Apparatus for Dual-Flow Countercurrent Extraction and Its Evaluation

Abstract

The dual-flow countercurrent extraction technique can be considered to be one of the true moving-bed (TMB) chromatographic methods. However, here we call it dual-flow countercurrent extraction, because the "stationary phase (bed)" is a liquid, and the principal structure of the column is to be categorized in the extractor.This method is a powerful tool for enantio-separation when 1) a suitable chiral separating agent exists, 2) recycling usage of the chiral separator is possible, and 3) a proper apparatus is procured with which continuous separation is to be performed. Although one can separate a mixture into only two fractions with this method, it is sufficient in most cases involving enantio-separations. Compared to chromatographic methods, it is advantageous because continuous separation can be performed by the technique, whereas intermittent separations are required by the chromatographic method. We planned to manufacture a proper apparatus for dual-flow countercurrent extraction for preparative use, though a countercurrent chromatograph 1 , which is not the dual-flow type, and a highspeed dual-countercurrent chromatograph 2 , which is not for the preparative use, are obtainable.We previously reported on an apparatus for dual-flow countercurrent extraction, with which the chiral separating agent can be recycled. 3 We also demonstrated that racemic β-blockers, such as propranolol and pindolol, could be extractively separated into their enantiomers in a chloroform-water two-phase system using didodecyl-L-tartrate as a chiral separator in the presence of boric acid. 4 However, with the vertical column of the previous apparatus, the efficient mixing of chloroform and water could not be attained, mainly because of a large difference in their densities. Also, the maximum flow rate of the extraction solvents was limited to about 3 ml/min with the apparatus. In order to overcome these problems, we designed an improved apparatus with a horizontal-type column. The principle of column separation is similar to that of Morris.5 Before preparing a long column, we investigated the optimal operation conditions using a short-column apparatus, because an experimental evaluation of the column becomes more difficult along with an increase in its efficiency. In this report we describe the structure of the manufactured short-column apparatus for dual-flow countercurrent distribution chromatography and a measurement of its efficiency by a simple graphical stage calculation method. Improved Apparatus for Dual-Flow CounterCurrent ExtractionA unit cell of the improved column comprises a mixer and a settler. All of the plastic parts of the column are made of polyfluoroethylene. The structure of the column is depicted in Figs. 1a, 1b, and a view of the whole apparatus is sketched in Fig. 2. In the mixing chamber, there is a stirring wheel in which a dipole button magnet (10 mmφ×5 mm) is inserted, and on which six cogs are placed. This can be rotated magnetically.The extraction column was prepared by inserting six pairs of mixing and se...

Simulation Study of the Separation of Binary Mixtures by the Continuous Dual-Flow Countercurrent Extraction Method

“…1 The efficiency did not decrease by the attachment of the recovery column. Thus, the further calculations were executed using the column efficiencies of 5+5+1 to 5+5+6 plates.…”

“…3). 1 The rest of the materials are to be present in the organic phase and they migrate to the recovery stage. In order to evaluate the present simulation program, the condition of S/(H+F) of 2.05 (indicated in Fig.…”

Practical Operation Procedure for a Continuous Dual-Flow Countercurrent Extraction Method

“…[3][4][5] The materials, the general experimental procedures and the HPLC conditions are detailed in those reports.…”

“…[1][2][3][4][5] When a binary mixture is subjected to separation by this method, the same solvent is used in both the separation and recovery (backextraction) stage, where a much larger amount of solvents should be required than in the former stage. It must be very economical if a part of the back-extracts can be diverted directly to the separation stage instead of a fresh solvent, without lowering the purities of the raffinates and those of the backextracts.…”