Distillation of Ethanol
Keikhosro Karimi
Department of Chemical
Engineering
I f h University
Isfahan U i it off Technology
T h l
Content
- Whyy p
purification?
- What is distillation?
- A short review on distillation?
- Eth
Ethanol
l Di
Distillation
till ti
- Ethanol Dehydration
Fe mentation
Fermentation
C6H12O6 2 C2H5OH + 2 CO2
Fermented broth or “mash” typically
t i
contains:
- Ethanol (2-12%)
- Microbial biomass
- Fusel oil
- Volatile components
- Stillage
Fusel oil
Fusel oil is a mixture of primary methylbutanols
andd methylpropanols
th l l formed
f d from
f k t id and
ketoacids d
derived from or leading to amino acids.
Depending on the resources used, important
components of fusel oil can be isoamylalcohol, n-
propylalcohol, sec-butylalcohol, isobutylalcohol,
n-butlyalcohol, active amylalcohol, and n-
amylalcohol.
Amount and Application
of Fusel Oil
The amount of fusel oil in mash highly
depends on the pH of the fermentor. Typically,
1–5 L of fusel oil are produced per 1000 L of
ethanol
Fusell oil
F il is
i usedd in
i solvents
l t forf paints,
i t
polymers, varnishes, and essential oils.
Aldehyde and other volatile
components
Acetaldehyde and trace amounts of
other aldehydes and volatile esters are
usually produced.
Typically, 1 L of acetaldehyde are
produced per 1000 L of ethanol
Odor of ethanol
Stillage
- Stillage consists of nonvolatile fraction of materials
remaining after alcohol distillation.
- Composition: depends on the type of feedstock used for
fermentation. Stillage generally contains:
Solids (Originated from feedstock proteins and spent
cells)
Residual sugars, residual ethanol, glycerol
Waxes
Fats
Fibers
ib
Mineral salts
Microbial biomass
Mash is usually
g or
centrifuged
settled in order to
p
separate the
microbial biomass
q
from the liquid and
then the liquid sent
to the ethanol
recovery system.
Purification of ethanol
Mash
95% - 99%
- Ethanol (2-12%)
-Water
-Fusel oil Ethanol
-Volatile
Volatile components
-Stillage
95%, E10, E30, …
Distillation process
- Distillation is the king of separation process,
p
and the most important and most visible
separation technology.
- Basis: difference in volatilities or separation
of more volatile materials from those less
volatile or non-volatile
non volatile materials
materials.
- Distillation is typically used for the separation
of ethanol,
ethanol fusel oiloil, aldehydes,
aldehydes and stillage.
stillage
Ethanol distillation
Various industrial distillation systems
f ethanol
for h l purification
ifi i are
- Simple two-column systems
- Three- or four-column Barbet
- Three-column Othmer system
- Vacuum
acuu rectification
ect cat o
- Vapor recompression
- Multieffect distillation
- Six-column reagent alcohol system.
Parameters in selection of the industrial distillation
systems:
Energy consumption (e.g., steam and cooling water
consumption)
-Quality of ethanol (complete separation of fusel oil
and light components).
- How to deal with the problem associated with
clogging of the first distillation column
- Simplicity in controlling the system
- Simplicity in opening column parts and cleaning
the columns.
- Of course, lower capital investment
Simple two-column system
Othmer system
Barbet system
Thermodynamic of
Ethanol-Water Mixture
- Ethanol-Water mixture (EWM) is a non-ideal mixtures and show a
large positive deviation from Raoult's Law.
- EWM has a high vapour pressure it means that it will have a low
boiling point. This means that the molecules are escaping easily and it
is not necessary to heat the mixture much to overcome the
intermolecular attractions completely.
- The boiling
g point
p / composition
p curve have a minimum value lower
than the boiling points of either water or ethanol.
- This minimum occurs with 95.6% by mass of ethanol in the mixture.
- The boiling point of this mixture is 78.2°C, compared with the boiling
point of pure ethanol at 78.5°C, and water at 100°C.
http://www.chemguide.co.uk/physical/phaseeqia/nonideal.html
References
- MJ.
MJ Taherzadeh and K.
K Karimi,
Karimi “Bioethanol:
Bioethanol: Market
and Production Processes”, In “Biofuels Refining and
Performance” by Ahindra Nag, Mc Graw Hill, 2008.
- B. L. Maiorella. Ethanol, In: Comprehensive
gy, Moo-Young,
Biotechnology, g, M. (Ed.),
( ), First ed.,,
Oxford: Pergamon Press Ltd., 1985.
Dehydration Process
Ethanol (90-95%) Ethanol (99%)
Pressure swing adsorption (PSA) with
molecular sieve is selected for ethanol
dehydration. PSA is a modern technology for
ethanol dehydration that is commercialized in
the
h 1980s.
1980
This process uses the adsorption and
d
desorption
ti nature
t off special
i l molecular
l l sieve
i
toward the water
Why Molecular Sieve?
Low operating cost and energy consumption
It can produce fuel ethanol with water content less
than 0.01% (v/v).
PSA for ethanol dehydration is just a physical
process with no addition of chemical components to
process,
the system and no discharge to environment.
High yield of recovery for ethanol.
Less capital investment.
Advanced and proven technology with sate and
reliable operation.
operation
Process Principle
Molecular sieve:
Absorb water vapor from ethanol vapor
M l
Molecular
l sieve:
i
A type of white clay
Manufactured in granule form
Synthetic zeolite of type 3Å is used for this application
The ppores are 3Å in diameter
Water molecules are 2.8Å
Ethanol molecules are 4.4Å
Therefore, water molecules are strongly attracted into the
pores but ethanol molecules are excluded.
http://www.alibaba.com/product-gs/208496770/Molecular_Sieve_3A.html
Good luck
