Concentrating aqueous acetate solutions with tertiary amines

Abstract

Water may be extracted from aqueous calcium acetate or sodium acetate solutions using low miscibility, low molecular weight tertiary amines, e.g. triethylamine (TEA) and N,N- dietliylmethylaniine (DEMA). This novel extraction technology was originally applied to water desalination in which water was extracted from aqueous sodium chloride solutions. Here, we explore its potential to recover acetate produced via fermentation. At 40C 55C, which corresponds to typical fen-fermentation temperatures, these low molecular weight tertiary an-amines, or their mixtures, can extract large amounts of water, but not much acetate salt, from dilute aqueous solutions. Thus, dilute acetate solutions can be concentrated by selectively removing water. At lower temperatures, the amine phase contains 20-35% water and negligible acetate salt. When the temperature is raised, water phases out of the amine, allowing the amine to be recycled and reused to extract additional water. Using this approach, about 82.5% of water can be removed from a 3% dilute solution using conventional multi-stage, counter- current extraction, thus providing a 15% concentrated acetate salt solution. Sodium acetate/water/TEA&DEMA equilibria were compared with calcium acetate/water/TEA&DEMA equilibria. The former system has a lower extraction temperature range; however, it does not have serious Iii-lime precipitation or phase interface emulsion problems as in the latter system-n. This work correlates the distribution coefficients with the organic-phase water content to help process design.