Introduction to Ethanol Production – No, Not the Drinking Kind!

1. Introduction to Ethanol Production – No, Not the Drinking Kind! Bia H. Thomas, Ph.D. ChE 473A Lecture October 19th, 2011 St. Louis, MO

2. Outline • Why is Ethanol Important? • How is Ethanol Made? • The Monod Model • The Wonderful World of Kinetics • The Bioreactor Setup • Some Analytical Techniques • Sample Results • Modeling • Some Final Thoughts

3. The Renewable Energy Question • Current world oil consumption is 88 million barrels/day which will continue to grow rapidly • By 2050 the world population will 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

4. Ethanol Production From Corn • 2010: 13 billion gallons of ethanol Source: www.ethanolrfa.org/industry/locations

5. The Case for Ethanol • 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 • Bio-ethanol is derived from cellulosic and lignocellulosic biomass via the following processes: Cellulosic Milling Liquefaction Saccharification Fermentation Lignocellulosic Pretreatment Saccharification Fermentation (C6 and C5) • 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

6. The Dry Grind Process • Dry grind: • Corn processed whole • Less complex • Lower initial capital cost • Fewer unit operations • 3 products: ethanol, CO2, and DDGS • Wet milling: • Only 30% of facilities are wet milling • Fractionation of corn kernel into starch, gluten, fiber, germ • Separation: chemically or enzymatically • Products: ethanol, gluten meal, gluten feed, oil • Starch component can be processed into many products

7. Fermentation Processes • Ideal fermentation processes • Growing cells are consuming the substrate (sugars) and producing more cells • rsx = rate of substrate consumption rx = rate of cell growth s = substrate concentration x = cell concentration P = ethanol concentration (in anaerobic case) rsx rx Cells (x) P Cells (x)

8. The Monod Model • Monod's model describes the relationship between the specific growth rate and the growth limiting substrate concentration as: where µm is the maximum specific growth rate and Ks is a saturation constant • Despite its empirical nature Monod's model is widely used to describe the growth of many organisms. Basically because it does adequately describe fermentation kinetics • Model has been modified to describe complex fermentation systems

9. Assumptions and Constraints • Monod model represents a very simple model of cell growth and product formation • Fermentation processes are often much more complex • Modifications may need to be introduced to handle more complicated systems • Additional equations would be required to handle multiple products and multiple organisms • The model has also assumed that product formation is linked to biomass growth • In reality, many commercially important products are produced in a non-growth associated manner • The model assumes that biomass and product formation can be represented by averaged yield coefficients • These assumptions may sometimes be an oversimplification and such a model would give unrealistic results

10. Why Is It Important? • When the model is solved numerically, a number of curves are obtained • With the model it is possible to: • Determine the number of fermentations that can be performed per year • Amount of profit that can be made.

11. dS q = = - P r X S dt Y P / S m 1 dX S m = = m + x dt K S S 1 - dX X X = = o Y X S - dS S S o - P P dP = = o Y P S - dS S S o Kinetics, Kinetics, More Kinetics • The rates of microorganisms’ growth, the consumption of glucose, and the formation of products are: Rate of reaction relative to cell mass concentration (1) Rate of reaction relative to ethanol concentration (2) Rate of reaction relative to glucose concentration (3) Specific growth rate without inhibition effect Monod’s model (4) (5) Yield coefficient (X w.r.t. S) (6) Yield coefficient (P w.r.t. S)

12. The Bioreactor Setup

13. The Bioreactor Setup Bench-scale 37L Stirred Fermentor (active volume: 16 L) Automatic temperature control via draft tube pH meter for optimum pH control Temperature Read Out Online biochemistry analyzer for ethanol concentration detection Fraction collector for automatic sampling system Turbine impeller for uniform yeast distribution

14. Analytical and Measurement Techniques • YSI analyzer • Takes online samples every hour to measure ethanol and glucose concentrations • Automatically samples test tubes for substrate concentration • Spectrophotometer • Absorbance measurement for each test tube • Absorbance used for calculating yeast concentration in each test tube using calibration curve • Gas Meter: • Measures the volume of CO2 evolved during fermentation • Volume used to calculate number of moles of ethanol produced • Other methods such as Brix Glucose Test and Ethanol Reagent Kits can be used to determine sample composition

15. Sample Results • 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

16. 1 Glucose 50 g/L 0.9 Glucose 100 g/L 0.8 Glucose 150 g/L 0.7 Glucose 200 g/L 0.6 Yeast concentration inside the reactor (g/L) Glucose 250 g/L 0.5 0.4 0.3 0.2 0.1 0 0 10 20 30 40 50 Time (hr) Yeast concentration inside the fermentor throughout the experimentation time Sample Results • 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

17. 8 Glucose 50 g/L 7 Glucose 100 g/L 6 Glucose 150 g/L Glucose 200 g/L 5 Ethanol Concentration inside the reactor (g/L) Glucose 250 g/L 4 3 2 1 0 0 10 20 30 40 50 Time (hr) Ethanol production throughout the experimentation time Sample Results • 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

18. Slight Problems • What can go wrong? • Errors given by the analytical equipment • Error in reading gas meter • Water bath can stop working • Error given by misuse of analyzer • Faulty impeller motor shaft • Faulty pumps

19. Kinetic Modeling μm = maximum specific growth rate KI = saturation coefficient for cell growth qP = specific ethanol production rate qS = specific glucose production rate • Experimental data consistent with basic Monod model • Kinetic parameters are obtained from Baltes (1994, Biotechnol. Prog.)

20. Final Thoughts • Ethanol is NOT the answer – As fuel or to drown your sorrows! • Multi-prong approach is necessary to solve world’s energy problems • Solar, Wind, Biogas, Bio-oil, Biodiesel, Biochemicals, … • Multidisciplinary efforts are necessary to make it work • Applied engineering and scale-up research will make solutions feasible and cost effective • Alternative energy technologies must have legs of its own to survive • No tax credits • No government incentives • What you learn in this class will help solve the problems of today and of the future

21. Questions