A method for producing polyethylene resin for geomembranes

Abstract

This invention relates to the field of polymer technology and discloses a method for producing polyethylene resin for geomembranes. A dual-loop reactor is used, with ethylene as the raw material, 1-hexene as the comonomer, isobutane as the diluent, and an aluminum-modified supported chromium catalyst for catalysis; the chromium catalyst has a specific surface area of ​​280–330 m². 2 / g, pore volume of 2.3-2.8mL / g, chromium content of 2-4wt%, aluminum content of 1-5wt%; slurry density of the first reactor is 510-520kg / m³ 3 The slurry density in the second reactor is 530-540 kg / m³. 3 The ethylene concentration in the first reactor is 3.5-4.5 mol%, and the ethylene concentration in the second reactor is controlled at 6-6.5 mol%. The temperature in the first reactor is controlled at 94-96℃, and the temperature in the second reactor is controlled at 93-95℃. The pressure in the first reactor is controlled at 3.7-3.9 MPa, and the pressure in the second reactor is controlled at 3.9-4.1 MPa. The residence time in the first reactor is 70-90 min, and the residence time in the second reactor is 40-50 min. The polyethylene resin used in the geomembrane has low density and soft material, which is beneficial for downstream construction and has good processing performance.

Description

Technical Field

[0001] This invention relates to the field of polymer technology, specifically disclosing a method for producing polyethylene resin for geomembranes. Background Technology

[0002] In recent years, with the rapid development of my country's plastics industry and the country's emphasis on environmental protection and water conservancy construction, plastic films have been increasingly used in landfills, sewage treatment ponds, and other fields. The key to these applications lies in the lining system, which must withstand the long-term corrosion of most types of waste, chemical extracts, and various hazardous wastes. Therefore, it must possess properties such as acid resistance, corrosion resistance, and aging resistance to prevent the penetration of various pollutants into the soil and groundwater. High-density polyethylene (HDPE) is an engineering plastic that can meet these requirements, thus its market prospects are very broad.

[0003] With the rapid development of my country's plastics industry and the country's emphasis on environmental protection and water conservancy construction, geomembranes are increasingly being used in landfills, sewage treatment plants, and other fields, mainly including the following aspects:

[0004] Firstly, there are applications in the environmental protection and sanitation industries, such as municipal solid waste landfills, sewage treatment plants, power plant regulating ponds, and solid waste treatment in mining and hospitals. The key to these applications lies in the lining system, which must withstand long-term corrosion from most types of waste, chemical extracts, and various hazardous wastes. Therefore, it must possess properties such as acid resistance, corrosion resistance, and aging resistance to prevent the penetration of various pollutants into the soil and groundwater and to avoid mineral loss. HDPE geomembranes are commonly used in these applications. HDPE geomembranes have good tensile strength, excellent impact resistance, tear resistance, and puncture resistance. Their disadvantages include a relatively hard texture and difficult construction. They are suitable for applications requiring excellent chemical resistance, such as large-area landfills and chemical plant linings.

[0005] Secondly, it's used in the transportation engineering industry, such as railway subgrades and various highway tunnels. In railway subgrades, it primarily serves to reinforce, isolate, and enclose the subgrade. It can be used for both new railway subgrades and railway maintenance, acting as an isolation barrier to prevent mudslides and to prevent expansive soil from absorbing water, swelling, shrinking, and cracking. Currently, the most commonly used structure in modern railway and highway tunnels is concrete / waterproof membrane / concrete structure, with tunnels employing this type of structure. In these applications, the geomembrane must possess excellent puncture resistance, animal bite resistance, and microbial resistance to ensure the tunnel remains dry, reduce maintenance costs, and extend its service life. Therefore, low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) composite geomembranes are generally used. These geomembranes have higher mechanical strength, are more elastic than HDPE geomembranes, and have better flexibility and weldability, making construction easier. The disadvantage is that their chemical resistance is lower than that of HDPE.

[0006] Thirdly, geomembranes are used as liquid lining systems, such as in artificial lakes, reservoir dams, aquaculture, and irrigation canals. A major application of geomembranes is fluid control; as linings for ponds, they prevent pollutants from entering groundwater or rivers. Furthermore, because geomembranes prevent seepage losses, their application saves tens of thousands of tons of water annually. These applications require geomembranes with excellent impermeability and good construction performance, often using composite geomembranes of HDPE and LLDPE.

[0007] Among the aforementioned materials, HDPE has the disadvantage of generally high density, resulting in relatively stiff geomembranes that pose significant difficulties during on-site construction. Therefore, medium- and low-density HDPE products are ideal raw materials for geomembranes. Currently, the industrial development of HDPE-specific materials in China mainly focuses on two aspects: polymerization process innovation and catalyst innovation. Significant breakthroughs in domestic HDPE polymerization processes are difficult to achieve, while catalyst innovation faces a contradiction between research and development risks and the stability of equipment operation.

[0008] Patent CN104744796 discloses a blown geomembrane material with high hexene grafting and high density polyethylene, but the NTR-975 chromium catalyst used in this patent is a traditional chromium catalyst.

[0009] Patent CN103788446B discloses a polyethylene resin composition and its preparation method for use as a special material for geomembranes. It employs a blend of linear low-density polyethylene (LDPE) and high-density polyethylene (HDPE), with LDPE comprising 10–50 wt% and HDPE comprising 50–90 wt%. It also includes a blend of antioxidants at 1–5 wt% of the HDPE weight. However, this method, which involves blending and then adding additives, is complex, cumbersome, and increases production costs.

[0010] Therefore, there is an urgent need to develop a simple and efficient production method for preparing polyethylene resin for geomembranes that does not require mixing. Summary of the Invention

[0011] This invention employs an improved Innovene S low-pressure slurry process applied to a high-density polyethylene (HDPE) plant. This plant utilizes a dual-loop low-pressure slurry process, capable of producing both single-peak and bi-peak HDPE products. The plant includes a raw material supply and refining unit, a catalyst activation unit, a catalyst feeding and reaction unit, a powder degassing and conveying unit, a solvent recovery unit, an extrusion granulation unit, a granule homogenization and conveying unit, as well as utilities and auxiliary facilities.

[0012] The technical solution adopted in this invention is as follows:

[0013] In a first aspect, the present invention provides a method for producing polyethylene resin for geomembranes, which employs a double-loop reactor, uses ethylene as raw material, hexene-1 as comonomer, isobutane as diluent solvent, and aluminum-modified supported chromium catalyst for catalysis.

[0014] The specific surface area of ​​the chromium-based catalyst is 280–330 m². 2 / g, with a pore volume of 2.3-2.8 mL / g, wherein the chromium-based catalyst contains 2-4 wt% chromium and 1-5 wt% aluminum by mass;

[0015] The density of the slurry in the first reactor is 510-520 kg / m³. 3 The slurry density in the second reactor is 530-540 kg / m³. 3 The ethylene concentration in the first reactor is 3.5-4.5 mol%, and the ethylene concentration in the second reactor is controlled at 6-6.5 mol%. The amount of hexene-1 added in the first reactor is 40-50 kg / t of hexene-1 / ethylene, and the amount of hexene-1 added in the second reactor is 60-70 kg / t of hexene-1 / ethylene. The temperature in the first reactor is controlled at 94-96℃, and the temperature in the second reactor is controlled at 93-95℃. The pressure in the first reactor is controlled at 3.7-3.9 MPa, and the pressure in the second reactor is controlled at 3.9-4.1 MPa. The residence time in the first reactor is 70-90 min, and the residence time in the second reactor is 40-50 min.

[0016] Preferably, the geomembrane is polymerized and granulated using polyethylene resin and an antioxidant, wherein the antioxidant addition amount is 6 kg / t of antioxidant / polyethylene powder.

[0017] In a second aspect, the present invention provides a polyethylene resin for geomembranes, prepared by the method described in the first aspect.

[0018] Preferably, the melt flow rate of the polyethylene geomembrane resin under a 21.6 kg load test is 8–14 g / 10 min.

[0019] Furthermore, the tensile yield stress of the resin used in the polyethylene geomembrane is 18-30 MPa, and the tensile elongation at break is ≥500%.

[0020] Furthermore, the environmental stress cracking time (ESCR) of the polyethylene geomembrane resin is ≥1500h.

[0021] Furthermore, the density of the resin used in the polyethylene geomembrane is 0.936 ± 0.002 g / cm³. 3 .

[0022] The beneficial effects achieved by this invention are as follows:

[0023] The polyethylene resin used to produce geomembranes using the method of this invention has a lower density and a softer material, which is more conducive to downstream construction. It has better processing performance than other similar products, is less likely to cause blockage of downstream processing equipment, and produces less odor than similar products on the market. It has a high balance of rigidity and toughness and resistance to environmental stress cracking, good creep resistance, oxidation resistance and chemical corrosion resistance, and is suitable for the processing and molding of various geomembranes, especially slip-faced geomembranes. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the following embodiments. It should be noted that this invention is not limited to the following embodiments.

[0025] The following Examples 1-3 of the present invention are used to prepare the polyethylene geomembrane, specifically using the improved Iinnovene S low-pressure slurry process, and the amount of aluminum-modified supported chromium catalyst used is the same as the amount of Ziegler-Natta catalyst used in the conventional Iinnovene S process.

[0026] Example 1

[0027] The specific production steps for the resin used in this polyethylene geomembrane are as follows:

[0028] An improved Iinnovene S low-pressure slurry process was employed, using ethylene as the raw material, 1-hexene as the comonomer, and isobutane as the diluent, in a dual-loop reactor. An aluminum-modified supported chromium catalyst with a specific surface area of ​​300 m² was selected. 2 / g, with a pore volume of 2.5mL / g, the chromium content in this aluminum-modified chromium catalyst is 3wt% and the aluminum content is 3wt%.

[0029] The ethylene concentration in reactor one is controlled at 4 mol%, and the ethylene concentration in reactor two is controlled at 6 mol%. The slurry density in reactor one is 515 kg / m³. 3 The density of the slurry in the second reactor is 535 kg / m³. 3 The temperature of reactor one is controlled at 95℃, and the temperature of reactor two is controlled at 94℃. The pressure of reactor one is controlled at 3.8MPa, and the pressure of reactor two is controlled at 4.0MPa. The residence time of reactor one is 80min, and the residence time of reactor two is 45min. The amount of hexene-1 added in reactor one is 45kg / t of hexene-1 / ethylene, and the amount of hexene-1 added in reactor two is 65kg / t of hexene-1 / ethylene.

[0030] After the resin for polyethylene geomembrane is produced into powder during the polymerization stage, it enters the granulation stage. During the granulation stage, a composite antioxidant needs to be added, and the amount of antioxidant added is 6 kg / t of polyethylene powder.

[0031] Example 2

[0032] The specific production steps for the resin used in this polyethylene geomembrane are as follows:

[0033] An improved Innovene S low-pressure slurry process was employed, using ethylene as the raw material, 1-hexene as the comonomer, and isobutane as the diluent, in a dual-loop reactor. An aluminum-modified supported chromium catalyst with a specific surface area of ​​280 m² was selected. 2 / g, with a pore volume of 2.3mL / g, the chromium content in this aluminum-modified chromium catalyst is 2wt%, and the aluminum content is 2wt%.

[0034] The ethylene concentration in reactor one is controlled at 3.5 mol%, and the ethylene concentration in reactor two is controlled at 6 mol%. The slurry density in reactor one is 510 kg / m³. 3 The density of the slurry in the second reactor is 530 kg / m³. 3 The temperature of reactor one is controlled at 94℃, and the temperature of reactor two is controlled at 93℃. The pressure of reactor one is controlled at 3.7MPa, and the pressure of reactor two is controlled at 3.9MPa. The residence time of reactor one is 70min, and the residence time of reactor two is 40min. The amount of hexene-1 added in reactor one is 40kg / t of ethylene, and the amount of hexene-1 added in reactor two is 60kg / t of ethylene.

[0035] After the resin for polyethylene geomembrane is produced into powder during the polymerization stage, it enters the granulation stage. During the granulation stage, a composite antioxidant needs to be added, and the amount of antioxidant added is 6 kg / t of polyethylene powder.

[0036] Example 3

[0037] The specific production steps for the resin used in this polyethylene geomembrane are as follows:

[0038] An improved Innovene S low-pressure slurry process was employed, using ethylene as the raw material, 1-hexene as the comonomer, and isobutane as the diluent, in a dual-loop reactor. An aluminum-modified supported chromium catalyst with a specific surface area of ​​330 m² was selected. 2 / g, with a pore volume of 2.8mL / g, the aluminum-modified chromium catalyst contains 4wt% chromium and 5wt% aluminum.

[0039] The ethylene concentration in reactor one is controlled at 4.5 mol%, and the ethylene concentration in reactor two is controlled at 6.5 mol%. The slurry density in reactor one is 520 kg / m³. 3 The density of the slurry in the second reactor is 540 kg / m³. 3The temperature of reactor one is controlled at 96℃, and the temperature of reactor two is controlled at 95℃. The pressure of reactor one is controlled at 3.9MPa, and the pressure of reactor two is controlled at 4.1MPa. The residence time of reactor one is 90min, and the residence time of reactor two is 50min. The amount of hexene-1 added in reactor one is 50kg / t of hexene-1 / ethylene, and the amount of hexene-1 added in reactor two is 70kg / t of hexene-1 / ethylene.

[0040] After the resin for polyethylene geomembrane is produced into powder during the polymerization stage, it enters the granulation stage. During the granulation stage, a composite antioxidant needs to be added, and the amount of antioxidant added is 6 kg / t of polyethylene powder.

[0041] Comparative Example 1

[0042] All other conditions are the same as in Examples 1-3, except as follows:

[0043] An improved Innovene S low-pressure slurry process was employed, using ethylene as the raw material, 1-hexene as the comonomer, and isobutane as the diluent, in a dual-loop reactor. A conventional Ziegler-Natta catalyst was selected.

[0044] The ethylene concentration in reactor one is controlled at 5 mol%, and the ethylene concentration in reactor two is controlled at 6 mol%. The slurry density in reactor one is 500 kg / m³. 3 The density of the slurry in the second reactor is 510 kg / m³. 3 The temperature of reactor one is controlled at 95℃, and the temperature of reactor two is controlled at 94℃. The pressure of reactor one is controlled at 3.7MPa, and the pressure of reactor two is controlled at 3.9MPa. The residence time of reactor one is 70min, and the residence time of reactor two is 50min. The amount of hexene-1 added in reactor one is 60kg / t of hexene-1 / ethylene, and the amount of hexene-1 added in reactor two is 70kg / t of hexene-1 / ethylene.

[0045] After the resin for polyethylene geomembrane is produced into powder during the polymerization stage, it enters the granulation stage. During the granulation stage, a composite antioxidant needs to be added, and the amount of antioxidant added is 6 kg / t of polyethylene powder.

[0046] Table 1 Test Results

[0047]

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing polyethylene resin for geomembranes, characterized in that, A dual-loop reactor was used, with ethylene as the raw material, hexene-1 as the comonomer, isobutane as the diluent solvent, and an aluminum-modified supported chromium catalyst for catalysis. The specific surface area of ​​the chromium-based catalyst is 280–330 m². 2 / g, with a pore volume of 2.3-2.8 mL / g, wherein the chromium-based catalyst contains 2-4 wt% chromium and 1-5 wt% aluminum. The slurry density in the first reactor is 510-520 kg / m³. 3 The slurry density in the second reactor is 530-540 kg / m³. 3 The ethylene concentration in the first reactor is 3.5-4.5 mol%, and the ethylene concentration in the second reactor is controlled at 6-6.5 mol%. The amount of hexene-1 added in the first reactor is 40-50 kg / t of hexene-1 / ethylene, and the amount of hexene-1 added in the second reactor is 60-70 kg / t of hexene-1 / ethylene. The temperature in the first reactor is controlled at 94-96℃, and the temperature in the second reactor is controlled at 93-95℃. The pressure in the first reactor is controlled at 3.7-3.9 MPa, and the pressure in the second reactor is controlled at 3.9-4.1 MPa. The residence time in the first reactor is 70-90 min, and the residence time in the second reactor is 40-50 min.

2. The method for producing polyethylene resin for geomembranes according to claim 1, characterized in that, The geomembrane is granulated using polyethylene resin and an antioxidant, wherein the antioxidant addition amount is 6 kg / t of antioxidant / polyethylene resin.

3. A polyethylene resin for geomembranes prepared by the method described in claim 1 or 2.

4. The polyethylene resin for geomembranes according to claim 3, characterized in that, The melt flow rate of the polyethylene resin used for the geomembrane was 8~14 g / 10 min under a 21.6 kg load test.

5. The polyethylene resin for geomembranes according to claim 4, characterized in that, The tensile yield stress of the polyethylene resin used in the geomembrane is 18~30MPa, and the tensile elongation at break is ≥500%.

6. The polyethylene resin for geomembranes according to claim 5, characterized in that, The environmental stress cracking time (ESCR) of the polyethylene resin used in the geomembrane is ≥1500h.

7. The polyethylene resin for geomembranes according to claim 6, characterized in that, The density of the polyethylene resin used in the geomembrane is 0.936±0.002 g / cm³.

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