Simple Separation Methods

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Terminology

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Properties of matter

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Simple Separation Methods

Distillation

Distillation as the Precursor to Gas Chromatographic Methods

non- volatile components

HPLC

volatile components

separated on a packed or capillary column

Phases in Distillation

Forms and Modes of distillation

Azeotropic/Extractive distillation

Example

Formation of two immiscible liquid phases by addition of benzene to water and ethanol.

To separate mixtures whose components boil too close together for economic fractional distillation.

Adding another component to alter the relative volatility of the mixture substances and form lower-boiling azeotrope that is heterogeneous.

Any technique used to break an azeotrope (mixtures that are difficult to separate) in distillation.

steam distillation

The mixture boiling point tempreture is reduced by vaporixing it into a stream of carrier vapor

vacuum distillation

Applications

To separate

materials that decompose below their normal boiling points.

high-boiling mixtures.

It is distillation under decreased pressure to reduces the boiling temperatures.

Flash distillation

It is instantaneous and continuous vaporization of a definite fraction of the liquid mixture in such a way that the total vapor produced is in equilibrium with the residual liquid.

Fractional distillation

It is based on the condensation of the hot vapor at verious levels in the column and the resulting liquid refluxes to a lower level where it is vaporized, which corresponds roughly to a re- distillation.

It depends on the distribution of constituents between the liquid mixture and vapor in equilibrium with the mixture.

less volatile ones are in greater concentration in the liquid.

more volatile components concentrated in the vapor

used

for separation of the components of liquid mixtures.

related to

solids

sublimation (highly specialized distillation method), is used to volatilize their component if possible .

evaporation but all the components of interest are volatile. while volatile components are separated from non-volatile ones in evaporation.

Extraxtion

Countercurrent Extraction Versus Differential Column System

Multiple Extractions

Craig Apparatus

method of multiple liquid-liquid extractions is countercurrent extraction, which permits the separation of substances with different distribution coefficients (ratios)

Extraction of Mixtures

Successive Extractions

If Kc < 1000 -> divide some of the extraction solvent into smaller portions and for each portion use successive extractions.

If Kc >1000 -> 1 signal extraction stage is enough to extract all of the target species.

Distribution ratio D

Excluding all complications according the interactions between the extracted species and the used solvents; these interactions should be ignored to simplify the calculations. D = total concentration of solvent in organic phase/total concentration of solvent in aqueous phase

Distribution Coefficient of a Species

Distribution Coefficient is used for one species.

Distribution Coefficient Kc

Distribution of a solute concentration (C) between two solvents ( 1 and 2) during extraction can be represented by the following equation: Kc = C1/C2

Distribution of solute between two immiscible solvents

Filtration

Types of filtration

Simple filtration

Using gravitational force to separate solids from the liquid.

Using simple filter papers (made from cellulose) and exhibit particle retention levels down to 2.5 μm.

Filtration under vacuum

Using Membrane Filters

Using Buchner funnel

used to

separate solids from liquids.

Porous material with a certain particle sizes (such as filter paper or membranes) allow the solvent to pass through while retaining the solids with particle sizes higher than the pore sizes.

Precipitation

Precipitation by Adjustment of pH

Mainly organic & inorganic weak acids & bases

Precipitation via Chemical Reaction

Common ion effect

Addition of a species that form a lower solubility salt with the target species.

Solvent Precipitation

Addition of another miscible solvent to the solution which lower the solubility of the component of interest

formation of pure crystals

By carried out in (a proper solvent & a controlled manner)

formation of precipitate (PPT)

By Increase the concentration of a solute in a solution to a higher level than its solubility

Evaporation

t is the process of removing the solvent from a sample by heating or by utilizing air currents which lead to concentrate the sample or transfer it into a solid state.

example

evaporation of seawater to get sea salt salt (NaCl)

Application of heat

Using an open container for a period of time

Usage

As final step for obtaining an isolated material as a residue

As a first preparation step for further separation.

Membrane Separation

Methods

Membrane-Based Separation Methods

Electrodialysis

Ultra filtration

The process

Application of hydrostatic pressure between 1 & 10 atm to separate solutes with diameters > 20 Aْ

Structure and properties

Various semipermeable membranes

Charged Membranes

The separation is accomplished by:

exclusion of coions (ions of the same charge as The fixed ions) from the membrane

pore size as well as

Thin Membranes

The thinner the membrane; the faster the transport rates through membranes.

Homogeneous Membranes

Particles of exactly the same size can be separated with homogeneous diffusive-type membranes when their solubilities in the film or their concentrations differ significantly

Composition

a homogeneous film or interphase through which a mixture of chemical species can be carried by molecular diffusion

Microporous Membranes

The principle

intermediate pore size -> partially rejected

<< pore size -> allowed to pass

If the size of particles (or molecules): >>pores sizes -> rejected to pass

Separate particles that differ significantly in size.

General important properties of membranes

Good chemical stability.

Good mechanical stability

Examples

Reverse Osmosis

Dialysis

Ultrafiltration

Some Applications

Separate azeotropic mixtures

Removal of urea from blood

Convert salt water to drinkable water

Definition

It a separation process that utilize semipermeable membranes to allow passage of certain chemical species completely, while stopping or strongly restrict the permeation of others.

Crystallization

Optimal solvent composition

s designed to minimize contamination of the crystals with other materials.

oncentrating a solution containing the component of interest by

allowing it to stand

heating it

Used to

obtain pure material in the crystalline state.