IMPROVED PROCESS AND SYSTEM FOR VAPOR PHASE POLYMERIZATION OF OLEFIN MONOMERS

Abstract

The present invention relates to a continuous vapor phase olefin polymerization process comprising polymerization of at least one olefin monomer in at least two serial polymerization reactors containing an agitated bed of forming polymer particles, wherein forming polymer particles are transferred from an upstream reactor to a downstream reactor, wherein the upstream reactor is a horizontal stirred reactor containing multiple reaction zones, each reaction zone having at least one inlet for a gaseous stream and optionally additionally an inlet for a liquid stream, wherein said process reduces the carry-over of undesired reactive gases from the upstream reactor to the downstream reactor. The present invention further relates to a system suitable for the present continuous vapor phase olefin polymerization process. The present invention further relates to the use of the present process and system for producing heterophasic polypropylene.

Claims

1. A continuous vapor phase olefin polymerization process comprising polymerization of at least one olefin monomer in at least two serial vapor phase polymerization reactors containing an agitated bed of forming polymer particles, wherein forming polymer particles are transferred from an upstream reactor to a downstream reactor, wherein the upstream reactor is a horizontal stirred reactor containing multiple reaction zones, each reaction zone having at least one inlet for a gaseous stream and optionally additionally an inlet for a liquid stream and, wherein one reaction zone comprised in the upstream reactor vessel is a polymer discharge reaction zone from which forming polymer particles are discharged and subsequently transported to the downstream reactor and wherein the ratio of the hydrogen concentration to the olefin monomer concentration in the polymer discharge reaction zone ([H.sub.2].sub.discharge zone/[Olefin monomer].sub.discharge zone) is reduced compared to the ratio of the hydrogen concentration to the olefin monomer concentration in the preceding reactor zone ([H.sub.2].sub.receding zone/[Olefin monomer].sub.preceding zone).

2. The process according to claim 1, wherein the ratio $\frac{{\left[H_2\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}}{{\left[H_2\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}}$ is 1.5-15.

3. The process according to claim 1, wherein one or more liquid streams to one or more reaction zones and/or one or more gaseous streams to one or more reaction zones are controlled to achieve the desired ratios of the hydrogen concentration to the olefin monomer concentration in the reaction zones.

4. The process according to claim 3, wherein the liquid stream to at least one reaction zone is a liquid reactor recycle stream further comprising an inert diluent or the olefin monomer.

5. The process according to claim 3, wherein the gaseous stream to at least one reaction zone comprises a gaseous recycle stream further comprising an inert diluent or the olefin monomer.

6. The process according to claim 1, wherein the liquid stream to the polymer discharge reaction zone and/or the gaseous to the polymer discharge reaction zone is propylene.

7. The process according to claim 3, wherein the propylene is polymer grade propylene consisting of at least 99.7 wt-% propylene.

8. The process according to claim 1, wherein the upstream reactor comprises an internal barrier to prevent back-mixing of the forming polymer product from the polymer discharge reaction zone to one or more other reaction zones comprised in the upstream reactor.

9. The process according to claim 1, wherein forming polymer particles are transferred from the upstream reactor to the downstream reactor in a forming polymer particles transport step comprises in a repeating sequence the steps of: (a) discharging at least one charge of forming polymer powder and reactive gases from the upstream reactor into a gas-solid separator wherein the polymer powder is separated from the reactive gases; (b) collecting the polymer powder separated in the gas-solid separator in a pressure transfer chamber; (c) increasing the pressure in the pressure transfer chamber with a pressurizing gas to a pressure that is higher than the operating pressure of the downstream reactor; and (d) discharging the polymer powder from the pressure transfer chamber into the downstream reactor, and (e) opening the valve between the gas-solid separator and the pressure transfer chamber, wherein the pressure in the pressure transfer chamber before said discharging at least one charge of forming polymer powder and reactive gases from the upstream reactor into the gas-solid separator is 10-700 kPaa.

10. A system suitable for a continuous vapor phase olefin polymerization process according to claim 1, comprising at least two serial vapor phase polymerization reactors containing an agitated bed of forming polymer particles and a means to transfer forming polymer particles from an upstream reactor to a downstream reactor, wherein the upstream reactor is a horizontal stirred reactor containing multiple reaction zones, each reaction zone having at least one inlet for a gaseous stream said reactor comprising multiple inlets for a gaseous stream to set different hydrogen to olefin ratios and optionally additionally an inlet for a liquid stream and wherein one reaction zone comprised in the upstream reactor is a polymer discharge reaction zone comprising an outlet for forming polymer particles to the means to transfer the forming polymer particles to the downstream reactor.

11. The system according to claim 10, wherein the means to reduce the ratio of the hydrogen concentration to the olefin monomer concentration in the polymer discharge reaction zone comprises an inlet for a liquid reactor recycle stream optionally further comprising an inert diluent or the olefin monomer.

12. The system according to claim 10, wherein the means to reduce the ratio of the hydrogen concentration to the olefin monomer concentration in the polymer discharge reaction zone comprises an inlet for a gaseous recycle stream optionally further comprising an inert diluent or the olefin monomer.

13. The system according to claim 10, wherein the upstream reactor comprises an internal barrier to prevent back-mixing of the forming polymer product from the polymer discharge reaction zone to one or more other reaction zones comprised in the upstream reactor.

14. The system according to claim 10, wherein the forming polymer particles are transferred from the upstream reactor to the downstream reactor using a polymer particles transport means comprising a gas-solid separator, a pressure transfer chamber and an offgas gas compressor, wherein the inlet of said offgas gas compressor is in continuous open gas communication with the gas-solid separator.

15. (canceled)

16. The process according to claim 1, wherein the ratio $\frac{{\left[H_2\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}}{{\left[H_2\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}}$ is 2-10 wherein one or more liquid streams to one or more reaction zones and/or one or more gaseous streams to one or more reaction zones are controlled to achieve the desired ratios of the hydrogen concentration to the olefin monomer concentration in the reaction zones, wherein the liquid stream to at least one reaction zone is a liquid reactor recycle stream further comprising an inert diluent, wherein said inert diluent is one or more selected from the group consisting of nitrogen, fuel gas, methane, ethane and propane, wherein the gaseous stream to at least one reaction zone comprises a gaseous recycle stream further comprising an inert diluent, wherein said inert diluent is one or more selected from the group consisting of nitrogen, fuel gas, methane, ethane and propane, wherein the liquid stream to the polymer discharge reaction zone and/or the gaseous to the polymer discharge reaction zone is propylene, wherein the upstream reactor comprises an internal barrier to prevent back-mixing of the forming polymer product from the polymer discharge reaction zone to one or more other reaction zones comprised in the upstream reactor,

17. The process according to claim 16, wherein forming polymer particles are transferred from the upstream reactor to the downstream reactor in a forming polymer particles transport step comprises in a repeating sequence the steps of: (a) discharging at least one charge of forming polymer powder and reactive gases from the upstream reactor into a gas-solid separator wherein the polymer powder is separated from the reactive gases; (b) collecting the polymer powder separated in the gas-solid separator in a pressure transfer chamber; (c) increasing the pressure in the pressure transfer chamber with a pressurizing gas to a pressure that is higher than the operating pressure of the downstream reactor; and (d) discharging the polymer powder from the pressure transfer chamber into the downstream reactor, and (e) opening the valve between the gas-solid separator and the pressure transfer chamber, wherein the pressure in the pressure transfer chamber before said discharging at least one charge of forming polymer powder and reactive gases from the upstream reactor into the gas-solid separator is 10-700 kPaa, preferably 90-500 kPaa and most preferably 105-200 kPaa.

18. The process according to claim 16, wherein the ratio $\frac{{\left[H_2\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}}{{\left[H_2\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}}$ is 3-7.

19. The process according to claim 16, wherein the propylene is polymer grade propylene consisting of at least 99.7 wt-% propylene.

Description

EXAMPLES

[0094] The development of a detailed model of the first polymerization reactor enabled the understanding of the thermodynamic and transport phenomena occurring in this system. This model was developed in Mobatec Modeller employing correlations derived from literature (for the mass transport phenomena) and from in-house developed models (namely thermodynamic models, based on PC-SAFT) and it was fitted with plant data. The sorption of the different gas components in the amorphous PP was estimated by developing simplified empirical correlations able to mimic the behaviour predicted by PC-SAFT.

[0095] In the examples, the results on the amount of hydrogen still present in the powder at the inlet of the downstream reactor are expressed as hydrogen Take-over, which is the excess of hydrogen in the downstream reactor. In other words, hydrogen Take-over is hydrogen carry-over from pressure chamber to downstream reactor minus hydrogen consumption in downstream reactor. This means the hydrogen Take-over could also be a negative value and additional hydrogen would need to be fed to the downstream reactor. This is a preferred situation with respect to the hydrogen/olefin control in downstream reactor.

[0096] The hydrogen Take-over in the base case is 712 g/h.

[0097] In the Examples the reactor is divided into four imaginary zones, each being or 25% of the reactor volume. The discharge zone is the last zone and comprises or 25% of the total reactor volume.

Example 1

[0098] No gas injection in polymer discharge reaction zone.

[00006]$\frac{{\left[H_2\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}}{{\left[H_2\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}}=5.4$

[0099] Hydrogen Take-over after applying this modification: 141 g/h

[0100] Reduction in hydrogen Take-over: 80%

Example 2

[0101] Manipulate the inlet of liquid and gas recycle streams is each zone of the first reactor.

[0102] Inject the minimum gas flow rate in polymer discharge reaction zone.

[0103] Injecting the minimum gas flow rate copes with the requirements associated with the nozzle operation.

[00007]$\frac{{\left[H_2\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}}{{\left[H_2\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}}=3.Math.\mathrm{.2}$

[0104] Hydrogen Take-over after applying this modification: 226 g/h

[0105] Reduction in hydrogen Take-over: 68%

Example 3

[0106] Inject pure gaseous propylene at the bottom of the polymer bed, instead of recycled gas.

[0107] Inject pure gaseous propylene in the polymer discharge reaction zone.

[0108] The recycled gas is injected in all 3 preceding reaction zones. The flow of pure propylene is the minimum gas flow required to avoid the nozzle blockage.

[00008]$\frac{{\left[H_2\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}}{{\left[H_2\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}}=5.6$

[0109] Hydrogen Take-over after applying this modification: 140 g/h

[0110] Reduction in hydrogen Take-over: 80%

Example 4

[0111] Inject pure gaseous propylene at the bottom of the polymer bed (instead of recycled gas) and inject pure liquid propylene as quench, at the top of the reactor (instead of the recycled liquid).

[00009]$\frac{{\left[H_2\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{preceding}.Math..Math.\mathrm{zone}}}{{\left[H_2\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}/{\left[\mathrm{Olefin}.Math..Math.\mathrm{monomer}\right]}_{\mathrm{discharge}.Math..Math.\mathrm{zone}}}=7.Math.\mathrm{.6}$

[0112] Hydrogen Take-over after applying this modification: 26 g/h

[0113] Reduction in hydrogen Take-over: 104%