(408c) Intensification of Carboxylic Acid Isolation Processes By Emulsification

Authors: 
Toth, A., Graz University of Technology
Macher-Ambrosch, R., Graz University of Technology
Lux, S., Graz University of Technology
Siebenhofer, M., Graz University of Technology
Process intensification holds a central role in the biorefinery, as the substitution of crude oil by renewable feedstock overstrains standard processes in terms of economy and efficiency. Intensification can be achieved by applying heuristic methods to develop innovative processes in biomass refining. While conversion of biomass to any desired extend is the lesser problem (at least from the point view of downstream processing), the downstream processing of effluents is energy and resource demanding. Therefore, low grade carboxylic acids or low grade alcohols are rarely processed. Within isolation, low concentration and unfavorable combinations of separation relevant substance properties form the most troublesome problems. A promising concept to deal with this economic problem is the change of properties like solubility or relative volatility by chemical conversion.

The change of properties, a tool of process intensification, can be combined within existing processes and equipment. Esterification of low grade carboxylic acids for example does change physical properties significantly. For esterification of carboxylic acids (e.g. acetic acid or formic acid) high excess of water is a major obstacle. Superimposition of the chemical conversion with liquid-liquid extraction can be used to overcome this limitation. Enhancement of the reaction rate as well as mass transfer, may be attained by catalyst-induced emulsification. Surface active, acidic catalysts like sulfonic acids (e.g. 4-dodecylbenzenesulfonic acid) accord with these requirements.

As a test system 60 g L-1 acetic acid was chosen with n-octanol as reactant and n-undecane as diluent. 4-dodecylbenzenesulfonic acid was used as catalyst, due to its good performance in esterification catalysis and due to its emulsification properties. Experiments were performed in order to determine the influence of catalyst, reaction temperature and solvent composition on the reaction kinetics and separation efficiency. Experimental results for esterification of dilute acetic acid with n-octanol in the emulsion regime have shown the applicability of pseudo-homogeneous rate laws for modeling the reaction kinetics. This implies a quasi-homogeneous state as a result of emulsification. For implementation of this intensified process, a mixer-settler setup is suitable as it allows higher conversions and separation efficiencies through multi-stage operation. Phase separation can be achieved through centrifugation or electrical splitting.