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HETEROGENEOUS AZEOTROPIC
DEHYDRATION OF ETHANOL TO OBTAIN
A CYCLOHEXANE-ETHANOL MIXTURE
Vicente GomisMª Dolores Saquete
Alicia Font
Ricardo Pedraza
Victoria Pastor-Matea
Chemical Engineering DepartmentUniversity of Alicante (Spain)e-mail: [email protected]
OBJECTIVE
Study the viability of cyclohexane in
the ethanol dehydration to obtain an
ethanol + cyclohexane mixture from
an azeotropic distillation column.
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� 1997 White Paper "Energy for the future"
•Doubling the share of renewable energy from 6%
(1997) to 12% (2010)
� 2003 EU Biofuels Directive (2003/30/EC)
•Target for biofuels in transport: 2% by 2005,
5.75% by 2010
� 2009 Directive „on the promotion of the use of
energy from renewable sources“ (2009/28/EC)
•Overall EU target : 20% renewable energy in
gross final energy consumption in 2020
•Target of 10% renewable energy in transport in
2020 for all member states
INTRODUCTION
Key renewable energy policy documents of the EU
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INTRODUCTION
Sectored emissions in Europe
Waste
2%
Agriculture
8%
Energy
48%
Transport
34%
Industry
8%
Benefits of biofuels
• Reduce GHG emissions
• Improve air quality
• Reduce petroleum dependence
• Improve energy security
Ethanol Production
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Ethanol Production
INTRODUCTION
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Ethanol dehydration
Pressure Swing Adsorption Azeotropic distillation
INTRODUCTION
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Azeotropic distillation
FEED
Ethanol/Water +
Benzene
ALCOHOLABSOLUTE
AZEOTROPETERNARY
(E)
(C)
(G)
(D)
(B)
(N)
(M)
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Ethanol
Water Benzene
E
G
N M
D
C
B
A
Heterogeneous region
INTRODUCTION
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Benzene (Young, 1902)
Pentane
Acetone
Hexane
Heptane
Toluene
Isooctane
Cyclohexane
Possible entrainers
Gaso
linecomponents
INTRODUCTION
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Conventional Process
Raw
materials
Ethanol
Production
FuelMixing
with
gasoline
Raw
materials
Ethanol + Gasoline
Production
Fuel
INTRODUCTION
Proposed Process
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Cost diminution of:
- Mixing
- Transportation
- Storage
Advantages
INTRODUCTION
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EXPERIMENTAL DESIGN
Study in an experimental
semi-pilot plant columnSimulation of the industrial process
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Cyclohexane
Semi-Pilot Plant Column study
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Semi-Pilot Plant Column study
� Simulated in Chemcad 6
� Rigorous calculation using the SCDS module (simultaneous correction
method for rigorous fractionation simulation)
� Thermodynamic model: UNIFAC
Operation Variables
Simulation Variables
• Feed 1: pure cyclohexane. Temperature = 66 ± 1ºC
Flow rate = 41.00 g/min
• Feed 2: water + ethanol mixture (94% wt. of ethanol). Temperature: 63 ±1ºC
Flow rate = 4.38 g/min
• Condenser: Temperature = 35ºC
• Heat exchanger 3: Temperature of the stream leaving HE-3 = 66 ±1ºC
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Reboiler Heat Duty (W)
0 50 100 150 200 250
Weig
ht
Fra
ctio
n
0.0
0.2
0.4
0.6
0.8
1.0
Ethanol Simulation
Cyclohexane Simulation
Cyclohexane
Ethanol
Semi-Pilot Plant Column study
• The ethanol concentration depends on the heat duty
• Only values ranging from 80-100 W permit ethanol concentrations close to 5 % wt.
Bottoms Product
The trends
observed in the
experimental
results resemble
their simulated
counterpartsOptimal
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Reboiler Heat Duty (W)
0 50 100 150 200 250
We
igh
t F
ractio
n
0.000
0.001
0.002
0.003
0.004
0.005
Water Simulation
Water
Semi-Pilot Plant Column study
• The concentration of water in the residue stream does vary considerably with respect to
the reboiler heat duty
• As the heat duty increases, the concentration of the water gradually decreases, reaching
values lower than 50 ppm.
Too high
Bottoms Product
< 50ppm
The trends
observed in the
experimental
results resemble
their simulated
counterparts
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Reboiler Heat Duty (W)
0 50 100 150 200 250
We
igh
t F
ractio
n
0.0
0.2
0.4
0.6
0.8
1.0
Semi-Pilot Plant Column study
Aqueous phase
• The composition of the aqueous layer is also dependent on the heat duty
• The composition tends to approach that of the plait point of the system.
The simulation adequately
reproduces neither the flow
rate values of the bottom
product and aqueous layer
obtained experimentally nor
the composition of the
streams
Water Simulation
Ethanol Simulation
Water Simulation
Water
Ethanol
Cyclohexane
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Reboiler Heat Duty (W)
0 50 100 150 200 250
Flow (g/m
in)
0
10
20
30
40
50
Simulation
Aqueous decant
Bottoms Product
Semi-Pilot Plant Column study
Flows
• The flow rate of the residue is always higher than that of the aqueous layer
• Both flow rates become more similar when the reboiler heat duty increases.
The simulation
adequately reproduces
neither the flow rate
values of the bottom
product and aqueous
layer obtained
experimentally nor the
composition of the
streams
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Ethanol
Water Cyclohexane
Semi-Pilot Plant Column study
UNIFAC non isothermal binodal curve
Experimental non isothermal binodal curve
Plait Point
UNIFAC phase split prediction
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Etanol
Agua Ciclohexano
UNIFAC
Experimental
UNIFAC Dortmund
UNIFAC LLE
Semi-Pilot Plant Column study
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Etanol
Agua Ciclohexano
UNIQUAC
Experimental
NRTL α variable
NRTL α constante
Semi-Pilot Plant Column study
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CONCLUSIONS
� It is possible, through azeotropic distillation, to obtain a mixture of cyclohexane
+ ethanol with concentrations of water lower than 50 ppm without the need
to distill absolute ethanol beforehand. Afterward, the mixture could be directly
employed as a carburant in car engines with no further modifications.
� The most critical parameter of the process is the reboiler heat duty. At lower
values, this produces a mixture of cyclohexane + ethanol with excessive
amounts of water. Whereas, at higher values the azeotropic distillation column
does not work properly, since the top stream condenses giving only one liquid
phase.
� Significant differences in some values are encountered between experimental
and simulated data which can be attributed to the calculation of the liquid-liquid
equilibrium. It is therefore necessary to improve the correlation of the
experimental equilibrium data for determined regions of the ternary system
diagram.
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CONCLUSIONS
The production of dry mixture of
ethanol + cyclohexane seems to be
technically and economically viable
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