Distillation and Absorption Flashcards

Flashcards about distillation and absorption principles.

What is the fundamental principle behind distillation and absorption?

Distillation and absorption rely on components of a mixture having different volatilities, resulting in different vapor and liquid compositions.

What does volatility characterize?

The tendency of a substance to vaporize.

List examples of pure substances and their vapor pressures (kPa).

Ethylene glycol (0.007 kPa), Phenol (0.05 kPa), Acetic acid (2.1 kPa), Water & Milk (2.4 kPa), Toluene (3.8 kPa), Ethanol (5.95 kPa), Benzene (14 kPa), Acetone (30 kPa).

What is a binary mixture or system?

A mixture consisting of two components, typically a more-volatile component (MVC) and a less-volatile component (LVC), where component A is usually the MVC.

What are the essential laws for a binary mixture?

PA + PB = P, yA + yB = 1, xA + xB = 1

What is Dalton's Law?

PA = yAP, where PA is the partial pressure of component A, yA is the mole fraction of A in the vapor phase, and P is the total pressure.

What is Raoult's Law?

PA = xAPAθ, where xA is the mole fraction of A in the liquid phase, and PAθ is the vapor pressure of pure A.

What is Henry's Law?

PA = HxA, where H is Henry's Constant. (Raoult’s law usually applies at high values of xA while Henry’s law applies at low concentrations.)

How does pressure affect separations generally?

Separations become more difficult as pressure increases since relative volatilities decrease, and the x-y plot gets closer to the 45º line.

What is the phase rule?

F = C - P + 2, where F is degrees of freedom, C is components, and P is the number of phases.

What is an azeotrope?

A mixture that exhibits the same concentration in the vapor phase and the liquid phase, preventing separation via distillation.

What happens when a mixture's total pressure is greater than computed for ideality (positive deviations from Raoult's law)?

A positive deviation, resulting in a minimum boiling azeotrope, such as the ethanol-water azeotrope.

What happens when the total pressure of a system at equilibrium is less than the ideal value (negative deviations from Raoult's law)?

A negative deviation, resulting in a maximum boiling azeotrope, such as the acetone-chloroform azeotrope.

How can azeotropic mixtures be separated?

Changing the pressure, or the addition of a third component (entrainer).

What happens when a liquid mixture at high pressure is brought to a lower pressure such that the temperature is now above the mixture’s boiling point in flash distillation?

Vaporizes until a new equilibrium is established, with a certain amount of vapor (V) and liquid (L) with compositions y and x, respectively.

What does simple batch distillation (Rayleigh distillation) involve?

It involves boiling a batch of liquid and immediately condensing and collecting the resultant vapor, often used for multi-component systems or small quantities.

What is the McCabe-Thiele graphical method?

A mathematical-graphical method for determining the number of theoretical trays or stages needed for a given separation of a binary mixture.

What is the main assumption made in the McCabe-Thiele method?

Constant molar overflow along the column, resulting from nearly equal molar heats of vaporization.

How can operation be analyzed for systems where a pseudo- or quasi- steady state can be assumed during batch rectification?

The same balance equation applies as for the single stage, and the internal recycle due to vaporization, condensation and reflux does not affect the overall balance.

What are two common methods of operating batch distillation?

Maintaining a constant R (i.e. variable xd) or maintaining a constant xd, where the reflux ratio must be continually increased.

What two sections does a continuous distillation system consist of?

Enrichment section and Stripping section.

The minimum reflux ratio is given when the _

ESOL intersects the equilibrium line.

What does HETP mean?

Height equivalent to a theoretical plate, helps with finding a relationship when mass transfer is as effective as possible.