Extraction of carboxylic acids by amine extractants.

摘要

This work examines the chemistry of solvent extraction by long-chain amines for recovery of carboxylic acids from dilute aqueous solution. Long-chain amines act as complexing agents with the acid, which facilitates distribution of the acid into the organic phase. This complexation is reversible, allowing for recovery of the acid from the organic phase and regeneration of the extractant.;Batch extraction experiments were performed to study the complexation of acetic, lactic, succinic, malonic, fumaric, and maleic acids with Alamine 336, an aliphatic, tertiary amine extractant, dissolved in various diluents. The diluents were selected from a variety of chemical classes, including halogenated hydrocarbons, alcohols, ketones, substituted aromatics, and alkanes.;The results of batch extraction experiments were interpreted by a "chemical" model, in which stoichiometric ratios of acid and amine molecules are assumed to form complexes in the solvent phase. From fitting of the extraction data, the stoichiometry of complexes formed and the corresponding equilibrium constants were obtained. The results of the model were combined with infrared spectroscopic experiments and results of past studies to analyze the chemical interactions that are responsible for extraction behavior.;Factors found to affect extraction include the acidity and structural characteristics of the acid extracted, the nature of the diluent, and temperature. Extraction increases with acid strength. Monocarboxylic acids form a higher ratio of multiacid to single acid complexes and show less aggregation of complexes than do dicarboxylic acids. The stoichiometries of complexes of dicarboxylic acids are influenced by intramolecular hydrogen bonding. Hydrogen-donating diluents, such as chloroform, promote formation of strong complexes with a single acid and amine, ketones promote multiacid per amine complexes, and inert diluents promote aggregation. An increase in temperature decreases the amount of acid extracted.;The information from the equilibrium studies was used to develop guidelines for large-scale staged extraction and regeneration schemes. A novel scheme, in which the diluent composition is shifted between extraction and regeneration, was developed which could achieve both high solute recovery and high product concentration.