PROCESS FOR THE PREPARATION OF ETHYLENE HOMO- OR COPOLYMERS IN A TUBULAR REACTOR

Abstract

The invention relates to a process for the preparation of low density polyethylene (LDPE) wherein the polymerisation takes place in a tubular reactor at peak temperatures ranging from 180° C. to 350° C. and at pressures ranging from 150 to 350 MPa and wherein the total effective length of the polymerisation reactor divided by the number of reaction zones is in the range from 230 to 350 m.

Claims

1. A process for the preparation of low density polyethylene (LDPE) wherein the polymerisation takes place in a tubular reactor at peak temperatures ranging from 180° C. to 350° C. and at pressures ranging from 150 to 350 MPa and wherein the total effective length of the polymerisation reactor divided by the number of reaction zones is in the range from 230 to 350 m.

2. A process according to claim 1 wherein the average ΔT is ≤55° C. and wherein the sum of all ΔT's (ΣΔT) is in the range from 100 to 350° C.

3. A process according to claim 1 wherein a reactor efficiency is >0.36, wherein the reactor efficiency is defined as the conversion in wt % multiplied by the number of reaction zones and divided by the average length of the reaction zones.

4. A process according to claim 1, wherein ethylene is fed into the reactor by a single ethylene feed stream and wherein the ethylene is fed to the first reaction zone.

5. A process according to claim 1, wherein one or more peroxides are used as initiator.

6. A process according to claim 1, wherein the LDPE has a long chain branching (LCB) content of ≥1.5/1000 C.

7. A process according to claim 1, wherein the comonomer is selected from the group consisting of acrylates, methacrylates, alkenes, dienes, carbon monoxide and combinations thereof.

8. A process according to claim 1, wherein the LDPE is a copolymer of ethylene and a comonomer, and the comonomer is selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2,3-dihydroxypropyl acrylate, 2,3-dihydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, poly(propylene glycol) monoacrylate, poly(propyleneglycol) monomethacrylate, poly(ethylene glycol) monoacrylate, poly(ethylene glycol) monomethacrylate, poly(ethylenepropyleneglycol) monomethacrylate, 2-hydroxyethyl vinyl ether, vinylacetate and combinations thereof.

9. A process according to claim 1, wherein the LDPE is a copolymer of ethylene and a comonomer, and the comonomer is selected from the group consisting of 4-butanediol dimethacrylate, hexanediol dimethacrylate, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, dodecanediol dimethacrylate, glycerol dimethacrylate, 1,4-butanediol diacrylate, hexanediol diacrylate, ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, dodecanediol diacrylate, glycerol diacrylate, glycerol 1,3-diglycerolate diacrylate, glycerol 1,3-diglycerolate dimethacrylate, poly(ethylene glycol) dimethacrylate, poly(propylene glycol) dimethacrylate, poly(ethylenepropyleneglycol) dimethacrylate, trimethylol propane trimethacrylate, trimethylol propane triacrylate, 1,4-butanediol divinyl ether, poly(ethylene glycol) divinyl ether, di(ethyleneglycol) divinyl ether, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene, 1,13-tetradecadiene and combinations thereof.

10. A process according to claim 1, wherein the reactor inlet pressure is between 150 MPa and 350 MPa.

11. A LDPE obtained by or obtainable by the process according to claim 1.

12. An extrusion coating composition comprising the LDPE obtained by or obtainable by the process according to claim 1.

13. An article comprising the LDPE obtained by or obtainable by the process according to claim 1.

14. A foam, film, blown film, cast film, extrusion coated laminate or sheet comprising the LDPE obtained by or obtainable by the process according to claim 1.

15. A process for making an article comprising the LDPE obtained by or obtainable by the process according to claim 1.

16. (canceled)

17. A process according to claim 1 wherein the average ΔT is ≤55° C. and wherein the sum of all ΔT's (ΣΔT) is in the range from 110 to 320° C.

18. A process according to claim 1 wherein a reactor efficiency is >0.4, and the reactor efficiency is defined as the conversion in wt % multiplied by the number of reaction zones and divided by the average length of the reaction zones.

19. A process according to claim 8, wherein an amount of units derived from the comonomer in the copolymer ranges from ≥0.10 to ≤20.0 mol %.

20. A process according to claim 1, wherein the LDPE has a long chain branching (LCB) content of ≥1.7/1000 C.

Description

EXAMPLES

[0108] Calculations of ethylene homopolymerisation have been performed based on deterministic and stochastic modelling as outlined by Kiparissides (A COMPREHENSIVE MATHEMATICAL MODEL FOR A MULTIZONE TUBULAR HIGH PRESSURE LDPE REACTOR, C. KIPARISSIDES, G. VERROS, G. KALFAS, M. KOUTOUDI & C. KANTZIA, Chem. Eng. Comm 1993, Vol 121, Pages 193-217, Publishers Gordon and Breach Science Publishers S.A.) and by M. Busch (Busch, M., Macromolecular Theory and Simulations, 2001, 10, 408-429).

[0109] Calculations were made for 4, 6 and 7 initiator injection points, total effective reactor length is 1940-2100 meter and an internal diameter of 59 mm. The calculations were carried out using the following conditions:

[0110] Feed of ethylene: 70636 kg/h

[0111] Starting temperature T: 159° C.

[0112] Pressure at inlet: 259 MPa

Comparative Example 1

[0113]

TABLE-US-00001 TABLE 1 Overview of calculation parameters and obtained molecular characteristics for a reactor with 4 reaction zones. number of reaction zones — 4 4 4 4 4 average length/reaction zone m 445 445 445 445 445 peak temperature ° C. 300 290 280 260 255 average temperature ° C. 273 266 259 244 240 Average ΔT ° C. 61 56 51 39 36 Sum of ΔT (ΣΔT) ° C. 242 222 203 154 142 Conversion % 26 24 22 19 18 reactor efficiency 0.23 0.22 0.20 0.17 0.16 LCB content /1000 C 3.0 2.4 2.0 1.4 1.2 Mn dalton 11287 11252 11271 11285 11293

Inventive Example 1

[0114]

TABLE-US-00002 TABLE 2 Overview of calculation parameters and obtained molecular characteristics for a reactor with 6 reaction zones. number of reaction zones — 6 6 6 6 6 6 average length/reaction zone m 297 297 297 297 297 297 peak temperature ° C. 300 290 285 280 273 260 average temperature ° C. 282 274 269 265 259 248 Average ΔT ° C. 50 46 44 42 39 32 Sum of ΔT (ΣΔT) ° C. 302 274 262 249 231 190 Conversion % 32 29 28 27 25 23 reactor efficiency 0.65 0.58 0.56 0.54 0.51 0.46 CTA feed vol % 1.5 1.8 2.0 2.1 2.3 2.6 LCB content /1000 C 3.8 3.09 2.79 2.53 2.21 1.75 Mn dalton 11286 11251 11272 11254 11259 11264

Inventive Example 2

[0115]

TABLE-US-00003 TABLE 3 Overview of calculation parameters and obtained molecular characteristics for a reactor with 7 reaction zones. number of reaction zones — 7 7 7 7 7 average length/reaction zone m 277 277 277 277 277 peak temperature ° C. 290 280 270 260 255 average temperature ° C. 272 266 257 252 244 Average ΔT ° C. 43 38 33 28 26 Sum of ΔT (ΣΔT) ° C. 201 177 150 122 110 Conversion % 32 29 27 25 23 reactor efficiency 0.81 0.74 0.68 0.63 0.59 CTA feed vol % 1.8 2.0 2.3 2.5 2.7 LCB content /1000 C 3.5 2.83 2.32 1.91 1.7 Mn dalton 11290 11277 11322 11312 11282

[0116] The conditions used for comparative example 1 result in a material which is called the base case. The molecular characteristics were calculated for four peroxide dosing points. Subsequently, additional peroxide dosing points were added within the same reactor length. From these results, it is evident that with increasing number of additional dosing points the conversion increases and the average temperature, too. Moreover, the number of LCB/1000 C (long chain branches/1000 carbons) significantly increases. This improves melt strength and processability of the material. Further the reactor efficiency can be increased as shown in FIG. 1. In FIG. 1, 1 (□) refers to the comparative example, 2 (∘) refers to inventive example 1 and 3 (Δ) refers to inventive example 2.