More class material - SOLVENT BASED SEPARATION Solvent...

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1 SOLVENT BASED SEPARATION Solvent Selection Rafiqul Gani, Peter M. Harper & Martin Hostrup CAPEC, Department of Chemical Engineering, Technical University of Denmark, DK-2800 Lyngby, Denmark. The objective of this article is to highlight the important issues related to selection/design of solvents for different types of solvent based separation techniques. The properties of the solvent are closely related to the design/operation of a solvent based separation technique that is employed to perform a specified separation task. The solvent selection problem formulation together with methods and tools that can be employed to solve such problems are highlighted. Practical examples illustrating the important solution steps are presented. INTRODUCTION Separation involves removal of one or more of the constituent parts from a mixture. A solvent is that constituent of a solution that is liquid in the pure state, is usually present in the larger amount and has dissolved the other constituent (a solute) of the solution. The solute may be a solid, a liquid or a gas. The solvent may be a single compound or a mixture of compounds. Solvent based separation techniques become necessary when separation or removal of a solute(s) from a mixture become difficult or
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2 infeasible by conventional separation techniques such as distillation. If the addition of a solvent causes a totally miscible liquid to split into two liquid phases and produce the necessary property difference, the solvent based separation technique is commonly known as liquid-liquid extraction. If the addition of a solvent causes the coexisting vapour and liquid phases to have different properties, the solvent based separation technique is called extractive distillation. Figures 1a & 1b highlight the change of the mixture properties as a result of the addition of a solvent. In Figure 1a , the difference between the properties of the liquid and vapour for the binary azeotropic mixture of ethanol-water with and without the addition of solvents is highlighted. It is clear from Figure 1a that addition of a solvent removes the barrier of the azeotropic condition. Figure 1b highlights through a ternary diagram that addition of the solvent causes the totally miscible binary liquid mixture (components A and B) to split into two liquid phases, a solvent-rich phase and a solute-rich (A or B) phase. << Figures 1a & 1b >> Examples of industrial processes employing solvent based separation techniques are numerous. Almost all chemical, petrochemical, biochemical and pharmaceutical processes employ one or more solvent based separation techniques. In chemical and petrochemical processes, solvents are used mainly to separate components from liquid and/or gaseous mixtures. While in biochemical and pharmaceutical processes, solvents are typically employed for dissolving or removing solids. Use of a solvent to extract aromatic compounds from a petroleum by-product or removal of a chemical species
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More class material - SOLVENT BASED SEPARATION Solvent...

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