Barring a few exceptions, almost every element or compound is found in an impure state i.e. as a mixture of two or more substances - thus the need to separate it into its individual components so as to make it more productive. Its applications in the field of chemical engineering can be very important. The best example that can be cited here is that of crude. Crude is a mixture of various hydrocarbons (though valuable in itself), there is a greater demand for the various hydrocarbons that it is a mixture of, viz. gasoline, diesel, etc. Enter separation processes!!

These processes can essentially be termed as a mass-transfer process. The classification can be based on the means of separation, i.e. purely mechanical or chemical. Ordinarily the choice of separation depends on the pros and cons of each. For systems that can not be separated by purely mechanical means (eg. crude), chemical separation is the way out. The mixture at hand could be a solid-solid, solid-liquid, solid-gas, liquid-liquid or liquid-gas mixture.

Like already mentioned above the phases could exist as a combination of any two or more states (solid, liquid or gas). Depending on the combination, various processes like distillation, absorption, adsorption, stripping, extraction, leaching, crystallization etc. can be employed to separate the mixtures. Some times two or more of these processes have to be used in combination to obtain the desired separation. In addition to these 'chemical' processes, other purely mechanical processes such as filtration, gravity separation etc. can also be applied where possible.