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
  • C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
  • C08F10/02—Ethene

Definitions

• the present invention relates to a process for manufacturing polyethylene by high-pressure polymerization in a tubular reactor.
• Low density polyethylene is generally made by high pressure polymerization in either an autoclave reactor (a high pressure continuously stirred tank reactor) or a tubular reactor.
• the choice of reactor affects the properties of the LDPE.
• the extent of branching of "autoclave LDPE” is higher than of "tubular LDPE”. This is due to the residence time in the reactors.
• a tubular reactor operates under plug flow conditions, meaning that the entire reaction mixture has the same residence time. In autoclave reactors, back mixing results in a spread of residence times. The result is a higher degree of branching of autoclave LDPE compared to tubular LDPE.
• Organic peroxides are generally used to initiate the polymerisation of ethylene, both in autoclave reactors and in tubular reactors. In both reactors, several different organic peroxides are generally used.
• diacyl peroxides such as di(3,5,5-trimethylhexanoyl)peroxide are at least one of the types to be used; in tubular reactors, peroxyesters like tert-butyl peroxy-2- ethylhexanoate and tert-butyl peroxypivalate are conventionally present.
• peroxides decompose by unimolecular homolysis of the 0-0 bond.
• various rearrangement and non-radical decomposition reactions reduce the initiator efficiency.
• diacyl peroxides may undergo non-radical decomposition via the so-called carboxy inversion process, yielding acyl carbonates.
• Peroxyesters may undergo non-radical decomposition via the Criegee rearrangement, a process analogues to carboxy inversion. It has now surprisingly been found that carboxy inversion can be reduced by using bis(n-butanoyl)peroxide as initiator:
• this peroxide is more efficient than conventionally used peroxides.
• this peroxide due to its low molecular weight, this peroxide has a high active oxygen content and its decomposition products are volatile and therefore don't end up in the resulting polymer.
• the present invention therefore relates to a process for manufacturing a polyethylene homo- or copolymer by conducting polymerization of ethylene, optionally in combination with one or more co-monomers, at a pressure in the range 500-5000 bar, wherein bis(n-butanoyl) peroxide is used as polymerization initiator.
• the polymerization is carried out at pressures that are in the range 500-5000 bar, preferably 1000-5000 bar, more preferably 1500-3500 bar, and most preferably 2000-3300 bar.
• the reaction temperature is preferably in the range 100-350°C, more preferably 130-330°C, and most preferably 160-320°C.
• the process can be performed in tubular and autoclave (i.e. high pressure stirred tank) reactors, preference is given to the performance in an autoclave reactor.
• Bis(n-butanoyl)peroxide can be dosed to the reactor 100% pure or, more preferably, as a solution in hydrocarbons, such as odorless mineral spirit, isododecane, chain transfer agents (e.g. butane, propylene, propionaldehyde), or one or more reactive diluents.
• a reactive diluent is a liquid unsaturated hydrocarbon that can copolymerize with ethylene. Examples of reactive diluents are olefins, more preferably C 6 -12 alpha-olefins.
• the bis(n-butanoyl)peroxide concentration in such solutions is preferably in the range 5-50 wt%, more preferably 20-40 wt%.
• bis(n-butanoyl)peroxide is preferably added to the reactor in amounts of 100 to 1000 ppm (weight parts per million weight parts), more preferably 100-500 ppm, calculated as pure peroxide and based on the weight of monomer.
• the process of the present invention can be used both for the homo- polymerization of ethylene and for the co-polymerization of ethylene with other monomers, provided that these monomers undergo free-radical polymerization with ethylene under high pressure.
• suitable co-polymerizable monomers are ⁇ , ⁇ -ethylenically unsaturated Ca-Ce-carboxylic acids (e.g. maleic acid, fumaric acid, itaconic acid, citraconic acid, acrylic acid, methacryiic acid, or crotonic acid), ⁇ , ⁇ -ethylenically unsaturated C 3 -Ci 5 -carboxylic esters or anhydrides (e.g.
• Ca-Ce-carboxylic acids e.g. maleic acid, fumaric acid, itaconic acid, citraconic acid, acrylic acid, methacryiic acid, or crotonic acid
• C 3 -Ci 5 -carboxylic esters or anhydrides e.g.
• vinyl carboxylates particularly preferably vinyl acetate, as co-monomers.
• the proportion of co-monomers in the reaction mixture is preferably in the range 0-45 wt%, more preferably 3-35 wt%, based on the weight of ethylene monomer.
• the process is used for the manufacture of ethylene homopolymer, more in particular low density polyethylene homopolymer (LDPE).
• LDPE low density polyethylene homopolymer
• the polymer resulting from the process of the present invention preferably has a density in the range 910-940 kg/m 3 , more preferably 918-926 kg/m 3 and most preferably 920-925 kg/m 3 .
• the density is mostly controlled by the reactor pressure and temperature profile and can also be influenced by means of the chain regulators and/or co-monomers.
• Low density polyethylene is defined as having a density in the range 0.910-0.940 g/cm 3 .
• the melt flow index of the resulting polymer in accordance with DIN 53 735 is preferably less than 50 g/10 min, more preferably less than 10 g/10 min, and most preferably less than 5 g/10 min.
• the polymerization initiator(s) is/are preferably introduced into the tubular reactor along the length of the tube at from 1 to 6 inlet points, so that from 1 to 6 reaction zones are obtained in which polymerization is initiated. More preferably 2-6, and most preferably 3-5 initiator inlet points are used and preferably 2-6, and most preferably 3-5 reaction zones are created.
• Each of the reaction zones has its own temperature profile.
• Bis(n-butanoyl)peroxide is introduced in at least one of the reaction zones. It preferably is introduced in a plurality of reaction zones, alone or in admixture with other peroxides (co-initiators). Most preferably, it is introduced in every reaction zone.
• the peroxide or mixture of peroxides that is introduced in each reaction zone can be the same or can differ per zone.
• An autoclave reactor generally also contains multiple (preferably 1 -6, more preferably 2-4) reaction zones, each zone being isothermal. As a result of this constant temperature per zone, only one type of peroxide is introduced in each zone. Bis(n-butanoyl)peroxide is introduced in one of the reaction zones.
• co-initiators can be used in the process of the present invention.
• Such co-initiator may have a higher reactivity (i.e. shorter half-life) or a lower reactivity (i.e. longer half-life) than bis(n-butanoyl)peroxide at a specific temperature.
• Co-initiators are preferably selected from the following groups. It is noted that bis(n-butanoyl)peroxide is used at temperatures up to about 200°C.
• Di(2-ethylhexyl)peroxydicarbonate and tert-butyl peroxyneodecanoate are the preferred co-initiators of group 1 .
• Group 2 suitable up to about 240°C: tert-butylperoxy 2-ethylhexanoate
• Group 3 suitable in the range 240-280°C: tert-butylperoxy-3,5,5- trimethylhexanoate, tert-butylperoxybenzoate, tert-butyl peroxyacetate, and 2,2- di(tert-butylperoxy)butane.
• Tert-butylperoxy-3,5,5-thmethylhexanoate and tert- butylperoxybenzoate are the preferred co-initiators of group 3.
• Group 4 - suitable above about 280°C di-tert-butyl peroxide and 3,6,9-triethyl- 3,6,9,-trimethyl-1 ,4,7-triperoxonane.
• tubular reactors it is conventional to use a mixture of peroxides covering the entire temperature profile.
• LDPE low density polyethylene
• One of these peroxides is bis(n- butanoyl)peroxide, the other are chosen from each of groups 2, 3, and 4.
• bis(n-butanoyl)peroxide co-initiators from each of groups 1 , 2, and 3.
• one peroxide is usually added per zone, although it is also possible to add a mixture of peroxides per zone.
• Each zone is at constant temperature: the temperature may, however, differ per zone. If the autoclave contains more than one zone, the most reactive peroxides - i.e. bis(n- butanoyl)peroxide and optionally a co-initiator of group 1 - is used in the top zone(s), whereas the least reactive co-initiators (groups 3 and/or 4) are used in the bottom zone(s).
• the most reactive peroxides - i.e. bis(n- butanoyl)peroxide and optionally a co-initiator of group 1 - is used in the top zone(s)
• the least reactive co-initiators groups 3 and/or 4
• the molar mass of the polyethylene to be prepared can be regulated in conventional ways by the addition of molecular weight regulators.
• molecular weight regulators are aliphatic and olefinic hydrocarbons (e.g. pentane, hexane, cyclohexane, propene, pentene, or hexene), ketones (e.g. acetone, diethyl ketone, or diamyl ketone), aldehydes (e.g. formaldehyde or acetaldehyde), and saturated aliphatic alcohols (e.g. methanol, ethanol, propanol, or butanol).
• saturated aliphatic aldehydes in particular propionaldehydes, or a-olefins such as propene or hexene.
• the reaction mixture After the last introduction of polymerization initiator, the reaction mixture is cooled in order to allow discharge of the product from the reactor. After discharge of the reaction mixture, the polymer is separated from any unreacted monomers by depressurization, after which the monomers can be re-circulated to the reactor.
• the resulting polyethylene is highly suitable to make high clarity polyethylene films (tubular LDPE), for injection molding applications, wire and cable production, and extrusion coating.
• Carboxy inversion products of bis(n-butanoyl)peroxide would be propyl-butanoyi carbonate, propane-propanoic anhydride, and mixed carboxylic carbonic anhydrides. However, no such products were detected.
• Carboxy inversion products of bis(3,5,5-trimethylhexanoyl)peroxide are 2,4,4- trimethylpentyl-3,5,5-trimethylhexanoyl carbonate, 2,4,4-trimethylpentane-2,4,4- trimethylpentanoic anhydride, and mixed carboxylic carbonic anhydrides. These products were indeed detected and listed in the Table below as “carboxy inversion products”. The results of Tables 1 and 2 show that bis(n-butanoyl)peroxide gives no carboxy inversion products.

Landscapes

• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=58745053

Family Applications (1)

Country Status (2)

Cited By (2)

Citations (3)

• 2018
  • 2018-05-14 WO PCT/EP2018/062313 patent/WO2018210712A1/en active Application Filing
  • 2018-05-15 TW TW107116433A patent/TW201900686A/zh unknown

Patent Citations (3)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events