In Part I of this study a theoretical model was recommended describing the hydraulic characteristics, being Sauter drop diameter, hold-up, operating regimes, and operational window, of caprolactam extraction in a pulsed disc and doughnut column. In order to confirm the theoretical model pilot plant experiments for the caprolactam forward and back-extraction were performed to determine the hydraulic characteristics as a function of the operating conditions. The experimental conditions covered the industrial operating range. All hydraulic experiments were performed at equilibrium conditions in order to avoid the influence of mass transfer.In the determination of the operational window flooding because of too low pulsation was qualitatively observed, while it was found that at high pulsation phase inversion was limiting for the back-extraction process and flooding for the forward extraction process. Application of the in Part I recommended theoretical model for the description of the obtained hydraulic data resulted in an accurate description after fitting the drop diameter, hold-up, and phase inversion data.
In a previous study a solvent mixture of heptane containing 40 mass % heptanol was selected as an alternative in the industrial extraction of caprolactam to replace benzene, toluene, or chlorinated hydrocarbons. This work reports the equilibrium distribution ratio of caprolactam and four model impurities of organic nature, namely, cyclohexanone, aniline, n-methylcaprolactam, and cyclohexane-carboxamide, comparing the mixed solvents with toluene as a reference. The resulting phase equilibria were interpreted using the equilibrium stage model. Based on these calculations it was found that, compared to toluene, the co-extracted fraction of cyclohexanone and aniline was higher, that of n-methylcaprolactam was comparable, and that of cyclohexane-carboxamide was lower using the mixed solvent. Overall, the mixed solvent reduced the fraction of coextracted impurities by almost 10 %.
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