Green chemistry–based synthesis, physicochemical characterization, and kinetic–chemical modeling of a sustainable soot-suppressing bioadditive

Abstract: Within the framework of the Sustainable Development Goals, the replacement of fossil fuels and the mitigation of their emissions represent priority global challenges. Renewable oxygenated additives have emerged as a promising strategy to reduce atmospheric pollutants. This study presents a green synthesis route for the production of dimethyl carbonate (DMC) and diethyl carbonate (DEC) from biomethanol or bioethanol and captured carbon dioxide, applying nine principles of Green Chemistry (GC) and using Ni/Cu catalysts supported in coffee carbon grounds. An experimental design based on green engineering was employed to evaluate the impact of these additives on the reduction of polycyclic aromatic hydrocarbons (PAHs) and soot in diesel combustion engines. The experiments were conducted in an atmospheric-pressure counterflow diffusion flame. The soot volume fraction was measured using light extinction and scattering techniques, while PAH concentrations were determined through advanced optical diagnostics such as laser-induced fluorescence and laser-induced incandescence, complemented by physicochemical characterization using NMR, FTIR, and GC. The results revealed a differential synergistic effect: DMC promoted greater PAH formation compared to DEC under equivalent conditions, a behavior not previously reported. To further elucidate the reaction mechanisms, a kinetic–chemical model supported by computational chemistry methods was developed, incorporating PAH growth up to A7 species (seven aromatic rings, including coronene C24H12). Experimental validation confirmed that DEC was more effective than DMC in reducing soot under equivalent conditions in ethylene flames. This work provides new evidence of how green chemistry enables the synthesis, characterization, and development of kinetic mechanisms of organic carbonates as oxygenated additives and identifies DEC as a sustainable product for emission mitigation, with prospects for technological optimization and industrial implementation aligned with environmental, economic, and social benefits.