History of LDPE development
- Nov 14, 2018 -

The development history

1. Polyethylene is the most important downstream product of ethylene. Polyethylene (PE) accounts for 70% of the world's consumption of polyolefin, 44% of the total consumption of thermoplastic general plastics, and 52% of the world's ethylene production. Polyethylene is divided into three categories, namely high voltage low density polyethylene (LDPE), high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). Film is its main processing products, followed by sheet and coating, bottles, tanks, barrels and other hollow containers and other injection and blow molding products, pipe and wire, cable insulation and sheath. Mainly used in packaging, agriculture and transportation departments. Compared with other countries in the world, China has more LDPE and LLDPE used in agricultural film. China is the largest agricultural film production country in the world, which is determined by the characteristics of China's big agricultural country.

By the end of 1998, China had completed 26 sets of polyethylene plants with a total capacity of 2.51 million tons.

3. The production method briefly describes that HP-LDPE is produced by two high pressure liquid phase processes, namely the kettle method and the pipe method. The polymer produced by cauldron process has narrow molecular weight distribution and more branched chains. The molecular weight distribution is wider and the branched chain is less. In addition to polymerization reactor, the process steps of the reactor and tube method are similar. The pipe method has a maximum single-line reactor capacity of 200,000 tons/year (e.g., Exxon's plant in Belgium and DSM's plant in the Netherlands), the kettle method has a maximum single-line reactor capacity of 180,000 tons/year (possibly up to 200,000 tons/year), and it is the plant built in Qatar by QGPC using Orchem(CdF) technology. There are different technologies of the kettle and the tube. Generally speaking, the tube method is preferred for large-scale devices. The device for producing the special brand is more inclined to use the kettle method. The LDPE device of qilu petrochemical company, which was put into operation in November 1998, adopts the high-pressure pipe process of DSM of the Netherlands, and is the device with the largest product brand and single line production capacity among similar devices in China at present. Yanshan petrochemical company will also build a LDPE device of 200,000 tons/year, using the technology of Exxon company, and the contract has been signed. Linear polyethylene (HDPE/LLDPE) is produced by low pressure liquid phase method and gas phase method.

At present, two kinds of liquid phase methods, namely slurry method and solution method, still dominate in terms of total production. The important solution-method processes are the medium-pressure process of DuPont(now Novacor) in Canada, the low-pressure cooling process of Dow and the technology of the Dutch mining company (DSM). These devices can be used to produce HDPE and LLDPE alternately. The two most widely used slurry processes are the light-diluent loop reactor processes (Phillips and Solvay) and the heavy diluent stirring tank processes (Hoechst, Nissan, mitsui). The main product of slurry technology is HDPE, but some MDPE can be produced as a secondary product. UCC and BP are the main holders of the production line polyethylene gas phase technology. The gas phase device is usually a convertible device, which can produce LLDPE and HDPE alternately, but it is limited by patent agreement. Devices that are licensed to produce two products often have the priority of producing one product over the other over a longer period of time. Even for convertible devices, frequent swaps between HDPE and LLDPE products are uneconomical and do not actually do so. In 1997, the world polyethylene peace capacity was about 50.7 million tons per year, with North America and Western Europe accounting for more than half of the world's total capacity. Asian countries (including Japan) account for about a quarter of the world's total capacity.

In terms of technology, high pressure polyethylene accounts for about 38%, and pipe and kettle methods account for nearly half. The slurry process accounts for about half of the 62 percent of the total line polyethylene. In 1998, the proportion of China's total production capacity of polyethylene by kettle method, tube method, slurry method, gas phase method and solution method was 9%, 18%, 26%, 43% and 3.2%, respectively. Compared with the world average ratio of production capacity of various process methods (19%, 19%, 30%, 24% and 8), the gas-phase method is high, the tubular method is similar, and other methods are low. In recent years, China's polyethylene industry has also made gratifying achievements in the development of catalysts, process equipment and new products. The localization of catalyst has made remarkable progress 30 tons/year. At present, the application rate of domestic catalysts in the slurry HDPE device has exceeded 80%. Made gratifying progress in the research of the metallocene catalysts in China, until 1996 years, has developed five mold trial or patent technology, has won five Chinese patent application Numbers, Beijing petrochemical research institute, lanzhou chemical industry company and the Shanghai chemical industry research institute has been made in the gas phase fluidized bed model test device with a bimodal molecular weight distribution of metallocene LLDPE, ripp also synthesized can produce high density, low density, low density and long chain branched polyethylene resin metallocene catalysts, developed by ripp load type bridge league alum zirconium catalyst has different sizes of pilot verification. APE - 1 s hospital development of metallocene catalyst in pilot test in LiaoHua passed successfully, and cooperate with American Phillips corporation completed a continuous slurry method with loop reactor pilot test, the test showed that the catalyst is highly active and better catalytic ability of 1 - hexene copolymerization, polymerization products have good particle size distribution and higher bulk density. In March 1999, the catalyst was identified by China petrochemical corporation and China national petroleum corporation. Great achievements have been made in the process development. Shanghai pharmaceutical industry research institute, design institute of yangzi petrochemical company and yanshan petrochemical company have developed the slurry high-density polyethylene process. The 140,000-ton/year high-density polyethylene plant of yanhua company was designed and built by China itself. From June 1, 1992 to September 26, 1994, the plant was completed and put into production, which only took 27 months and 25 days, saving foreign exchange 47.43 million yuan compared with the imported technology and equipment construction. After that, another 70,000 tons/year production line was built in lanzhou chemical industry company with this process. Yangzi petrochemical company has completed the "high density and low pressure polyethylene complete technology package of slurry method with annual capacity of 200,000 tons", which has been appraised by China petrochemical corporation in 1997. By adopting this technology, the engineering cost of new polyethylene plant can be greatly reduced, and the capacity expansion and transformation of existing plant can be effectively guided. Shanghai pharmaceutical industrial design institute and yanshan petrochemical company have jointly developed a new production process of full-density polyethylene by slurry method and horizontal gas phase kettle. Some achievements have been made in the development of new products. Qilu petrochemical company produces high strength film, tubing and large hollow container has become the fist of the company products, HDPE material for cladding tube after natural gas gathering and transferring in the national key project of shan - Beijing after successful application in engineering, and recently in the international bidding beat several well-known large companies abroad, implementation to the Egyptian pipeline preservation plant export, broke the European and American companies fully control the situation of the Middle East special synthetic resin material. Yanshan petrochemical company has piloted the production of 6000M pipe material with high molecular weight, wide molecular weight distribution and good ESCR performance. The Beijing institute of chemical technology has successfully developed HDPE material that can be used in the automobile oil tank. The simulated two-pot series method is used to conduct ethylene two-pot polymerization in the 2-liter polymerization reactor to prepare the high-molecular weight butadiene copolymerization type HDPE resin with bimodal distribution. The performance index is equivalent to the basic resin performance of foreign single-layer automobile oil tank special material.

4. In 1998, China produced 2.3 million tons of polyethylene, including 74.0 million tons of HDPE, 591,000 tons of LDPE and 971,000 tons of LLDPE(including HDPE produced in full-density polyethylene). In 1998, China imported 2.42 million tons of polyethylene and consumed 4.72 million tons. In 1998, China's polyethylene production capacity was about 4.5% of the world's production capacity (5523 million tons), and its apparent consumption was 10.8% of the world's consumption (43.7 million tons). Because a significant proportion of the polyethylene imported into China is imported for processing, but half of the resin that is imported is often left in China. When the demand is calculated, 60% of the imported resin is imported for processing, and half of the polyethylene from the imported material is left in China, that is, 70% of the import is calculated to meet the domestic demand.

5. The average annual growth rate of polyethylene consumption in China from 1983 to 1998 was 15.2%, 1.5 times the GDP growth rate (10.3%). The average operating rate of polyethylene plant in China from 1993 to 1997 was 90.5%.

6. The largest amount of LDPE used is film and sheet, followed by extrusion coating, injection molding, wire and cable. These four applications together account for 90% of LDPE applications. Film is LDPE's largest market, packaging and non - packaging applications roughly 50% each. Extrusion coating is the second largest market of LDPE in the world, and it is the application field of LDPE with rapid growth. The application of thin films and sheets accounts for 75% of the total LLDPE consumption in the world. Injection molding and wire and cable are the second and third largest application areas of LLDPE respectively, but only take up 7%~15% of the total amount of LLDPE. Stretch wrap is the fastest growing market for LLDPE in packaging in the world, replacing packing tape, corrugated sheet, wrapping paper and shrink wrap. Packaging accounts for 75% of HDPE resin consumption, construction accounts for 10%~15%, and the remaining 10%~15% are used in other consumer and industrial products. Blow molding and injection molding are the main application areas in the United States and Western Europe, accounting for about 60%~50% of the total consumption. However, in Japan and other Asian countries, HDPE consumption in these sectors only accounts for 1/3 of the total consumption. In terms of consumption proportion, the proportion of thin film consumption in Asian countries is twice that in the United States and Western Europe. Take the us market as an example, the departments with the largest consumption of HDPE are all kinds of bottles, barrels, cans and bags, followed by sheet materials, pipes, packing boxes, trays, wires and cables, etc., but the applications with the highest expected annual growth rate are automobile fuel tanks, barrels and cans, followed by lining boards, water supply and irrigation water pipes and geotextiles. Thin film accounts for almost 60% of China's polyethylene consumption (see table), of which agricultural film accounts for 20.4%. In 1998, over 700,000 tons of polyethylene resin was consumed in agricultural film in China. China has the highest agricultural film production in the world, which is determined by the characteristics of China's major agricultural country. Other applications of polyethylene include pipes, plates, hollow vessels, single filaments, braided products, injection molded parts, wires and cables, etc. Domestic pipe consumption is mainly agricultural pipe, followed by water pipe and gas pipe; The hollow container is mainly used for the packaging of beverage, cosmetics, edible oil and medicine. In 1997, about 60,000 tons of resin was consumed for vessels over 100 liters. Single silk and weaving products are mainly used for rope, fishing net silk and color striped cloth; The cable material is mainly used for insulation material, crosslinking cable material and sheath material. Plastic injection is mainly used in the production of turnover boxes, plastic pallets, plastic caps and other products; Others include polyethylene coating and chlorinated polyethylene, etc.

For many years, China's production of polyethylene has been unable to meet the market demand, with imports accounting for about half of the apparent demand. From 1983 to 1997, the average apparent demand satisfaction rate of polyethylene in China was 46%, and the average satisfaction rate was 54%. If the transformation of China's large and medium ethylene can be completed in 2002, the polyethylene capacity is expected to reach 3.7 million tons, and the output will be 3.3 million tons according to the operation rate of 90%. According to the historical demand changes and the development forecast of China's national economy, the polyethylene demand in China is estimated to be 5.86 million tons (apparent demand is 7 million tons) in 2002, 790(9.5 million tons) in 2005 and 1220(14.8 million tons) in 2010. It is speculated that the content and apparent content of polyethylene in China in 2002 were 56% and 47% respectively. That's on par with the 1983-1997 average. Polyethylene has considerable market potential in China and is a promising petrochemical product.

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