Process and plant for manufacturing polyethylene-silane-copolymers

1. A process for manufacturing polyethylene-silane copolymer conducted in a plant comprising at least one compressor unit and at least one reactor being downstream of the compressor unit,

the process comprising the steps of:

a) feeding a first feed stream comprising ethylene into the at least one compressor unit and subsequently to the at least one reactor, and

b1) feeding a second feed stream comprising at least one silane comonomer to the first feed stream only after the first feed stream comprising ethylene leaves the compressor unit and feeding the combined feed stream comprising ethylene and the at least one silane comonomer to the at least one reactor as front feed and/or

b2) feeding another second feed stream comprising at least one silane comonomer to the at least one reactor at at least one location along the reactor.

2. The process according to claim 1 , wherein the concentration of the silane comonomer being fed at a location along the reactor is the same as or differs from the concentration of the silane comonomer entering the reactor at the front.

3. The process according to claim 1 , wherein the concentration of the silane comonomer being fed at the front of reactor is more than 50 wt % of the concentration of the silane comonomer entering the reactor in total.

4. The process according to claim 1 , wherein the at least one silane comonomer if fed to the reactor at a location along the reactor is added to the reactor using at least one high pressure plunger pump.

5. The process according to claim 1 , wherein the silane comonomer comprises an unsaturated silane compound represented by the general formula

RSiR′ n Y 3 - n

wherein R is an ethylenically unsaturated hydrocarbyl, hydrocarbyloxy or (meth)acryloxy hydrocarbyl group, R′ is an aliphatic saturated hydrocarbyl group, Y is a hydrolysable organic group, and n is 0, 1 or 2.

6. The process according to claim 5 , wherein the unsaturated silane compound is a compound represented by the formula

CH 2 ═CHSi(OA) 3

wherein A is a hydrocarbyl group having 1-8 carbon atoms.

7. The process according to claim 5 , wherein the unsaturated silane is selected from a group consisting of vinyl trimethoxysilane (VTMS), vinyl dimethoxyethoxy silane, vinyl triethoxysilane, gamma-(meth)acryloxypropyltrimethoxy-silane, gamma(meth)acryloxypropyltriethoxysilane, vinyl triacetoxysilane, and any combinations thereof.

8. The process according to claim 1 , wherein at least one further polar comonomer is additionally fed to the feed stream comprising ethylene before said feed stream enters the compressor unit, is fed to the feed stream comprising ethylene before entering the at least one reactor as front feed and/or is fed to the reactor at at least one location along the reactor.

9. The process according to claim 8 , wherein the at least one additional polar comonomer is selected from the group consisting of vinyl carboxylate esters; alpha-olefins; (meth)acrylates; vinyl ethers; aromatic vinyl compounds and any combination thereof.

10. The process according to claim 8 , wherein the at least one additional polar comonomer is selected from a group consisting of vinyl acetate (EVA), methacrylates maleic anhydride (MAH), and acrylamide.

11. The process according to claim 1 , wherein a third feed stream comprising at least one chain transfer agent is fed to the feed stream comprising ethylene before said feed stream enters the compressor unit, is fed to the feed stream comprising ethylene before entering the at least one reactor as front feed and/or is fed to the reactor at at least one location along the reactor.

12. The process according to claim 11 , wherein the chain transfer agent is selected from a group consisting of propionaldehyde, propylene, propane, methyl ethyl ketone, isopropanol, methyl vinyl sulfide, n-butyronitrile, butene-1,4-methylpentane-1, isobutylene, diisobutylene, acetaldehyde and mixtures thereof.

13. The process according to claim 1 , wherein the at least one reactor is operated above a critical pressure of between 1000 and 3500 bar and at temperatures between 165 and 340° C., the feed temperature of either or both first and second feed streams of the reactor being in the range of 165 to 200° C.

14. The process according to claim 11 , wherein the chain transfer agent and/or comonomers are separated from the volatile part of the reaction mixture from the reactor in a gas purification unit.

15. The process according to claim 1 , wherein the ethylene of the first feed stream is fresh ethylene, ethylene recycled from the reactor without any further purification and/or ethylene recycled from the reactor, which underwent gas purification.

16. The process according to claim 1 , wherein the concentration of the silane comonomer being fed at the front of the reactor is more than 75% of the concentration of the silane comonomer entering the reactor in total.

17. The process according to claim 4 , wherein the at least one high pressure plunger pump is of the type of LEWA plunger pumps.

18. The process according to claim 5 , wherein the unsaturated silane compound is a compound represented by the formula

CH 2 ═CHSi(OA) 3

wherein A is a hydrocarbyl group having 1-4 carbon atoms.

19. The process according to claim 10 , wherein the methacrylates are selected from a group consisting of methyl acrylate (EMA), ethyl acrylate (EEA), butyl acrylate (EBA), methyl methacrylate (EMMA), and glycidyl methacrylate (GMA).

20. The process according to claim 1 , wherein the at least one reactor is operated above a critical pressure of between 2000 and 3200 bar, and at temperatures between 165 and 340° C., the feed temperature of either or both first and second feed streams of the reactor being in the range of 165 to 200° C.