Extraction of Bio-Butanol using Supercritical Carbon Dioxide A Major Qualifying Project submitted to the faculty of the Chemical Engineering Department at WORCESTER POLYTECHNIC INSTITUTE in partial fulfillment of the requirements for the degree of Bachelor of Science. Submitted by: Chelsea Conlon David Knutson Mark Overdevest Allison Rivard Professor Michael Timko, Advisor Associate Professor Geoffrey Tompsett Abstract Renewable biofuels such as butanol are being researched due to the continued depletion of fossil fuels. Researchers at MIT have recently discovered a B. Megaterium bacteria that survives under high pressure and anaerobic conditions. They are genetically manipulating the bacteria to produce biofuels such as butanol. Butanol is potentially a great alternative for the ethanol dominated biofuel market since it is more energy dense and less flammable than ethanol. At WPI we are operating a supercritical carbon dioxide extraction system compatible with the organism. Throughout the course of our project our team made many improvements to the system set up and procedure for operation. This paper focuses on the extraction results, trends, and models that were generated when operating the high- pressure extraction system. Overall the system showed a slight increase in the extraction rate when the initial butanol concentration was increased from 1 wt.% to 3 wt.% and when the flow rate of scCO2 was increased. On the other hand, no change in the extraction rate was observed when the pressure of the system was varied from 1500 PSI to 2000 PSI. With the experimental data our team concluded that the extraction unit can extract about 80- 85% of butanol in the first 30 minutes. In order to further the future research of this project, experimental and theoretical models were created. The models allowed us to predict extraction rates and overall mass transfer coefficients for runs that were not completed. Therefore, the models reduce the amount of experimental runs that need to be performed. 2 Table of Contents Abstract .................................................................................................................................................... 2 Table of Contents ................................................................................................................................... 3 Acknowledgements .............................................................................................................................. 5 Table of Figures ..................................................................................................................................... 6 Table of Tables ....................................................................................................................................... 8 Chapter 1: Introduction ...................................................................................................................... 9 Chapter 2: Background ..................................................................................................................... 12 2.1 Biofuels in the United States ............................................................................................................... 12 2.1.1 Energy Consumption in the United States ............................................................................................. 12 2.1.2 Non-renewable and Renewable Energy Sources ................................................................................ 13 2.1.3 US Government Support of Biofuels ......................................................................................................... 13 2.1.4 Advantages and Disadvantages of the Most Common Types of Biofuels .................................. 14 2.1.5 A Comparison of Butanol and Ethanol .................................................................................................... 14 2.1.6 Bio-butanol Companies in Industry ......................................................................................................... 17 2.2 Supercritical Fluid Extraction ............................................................................................................ 17 2.2.1 Advantages and Disadvantages of SFE .................................................................................................... 18 2.2.2 Supercritical Carbon Dioxide as an Extraction Solvent .................................................................... 18 2.2.3 SFE of Butanol using scCO2 .......................................................................................................................... 19 2.2.4 SFE of Butanol from Fermentation Broths ............................................................................................ 19 2.3 Phase Equilibrium Modeling .............................................................................................................. 20 2.3.1 Bulk Mass Transportation ............................................................................................................................ 20 2.3.2 Transportation Through a Cell Membrane............................................................................................ 22 2.3.3 Butanol Phase Equilibrium .......................................................................................................................... 22 2.3.4 Ideal Conditions for Extraction .................................................................................................................. 23 2.4 Supercritical Fluid Extraction Equipment ..................................................................................... 24 2.5 Extraction Safety Hazards ................................................................................................................... 26 Chapter 3: Methodology .................................................................................................................... 29 3.1 Reactor ....................................................................................................................................................... 29 3.1.1 Experimental Plan ........................................................................................................................................... 29 3 3.1.2 Set Up .................................................................................................................................................................... 30 3.1.3 Operating the system ..................................................................................................................................... 31 3.1.4 Shut Down ........................................................................................................................................................... 31 3.2 Gas Chromatography ............................................................................................................................. 33 3.2.1 Calibration .......................................................................................................................................................... 33 3.2.2 Analyzing Samples ........................................................................................................................................... 33 3.3 Experimental Model .............................................................................................................................. 33 3.3.1 Model Procedure .............................................................................................................................................. 34 3.4 Theoretical Model .................................................................................................................................. 34 Chapter 4: Results ............................................................................................................................... 36 4.1 Gas Chromatography ............................................................................................................................. 36 4.1.1 Calibration Curves ........................................................................................................................................... 36 4.2 Experimental Results ............................................................................................................................ 38 4.2.1 Mass Balances .................................................................................................................................................... 38 4.2.2 Raw Data Results on Extraction Rates for Different Parameters ................................................. 39 4.3 Experimental Model .............................................................................................................................. 46 4.3.1 The Effects of Concentration on Kla ......................................................................................................... 48 4.3.2 The Effects of Pressure on Kla..................................................................................................................... 50 4.3.3 The Effects of Mass Flow Rate on Kla ....................................................................................................... 52 4.4 Theoretical Model Results of Correlations for Kla ...................................................................... 53 4.4.1 Calculation for Kla from Kl and Some Assumptions ........................................................................... 53