Process for manufacturing polyolefins with low volatile matter content

Abstract

A process for separating at least one polyolefin from a product stream from a solution polymerization process, wherein the product stream comprises a mixture of at least one polyolefin and a volatile substance, and the process comprises the steps of: separating the product stream into a first polyolefin-lean vapor stream and a first condensed polyolefin-rich stream; separating the first condensed polyolefin-rich stream into a second polyolefin-lean vapor stream and a second condensed polyolefin-rich stream; and separating the second condensed polyolefin-rich stream into a final polyolefin-lean vapor stream and a final condensed polyolefin-rich stream; wherein the first polyolefin-lean vapor stream and the second polyolefin-lean vapor stream are introduced as an initial feed stream of the solution polymerization process without any additional purification step.

Description

Technology Field

[0001] The present invention relates to a process for separating polyolefins from a product stream of a solution polymerization process. In particular, the present invention relates to a process simplification in that at least a portion of the residual overhead stream of the separation step can be returned directly to the feed stream of the solution polymerization process, i.e., without any additional purification. Furthermore, the present invention relates to a polyolefin obtainable from such a process. Background Technology

[0002] In polyolefin polymerization technology, particularly in polyolefin polymerization technology based on solution techniques, downstream processing of the product stream is essential for producing products with low volatile matter content in terms of solvent and / or unreacted (co)monomers.

[0003] Downstream processing takes place through several separation steps, typically pressure flashing steps. Typically, these separation steps are repeated at least once to produce a polyolefin with a low content of volatile substances. Each of these steps produces a polymer-rich phase and a polymer-lean phase, while the latter is typically reintroduced into the polymerization process after undergoing at least one purification step.

[0004] WO 2020 / 060745 A1 aims for the devolatilization of polymers. It discloses that the feed stream of a reactor is temperature-controlled, pressure-controlled, and separated into a polymer-lean phase and a polymer-rich phase. The separator is generally described as a high-pressure liquid-liquid separator (HPS). Subsequently, the polymer-rich phase is again temperature-controlled and fed to a second separator, which is a flash separator. WO 2020 / 060745 facilitates flash separation by using high-pressure injection of volatile substances into the second separator to lower the partial pressure of the volatile substance composition within the polymer. Subsequently, the polymer-rich phase from the second separator is added to a devolatilization extruder as a final step. However, WO 2020 / 060745 does not provide any specific instruction regarding the easy return of the polymer-lean phase from these separation steps to the feed stream of the polymerization process.

[0005] WO 2009 / 126277 A2 discloses a polymer production process using a subsequent LCST separator, wherein a low critical solution temperature boundary crosses the inlet stream to form two fluid phases. The subsequent process includes one or more flash vessels and devolatilization extruders connected in series. However, again, WO 2009 / 126277 A2 does not provide any particular instruction regarding the easy return of the polymer-lean phase from this separation step to the feed stream of the polymerization process.

[0006] [Problem of the Invention]

[0007] One of the primary concerns in modern solution polymerization processes is energy efficiency and cost considerations. In conventional polymerization processes, ideally, the overhead phase of each separation stage is returned to the initial feed stream of the solution polymerization process. However, in typical equipment for conventional processes, the feed stream is purified before return, which further increases energy consumption, setup complexity, and costs while reducing the overall process efficiency. This is because impurities introduced into the recirculation stream can lead to a decrease in catalytic activity within the reactor. Furthermore, after adjusting the temperature and pressure to meet the requirements of the polymerization reaction, spontaneous polymerization of the mixture within the stream induced by these impurities can result in equipment fouling. Finally, the influx of polymer particles originating from the separation stage can cause fouling of downstream equipment in the recirculation stream, such as heat exchangers.

[0008] [Purpose of the Invention]

[0009] Therefore, there is a need for a process to separate polyolefins from the product stream of a solution polymerization process that produces polyolefins containing low-volatility substances, and this process is more energy-efficient, less complex, less prone to fouling, and less expensive than known in the prior art.

[0010] [Summary of the Invention]

[0011] Now, surprisingly, it has been discovered that the aforementioned objective can be achieved by a process for separating at least one polyolefin from a product stream from a solution polymerization process, wherein the product stream comprises a mixture of at least one polyolefin and a volatile substance, said process comprising the steps of: separating the product stream into a first polyolefin-lean vapor stream and a first condensed polyolefin-rich stream; separating the first condensed polyolefin-rich stream into a second polyolefin-lean vapor stream and a second condensed polyolefin-rich stream; separating the second condensed polyolefin-rich stream into a final polyolefin-lean vapor stream and a final condensed polyolefin-rich stream, and wherein the first polyolefin-lean vapor stream and the second polyolefin-lean vapor stream are introduced as an initial feed stream of the solution polymerization process without any additional purification steps.

[0012] More surprisingly, it has been discovered that the aforementioned objective can be achieved by a polyolefin obtained by a process of separating at least one polyolefin from a product stream from a solution polymerization process, wherein the product stream comprises a mixture of at least one polyolefin and a volatile substance, and the process comprises the steps of: separating the product stream into a first polyolefin-lean vapor stream and a first condensed polyolefin-rich stream; separating the first condensed polyolefin-rich stream into a second polyolefin-lean vapor stream and a second condensed polyolefin-rich stream; separating the second condensed polyolefin-rich stream into a final polyolefin-lean vapor stream and a final condensed polyolefin-rich stream, wherein the first polyolefin-lean vapor stream and the second polyolefin-lean vapor stream are introduced as an initial feed stream of the solution polymerization process without any additional purification steps.

[0013] [definition]

[0014] 'Volatile substances' as used in this specification ( volatiles) or 'volatile compounds ( volatile compounds The expression )’ should be understood as a compound having a significantly lower molecular weight compared to the polyolefin separated in the process of the present invention. Such compounds typically exist in gaseous form when exposed to a flash separator. Generally, volatile compounds are mixtures of volatile hydrocarbons. Preferably, the mixture of volatile hydrocarbons comprises at least one solvent, optionally a monomer, and a comonomer.

[0015] Flash separator ( Flash separators The 'low-pressure separator' has been known in the prior art for decades (also referred to as a low-pressure separator). As is well known in the art, a liquid feed is passed through a flash vessel operated at reduced pressure. This allows a portion of the liquid phase to vaporize and be withdrawn from the low-pressure separator as a top stream (or vapor stream). The portion remaining in the liquid phase is subsequently withdrawn from the flash vessel as a bottom stream or liquid stream. Operating the low-pressure separator so that both the vapor and liquid phases exist in the flash vessel describes this situation.

[0016] The term 'condensation point' as used in this specification ( condensation point )' should be understood as a combination of conditions that lead to the condensation of a compound from a vaporized mixture. In particular, the condensation point depends on a combination of pressure, temperature, and hydrocarbons, such as the solvent, monomer, and optionally comonomer, and any other gaseous component of the system.

[0017] The term 'separation efficiency' as used in this specification ( separation efficiency )’ is defined as the value obtained by dividing the mass flow rate of a component extracted from a polymer-lean stream or vapor stream by the (theoretical) mass flow rate of a component in a polymer-rich stream or condensed stream under equilibrium conditions.

[0018] The term 'vacuum pressure condition' as used in this specification ( vacuum pressure conditions ')' indicates a vacuum pressure of less than 1500 mbara, preferably less than 800 mbara, and most preferably less than 200 mbara. Preferably, the pressure is 1 mbara or higher, more preferably 5 mbara or higher, and most preferably 20 mbara or higher. Pressures lower than the given range are disadvantageous in terms of energy consumption and resulting costs. Pressures higher than the given range result in too much volatile material in the final polymer.

[0019] The 'average time of stay' provided here ( average residence time )' should be understood as the average residence time of the contents of a polymerization reactor containing a catalyst.

[0020] The term 'polyolefin-rich stream' as used in this specification ( polyolefin-lean stream )' and 'polyolefin-lean stream( polyolefin-lean stream )’ refers to two streams coming from a separation device that separates the output streams of a polymerization reactor, where the polymer-rich stream has a higher polymer content than the polymer-lean stream. Accordingly, the minimum concentration of polyolefin in the polymer-rich stream is 60% by weight or more relative to the total weight of the polymer-rich stream. Likewise, the maximum concentration of polyolefin in the polymer-lean stream is less than 10% by weight relative to the total weight of the polymer-lean stream. Brief explanation of the drawing

[0021] Figure 1 shows a schematic layout of the process of the present invention. 참조 부호 A: 1st separation step (Step A) B: Second separation step (Step B) C: Third separation step (Step C) a: product stream a': Initial supply stream b: First polymer-lean vapor stream of Step A c: First condensed polymer-rich stream of Step A b': Second polymer-lean vapor stream of stage B c': Second condensed polymer-rich stream of Step B b*: Final polymer-lean vapor stream of step C c*: Final condensed polymer-rich stream of step C Specific details for implementing the invention

[0022] The present invention will be described in detail below.

[0023] General process of the present invention ( General process of the invention)

[0024] Generally, the process of the present invention relates to a solution polymerization process. The process of the present invention is used to remove volatile compounds from a product polymer and to recirculate a stream of components removed from said polymer. Accordingly, the solution polymerization process should be described as follows.

[0025] Solution polymerization process ( Solution polymerization process)

[0026] Preferably, the present invention can be applied to supercritical, solution, and advanced solution polymerization processes. More preferably, it is a continuous supercritical, solution, and advanced solution polymerization process. Most preferably, the production process comprises a continuous solution polymerization process.

[0027] The polymer produced by the solution polymerization process is a polyolefin. Preferably, the polyolefin is polyethylene (PE), particularly high-density polyethylene (HDPE), low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), or polypropylene (PP). Most preferably, the polyolefin is a polyethylene copolymer or a polyethylene homopolymer.

[0028] When the polymer is a copolymer, the comonomer is different from the α-olefin monomer and is selected from the group consisting of linear and cyclic olefins, α-olefins having 2 to 12 carbon atoms, and mixtures thereof. Preferably, the comonomer is an α-olefin different from the α-olefin monomer and is selected from the group consisting of linear α-olefins having 2 to 12 carbon atoms and mixtures thereof, preferably 4 to 10 carbon atoms, most preferably 1-butene and 1-octene.

[0029] In the most preferred embodiment, the polyolefin is produced by a solution polymerization process as disclosed below.

[0030] Polymerization is typically carried out in the presence of an olefin polymerization catalyst. Preferably, the olefin polymerization catalyst is a metallocene catalyst. Preferably, the polymerization catalyst comprises a metallocene complex and a co-catalyst and / or aluminoxane co-catalyst comprising boron. More preferably, the metallocene catalyst comprises a hafnocene catalyst. Even more preferably, the hafnocene catalyst comprises a hafnocene complex comprising a cyclopentadienyl (Cp) ligand, a fluorenyl (Flu) ligand, and a covalent bridge connecting the two ligands.

[0031] Accordingly, more preferably, the polymerization catalyst comprises at least one metallocene complex selected from complexes M1, M2 and M3 or a mixture thereof, which is described in detail as follows.

[0032] Metallocene complex M1 is a metallocene complex of chemical formula (I).

[0033]

[0034] Here,

[0035] If more than 50 mol% of the complex of Formula II has M = Hf, then M is a mixture containing Hf or Zr, and

[0036] X is a sigma ligand, and

[0037] R are identical or different from each other, and are saturated linear or branched C1-C 10 Alkyl, C5-C 10 Aryl, C6-C 20 Alkylaryl or C6-C 20 It may be an arylalkyl group, which may optionally contain up to two heteroatoms or silicon atoms, and

[0038] R 1 C6-C 20 - It is an aryl, and this consists of one or up to five linear or branched C1-C 10 It can be substituted or unsubstituted with alkyl group(s), and

[0039] R 2 is a saturated linear or annular C3-C 20 Alkyl group or branched CR 3 R 4 R 5 And, here, R 3 Silver, hydrogen, or C1-C 20 It is an alkyl group, and R 4 and R 5 is identical or different, and C1-C 20 It can be an alkyl group.

[0040] Metallocene complex M2 is a metallocene complex of chemical formula (I).

[0041] Here,

[0042] If more than 50 mol% of the complex of Formula II has M = Hf, then M is a mixture containing Hf or Zr, and

[0043] X is a sigma ligand, and

[0044] R are identical or different from each other, and are saturated linear or branched C1-C 10 Alkyl, C5-C 10 Aryl, C6-C 20 Alkylaryl or C6-C 20 It may be an arylalkyl group, which may optionally contain up to two heteroatoms or silicon atoms, and

[0045] R 1 Optionally up to two heteroatoms or silicon atoms or C4-C 10 C6-C containing heteroaryl groups 10 Aryl or C6-C 20 It is an alkylaryl group, and

[0046] R 2 is a C4-C of chemical formula (II) that optionally carries an alkyl substituent at the β-position. 20 It is a cycloalkyl group.

[0047]

[0048] Metallocene complex M3 is a metallocene complex of chemical formula (III).

[0049]

[0050] Here,

[0051] M is Hf and,

[0052] X is a sigma-donor ligand, and

[0053] R 1 , R 2 , R 3 is identical or different, hydrogen or saturated linear or branched C1-C 10 It may be an alkyl group, and thereby the alkyl group may selectively contain up to two heteroatoms belonging to groups 14 to 16 of the periodic table, or R 1 and R 2 or R 2 and R 3 It can form a ring having 4 to 6 carbon atoms and 1 to 3 double bonds, and

[0054] R 4 and R 5 are identical or different from each other, and are saturated linear or branched C1-C 10 Alkyl, C5-C 10 Aryl, C6-C 20 Alkylaryl or C6-C 20It may be an arylalkyl group, which may optionally contain up to two heteroatoms belonging to groups 14 to 16 of the periodic table, and

[0055] n can be 1 to 5, and

[0056] Ar is C6-C 20 -aryl or -heteroaryl group, which is a linear or branched C1-C of 1 to 5 10 It can be substituted or unsubstituted with alkyl group(s).

[0057] Accordingly, preferably, the polymerization process is carried out in the presence of an olefin polymerization catalyst selected from the list consisting of catalysts C1, C2, C3, and C4 described below.

[0058] Catalyst C1 comprises at least one metallocene complex M1 and a co-catalyst containing boron. For details regarding the preparation of such catalyst and further details, refer to WO 2018 / 108917 A1 incorporated herein by reference.

[0059] Catalyst C2 comprises at least one metallocene complex M2 and a co-catalyst containing boron. For details regarding the preparation of such catalyst and further details, refer to WO 2018 / 108918 A1 incorporated herein by reference.

[0060] Catalyst C3 comprises at least one metallocene complex M3 and an aluminoxane co-catalyst and optionally an aluminum alkyl compound Al(R7)3, where R7 is linear or branched It is a C2-C8-alkyl group. For the preparation of such catalysts and more detailed information, refer to WO 2018 / 178151 A1 incorporated herein by reference.

[0061] Catalyst C4 comprises at least one metallocene complex M3 and a co-catalyst containing boron. For the preparation of such catalyst and more details, refer to WO 2018 / 178152 A1 incorporated herein by reference.

[0062] A solvent is also present in the solution polymerization process. Under polymerization conditions, the solvent is in a liquid or supercritical state. The solvent is typically and preferably a hydrocarbon solvent. The liquid hydrocarbon solvent used is preferably C 5-12 - It is a hydrocarbon, which is C such as pentane, methylpentane, hexane, heptane, octane, cyclohexane, methylcyclohexane, and hydrogenated naphtha. 1-4 It may be substituted or unsubstituted with an alkyl group. More preferably, unsubstituted C 6-10 - Hydrocarbon solvents are used, and more preferably, unsubstituted C 5-7 - Hydrocarbon solvents are used. Most preferably, hexane is used.

[0063] Other components may also be added to the reactor. It is known that hydrogen is supplied to the reactor to control the molecular weight of the polymer formed during polymerization.

[0064] Typically, the content of the polymer in the stream extracted from the solution polymerization process comprising a solvent, polymer, unreacted monomer, and optionally a comonomer is 10 to 35 weight%, preferably 12.5 to 30 weight%, more preferably 15 to 25 weight%, and most preferably 19 to 24 weight%.

[0065] Preferably, to deactivate the polymerization catalyst, the stream withdrawn from the solution polymerization reactor is heated to a temperature at least 5°C higher than the temperature of the reaction mixture at the reactor outlet for a period of 1 to 250 seconds.

[0066] By heating the stream withdrawn from the solution polymerization reactor to a predetermined temperature for a predetermined period to sufficiently deactivate the polymerization catalyst, uncontrolled polymerization reactions in the low-pressure separator can be avoided. Therefore, there is no need to add a deactivating agent to the reactor outlet stream, and the disadvantage of transporting such agents accompanied by recycled monomers and / or solvents to the reactor, as described above, is avoided.

[0067] Therefore, in the present invention, it is preferable not to add a catalyst deactivator before supplying the stream extracted from the solution polymerization reactor to the separation process of the present invention.

[0068] In a preferred embodiment, the stream withdrawn from the solution polymerization reactor is heated to a temperature at least 10°C higher than the temperature of the reaction mixture at the reactor outlet, more preferably at least 15°C higher than the temperature of the reaction mixture at the reactor outlet, more preferably at least 20°C higher than the temperature of the reaction mixture at the reactor outlet, more preferably at least 30°C higher than the temperature of the reaction mixture at the reactor outlet, more preferably at least 40°C higher than the temperature of the reaction mixture at the reactor outlet, and most preferably at least 50°C higher than the temperature of the reaction mixture at the reactor outlet.

[0069] Typically, the temperature at which the stream extracted from the solution polymerization reactor is heated is up to 100°C higher than the temperature of the reaction mixture at the outlet of the reactor, more preferably up to 90°C higher than the temperature of the reaction mixture at the outlet of the reactor, and most preferably up to 70°C higher than the temperature of the reaction mixture at the outlet of the reactor.

[0070] Preferably, the stream withdrawn from the solution polymerization reactor is heated to the temperature described herein for a period of 10 to 200 seconds, more preferably 15 to 180 seconds, even more preferably 20 to 180 seconds, even more preferably 40 to 170 seconds, even more preferably 50 to 160 seconds, and most preferably 60 to 150 seconds.

[0071] The stream withdrawn from the solution polymerization reactor is preferably heated to a temperature of at least 180°C, more preferably at least 190°C, even more preferably at least 200°C, and most preferably at least 210°C.

[0072] The stream withdrawn from the solution polymerization reactor is preferably heated to a temperature of up to 275°C, more preferably up to 260°C, and most preferably up to 250°C.

[0073] In principle, when heating is applied for a longer period, a lower temperature may be used, and when applied for a shorter period, a higher temperature must be used to deactivate the catalyst.

[0074] Accordingly, in a preferred embodiment of the process of the present invention, the outlet stream of the reactor is given by the following relationship:

[0075] t * x >0.05,

[0076] In an additional embodiment, the reaction mixture at the outlet of the reactor is heated for a period t (min) such that the temperature is at least x°C higher than the temperature according to the relationship t * x > 0.1, in another embodiment t * x > 0.2, and in yet another embodiment t * x > 0.5.

[0077] After heat treatment of the stream withdrawn from the solution polymerization reactor, preferably 10% by weight or less of the catalyst, more preferably 5% by weight or less, even more preferably 4% by weight or less, and most preferably 2% by weight or less is in an active state. Consequently, in this setting, catalyst deactivators are avoided, and the incorporation of such catalyst deactivators into the recirculation stream can be significantly reduced.

[0078] In a preferred embodiment of the present invention, the residence time of the catalyst in the reactor is further optimized, which means that the residence time is adjusted to be sufficiently long to ensure that the catalyst is already sufficiently deactivated in the reactor outlet stream leaving the reactor.

[0079] On the other hand, since an excessively long residence time can result in a large amount of already deactivated catalyst in the reactor, which has negative consequences for process economics, the present invention also enables adjusting the residence time to be as short as possible to minimize the impact on process economics.

[0080] To optimize the catalyst residence time, the following mathematical formula can be used. After time t, the concentration of the active catalyst inside the reactor can be described by the following empirical formula (1):

[0081]

[0082] Here, C* cat is the concentration of the active catalyst, and C* cat,0 is the initial active concentration, and k d ε is the kinetic rate constant of the inactive reaction and t is time.

[0083] Catalytic deactivation constant k d It can be modeled as a temperature-dependent equation through the Arrhenius equation shown in Equation (2):

[0084]

[0085] Here, E a,d is the activation energy constant, and R silver It is the ideal gas constant, and T is the temperature.

[0086] To explain the residence time distribution (RTD), the details of the reactor setup must be considered, as is well known to those skilled in the art.

[0087] As an example, and in a preferred embodiment of the present invention, the actual reactor can be approximated by two consecutive stirred tank reactors connected by a plug-flow reactor.

[0088] The RTD function X(t) for this configuration is described by Equation (3):

[0089]

[0090] Here, t is time (unit: minutes), t1 is the residence time in the first part of the reactor, t2 is the residence time in the second part of the reactor, and t3 is the dead time between sections.

[0091] Preferably, the average residence time in the reactor is selected between 0.5 and 15 minutes, more preferably between 1 and 15 minutes.

[0092] The calculation according to the above formula leads to a preferred embodiment of the process of the present invention, wherein the average residence time in the reactor t average follows the following relationship:

[0093] 2900 / T reactor -13 < t average < 4200 / T reactor - 13,

[0094] Preferably, the following relationship is followed:

[0095] 3000 / T reactor -13 < t average < 3500 / T reactor - 13

[0096] Here T reactor is the temperature inside the polymerization reactor, and the reactor is approximated by two continuous stirred tank reactors connected by a plug-flow reactor.

[0097] Preferably, in the process of the present invention, 4% by weight or less of the catalyst in an active state, more preferably 3% by weight or less of the catalyst in an active state, leaves the reactor. Consequently, in this setup, catalyst deactivators can be avoided, thereby significantly reducing the incorporation of such catalyst deactivators into the recirculation stream. Additionally, typically, a stream containing hydrocarbons withdrawn from the reactor—that is, not the product stream—is further recirculated, i.e., fed downstream of the separation process, in an amount exceeding 20%, preferably exceeding 40%, and most preferably exceeding 60% of the total stream withdrawn from the reactor.

[0098] The above stream is introduced into a separation process according to the present invention as follows.

[0099] Separation process of the present invention

[0100] In the most general embodiment of the present invention, the separation process of the present invention is a process for separating at least one polyolefin from a product stream from a solution polymerization process, wherein the product stream (a) comprises a mixture of at least one polyolefin and a volatile substance, and

[0101] A) a step of separating the product stream (a) into a first polyolefin-lean vapor stream (b) and a first condensed polyolefin-rich stream (c);

[0102] B) A step of separating the first condensed polyolefin-rich stream (c) into a second polyolefin-lean vapor stream (b') and a second condensed polyolefin-rich stream (c');

[0103] C) A step of separating the second condensed polyolefin-rich stream (c') into a final polyolefin-lean vapor stream (b*) and a final condensed polyolefin-rich stream (c*);

[0104] Includes,

[0105] The first polyolefin-lean vapor stream (b) and the second polyolefin-lean vapor stream (b') are characterized by returning to the initial feed stream (a') of the polyolefin polymerization process without any additional purification steps.

[0106] Preferably, the mixture of volatile substances comprises volatile substances, such as solvent(s), monomer(s), and comonomer(s).

[0107] Generally, the solvent must be able to dissolve the polyolefin, particularly the polyolefin to be separated in the process of the present invention. Therefore, the solvent is preferably a non-polar solvent. Accordingly, the solvent is preferably a hydrocarbon. More preferably, the solvent is a paraffinic solvent (' Similia similibus solventum Aromatic hydrocarbon solvents may also be considered as they are known to have excellent solvent properties. Therefore, preferably, the solvent is selected from a list of low-boiling point solvents and high-boiling point solvents. Low-boiling point solvents include n-alkanes and aromatic hydrocarbons, such as toluene and xylene. The advantage of low-boiling point solvents is that they can be separated from the dissolved polyolefin with less energy consumption. High-boiling point solvents include paraffinic gas oils or vacuum gas oils. These solvents have the disadvantage of being difficult to remove from the product. Therefore, preferably, the solvent is an alkane selected from a list consisting of C4, C5, C6, C7, C8, C9, and C10 alkanes or a mixture thereof, more preferably an n-alkane selected from a list consisting of C4, C5, C6, C7, C8, C9, and C10 n-alkanes, or a mixture thereof.

[0108] Typically, the content of the polymer in the product stream (a) extracted from a solution polymerization process comprising a solvent, a polymer, an unreacted monomer, and optionally a comonomer is 10 to 35 weight%, preferably 12.5 to 30 weight%, more preferably 15 to 25 weight%, and most preferably 19 to 24 weight%.

[0109] In a preferred embodiment of the present invention, in step A), 55 to 90 weight percent, preferably 60 to 70 weight percent, of a mixture of volatile substances is removed from the product stream (a). Likewise, in a preferred embodiment of the present invention, in step B), 10 to 40 weight percent, preferably 25 to 30 weight percent, of a mixture of volatile substances is removed from the first condensed polyolefin-rich stream (c). Furthermore, in a preferred embodiment of the present invention, in step C), up to 5 weight percent, preferably 0.2 to 5 weight percent, of the mixture of volatile substances is removed from the second condensed polyolefin-rich stream (c'). Accordingly, most preferably, in step A), 60 to 90 weight percent of the mixture of volatile substances is removed from the product stream (a), in step B), 25 to 40 weight percent of the mixture of volatile substances is removed from the first condensed polyolefin-rich stream (c), and in step C), 0.2 to 5 weight percent of the mixture of volatile substances is removed from the second condensed polyolefin-rich stream (c').

[0110] Step A)

[0111] Preferably, the first polyolefin-lean vapor stream (b) generated in step A) is superheated. Preferably, step A) is carried out under conditions that cause volatile compounds in the effluent stream to evaporate from a condensed phase containing mainly a polymer. Preferably, the temperature used in step A) is 150 to 300°C, more preferably 175 to 275°C, and even more preferably 200 to 250°C. Furthermore, step A) is carried out at a pressure of preferably 1 to 15 bara, more preferably 2 to 12 bara, and most preferably 2.5 to 10 bara. Most preferably, in this case, step A) is carried out at a temperature of 200 to 250°C and a pressure of 2.5 to 10 bara. Thus, the conditions found in the first polyolefin-lean vapor stream (b) are set so that a mixture of volatile substances, i.e., solvent, unreacted monomer, and / or comonomer, is not at its condensation point. Accordingly, the mixture of compounds in the first polyolefin-lean vapor stream (b) is generally found to exist in gaseous form. Therefore, preferably, step A) is a flash separation step. The first polyolefin-lean vapor stream (b) is introduced into the initial feed stream (a') of the polymerization zone without the need for an additional purification step after adjusting the temperature and pressure to the requirements of the polymerization reaction. With the high pressure drop realized in this first separation step, it is believed that only components that do not cause problems for the polymerization reaction and / or the composition of the first polyolefin-lean vapor stream (b) are evaporated in this step. Thus, this stream consists mainly of solvent(s), monomer(s), and comonomer(s).

[0112] As described above, the first polyolefin-lean vapor stream (b) contains a major portion of the non-reactive solvent and a large portion of the unreacted comonomer following the unreacted monomer. Meanwhile, preferably, the polyolefin solution concentration in the first condensed polyolefin-rich stream (c) is greater than 60 wt%, preferably greater than 65 wt%, and most preferably greater than 70 wt%. If the polymer concentration in the first condensed polyolefin-rich stream (c) is less than 60 wt%, the amount of volatile substances in the final polymer product will be at a higher level. The polymer concentration in the first condensed polyolefin-rich stream (c) depends on the separation efficiency in step A) or generally in the flash separation step. Next, it is explained why it is important to have the required temperature of the stream introduced into the flash separation step, i.e., the product stream (a) entering step A).

[0113] The following is similar to polyethylene elastomer, for example, 855 kg / m² 3An example is provided for a solution polymerization process of a polymer having a very low density, up to 150°C. This process is carried out at a lower polymerization temperature. Consequently, due to the lower temperature of the product stream (a), the polymer solution concentration in the first condensed polyolefin-rich stream (c) is reduced to less than 60 wt%. This is because the separation efficiency depends not only on the pressure drop in step A) but also on the temperature of the stream entering the flash separation stage. If the pressure drop is kept constant and the temperature is low (down to 150°C), the separation efficiency of the flash separation stage decreases. To avoid a lower polymer concentration, the pressure in step A) can be lowered, and the pressure drop increases accordingly. However, as an additional result, the condensation temperature of the composition of the first polyolefin-lean vapor stream (b) is lowered, and generally low-pressure steam is generated in the first heat exchanger. Secondly, the first polyolefin lean vapor stream (b) has too low a pressure, which is less favorable for return to the process or local system, especially when the pressure is generally less than 4 bara.

[0114] Therefore, in the process of the present invention, for the production of low-density polyethylene elastomers, more energy can be recovered by adopting the conditions of step A). ​​It is important to sufficiently heat the reactor product stream (a) to generate steam at a normal pressure level for the polymerization of a very low-density polymer. Then, the pressure level of step A) can be increased, and the pressure level of the steam generated in the first polyolefin-lean steam stream (b) can be increased.

[0115] Another advantage of higher pressure at the same polyethylene solution concentration is that the volume of the vapor flow is reduced, creating a lower vapor velocity in the first polyolefin-lean vapor stream (b). This has the effect of reducing polyethylene incorporation into the first polyolefin-lean vapor stream (b).

[0116] Step B)

[0117] Preferably, the second polyolefin-lean vapor stream (b') generated in step B) is superheated. Preferably, step B) is performed under conditions that cause volatile compounds in the effluent stream to evaporate from the first condensed polyolefin-rich stream (c), which mainly contains the polymer. Preferably, the temperature used in step A) is 150 to 300°C, more preferably 175 to 275°C, and even more preferably 200 to 250°C. Furthermore, step B) is preferably performed at a pressure of 1 to 15 bara, more preferably 1 to 12 bara, and most preferably 1.5 to 10 bara. If the flash separation step is performed multiple times, the pressure is lowered with each step, and the temperature of the polyolefin is usually increased with each step. Thus, if step A) is performed as a flash separation step, the pressure in step B) is lower than the pressure in step A). Furthermore, if step A) is performed as a flash separation step, the temperature in step B) is higher than the temperature in step A). ​​In such a case, most preferably, step B) is performed at a temperature of 200 to 250°C and a pressure of 1.5 to 10 bara. Preferably, the second polyolefin-lean vapor stream (b') is returned to the polymer recirculation process after adjusting the pressure and temperature to the requirements of the recirculation process. The second polyolefin-lean vapor stream (b') is returned to the recirculation process without any additional purification.

[0118] Accordingly, the conditions found in the second polyolefin-lean vapor stream (b') are set so that a mixture of volatile substances, namely solvent, unreacted monomer, and / or comonomer, is not at its condensation point. Thus, it has been found that the mixture of compounds in the second polyolefin-lean vapor stream (b') generally exists in gaseous form. Therefore, preferably, step B) is a flash separation step. The second polyolefin-lean vapor stream (b') extracted in step B) can be introduced into the initial feed stream (a') of the polymerization zone without the need for an additional purification step after controlling the temperature and pressure to meet the requirements of the polymerization reaction. It is believed that problematic active species, such as the active catalyst, are decomposed in step B). Therefore, these impurities will not reduce the activity of the catalyst within the reactor. In addition, these impurities will also prevent the monomer / comonomer mixture in the second polyolefin-lean vapor stream (b') from spontaneously polymerizing after the temperature and pressure are adjusted as required conditions for the polymerization reaction. Thus, fouling of the equipment and degradation of the quality of the polymer produced in the polymerization reaction can be avoided.

[0119] Step C)

[0120] In a preferred embodiment of the present invention, step C) is preferably a flash separation step or an extruding / degassing step involving a preceding addition of a stripping agent to a second condensed polyolefin-rich stream (c').

[0121] If step C) is a flash separation step, stripping is preferably added to the second condensed polyolefin-rich stream (c') before being introduced into step C). More preferably, the stripping agent is added in an amount of 2 to 4 weight percent relative to the total weight of the second condensed polyolefin-rich stream (c'). Preferably, if step C) is a flash separation step, step C) is performed at a temperature of 200 to 250°C. Furthermore, in this case, step C) is preferably performed under vacuum pressure conditions. If the flash separation step is performed multiple times, the pressure is lowered with each step and the temperature is usually increased with each step. Thus, if step C) is performed as a flash separation step, the pressure in step C) is lower than the pressure in step B). Furthermore, if step C) is performed as a flash separation step, the temperature in step C) is higher than in step B). Preferably, if step C) is a flash separation step, step C) is performed at a temperature of 150 to 300°C, preferably 175 to 275°C, and most preferably 200 to 250°C. Furthermore, in this case, step C) is preferably performed under vacuum pressure conditions. Thus, most preferably, if step C) is a flash separation step, a stripping agent is supplied to the second condensed polyolefin-rich stream (c') in an amount of 2 to 4 weight% relative to the total weight of the second condensed polyolefin-rich stream (c') before it enters the flash separator, and step C) is performed at a temperature of 200 to 250°C and under vacuum pressure conditions.

[0122] If step C) is an extrusion / degassing step, the second condensed polyolefin-rich stream (c') is preferably introduced into a devolatilization extruder. Preferably, the extruder has backward degassing at a pressure in the range of greater than 0.5 bar above atmospheric pressure and less than 0.5 bar above atmospheric pressure, preferably at atmospheric pressure, where atmospheric pressure refers to the natural atmospheric pressure of the Earth's atmosphere varying at about 1 atm, and refers to forward degassing domes under vacuum conditions. Most preferably, the extruder uses a stripping agent introduced between the degassing domes.

[0123] The stripping agent is preferably selected from a list consisting of carbon dioxide, nitrogen, and water. Most preferably, the stripping agent is water.

[0124] The final condensed polyolefin-rich stream (c*) consists mainly of polyolefins produced from the polymerization reaction.

[0125] Preferably, the final polyolefin-lean vapor stream (b*) extracted from step C) is purified in the recovery zone and optionally returned to the initial feed stream (a) of the polymerization zone.

[0126] polyolefin

[0127] The polyolefin obtainable by the process according to the process of the present invention preferably contains less than 500 ppm of volatile substances from a mixture of volatile substances, preferably less than 200 ppm of volatile substances, and most preferably 150 ppm or less of volatile substances.

[0128] [Test Method]

[0129] a) Volatile substance content

[0130] The volatile matter content of polyolefins was measured using gas chromatography and headspace extraction according to VDA 277:1995 using the headspace method. The equipment was an Agilent gas chromatograph equipped with a WCOT-capillary column (wax type) 30 m in length and 0.25 mm x 1.0 micrometer inner diameter (1 μm membrane thickness). A flame ionization detector was used with hydrogen as the fuel gas. The GC setup was as follows: isotherm at 50°C for 3 min, heating to 200°C at 12 K / min, isotherm at 200°C for 4 min, injection temperature: 200°C, detection temperature: 250°C, carrier helium, flow mode splitting of 1:20, and a carrier gas flow rate of 1 ml / min. The emission potential was measured based on the sum of all values ​​provided by the substance emitted after gas chromatography analysis and flame ionization detection using acetone as a calibration standard. Sample introduction (pellet, approx. 2 g) was conditioned at 120°C for 5 hours prior to measurement and then subjected to headspace analysis (20 ml headspace vial). The units were micrograms of carbon per gram of sample, each in ppm.

[0131] [Example]

[0132] In the following embodiments of the present invention, the present invention is exemplified by using calculations involving Aspen HYSYS.

[0133] Example of the invention IE1

[0134] A typical product stream obtained from the polymerization zone of a polyethylene solution polymerization process is modeled as 20 wt% polyethylene and 80 wt% n-hexane at a temperature of 250°C and a pressure of 85 barg. This mixture is separated in a first flash separation step, and the polyethylene-rich phase is removed and used in the next separation step. The polyethylene-lean phase is returned directly to the polymerization zone of the recirculation process without any further purification. In the first flash separation step, the pressure is lowered to 10 bara while the temperature is lowered to 198°C.

[0135] Subsequently, the polyolefin-rich phase of the first flash separation stage, containing 68 wt% polyethylene, is heated again to 250°C and introduced into a second flash separation stage operated at a pressure of 1.5 bara. Due to the flashing operation, the temperature of the polyolefin-rich phase is lowered to 217°C. Again, the polyolefin-lean vapor phase of the second flash separation stage is condensed and returned to the polymerization zone of the direct polymerization process without any further purification.

[0136] The polyolefin-rich phase of the second flash separation stage, containing 98 wt% polyethylene, is heated again to 250°C, and water is mixed into the polyolefin-rich phase in an amount of 3 wt% relative to the total weight of the polyolefin-rich phase. The final portion of the hydrocarbons is removed using a third flash vessel operated under strong vacuum pressure conditions. The level of volatile substances in the polyolefin is less than 150 ppm. The polyolefin-lean phase of the third flash separation stage is introduced into a recovery zone to separate the solvent, comonomer (if present), and light and heavy hydrocarbons.

Claims

Claim 1 A process for separating at least one polyolefin from a product stream (a) from a solution polymerization process, wherein the product stream (a) comprises a mixture of at least one polyolefin and a volatile substance, and the process comprises: A) separating the product stream (a) into a first polyolefin-lean vapor stream (b) and a first condensed polyolefin-rich stream (c); B) separating the first condensed polyolefin-rich stream (c) into a second polyolefin-lean vapor stream (b') and a second condensed polyolefin-rich stream (c'); C) separating the second condensed polyolefin-rich stream (c') into a final polyolefin-lean vapor stream (b*) and a final condensed polyolefin-rich stream (c*); wherein the first polyolefin-lean vapor stream (b) and the second polyolefin-lean vapor stream (b') are any additional A process characterized by being introduced as an initial feed stream (a') of a solution polymerization process without a purification step, wherein the product stream (a) is heated for a period t (min) such that the temperature of the reaction mixture at the outlet of the solution polymerization reactor is at least x (°C) higher than the temperature of the reaction mixture at the outlet of the solution polymerization reactor in accordance with the following relationship, and wherein no catalyst deactivator is added before the product stream (a) is introduced into the separation steps: [Relationship] t * x > 0.

05. Claim 2 A process according to claim 1, wherein the mixture of volatile substances comprises a solvent, a monomer, and a comonomer. Claim 3 A process according to paragraph 2, wherein the solvent is selected from the group consisting of C4, C5, C6, C7, C8, C9 and C10 alkanes or mixtures thereof. Claim 4 A process according to claim 1, wherein in step A), 60 to 90 weight percent of the mixture of volatile substances is removed from the product stream (a). Claim 5 A process according to claim 1, wherein in step B), 25 to 40 weight percent of the mixture of volatile substances is removed from the first condensed polyolefin-rich stream (c). Claim 6 A process according to claim 1, wherein in step C), 0.2 to 5 weight percent of the mixture of volatile substances is removed from the second condensed polyolefin-rich stream (c'). Claim 7 In paragraph 1, the process in which step A) is a flash separation step. Claim 8 In claim 7, step A) is performed at a supply temperature of 200 to 250°C and a pressure of at least 2.5 to 10 bara, a process. Claim 9 In paragraph 1, the process in which step B) is a flash separation step. Claim 10 In claim 9, the process wherein step B) is performed at a supply temperature of 200 to 250°C and a pressure of 1.5 to 10 bara. Claim 11 A process according to claim 1, wherein step C) is a flash separation step or an extrusion / degassing step in which a stripping agent is pre-added to the second condensed polyolefin-rich stream (c'). Claim 12 In claim 11, step C) is a flash separation step and is performed under vacuum pressure conditions and a supply temperature of 200 to 250°C, the process. Claim 13 A process according to any one of claims 1 to 12, wherein the solution polymerization process is performed in the presence of a metallocene catalyst.

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