Process of separating a polymer-monomer mixture

Abstract

A process of separating a polymer-monomer mixture into a solid fraction comprising the polymeric components and a gaseous fraction comprising the gaseous components containing monomers; the process comprising the step of: introducing the polymer-monomer mixture into a separation vessel comprising at least a filter bag, a first outlet for the gaseous fraction and second outlet for the solid fraction, which is on an opposite side of the filter bag with respect to the first outlet; applying a depression inside the filter bag so that the gaseous fraction passes through the filter bag and goes out of the vessel through the first outlet; and discharging the solid fraction through the second outlet; the filter bag comprises a filtering layer 9, which is comprises aramid fibers superficially coated with at least one perfluorocarbon.

Description

Basell Poliolefine Italia Sri FE7544-WO-01 FE050 / 23PROCESS OF SEPARATING A POLYMER-MONOMER MIXTUREDESCRIPTIONTECHNICAL FIELD

[0001] The present invention relates to a process of separating a polymermonomer mixture and a method of preparing an olefin polymer. The present invention further relates to a separation apparatus for separating the polymermonomer mixture and plant for preparing the olefin polymer comprising such a separation apparatus.BACKGROUND OF THE INVENTION

[0002] In a typical polymerization system, monomer (and possibly comonomer, diluents, and catalyst) are fed into a continuously stirred reactor or a gas-phase polymerization reactor. The monomer (and possibly co-monomer) reacts to produce a product effluent containing solid polymer particles of various sizes, diluents (if used), unreacted monomer, and possibly catalyst. The effluent is removed from the reactor, and typically contains a good amount of unreacted monomer. For economical operation of this process the unreacted monomer and / or diluents are separated from the polymer solids and then returned to the reactor(s).

[0003] The reactors that are currently used are of different types.

[0004] WO2018087209A1 discloses a process for preparing an olefin polymer in the presence of hydrogen in a gas-phase polymerization reactor comprising three or more polymerization zones and at least two thereof are sub-zones of a polymerization unit, in which the growing polymer particles flow downward in a densified form.

[0005] WO2019154756A1 discloses gas-phase polymerization reactor for the gas-phase polymerization of olefins comprising at least one polymerization zone which is equipped with a recycle line for withdrawing reaction gas from the reactor, leading the reaction gas through a heat-exchanger for cooling and feeding the reaction gas back to the reactor. The recycle line is equipped with the heatexchanger, a centrifugal compressor comprising variable guide vanes, and a butterfly valve.

[0006] W02008095807A1 discloses an apparatus for the liquid-phase polymerization of one or more a-olefins comprising: a first reactor selected from aloop reactor or a continuously stirred tank reactor; at least a downstream loop reactor; and a connection line for transferring a polymer slurry from said first reactor to said downstream loop reactor.

[0007] US 6,110,243 B1 describes filter bags comprising expanded PTFE membranes and optional aramid or polyester covers for industrial dust filtration.

[0008] CN 102166455 A discloses high-temperature needle-felt filter materials, including aramid fibers and possible PTFE coatings, for flue gas filtration.

[0009] US 2003 / 0156999 A1 relates to separating unreacted monomer from polymerization effluent using bag filters at high pressure.

[0010] CN 106390623 describes ultra-fine aramid fiber filter bags with PTFE-based protective layers for dust collection.

[0011] EP 2 090 828 A2 discloses filters for combustion gases using various materials, including aramid and PTFE.

[0012] CN 110545890 A describes bag filters, possibly of PTFE, for removing polymer fines from reactor effluent.

[0013] US 7,098,301 B1 discloses high-pressure bag filtration for separating polymer solids and unreacted monomer.

[0014] EP 2 253 375 B1 describes the use of bag filters, including PTFE membranes, for removing fine powders in water-absorbing resin production.

[0015] It is known to separate polymer solids from unreacted monomer by feeding the effluent to a separation apparatus provided with a plurality of filter bags (for example, as disclosed in US7098301).

[0016] Filter bags material has significant impact on the filtration performance and on the life of the bags themselves. Goretex® is usually used as bags material in polypropylene plants due to it good resistance on metalloorganic chemicals used in the polymerization reactions and that can be present in the filtration environment. Unfortunately Goretex® tissue can adsorb the polymer fines that are easily nested in the filtration media reducing suddenly the filtration efficiency and the life time of the bags, that must be changed with a certain frequency.

[0017] The object of the present invention is to provide a process of separating a polymer-monomer mixture, a method of preparing an olefin polymer, a separation apparatus for separating the polymer-monomer mixture and a plant for preparing the olefin polymer, that allow the drawbacks of the known art to be at least partially overcome, and which eventually are, at the same time, simple and inexpensive to implement.SUMMARY

[0018] According to the invention there is provided a process of separating a polymer-monomer mixture, a method of preparing an olefin polymer, a separation apparatus and a plant according to the appended independent claims and, preferably, according to any one of the claims directly or indirectly depending on the independent claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention is hereinafter described with reference to the accompanying drawings, which depict a non-limiting embodiment thereof, wherein:

[0020] - figure 1 is schematic and side view of a separation apparatus and a plant in accordance with the present disclosure;

[0021] - figure 2 is a perspective view of a component of the apparatus of figure 1.-DETAILED DESCRIPTION

[0022] With reference to figure 1, in accordance with a first aspect of the present invention, it is herein provided a separation apparatus 1 for separating a polymer-monomer mixture, which comes from a polymerization reactor 2 and comprises polymeric components and gaseous components, into a solid fraction comprising the polymeric components and a gaseous fraction comprising the gaseous components containing monomers.

[0023] The separation apparatus 1 comprises:

[0024] a separation vessel 3 provided with at least a filter bag 4 (in particular, filter bags 4 - in the embodiment of figure 1 three filter bags 4 are depicted), a first outlet 5 for the gaseous fraction and second outlet 6 for the solid fraction, which is on an opposite side of the filter bag 4 with respect to the first outlet 5; and

[0025] a suction device 7 for applying a depression inside the filter bag(s) 4 so that the gaseous fraction passes through the filter bag(s) 4 and goes out of the vessel 3 through the first outlet 5. The suction device can be, e.g. a pump or a compressor and does not need to be directly connected to the separation vessel 3.

[0026] The second outlet 6 is designed for discharging the solid fraction through the second outlet 6.

[0027] Making particular reference to figure 2, the filter bag 4 comprises a structural support 8 (in particular, a bag filter cage) and a filtering layer 9, which ismounted on the structural support 8 and comprises (in particular, consists of) aramid fibers superficially coated with at least one perfluorocarbon (in particular, polytetrafluoroethylene - PTFE).

[0028] It has been experimentally observed that in this way the filtering layer 9 surprisingly absorbs very little polymer fines and have, also for this reason, a very long lifetime, in particular significantly longer than that of corresponding layers of Goretex®.

[0029] It has also been observed that the filtering layer 9 has an unexpected resistance to the polymer-monomer mixture coming from a polymerization reactor 2. Please note that such a polymer-monomer mixture is a particularly aggressive composition, as it typically contains a portion of polymerization catalyst / s (in particular, organometallic compounds; more in particular, alkylaluminium compounds - the polymerization catalyst / s is / are disclosed in are detail below).

[0030] Figure 2 depicts an embodiment of the filter bag 4. However, please note that in order to better show the structure of the structural support 8 the filtering layer 9 is slightly moved with respect to its proper position. The filtering layer 9 usually covers the structural support 8 (bag filter cage) substantially entirely (so that the gaseous fraction that goes inside the filter 4 must necessarily pass through the filtering layer 9.

[0031] In the present text, the term “superficially coated” indicates that the aramid fibers are at least partially (in particular, predominantly) covered with the at least one perfluorocarbon (in particular, polytetrafluoroethylene - PTFE). In some non-limiting instances, the aramid fibers are substantially completely covered with at least one perfluorocarbon (in particular, polytetrafluoroethylene - PTFE).

[0032] Advantageously but not necessarily, the filtering layer 9 has an air permeability lower than 300 (in particular, lower than 200; more in particular lowerthan 160) . More precisely but not necessarily, the filtering layer 9 has anair permeability from about 80 (in particular, from about 100; more in particular, from about 140) to about 290 (in particular, to about 220; more in particular, toabout 170) — — .dm^xmin

[0033] In particular, the air permeability is measured according to EN ISO 9237:1995 (@ 200 Pa).

[0034] In carried out experiments, the filtering layers 9 with the above identified permeabilities have surprisingly shown to properly work for separating the two fractions, achieving a good separation, while, at the same time, to have a lower absorption of polymer fines.

[0035] Advantageously but not necessarily, the filtering layer 9 comprises (in particular, consists of) meta-aramid fibers.

[0036] Advantageously but not necessarily, the filtering layer 9 comprises (in particular, consists of) aramid fibers (in particular, meta-aramid fibers) superficially coated with polytetrafluoroethylene.

[0037] Advantageously but not necessarily, the aramid fibers of the filtering layer 9 are needle felted. In other words, the filtering layer 9 is (consists of) needle felt.

[0038] According to some non-limiting embodiments, the filtering layer 9 has a tensile strength of at least about 300 N. More precisely, the filtering layer 9 has longitudinal tensile strength of at least about 400 N up to about 1000 N (in particular, up to about 800 N; more in particular, up to about 600 N) and / or a cross strength of at least about 700 N (in particular, of at least about 900 N; more in particular, of at least 1100 N) possibly up to about 2000 N.

[0039] In particular, the tensile strength is measured according to EN ISO 9073-3:1989 (sample size 200 mm-50 mm; sampling parallel to the scrim threads; deformation rate 200 mm / min).

[0040] Advantageously but not necessarily, the filtering layer 9 has a thickness (BWF Envirotec standard 01) from about 1.5 mm (in particular, from about 2 mm; more in particular, from 2.1) to about 3 mm (in particular, to about 2.5 mm).

[0041] In addition or alternatively, the filtering layer 9 has an area weight (BWF Envirotec standard 04) from about 400 g / m2(in particular, from about 450 g / m2) to about 600 g / m2(in particular, to about 550 g / m2).

[0042] In addition or alternatively, the filtering layer 9 has a density (BWF Envirotec standard 01) from about 0.15 g / cm3(in particular, from 0.2 g / cm3; more in particular, from 0.21 g / cm3) to about 0.3 g / cm3(in particular, to about 0.25 g / cm3).

[0043] In particular, the filtering layer 9 has a separation efficiency (maximum dust content in outlet gas) not higher than 35 mg / m3(more in particular, not higher than 30 mg / m3).

[0044] Please note that according to different embodiments the polymerization reactor 2 may be a single reactor or a plurality of reactors arranged, for example, in parallel or in succession (one downstream of another).

[0045] Examples of the polymerization reactor 2 are disclosed in US2018178180A1, US20200031957A1 , US20110054127A1, W02018087209A1, WO2019154756A1 and W02008095807A1.

[0046] In accordance with a second aspect of the present invention, a plant 15 for preparing an olefin polymer is also herein provided. The plant 15 comprises the polymerization reactor 2 (as above disclosed), the separation apparatus 3 (as above disclosed), a first connection 13 for feeding the polymer-monomer mixture from the polymerization reactor 2 to the separation apparatus 3 and a second connection 14 for conveying said gaseous fraction from the separation apparatus 3 back the polymerization reactor 2.

[0047] According to some non-limiting embodiments, the plant 15 comprises also a separation vaporizer 11 , which is designed to treat the polymer-monomer mixture so that at least (part of) the monomers vaporize(s). In this case, the reactor 2 is typically designed to implement a liquid-phase polymerization.

[0048] According to some non-limiting embodiments, the plant 15 also comprises a pump (known per se and not depicted) arranged at the second connection 14 for conveying the polymer-monomer mixture along the second connection 14.

[0049] In accordance with a third aspect of the present invention, it is herein provided a process of separating a polymer-monomer mixture, which comes from a polymerization reactor 2 and comprises polymeric components and gaseous components, into a solid fraction comprising the polymeric components and a gaseous fraction comprising the gaseous components containing monomers.

[0050] The process comprises the steps of: introducing the polymer-monomer mixture into a separation vessel 3 comprising at least a filter bag 4, a first outlet 5 for the gaseous fraction and a second outlet 6 for the solid fraction, which is on an opposite side of the filter bag 4 with respect to the first outlet 5; applying a depression inside the filter bag 4 (in particular, by means of a suction device 7) so that the gaseous fraction passes through the filter bag 4 and goes out of the separation vessel 3 through the first outlet 5; and discharging the solid fraction through the second outlet 6.

[0051] The filter bag 4 comprises a structural support 8 and a filtering layer 9, which is mounted on the structural support 8 and comprises aramid fibers superficially coated with at least one perfluorocarbon.

[0052] In particular, the separation vessel 3 and its components (e.g. the filter bag 4, the outlets 5 and 6 and possibly the suction device) are as defined above with respect to the first aspect of the present invention.

[0053] Advantageously but not necessarily, during the step of applying, the applied depression inside the filter bag is at least about 10 bar (in particular, at least about 15 bar; more in particular, at least about 18 bar). In the contest of thepresent disclosure, for “depression” it is intended the differential pressure between the filter bag and the upstream polymerization reactor.

[0054] Alternatively or in addition, during the step of applying, the applied depression inside the filter bag is up to about 28 bar (in particular, to about 25 bar; more in particular, to about 20 bar).

[0055] With the selected pressures it is possible to more efficiently separate the solid fraction and the gaseous fraction. In particular, it has been observed that the filtering layer 9 as herein defined is particularly resistant to relatively high depressions.

[0056] Advantageously but not necessarily, during the step of applying, the temperature inside the filter bag is from about 35°C (in particular, from about 50°C; more in particular, from about 65°C) to about 120°C (in particular, to about 100°C, more in particular, to about 90°C; still more in particular, to about 80°C).

[0057] According to some non-limiting embodiments, the polymeric component comprises (in particular, is) homo-polymer(s) and / or co-polymer(s) of propylene and the monomers comprise (are) propylene.

[0058] In addition or alternatively, the polymeric component comprises (in particular, is) homo-polymer(s) and / or co-polymer(s) of ethylene and the monomers comprise (are) ethylene.

[0059] In accordance with a fourth aspect of the present invention, it is herein also provided a method of preparing an olefin polymer comprising a polymerization step, during which an olefin homopolymerize or copolymerize together with one or more other olefins in the polymerization reactor 2 in the presence of a polymerization catalyst; the method comprises a process as above described (in accordance with the first aspect of the present invention), wherein the polymermonomer mixture comes from the polymerization reactor 2.

[0060] Advantageously but not necessarily, the gaseous fraction, which comprises the gaseous components containing monomers and is obtained by the process of separation, is recycled to the polymerization reactor 2.

[0061] Please note that according to different embodiments the polymerization step may be carried out in a single reactor or a plurality of reactors arranged, for example, in parallel or in succession (one downstream of another).

[0062] In some non-limiting cases, the polymerization step is carried out at temperatures of from 20 to 200°C and pressures of from 0.5 to 10 MPa.

[0063] Examples of how polymerization step is carried out are disclosed in US2018178180A1, US20200031957A1 , US20110054127A1, W02018087209A1, WO2019154756A1 and W02008095807A1.

[0064] More precisely, the polymerization step may be carried out in gasphase or in liquid-phase.

[0065] Where the polymerization step is carried out in the liquid phase. The method comprises also a vaporization step, during which the polymer-monomer mixture is treated so that at least (part of) the monomers vaporize(s). In these cases, the polymer-monomer mixture is fed to the separation vessel 3 (only) after having undergone the vaporization step.

[0066] In particular, the vaporization step is carried out by a vaporizer 11 connecting the reactor 2 to the separation apparatus 1 (in particular to the separation vessel 3). In particular, the vaporizer 11 is arranged at the second connection 14.

[0067] More precisely, the vaporization step is carried out when the polymerization step is liquid-phase polymerization (as disclosed in W02008095807A1).

[0068] In some non-limiting embodiments, the polymerization step is carried out by using olefin polymerization catalysts, alternatively titanium-based Ziegler-Natta-catalysts, Phillips catalysts based on chromium oxide, or single-site catalysts. As used herein, single-site catalysts are catalysts based on chemically uniform transition metal coordination compounds, such as metallocene catalysts. In some non-limiting embodiments, mixtures of two or more different catalysts are used. In some non-limiting embodiments, the mixed catalyst systems are designated as hybrid catalysts.

[0069] In particular, the polymerization step is carried out in the presence of Ziegler-Natta catalysts made from or containing:i. a solid catalyst component made from or containing Mg, Ti, a halogen and an electron donor compound (internal donor),ii. an alkylaluminium compound, andiii. optionally, an electron-donor compound (external donor).

[0070] In some non-limiting embodiments, component (i) is prepared by contacting a magnesium halide, a titanium compound having at least a Ti-halogen bond, and optionally an electron donor compound. In some non-limiting embodiments, the magnesium halide is MgCh in active form as a support for Ziegler-Natta catalysts. In some non-limiting embodiments, the titanium compounds are TiCU, TiCh, or Ti-haloalcoholates of formula Ti(OR)n-yXy, where n is the valence of titanium, y is a number between 1 and n— 1 , X is a halogen and R is a hydrocarbon radical having from 1 to 10 carbon atoms, can also be used.

[0071] In some non-limiting embodiments, electron donor compounds for preparing Ziegler type catalysts are selected from the group consisting of alcohols, glycols, esters, ketones, amines, amides, nitriles, alkoxysilanes and aliphatic ethers. In some non-limiting embodiments, these electron donor compounds are used alone or in mixtures with other electron donor compounds.

[0072] In some non-limiting embodiments, other solid catalyst components used are based on a chromium oxide supported on a refractory oxide, such as silica, and activated by a heat treatment. Catalysts obtainable from those components consist of chromium (VI) trioxide chemically fixed on silica gel. These catalysts are produced under oxidizing conditions by heating the silica gels that have been doped with chromium (III) salts (precursor or precatalyst). During this heat treatment, the chromium (III) oxidizes to chromium (VI), the chromium (VI) is fixed and the silica gel hydroxyl group is eliminated as water.

[0073] In some non-limiting embodiments, other solid catalyst components used are single-site catalysts supported on a carrier, such as metallocene catalysts, made from or containing:i. at least a transition metal compound containing at least one n bond; and ii. at least a cocatalyst selected from an alumoxane or a compound able to form an alkyl-metallocene cation.

[0074] In some non-limiting embodiments, when the catalyst includes an alkylaluminium compound, such as in Ziegler-Natta catalysts, the molar ratio of solid catalyst component to alkylaluminium compound introduced into the polymerization reactor is in the range from 0.05 to 3, alternatively from 0.1 to 2, alternatively from 0.5 to 1.

[0075] In particular (as a consequence), the polymer-monomer mixture, which undergoes the (separation) process (according with the third aspect of the invention) contains (some amounts of) the above presented catalyst(s) (in particular one or more organometallic compounds; more in particular, alkylaluminium compounds).

[0076] Advantageously but not necessarily, the process in accordance with the third aspect of the present invention is implemented by the apparatus 1 of the first aspect of the invention.

[0077] Analogously, not necessarily, the apparatus 1 of the first aspect of the invention is configured to implement the process of the third aspect of the present invention.

[0078] In addition or alternatively, the method in accordance with the fourth aspect of the present invention is implemented by the plant 15 of the second aspect of the invention.

[0079] Analogously, not necessarily, the plant 15 of the second aspect is configured to implement the method of the fourth aspect of the present invention.

Claims

CLAIMS1. A process of separating a polymer-monomer mixture, which comes from a polymerization reactor (2) and comprises polymeric components and gaseous components, into a solid fraction comprising the polymeric components and a gaseous fraction comprising the gaseous components containing monomers; the process comprising the steps of:introducing the polymer-monomer mixture into a separation vessel (3) comprising at least a filter bag (4), a first outlet (5) for the gaseous fraction and a second outlet (6) for the solid fraction, which is on an opposite side of the filter bag (4) with respect to the first outlet (5);applying a depression inside the filter bag (4) so that the gaseous fraction passes through the filter bag (4) and goes out of the separation vessel (3) through the first outlet (5); anddischarging the solid fraction through the second outlet (6);the filter bag (4) comprising a structural support (8) and a filtering layer (9), which is mounted on the structural support (8) and comprises aramid fibers superficially coated with at least one perfluorocarbon.

2. The process of claim 1, wherein, during the step of applying, the applied depression inside the filter bag (4) is from 10 bar to 28 bar.

3. The process of claim 1 or 2, wherein, during the step of applying, the applied depression inside the filter bag (4) is from 18 bar to 20 bar.

4. The process of any one of claims 1 to 3, wherein, during the step of applying, the temperature inside the filter bag (4) is from 35°C to 120°C.

5. The process of any one of claims 1 to 4, wherein the filtering layer (9) has an air permeability from 80 to 300 — — .

6. The process of any one of claims 1 to 5, wherein the perfluorocarbon is polytetrafluoroethylene (PTFE).

7. The process of any one of claims 1 to 6, wherein the filtering layer (9) consists of meta-aramid fibers superficially coated with polytetrafluoroethylene (PTFE).

8. The process of any one of claims 1 to 7, wherein the polymeric component is homo-polymer and / or co-polymer of propylene and the monomers comprise propylene.

9. The process of any one of claims 1 to 8, wherein the polymer-monomer mixture comprises a polymerization catalyst.

10. A method of preparing an olefin polymer comprising homopolymerizing an olefin or copolymerizing the olefin together with one or more other olefins in a polymerization reactor in the presence of a polymerization catalyst; the method comprises a process of separation according to any one of claims 1 to 9; the polymer-monomer mixture coming from the polymerization reactor.

11. The method according to claim 10, wherein the gaseous fraction, which comprises the gaseous components containing monomers and is obtained by the process of separation, is recycled to the polymerization reactor (2).

12. A separation apparatus (1) for separating a polymer-monomer mixture, which comes from a polymerization reactor (2) and comprises polymeric components and gaseous components, into a solid fraction comprising the polymeric components and a gaseous fraction comprising the gaseous components containing monomers; the separation apparatus (1) comprising:a separation vessel (3) provided with at least a filter bag (4), a first outlet (5) for the gaseous fraction and second outlet (6) for the solid fraction, which is on an opposite side of the filter bag (4) with respect to the first outlet (6); anda suction device (7) for applying a depression inside the filter bag (4) so that the gaseous fraction passes through the filter bag (4) and goes out of the separation vessel (3) through the first outlet (5);the second outlet (6) being designed for discharging the solid fraction; the filter bag (4) comprising a structural support (8) and a filtering layer (9) mounted on the structural support (8), which comprises aramid fibers superficially coated with at least one perfluorocarbon.

13. The separation apparatus of claim 12, wherein the filtering layer (9) has an air permeability from 80 to 30014. The separation apparatus of claim 12 or 13 , wherein the aramid fibers superficially coated with polytetrafluoroethylene (PTFE); in particular, the filtering layer (9) consists of Meta-aramid fibers superficially coated with polytetrafluoroethylene.

15. A plant for preparing an olefin polymer comprising a polymerization reactor, a separation apparatus according to any one of claims 12 to 14, a first connection for conveying the polymer-monomer mixture comes from the polymerization reactor to the separation apparatus and a second connection for conveying said gaseous fraction from the separation apparatus back the polymerization reactor.

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