Energy & Fuels 2000, 14, 1333
1333
Book Reviews The Desulfurization of Heavy Oils and Residua, 2nd Edition. By James G. Speight, Marcel Dekker: New York; 2000. 480 pp. ISBN 0-8247-8921. $175.00. Considerable progress has been made in the processing of high-sulfur heavy crude oils and residues over the past twenty years; therefore, the second edition of James Speight’s 1981 book on desulfurization is a welcome volume. The title is actually quite misleading, because Speight’s definition of desulfurization includes any process that changes the sulfur content of the product streams relative to the feed. Consequently, the subject area is much broader than the title would suggest, including an introduction to refinery distillation, visbreaking, and coking processes. Similarly, the discussion ranges over process concepts for both distillate fractions and residues, contrary to what the title would indicate. Much of the flowsheet of a modern refinery is covered, with the exception of process steps such as alkylation and reforming. Although sulfur is a major theme, a more accurate title to indicate the full scope of this book would be along the lines of “refinery processes for heavy distillates and residues”. The overall intent of the book is to provide an introduction to refinery processes, with an emphasis on the underlying chemistry of the feed stocks and the process transformations. The opening chapter reviews the history and general terminology, followed by a section on the characterization of petroleum fractions, including elemental analysis, physical properties and molecular weight. A chapter on feedstock composition covers the chemical constituents of petroleum fractions, including a useful discussion of molecular weight-solubility parameter maps for understanding class fractionation of crude oils and residues. A disappointment in this section was the brief coverage of the chemistry of the sulfur species in distillate and petroleum fractions. The past twenty years has seen significant advances in understanding the steric factors that control reactions of thiophenic compounds, the distribution of sulfur between thiophenic and thioether forms, and the structure of sulfur in asphaltenes. Steric effects in hydrotreating are mentioned in a subsequent chapter, but the importance of the nature of the sulfur species and the tools for differentiating them is not mentioned. This gap is surprising given the importance of thioethers and disulfides in achieving modest levels of sulfur removal in processes such as visbreaking and thermal cracking of heavy residues in the presence of hydrogen. Given Speight’s broad definition of desulfurization, the chapter on desulfurization chemistry (Chapter 4) actually includes considerable valuable discussion of thermal and catalytic cracking and coke formation, as well as hydrotreating reactions of sulfur compounds. The chapter on the desulfurization process (Chapter 5) focuses on catalytic hydroprocesses: hydrotreating in fixed-bed reactors and hydroconversion in ebullated-bed reactors. The relationships between the process variables such as temperature, hydrogen pressure, residence time and hydrogen consumption are presented well, although the role of hydrogenation of aromatic carbon in increasing hydrogen consumption is not discussed. The chemistry and characteristics of the industry-standard catalysts are described effectively, with a brief summary of current views of the active sites of Ni/Mo and Co/Mo sulfide catalysts. The section on plugging of catalyst beds is confusing in that two distinct problems are combined interchangeably, i.e., plugging of packed-bed hydrogenation reactors by particulates such as iron sulfide, and deposition of coke and vanadium sulfide within the porous structure of supported-metal catalysts. The introductory section on the key process variables and characteristics is then followed by an interesting and effective discussion of the role of feedstock properties in altering process and catalyst performance (Chapter 6).
The next chapter is possibly the most unusual, following as it does Speight’s definition of desulfurization processes. Chapter 7, on desulfurization during refining, includes coverage of processes where alterations in sulfur content are strictly secondary objectives. These process steps include distillation, fluid catalytic cracking, visbreaking, and coking. Confusing this classification is coverage of hydroprocessing and deasphalting in this chapter, even though these steps are covered in much more detail in subsequent chapters. The organization of this section would be improved by moving the coverage of these topics to subsequent chapters. The unwary reader will be thoroughly confused by the usage of the term “hydrocracking” in this text. Unfortunately, this term is used to describe both thermal cracking processes that use a catalyst to control coke formation during conversion of residues, and processes for converting distillates into gasoline and diesel fractions using bifunctional metal-zeolite catalysts. Speight uses both definitions interchangeably, in some cases in the same section. For example, in section 7.6, hydrocracking is first defined as thermal decomposition with hydrogen and catalyst to remove heteroatoms and mitigate coke formation. Further down the same page, hydrocracking is described as useful for cycle oils and straight run naphtha, then subsequently as a one- or two-stage process for making gasoline or middle distillates from a heavy vacuum gas oil. The latter applications are for the bifunctional catalyst types which require careful control of nitrogen content. Luckily, much of the discussion of hydrocracking is on residue feeds, rather than zeolite-based catalysis of cracking. The final chapters on process technologies give summary descriptions of a wide range of processes for processing residue fractions, including thermal cracking, fluid catalytic cracking, deasphalting (Chapter 8) and hydrogen-based processes (Chapter 9). These sections provide an excellent quick reference for brief descriptions of proprietary process technologies. The processes are all from the recent literature, therefore, these chapters capture the current thinking in the design of processes for heavy residue fractions. The only minor concern with this section is that a reader who is new to the field may not realize that while some of the processes are widely used, some are only at the pilot or demonstration stage. Speight clearly points out this issue on the opening remarks in Chapter 9, but some additional remarks as to which processes are widely used would be helpful. The final chapter of the book is a useful discussion of various technologies for hydrogen production, including partial oxidation, gasification and steam reforming. Unfortunately, the material on cleanup of refinery gases and the environmental effects of sulfur containing gases, which was promised in the preface to the second edition, seems to have been omitted. This oversight is unfortunate, because after all of the discussion on desulfurization it would be ideal to consider the fate of the hydrogen sulfide that is liberated. Finally, the book concludes with a valuable glossary of refining and petroleum chemistry terms. This feature is particularly welcome in an introductory text. Overall, “The Desulfurization of Heavy Oils and Residua, 2nd Edition” by James G. Speight is a welcome addition to any reference collection on petroleum processing. It is particularly aimed at readers who are new to the field, and it succeeds in providing both factual content and a summary of the trends and unresolved issues in processing of heavy oil and residue materials. Murray R. Gray, Department of Chemical and Materials Engineering, University of Alberta EF000034S 10.1021/ef000034s
