Many processes in chemical engineering require the separation of one or more of the components of a liquid mixture by treating the mixture with an immiscible solvent in which these components are preferentially soluble. In some cases purification of a liquid may be the function of the process, in others the extraction of a dissolved component for subsequent processing may be the important aspect. An example of the former is the preparation of pure organic liquids from products of the oil industry. Liquid/liquid extractions may also be used as energy-saving processes by, for example, eliminating distillation stages. It is possible, of course that the substance of interest may be heat-sensitive anyway and that distillation is accordingly an unacceptable process. The rate at which a soluble component is transferred from one solvent to another will be dependent, amongst other things on the area of the interface between the two immiscible liquids. Therefore it is very advantageous for this interface to be formed by droplets and films, the situation being analogous to that existing in packed distillation columns. The Armfield Liquid/Liquid Extraction Unit takes the form of a vertically-oriented packed column which may be operated either, by filling the column with water and allowing a solvent to flow down the column over the packing, or filling the column with solvent and allowing water to flow up the column over the packing. In either case the process is continuous, both liquids being pumped into the column. Sensing electrodes at the top and bottom of the column determine whether the column is filled with water or with solvent. This is achieved by sensing and maintaining the position of the water level at the appropriate height. A solenoid valve controlling the flow of solvent under gravity from the column is operated by the sensing electrode system.A distillation unit with a fractionating column is included to allow the reclamation of solvent where appropriate.
- Description of apparatus
The apparatus consist of:
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Floor-standing and welded steel framework fitted with adjustable feet.
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The stainless steel glass liquid/liquid extraction columns.
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Water for the column is stored in the supply tank from where it is pumped by the centrifugal pump.
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Polythene tank to collect the water leaves the top of the column.
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The organic solvent supply tank provides the feed for the solvent metering pump.
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The level of the water/solvent interface in the column is determined by the operation of the solenoid valve.
- Experiments done on it:
- Determination of Distribution Coefficient :The objective of this experiment is to determine the distribution coefficient for the system organic solvent-Propionic Acid-Water and to show its dependence on concentration. The solvent (water) and solution (organic solvent/propionic acid) are mixed together and then allowed to separate into the extract phase and the raffinate phase. The extract phase will be water and propionic acid and the raffinate, organic solvent with a trace of propionic acid. The distribution coefficient, K, is defined as the ratio.It is assumed that equilibrium exists between the two phases. At low concentrations, the distribution coefficient is dependent on the concentration and thus Y = KX.
- Basic Operation of the Liquid/Liquid Extraction Column: The objective of this experiment is to observe the hydraulics of counter current flow in a packed column.The experiment will be carried out using the two immiscible liquids organic solvent and water and the column will be operated in the two modes: (a) The aqueous phase as the continuous medium. (b) The organic phase as the continuous medium.
- Overall Mass Balance and Mass Transfer Coefficients with the Aqueous Phase as the Continuous Medium:The objective of this experiment is to demonstrate how a mass balance is performed on the extraction column, and to measure the mass transfer coefficient with the aqueous phase as the continuous medium.
- Overall Mass Balance and Mass Transfer with the Organic Phase as the Continuous Medium:The objective of this experiment is to demonstrate how a mass balance is performed on the extraction column, and to measure the mass transfer coefficient with the organic phase as the continuous medium.
- Demonstration of Solvent Recovery:The objective of this experiment is to recover the solvent used in the liquid/liquid extraction experiments using the distillation column