Fast solvent screening for counter-current liquid-liquid extraction columns

Liquid-liquid extraction (LLEx) provides the separation of a certain solute present in a stream when adding a solvent that produces a phase split. Then the raffinate is collected free of solute, which in turn is to be found in the extract. The solute is separated from one phase and mixed in another phase from which it is recovered, in most cases, by distillation. The main difficulty of the process is to find a suitable solvent. When an immiscible solvent is not found, in some cases, the extractive distillation is an alternative. The present work compares the LLEx process with extractive distillation process. Furthermore, two parameters are provided to rank the solvents useful for LLEx, one related to the solvent aqueous toxicity impact, and another related to the energy required for solvent recovery. Both parameters for a counter-current LLEx column are calculated using a simple decanter, i.e. a single liquid-liquid equilibrium stage. The first parameter depends on the solvent lost in the raffinate, and its aqueous toxicity is represented by LC50 (lethal concentration required to kill half the members of a tested population). The second parameter depends on the minimum solvent flow rate and its boiling point. Hence, the proposed parameters are suitable to easily check when new proposed solvents are more environmental friendly.