Abstract
In many complex systems in solvent extraction a second solute is often present or is added to promote extraction of the first solute. Previous studies showed that the electrolyte sulfuric acid can be considered as a salting‐out agent for extraction of formic acid from water by methyl isobutyl ketone.
In the present work two systems were studied: (I) hydrochloric acid‐formic acid‐water‐methyl isobutyl ketone and (II) sulfuric acid‐acetic acid‐water‐methyl isobutyl ketone. Selectivities of over 200 were found favoring the extraction of formic over hydrochloric acid, and values of over 6,000 favoring the acetic over the sulfuric acid were found. The data for extraction of formic acid were correlated by the Setschenow equation. A similar type of equation was found for extraction of acetic acid in system II.
The results indicate that the electrolyte hydrochloric acid can also be considered as a salting‐out agent for formic acid. The data show that sulfuric is more effective than hydrochloric acid in salting‐out the formic acid. This is in qualitative agreement with experimental data in other systems employing sulfate and chloride electrolytes and with the theoretical equation derived by Debye and McAuley. About 28% less sulfuric acid is needed to salt‐out a given amount of acetic acid when compared with salting‐out the same amount of formic acid.
The changes in activity coefficient of the acetic acid in the aqueous phase with additions of sulfuric acid were measured in system II. These activity coefficient changes could account for only about 39% of the increase in distribution ratio of the acetic acid. A possible explanation for this is that the molecular species of the acetic acid in the organic and aqueous phases changed when sulfuric acid was added to the water phase.