Fuel Etanol from Cellulosic Biomass

Fuel Etanol from Cellulosic Biomass

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Monte, CA, 1988). 27. T. Y. Chang, S. J. Rudy, G. Kuntasal, R. A. Gorse, Atmos. Environ. 23, 1629 (1989). 28. G. Z. Whitten, "Comparative ranking of the environmental impacts of alternative fuels" (Systems Applications, Inc., San Rafael, CA, 1989). 29. The difference between feedstock cost and by-product credits is the lower limit for the net feedstock cost in that capital and operating costs associated with coproduct production are not considered.

30. Ethanol's Role in CleanAir (Backgrounder Ser 1102-89, USDA, Washington, DC, 1989).

31. Energyfrom Biological Processes, vol. 2, Technical and Environmental Analyses (Office ofTechnology Assessment, Washington, DC, 1980).

32. Report of the New Farm and Forest Products Task Force to the Secretary (USDA, Washington, DC, 1987).

3. A. E. Humphrey, A. Moreira, W. Armiger, D. Zabriske, Biotechnol. Bioeng. Symp. 7, 45 (1977); T. W. Jeffries, Adv. Biochem. Eng.-Biotechnol. 27, 1 (1983); T. K. Ng, R. M. Busche, C. C. McDonald, R. W. F. Hardy, Science 219, 733 (1983); J. Young, E. Griffin, J. Russell, Biomass 10, 9 (1986).

34. "Short rotation woody crops program annual progress report," Oak Ridge Nati. Lab. Environ. Sci. Div. Publ. 3030 (1988).

35. D. H. Strauss and L. L. Wright, in Energyfrom Biomass and Wastes XIV, D. L. Klass, Ed. (Institute of Gas Technology, Chicago, in press).

36. D. J. Parish, D. D. Wolf, W. L. Daniels, D. H. Vaughan, J. S. Cundiff, "Perennial species for optimum production of herbaceous biomass in the Piedmont, final report 1985-89," Oak Ridge Natl. Lab. Publ. 85-27413/5 (1990); J. H. Cherney, K. D. Johnson, J. J. Volenec, E. J. Kladivko, D. K. Green, "Evaluation ofpotential herbaceous biomass crops on marginal crop lands, final report 1985-1989," Oak Ridge Natl. Lab. Publ. 85-27412 (1990). 37. J. D. Wright, Energy Prog. 8 (no. 2), 71 (1988); Chem. Eng. Prog. 84 (no. 8), 62 (1988).

38. "Current SERI wood feedstock-based simultaneous saccharification and fermentation (SSF) process design." 39. Based on a 35-mile average travel distance and transport of biomass with 50% moisture by diesel truck requiring 2000 Btu per ton per mile; see (40).

40. M. DeLuchi, thesis, University of California, Davis (1990). 41. Chemical requirements are design specific, but corresponding energy flows are small in all cases that we have examined. For the SSF design considered here (42), the significant chemical flows are for H2S04 and Ca(OH)2 used in pretreatment.

H2S04 manufacture is an energy-yielding process [R. N. Shreve and J. A. Brink, Chemical Process Industries (McGraw-Hill, New York, 1977), p. 301]. The value given is essentially all for Ca(OH)2 manufacture [F. Schwarzkopf, Lime Burning Technology, A Manualfor Plant Operators (Kennedy Van Saun Corp., Danville, PA, 1974)]. The energy required for manufacture ofammonia and other chemicals used as nutrients for yeast growth is an insignificant contribution.

42. N. D. Hinman, J. D. Wright, W. Hoagland, C. E. Wyman, Appl. Biochem. Biotechnol. 20/21, 391 (1989).

43. From (40), consistent with a large plant able to use pipeline transport to a significant extent.

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4. Value used in (45) for a corn-based ethanol plant; believed to be conservative for an economical cellulose-to-ehanol process. 45. R. S. Chambers, R. A. Herendeen, J. J. Joyce, P. S. Penner, See 206,789 (1979). 46. M. A. Johnson, Energy 8, 225 (1983); J. M. Krochta, in Proceedings ofthe Second

International Conference on Energy Use Management (Pergamon, Elansford, NY, 1979), p. 1956-1963); F. Parisi,Adv. Biochem. Eng.-Biotechnol. 28, 41 (1983); T. Yorifugi, Energy Dev.J. 3, 195 (1981). 47. Based on heat of combustion for petroleum liquids [Basic Pet. Data Book

[(American Petroleum Institute, Washington, DC, 1989), vol. 9, no. 3], adding 19% for oil recovery, refining, and distribution (40).

48. R. C. Loehr and M. Sengupta, Environ. Sanit. Rev. 16 (1985); E. D. Waits and J.

L. Elmore, Environ. Int. 9, 325 (1983). 49. Threshold Limit Values for Chemical Substances and Physical Agents in the

Workman Environment with Intended Changes for 1980s (American Conference of Government Industrial Hygienists, Cincinnati, OH, 1980). 50. Hydrocarb. Process. 68 (no. 1), 85 (1989); ibid. 67 (no. 9), 61 (1988). 51. L. Lynd, Appl. Biochem. Biotechnol. 24/25, 695 (1990). 52. M. K. Veldhuis, L. M. Christensen, E. I. Fulmer, Ind. Eng. Chem. 28,430 (1936);

T. K. Ng, P. J. Weimer, J. G. Zeikus, Arch. Microbiol. 114, 1 (1977). 53. L. R. Lynd, H. E. Grethlein, R. H. Wolkin, Appl. Environ. Microbiol. 5, 3131 (1989). 54. J. N. Van Arsdell et al., BiolTechnology 5, 60 (1987); B. Surbriggen, M. J. Bailey,

M. E. Pentrila, K. Poutanen, M. Linko,J. Biotechnol. 13, 267 (1990); M. E. Penttila, P. Lehtovaara, M. Bailey, T. T. Teer, J. K. C. Knowles, Gene 63, 103

5. National Assessment of Undiscovered Conventional Oil Gas Resources, Working-

Paper (Working pap., U.S. Geological Survey and Minerals Management Service, March 1989); R. A. Kerr, Science 245, 1330 (1989).

56. M. Grathwohl, World Energy Supply (de Gruyter, Berlin, 1982). 57. L. R. Lynd, Adv. Biochem. Eng.-Biotechnol. 38, 1 (1989).

58. The indicated range is consistent with the evaluation of the DOE Biofuels

Feedstock Development Program [R. D. Perlack andJ. W. Ranney, Enery 12 (no. 12), 1217 (1987); (35)]. 59. S. Kane, J. Reilly, M. LeBlanc, J. Hrubovcak, Agribusiness 5, 505 (1989); Feed

Situation and Outlook Report (USDA, FDS-314, Washington, DC, 1990). 60. C. E. Wyman and N. D. Himman,Appl. Biochem. Biotechnol. 24/25, 735 (1990). 61. J. D. Ferchak and E. K. Pyc, Sol. Energy 26,9 (1981); J. W. Ranney, L. L. Wright,

P. Layton,J. For. 85 (no. 8), 17 (1987); N. Smith and T. J. Corcoran, Am. Chem. Soc. Symp. Ser. 144,433 (1981). 62. G. Marland and A. Turhollow, Oak Ridge Natl. Lab. Environ. Sci. Div. Publ. 3301

(1990). 63. Agricultural Resources-Cropland, Water, and Conservation, Situational Outlook and

Report (USDA, Washington, DC, 1988). 64. 'Basic Statistics, 1982 National Resources Inventory," USDA Soil Conserv. Serv.

Stat. Bull. 756 (1987). 65. H. E. Grethlein, D. C. Allen, A. 0. Converse, Biotechnol. Bioeng. 26,1498 (1984). 6. We thank M. DeLuchi, P. Lorang, R. Moorer, and A. Turhollow for useful discussions and information. Publication 3644, Environmental Sciences Division, Oak Ridge National Laboratory.

Withy Gases Dissolve in Liquids GERALD L. POLLACK

The thermodynamics and statistical mechanics ofsolubility are fairly well understood. It is still very difficult, however, to make quantitative predictions of solubility for real systems from first principles. The purposes ofthis article are to present the results of solubility experiments in some prototype solute-solvent systems, to show how far they may be understood from molecular first principles, and to discuss some of the things that are still missing. The main systems used as examples have the inert gas xenon as solute and some simple organic liquids as solvents.L GASES DISSOLVE AL LIQUIDS, BUT THE ACTUAL solubilities range over many orders ofmagnitude. For inert gases at room temperature, for example, the solubility ofXe in n-octane, a common hydrocarbon liquid, is 470 times that ofHe in water. Gas solubility can vary much more for complex solutes and solvents. As an example, the solubility of the anesthetic gas halothane in olive oil is more than 106 times the solubility of common gases in liquid mercury.

Can the solubilities of gases in liquids be quantitatively understood from molecular first principles? The question can be generalized with the help of the Gibbs phase rule, according to which systems such as these with two components and two phases have two degrees of freedom, such as temperature and pressure. There- fore, the question may be enlarged to include: Can the temperature and pressure dependence of these solubilities be understood from molecular first principles?

One purpose ofthis article is to discuss how far we can go, using current experiments and modern theory, in answering these questions. Also discussed with the same ideas are some applications of solubility. Finally, there are some suggestions of what natural next steps would advance our understanding of the subject.

Solubility is an old subject, although most ofthe early interest was in solubility of solids in water, which is still an important area of research and applications. Aristotle knew that evaporation ofseawater would recover dissolved salts, and there are records of a systematic study by Pliny the Elder of the relative solubilities of many solids in water.

Early quantitative measurements ofthe solubility ofgases, a more difficult measurement, were made by William Henry (1), as well as by Cavendish, Priestley, and others. Henry studied the pressure and temperature dependence of air, H2, N2, 02, and other gases in water. He discovered, among other things, that 02 is more soluble than N2 in water. This is an early example ofthe principle that is the basis ofpreferential extraction ofone gas from a mixture ofgases by use ofa solvent. Since that time, the subject has been actively studied because of its fundamental interest and applications. More recently, extensive contributions to understanding gas solubility have been made by Hildebrand and his co-workers and by many others (2, 3). Review articles give comprehensive discussions ofthe subject as well as results for many solute-gas, solvent-liquid systems (4, 5).

Ostwald solubility (L) is an especially useful and also intuitive measure of gas solubility (6). It is defined as the ratio of the concentration ofgas molecules dissolved at equilibrium in the liquid solvent to their concentration in the gas phase. In other words, L is the ratio: (moles ofsolute per liter of solution)/(moles of solute per liter of gas). We then can write where p is the number density and subscripts 1 and 2 stand for, respectively, solvent and solute.

ARTICLES 1323

The author is in the Department ofPhysics and Astronomy, Michigan State University, East Lansing, MI 48824.

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