Polyethylene is the most important downstream product of ethylene. Polyethylene (PE) accounts for 70% of world polyolefin consumption, 44% of total thermoplastic consumption and 52% of world ethylene production. Polyethylene is basically divided into three categories, namely high-pressure low-density polyethylene (LDPE), high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). Film is its main processing product, followed by sheets and coatings, hollow containers such as bottles, cans and barrels, and other various injection and blow molding products, insulation and sheathing of pipes, wires and cables. Mainly used in packaging, agriculture and transportation sectors. Compared with other countries in the world, China uses more low-density polyethylene and LLDPE in agricultural films. China is the country with the largest output of agricultural film in the world, which is determined by the characteristics of China as a big agricultural country. 2. Capacity and output By the end of 1998, China had built 26 sets of polyethylene plants with a total capacity of 2,565,438+0,000 tons. 3. Brief description of production methods HP-LDPE is produced by two high-pressure liquid phase methods, namely kettle method and tube method. The polymer produced by kettle process has narrow molecular weight distribution and many branches; However, the products produced by tubular process have wider molecular weight distribution and fewer branched chains. Except for the polymerization reactor, the process steps of the kettle method and the tubular method are similar. The maximum single-line reactor capacity of the tubular process is 200,000 tons/year (for example, Exxon's factory in Belgium and DSM's factory in the Netherlands), and the maximum single-line reactor capacity of the kettle process is 6,543,800 tons/year (possibly reaching 200,000 tons/year), which is a device built by QGPC Company in Qatar using Orchem(CdF) technology. Both kettle process and tubular process have their own advantages. Generally speaking, large equipment tends to use tubular process. Kettle method is the first choice to produce special brand equipment. The LDPE plant 1998 1 1 put into operation in June in Qilu Petrochemical Company adopted the high-pressure tubular process of DSM company in the Netherlands, which is the one with the largest product brand and single-line capacity among similar plants in China at present. Yanshan Petrochemical Company will also build a 200,000-ton/year low-density polyethylene plant with Exxon technology, and the contract has been signed. Linear polyethylene (HDPE/LLDPE) is produced by low pressure liquid phase method and gas phase method. At present, the two liquid-phase methods in the world, namely slurry method and solution method, still dominate the total output. The important solution processes are medium pressure process of DuPont (now Novacor), low pressure cooling process of Dow and DSM process. These devices can alternately produce HDPE and LLDPE (called convertible devices in industry and full density polyethylene in China). The two most widely used slurry methods are loop reactor method using light diluent (Phillips and Solvay) and stirred tank method using heavy diluent (Hoechst, Nissan and Mitsui). The main product of slurry process is high density polyethylene, but some MDPE can also be produced as a by-product. UCC and BP are the main holders of gas phase technology in polyethylene production line. Gas phase process equipment is generally convertible equipment, which can alternately produce LLDPE and HDPE, but it is limited by some patent agreements. Equipment licensed to produce two products must usually give priority to producing one product for a long time. Even for convertible devices, frequent interchange between HDPE and LLDPE products is uneconomical, and it is not actually done. From 65438 to 0997, the world's peaceful polyethylene production capacity was about 50.7 million tons/year, and the production capacity of North America and Western Europe accounted for more than half of the world's total production capacity. Asian countries (including Japan) account for 1/4 of the world's total capacity. As far as technology is concerned, high-pressure polyethylene accounts for about 38%, and pipeline method and kettle method account for almost half each. Slurry method accounts for about half of the 62% share of bus polyethylene. In China, the kettle method, tube method, slurry method, gas phase method and solution method accounted for 9%, 18%, 26%, 43% and 3.2% of the total polyethylene production capacity from 65438 to 0998 respectively. Compared with the average productivity ratios of various process methods in the world (19%, 19%, 30%, 24%, 8), the gas phase method is higher, the tubular method is similar, and other methods are lower. In recent years, China's polyethylene industry has also made gratifying achievements in catalyst development, localization of process equipment and new product development. Remarkable progress has been made in the localization of catalysts. Yanshan Petrochemical Company has built a 30-ton/year domestic HDPE catalyst production plant, and the catalyst produced has been used in large industrial plants. At present, the coverage rate of domestic catalyst in slurry HDPE plant has exceeded 80%. The research of metallocene catalysts in China has made gratifying progress. By the middle of 1996, * * had developed five model tests or patented technologies and obtained five China patent application numbers. Metallocene -LLDPE with bimodal molecular weight distribution was prepared by Beijing Institute of Petrochemical Technology, Lanzhou Chemical Company and Shanghai Institute of Chemical Technology in a gas-phase fluidized bed model test device, and the Institute of Stone Science also synthesized products with high density, low density, ultra-low density and long chain. The metallocene catalyst APE- 1S developed by the institute successfully passed the pilot test in Liao Hua, and completed the pilot test of loop slurry continuous reactor in cooperation with Phillips Company of the United States. The results show that the catalyst has high activity and good catalytic ability for the polymerization of 1- hexene, and the polymer product has good particle size distribution and high bulk density. 1March, 1999, the catalyst passed the appraisal organized by Sinopec Group and China Petroleum and Natural Gas Group Company. The process development has achieved fruitful results. Shanghai Institute of Pharmaceutical Industry, Design Institute of Yangzi Petrochemical Company and Yanshan Petrochemical Company have developed slurry high density polyethylene. The 65,438+400,000 tons/year HDPE plant of Yanhua Company was designed and built by our country. From 1 June 1992 1 scheme determination to1September 26, 19941completion and production, it only took 27 months and 25 days, saving 47.43 million yuan in foreign exchange compared with imported technology and equipment construction. After that, a 70,000-ton/year production line was built in Lanzhou Chemical Company. Yangzi Petrochemical Company has completed the "Complete Technical Package of Slurry HDPE with an annual output of 200,000 tons" and passed the appraisal of sinopec group 1997. This technology can greatly reduce the project cost of newly-built polyethylene plant and effectively guide the expansion and transformation of existing plants. The new technology of producing full density polyethylene by slurry method and horizontal gas-phase kettle jointly developed by Shanghai Pharmaceutical Industry Design Institute and Yanshan Petrochemical Company has applied for China patent and will be implemented in Yanshan industrial plant soon. Some achievements have been made in the development of new products. The high-strength membranes, pipes and large hollow containers produced by Qilu Petrochemical Company have become the company's fist products. After the successful application of HDPE-coated pipeline special material in Shaanxi-Beijing natural gas gathering and transportation project, it recently defeated many well-known foreign companies in international bidding, realized the export to Egypt pipeline anticorrosion plant, and broke the situation that European and American companies completely controlled the synthetic resin special material in the Middle East. Yanshan Petrochemical Company trial-produced 6000M high molecular weight, wide molecular weight distribution and good ESCR performance. Beijing Research Institute of Chemical Technology has successfully developed HDPE material which can be used in automobile fuel tanks. The institute simulated the two-kettle series polymerization of ethylene in a 2-liter polymerization kettle, and prepared high molecular weight butene * * * HDPE resin with bimodal molecular weight distribution. Its performance index is equivalent to that of foreign basic resin for single-layer automobile fuel tank. 4. Demand 1.998 China's polyethylene output is 2.3 million tons, including 740,000 tons of HDPE, 5965438+10,000 tons of LDPE and 9765438+10,000 tons of LLDPE (including HDPE produced by full-density polyethylene plant). From 65438 to 0998, China imported 2.42 million tons of polyethylene, with an apparent consumption of 4.72 million tons. 1998 the polyethylene production capacity in China is about 4.5% of the world production capacity (55.23 million tons), and the apparent consumption is 10.8% of the world consumption (43.7 million tons). Because a considerable part of polyethylene imported from China is used for feed processing, half of the resin used for feed processing is often left at home. When calculating the demand, it is calculated that 60% of the imported resin is imported and processed, and half of the imported polyethylene stays at home, that is, 70% of the imported resin meets the domestic demand. 5. Growth rate 1983- 1998 The average annual growth rate of polyethylene consumption in China is 15.2%, which is 1.5 times the GDP growth rate (10.3%). From 1993 to 1997, the average operating rate of polyethylene plants in China is 90.5%. 6. The largest amount of 6.LDPE is film and sheet, followed by extrusion coating, injection molding, wire and cable. These four applications account for 90% of LDPE applications. Film is the largest market for low density polyethylene, with packaging and non-packaging applications accounting for 50% and 50% respectively. Extrusion coating is the second largest market of LDPE in the world, and it is a rapidly growing application field of LDPE, which is mainly conducive to the development of packaging technology and the continuous innovation of packaging style. The application of film and sheet accounts for 75% of LLDPE consumption in the world. Injection molding and wire and cable are the second and third largest application fields of LLDPE respectively, but they only account for 7% ~ 65% of the total consumption of LLDPE. Stretched film is the fastest growing market of LLDPE in the global packaging field, which is replacing packaging tape, corrugated board, wrapping paper and shrink packaging. Packaging accounts for 75% of HDPE resin consumption, construction accounts for 10%~ 15%, and the rest 10%~ 15% is used for other consumer goods and industrial supplies. Blow molding and injection molding are the main application fields in the United States and western Europe, accounting for about 60%~50% of the total consumption. However, in Japan and other Asian countries, the consumption of HDPE in these areas only accounts for 65,438+0/3 of the total consumption. According to the proportion of consumption, the proportion of film consumption in Asian countries is twice that of the United States and Western Europe. Taking the American market as an example, the departments with the largest consumption of HDPE are all kinds of bottles, barrels, cans and packaging bags, followed by sheets, pipes, packaging boxes, trays, wires and cables. However, the applications with the highest annual growth rate are expected to be automobile fuel tanks, barrels and tanks, followed by linings, water supply and irrigation pipes and geotechnical films. Film accounts for almost 60% of polyethylene consumption in China (see table), of which agricultural film accounts for 20.4%. From 65438 to 0998, China consumed more than 700,000 tons of polyethylene resin for agricultural film. China is the country with the highest output of agricultural film in the world, which is determined by the characteristics of China as a big agricultural country. Other applications of polyethylene include pipes, plates, hollow containers, monofilaments, woven products, injection molded parts, wires and cables. Domestic pipes are mainly agricultural pipes, followed by drinking water pipes and gas pipes; Hollow containers are mainly used for packaging beverages, cosmetics, edible oil and medicines. 1997 About 60,000 tons of resin is consumed for containers with a capacity of 100 liter; Monofilament and woven products are mainly used for ropes, fishing nets and colored striped cloth; Cable materials are mainly used for insulation materials, cross-linked cable materials and sheath materials; Injection molding is mainly used to produce turnover boxes, plastic trays, plastic bottle caps and other products; Others include polyethylene coatings and chlorinated polyethylene. 7. Development Prospects For many years, China's polyethylene production has been unable to meet the market demand, and the import volume accounts for about half of the apparent demand. 1983- 1997 The average apparent demand satisfaction rate of polyethylene in China is 46%, and the average satisfaction rate is 54%. If China's large and medium-sized ethylene can be reformed in 2002, it is estimated that the polyethylene production capacity will reach 3.7 million tons, and the output will be 3.3 million tons according to the operating rate of 90%. According to the historical demand change and the forecast of China's national economic development, it is predicted that the polyethylene demand in China will be 5.86 million tons in 2002, 7.9 million tons in 2005 and 1.220( 1.480) tons in 2065. It is estimated that the satisfaction rate and apparent satisfaction rate of polyethylene in China in 2002 are 56% and 47% respectively. It is equivalent to the average level of 1983- 1997. Polyethylene has considerable market potential in China, and it is a petrochemical product with great development prospects.