N.J.M. Kuipers

Extraction of Caprolactam with Toluene in a Pulsed Disc and Doughnut Column—Part I: Recommendation of a Model for Hydraulic Characteristics

Abstract Caprolactam, the monomer for Nylon‐6, is industrially recovered from an aqueous feed containing ammonium sulphate by extraction with organic solvents like benzene, toluene, or chlorinated hydrocarbons followed by back‐extraction with water. Extraction columns like the Rotating Disk Contactor and Pulsed Packed Column are industrially applied. In this paper a model is recommended for the description of the hydraulic characteristics of a pulsed disc and doughnut column for caprolactam extraction with toluene. In Part II and III the hydraulic and mass transfer characteristics, respectively, are determined and described with the developed models. The hydraulic characteristics are correlated as a function of the operating conditions for the experimental conditions covering the industrial operating range. The model is derived for equilibrium conditions in order to avoid the influence of mass transfer. The final model describes the operational window via equations describing flooding due to insufficient pulsation, and flooding due to a too small relative velocity between both phases and phase inversion. In the operational window several operational regimes can be distinguished, being mixer‐settler, dispersion, and emulsion type operation. Finally, two equations are presented for the description of the Sauter drop diameter and hold‐up at each operational point. The hydraulic characteristics are correlated using physical properties, operational parameters, and geometrical characteristics of the column.

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=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=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.

Reactive Extraction of Alcohols from Apolar Hydrocarbons with Aqueous Solutions

The aqueous solutions are evaluated as sustainable reactive extraction solvents for the recovery of monohydroxyl alcohols (benzyl alcohol, 1-hexanol, cyclohexanol) present in few-percent concentrations in apolar hydrocarbons (toluene, n-hexane, and cyclohexane) by considering two approaches. An aqueous solution containing a reactive extractant, like borate salts, borate complexes, a monosalt of dicarboxylic acid, hydroxypropyl-cyclodextrins, and silver nitrate, shows limited potential to be used. Another approach, in which the alcohol is chemically modified prior to the extraction into an easy-extractable form, in this case a monoester/carboxylic acid, shows much more potential. An environmentally benign aqueous solution of sodium hydrogen carbonate can provide a distribution ratio of benzyl alcohol up to 200, leaving the solubility of the organic solvent in the aqueous solution unchanged relative to pure water and therefore increasing the selectivity with two orders of magnitude. The modification of aromatic, cyclo-aliphatic, and linear aliphatic alcohols can be performed efficiently in the apolar organic solvent without need for a catalyst. The recovery of the modified alcohol can be performed by back-extraction in combination with a spontaneous hydrolysis.

Performance analysis and optimization of enantioselective fractional extraction with a multistage equilibrium model

Chiral compounds are important products in the pharmaceutical and fine chemical industry. Fractional reactive extraction (FREX) is a promising enantiomer separation method but knowledge on translation into industrial practice is very scarce. In this work the combinations of process and product parameters that generate a specified yield and product purity have been evaluated using a multi-stage equilibrium model. The simulations demonstrated that the influence of changes in process parameters (pH, T, concentrations) can be predicted with the multistage equilibrium model for reactive extraction of phenylglycinol and phenylethylamine. A higher pH, lower temperature, higher concentrations and a higher excess of extractant all result in higher purities. Implementation of reflux results in somewhat higher product purities (or less stages), but a significant loss in capacity. Recovery of product and extractant by backextraction should be carried out by pH shift, preferably with CO2 to prevent salt formation. For separating racemic mixtures with a minimal single stage selectivity of 1.5 a multiproduct extractor should contain 50 stages, evenly distributed over the wash and strip section.