Bio Combustibles

Source: Biofuels Engineering Process Technology

PART

1

The Basics
CHAPTER 1 Introduction CHAPTER 2 Harvesting Energy from Biochemical Reactions CHAPTER 3 Microbial Modeling of Biofuel Production

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2009 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Termsof Use as given at the website.

The Basics

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2009 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.

Source: Biofuels Engineering Process Technology

CHAPTER

1

Introduction
1.1 Biorefinery
Renewable energyderiving from solar, wind, and biomass sources has great potential for growth to meet our future energy needs. Fuels such as ethanol, methane, and hydrogen are characterized as biofuels because they can be produced by the activity of biological organisms. Which of these fuels will play a major role in our future? The answer is not clear, as factors such as land availability, future technical innovation,environmental policy regulating greenhouse gas emissions, governmental subsidies for fossil fuel extraction/ processing, implementation of net metering, and public support for alternative fuels will all affect the outcome. A critical point is that as research and development continue to improve the efficiency of biofuel production processes, economic feasibility will continue to improve. Biofuelproduction is best evaluated in the context of a biorefinery (Fig. 1.1). In a biorefinery, agricultural feedstocks and by-products are processed through a series of biological, chemical, and physical processes to recover biofuels, biomaterials, nutraceuticals, polymers, and specialty chemical compounds.2,3 This concept can be compared to a petroleum refinery in which oil is processed to producefuels, plastics, and petrochemicals. The recoverable products in a biorefinery range from basic food ingredients to complex pharmaceutical compounds and from simple building materials to complex industrial composites and polymers. Biofuels, such as ethanol, hydrogen, or biodiesel, and biochemicals, such as xylitol, glycerol, citric acid, lactic acid, isopropanol, or vitamins, can be produced for usein the energy, food, and nutraceutical/pharmaceutical industries. Fibers, adhesives, biodegradable plastics such as polylactic acid, degradable surfactants, detergents, and enzymes can be recovered for industrial use. Many biofuel compounds may only be economically feasible to produce when valuable coproducts are also recovered and when energyefficient processing is employed. One advantage ofmicrobial conversion processes over chemical processes is that microbes are

3
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Introduction

4

The Basics
able to select their substrate among a complex mixture ofcompounds, minimizing the need for isolation and purification of substrate prior to processing. This can translate to more complete use of substrate and lower chemical requirements for processing. Early proponents of the biorefinery concept emphasized the zeroemissions goal inherent in the plan—waste streams, water, and heat from one process are utilized as feed streams or energy to another, to fullyrecover all possible products and reduce waste with maximized efficiency.2,3 Ethanol and biodiesel production can be linked effectively in this way. In ethanol fermentation, 0.96 kg of CO2 is produced per kilogram of ethanol formed. The CO2 can be fed to algal bioreactors to produce oils used for biodiesel production. Approximately 1.3 kg CO2 is consumed per kilogram of algae grown, or 0.5 kg...