March 24, A DePriester Chart DePriester Charts provide an efficient method to find the vapor-liquid equilibrium ratios for different substances at different conditions of pressure and temperature. The original chart was put forth by C. DePriester in an article in Chemical Engineering Progress in These nomograms have two vertical coordinates, one for pressure , and another for temperature. Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.
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Engineering - Relative volatility. Relative volatility is a measure of the difference between the vapor pressure of the more volatile components of a liquid mixture and the vapor pressure of the less volatile components of the mixture. This measure is widely used in designing large industrial distillation processes.
In other words, the higher is the relative volatility of a liquid mixture, the easier it is to separate the mixture components by distillation. By convention, relative volatility is typically denoted as the Greek letter alpha,. When the volatilities of both key components are equal, it follows that. Typically, the overhead fraction from the distillation column consists predominantly of the more volatile component and some small amount of the less volatile component and the bottoms fraction consists predominantly of the less volatile component and some small amount of the more volatile component.
Relative volatility of multi- component mixtures. A liquid mixture containing many components is called a multi- component mixture. When a multi- component mixture is distilled, the overhead fraction and the bottoms fraction typically contain much more than one or two components. For example, some intermediate products in a petroleum refinery are multi- component liquid mixtures that may contain the alkane, alkene and alkyne hydrocarbons ranging from methane having one carbon atom to decanes having ten carbon atoms.
For distilling such a mixture, the distillation column may be designed for example to produce: An overhead fraction containing predominantly the more volatile components ranging from methane having one carbon atom to propane having three carbon atoms A bottoms fraction containing predominantly the less volatile components ranging from isobutane having four carbon atoms to the decanes having ten carbon atoms.
Such a distillation column is typically called a depropanizer. The column designer would designate the key components governing the separation design to be propane as the so- called light key LK and isobutane as the so- called heavy key HK. In that context, a lighter component means a component with a lower boiling point or a higher vapor pressure and a heavier component means a component with a higher boiling point or a lower vapor pressure.
Thus, for the distillation of any multi- component mixture, the relative volatility is often defined as: Large- scale industrial distillation is rarely undertaken if the relative volatility is less than 1.
Priester charts. Since an increase in the pressure requires an increase in the temperature, then an increase in temperature also effects the relative volatility.
The adjacent diagram is based on the vapor- liquid equilibrium of a hypothetical binary liquid mixture and illustrates how an increase in either the pressure or temperature decreases the relative volatility of the mixture.
Using the Depriester chart? T, Hz-CH4 20 Flash calculation for a plastic waste pyrolysis process. Tape - Tunnels And Trolls 7. The diagram depicts four sets of vapor- liquid equilibrium for a hypothetical binary mixture of liquids for example, acetone and water or butane and pentane , each set at a different condition of temperature and pressure.
Since the relative volatility of a liquid mixture varies with temperature and pressure, each of the four sets is also at a different relative volatility. Condition 1 is at a temperature and pressure where the relative volatility of the hypothetical binary solution is high enough to make the distillation quite easy. As can be seen in the diagram at. Green 1. Henley 1.
Priester 1. Sinnott 2. ISBN 0- 7. Multicomponent Flash Drum Calculation. The aim of this site is to impart a basic understanding of thermodynamics, not only to. Users can obtain a brief overview of this site by looking at the linked PDF file.
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