Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By addition of entire unsaturated molecules – e.g.,...
Reexamination Certificate
2003-07-23
2004-11-09
Teskin, Fred (Department: 1713)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By addition of entire unsaturated molecules, e.g.,...
C585S009000, C585S946000, C526S208000
Reexamination Certificate
active
06815571
ABSTRACT:
The present invention relates to a process for preparing ethylene polymers by the high-pressure method, which comprises dissolving one or more free-radical initiators in one or more ketones of the formula I
where R
1
and R
2
are identical or different and are selected from among C
1
-C
6
-alkyl and C
3
-C
12
-cycloalkyl and R
1
and R
2
may also be covalently linked to one another to form a 4- to 13-membered ring, prior to the polymerization,
compressing the solution, metering it into the polymerization reactor at one or more points and subsequently carrying out the polymerization at from 150 to 380° C. and from 500 to 4500 bar.
Ethylene polymers can be prepared by various methods which can be subdivided broadly into low-pressure processes carried out at from 20 to 100 bar and temperatures up to 110° C., and high-pressure processes carried out at from 500 to 4000 bar and temperatures of 150° C. and above. The high-pressure method is a free-radical polymerization process which can generally make do without a catalyst (cf., for example:
Ullmann's Enyclopädie der technischen Chemie
, 4
th
edition, keywords: waxes, Vol. 24, p. 36 ff., Thieme Verlag Stuttgart, 1977). To initiate the free-radical chain reaction, use is usually made of one or more organic peroxides, for example the Trigonox® or Perkadox® grades from Akzo Nobel, or else air or atmospheric oxygen. The process is generally carried out in high-pressure autoclaves or in tube reactors. High-pressure autoclaves are known in squat or elongated designs. The frequently used tube reactors (
Ullmanns Encyclopädie der technischen Chemie
, Volume 19, p. 169 and p. 173 ff (1980), Verlag Chemie Weinheim, Deerfield Beach, Basle, and
Ullmann's Enyclopädie der technischen Chemie
, 4
th
edition, keywords: waxes, Vol. 24, p. 36 ff., Thieme Verlag Stuttgart, 1977) are easy to handle and have a low maintenance requirement.
To set the appropriate molecular weight, use is made of substances known as molecular weight regulators or simply regulators. When a substance is used as regulator, it has to be ensured that it is sufficiently efficient because the introduction of very large amounts of regulators is uneconomical.
A frequently used regulator is hydrogen, but when air or atmospheric oxygen is used as free-radical initiator in free-radical polymerization processes it can lead to the formation of explosive hydrogen/oxygen mixtures and is therefore of concern for safety reasons.
Gaseous regulators such as the frequently used alkanes ethane and propane likewise require strict safety regulation.
Ketones are known as particularly advantageous regulators because they are suitable for preparing excellent products having advantageous organoleptic properties, as has been demonstrated, for example, in DE-A 100 64 752, DE-A 100 64 799 and DE-A 100 64 800, published on Jun. 27, 2002. However, the consumption of ketones should be kept as low as possible for cost reasons.
The use of ketones as molecular weight regulators in the preparation of high molecular weight LDPE is likewise known. EP-A 0 928 797 proposes a process using methyl ethyl ketone as regulator, by means of which an LDPE suitable for extruded products, for example for films having a good puncture resistance, are prepared. However, the consumption of regulators is very high, which represents an economic disadvantage. If one wished to prepare waxes by the process described in EP-A 0 928 797, the consumption of regulators would be substantially higher still.
DE-A 1 908 964 discloses a process by means of which ethylene homopolymers can be prepared by the high-pressure method. The process described uses a peroxidic free-radical initiator, advantageously dissolved in an inert solvent (p. 4), in the first reaction zone and air in the second. As regulators, propionaldehyde or methyl ethyl ketone are recommended. In this process, ethylene, free-radical initiator and regulator are metered simultaneously into the first reaction zone of the reactor while air and a further regulator are metered into a second reaction zone. The process described is costly from a logistic and process engineering point of view.
U.S. Pat. No. 3,334,081 describes a high-pressure polymerization process having an increased conversion which is based on feeding ethylene into the reactor at at least two different places. A large number of organic peroxides are recommended as free-radical initiators and a large number of organic compounds, preferably ketones such as methyl ethyl ketone, are recommended as regulators. However, a disadvantage of the process described is the high capital cost resulting from the numerous metering points which all have to be designed so as to be extremely pressure-stable and leak-free. This makes the capital cost of a polymerization plant very high.
It is an object of the present invention to provide a process by means of which polyethylene, for example polyethylene waxes or high molecular weight polyethylene, can be prepared by the high-pressure method and in which both the consumption of process solvents and regulators, in particular of ketones as regulators, and the number and amount of various process chemicals is very low.
We have found that this process is achieved by dissolving one or more free-radical initiators directly in a ketone or a mixture of a plurality of ketones, subsequently compressing the solution and metering it into the polymerization apparatus and then carrying out the polymerization under high-pressure conditions.
Regulators used are one or more aliphatic, cycloaliphatic or alicyclic ketones of the formula I
In this formula, the radicals R
1
and R
2
are identical or different and are selected from among
C
1
-C
6
-alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl, isohexyl, sec-hexyl, particularly preferably C
1
-C
4
-alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl;
C
3
-C
12
-cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl and cyclododecyl; preferably cyclopentyl, cyclohexyl and cycloheptyl.
In a particular embodiment, the radicals R
1
and R
2
are covalently joined to one another to form a 4- to 13-membered ring. Thus, for example, R
1
and R
2
can together be:
—(CH
2
)
4
—, —(CH
2
)
5
—, —(CH
2
)
6
, —(CH
2
)
7
—, —CH(CH
3
)—CH
2
—CH
2
—CH(CH
3
)—
or
—CH(CH
3
)—CH
2
—CH
2
—CH
2
—CH(CH
3
)—.
Preferred examples are acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), 2-pentanone, 3-pentanone and cyclopentanone, cyclohexanone and cycloheptanone. Particularly preferred examples are acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; very particular preference is given to methyl ethyl ketone and cyclohexanone.
Free-radical initiators used are one or more peroxides selected from among the commercially available substances
didecanoyl peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, tert-amyl peroxy-2-ethylhexanoate, dibenzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxydiethylacetate, tert-butyl peroxydiethylisobutyrate, 1,4-di(tert-butylperoxycarbo)cyclohexane as isomer mixture, tert-butyl perisononanoate, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-butylperoxy)cyclohexane, methyl isobutyl ketone peroxide, tert-butyl peroxyisopropylcarbonate, 2,2-di(tert-butylperoxy)butane or tert-butyl peroxyacetate;
tert-butyl peroxybenzoate, di-tert-amyl peroxide, dicumyl peroxide, the isomeric di(tert-butylperoxyisopropyl)benzenes, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, tert-butyl cumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hex-3-yne, di-tert-butyl peroxide, 1,3-diisopropyl monohydroperoxide, cumene hydroperoxide or tert-butyl hydroperoxide; or
dimeric or trimeric ketone peroxides of the formulae IIa to IIc.
In these formulae, the radicals R
3
to R
8
are identical or different and are selected from among
C
1
-C
8
-alkyl su
Deckers Andreas
Dröge Thomas
Gonioukh Andrei
Mähling Frank-Olaf
Weber Wilhelm
BASF - Aktiengesellschaft
Teskin Fred
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