heterogeneous azeotropic dehydration of ethanol … · heterogeneous azeotropic dehydration of...

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.

EQUIFASE 2009EQUIFASE 2009

� 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


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


Ethanol Production

INTRODUCTION


Ethanol dehydration

Pressure Swing Adsorption Azeotropic distillation

INTRODUCTION


Azeotropic distillation

FEED

Ethanol/Water +

Benzene

ALCOHOLABSOLUTE

AZEOTROPETERNARY

(E)

(C)

(G)

(D)

(B)

(N)

(M)

0255075100

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50

25

0

100

100

75

50

0

25

Ethanol

Water Benzene

E

G

N M

D

C

B

A

Heterogeneous region

INTRODUCTION


Benzene (Young, 1902)

Pentane

Acetone

Hexane

Heptane

Toluene

Isooctane

Cyclohexane

Possible entrainers

Gaso

linecomponents

INTRODUCTION


Conventional Process

Raw

materials

Ethanol

Production

FuelMixing

with

gasoline

Raw

materials

Ethanol + Gasoline

Production

Fuel

INTRODUCTION

Proposed Process


Cost diminution of:

- Mixing

- Transportation

- Storage

Advantages

INTRODUCTION


EXPERIMENTAL DESIGN

Study in an experimental

semi-pilot plant columnSimulation of the industrial process


Cyclohexane

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


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


• 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



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


• 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



0 50 100 150 200 250

We

igh

t F

ractio

n

0.0

0.2

0.4

0.6

0.8

1.0


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



0 50 100 150 200 250

Flow (g/m

in)

0

10

20

30

40

50

Simulation

Aqueous decant

Bottoms Product


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


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



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Etanol

Agua Ciclohexano

UNIQUAC

Experimental

NRTL α variable

NRTL α constante



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.


CONCLUSIONS

The production of dry mixture of

ethanol + cyclohexane seems to be

technically and economically viable


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