Sustainable Production of Furfural in Biphasic Reactors Using Terpenoids and Hydrophobic Eutectic Solvents

Furfural comes from lignocellulosic biomass that, together with its derived products, has many useful applications in several industries. Furfural is usually obtained via pentose dehydration using a biphasic reactor to extract furfural in situ from its reaction medium. However, the conventional solvents used so far, mainly toluene and methyl isobutyl ketone (MIBK), are harmful to health and the environment. Therefore, hydrophobic natural solvents have been successfully tested in this work to improve the performance of the process from a sustainable point of view. First, 30 natural solvents were screened using the conductor-like screening model for real solvents (COSMO-RS) method to select solvents with high affinity to furfural. From the results obtained in the screening, 14 natural and 2 conventional solvents were selected for experimentation, including thymol, eugenol, toluene, MIBK, and several hydrophobic eutectic solvents formed by thymol. Then, the liquid-liquid extraction of furfural was carried out both in vials and in a reactor, simulating the usual temperature and pH conditions for obtaining furfural. Thymol and eugenol showed extraction yields of 95 and 91%, significantly higher than those of conventional solvents MIBK and toluene, which were 85 and 81%, respectively. Finally, the in situ reaction and extraction of furfural from xylose were performed using the natural solvents eugenol and thymol and the conventional solvent MIBK. Under operating conditions, namely, microwave heating to 443.2 K, 10 min of reaction, and a solvent-to-feed ratio of 1.00, xylose conversion of 96.7%, furfural selectivity of 75.3%, and a furfural production yield of 72.8% from xylose were obtained using eugenol as the organic solvent, with improved outcomes over MIBK and thymol cases, pointing an adequate approach to improve both the effectiveness and the sustainability of the process.