Types Of Distillation

Types Of DistillationName Marui UqailiRoll No 13CH56Presented To Prof Dr Aziza AftabDepartment Of Chemical EngineeringMehran University Of Engineering And Technology JamshoroContentsDistillation processTypes of distillationDistillation equipments and their propertiesTypes: Simple, Fractional, Vacuum, Steam And Azeotropic Applications DistillationDistillation is a kind of separation technique of two or more volatile liquid compounds by using the difference in boiling points and relative volatility.The process takes place in a column, and two heat exchangers.In the column two phases, liquid and gas, are distributed to enrich the vapour in more volatile compounds and enrich the liquid phase on less volatile compounds.Mass transfer is the key to a successful distillation.

Advantages And DisadvantagesAdvantagesIt has simple flow sheet, low capital investment, and low risk. If components to be separated have a high relative volatility difference and are thermally stable, distillation is hard to beat. DisadvantagesDistillation has a low energy efficiency and requires thermal stability of compounds at their boiling points. It may not be attractive when azeotropes are involved or when it is necessary to separate high boiling components, present in small concentrations, from large volumes of a carrier, such as water.

Continuous DistillationLiquid mixture runs down the column while vapour goes up.Vapour is produced by partial vaporisation of the mixture which is heated in reboiler.The mixture which is to be separated is fed to column at one or more points.Then vapour is partially condensed to earn back the less volatile compounds to the column to separate as bottom product. (reflux

Batch Distillation The oldest operation used for separation of liquid mixtures.Feed is fed from bottom, where includes reboiler, to be processed.Numbers of accumulator tanks are connected to collect the main and the intermediate distillate fractions.

Semi Batch Distillation

Semi-batch distillation is very similar to batch distillation.Feed is introduced to column in a continuous or semi-continuous mode. It is suitable for extractive and reactive distillations.

Comparison Of Distillation TypesFor batch distillation, it is enough to use only one column to separate multi component liquid mixtureOne sequence of operation is enough to separate all the components in a mixture.

Equipment DesignsPlate Columns (Tray Columns)Packed Beds

Plate Columns (Tray Columns)It is the most widely used kind of distillation column. Trays are shaped to maximize the liquid-vapour contact and increase the mass transfer area. Tray types include sieve, valve and bubble cap.

Advantages And Disadvantages Advantages Least expensive column for diameters greater than 0.6mThe liquid-vapour contact in the cross-flow of plate columns is more effective than counter current-flow in packed columns.Cooling coils can be easily added to the plate column Can handle high liquid flow rates.DisadvantagesHigher pressure drops than packed columnsFoaming can occur because the liquid is agitated by the vapour flowing up through it Packed BedsPackings can be provided either as dumped or stacked.Dumped packing constitutes of bulk inert materials.Stacked packing is includes meshwork which has the same diameter with the column. Important criteria for packings are efficient contact (liquid-vapour), resistance to flow, flow capacity, resistance of packing against corrosion.

Advantages And DisadvantagesAdvantagesWhen the diameter is less than 0.6m it is less expensive than the plate column.Packing is able to handle corrosive materials. Lower pressure drop than in plate columns. Good for thermally sensitive liquidsDisadvantagesCan break during installation or due to thermal expansion.Not cost efficient for high liquid flow rates.Contact efficiencies are decreased when the liquid flow rate is too lowSimple DistillationInsimple distillation, the vapor is immediately channeled into a condenser. Consequently, the distillate is not pure but rather its composition is identical to the composition of the vapors at the given temperature and pressure. That concentration followsRaoult's law.As a result, simple distillation is effective only when the liquid boiling points differ greatly (rule of thumb is 25C)[18]or when separating liquids from non-volatile solids or oils. For these cases, the vapor pressures of the components are usually different enough that the distillate may be sufficiently pure for its intended purpose.

Fractional DistillationFractional distillation differs from distillation only in that it separates a mixture into a number of different parts, calledfractions. A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top. Like distillation, fractional distillation works because the different substances in the mixture have different boiling points.

Vacuum DistillationLaboratory-scale vacuum distillation is used when liquids to be distilled have high atmospheric boiling points orchemically changeat temperatures near their atmospheric boiling points. Temperature sensitive materials (such asbeta carotene) also require vacuum distillation to removesolventsfrom the mixture without damaging the product. Another reason vacuum distillation is used is that compared tosteam distillationthere is a lower level of residue build up. This is important in commercial applications whereheat transferis produced usingheat exchangers.There are many laboratory applications for vacuum distillation as well as many types of distillation set-ups and apparatuses.Safety is an important consideration when using glassware as part of the set-up. All of the glass components should be carefully examined for scratches and cracks which could result in implosions when the vacuum is applied. Wrapping as much of the glassware with tape as is practical helps to prevent dangerous scattering of glass shards in the event of an implosion.

Steam DistillationWhen a mixture of two practicallyimmiscibleliquids is heated while being agitated to expose the surface of one liquid to the vapor phase, each constituent independently exerts its ownvapor pressureas a function of temperature as if the other constituent were not present. Consequently, the vapor pressure of the whole system increases. Boiling begins when the sum of thepartial pressuresof the two immiscible liquids just exceeds theatmospheric pressure(approximately 101kPaat sea level). In this way, many organic compounds insoluble in water can be purified at a temperature well below the point at which decomposition occurs. For example, the boiling point of bromo benzeneis 156Cand the boiling point of water is 100C, but a mixture of the two boils at 95C. Thus, bromo benzene can be easily distilled at a temperature 61C below its normal boiling point.

Azeotropic DistillationInchemistry,Azeotropic distillationis any of a range of techniques used to break anazeotropein distillation. Inchemical engineering,Azeotropic distillationusually refers to the specific technique of adding another component to generate a new, lower-boiling azeotrope that is heterogeneous (e.g. producing two, immiscible liquid phases), such as the example below with the addition of benzene to water and ethanol. This practice of adding an entrained which forms a separate phase is a specific sub-set of (industrial)Azeotropic distillation methods, or combination thereof. In some senses, adding an entrained is similar toextractive distillation.

Applications Of DistillationSimple distillation is still used to obtain pure drinking water out of hard or contaminated water and also used to make homemade perfumes, liquor, and soaps.Fractional distillation is used for the alcohol purification and gasoline purification in petroleum refining industries Steam distillation is widely used for large-scale separation of essential oils, fats, waxes, and perfumes.For the separation of some aromatic compounds, vacuum distillation is used along with steam distillation. When vacuum distillation is combined with fractional distillation method, components of a mixture get separated very easily.Azeotropic distillation of ethanol forgasolineaddition, the most common means of breaking the azeotrope is the use ofmolecular sieves. Ethanol is distilled to 96%, then run over a molecular sieve which adsorbs water from the mixture. The concentration is now above 96% and can be further distilled. The sieve is heated to remove the water and reused