PROCESS FOR MANUFACTURING POLYETHYLENE

Abstract

Process for manufacturing a polyethylene homo- or copolymer by conducting high-pressure polymerization of ethylene, optionally in combination with one or more co-monomers, in a tubular reactor, wherein tert-amyl peroxyisobutyrate is used as polymerization initiator.

Claims

1. Process for manufacturing a polyethylene homo- or copolymer by conducting high-pressure polymerization of ethylene, optionally in combination with one or more co-monomers, in a tubular reactor, wherein tert-amyl peroxyisobutyrate is used as polymerization initiator.

2. Process according to claim 1 wherein the polymerization is conducted at a temperature in the range 160-350 C.

3. Process according to claim 1 wherein the polymerization is conducted at a pressure in the range 500-5000 bar.

4. Process according to claim 1 wherein the polyethylene is low density polyethylene (LDPE).

5. Process according to claim 1, wherein one or more co-initiators are used.

6. Process according to claim 5, using, as co-initiator, a peroxide selected from the group consisting of di(2-ethylhexyl)peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, tert-amyl peroxypivalate, and tert-butyl peroxypivalate.

7. Process according to claim 6 wherein the co-initiator is tert-butyl peroxypivalate.

8. Process according to claim 6 wherein the co-initiator is di(2-ethylhexyl)peroxydicarbonate or tert-butyl peroxyneodecanoate.

9. Process according to claim 5, using, as co-initiator, a peroxide selected from the group of tert-butyl peroxy-3,3,5-trimethylhexanoate, tert-butyl peroxybenzoate, 2,2-di(tert-butylperoxy)butane, tert-butyl peroxyacetate, tert-butyl peroxy isopropyl carbonate, di-tert-butyl peroxide, and 3,3,5,7,7-pentamethyl-1,2,4-trioxepane.

10. Process according to claim 9 wherein the co-initiator is di-tert-butyl peroxide or tert-butyl peroxy-3,3,5-trimethylhexanoate.

Description

EXAMPLE

[0059] In this example, the decomposition of tert-butyl peroxy-2-ethylhexanoate, tert-amyl peroxy-2-ethylhexanoate, and tert-amyl peroxyisobutyrate under conditions comparable to those in an ethylene polymerization process was studied.

[0060] Solutions of the peroxides in n-nonane (0.1 M) were prepared and the peroxides were completely decomposed in a continuous flow reactor at a temperature of 175 C. and a pressure of 2000 bar.

[0061] To compare the selected peroxides, the amount of acetone formed during total decomposition was taken as a measure for the amount of 1-scission. The results are displayed in Table 1, which shows that tert-amyl peroxyisobutyrate undergoes significantly more 1-scission than the other two peroxides. Tert-amyl peroxyisobutyrate thus forms a higher number of selective alkyl-radicals and gives reduced hydrogen abstraction. This will result in less branching.

TABLE-US-00001 TABLE 1 Acetone (mol/mol peroxide) tert-amylperoxy isobutyrate 0.515 tert-butylperoxy 2-ethylhexanoate 0.094 tert-amylperoxy 2-ethylhexanoate 0.301

[0062] The in-cage termination reactions affect the efficiency of peroxides. If the radicals that are formed upon peroxide dissociation are directly consumed inside the solvent cage to form ethers (through in-cage decarboxylation) and alkenes (through in-cage disproportionation), the efficiency drops, simply because these radicals are not available for polymerization initiation. Hence, the formation of alkenes and ethers is an indicator for the efficiency.

TABLE-US-00002 TABLE 2 Ether Alkene (mol/mol (mol/mol peroxide) peroxide) tert-amylperoxy isobutyrate 0.13 0.03 tert-butylperoxy 2-ethylhexanoate 0.14 0.42 tert-amylperoxy 2-ethylhexanoate 0.21 0.37

[0063] Table 2 shows that tert-amyl peroxyisobutyrate gives less in-cage reactions than the other two peroxides, indicating a higher efficiency.