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A Bioenergy-Based Bench-Scale

Experiment for Undergraduate

Engineering Students

Bia Henriques, Fan Mei, Khursheed Karim, Steve Picker

Muthanna Al-Dahhan

Department of Chemical Engineering

Washington University

ACS 229th Annual Meeting

Going Green: Lecture Assignments and Lab

Experiences for the College Curriculum

San Diego, California

March 13th-17th, 2005

Chemical Reaction Engineering Laboratory

Current world oil consumption is 80 million barrels/day which

will continue to grow rapidly

By 2050 the world population would reach 9-10 billion and

current reserves of both oil and natural gas will be exhausted

How to supply the vast quantities of energy, fuels and chemicals

when oil, gas and coal are no longer readily available is one of

the most challenging and important problems now facing

humanity

Renewable sources of energy and chemicals will replace the

fossil-based fuels and products

Ethanol is one of the renewable sources of energy which is

considered a cleaner source of bioenergy

Introduction/Motivation


Demand for ethanol is increasing with ever mounting pace: In

2003, the US production of bioethanol was 2.8 billion gallons

from 175 million gallons in 1980 and 1.77 billion gallons in 2001

and as of 8/04, the production has reached 3.4 billion/year

Bio-ethanol is derived from cellulosic and lignocellulosic

biomass via the following processes:

Introduction/Motivation


Cellulosic

Milling

Liquefaction

Saccharification

Fermentation

Lignocellulosic

Pretreatment

Saccharification

Fermentation (glucose and pentoses)

Ethanol can be produced from corn, a starch-based cellulosic

biomass, according to the reaction:

yeast (X), 36°C

C6H12O6 _ 2C2H5OH + 2CO2

Glucose (S) _ 2 Ethanol (P) + 2 Carbon Dioxide

Develop an open-ended bio-energy based experiment

for bioethanol production:

To expose Chemical Engineering and other

undergraduate students to one of the bioenergy

sources

To bring to their attention the issues regarding the

future of energy

To give students experience with a flexible bench

scale experiment that can be used to study the

processes of liquefaction, saccharafication and

fermentation for bioethanol production

To introduce students to various analytical and

measurement techniques


Objectives

Establish an interactive learning approach to allow students to studyvarious parameters that affect bioethanol production. This approachconsists of:

All the students review the previous lab reports and summarizetheir conditions and findings

Each group of students proposes the task to be conducted and theparameter to be investigated

Prior to experiment, workshop for the groups is arranged tofacilitate the interaction among the groups by presenting theirproposed study and to conduct discussion among them to finalizethe conditions and parameters to be investigated by each groupthat complement each other and complement the previous labreports findings

After experiments are conducted all groups share their data, resultsand any problems in an interactive manner

Each group of students prepares a final lab report that uses the datafrom all the groups along with the findings from previous labreports for the results analysis and discussion

All the lab reports and findings will be available for future studentsto conduct experiments that investigate new parameters andconditions


Objectives Cont. Schematic Diagram of the Setup


Thermostatically controlled

heating/cooling

water bath

Variable Speed Drive

Gas Meter

Analyzer

Fraction Collector

Bidirectional Pump

37L Reactor

Inoculum Port

Thermocouple

Drive Belt

Draft Tube

for heating/cooling

Experimental Setup

Online biochemistry

analyzer for ethanol

concentration detection

Automatic

temperature

control via

draft tube


pH meter for

optimum pH

control

Fraction collector for

automatic sampling

system

Turbine impeller for

uniform yeast

distribution

Temperature

Read Out

Bench-scale 37L Stirred Fermentor (active volume: 16 L) YSI analyzer

1) took online samples every hour to measure ethanol

concentration

2) automatically sampled test tubes for substrate concentration

Spectrophotometer:

1) absorbance measurement for each test tube

2) absorbance used for calculating yeast concentration in each

test tube using calibration curve

Gas Meter:

1) measured the volume of CO2 evolved during fermentation

2) volume used to calculate number of moles of ethanol produced

Analytical and Measurement Techniques


Results of the base line study (20 g/L of glucose and 4 g/L yeast) at 36°C

pH kept between 5.5 and 4.0

Samples taken every 45 minutes

Preliminary Results


TA Results

0

5

10

15

20

0 500 1000 1500Time (min)

Su

bst

rate

Co

nce

ntr

atio

n (

g/L

)

0

1

2

3

4

5

6

7

8

9

10

Eth

an

ol

Co

ncen

trati

on

(g

/L)

Substrate Concentration Ethanol Concentration

The students proposed to achieve in an interactive manner the followinggoals:

1) Study and analyze the ethanol yield at different initial glucoseconcentrations

2) Review the yeast fermentation kinetic models available in the literature,with and without substrate and product inhibition

The students suggested to study the effect of the following sugar (substrate)concentrations according to the table below:

Such different set of conditions allow the groups to share their experimentaldata to discuss the effect of substrate concentration and inhibition on ethanolproduction

Parameters Studied – Fall 2004


250 g/l of sugar

200 g/l of sugar

150 g/l of sugar

100 g/l of sugar

50 g/l of sugar

Concentration

Group 5

Group 4

Group 3

Group 2

Group 1

Groups

Temperature = 36ºC

pH = 4.0-5.5

Yeast = Saccharomyces cerevisiae

Agitation = 92.5 rpm

The plot shows that at high initial glucose concentrations the

growth of the yeast gets affected and thus, the yeast takes longer

time to inhibit the growth.

Student’s Sample Results


Yeast concentration inside the fermentor throughout

the experimentation time

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50Time (hr)

Yeast concentr

ation insid

e the

reacto

r (g

/L)

Glucose 50 g/L

Glucose 100 g/L

Glucose 150 g/L

Glucose 200 g/L

Glucose 250 g/L

Yeast was not incubated prior to experiment which explains the delay in

the production of ethanol for all groups

From the figure initial glucose concentrations of 50, 100, and 150 g/L

allowed fermentor to reach its maximum capacity

For the 2 highest glucose concentrations students believe that the time for

the experiment was not long enough

Student’s Sample Results


Ethanol production throughout the experimentation

time

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50Time (hr)

Eth

anol C

oncentr

ation insid

e

the r

eacto

r (g

/L)

Glucose 50 g/L

Glucose 100 g/L

Glucose 150 g/L

Glucose 200 g/L

Glucose 250 g/L

Group 1 (50 g/L):

1. Errors given by the analytical equipment

2. Error in reading gas meter

Group 2 (100 g/L):

1. Water bath stopped working after 30 hours

2. Error given by misuse of analyzer

Group 3 (150 g/L):

1. faulty impeller motor shaft

2. faulty pumps

Problems Encountered


The rates of microorganisms’ growth, the consumption of

glucose, and the formation of products are:

Bioethanol Production/ Kinetics Rate


Xrdt

dXX

µ==

Xqrdt

dPPP ==

(1)

(3)

(2)

(4)

Rate of reaction relative to cell mass

concentration

Rate of reaction relative to ethanol

concentration

Rate of reaction relative to glucose

concentration

Specific growth rate without inhibition effect

Monod’s model

(5)

(6)

Yield coefficient (X w.r.t. S)

Yield coefficient (P w.r.t. S)SS

PP

dS

dPY

SS

XX

dS

dXY

SK

S

dt

dX

x

XY

qr

dt

dS

o

o

SP

o

o

SX

S

m

SP

P

S

!

!==

!

!==

+==

!==

1

/

1 µµ

Other Models


_m = maximum specific growth rate

X = cell mass concentration

S = glucose concentration

P = ethanol concentration

qP = specific ethanol production rate

YP/S = ethanol yield factor

Ks1= saturation coefficient for cell growth on glucose

Ks2 = saturation coefficient for ethanol on glucose

K1 = Aiba’s exponent for cell formation (L/g)

K2 = Aiba’s exponent for ethanol formation (L/g)

a = Luong constant for cell formation (L/hour)

b = Luong’s constant for ethanol formation (g/L)

1

2

1/

SIS

m

KSSK

S

++=

µµ (5)

(6 & 7)

(8 & 9)

Substrate inhibition (Haldane Model)

Aiba Model (Aiba et al, 1968)

Luong Model ( Loung, 1985)

()22PPSSqekPKS!="+

()11mSSekPKSµµ=!+

112211ammSbppmSSPPKSSPqPKSµµ!"#$%=&'()*++,'(-."#$%=&'()*++,'(-.

Experimental data consistent with basic Monod model

Kinetic parameters are obtained from Baltes, M.(1994, Biotechnol. Prog.)

Analytical technique to measure cell concentration not available at the

time

TA Results With Modeling


Glucose and Ethanol Concentration vs Time

0

5

10

15

20

0 500 1000 1500Time (min)

Su

bstr

ate

Co

ncen

trati

on

(g

/L)

0

1

2

3

4

5

6

7

8

9

10

Eth

an

ol

Co

ncen

trati

on

(g

/L)

Substrate Concentration Model-SEthanol Concentration Model-P

Xrdt

dXX

µ==

Xqrdt

dSSS !==

Xqrdt

dPPP ==

2.5

44.12

1.0

386.0

=

=

=

=

+=

P

S

I

m

I

m

q

q

K

SK

S

µ

µµ

_m = maximum specific growth rate

KI = saturation coefficient for cell growth

qP = specific ethanol production rate

qS = specific glucose production rate

Flexible experimental setup has been developed and tested for

an open-ended study to produce ethanol as a bioenergy source

An interactive learning approach to teach a laboratory

experiment for undergraduate Chemical Engineering and other

students has been established

The effect of substrate concentration on corn syrup

fermentation using a specific strain of Saccharomyces

cerevisiae has been studied during Fall 2004

Future students will be able to study different parameters such

as temperature, degree of agitation, pH range, different culture

types (yeast strains) and others or repeat questionable results

Summary


Extend the utilization of the bioreactor setup to investigate in thefuture liquefaction, saccharification and Simultaneoussaccharification and fermentation (SSF) processes

Elucidate the nature of the fermentation process, its biological,chemical, or physical basis

Modify the bioreactor setup for automatic pH control

Future Work


References:

http://www.meadmadecomplicated.org/science/fermentation.html

http://www.andrew.cmu.edu/user/jitkangl/Fermentation%20of%20Ethanol/Fermentation%20of%20Ethanol.htm

http://www.ifp.fr/IFP/en/IFP02OGS.nsf/(VNoticesOGST)/FDD676FDF98DDE0EC1256CDE00582457/$file/ogiers_v54n1.pdf?openelement

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