The continuous production ofbioethanol: One, two and three tank

reactor designsS.D. Watt

�

H.S. Sidhu

�

, M.I. Nelson

�

, A.K. Ray

�

(1) School of Physical, Environmental and Mathematical Science, UNSW@ADFA,

AUSTRALIA.

(2) School of Mathematics & Applied Statistics, University of Wollongong, AUSTRALIA.

(3) Department of Chemical and Biochemical Engineering, University of Western Ontario,

CANADA

Bioethanol production – p.1/15

Talk Outline

Brief background.

Model description.

Results — dynamical & optimal performance.

Conclusion and future work.

Work supported from a grant from the Australian Research

Council (DP0559177)

Bioethanol production – p.2/15

Background — bioethanol

What is bioethanol?

Bioethanol is ethanol that is made from a starch- orsugar-based feedstock, such as corn and sugar cane.Why manufacture bioethanol?

The energy content of ethanol is approximatelytwo-thirds that of petrol by volume.

Ethanol contains 35% oxygen and when blended withpetrol results in a more even and complete combustionof fuels — reduces knocking and improves performance

Reduced emissions — greenhouse gas emissionsreduced by up to 19%, tailpipe carbon monoxide by asmuch as 30%

It takes only six months to harvest a substantial crop forfuel.

Bioethanol production – p.3/15

Background — bioethanol

What is bioethanol?Bioethanol is ethanol that is made from a starch- orsugar-based feedstock, such as corn and sugar cane.Why manufacture bioethanol?

The energy content of ethanol is approximatelytwo-thirds that of petrol by volume.

Ethanol contains 35% oxygen and when blended withpetrol results in a more even and complete combustionof fuels — reduces knocking and improves performance

Reduced emissions — greenhouse gas emissionsreduced by up to 19%, tailpipe carbon monoxide by asmuch as 30%

It takes only six months to harvest a substantial crop forfuel.

Bioethanol production – p.3/15

Background — bioethanol

What is bioethanol?Bioethanol is ethanol that is made from a starch- orsugar-based feedstock, such as corn and sugar cane.Why manufacture bioethanol?

The energy content of ethanol is approximatelytwo-thirds that of petrol by volume.

Ethanol contains 35% oxygen and when blended withpetrol results in a more even and complete combustionof fuels — reduces knocking and improves performance

Reduced emissions — greenhouse gas emissionsreduced by up to 19%, tailpipe carbon monoxide by asmuch as 30%

It takes only six months to harvest a substantial crop forfuel.

Bioethanol production – p.3/15

Background — bioethanol

What is bioethanol?Bioethanol is ethanol that is made from a starch- orsugar-based feedstock, such as corn and sugar cane.Why manufacture bioethanol?

The energy content of ethanol is approximatelytwo-thirds that of petrol by volume.

Ethanol contains 35% oxygen and when blended withpetrol results in a more even and complete combustionof fuels — reduces knocking and improves performance

Reduced emissions — greenhouse gas emissionsreduced by up to 19%, tailpipe carbon monoxide by asmuch as 30%

It takes only six months to harvest a substantial crop forfuel.

Bioethanol production – p.3/15

Background — bioethanol

What is bioethanol?Bioethanol is ethanol that is made from a starch- orsugar-based feedstock, such as corn and sugar cane.Why manufacture bioethanol?

The energy content of ethanol is approximatelytwo-thirds that of petrol by volume.

Ethanol contains 35% oxygen and when blended withpetrol results in a more even and complete combustionof fuels — reduces knocking and improves performance

Reduced emissions — greenhouse gas emissionsreduced by up to 19%, tailpipe carbon monoxide by asmuch as 30%

It takes only six months to harvest a substantial crop forfuel.

Bioethanol production – p.3/15

Background — bioethanol

What is bioethanol?Bioethanol is ethanol that is made from a starch- orsugar-based feedstock, such as corn and sugar cane.Why manufacture bioethanol?

The energy content of ethanol is approximatelytwo-thirds that of petrol by volume.

Ethanol contains 35% oxygen and when blended withpetrol results in a more even and complete combustionof fuels — reduces knocking and improves performance

Reduced emissions — greenhouse gas emissionsreduced by up to 19%, tailpipe carbon monoxide by asmuch as 30%

It takes only six months to harvest a substantial crop forfuel.

Bioethanol production – p.3/15

Model — biochemistry

A.B. Jarzebski. (1992). “Modelling of oscillatory behaviourin continuous ethanol fermentation”. Biotechnology Letters,14(2), 137–142.

Substrate (

�

).

Product - ethanol - (

�

)

Biomass (Zymomonos mobilis)Viable cells (

��� )Non-viable cells (

���� ) — non-growing, but still retainthe ability to produce ethanol.Dead cells (

�� ) — eqn uncouples.

Bioethanol production – p.4/15

Model — single reactor

� � ��� � � � ��� � � � � � ��� ����

� �� ��� � �

� � ���� � � � �� � � � � � � � � � �� �

� � � � ��� � � � � � � � � � � � �� � � � � � �

� � ���� � � � �� � � � � �� � � � � �

� � ��� � � � � � � � �������

� �� � � � �

Bioethanol production – p.5/15

Model — rate expressions

� � �� ��

���� � �

� ��

��

��� � � �

� � � � ��

�� � � �

� ��

��

��� � � �

� � � �� ��

���� � �

� ��

� ��

�� � � � � �

Reaction rates can not be negative.

Substrate limitation.

Product inhibition.

Bioethanol production – p.6/15

Results — ethanol concentration

0 5 10 15 20−10

0

10

20

30

40

50

Residence time (h)

Eth

anol

con

cent

ratio

n (g

/l)

Figure 0:

��� � �� �

g l

� �

. � � �� �

hr.Bioethanol production – p.7/15

Results — productivity (Pr � �)

0 5 10 15 20−1

0

1

2

3

4

Residence time (h)

Prod

uctiv

ity (

g/l/h

)

Figure 0:��� � �� �

g l

� �

. Pr � �� � � � �

g l

� �

hr

� �

at

� � �� �

hr. Bioethanol production – p.8/15

Results — single reactor

Two hopf bifurcations if

�� � � � � g l

� � � �� �

.

One hopf bifurcation if g l .

Period doubling bifurcations.( g l , hr)

Period doubling route to chaos.Large residence times ( g l , hr).

Maximum productivity: system operated at a staticsteady-state.

If g l then

Pr g l hr

Bioethanol production – p.9/15

Results — single reactor

Two hopf bifurcations if

�� � � � � g l

� � � �� �

.

One hopf bifurcation if

�� � � � � g l

� �

.

Period doubling bifurcations.( g l , hr)

Period doubling route to chaos.Large residence times ( g l , hr).

Maximum productivity: system operated at a staticsteady-state.

If g l then

Pr g l hr

Bioethanol production – p.9/15

Results — single reactor

Two hopf bifurcations if

�� � � � � g l

� � � �� �

.

One hopf bifurcation if

�� � � � � g l

� �

.

Period doubling bifurcations.(

� � � �� �

g l

� �

, � � �� � � � � � � � �

hr)

Period doubling route to chaos.Large residence times ( g l , hr).

Maximum productivity: system operated at a staticsteady-state.

If g l then

Pr g l hr

Bioethanol production – p.9/15

Results — single reactor

Two hopf bifurcations if

�� � � � � g l

� � � �� �

.

One hopf bifurcation if

�� � � � � g l

� �

.

Period doubling bifurcations.(

� � � �� �

g l

� �

, � � �� � � � � � � � �

hr)

Period doubling route to chaos.Large residence times (

� � � �� �

g l

� �

, � � � �

hr).

Maximum productivity: system operated at a staticsteady-state.

If g l then

Pr g l hr

Bioethanol production – p.9/15

Results — single reactor

Two hopf bifurcations if

�� � � � � g l

� � � �� �

.

One hopf bifurcation if

�� � � � � g l

� �

.

Period doubling bifurcations.(

� � � �� �

g l

� �

, � � �� � � � � � � � �

hr)

Period doubling route to chaos.Large residence times (

� � � �� �

g l

� �

, � � � �

hr).

Maximum productivity: system operated at a staticsteady-state.

If g l then

Pr g l hr

Bioethanol production – p.9/15

Results — single reactor

Two hopf bifurcations if

�� � � � � g l

� � � �� �

.

One hopf bifurcation if

�� � � � � g l

� �

.

Period doubling bifurcations.(

� � � �� �

g l

� �

, � � �� � � � � � � � �

hr)

Period doubling route to chaos.Large residence times (

� � � �� �

g l

� �

, � � � �

hr).

Maximum productivity: system operated at a staticsteady-state.

If

�� � � � � g l� � � �� �

then

Pr� �� � � � �� � �

g l

� �

hr

� � � � � � �� � � �� � �

Bioethanol production – p.9/15

Results — reactor cascade

Infl

ow

Reactor 1 Reactor 2

Outflow

Reactor 3

Pr �

��� � �

Pr � �

��

�� � � � � �

Bioethanol production – p.10/15

Results — double reactor cascade

0 2 4 6 8

Prod

uctiv

ity (

mg

per

litre

per

hou

r)

Residence time in first tank (hours)10

0

1

2

3

4

5

Figure 0: Total residence � �

� � � � � � �

h

�

.

��� � � � �

g l

� �

.Bioethanol production – p.11/15

Results - optimal double reactor cascade

0 5 10 15 200

1

2

3

4

5

6

Total residence time (hours)

Opt

imal

pro

duct

ivity

(m

g pe

r lit

re p

er h

our)

Optimal single tank productivity

Figure 0: Optimal performance of a cascade of two (un)equal reactors.

�� � � � �

g l

� �

.Bioethanol production – p.12/15

Results — scatter plot

3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.27

8

9

10

11

12

13

14

15

16

Optimal productivity (grams per litre per hour)

Tot

al r

esid

ence

tim

e (h

ours

)

one reactor

2 equal reactors

3 equal reactors2 unequal reactors

3 unequal reactors

Figure 0: Optimal performance of a cascade of various reactor configura-tions.

�� � � � �

g l� �

.

Bioethanol production – p.13/15

What’s next?

Feed concentration : Extensive investigation.

Reactor costs : Can we afford to optimise production?

Recycle : Improves performance.

Performance : Maximise product concentration.

Undergraduate lab : Department of Chemical Engineering,Monash University.

Bioethanol production – p.14/15

Conclusions

1. Ethanol production using verified model.

2. Investigated single-reactor.

3. Investigated double- and triple- reactor cascades.

4. Double reactor cascade can outperform single reac-tor by upto 34%.

5. Triple reactor cascade can outperform single reactorby upto 36%.

6. Equal double reactor cascade can outperform singlereactor by 27%.

7. Equal triple reactor cascade can outperform single re-actor by 28%.

Bioethanol production – p.15/15

Conclusions

1. Ethanol production using verified model.

2. Investigated single-reactor.

3. Investigated double- and triple- reactor cascades.

4. Double reactor cascade can outperform single reac-tor by upto 34%.

5. Triple reactor cascade can outperform single reactorby upto 36%.

6. Equal double reactor cascade can outperform singlereactor by 27%.

7. Equal triple reactor cascade can outperform single re-actor by 28%.

Bioethanol production – p.15/15

Conclusions

1. Ethanol production using verified model.

2. Investigated single-reactor.

3. Investigated double- and triple- reactor cascades.

4. Double reactor cascade can outperform single reac-tor by upto 34%.

5. Triple reactor cascade can outperform single reactorby upto 36%.

6. Equal double reactor cascade can outperform singlereactor by 27%.

7. Equal triple reactor cascade can outperform single re-actor by 28%.

Bioethanol production – p.15/15

Conclusions

1. Ethanol production using verified model.

2. Investigated single-reactor.

3. Investigated double- and triple- reactor cascades.

4. Double reactor cascade can outperform single reac-tor by upto 34%.

5. Triple reactor cascade can outperform single reactorby upto 36%.

6. Equal double reactor cascade can outperform singlereactor by 27%.

7. Equal triple reactor cascade can outperform single re-actor by 28%.

Bioethanol production – p.15/15

Conclusions

1. Ethanol production using verified model.

2. Investigated single-reactor.

3. Investigated double- and triple- reactor cascades.

4. Double reactor cascade can outperform single reac-tor by upto 34%.

5. Triple reactor cascade can outperform single reactorby upto 36%.

6. Equal double reactor cascade can outperform singlereactor by 27%.

7. Equal triple reactor cascade can outperform single re-actor by 28%.

Bioethanol production – p.15/15

Conclusions

1. Ethanol production using verified model.

2. Investigated single-reactor.

3. Investigated double- and triple- reactor cascades.

4. Double reactor cascade can outperform single reac-tor by upto 34%.

5. Triple reactor cascade can outperform single reactorby upto 36%.

6. Equal double reactor cascade can outperform singlereactor by 27%.

7. Equal triple reactor cascade can outperform single re-actor by 28%.

Bioethanol production – p.15/15

Conclusions

1. Ethanol production using verified model.

2. Investigated single-reactor.

3. Investigated double- and triple- reactor cascades.

4. Double reactor cascade can outperform single reac-tor by upto 34%.

5. Triple reactor cascade can outperform single reactorby upto 36%.

6. Equal double reactor cascade can outperform singlereactor by 27%.

7. Equal triple reactor cascade can outperform single re-actor by 28%.

Bioethanol production – p.15/15

Conclusions

1. Ethanol production using verified model.

2. Investigated single-reactor.

3. Investigated double- and triple- reactor cascades.

4. Double reactor cascade can outperform single reac-tor by upto 34%.

5. Triple reactor cascade can outperform single reactorby upto 36%.

6. Equal double reactor cascade can outperform singlereactor by 27%.

7. Equal triple reactor cascade can outperform single re-actor by 28%.

Bioethanol production – p.15/15