A few days ago, the reporter interviewed Zhou Xueshuang, a senior engineer of the Environmental Engineering Evaluation Center of the Ministry of Environmental Protection, and some chemical experts, asking them to give us an objective and scientific answer.
â—†In many countries, PX is not a dangerous chemical
A chemical expert at Tianjin University said that PX chemical name is para-xylene, a colorless transparent liquid, and its appearance is similar to that of ordinary gasoline. In fact, ordinary gasoline contains about 10% of PX, which is stable in nature and belongs to the fourth grade (mild hazard indicator) of the national occupational exposure to toxicant hazard classification, which is the same level as gasoline.
He said that PX is insoluble in water and has strong volatility. It usually evaporates in 3 to 5 days, can be photolyzed in the air, and is not a persistent pollutant in surface water. According to the Globally Harmonized System of Classification and Labelling of Chemicals and the List of Hazardous Chemicals, PX is not considered a hazardous chemical in many countries. The EU lists PX as a harmful product because it stimulates the eye and upper respiratory tract when the body inhales excessive PX. A particularly high concentration of PX has an anesthetic effect on the central nervous system. The maximum allowable concentration of xylene in the air of China (TJ36-79) workshop is 100mg/m3, and the maximum allowable concentration in the atmosphere of residential areas is 0.30mg/m3. Under normal circumstances, these limits will not be reached.
He introduced that although the benzene and hydrogen sulfide produced in the PX production process are highly toxic and carcinogenic, they are important atmospheric pollutants. However, domestic enterprises are mostly introduced into the world's more mature and advanced technology. The benzene produced in the PX production process is recycled, and the hydrogen sulfide waste gas produced will be discharged after desulfurization and harmless treatment.
In response to rumors that PX is carcinogenic and can cause invisible poisoning, Jin Yong, an academician of the Chinese Academy of Engineering and a professor of chemical engineering at Tsinghua University, said that in 2007, the WHO International Agency for Research on Cancer (IARC) defined PX as “the third group of carcinogensâ€. "The existing evidence does not prove that it is carcinogenic to humans." The weighted average maximum allowable concentration of PX in air is 100 ppm, and the lowest concentration of odor is 0.44 ppm, so people will not be unknowingly poisoned.
â—†PX is widely used
An expert from Tianjin University introduced that PX is widely used in the production of polyester, and electronic information products such as film base, tape base, capacitor film, optical disk and magnetic card are used. PX is also an important raw material for the production of polyester and plastic. In 2010, China's polyester production accounted for 81.4% of chemical fiber production. The production of daily necessities such as shirts and mineral water bottles is inseparable from PX. The most important downstream product of PX is PET, which is increasingly replacing aluminum, glass, ceramic, paper and other materials. Therefore, PX has become an indispensable important chemical raw material.
It is understood that in 2010, China has become the world's largest PX production and consumption country, with production capacity accounting for 24% of the world, consumption accounting for 32% of the world, and the demand gap of PX is still very large. Experts predict that in order to meet domestic demand, China needs PW production of about 12.84 million tons and 16.39 million tons in 2015 and 2020. There is still much room for development in China's production capacity.
Not only China, but the demand gap for PX in the world is very large, so the PX project means huge GDP. This is also the reason why countries are keen on launching the PX project. At the end of August, the world's largest PX project started in Singapore with an investment of 2.4 billion US dollars and can produce 800,000 tons of PX per year. It is expected to be completed in 2014. If it has not been produced, it has already received an order of $2.2 billion.
In September this year, experts and scholars at the China Petroleum and Chemical Industry Federation said that PX production has been in the world for decades. Countries such as the United States, Britain, Japan, Germany, and France, which attach great importance to environmental protection, have spared no effort to develop petrochemicals, many of which have PX projects. Japan has been a major exporter of PX in recent years, with an annual export volume of around 2.2 million tons. Even some PX projects are close to residential areas. For example, the PX installation in Yokohama, Japan is only one way away from the residential area; the PX installation in Busan, South Korea is 4 kilometers from the city center; the Jurong Petrochemical District in Singapore also has a PX installation, about from the city. 10 kilometers; there has not been a pollution accident in this country where PX production has caused serious harm to the environment and residents.
â—†PX projects must be strictly environmentally reviewed and managed
“Although the risk of PX production can be prevented and controlled, like other petrochemical projects, the risk of harm to the environment is objective and cannot be ignored.†Zhou Xueshuang said that PX plants and other large-scale chemical projects must be strictly implemented before the plant is put into production. Environmental review, in line with environmental standards. In September this year, the National Development and Reform Commission, the Ministry of Industry and Information Technology, the Ministry of Environmental Protection, the General Administration of Safety Supervision, and the Ministry of Land and Resources have issued notices requiring local authorities to conduct safety and environmental protection inspections on sensitive products such as PX, especially highly toxic chemicals. Appropriately expand the safety protection distance and environmental margin, and take social risk assessment as a precondition for project approval. After completion, it must pass the inspection and acceptance of safety and environmental protection departments before it can be put into production. The key is that local governments and enterprises must implement national policies.
Zhou Xueshuang said that the people are more sensitive to the PX project, probably because the local government is not daring to introduce the PX project, and the project is not transparent. And very few chemical companies neglect the safe production management of dangerous chemicals, resulting in production safety and environmental pollution accidents, causing adverse effects. He suggested that from the perspective of environmental safety, appropriate protection distance should be set between chemical projects such as enterprise PX and residential areas. On the one hand, the length of the sanitary protection distance depends on the size of the factory. On the other hand, it depends on the local meteorological conditions, such as the wind direction. Based on the above two conditions, the corresponding protection distance is calculated according to the relevant national standards.
“The harm of PX itself is not great, but many of its production processes and processes are in a high temperature and high pressure environment. Therefore, in actual production, it is necessary to strictly abide by the laws, regulations and operating procedures concerning the management of hazardous chemicals, and carry out scientific research on production equipment. Design and construction are also very important, and can not blindly pursue the project schedule and PX production. In addition, PX has the characteristics of flammability, and must strictly implement the relevant national rules and regulations during storage and transportation.†Tianjin University Experts said that in 1949 By 2010, there were 35 major accidents involving the production, use, storage or transportation of chemicals in the country. Among them, 60% of the major accidents were caused by violations and violations, and 29% were caused by unreasonable equipment and design.
A senior executive of BASF, a well-known German chemical company, said that it is not only developing countries that are developing chemical projects such as PX. Germany and other developed countries also have many chemical companies. However, the concept of safety and environmental protection has become a consensus within the industry. The production process of the product is mostly monitored in real time, and hidden dangers can be discovered in advance. The production in some workshops is transparent and open, and local residents can visit them at any time. At the same time, the company pays great attention to the employees' usual emergency drills, simulates the accidents, and trains the employees' ability to solve practical problems, so that even if there is a problem, the damage can be minimized.
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