Abstract: A method for the copolymerization of ethylene and a C3+ olefin copolymer in a loop reactor system and polymers formed therefrom are described herein.

Abstract: An apparatus for manufacturing a polymer resin comprises a polymerization vessel, a bearing part, a protection part, a circulating cooling means, a raw material-injecting nozzle and a flow path-constituting part. The protection part forms a first flow path between the protection part and the side face of the agitation axis. The circulating cooling means includes a circulating inlet nozzle provided on a side face of the protruding part so as to be opposite to the protection part. The flow path-constituting part is provided between the bearing part and the protection part so as to cover the side face of the agitation axis, to fix the bearing part and the protection part. This flow path-constituting part forms a second flow path between the side face of the agitation axis and the flow path-constituting part and a third flow path for coupling the second flow path with the raw material-injecting nozzle.

Abstract: The disclosure relates to a device for removing and analyzing a sample from a polymerization reactor including one or more sample conduits for removing a sample from the reactor and transferring the sample to a sample flash tank, whereby the conduits are in communication with the reactor and are provided with at least two sampling valves; a sample flash tank for separating said solid particles and evaporated gas, whereby the sample flash tanks are connected to the conduits and provided with a device for analyzing evaporated gas, and including a sample receiver for purifying the solid particles. The receivers are connected to the sample flash tanks and provided with an apparatus for analyzing the solid particles. The disclosure includes a method for improving a polymerization reaction.

Abstract: The present invention discloses a slurry loop reactor comprising at least two loop reactors connected in series and wherein the line connecting the two loops is subject to a dynamic pressure difference.

Abstract: The present invention relates the use of a pump in a loop reactor for the production of polyethylene, as well as a reactor comprising such pump and methods for producing polyolefin by means of such reactor. The pump according to the invention is characterized in that it is an axial flow impeller circulation pump, wherein the impeller comprises 6 blades and wherein the pump is fixed on a spring supported frame. Use of the pump according to the present invention allows for preparation of homogeneous polyethylene products that meet high quality standards from the complicated ethylene polymerization mixtures while at the same time being produced with low energy consumption.

Abstract: The present invention relates to a process for improving the polymerization of ethylene and one or more optional co-monomer(s) in a polymerization loop reactor characterized in that said process comprises the step of controlling the hydrogen/monomer ratio along the path of the reactor by multiple, spatially separated, feeding of hydrogen along the path of the loop reactor. In particular, the invention provides a process for controlling, and preferably narrowing, the molecular weight distribution of the produced polymer particles. In another aspect, the invention relates to a polymerization loop reactor suitable for the polymerization process of ethylene and an optional olefin co-monomer, wherein the molecular weight distribution of the produced ethylene polymer can be controlled.

Abstract: An emulsion polymerization process using a redox initiator comprising a reductant and an oxidant, wherein monomers are mixed into a carrier liquid, e.g. water, to make a pre-emulsion, which is then supplied to a reactor comprising one or more circulation loops, an outlet, and a circulation pump for circulating a reactor charge within the circulation loop, characterized in that the reductant is added to the pre-emulsion before it is mixed into the reactor charge and the oxidant is mixed into the reactor charge, e.g., via the water-phase feed.

Abstract: A method of extracting the contents from the inside of a reactor kept at high temperature and high pressure includes the steps of introducing the contents of the reactor into a pipe having an internal space which communicates with the reactor, closing the pipe to enclose the contents in the internal space, removing unnecessary gas from the internal space, and supplying an inert gas to the internal space, thereby replacing the contents enclosed in the internal space with the inert gas. The contents are discharged from the internal space by replacing the contents enclosed in the internal space with the inert gas.

Abstract: A process for feeding ethylene into a polymerization system includes providing a low-pressure ethylene stream, one or more low-pressure C3 to C20 monomer streams, an optional low-pressure inert solvent/diluent stream, and one or more reactors; metering the low-pressure ethylene stream, the one or more low-pressure C3 to C20 monomer streams, and the optional low-pressure inert solvent/diluent stream; blending the metered low-pressure ethylene stream, the metered one or more low-pressure C3 to C20 monomer streams, and the metered low-pressure optional inert solvent/diluent stream to form an ethylene-carrying low-pressure blended liquid feed stream; pressurizing the ethylene-carrying low-pressure blended liquid feed stream to the polymerization system pressure with one or more high-pressure pumps to thrm an ethylene-carrying high-pressure blended reactor feed stream; and feeding the ethylene-carrying high-pressure blended reactor feed stream to the one or more reactors.

Abstract: The present invention relates to a process for improving the devolatilization of polymer slurry produced in an olefin polymerization reactor. The process is characterized in that it involves an adjustment of the temperature of the interior surface of the flash line for periodically transferring polymer slurry from the polymerization reactor to a downstream processing unit. In particular, in accordance with the present process, the temperature of the interior surface of the flash line is adjusted to a temperature which is equal to or higher than the softening temperature of the polymer passing through said flash line whereby said temperature is higher in a first half of the length of the flash line than in the remaining length of the flash line.

Abstract: Organopolysiloxanes with consistent product properties are prepared while minimizing alcohol usage in the hydrolysis of chlorosilanes by use of a vertical continuous loop reactor having a heating unit on an ascending side of the loop which is regulated such that the temperature of the reactant mixture is within ±5° C. of a set value.

Abstract: The invention relates to a process for preparing polyolefin in a loop reactor. The polymer is prepared by polymerizing olefin monomers in the presence of a catalyst to produce a polyolefin slurry while pumping said slurry through said loop reactor by means of a pump. The present process is characterized in that the catalyst is fed in the loop reactor at a distance to the pump. The invention allows production of the polymer with advantageous properties while leading to fewer blockages of the reactor.

Abstract: Embodiments of the present invention are directed to automated-polymer-synthesis systems that include discrete reagent-solution-addition, wait-time, and reagent-solution-draining sub-systems which together significantly increase throughput and decrease sub-system idle time. The automated-polymer-synthesis systems that represent embodiments of the present invention additionally include switches at points in which carriers can be received from multiple input paths or output to multiple different output paths. The automated-polymer-synthesis systems that represent embodiments of the present invention generally include an input spur and output spur in addition to a main loop, allowing carriers containing only completed polymers to be removed and new carriers input, so that carriers traverse the automated-polymer-synthesis systems independently from one another.

Abstract: An axial pump system cooperative with an elbow or other pipe section improves conversion of tangential to axial flow of a slurry flowing through a loop reactor by including both primary and secondary outlet guide vanes in the pipe section. The secondary guide vanes have “see through” access from the outlet end of the pipe section, while the primary guide vanes have “see through” access from the inlet side of the pipe section. Pump energy efficiency is improved, and friction of polymer particles on the reactor loop and pump sidewalls is reduced, thereby reducing the amount of polymer decay and increasing the percentage of useable and saleable product obtained from the reactor. Guide vanes can be straight or curved. Curved guide vanes can have inlet angles approximating the absolute flow angle of the fluid, and/or outlet angles approximating 0 degrees relative to the meridianal axis of the pipe section.

Abstract: Disclosed herein are an apparatus for producing liposomes and a method of producing liposomes by which it is made possible to produce liposomes under sterile conditions during the manufacturing process while monitoring in line the particle diameter of liposomes.

Abstract: The present invention provides a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included); a method for producing (meth)acrylic acid from at least one reactant selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, in which a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included) is used as a catalyst; and a reactor used for producing (meth)acrylic acid from at least one reactant selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, in which a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included) is used as a catalyst. Further, the present invention provides a method for producing the (meth)acrylic acid without any additional process of converting (meth)acrolein into (meth)acrylic acid.

Abstract: An olefin polymerization process and apparatus wherein a fluid slurry comprising monomer, diluent and catalyst is circulated in a continuous loop reactor by two or more pumps. The process and apparatus allow operating the reaction at significantly higher solids content in the circulating fluid slurry. In a preferred embodiment, the fluid slurry is circulated by two impellers arranged so that the downstream impeller benefits from the rotational energy imparted by the upstream impeller. An olefin polymerization process operating at higher reactor solids by virtue of more aggressive circulation has improved efficiencies, particularly in larger-volume reactors.

Abstract: Techniques and systems for producing a polyolefin using reactors in series are described. Described embodiments include techniques and systems for polymerizing a monomer in a first polymerization reactor to form a first polyolefin, discharging a first slurry continuously from the first polymerization reactor to a second polymerization reactor, and discharging a second slurry continuously from the second polymerization reactor. Using continuous take-off devices disposed on either or both reactors, pressure control may be attained such that the rate of transfer between and withdrawal from both reactors are within a desired range.

Abstract: An apparatus defined as a set of loop reactors suitable for the polymerization process of a monomer, preferably ethylene and optionally an olefin co-monomer, comprising for each of said reactors: a plurality of interconnected pipes P defining a flow path for a polymer slurry, said slurry consisting essentially of ethylene, optionally a co-monomer, a polymerization catalyst, liquid diluent and solid olefin polymer particles, means for feeding monomer, optionally a co-monomer, diluent and optionally hydrogen in the reactor, means for feeding a polymerization catalyst in the reactor, a pump suitable for maintaining the polymer slurry in circulation in such reactor, one or more settling legs connected to the pipes P of such reactor for settling of polymer slurry, one or more control valves connected to the outlet of such settling legs, and one or more flash lines for discharging settled polymer slurry out of the reactor characterized in that each of said loop reactors comprises a three-or-more-way valve defini

Abstract: The present invention relates to a process which comprises preparing polymers. The process uses an appropriate installation, and may comprise determining at least one parameter of a physical and/or chemical conversion. The invention also relates to a corresponding screening process. According to this process, a polymerization reaction medium is made to flow in a tubular flow member.

Abstract: The present invention provides a multiple loop reactor suitable for polymerizing olefins comprising at least two interconnected loop reactors, whereby said connection essentially consists of one or more transfer lines suitable for transferring polymer slurry from a reactor to another reactor and whereby said transfer line extends substantially horizontally. The invention further relates to a process for producing olefin polymers in a multiple loop reactor according to the invention. The invention also relates to the use of a transfer line for transferring polymer slurry from a reactor to another reactor in a multiple loop reactor comprising at least two interconnected loop reactors, whereby said transfer line extends substantially horizontally.

Abstract: A polymerization reactor comprising one or more circulation loops with one or more inlets for raw material, one or more outlets, and a circulation pump for circulating a reactor charge within the circulation loop. A by-pass line for by-passing the circulation pump connects a point of the loop upstream of the pump with a point downstream of the pump.

Abstract: After various sugar nucleotide solutions and glycosyltransferases (or primers) have been mixed, they are introduced into a reaction tank (column) with primers (or glycosyltransferases) immobilized thereon. Then solutions coming out of the reaction tank are led to an ultrafiltration column. The oligosaccharide synthesizer according to the present invention is equipped with a flow path for ensuring that glycosyltransferases or primers separated by the ultrafiltration column are returned into a container for storing each solution in a sample injector.

Abstract: A system and method for measuring pressure and flow rate of polymer slurry circulating in a loop reactor. For flow rate measurement, the loop reactor has a pressure tap on an outside radius of an elbow of the loop and a pressure tap on an inside radius of the elbow. The pressure taps incorporate diaphragms. Sensing legs couple the pressure taps with a differential pressure meter configured to provide a signal indicative of the flow rate of the polymer slurry. For pressure measurement, pressure taps without diaphragms at the loop reactor wall may be disposed at various points along the loop reactor, the pressure taps coupled to pressure sensing lines. A diluent flush line having a screen disposed therein may provide diluent to the pressure taps. The screen may reduce fouling of the pressure tap and sensing line with solids from the reactor.

Abstract: Process for producing a multimodal polyethylene in at least two reactors connected in series, in which 20-80 wt % of a first polymer is made in suspension in a first reactor and 80-20 wt % of a second polymer is made in suspension in a second reactor in the presence of the first polymer, and a stream or slurry containing the resulting polymer is withdrawn from the second reactor and transferred to a flash tank operating at a pressure and temperature such that at least 50 mol % of the liquid component of the slurry, or the non-polymer component of the stream entering the flash tank, is withdrawn from the flash tank as a vapour, wherein the concentration in the stream or slurry entering the flash tank of components having a molecular weight below 50 g/mol, Clights (mol %), satisfies the equation Clights<7+0.07(40?Tc)+4.4(Pc?0.8)?7(CH2/CEt) where Tc and Pc are respectively the temperature (in ° C.

Abstract: Process for producing a multimodal polyethylene in at least two loop reactors connected in series. In the process 20-80 wt % of a high molecular weight (HMW) polymer is made in suspension in a first reactor and 20-80 wt % of a low molecular weight (LMW) polymer is made in suspension in a second reactor, one polymer being made in the presence of the other in either order. The ratio of the average activity in the LMW reactor to the average activity in the HMW reactor is from 0.25 and 1.5, where average activity in each reactor is defined as the rate of polyethylene produced in the reactor (kgPE/hr)/[ethylene concentration in the reactor (mol %)×residence time in the reactor (hours)×feed rate of catalyst into the reactor (g/hr)], residence time being defined as the mass of the polymer in the reactor (kg)/the output rate of polymer from the reactor (kg/hr), and the volumes of the two reactors differ by less than 10%.

Abstract: Process for providing a flow of particulate matter to a reactor, by intermittently adding the particulate matter and a diluent to a mixing tank, and continuously withdrawing a slurry of particulate matter in diluent from the mixing tank for introduction into the reactor. Prior to each addition of particulate matter and diluent to the mixing tank, the concentration of particulate matter in the diluent already in the mixing tank is measured or calculated, and the amount of particulate matter and diluent subsequently added is measured so as to achieve the same concentration at the end of the addition as that measured or calculated prior to the addition.

Abstract: A process for the gas-phase polymerization of ?-olefins carried out in two interconnected polymerization zones, wherein the growing polymer particles flow through the first of said polymerization zones (riser) under fast fluidization conditions, leave said riser and enter the second of said polymerization zones (downcomer) through which they flow downward in a densified form, the process being characterized in that: (a) the gas mixture present in the riser is totally or partially prevented from entering the downcomer by introducing into the upper part of said downcomer a liquid stream LB having a composition different from the gaseous mixture present in the riser; (b) the ratio R between the flow rate Fp of polymer circulated between said downcomer and said riser and the flow rate LB of said liquid being adjusted in a range from 10 to 50.

Abstract: A polyester production system employing a vertically elongated esterification reactor. The esterification reactor of the present invention is an improvement over conventional CSTR esterification reactors because, for example, in one embodiment, the reactor requires little or no mechanical agitation. Further, in one embodiment, the positioning of the inlets and outlets of the reactor provides improved operational performance and flexibility over CSTRs of the prior art.

Abstract: Techniques are provided for producing polymer particles of a size just slightly larger than the size of polymer fines. The technique may prevent or limit the occurrence of reactor fouls associated with large polymer particles. The technique also may provide a greater weight percentage of solids in the reactor. The desired polymer particle size may be achieved by employing a catalyst having particles of a size determined based on the expected catalyst productivity. In certain embodiments, the catalyst particle size may be determined based on the expected catalyst productivity, the polymer particle density, the catalyst particle density, and/or the polymer particle size.

Abstract: Process for producing a multimodal polyethylene in at least two reactors connected in series, in which 20-80 wt % of a high molecular weight (HMW) polymer is made in suspension in a first reactor and 20-80 wt % of a low molecular weight (LMW) polymer is made in suspension in a second reactor in the presence of the HMW polymer, wherein the solids concentration in the second LMW reactor, defined as the mass of polymer divided by the total mass of slurry, is at least 35 wt %, most preferably between 45 wt % and 60 wt %, and/or the ratio of solids concentration in the first reactor to that in the second reactor is maintained at less than 1.0, preferably between 0.6 and 0.8, and further wherein the volume of the second reactor is at least 10%, preferably at least 30% and more preferably at least 50% greater than the volume of the first reactor.

Abstract: Process for producing a multimodal polyethylene in at least two reactors connected in series, in which 20-80 wt % of a high molecular weight (HMW) polymer is made in suspension in a first reactor and 20-80 wt % of a low molecular weight (LMW) polymer is made in suspension in a second reactor. The ratio of the average activity in the LMW reactor to the average activity in the HMW reactor is from 0.25 and 1.5, where average activity in each reactor is defined as the rate of polyethylene produced in the reactor (kgPE/hr)/[ethylene concentration in the reactor (mol %)×residence time in the reactor (hours)×feed rate of catalyst into the reactor (g/hr)], residence time being defined as the mass of the polymer in the reactor (kg)/the output rate of polymer from the reactor (kg/hr). The volume of the second reactor is at least 10% greater than the volume of the first reactor, and the ratio of length to diameter of the first reactor, L/D(1), is greater than that of the second reactor, L/D(2).

Abstract: An olefin polymerization reactor according to the present invention comprises: a vertically extending cylinder; a decreasing diameter portion on the cylinder, having an inside diameter that decreases progressively downward, and having a gas inlet orifice at a bottom end thereof; and a plurality of through holes passing through from an outside surface towards an inside surface of the decreasing diameter portion. Inside a reaction zone enclosed by an inside surface of the decreasing diameter portion and an inside surface above the decreasing diameter portion of the cylinder, a spouted-fluidized bed or a spouted bed is formed.

Abstract: The present invention provides a multiple loop reactor suitable for polymerizing olefins comprising at least two interconnected loop reactors, whereby said connection essentially consists of one or more transfer lines suitable for transferring polymer slurry from a reactor to another reactor and whereby said transfer line extends substantially horizontally. The invention further relates to a process for producing olefin polymers in a multiple loop react or according to the invention. The invention also relates to the use of a transfer line for transferring polymer slurry from a reactor to another reactor in a multiple loop reactor comprising at least two interconnected loop reactors, whereby said transfer line extends substantially horizontally.

Abstract: A gas treatment apparatus for treating a gas by bringing the gas into contact with a treatment liquid. The gas treatment apparatus includes a gas-liquid contact chamber for a gas-liquid contact of the gas with the treatment liquid, a storage chamber, located over the gas-liquid contact chamber, for storing the treatment liquid, and a treatment liquid supplying unit for supplying the treatment liquid stored in the storage chamber to an inside of the gas-liquid contact chamber with a gravity-drop.

Abstract: Process for transferring a slurry stream containing polymer through a transfer line from a polymerisation reactor to a downstream vessel by, prior to entry into the downstream vessel, separating the slurry stream into two flows, the first flow being recycled upstream of the flow separation and the second flow being passed into the downstream vessel. The flow separation is located more than halfway along the transfer line between the reactor and the downstream vessel.

Abstract: Techniques are provided for producing polymer particles of a size just slightly larger than the size of polymer fines. The technique may prevent or limit the occurrence of reactor fouls associated with large polymer particles. The technique also may provide a greater weight percentage of solids in the reactor. The desired polymer particle size may be achieved by employing a catalyst having particles of a size determined based on the expected catalyst productivity. In certain embodiments, the catalyst particle size may be determined based on the expected catalyst productivity, the polymer particle density, the catalyst particle density, and/or the polymer particle size.

Abstract: The present invention relates to a loop reactor suitable for olefin polymerization process comprising: a plurality of interconnected pipes defining a flow path for a polymer slurry, said slurry consisting essentially of an olefin reactant, a polymerization catalyst, liquid diluent and solid olefin polymer particles, means for introducing olefin reactant, polymerization catalyst and diluent into said reactor, a pump suitable for maintaining the polymer slurry in circulation in said reactor, and single settling leg connected to said loop reactor through (a) a take off line extending from said reactor to said settling leg and configured to remove said polymer slurry from said reactor, and (b) a return line extending from said settling leg to said reactor, characterized in that said take off line is radially connected to said single settling leg.

Abstract: A continuous gas phase circulating bed reactor, including: a riser for contacting a catalyst and a first gas composition comprising an olefin to form a polyolefin under fast-fluidization regime or a dilute-phase pneumatic conveying regime conditions; a downer for contacting the catalyst and a second gas composition comprising an olefin to form additional polyolefin under fast fluidization regime or a dilute-phase pneumatic conveying regime conditions; and a transport section for conveying at least a portion of the catalyst, polyolefin, and additional polyolefin from the downer to the riser. Also disclosed is a polymerization process using such a circulating bed reactor.

Abstract: The pump assembly includes an impeller rotatably mounted in a pipe of the reactor having blades that generate a flow of fluid slurry through the pipe, a nosecone protruding in an upstream direction in front of the impeller blades that rotates along with the blades, and a plurality of stationary guide vanes connected to the housing upstream of the impeller blades and having free ends that are radially spaced apart from the nosecone. The leading edges of the stationary vanes are shaped to direct any stringy material into the radial gaps between the free ends of the stationary vanes and the rotating nose cone to be shredded and thus prevent fouling and clogging of the pump assembly when such stringy material is generated during the polymerization process.

Abstract: A process comprising polymerising in a loop reactor of continuous tubular construction an olefin monomer optionally together with an olefin comonomer in the presence of a polymerisation catalyst in a diluent to produce a slurry comprising solid particulate olefin polymer and the diluent wherein the internal diameter of at least 50% of the total length of the reactor is at least 700 millimeters and the solids concentration in the reactor is at least 20 volume % is disclosed.

Abstract: A process for the multistage polymerization of olefins in a sequence of an upstream slurry reactor and a downstream gas-phase reactor, the transfer of polymer from the upstream reactor to the downstream reactor comprising the following steps: a) heating the slurry of polyolefin particles to evaporate the liquid polymerization medium; b) separating the polyolefin particles from the obtained gaseous phase in at least a separation chamber; c) transferring the polyolefin particles to said downstream reactor by means of a couple of lock hoppers working intermittently in parallel, where one of said lock hoppers is continuously filled with the polymer coming from said separation chamber, while simultaneously the other one is continuously pressurized by means of a gas comprising the reaction mixture coming from said downstream reactor.

Abstract: There are disclosed polymerization processes and associated apparatuses. The polymerization processes involve both making a polymeric material in a fluidized bed reactor having a feed distributor and catching a spitwad with a spitwad catcher, and the apparatuses are those corresponding to such processes.

Abstract: A process for the polymerization of olefin's, including: introducing an olefin and a polymerization catalyst into a polymerization reactor to form a polyolefin, the polymerization reactor including: a fluidized bed region having a top and a bottom; and a motive bed region; wherein a first end of the motive bed region is fluidly connected to the top of the fluidized bed region; and wherein a second end of the motive bed region is fluidly connected to the bottom of the fluidized bed region; and wherein a diameter of the fluidized bed region is greater than a diameter of the motive bed region; circulating at least a portion of the olefin, the catalyst, and the polyolefin through the fluidized bed region and the motive bed region; maintaining a dense-phase fluidized bed within the fluidized bed region; recovering polyolefin from the fluidized bed region, is provided. A reactor system directed to the process is also provided.

Abstract: Techniques and systems for producing a polyolefin using reactors in series are described. Described embodiments include techniques and systems for polymerizing a monomer in a first polymerization reactor to form a first polyolefin, discharging a first slurry continuously from the first polymerization reactor to a second polymerization reactor, and discharging a second slurry continuously from the second polymerization reactor. Using continuous take-off devices disposed on either or both reactors, pressure control may be attained such that the rate of transfer between and withdrawal from both reactors are within a desired range.

Abstract: There are disclosed polymerization processes and associated apparatuses. The polymerization processes involve both making a polymeric material in a fluidized bed reactor having a feed distributor and catching a spitwad with a spitwad catcher, and the apparatuses are those corresponding to such processes.

Abstract: Techniques are provided for producing polymer particles of a size just slightly larger than the size of polymer fines. The technique may prevent or limit the occurrence of reactor fouls associated with large polymer particles. The technique also may provide a greater weight percentage of solids in the reactor. The desired polymer particle size may be achieved by employing a catalyst having particles of a size determined based on the expected catalyst productivity. In certain embodiments, the catalyst particle size may be determined based on the expected catalyst productivity, the polymer particle density, the catalyst particle density, and/or the polymer particle size.

Abstract: A composition for acrylic artificial stone, the composition including a (meth)acrylic monomer and an inorganic material. At least one of the (meth)acrylic monomer and the inorganic material may be contained in a component generated by decomposing a polymeric (meth)acrylic resin.

Abstract: The present invention discloses a transfer system between the first and second reactors in a double loop reactor that is equipped to reduce clogging in the transfer lines by providing a regulation mechanism arranged to insure equivalent flushing in each transfer line.

Abstract: An olefin polymerization reaction unit includes a multistage gas phase polymerization reactor which is divided into two or more polymerization stages, in which polyolefin particles move from an initial stage to a final stage, and in which an olefin monomer-containing gas is fed from the final stage toward the initial stage. The reaction unit also includes first circulating means for feeding to the final stage a gas that is discharged from the initial stage and then cooled with a first heat exchanger, and second circulating means for feeding to one of the polymerization stages a condensate formed by condensing, with a second heat exchanger different from the first heat exchanger, a gas removed from one of the polymerization stages.