Handbook on Bioethanol

Production and Utilization

Charles Wyman

• Publisher: Routledge
• Year: 2018
• ISBN:
  9781351441766
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Bioethanol is a versatile transportation fuel and fuel additive that offers excellent performance and reduced air pollution compared to conventional fuels. Its production and use adds little, if any, net release of carbon dioxide to the atmosphere, dramatically reducing the potential for global climate change. Through a sustained research program and an emerging economic competitiveness, the technology for bioethanol production is poised for immediate widespread commercial applications. Written by engineers and scientists providing a technical focus, this handbook provides the up-to-date information needed by managers, engineers, and scientists to evaluate the technology, market, and economics of this fuel, while examining the development of production required to support its commercial use.

CHAPTER
1

ETHANOL PRODUCTION FROM LIGNOCELLULOSIC BIOMASS: OVERVIEW

Charles E. Wyman

1.1 INTRODUCTION

1.1.1 Economic and Environmental Issues

The United States and much of the world are faced with complex economic and environmental issues associated with energy use that must be addressed if we are to maintain and improve our lifestyles. Our economy depends on low-cost energy. The largest single portion (about 40%) of the energy used in this country is derived from petroleum, more than half of which is imported [1]. Because much of this oil is produced in unstable regions of the world, our high dependence on outside sources of oil resulted in severe price shocks and shortages that caused considerable damage to the economy during the 1970s. As a result, the United States and many other countries sought to develop new sources of energy that would reduce oil imports and improve their strategic and economic strength. However, interest (and funding) for such work waned when oil prices dropped, and few petroleum substitutes have advanced to commercial use. In the interim, imports have now mounted again to the point that dependence on OPEC oil is reaching levels witnessed during previous disruptions, and some sources are beginning to predict a recurrence of past economic events that could again severely disrupt our economy.

As pressing as these economic issues could become in the near future, we are also faced with potentially even greater environmental consequences if we do not change our energy use patterns. Thirty-nine cities in the United States reached excessively high levels of carbon monoxide (CO), and nine exceeded tolerable concentrations of ozone in the air [2]. Looming in the background is mounting concern about the buildup of carbon dioxide (CO₂) and other so-called greenhouse gases in the atmosphere, which could trap the heat that usually radiates from the earth, and cause global climate change [3]. Although there is some uncertainty in such predictions, consensus is building that global climate change is beginning, and if these predictions prove true, the consequences of the resulting climatic changes will be substantial, widely felt, and difficult (perhaps impossible) to reverse if we continue on our current path [4,5,6]. The economic and social effects of global climate change would likely pale anything that has occurred in recent times.

1.1.2 The Link between Petroleum and Transportation

If we examine these economic and environmental issues, we find that they emanate from our great dependence on fossil fuels and on petroleum in particular. In addition to its being our largest single energy source, petroleum is the only one of which we import a substantial fraction; the United States has an abundance of coal and major supplies of natural gas, the other major fossil energy forms [1]. Further, the transportation sector consumes about two-thirds of the petroleum we use, by far the largest fraction. Most energy for that market (about 97%) is derived from oil, unlike other sectors such as electricity production that are well diversified. Therefore, if we seek to reduce our use of petroleum, we must expand our energy options for transportation.

Beyond its impact on petroleum consumption, the transportation sector also has a large impact on the environment. About two-thirds of the CO pollution in our cities comes from vehicular traffic. In addition, about 40% of the compounds released into the atmosphere that lead to ozone formation and smog is due to transportation [2]. Because of its almost total dependence on petroleum, the transportation sector is responsible for about one-third of the CO₂ emissions in the United States [1]. Thus, once again, we must change our energy use patterns for transportation if we hope to address these critical environmental issues that severely affect our health and ultimately our economic and social well-being.

1.1.3 Strategies for Transportation

Three strategies can be employed to reduce our dependence on petroleum, improve air quality, and reduce the accumulation of greenhouse gases for the transportation sector:

• We can reduce the number of vehicle miles traveled (VMT) and associated fuel use by using public transportation instead of individual vehicles, or by working from our homes via the expanding information highway. Although improvements are desirable, many believe we are limited in the reductions we can achieve in VMTs before the economy suffers, and there are indications that fuel is used in other ways even if people work out of their homes.

• We can improve the efficiency of our vehicles so they consume less fuel. Improvements in this area seem both desirable and likely; however, the technology will reach a point of diminishing returns, and our current preference for large cars limits the impact of this avenue.

• We can address the environmental and economic issues by developing tranportation fuels that can be produced domestically in large quantities, burn cleanly, and do not contribute to CO₂ buildup in the atmosphere.

Finding cost-effective, environmentally sound substitutes for petroleum in the transportation sector is not easy, or we would have done it already. Petroleum has a number of very desirable attributes such as a high energy density in a liquid form that is extremely convenient for mobile applications. To some degree, attempts to use natural gas and electricity have suffered from more difficult infrastructure requirements. In addition, petroleum provides high performance that is very difficult to duplicate by other fuels or vehicle systems. The inability to match the attributes of gasoline, diesel fuel, aviation fuel, and other liquid fuels derived from petroleum, particularly at a low price, has impeded any attempts to introduce substitutes into the marketplace.

1.1.4 Why Bioethanol?

One fuel that has the potential to match the convenient features of petroleum at a low price is ethanol produced from lignocellulosic biomass resources—conveniently referred to as bioethanol. Bioethanol can be produced from domestically abundant sources of biomass including agricultural and forestry residues, wastepaper and other sizeable portions of municipal solid waste (MSW), various industrial waste streams, and ultimately woody and herbaceous crops grown on underutilized land to support large-scale bioethanol production [7]. Because few, if any, fossil fuel inputs are needed to grow such materials and convert them into bioethanol, a high ratio of energy production is achieved compared to fossil energy inputs, and the net release of CO₂ that can contribute to global climate change can be practically zero [8]. When added to gasoline, ethanol improves fuel combustion, thereby reducing tailpipe emissions of CO and of unburned hydrocarbons that form smog. As a neat or pure fuel, ethanol has extremely favorable properties that can reduce smog-forming emissions. A properly tuned engine can also achieve higher efficiency on pure ethanol than on gasoline, which compensates to a large extent for its somewhat lower energy content [7]. By applying the rapidly advancing sources of biotechnology to bioethanol production over the past few years, the technology has been improved to the point that bioethanol is now competitive for blending with gasoline with ethanol currently manufactured from corn in the United States [9]. Furthermore, when low-cost waste streams and other niche market advantages are employed, the cost of bioethanol production can be very low with current technology. In addition, opportunities have been identified to further improve the bioethanol technology to the point that it can compete with the price of gasoline as a neat or pure fuel without the tax incentives now employed to make corn ethanol competitive as a blending agent.

This handbook is dedicated to providing a concise summary of the need for bioethanol, the effects of its use, the market, and its technology to aid the reader in quickly understanding the key features of bioethanol. Extensive references are provided in each chapter to aid in obtaining more information when desired. In this chapter, an overall summary of the technology is offered based largely on summaries of each chapter.

1.2 BIOTHANOL AS A TRANSPORTATION FUEL

1.2.1 Changes in Transportation

Chapter 2 provides information on the changes the transportation sector is currently undergoing in the United States, including reformulating fuel, implementing tighter emission standards for vehicles, developing alternative fuels and alternative fuel vehicles (AFVs), and establishing new transportation system technologies in an attempt to reduce petroleum use, improve air quality, and reduce greenhouse gas emissions. Passage of the Alternative Motor Fuels Act (AMFA) in 1988, the Clean Air Act and its amendments in 1990 (CAAA-90), and the Energy Policy Act (EPACT) in 1992 have created more stringent environmental regulations and fostered the development and use of alternative fuels and AFVs. In particular, the CAAA-90 require that gasoline in CO nonattainment areas contain 2.7% oxygen during winter months and that reformulated gasoline (RFG) in ozone nonattainment areas contain 2.0% oxygen. Federal and state tax incentives were developed in the late 1970s and early 1980s to promote ethanol use in response to the petroleum price disruptions of the time, and a $0.14/L federal tax reduction is now provided to make ethanol production from corn economically viable. These incentives were initially restricted to 10% blends of ethanol with gasoline (3.5% oxygen) but have been extended to suitable blend levels for CO and ozone nonattainment areas on a prorated basis. As a result, corn ethanol production has increased from virtually nothing in the late 1970s to about 5.7 billion L annually now.

Changing priorities in national security could drive the development of a better transportation infrastructure, domestic fuel sources, and high-technology transportation systems. The Climate Convention and President Clinton’s Global Climate Change Action Plan encourage the nation to develop fuels and vehicles that minimize or eliminate greenhouse gas emissions. However, the economics must be improved and the infrastructure developed before the use of alternative transportation fuels will likely reach the point that they can reduce the strategic, economic, and environmental impacts of petroleum use.

1.2.2 Ethanol as a Transportation Fuel and Fuel Additive

Ethanol is a versatile transportation fuel and fuel additive, as shown in Chapter 3. Ethanol is currently blended typically at 10% levels with gasoline to extend the U.S. gasoline supply, and Brazil employs 22% blends of ethanol in all gasoline used. Because ethanol has a higher octane than gasoline, it also boosts the octane of the blend, reducing the need to use toxic additives such as benzene in this role. Furthermore, as noted before, ethanol provides oxygen to the fuel, reducing tailpipe emissions of CO and unburned hydrocarbons that pollute our air. However, even though ethanol has a much lower vapor pressure than gasoline, the vapor pressure of blends actually increases compared to the gasoline to which the ethanol is added, causing concerns about the impact of greater evaporative emissions on smog formation. The vapor pressure of the gasoline blending stock to which ethanol is added can be reduced to compensate for this small (about 1 psi) vapor pressure change, but current economic and market forces do not favor such an approach. Alternatively, ethanol can be reacted with isobutylene to form ethyl tertiary butyl ether (ETBE), which provides all the favorable properties of direct addition of ethanol and lowers the vapor pressure of the blend. In addition, ETBE is more easily integrated into the gasoline distribution system because it is very similar to gasoline and doesn’t suffer from limitations such as the tendency to phase separate with water that ethanol does.

Ethanol has a number of very favorable properties that are desirable for use as a neat or pure fuel. Its high heat of vaporization, low flame temperature, greater gas volume change, high specific energy, high octane, and other characteristics make it possible to achieve about a 15% higher efficiency for ethanol than for gasoline in properly optimized spark-ignition engines. This improvement can largely compensate for the fact that ethanol has about two-thirds of the volumetric energy content of gasoline, and a vehicle should be able to travel about 75% to 80% of the distance on a given volume of ethanol as on the same volume of gasoline. From an economic perspective, this means neat or pure ethanol is worth about 75% to 80% of the pump price of gasoline. With some modifications, ethanol can also be used in compression-ignition engines to achieve lower emissions of particulates, oxides of nitrogen (NO_x), and aromatics, although CO, volatile organic compounds, and aldehyde emissions appear to be higher.

Because of its excellent fuel properties, ethanol from cane sugar is used extensively in Brazil as a pure fuel. New flexible fuel vehicles (FFVs) that can run on any mixture of gasoline and ethanol are also being sold now in the United States, although they cannot be optimized to take advantage of ethanol’s superior fuel properties and still accommodate gasoline use. However, both require the implementation of tax policies to be economical at this time.

1.2.3 Ethanol Market Forces

The extent to which bioethanol will penetrate the transportation fuels market depends on the interaction of supply and demand in that market. Chapter 4 examines these market forces with respect to the use of ethanol in the transportation fuels market.

On the demand side, the interaction between the price of and demand for ethanol in two distinct submarkets—one for gasoline blending components and one for neat fuels for internal combustion engines in passenger vehicles—is described. The price the refiner is willing to pay for ethanol (its value) should be roughly proportional to the price of oil when ethanol is directly blended with conventional gasoline and to the price of methanol when used to produce ethers in markets such as California that are concerned with minimizing the vapor pressure to reduce smog formation. However, the value of ethanol in the blend submarket could be significantly increased if the national or a regional refining system were to replace or upgrade its capital stock over time with the use of ethano...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Foreword
• Preface
• Acknowledgments
• CHAPTER 1: ETHANOL PRODUCTION FROM LIGNOCELLULOSIC BIOMASS: OVERVIEW
• CHAPTER 2: STRATEGIC, ECONOMIC, AND ENVIRONMENTAL ISSUES FOR TRANSPORTATION FUELS
• CHAPTER 3: PERFORMANCE OF ETHANOL AS A TRANSPORTATION FUEL
• CHAPTER 4: BIOETHANOL MARKET FORCES
• CHAPTER 5: ENVIRONMENTAL IMPACTS OF BIOETHANOL
• CHAPTER 6: BIOMASS FEEDSTOCK RESOURCES AND COMPOSITION
• CHAPTER 7: HEMICELLULASES: DIVERSITY AND APPLICATIONS
• CHAPTER 8: CELLULASES: STRUCTURE, FUNCTION, AND APPLICATIONS
• CHAPTER 9: BIOCATALYST DEVELOPMENT FOR BIOETHANOL PRODUCTION FROM HYDROLYSATES
• CHAPTER 10: PRETREATMENT OF BIOMASS
• CHAPTER 11: CELLULASE PRODUCTION
• CHAPTER 12: CELLULOSE BICONVERSION TECHNOLOGY
• CHAPTER 13: HEMICELLULOSE CONVERSION TO ETHANOL
• CHAPTER 14: ADVANCED PROCESS OPTIONS FOR BIOETHANOL PRODUCTION
• CHAPTER 15: ETHANOL FROM CORN: TECHNOLOGY AND ECONOMICS
• CHAPTER 16: INTEGRATED BIOPROCESS DEVELOPMENT FOR BIOETHANOL PRODUCTION
• CHAPTER 17: REVIEW OF PILOT PLANT PROGRAMS FOR BIOETHANOL CONVERSION
• CHAPTER 18: METHODS FOR THE CHEMICAL ANALYSIS OF BIOMASS PROCESS STREAMS
• INDEX