(597e) Efficient and Selective Recovery of Formic Acid and Acetic Acid from Their Mixed Solutions

Formic and acetic acids are among the low molecular weight carboxylic acids that have wide applications in various industries. They co-exist in the media of several biological productions and wastewater streams. Their high production amounts and costs make their low-cost and efficient recovery very significant and beneficial.

Selective recovery of carboxylic acids from their binary acid aqueous solutions with high efficiency is so important. One of the most advantageous methods for the purpose is reactive extraction, a modified version of traditional liquid-liquid extraction process. It is superior to various types of separation techniques with its high distribution coefficients (K_D), low energy requirements, thermal stability and ease of process. Despite there are several studies on reactive extraction in the literature, most of them were carried out using single acid synthetic solutions. On the other hand, several types of aqueous solutions contain carboxylic acids, e.g., biological production media and wastewater streams are multi-acid solutions.

In the present study, selective recovery of formic and acetic acid from their mixed solutions by reactive extraction was aimed. In order to have a successful operation, system variables should be operated at optimum values. Firstly, both acids were recovered from their single acid solutions using tertiary amines dissolved in 10 different types of organic diluents. These diluents or solvents were selected from different types of chemical classes. The K_D and extraction efficiency (E%) values were compared and most efficient solvents for the operation were determined. In addition, separation factor values were calculated using the K_D values of each acid obtained in their separate solutions. For both acid types, the highest K_D and E% values were attained with intermediate molecular weight alcohols. In addition, highest separation factors were also obtained with them, too. Furthermore, separation factors increased with the increase in initial concentration of the extractant.

In the second part of the experimental part, formic and acetic acids were recovered via reactive extraction from their binary acid solutions. Highest separation factors were obtained with 0.5 M TOA in alcohols while the lowest were with 0.1 M TOA level, which is consistent with the results, obtained using single acid solutions. The effect of initial pH on the selective recovery was also probed. The highest recovery rates were obtained with the solutions; pH was not adjusted (pH~2.2) and with the organic phases, 1-hexanol was used as the diluent. Moreover, effects of the acid ratio and total acid concentration (where the acid ratio is 1) were also investigated. Highest selective extraction efficiencies (separation factor~8) were obtained with total acid concentration of 0.5 M (0.25 M each acid in aqueous solution). According the results, selective recovery was not influenced from the acid ratio at this total acid level.