Reactive extraction of carbonyl compounds from apolar hydrocarbons using aqueous salt solutions

Several aqueous salt solutions are evaluated as reactive extraction solvents for the recovery of aldehydes and ketones, present in few-percent concentrations in apolar hydrocarbons. The influence of the type (amino, hydrazine, or bisulfite) and structure of the salt on the extraction performance toward aromatic and linear aliphatic aldehydes, as well as toward cycloaliphatic and linear aliphatic ketones, was analyzed. The results show that some of the aqueous salt solutions enable distribution ratios of carbonyl as high as 300, which are much higher than the values obtained in most conventional solvents. We observed that bisulfite and hydrazine salt solutions have much higher capacities than solutions of amine salts. Furthermore, the presence of a carboxylic group instead of a sulfonic group, but also a larger distance of the acidic group from the reacting amino center, makes an amine a better extractant. Generally, it was noticed that the extractability using aqueous salt solutions decreases in the order linear aldehyde > aromatic aldehyde > cyclic ketone > linear ketones. Most of the evaluated salt solutions showed a decrease in the carbonyl distribution ratio with increasing temperature, indicating that a temperature shift might be a feasible option for reextraction. The losses of organic solvent in extract or water in raffinate are not significantly influenced by the presence of salt. Therefore, aqueous salt solutions show great potential to be used as reactive extraction solvents for the recovery of carbonyl compounds from apolar organic solvents.