Green monoterpenes based deep eutectic solvents for effective BTEX absorption from biogas

Abstract

The combustion of biogas which contains significant amounts of monoaromatic hydrocarbons, i.e. benzene, ethylbenzene, toluene, and xylene (BTEX) can cause many technological, environmental, and health problems. Therefore, in these studies, a new physical absorption method based on deep eutectic solvents (DES) consisting of monoterpenes and carboxylic acids was developed for BTEX removal. A total of 39 DES were synthesized, of which seven were selected based on their affinity to BTEX, favorable physicochemical properties, and “green” character. Detailed structural (i.e. 1H NMR, 13C NMR, and FT-IR) and physicochemical experiments (i.e. melting point, density, viscosity, and surface tension) were performed for the DES. Then, DESs were used for the absorption process in both the laboratory and enlarged scale. BTEX absorption was monitored using two methods, including "in-situ" gas chromatography, and "online" sensors matrices. The crucial absorption parameters i.e. type of DES, temperature, and regeneration possibility were carefully studied. The mechanism of BTEX absorption was explained using experimental spectroscopic techniques and theoretical analysis based on the COSMO-RS model. The obtained results indicate that Eucalyptol:Octanoic acid can selectively capture BTEX from a biogas mixture due to the formation of electrostatic interaction. DES absorption capacity is 53.96 mg/g, which is comparable with commercially available absorbents.