g / t of PE produced, preferably from 100 to 600 g / t of PE produced.
Das strömende Fließmedium, zu dem die vorstehend genannten Radikalkettenstarter erfindungsgemäß zugeleitet werden, kann neben Ethylen als Comonomer zusätzlich 1-Olefine mit 3 bis 20 C-Atomen, vorzugsweise mit 3 bis 10 C-Atomen, in einer Menge im Bereich von 0 bis 10 Gew.-%, bezogen auf die Menge an Ethylenmonomer, enthalten, vorzugsweise in einer Menge im Bereich von 1 bis 5 Gew.-%. Zusätzlich kann das strömende Fließmedium erfindungsgemäß Polyethylen in einer Menge im Bereich von 0 bis 40 Gew.-%, bezogen auf das Gesamtgewicht der Monomere, enthalten, vorzugsweise von 1 bis 30 Gew.-%.The flowing flow medium to which the above-mentioned radical chain initiators are fed according to the invention can, in addition to ethylene as a comonomer, additionally 1-olefins having 3 to 20 C atoms, preferably having 3 to 10 C atoms, in an amount in the range from 0 to 10% by weight .-%, Based on the amount of ethylene monomer, preferably in an amount in the range of 1 to 5 wt .-%. In addition, the flowing fluid medium according to the invention Contain polyethylene in an amount in the range of 0 to 40 wt .-%, based on the total weight of the monomers, preferably from 1 to 30 wt .-%.
In einer besonders bevorzugten Variante des erfindungsgemäßen Verfahrens wird die Zuleitung der Radikalkettenstarter in einem Bereich des Rohrreaktors vorgenommen, in dem durch eine Reduzierung des Durchmessers des Rohrreaktors auf einen Wert von etwa dem 0,6- bis 0,9-fachen des Durchmessers D des Reaktors in der Zulaufzone die Strömungsgeschwindigkeit des strömenden Fließmediums auf das 1 ,2- bis 2,8-fache, vorzugsweise auf das 1 ,8- bis 2,5-fache, der Strömungsgeschwindigkeit innerhalb der Zulaufzone des Rohrreaktors erhöht ist. In Absolutzahlen ausgedrückt liegt dieIn a particularly preferred variant of the method according to the invention, the radical chain starters are supplied in a region of the tubular reactor in which the diameter of the tubular reactor is reduced to a value of approximately 0.6 to 0.9 times the diameter D of the reactor in the feed zone, the flow rate of the flowing fluid medium is 1.2 to 2.8 times, preferably 1.8 to 2.5 times, the flow rate within the feed zone of the tubular reactor is increased. Expressed in absolute numbers
Strömungsgeschwindigkeit des strömenden Fließmediums im Zuleitungsbereich der Radikalkettenstarter erfindungsgemäß im Bereich von 10 bis 40 m/s, vorzugsweise von 15 bis 30 m/s, besonders bevorzugt von 20 bis 25 m/s.Flow velocity of the flowing flow medium in the supply area of the radical chain starters according to the invention in the range from 10 to 40 m / s, preferably from 15 to 30 m / s, particularly preferably from 20 to 25 m / s.
Das erfindungsgemäße Verfahren hat den Vorteil, dass ein stabiler Reaktorbetrieb bei ungewöhnlich hohen Maximaltemperaturen von bis zu 350 °C aufrecht erhalten werden kann, ohne dass eine Zersetzungsneigung auftritt.The process according to the invention has the advantage that stable reactor operation can be maintained at unusually high maximum temperatures of up to 350 ° C. without a tendency to decompose.
Ein weiterer Vorteil des erfindungsgemäßen Verfahrens ist darin zu sehen, dass der Start der Polymerisation bei tieferen Temperaturen einsetzt und dass danach der Temperaturanstieg der Reaktionsmischung kontrolliert erfolgt. Dadurch wird die Lebensdauer der Radikalkettenstarter, die gewöhnlich nur eine relativ kurze Halbwertszeit haben, besser für die Polymerisation und damit für die Herstellung von LDPE ausgenutzt.Another advantage of the process according to the invention is that the start of the polymerization starts at lower temperatures and that the temperature rise of the reaction mixture then takes place in a controlled manner. As a result, the service life of the radical chain starters, which usually have only a relatively short half-life, is better utilized for the polymerization and thus for the production of LDPE.
In Praxisversuchen wurde deutlich, dass durch das erfindungsgemäße Verfahren der Umsatz und vor allem die Produkteigenschaften wie Dichte und MFR verbessert werden. Die einzusetzende Menge an Radikalkettenstarter konnte erfindungsgemäß um ca. 15 % gesenkt werden und die Betriebskonstanz des Rohrreaktors wurde erhöht. AusführungsbeispielIn practical tests, it became clear that the process according to the invention improves sales and above all product properties such as density and MFR. According to the invention, the amount of radical chain starter to be used could be reduced by approximately 15% and the operating constancy of the tubular reactor was increased. embodiment
In einem Rohrreaktor mit einem L/D-Verhältnis von 30 000 wurde einem Gemisch aus 98 Vol.-% Ethylen, 1 ,5 Vol.-% Propylen als Moderator und 1 ,5 ppm Sauerstoff am Reaktoreintritt nach Erwärmung auf eine Temperatur von 150 °C eine Menge von 28,5 ppm di-tert.-Butylperoxy-2-ethylhexanoat und 200 ppm Hexan (Lösungsmittel) eingespritzt. In der ersten Reaktionszone wurde die Temperatur des Kühlwassers auf 195 °C eingestellt, in der zweiten Reaktionszone wurde durch weitere Zugabe von Kühlwasser auf eine Wassertemperatur von 154 °C gekühlt. Der Druck im Innern des Reaktors betrug 233 MPa (= 2330 bar).In a tubular reactor with an L / D ratio of 30,000, a mixture of 98% by volume ethylene, 1.5% by volume propylene as moderator and 1.5 ppm oxygen at the reactor inlet after heating to a temperature of 150 ° C an amount of 28.5 ppm of di-tert-butylperoxy-2-ethylhexanoate and 200 ppm of hexane (solvent) were injected. In the first reaction zone, the temperature of the cooling water was set to 195 ° C., in the second reaction zone cooling was carried out to a water temperature of 154 ° C. by further addition of cooling water. The pressure inside the reactor was 233 MPa (= 2330 bar).
Das am Ende des Reaktors in bekannter Weise aufgearbeitete Polyethylen hatte eine Dichte von 0,924 g/cm3 und einen MFR von 0,65 dg/min. The polyethylene worked up at the end of the reactor in a known manner had a density of 0.924 g / cm 3 and an MFR of 0.65 dg / min.

Claims

Patentansprüche claims
l . Verfahren zur Herstellung von Ethylenhomo- und -copolymeren in einem Rohrreaktor bei Drücken oberhalb von 1000 bar und Temperaturen im Bereich von 100 bis 400 °C durch radikalische Polymerisation, bei dem einem strömenden Fließmedium enthaltend Ethylen, Molmassenregler und ggf. Polyethylen zunächst geringe Mengen von Radikalkettenstarter zugeleitet werden, wonach dann die Polymerisation durchgeführt wird, dadurch gekennzeichnet, dass die Polymeristaion bei einem Druck im Bereich von 2000 bis 3500 bar durchgeführt wird und dass die Reaktionsmischung innerhalb des Rohrreaktors ein Temperaturprofil im Bereich von 100 bis 350 °C durchläuft.l. Process for the production of ethylene homopolymers and copolymers in a tubular reactor at pressures above 1000 bar and temperatures in the range from 100 to 400 ° C by free-radical polymerization, in which a flowing fluid medium containing ethylene, molecular weight regulator and possibly polyethylene initially contains small amounts of free radical initiators are fed in, after which the polymerization is then carried out, characterized in that the polymerization is carried out at a pressure in the range from 2000 to 3500 bar and in that the reaction mixture within the tubular reactor runs through a temperature profile in the range from 100 to 350 ° C.
2 . Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Reaktionsmischung aus Inertgas, Molmassenregler, Ethylen und Comonomer zunächst auf einen Druck von 2800 bar komprimiert und dann auf eine Temperatur von 120 °C erhitzt wird.2nd A method according to claim 1, characterized in that the reaction mixture of inert gas, molecular weight regulator, ethylene and comonomer is first compressed to a pressure of 2800 bar and then heated to a temperature of 120 ° C.
3 . Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die heiße Reaktionsmischung dann in den Rohrreaktor eingespeist wird, wo unverzüglich über Hochdruckkolbenpumpen Peroxidinitiator in einer Menge von 10 bis 400 ppm, bezogen auf das Gewicht der Reaktionsmischung, zugegeben wird.3rd A method according to claim 1 or 2, characterized in that the hot reaction mixture is then fed into the tubular reactor, where peroxide initiator in an amount of 10 to 400 ppm, based on the weight of the reaction mixture, is immediately added via high-pressure piston pumps.
4 . Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass die sofort frei werdende Reaktionswärme durch Wasserkühlung abgeführt wird.4th Method according to one of claims 1 to 3, characterized in that the immediately released heat of reaction is removed by water cooling.
5. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass die Wasserkühlung so eingestellt wird, dass für die Herstellung von5. The method according to any one of claims 1 to 4, characterized in that the water cooling is set so that for the production of
Ethylenhomopolymer in zwei Zonen, von denen Zone 1 die vorderen zwei Drittel der gesamten Rohrlänge des Rohrreaktors umfasst und von denen Zone 2 das hintere Drittel der gesamten Rohrlänge des Rohrreaktors umfasst, die bevorzugte Wassertemperatur für die Kühlung nach folgender Formel berechnet wird:Ethylene homopolymer in two zones, of which zone 1 is the front two thirds of the total tube length of the tube reactor and of which zone 2 comprises the rear third of the total tube length of the tube reactor, the preferred water temperature for cooling is calculated using the following formula:
T(H2O) [°C] Zone 1 = 200 - 7,77 ■ MFR und T(H2O) [°C] Zone 2 = 159 - 7,62 ■ MFR,T (H 2 O) [° C] Zone 1 = 200 - 7.77 ■ MFR and T (H 2 O) [° C] Zone 2 = 159 - 7.62 ■ MFR,
wobei MFR den Schmelzindex des am Ende des Reaktors erhaltenen Homopolymers in [dg/min] darstellt, gemessen nach ASTM D-1238, Conditionwhere MFR represents the melt index of the homopolymer obtained at the end of the reactor in [dg / min], measured according to ASTM D-1238, Condition
(E).(E).
6. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass die Wasserkühlung so eingestellt wird, dass für die Herstellung von6. The method according to any one of claims 1 to 4, characterized in that the water cooling is set so that for the production of
Ethylencopolymer in zwei Zonen, von denen Zone 1 die vorderen zwei Drittel der gesamten Rohrlänge des Rohrreaktors umfasst und von denen Zone 2 das hintere Drittel der gesamten Rohrlänge des Rohrreaktors umfasst, die bevorzugte Wassertemperatur für die Kühlung nach folgender Formel berechnet wird:Ethylene copolymer in two zones, of which zone 1 comprises the front two thirds of the total tube length of the tubular reactor and of which zone 2 comprises the rear third of the total tube length of the tubular reactor, the preferred water temperature for cooling is calculated using the following formula:
T(H2O) [°C] Zone 1 = 130 - 1 ,77 • MFR und T(H2O) [°C] Zone 2 = 120 - 3,0 - MFR,T (H 2 O) [° C] zone 1 = 130 - 1, 77 • MFR and T (H 2 O) [° C] zone 2 = 120 - 3.0 - MFR,
wobei MFR den Schmelzindex des am Ende des Reaktors erhaltenen Copolymers in [dg/min] darstellt, gemessen nach ASTM D-1238, Condition (E).where MFR represents the melt index of the copolymer obtained at the end of the reactor in [dg / min], measured according to ASTM D-1238, Condition (E).
7. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass die Polymerschmelze nach dem Austritt aus dem Reaktor durch schrittweises Entspannen von nicht umgesetzten Reaktionsgasen befreit, granuliert und abgefüllt wird. 7. The method according to any one of claims 1 to 6, characterized in that the polymer melt is freed from granules and filled by stepwise expansion of unreacted reaction gases after leaving the reactor.
. Verfahren nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass als Molmassenregler polare oder unpolare organische Verbindungen wie Ketone, Aldehyde, Alkane oder Alkene mit 3 bis 20 C-Atomen eingesetzt werden, vorzugsweise Aceton, Methylethylketon, Propionaldehyd, Propan, Propen, Butan, Buten oder Hexen., Method according to one of claims 1 to 7, characterized in that polar or non-polar organic compounds such as ketones, aldehydes, alkanes or alkenes having 3 to 20 carbon atoms, preferably acetone, methyl ethyl ketone, propionaldehyde, propane, propene, butane, are used as molecular weight regulators , Butene or witches.
9. Verfahren nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, dass als Radikalkettenstarter Peroxide wie tertiär-Butylperoxypivalat (TBPP), tertiär- Butylperoxy-3,5,5-trimethylhexanoat (TBPIN), Di-tertiärbutylperoxid (DTBP), tertiär-Butylperisononat oder Gemische oder Lösungen von diesen in geeigneten Lösemitteln in Mengen im Bereich von 10 bis 1000 g/t erzeugtes PE, vorzugsweise von 100 bis 600 g/t PE, zugeleitet werden. 9. The method according to any one of claims 1 to 8, characterized in that as free radical initiators peroxides such as tertiary-butylperoxypivalate (TBPP), tertiary-butylperoxy-3,5,5-trimethylhexanoate (TBPIN), di-tertiary butyl peroxide (DTBP), tertiary Butyl perisononate or mixtures or solutions of these in suitable solvents in amounts in the range from 10 to 1000 g / t PE, preferably from 100 to 600 g / t PE, are supplied.
EP02743142A 2001-06-11 2002-06-04 Method for producing ethylene homopolymers and copolymers by means of radical high pressure polymerization Withdrawn EP1395618A1 (en)

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