(300g) Esterification and Extraction with Supported Liquid Membrane Permeation

Wood pulping processes often generate aqueous effluents containing carboxylic acids; particularly acetic acid. Biorefinery concepts increasingly target integrated material loops including side streams and side stream constituents, and value added products, such as esters, are desired approaches. Esterification of carboxylic acids from pulping effluents may enable production of added value products from pulping effluents. In the present project liquid supported membrane permeation is used to combine esterification reaction with subsequent extraction of the reaction product. Teerachaiyapat et al [1] showed that a hollow fiber membrane module can be used as esterification reactor in principle. The set up used in the present work, originially developed behind the background of heavy metal recycling, has been adapted for reactive membrane separations. The membrane unit offers challenging technological features in isolating value-added products from dilute effluents with a complex matrix. Since cross flow operation is applied, fouling as well as scaling is not a serious issue of process stability limiting significance [2]. The flexibility in membrane composition gives access to the transfer of non-ionogenic as well as ionogenic species. Even highly water soluble solvents, reactants and catalysts may be applied without need of raffinate treatment, since loss of solvent is limited by the physical barrier of the membrane.

The results confirm applicability of the membrane process for the combination of separation by membrane permeation with rigid membranes and esterification of acetic acid with octanol. Via combination of membrane permeation and esterification, the reaction equilibrium related to the aqueous phase may be overcome because of limited solubility of water in the membrane phase. Acetic acid is transferred from the aqueous bulk phase to the rigid interface of the membrane where it converts to the nearly water insoluble ester by releasing water to the aqueous phase while the ester diffuses into the membrane bulk phase. Esterification in the aqueous phase would need the catalyst sulfuric acid which cannot be recycled. In phase transfer catalysis diethylhexylphosphoric acid (DEHPA) or sulfonates (e.g. Dodecylbenzenesulfonic acid) may be used as catalyst in the solvent phase. DEHPA is not catalyzing this reaction sufficiently while dodecylbenzenesulphonic acid (DBSA) is catalyzing the esterification reaction to a sufficient extent. Emulsion formation of DBSA in the solvent phase is avoided by separation from the aqueous phase with the rigid membrane.

[1] T. Teerachaiyapat and P. Ramakul, â??Application of hollow fiber supported liquid membrane as a chemical reactor for esterification of lactic acid and ethanol to ethyl lactate,â? Korean J. Chem. Eng., vol. 33, no. 1, pp. 8â??13, 2016.

[2] M. Siebenhofer, H. Noll, and M. Kienberger, â??Liquid Membrane Permeation with Supported Liquid Membranes and their Application in Li-ion Battery Recycling,â? Sep. Sci. Technol., vol. 50, no. 18, pp. 2937 â?? 2947, 2015.