Key Takeaways & Executive Findings
- •• • At 60 cm spray distance, ScCO2 spraying achieved average VOCs emission reduction rates of (62.10±1.59)% across three industrial coating systems, compared to high-pressure airless spraying, demonstrating significant source reduction potential for compliance with tightening VOC regulations. • • Coating efficiency improvements were consistently above 20% for all tested systems at both 40 cm and 60 cm distances, with averages of (30.62±8.75)% and (31.74±12.83)%, respectively, directly reducing coating consumption and waste. • • VOCs content reduction rates varied by coating system: 46.03% for wooden furniture-polyurethane, 23.80% for wooden furniture-acrylic, and 37.60% for metal parts-fluorocarbon, indicating that formulation compatibility is critical for maximizing abatement. • • Diluent substitution rate reached 83% (from 60% to 10% addition), but complete elimination of diluent was not feasible under the tested parameters due to excessive viscosity, highlighting a practical operational limit for ScCO2 technology.
Abstract
Source reduction of volatile organic compounds (VOCs) from industrial emissions is a core task for air quality improvement during China's 15th Five-Year Plan period. Supercritical carbon dioxide (ScCO2) spraying technology emerges as a cutting-edge VOCs abatement approach, as it reduces both VOCs content in coatings and coating consumption. However, empirical research on coating efficiency enhancement and VOCs emission reduction at demonstration scale remains scarce. This study selected three solvent-based coating systems widely used in Chinese industry: wooden furniture-polyurethane, wooden furniture-acrylic, and metal parts-fluorocarbon. A calculation method for ScCO2 spraying efficiency and VOCs emission reduction rate was established, and emission reduction performance was systematically measured. Results indicated that compared with high-pressure airless spraying, average coating efficiency improvement rates of ScCO2 spraying at spray distances of 60 cm and 40 cm across the three scenarios were (30.62±8.75)% and (31.74±12.83)%, respectively. Correspondingly, average VOCs emission reduction rates were (62.10±1.59)% (60 cm) and (53.73±11.78)% (40 cm). VOCs content reduction rates for the three systems were 46.03%, 23.80%, and 37.60%, respectively. Diluent addition was reduced from 60% to 10%, achieving a substitution rate of 83%. The study confirms that ScCO2 spraying can achieve significant reductions in VOCs and solvent emissions in wooden furniture and metal parts coating processes, providing empirical support for industrial promotion.
1. Introduction
Industrial surface coating is a major source of anthropogenic volatile organic compounds (VOCs), which contribute to PM2.5 and ground-level ozone formation. While end-of-pipe treatment has been the dominant control strategy, its incremental abatement potential is diminishing, prompting a shift toward source reduction. Supercritical carbon dioxide (ScCO2) spraying offers a dual benefit: it replaces a portion of organic solvents in coatings and improves transfer efficiency, thereby reducing both VOC content and coating usage. Despite its promise, industrial adoption has been slow due to high upfront costs and a lack of empirical performance data at demonstration scale.
This study addresses the critical gap by systematically evaluating ScCO2 spraying across three representative solvent-based coating systems used in Chinese furniture and metal parts manufacturing. By establishing a rigorous calculation methodology and conducting controlled comparative tests against high-pressure airless spraying, the research quantifies coating efficiency improvements and VOC emission reductions under realistic operating conditions. The findings provide the first comprehensive field-level evidence needed to assess the technical and economic viability of ScCO2 spraying as a source reduction technology, thereby informing policy and industrial decision-making.
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LI Yawen, DING Shiwen, LI Kaiqi (2026). VOCs Abatement Evaluation of Supercritical Carbon Dioxide Green Spraying in Industrial Surface Coating. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202604020
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Frequently Asked Questions
What are the specific VOCs emission reduction rates achieved by ScCO2 spraying compared to high-pressure airless spraying, and how do they vary with spray distance?
At a spray distance of 60 cm, the average VOCs emission reduction rate across the three tested coating systems was (62.10±1.59)%. At 40 cm, the average reduction was (53.73±11.78)%. These values indicate that a longer spray distance enhances the relative benefit of ScCO2 spraying, likely due to improved atomization and reduced overspray.
How does the coating efficiency improvement of ScCO2 spraying translate into material savings and waste reduction in industrial operations?
Coating efficiency improvements averaged (30.62±8.75)% at 60 cm and (31.74±12.83)% at 40 cm across the three systems. This means that for a given coating job, ScCO2 spraying uses approximately 30% less paint compared to high-pressure airless spraying, directly reducing both material costs and the volume of VOC-containing waste requiring disposal.
What is the maximum diluent substitution rate achievable with ScCO2 spraying without compromising coating quality?
In this study, the diluent addition was reduced from 60% to 10%, achieving a substitution rate of 83%. However, complete elimination of diluent was not feasible because the coating viscosity became too high for successful spraying under the tested parameters. This suggests that while ScCO2 can significantly reduce solvent use, a small amount of diluent may still be necessary for certain formulations.
Are there differences in VOCs content reduction rates among different coating systems, and what implications do these have for technology adoption?
Yes, VOCs content reduction rates varied: 46.03% for wooden furniture-polyurethane, 23.80% for wooden furniture-acrylic, and 37.60% for metal parts-fluorocarbon. These differences highlight that the effectiveness of ScCO2 spraying depends on the coating formulation's compatibility with supercritical CO2. Industries using polyurethane systems may see greater benefits, while acrylic systems may require formulation adjustments to maximize reductions.
What are the main barriers to industrial adoption of ScCO2 spraying, and how does this study address them?
Barriers include high initial capital investment for ScCO2 equipment and a lack of empirical performance data. This study provides quantitative evidence of VOCs reduction and coating efficiency improvements across multiple real-world coating systems, which can help companies assess the return on investment. However, a comprehensive techno-economic analysis is still needed to fully evaluate cost-effectiveness compared to conventional methods.
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