Extraction of Caprolactam with an Alternative Benign Solvent in a Pulsed Disc and Doughnut Column

Abstract

Caprolactam is obtained by extraction using organic solvents like benzene, toluene, or chlorinated hydrocarbons. As an alternative solvent, the mixed solvent heptane-heptanol (40 mass %) was selected in previous studies based on a relatively high distribution ratio of caprolactam, a low mutual solvent solubility, beneficial physical properties, and a low distribution ratio of impurities. Now, the hydraulic and mass transfer characteristics of the extraction of caprolactam in a pulsed disc and doughnut column (PDDC) were investigated using the benign solvent. The results were compared to those for toluene.The PDDC showed qualitatively comparable operational characteristics for both solvents. In the hydraulic experiments the mixed solvent showed smaller drop diameters and hold-ups, required lower pulsation intensities for regime transitions, but the operational windows are slightly smaller. For both solvents, mass transfer resulted in increasing drop diameters and pulsation intensities required for regime transition. In the forward extraction the mixed solvent was superior, where HETS/m ¼ 0.26 to 0.37, compared to 0.42 to 0.67 for toluene, while less theoretical stages are required as well. For the back-extraction HETS/m ¼ 0.33 to 0.40 for the mixed solvent compared to 0.30 to 0.37, but toluene requires the lower amount of theoretical stages.The hydraulic characteristics at equilibrium and concentration profiles in both the forward and back-extraction were described accurately using the developed models.

Mass transfer performance in pulsed disc and doughnut extraction columns

“…Since no published correlations are available for prediction of mass transfer coefficient in pulsed disc and doughnut columns, the Kumar and Hartland correlations are commonly used for description of the mass transfer performance in pulsed disc and doughnut columns (Van Delden et al, 2006;Grinbaum, 2006). In the present work, the possibility of using these correlations for prediction of the overall mass transfer coefficient is examined.…”

“…The comparison of experimental results with those calculated by the Kumar and Hartland correlations is shown in Figure 5. Van Delden et al (2006) also used these correlations for description of mass transfer performance of extraction of caprolactam with toluene in a pulsed disc and doughnut column. Vol.…”

Extraction of samarium and gadolinium from aqueous nitrate solution with D2EHPA in a pulsed disc and doughnut column

“…Among the various types of extraction columns, the pulsed disc and doughnut extraction column is one type of extractor whose application has rarely been referred to the literature [13][14][15][16]. An installation of the pulsed disc and doughnut columns to treat the uranium solutions from Western Mining Corporations in South Australia has shown that these columns have a clear advantage over the mixer-settlers.…”

Axial Mixing and Mass Transfer Performance of an Annular Pulsed Disc-and-Doughnut Column

“…[8] The axial dispersion and backflow model are most appropriate for describing axial mixing and mass transfer for column scale-up designs, [9] and have been applied to the PDDC. [10][11][12][13][14][15] The most widely used model, the ADM, was proposed by Danckwerts, and is an intuitive and simple solution. [5] In this model, mass transfer factors are considered in terms of the number of mass transfer units (N oc ), whereas all nonideal factors are considered in terms of a single parameter, namely the axial dispersion coefficient, which is consistent with Fick's law with a clear physical meaning.…”