As a critical production process in industries such as printing and packaging, new energy batteries, and electronic materials, coating technology is widely used in the manufacturing of release paper, protective films, optical films, lithium battery separators, and other products. During the coating process, large quantities of organic solvents—such as ethyl acetate, toluene, MEK (methyl ethyl ketone), and methanol—evaporate under high temperatures during the drying stage, generating VOC exhaust gases with highly complex compositions. Challenges including difficulty in meeting emission standards, high energy consumption costs, and unstable treatment performance continue to trouble many coating enterprises. CADAIR has extensive experience in VOC treatment for the coating industry and, leveraging its core strengths in stable compliance and significant energy savings, has successfully served many leading companies in the sector.
I. Characteristics of Industry Exhaust Gas
The primary prerequisite for VOC treatment in the coating industry is the accurate identification of exhaust gas characteristics. The core features of industry emissions are as follows:
- Complex composition: Primarily composed of esters, ketones, alcohols, and benzene-series compounds. Ethyl acetate, MEK, and toluene are the most frequently used solvents. Some processes also involve high-boiling-point solvents such as acetylacetone and ethylene glycol monomethyl ether.
- High air volume with low concentration: This is a common industry condition. A single coating line often generates exhaust airflow ranging from tens of thousands to hundreds of thousands of cubic meters per hour.
- Large concentration fluctuations: VOC concentration levels vary widely, ranging from several hundred mg/m³ to over ten thousand mg/m³.
- Continuous production operation: Coating lines typically operate continuously 24 hours a day. Any malfunction in the treatment equipment can directly affect production capacity.
II. Key Treatment Challenges
Due to the unique nature of coating industry exhaust gases, conventional treatment solutions often prove inadequate. The major treatment challenges are summarized below:
- Complex and variable solvent composition: When switching between different product types, exhaust gas compositions change significantly, making it difficult for a single treatment technology to fully adapt and effectively process all conditions.
- Stringent emission standards: Environmental regulations in China continue to tighten. Some regions require non-methane hydrocarbon concentrations below 20 mg/m³, far stricter than national baseline standards.
- High energy consumption pressure: The industry commonly operates under high-airflow conditions, resulting in substantial energy costs for VOC treatment systems and directly impacting manufacturing competitiveness.
- Strict safety requirements: Solvents such as toluene are flammable, while some solvents are toxic, placing stringent demands on safety protection design within treatment systems.
- Zeolite rotor clogging issues: Coating exhaust gases often contain silicon-based substances that can adhere to the rotor surface, causing adsorption performance degradation. This places extremely high requirements on the pretreatment stage.
III. Recommended Solutions
To address the unique characteristics of coating industry exhaust gases, CADAIR recommends mature process solutions centered on zeolite rotor systems or three-bed RTO systems. Based on exhaust composition, concentration, airflow volume, and local emission standards, treatment technologies can be flexibly combined to suit different operating conditions.
(1) Customized Treatment Processes for Different Conditions
- High-airflow, low-concentration conditions:
Adopt a zeolite rotor + RTO combined process. The concentration ratio can reach 10:1–15:1, significantly reducing downstream treatment airflow and delivering excellent energy-saving performance. - Medium-to-high concentration mixed solvent conditions:
Use a three-bed RTO process without the need for pre-concentration treatment. The system structure is simple, thermal efficiency exceeds 95%, and long-term operating costs are low. - Strict emission requirement conditions:
Adopt a zeolite rotor + five-bed RTO combined process. The five-bed structure provides higher purification efficiency and can meet stringent regional environmental standards. - Recoverable single-solvent conditions (such as ethyl acetate):
Use an activated carbon fiber (K-FILTER) adsorption recovery process. Solvent recovery rates exceed 97%, recovered solvent quality is high enough for direct reuse in production, and equipment investment payback periods are short.
(2) Key Technical Features
CADAIR’s core treatment equipment is designed for the complex operating conditions of the coating industry:
- The zeolite rotor uses imported zeolite molecular sieves with strong hydrophobicity and the ability to continuously withstand temperatures up to 200°C. Adsorption efficiency is over 40% higher than conventional activated carbon systems and effectively resists interference from silicon-based substances in coating exhaust gases.
- The RTO system adopts an optimized multi-bed design with thermal efficiency exceeding 95% and purification efficiency above 99%. Its ceramic heat storage media feature a modular structure for convenient disassembly and maintenance.
- In addition, based on coating exhaust characteristics, the system incorporates pretreatment units such as front-end filtration and spray scrubbing to prevent impurity clogging and ensure the long-term stable operation of the rotor.
(3) Specialized Solvent Recovery Solutions
For coating manufacturers using large amounts of single solvents such as ethyl acetate, CADAIR provides customized activated carbon fiber (K-FILTER) adsorption recovery technology. The standardized process route consists of “adsorption → steam desorption → condensation recovery,” enabling high-quality solvent recovery and recycling.
This technology achieves treatment efficiency above 97%, with outlet concentrations as low as 30 ppm—far superior to standard industry emission requirements. The recovered ethyl acetate features high purity and can be directly reused in production processes, substantially reducing solvent procurement costs. Most projects recover equipment investment within 1–2 years.
For special operating conditions with high moisture content, an SD-type dehydration unit can be added to further improve recovered solvent quality.
IV. Benchmark Case Studies
CADAIR has deeply specialized in VOC treatment for the coating industry and has served thousands of customers. The following are representative benchmark projects from its project database.
(1) Mixed Exhaust Gas Treatment Cases
- A well-known coating enterprise in Mianyang, Sichuan:
The exhaust gas contained multiple organic solvents including ethyl acetate, toluene, methanol, MEK, and acetylacetone. The exhaust airflow reached 220,000 Nm³/h. A zeolite rotor + RTO process was adopted, achieving stable compliant emissions during operation. This project has become a benchmark VOC treatment project for the coating industry in Southwest China. - A new materials enterprise in Qingdao, Shandong:
The exhaust gas contained solvents such as MEK, N-methyl-2-pyrrolidone (NMP), and ethylene glycol monomethyl ether, with an airflow volume of 5,000 m³/h. A three-bed RTO process was selected, eliminating the need for rotor pre-concentration. The system is simple, efficient, and has operated stably without faults over the long term.
(2) Specialized Solvent Recovery Cases
CADAIR has extensive project experience in ethyl acetate recovery. Leveraging its activated carbon fiber (K-FILTER) adsorption recovery technology, the company has successfully served leading enterprises such as Yongxin Huangshan, Kunshan Jiapu, Dongguan Qimiao, Guangzhou Yongxin, and Zhongjin Matai.
Among these projects:
- China Tobacco Anhui (Lucky Optoelectronics) Project:
The exhaust gas contained dichloromethane and methanol, with an airflow volume of 29,000 Nm³/h. Officially commissioned in 2025, the project adopted a KF + KB series process (carbon fiber adsorption + rotor concentration) to achieve highly efficient solvent recovery.
Measured data show that CADAIR’s ethyl acetate recovery system achieves a treatment efficiency of 97%, with outlet concentrations as low as 30 ppm. The recovered solvent can be directly reused in production.
V. FAQ – Frequently Asked Questions
Q1: How should coating industry VOC treatment processes be selected?
A1: Process selection should comprehensively consider exhaust composition, concentration, airflow volume, local emission standards, and solvent recovery value. General selection principles are as follows:
- For high-airflow, low-concentration exhaust gas, prioritize a zeolite rotor + RTO combined process to reduce downstream treatment load through concentration.
- For medium-to-high concentration mixed solvent exhaust gas, choose a three-bed RTO system due to its simplicity and low operation and maintenance costs.
- In regions with strict emission standards, use a zeolite rotor + five-bed RTO process to ensure compliant emissions.
- If the exhaust gas mainly contains recoverable single solvents such as ethyl acetate, prioritize activated carbon fiber (K-FILTER) adsorption recovery technology. The recovered solvent can be reused, and equipment investment can typically be recovered within 1–2 years.
CADAIR’s technical team can provide free solution comparison and selection services based on customer VOC testing reports.
Q2: How are silicon-based substances in coating exhaust gases handled?
A2: Silicon-based substances in coating exhaust gases mainly originate from release agent residues. These substances easily adhere to the surface of zeolite rotors, reducing adsorption performance.
To address this issue, CADAIR optimizes the pretreatment system by adding a combined purification device consisting of metal mesh filtration and activated carbon adsorption to intercept silicon-based impurities and improve the cleanliness of gas entering the rotor.
At the same time, the system uses zeolite rotors made with hydrophobic imported molecular sieve materials. Their anti-fouling performance significantly exceeds that of conventional activated carbon systems, effectively extending maintenance cycles and ensuring long-term stable operation.
