Polyoxymethylene

This post was last edited by QXZ-1966 on 2010-1-13 at 21:47. Polyoxymethylene was developed by DuPont in the 1950s, and it is one of the three major general-purpose engineering plastics in the world today. As an engineering plastic with excellent properties, polyoxymethylene can be divided into two main categories. The first is the homopolymer of trioxymethylene or formaldehyde, known as homopolymerized polyoxymethylene. This material possesses high rigidity and strong tensile strength; its tensile strength per unit mass is higher than that of zinc and brass, and it is close to that of steel. It also has good wear resistance and a low coefficient of friction. However, it has poor thermal stability and is not resistant to acids and alkalis. The second is a copolymer of trimethylolpropane and a small amount of pentane ring, known as copolymerized formaldehyde. The conditions required for processing copolymerized formaldehyde are not as stringent as those for homopolymerized formaldehyde; less formaldehyde gas is released during the processing due to thermal decomposition, and this gas can be recovered and reused. Therefore, the development momentum of homopolymerous polyoxymethylene will gradually decline in the future, while copolymerous polyoxymethylene will become the direction for future development. Currently, the production capacity of copolymerized polyoxymethylene accounts for about 80% of the total polyoxymethylene production capacity. 　　Production and Market The world’s production and consumption of polyoxymethylene are concentrated in industrially developed countries and regions such as the United States, Western Europe, and Japan. Since its introduction, polyoxymethylene has seen rapid development due to its excellent properties, with growing global demand. In 2001, the world’s total production capacity for polyoxymethylene was approximately 800,000 tons, and the average annual growth rate of global consumption of this material from 1995 to 2000 was around 5%. 　　Currently. The development of the global polyoxymethylene industry is characterized by two main trends: first, production is becoming more concentrated and monopolized. The companies Heraeus-Sellinus, DuPont, BASF, and Mitsubishi Gas account for 83% of the world’s total polyoxymethylene production capacity. These companies control the production and market of polyoxymethylene worldwide, thus determining its fate. Secondly, Asia is developing rapidly with fast-growing consumption. Before 1995, about 90% of the world’s polyoxymethylene production facilities were located in industrially developed regions such as the United States, Western Europe, and Japan. In recent years, as Asia’s economy has gradually recovered and the economies of China and ASEAN have continued to develop steadily, the demand for engineering plastics has grown stronger, and world-renowned polyoxymethylene manufacturers are optimistic about the Asian market. Companies flocked to Asia to invest in building factories; between 1995 and 2001, Asia, particularly Malaysia, Singapore, South Korea, and Taiwan, saw a new production capacity of 163,000 tons. Together with the increase in Japan’s capacity, Asia’s new capacity accounted for about 65% of the global increase. 　　At the end of the 1970s, China developed its first set of polyoxymethylene production facilities on its own. After more than 20 years of development that progressed slowly, there are now only two manufacturing enterprises in China: the Shanghai Solvent Factory and the Shijinggou Joint Chemical Plant of Jihua Corporation. Their production capacities are 1,700 tons per year and 1,000 tons per year respectively. Both use the trioxymethylene-based production process; however, their copolymerization technology lags far behind that of foreign countries. The consumption of raw materials and auxiliary materials is high, and the quality of the product is unstable. The main reasons for this are the low conversion rate of trioxymethylene in these processes sowie inadequate techniques for the recovery and purification of formaldehyde. Moreover, the polyoxymethylene technology developed in China has many shortcomings from an engineering perspective, preventing the achievement of economies of scale and thus restricting the development of China’s polyoxymethylene industry. China’s polyoxymethylene industry is underdeveloped and is far from able to meet domestic demand. In 2000, Yunnan Natural Gas Chemical Group Company introduced a polyoxymethylene production technology and facility with an annual capacity of 10,000 tons from the Polish company ZAT; this facility has now been built and put into operation. By then, the domestic production capacity for polyoxymethylene will reach 12,700 tons per year. 　　In recent years, the consumption of polyoxymethylene in China has increased rapidly; in 2000, the apparent domestic consumption amounted to 88,400 tons per year. The distribution of consumption was as follows: 55% for the electronics and electrical industry, 15% for the automotive industry, 20% for consumer goods, 8% for industrial equipment, and 2% for other sectors. Due to low domestic production, the country relies mainly on imports from abroad to meet domestic demand; import volumes have been increasing year by year in recent years, with figures of 63,400 tons, 90,600 tons, 108,300 tons, and 109,000 tons for the years 1998, 1999, 2000, and 2001 respectively. 　　In our country, polyoxymethylene is primarily used in the electronics and electrical industry. In recent years, the electronics and electrical industry here has developed rapidly, and the automotive industry has gradually become a key industry in our country as well; therefore, the demand for polyoxymethylene will continue to increase. It is estimated that the demand for polyoxymethylene in our country will reach 100,000 tons by 2002, and exceed 120,000 tons by 2005. Even if all three domestic plants operate at full capacity, it is still far from meeting domestic demand. Given the huge size of China’s polyoxymethylene market and the increasingly fierce competition among various brands from international companies in this domestic market, foreign manufacturers are employing various methods to expand their share of the market in China. It is reported that both DuPont and Mitsubishi Gas Chemical plan to invest in building polyoxymethylene production plants with a capacity of 10,000 tons each in China. Nippon Boride Plastic, Mitsubishi Gas Chemical, and Ticona will jointly invest $128 million to build a 60,000-ton/year polyoxymethylene plant in Nantong, Jiangsu, with completion and operation scheduled for 2004. Additionally, the polyoxymethylene project with an annual production capacity of 20,000 tons proposed by the methanol plant in Daqing Oilfield has been **approved** ； The polyoxymethylene production project of Shanxi Jincheng Orchid Science and Technology Co., Ltd., with a total investment of 580 million yuan and an annual production capacity of 20,000 tons, has also been approved for implementation by the Planning Commission. 　　Problems and Development Strategies The polyoxymethylene market in China holds great potential. Polyoxymethylene is primarily used in industries such as automobiles and electronics, which are all strategic sectors vital to the country’s economy and people’s livelihoods. Foreign companies pay close attention to this potentially huge market in China, and thus China’s polyoxymethylene industry will face fierce competition. Therefore, domestic enterprises should seize the opportunities to develop rapidly; otherwise, they risk being eliminated in the increasingly competitive global market. It is thus extremely urgent and important to develop China’s polyoxymethylene industry. 　　At present, the development of the polyoxymethylene industry in our country is far behind the advanced levels abroad, with demand for such products relying almost 100% on imports. Although our country began developing polyoxymethylene quite early on, after several decades of development, no significant breakthroughs have been achieved in terms of technology. Compared to foreign companies, it is too small in scale. At present, polyoxymethylene in China can only be operated in pilot-scale plants; the scale-up to industrial levels has not been successful, making it impossible to design and build production facilities with a capacity of tens of thousands of tons. 　　In our country, the optimal operating conditions for polyoxymethylene have not yet been identified; the performance of catalysts is not high, companies are unable to control the molecular weight and its distribution independently, there are few product grades available, and the quality is unstable – all of these are major challenges that hinder the development of domestically produced polyoxymethylene. Furthermore, the introduction of technology is also quite difficult; since the 20th century, efforts have been made to conduct tough negotiations with foreign companies in an attempt to acquire foreign technology, but these attempts have not been successful for various reasons. Foreign companies all wish to build polyoxymethylene plants in China on a wholly-owned or absolutely controlling basis, in order to maintain control and achieve higher profits. In recent years, Yuntianhua has successfully introduced 10,000-ton polyoxymethylene production facilities from the Polish company ZAT. However, the technology used is not very advanced, and qualified products have yet to be produced; the date of commissioning keeps being postponed, and there are still some production-related technical issues that have not been resolved. As a high-tech product characterized by high investment and high output values, the production and processing of polyoxymethylene involve advanced technical skills and generate substantial profits; it is therefore one of the key areas of interest for multinational companies. In China, where no breakthroughs have been achieved in the core technologies related to polyoxymethylene, foreign companies are reluctant to transfer such technologies to China or establish joint ventures there. For example, a major foreign company that produces polyoxymethylene preferred to invest heavily in building a plant in Shenzhen capable of producing 10,000 tons per year of polyoxymethylene pellets and plastic alloys, rather than establishing a joint venture in Shanghai to produce 45,000 tons per year of polyoxymethylene. With China’s accession to the WTO, some foreign companies, driven by competitive needs, have decided to build large-scale polyoxymethylene production facilities in China on a wholly-owned basis; however, they are not yet able to transfer technology to our country. 　　As a high-performance engineering plastic, polyoxymethylene is a strategic product for our country, and its development should be promoted actively. It is highly necessary and important for our country to develop technology for producing 10,000 tons of polyoxymethylene with independent intellectual property rights as soon as possible. 　　Firstly, China’s energy structure is dominated by coal, and methanol, the starting material for polyoxymethylene, is one of the coal chemical products that can be manufactured on a large scale in the country. Therefore, from the perspective of the energy structure, it holds strategic significance for China to develop polyoxymethylene vigorously. It is conducive to establishing a new coal chemical industry in our country for the 21st century. 　　Secondly, as a pillar industry in our country, the automotive industry is developing rapidly at present. However, the proportion of polyoxymethylene used in China’s automotive sector is far below the world average. Therefore, it is necessary to increase the use of polyoxymethylene in this industry; this will not only promote the development of China’s polyoxymethylene industry but also contribute to the localization of automobile production. As the process of localizing China’s automotive industry accelerates, this sector will be one of the areas with the fastest growth in polyoxymethylene consumption in the future. 　　It is recommended that **the relevant departments organize experts to digest and absorb the introduced technologies, and then bring together various resources to work on overcoming the challenges, so as to develop domestic production facilities capable of producing tens of thousands of tons per year as soon as possible, with a focus on advancing technology related to copolymerized formaldehyde. The top priority is to invest considerable funds in improving various supporting processes, and to ensure the proper operation of the 10,000-ton per year polyformaldehyde production plants that have already been introduced in the country. With the coordination and support of relevant authorities, it is necessary to produce qualified products as soon as possible. In addition, relevant research institutions in our country should accelerate research on the application of polyoxymethylene alloys, in order to provide technical support for the production and use of polyoxymethylene in our country. Even if it is difficult to make breakthroughs in domestic production technology for polyoxymethylene on a ten-thousand-ton scale in the short term, given the current market demand and future trends in demand growth, it is necessary to take various measures—such as setting up wholly-owned enterprises—to introduce more advanced foreign polyoxymethylene copolymerization technologies and build several production facilities capable of handling ten-thousand tons per year. The development of China’s polyoxymethylene industry is an urgent matter that cannot wait.

I heard that the technology for an annual production of 60,000 tons is now quite mature.

Polyoxymethylene (POM) is divided into two main categories: one is the homopolymer of trimethylolpropane or formaldehyde, known as homopolyoxymethylene; the other is a copolymer of trimethylolpropane with a small amount of cyclic compounds, known as copolyoxymethylene. ) S+ s! i! S+ J( K/ K; z! L The production process for homopolymerized polyoxymethylene is represented by DuPont Company. Its products have a relative density of around 1.4 and a melting point of 170–185°C. They feature excellent rigidity, with a tensile strength of up to 68.9 MPa; their tensile strength per unit mass is higher than that of zinc and brass. Additionally, they have good wear resistance and a low friction coefficient. However, they lack thermal stability and are not resistant to acids. In the homopolymerization process, 50% formalin solution is first reacted with isooctanol to produce a hemiacetal solution. Refined formaldehyde is obtained through dehydration and thermal pyrolysis, followed by liquid-phase polymerization in a reactor. After filtration, separation, and drying of the polymerization product, it is further terminated by esterification with acetic anhydride. High-purity nitrogen is required for protection during the process. The formaldehyde purification process in this technique is complex; the post-treatment end-capping process presents certain difficulties. The process flow is lengthy, there are many pieces of equipment, and corrosion is severe, requiring expensive alloy materials for the synthesis reactors. The production process for copolymerized formaldehyde is typically represented by the technology of Heraeus Selenia; companies such as BASF and Mitsubishi Gas Chemical also have their own technologies. Yubari Kogyo’s solvent-free gas-phase polyoxymethylene copolymerization process during the polymerization stage is also distinctive. A 50% formaldehyde solution was concentrated to 65%, and a triomethylenemethane solution was synthesized in the presence of sulfuric acid; polymeric-grade triomethylenemethane was obtained through extraction and purification with a solvent (benzene or dichloroethane). Then, polymeric trimethylolpropane was used as the polymerization monomer, and ethylene oxide (or dioxolane) was used as the copolymerization monomer, to carry out bulk continuous copolymerization using a twin-screw reactor. The resulting copolymer is crushed, subjected to continuous and batch stabilization to remove thermally unstable components, dried, and then mixed with additives for granulation. Asahi Kasei has developed a new process for the direct synthesis of 70% high-concentration formaldehyde through the oxidation of methylal, eliminating the need for formaldehyde concentration and the recovery of dilute formaldehyde. The formaldehyde produced in the synthesis of triomethylenemethane can be recycled back to the methoxal synthesis reactor. Its methyl acetal synthesis occurs at a low temperature (60–90°C), with almost no formic acid produced, and thus no equipment corrosion occurs. Furthermore, since the formaldehyde content obtained from the reaction reaches 70%, this facilitates an increase in the reaction rate of paraformaldehyde synthesis and reduces side reactions. The gas-phase copolymerization of formaldehyde technology developed by Ube Industries consists mainly of formaldehyde synthesis, monomer preparation, copolymerization, stabilization, and solvent recovery. The process route is as follows: The raw material methanol is oxidized with air to produce 50% formaldehyde, which then reacts with polyethylene glycol; after dehydration, thermal decomposition, and purification, purified formaldehyde gas is obtained. The purified formaldehyde gas is mixed with the gaseous comonomer octacyclotriene and then fed into a twin-screw reactor for copolymerization. The high-temperature cyclic polyoxymethylene powder discharged from the polymerization reactor is cooled and returned to the reactor for recycling in order to control the polymerization temperature; thereafter, the polyoxymethylene powder is conveyed by a screw conveyor to the stabilization process. This technology has low requirements for materials, a simple process, and low corrosivity. The copolymerization technique using triomethyleneperoxide as the polymerization monomer accounts for 80% of the world’s polyoxymethylene production capacity. In the technology for producing trioxane, the sulfuric acid catalysis method and the solid acid catalysis method currently coexist. The production of 70% concentrated formaldehyde through the oxidation of methylal, developed by Asahi Kasei, represents a significant improvement in the copolymerization process; it eliminates the need for formaldehyde concentration and the recovery of diluted formaldehyde, thereby **reducing energy consumption and costs**. In terms of stabilization technologies, melt processes and liquid-phase hydrolysis processes coexist currently, with the latter holding development potential. For reference: http://bbs.hcbbs.com/viewthread.php?tid=116015

The process flows for copolymerization and homopolymerization are different

It’s so detailed; now I understand the situation of polyoxymethylene in China.