Economic and environmental benefits of novel process of ionic liquids-based toluene absorption from exhaust gas at atmospheric pressure

Abstract

The traditional toluene absorption process typically operates at high absorption pressure and desorption temperature, imposing a significant burden on the process. In this work, a novel process of atmospheric pressure toluene absorption using ionic liquids (ILs) is first proposed, which involves introducing a stripping column after the desorption unit to perform secondary purification of the circulating ILs, further decreasing the toluene content in ILs from 106–215 ppm to 5–13 ppm. Moreover, the novel process reduces the absorption pressure from 18 bar to 1 bar, and decreases the desorption temperature from 310 °C to approximately 150 °C. A comprehensive comparison of the traditional and novel process is carried out using nine ILs composed of imidazolium cations ([BMIM]+, [HMIM]+, [OMIM]+) and anions ([BF4]-, [PF6]-, [NTf2]-), considering both process economics and life cycle environmental impacts. The results indicate that in comparison to the traditional process using same ILs, the proposed novel processes exhibit superior economic performance and lower environmental impact, achieving savings of 68.9–76.9% in total annual cost and reducing global warming potential by 56.4–74.8%.