Distillation and Alcohol Production Application Distillation and Alcohol Production Applicaiton

Distillation and Alcohol Production Application Distillation process Types of distillation Distillation equipments and properties of them Alcohol production Distillation of alcohol Types of alcohol distillation

Distillation Distillation is a kind of seperation technique of two or more volatile liquid compunds 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 vapor in more volatile compounds and enrich the liquid phase on less volatile compounds. Mass transfer is the key to a successful distillation.

Advantages & Disadvantages It has simple flowsheet, 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. Disadvantages Distillation 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.

Types of Distillation Continous Distillation Batch Distillation Semi-Batch Distillation

Continous Distillation The mixture which is to be seperated is fed to column at one or more points. Liquid mixture runs down the column while vapor goes up. Vapor is produced by partial vaporisation of the mixture which is heated in reboiler. Then vapor is partially condensed to earn back the less volatile compounds to the column to seperate as bottom product. (reflux)‏

Batch Distillation The oldest operation used for seperation 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 continous or semi-continous mode. It is suitable for extractive and reactive distillations.

Comparsion of Distillation Types For batch distillation, it is enough to use only one column to seperate multicomponent liquid mixture. One sequence of operation is enough to seperate all the components in a mixture. For continous distillation, to seperate multicomponent liquid mixtures, more than one columns are necessary to be used. One column is dedicated to seperate a specific mixture and specific operation.

Equipment Designs Plate 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-vapor contact and increase the mass transfer area. Tray types include sieve, valve and bubble cap.

Advantages & Disadvantages Least expensive colum for diameters greater than 0.6m The liquid-vapor contact in the cross-flow of plate columns is more effective than countercurrent-flow in packed columns. Cooling coils can be easily added to the plate column Can handle high liquid flow rates. Disadvantages Higher pressure drops than packed columns Foaming can occur because the liquid is agitated by the vapor flowing up through it.

Packed Beds Packings can be provided either as dumped or stacked. Dumped packing consistutes of bulk inert materials. Stacked packing is includes meshwork which has the same diameter with the column. Important criterias for packings are efficent contact (liquid-vapor), resistence to flow, flow capacity, resistance of packing against corrosion.

Advantages & Disadvantages When 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 liquids. Can 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 low.

Making of Alcohol Alcohols, generally can be created by reduction of aldehydes or twice reduction of ketones. Ethanol (C2H5OH) can produced by fermantation of molases. Fermantation is done in a tank and it is cleaned and sterilized before the fermantation begins.

Molases have strong concentration of sugar which doesn't provide the adequate conditions for fermantation. Consequently it must be dilluted to concentration of %17 sugar. Optimum enviromental pH range is between 4.0 and 5.0; and optimum temperature is 76°F(25°C). Fermantated molases is called beer and it contains %6.5 to %11 alcohol by volume.

Distillation of Alcohol Under 1 athmosphere pressure boiling points of water and alcohol are 100°C and 78.3°C. Water and ethyl alcohol mixture forms an azeotrope in athmospheric pressure at a mole fraction of %89.4 of ethyl alcohol which means that by simple distillation of ethyl alcohol, it cannot be purified more than %95.6 w. As distillation equipments, bubble cap trays and tray columns are mostly used in alcohol distillation.(Figure on left)‏

Pot Distillation Process (Batch Distillation)‏ Entire batch of beer is heated in a large container and alcohol/water vapors are chanelled into a distillation column. After all the boiling and reflux operations, when almost all alcohol is boiled, process is stopped and stillage is removed.

The basic advantage of pot distillation is its simplicity The basic advantage of pot distillation is its simplicity. It has simple equipment system. Fermantation and boiling for distillation can take place at the same pot, which makes it more practical The disadvantage of the pot distillation is low distillation efficiency. It requires about three times more energy comparing to continous distillation.

Continous-Feed Distillation Process Typically it is also known as continous distillation. Alcohol/liquid mixture is fed to column and it flows. Flow rate is decreased by trays. Mixture boils up in the reboiler and goes up of the column to condenser as it contacts with the condensed liquid. The vapor with high alcohol percent leaves the condenser to be collected in accumulator.

The advantage of the continous feed distillation process is it's high energy efficiency comparing to the pot distillation process. Eventually amount of energy required for per liter of alcohol is less than in pot distillation. On the other hand it can operate for long hours (almost 8000 hours per annum)‏ The disadvantage of continous feed distillation is it needs a little more complicated equipment system comparing to the batch distillation.

Vacuum Distillation Low temperature allows us to achieve higher alcohol concentrations. At a pressure below 0.1 athmosphere azeotrope disappears and enables to distillate to almost 100 percent alcohol.

Because of the high operation and installation costs, low energy efficiency, vacuum distillation appears to be uneconomical in the commercial applications.

Azeotropic Distillation This type of distillation is used for processes that produce almost 100 percent alcohol with help of an organic solvent and two additional distillations. A solvent (pentane, gasoline etc.) is added to distillation product comming out of the usual distillation column. Mixture is fed to another distillation column which seperates it into a top product and a bottom product. Distillate of this column is fed to a third column which distills out the solvent leaving the mixture of alcohol-water. Solvent is recycled and never gets out. System is hard to design and it is more complicated comparing to ordinary distillation system.