Equilibrium studies on butane-1,4-diamine extraction with 4-nonylphenol

BACKGROUND: The extraction of butane-1,4-diamine (BDA) from aqueous solutions with undiluted 4-nonylphenol (4NP) has been studied at three temperatures (298 K, 310 K and 323 K) in a batch system. A reactive extraction model based on mass action law was applied to describe the experimental data.

RESULTS: The model developed describes the distribution of BDA between the 4NP phase and the aqueous phase, and the average stoichiometry of the complexation due to interactions between the two amine groups of BDA and 4NP, as well as the complexation constant were fitted to experimental data with good accuracy for each of the three temperatures, the largest error at the confidence limit of the estimated parameters being 6%. Using a Van't Hoff plot, the thermodynamic parameters of the equilibrium constant were determined and used to estimate that in a single stage with only S/F = 0.5, over 99% of the BDA can be extracted from a 1.146 wt% aqueous solution. High distribution ratios at low BDA concentrations hampered the effective recovery by back-extraction in a single stage, therefore multistage processing was considered and short-cut calculations revealed a maximum concentration factor of 3.6.

CONCLUSION: Good agreement between single stage equilibrium data and the model was obtained and the model developed was used in short-cut calculation of a coupled multistage forward and back-extraction process showing a maximum concentration factor of only 3.6, therefore an alternative, more effective recovery strategy, e.g. through anti-solvent addition is suggested.