Polymerisation process and polymerisation unit comprising a degassing section
Polymerization unit for producing polymer powder having at least one polymerization reactor for the polymerization of light (co)monomer(s) having less than 7 carbon atoms, and heavy comonomer(s) having at least 7 carbon atoms, and a degassing section including two (and optionally a third) cylindrical degassing vessels in series. Light (co)monomer(s) are degassed in the first degassing vessel (V 1 ) and recovered, and heavy comonomers are degassed in the second degassing vessel (V 2 ) and recovered. The active polymer powder is optionally polished and/or optionally deactivated in the optional third degassing vessel (V 3 ). The cross-sectional area (S 2 ) of the second degassing vessel is greater than 1.5 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 >1.5×S 1 ], and vessels V 1 and V 2 are equipped with a vent recovery unit (VR) for respectively recovering the light (co-)monomer(s) (VR 1 ) and the heavy comonomer(s) (VR 2 ) from the gases exiting the vessels.
1. Polymerisation unit for producing polymer powder comprising
at least one polymerisation reactor for the polymerisation of
light (co)monomer(s), being (co)monomer(s) having less than 7 carbon atoms; and
heavy comonomer(s), being comonomers having at least 7 carbon atoms,
and a degassing section comprising two (and optionally a third) cylindrical degassing vessels in series, wherein
light (co)monomer(s) are degassed in the first degassing vessel (V 1 ) and recovered,
heavy comonomers are degassed in the second degassing vessel (V 2 ) and recovered,
the active polymer powder is optionally polished and/or optionally deactivated in the optional third degassing vessel (V 3 ), and
wherein the cross-sectional area (S 2 ) of the second degassing vessel is greater than 1.5 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 >1.5×S 1 ], and
further wherein vessels V 1 and V 2 are equipped with a vent recovery unit (VR) for respectively recovering the light (co-)monomer(s) (VR 1 ) and the heavy comonomer(s) (VR 2 ) from the gases exiting the vessels.
2. Polymerisation process in a polymerisation unit for producing polymer powder comprising
at least one polymerisation reactor for the polymerisation of
light (co)monomer(s), being (co)monomer(s) having less than 7 carbon atoms; and
heavy comonomer(s), being comonomers having at least 7 carbon atoms,
and a degassing section comprising two (and optionally a third) cylindrical degassing vessels in series V 1 V 2 V 3 ,
wherein the process comprises alternate sequences of
polymerisation of light (co)monomer(s) in the absence of heavy comonomer(s), and of
polymerisation of heavy comonomer(s), and
wherein
light (co)monomer(s) are degassed in the first degassing vessel V 1 by passing a counter current purging gas in the said vessel and recovered,
heavy comonomer(s) are degassed in the second degassing vessel V 2 by passing a counter current purging gas in the said vessel and recovered, and
the active polymer powder is optionally polished and/or optionally deactivated in the optional third degassing vessel V 3 ,
and further wherein
the flow rate (Q 2 ) of the purging gas in the second vessel V 2 is higher than 1.5 times the flow rate (Q 1 ) of the purging gas in the first vessel V 1 [Q 2 >1.5×Q 1 ] during the heavy comonomers(s) polymerisation sequences.
3. Unit according to claim 1 wherein the cross-sectional area (S 2 ) of the second degassing vessel is greater than 2 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 >2×S 1 ].
4. Unit according to claim 1 wherein the cross-sectional area (S 2 ) of the second degassing vessel is smaller than 10 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 <10×S 1 ].
5. Unit according to claim 1 wherein the ratio between [the ratio between the height (H 2 ) and the diameter (D 2 ) of the second degassing vessel] and [the ratio between the height (H 1 ) and the diameter (D 1 ) of the first degassing vessel] is lower than 1, i.e. [(H 2 /D 2 )/(H 1 /D 1 )]<1.
6. Unit according to claim 1 wherein the ratio between [the ratio between the height (H 2 ) and the diameter (D 2 ) of the second degassing vessel] and [the ratio between the height (H 1 ) and the diameter (D 1 ) of the first degassing vessel] is higher than 0.3, i.e. [(H 2 /D 2 )/(H 1 /D 1 )]>0.3.
7. Unit according to claim 1 wherein vessel V 2 is used as a surge silo for such polymer powders which do not contain heavy comonomer(s).
8. Unit according to claim 1 wherein VR 1 and VR 2 include compression stages and the pressure—after the compression stage—of VR 2 is lower than the pressure—after the compression stage—of VR 1 (pVR 2 <pVR 1 ).
9. Process according to claim 2 wherein, when the polymerisation unit does not produce heavy comonomer(s) containing polymers and/or the second degassing vessel V 2 is by-passed by the polymer coming from V 1 .
10. Process according to claim 2 wherein the flow rate (Q 2 ) of the purging gas in the second vessel V 2 is lower than 10 times the flow rate (Q 1 ) of the purging gas in the first vessel V 1 [Q 2 <10×Q 1 ] during the heavy comonomers(s) polymerisation sequences.
11. Process according to claim 2 wherein the cross-sectional area (S 2 ) of the second degassing vessel is greater than 1.5 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 >1.5×S 1 ].
12. Process according to claim 2 wherein the cross-sectional area (S 2 ) of the second degassing vessel is smaller than 10 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 <10×S 1 ].
13. Process according to claim 2 wherein the ratio between [the ratio between the height (H 2 ) and the diameter (D 2 ) of the second degassing vessel] and [the ratio between the height (H 1 ) and the diameter (D 1 ) of the first degassing vessel] is lower than 1, i.e. [(H 2 /D 2 )/(H 1 /D 1 )]<1.
14. Process according to claim 2 wherein the ratio between [the ratio between the height (H 2 ) and the diameter (D 2 ) of the second degassing vessel] and [the ratio between the height (H 1 ) and the diameter (D 1 ) of the first degassing vessel] is higher than 0.3, i.e. [(H 2 /D 2 )/(H 1 /D 1 )]>0.3.
15. Process according to claim 2 wherein vessel V 2 is used as a surge silo for such polymer powders which do not contain heavy comonomer(s).
16. Process according to claim 2 wherein vessels V 1 and V 2 are equipped with a vent recovery unit (VR) for respectively recovering the light (co-)monomer(s) (VR 1 ) and the heavy comonomer(s) (VR 2 ) from the gases exiting the vessels.
17. Process according to claim 16 wherein VR 1 and VR 2 include compression stages and the pressure—after the compression stage—of VR 2 is lower than the pressure—after the compression stage—of VR 1 (pVR 2 <pVR 1 ).
18. Unit according to claim 14 wherein the cross-sectional area (S 2 ) of the second degassing vessel is greater than 2.5 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 >2.5×S 1 ].
19. Unit according to claim 4 wherein the cross-sectional area (S 2 ) of the second degassing vessel is less than 8 times the cross-sectional area (S 1 ) [S 2 <8×S 1 ].
20. Process according to claim 11 wherein the cross-sectional area (S 2 ) of the second degassing vessel is greater than 2 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 >2×S 1 ].
21. Process according to claim 20 wherein the cross-sectional area (S 2 ) of the second degassing vessel is greater than 2.5 times the cross-sectional area (S 1 ) of the first degassing vessel [S 2 >2.5×S 1 ].
22. Process according to claim 12 wherein the cross-sectional area (S 2 ) of the second degassing vessel is less than 8 times the cross-sectional area (S 1 ) [S 2 <8×S 1 ].