SU734217A1 - Method of preparing ethylene (co)polymers - Google Patents

Description

The invention relates to the plastics industry, in particular, to the production of ethylene homo - or copolymers in a tubular reactor, which are used to make rt coating films, etc. In the homo- and copolymerization of ethylene by a radical mechanism, a polymer with an ultrahigh molecular weight is formed with the target product. This part of the product forms films on the walls of the reactor and is a source for the production of microgels. With further processing, especially when producing films, coating and using in the cable industry, this part of the product becomes noticeable, which spoils the appearance of thin films and, moreover, due to uneven product structure. may cause breakage during film expansion and coating. The known method of homo - or copolymerization of ethylene in the presence of radical initiators. In order to eliminate the formation of a polymer film on the walls of the reactor, the reaction pressure is periodically released 1 By increasing the flow rate of the reaction mixture, the polymer film is broken off the walls of the reactor. In a known manner, the gel content in the product is reduced, however, simultaneously with pressure drops, the reaction process is noticeably disturbed temperature and pressure fluctuations. In order to reduce the formation of film on the walls of the reactor during the homoi copolymerization of ethylene, butane 2 is introduced into the reactor. A product with improved film properties (lower turbidity, improved film gloss) is obtained, however, the gelation is completely eliminated. The closest is the method of producing ethylene (co) polymers by polymerizing ethylene or copolymerizing it with vinyl acetate in a tubular reactor in the presence of a radical initiator and inhibitor 3J. The inhibitor is introduced in an amount of 0.02-0.5 weight. in the process of (co) polymerization. The inhibiting compound is a low molecular weight; 1 times the condensation product of paratret1 kilphenols with jurmaldehyde. Get polymer with

llotnostyo 0.916-0.920 g / cm, melt index 1.26-6.25 g 10 min with a reduced content of microgels. Entering a large amount of inhibitor leads to undesirable color (from yellow to dark brown) polymer. In addition, the inhibitor injected only partially acts in the system of separation of the reaction mixture (where a polymer film is also formed on the walls of the separator), since already in the polymerization zone most of it turns into an inactive compound.

The purpose of the invention is to increase the transparency of the final product.

The goal is achieved by the fact that in a known method of producing ethylene (co) polymers by polymerizing ethylene or copolymerising it with vinyl acetate in a tubular reactor in the presence of a radical initiator and inhibitor, 0.0005-0.005% of the monomers of the phenol derivative is used as an inhibitor, and Before the reduction of the reaction pressure, the stabilized mixture is additionally introduced into the initial mixture into the reaction mixture or directly into the reaction pressure compressor and into the reaction mixture. iziruyushchy additive.

As inhibitory compounds, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-4-methylphenol 4, 4-meth and flax bis (2, 6-di- tert-butylphenol), 2,4-dimethyl-b-tert-butyl-phenol-4-tert-butylpyrocatechin and others.

Dialkyl or diacyl peroxides, oxygen, peroxydicarbonates or mixtures thereof, etc. are used as initiators.

For example, hydrocarbons are used as chain regulators. As stabilizing additives, compounds such as 4,4-thio-bis (3-methyl-B-tert-butylphenol), 2, 2 methylene bis-4- methyl-6 (, 1-methylcyclohexyl) phenol, substituted amines or diamines, for example N-phenyl-p-Japhylamine, condensation products of diamines with ketones, for example, cyclohexanone-diphenylamine condensates, phosphoric acid esters with mono- and polyfunctional alcohols, for example, trinynyl-phenylphosphite, thio-carboxylic acid esters, for example, di-octadecyl ef p tiodipropionovoy- acid.

You can also use a mixture of the above stabilizing additives, and the individual components should have the lowest possible volatility.

Example 1. In a tubular reactor with a diameter / length ratio of 1: 15,000 divided into 2 zones, moreover, the ratio of the length of zone I to length

Zone II is 1: 2, and the load amount distribution is 1: 1, a mixture of 21.5000 t / h of ethylene, 0.385 t / h of butane, 0.150 t / propane is introduced. 0.001 t / h (corresponding to 0.005 wt.%) 2, b-di-tert-butyl-4-methylphenol is added to the lubrication of the two-stage reaction pressure compressor and injected directly into the reaction compressor. The inlet pressure in zone I of the reactor is 2300 atm, the temperature of the heat transfer medium in the first zone, and in zone II -. A mixture of diisopropyl peroxydicarbonate, tert-butyl perbenzoate and dilauryl peroxide in a ratio of 1: 2: 1 in the amount of 1.6 kg / h is introduced into the first zone of the reactor and

2.3 kg / h in zone II, in the form of a 15% solution in paraffin oil (as initiator). In the I zone of the reactor, the maximum temperature is set at 300 ° C, and in the II - 320 ° C. In front of the reducing valve, zone II is added to the reaction mass

10 kg / h (which corresponds to 0.05 wt.%) A mixture of equal parts of the product of condensation of diphenylamine with cyclohexane, as well as trinonylphenylphosphite in the form of a 50% dispersion in paraffin oil.

Plant capacity 4.73 tons / hour.

The polyethylene obtained has a density of 0.925 g / cm, a melt index of 1.9 g / 10 min.

Films made from polyethylene

By blowing, they are characterized by a finite gloss, a very low degree of turbidity (0.07), do not contain a high molecular weight fraction, have increased strength at break, suitable for printing.

Example 2. The experiment was carried out in a reactor; described in example 1.

Under a pressure of 2500 atm, a mixture consisting of 20,500 tons / hour of ethylene, 1,900 tons / hour of vinyl acetate (i.e. 8.5%) and 0.0001 tons / hour (corresponding to 0.0005 wt.%) Is introduced into the reactor. ) 4,4-methylene bis- (2,6-di-t-butylphenol), which is added to the reaction mixture before it enters the reaction compressor.

Oxygen in the amount of 200 silt / hour is added to the stream directed to the II of the reactor. In the I zone of the reactor, as described in Example 1, a mixture of peroxides is added in the amount of

1.4kg / hour 0.5 kg / h of diieopropyl peroxydicarbonate is introduced into the beginning of zone II of the reactor in the form of a solution

in paraffin oil. The temperature of the coolant in the I reaction zone is - and in zone II - 180 ° C. The maximum temperature in 1 reaction zone is 260 ° C, and in II -.

40 kg / h (which is 0.002% by weight of a mixture of 4,4-thio-bis (3-methyl-6-tert-butylphenol), dodecyl thiodipropionic acid diododecyl ester and triphenylphosphite) are added to the reaction mixture by lowering the reaction pressure. 2: 1: 1 as a 25% dispersion in paraffin oil. The yield of a copolymer of ethylene with vinyl acetate is 4.21 tons / hour. The melt index of the copolymer is 2.0 g / 10 min, the density is 0.937 g / cm.

Films obtained from these copolymers are characterized by good gloss, low flawability, good mechanical properties, suitable for printing. The films are transparent and do not contain high molecular non-homogeneous products, the turbidity of the films is 0.11.

Claims (3)

1.Patent UK No. 891903, cl. 2/6 /, P, publ. 1959. 0 2. US patent 3119804, cl. 260-94.9, publ. 1968. 3. US Patent 3157629, cl. 260-94.9, publ. 1970. (prototype).