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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

    Chemical Reaction Engineering Laboratory

    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

    Chemical Reaction Engineering Laboratory

    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), 36C

    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

    Chemical Reaction Engineering Laboratory

    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

    Chemical Reaction Engineering Laboratory

    Objectives Cont. Schematic Diagram of the Setup

    Chemical Reaction Engineering Laboratory

    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

    Chemical Reaction Engineering Laboratory

    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

    Chemical Reaction Engineering Laboratory

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

    pH kept between 5.5 and 4.0

    Samples taken every 45 minutes

    Preliminary Results

    Chemical Reaction Engineering Laboratory

    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

    Chemical Reaction Engineering Laboratory

    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 = 36C

    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.

    Students Sample Results

    Chemical Reaction Engineering Laboratory

    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

    Students Sample Results

    Chemical Reaction Engineering Laboratory

    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

    Chemical Reaction Engineering Laboratory

    The rates of microorganisms growth, the consumption of

    glucose, and the formation of products are:

    Bioethanol Production/ Kinetics Rate

    Chemical Reaction Engineering Laboratory

    Xrdt

    dXX

    ==

    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

    Monods 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

    Other Models

    Chemical Reaction Engineering Laboratory

    _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 = Aibas exponent for cell formation (L/g)

    K2 = Aibas exponent for ethanol formation (L/g)

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

    b = Luongs constant for ethanol formation (g/L)

    1

    2

    1/

    SIS

    m

    KSSK

    S

    ++=

    (5)

    (6 & 7)

    (8 & 9)

    Substrate inhibition (Haldane Model)

    Aiba Model (Aiba et al, 1968)

    Luong Model ( Loung, 1985)

    ()22PPSSqekPKS!="+

    ()11mSSekPKS=!+

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

    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

    Chemical Reaction Engineering Laboratory

    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

    ==

    Xqrdt

    dSSS !==

    Xqrdt

    dPPP ==

    2.5

    44.12

    1.0

    386.0

    =

    =

    =

    =

    +=

    P

    S

    I

    m

    I

    m

    q

    q

    K

    SK

    S

    _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

    Chemical Reaction Engineering Laboratory

    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

    Chemical Reaction Engineering Laboratory

    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