Multistage Distillation

Batch-wise or continuously

Multistage processes can be carried out ____________ or ____________

distillation

This process utilizes vapor and liquid phases at essentially the same temperature and pressure for the coexisting zones.

random or structured packings

Various kinds of devices such as _________________________ and plates or trays are used to bring the two phases into intimate contact.

Trays, column

_________ are stacked one above the other and enclosed in a cylindrical shell to form a _________

Packings

_____________ are also generally contained in a cylindrical shell between hold-down and support plates.

• Packing column

• Tray column

Types of Distillation columns

Packing column

In this type of distillation column, Packings are generally contained in a cylindrical shell between hold down and support plates.

allows intimate contact between vapor and liquid phases.

What is the purpose of packings?

They are typically randomly oriented within the column to allow uniform flow of both phases.

Tray column

In this type of distillation columns, trays are stacked one above the other and enclosed in a cylindrical shell to form a column.

liquid - downwards

vapor - upwards

In tray columns, flow of __________ is down at one side of the tray, whereas flow of _______ is upwards.

one or more points

The feed material, which is to be separated into fractions, is introduced at ______________ along the column shell.

boil up

Liquid reaching the bottom of the column is partially vaporized in a heated reboiler to provide _________, which is sent back up the column.

overhead condenser

Vapor reaching the top of the column is cooled and condensed to liquid in the _________________

reflux

Part of this liquid is returned to the column as ___________ to provide liquid overflow.

distillate

The remainder of the overhead stream is withdrawn as ____________, or overhead product

1. a second phase be formed so that both liquid and vapor phases are present and can contact each other on each stage within a separation column

2. the components have different volatilities so that they will partition between the two phases to different extents

3. the two phases can be separated by gravity or other mechanical means.

The separation requires that:

rectifying section

If the feed is introduced at one point along the column shell, the column is divided into an upper section, which is often called the _________________

Stripping section

Lower section of the column

• McCabe-Thiele Method

• Ponchon-Savarit Method

What are the two methods of solving parameters in Multistage Tray towers?

Continuous contact towers or differential columns

Packed columns are also called ___________ and _______

The feed mixture only has two components

Graphical techniques can only be used when ________________

McCabe-Thiele Method

Uses the x-y diagram method requiring only phase equilibrium and mole balance relationships.

McCabe-Thiele Method

assumes an adiabatic column and constant latent heat for the binary mixture at all compositions

• Adiabatic column

• Constant latent heat for the mixture at all compositions

• Constant molar overflow

What are the assumptions in McCabe Thiele method?

McCabe-Thiele

It is simple and gives a useful first estimate of the column design

Fenske Equation

This is an equation used for calculating the minimum number of theoretical plates

Ponchon Savarit

This approach uses the energy balance in addition to mole balance and phase equilibrium relationships

Ponchon Savarit

This method provides also information on the condenser and reboiler duties.

RUHEMANN, PONCHON, and SAVARIT

Who developed the Ponchon-Savarit Method?

• Heat capacity as a function of temperature, composition and pressure.

• Heat of mixing and dilution as a function of temperature and composition.

• Latent heats of vaporization as a function of composition and pressure or temperature.

• Bubble-point temperature as a function of composition and pressure.

What data are needed in doing the Ponchon-Savarit Method?