(495f) Isolation of Carboxylic Acids from Dilute Aqueous Solutions – Intensifying Approach By Conversion in Emulsified Reactive Solvents

Authors: 
Toth, A., Graz University of Technology
Siebenhofer, M., Graz University of Technology
Lux, S., Graz University of Technology
Macher-Ambrosch, R., Graz University of Technology
Painer, D., Graz University of Technology
The focus on the production of biobased bulk chemicals as well as the progress in the biorefinery require innovative downstream processing of the product effluents. Examples are provided by different cellulose pulping processes with varying yields of carboxylic acids (e.g. acetic acid or formic acid). The effluents from such processes are usually characterized by low concentration of the constituents in aqueous solution. Conventional separation techniques quickly reach economic limits. The requirements for downstream processes capable of dealing with such feed specification, must suffice effective separation to ensure economic utilization of the valuable constituents.

The intensification of conventional separation techniques by combining with chemical reaction provides high potential in overcoming these obstacles. Two approaches, reactive distillation for the isolation of carboxylic acids and chemical conversion of the target constituents in both phases of a liquid-liquid extraction process, may offer a feasible option. Reactive conversion of choice for isolation of carboxylic acids is the esterification with an aliphatic alcohol, whereby the market value of the carboxylic acids can be significantly increased and the significant change of physical properties favorably influences the separation process.

As the partition behavior of the reactants is supportive when using higher aliphatic alcohols (e.g. nâ??butanol or 1-octanol), the use of these alcohols, either dissolved in corresponding esters or hydrocarbon based solvents has been investigated. Catalysis and elevated temperature are provided to increase the reaction rate of the esterification reaction. 4â??dodecylbenzenesulfonic acid (4DBSA), a strong anionic surfactant and highly active homogeneous catalyst, has been used in the experimental validation in order to highly increase the contact between the reactants and the catalyst by emulsification. After having finished the reaction the emulsion is separated from the aqueous phase by settling and split by coalescence. A continuous process has been designed by altering conversion, phase separation, emulsion splitting and isolation of the product. Exemplarily 80% separation efficiency was obtained for acetic acid separation from aqueous feed by esterification with octanol in the emulsified solvent phase in single stage isolation.