VLE nonideality

This geometric relationship is derived from the overall molar balance and the two overall component balances around the column. 

Substituting the first equation into the second and third gives 

Rearranging these two equations to solve for the ratio of B over D gives 

As we will see in subsequent chapters, this straight-line relationship is quite useful in representing what is going on in a ternary distillation system. This straight line is called the component-balance line. 

An azeotrope is defined as a composition at which the liquid and vapor compositions are equal. Obviously when this occurs, there can be no change in the liquid and vapor compositions from tray to tray in a distillation column. Therefore, an azeotrope represents a distillation boundary.  

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Carbon tetrachloride Trichloroethylene (TCE) and carbon tetrachloride (CTC) separation The concentration of TCE in CTC was hi er than expected. A total reflux test showed that separation near the column bottom was worse than expected. Either VLE nonideality or decomposition of chlorinated ethanes at the reboiler temperature was the culprit. Total reflux tests can give valuable insist into poor performance. Watch out when extrapolating VLE data. 

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