Process for reducing the production of transition material in the conversion of titanium-based polyethylene to polyolefin elastomer

Abstract

The present application relates to a kind of production methods for reducing transition material in titanium polyethylene production polyolefin elastomer, belong to the technical field of petrochemical industry.The production method includes the following steps: 1) control the differential pressure of distribution plate of the gas phase reactor to be converted, increase the discharge frequency of discharge system;2) cut off the injection of cocatalyst, then stop the injection of main catalyst in titanium catalyst;3) injection terminator;4) replacement is carried out to the gas phase reactor to be converted;5) injection pretreatment agent, re-establish the gas phase component of POE production;6) injection POE catalyst initiates the polymerization reaction of POE production, while carrying out bed replacement;7) after bed replacement is completed, continue polymerization reaction to complete conversion.The production method proposed in the present application adopts the production mode without exiting condensation state, without adjusting pentane concentration, reduce the production of transition material;In addition, the production method does not add water, avoid the risk of lumping and pipeline plugging in the gas phase reactor to be converted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of petrochemical industry, and relates to a production method for reducing transition material in titanium-based polyethylene conversion into polyolefin elastomer. BACKGROUND

[0002] Polyolefin elastomer (POE for short) is an elastomer obtained by polymerization of ethylene and alpha-olefin under the action of homogeneous metal catalyst, has wide application, can be used as rubber, can be used as thermoplastic elastomer, and can be used as plastic impact modifier and toughening agent, and has been well applied in the toughening modification of various plastics and has constituted a strong competition to traditional toughening agents.

[0003] POE can replace general-purpose polymers such as EPM, EPDM, EVA, SBC (styrene bulk copolymer), TPU, PVC, LDPE and EMA, and is widely used in medical packaging materials, automobile parts, electric wires and cables, daily necessities and toys. Because the vulcanization process can be omitted in the use process, energy consumption can be saved by 25% to 40%, and processing efficiency can be improved by 10 to 20 times.

[0004] At present, the most commercialized POE is ethylene-octene copolymer, and the mass fraction of octene in the ethylene-based copolymer is greater than 35% (the mass fraction of octene is less than 20% when it is a plastic body), and the market share of Dow Chemical, Mitsui and Exxon Mobil is higher. The solution method is used for production. Although the POE product prepared by the solution method has advantages in performance, the solution method has the following disadvantages:

[0005] ①High solvent recovery cost: a large amount of organic solvent is needed in the production process, and the recovery and treatment of the solvent requires high cost and energy consumption;

[0006] ②Complex process flow: involves multiple steps such as solvent addition, separation and recovery, making the whole production process more complicated;

[0007] ③Large environmental impact: the use and discharge of solvents may cause certain pollution and harm to the environment;

[0008] ④Low production efficiency: compared with the conventional polyolefin production method, the production speed of the solution method is slow, and the production capacity is limited;

[0009] ⑤Large equipment investment: due to the complexity of the process flow and the requirements of solvent treatment, relatively expensive and complex production equipment is needed.

[0010] Due to the above-mentioned disadvantages of the process method and equipment and facilities, the price of POE is high.

[0011] In order to solve the complex process and complex equipment of the solution method POE production method, some researchers also studied the method of using titanium catalyst to produce metallocene catalyst, but there are still some shortcomings such as complex production process, long material qualification time, too many transition materials, easy pipeline blockage, short production cycle and so on. The following is an example.

[0012] Patent CN 117567676 B discloses a production method for converting titanium-based polyethylene to metallocene polyethylene, which comprises: adjusting the to-be-converted gas phase reactor from condensation state production mode to dry state operation mode; reducing the discharge frequency of the to-be-converted gas phase reactor discharge system in dry state operation mode; reducing the catalyst injection amount to half of the original injection amount, and cutting off the cocatalyst; when the cocatalyst is consumed, gradually reduce the catalyst to zero; inject a terminating agent into the to-be-converted gas phase reactor; reduce the pressure of the to-be-converted gas phase reactor and inject steam; replace the to-be-converted gas phase reactor, and then inject a pretreatment agent; according to the initiation conditions of metallocene polyethylene, re-establish the concentration of gas phase components, and then inject a metallocene catalyst to complete the conversion. This method can complete the start-up of metallocene polyethylene without using a metallocene polyethylene seed bed, and the start-up time of metallocene polyethylene is reduced.

[0013] Patent CN 117567675 B relates to a production method for converting chromium-based polyethylene to metallocene polyethylene, belonging to the technical field of petroleum chemical industry; the method comprises: adjusting the to-be-converted gas phase reactor to a conversion state, and then injecting a terminating agent; replacing the to-be-converted gas phase reactor, and then injecting a pretreatment agent; according to the initiation conditions of metallocene polyethylene, re-establishing the concentration of gas phase components, and then injecting a metallocene catalyst to initiate the reaction and complete the conversion; wherein the pretreatment agent comprises an antistatic agent. This method can complete the start-up of metallocene polyethylene without using a metallocene polyethylene seed bed, thereby minimizing the cost of seed bed extraction and loading, avoiding the construction cost of additional metallocene polyethylene seed bin, and reducing the start-up time of metallocene polyethylene.

[0014] Patent CN 108948248 B discloses a method and device for producing polyolefin elastomer by gas phase method, and application of the polyolefin elastomer. The method is to react in a reactor with polyethylene particles as seed bed, pass raw material mixed gas including ethylene, hydrogen and nitrogen into the reactor, make the polyethylene particles in the seed bed flow and reach fluidized state, then add catalyst and pass in atomized liquid droplet-shaped comonomer to react. The comonomer is long-chain alkene with carbon atom number of 6-18, and the prepared polymerization product has density of 0.865-0.910 g / cm 3 , and long-chain alkene content of 6-40 wt%.

[0015] However, the above patent uses gas phase method to produce POE product, although it can solve the problems of high solvent recovery cost, complex process flow, large environmental impact, relatively low production efficiency, and large equipment investment in solution method for preparing POE product, but the above patent only relates to the method for switching different catalyst systems in the preparation of polyethylene by gas phase method, and the problems of complex transition process, large amount of transition material and easy pipeline blockage in the existing transition of POE are not solved. SUMMARY

[0016] In order to solve the problems in the prior art, the present application provides a production method for reducing transition material in the transition of titanium-based polyethylene to polyolefin elastomer, which can greatly reduce the POE transition time, reduce the amount of transition material, keep the material pipeline unobstructed, and prolong the POE production operation cycle.

[0017] In the first aspect, the present application provides a production method for reducing transition material in the transition of titanium-based polyethylene to polyolefin elastomer, which comprises the following steps:

[0018] 1) Control the pressure difference of the distribution plate of the gas phase reactor to be transitioned, so that the gas holes of the distribution plate of the gas phase reactor to be transitioned are in unobstructed state; increase the discharge frequency of the discharge system of the gas phase reactor to be transitioned, so as to reduce the bed height of the titanium-based polyethylene product powder, and make the titanium-based polyethylene product powder to be replaced at the lowest bed height (or material level);

[0019] 2) Cut off the injection of the cocatalyst, stop the injection of the main catalyst in the titanium-based catalyst after the cocatalyst in the gas phase reactor to be transitioned is consumed, so as to naturally consume the residual titanium-based catalyst and reduce the reaction load;

[0020] 3) Maintain the reaction temperature, reaction pressure and fluidization state in the gas phase reactor to be transitioned, and inject a terminating agent into the gas phase reactor to be transitioned, so as to completely terminate the reaction in the gas phase reactor to be transitioned;

[0021] 4) After the reaction is completely terminated, keep the partial pressure and total pressure of each component in the gas phase reactor to be transitioned unchanged, and maintain the reaction temperature, and replace the gas phase reactor to be transitioned;

[0022] 5) Inject a pretreatment agent to pretreat the bed layer powder in the gas phase reactor to be transitioned (i.e. inject the pretreatment agent for preloading (or advance addition) to quickly and smoothly release the activity after the injection of POE catalyst), and reestablish the gas phase components for producing POE according to the polymerization initiation conditions of POE;

[0023] 6) After the gas phase components are established in place, inject the POE catalyst to initiate the polymerization reaction for producing POE, and at the same time, replace the bed layer;

[0024] 7) After the bed replacement is completed, the bed height is lifted to the position of the enlarged section of the gas phase fluidized bed, the bed height is maintained, and the polymerization reaction is continued to complete the production changeover.

[0025] In the present application, the titanium-based polyethylene product refers to a polyethylene product produced by using a titanium-based catalyst, for example, polyethylene plastic and polyethylene-α-olefin copolymer.

[0026] As an optional embodiment, the polyolefin elastomer is obtained by polymerization of ethylene and α-olefin using a metallocene catalyst, wherein the α-olefin includes at least one of octene, hexene and butene; the density of the polyolefin elastomer is <0.89 g / cm 3 .

[0027] As an optional embodiment, the gas phase reactor to be changed over includes a gas phase fluidized bed, and the gas phase fluidized bed includes a straight section and an enlarged section.

[0028] There are many small holes on the distribution plate of the gas phase reactor to be changed over, which may be blocked by powder or sticky material. By adjusting the working condition of the gas phase reactor to be changed over, for example, increasing the fluidization gas velocity, or / and increasing the concentration of condensate, the blockage in the small holes can be flushed away, so as to ensure that the gas holes of the distribution plate of the gas phase reactor to be changed over are unobstructed.

[0029] As an optional embodiment, the pressure difference of the distribution plate is controlled in a minimum range of 15-45 kPa. Preferably, the pressure difference of the distribution plate is controlled in a range of 18-24 kPa.

[0030] In the present application, when the pressure difference of the distribution plate is too large, many small holes on the distribution plate are blocked by the polymer, the fluidization circuit is not unobstructed, and thus the heat removal is not timely, which easily causes the phenomenon of explosive polymerization.

[0031] As an optional embodiment, in the step 1), the titanium-based polyethylene product powder to be replaced is in a minimum bed height, and the minimum bed height is 7.5-9.5 m.

[0032] As an optional embodiment, the bed height of the titanium-based polyethylene powder to be replaced is 75%-90% of the straight section of the gas phase fluidized bed.

[0033] As an optional embodiment, the titanium-based catalyst is a conventional titanium-based catalyst in the art, including any one of a silica supported titanium-based catalyst and a magnesium chloride supported titanium-based catalyst.

[0034] As an optional embodiment, the activity of the titanium catalyst is 3 to 5 times of the activity of the POE catalyst. Optionally, the POE catalyst is a conventional metallocene catalyst in the art, including one of dichlorobis-cyclopentadienyl zirconium (Cp2ZrCl2) catalyst and bridged metallocene catalyst, wherein Cp represents cyclopentadienyl; the bridged group can be an alkylidene group (such as -CH2-) or a silane group (such as -SiMe2-, Me represents methyl).

[0035] As an optional embodiment, the co-catalyst includes at least one of monochloro diethyl aluminum and tri-n-hexyl aluminum.

[0036] As an optional embodiment, the pre-treatment agent is 10 ppm to 80 ppm of the mass concentration of the ethylene feed.

[0037] As an optional embodiment, the pre-treatment agent is circulated in the gas phase reactor to be converted for 0.5 h to 8 h.

[0038] As an optional embodiment, the pre-treatment agent includes at least one of a stearate pre-treatment agent, a composite stearate pre-treatment agent, and dodecyl benzene sulfonic acid.

[0039] In the present application, the main components of the stearate pre-treatment agent are aluminum stearate, oil-soluble alkyl alcohol amine, and mineral oil solvent, with a ratio of 10% to 30%: 15% to 25%: 65% to 90%. The main components of the composite stearate pre-treatment agent are aluminum stearate, oil-soluble alkyl alcohol amide, mineral oil solvent, and stearate, with a ratio of 10% to 30%: 15% to 25%: 65% to 90%: 1% to 3%.

[0040] As an optional embodiment, the components of the termination agent include at least one of ethanol and toluidine. Preferably, the components of the termination agent include toluidine.

[0041] As an optional embodiment, the end timing of the replacement is that ethanol < 10 ppm and toluidine < 15 ppm in the gas phase reactor to be converted.

[0042] As an optional embodiment, in step 4), the replacement uses a pressure swing method. The low pressure of the pressure swing method is 600 kPa to 900 kPa; the high pressure of the pressure swing method is 1100 kPa to 1400 kPa.

[0043] As an optional embodiment, in step 7), after the completion of the bed replacement, the bed height is quickly raised to the gas phase fluidized bed expansion section, and the bed height (or material level) is maintained at 11.5 m to 15.5 m, and the polymerization reaction is continued to complete the conversion.

[0044] As an optional embodiment, the transition material produced by the method is 90-130 t.

[0045] The production method provided by the application adopts a non-exit condensed state production mode, the co-catalyst is cut off in advance, the high-activity catalyst injection is cut off after the co-catalyst is close to complete consumption, the catalyst is naturally deactivated, the load is reduced, the main catalyst activity is consumed until the reaction heat load is reduced to the target value, in the case that the bed powder is not emptied and the reactor is not cleaned, after replacement, a pretreatment agent is added to eliminate the influence of residual components in the bed on the POE catalyst, and then the gas phase is established, the POE catalyst is injected to initiate the reaction, and the production transition is completed.

[0046] The entire process does not need to use water to eliminate the co-catalyst in the gas phase reactor to be transitioned, the original high-activity titanium catalyst can be used to completely consume the co-catalyst, the large amount of transition material generated by replacing the excess water from the gas phase reactor to be transitioned is avoided, and the transition material during POE production is reduced. After water is added in the prior art, the water is in a liquid state in the reactor, and the water is adsorbed by the powder, so that the water is not uniformly distributed in the reactor, the poison is not uniformly distributed, and the catalyst activity release is not uniform, which increases the risk of caking in the gas phase reactor to be transitioned and pipeline blockage. The application avoids the above risks, thereby improving the device operation efficiency.

[0047] In the application, the above technical features can be freely combined to form new technical solutions without conflict.

[0048] Compared with the prior art, the technical solution of the application has the following beneficial technical effects:

[0049] (1) The production method provided by the application adopts a non-exit condensed state production mode, compared with the production mode of the prior art in which the condensed state is exited, the pentane concentration does not need to be adjusted, and therefore the transition material is reduced;

[0050] (2) The production method provided by the application does not need to use water to eliminate the co-catalyst in the gas phase reactor to be transitioned during the entire process, the co-catalyst in the gas phase reactor to be transitioned is consumed by the main catalyst with higher activity, the large amount of transition material generated by replacing the excess water from the reactor is avoided, and the transition material during POE production is reduced;

[0051] (3) The production method provided by the application does not add water during the transition process, avoids the uneven distribution of the powder and the uneven distribution of the poison in the gas phase reactor to be transitioned, and avoids the risk of uneven release of the catalyst activity, caking in the gas phase reactor to be transitioned, and pipeline blockage, thereby improving the device operation efficiency and prolonging the operation cycle. DETAILED DESCRIPTION

[0052] To make the purposes, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in a clear and complete manner in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0053] The catalyst commonly used in POE production is mainly a constrained geometry metallocene catalyst (CGC), which is generally a kind of metal organic complex formed by a transition metal element (such as a group IVB element Ti, Zr, Hf, etc.) or a rare earth metal element and at least one cyclopentadienyl or its derivative through covalent or coordination bond interaction. Currently, the catalysts mainly used in commercial POE production are bridged metallocene catalysts and CGC catalysts, which are quite different from the components of traditional Ziegler-Natta catalysts and chromium-based catalyst systems and are more sensitive to impurities in raw materials. Therefore, in the process of converting the titanium-based catalyst to the metallocene catalyst for producing POE in the gas phase polymerization process, water is mainly used as an alkyl aluminum deactivator for deactivation treatment in China, but this production method has the following disadvantages:

[0054] ①After excessive water is injected into the reactor to be converted, it is adsorbed on the surface of the powder and is difficult to displace out of the reactor to be converted, which will produce a large amount of transition material;

[0055] ②The activity of the titanium-based main catalyst (generally alkyl aluminum) is not high enough, and the alkyl aluminum that is not completely deactivated will become a poison for the metallocene catalyst, which will affect the gel and crystal points of the subsequent metallocene product (for example, POE product);

[0056] ③The excess water is not uniformly distributed in the reactor to be converted, which leads to uneven release of catalyst activity, easy caking and blocking of system pipelines.

[0057] To this end, the inventors intend to provide a method for reducing the transition material of a titanium-based polyethylene copolymer to polyolefin elastomer POE production, by first cutting off the cocatalyst, reducing the powder bed height, and then cutting off the high-activity catalyst injection, allowing the catalyst to naturally deactivate, reducing the load, and allowing the main catalyst activity to be consumed until the reaction heat load is reduced to the target value (11.5±2 t / h), without emptying the bed layer powder or cleaning the gas phase reactor to be converted, and after replacement, by adding a pretreatment agent to eliminate the influence of residual components in the bed on the production of POE metallocene catalyst, and then establishing a gas phase, injecting a metallocene catalyst to initiate a reaction, and after the bed replacement is completed, the bed height is raised to 13.5±2 m, the bed height is maintained, and the polymerization reaction is continued to complete the conversion. The entire process does not require the use of water to eliminate the cocatalyst in the gas phase reactor to be converted, and the cocatalyst is consumed by the chemical reaction of the high-activity titanium-based catalyst (i.e., the main catalyst added first) and the cocatalyst, avoiding the use of water to eliminate the cocatalyst, which requires the displacement of a large amount of transition material from the gas phase reactor to be converted, thereby reducing the transition material during POE production. In addition, since no water is added, there is no problem of uneven activity of the catalyst due to water adsorbed onto the powder, thereby avoiding the risk of caking and pipeline blockage in the gas phase reactor to be converted, and the operating cycle can be extended.

[0058] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. The experimental methods in the following examples are not specified, and the methods are generally determined according to the national standards. If there is no corresponding national standard, the methods are performed according to the general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0059] Unless otherwise specified, all materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods.

[0060] Example 1

[0061] A production method for reducing the transition material of a titanium-based polyethylene to polyolefin elastomer, comprising the following steps:

[0062] S1: make the distribution plate gas hole of the standby production gas phase reactor in a smooth state, and control the differential pressure of the distribution plate at 23 kPa; increase the discharge frequency of the discharge system of the standby production gas phase reactor to reduce the height of the titanium polyethylene product powder bed layer to 85% of the height of the straight cylinder section. By reducing the height of the titanium polyethylene product powder bed layer, the powder of the original product in the standby production gas phase reactor is reduced, thereby reducing the product powder that needs to be replaced, so that the indicators of bed replacement quickly meet the qualified requirements, the production conversion process is accelerated, and the production conversion time is reduced.

[0063] S2: cut off the injection of the cocatalyst dichlorodiethylaluminum, and after the cocatalyst is consumed in the reactor, gradually reduce the main catalyst in the titanium catalyst to 0, so that the residual catalyst is naturally consumed and the reaction load is reduced; the activity of the main catalyst is 4.5 times that of the subsequent POE catalyst. The composition of the main catalyst includes: silicon dioxide > 70, titanium tetrachloride < 11, tetraoxysilane < 11, and magnesium chloride < 8.

[0064] S3: maintain the reaction temperature, reaction pressure and fluidization state in the reactor, inject the terminating agent ethanol, gradually reduce the ethylene feed amount and increase the nitrogen injection amount according to the inactivation speed of ethanol on the catalyst, keep the total pressure in the reactor unchanged, and avoid the adverse effects of pressure changes on the activity of the catalyst.

[0065] S4: after the reaction is completely terminated, keep the partial pressure and total pressure of each component in the reactor unchanged, maintain the reaction temperature, and use nitrogen to displace the impurities in the reactor, with a displacement standard of 0.8 ppm of ethanol content in the reactor.

[0066] S5: pretreat the bed layer powder in the reactor and reestablish the gas phase components; wherein a composite stearate pretreatment agent is selected as the bed layer pretreatment agent to treat the residual catalyst and impurities in the bed layer, so as to avoid the influence of the residual catalyst and impurities on the activity of the subsequent metallocene catalyst, so that the activity of the subsequent POE catalyst is quickly released and the activity is stable; the injection amount of the bed layer pretreatment agent is 76 ppm of the mass concentration of ethylene, and the circulation time after injection is 2 h.

[0067] S6: after the gas phase components are established, the metallocene catalyst is injected to initiate the polymerization reaction for POE production, and an upward trend can be seen within 10 min after the reactor is stabilized; at the same time, the transition material generated during the polymerization reaction is replaced.

[0068] S7: after 3 h of polymerization reaction, the titanium powder in the reactor is completely replaced, the bed height is increased to the junction of the expansion section and the straight cylinder section, and the bed height is kept unchanged, and the production conversion is completed.

[0069] Example 2

[0070] A production method for reducing transition material in titanium-based polyethylene to polyolefin elastomer conversion, comprising the following steps:

[0071] S1: make the distribution plate air hole of the gas phase reactor to be converted into a smooth state, and control the distribution plate pressure difference in the lowest range of 22 kPa; increase the discharge frequency of the reactor discharge system, and reduce the height of the powder bed layer to 80% of the height of the straight cylinder section.

[0072] S2: cut off the injection of co-catalyst tri-n-hexyl aluminum, and gradually reduce the main catalyst to 0 after the co-catalyst is consumed in the reactor, so that the residual catalyst is naturally consumed and the reaction load is reduced. The activity of the main catalyst is 4 times that of the subsequent POE catalyst. The main catalyst uses the co-catalyst in Example 1.

[0073] S3: maintain the reaction temperature, reaction pressure and fluidization state in the reactor, inject the terminator toluene amine, gradually reduce the ethylene feed amount according to the inactivation speed of toluene amine to the catalyst, increase the nitrogen injection amount, and keep the total pressure in the reactor unchanged.

[0074] S4: after the reaction is completely terminated, the partial pressure and total pressure of each component in the reactor are kept unchanged, the reaction temperature is maintained, and nitrogen is used to displace the impurities in the reactor. The displacement standard is that the toluene amine content in the reactor is 0.4 ppm.

[0075] S5: pretreat the bed layer powder in the reactor and reestablish the gas phase components; wherein a stearate salt pretreatment agent is selected as the bed layer pretreatment agent to quickly release the activity of the subsequent POE catalyst and stabilize the activity. The injection amount of the bed layer pretreatment agent is 45 ppm of the mass concentration of ethylene, and the circulation time after injection is 3.5 h.

[0076] S6: after the gas phase components are established in place, the POE catalyst is injected to initiate the polymerization reaction of POE production. Usually, within 15 min after the reactor is stabilized, an upward trend can be seen; at the same time, the transition material generated during the polymerization reaction is displaced.

[0077] S7: after 4.5 h of polymerization reaction, the titanium-based powder in the reactor is completely displaced, the bed height is raised to the junction of the expansion section and the straight cylinder section, the bed height is kept unchanged, and the conversion is completed.

[0078] Example 3

[0079] A production method for reducing transition material in titanium-based polyethylene to polyolefin elastomer conversion, comprising the following steps:

[0080] S1: make the distribution plate air hole of the gas phase reactor to be converted into a smooth state, and control the distribution plate pressure difference in the lowest range of 22 kPa; increase the discharge frequency of the reactor discharge system, and reduce the height of the powder bed layer to 80% of the height of the straight cylinder section.

[0081] S2: cut off the injection of the co-catalyst dichloroethyl aluminum, after the co-catalyst is consumed in the reactor, gradually reduce the main catalyst to 0, and allow the residual catalyst to naturally consume and reduce the reaction load. The activity of the main catalyst is 3.5 times that of the subsequent POE catalyst. Among them, the main catalyst uses the co-catalyst in Example 1.

[0082] S3: maintain the reaction temperature, reaction pressure and fluidization state in the reactor, inject the terminating agent ethanol, gradually reduce the ethylene feed amount and increase the nitrogen injection amount according to the inactivation speed of ethanol on the catalyst, and keep the total pressure in the reactor unchanged.

[0083] S4: after the reaction is completely terminated, keep the partial pressure and total pressure of each component in the reactor unchanged, maintain the reaction temperature, and use nitrogen to displace the impurities in the reactor. The displacement standard is that the ethanol content in the reactor is 0.6 ppm.

[0084] S5: pretreat the bed powder in the reactor and reestablish the gas phase components; among them, dodecyl benzene sulfonic acid is selected as the bed pretreatment agent to quickly release the activity of the subsequent POE catalyst and stabilize the activity. The injection amount of the bed pretreatment agent is 18 ppm of the mass concentration of ethylene, and the circulation time after injection is 6 h.

[0085] S6: after the gas phase components are established, the POE catalyst is injected to initiate the polymerization reaction of POE production. Generally, within 20 min after the reactor is stabilized, an upward trend can be seen; at the same time, the transition material generated during the polymerization reaction is replaced.

[0086] S7: after 4 h of polymerization reaction, the titanium powder in the reactor is completely replaced, the bed height is raised to the junction of the expansion section and the straight section, the bed height is kept unchanged, and the production is completed.

[0087] Comparative Example 1

[0088] This comparative example provides a method for reducing the production of transition material in the production of polyethylene to polyolefin elastomer, which is only different from Example 1 in that step S1 is different, and other processes and conditions are the same as those in Example 1. Specifically,

[0089] Step S1: keep the distribution plate gas holes of the gas phase reactor to be converted to be unobstructed, and control the pressure difference of the distribution plate in the lowest range of 26 kPa; the discharge frequency of the reactor discharge system is unchanged, and the powder bed height of the reactor is still maintained at the highest position, which is located at the expansion section of the reactor.

[0090] Comparative Example 2

[0091] The comparative example 2 provides a production method of titanium-based catalyst for producing polyolefin elastomer POE, which is different from the example 2 only in that step S2 is different, and other processes and conditions are the same as those of the example 2. Specifically,

[0092] Step S2: cut off the injection of the main catalyst, cut off the cocatalyst at the same time, and inject steam into the reactor after the cocatalyst tri-n-hexyl aluminum in the reactor is completely consumed, so that the residual catalyst is naturally consumed and the reaction load is reduced.

[0093] Comparative example 3

[0094] The comparative example 2 provides a production method of titanium-based catalyst for producing polyolefin elastomer POE, which is different from the example 2 only in that step S2 is different, and other processes and conditions are the same as those of the example 2. Specifically,

[0095] S3: maintain the reaction temperature, reaction pressure and fluidization state in the reactor, inject the terminating agent carbon monoxide, gradually reduce the feeding amount of ethylene and increase the injection amount of nitrogen according to the inactivation speed of carbon monoxide on the catalyst, and keep the total pressure in the reactor unchanged.

[0096] S4: after the reaction is completely terminated, keep the partial pressure and total pressure of each component in the reactor unchanged, maintain the reaction temperature, and use nitrogen to displace the impurities in the reactor, and the displacement standard is that the content of carbon monoxide in the reactor is 0.5 ppm.

[0097] Table 1 shows the transition time, transition weight and block weight of the degassing system per 8 hours of the titanium-based polyethylene for producing polyolefin elastomer in the examples 1 to 3 and the comparative examples 1 to 3.

[0098] Table 1:

[0099]

[0100] As shown in Table 1, compared with the comparative examples 1 to 3, the production method for reducing the transition material in the titanium-based polyethylene for producing polyolefin elastomer provided by the examples 1 to 3 has shorter transition time, less transition material, less block material generated by the system and lower risk of pipeline blockage.

[0101] Various embodiments of the present application can take on a variety of scopes; it should be understood that a description in one scope is merely for convenience and brevity and should not be construed as a limitation of the present application; therefore, it should be considered that the description of the scope has specifically disclosed all possible sub-scopes and single values within the scope. For example, it should be considered that the description of the scope from 1 to 6 has specifically disclosed sub-scopes, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single values within the scope, such as 1, 2, 3, 4, 5, and 6, regardless of the scope. In addition, whenever a numerical range is indicated in this text, it refers to any cited number (fraction or integer) within the indicated range.

[0102] In the present application, the terms "include", "contain" and the like mean "including but not limited to". In this text, relational terms such as "first" and "second" and the like are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. In this text, "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent: A exists alone, A and B exist together, and B exists alone. Where A and B can be singular or plural. In this text, "one or more" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single or multiple items.

[0103] The above description is only a specific embodiment of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A process for reducing the production of a transition material in the conversion of a titanium-based polyethylene to a polyolefin elastomer, characterized by, The production method comprises the following steps: 1) controlling the pressure difference of the distribution plate of the to-be-replaced gas phase reactor, increasing the fluidization gas velocity or / and increasing the condensate concentration, so that the gas holes of the distribution plate of the to-be-replaced gas phase reactor are in an unobstructed state; increasing the discharge frequency of the discharge system of the to-be-replaced gas phase reactor to reduce the bed height of the titanium-based polyethylene product powder, so that the titanium-based polyethylene product powder to be replaced is in the lowest bed height; the to-be-replaced gas phase reactor comprises a gas phase fluidized bed, and the gas phase fluidized bed comprises a straight section and an enlarged section; the pressure difference ranges from 15 kPa to 45 kPa, and the lowest bed height ranges from 7.5 m to 9.5 m; 2) cutting off the injection of the cocatalyst, and stopping the injection of the main catalyst in the titanium-based catalyst after the cocatalyst in the to-be-replaced gas phase reactor is consumed; 3) maintaining the reaction temperature, the reaction pressure and the fluidization state in the to-be-replaced gas phase reactor, and injecting a terminating agent into the to-be-replaced gas phase reactor, wherein the terminating agent comprises at least one of ethanol and toluidine; 4) after the reaction is completely terminated, keeping the partial pressure and the total pressure of each component in the to-be-replaced gas phase reactor unchanged, maintaining the reaction temperature, and replacing the to-be-replaced gas phase reactor; 5) injecting a pretreatment agent to pretreat the bed powder in the to-be-replaced gas phase reactor, and re-establishing the gas phase components for producing POE according to the polymerization initiation conditions of POE; 6) after the gas phase components are established, injecting a POE catalyst to initiate the polymerization reaction for producing POE, and simultaneously replacing the bed; 7) after the bed replacement is completed, raising the bed height to the enlarged section of the gas phase fluidized bed, maintaining the bed height, and continuing the polymerization reaction to complete the replacement.

2. The production method for reducing the transition material in the titanium-based polyethylene replaced by the polyolefin elastomer according to claim 1, wherein the polyolefin elastomer is obtained by polymerization of ethylene and α-olefin using a metallocene catalyst, and the α-olefin comprises at least one of octene, hexene and butene.

3. The production method for reducing the transition material in the titanium-based polyethylene replaced by the polyolefin elastomer according to claim 2, wherein the POE catalyst is a metallocene catalyst.

4. The production method for reducing the transition material in the titanium-based polyethylene replaced by the polyolefin elastomer according to claim 1, wherein the activity of the titanium-based catalyst is 3-5 times the activity of the POE catalyst. The polyolefin elastomer has a density < 0.89 g / cm 3 .

5. The production method for reducing the transition material in the titanium-based polyethylene replaced by the polyolefin elastomer according to claim 1, wherein the bed height of the titanium-based polyethylene powder to be replaced in step 1) is 75%-90% of the straight section of the gas phase fluidized bed.

6. The production method for reducing the transition material in the titanium-based polyethylene replaced by the polyolefin elastomer according to claim 1, wherein the cocatalyst in step 2) comprises at least one of monochlorodioethylaluminum and tri-n-hexylaluminum.

7. The production method for reducing the transition material in the titanium-based polyethylene replaced by the polyolefin elastomer according to claim 1, wherein the terminating agent in step 3) comprises at least one of ethanol and toluidine. ​ ​ ​ ​ The end time of the displacement in the step 4) is when ethanol < 10 ppm and toluidine < 15 ppm in the to-be-converted gas phase reactor. 8.The method of claim 1, wherein the low pressure of the swing pressure method is 600 kPa to 900 kPa, and the high pressure of the swing pressure method is 1100 kPa to 1400 kPa. 9.The method of claim 1, wherein the pretreatment agent is 10 ppm to 80 ppm of the mass concentration of ethylene feed. 10.The method of claim 1, wherein the pretreatment agent is circulated in the to-be-converted gas phase reactor for 0.5 h to 8 h. 11.The method of claim 1, wherein the pretreatment agent comprises at least one of a stearate pretreatment agent, a composite stearate pretreatment agent, and dodecyl benzene sulfonic acid. 12.The method of claim 1, wherein after the bed displacement is completed, the bed height is quickly raised to the expansion section of the gas phase fluidized bed, the bed height is maintained at 11.5 m to 15.5 m, and the polymerization reaction is continued to complete the conversion. The transition material produced by the production method is 90 t to 130 t. ​ ​ ​ ​ 13. The process for reducing the production of transition material in the conversion of a titanium-based polyethylene to a polyolefin elastomer of any one of claims 1-12, wherein, ​

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