Biorenewable Resources: Engineering New Products from Agriculture. Robert C. Brown. Iowa State Press, Ames, 2003. 286 pp., illus. $74.99 (ISBN 0813822637 paper).
Recent years have seen a remarkable growth of interest in the use of biologically produced fuels and materials, in part because of concerns that humans have become overreliant on fossil fuels and in part because of apprehension about increasing atmospheric levels of greenhouse gases. Although several academic disciplines address aspects of the emerging field of biobased resource utilization, industry needs employees with an appreciation of how these disciplines can be integrated. Until now, textbooks have seldom offered the broad perspective necessary to train students to conduct research and be effective managers in this growing field. Robert C. Brown's fine book fills this gap by providing a logical overview of the relevant areas of engineering, thermodynamics, and chemistry, as well as a clear account of the range of raw materials and processes available.
Brown, who holds the Bergles chair in thermal sciences at Iowa State University, is professor of mechanical and chemical engineering and director of the university's Center for Sustainable Environmental Technologies. His book is intended for upper-level undergraduate and first-year graduate students in science and engineering, but I suspect it may well find broader use as a general reference among professionals.
Brown begins by defining what constitutes biorenewable resources— anything containing organic material that uses sunlight for energy, from crops to trees. He then discusses what drives the growing interest in bioenergy and biobased products. Aside from the fears about the greenhouse effect and overreliance on fossil fuels, which lead to national security concerns, are worries about pollution from acid rain and stratospheric ozone depletion. To his credit, Brown does not shrink from describing the challenges that stand in the way of converting a primarily petroleum-based economy back to one at least partially based on renewable resources.
The book provides all the scientific foundation needed for an understanding of how biobased raw materials are converted into finished products. The broad sweep of the work is evident in its treatment of the conversion of a wide range of raw materials to energy and in its description of a wide range of production processes. Brown also considers harvesting and storage of herbaceous and woody crops, ranging from annual cereals, switchgrass, and alfalfa to hybrid poplar and eucalyptus.
Chapters five through eight cover conversion of biorenewable resources into a variety of products, such as fuels, chemicals, solvents, plastics and fibers. Brown reviews furnace designs and explains how they can best be applied in boiler systems, detailing power cycles of relevance to bioenergy. Happily, he provides enough theory for the student to understand how limits to efficiency come about. Brown rightly gives a considerable amount of space to fuel cells, which are one of the recently publicized new energy technologies. Although carbonaceous fuels must first be reformed to hydrogen before they are suitable for use in such cells, the high thermodynamic efficiency of fuel cells makes them attractive when other fuels are relatively costly. Still, the initial requirement for fossil fuel generation of energy does not necessarily help reduce reliance on petroleum or coal.
Almost as many important intermediate chemicals can be manufactured using biomaterials as can be produced with petroleum. Brown presents a list of the top 60 (by annual production) commodity chemicals in the United States and considers which of them can most efficiently be produced with biorenewable materials. This very worthwhile exercise demonstrates that increasing the use of biorenewable materials will depend more on bringing about changes in the manufacturing infrastructure than on finding new chemical pathways.
Brown evaluates the co-firing of biomass with coal, as well as the other mechanical and chemical processes for producing fuel gas from biomass with heat. He gives a valuable assessment of the potential of anaerobic digestion for producing “biogas,” a mixture of methane and carbon dioxide, and provides a full discussion of the production of ethanol, methanol, and “biodiesel” as transportation fuels. His presentation of the arguments for and against the last of these, in particular, is evenhanded. Production of biodiesel entails the chemical conversion of several oilseed triglycerides into methyl or ethyl esters of the fatty acids. The resulting fuel has properties very similar to those of petroleum-based diesel.
Brown concludes that, although the production of the fuel ethanol from starch is straightforward, the economics are critically dependent on efficient utilization of by-products or their conversion to higher-value final products. This insight could well provide opportunities for innovators. For example, conversion of cellulosic, hemicellulosic, and lignocellulosic materials to sugars for fermentation is a critical limiting step for the utilization of many biomaterials; Brown describes several pretreatment processes that can be used to convert cellulose and lignocellulose to fermentable five-carbon and six-carbon sugars, but opportunities to further improve efficiencies at this key process bottleneck still exist.
Chemical building blocks used by the petroleum industry include syngas (a mixture of carbon monoxide and hydrogen), ethylene, propylene, butadiene, and a mixture of monocyclic aromatic hydrocarbons known as BTX (benzene, toluene, and xylene). It is impractical to simply replace these with building blocks derived from biorenewable resources—many are hard to manufacture economically from biological resources—but it may well be feasible to create substitutes. Oxygenated organic compounds can be used as building blocks in the production of fuels and commodity chemicals, for example. The book gives an expert survey of biological and enzymatic processes that can yield such valuable intermediates.
One particularly valuable aspect of this work is that Brown does not give short shrift to the mechanical and chemical pulping processes that are an essential facet of the production of natural fibers. Herbaceous materials contain less lignin than does woody material, which makes pulping herbaceous material easier, but the paper that is produced lacks the strength of paper made from woody raw materials. Needless to say, the considerations quickly become more complicated in more complex processes.
In the latter part of the book, Brown provides a valuable account of the environmental and economic issues confronted by the bioprocessing industry. One of the most exciting new frontiers is the use of genetic engineering to produce materials optimized for efficient use. Despite some public resistance to genetic engineering of crop plants, especially in Europe, Brown is skeptical about one commonly heard argument against the technology: that it will lead to a loss of biodiversity. Agriculture in general leads to a loss of biodiversity, he notes. Moreover, Brown is just as dubious about another feared threat, that transgenes in food crops might jump into human DNA. Although he states that this scenario is highly unlikely, he (surprisingly) offers a diagram that depicts it.
The final two chapters include an effective comparison of biorenewable and fossil-based resources in terms of their nitrogen, sulfur, and chlorine content. Brown demonstrates the use of “life-cycle analysis” to show how it is possible to anticipate the environmental impact of a new product. These final chapters also include an introduction to methods for determining the cost of producing a crop and for analyzing cash flow. In examples, Brown estimates the cost of manufacturing various biologically based chemicals and of producing electricity from several biorenewable resources.
Throughout the book, plentiful illustrations help the student visualize complex processes. Process diagrams are particularly helpful, and problems at the end of each chapter will aid study.
Brown's book is a valuable resource. I found a few typographical errors that could be confusing to a student, but that was the only shortcoming I identified. Teachers, students, and practitioners are fortunate to have access to this impressive compilation on such a vital field.
