Automotive paint sludge contains pigments, resins, solvents, curing agents, and other compounds, and is widely regarded as a VOC-rich hazardous waste. Previous research has shown that VOC emissions from paint sludge are mainly governed by diffusion, and that higher temperatures can accelerate emissions from porous or organic materials. However, existing studies have largely relied on empirical observations, while the physical mechanism connecting temperature with key emission parameters remains insufficiently understood. This gap makes it difficult to predict VOC release under changing environmental conditions, especially during storage, transport, and treatment of sludge generated by the automotive industry.
A study (DOI: 10.48130/een-0026-0010) published in Energy & Environment Nexus on 04 June 2026 by Mingqian Cheng's team, Kunming University of Science and Technology, reports that temperature-dependent VOC emissions can be quantitatively described by theoretical correlations for the diffusion coefficient and initial releasable concentration.
To build the framework, the researchers first used statistical physics to derive temperature-dependent relationships for two core parameters: the diffusion coefficient, Dₘ, which reflects how rapidly VOCs migrate through the solid matrix, and the initial emittable concentration, Cₘ,₀, which represents the VOC fraction available for release. Their derivation showed that ln(Dₘ/T¹·²⁵) varies linearly with 1/T, while ln(Cₘ,₀·T⁰·⁵) also follows a linear relationship with 1/T. The team then selected oil-based dry paint sludge from an automobile manufacturing plant in Changchun, China, and characterized its physical and chemical properties. Because the sludge had very low water content, the influence of internal moisture on VOC diffusion could be minimized. Emission tests were conducted in a VOC release chamber at four temperatures: 18, 23, 28, and 33 °C, with relative humidity maintained at 50% and ventilation at two air changes per hour. Seven representative VOCs were analyzed, including 1-butanol, butyl acetate, 1,2,4-trimethylbenzene, 1-ethyl-4-methylbenzene, 1,2,3-trimethylbenzene, M&P-xylene, and O-xylene. The results showed that emission rates rose sharply with temperature, but declined after several hours and nearly stopped after about 15 hours. Compared with 18 °C, total VOC release at 33 °C increased by 77.84%–287.35%. Both Cₘ,₀ and Dₘ generally increased with temperature, and the fitted emission parameters showed strong agreement with the diffusion model, with determination coefficients mostly above 0.93. Further validation confirmed that the theoretical correlations predicted temperature-driven changes well, with most regression results showing R² values above 0.9. The team also tested six machine-learning models, finding that ridge regression performed best, although the physical model was more robust under limited data conditions.
Overall, the study provides a clearer explanation of why warmer conditions intensify VOC emissions from automotive paint sludge and offers a predictive tool for short-term emission assessment. While the authors note that long-term emissions may involve additional chemical processes such as aging or hydrolysis, their framework marks an important step toward more reliable hazardous-waste emission modeling and cleaner industrial-process control.
###
References
DOI
10.48130/een-0026-0010
Original Source URL
https://doi.org/10.48130/een-0026-0010
Funding information
This research was supported by the Yunnan Fundamental Research (No. 202401CF070139), the National Natural Science Foundation of China (No. 22406076), and the Central Government Guides Local Science and Technology Development Fund (No. 24ZYQA025).
About Energy & Environment Nexus
Energy & Environment Nexus (e-ISSN 3070-0582) is a multidisciplinary journal for communicating advances in the science, technology and engineering of energy, environment and their Nexus.