Method of splitting the return fluidization gas in a gas solids olefin polymerization reactor

Abstract

The present invention relates to a process for polymerizing olefin monomer(s) in a gas solids olefin polymerization reactor wherein the fluidization gas is split and returned to the reactor into the bottom zone of the reactor and directly into the dense phase formed by particles of a polymer of the olefin monomer(s) suspended in an upwards flowing stream of the fluidization gas in the middle zone of the reactor.

Claims

1. A process for polymerizing olefin monomer(s) in a gas solids olefin polymerization reactor comprising: a top zone; a middle zone, which comprises a top end in direct contact with said top zone and which is located below said top zone, the middle zone having a generally cylindrical shape; and a bottom zone, which is in direct contact with a bottom end of the middle zone and which is located below the middle zone; comprising the following steps: a) introducing a first stream of fluidization gas into the bottom zone; b) polymerizing olefin monomer(s) in the presence of a polymerization catalyst in a dense phase formed by particles of a polymer of the olefin monomer(s) suspended in an upwards flowing stream of the fluidization gas in the middle zone; c) withdrawing a second stream comprising the fluidization gas from the top zone; d) introducing the second stream into a cooler; e) withdrawing the cooled second stream from the cooler; and f) splitting the cooled second stream into a cooled third stream and the first stream; and g) introducing the cooled third stream through one or more feeding ports in a feeding area of the middle zone at the dense phase in the middle zone of the gas solids olefin polymerization reactor wherein the feeding area of the middle zone is located on the surface of the middle zone between the top end and 50% of the total height of the middle zone, whereas the bottom end corresponds to 0% and the top end corresponds to 100% of the total height of the middle zone, and wherein the cooled third stream comprises from 1 to 30 wt % condensed fluidization gas, and wherein the cooled third stream is introduced through the one or more feeding ports into the dense phase in the middle zone of the gas solids olefin polymerization reactor in an introduction angle of 5° to 75°, whereas the introduction angle is the angle between the projection of the direction of the cooled third stream after introduction into the reactor on a projection plane, which crosses a tangent plane of the generally cylindrical shape of the middle zone at the location of the one or more feeding ports and along an intersection line between the tangent plane and the generally cylindrical surface of the middle zone, whereas the projection plane is located perpendicular to the tangent plane, and a perpendicular line, which crosses the generally cylindrical surface of the middle zone at the location of the one or more feeding ports, is located parallel to the projection plane, and is perpendicular to the tangent plane.

2. The process according to claim 1, wherein the feeding area of the middle zone is located in between the top end of the middle zone and 70% of the height of the middle zone in relation to the top end of the middle zone.

3. The process according to claim 1, wherein number of feeding ports for introducing the cooled third stream is in the range of 1 to 15.

4. The process according to claim 1, wherein the feeding ports are distributed across the feeding area of the middle zone of the gas solids olefin polymerization reactor in axial and/or radial direction with the proviso that the cooled third stream is introduced into the dense phase.

5. The process according to claim 1, wherein the cooled second stream is split into the cooled third stream and the first stream at a ratio of 5:95 (v/v) to 75:25 (v/v).

6. The process according to claim 1, wherein the pressure difference between the cooled third stream and the polymerization pressure in the gas solids polymerization reactor, ΔP, is at least 0.1 bar.

7. The process according to claim 1, wherein the superficial gas velocity of the upwards flowing stream of the fluidization gas in the middle zone is from 0.35 to 1.2 m/s.

8. The process according to claim 7 wherein the superficial gas velocity of the first stream of fluidization gas introduced into the bottom zone is lower than the superficial gas velocity of the upwards flowing stream of the fluidization gas in the middle zone and is in the range of from 0.1 to 1.3 m/s.

9. The process according to any of the preceding claims wherein the bulk density of the dense phase during polymerization is in the range of from 100 to 500 kg/m.sup.3.

10. A reactor assembly for polymerizing olefin monomer(s) comprising a gas-solids olefin polymerization reactor (1) comprising: a top zone (4); a middle zone (3), which comprises a top end in direct contact with said top zone (4) and which is located below said top zone (4), the middle zone (3) having a generally cylindrical shape; and a bottom zone (2), which is in direct contact with a bottom end of the middle zone (3) and which is located below said middle zone (3); a first line (7) for withdrawing a second stream comprising fluidization gas from the top zone (4) of the gas-solids olefin polymerization reactor (1), a cooler (10) for cooling the second stream; a second line (11) for withdrawing the cooled second stream from the cooler (10); a third line (6) connecting the second line (11) and the bottom zone (2) of the gas-solids olefin polymerization reactor (1) for introducing a first stream of fluidization gas into the bottom zone (2) of the gas-solids olefin polymerization reactor (1), one or more feeding ports (13) located in a feeding area of the middle zone; a fourth line (12) connecting the second line (11) and the one or more feeding ports (13) for introducing a cooled third stream into the middle zone (3) of the gas-solids olefin polymerization reactor (1) wherein the feeding area of the middle zone is located on the surface of the middle zone between the top end and 50% of the total height of the middle zone, whereas the bottom end corresponds to 0% and the top end corresponds to 100% of the total height of the middle zone; and wherein the cooled third stream comprises from 1 to 30 wt % condensed fluidization gas, and wherein the cooled third stream is introduced through the one or more feeding ports into the dense phase in the middle zone of the gas solids olefin polymerization reactor in an introduction angle of 5° to 75°, whereas the introduction angle is the angle between the projection of the direction of the cooled third stream after introduction into the reactor on a projection plane, which crosses a tangent plane of the generally cylindrical shape of the middle zone at the location of the one or more feeding ports and along an intersection line between the tangent plane and the generally cylindrical surface of the middle zone, whereas the projection plane is located perpendicular to the tangent plane, and a perpendicular line, which crosses the generally cylindrical surface of the middle zone at the location of the one or more feeding ports, is located parallel to the projection plane, and is perpendicular to the tangent plane.

11. The reactor assembly according to claim 10 wherein the gas solids olefin polymerization reactor is a fluidized bed reactor comprising a fluidization grid.

12. The reactor assembly according to claim 10 wherein the gas solids olefin polymerization reactor is a fluidized bed reactor comprising a top zone having a generally conical shape, a middle zone in direct contact and below said top zone having a generally cylindrical shape, a bottom zone in direct contact with and below the middle zone and having a generally conical shape which does not contain a fluidization grid.

Description

FIGURES

(1) FIG. 1 shows an embodiment of the polymerization process according to the present invention in a fluidized bed reactor with a fluidization grid.

REFERENCE SIGNS

(2) 1 fluidized bed reactor 2 bottom zone 3 zone 4 top zone (disengaging zone) 5 fluidized bed (dense zone) 6 first stream of fluidized gas 7 second stream of fluidized gas 8 compressor 9 compressed second stream of fluidized gas 10 cooler 11 cooled second stream of fluidized gas 12 cooled third stream of fluidized gas 13 feeding ports for the cooled third stream of fluidized gas 14 feeding port for polymerization catalyst 15 polymer withdrawal 16 fluidization grid
Description of FIG. 1

(3) FIG. 1 shows an embodiment of the gas solids olefin polymerization reactor system according to the present invention. The fluidized bed reactor (1) comprises a bottom zone (2), a middle zone (3) and a disengaging zone as top zone (4). The middle zone (3) and the bottom zone (2) are separated by the fluidization grid (16). The first stream of fluidized gas (6) enters the fluidized bed reactor (1) through the bottom zone (2) and flows upwards, thereby passing the fluidization grid (16) and entering the middle zone (3). Due to the substantially cylindrical shape of the middle zone (3) the gas velocity is constant so that above the fluidization grid (16) the fluidized bed (5) is established in the middle zone (3). Due to the conical shape of the disengaging zone (4) the gas entering the disengaging zone (4) expands so that the gas disengages from the polyolefin product of the polymerization reaction so that the fluidized bed (5) is confined in the middle zone (3) and the lower part of the disengaging zone (4). The polymerization catalyst together with optional polyolefin powder polymerized in previous polymerization stage(s) is introduced into the fluidized bed reactor (1) through feeding port (14) directly into the fluidized bed (5). The polyolefin product of the polymerization process is withdrawn from the fluidized bed reactor through outlet (15).

(4) The fluidized gas is withdrawn from the disengaging zone (4) as second stream of fluidization gas (7) and introduced into a compressor (8). The compressed second stream (9) is withdrawn from the compressor (8) and introduced into a cooler (10). The cooled second stream (11) is withdrawn from the cooler (10) and split into a third cooled stream (12) and the first stream (6). The cooled third stream (12) is introduced into fluidized bed (5) of the fluidized bed reactor (1) through one or more feeding ports (13) as such that the fluidized gas of the cooled third stream (12) is directed into the fluidized bed (5).

(5) FIG. 2 shows the definition of the introduction angle of the cooled third stream.

REFERENCE SIGNS

(6) a projection of the direction of the cooled third stream b perpendicular line c projection plane d tangent plane e location of the feeding port f intersection line g generally cylindrical surface of the middle zone α introduction angle γ angle between planes (c) and (d)
Description of FIG. 2

(7) FIG. 2 demonstrates the definition of the introduction angel α of the cooled third stream. Said introduction angle (α) is the angle between a projection (a) and a perpendicular line (b), whereas the projection (a) is the projection of the direction of the cooled third stream after introduction into the reactor on a projection plane (c), which crosses the tangent plane (d) of the generally cylindrical shape (g) of the middle zone at the location of the one or more feeding ports (e) and along an intersection line (f) between the tangent plane (d) and the generally cylindrical surface (g) of the middle zone, whereas the projection plane (c) is located perpendicular to the tangent plane (d) (γ=90°) and whereas the perpendicular line (b) crosses the generally cylindrical surface (g) of the middle zone at the location of the feeding port (e), is parallel to projection plane (c) and is perpendicular to tangent plane (d).

EXAMPLES

(8) A gas phase reactor equipped with a fluidization grid and a disengaging zone was employed to assess the effect of splitting the recirculation gas in the solids carry over. The reactor had a diameter equal to 0.3 m and height equal to 1.5 m. The following experimental procedure steps were followed for all the gas experiments: i) Starting to inject fluidization gas (FG) into the bottom of the fluidized bed reactor to form the bottom of the fluidized bed (FB) ii) Feeding polyolefin powder with a powder feed of 7.65 kg/min through the catalyst feeding port to form the fluidized bed (FB) iii) Increasing the bulk density (BD) of the fluidized bed in the middle zone of the fluidized bed reactor (bulk density=mass of polymer powder divided by the volume of the reactor, excluding the disengaging zone) to about 300 kg/m.sup.3 iv) Starting to inject fluidization gas (i.e. jet gas (JG)) through one feeding port situated in the middle zone of the fluidized bed reactor at an introduction angle of 20° directly into the fluidized bed (FB) v) Stopping polymer powder feed vi) Keeping fluidization gas (FG) feed constant while the bulk density (BD) decreases over time due to polymer powder entrainment

Reference Example 1

(9) In this example a fluidization experiment following the procedure described above was performed without using jet gas (JG) so that all fluidization gas was injected from the bottom of the fluidized bed reactor. The conditions and results for the reference fluidization experiment (i.e. fluidization gas split, superficial gas velocity of the fluidization gas (FG) just above the fluidization grid (SGV.sub.FG), the combined superficial gas velocity of the fluidization gas (FG) and the jet gas (JG) in the middle zone (SGV.sub.total), FG flow and BD) are illustrated in Table 1.

(10) TABLE-US-00001 TABLE 1 Experimental fluidization conditions without jet gas (JG). Conditions Values JG Pressure difference [bar] 0 JG Flow [m.sup.3/h] (% Split (v/v)) 0 (0% split) JG Velocity [m/h] 0 FG Flow [m.sup.3/h] (% Split (v/v)) 150.6 (100% Split) Overall Gas Feed [m.sup.3/h] 150.6 SGV.sub.FG [m/s] 0.61 SGV.sub.total [m/s] 0.61

(11) It was found that at a constant FG flow the bulk density decreases from about 300 kg/m.sup.3 to about 110 kg/m.sup.3 over a time of about 40 min due to polymer powder entrainment.

Inventive Example 2

(12) Example 1 was repeated by splitting the fluidization gas flow into a jet gas (JG) flow and a fluidization gas (FG) flow with a split of 45:55 (v/v). The conditions and results for the reference fluidization experiment (i.e. fluidization gas split, superficial gas velocity of the fluidization gas (FG) just above the fluidization grid (SGV.sub.FG), the combined superficial gas velocity of the fluidization gas (FG) and the jet gas (JG) in the middle zone (SGV.sub.total), FG flow and BD) are illustrated in Table 2.

(13) TABLE-US-00002 TABLE 2 Experimental fluidization conditions with a JG:FG split of 45:55 (v/v). Conditions Values JG Pressure difference [bar] 5 JG Flow [m.sup.3/h] (% Split (v/v)) 68.0 (45.3% split) JG Velocity [m/h] 1053 JG Temperature [° C.] 25 FG Flow [m.sup.3/h] (% Split (v/v)) 82.1 (54.7% Split) Overall Gas Feed [m.sup.3/h] 150.1 SGV.sub.FG [m/s] 0.33 SGV.sub.total [m/s] 0.61

(14) It was found that at a constant FG flow the additional JG flow minimizes the polymer powder entrainment which can be seen in the bulk density that only decreases from about 300 kg/m.sup.3 to about 200 kg/m.sup.3 over a time of about 44 min.

Inventive Example 3

(15) Example 1 was repeated by splitting the fluidization gas flow into a jet gas (JG) flow and a fluidization gas (FG) flow with a split of 15:85 (v/v). The conditions and results for the reference fluidization experiment (i.e. fluidization gas split, superficial gas velocity of the fluidization gas (FG) just above the fluidization grid (SGV.sub.FG), the combined superficial gas velocity of the fluidization gas (FG) and the jet gas (JG) in the middle zone (SGV.sub.total), FG flow and BD) are illustrated in Table 3.

(16) TABLE-US-00003 TABLE 3 Experimental fluidization conditions with a JG:FG split of 15:85 (v/v). Conditions Values JG Pressure difference [bar] 1 JG Flow [m.sup.3/h] (% Split (v/v)) 23.3 (15.3% split) JG Velocity [m/h] 515 JG Temperature [° C.] 25 FG Flow [m.sup.3/h] (% Split (v/v)) 129.1 (84.7% Split) Overall Gas Feed [m.sup.3/h] 152.3 SGV.sub.FG [m/s] 0.52 SGV.sub.total [m/s] 0.62

(17) It was found that at a constant FG flow even a lower amount of JG flow minimizes the polymer powder entrainment which can be seen in the bulk density that only decreases from about 320 kg/m.sup.3 to about 160 kg/m.sup.3 over a time of about 46 min.

Additional Experiments

(18) The gas phase reactor mentioned above was further employed with the following experimental procedure steps: i) Starting to inject fluidization gas (FG) into the bottom of the fluidized bed reactor to form the bottom of the fluidized bed (FB) ii) Feeding polyolefin powder with a powder feed of 7.65 kg/min through the catalyst feeding port to form the fluidized bed (FB) iii) Increasing the bulk density (BD) of the fluidized bed in the middle zone of the fluidized bed reactor (bulk density=mass of polymer powder divided by the volume of the reactor, excluding the disengaging zone) to about 350 kg/m.sup.3 iv) Starting to inject fluidization gas (i.e. jet gas (JG)) through one feeding port situated in the disengaging zone of the fluidized bed reactor having an introduction angle of 20° As the disengaging zone does not have a cylindrical shape, the introduction angle is defined in that the perpendicular line (b) is not perpendicular to the tangent plane (d), but to a line crossing the location of the one or more feeding ports (e) and extending parallel to the generally cylindrical surface (g) of the middle zone. v) Stopping polymer powder feed v) Keeping fluidization gas (FG) feed constant while the bulk density (BD) decreases over time due to polymer powder entrainment

Reference Example 4

(19) In this example a fluidization experiment following the procedure described above was performed without using jet gas (JG) so that all fluidization gas was injected from the bottom of the fluidized bed reactor. The conditions and results for the reference fluidization experiment (i.e. fluidization gas split, superficial gas velocity of the fluidization gas (FG) just above the fluidization grid (SGV.sub.FG), the combined superficial gas velocity of the fluidization gas (FG) and the jet gas (JG) in the middle zone (SGV.sub.total), FG flow and BD) are illustrated in Table 4.

(20) TABLE-US-00004 TABLE 4 Experimental fluidization conditions without jet gas (JG). Conditions Values JG Pressure difference [bar] 0 JG Flow [m.sup.3/h] (% Split (v/v)) 0 (0% split) JG Velocity [m/h] 0 FG Flow [m.sup.3/h] (% Split (v/v)) 150 (100% Split) Overall Gas Feed [m.sup.3/h] 150 SGV.sub.FG [m/s] 0.60 SGV.sub.total [m/s] 0.60

(21) It was found that at a constant FG flow the bulk density decreases from about 350 kg/m.sup.3 to about 150 kg/m.sup.3 over a time of about 30 min due to polymer powder entrainment.

Comparative Example 5

(22) Example 4 was repeated by splitting the fluidization gas flow into a jet gas (JD) flow and a fluidization gas (FD) flow with a split of 16:84 (v/v). The conditions and results for the reference fluidization experiment (i.e. fluidization gas split, superficial gas velocity of the fluidization gas (FG) just above the fluidization grid (SGV.sub.FG), the combined superficial gas velocity of the fluidization gas (FG) and the jet gas (JG) in the middle zone (SGV.sub.total), FG flow and BD) are illustrated in Table 5.

(23) TABLE-US-00005 TABLE 5 Experimental fluidization conditions with a JG:FG split of 16:84 (v/v). Injection port of JG is located at the disengaging zone in downwards direction towards the bottom part of that zone. Conditions Values JG Pressure difference [bar] 1 JG Flow [m.sup.3/h] (% Split (v/v)) 24 (16% split) JG Velocity [m/h] 156 JG Temperature [° C.] 25 FG Flow [m.sup.3/h] (% Split (v/v)) 126 (84% Split) Overall Gas Feed [m.sup.3/h] 150 SGV.sub.FG [m/s] 0.504 SGV.sub.total [m/s] 0.60

(24) It was found that at a constant FG flow the addition of the JG flow maximizes the polymer powder entrainment which can be seen in the bulk density that further decreases from about 350 kg/m.sup.3 to about 110 kg/m.sup.3 over a time of about 30 min. It was made clear that introducing the JG flow into the disengaging zone of the gas phase reactor has a negative effect of solids carry over.