PRELIMS - Sepa

Separation Processes

Defined as those operations which transform a mixture or substances into two or more products which differ from each other in composition

Distillation

separates various chemical component according to volatility.
Involves multiple contacts between counter currently flowing liquid and vapor
Separating agent: ESA and sometimes work transfer
Example: Purification Of Styrene

alkylation

to react small hydrocarbon molecules to create larger ones

Catalytic reforming

to modify the structure Of medium-sized hydrocarbo ns.

fluid catalytic cracking

to break apart very large hydrocarbon molecules.

Hydrocracking

to break apart very large hydrocarbon molecules

phase creation

The most cmunon industrial technique involves the creation ofa second phasc (vapor. liquid, or solid) that is inunisciblc with the feed phase. The creation is accomplished by energy transfer to or from thc process or by prcsqzre reduction.

phase addition

introduce the second phase into the System in the form of a solvent that selectively dissolves some of the species in the feed

barrier

less common, but of growing importance, is the use ofbarrier, which restricts or enhances the movemalt of a certain chemical species with resFt to other species

solid agent

addition of solid particles which act directly or as inert carriers for other substances so as to cause separation.

force field or gradient

extemal fields of various types are applied for specialized separations

Partial condensation or vaporization

The feed mixture include species that Widely in tendency to vaporize
ESA
Example: Recovery of H2 and N2 from ammonia by partial condensation by high-pressure phase separation

Flash vaporization

Caused by reducing the pressure of the feed with a valve. The resulting phase is enriched with respect to the species that are most volatile while the liquid phase is enriched wiith respect to the least volatile species
Separating agent: prßwre reduction
Example: Recovery of water from sa water

extractive distillation

When volatility differences between species to be separated are so small
Separating agent: Liquid solvent (MSA) and heat transfer
Example: Separation Of acetone and methanol

Absorption

If the feed is all vapor and the stripping section of the column is not needed to achieve the desired operation.
Separating agent: Liquid absorbent (MSA)

Example: Separation Of carbon dioxide from combustion products by absorption With aqueous solutions Of an ethanolamine

Stripping

A liquid mixture is separated, generally at elevated temperature and ambient pressure, by contacting liquid feed with a stripping agent.
Separating agent: Stripping vapor (MSA)
Example: Stream stripping Of naphtha, kerosene, and gas Oil side cuts from crude distillation unit to remove light ends

Azeotropic Distillation

Formation of minimum-boiling azeotropic mixtures
Separating agent: Liquid (MSA) and heat transfer (ESA)
Example: Separation of acetic acid from water using n-butyl acetate as entrainer to form with water

Liquid-liquid extraction

Widely used when distillation is impractical, especially when the mixture to be separated is temperature sensitive
Soar-ating agent: Liquid solvent (MSA)

Example: Recovery Of Aromatics

Liquid-liquid extraction (two solvent)

Each solvent has its own specific selectivity for dissolving the components of the feed mixture. Separating agent: Two liquid solvents

Example: Use of propane and cresylic acid as solvents to separate paraffins from aromatics and naphthene’s

Leaching

Referred to as Widely used in the metallurgical, natural product, and food industries. To promote diffusion of the solute out of the solid and into the liquid solvent
Separating agent: Liquid solvent
Example: Extraction of sucrose from sugar beets with hot water

Osmosis

Involves transfer, by a concentration gradient, of a solvent through a membrane into a mixture of solute and solvent. The membrane is almost nonpermeable to the solute.
Separating agent: Nonporous membrane

Reverse osmosis

Transport of solvent in the opposite direction and is affected by imposing a pressure, higher than osmotic pressure on the feed side.

Separating agent: Nonporous membrane with pressure gradient

Example: Desalination Of Sea water

Dialysis

Transport, by concentration gradient, of small solute sometimes called crystalloids. through a porus membrane.

Separating agent: Porous membrane with pressure gradient

Example: Recovery of caustic from hemicellulose

Microfiltration

Retention of molecules typically in the size range from 0.02 to 10 Separating agent: Microporous membrane with gradient

Example: Removal of bacteria from drinking water

Ultrafiltration

Retention of molecules typically in the size range from I to 20 nm

Separating agent: Microporous membrane with pressure gradient Example: Separation of whey from cheese

Pervaporation

The species being absorbed by and transported through the nonporous membrane are evaporated Uses lower pressures than RO

Separating agent: Nonporous membrane with pressure gradient

Example: Separation of azeotropic mixtures

Gas permeation

Separation of gas mixtures through membranes, using pressure as the driving force

Separating agent: Nonporous membrane With pressure gradient

Example: Hydrogen enrichment

adsorption

Used to remove present in low concentrations in non- adsorbing solvents or gases and to separate the components in gas or liquid mixtures

Separating agent: Solid adsorbent

Example: Purification of p xylene

Adsorbent: Activated carbon, Aluminum oxide, Silica gel, Zeolite adsorbents (Molecular sieve)

Regeneration methods: thermal Swing, pressure Swing, Inert purge stripping, Displacement desorption

chromatography

a method for separating the components of a gas feed or liquid mixture by passing the feed through a bed of packing.
Separating agent: solid adsorbent
Example: separation of xylene isomers and ethyl benzen

Ion exchange

Resembles adsorption in that solid particle. arc used and regeneration is necessary, however involves chemical reactiom

Separating agent: Resin With ion-active sites

Example: Demineralization of water

Centrifugation

Establishes a pressure field that separates fluid mixtures according to molecular weight. Force field or gradient: Centrifugal force field Example: Separation of uranium isotopes

electrolysis

When water is decomposed into hydrogen at the cathode and oxygen at the anode. Force field or gradient: Electrical force field Example: Concentration Of heavy wate

electrodialysis

Cation and anion-permeable membranes Carty a fixed charge, preventing the migration Of species of like charge. Force field or gradient: Electrical force field and membrane Example: Desalinization of sea wate

saturated conditiona

A condition wherein the maximum possible composition is reached given the set Of conditions.

Phase

Defined as any homogeneous portion or a system that has uniform physical and chemical characteristics.

phase diagram

A graphical representation which details the form(s) the material takes under specific conditions

triple point

the point on a phase diagram at which the three states coexist

critical point

the point on a phase diagram at which the substance is indistinguishable between liquid and gaseous States

fusion curve

the curve on a phase diagram which represents the transition between liquid and solid states

vaporization curve

— the curve on a phase diagram which represents the transition between gaseous and liquid states

sublimation curve

the curve on a phase diagram which represents the transition between gaseous and solid state

gibbs phase rule

Predicts the number of phases that Will coexist within a System at equilibrium. It does not apply in non- equilibrium situations.

constant operating condition

there are no changes in temperature and pressure

constant saturated conditions

composition of components does not change

ideal stage

refers to the contact stage or a medium which means that the resulting products are in saturated condition or the maximum composition.