Extraction Processes (Lecture 7) PDF

## Extraction - Extraction; - It is the removal of soluble materials (liquids or solids) from a solid or from a liquid mixture by treatment with a selective solvent. - The extraction may be classified according to the mechanism of extraction into: - Solid-liquid extraction (leaching). - Liqu...

## Extraction - Extraction; - It is the removal of soluble materials (liquids or solids) from a solid or from a liquid mixture by treatment with a selective solvent. - The extraction may be classified according to the mechanism of extraction into: - Solid-liquid extraction (leaching). - Liquid-liquid extraction. ## Importance of extraction 1. Potency is readily controlled. 2. Deterioration by enzyme action is diminished. 3. Preparations of the drug are more easily formulated, more stable, more palatable, and more elegant. 4. Tabletting of the crude material may not be possible. 5. Injection of the crude material may be undesirable or dangerous. 6. Smaller bulk facilitates storage and transport. ## Solid-liquid extraction (leaching) - Extraction of soluble valuable materials from solid substance, or to free valuable insoluble substance from less valuable soluble one. - E.g. Extraction of tea leaves, coffee seeds, isolation of fixed oil from seeds, strychnine from nux vomica seeds. - Isolation of enzymes or hormones. - E.g. Insulin from animal source. ## Extraction always involves __2__ steps: 1. Contact of the solvent with the solid to be treated so as to transfer the soluble constitute (solute) to the solvent. 2. Separation or washing of the solution from the residual solid. ## Factors affecting the rate of leaching 1. __Particle size:__ - Reduction of solid particle size increases the surface area available for extraction and decreases the distance which the solute transfers from the inside of particles to outside. - Reduction of particle size should be controlled since very fine particle may: 1. Inhibit the solvent circulation. 2. Increase electrostatic charges on the surface of the particles, which adsorb the extracted solute on their surfaces and decrease the efficiency of extraction. 2. __Temperature:__ - Increasing the temperature leads to an increase in the solubility and diffusion of most solutes, so increases the extraction rate. Also, an increase in temperature leads to a decrease in the viscosity of solvent and facilitates its diffusion to the solid to be extracted, so increasing the extraction rate. - But also temperature should be controlled to avoid: 1. Inhibition of enzymatic activity 2. Decomposition of active constituents 3. __Agitation:__ - Agitation facilitates diffusion of solute to the bulk of solvent, so increasing the rate of extraction. - Agitation keeps fine particles in suspension and facilitates solvent penetration, and also prevents sedimentation of particles. 4. __Solvent:__ - Should be selective to dissolve the material intended to be extracted. In this concern, like dissolves like (meaning polar solvent dissolves polar materials, and vice versa). - Cheap, non-toxic, stable, i.e. not volatile and non-inflammable. - **N.B.** as the extraction process precedes, the concentration gradient between the solvent and solid substances will decrease, and also the solvent viscosity will increase; these may result in hindering the extraction process. ## Liquid-liquid extraction - Liquid-liquid extraction is the term applied to any operation in which a material dissolved in one liquid phase is transferred to a second liquid phase. - __Requirements for liquid-liquid extraction:__ - Selectivity of solvent. - Differential solubility of the two liquids in the solvent. - The solvent used must be immiscible with the solution to be extracted. - Liquid-liquid extraction consists of the same basic steps as solid-liquid extraction: 1. Intimate mixing or contact of the solvent with the solution to be treated, so as to transfer the solute from the solution to the solvent. 2. Separation of the liquid solution phase from other liquid solution phase. 3. Recovery of the solvent (distillation). - The separation and recovery of the solvent may be carried out by various methods such as distillation or simple heating or cooling. - Liquid-liquid extraction is widely used for separation of the components of a solution, particularly when: 1. The components are relatively non-volatile. 2. The components are sensitive to the temperature required for separation by distillation. 3. The desired, less volatile component is present in the solution only in a relatively small amount. In such a case, the less volatile component may be extracted to a second solvent, producing a more concentrated solution from which it may be recovered more economically.