1. Biomass and Biofuels MECH 5970 25 April 2011

2. Background Biomass: material of recent biological origin. Provides (directly or via processing) HC fuel for combustion applications. Very long history – Wine, beer making: fermentation methods – Wood (a biofuel) was the original fuel. – Whaling: provided the original lamp oil.

3. Current status

4. 2005-2008: ethanol is gasoline increased from 3.8 to 5.5%, and biodiesel in diesel increased from 0.9 to 1.5%

5. Competition of resources: – Water – Agricultural land – Agricultural products: food vs. fuel. Effect of extensive energy crop farming on ecosystem and climate. Net energy return: are fossil fuels saved? CO 2 neutrality of biofuels is not always obvious. Critical issues

6. Types of biofuels Plant oil based (sunflower, palm, waste oil,…) – Straight use of oil with minor modifications (water removal, viscosity reduction) in diesel cycles. – Biodiesel: transesterfication of plant oil to provide fatty acid methyl ester (FAME). – “Green diesel”: traditional fractional distillation of plant oil.

7. Alcohol based fuels Ethanol from agricultural crops (carbohydrate feed stock): corn, cereals, sugar cane, beets, cassava,… – Fermentation to ethanol/water mix. – Distillation to ethanol.

8. Alcohol based fuels Ethanol from herbaceous and woody crops (cellulosic biomass): grasses, corn stover, wood,… – Breakdown (digestion) of cellulosic biomass in several steps to form sugars. – Fermentation of sugars to ethanol/water mix. – Distillation to ethanol. Methanol: chemical, rather than biochemical, process.

9. Gas fuels Biogas: primarily CH 4, CO 2 – Produced by anerobic digestion and/or fermentation of biodegradable materials. – Swamp gas, landfill gas. Syngas: H 2 and CO – Produced by partial oxidation (pyrolosis) of biomass.

10. Cellulosic ethanol Biological approach: – Cellulose hydrolysis: pretreatment and digestion of cellulose into sugars – Fermentation to ethanol, followed by distillation, purification Thermochemical approach: – Partial oxidation of cellulose to CO, CO 2, H 2 – Fermentation using Clostridium ljungdahlii to ethanol

11. Algae—based fuels Advantages over crop—based fuels: – Better use of water resources (can use salt, waste water) – Theoretically yield 10-100 times more energy per unit area than croplands. – Simplified process: algae consume CO 2, produce fuel (oils or alcohols).