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EP-4739429-A1 - PROCESS FOR THE POLYMERIZATION OF OLEFINS IN LOOP REACTOR WITH VARIABLE SLURRY VELOCITY

EP4739429A1EP 4739429 A1EP4739429 A1EP 4739429A1EP-4739429-A1

Abstract

A process and an apparatus for the slurry polymerization of one or more α-olefins in at least one loop reactor under circulation of the polymer slurry by means of an axial flow pump coupled to a variable speed drive, providing a substantially constant flow velocity of the polymer slurry variable from 1 to 11.5 m/s.

Inventors

  • DI FEDERICO, PIER LUIGI
  • BALESTRA, ENRICO
  • ZANDEGIACOMO RIZIO, Anna
  • MACCABIANI, Guido
  • VITALE, FRANCESCO

Assignees

  • Basell Poliolefine Italia S.r.l.

Dates

Publication Date
20260513
Application Date
20240703

Claims (10)

  1. 1. Process for the slurry polymerization of one or more a-olefins carried out in at least a loop reactor under circulation of the polymer slurry by means of an axial flow pump, characterized in that said axial flow pump provides a flow velocity of the polymer slurry variable from 1 to 11.5 m/s, wherein said velocity is kept substantially constant throughout the whole loop reactor, and wherein said axial flow pump is coupled to a variable speed drive whereby the rotational speed of said axial flow pump is adjusted to maintain the average circulating velocity of the polymer slurry at the desired value.
  2. 2. Process according to claim 1, characterized in that said axial flow pump provides a flow velocity of the polymer slurry from 3 to 10.5 m/s.
  3. 3. Process according to claim 1 or 2, characterized in that said axial flow pump provides a flow velocity of the polymer slurry from 5 to 9.5 m/s.
  4. 4. Process according to any of claims 1 to 3, characterized in that said axial flow pump provides a flow velocity of the polymer slurry from 6.0 to 9.0 m/s.
  5. 5. Process according to any of claims 1 to 4, carried out in a sequence of at least two loop reactors interconnected by means of a transfer line, wherein by means of said transfer line the polymer is transferred from a first loop reactor to a second loop reactor and a fraction of polymer slurry is withdrawn from said second loop reactor and is continuously recycled back to it; characterized in that the flow velocity of the polymer slurry in at least said first loop reactor is variable from 1 to 11.5 m/s, preferably from 3 to 10.5 m/s, more preferably from 5 to 9.5 m/s, by means of said axial flow pump.
  6. 6. Process according to claim 5, characterized in that the flow velocity of the polymer slurry in both said first and second loop reactors is variable from 1 to 11.5 m/s, preferably from 3 to 10.5 m/s, more preferably from 5 to 9.5 m/s, by means of axial flow pumps located in each of said reactors.
  7. 7. Process according to any of claims 1 to 6, wherein the loop reactor comprises at least two vertical legs joined each other by means of a top bend and a bottom bend.
  8. 8. Apparatus for the slurry polymerization of olefins, comprising at least one loop reactor (10) comprising at least two vertical legs (11,11a) joined each other by means of a top bend (13) and a bottom bend (13a), and an axial flow pump (14) located at the bottom bend (13a) of said loop reactor, characterized in that said axial flow pump (14) is connected to a variable speed drive (16) to adjust the flow velocity of said slurry circulating within said loop reactor.
  9. 9. Apparatus according to claim 8, characterized in that said variable speed drive (16) varies the rotational speed of the pump 14 by electrical means or by hydraulic means.
  10. 10. Apparatus according to any of claims8 to 9, characterized in that said variable speed drive (16) is connected to a speed controller (36) and a speed sensor (38) mounted on a shaft (34) of said pump (14), whereby the speed of rotation of the pump (14) is detected and controlled.

Description

PROCESS FOR THE POLYMERIZATION OF OLEFINS IN LOOP REACTOR WITH VARIABLE SLURRY VELOCITY [0001] The present invention relates to a process for the liquid-phase polymerization of olefins carried out in at least one loop reactor with variable velocity of the circulating slurry. The invention also relates to an apparatus for polymerizing olefins comprising at least one loop reactor provided with means to vary the slurry velocity. BACKGROUND OF THE DISCLOSURE [0002] It is known to carry out the olefin polymerization under slurry conditions in one or more loop reactors. This type of reactor is widely used in the production of polyethylene and polypropylene. The obtained product consists of solid polymer particles in a suspension of liquid monomers (bulk polymerization), or alternatively, polymer particles in a suspension of liquid monomers mixed with an inert solvent, as the polymerization diluent. Propylene (co)polymers are typically produced by using liquid propylene as the polymerization medium, in order to maximize the rate of the polymerization reaction by providing a high monomer concentration. [0003] The polymer slurry is continuously circulated in the loop reactor by a pump to maintain a homogeneous dispersion of the solid polymer in the liquid reaction medium. A polymer slurry is withdrawn from the reactor and may be concentrated so that the solid content at the reactor outlet is higher than the solid content inside the loop reactor. Traditionally, this has been done by using settling legs at the discharge from the loop reactor. Settling legs operate on a batch principle to recover the product. The concentrated polymer slurry is successively transferred to a flash tank, where most of the diluent and unreacted monomers are flashed off, so as to separate the solid polymer at the bottom of the flash tank. [0004] It has also been known to use a second loop reactor that receives the polymer slurry from the first loop reactor to continue the polymerization reaction, possibly under different polymerization conditions, to produce olefin polymers and copolymers having desired composition and properties. [0005] During the standard working of the polymerization apparatus, a predefined pressure gradient along the transfer line ensures a continuous transfer of polymer slurry between the first loop reactor and the second loop reactor. [0006] WO 2009/027197 Al discloses a process for the slurry polymerization of one or more a-olefins in a sequence of at least two loop reactors interconnected by means of a transfer line, wherein a fraction of polymer slurry produced in the first loop reactor is discharged into said transfer line and transferred to said second loop reactor, and a fraction of polymer slurry withdrawn from said second loop reactor is continuously recycled back to it also by means of said transfer line. [0007] When the process is carried in a loop reactor, however, it has been found that under certain operating conditions a slugging phenomenon can occur. Slurry slugging shows a segregation of the solid phase from the liquid phase, especially in the bends of the loop reactor, where a change of direction of the slurry flow occurs, possibly due to unbalanced energy exchange between the suspended polymer and the suspending liquid. [0008] Slurry slugging causes an accumulation of some circulating polymer, which starts flowing in a concentrated form inside the loop reactor. This generates fluctuations and instability in the operating conditions, which may limit the concentration of solids that the loop reactor can manage. [0009] In view of the foregoing, there is a need of improving the operation of the liquid-phase olefins polymerization process carried out in one or more loop reactors, so as to prevent or minimize the slugging of the slurry and the associated fluctuations in the operating conditions of the process, whereby ensuring a reliable working of the polymerization plant. SUMMARY OF THE DISCLOSURE [00010] It is therefore an object of the present invention a process for the slurry polymerization of one or more a-olefins carried out in one or more loop reactors, wherein the polymer slurry is circulated in the loop reactor by means of an axial flow pump that provides a flow velocity of the circulating slurry variable from 1 to 11.5 m/s, preferably from 3 to 10.5 m/s, more preferably from 5 to 9.5 m/s, even more preferably from 6.0 to 9.0 m/s, wherein said velocity is kept substantially constant throughout the whole loop reactor, and wherein said axial flow pump is coupled to a variable speed drive whereby the rotational speed of said axial flow pump is adjusted to maintain the average circulating velocity of the polymer slurry at the desired value. [00011] Another object of the invention is an apparatus for the slurry polymerization of olefins, comprising at least one loop reactor, said loop reactor comprising at least two vertical legs joined each other by means of a top bend and a bottom bend, and an