Separation of low molecular weight alcohols from dilute aqueous solutions by reversible chemical complexation

Abstract

The removal of alcohols from dilute solutions has traditionally been performed by distillation. Since this is an energy intensive process, a large amount of the total processing cost is due to the separation and purification of the alcohol. As an alternative to distillation, extraction is investigated from both a process and a chemistry point of view for several alcohols. The goals of the project were to find effective solvent systems for removal of alcohols and to investigate the interactions occurring in the organic phase during extraction. Ethanol was examined both as a model compound and because of the interest in its production by fermentation. The four butanols were extracted in order to investigate the differences in extraction of the various isomers. Several propanols and propanediols were used also. Phenols were found to provide much higher distribution ratios for extraction of ethanol than do other common solvents. Since most phenols are solids at room temperature, a mixed solvent system was employed. It was found that the type of diluent used could have a very large effect on the distribution ratio for the alcohol as well as on the water co-extraction and the solvent loss to the aqueous phase. In extracting the butanol isomers it was found that the indicated activity coefficients in the organic phase were approximately the same when large concentrations of m-cresol were present. This indicates 1 that the majority of the difference in the distribution ratios of the isomers is due to the differences in solvation of butanol in the aqueous phase. A mass-action-law model was used to obtain indicated stoichiometries for the complexes formed in the organic phase between the alcohol and m-cresol. Both multiple linear regression and curvefitting methods were used to find the stoichiometries. The results seem to indicate the presence of a 1:1 alcohol:m-cresol complex with solvation modifications due to the changing concentrations of the components of the organic phase. From the complex formation constants at different temperatures, the enthalpy of complex formation was calculated for the interaction between ethanol and m-cresol. 2 i DEDICATION To Shelley for making it all worthwhile ii ACKNOWLEDGMENTS I would like to acknowledge the support I have received from Professor C. Judson King. His knowledge and experience were invaluable during my graduate career. He allowed both the freedom to pursue ideas and the guidance to keep from straying to far.