Extraction of betaine from beet molasses using membrane contactors

An experimental study of betaine separation involving non-dispersive solvent extraction using hollow fibers is described. The extractant was a solution of dinonylnaphthalene sulfonic acid (DNNSA) in n-heptane and stripping was performed with sodium hydroxide solution. Different operating conditions for the extraction and stripping processes were tested using a single hollow fiber contactor and then both processes were operated simultaneously using two contactors in series. The experimental results were fitted using a kinetic model with two design parameters, namely the overall mass-transfer coefficients referred to the feed and stripping phases. The overall coefficients were also estimated using the conventional diffusion model and the relative contribution of in-series resistances was evaluated using a reaction–diffusion model that takes into account interfacial reactions. A comparison of the individual resistances in the extraction and stripping contactors showed that the complex-formation reaction is slower than the decomposition reaction. This non-dispersive extraction technology was applied to beet molasses betaine/sucrose separation under the conditions identified previously. The results were correctly simulated by the mathematical model developed previously using synthetic solutions.

Research highlights► An experimental study of betaine non-dispersive extraction using hollow fibers is described. ► DNNSA and sodium hydroxide were used as extractant and stripping agents, respectively. ► Mass transfer rate was evaluated using a reaction–diffusion model that takes into account interfacial reactions. ► The extraction-stripping integrated process required acid pH for extraction of the cationic betaine species, in accordance with the equilibrium model. ► The presence of sucrose in the feed phase (the main component of bet molasses) yields an increased chemical reaction resistance in the stripping contactor.