Thread Content
The production methods of polyethylene (LDPE): HP-LDPE is manufactured using two high-pressure liquid-phase processes, namely the batch process and the tubular process. Polymers produced by the batch process have a narrow molecular weight distribution and numerous side chains ； The products obtained by the tubular process have a wider molecular weight distribution and fewer side chains. Except for the polymerization reactor, the process steps of the batch and tubular methods are similar. The maximum capacity of a single reactor in the tubular process is 200,000 tons per year (such as Exxon’s facility in Belgium and DSM’s facility in the Netherlands), while the maximum capacity for a single reactor in the batch process is 180,000 tons per year (with the possibility of reaching 200,000 tons per year); this refers to the facility built by QGPC in Qatar using Orchem (CdF) technology. Both the kettle process and the tubular process have their advantages. Generally speaking, large-scale plants tend to use the tubular process, while plants that produce specific grades of products prefer the kettle process. The LDPE plant of Qilu Petrochemical Company, which came online in November 1998, uses the high-pressure tubular process developed by the Dutch company DSM. It is the plant in China with the widest range of product grades and the highest single-line production capacity among similar plants currently in operation. Yanshan Petrochemical will also build an LDPE plant with a capacity of 200,000 tons per year, using Exxon’s technology; the contract has already been signed. Linear polyethylene (HDPE/LLDPE) is produced by the low-pressure liquid phase method and the gas phase method. The two current liquid-phase methods in the world, namely the slurry method and the solution method, still hold a dominant position in terms of total production. Important solution-based processes include DuPont’s (now Novacor) medium-pressure process in Canada, Dow’s low-pressure cooling process, and the DSM process from the Dutch mining company. These units can alternately produce HDPE and LLDPE (industrially known as convertible units; in China, they are referred to as full-density polyethylene). The two most widely used slurry process methods are the loop reactor process using a light diluent (Phillips? and? Solvay), and the batch reactor process using a heavy diluent (Hoechst, Nissan, Mitsui). The main product of the slurry process is HDPE, but some MDPE can also be produced as a secondary product. UCC and BP are the main holders of the linear polyethylene gas-phase process technology. Vapor-phase plants are generally convertible units that can produce LLDPE and HDPE alternately, but they are subject to certain restrictions under patent agreements. Facilities licensed to produce two types of products usually also have to prioritize the production of one type of product for a longer period of time. Even for convertible devices, frequent switching between HDPE and LLDPE products is uneconomical, and in practice this is not done. In 1997, the world’s polyethylene production capacity was approximately 50.7 million tons per year, with North America and Western Europe accounting for more than half of the global total capacity. Asia **(including Japan) accounts for about 1/4 of the world’s total capacity. In terms of manufacturing processes, high-pressure polyethylene accounts for about 38%, while the tubular and batch methods each account for roughly half. The slurry process accounts for about half of the 62% share held by linear polyethylene as a whole. In 1998, in China, the respective shares of the kettle process, tubular process, slurry process, gas-phase process, and solution process in the total polyethylene production capacity were 9%, 18%, 26%, 43%, and 3.2%. Compared with the average ratios of production capacity for various processes worldwide (19%, 19%, 30%, 24%, and 8), the vapor-phase method has a high value, the tubular method is similar, while the other methods have lower values. In recent years, China’s polyethylene industry has also achieved remarkable results in areas such as catalyst development, the localization of process equipment, and the development of new products. Significant progress has been made in the localization of catalysts. A production facility for HDPE catalysts with an annual capacity of 30 tons has been built at Yanshan Petrochemical Company, and the catalysts produced there are already being used in large-scale industrial plants. At present, the utilization rate of domestic catalysts in slurry-based HDPE plants has exceeded 80%. Remarkable progress has been made in the research of metallocene catalysts in our country. By mid-1996, five pilot-scale or patented technologies had been developed, and 5 Chinese patent application numbers had been obtained. The Beijing Research Institute of Petrochemical Technology, Lanzhou Chemical Industry Company, and Shanghai Research Institute of Chemistry have produced metallocene-LLDPE with a bimodal molecular weight distribution using gas-phase fluidized-bed pilot-scale reactors. The Research Institute of Chemistry has also synthesized metallocene catalysts that can be used to produce high-density, low-density, ultra-low-density, and long-chain branched polyethylene resins. The supported bridged metallocene-zirconium catalyst developed by the Research Institute of Chemistry has undergone pilot-scale tests on various scales. The metallocene catalyst APE-1S developed by this institute successfully passed pilot-scale tests at Liaoning Chemical Industry Corporation. In collaboration with the American company Phillips, pilot-scale evaluation tests were conducted using a continuous loop-slurry reactor, and the results showed that this catalyst possesses high activity as well as excellent catalytic efficiency for the copolymerization of 1-hexene. The polymer products obtained had a favorable particle size distribution and high bulk density. In March 1999, this catalyst passed the evaluation organized by Sinopec Group Corporation and CNPC Group Corporation. Significant achievements have been made in process development; institutions such as the Shanghai Pharmaceutical Industry Research Institute, the Design Institute of Yangzi Petrochemical Company, and Yanshan Petrochemical Company have developed a slurry-process for high-density polyethylene production. Yanhua Company’s 140,000 tons per year high-density polyethylene plant was designed and constructed in China. From the date the plan was finalized on June 1, 1992, to the day the plant began operation on September 26, 1994, it took only 27 months and 25 days; this approach saved 47.43 million yuan in foreign exchange compared to using imported technologies and equipment for construction. Subsequently, using this process, a 70,000-ton/year production line was built at Lanzhou Chemical Industry Company. Yangzi Petrochemical Corporation developed a \"set of technical processes for annual production of 200,000 tons of slurry-process high-density low-pressure polyethylene\", which is at an advanced level among similar facilities; this system was approved by Sinopec in 1997. By adopting this technology, the construction cost of new polyethylene plants can be significantly reduced, and it can also provide effective guidance for the expansion and renovation of existing plants. The Shanghai Pharmaceutical Industry Design Institute and Yanshan Petrochemical Company have jointly developed a new production process for full-density polyethylene using a slurry method in combination with a horizontal gas-phase reactor; a Chinese patent has been applied for, and implementation is planned at the industrial facility in Yanshan. Certain achievements have been made in the development of new products. The high-strength films, pipes, and large and medium-sized hollow containers produced by Qilu Petrochemical Company have become its flagship products. After being successfully used in the **key Shaanxi-Beijing natural gas transmission project**, the special material for HDPE-coated pipes has recently defeated several well-known foreign companies in international bidding, enabling its export to an anti-corrosion pipe manufacturing plant in Egypt and breaking the monopoly of European and American companies on special materials for synthetic resins in the Middle East. Yanshan Petrochemical Company has trial-produced the pipe material 6000M, which features a high molecular weight, a wide molecular weight distribution, and good ESCR properties. The Beijing Research Institute of Chemical Technology has developed HDPE material suitable for use in automobile fuel tanks. By using a two-reactor series method in a 2-liter polymerization reactor, the institute carried out the polymerization of ethylene in two stages, resulting in high-molecular-weight butene copolymerized HDPE resin with a bimodal molecular weight distribution; the performance characteristics of this resin are comparable to those of the base resins used for single-layer automobile fuel tanks abroad.