SYSTEM

FIELD OF THE INVENTION

[0001] The present disclosure relates to a process for ethylene polymerization. More particularly, the present disclosure relates to an ethylene slurry polymerization process having reduced fouling through an improved ethylene feed system.

BACKGROUND OF THE INVENTION

[0002] The use of polyethylene-containing products is known. Various processes can be used to produce polyethylene, including gas phase processes, solution processes, and slurry processes. In ethylene slurry polymerization processes, diluents such as hexane or isobutane may be used to dissolve the ethylene monomer, comonomers and hydrogen, and the monomer(s) are polymerized with a catalyst. Following polymerization, the polymer product formed is present as a slurry of polyethylene particles suspended in the liquid medium.

[0003] In typical multi-reactor cascade processes, shown e.g., in WO 2005/077992 Al or WO 2012/028591 Al, the reactors can be operated in parallel or in series, and the types and amounts of monomer and conditions can be varied in each reactor to produce a variety of polyethylene materials, including unimodal or multimodal polyethylene material. Such multimodal compositions are used in a variety of applications; e.g., WO 2012/069400 Al discloses trimodal polyethylene compositions for blow moldings.

[0004] A challenge sometimes encountered by continuous stirred tank reactors in ethylene slurry polymerization systems is fouling that can occur on the reactor internals. Ethylene monomer is introduced into the reactor in gaseous form and dissolves in the diluent. The solid catalyst component is dosed into the reactor and is suspended in the diluent. When the dissolved ethylene comes into contact with the catalyst particles, polyethylene is formed. The reaction occurs everywhere within the reactor, including near the interior reactor surfaces and reactor internals. Of special concern is the area around the ethylene inlet nozzles since the local concentration of ethylene is at its highest at the discharge of the inlet nozzle. Ideally, the ethylene feed would immediately dissolve and be mixed so as to form a uniform concentration in the diluent in contact with uniformly distributed catalyst particles. However, if dissolution of the ethylene and mixing of the reactor contents is not adequate, solid polyethylene can adhere to interior reactor surfaces and reactor internals. If such adhesion is ongoing, the accumulated material can form solid lumps and interfere with reactor performance. Ultimately, if not remedied, this process of fouling may lead to a unit shutdown for cleaning.

[0005] Conventional systems in the past have fed the ethylene through a nozzle without a length of pipe in the bottom of the reactor. The ethylene entered the reactor directly at the reactor wall, which led to fouling around this nozzle due to the very high concentration of ethylene and in the suspension. Fouling also occurred inside the nozzle itself. Due to low velocities of ethylene at the exit of the nozzle, catalyst-containing suspension would migrate into the nozzle and react with the ethylene to form polyethylene particles. To prevent total plugging of the nozzle, it would have to be frequently cleaned.

[0006] Therefore, a continuing need exists for ethylene slurry polymerization processes having improved performance through more efficient ethylene dissolution and mixing, resulting in reduced internal reactor fouling.

SUMMARY OF THE INVENTION

[0007] The present disclosure provides processes for ethylene slurry polymerization using an ethylene distribution system.

[0008] The disclosure provides processes for the preparation of polyethylene by polymerizing in a slurry ethylene and optionally one or more C ₃ to C ₁₀ alpha-olefins at a temperature from 60°C to 95°C and a pressure from 0.15 MPa to 3 MPa, where the polymerization is carried out in a cylindrical polymerization reactor having a cylindrical reactor wall, a bottom reactor head and a top reactor head, which reactor has an inner diameter D and is equipped with an agitator for mixing the contents of the reactor and inducing a flow of the slurry, wherein the ethylene is fed into the reactor by an ethylene injection system comprising one or more injection nozzles which project through the bottom reactor head or through the reactor wall and extend from 0.02 times to 0.5 times the inner diameter D into the reactor and wherein the ethylene exits the injection nozzle with an exit velocity from 10 m/s to 200 m/s.

[0009] In some embodiments, the injection nozzles projecting through the bottom reactor head or through the reactor wall have a direction into the reactor, a sloped ethylene outlet with an outlet tip and an outlet base, and an angle between the direction of the injection nozzle and the line connecting the outlet tip and the outer base of from 20° to 80° and the slope of the ethylene outlet is oriented in a way with respect to the flow of the slurry that the outlet tip is in an upstream position and the outlet base is in a downstream position with respect to the flow of the slurry.

[0010] In some embodiments, the agitator comprises a motor, a vertical rotating shaft, which is centrally located in the reactor, and one or more stages of agitator blades attached to the rotating shaft; and wherein the agitator induces primarily a vertical flow of the slurry in a circular cross-section around the agitator shaft.

[0011] In some embodiments, the vertical flow of the slurry in the circular cross-section is a downward flow.

[0012] In some embodiments, the one or more injection nozzles project through the bottom reactor head and extend vertically from 0.04 times to 0.2 times the inner diameter D into the reactor and the horizontal distance from the center of the reactor to the outlet of the injection nozzles is from 0.1 times to 0.45 times the inner diameter D.

[0013] In some embodiments, the ethylene injection system comprises at least two injection nozzles and all injection nozzles are arranged on a circular line around the reactor center.

[0014] In some embodiments, the injection nozzles are uniformly distributed on the circular line.

[0015] In some embodiments, the one or more injection nozzles project through the cylindrical reactor wall at a wall passing point positioned in the lower two thirds of the reactor and extend from 0.02 times to 0.48 times the inner diameter D into the reactor.

[0016] In some embodiments, the injection nozzles are inclined downward.

[0017] In some embodiments, the horizontal angle between the direction of the injection nozzle and the horizontal is of from 5° to 60°.

[0018] In some embodiments, the flow of the slurry in the polymerization reactor has a circular component and the injection nozzles are inclined towards the downstream direction of the circular flow.

[0019] In some embodiments, the radial angle between the direction of the injection nozzle and a line running from the wall passing point to the center of the reactor is from 5° to 60°.

[0020] In some embodiments, the outlets of the injection nozzles are located at a position below the agitator. [0021] In some embodiments, the wall passing points are arranged at the same height of the reactor and uniformly distributed around the reactor.

[0022] In some embodiments, the reactor is one of a multi -reactor polymerization system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings, wherein:

[0024] Figure 1 depicts a side view of an ethylene feed injection nozzle.

[0025] Figure 2 depicts a side view of an ethylene slurry polymerization reactor with a bottom feed ethylene injection system.

[0026] Figure 3 depicts a top view of an ethylene slurry polymerization reactor with a bottom feed ethylene injection system.

[0027] Figure 4 depicts a side view of an ethylene slurry polymerization reactor with a side feed ethylene injection system.

[0028] Figure 5 depicts a top view of an ethylene slurry polymerization reactor with a side feed ethylene injection system.

DETAILED DESCRIPTION OF THE INVENTION

Polyethylene Slurry Production Process

[0029] The process of the present disclosure to produce polyethylene includes the slurry polymerization of ethylene and optionally one or more C ₃ to C ₁₀ alpha-olefins as comonomers in the presence of an ethylene polymerization catalyst, a diluent, such as hexane or isobutane, and optionally hydrogen. The polymerization proceeds in a suspension of particulate polyethylene in a suspension medium comprising the diluent, unreacted ethylene and optionally one or more comonomers. Polyethylene polymers obtained by the process described in the present disclosure can be ethylene homopolymers or copolymers of ethylene containing up to 40 wt. , more preferably from 0.1 to 10 wt. % of recurring units derived from C ₃ -Cio-l-alkenes. Preferably, the comonomers are chosen from propylene, 1-butene, 1-pentene, 1-hexene, 1-octene or mixtures thereof. The slurry polymerization occurs at reactor temperatures from 60°C to 95°C, preferably from 65°C to 90°C, and more preferably from 70°C to 85°C, and at reactor pressures from 0.15 MPa to 3 MPa, preferably from 0.2 MPa to 2 MPa, more preferably from 0.25 MPa to 1.5 MPa. [0030] Preferably, the polyethylene polymers produced by the polymerization process are high density polyethylene resins preferably having a density in the range from 0.935 g/cm to

0.970 g/cm 3. More preferably, the density is in the range from 0.940 g/cm 3 ^J to 0.970 g/cm 3 ^J .

Most preferably, the density is in the range from 0.945 g/cm 3 to 0.965 g/cm 3. Density is measured according to DIN EN ISO 1183-1:2004, Method A (Immersion) with compression molded plaques of 2 mm thickness which were prepared with a defined thermal history: Pressed at 180°C, 20 MPa for 8 min with subsequent crystallization in boiling water for 30 min.

[0031] Preferably, the polyethylene polymers produced by the polymerization process have a melt index (MI _21.6 ) from 1 dg/min to 300 dg/min, more preferably from 1.5 dg/min to 50 dg/min, and most preferably from 2 dg/min to 35 dg/min. The MI _21.6 is measured according to DIN EN ISO 1133:2005, condition G at a temperature of 190°C under a load of 21.6 kg.

Catalyst

[0032] The polymerization can be carried out using all customary ethylene polymerization catalysts, e.g., the polymerization can be carried out using Phillips catalysts based on chromium oxide, using titanium-based Ziegler-type catalysts, i.e., Ziegler-catalysts or Ziegler- Natta-catalysts, or using single-site catalysts. For the purposes of the present disclosure, single-site catalysts are catalysts based on chemically uniform transition metal coordination compounds. Particularly suitable single-site catalysts are those comprising bulky sigma- or pi- bonded organic ligands, e.g. catalysts based on mono-Cp complexes, catalysts based on bis- Cp complexes, which are commonly designated as metallocene catalysts, or catalysts based on late transition metal complexes, in particular iron-bisimine complexes. Furthermore, it is also possible to use mixtures of two or more of these catalysts for the polymerization of olefins. Such mixed catalysts are designated as hybrid catalysts. The preparation and use of these catalysts for olefin polymerization are generally known.

[0033] Preferred catalysts are of the Ziegler type, preferably comprising a compound of titanium or vanadium, a compound of magnesium and optionally a particulate inorganic oxide as support.

[0034] The titanium compounds are preferably selected from the halides or alkoxides of trivalent or tetravalent titanium, with titanium alkoxy halogen compounds or mixtures of various titanium compounds. Examples of suitable titanium compounds are TiBr ₃ , TiBr ₄ , T1CI ₃ , TiCl ₄ , Ti(OCH ₃ )Cl ₃ , Ti(OC ₂ H ₅ )Cl ₃ , Ti(0-i-C ₃ H ₇ )Cl ₃ , Ti(0-n-C ₄ H ₉ )Cl ₃ , Ti(OC ₂ H ₅ )Br ₃ , Ti(0-n-C ₄ H ₉ )Br ₃ , Ti(OCH ₃ ) ₂ Cl ₂ , Ti(OC ₂ H ₅ ) ₂ Cl ₂ , Ti(0-n-C ₄ H ₉ ) ₂ Cl ₂ , Ti(OC ₂ H ₅ ) ₂ Br ₂ , Ti(OCH ₃ ) ₃ Cl, Ti(OC ₂ H ₅ ) ₃ Cl, Ti(0-n-C ₄ H ₉ ) ₃ Cl, Ti(OC ₂ H ₅ ) ₃ Br, Ti(OCH ₃ ) ₄ , Ti(OC ₂ H ₅ ) ₄ or Ti(0-n-C ₄ H ₉ ) ₄ . Preference is given to using titanium compounds which comprise chlorine as the halogen. Preference is likewise given to titanium halides which comprise only halogen in addition to titanium, and among these especially titanium chlorides and in particular, titanium tetrachloride. Among the vanadium compounds, preferable are the vanadium halides, the vanadium oxyhalides, the vanadium alkoxides and the vanadium acetylacetonates. Preference is given to vanadium compounds in the oxidation states 3 to 5.

[0035] In the production of the solid component, preferably at least one compound of magnesium is used. Suitable compounds of this type are halogen-comprising magnesium compounds such as magnesium halides, and in particular the chlorides or bromides, and magnesium compounds from which the magnesium halides can be obtained in a customary way, e.g., by reaction with halogenating agents. Preferably, the halogens are chlorine, bromine, iodine or fluorine, or mixtures of two or more of the halogens. More preferably, the halogens are chlorine or bromine. Most preferably, the halogens are chlorine.

[0036] Possible halogen-containing magnesium compounds are magnesium chlorides or magnesium bromides. Magnesium compounds from which the halides can be obtained are, for example, magnesium alkyls, magnesium aryls, magnesium alkoxy compounds or magnesium aryloxy compounds or Grignard compounds. Suitable halogenating agents are, for example, halogens, hydrogen halides, SiCl ₄ or CC1 ₄ . Preferably, chlorine or hydrogen chloride is the halogenating agents.

[0037] Examples of suitable, halogen-free compounds of magnesium are diethylmagnesium, di-n-propylmagnesium, diisopropylmagnesium, di-n-butylmagnesium, di-sec-butylmagnesium, di-tert-butylmagnesium, diamylmagnesium, n-butylethylmagnesium, n-butyl-sec-butylmagnesium, n-butyloctylmagnesium, diphenylmagnesium, diethoxymagnesium, di-n-propyloxymagnesium, diisopropyloxymagnesium, di-n-butyloxymagnesium, di- sec-butyloxymagnesium, di-tert-butyloxymagnesium, diamyloxymagnesium, n-butyloxyethoxymagnesium, n-butyloxy- sec-butyloxymagnesium, n-butyloxyoctyloxymagnesium and diphenoxymagnesium. Among these, preference is given to using n-butylethylmagnesium or n-butyloctylmagnesium. [0038] Examples of Grignard compounds are methylmagnesium chloride, ethylmagnesium chloride, ethylmagnesium bromide, ethylmagnesium iodide, n-propylmagnesium chloride, n-propylmagnesium bromide, n-butylmagnesium chloride, n-butylmagnesium bromide, sec-butylmagnesium chloride, sec-butylmagnesium bromide, tert-butylmagnesium chloride, tert-butylmagnesium bromide, hexylmagnesium chloride, octylmagnesium chloride, amylmagnesium chloride, isoamylmagnesium chloride, phenylmagnesium chloride and phenylmagnesium bromide.

[0039] As magnesium compounds for producing the particulate solids, preference is given to using, apart from magnesium dichloride or magnesium dibromide, the di(Ci-Cio-alkyl)- magnesium compounds. Preferably, the Ziegler-type catalyst comprises a transition metal selected from titanium, zirconium, vanadium, and chromium.

[0040] The Ziegler-type catalyst is preferably added to the slurry reactor by first mixing the catalyst with the diluent used, such as hexane, in a mixing tank to form a slurry suitable for pumping. Preferably, a positive displacement pump, such as a membrane pump is used to transfer the catalyst slurry to the slurry polymerization reactor.

[0041] Catalysts of the Ziegler type are commonly used for polymerization in the presence of a cocatalyst. Accordingly, the slurry polymerization of the present disclosure is preferably carried out in the presence of a cocatalyst. Preferred cocatalysts are organometallic compounds of metals of groups 1, 2, 12, 13 or 14 of the Periodic Table of Elements, in particular organometallic compounds of metals of group 13 and especially organoaluminum compounds. Preferred organoaluminum compounds are selected from aluminum alkyls. The aluminum alkyls are preferably selected from trialkylaluminum compounds. More preferably, the aluminum alkyls are selected from trimethylaluminum (TMA), triethylaluminum (TEAL), tri-isobutylaluminum (TIBAL), or tri-n-hexylaluminum (TNHAL). Most preferably, the aluminum alkyl is TEAL. The cocatalyst(s) are preferably miscible with the diluent and thus comprised in the suspension medium.

[0042] The cocatalyst can be added to the slurry reactor as such. Preferably, the cocatalyst is added by first mixing the cocatalyst with the diluent used, such as hexane or isobutane, in a mixing tank. Preferably, a positive displacement pump, such as a membrane pump is used to transfer the cocatalyst to the slurry polymerization reactor.

[0043] The process of the present disclosure is carried out in at least one polymerization reactor. It may include a polymerization in a stand-alone polymerization reactor or it may include a polymerization in a polymerization reactor of a multi-reactor system. Such multi- reactor systems may be operated in parallel or in series. It is possible to operate two, three or more polymerization reactors in parallel. Preferably, the polymerization reactors of the multi- reactor system are operated in series; i.e. the reactors are arranged as cascade. Preferably such a series includes two or three reactors operating in series, more preferably three reactors operating in series.

[0044] The process of the present disclosure is carried out in a cylindrical polymerization reactor which comprises a cylindrical reactor wall, a bottom reactor head connected to the cylindrical reactor wall at a bottom tangent and a top reactor head connected to the cylindrical reactor wall at a top tangent. The cylindrical polymerization reactor has an inner diameter D which corresponds to the inner diameter of the cylindrical reactor wall and a height H which is the distance from the bottom tangent to the top tangent measured along the central axis of the cylindrical polymerization reactor. The reactor has preferably a height/diameter ratio (H/D) of from 1.5 to 4 and more preferably a height/diameter ratio (H/D) of from 2.5 to 3.5.

[0045] The reactor is equipped with an agitator for mixing the contents of the reactor and inducing a flow of the slurry. In a preferred embodiment of the present disclosure, the agitator is arranged centrally in the reactor and preferably comprises a motor located on the top reactor head, a rotating shaft which is extending along the reactor' s central axis and one or more stages of agitator blades. Preferably, there are 2 to 6 stages of agitator blades attached to the rotating shaft. More preferably, there are 4 or 5 stages of agitator blades. A stage of agitator blades usually comprises several agitator blades. Preferred stages of agitator blades comprise from 2 to 4 blades.

[0046] In the preferred embodiment the motor rotates the agitator shaft and the attached agitator blades. The rotation of the blades induces primarily a vertical flow of the slurry in a circular cross-section around the agitator shaft. This vertical flow of the slurry is preferably a downward flow. At the bottom head, this flow changes direction, and flows first outward toward the reactor wall and then back upward to the top, changes direction again and then back to the center of the polymerization reactor. The rotation of the agitator also results in a secondary flow pattern of slurry in the reactor. This secondary flow is a circular flow in the direction of rotation of the agitator. To control this circular flow, the polymerization reactor is usually equipped with one or more baffles. [0047] According to the process of the present disclosure, the ethylene is fed into the polymerization reactor by an ethylene injection system comprising one or more injection nozzles which project through the bottom reactor head or through the reactor wall and extend from 0.02 times to 0.5 times the inner diameter D into the reactor. The length by which the injection nozzles extend into the reactor has to be understood as the distance from the point where the injection nozzle center line exits the injection nozzle at its ethylene outlet to the point where the injection nozzle center line passes the inner surface of the reactor wall or the inner surface of the bottom reactor head.

[0048] The ethylene is provided to the injection nozzles from the outside of the reactor, passes the reactor wall at the wall passing points of the injection nozzles and exits the injection nozzles through the outlets of the injection nozzles arranged within the polymerization reactors. Preferably, the injection nozzles are straight pipes of an inner diameter D with a certain direction into the reactor. This direction of the injection nozzles correspond to the direction of the injection nozzle center lines. According to the present disclosure the ethylene is fed to the reactor with an ethylene exit velocity of from 10 m/s to 200 m/s, preferably of from 25 m/s to 150 m/s. The desired ethylene exit velocity is achieved by designing diameter D of the one or more injection nozzles in an appropriate way so that the targeted ethylene flow rate to the slurry polymerization results in the desired ethylene exit velocity. The relatively high exit velocity provides high differential speed with respect to the circulating reactor contents, and higher turbulence, which provides improved mixing.

[0049] In a preferred embodiment of the present disclosure, the end of the injection nozzle arranged within the polymerization reactor; that means the ethylene outlet of the injection nozzle, is sloped and has accordingly an outlet tip and an outlet base. The slope is preferably in a way that the angle between the direction of the injection nozzle and the line connecting the outlet tip and the outlet base, i.e. the angle between the injection nozzle center line and the line connecting the outlet tip and the outlet base, is from 20° to 80°, more preferably from 30° to 60°. The slope of the ethylene outlet is preferably oriented in a way with respect to the flow of the slurry that the outlet tip is in an upstream position and the outlet base is in a downstream position with respect to the flow of the slurry. Orientation of the nozzle in this manner minimizes migration of slurry into the nozzle, so as to prevent fouling. For injection nozzles having a sloped ethylene outlet, the point where the injection nozzle center line exits the injection nozzle is the point where the center line meets the line connecting the outlet tip and the outlet base.

[0050] Reference is now made to Figure 1 which illustrates an embodiment of an injection nozzle of the present disclosure. Injection nozzle 110 projects through reactor wall 101, which can be either the wall of the reactor bottom head or the cylindrical side wall of the reactor, and has an outlet 111 which has an outlet tip 112 and an outlet base 113. Angle a is the angle between line 114 connecting outlet tip 112 and outlet base 113 and center line 115 of injection nozzle 110. Angle a is preferably from 20 to 80°. Distance 116 is the extension of injection nozzle 110 into the polymerization reactor.

[0051] For injection nozzle 110 shown in Figure 1, ethylene is provided from below and exits the injection nozzle through outlet 111. The slurry flows in direction 130 corresponding to a flow from an upstream point 131 to a downstream point 132. According to the preferred embodiment shown in Figure 1, the slope of the ethylene outlet 111 as defined by line 114 is oriented in a way with respect to the flow of the slurry that the outlet tip 112 is in an upstream position and the outlet base 113 is in a downstream position with respect to direction 130 of the flow of slurry.

[0052] In a preferred embodiment of the present disclosure, the one or more injection nozzles project through the bottom reactor head. In this embodiment the injection nozzles extend vertically from 0.04 times to 0.2 times the inner diameter D into the reactor, more preferably from 0.07 times to 0.15 times the inner diameter D into the reactor and the horizontal distance from the center of the reactor to the outlet of the injection nozzles is from 0.1 times to 0.45 times the inner diameter D, more preferably from 0.2 times to 0.4 times the inner diameter D. Consequently, the outlets of the injection nozzles are located below the agitator at positions where the downward flow of the slurry induced by the agitator has changed direction and flows primarily outward towards the reactor wall. Accordingly, the outlets of sloped injection nozzles are oriented in a way that the outlet tip are positioned in direction to the reactor center and the outlet bases are positioned in direction to the reactor walls. When the ethylene injection system comprises two or more injection nozzles, all injection nozzles are preferably arranged on a circular line around the reactor center. It is especially preferred that the injection nozzles are uniformly distributed on the circular line and have uniform spacing, so that with two nozzles there is a 180 degree spacing between the nozzles; when there are three nozzles, there is a 120 degree spacing between the nozzles; and when there are four nozzles, there is a 90 degree spacing between the nozzles.

[0053] Reference is now made to Figures 2 and 3 which illustrate a preferred embodiment in which two injection nozzles project through the bottom reactor head.

[0054] Reactor 100 shown in Figure 2 includes a cylindrical reactor wall 102 that extends from a bottom tangent 103 to a top tangent 104; a bottom reactor head 105 connected to the cylindrical reactor wall 102 at the bottom tangent 103; a top reactor head 106 connected to the cylindrical reactor wall 104 at the top tangent 104; and an agitator 120 for mixing the contents of the reactor 100. The agitator 120 has a motor 121, a rotating shaft 122 which is centrally located in the reactor 100, extending along the reactor's central axis and is driven by motor 121 in a direction of rotation 123, and three stages of agitator blades 124 attached to the rotating shaft 122. The reactor has a height, H, measured along its central axis from the bottom tangent 103 to the top tangent 104, and an inner diameter D.

[0055] The blades of agitator stages 124 convey the contents of the reactor 100 in a primary flow pattern 133 with a flow vector 133a initially oriented downward along the central axis of the reactor 100 to the bottom head 105, where it changes direction and flows first outward toward the reactor wall 102 and then back upward to the top head 106, changes direction again and then back to the impeller(s) 103. The rotation of the blades of stages 124 also result in a secondary flow pattern 134 in the reactor. The secondary flow 134 is a circular motion in the direction of rotation 123 of the rotating shaft 122.

[0056] The reactor 100 also contains an ethylene injection system for feeding ethylene into the reactor 100. The embodiment shown in Figure 2 has two injection nozzles 110 that project inward through the bottom reactor head 105. The injection nozzles 110 have sloped ethylene outlets 111 which are oriented in a way that the outlet tips are positioned in direction to the reactor center and the outlet bases are positioned in direction to the reactor wall. The diameter of injection nozzles 110 is adapted to maintain an ethylene exit velocity from 10 m/s to 200 m/s.

[0057] Figure 3 is a top view of reactor 100 shown in Figure 2. The depicted agitator stage 124 has four agitator blades attached to rotating shaft 122. The rotation of the agitator blades of stages 124 defines a circular cross-section 125. The two ethylene outlets 111 of the two injection nozzles used in the embodiment shown in Figure 3 have the same distance from the center of the reactor and thus also from rotating shaft 122 and are accordingly positioned on circle 117.

[0058] In another preferred embodiment of the present disclosure, the one or more injection nozzles project through the cylindrical reactor wall. In this embodiment the injection nozzles extend from 0.02 times to 0.48 times the inner diameter D into the reactor, more preferably from 0.1 times to 0.4 times the inner diameter D into the reactor, and the injection nozzles project through the wall at a wall passing point positioned in the lower two third of the reactor; i.e., a point with a distance of not more than H*2/3 from the bottom tangent which connects the cylindrical reactor wall and the bottom tangent. More preferably the wall passing point, at which the injection nozzles projects through the cylindrical reactor wall, is positioned at a point in the lower half of the reactor, i.e. at a point with a distance of not more than H/2 from the bottom tangent and most preferably, the wall passing point is positioned in the lower third of the reactor, i.e., a point with a distance of not more than H/3 from the bottom tangent.

[0059] The injection nozzles projecting through the cylindrical reactor wall may incline downward. For inclining injection nozzles, the horizontal angle between the direction of the injection nozzle and the horizontal, i.e. the angle between the center line of the injection nozzle and the horizontal, is preferably from 5° to 60°, more preferably from 7.5° to 45° and especially preferred from 10° to 30°. The injection nozzles projecting through the cylindrical reactor wall may also have a radial deviation; that means the center line of the injection nozzles is not passing through the reactor center. This deviation is preferably towards the downstream direction of the circular flow of the slurry which is normally induced as secondary flow pattern by the rotation of the agitator. Injection nozzles not directed to the reactor center have preferably a radial angle between the direction of the injection nozzle, i.e. the center line of the injection nozzle, and a line running from the wall passing point to the center of the reactor of from 5° to 60°, more preferably from 7.5° to 45° and especially preferred from 10° to 30°. The outlets of the injection nozzles are preferably arranged at a height which differs from the height of a stage of agitator blades attached to the agitator shaft. Preferably the outlets of the injection nozzles are arranged below at least one stage of agitator blades. Most preferably the outlets of the injection nozzles are located at a position below the agitator, i.e. below all stages of agitator blades. Consequently, the outlets of the injection nozzles are preferably located at positions where the primary flow pattern is a downward flow of the slurry with an additional, smaller, circular flow. Accordingly, the outlets of sloped injection nozzles are preferably arranged in a way that the outlet tip is in upstream position with respect to the primary flow pattern.

[0060] The injection nozzles projecting through the cylindrical reactor wall are preferably positioned in a way that all wall passing points are arranged at the same height of the reactor. It is especially preferred that the injection nozzles are uniformly distributed around the reactor and have uniform spacing, so that with two nozzles there is a 180 degree spacing between the nozzles; when there are three nozzles, there is a 120 degree spacing between the nozzles; and when there are four nozzles, there is a 90 degree spacing between the nozzles. Orienting the nozzles in this way prevents solids from entering the nozzles if solids settle in the reactor, as well as maximizing the number of nozzles that can be installed relative to an installation on the bottom of the reactor. Higher numbers of nozzles provides even more improved mixing and distribution of the ethylene.

[0061] Reference is now made to Figures 4 and 5 which illustrate a preferred embodiment in which two injection nozzles project through the cylindrical reactor wall. The reactor shown in Figures 4 and 5 is identical to that depicted in Figures 2 and 3 and agitated in the same manner.

[0062] The ethylene injection system for feeding ethylene into the reactor 100 shown in Figure 4 has two injection nozzles 110 that project inward through the cylindrical reactor wall 102 at wall passing points 118 positioned at the same height in the lower third of the reactor. The injection nozzles 110 may incline downward with a horizontal angle β between the center lines 115 and the horizontal 135. When injection nozzles 110 incline downward, angle β is preferably from 5 to 60°. The ethylene outlets 111 of the injection nozzles 110 are located at a position below the agitator 120, i.e. below all stages of agitator blades 124. Distances 119 are the horizontal distances of the outlets of the injection nozzles to the center of the reactor. The injection nozzles 110 have sloped ethylene outlets 111 which are oriented in a way that the outlet tips are positioned in an upward position corresponding to the primarily downward flow in the circular cross-section defined by the rotation of the agitator blades. The diameter of injection nozzles 110 is adapted to maintain an ethylene exit velocity from 10 m/s to 200 m/s.

[0063] Figure 5 is a top view of reactor 100 shown in Figure 4. The two injection nozzles 110 may have a tangential deviation towards the downstream direction of the circular flow of the slurry 134 which deviation has a radial angle γ between the center lines 115 of the injection nozzle 110 and a line 136 running from the wall passing point 118 to the center of the reactor thus to rotating shaft 122. When injection nozzles 110 have a tangential deviation, angle γ is preferably from 5 to 60°.

[0064] Other features, advantages and embodiments of the subject matter disclosed herein will be readily apparent to those exercising ordinary skill after reading the foregoing disclosure. In this regard, while specific embodiments of the present subject matter have been described in considerable detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the present subject matter as described and claimed.