Polyethylene fractionation method, polyethylene obtained by the polyethylene fractionation method, system for polyethylene fractionation, and its applications

Abstract

The present invention relates to the field of polymer classification and discloses a polyethylene classification method, polyethylene obtained by the polyethylene classification method, a polyethylene classification system, and applications thereof. The polyethylene classification method, based on a preparative-grade high-temperature liquid chromatography column, employs two splits and controls the flow ratio of the second split, achieving precise and targeted classification of polyethylene raw materials and achieving precise and targeted control of the average molecular weight, molecular weight distribution curve, and branching structure of polyethylene, particularly low-density polyethylene.

Description

Technical Field

[0001] The present invention relates to the field of polymer classification, and in particular to a polyethylene classification method, polyethylene obtained by the polyethylene classification method, a system for polyethylene classification and applications thereof. Background Art

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

[0003] Existing methods for regulating the molecular structure of polyethylene can be roughly divided into two categories: direct preparation and fractional extraction. (1) Direct preparation methods usually require the use 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 cost (usually requiring the use of expensive catalysts), poor universality of the method (special polymerization systems usually limit the structures that can be obtained), and because its polymerization mechanism is not free radical polymerization, the molecular structure of the product is not completely consistent with LDPE. (2) Fractional extraction methods start from existing LDPE samples, separate the different molecular weight parts in LDPE, and selectively obtain one or some components, thereby achieving molecular structure regulation. In contrast, fractional extraction methods have greater practicality, flexibility and universality. The most representative technology in this regard is temperature-rising fractional elution (TREF), which can achieve the fractionation of different molecular weight components based on differences in crystallinity; however, to date, this type of technology still has problems such as low separation resolution and long time consumption. Summary of the Invention

[0004] The present invention aims to overcome the existing problems of difficulty in directing and regulating the molecular structure of polyethylene and obtaining polyethylene samples with a single structural variable. The present invention provides a polyethylene fractionation method, polyethylene produced by the polyethylene fractionation method, a polyethylene fractionation system, and applications thereof. This polyethylene fractionation method, based on a preparative-grade high-temperature liquid chromatography column, employs two splits and controls the flow ratio of the second split, achieving precise, directed fractionation of the polyethylene raw material and achieving precise, directed regulation of the average molecular weight, molecular weight distribution curve, and branching structure of polyethylene, particularly low-density polyethylene.

[0005] A first aspect of the present invention provides a polyethylene classification method, wherein the method comprises:

[0006] S1. Transferring the polyethylene solution to a preparative-grade liquid chromatography column for separation, and then performing 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;

[0007] S2. Testing the first material stream to obtain the retention time t;

[0008] S3, performing 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;

[0009] When the retention time is t1, V3 is controlled to decrease from V3=V2 to 0 mL / min; when the retention time is t2, V3 is increased to V3=V2, and the components with retention time in the range of t1 to t2 in the fourth stream are collected, i.e., the target product;

[0010] Alternatively, when the retention time is t1, V3 is controlled to increase from 0 mL / min to V3'; when the retention time is t2, V3' is reduced to 0 mL / min, and the component with a retention time between t1 and t2 in the fourth stream is collected, i.e., the target product;

[0011] Alternatively, when the retention time is less than t1, V3 is controlled to be equal to V2, and when the retention time is t1, V3 is reduced to 0 mL / min; the components in the fourth stream with a retention time between t1 and the end of elution are collected, i.e., the target product;

[0012] Alternatively, when the retention time is less than t2, V3 is controlled to 0 mL / min, and when the retention time is t2, V3 is increased to V3=V2; the components in the fourth stream whose retention time is within the range from the start of elution to t2 are collected, i.e., the target product;

[0013] Among them, 0s<t1<t2≤t.

[0014] In a second aspect, the present invention provides a polyethylene obtained by the above-mentioned classification method, wherein the weight average molecular weight of the polyethylene is 10-1000 kDa, and the molecular weight distribution PDI of the polyethylene is 1.2-20.

[0015] A third aspect of the present invention provides a system for polyethylene classification, wherein the system comprises:

[0016] Feeder 4, preparative liquid chromatography column 5, first splitter 6, detector 7, second splitter 8, syringe pump 10, fraction collection bottle 11;

[0017] The polyethylene solution from the feed system is transported to the preparative-grade liquid chromatography column 5 for separation, and then transported to the first splitter 6 for first splitting 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;

[0018] The first stream is transported to the detector 7 for testing to obtain the retention time t;

[0019] The second material flow is conveyed to the second splitter 8 for second splitting to obtain a third material flow and a fourth material flow, wherein the flow rate of the third material flow is V3;

[0020] When the retention time is t1, V3 is reduced from V3=V2 to 0 mL / min by adjusting the syringe pump 10; when the retention time is t2, V3 is increased to V3=V2 by adjusting the syringe pump 10, and the components with retention times between t1 and t2 in the fourth stream are collected in the fraction collecting bottle 11;

[0021] Alternatively, when the retention time is t1, V3 is increased from 0 mL / min to V3' by adjusting the syringe pump 10; when the retention time is t2, V3' is reduced to 0 mL / min by adjusting the syringe pump 10, and components in the fourth stream with a retention time between t1 and t2 are collected in a fraction collection bottle;

[0022] Alternatively, when the retention time is less than t1, the syringe pump 10 is adjusted so that V3=V2; when the retention time is t1, the syringe pump 10 is adjusted to reduce V3 to 0 mL / min, and the components with retention times between t1 and the end of elution in the fourth stream are collected in the fraction collection bottle;

[0023] Alternatively, when the retention time is less than t2, the syringe pump 10 is adjusted to make V3 = 0 mL / min; when the retention time is t2, the syringe pump 10 is adjusted to increase V3 to V3 = V2, and the components in the fourth stream with a retention time ranging from the start of elution to t2 are collected in the fraction collection bottle;

[0024] Among them, 0s<t1<t2≤t.

[0025] A fourth aspect of the present invention provides an application of the above system in polyethylene classification.

[0026] Through the above technical solution, the polyethylene classification method provided by the present invention, the polyethylene obtained by the polyethylene classification method, the system for polyethylene classification and the application thereof achieve the following beneficial effects:

[0027] The polyethylene fractionation method provided by the present invention is based on a preparative-grade high-temperature liquid chromatography column, adopts two splits and controls the flow ratio of the second split, thereby realizing precise directional fractionation of polyethylene raw materials and achieving the goal of precisely controlling the average molecular weight, molecular weight distribution curve, and branched structure of polyethylene, especially low-density polyethylene (LDPE). This method breaks through the limitations of the existing technology of the difficulty in controlling the molecular structure of polyethylene and the large number of molecular structure variables, and provides a new idea for the precise control of the molecular structure of polyethylene and the study of structure-macrostructure-activity relationship.

[0028] Furthermore, the polyethylene fractionation method provided by the present invention has the characteristics of high separation resolution and online continuous operation. It can continuously and accurately control the collection amount of each fraction and obtain samples with the required average molecular weight and molecular weight distribution curve online in a targeted manner, which is convenient and efficient.

[0029] Furthermore, the polyethylene classification method provided by the present invention has wide applicability. In addition to the polyethylene cable insulation material used in the present invention, it can be extended to the molecular design and performance optimization of other polymer materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the polyethylene classification method;

[0031] Figure 2 is a schematic diagram of a system used for polyethylene grading;

[0032] Figures 3(a) to 3(c) are schematic diagrams of directional fractionation of average molecular weight of polyethylene or narrowing of molecular weight distribution;

[0033] Figures 4(a) to 4(c) are schematic diagrams showing the broadening of the molecular weight distribution of polyethylene;

[0034] Figures 5(a) to 5(c) are schematic diagrams of selective removal of macromolecular components from polyethylene;

[0035] Figure 6 (a)-Figure 6 (c) are schematic diagrams of the selective removal of small molecular components in polyethylene.

[0036] Description of Reference Numerals

[0037] 1-Mobile phase storage tank; 2-Transfer 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 DESCRIPTION

[0038] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0039] A first aspect of the present invention provides a method for polyethylene classification, wherein the method comprises:

[0040] S1. Transferring the polyethylene solution to a preparative-grade liquid chromatography column for separation, and then performing 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;

[0041] S2. Testing the first material stream to obtain a retention time t;

[0042] S3, performing 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;

[0043] When the retention time is t1, V3 is controlled to decrease from V3=V2 to 0 mL / min; when the retention time is t2, V3 is increased to V3=V2, and the components with retention time in the range of t1 to t2 in the fourth stream are collected, i.e., the target product;

[0044] Alternatively, when the retention time is t1, V3 is controlled to increase from 0 mL / min to V3'; when the retention time is t2, V3' is reduced to 0 mL / min, and the component with a retention time between t1 and t2 in the fourth stream is collected, i.e., the target product;

[0045] Alternatively, when the retention time is less than t1, V3 is controlled to be equal to V2, and when the retention time is t1, V3 is reduced to 0 mL / min; the components in the fourth stream with a retention time between t1 and the end of elution are collected, i.e., the target product;

[0046] Alternatively, when the retention time is less than t2, V3 is controlled to 0 mL / min, and when the retention time is t2, V3 is increased to V3=V2; the components in the fourth stream whose retention time is within the range from the start of elution to t1 are collected, i.e., the target product;

[0047] Among them, 0s<t1<t2≤t.

[0048] The polyethylene fractionation method provided by the present invention is based on a preparative-grade high-temperature liquid chromatography column, adopts two splits and controls the flow ratio of the second split, thereby realizing precise directional fractionation of polyethylene raw materials and achieving the goal of precisely controlling the average molecular weight, molecular weight distribution curve, and branched structure of polyethylene, especially low-density polyethylene (LDPE). This method breaks through the limitations of the existing technology of the difficulty in controlling the molecular structure of polyethylene and the large number of molecular structure variables, and provides a new idea for the precise control of the molecular structure of polyethylene and the study of structure-macrostructure-activity relationship.

[0049] Furthermore, the polyethylene fractionation method provided by the present invention has the characteristics of high separation resolution and online continuous operation. It can continuously and accurately control the collection amount of each fraction and obtain samples with the required average molecular weight and molecular weight distribution curve online, which is convenient and efficient.

[0050] Furthermore, the polyethylene classification method provided by the present invention has wide applicability. In addition to the polyethylene cable insulation material used in the present invention, it can be extended to the molecular design and performance optimization of other polymer materials.

[0051] In the present invention, the retention time t refers to the time it takes for the target component after polyethylene fractionation to flow through the liquid chromatography column and finally reach the detector.

[0052] In the present invention, by testing the first material stream, the content of each component obtained after separation by a preparative-grade liquid chromatography column, as well as molecular structural information of polyethylene such as average molecular weight, molecular weight distribution curve or branching structure can be obtained.

[0053] In the present invention, retention time t1 refers to the start time of collecting the fourth stream component, retention time t2 is the end time of stopping collecting the fourth stream component, and retention time t2 refers to any specific retention time within the range of retention time t.

[0054] In the present invention, the start time for starting to collect the fourth material flow component and the start time for stopping to collect the fourth material flow component can be selected according to actual needs, as long as the start time for stopping to collect the fourth material flow component is greater than the start time for starting to collect the fourth material flow component.

[0055] In the present invention, multiple t1 and t2 can be selected as needed, for example, t 1j and t 2k , wherein j and k are integers greater than or equal to 1, representing different starting times for starting to collect the fourth material stream component and ending times for starting to collect the fourth material stream component, respectively.

[0056] In the present invention, the flow rate of the fourth stream is V4.

[0057] In one embodiment of the present invention, when retention time is t1, V3 is controlled to decrease from V3=V2 to 0 mL / min; when retention time is t2, V3 is increased to V3=V2, and the components in the fourth stream with retention times between t1 and t2 are collected, i.e., the target product. This embodiment can not only produce the target product with a narrowed molecular weight distribution, but also produce polyethylene with a specific weight-average molecular weight or number-average molecular weight.

[0058] In one embodiment of the present invention, when retention time is t1, V3 is controlled to increase from 0 mL / min to V3'; when retention time is t2, V3' is reduced to 0 mL / min, and the components in the fourth stream with retention times between t1 and t2 are collected, i.e., the target product. This embodiment can produce a target product with a broadened molecular weight distribution.

[0059] In one embodiment of the present invention, when the retention time is less than t1, V3 is controlled to equal V2. When the retention time is t1, V3 is reduced to 0 mL / min. Components in the fourth stream with a retention time between t1 and the end of elution are collected as the target product. This embodiment can selectively remove high molecular weight components from polyethylene.

[0060] In the present invention, there is no particular requirement for the time required to reduce V3 to 0 mL / min at the retention time t1, as long as V3 begins to decrease at the retention time t1, preferably V3 is reduced from V2 to 0 mL / min within 30 s. For example, V3 can be reduced from V2 to 0 mL / min 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, or 30 s.

[0061] In one embodiment of the present invention, when the retention time is less than t2, V3 is controlled to 0 mL / min. When the retention time is t2, V3 is increased to V3 = V2. Components in the fourth stream whose retention time falls within the elution start time range t2 are collected as the target product. This embodiment can selectively remove low molecular weight components from polyethylene.

[0062] In the present invention, there is no particular requirement for the time required to increase V3 to V3=V2 when the retention time is t2. As long as V3 begins to increase when the retention time is t2, it is preferred that V3 be increased from 0 mL / min to V2 within 30 s. For example, V3 can be increased from 0 mL / min to V2 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, or 30 s.

[0063] According to the present invention, V2 / V1 is 10-50:1.

[0064] In the present invention, when V2 / V1 is controlled to meet the above range, polyethylene fractions with appropriate flow rates can be tested, and the retention time t can be obtained without affecting the recovery yield and ensuring the test accuracy of the detector.

[0065] According to the present invention, the flow rate of the polyethylene solution delivered to the preparative-grade liquid chromatography column is V0, wherein V0 is greater than or equal to 5 mL / min.

[0066] In the present invention, when the flow rate of the polyethylene solution delivered to the preparative-grade liquid chromatography column is controlled to meet the above range, the optimal working flow rate range can be provided for the preparative-grade liquid chromatography column, thereby achieving efficient fractionation of the polyethylene components.

[0067] Furthermore, V0 is 5-50 mL / min.

[0068] In the present invention, the flow rate of the polyethylene solution in the preparative liquid chromatography column does not suffer loss, 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 transported to the preparative liquid chromatography column.

[0069] According to the present invention, the temperature of the preparative-grade liquid chromatography column is greater than or equal to 25°C.

[0070] In the present invention, when the temperature of the polyethylene solution is controlled to meet the above range, it can ensure that the polyethylene segments are fully dissolved in the mobile phase of the preparative-grade liquid chromatography column, and ensure that each component in the polyethylene is fully separated.

[0071] Furthermore, the temperature of the preparative-grade liquid chromatography column is 80-220°C.

[0072] According to the present invention, the inner diameter of the preparative-grade liquid chromatography column is greater than or equal to 4 mm.

[0073] In the present invention, the use of a preparative-grade liquid chromatography column with an inner diameter greater than or equal to 4 mm can ensure sufficient sample capacity and provide sufficient injection volume and concentration for the polyethylene solution.

[0074] Furthermore, the preparative-grade liquid chromatography column is a size exclusion mode gel permeation chromatography (GPC) column with an inner diameter of 4.6-50 mm.

[0075] In the present invention, the size exclusion mode gel permeation chromatography (GPC) column is selected to efficiently fractionate the polyethylene components based on the differences in molecular weight.

[0076] 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.

[0077] In the present invention, there is no particular limitation on the specific rate of linear decrease or linear increase of V3, as long as V3 can be reduced from V2 to 0 mL / min and then increased from 0 mL / min to V2 within the retention time range of t1 to t2.

[0078] In another preferred embodiment of the present invention, when the retention time is t1, V3 is controlled to increase linearly from 0 mL / min to V3'; when the retention time is t2, V3' is controlled to decrease linearly to 0 mL / min.

[0079] In the present invention, there is no particular limitation on the specific rate of linear increase of V3 or linear decrease of V3', as long as the change process of V3 increasing from 0 mL / min to V3' and then decreasing from V3' to 0 mL / min can be achieved within the retention time range of t1 to t2.

[0080] In another preferred embodiment of the present invention, when the retention time is less than t1, V3 is controlled to be equal to V2, and when the retention time is t1, V3 is linearly reduced to 0 mL / min within 30 s.

[0081] In the present invention, there is no particular limitation on the rate at which V3 is linearly reduced to 0 mL / min, as long as V3 is reduced from V2 to 0 mL / min within 30 s.

[0082] In another preferred embodiment of the present invention, when the retention time is less than t2, V3 is controlled to be 0 mL / min, and when the retention time is t2, V3 is linearly increased to V3=V2 within 30 s.

[0083] In the present invention, there is no particular limitation on the rate at which V3 is linearly increased to V2, as long as V3 is increased from 0 mL / min to V2 within 30 s.

[0084] In the present invention, by adjusting V3 at different retention times, the collection amount of the fraction collection end, that is, the components within a specific retention time range in the fourth stream, can be dynamically controlled, thereby accurately controlling the average molecular weight, molecular weight distribution curve, branched structure and other characteristics of the polyethylene component in the target product as needed.

[0085] In the present invention, the classification method can be applied to different types of polyethylene and can be adapted to different instruments and equipment and different test conditions. The retention time t can vary within a large range, for example, the retention time t is 300-3600s, preferably 600-1200s.

[0086] In the present invention, the classification method can be applied to polyethylenes with various weight average molecular weights and molecular weight distributions. For example, the weight average molecular weight of the polyethylene in the polyethylene solution is 50-500 kDa, and the molecular weight distribution PDI of the polyethylene in the polyethylene solution is 5-15.

[0087] According to the present invention, the polyethylene in the polyethylene solution is at least one selected from low-density polyethylene, linear low-density polyethylene, high-density polyethylene and ethylene copolymers.

[0088] In the present invention, the ethylene copolymer is a conventional ethylene copolymer in the art, including but not limited to a copolymer of ethylene and α-olefin.

[0089] In the present invention, the polyethylene can be prepared by conventional processes in the art, for example, by free radical polymerization.

[0090] According to the present invention, the concentration of the polyethylene solution is 0.1-5 wt %.

[0091] In the present invention, when the concentration of the polyethylene solution is controlled to meet the above range, a larger preparation amount can be achieved on the basis of ensuring a good classification effect.

[0092] In the present invention, there is no particular limitation on the solvent in the polyethylene solution, and conventional organic solvents in the art, such as trichlorobenzene, can be used.

[0093] In the present invention, the classification method further comprises: 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.

[0094] In the present invention, the classification method further comprises concentrating the collected target product to obtain polyethylene.

[0095] In the present invention, there is no particular limitation on the concentration method, and conventional concentration methods in the art, such as rotary evaporation, freeze drying, etc., can be used.

[0096] In a specific embodiment of the present invention, as shown in Figure 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 Figure 3(b), the flow rate V4 of the fourth material stream linearly increases from 0 mL / min to V2 when the retention time is t1, and linearly recovers to 0 mL / min when the retention time is t2. The components in the fourth material stream with a retention time in the range of t1 to t2, i.e., the target product, are collected. As can be seen from Figure 3(c), the molecular weight distribution of the target product is narrower than that of the polyethylene raw material.

[0097] In another specific embodiment of the present invention, as shown in Figure 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 Figure 4 (b), the flow rate V4 of the fourth material stream begins to linearly decrease from V2 to V2-V3' when the retention time is t1, and when the retention time is t2, V4 linearly recovers to V2, and the components in the fourth material stream with a retention time in the range of t1 to t2, i.e., the target product, are collected. As can be seen from Figure 4 (c), the molecular weight distribution of the target product is wider than that of the polyethylene raw material.

[0098] In another specific embodiment of the present invention, as shown in Figure 5 (a), when the retention time is less than t1, V3=V2, and when the retention time is t1, V3 decreases from V2 to 0 mL / min; correspondingly, as shown in Figure 5 (b), the flow rate V4 of the fourth material stream is V4=0 mL / min when the retention time is less than t1, and increases to V2 when the retention time is t1. The components in the fourth material stream with a retention time in the range from t1 to the end of elution are collected, that is, the target product. It can be seen from Figure 5 (c) that compared with the polyethylene raw material, the content of macromolecular components in the target product is reduced.

[0099] In another specific embodiment of the present invention, as shown in Figure 6 (a), when the retention time is less than t2, V3=0 mL / min, and when the retention time is t2, V3 is increased to V3=V2. Correspondingly, as shown in Figure 6 (b), when the retention time is less than t2, the flow rate of the fourth material stream is V4=V2, and when the retention time is t2, V4 is reduced to 0 mL / min, and the components in the fourth material stream with a retention time between the start of elution and t2 are collected, i.e., the target product. It can be seen from Figure 6 (c) that compared with the polyethylene raw material, the content of small molecular components in the target product is reduced.

[0100] A second aspect of the present invention provides a polyethylene obtained by the above-mentioned classification method.

[0101] In the present invention, by adopting the above-mentioned classification method, polyethylene with different weight average molecular weight and / or molecular weight distribution can be obtained in a directional manner 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 molecular weight distribution PDI of the polyethylene is 1.2-20.

[0102] In a preferred embodiment of the present invention, the polyethylene is polyethylene for DC cables.

[0103] A third aspect of the present invention provides a system for polyethylene classification, wherein the system comprises:

[0104] Injector 4, preparative liquid chromatography column 5, first splitter 6, detector 7, second splitter 8, syringe pump 10, fraction collection bottle 11;

[0105] The polyethylene solution from the feed system is transported to the preparative-grade liquid chromatography column 5 for separation, and then transported to the first splitter 6 for first splitting 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;

[0106] The first stream is transported to the detector 7 for testing to obtain the retention time t;

[0107] The second material flow is conveyed to the second splitter 8 for second splitting to obtain a third material flow and a fourth material flow, wherein the flow rate of the third material flow is V3 and the flow rate of the fourth material flow is V4;

[0108] When the retention time is t1, V3 is reduced from V3=V2 to 0 mL / min by adjusting the syringe pump 10; when the retention time is t2, V3 is increased so that V3=V2 by adjusting the syringe pump 10, and the components with retention times between t1 and t2 in the fourth stream are collected in the fraction collecting bottle 11;

[0109] Alternatively, when the retention time is t1, V3 is increased from 0 mL / min to V3' by adjusting the syringe pump 10; when the retention time is t2, V3' is reduced to 0 mL / min by adjusting the syringe pump 10, and components in the fourth stream with a retention time between t1 and t2 are collected in a fraction collection bottle;

[0110] Alternatively, when the retention time is less than t1, the syringe pump 10 is adjusted so that V3=V2; when the retention time is t1, the syringe pump 10 is adjusted to reduce V3 to 0 mL / min, and the components with retention times between t1 and the end of elution in the fourth stream are collected in the fraction collection bottle;

[0111] Alternatively, when the retention time is less than t2, the syringe pump 10 is adjusted to make V3 = 0 mL / min; when the retention time is t2, the syringe pump 10 is adjusted to increase V3 to V3 = V2, and the components in the fourth stream with a retention time ranging from the start of elution to t2 are collected in the fraction collection bottle;

[0112] Among them, 0s<t1<t2≤t.

[0113] The polyethylene system provided by the present invention is based on a preparative-grade high-temperature liquid chromatography column, utilizes a first splitter and a second splitter, and accurately controls the flow rate of the third material stream through an injection pump 10, thereby realizing online continuous directional classification of polyethylene, especially low-density polyethylene, and can continuously and accurately control the collection amount of each fraction, and obtain samples with the required average molecular weight and molecular weight distribution curve online, which is convenient and efficient.

[0114] In the present invention, the injector 4 is used to pass the polyethylene solution into the preparative-grade liquid chromatography column 5 .

[0115] In the present invention, preferably, the injection pump 10 is a precision injection pump, which is used to accurately control the flow rate V3 of the third material flow to achieve directional classification of polyethylene.

[0116] In the present invention, the injection needle and / or syringe of the injection pump is 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 achieve dynamic regulation of the flow rate V3 of the third material flow.

[0117] According to the present invention, the system further comprises a mobile phase storage tank 1 and a delivery pump 2 .

[0118] In the present invention, the mobile phase storage tank 1 is used to store the mobile phase for elution and fractionation of a preparative-grade liquid chromatography column. For example, the mobile phase is trichlorobenzene.

[0119] 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-grade liquid chromatography column 5 .

[0120] According to the present invention, the flow rate V0 of the delivery pump 2 is greater than or equal to 5 mL / min.

[0121] In the present invention, when the flow rate of the delivery pump 2 is controlled to meet the above range, an optimal working flow rate range can be provided for the preparative-grade liquid chromatography column, thereby achieving efficient fractionation of the various components of polyethylene.

[0122] Furthermore, the flow rate V0 of the delivery pump 2 is 5-50 mL / min;

[0123] According to the present invention, the pressure of the delivery pump 2 is greater than or equal to 5 MPa.

[0124] In the present invention, when the pressure of the delivery pump 2 is controlled to meet the above range, a sufficient delivery pump working flow rate can be provided (ie, the requirement of V0 being greater than or equal to 5 mL / min is met).

[0125] Furthermore, the pressure of the delivery pump 2 is 5-40 MPa.

[0126] According to the present invention, the system further comprises a buffer tube 9 , which is connected between the second flow divider 8 and the injection pump 10 .

[0127] In the present invention, the buffer tube 9 is used to temporarily store components other than the target components in the second material flow to prevent them from entering a low-temperature environment and precipitating.

[0128] According to the present invention, the capacity of the buffer tube 9 is greater than or equal to 100 mL.

[0129] 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.

[0130] According to the present invention, the system further comprises a temperature control system 3 for controlling the temperature of the sample injector 4, the preparative liquid chromatography column 5, the first splitter 6, the second splitter 8, the buffer tube 9 and the fraction collecting bottle 11.

[0131] In the present invention, the temperature control system 3 makes the temperature of the sample 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 greater than or equal to 25°C, preferably 80-220°C.

[0132] According to the present invention, the inner diameter of the preparative-grade liquid chromatography column is greater than or equal to 4 mm, and preferably is a size exclusion mode gel permeation chromatography column with an inner diameter of 4.6-50 mm.

[0133] 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.

[0134] A fourth aspect of the present invention provides an application of the above system in polyethylene classification.

[0135] like Figure 1 As shown, the classification method of the present invention includes:

[0136] Pre-treating the low-density polyethylene raw material, specifically, dissolving the polyethylene in an organic solvent under high temperature conditions to obtain a polyethylene solution;

[0137] The polyethylene solution is transported to a preparative-grade liquid chromatography column for separation, and then subjected to a first splitter for first splitting to obtain a first material stream and a second material stream;

[0138] Performing molecular structure determination on the first material stream to obtain a retention time t;

[0139] The second stream is split through a second splitter to obtain a third stream and a fourth stream;

[0140] By performing online flow control on the third material stream, the fraction in the fourth material stream is selectively collected, and the collected fraction is concentrated to obtain the target polyethylene.

[0141] 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 conventional high temperature GPC method equipped with a differential refractive index detector; the polyethylene raw material used was commercially available low-density polyethylene granular resin.

[0142] Example 1 - Polyethylene average molecular weight directional classification

[0143] 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. The solution is stored in polyethylene solution storage tank 1 and then transferred to a preparative liquid chromatography column 5 via a transfer pump 2 and an injector 4. The preparative liquid chromatography column is a high-temperature gel permeation chromatography (GPC) column in size exclusion mode with an inner diameter of 7.5 mm. The transfer pump has a flow rate V0 of 10.5 mL / min and a pressure of 15 MPa. The components separated by the preparative liquid chromatography column are transferred to a first splitter 6 for a first split, resulting in a first stream and a second stream. 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.

[0144] S2. The first material stream is transported to the detector 7, and the retention time t is obtained to be 720-1080s.

[0145] 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, wherein the flow rate of the third material flow is V3, and the precise control of V3 is achieved by controlling the extraction rate of the precision syringe pump, specifically:

[0146] (i) When the retention time is t 11 =750s, the extraction rate of the precision syringe pump is controlled so that the flow rate V3 of the third stream decreases linearly from 10mL / min to 0mL / min. When the retention time is t 21=750+90s, control the extraction rate of the precision syringe pump so that the flow rate V3 of the third stream is linearly increased from 0 mL / min to 10 mL / min, and collect the fourth stream in the fraction collection bottle 11 with a retention time of t 11 to t 21 The components within the range are obtained to obtain target fraction 1;

[0147] (ii) When the retention time is t 12 =840s, the extraction rate of the precision syringe pump is controlled so that the flow rate V3 of the third stream decreases linearly from 10mL / min to 0mL / min. When the retention time is t 22 =840+90s, the extraction rate of the precision syringe pump was controlled so that the flow rate V3 of the third stream was linearly increased from 0 mL / min to 10 mL / min, and the fractions of the fourth stream with a retention time of t 12 to t 22 The components within the range are obtained to obtain target fraction 2;

[0148] (iii) When the retention time is t 13 =930s, the extraction rate of the precision syringe pump is controlled so that the flow rate V3 of the third stream decreases linearly from 10mL / min to 0mL / min. When the retention time is t 23 =930+90s, the extraction rate of the precision syringe pump was controlled so that the flow rate V3 of the third stream was linearly increased from 0 mL / min to 10 mL / min, and the fractions of the fourth stream with a retention time of t 13 to t 23 The components within the range are obtained to obtain target fraction 3;

[0149] The temperature of the sample injector 4, the preparative liquid chromatography column 5, the first splitter 6, the second splitter 8, the buffer tube 9 and the fraction collecting bottle 11 is controlled to be 150°C by the temperature control system 3.

[0150] Target fraction 1, target fraction 2, and target fraction 3 were concentrated to obtain polyethylene S1, polyethylene S2, and polyethylene S3, respectively. The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (PDI) of polyethylenes S1-S3 are shown in Table 1.

[0151] Table 1

[0152]

[0153] As can be seen from Table 1, polyethylenes having different weight average molecular weights (Mw) and number average molecular weights (Mn) but similar molecular weight distributions (PDI) can be obtained by the fractionation method of the present invention.

[0154] Example 2 - Polyethylene Molecular Weight Distribution Control

[0155] S1. Proceed as in step S1 of Example 1, except that: LDPE has Mw = 167810 Da, Mn = 16208 Da, and PDI = 10.35.

[0156] S2. The first material stream is transported to the detector 7, and the retention time t obtained is 690-1020s.

[0157] 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, wherein the flow rate of the third material flow is V3, and the precise control of V3 is achieved by controlling the extraction rate of the precision syringe pump, specifically:

[0158] (i) When the retention time is t 11 =730s, the extraction rate of the precision injection pump is controlled so that the flow rate V3 of the third stream decreases exponentially from 10mL / min to 0mL / min. When the retention time is t 21 =730+100s, the extraction rate of the precision syringe pump is controlled so that the flow rate V3 of the third stream increases exponentially from 0 mL / min to 10 mL / min, and the fractions of the fourth stream with a retention time of t 11 to t 21 The components within the range are obtained to obtain target fraction 1;

[0159] (ii) When the retention time is t 12 =690s, the extraction rate of the precision injection pump is controlled so that the flow rate V3 of the third stream increases exponentially from 0mL / min to 5mL / min. When the retention time is t 22 =1020s, the extraction rate of the precision syringe pump is controlled so that the flow rate V3 of the third stream is restored from 5 mL / min to 0 mL / min in an exponential manner, and the fractions of the fourth stream with a retention time of t 12 to t 22 The components within the range are obtained to obtain target fraction 2;

[0160] Target fraction 1 and target fraction 2 were concentrated to obtain polyethylene S4 and polyethylene S5, respectively. The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (PDI) of the polyethylene are shown in Table 2.

[0161] Table 2

[0162]

[0163] As can be seen from Table 2, the fractionation method of the present invention can produce polyethylene components with narrower molecular weight distribution (such as polyethylene S4 obtained by concentrating target fraction 1) and wider molecular weight distribution (such as polyethylene S5 obtained by concentrating target fraction 2).

[0164] Example 3 - Selective filtration of macromolecular or small molecular components

[0165] S1. Proceed according to step S1 of Example 2.

[0166] S2. The first material stream is transported to the detector 7, and the retention time t obtained is 690-1020s.

[0167] 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, wherein the flow rate of the third material flow is V3, and the precise control of V3 is achieved by controlling the extraction rate of the precision syringe pump, specifically:

[0168] (i) When the retention time is t1 = 750 s, the extraction rate of the precision syringe pump is controlled so that the flow rate V3 of the third stream is linearly reduced from 10 mL / min to 0 mL / min within 30 s until the elution is completed, and the components of the fourth stream with a retention time between t1 and the end of elution are collected in a fraction collection flask 11 to obtain target fraction 1;

[0169] (ii) When the retention time is t2 = 910 s, the extraction rate of the precision syringe pump is controlled so that the flow rate V3 of the third stream is linearly increased from 0 mL / min to 10 mL / min until the elution is completed, and the components of the fourth stream with retention times between the start of elution and t2 are collected in the fraction collection flask 11 to obtain the target fraction 2;

[0170] Target fractions 1 and 2 were concentrated to yield polyethylenes S6 and S7, respectively. The weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (PDI) of the polyethylenes, as well as the proportions of macromolecular and micromolecular components in polyethylenes before fractionation, polyethylenes S6, and polyethylenes S7, are shown in Table 3.

[0171] Table 3

[0172]

[0173] As can be seen from Table 3, the fractionation method of the present invention can selectively filter out high molecular weight components (such as polyethylene S6 obtained by concentrating target fraction 1) or low molecular weight components (such as polyethylene S7 obtained by concentrating target fraction 2) in polyethylene.

[0174] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A polyethylene classification method, characterized in that: The method comprises: S1. Transferring the polyethylene solution to a preparative-grade liquid chromatography column for separation, and then performing 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. Testing the first material stream to obtain a retention time t; S3, performing 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, V3 is controlled to decrease from V3=V2 to 0 mL / min; when the retention time is t2, V3 is increased to V3=V2, and the components with retention time in the range of t1 to t2 in the fourth stream are collected, i.e., the target product; Alternatively, when the retention time is t1, V3 is controlled to increase from 0 mL / min to V3'; when the retention time is t2, V3' is reduced to 0 mL / min, and the component with a retention time between t1 and t2 in the fourth stream is collected, i.e., the target product; Alternatively, when the retention time is less than t1, V3 is controlled to be equal to V2, and when the retention time is t1, V3 is reduced to 0 mL / min; the components in the fourth stream with a retention time between t1 and the end of elution are collected, i.e., the target product; Alternatively, when the retention time is less than t2, V3 is controlled to 0 mL / min, and when the retention time is t2, V3 is increased to V3=V2; the components in the fourth stream whose retention time is within the range from the start of elution to t2 are collected, i.e., the target product; Wherein, retention time t1 refers to the start time of collecting the fourth material stream component, retention time t2 is the end time of stopping collecting the fourth material stream component, and retention time t2 refers to any specific retention time within the range of retention time t.

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

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

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

5. The classification method according to claim 1 or 2, wherein: When the retention time is t1, V3 is linearly reduced from V2 to 0 mL / min; when the retention time is t2, V3 is linearly increased to V2; Alternatively, when the retention time is t1, V3 is controlled to increase linearly from 0 mL / min to V3'; when the retention time is t2, V3' is controlled to decrease linearly to 0 mL / min; Alternatively, when the retention time is less than t1, V3 is controlled to be equal to V2, and when the retention time is t1, V3 is linearly reduced to 0 mL / min within 30 s; Alternatively, when the retention time is less than t2, V3 is controlled to be 0 mL / min, and when the retention time is t2, V3 is linearly increased to V3=V2 within 30 s.

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

7. The classification method according to claim 1 or 2, wherein: The weight average molecular weight of the polyethylene in the polyethylene solution is 50-500 kDa, and the molecular weight distribution PDI of the 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 copolymers; And / or, the concentration of the polyethylene solution is 0.1-5wt%.

8. A system for polyethylene classification, characterized in that The system comprises: an injector (4), a preparative-grade liquid chromatography column (5), a first splitter (6), a detector (7), a second splitter (8), a syringe pump (10), and a fraction collection bottle (11); The polyethylene solution from the feed system is transported to a preparative-grade liquid chromatography column (5) for separation, and then transported to a first splitter (6) for first splitting 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 a detector (7) for testing to obtain a retention time t; The second material flow is transported to a second splitter (8) for second splitting to obtain a third material flow and a fourth material flow, wherein the flow rate of the third material flow is V3; When the retention time is t1, the syringe pump (10) is adjusted so that V3 is reduced from V3=V2 to 0 mL / min; when the retention time is t2, the syringe pump (10) is adjusted so that V3 is increased to V3=V2, and the components with retention times between t1 and t2 in the fourth stream are collected in the fraction collection bottle (11); Alternatively, when the retention time is t1, V3 is increased from 0 mL / min to V3' by adjusting the syringe pump (10); when the retention time is t2, V3' is reduced to 0 mL / min by adjusting the syringe pump (10), and components with retention times ranging from t1 to t2 in the fourth stream are collected in a fraction collection bottle; Alternatively, when the retention time is less than t1, the syringe pump (10) is adjusted so that V3=V2; when the retention time is t1, the syringe pump (10) is adjusted to reduce V3 to 0 mL / min, and the components with retention times ranging from t1 to the end of elution in the fourth stream are collected in the fraction collection bottle; Alternatively, when the retention time is less than t2, the syringe pump (10) is adjusted so that V3 = 0 mL / min; when the retention time is t2, the syringe pump (10) is adjusted to increase V3 to V3 = V2, and components in the fourth stream having a retention time ranging from the start of elution to t2 are collected in a fraction collection bottle; Wherein, retention time t1 refers to the start time of collecting the fourth material stream component, retention time t2 is the end time of stopping collecting the fourth material stream component, and retention time t2 refers to any specific retention time within the range of retention time t.

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

10. The system according to claim 9, 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.

11. The system according to any one of claims 8 to 10, wherein: The system further comprises a temperature control system (3), wherein the temperature control system (3) is used to control the temperature of the sample 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).

12. The system according to any one of claims 8 to 10, wherein: The inner diameter of the preparative-grade 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.

13. Use of the system according to any one of claims 8 to 12 in polyethylene classification.

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