Distillation
 Distillation
is an operation whereby the vaporization of a liquid mixture yields
a vapor phase containing more than one component, and it is desired
to recover one or more of these components in a pure state. This is
distinct from evaporation which is not discussed in this section.
Distillation as such is a
major unit operation in the chemical processing industry for the purification
or separation of liquid mixtures. Other principle unit operations of
separation are evaporation and extraction. Distillation and evaporation
are often considered simultaneously because of their use of heat to
achieve separation.
Distillation in practical
operations can be effected on either a continuous or a batch mode of
operation. A simple reboiler and condenser arrangement with an unpacked
column provides one theoretical stage of separation. This is suitable
for mixtures containing a volatile solvent with non volatile impurities.
Columns which are packed or fitted with trays provide several theoretical
stages of separation. Such arrangements are valuable for liquid mixtures
in which both components have similar relative volatilities.
Although the effectiveness
of the distillation operation is dependent upon such theoretical considerations
as the relative volatility of the components. In practice, the design
of a distillation unit is extremely important.
Borosilicate glass equipment
has been used successfully for many years in the field of distillation
operations. Many units have been installed using the distillation operation,
especially for the recovery of solvents. However, details on this particular
aspect are not covered in this section.
Glass distillation columns
are normally filled with packing materials made of borosilicate glass,
but other packing materials can also be supplied. Cooling arrangements
for the distillate can use either shell and tube or coil type heat exchangers.
Specific advice on both the optimum packing material and the method
of operation can be given by our Chemical Engineers.
Glass columns can vary in
diameter from 80 to 1000 mm and columns have been erected to heights
of up to 30 meters. Glass distillation units can operate at atmospheric
pressure or at high vacuum, using special low pressure loss packings.
Distillation Unit with
Coil Type Condenser
|
The distillation arrangement
with descending type coil condenser is one of the simplest types
of condenser arrangements and includes a total condenser, product
cooler and vent condenser.
By combining glass
process plant equipment with other materials, we can offer well
proven units in a a variety of sizes. Glass reaction vessels are
available up to 400 liters in capacity and, where larger units
are required, glass-lined and stainless steel vessels are commonly
used. Coil type condensers have surface areas from 0.2m2
up to 12m2. Using cooling water
at 20°C these condensers have heat transfer coefficients of
up to 250 kcal/m2/h°C.
This up and over type
distillation unit is suitable for use under vacuum conditions
and is an ideal facility for reactions involving total reflux.
|
 |
Distillation Unit with
Shell and Tube Condenser
|
This distillation arrangement
is virtually identical to the previous arrangement. The main difference
is that shell and tube heat exchangers have been incorporated
instead of coil condensers. Shell and tube type condensers have
surface areas from 3m2 to 26m2.
Using cooling water at 20°C these condensers have heat transfer
coefficients of up to 900 kcal/m2h°C.
The most important
feature of this arrangement is the low installation height.
|
 |
Distillation Unit with
Phase Separation
|
This distillation arrangement
illustrates the use of a horizontal separation vessel in a distillation
unit.
In this arrangement,
the light phase flows back into the boiler as the reflux and the
heavy phase flows through a condenser into the receiver as the
product. It is easy to reverse the system to enable the heavy
phase to become the reflux.
The arrangement can
be operated under vacuum and the illustration shows suitable receivers.
|
 |
Batch Distillation Column
|
Batch distillation
columns always have a reboiler vessel sized to accommodate the
entire batch of the material to be distilled.
For small batch operations,
glass vessels up to 200 liters in capacity are normally used and,
where larger batches are required, glass-lined or stainless steel
vessels are available.
Glass distillation
columns are available from 80 to 100 mm in nominal bore and are
ideal for operation under both atmospheric and vacuum conditions.
Columns of this nature
are operated under conditions of either fixed reflux ratio or
variable reflux ratio. This illustration shows a batch distillation
column which includes a total condenser, product cooler and the
facility for providing reflux at the top of the column by means
of the control valve. Reflux timers are also available.
|
 |
Continuous Distillation
Column
|
Continuous distillation
columns always have this same basic construction. For the reboiler,
a circulatory evaporator is often selected and, as pre-heaters,
our HEB type boilers are ideal.
The main point to consider
in continuous distillation columns is the automatic control system.
Many standard systems are available and, in this illustration
an electro-magnetically controlled reflux divider with timer is
shown.
Glass distillation
columns are available from 80 to 1000 mm in nominal bore and ideal
for operation under both atmospheric and vacuum conditions.
|
 |
|
