class14_w08

Class14_w08 - Biomass as renewable energy Carbon cycling in the biosphere CO2 H2O hv CH2O O2 CH2O O2 CO2 H2O Biomass is burned but no net CO2 is

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Carbon cycling in the biosphere : CO 2 + H 2 O + hv CH 2 O + O 2 CH 2 O + O 2 CO 2 + H 2 O Biomass is burned, but no net CO 2 is introduced into the atmosphere. Biomass as renewable energy Energy density is lower than fossil fuel Sources : agricultural waste explicit energy crops
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Production of ethanol from biomass Ethanol fermentation ; starts from pyruvate – CO 2 production makes the resulting mixture carbonated (beer), or causes dough to rise (bakers yeast). Pyruvate is the product of a 10-step enzyme pathway that breaks down glucose (glycolysis) Ethanol production is based on (anaerobic) fermentation of sugars Ethanol is mixed with gasoline (improve octane) or used as E85 Very successful in Brazil (sugar cane)
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Production of ethanol from biomass Crops are harvested and processed to yield glucose or other sugars that can be fermented to ethanol. Processing to glucose from non-cellulosic material is much easier (amylase) Cellulase enzymes are found only in certain fungi and bacteria and are much harder to adapt in industrial processes
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Efficiency of energy conversion from corn ethanol is extremely poor. Why? Fermentation plant requires fossil fuel input Corn harvesting and ethanol transport Fertilizers! Ultimately depend on CH 4 Corn ethanol interest in the US is driven by politics, not science
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Processing from cellulosic ethanol is difficult : Cellulose is covered in hemicellulose requiring acid treatment Hemicellulose = lignin + 5-carbon sugar polymer Once uncovered cellulose has to be processed with cellulases glucose Xylose requires separate fermentation from glucose lignin xylose This processing currently limits noncellulosic ethanol production to pilot-scale Dedication of land to biomass production also is limiting
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Hydrogen Economy 16 May 1937 Lakehurst, NJ Hindenberg H 2 explosion POSSIBLE H 2 INFRASTRUCTURES H 2 fuel cells in vehicles
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This note was uploaded on 08/06/2008 for the course CHEM 123 taught by Professor Perona during the Winter '08 term at UCSB.

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Class14_w08 - Biomass as renewable energy Carbon cycling in the biosphere CO2 H2O hv CH2O O2 CH2O O2 CO2 H2O Biomass is burned but no net CO2 is

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