Current situation and existing problems of environ

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The current situation and existing problems of environmental pollution in China's coating industry. This paper introduces the development situation and main production process of China's coating industry, analyzes its pollution status, mainly including wastewater, waste gas and solid waste generated in the production process, discusses the main standards related to the production of China's coating industry, and the existing problems of environmental pollution, and points out that the transformation of the coating industry to green development and sustainable development is its inevitable trend

[key words] coating industry; Pollution status; Volatile organic compounds (VOC); Control standards; Sustainable development

1 overview of China's coating industry

1.1 development process

coating is a kind of material coated on the surface of objects, which can form a solid film with firm adhesion and certain strength and continuity. The formed film is called film, paint film or coating [1] coating. Coatings have a long history of development in China. The development process of coating names in China has experienced the transformation of "paint paint coating" [2] (see Table 1). Paint technology has long been recorded in ancient China. Paint liquid first appeared in the stone age, Xia, Shang and Zhou dynasties as adhesive, preservative and decorative lines. In 1915, the establishment of Shanghai Kailin pigment and paint factory announced the birth of China's modern coating industry; In 2000, for about ten years, China's coating enterprises gradually changed from the operation mode of "state-owned enterprises, private enterprises and foreign enterprises" to a new operation mode of "state-owned enterprises, private enterprises and foreign-funded enterprises" [3]; In 2009, China's coating industry ushered in a golden period of development [4]. Under the impact of the global financial crisis, China's coating industry bucked the trend and became the country with the largest coating production in the world. China's annual coating production gradually increased [5]. According to the latest statistical data of the National Bureau of statistics, as of the first half of 2018, the total output of coatings of Enterprises above Designated Size in China had reached 8.3949 million tons, an increase of 0.6% over the same period last year [6]. Now we have ushered in the spring and Autumn period, the Han Dynasty, the Tang Dynasty after the fourth paint industry heyday

1.2 distribution overview

China's coating industry is mainly concentrated in economically developed areas and raw materials gathering areas. In 2014, there were 1344 Enterprises above the scale of coating in China, and the number of coating enterprises in various provinces and cities is shown in table 2[7]. By 2018, the number of Enterprises above Designated Size in the national coating industry had increased to 1906, mainly concentrated in 8 provinces and cities including Zhejiang, Jiangsu, Shandong, Guangdong, Hebei, Shanghai, Beijing and Tianjin. The coating output of these 8 provinces and cities accounted for 76.5% of China's total coating output [8]. To sum up, China's coating enterprises are mainly concentrated in economically developed provinces and cities, mainly in the Yangtze River Delta, the Pearl River Delta and the Bohai rim, which is related to the regional economic development and resource endowment advantages

2 the main production process of China's coating industry

the production process of coating is mainly physical dispersion and mixing process [9]. The process flow of different types of coating is different. The specific process is shown in Figure 1. Different processes produce different pollution. See Table 3 for specific examples. Solvent based coatings face serious environmental pollution, serious energy waste and high cost. However, compared with traditional coatings, solvent based coatings have their own obvious advantages and occupy an important position in China's coating industry. As a sunrise industry in the coating industry, water-based coatings, powder coatings and high solid coatings are characterized by low pollution, low "three wastes"/"no" three wastes "and energy conservation. They are environmentally friendly coatings that respond to the national cleaner production strategy

3 environmental pollution in China's coating industry

pollutants involved in the coating industry include wastewater, waste gas, dust, solid waste gas, ammonia nitrogen, petroleum, volatile phenol, chemical oxygen demand, total phosphorus, hexavalent chromium, cadmium, lead and arsenic [14]. Pollution to the environment and threat to human health can not be avoided in the process of coating production and the use of coating

3.1 wastewater

the water pollution of the coating industry includes the production wastewater of the coating industry, the wastewater pollution from the cleaning of coating production equipment and production sites. Most of the coating production is related to resin synthesis and uses a large number of organic solvents, pigments, additives and other chemical materials, so the discharge of industrial wastewater is not possible in the production process. Now let's learn about the operation method of the pneumatic pipe joint tensile testing machine [15]. The washing of water-based coating equipment causes great water pollution. In the production process of solvent based coating, it is not allowed to wash the production equipment with water, so in general, there is less washing wastewater in the production of solvent based coating. Washing wastewater (such as amino resin wastewater, alkyd resin wastewater and oil bleaching wastewater) mainly comes from resin reaction [16]. The wastewater from the coating industry has the characteristics of great changes and poor biodegradability, and the wastewater with normal color ----- associate professor xupiming of Far East University of science and technology contains toxic organic compounds, the composition of pollutants is complex, and the wastewater produced by different coating processes is different [17]. The national mandatory standard GB limits of harmful substances in solvent based wood coatings for interior decoration materials has specified the limits of four soluble harmful elements: lead, cadmium, chromium and mercury [18]. Harmful substances contained in coatings can directly or indirectly damage human health [19]

3.2 the harmful substances in the exhaust gas

paint will lead to the decline of indoor air quality and affect human health. The policy formulation focus of the coating industry in the comprehensive directory of environmental protection is mainly focused on coatings containing high organic compounds, heavy metals such as lead, and raw material products [19]. VOC is a recognized precursor [20]. Organic solvents are widely used in solvent based coatings, making the coating industry an important industrial pollution source for the generation and emission of atmospheric VOC. According to relevant data, in 2014, China's paint output reached 12.7891 million tons, and the solvent consumption of the paint industry was about 7million tons, accounting for about 13% of China's total VOC emissions [21]. Paint waste gas mainly comes from organic solvents and diluents used in paint production. Once the film is formed, the organic volatiles eventually enter the atmosphere, causing serious environmental problems. The VOC emitted by Chinese coatings is about 1883 KT, mainly including benzene series compounds, alcohols, esters, ethers and ketones. The average incremental reactivity index (based on o3/voc) is about 36 kg, and 31% of volatile organic compounds are toxic substances [22]. VOC produced by the coating industry causes serious pollution and impact on the atmosphere [23]; It also indirectly affects the global climate and human health [24]

3.3 solid waste

no matter what construction method is adopted, the coating can not be fully utilized, and the unrecoverable and lost coating will form waste residue. The waste residues of the coating industry mainly include: waste mother liquor, waste residue, waste water treatment sludge, waste adsorbent, waste organic solvent, waste paper recycling, intermediate waste, etc. produced in the production of dyes, pigments, coatings, paints, etc. except for water-based coatings; Deinking slag produced during processing; Invalid, deteriorated, counterfeit and substandard inks, dyes and pigments produced during the production, sales and use of coatings. The coating waste residue is not only difficult to treat, but also difficult to collect, which increases the difficulty of pollution control in the coating industry [25]

4 main standards of China's coating industry

the General Administration of quality supervision, inspection and Quarantine of the people's Republic of China and the National Standards Committee have issued 30 relevant standards for coatings and pigments as of 2017, including test methods, technical specifications and product categories. The new standard proposed at the executive meeting of the Ministry of ecological environment in march2019 stipulates that the wastewater pollutants, odor pollutants (except styrene) and environmental noise generated by coating enterprises or production facilities shall comply with the corresponding national pollutant discharge standards, and the identification, treatment and disposal of solid wastes shall comply with the corresponding national solid waste pollution control standards; The emission limits, monitoring, supervision and management requirements of air pollutants generated by the coating industry are applicable to GB emission standard of air pollutants for coating, ink and adhesive industry. The new standard will be officially implemented on July 1, 2019. The production units involved in the production and modification of synthetic resin in the coating industry shall comply with GB emission standard of pollutants for synthetic resin industry [27], and the manufacturing of lotion shall also comply with this standard. With the rapid economic development, China has become a large paint manufacturing country, but the VOC emissions also increase. VOC produced by the coating industry is the focus of pollutant control, and enterprises should manufacture in strict accordance with China's standards. See table 4[28] for specific standards

5 problems of environmental pollution in China's coating industry

5.1 the development level is low and the pollution control is difficult

there are many coating enterprises in China, but they are small in scale and lack of ACE products and enterprises [31]. In 2025, the overall industrial scope will exceed 100 billion yuan. It is understood that China's small coating enterprises with an annual output of less than 1000 tons account for the majority, and their products are concentrated in the middle and low-end market. The phenomenon of blind construction, repeated construction, small workshop production, intermingled good and bad, and low overall development level in coating enterprises has led to greater difficulties in governance and prominent environmental protection problems

5.2 there are few cleaner production enterprises in coatings and serious pollution

cleaner production refers to the use of advanced technology and equipment, clean energy and raw materials to reduce pollution at the source, improve resource utilization efficiency, reduce or avoid the generation and emission of pollutants in production and use, and reduce the harm to the environment and human health. By 2015, there were about ten coating enterprises with the ten ring marks in China, accounting for only 1% of the national coating enterprises [32]. There are few clean production enterprises of coatings, which cause serious pollution

5.3 a large amount of VOC is produced, which pollutes the environment and endangers human health.

China's coating industry is still dominated by the production of solvent based coatings, which account for about half of China's coating industry. The preparation of solvent based coatings requires the use of a large number of volatile solvents, such as benzene, toluene, xylene, heavy metals (lead, mercury, cadmium, etc.), most of which pollute the environment and endanger human health [33]. If toluene and xylene are inhaled for a long time, fatigue, headache and dizziness, chronic dermatitis, conjunctival congestion, memory impairment and other neurasthenic syndromes will be caused, while benzene poisoning can cause leukemia [34]. The coating industry has become an important industrial pollution source for the generation and emission of atmospheric VOC. Especially in household coatings, volatile organic compounds at room temperature have become a public hazard to the environment and human health. The serious problems such as the large amount of VOC, the large number of high-power energy consumption equipment and the serious noise and dust pollution are the challenges on the road of sustainable development of China's coating industry [35]

6 outlook

from tung oil more than 2000 years ago to chemical synthetic coatings today, China's coating industry has developed rapidly and has become a major coating production country. China is the largest paint market in the world. The paint industry has promoted China's economic growth, but its production and use have also brought pollution to China's water environment and atmospheric environment. At the same time, it also endangers human health. In particular, the volatile organic compounds produced by it will have a great impact on human health and hinder China's sustainable development to a great extent. Industry environmental protection is the main challenge faced by China's coating industry. It is an inevitable trend for coating consumption to change from "oil" to "water" during the "13th five year plan"

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