Handbook of Cellulosic Ethanol
The inevitable decline in petroleum reserves and the rise in demand for oil from rapidly growing economies have caused soaring oil prices, and coupled with climate change concerns have contributed to the current interest in renewable energy resources. In some parts of the world this interest has resulted in the introduction of legislations promoting the use of renewable energy resources and increasing government incentives for commercialization of renewable energy technologies. Development of science and technologies for efficient conversion of lignocellulosic biomass to renewable liquid transportation fuels has become one of the high priority research areas of the day, and bioethanol is the most successful biofuel to date. Corn - and sugarcane-derived first generation bioethanol is currently in wide use as a blend-in fuel in gasoline sold in the United States, Brazil, and in a few other countries. However, there are a number of major drawbacks to these first generation fuels such as the effect on food prices as traditional food resources are utilized as raw materials, net energy balance, and poor greenhouse gas mitigation.
Cellulosic ethanol is a second generation biofuel produced from agricultural wastes, grasses, municipal wastes, and other feedstocks that do not double as food, so unlike traditional corn-based ethanol, it promises to avoid encroaching upon and destabilizing the human food supply. In addition, cellulosic ethanol can be produced from a variety of abundant lignocellulosic biomass feedstocks, and should be able to be produced in substantial amounts to meet the growing global energy demand. There are two fundamental routes to produce cellulosic ethanol from renewable biomass: the aqueous-phase biomass saccharification-fermentation route, and thermochemical gasification route. The thermochemical route can be divided into two paths as syngas produced from biomass can be converted to ethanol by chemical or enzymatic methods.
This handbook is a comprehensive up-to-date guide to cellu - losic ethanol, divided into five parts: introduction to cellulosic ethanol, aqueous-phase biomass hydrolysis route, biomass gasification route, processing of fuel grade ethanol, and techno-economical evaluation of the processes. The first part covering Chapters 1 to 3 introduces the reader to cellulosic ethanol, presenting the advantages over first generation corn or sugarcane ethanol. In the United States, the gradual transition to renewable energy sources is supported by a series of legislations and government incentives, and these aspects of bioethanol are also discussed in this part. Then, various types of cellulosic ethanol feedstocks are presented in the third chapter, including agricultural wastes, fast growing grasses such as switchgrass and trees like poplar, forestry residues and municipal wastes.
The second part of the book covering Chapters 4 to 10 presents the cellulolysis processes or aqueous-phase biomass saccharification-fermentation route. Chapters 4 and 5 detail the challenges in biomass saccharification, or recalcitrance, as well as various pretreatment techniques such as physical, physicochemical, chemical, and biological pretreatments, and applications to different feedstocks. Chapter 6 covers the enzymatic saccharification, including cellulases, hemicellulase families, mechanisms, enzyme preparation methods, and immobilization of enzymes. Chapter 7 is dedicated to acid hydrolysis, or direct saccharification, using various acid catalysts: concentrated, dilute mineral acids, progress in ionic liquid-based systems, acid group functionalized ionic liquids, and solid acids. Fermentation of the sugar solution to "beer" is presented in Chapters 8 and 9. The microorganisms used in the fermentations, including recent advances in genetic modifications of microorganisms, separate hydrolysis fermentation (SHF), simultaneous saccharification and fermentation (SSF), consolidated bioprocessing (CBP), and surface-engineered and immobilized yeasts are covered in detail in Chapter 8. Fermentation configurations and engineering aspects of fermenter design are presented in Chapter 9. In addition, separation and utilization of lignin byproduct is also covered in this section, under Chapter 10, introducing the total biorefinery concept.
The third part of the book (Chapters 11-13) is dedicated to the biomass gasification route, which is an alternative approach for producing ethanol from lignocellulosic biomass. Pyrolysis chemistry, gasifier designs, and syngas cleaning are covered in Chapter 11, whereas the conversion of syngas to ethanol using microorganisms and their metabolic pathways are presented in Chapter 12. Syngas produced from biomass can be transformed into ethanol using metal catalysts such as Rh-, Mo - or Cu-based systems as well, and this route is presented in Chapter 13.
Processing of ethanol produced thorough various paths is presented in Part 4 of the book. Concentration of ethanol to approximately 90% ethanol by distillation is the first step in purification of ethanol. Technologies used in the current first generation ethanol industry for distillation of the "beer" to an azeotrope mixture, and then dehydration to > 99.5% fuel grade ethanol, are adoptable to cellulosic ethanol as well. Engineering aspects of the industrial three column distillation set up and recent technological advances like pervaporation are discussed in Chapters 14 and 15. Part 5 provides the details of fuel ethanol standards and process evaluation. Fuel grade ethanol standards in the US and EU, testing methods, and quality control are some of the sections in Chapter 16. Finally, the techno-economic aspects of cellulosic ethanol, a list of current and under-construction cellulosic ethanol plants around the world as of June, 2013, and the future prospects of cellulosic ethanol are presented in Chapter 17.
It is my great pleasure to thank Scrivener Publishing and John Wiley & Sons for kindly agreeing to publish this book. Finally, I wish to thank my wife Preethika, daughter Hiruni, and son Hasun for their love, support, encouragement, and patience during the writing of this book.
Ananda S. Amarasekara June, 2013