Perry´s chemical engeneers handbook

Perry´s chemical engeneers handbook

(Parte 1 de 7)

Biological Concepts24-4
Isolated Plant and Animal Cells24-4
Mutation and Genetic Engineering24-6
Additional References24-6
Cell and Tissue Cultures24-6
Mammalian Cells24-6
Plant Cells and Tissues24-6
Primary Growth Requirements24-6
Secondary Metabolic Requirements24-7
Additional References24-7
Process Considerations24-10
Oxygen Transfer24-10
Sparger Systems24-1
Cell Culture24-14
Additional References24-15
Additional References24-16
Structured Models24-17
Continuous Culture24-17
Mathematical Analysis24-17
Computer Aids for Analysis and Design24-18
Plant Cell and Tissue Cultures24-18
Additional References24-19
Mixed Cultures24-19
Bioprocess Control24-20
Enzymatic Reaction Kinetics24-21
Immobilized Enzymes24-21
Enzymatic Reactors24-2
Additional References24-2


Section 24 Biochemical Engineering

Henry R. Bungay, P.E., Ph.D.,Professor of Chemical and Environmental Engineering, Rensselaer Polytechnic Institute; Member, American Institute of Chemical Engineers, American Chemical Society, American Society for Microbiology, American Society for Engineering Education, Society for General Microbiology. (Section Editor)

Arthur E. Humphrey, Ph.D.,Retired, Professor of Chemical Engineering, Pennsylvania State University; Member, U.S. National Academy of Engineering, American Institute of Chemical Engineers, American Chemical Society, American Society for Microbiology.

George T. Tsao, Ph.D.,Director, Laboratory for Renewable Resource Engineering, Purdue University; Member, American Institute of Chemical Engineers, American Chemical Society, American Society for Microbiology.

Assisted by David T. Tsao.


Nomenclature and Units SymbolDefinitionSI unitsU.S. customary units

A Empirical constant Dimensionless Dimensionless C Concentration (mass) kg/m lb/ft C Concentration mol/m (lb× mol)/ft D Diameter m ft D Effective diffusivity m /s ft /h DF /V s h

DRTDecimal reduction time forsh sterilization

E Activation energy cal/mol Btu/(lb× mol) FFlow or feed ratem/sft/h HConcentration of host organismskg/mlb/ft KRate coefficientUnits dependent on order of reactionUnits dependent on order of reaction K Michaelis constant kg/m lb/ft KaLumped mass-transfer coefficientsh K Death-rate coefficient s h K Monod coefficient kg/m lb/ft kKinetic constantsDependent on reaction orderDependent on reaction order M Coefficient for maintenance energy Dimensionless Dimensionless NNumbers of organisms or sporesDimensionlessDimensionless P Product concentration kg/m lb/ft QSpecific-respiration-rate coefficientkg O/(kg organism×s)lb O/(lb organism×h) R Universal-gas-law constant 8314 J/(mol× K) 0.7299 (ft )(atm)/(lb× mol× R) rRadial positionmft S Substrate concentration kg/m lb/ft S Shear N/m lbf/ft SSubstrate concentration in feedkg/mlb/ft T Temperature K ° F t Time s h VVelocity of reactionmol/s(lb×mol)/h VMaximum velocity of reactionmol/s(lb×mol)/h V Air velocity m/s ft/h V Fermenter volume m ft

VVMVolume of air/volume of fermentationDimensionlessDimensionless broth per minute

X Organism concentration kg/m lb/ft Y Yield coefficient kg/kg lb/lb

Greek symbols b Dimensionless Michaelis constant Dimensionless Dimensionless m Specific-growth-rate coefficient s h m or m Maximum-specific-growth-rate s h coefficient w Recycle ratio Dimensionless Dimensionless f Thiele modulus Dimensionless Dimensionless

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Press, Washington, DC, 1993. 5.Bu’Lock, J. D., and B. Kristiansen (eds.), Basic Biotechnology,Academic

Press, London, 1987. 6.Bungay, H. R., Energy: The Biomass Options,Wiley, 1981. 7.Bungay, H. R., BASIC Biochemical Engineering,BiLine Assoc., Troy, New

York, 1993. 8.Bungay, H. R., BASIC Environmental Engineering,BiLine Assoc., Troy,

New York, 1992. 9.Coombs, J., Dictionary of Biotechnology,Stockton Press, New York, 1992. 10.Demain, A., and N. Solomon, Biology of Industrial Microorganisms,Butterworth/Heinemann, Stoneham, Massachusetts, 1985. 1.Dibner, M. D., Biotechnology Guide U.S.A.: Companies, Data, and Analysis,Stockton Press, New York, 1991. 12.Dunn, I. J., E. Heinzele, J. Ingham, and J. E. Prenosil, Biological Reactor

Engineering—Principles, Applications, and Modelling with PC Simulation,VCH, Weinheim, New York, 1992. 13.Fiechter, A., H. Okada, and R. D. Tanner (eds.), Bioproducts and Bioprocesses, Springer-Verlag, Berlin, 1989. 14.Finkelstein, D. B., and C. Ball, Biotechnology of Filamentous Fungi,Butterworth/Heinemann, Stoneham, Massachusetts, 1992. 15.Fleschar, M. H., and K. R. Nill, Glossary of Biotechnology Terms,Technomic Pub. Co., Lancaster, PA, 1993. 16.Glick, B. R., and J. J. Pasternak, Molecular Biotechnology,ASM Press,

Washington, DC, 1994. 17.Ho, C. S., and D. I. C. Wang, Animal Cell Bioreactors,Butterworth/

Heinemann, Stoneham, Massachusetts, 1991. 18.Jackson, A. T., Process Engineering in Biotechnology,Prentice Hall, Englewood Cliffs, New Jersey, 1991.

19.Lancini, G., and R. Lorenzetti, Biotechnology of Antibiotics and Other

Bioactive Microbial Metabolites,Plenum, New York, 1993. 20.Laskin, A., Enzymes and Immobilized Cells in Biotechnology,Butterworth/Heinemann, Stoneham, Massachusetts, 1985. 21.Lee, J. M., Biochemical Engineering,Prentice Hall, Englewood Cliffs,

New Jersey, 1991. 2.Lydersen, B., N. A. D’Elia, and K. L. Nelson, Bioprocess Engineering,

Wiley, New York, 1994. 23.McDuffie, N. G., Bioreactor Design Fundamentals,Butterworth/Heinemann, Stoneham, Massachusetts, 1991. 24.Moo-Young, M. (ed.), Comprehensive Biotechnology: The Principles,

Applications and Regulations of Biotechnology in Industry, Agriculture and Medicine,Pergamon Press, Oxford, 1985. 25.Murooka, Y., and T. Imanaka, Recombinant Microbes for Industrial and

Agricultural Applications,M. Dekker, New York, 1993. 26.Nielsen, J., and J. Villadsen, Bioreaction Engineering Principles,Plenum,

New York, 1994. 27.Pons, M.-N. (ed.), Bioprocess Monitoring and Control,Hanser, 1991. 28.Richardson, J. F., and D. G. Peacock, Chemical Engineering,vol. 3, Pergamon/Elsevier, Oxford, 1994. 29.Solomons, G. L., Materials and Methods in Fermentation,Academic

Press, 1969. 30.Shuler, M. L. (ed.), Chemical Engineering Problems in Biotechnology,Am.

Inst. Chem. Engr., New York, 1989. 31.Thilly, W., Mammalian Cell Technology,Butterworth/Heinemann, Stoneham, Massachusetts, 1986. 32.Twork, J. V., and A. M. Yacynych, Sensors in Bioprocess Control,Dekker,

New York, 1993. 3.Vanek, Z., and Z. Hostalek, Overproduction of Microbial Metabolites,

Butterworth/Heinemann, Stoneham, Massachusetts, 1986. 34.Vieth, W. R., Bioprocess Engineering: Kinetics, Mass Transport, Reactors, and Gene Expression,Wiley, New York, 1994. 35.Vogel, H. C., Fermentation and Biochemical Engineering Handbook: Principles, Process Design, and Equipment,Noyes Publications, Park Ridge, New Jersey, 1983. 36.Volesky, B., and J. Votruba, Modeling and Optimization of Fermentation Processes, Elsevier, 1992.

The differences between biochemical engineering and chemical engineering lie not in the principles of unit operations and unit processes but in the nature of living systems. The commercial exploitation of cells or enzymes taken from cells is restricted to conditions at which these systems can function. Most plant and animal cells live at moderate temperatures and do not tolerate extremes of pH. The vast majority of microorganisms also prefer mild conditions, but some thrive at temperatures above the boiling point of water or at pH values far from neutrality. Some can endure concentrations of chemicals that most other cells find highly toxic. Commercial operations depend on having the correct organisms or enzymes and preventing inactivation or the entry of foreign organisms that could harm the process.

The pH, temperature, redox potential, and nutrient medium may favor certain organisms and discourage the growth of others. For example, pickles are produced in vats by lactobacilli well-suited to the acid conditions and with small probability of contamination by other organisms. In mixed culture systems, especially those for biological waste treatment, there is an ever shifting interplay between microbial populations and their environments that influences performance and control. Although open systems may be suitable for hardy organisms or for processes in which the conditions select the appropriate culture, many bioprocesses are closed and have elaborate precautions to prevent contamination. The optimization of the complicated biochemical activities of isolated strains, of aggregated cells, of mixed populations, and of cell-free enzymes or components presents engineering chal- lenges that are sophisticated and difficult. Performance of a bioprocess can suffer from changes in any of the many biochemical steps functioning in concert, and genetic controls are subject to mutation. Offspring of specialized mutants that yield high concentrations of product tend to revert during propagation to less productive strains— a phenomenon called rundown.

This section emphasizes cell cultures and microbial and enzymatic processes and excludes medical, animal, and agricultural engineering systems. Engineering aspects of biological waste treatment are covered in Sec. 25.

Biotechnology has a long history—fermented beverages have been produced for several thousand years. But biochemical engineering is not yet fully mature. Developments such as immobilized enzymes and cells have been exploited partially, and many exciting advances should be forthcoming. Genetic manipulations through recombinant DNA techniques are leading to practical processes for molecules that could previously be found only in trace quantities in plants or animals. Biotechnology is now viewed as a highly profitable route to relatively valuable products. In the near future, costs of environmental protection may force more companies to switch from chemical processing that generates wastes that are costly to treat to biochemical methods with wastes that are easily broken down by biological waste treatment processes and that present much less danger to the environment. Some commercial bioprocesses could have municipal and industrial wastes as feedstocks, and the credits for accepting them should improve the economic prospects. When petroleum runs out and the prices soar for petrochemicals, there will be large profits for fermentations that produce equivalent compounds.

CellsThe cell is the unit of life. Cells in multicellular organisms function in association with other specialized cells, but many organisms are free-living single cells. Although differing in size, shape, and functions, there are basic common features in all cells. Every cell contains cytoplasm, a colloidal system of large biochemicals in a complex solution of smaller organic molecules and inorganic salts. The cytoplasm is bounded by a semielastic, selectively permeable cell membrane that controls the transport of molecules into and out of the cell. There are biochemical transport mechanisms that spend energy to bring substances into the cell despite unfavorable concentration gradients across the membrane. Cells are protected by rigid cell walls external to the cell membranes. Certain bacteria, algae, and protozoa have gelatinous sheaths of inorganic materials such as silica.

Sequences of genes along a threadlike chromosome encode information that controls cellular activity. As units of heredity, genes determine the cellular characteristics passed from one generation to the next. In most cells, the chromosomes are surrounded by a membrane to form a conspicuous nucleus. Cells with organized nuclei are described as eukaryotic. Other intracellular structures serve as specialized sites for cellular activities. For example, photosynthesis is carried out by organelles called chloroplasts. In bacteria and cyanobacteria (formerly called blue-green algae), the chromosomes are not surrounded by a membrane, and there is little apparent subcellular organization. Lacking a discrete nucleus, these organisms are said to be prokaryotic.

Microorganisms of special concern to biochemical engineering include yeasts, bacteria, algae, and molds. The protozoa can feed on smaller organisms in natural waters and in waste-treatment processes but are not useful in producing materials of commercial value. Certain viruses called phages are also important in that they can infect microorganisms and may destroy a culture. A beneficial feature of microbial viruses is the ability to convey genetic materials from other sources into an organism. This is called transduction. Each species of microorganisms grows best within certain pH and temperature ranges, commonly between 20 and 40°C (68–104°F) and not too far from neutral pH.

BacteriaThe bacteria are tiny single-cell organisms ranging from 0.5–20 m in size, although some may be smaller, and a few exceed 100 m in length. The cell wall imparts a characteristic round or ovoid, rod, or spiral shape to the cell. Some bacteria can vary in shape, depending on culture conditions; this is termed pleomorphism.Certain species are further characterized by the arrangement of cells in clusters, chains, or discrete packets. Some cells produce various pigments that impart a characteristic color to bacterial colonies. The cytoplasm of bacteria may also contain numerous granules of storage materials such as carbohydrates and lipids. Bacteria can contain plasmids that are pieces of genetic material existing outside the main genome. Plasmids can be used as vectors for introducing foreign genes into the bacteria that can impart new synthetic capabilities to an otherwise “wild” bacterial strain. Many bacteria exhibit motility by means of one or more hairlike appendages called flagella. Bacteria reproduce by dividing into equal parts, a process termed binary fission.

Under adverse conditions, certain microorganisms produce spores that germinate upon return to a favorable environment. Spores are a particularly stable form or state of bacteria that may survive dryness and temperature extremes. Some microorganisms form spores at a stage in their normal life cycle.

Many species may, under appropriate circumstances, become surrounded by gelatinous material that provides a means of attachment and some protection from other organisms. If many cells share the same gelatinous covering, it is called a slime; otherwise each is said to have a capsule.

AlgaeAlgae are a very diverse group of photosynthetic organisms that range from microscopic size to giant kelp that may reach lengths of 20 m (6 ft). Some commercial biochemicals come from algal sea- weeds, and algae supply oxygen and consume nutrients in some processes used for biological waste treatment. Although their rapid growth rates relative to other green plants offer great potential for producing biomass for energy or a chemical feedstock, there is little industrial use of algae. One proposed process uses Dunaliella, a species that grows in high salinity and accumulates glycerol internally to counter the high external osmotic pressure. Outdoor ponds are most suitable for growing algae because vast surfaces and high illumination are needed.

FungiAs a group, fungi are characterized by simple vegetative bodies from which reproductive structures are elaborated. All fungal cells possess distinct nuclei and produce spores in specialized fruiting bodies at some stage in their life cycles. The fungi contain no chlorophyll and therefore require sources of complex organic molecules for growth: Many species grow on dead organic material; others live as parasites.

Yeasts are one kind of fungi. They are unicellular organisms surrounded by a cell wall and possessing a distinct nucleus. With very few exceptions, yeasts reproduce by a process known as budding, where a small new cell is pinched off the parent cell. Under certain conditions, an individual yeast cell may become a fruiting body, producing spores.

Isolated Plant and Animal CellsBiotechnology includes recovery of biochemicals from intact animals and plants, but the care and feeding of them is beyond the scope of this section. Processes with their isolated cells have much in common with processes based on microorganisms. The cells tend to be much more fragile than microbial cells, and allowable ranges of pH and temperature are quite narrow. These cells occur in aggregates and usually require enzymes to free them. There is a strong tendency for the cells to attach to something, and cell cultures often exploit attachment to surfaces.

Plant and animal cells have numerous chromosomes. Growth rates are relatively slow. A typical nutrient medium will contain a large number of vitamins and growth factors in addition to complex nitrogen sources, because other specialized cells in the original structures supply these needs. A plant or animal cell is not like a microbial cell in its ability to function independently.

VirusesViruses are particles of a size below the resolution of the light microscope and are composed mainly of nucleic acid, either DNA or RNA, surrounded by a protein sheath. Lacking metabolic machinery, viruses exist only as intracellular highly host-specific parasites. Many bacteria and certain molds are subject to invasion by virus particles. Those that attack bacteria are called bacteriophages. They may be either virulent or temperate (lysogenic). Virulent bacteriophages divert the cellular resources to the manufacture of phage particles; new phage particles are released to the medium as the host cell dies and lyses. Temperate bacteriophages have no immediate effect upon the host cell; they become attached to the bacterial chromosome. They may be carried through many generations before being triggered to virulence by some physical or chemical event.

BiochemistryAll organisms require sources of carbon, oxygen, nitrogen, sulfur, phosphorus, water, and trace elements. Some have specific vitamin requirements as well. Green plants need only carbon dioxide, nitrate or ammonium ions, dissolved minerals, and water to manufacture all of their cellular components. Photosynthetic bacteria require specific sources of hydrogen ions, and the chemosynthetic bacteria must have an oxidizable substrate. Some microorganisms have the ability to “fix” atmospheric nitrogen by reduction. Organisms that use only simple inorganic compounds as nutrients are said to be autotrophic (self-nourishing).

(Parte 1 de 7)