PROCESS FOR PREPARATION OF MULTIMODAL POLYOLEFIN

Abstract

The invention relates to a process for the preparation of a multimodal polyolefin polymer in a first polymerization reactor and a second polymerization reactor connected in series, wherein a first polyolefin polymer is prepared in the first polymerization reactor in suspension in the presence of hydrogen and a second polyolefin polymer is prepared in the second polymerization reactor in the presence of a lower concentration of hydrogen than in the first polymerization reactor, the process comprising: a) withdrawing a suspension of solid polyolefin particles in a suspension medium from the first polymerization reactor, wherein the suspension medium comprises hydrogen and a hydrocarbon mixture having an initial boiling point of at least 50 C. and a final boiling point of at most 120 C.; b) feeding the suspension to a flash drum having a pressure controlled by a vacuum pump, wherein the pressure of the flash drum is less than 0.1 MPa; c) vaporizing a part of the suspension medium in the flash drum to obtain a hydrogen-depleted suspension and d) withdrawing the hydrogen-depleted suspension from the flash drum and feeding it to the second polymerization reactor.

Claims

1. A process for the preparation of a multimodal polyolefin polymer in a first polymerization reactor and a second polymerization reactor connected in series, wherein a first polyolefin polymer is prepared in the first polymerization reactor in suspension in the presence of hydrogen and a second polyolefin polymer is prepared in the second polymerization reactor in the presence of a lower concentration of hydrogen than in the first polymerization reactor, the process comprising: a) withdrawing a suspension of solid polyolefin particles in a suspension medium from the first polymerization reactor, wherein the suspension medium comprises hydrogen and a hydrocarbon mixture having an initial boiling point of at least 50 C. and a final boiling point of at most 120 C.; b) feeding the suspension to a flash drum having a pressure controlled by a vacuum pump, wherein the pressure of the flash drum is less than 0.1 MPa; c) vaporizing a part of the suspension medium in the flash drum to obtain a hydrogen-depleted suspension and d) withdrawing the hydrogen-depleted suspension from the flash drum and feeding it to the second polymerization reactor.

2. The process according to claim 1, wherein the polyolefin polymer is selected from ethylene homopolymer, an ethylene copolymer of ethylene and C3-C12 -olefin, propylene homopolymer and a propylene copolymer of propylene and ethylene or C4-C12 -olefin.

3. The process according claim 1, wherein a further reactor is connected to upstream of the first polymerization reactor and/or downstream of the second polymerization reactor.

4. The process according to claim 3, wherein the further reactor is equipped with a hydrogen degassing system.

5. The process according to claim 1, wherein the hydrocarbon mixture comprises hydrocarbons selected from the group of C6 to C12 hydrocarbons.

6. The process according to claim 1, wherein the first polymerization reactor is carried out at pressures of 0.1 to 5 MPa and temperatures of 40 C. to 130 C., and/or the second polymerization reactor is carried out at pressures of 0.1 to 5 MPa and temperatures of 40 C. to 130 C.

7. The process according to claim 1, wherein the pressure in the flash drum is 0.05 to 0.09 MPa.

8. The process according to claim 1, wherein gas from the gas-phase of the flash drum is withdrawn from the flash drum and fed to a heat exchanger present between the flash drum and the vacuum pump, to be condensed.

9. The process according to claim 8, wherein the liquid obtained in the heat exchanger is fed to a point in the process where suspension is present.

10. The process of claim 8, wherein the liquid obtained in the heat exchanger is fed to a point in the process downstream of the second polymerization reactor where no suspension is present.

11. The process according to claim 1, wherein the heat exchanger is a vertical reflux condenser and the condensed liquid flows down back to the flash vessel by gravity.

12. A system for preparing a multimodal polyolefin polymer, comprising i) a first polymerization reactor designed for polymerizing olefins in suspension; ii) a flash drum downstream of the first polymerization reactor; iii) a vacuum pump configured to control the pressure of the flash drum to a pressure of less than 0.1 MPa durin operation; and iv) a second polymerization reactor designed for polymerizing olefins in suspension down-stream of the flash drum.

13. The system according to claim 12, further comprising v) a heat exchanger designed for condensing gas, connected to the flash drum by a conduit for transferring gas from the flash drum to the heat exchanger; and vi) a conduit, connected to the heat exchanger for returning the liquid obtained in the heat exchanger to a point in the system where suspension is present, such as the flash drum, the first polymerization reactor and/or the second polymerization reactor.

14. The system according to claim 12, further comprising v) a heat exchanger designed for condensing gas, connected to the flash drum by a conduit for transferring gas from the flash drum to the heat exchanger; and vi) a conduit, connected to the heat exchanger for returning the liquid obtained in the heat exchanger to a point in the system downstream of the second polymerization reactor where no suspension is present.

15. The process according to claim 8, wherein the liquid obtained in the heat exchanger is fed to the flash drum, the first polymerization reactor and/or the second polymerization reactor.

Description

[0066] The invention is now elucidated with reference to FIG. 1 which schematically illustrates an embodiment of the system of the invention.

[0067] FIG. 1 shows an example of a schematic of the process according to the invention. The first polymerization reactor (21) receives a feed stream 1 containing diluent, monomers, catalyst, co-catalyst, and hydrogen. Feed injection can be done with one stream (as shown) or via multiple inlet streams. The reactor outlet, stream 2, is partially recirculated back to the reactor via a pump (22) and a heat exchanger (23). The net outlet, stream 5, is depressurized via a valve (24) to form a liquid-vapour stream (6). Vapours from stream 6 are separated in the flash vessel (25), to form stream 7. Steam 7 is partially condensed in a heat exchanger (26). Liquid condensate, stream 8, can be recycled back to the flash (25) or back to the first reactor (21), or it can sent forward to the second reactor (29), or even further downstream to a point in the process where only diluent, and no polymer, is present. Non-condensable gases, stream 9, are sent to a vacuum pump (27). Compressed gases, stream 10, can be sent to a monomer recovery unit, or to a different plant. The bottom outlet of the flash vessel (stream 11) is sent via a pump (28) to the second reactor (29), which can receive additional feed components via stream 13. The net outlet of the second reactor (stream 17) can be flashed following a similar process as that undergone by stream 5.