Sometimes we have to separate a chemical compound from a mixture. We use different physical characteristics such as boiling point, polarity of compounds to separate chemical compounds from mixtures. But sometime we cannot obtain 100% pure compound after separating.
Example
You know, there are a lot of salts are in the sea water such as NaCl, KCl, MgBr22 and more. But we want to separate NaCl from other chemicals (or decrease amount of other chemicals). We use EVAPORATION to remove water and then CRYSTALLIZATION to remove other salts.
Removing water from a solid is also an example to separating compounds. Follwing chemical industries use separation methods to prepare their products.
Transferring of materials from one homogeneous phase to another is defined as separating of mixtures.
Petroleum is a complex mixture of alkanes, cyclo alkane and aromatic compounds. Crude oil is not worth until it is separated into different compounds such as petrol, diesel, kerosene and many more.
Crude oil contains thousands of compounds. Composition of crude oil is classified according to their range of boiling points. These hydrocarbons are separated on the basis of their molecular mass by fractional distillation.
Valuable materials may be mixed with dirt or waste. But we need to recover or separate that valuable material. Therefore we have to follow a specific separating method to recover that material from initial mixture.
Removing unwanted materials from a mixture will reduce the weight of mixtures. It is very important in transporting. So reducing weight will decrease the cost of transportation.
These unit operations (separation methods) will be explained in detail later in this tutorial.
Density or particle size is used when we use mechanical separating methods.
In distillation, boiling point is used to separate chemical compounds. The most industrial use of this is, petroleum refining process. Petroleum contains so many organic chemicals and they have different boiling point values.
Some compounds dissolve very well in some solvents than another solvent. In such cases, extraction is used to separate chemicals.
There are so many unit operations in Chemical Engineering which are helpful to separate one or more chemicals from a mixture. Now we are going to study those unit operations briefly.
Adsorption occurs, when a solid surface is exposed to fluid (a gas or a liquid). Also adsorption is defined as the enrichment of material or increase of density of the fluid in the vicinity of an interface
Adsorption occurs in two ways, physical (physisorption) and chemical (chemisorption).
Transfer of one or more species from the gas phase to a liquid solvent is defined as absorption.
final removal of water, or another solute, and the operation often follows evaporation, filtration, or crystallisation. Drying has more advantages than reducing weight.
Drying is used in lot of chemical industries in the world.
Distillation is one of the most common unit operation in the world and uses in so many industries to separate one or more chemicals from a mixture.
The separation of liquid mixtures into their various components is defined as distillation.
Distillation is the major unit operation in petroleum refining industry.
The separation of the components of a liquid mixture by treatment with a solvent in which one or more of the desired components is preferentially soluble is known as liquid–liquid extraction.
One of the uses of liquid liquid extraction is, separation of aromatics from kerosene-based fuel oils to improve their burning qualities and the separation of aromatics from paraffin and naphthenic compounds to improve the temperature-viscosity characteristics of lubricating oils.
There are three steps in liquid liquid extraction
removal of water from a solution by boiling the liquor in a suitable vessel, an evaporator, and withdrawing the vapour. Heat is supplied to vaporize the solvent.
When evaporation occurs, concentration of material in the solution increases.
If solution contains solids, after evaporated, liquid will become saturated and crystals were deposited.
Crystallization is a separation technique where a solid phase is separated from a mother liquor where the atoms or molecules are highly organized into a structure known as a crystal.
Forming a NaCl precipitation from ocean water is an example to crystallization. Also crystallization is used to large-scale productions of food additives.
Chromatography is used to separation, identification and quantitative analysis of a mixture of compounds. This separation method was originally used to separate the different types of pigments in leaf extracts.
Also with new instruments chromatography can be used to identify components present in a mixture and to measure concentrations of components.
Dangerous drugs like heroin can be identified with quantitatively. Also chromotography is helpful to separate amino acids
