Polyethylene grading method, polyethylene obtained by polyethylene grading method, system for grading polyethylene and application thereof

Abstract

The invention relates to the field of polymer grading, and discloses a polyethylene grading method, polyethylene obtained through the polyethylene grading method, a system for polyethylene grading and application of the system. According to the polyethylene grading method, on the basis of preparing a high-temperature liquid chromatographic column, two-time flow division is adopted, and the flow ratio of second flow division is controlled, so that accurate and directional grading of a polyethylene raw material is realized, and the purposes of accurate and directional regulation and control of the average molecular weight, the molecular weight distribution curve and the branched structure of polyethylene, especially low-density polyethylene, are realized.

Description

Technical Field

[0001] The present invention relates to the field of polymer fractionation, and particularly relates to a polyethylene fractionation method, polyethylene obtained by the polyethylene fractionation method, a system for polyethylene fractionation, and its applications. Background Art

[0002] Low-density polyethylene (LDPE), as a key insulating base material for high-voltage cables, its microscopic molecular structure directly determines its macroscopic properties. However, traditional industrial synthesis methods, such as free radical polymerization, are difficult to precisely control microscopic molecular structure parameters such as average molecular weight, molecular weight distribution curve, and branching structure during the production process. This results in multiple structural variables among LDPE samples of different grades. This structural uncertainty makes it very difficult to establish an accurate structure-property relationship between the LDPE molecular structure and its macroscopic properties. Therefore, achieving directional regulation of the LDPE molecular structure is crucial for understanding its structure-property relationship.

[0003] Existing polyethylene molecular structure regulation methods can be roughly divided into two categories: direct preparation and fractional extraction. (1) Direct preparation methods usually require the aid of special catalysts and / or specially designed polymerization systems to regulate the molecular structure within a certain range. The problems with this type of technology are high costs (usually expensive catalysts are required), poor universality of the method (special polymerization systems usually limit the structures that can be obtained), and since its polymerization mechanism is not free radical polymerization, the molecular structure of the product is not exactly the same as that of LDPE. (2) Fractional extraction methods start from existing LDPE samples, split different molecular weight parts in LDPE, and selectively obtain one / some of the components to achieve molecular structure regulation. In contrast, fractional extraction methods have stronger practicality, flexibility, and universality. The most representative technology in this regard is temperature rising elution fractionation (TREF), which can achieve fractionation of different molecular weight components based on differences in crystallinity; however, up to now, such technologies still have problems such as low separation resolution and long time consumption. Summary of the Invention

[0004] The object of the present invention is to overcome the problems in the prior art that the polyethylene molecular structure is difficult to be directionally regulated and it is difficult to obtain polyethylene samples with a single structural variable, and to provide a polyethylene fractionation method, polyethylene prepared by the polyethylene fractionation method, a system for polyethylene fractionation, and its applications. Based on a preparative high-temperature liquid chromatography column, this polyethylene fractionation method adopts two shunts and controls the flow ratio of the second shunt to achieve precise and directional fractionation of polyethylene raw materials, and realizes the goal of precisely and directionally regulating the average molecular weight, molecular weight distribution curve, and branching structure of polyethylene, especially low-density polyethylene.

[0005] The first aspect of the present invention provides a method for fractionating polyethylene, wherein the method comprises: S1. After transporting the polyethylene solution to a preparative liquid chromatography column for separation, perform a first split to obtain a first stream and a second stream; wherein, the flow rate of the first stream is V1, and the flow rate of the second stream is V2; S2. Test the first stream to obtain the retention time t; S3. Perform a second split on the second stream to obtain a third stream and a fourth stream, wherein the flow rate of the third stream is V3; When the retention time is t1, control V3 to decrease from V3 = V2 to 0 mL / min; when the retention time is t2, increase V3 to V3 = V2, and collect the components in the fourth stream with retention times in the range of t1 to t2, which are the target products; Or, when the retention time is t1, control V3 to increase from 0 mL / min to V3'; when the retention time is t2, decrease V3' to 0 mL / min, and collect the components in the fourth stream with retention times in the range of t1 to t2, which are the target products; Or, when the retention time is less than t1, control V3 = V2, and when the retention time is t1, decrease V3 to 0 mL / min; collect the components in the fourth stream with retention times in the range of t1 to the end of elution, which are the target products; Or, when the retention time is less than t2, control V3 = 0 mL / min, and when the retention time is t2, increase V3 to V3 = V2; collect the components in the fourth stream with retention times in the range of the start of elution to t2, which are the target products; Wherein, 0 s < t1 < t2 ≤ t.

[0006] The second aspect of the present invention provides a polyethylene obtained by the above fractionation method, wherein the polyethylene has a weight average molecular weight of 10 - 1000 kDa, and the molecular weight distribution PDI of the polyethylene is 1.2 - 20.

[0007] The third aspect of the present invention provides a system for polyethylene fractionation, wherein the system comprises: A feeder 4, a preparative liquid chromatography column 5, a first splitter 6, a detector 7, a second splitter 8, an injection pump 10, and a fraction collection bottle 11; Wherein, the polyethylene solution from the feeding system is transported to the preparative liquid chromatography column 5 for separation and then transported to the first splitter 6 for a first split to obtain a first stream and a second stream, wherein the flow rate of the first stream is V1, and the flow rate of the second stream is V2; The first stream is transported to the detector 7 for testing to obtain the retention time t; The second material flow is transported to the second diverter 8 for second diversion to obtain a third material flow and a fourth material flow, where the flow rate of the third material flow is V3; When the retention time is t1, the injection pump 10 is adjusted to reduce V3 from V3 = V2 to 0 mL / min; when the retention time is t2, the injection pump 10 is adjusted to increase V3 to V3 = V2, and the components in the fourth material flow with a retention time in the range of t1 to t2 are collected in the fraction collection bottle 11; Alternatively, when the retention time is t1, the injection pump 10 is adjusted to increase V3 from 0 mL / min to V3'; when the retention time is t2, the injection pump 10 is adjusted to reduce V3' to 0 mL / min, and the components in the fourth material flow with a retention time in the range of t1 to t2 are collected in the fraction collection bottle; Alternatively, when the retention time is less than t1, the injection pump 10 is adjusted to make V3 = V2; when the retention time is t1, the injection pump 10 is adjusted to reduce V3 to 0 mL / min, and the components in the fourth material flow with a retention time in the range of t1 to the elution termination are collected in the fraction collection bottle; Alternatively, when the retention time is less than t2, the injection pump 10 is adjusted to make V3 = 0 mL / min; when the retention time is t2, the injection pump 10 is adjusted to increase V3 to V3 = V2, and the components in the fourth material flow with a retention time in the range of the elution start to t2 are collected in the fraction collection bottle; Wherein, 0 s < t1 < t2 ≤ t.

[0008] The fourth aspect of the present invention provides an application of the above system in polyethylene fractionation.

[0009] Through the above technical solutions, the polyethylene fractionation method, the polyethylene obtained by the polyethylene fractionation method, the system for polyethylene fractionation and its application provided by the present invention achieve the following beneficial effects: Based on the preparation of a preparative high-temperature liquid chromatography column, the polyethylene fractionation method provided by the present invention adopts two-stage diversion and controls the flow rate ratio of the second diversion, realizing precise and directional fractionation of polyethylene raw materials, achieving the goal of precisely regulating the average molecular weight, molecular weight distribution curve, and branching structure of polyethylene, especially low-density polyethylene (LDPE), breaking through the limitations of the difficult molecular structure regulation and many molecular structure variables in the prior art, and providing a new idea for the precise regulation of polyethylene molecular structure and the study of the structure-macroscopic structure-activity relationship.

[0010] Furthermore, the polyethylene fractionation method provided by the present invention has the characteristics of high separation resolution and on-line continuous operation, can continuously and precisely control the collection amount of each fraction, on-line obtain samples with the desired average molecular weight and molecular weight distribution curve, and is convenient and efficient.

[0011] Furthermore, the polyethylene fractionation method provided by the present invention has wide applicability. Besides the polyethylene cable insulation material applied in the present invention, it can be popularized and applied to the molecular design and performance optimization of other polymer materials. Description of the Drawings

[0012] Figure 1 is a flow chart of the polyethylene fractionation method; Figure 2 is a schematic diagram of the system for polyethylene fractionation; Figures 3(a) - 3(c) are schematic diagrams of the directional fractionation of the average molecular weight of polyethylene or the narrowing of the molecular weight distribution; Figures 4(a) - 4(c) are schematic diagrams of the broadening of the polyethylene molecular weight distribution; Figures 5(a) - 5(c) are schematic diagrams of selectively removing macromolecular components from polyethylene; Figures 6(a) - 6(c) are schematic diagrams of selectively removing low molecular weight components from polyethylene.

[0013] Description of the Reference Numerals 1 - mobile phase storage tank; 2 - delivery pump; 3 - temperature control system; 4 - injector; 5 - preparative liquid chromatography column; 6 - first splitter; 7 - detector; 8 - second splitter; 9 - buffer tube; 10 - syringe pump; 11 - fraction collection bottle. Detailed Embodiments

[0014] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0015] The first aspect of the present invention provides a method for polyethylene fractionation, wherein the method includes: S1. After transporting the polyethylene solution to the preparative liquid chromatography column for separation, perform a first split to obtain a first stream and a second stream, wherein the flow rate of the first stream is V1 and the flow rate of the second stream is V2; S2. Test the first stream to obtain the retention time t; S3. Perform a second split on the second stream to obtain a third stream and a fourth stream, wherein the flow rate of the third stream is V3; When the retention time is t1, control V3 to decrease from V3 = V2 to 0 mL / min; when the retention time is t2, increase V3 to V3 = V2, and collect the components in the fourth stream with retention times in the range of t1 to t2, which are the target products; Alternatively, when the retention time is t1, control V3 to increase from 0 mL / min to V3'; when the retention time is t2, reduce V3' to 0 mL / min, and collect the components in the fourth stream with retention times in the range from t1 to t2, which are the target products; Alternatively, when the retention time is less than t1, control V3 = V2; when the retention time is t1, reduce V3 to 0 mL / min; collect the components in the fourth stream with retention times in the range from t1 to the end of elution, which are the target products; Alternatively, when the retention time is less than t2, control V3 = 0 mL / min; when the retention time is t2, increase V3 to V3 = V2; collect the components in the fourth stream with retention times in the range from the start of elution to t1, which are the target products; Wherein, 0 s < t1 < t2 ≤ t.

[0016] Based on the preparation of a high-temperature liquid chromatography column, the polyethylene fractionation method provided by the present invention adopts two-stage splitting and controls the flow ratio of the second split, achieving precise and directional fractionation of polyethylene raw materials, and realizing the goal of precisely regulating the average molecular weight, molecular weight distribution curve, and branching structure of polyethylene, especially low-density polyethylene (LDPE). It breaks through the limitations of the large difficulty in regulating the molecular structure of polyethylene and the large number of molecular structure variables in the prior art, providing a new idea for the precise regulation of the polyethylene molecular structure and the study of the structure-macroscopic structure-activity relationship.

[0017] Furthermore, the polyethylene fractionation method provided by the present invention has the characteristics of high separation resolution and on-line continuous operation, can continuously and precisely control the collection amount of each fraction, and on-line obtain samples with the required average molecular weight and molecular weight distribution curve, which is convenient and efficient.

[0018] Furthermore, the polyethylene fractionation method provided by the present invention has wide applicability. In addition to the polyethylene cable insulation material applied in the present invention, it can be popularized and applied to the molecular design and performance optimization of other polymer materials.

[0019] In the present invention, the retention time t refers to the time for the target component after polyethylene fractionation to flow through the liquid chromatography column and finally reach the detector.

[0020] In the present invention, by testing the first stream, the content of each component obtained after separation by the preparative liquid chromatography column and the molecular structure information of polyethylene such as the average molecular weight, molecular weight distribution curve, or branching structure can be obtained.

[0021] In the present invention, the retention time t1 refers to the starting time for collecting the components of the fourth stream, the retention time t2 refers to the ending time for stopping collecting the components of the fourth stream, and the retention time t2 refers to any specific retention time within the range of the retention time t.

[0022] In the present invention, the starting time for starting to collect the fourth stream component and the starting time for stopping to collect the fourth stream component can be selected according to actual needs, as long as the starting time for stopping to collect the fourth stream component is greater than the starting time for starting to collect the fourth stream component.

[0023] In the present invention, multiple t1 and t2 can be selected as needed, such as t 1j and t 2k , where j and k are integers greater than or equal to 1, representing the starting time for starting to collect the fourth stream component and the ending time for starting to collect the fourth stream component respectively.

[0024] In the present invention, the flow rate of the fourth stream is V4.

[0025] In a specific embodiment of the present invention, when the retention time is t1, control V3 to decrease from V3 = V2 to 0 mL / min; when the retention time is t2, increase V3 to V3 = V2, and collect the components in the fourth stream with retention times in the range of t1 to t2, that is, the target product. By adopting the above embodiment, not only can the target product with a narrower molecular weight distribution be obtained, but also polyethylene with a specific weight average molecular weight or number average molecular weight can be obtained.

[0026] In a specific embodiment of the present invention, when the retention time is t1, control V3 to increase from 0 mL / min to V3'; when the retention time is t2, decrease V3' to 0 mL / min, and collect the components in the fourth stream with retention times in the range of t1 to t2, that is, the target product. By adopting the above embodiment, a target product with a wider molecular weight distribution can be obtained.

[0027] In a specific embodiment of the present invention, when the retention time is less than t1, control V3 = V2, and when the retention time is t1, decrease V3 to 0 mL / min; collect the components in the fourth stream with retention times in the range of t1 to the elution termination, that is, the target product. By adopting the above embodiment, the high molecular weight components in polyethylene can be selectively removed.

[0028] In the present invention, there is no particular requirement for the time required to reduce V3 to 0 mL / min at a retention time of t1. As long as V3 starts to decrease at a retention time of t1, it is preferred to reduce V3 from V2 to 0 mL / min within 30 s. For example, it can be reduced within 1 s, 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s, 10 s, 11 s, 12 s, 13 s, 14 s, 15 s, 16 s, 17 s, 18 s, 19 s, 20 s, 21 s, 22 s, 23 s, 24 s, 25 s, 26 s, 27 s, 28 s, 29 s, 30 s.

[0029] In a specific embodiment of the present invention, when the retention time is less than t2, control V3 = 0 mL / min. When the retention time is t2, increase V3 to V3 = V2; collect the components in the fourth stream with a retention time within the range of t2 from the start of elution, that is, the target product. By adopting the above embodiment, small molecular weight components in polyethylene can be selectively removed.

[0030] In the present invention, there is no particular requirement for the time required to increase V3 to V3 = V2 at a retention time of t2. As long as V3 starts to increase at a retention time of t2, it is preferred to increase V3 from 0 mL / min to V2 within 30 s. For example, it can be increased within 1 s, 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s, 10 s, 11 s, 12 s, 13 s, 14 s, 15 s, 16 s, 17 s, 18 s, 19 s, 20 s, 21 s, 22 s, 23 s, 24 s, 25 s, 26 s, 27 s, 28 s, 29 s, 30 s.

[0031] According to the present invention, V2 / V1 is 10 - 50:1.

[0032] In the present invention, when controlling V2 / V1 to satisfy the above range, it is possible to test the polyethylene fractionation components with a suitable flow rate, and obtain the retention time t on the premise of not affecting the recovery yield and ensuring the test accuracy of the detector.

[0033] According to the present invention, the flow rate of the polyethylene solution delivered to the preparative liquid chromatography column is V0, where V0 is greater than or equal to 5 mL / min.

[0034] In the present invention, when controlling the flow rate of the polyethylene solution delivered to the preparative liquid chromatography column to satisfy the above range, it is possible to provide the optimal working flow rate range for the preparative liquid chromatography column and achieve efficient fractionation of each component of polyethylene.

[0035] Furthermore, V0 is 5 - 50 mL / min.

[0036] In the present invention, the flow rate of the polyethylene solution does not decrease in the preparative liquid chromatography column, that is, the flow rate of the components separated by the preparative liquid chromatography column flowing out of the preparative liquid chromatography column is the same as the flow rate of the polyethylene solution delivered to the preparative liquid chromatography column.

[0037] According to the present invention, the temperature of the preparative liquid chromatography column is greater than or equal to 25 °C.

[0038] In the present invention, when the temperature of the polyethylene solution is controlled to meet the above range, it can ensure that the polyethylene chain segments are fully dissolved in the mobile phase of the preparative liquid chromatography column, and ensure that each fraction in the polyethylene is fully separated.

[0039] Furthermore, the temperature of the preparative liquid chromatography column is 80 - 220 °C.

[0040] According to the present invention, the inner diameter of the preparative liquid chromatography column is greater than or equal to 4 mm.

[0041] In the present invention, selecting a preparative liquid chromatography column with an inner diameter greater than or equal to 4 mm can ensure a sufficient sample capacity and provide a sufficient injection volume and concentration for the polyethylene solution.

[0042] Furthermore, the preparative liquid chromatography column is a size exclusion mode gel permeation chromatography column (GPC) with an inner diameter of 4.6 - 50 mm.

[0043] In the present invention, selecting a size exclusion mode gel permeation chromatography column (GPC) can efficiently fractionate each component of the polyethylene based on the difference in molecular weight.

[0044] In a preferred embodiment of the present invention, when the retention time is t1, V3 is linearly decreased from V2 to 0 mL / min; when the retention time is t2, V3 is linearly increased to V2.

[0045] In the present invention, there is no particular limitation on the specific rate of the linear decrease or linear increase of V3. As long as V3 can achieve the change process of decreasing from V2 to 0 mL / min and then increasing from 0 mL / min to V2 within the range of the retention time from t1 to t2.

[0046] In another preferred embodiment of the present invention, when the retention time is t1, V3 is controlled to linearly increase from 0 mL / min to V3'; when the retention time is t2, V3' is controlled to linearly decrease to 0 mL / min.

[0047] In the present invention, there is no particular limitation on the specific rate of the linear increase of V3 or the linear decrease of V3'. As long as within the range of the retention time from t1 to t2, the change process of V3 from 0 mL / min to V3' and then from V3' to 0 mL / min can be achieved.

[0048] In another preferred embodiment of the present invention, when the retention time is less than t1, control V3 = V2. When the retention time is t1, linearly decrease V3 to 0 mL / min within 30 s.

[0049] In the present invention, there is no particular limitation on the rate of linearly decreasing V3 to 0 mL / min. As long as it is ensured that within 30 s, V3 is decreased from V2 to 0 mL / min.

[0050] In another preferred embodiment of the present invention, when the retention time is less than t2, control V3 = 0 mL / min. When the retention time is t2, linearly increase V3 to V3 = V2 within 30 s.

[0051] In the present invention, there is no particular limitation on the rate of linearly increasing V3 to V2. As long as it is ensured that within 30 s, V3 is increased from 0 mL / min to V2.

[0052] In the present invention, by adjusting V3 at different retention times, the collection amount at the collection end of fraction collection can be dynamically regulated, that is, the components within a specific retention time range in the fourth stream, and thus the average molecular weight, molecular weight distribution curve, branching structure, etc. of the polyethylene component in the target product can be precisely controlled as needed.

[0053] In the present invention, the fractionation method can be applicable to different types of polyethylene, and can adapt to different instrument devices and different test conditions. The retention time t can vary within a relatively large range. For example, the retention time t is 300 - 3600 s, preferably 600 - 1200 s.

[0054] In the present invention, the fractionation method can be applicable to polyethylenes with various weight-average molecular weights and molecular weight distributions. For example, the weight-average molecular weight of polyethylene in the polyethylene solution is 50 - 500 kDa, and the molecular weight distribution PDI of polyethylene in the polyethylene solution is 5 - 15.

[0055] According to the present invention, the polyethylene in the polyethylene solution is selected from at least one of low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and ethylene copolymers.

[0056] In the present invention, the ethylene copolymer is a conventional ethylene copolymer in the art, including but not limited to copolymers of ethylene and α-olefins.

[0057] In the present invention, the polyethylene can be prepared by conventional processes in the art, for example, by free radical polymerization.

[0058] According to the present invention, the concentration of the polyethylene solution is 0.1 - 5 wt%.

[0059] In the present invention, when the concentration of the polyethylene solution is controlled to meet the above range, a larger production amount can be achieved on the basis of ensuring good classification effect.

[0060] In the present invention, there is no particular limitation on the solvent in the polyethylene solution, and conventional organic solvents in the art can be used, such as trichlorobenzene.

[0061] In the present invention, the classification method further includes: a step of pre-treating the polyethylene raw material, for example, dissolving the polyethylene in an organic solvent under high temperature conditions to obtain a polyethylene solution.

[0062] In the present invention, the classification method further includes concentrating the collected target product to obtain polyethylene.

[0063] In the present invention, there is no particular limitation on the concentration method, and conventional concentration methods in the art can be used, such as rotary evaporation, freeze drying, etc.

[0064] In a specific embodiment of the present invention, as shown in Fig. 3(a), when the retention time is t1, V3 linearly decreases from V2 to 0 mL / min, and when the retention time is t2, V3 linearly recovers to V2. Correspondingly, as shown in Fig. 3(b), the flow rate V4 of the fourth stream linearly increases from 0 mL / min to V2 when the retention time is t1, and V4 linearly recovers to 0 mL / min when the retention time is t2. The components in the fourth stream with a retention time in the range of t1 to t2 are collected, that is, the target product. As can be seen from Fig. 3(c), compared with the polyethylene raw material, the molecular weight distribution of the target product becomes narrower.

[0065] In another specific embodiment of the present invention, as shown in Fig. 4(a), when the retention time is t1, V3 linearly increases from 0 mL / min to V3'; when the retention time is t2, V3' linearly recovers to 0 mL / min. Correspondingly, as shown in Fig. 4(b), the flow rate V4 of the fourth stream starts to linearly decrease from V2 to V2 - V3' when the retention time is t1, and V4 linearly recovers to V2 when the retention time is t2. The components in the fourth stream with a retention time in the range of t1 to t2 are collected, that is, the target product; as can be seen from Fig. 4(c), compared with the polyethylene raw material, the molecular weight distribution of the target product becomes wider.

[0066] In another specific embodiment of the present invention, as shown in Fig. 5(a), when the retention time is less than t1, V3 = V2. When the retention time is t1, V3 decreases from V2 to 0 mL / min. Correspondingly, as shown in Fig. 5(b), when the retention time is less than t1, the flow rate V4 of the fourth stream is 0 mL / min. When the retention time is t1, V4 increases to V2. The components in the fourth stream with a retention time in the range from t1 to the end of elution are collected, which are the target products. As can be seen from Fig. 5(c), compared with the polyethylene raw material, the content of macromolecular components in the target products decreases.

[0067] In another specific embodiment of the present invention, as shown in Fig. 6(a), when the retention time is less than t2, V3 = 0 mL / min. When the retention time is t2, V3 is increased to V3 = V2. Correspondingly, as shown in Fig. 6(b), when the retention time is less than t2, the flow rate V4 of the fourth stream is V2. When the retention time is t2, V4 decreases to 0 mL / min. The components in the fourth stream with a retention time in the range from the start of elution to t2 are collected, which are the target products. As can be seen from Fig. 6(c), compared with the polyethylene raw material, the content of small molecular components in the target products decreases.

[0068] The second aspect of the present invention provides a polyethylene obtained by the above fractionation method.

[0069] In the present invention, by using the above fractionation method, polyethylene with different weight-average molecular weights and / or molecular weight distributions can be obtained directionally as needed, and the weight-average molecular weight and / or molecular weight distribution of the obtained polyethylene can vary within a large range. For example, the weight-average molecular weight of the polyethylene is 10 - 1000 kDa, and the polydispersity index (PDI) of the polyethylene is 1.2 - 20.

[0070] In a preferred embodiment of the present invention, the polyethylene is polyethylene for DC cables.

[0071] The third aspect of the present invention provides a system for polyethylene fractionation. Among them, the system includes: Sampler 4, preparative liquid chromatography column 5, first splitter 6, detector 7, second splitter 8, syringe pump 10, fraction collector 11; Among them, the polyethylene solution from the feeding system is transported to the preparative liquid chromatography column 5 for separation, and then transported to the first splitter 6 for the first splitting to obtain a first stream and a second stream. Among them, the flow rate of the first stream is V1, and the flow rate of the second stream is V2; The first stream is transported to the detector 7 for testing to obtain the retention time t; The second stream is transported to the second splitter 8 for the second splitting to obtain a third stream and a fourth stream. Among them, the flow rate of the third stream is V3, and the flow rate of the fourth stream is V4; When the retention time is t1, adjust the injection pump 10 to reduce V3 from V3 = V2 to 0 mL / min; when the retention time is t2, adjust the injection pump 10 to increase V3 such that V3 = V2, and collect the components in the fourth stream with retention times in the range of t1 to t2 in the fraction collection bottle 11; Alternatively, when the retention time is t1, adjust the injection pump 10 to increase V3 from 0 mL / min to V3'; when the retention time is t2, adjust the injection pump 10 to reduce V3' to 0 mL / min, and collect the components in the fourth stream with retention times in the range of t1 to t2 in the fraction collection bottle; Alternatively, when the retention time is less than t1, adjust the injection pump 10 such that V3 = V2; when the retention time is t1, adjust the injection pump 10 to reduce V3 to 0 mL / min, and collect the components in the fourth stream with retention times in the range of t1 to the end of elution in the fraction collection bottle; Alternatively, when the retention time is less than t2, adjust the injection pump 10 such that V3 = 0 mL / min; when the retention time is t2, adjust the injection pump 10 to increase V3 to V3 = V2, and collect the components in the fourth stream with retention times in the range of the start of elution to t2 in the fraction collection bottle; Wherein, 0 s < t1 < t2 ≤ t.

[0072] Based on the preparative high-temperature liquid chromatography column, the polyethylene system provided by the present invention utilizes the first splitter and the second splitter, and precisely controls the flow rate of the third stream through the injection pump 10, realizing the on-line continuous directional fractionation of polyethylene, especially low-density polyethylene. It can continuously and precisely control the collection amount of each fraction, obtain samples with the desired average molecular weight and molecular weight distribution curve on-line, which is convenient and efficient.

[0073] In the present invention, the sampler 4 is used to introduce the polyethylene solution into the preparative liquid chromatography column 5.

[0074] In the present invention, preferably, the injection pump 10 is a precision injection pump, which is used to precisely control the flow rate V3 of the third stream to achieve the directional fractionation of polyethylene.

[0075] In the present invention, the injection needle and / or syringe of the injection pump are connected to the pipeline in the system through conventional interfaces and / or interfaces in the art, such as Luer connectors or other locking interfaces, and the extraction rate of the injection pump 10 is controlled by a program to realize the dynamic adjustment of the flow rate V3 of the third stream.

[0076] According to the present invention, the system further includes a mobile phase storage tank 1 and a delivery pump 2.

[0077] In the present invention, the mobile phase storage tank 1 is used to store the mobile phase for elution fractionation of the preparative liquid chromatography column. For example, the mobile phase is trichlorobenzene.

[0078] In the present invention, the delivery pump 2 is used to deliver the mobile phase in the mobile phase storage tank 1 to the preparative liquid chromatography column 5.

[0079] According to the present invention, the flow rate V0 of the delivery pump 2 is greater than or equal to 5 mL / min.

[0080] In the present invention, when the flow rate of the delivery pump 2 is controlled to meet the above range, the optimal working flow rate range can be provided for the preparative liquid chromatography column, and efficient fractionation of each component of polyethylene can be achieved.

[0081] Furthermore, the flow rate V0 of the delivery pump 2 is 5 - 50 mL / min; According to the present invention, the pressure of the delivery pump 2 is greater than or equal to 5 MPa.

[0082] In the present invention, when the pressure of the delivery pump 2 is controlled to meet the above range, sufficient working flow rate of the delivery pump can be provided (i.e., to meet the requirement that V0 is greater than or equal to 5 mL / min).

[0083] Furthermore, the pressure of the delivery pump 2 is 5 - 40 MPa.

[0084] According to the present invention, the system further includes a buffer tube 9, and the buffer tube 9 is connected between the second splitter 8 and the injection pump 10.

[0085] In the present invention, the buffer tube 9 is used to temporarily store the non-target components in the second stream to prevent them from entering the low-temperature environment and precipitating.

[0086] According to the present invention, the capacity of the buffer tube 9 is greater than or equal to 100 mL. In the present invention, when the capacity of the buffer tube 9 is ensured to meet the above range, sufficient buffer capacity can be provided for a single polyethylene fractionation with V0 greater than or equal to 5 mL / min.

[0087] According to the present invention, the system further includes a temperature control system 3, and the temperature control system 3 is used to control the temperatures of the injector 4, the preparative liquid chromatography column 5, the first splitter 6, the second splitter 8, the buffer tube 9 and the fraction collector 11.

[0088] In the present invention, the temperature control system 3 makes the temperatures of the injector 4, the preparative liquid chromatography column 5, the first splitter 6, the second splitter 8, the buffer tube 9 and the fraction collector 11 greater than or equal to 25°C, preferably 80 - 220°C.

[0089] According to the present invention, the inner diameter of the preparative liquid chromatography column is greater than or equal to 4 mm, and preferably a gel permeation chromatography column in size exclusion mode with an inner diameter of 4.6 - 50 mm.

[0090] According to the present invention, the detector 7 is selected from at least one of an ultraviolet detector, a differential refractive index detector, a light scattering detector, and a viscosity detector.

[0091] The fourth aspect of the present invention provides an application of the above system in the fractionation of polyethylene.

[0092] As Figure 1 shown, the fractionation method of the present invention includes: Pre-treat the low-density polyethylene raw material. Specifically, dissolve polyethylene in an organic solvent under high-temperature conditions to obtain a polyethylene solution. After transporting the polyethylene solution into the preparative liquid chromatography column for separation, perform a first split through a first splitter to obtain a first stream and a second stream. Determine the molecular structure of the first stream to obtain the retention time t. The second stream undergoes a second split through a second splitter to obtain a third stream and a fourth stream. By performing on-line flow control on the third stream, thereby achieving selective collection of fractions in the fourth stream, and concentrating the collected fractions to obtain the target polyethylene.

[0093] The present invention will be described in detail below through examples. In the following examples, the weight-average molecular weight and molecular weight distribution parameters of polyethylene were measured by a conventional high-temperature GPC method equipped with a differential refractive index detector; the polyethylene raw material used was a commercially available low-density polyethylene pellet resin.

[0094] Example 1 - Directional Fractionation of Polyethylene Average Molecular Weight S1. Dissolve 0.2 g of LDPE (Mw = 145,820 Da, Mn = 28,592 Da, PDI = 5.10) in trichlorobenzene to obtain a 1 wt% polyethylene solution, store it in the polyethylene solution storage tank 1, and transport it to the preparative liquid chromatography column 5 through the transfer pump 2 and the injector 4. Among them, the preparative liquid chromatography column is a high-temperature gel permeation chromatography column (GPC) in size exclusion mode, with an inner diameter of 7.5 mm. The flow rate V0 of the transfer pump is 10.5 mL / min, and the pressure is 15 MPa. The components separated by the preparative liquid chromatography column are transported to the first splitter 6 for the first split to obtain a first stream and a second stream. Among them, the flow rate V1 of the first stream is 0.5 mL / min, and the flow rate V2 of the second stream is 10 mL / min.

[0095] S2. Transport the first stream to the detector 7 to obtain a retention time t of 720 - 1080 s.

[0096] S3. The second material flow is transported to the second splitter 8 for second splitting to obtain a third material flow and a fourth material flow. Among them, the flow rate of the third material flow is V3. By controlling the extraction rate of the precision injection pump, precise control of V3 is achieved. Specifically: (i) When the retention time is t 11 = 750 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow linearly decreases from 10 mL / min to 0 mL / min. When the retention time is t 21 = 750 + 90 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow linearly increases from 0 mL / min to 10 mL / min. Collect the components in the fourth material flow with retention times within the range of t 11 to t 21 in the fraction collection bottle 11 to obtain the target fraction 1; (ii) When the retention time is t 12 = 840 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow linearly decreases from 10 mL / min to 0 mL / min. When the retention time is t 22 = 840 + 90 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow linearly increases from 0 mL / min to 10 mL / min. Collect the components in the fourth material flow with retention times within the range of t 12 to t 22 in the fraction collection bottle 11 to obtain the target fraction 2; (iii) When the retention time is t 13 = 930 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow linearly decreases from 10 mL / min to 0 mL / min. When the retention time is t 23 = 930 + 90 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow linearly increases from 0 mL / min to 10 mL / min. Collect the components in the fourth material flow with retention times within the range of t 13 to t 23 in the fraction collection bottle 11 to obtain the target fraction 3; Control the temperatures of the injector 4, the preparative liquid chromatography column 5, the first splitter 6, the second splitter 8, the buffer tube 9, and the fraction collection bottle 11 to be 150 °C through the temperature control system 3.

[0097] Concentrate the target fraction 1, the target fraction 2, and the target fraction 3 respectively to obtain polyethylene S1, polyethylene S2, and polyethylene S3. The weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution PDI of polyethylene S1 - S3 are shown in Table 1.

[0098] Table 1

[0099] As can be seen from Table 1, through the classification method described in the present invention, polyethylenes with different weight-average molecular weights (Mw) and number-average molecular weights (Mn), but with similar molecular weight distributions (PDI), can be obtained.

[0100] Example 2 - Control of Polyethylene Molecular Weight Distribution S1. The steps are carried out according to step S1 of Example 1, with the difference that: for LDPE, Mw = 167810 Da, Mn = 16208 Da, and PDI = 10.35.

[0101] S2. The first material flow is transported to the detector 7, and a retention time t of 690 - 1020 s is obtained.

[0102] S3. The second material flow is transported to the second diverter 8 for secondary diversion to obtain a third material flow and a fourth material flow. Among them, the flow rate of the third material flow is V3, and by controlling the extraction rate of the precision injection pump, the precise control of V3 is achieved. Specifically: (i) When the retention time is t 11 = 730 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow decreases exponentially from 10 mL / min to 0 mL / min. When the retention time is t 21 = 730 + 100 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow increases exponentially from 0 mL / min to 10 mL / min. Collect the components in the fourth material flow with retention times within the range of t 11 to t 21 in the fraction collection bottle 11 to obtain the target fraction 1; (ii) When the retention time is t 12 = 690 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow increases exponentially from 0 mL / min to 5 mL / min. When the retention time is t 22 = 1020 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third material flow returns exponentially from 5 mL / min to 0 mL / min. Collect the components in the fourth material flow with retention times within the range of t 12 to t 22 in the fraction collection bottle 11 to obtain the target fraction 2; Concentrate the target fraction 1 and the target fraction 2 respectively to obtain polyethylene S4 and polyethylene S5. The weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution PDI of the polyethylene are shown in Table 2.

[0103] Table 2

[0104] As can be seen from Table 2, through the fractionation method of the present invention, polyethylene components with a narrower molecular weight distribution (such as polyethylene S4 concentrated from target fraction 1) and a wider molecular weight distribution (such as polyethylene S5 concentrated from target fraction 2) can be respectively prepared.

[0105] Example 3 - Selective Filtration of Macromolecular or Small Molecular Components S1. Perform according to step S1 of Example 2.

[0106] S2. The first feed stream is transported to detector 7 to obtain a retention time t of 690 - 1020 s.

[0107] S3. The second feed stream is transported to the second splitter 8 for second splitting to obtain a third feed stream and a fourth feed stream. Among them, the flow rate of the third feed stream is V3, and by controlling the extraction rate of the precision injection pump, the precise control of V3 is achieved. Specifically: (i) When the retention time is t1 = 750 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third feed stream linearly decreases from 10 mL / min to 0 mL / min within 30 s until the elution ends, and collect the components in the fourth feed stream with a retention time within the range from t1 to the end of elution in the fraction collection bottle 11 to obtain target fraction 1; (ii) When the retention time is t2 = 910 s, control the extraction rate of the precision injection pump so that the flow rate V3 of the third feed stream linearly increases from 0 mL / min to 10 mL / min until the elution ends, and collect the components in the fourth feed stream with a retention time within the range from the start of elution to t2 in the fraction collection bottle 11 to obtain target fraction 2; Concentrate target fraction 1 and target fraction 2 to obtain polyethylene S6 and S7 respectively. The weight - average molecular weight (Mw), number - average molecular weight (Mn), and molecular weight distribution PDI of the polyethylene, as well as the proportion of macromolecular and small molecular components in the polyethylene before fractionation, polyethylene S6, and polyethylene S7 are shown in Table 3.

[0108] Table 3

[0109] As can be seen from Table 3, through the fractionation method of the present invention, macromolecular components (such as polyethylene S6 concentrated from target fraction 1) or small molecular components (such as polyethylene S7 concentrated from target fraction 2) in polyethylene can be selectively filtered out.

[0110] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A polyethylene fractionation method, characterized in that, The method includes: S1. After transporting the polyethylene solution to a preparative liquid chromatography column for separation, a first split is performed to obtain a first stream and a second stream, where the flow rate of the first stream is V1 and the flow rate of the second stream is V2; S2. Test the first stream to obtain the retention time t; S3. Perform a second split on the second stream to obtain a third stream and a fourth stream, where the flow rate of the third stream is V3; When the retention time is t1, control V3 to decrease from V3 = V2 to 0 mL / min; when the retention time is t2, increase V3 to V3 = V2, and collect the components in the fourth stream with retention times in the range from t1 to t2, which are the target products; Or, when the retention time is t1, control V3 to increase from 0 mL / min to V3'; when the retention time is t2, decrease V3' to 0 mL / min, and collect the components in the fourth stream with retention times in the range from t1 to t2, which are the target products; Or, when the retention time is less than t1, control V3 = V2, and when the retention time is t1, decrease V3 to 0 mL / min within 30 s; collect the components in the fourth stream with retention times in the range from t1 to the end of elution, which are the target products; Or, when the retention time is less than t2, control V3 = 0 mL / min, and when the retention time is t2, increase V3 to V3 = V2 within 30 s; collect the components in the fourth stream with retention times in the range from the start of elution to t2, which are the target products; Wherein, 0 s < t1 < t2 ≤ t.

2. The hierarchical method according to claim 1, wherein, V2 / V1 is 10 - 50:1; And / or, the flow rate of the polyethylene solution transported to the preparative liquid chromatography column is V0, where V0 is greater than or equal to 5 mL / min.

3. The grading method according to claim 1 or 2, wherein The temperature of the preparative liquid chromatography column is greater than or equal to 25 °C; And / or, the inner diameter of the preparative liquid chromatography column is greater than or equal to 4 mm.

4. The grading method according to claim 1 or 2, wherein, The preparative liquid chromatography column is a gel permeation chromatography column in size exclusion mode with an inner diameter of 4.6 - 50 mm.

5. The hierarchical method according to claim 1 or 2, wherein When the retention time is t1, make V3 linearly decrease from V2 to 0 mL / min; when the retention time is t2, make V3 linearly increase to V2; Or, when the retention time is t1, control V3 to linearly increase from 0 mL / min to V3'; when the retention time is t2, make V3' linearly decrease to 0 mL / min; Or, when the retention time is less than t1, control V3 = V2, and when the retention time is t1, make V3 linearly decrease to 0 mL / min within 30 s; Or, when the retention time is less than t2, control V3 = 0 mL / min, and when the retention time is t2, make V3 linearly increase to V3 = V2 within 30 s.

6. The hierarchical method according to claim 1 or 2, wherein The retention time t is 300 - 3600 s.

7. The grading method according to claim 1 or 2, wherein The weight average molecular weight of polyethylene in the polyethylene solution is 50 - 500 kDa, and the molecular weight distribution PDI of polyethylene in the polyethylene solution is 5 - 15; And / or, the polyethylene in the polyethylene solution is selected from at least one of low density polyethylene, linear low density polyethylene, high density polyethylene, and ethylene copolymer; And / or, the concentration of the polyethylene solution is 0.1 - 5 wt%.

8. Polyethylene obtained by the fractionation method according to any one of claims 1 - 7; Among them, The polyethylene has a weight average molecular weight of 10 - 1000 kDa, and the molecular weight distribution PDI of the polyethylene is 1.2 - 20.

9. A system for polyethylene fractionation, characterized in that, The system includes: a sampler (4), a preparative liquid chromatography column (5), a first splitter (6), a detector (7), a second splitter (8), an injection pump (10), and a fraction collection bottle (11); Among them, the polyethylene solution from the feeding system is transported to the preparative liquid chromatography column (5) for separation, and then transported to the first splitter (6) for the first splitting to obtain a first stream and a second stream, where the flow rate of the first stream is V1 and the flow rate of the second stream is V2; The first stream is transported to the detector (7) for testing to obtain the retention time t; The second stream is transported to the second splitter (8) for the second splitting to obtain a third stream and a fourth stream, where the flow rate of the third stream is V3; When the retention time is t1, by adjusting the injection pump (10), V3 is reduced from V3 = V2 to 0 mL / min; when the retention time is t2, by adjusting the injection pump (10), V3 is increased to V3 = V2, and the components in the fourth stream with a retention time in the range of t1 to t2 are collected in the fraction collection bottle (11); Or, when the retention time is t1, by adjusting the injection pump (10), V3 is increased from 0 mL / min to V3'; when the retention time is t2, by adjusting the injection pump (10), V3' is reduced to 0 mL / min, and the components in the fourth stream with a retention time in the range of t1 to t2 are collected in the fraction collection bottle; Or, when the retention time is less than t1, by adjusting the injection pump (10), V3 = V2; when the retention time is t1, by adjusting the injection pump (10), V3 is reduced to 0 mL / min, and the components in the fourth stream with a retention time in the range of t1 to the end of elution are collected in the fraction collection bottle; Or, when the retention time is less than t2, by adjusting the injection pump (10), V3 = 0 mL / min; when the retention time is t2, by adjusting the injection pump (10), V3 is increased to V3 = V2, and the components in the fourth stream with a retention time in the range of the start of elution to t2 are collected in the fraction collection bottle; Among them, 0 s < t1 < t2 ≤ t.

10. The system according to claim 9, wherein, The system further includes a mobile phase storage tank (1) and a delivery pump (2); And / or, the system further includes a buffer tube (9), and the buffer tube (9) is connected between the second splitter (8) and the injection pump (10).

11. The system according to claim 10, wherein, The flow rate V0 of the delivery pump (2) is greater than or equal to 5 mL / min And / or, the pressure of the delivery pump (2) is greater than or equal to 5 MPa; And / or, the capacity of the buffer tube (9) is greater than or equal to 100 mL.

12. The system according to any one of claims 9-11, wherein, The system further includes a temperature control system (3), and the temperature control system (3) is used to control the temperatures of the sampler (4), the preparative liquid chromatography column (5), the first splitter (6), the second splitter (8), the buffer tube (9), and the fraction collector bottle (11).

13. The system according to any one of claims 9 - 11, wherein, The inner diameter of the preparative liquid chromatography column (5) is greater than or equal to 4 mm; and / or, the detector (7) is selected from at least one of an ultraviolet detector, a differential refractive index detector, a light scattering detector, and a viscosity detector.

14. Use of the system according to any one of claims 9-13 in polyethylene fractionation.

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