RL Stevenson Presentation Biological Fuels Daniel M. Jenkins University of Hawai‘i, Mānoa April 27, 2007

Why Use Biologically Derived Fuels? Finite fossil fuel reserves (‘energy crisis’) Environmental impacts of fossil fuel combustion -release of sequestered CO 2 -climate change -volatile organic compounds, aromatic compounds, hydrocarbon ‘spills’

What are Biological Fuels? Fuels derived from biological materials (e.g. plants) or processes (e.g. methanogenic bacteria) Examples -Wood (undegraded cellulosic material) -Methane -Hydrogen -Ethanol -Oils (triglycerides)

Biological Fuels Wood (and other undegraded plant materials) -High energy content, low processing requirements -Often used for heating energy, and sometimes to power the boiler for steam turbine, but; -High ash content, high NO x -Rate of combustion difficult to control

Biological Fuels Wood (and other undegraded plant materials) -Can be processed to yield pure carbon (e.g. UH flash carbonization process -Carbon (e.g. coal) burns hotter, thermodynamically more efficient for generating electricity, but still -High ash content -Rate of combustion difficult to control

Biological Fuels Methane (often results from anaerobic decomposition of organic matter) -Can be recovered as off- gas from landfill and waste treatment operations, or from dedicated methane generating fermentation processes -Some coevolved gases may be corrosive (e.g. H 2 S); further processing/ purification may be required

Biological Fuels Hydrogen -Under certain conditions, may be derived from photosynthetic bacteria or algae (e.g., see Juanita Matthews thesis defense, Agr. Sci 219, 3:00 PM today) -Hydrogen production confers no biological benefit to organism, so difficult to sustain

Biological Fuels Ethanol -Produced by anaerobic fermentation of sugars by yeast -Controvertial: are energy inputs into cultivation and fermentation processes recovered? Should we process material that people can eat?

Biological Fuels Ethanol -Usually only small portion of plant has sugars directly available for fermentation

Biological Fuels Ethanol -Alternative is to use cultivate plants with higher fermentable sugar content

Biological Fuels Ethanol -Better alternative is to convert cellulosic materials to fermentable sugars- to enable utilization of all manner of crop residues Cellulose (problem- very difficult to hydrolyze bonds) Amylose (starch)- very easy to degrade to glucose

Biological Fuels Oils -Typically concentrated in seeds of grains, legumes, and trees (e.g., corn, sunflower, soy, peanut, olive, etc…)- so quantity is limited, but; -Vegetable oils are already extracted for food industry, and waste vegetable oil is readily available!

Biological Fuels Oils -Waste vegetable oil (after filtering, separating from water, free fatty acids, etc) can be burned directly in modified engines -Waste vegetable oil can be chemically converted to ‘biodiesel’, which can run an unmodified diesel engine

Biological Fuels Making Biodiesel -vegetable oil is composed of triglycerides- groups of three fatty acids esterified to glycerol Fatty acids: Triglyceride:

Biological Fuels Making Biodiesel -transesterification of tryglyceride with methoxide results in biodiesel and glycerol + (Potassium methoxide, prepared in advance by addition of KOH to methanol)

Biological Fuels Making Biodiesel -biodiesel (hydrophobic) and glycerol (hydrophilic) are immiscible- easy to separate at completion of transesterification

Biological Fuels Making Biodiesel -Reactor for transesterification have controlled temperature and agitation Temperature control provides activation energy to accelerate the reaction Agitation improves contact area between immiscible reactants, and improves mass transport at phase boundaries

Biological Fuels Making Biodiesel -Process considerations Stoichiometry of reactants must be close: -excess hydroxide (KOH) causes saponification and increases amount of free fatty acids (corrosive) -excess triglycerides result in mono and diglycerides which are difficult to burn cleanly

Biological Fuels Making Biodiesel -Safety considerations Methanol vapor is hazardous- need vapor trap? Use ethanol as an alternative? Pressure vessel? Combustible materials?