alcohol is an important product required by industry. As per IS
Specification it is nearly 100% pure / water free alcohol. Alcohol
as manufactured is rectified spirit, which is 94.68% alcohol, and
rest is water. It is not possible to remove remaining water from
rectified spirit by straight distillation as ethyl alcohol forms a
constant boiling mixture with water at this concentration and is
known as azeotrope. Therefore, special process for removal of water
is required for manufacture of absolute alcohol.
In order to extract water from alcohol it is necessary to use some
dehydrate, which is capable of separating, water from alcohol.
Simple dehydrate is unslacked lime, Industrial alcohol is taken in a
reactor and quick lime is added to that and the mixture is left over
night for complete reaction. It is then distilled in fractionating
column to get absolute alcohol. Water is retained by quick lime.
This process is used for small-scale production of absolute alcohol
by batch process.
used for dehydration of alcohol using molecular sieves is as follows:
MOLECULAR SIEVE DEHYDRATION:
salient features of the process are given herewith:
Dehydration with Molecular Sieve Process
The rectified spirit from the rectifier is superheated with steam in
feed super-heater. Super-heated rectified spirit from feed
super-heater is passed to one of the pair of molecular sieve beds
for several minutes. On a timed basis, the flow of superheated
rectified spirit vapor is switched to the alternate bed of the
pair. A portion of the anhydrous ethanol vapor leaving the fresh
adsorption bed is used to regenerate the loaded bed. A moderate
vacuum is applied by vacuum pump operating after condensation of the
regenerated ethanol water mixture. This condensate is transferred
from recycle drum to the Rectified Column in the hydrous
distillation plant Via Recycle pump. The net make of anhydrous
Absolute alcohol draw is condensed in product condenser and passed
to product storage.
The life of molecular sieve may be around five to seven years.
However, the operating cost is considerably less than azeotropic
MOLECULAR SIEVE ETHANOL
DEHYDRATION TECHNOLOGY FOR FUEL ETHANOL
Most of the ethanol dehydration plants for
production of absolute alcohol are based on Azeotropic
distillation. It is a mature and reliable technology capable of
producing a very dry product. However, its high capital cost,
energy consumption, reliance on toxic chemicals like benzene and
sensitivity to feedstock impurities, has virtually eliminated the
use of azeotropic distillation in modern ethanol plants. Benzene
has been used as entrainer of choice of ethanol dehydration but it
is now known to be a powerful carcinogen.
Advantages of MOLECULAR SIEVE technology for ethanol dehydration are
The basic process is very simple, making it easy to automate which
reduces Labour and training requirements.
The process is inert. Since no chemicals are used, there are no
material handling or liability problems, which might endanger
Molecular sieves can easily process ethanol-containing contaminants,
which would cause immediate upset in an azeotropic distillation
system. In addition to ethanol, a properly designed sieve can
dehydrate a wide variety of other chemicals, thereby providing added
flexibility in future operating options.
molecular sieve desiccant material has a very long potential service
life, with failure occurring only due to fouling of the media or by
mechanical destruction. A properly designed system should exhibit a
desiccant service life in excess of 5 years.
can be configured to function as a stand-alone system or to be
integrated with the distillation system. This lets the customer
make the trade-off between maximum operating flexibility versus
maximum energy efficiency.
If fully integrated with the
distillation system, steam consumption rate only slightly above the
absolute theoretical minimum for the separation can be achieved.
A properly designed molecular sieve can reliably dehydrate 160-proof
ethanol to 190 + proof, making strict control of rectifier overhead
product quality unnecessary.
From Feed Tank, rectified spirit is pumped to
the Stripper / Rectifier Column. A partial steam of vapors from the
Column are condensed in Condenser and sent back to the column as
reflux. Rest of the vapors are passed through a super-heater and
taken to the Molecular Sieve units for dehydration. The vapor
passes through a bed of molecular sieve beads and water in the
incoming vapor stream is adsorbed on the molecular sieve material
and anhydrous ethanol vapor exists from the Mol. Sieve Unit .
Hot anhydrous ethanol vapor from the Mol. Sieve Units is condensed
in the Mol. Sieve Condenser. The anhydrous ethanol product is
then further cooled down in the product cooler, to bring it close to
the ambient temperature.
The two Mol.
Sieve units operate sequentially and are cycled so that one is under
regeneration while the other is under operation, adsorbing water
from the vapor stream. The regeneration is accomplished by applying
vacuum to the bed undergoing regeneration. The adsorbed from the
molecular sieves material desorbs and evaporates into the ethanol
vapor stream. This mixture of ethanol and water is condensed and
cooled against cooling tower water in the Mol. Sieves Regenerant
Condenser. Any uncondensed vapor and entrained liquid leaving the
Mol. Sieve Regenerant Condenser enters the Mol. Sieve Regenerant
Drum, where it is contacted with cooled regenerant liquid.
regenerant liquid is weak in ethanol concentration, as it contains
all the water desorbed from the Molecular Sieve Beds. This low
strength liquid is recycled back to the Stripper Column for
recovering the ethanol. The water leaves from the bottom of the
column and contains only traces of alcohol.
THE SYSTEM ( molecular sieves )
Near theoretical recovery
consumption minimized by multi-stage preheating to permit
substantial heat recovery and reuse.
An advanced control system, developed through years of experience,
to provide sustained, stable, automatic operation.