Investigation of green solvents for the extraction of phenol and natural alkaloids: Solvent and extractant selection

Abstract

Green solvents have been gaining momentum to replace traditional volatile organic compounds (VOCs) in solvent extraction processes due to environmental and health concerns. In this work, phenol was used as a model compound for natural alkaloid extraction to find an appropriate alternative among green bio-derived solvents, including d-limonene, α-pinene, p-cymene, 2,5-dimethylfuran (DMF) and CyreneTM. Moreover, extractants including Cyanex 923®, trioctylphosphine oxide (TOPO), tri-butyl-phosphate (TBP) and Alamine 336 were evaluated to investigate the improvement to phenol extraction performance. The selection of extractants and green solvents is based on an evaluation matrix composing several criteria including toxicity, biodegradability, feedstock, market price, physicochemical properties and extraction performance. Hansen solubility parameters (HSPs) and conductor-like screening model (COSMO-SAC) with direction character of hydrogen bonding parameters (DHB) were used to assist the selection process. The COSMO predictions are in good agreement with the experimental data and within 20% deviation in most cases. Finally, d-limonene and Cyanex 923® were selected as the solvent replacement and extractant, respectively. 0.2 M and 0.6 M Cyanex 923® in d-limonene and xylene were further investigated via phenol and morphine isotherms at optimised pH values. It was found that d-limonene exhibits acceptable extraction performance for phenol extraction but is less efficient for morphine extraction as compared to xylene possibly due to emulsion formation during alkaloid extraction.