VOC pollution and prevention in coating production

Wang Fangyuan (Jinhua 321000, Zhejiang global paint Group Co., Ltd.) Sheng Yilin (321017, bioengineering branch, Jinhua Vocational and technical college, Zhejiang) Abstract: in view of the current situation of environmental protection in paint chemical enterprises, the causes of VOC and its toxicity were analyzed, and the prevention and treatment measures were put forward technically Key words: VOC pollution; prevention and control measures; coating production On June 5, 2003, the 31st World Environment Day, the State Environmental Protection Administration issued the 2002 China environmental situation bulletin and pointed out that the chemical industry should achieve a good combination of economic and environmental benefits through cleaner production to solve the contradiction between pollution and environment, as well as the coordinated development of economy and society Due to the late start of the environmental protection work in China, the environmental protection work in the coating industry is far behind that in foreign countries, especially the pollution and control of VOC, which is still dominated by solvent products in many domestic coating enterprises, has to be given priority in the industry 1 The production of VOC and toxic VOC are volatile hydrocarbon solvent based coatings Most diluents are xylene, toluene, benzene, 200 × gasoline, butyl ester, etc Most of the production of alkyd and amino resin uses volatile pentaerythritol, phthalic anhydride, benzene, alcohol and ester as organic raw materials, so that volatile toxic gases are constantly emitted in the production and construction environment Although the production process is carried out in a closed system, VOC pollution is inevitable due to uncontrollable factors such as production raw materials In gb8978-1997, the limit values of all kinds of volatile toxic and harmful substances that cause air pollution are stipulated VOC discharged into the atmosphere will cause photochemical pollution, that is, VOC and nitrogen oxides react under the sun's ultraviolet rays to generate ozone to increase the ground ozone concentration When the ground ozone concentration exceeds 1.0 μ L / L, it will cause harm to human health, causing headache, dry throat, weakness and other symptoms Now many cities have added an air pollution index forecast measure, which means people have more attention to the living environment Moreover, the solvents and diluents used by coating enterprises have strong flammability and explosiveness, and there are serious fire hazards in high temperature weather in summer 2 VOC prevention and control measures 2.1 strengthen publicity and education Employees in the paint industry should first carry out "three-level environmental protection and safety education" in the plant Department, workshop and post after entering the plant; In the process of production, regular safety training courses should be held to timely understand and master the production process, use methods and protective measures of new materials, and various forms of publicity should be taken to enhance the awareness of self-protection so that employees can fully understand the harm of VOC pollution At the same time, strict production and safety operation procedures shall be formulated to ensure that VOC in the production process is discharged less or not 2.2 strict on-site management On site management is a key measure of enterprise management, and on-site environmental management is an indispensable link In the production process, in addition to strictly implementing the production and safety operation procedures, regular VOC pollution measurement shall be carried out for the workplace and the test results shall be published If there is any over standard, rectification opinions and measures shall be put forward in time Control pollution at the source Qualified enterprises shall pass ISO14000 certification The implementation of ISO14000 environmental management system certification has a far-reaching impact on coating enterprises, which can improve the image, reputation and market access of enterprises, help to eliminate trade barriers, improve the management level of enterprises and the environmental awareness of employees, reduce environmental risks, and play an important role in enterprises 2.3 to reduce or eliminate VOC pollution, the process and formula must be improved For example, properly reduce the feeding temperature, change the feeding mode or use non-toxic and low-volatile raw materials; or use the microcomputer automatic control system to implement unmanned operation to reduce human error factors, so as to achieve accurate measurement and process control to avoid the responsibility accidents such as tank expansion and overflow At the same time, it is necessary to fully introduce foreign advanced equipment At present, many of the production equipment of the paint chemical enterprises in our country are obsolete equipment, which is very unfavorable for the effective control of VOC pollution For this reason, enterprises should increase investment to completely transform the current production equipment so that production can be carried out in a closed and pollution-free system as much as possible 2.4 development of new products at present, the world coatings are developing towards low VOC or environment-friendly coatings The special meeting of "healthy coatings" held in Brussels last year has attracted great attention of Chinese coating experts At present, domestic solventless nitrocellulose paint, epoxy paint and water-based paint are still far behind developed countries in technology For example, Germany's water-based paint has accounted for half of the total paint, while low odor and VOC content of Matt and bright interior wall emulsion paint has become a mature product As the representative of zero VOC coating, powder coating, like water-based coating, has attracted great attention in the coating industry The variety of high solid coatings has been greatly developed The coating R & D personnel need to make more exploration in this area The VOC pollution caused by solvent products of coating enterprises has become another important gas pollution source after flue gas pollution Therefore, enterprises must increase investment in the effective governance of VOC At present, there are many effective VOC governance technologies as follows 3.1 active adsorption is one of the most effective and widely used methods in organic waste gas treatment, including active carbon, diatomite, zeolite and so on Through the adsorption system, not only VOC concentration can be greatly reduced to achieve emission standard, but also the adsorbed products can be reused for production through stripping absorption 3.2 air induced high-altitude discharge is one of the most commonly used and simple methods for general enterprises in painting, sanding and other positions, with low cost, easy operation and obvious effect However, the high-altitude emission is only the transfer of pollution and does not really solve the problem of pollution, while the power of induced draft fan and the installation height of air outlet directly affect the effect of induced draft 3.3 combustion treatment VOC is organic volatile material, which is easy to burn The normal temperature or catalytic oxidation combustion treatment gas can be used to enter the boiler or incinerator from the induced air pipe for combustion, but the high temperature organic gas shall be subject to safety demonstration This method can convert VOC into CO2 and H2O basically 3.4 absorption and degassing: VOC is generally dissolved in diesel or 200 × gasoline and other organic solvents, which can be used as fuel or diluent after absorption of VOC by diesel or 200 × gasoline This method is easy to operate and low cost, but there are still some volatile gas residues after absorption treatment Because the organic solvent itself is volatile, it can not reduce VOC to zero If high temperature occurs, the absorption rate is lower 3.5 condensation collection: for the high temperature organic gas in the reactor, the method of condensation collection can be used first, direct condensation and then spiral condensation The degassing effect of this method is obviously easy to operate, with low operation cost, but the effect of low boiling point gas is not good 3.6 biological treatment of organic waste gas is the most economical and effective method with good effect and operation cost lower than any other treatment method, which is safe and easy to operate The biological purification methods of VOC include direct microbial purification, indirect microbial treatment (first water absorption and then wastewater biological treatment) and plant purification Direct biological purification includes biological absorption tank, biological washing tank, biological trickling filter and biological filter with good treatment effect and convenient operation, among which biological filter technology is more mature and applied For example, there are hundreds of waste gas biofilters built in Germany and the Netherlands with good operation results Indirect biological treatment is to use water or weak alkaline solution to absorb VOC containing alcohols, aldehydes and other substances, which are easily soluble in water after absorption, and then use biodegradation to make the wastewater discharge up to the standard The plant purification method is to increase the green area in the plant area and use the green plants to absorb and transform the pollutants in the air to purify the air This method is suitable for the pollution of the large environment with low concentration 3.7 the VOC pollutants in the solvent based coatings using alternative HAP solvent are mainly the volatile gases in toluene and xylene Although benzene diluent has many advantages in construction, its toxic effect is well known Therefore, some manufacturers are looking for a formula that can replace the solvent containing toluene and xylene to improve the environmental protection performance of the coating Conclusion: with the enhancement of people's awareness of environmental protection, many domestic enterprises have attached great importance to environmental protection work, but there are still many enterprises that only consider the immediate interests are often not thorough in governance, especially the VOC governance measures are not in place and lack of obvious results In general, there are problems of concentration exceeding standard in workplaces, although relevant standards and regulations have been issued However, in action, the VOC prevention and control standards or rules of the coating industry are often not consciously implemented