A process and apparatus for separating polyethylene wax from a heavies fraction of an ethylene tetramer product

Abstract

This invention relates to the field of selective tetramerization technology of ethylene, specifically a method and apparatus for separating polyethylene wax from the heavy components of ethylene tetramerization products. The method provided by this invention uses a specific cleaning agent to clean the mixture of high-boiling-point liquid components and polyethylene wax produced during the distillation of ethylene tetramerization products. The high-boiling-point liquid components and polyethylene wax are then separated using conventional separation methods, yielding polyethylene wax that meets usage specifications. Simultaneously, the mother liquor containing high non-boiling-point components and catalyst is fed into a cleaning agent recovery system for recycling. Experiments show that the PE wax separated using the separation method described in this invention, within the separation apparatus described in this invention, is a white granular material with a molecular weight of 3000–5000, a softening point of 108°C, and catalyst metal residues of less than 3 ppm Al and less than 1 ppm Cr, meeting commercially available requirements.

Description

Technical Field

[0001] This invention relates to the field of selective tetramerization technology of ethylene, specifically a method and apparatus for separating polyethylene wax from the heavy components of ethylene tetramerization products. Background Technology

[0002] 1-Octene, as an important organic raw material and chemical intermediate, is mainly used in the production of high-end polyethylene (PE) and polyolefin elastomer (POE). In the preparation process of 1-octene, the selective tetramerization of ethylene has advantages over traditional processes, such as high catalyst activity and high product selectivity, making it a research hotspot in China and currently being translated into industrial applications.

[0003] In the selective tetramerization of ethylene, ethylene, under the action of a catalyst, produces the main products 1-octene and 1-hexene, as well as C... 10 ~C 14 The reaction mixture, consisting of high-boiling-point liquid hydrocarbon components, PE wax, and high-molecular-weight PE, undergoes solid-liquid separation after quenching. The non-solid phase of high-molecular-weight PE is separated and then fed into a distillation unit for stepwise separation of the liquid phase products, recovering the solvent and refining the corresponding products. However, the high-boiling-point liquid components, PE wax, and quenching catalysts accumulate at the bottom of the last stage of the distillation unit or in the reboiler. While this material remains liquid and has good fluidity at high temperatures (>120°C), it precipitates during transport and storage as the temperature drops slightly, resulting in poor fluidity, severe blockage of pipelines and pumps, and solidification in storage tanks, making cleaning difficult. Manual cleaning generates a strong odor, increasing occupational hazards and safety risks. Therefore, it is necessary to separate the PE wax from the heavy components at the bottom of the final distillation unit. Separating qualified PE wax from the heavy components after distillation of ethylene tetramerization products can reduce operational instability and recover PE wax, increasing the economic value of the unit and greatly contributing to the industrialization of ethylene tetramerization.

[0004] However, because the PE wax in this material is mixed with high-boiling-point hydrocarbons, they are miscible at high temperatures, but solidify as a whole after cooling. Especially in the solidified state, the PE wax swells in the high-boiling-point hydrocarbons and cannot be filtered and separated. The catalyst residue also increases the metal residue in this material. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method and apparatus for separating polyethylene wax from the heavy components of ethylene tetramer products. The method provided by the present invention can separate high-purity polyethylene wax from the heavy components of ethylene tetramer products after distillation.

[0006] This invention provides a method for separating polyethylene wax from the heavy components of ethylene tetramer products, comprising:

[0007] S1) Mix the heavy components of the ethylene tetramer product with a cleaning agent to obtain a solid-liquid mixture; the cleaning agent is at least one of methanol or ethanol.

[0008] S2) Separate the solid substances in the solid-liquid mixture to obtain polyethylene wax.

[0009] This invention first mixes the heavy components of ethylene tetramerization product with a cleaning agent to obtain a solid-liquid mixture. The cleaning agent is at least one of methanol or ethanol, preferably selected from methanol or ethanol. The purity of the cleaning agent in this invention is 90-100%. The mass ratio of the cleaning agent to the heavy components of ethylene tetramerization product is 1-20. The mixing temperature is 20-100°C, preferably 40-45°C; the mixing time is 1-10 hours, preferably 3-5 hours.

[0010] The inventors of this application have creatively discovered that by using the cleaning agent described in this invention in a cleaning tank and dispersing and cleaning the heavy components of ethylene tetramerization products at the temperature described in this invention, the high-boiling-point liquid hydrocarbon components swollen in polyethylene wax (PE wax) can be removed, changing the morphology of PE wax so that it precipitates and disperses into fine particles, achieving the purpose of easy separation; at the same time, the cleaning agent washes out the quenching agents and catalysts attached to the PE wax, achieving the purpose of purifying the PE wax and meeting the requirements for commercial sale.

[0011] The ethylene tetramerization heavy component described in this invention refers to the component separated at the bottom of the last stage separation column of a distillation unit after the ethylene tetramerization reaction is carried out by rectification. Specifically, the tetramerization reaction is a selective tetramerization reaction of ethylene with 1-octene and 1-hexene as the main products under the action of a catalyst. In some embodiments of this invention, ethylene is subjected to a selective tetramerization reaction with 1-octene and 1-hexene as the main products under the action of a catalyst, the reaction is quenched with a quencher, and the resulting material is distilled. The ethylene tetramerization heavy component described in this invention is obtained at the bottom of the last stage separation column of the distillation unit. In some embodiments of this invention, the ethylene tetramerization heavy component includes C 10 ~C 14 The high-boiling-point liquid hydrocarbon components, polyethylene wax, quenching agents, and catalysts are used in this invention for the tetramerization of ethylene. The materials used in this invention, such as catalysts and quenching agents, are not particularly limited and are materials commonly used by those skilled in the art for the tetramerization of ethylene.

[0012] The temperature of the heavy component of the ethylene tetramer product described in this invention is 120℃~150℃. At high temperatures (>120℃), the heavy component of the ethylene tetramer product melts; as the temperature decreases, PE wax precipitates and solidifies, making transportation, storage, and transfer difficult. Therefore, in actual operation, heated pipelines are often used to maintain the temperature of the heavy component of the ethylene tetramer product to ensure its liquid flowability and prevent premature precipitation of polyethylene wax at excessively low temperatures.

[0013] This invention obtains a solid-liquid mixture and then separates the solid substances within it to obtain polyethylene wax. Specifically, the solid-liquid mixture is separated from the solid substances in a separation device to obtain polyethylene wax. This invention does not impose any particular limitation on the separation device or method; any separation device and solid-liquid separation method well-known to those skilled in the art is acceptable.

[0014] After separating the solid substances from the solid-liquid mixture, this invention further includes rinsing the separated solid substances with the cleaning agent described in this invention. The amount of the cleaning agent used in this invention is 10-20% of the mass of the cleaning agent used in step S1). This invention uses a small amount of cleaning agent for a secondary rinse in a centrifuge to further purify the PE wax and reduce the residue of liquid heavy components and catalyst. In some embodiments of this invention, the molecular weight of the polyethylene wax obtained by the separation method described in this invention is 3000-5000; the aluminum content of the polyethylene wax is less than 10 ppm; and the chromium content of the polyethylene wax is less than 5 ppm.

[0015] The cleaning agent described in this invention can be recovered and reused through distillation. Since the boiling point of the selected cleaning agent is much lower than that of the components in the mother liquor, conventional distillation can achieve the required purity for the recovered cleaning agent. The ethylene tetramer product heavy components of this invention, after PE wax removal and cleaning agent recovery, are liquid at room temperature, facilitating transportation and storage, and can be used for waste liquid treatment or supplied to other petrochemical plants for processing.

[0016] The present invention provides a method for separating polyethylene wax from the heavy components of ethylene tetramer products. PE wax is obtained from the wax-containing heavy components at the end of the distillation of ethylene tetramer products, which reduces the impact of PE wax on the instability of the equipment and increases profits.

[0017] The present invention also provides a separation apparatus that applies the above separation method, comprising: a cleaning system and a separation system connected to the cleaning system.

[0018] Specifically, the separation apparatus of the present invention using the above separation method includes:

[0019] Cleaning kettle;

[0020] A separator connected to the washing vessel;

[0021] The mother liquor tank is connected to the separator;

[0022] A cleaning agent recovery vessel connected to the mother liquor tank;

[0023] A cleaning agent recovery cooler and a heavy oil cooler are connected to the cleaning agent recovery vessel;

[0024] A cleaning agent recovery tank connected to the cleaning agent recovery cooler;

[0025] A heavy oil tank connected to the heavy oil cooler.

[0026] Both the cleaning axe and the cleaning agent recovery vessel described in this invention are equipped with jackets and agitators. All equipment used in this device is conventional chemical equipment with no special requirements. Combined with the bottom discharge from the distillation system, it can operate intermittently.

[0027] The cleaning vessel of this invention is equipped with an inlet for the heavy components of ethylene tetramerization, an inlet for the cleaning agent, and a bottom outlet. The separator of this invention is equipped with an inlet for the separated material, an inlet for the cleaning agent, and a mother liquor outlet. The mother liquor tank of this invention is equipped with an inlet for the mother liquor tank and a bottom outlet. The cleaning agent recovery tank of this invention is equipped with an inlet for the cleaning agent recovery tank and a bottom outlet. The cleaning agent recovery vessel of this invention is equipped with an inlet for the cleaning agent recovery vessel, a bottom outlet for the cleaning agent recovery vessel, and a distillation port for the cleaning agent recovery vessel.

[0028] The cleaning agent inlet of the cleaning vessel of this invention is connected to the bottom outlet of the cleaning agent recovery tank. The bottom outlet of the cleaning vessel of this invention is connected to the feed inlet of the separator. The cleaning agent inlet of the separator of this invention is connected to the bottom outlet of the cleaning agent recovery tank. The mother liquor outlet of the separator of this invention is connected to the inlet of the mother liquor tank. The inlet of the cleaning agent recovery vessel of this invention is connected to the bottom outlet of the mother liquor tank. The bottom outlet of the cleaning agent recovery vessel of this invention is connected to the heavy oil tank via a heavy oil cooler. The distillation port of the cleaning agent recovery vessel of this invention is connected to the cleaning agent recovery tank via a cleaning agent recovery cooler.

[0029] The feed inlet of the ethylene tetramer heavy component of the cleaning vessel described in this invention is connected to the bottom / reboiler of the last stage separation column of the ethylene tetramer distillation unit via a heated pipeline. The feed inlet is used to introduce the ethylene tetramer heavy component material from the bottom of the column into the cleaning vessel; the heated pipeline is used to maintain the temperature of the ethylene tetramer heavy component at 120°C to 150°C. In some embodiments of this invention, after the ethylene tetramer heavy component is obtained by the above method, it is directly transported from the bottom of the last stage separation column of the distillation unit to the cleaning vessel via a heated pipeline, maintaining the temperature of the ethylene tetramer heavy component at 120°C to 150°C, and then separated according to the above separation method.

[0030] In some embodiments of the present invention, a closed centrifuge is used to separate the solid-liquid mixture; the solid-liquid mixture in the cleaning device of the present invention is in a suspension state, and the use of a closed centrifuge to separate it ensures a good occupational health environment on site.

[0031] In some embodiments of the present invention, the present invention provides a method for separating polyethylene wax from heavy components of ethylene tetramer products using the above-described separation device, comprising the following steps:

[0032] 1) Add the cleaning agent from the cleaning agent recovery tank to the cleaning tank;

[0033] 2) The heavy component of ethylene tetramer product in the bottom of the last stage separation tower / reboiler of the ethylene tetramer product distillation unit is added to the cleaning tank through a heated pipeline.

[0034] 3) The cleaning agent added in steps 1) and 2) and the heavy components of ethylene tetramer are mixed in the cleaning tank for cleaning. The temperature of the cleaning tank is controlled by the jacket to obtain a solid-liquid mixture.

[0035] 4) The solid-liquid mixture obtained after cleaning in step 3) is fed into a separator for separation, and the solid material is rinsed with cleaning agent from the cleaning agent recovery tank. After the solid-liquid separation is complete, the separated mother liquor is fed into the cleaning agent recovery tank for cleaning agent recovery, and the separated solid material is polyethylene wax.

[0036] The selection and purity of the cleaning agent described in this invention are the same as described above; in some embodiments, the cleaning agent described in this invention is selected from at least one of methanol or ethanol, preferably one of methanol or ethanol; the purity of the cleaning agent recovered in the cleaning agent recovery vessel is 90% to 100%. The addition ratio of the cleaning agent and the heavy component of the ethylene tetramerization product described in this invention is the same as described above; in some embodiments, the mass ratio of the amount of cleaning agent added to the cleaning vessel to the mass of the material added to the bottom / reboiler of the last stage separation column of the ethylene tetramerization distillation unit is 1 to 20.

[0037] The cleaning temperature and time for mixing the cleaning agent and the ethylene tetramer product heavy component of the present invention are the same as those described above; in some embodiments, the cleaning temperature in the cleaning tank is 20-100°C, preferably 40-45°C, and the cleaning time for each batch of material is 1-10 hours, preferably 3-5 hours.

[0038] When the cleaning agent in the cleaning agent recovery tank is used to rinse solid materials, the amount of cleaning agent used is the same as described above; in some embodiments, the mass of cleaning agent used in the separator to rinse solid materials is 10% to 20% of the mass of cleaning agent in the cleaning tank.

[0039] In this invention, the mother liquor separated in step 4) above is recycled in a cleaning agent recovery vessel, and the recovery temperature is controlled by a jacket. The distilled cleaning agent is returned to the cleaning agent recovery tank through a cleaning agent recovery cooler, and the liquid heavy components remaining at the bottom of the vessel are sent to the heavy oil tank through a heavy oil cooler.

[0040] This invention discloses a method and apparatus for separating polyethylene wax from the heavy components of ethylene tetramerization products. The method uses a specific cleaning agent to clean the mixture of high-boiling-point liquid components and polyethylene wax produced during the distillation of ethylene tetramerization products. Conventional separation methods are then used to separate the high-boiling-point components and polyethylene wax, yielding polyethylene wax that meets usage specifications. Simultaneously, the mother liquor containing high non-boiling-point components and catalyst is fed into a cleaning agent recovery system for recycling. The separation apparatus provided by this invention solves the problem of separating high-boiling-point components and polyethylene wax using the separation method described herein. This avoids pipeline blockage, tank solidification, and cleaning difficulties caused by unseparated mixtures during subsequent transportation and storage, and also produces polyethylene wax as a byproduct, maximizing the utilization of the product's value. Experiments show that the PE wax separated using the method described in this invention and in the separation apparatus is a white granular material with a molecular weight of 3000-5000, a softening point of 108℃, and catalyst metal residues of less than 3 ppm Al and less than 1 ppm Cr, meeting commercial requirements. Attached Figure Description

[0041] Figure 1This is a schematic diagram of a device for separating polyethylene wax from the heavy components of the ethylene tetramer product described in this invention. Detailed Implementation

[0042] This invention discloses a method and apparatus for separating polyethylene wax from the heavy components of ethylene tetramerization products. Those skilled in the art can refer to this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0043] Embodiments 1 and 2 of the present invention use Figure 1 The apparatus shown was used to separate polyethylene wax, a byproduct of ethylene tetramerization.

[0044] Figure 1 This is a schematic diagram of a device for separating polyethylene wax from the heavy components of the ethylene tetramer product described in this invention.

[0045] In the diagram: 1 is the cleaning vessel, 2 is the separator, 3 is the mother liquor tank, 4 is the cleaning agent recovery vessel, 5 is the heavy oil tank, 6 is the cleaning agent recovery tank, 7 is the cleaning agent cooler, and 8 is the heavy oil cooler.

[0046] The present invention will be further described below with reference to the embodiments:

[0047] Example 1

[0048] Methanol was used as the cleaning agent, and 1000 kg of methanol (purity >99%) was added to the cleaning vessel. 100 kg of material from the bottom of the last stage separation tower / reboiler of the ethylene tetramerization distillation unit was slowly added to the cleaning vessel through a heated pipeline. The temperature inside the cleaning vessel was controlled at 40–45°C using the jacket, and the vessel was stirred and cleaned for 3 hours. After cleaning, the material in the vessel was transferred to a closed separator in three batches for separation, with 50 kg of methanol added each time. After thorough centrifugation, the solid material exiting the centrifuge was PE wax, which was then dried. The centrifuge mother liquor entered the cleaning agent recovery vessel for cleaning agent distillation recovery. The distillation temperature was controlled by the recovery vessel jacket. The purity of the recovered cleaning agent was 99.83%, and 1078 kg of methanol was recovered, a recovery rate of 93.74%. The distilled heavy oil, after cooling to room temperature, became a liquid with good fluidity and was stored in a heavy oil tank. This processing yielded 100 kg of wax-containing recombinant material (78% solid content), resulting in 72.36 kg of PE wax (after drying) and 33.34 kg of heavy oil. The PE wax is a white granular material with a molecular weight of 3000-5000, a softening point of 108℃, and residual catalyst metals of Al = 3 ppm and Cr = 1 ppm, meeting commercial requirements.

[0049] Example 2

[0050] Ethanol was used as the cleaning agent, and the material from the bottom of the last stage separation column / reboiler of the ethylene tetramer distillation unit, which was from the same source and batch as in Example 1, was used.

[0051] Add 1000 kg of ethanol (purity >99%) to the cleaning vessel. Slowly add 100 kg of material from the bottom of the last stage separation tower / reboiler of the ethylene tetramerization distillation unit to the cleaning vessel via a heated pipeline. Control the temperature inside the vessel at 40–45°C using the vessel jacket and stir for 5 hours. After cleaning, transfer the material in the vessel to a closed separator in three batches for separation, rinsing with 60 kg of ethanol each time. After thorough centrifugation, the solid material exiting the centrifuge is PE wax, which can be further dried. The centrifuge mother liquor enters the cleaning agent recovery vessel for cleaning agent distillation recovery. Control the distillation temperature using the recovery vessel jacket. The purity of the recovered cleaning agent is 99.65%, and 1054 kg of ethanol is recovered, a recovery rate of 91.65%. The distilled heavy oil, after cooling to room temperature, becomes a liquid with good fluidity and is stored in a heavy oil tank. This processing yielded 100 kg of wax-containing recombinant material (78% solid content), resulting in 75.12 kg of PE wax (after drying) and 36.34 kg of heavy oil. The PE wax was white granules with a molecular weight of 3000-5000 and a softening point of 108℃. The catalyst metal residue Al was 2 ppm, and Cr was not detected, meeting commercial requirements.

[0052] Comparative Example 1

[0053] The waxy heavy components in the bottom / reboiler of the last stage separation column of the ethylene tetramerization distillation unit were directly separated by filtration, pressure filtration and centrifugation respectively. The results showed that at room temperature, the waxy heavy components were solidified into wax, and no matter what method was used, filtration, pressure filtration and centrifugation could not completely separate the solid and liquid.

[0054] Comparative Example 2

[0055] Low-boiling-point hydrocarbon solvents such as cyclopentane, cyclohexane, and n-hexane, as well as the aromatic solvent toluene, were used as cleaning agents, and the same cleaning and separation methods as in Example 1 were employed. The results showed that while these solvents could dissolve most of the high-boiling-point hydrocarbons from the wax-containing heavy components in the bottom / reboiler of the last stage separation column of the ethylene tetramerization distillation unit, they also caused the PE wax in the heavy components to swell more easily. The swollen PE wax led to a dense filter cake layer, preventing the washing liquid / filtrate from passing through the filter cake layer, thus hindering solid-liquid separation. Furthermore, these solvents had poor solubility for the metal compound catalysts adsorbed on the PE wax, making it difficult to wash them off the PE wax and resulting in unqualified PE wax with low metal residue.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for separating polyethylene wax from the heavy components of ethylene tetramer products, characterized in that, include: S1) Mix the heavy components of ethylene tetramerization product with a cleaning agent to obtain a solid-liquid mixture; the cleaning agent is at least one of methanol or ethanol; the heavy components of ethylene tetramerization product include C 10 ~C 14 The mixture comprises a high-boiling-point liquid hydrocarbon component, polyethylene wax, a quenching agent, and a catalyst; the mixing temperature is 20~100℃; and the mixing time is 1~10 h. S2) Separate the solid substances in the solid-liquid mixture to obtain polyethylene wax.

2. The separation method according to claim 1, characterized in that, In step S1), the mass ratio of the cleaning agent to the ethylene tetramer product heavy component is 1~20.

3. The separation method according to claim 1, characterized in that, In step S1), the mixing temperature is 40~45℃; the mixing time is 3~5 h.

4. The separation method according to claim 1, characterized in that, In step S1), the temperature of the heavy component of the ethylene tetramer product is 120~150℃.

5. The separation method according to claim 1, characterized in that, In step S2), after separating the solid substances in the solid-liquid mixture, the method further includes rinsing the separated solid substances with the cleaning agent described in step S1. The amount of cleaning agent used in step S2) is 10-20% of the mass of the cleaning agent used in step S1).

6. The separation method according to claim 1, characterized in that, The molecular weight of the polyethylene wax obtained in step S2) is 3000~5000; The aluminum content of the polyethylene wax is less than 10 ppm; The chromium content of the polyethylene wax is less than 5 ppm.

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