Introduction: China is the world's largest producer and consumer of coatings. Coatings are widely used in buildings, automobiles, furniture, ships, hardware, and other key sectors of the national economy. While promoting industrial development and improving people's livelihood, the industry also faces significant organic waste gas pollution issues. During the coating production process, a large amount of organic solvents such as toluene, xylene, ethyl acetate, and acetone are used to ensure product performance. The resulting volatile organic compounds (VOCs), also known as organic waste gases, are the main process emissions in the coating industry. According to the World Health Organization (WHO), organic waste gas refers to a type of organic compound with a boiling point of 50–250°C and a saturated vapor pressure greater than 133.32 Pa at room temperature, existing as vapor in the air at ambient temperature, which may have irritant, toxic, and in some cases, carcinogenic properties.

Organic waste gases not only directly harm the respiratory and nervous systems of frontline workers, but long-term exposure can lead to asthma, leukemia, and other diseases. They also exacerbate PM2.5 and ozone pollution, becoming a key factor limiting air quality improvement in China. At the same time, with increasingly stringent national environmental policies and the enforcement of regulations such as the "Emission Control Standards for Unorganized Volatile Organic Compounds" and "Air Pollutant Emission Standards for the Coating Industry," the level of VOCs treatment in coating enterprises directly affects environmental approval, production operations, and industry competitiveness. This article, based on the core requirements of environmental impact assessment for coating manufacturing projects, discusses in detail the identification of VOC evaluation factors, emission calculation, and targeted control measures, providing professional reference for coating enterprises to achieve environmental compliance and green development.

01 Introduce Advanced Production Models to Reduce VOC Generation from the Source

The core operations of the coating industry include two major segments: coating production and resin synthesis, involving furnaces, chemical reaction devices, coating preparation units, mixing equipment, and filling equipment. All these facilities emit organic waste gases to varying degrees during operation. Among them, the coating preparation and filling processes produce VOCs characterized by "large volume, low concentration, and complex composition," making them the most difficult and key points for treatment across the industry.

Traditional coating production often adopts extensive management practices, with issues such as poorly sealed equipment, open handling during material transfer, and solvent evaporation during storage, leading to significant unorganized emissions. This not only increases the difficulty of subsequent treatment but also wastes solvent resources. To reduce VOC generation from the source and ensure compliant emissions, coating enterprises must abandon traditional extensive management and actively introduce advanced production technologies and environmental management models, achieving both environmental and economic benefits through scientific and refined management, which can be advanced in the following two aspects:

First, adopt a closed production model. Implement fully enclosed production processes for key equipment such as resin synthesis reactors, coating mixing tanks, and solvent storage tanks, equipped with specialized sealing devices to prevent material leakage and unorganized VOC emissions; material transfer should use sealed pipelines and containers to avoid open dumping and air exposure; the filling process should adopt sealed filling equipment with waste gas collection systems, directly collecting VOCs generated during filling into the treatment system, controlling unorganized emissions from the source. Additionally, automated and intelligent production equipment can reduce manual operation and lower the risk of VOC leakage caused by human factors.

Second, adopt scientific production management. Establish a comprehensive VOC control system, define environmental responsibilities at each production stage, strengthen environmental training for operators, and standardize operating procedures; optimize production processes by selecting low-VOC raw materials (such as water-based or solvent-free coating materials) to reduce VOC generation at the source; reasonably plan production schedules to avoid long-term storage and idle materials, reducing solvent evaporation losses; establish solvent usage ledgers to accurately manage consumption, achieving efficient resource use and providing reliable data for VOC emission calculations.

02 Optimize VOC Treatment and Purification to Improve Efficiency and Cost-effectiveness

VOCs generated during coating production are characterized by complex composition, large concentration fluctuations, and high volume. Single treatment methods often fail to achieve ideal results and are economically inefficient. Common VOC purification methods in the industry are classified into recovery and purification approaches. Enterprises need to select treatment schemes based on production scale, gas concentration, composition, and environmental requirements, balancing treatment effectiveness and cost.

Recovery methods physically or chemically recover solvents from VOCs for reuse, reducing pollution and raw material loss while improving economic benefits. Common methods include adsorption-freezing, extraction-distillation, and condensation recovery. The core requirement is that recovered solvents must meet purity standards for reuse, with further purification if necessary. However, the coating industry's VOCs are often low-concentration and high-volume; single recovery methods require large equipment investment and high costs, making them less economical for small- and medium-sized enterprises. Therefore, recovery methods are better suited for high-concentration, high-value solvents, such as special solvents used in premium coatings.

Purification methods decompose or transform VOC pollutants into harmless substances to achieve compliant emissions. Common methods include incineration, adsorption-desorption, and adsorption. Incineration is simple and highly efficient, decomposing VOCs into CO2 and water with purification efficiency exceeding 95%. However, for low-concentration, high-volume VOCs in the coating industry, incineration alone requires large equipment and high fuel consumption, limiting its use.

Adsorption-desorption is an optimized treatment for low-concentration, high-volume VOCs. VOCs are first adsorbed by materials such as activated carbon or zeolite, concentrated into high-concentration gas, and then desorbed. The high-concentration VOCs can be further treated by incineration or recovery, reducing equipment size, fuel consumption, and treatment cost. This combined approach is the most widely used solution in the coating industry.

Some small and medium-sized enterprises use single adsorption methods. While low-cost and easy to operate, limitations include saturation of traditional adsorbents, declining efficiency, and high maintenance costs, making it suitable