FEEDING OF LIQUID TO A REACTOR Background of the invention The present invention relates to gas phase reaction technology and concerns the feeding of liquid into a gas phase reactor. The invention can be used for instance in polymerizing processes, especially in olefin polymerizing processes, for feeding, liquified circulation gas into a fluidized bed gas phase reactor.

A fluidized bed polymerization reactor comprises a bed of solid polymer particles which is maintained in a fluidized state by inroducing a gas stream at the bottom of the bed. The gas stream flows upwards in the reactor at a velocity sufficient to support the solid particles. The unreacted gas is collected at the top of the reactor, compressed and reintroduced at the bottom of the bed. The reactor can also be provided with a rotating mixer. A gas phase reactor can be used for instance in polymerization processes.

In exothermic processes, the production capacity of a gas phase reactor is often restricted by the ability to remove heat from the reactor. Heat can be removed e. g. by cooling the circulation gas before reintroducing it into the reactor. It is also possible to cool the circulation gas to such an extent that some components present in the gas are condensed. When partially condensed circulation gas re-enters the reactor, the condensed components are evaporated thus cooling the reaction medium. One way of removing the heat and to control the temperature of the reactor is to condense the circulation gas before it is returned into the reactor. The condensate is fed through inlet openings in the bottom wall of the reactor.

Such a cooling system is proposed e. g. in US 4368291. The document discloses a process for preparing polyethylene, in which ethylene is first polymerized in a liquid reactor and thereafter in a gas phase reactor. Dispersion medium from the gas phase reactor can be removed and cooled, possibly condensed, and recycled into the reactor.

EP-B-89691 discloses a process for polymerizing monomers in a gas phase in which the circulation gas is cooled so that at least part of it is condensed. The two-phase mixture containing the gas and the condensed liquid is reintroduced into the bottom of the bed.

Also EP-B-699213 discloses a process for polymerizing olefins in a gas phase in which the circulation gas is cooled so that at least part of it is condensed. The gas and liquid fractions are then separated, the gas is reintroduced at the bottom of the bed, and the liquid is introduced directly into the bed. The liquid is injected into the bed by means of liquid only nozzles or gas assisted nozzles.

General description of the invention Now a method according to claim 1 has been invented. Some preferred embodiments of the invention are defined in the other claims.

In accordance with the invention, liquid is fed into the reactor through a mixer. Thus the liquid can be distributed very evenly into the reactor.

According to one embodiment of the invention, the objective of the liquid feed is to remove the heat of an exothermic reaction. Then, the liquid that is fed into the bed through the mixer is such as it is evaporated in the conditions present in the gas phase reactor thus removing the heat of polymerization. The liquid may be a fresh feed or it may be a component of the circulation gas which is obtained by cooling the circulation gas stream so that part of the stream is condensed and then separating the condensed component.

The reactor may be especially a fluidized bed reactor, and the gas is fed especially into the bed of such a reactor.

According to one embodiment of the invention, the recycle gas stream collected from the top of the reactor is cooled so that at least one component of the gas stream is condensed. The condensed component is then separated from the gas stream. The gas stream is reintroduced into the bottom of the fluidized bed and the liquid stream is led into the mixer and introduced through the mixer into the bed. In this way the condensed liquid is distributed evenly into the bed and it will not form solid blocks with the particles of the bed.

The invention is especially useful in polymerizing processes, for instance in olefin polymerizing processes. The olefin may be for instance a lower olefin such as propylene or ethylene or their mixture, optionally together with higher alpha-olefins and/or dienes like 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1,9- decadiene, 1,5-hexadiene and 1,7-octadiene. The gas phase polymerization process may also be a step in a multistage process. A special example of such is a two-stage

process in which the polymerization is first carried out in a liquid reactor, such as a loop reactor, and thereafter in the gas phase reactor.

The mixer is preferably rotating and is provided with a shaft. The shaft is preferably vertical and extends out of the bottom of the reactor. The liquid is preferably fed into the reactor through the shaft of the mixer. The reactor may be provided with a sealed chamber for feeding the liquid through a hollow of the shaft.

Brief description of the drawings The enclosed drawings form a part of the written description.

Figure 1 is a schematic representation of a fluidized bed polymerization process.

Figure 2 shows one embodiment of the invention, in which liquid together with purge gas may be fed into reactor.

Figure 3 shows a second embodiment of the invention, in which liquid may be fed into the reactor separately from the possible purge gas.

Figure 4 shows an alternative for the embodiment of Figure 3.

Detailed description of some preferred embodiments of the invention According to Figure 1, gas comprising gaseous monomer or monomers to be polym- erized are fed through a line 1 into a fluidized bed gas phase reactor 2. Fresh monomer (s) and other possible gaseous ingredients may be added to line 1 at a suitable point. The gas flow may also comprise for instance necessary catalysts for carrying out the polymerization in the reactor. Polymer particles form a bed on a gas distribution plate 3 at the bottom of the reactor. The gas distribution plate has small holes through which gas can be introduced evenly to the bottom of the bed. Polymer is removed from the bed through a line 4. The bed is maintained in a fluidized state by collecting the unreacted gas from the top of the reactor 2 via a line 5, compressing the gas in a compressor 6, and circulating the gas to the bottom reactor via the line 1.

The reactor can be used for instance for polymerizing olefins, such as propylene or ethylene. Additional monomers, such as comononers, or other reaction components, such as hydrogen, or other substances, such as aluminium alkyl cocatalysts, may be fed into the reactor 2 by combining the fresh feed with the circulation gas line 1.

The gas removed from the top of the reactor 2 is cooled and partially condensed in a heat exchanger 7, and the partially condensed flow is further led through a line 8 into a separator tank 9. The gas from the separator tank 9 is led through the line 1 to the bottom of the reactor 2. Catalyst is introduced into the reactor 2 through a line 10. The catalyst feed may also be in the form of polymer particles from a prior polymerization stage, which particles contain the active catalyst. The catalyst may comprise also some gas necessary to convey the catalyst or polymer particles into the reactor 2. The condensate from the tank 9 is led to the bottom of the reactor 2 through a separate line 11 by means of a pump 12.

The gas fed through the line 1 may comprise also polymer already formed in preceding steps.

The reactor 2 is provided with a rotating mixer 13 for stirring the polymer bed. The mixer comprises a vertical shaft 14 which extends below the bottom of the reactor 2. The shaft 14 is provided with a mechanism 15 for rotating the mixer 13. The upper end of the shaft 14 extends above the gas distribution plate 3 and is provided with radial arms 16 at the outer end of which there are blades 17.

The shaft 14 of the mixer 13 has a hollow, and the mixer above the gas distribution plate 3 is provided with holes for leading fluid from the hollow to the polymer bed.

The condensate feed line 11 leads into the hollow of the shaft 14 separately from the gas flow of the line 1. From the hollow of the shaft 14, the condensate is fed and mixed into the bed.

The reactor 2 of Fig. 2 has a bottom with a central inward extension 18 of conical shape. The extension 18 is thus surrounded by a bottom ring 19. The upper part of the extension 18 is separated by a sealing wall 20 so that a chamber 21 is formed.

The shaft 14.1 of the mixer 13 goes through the chamber 21 and the gas distribution plate 3 into the reactor 2. In the reactor 2, the shaft 14. 1 is provided with radial arms 16 and blades 17. The blades 17 are near the inner wall of the reactor. The mixer shaft seal, support bearings and rotating machinery 15.1 are placed in the extension 18 below the chamber 21.

The shaft 14.1 has a hollow with its ends closed. The portion of the hollow shaft 14.1 within the chamber 21 is provided with holes 22. The arms 16 have hollows connected with the hollow of the shaft 14.1 and holes 23 opening into the reactor 2.

The blades 17 have hollows connected with the openings of the arms 16 and provided with holes 24 on their inner or outer surfaces.

The feed line 11 for the condensed circulation flow is joined to the chamber 21.

Thus the condensate is fed through the holes 22 into the shaft 14.1 and therefrom through the holes 23 and 24 into the bed of the reactor.

The feed line 1 for the gaseous circulation flow is joined to the bottom of the bottom ring 19.

Additional purge gas may be led through a line 25 into the chamber 21.

The equipment according to Fig. 2 may be in principle similar as that described in EP-707513 for feeding gas into a reactor and comprising further means for feeding liquid together with the gas.

Also the reactor 2 of Fig. 3 has a bottom with an inward extension 18 and a bottom ring 19 with line 1 for feeding the gaseous circulation flow. The shaft 14.2 of the mixer 13 goes through the mixer shaft seal, support bearings and rotating machinery 15.2 and the gas distribution plate 3 into the reactor 2. The mixer shaft 14. 2 has a central opening 26 provided with a hollow inner shaft 27 extending through the mixer shaft. At the upper end of the inner shaft 27 there are radial arms 28, which have hollows connected with the hollow of the inner shaft and holes 29 opening into the reactor. The feed line 11 for the condensed circulation flow is connected via a liquid inlet seal 30 with the hollow of the inner shaft 27.

The upper part of the extension 18 is separated by a sealing wall 31 so that a chamber 32 is formed. The shaft 14.2 has a hollow surrounding coaxially the hollow of the inner shaft 27. The portion of the coaxial hollow of shaft 14.2 within the chamber 32 is provided with holes 22'which lead to holes in the upper part of the mixer within the reactor. Purge gas is led through line 25 into the chamber 32 and thereby into the reactor.

An alternative to the embodiment of Fig. 3 is shown in Fig. 4. Here the feed line 11 leads to a sealed feed chamber 33 between the mixer machinery 15. 3 and the seal wall 31. 1 of the chamber 32. From the feed chamber 33 there is a connection into the hollow of the inner shaft 14.3.