EVERY VITAL INDUSTRY IN AMERICA OWES AN ENORMOUS DEBT TO THE
INDUSTRIAL CHEMIST AND CHEMICAL ENGINEER
INTRODUCTION
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Just as the arts of tanning and dyeing were practiced long before the scientific principles upon which they depend were known, so also the practice of chemical engineering preceded any analysis or exposition of the princi les upon which such practice is based. The unit operations of cgemical engineering have in some instances been developed to such an extent in individual industries that the operation is looked upon as a special one adapted to these conditions alone, and is, therefore, not frequently used by other industries. All important unit o erations have much in common, and, if the underlying principres upon which the rational design and operation of basic types of engineering equipment depend are understood, their successful adaptation to manufacturing processes becomes a matter of good management rather than of good fortune. I n this book we have attempted to recall to the reader’s mind those principles of science upon which chemical engineering operations are based, and then to develop methods for applying these principles to the solution of such problems as present themselves in chemical engineering practice. We have selected for treatment basic operations common to all chemical industries, rather than details of specific processes, and so far as is now possible, the treatment is mathematically quantitative as well as qualitatively descriptive. We venture to hope that the book will stimulate engineers to design apparatus adapted for any particular purpose, rather than just t o build it and then to rely on arge scale experimentation with expensive changes in construction to effect efficient operation.
MONG all the fields of chemical endeavor the expression of
American talent is nowhere more striking than in the industrial application of our store of scientific knowledge. The countless natural riches of our nation have provided fertile soil indeed for the expression of those skills. The past 75 years reveal an astounding growth. Today, that growth has proliferated until virtually every major industry owes an important debt t o the industrial chemist and chemical engineer, and the chemical process industries have assumed the lead position on the American industrial scene. Accounts will be given of developments in many of the chemical process industries elsewhere in this historical series. However, the story is not complete without a description of the advances in basic technology, both engineering and chemical, that are the common denominator for many of the advances in a specific industry. This historical section is devoted t o that broad theme. It also includes histories of several important chemical process industries that do not fall within the logical scope of the other sections of the 75-year review.
T.
H. CHILTON
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HE concept of unit operations date8 back scarcely half way
in the 75 years’ history of the AMERICAN CHEMICAL SOCIETY. It was in 1915 that the late Arthur D. Little (11) introduced this conception, in a report to the Corporation of the Massachusetts Institute of Technology.
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W. A. Pardee
Any chemical process, on whatever scale conducted, may be resolved into a ooordinated series of what may be termed (tunit actions,” as pulverizing, mixing, heating, roasting, absorbing, cohdensing, lixiviating, precipitating, crystallizing, filtering, dissolving, electrolyzing, and so on. The number of these basic unit operations is not very large, and relatively few of them are involved in any particular process. The complexity of chemical results from the variety of conditions as to temperatWe,presswe, etc.,under which the unit actions must be carried and from the limitations as to materials outin different of construction and design of apparatusimposed by the hysical and chemical character of the reactingsubstances. An aiility to cope broadly with the demands of his profession can be attained only through the analysis of processes into the unit actions of which they are composed, and the close study of these basic unit actions as they are carried out on the commercial scale under the conditions imposed by practice.
Little did not clearly differentiate in his “unit actions” bctween “unit operations” and “unit processes.” Following the adoption of the first by Walker, Lewis, and McAdams, this term. “unit operations,” has come t o represent the primarily physical treatment steps that make up a chemical manufacturing process. Following the adoption of the title “Unit Processes in Organic Synthesis” by Groggins (4), this term has come t o imply the occurrence of a distinct chemical change, rather than a mere physical treatment. The unit operations concept formed the inspiration for the rcsearches that were reported in a memorable series of symposia held by the Division of Industrial and Engineering Chemistry in 1921 on drying (8); in 1922 on distillation (9);in 1924 on heat transfer ( 6 ) ; and in 1924, also, on absorption (14). Stine (17) stated in 1928: Perha s the characteristic which most differentiates the chemicarengineering of today from the earlier activities of those interested in this field is the quantitative treatment of these various unit operations, and it is this exact and quantitative treatment of these operations which constitutes the province of modern chemical There was, of course, chemical engineering before 1915, when the unit operations concept was formulated, There a chemical manufacturing industry before 1908, when the Division of Industrial and Engineering Chemistry was established (under the original name “Industrial Chemists and Chemical Engineers”), and the American Institute of Chemical Engineers was founded. There was a chemical industry, even in 1876 when the AMERICAN CHEMICAL SOCIETY was founded. But the concept of chemical engineering as a profession and as a body of science emerged
This concept found immediate acceptance a t M.I.T. It became the inspiration of a whole school of teaching and research, there and elsewhere. It formed the basis of the outline of a work on the principles of chemical engineering, developed over the course of several years as mimeographed notes, and finally as the text (18)bearing that title, with these historic words in the preface:
Coordinator: W. A. Pardee, Gulf Research and Development Co., Pittsburgh, Pa. T . H. Chilton, E. I. du Pont de Nemours & Co., Wilmington, Del.
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slowly during the period. development :
Little ( 1 1 ) records one h i e of this
Although industrial chemistry in its modern sense may be said to have begun as long ago as the French Revolution with the invention by Le Blanc of the soda process, it was nearly one hundred years thereafter before chemical engineering began to be dimly recognized as a distinct profession. I n Kovember 1887 the faculty of Massachusetts Institute of Technology appointed a committee “to consider instruction in engineering as relating especially to applied chemistry,” and in the faculty meeting of that year it was voted to establish a course in chemical engineering. The course schedule was adopted in February 1888 and went into effect the following autumn, the f i s t class in chemical engineering ever graduated receiving its diplomas from the institute in 1891.
Research chemical engineer operates experimental vacuum drying equipment
Only one other school had adopted a curriculum in chemical engineering up to the turn of the century-the Univerbity of Michigan. In England in 1880, a movement was instituted to form a “society of chemical engineers.” The society defined a chemical engineer as “a person possessing knowledge of chemistry, physics, and mechanics, and a h @employs that knowledge for the utilization of chemical reactions on a large scale” (a definition closely paralleling the one adopted in 1948 by the American Institute of Chemical Engineers). But the time was not then ripe, and what emerged was the now venerable Society of Chemical Industry. G. E. Davis, who took part in the movement referred to, gave a series of lectures on chemical engineering a t the Manchester Technical School in 188’7. These lectures were later enlarged and published (S), first in 1901. The following, refcrring t n thr period 1876-1901, has a strangely modern sound: There have been many changes in manufacturing chemistry during the last quarter of a century. . .During the period under review, there has been no change in the chemistry of the situation. Chemists, i t is true, have a much greater knowledge of the methods of substitution, of isolation, and of recombining different and various organic radicals, and to their researches we owe much of our present prosperity in the chemical trade; but the greatest progress has been made in the mechanism of plant and in the way in which chemical operations have been carried out on the large scale. Though chemical operations are now much more intricate than they were a quarter of a century ago, they are carried out less expensively, and with greater safety to the workpeople, and a t least the moiety of this improvement must be credited to the chemical engineer.
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Filtration section at Corn Products Refining plant. room i s only partially enclosed
The
The chapter headings of Davis’s two-volume work published in 1904 would not look unfamiliar if they aere used in a 1950 text, on unit operations: Moving solids, liquids, and ases Treating and preparing soli& Application of heat and cold Separating solubles from insolubles Absorbing and compressing gases Evaporation and distillation Crystallization and dialysis
Fundamental u n i t operation, mixing, i s put into practice
in sparkling new industrial plant
He even included a section on safety practices. But most of the treatment was descriptive, and its essentially qualitative character can be inferred from the statement accompanying an illustration of a rectifying column: “The dimensions of the dephlegmating column cannot well be calculated, except from the results of previous experience.” The quantitative treatment that differentiates the unit operations from the earlier rule-of-thumb approach to chemical plant design, strangely enough, was slow in developing. The quantitative basis of rectification calculations was formulated by Sorel (16)in 1880, and made available in a book in 1893. Rut Young’s ( d o ) book in 1903, even as revised ( 1 9 ) in 1922, makes no reference to it, and has a singularly unilluminating treatment of reflux and its relation to number of plates. Lewis (7), a t the Distillation Symposium of 1922, based his treatment on Sorel, but it was through the classic paper of SlcCabe and Thiele ( 1 2 )in 1925 that
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the matter was brought to a point of real usefulness to the chemical engineer. The groundwork for other unit operations was, of course, being laid. Hausbrand’s work ( 5 ) , the first German edition of which appeared in 1899, did give tables of data which could be used for design of heaters, coolers, and condensers, though nothing very fundamental. The fundamental data were beginning to be supplied, however, by various workers-for example, Stanton (16) in England. The period from 1924 to 1934 witnessed the flowering of quantitative researches in chemical engineering, and by 1933 Little ( 1 1 ) was able to conclude that the concept of unit operations he had introduced “is now generally accepted.” , Oddly enough, the Division of Industrial and Engineering Chemistry gave no formal attention to unit operations in that decade. I n 1934, under the chairmanship of W. H. McAdams, a Symposium on Diffusional Processes was held, and during that year, under the leadership of D. B. Keyes, the Chemical Engineering Symposium was organized, and the first symposium held, during the Christmas holidays, on the topic of distillation. Devoted primarily to unit operations, this series of Christmas symposia has done a great deal to foster and strengthen this treatment of the principles of chemical engineering. A listing of the topics covered in successive years is an essential part of the history of unit operations and of the Division of Industrial and Engineering Chemistry. Such a list is given i n the divisional history a t the end of the section on industrial and engineering chemistry (page 310). The 1901 “Handbook of Chemical Engineering” ( 3 )by Davis, essentially qualitative and descriptive in character, is forgotten, except for historical interest. The 1922 work (10)by Liddell was written on a comparable level. But the 1934 “Chemical Engineers’ Handbook” ( I S ) , based on the quantitative approach inherent in the unit operations concept and built on the researches of the preceding 15 or 20 years, has become the indispensable reference work of the profession. The pioneering treatise (18)of 1923 and the other of consequence that has followed it (1) have uniformly adopted this treatment. The final triumph of Little’s concept may now be said to have come in the unabashed adoption for the latest chemical engineering text ( 2 ) of the simple title: “unit operations.” LITERATURE CITED
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(1) Badger, W. L., and McCabe, W. L., “Elements of Chemical Engineering,” New York, McGraw-Hill Book Co., 1931. (2) Brown, G. G., and associates, “Unit Operations,” New York, John Wiley & Sons, 1950. (3) Davis, G. E., “Handbook of Chemical Engineering,” Manchester, Davis Bros., 1st ed., 1901; 2nd ed., 1904. (4) Groggins, P. H., “Unit Processes in Organic Synthesis,” New York, McGraw-Hill Book Co., 1935. (5) Hausbrand, Eugen, “Evaporating, Condensing, and Cooling Apparatus,” tr. by A. C. Wright, London, Scott, Greenwood & Son, 1903. (6) HeiIman, R. H., et al., IND.ENG.CHEM.,16,451-93 (1924). (7) Lewis, W. K., J. IND. ENG.CHEM.,14,492-7 (1922). (8) Lewis, W.K., et al. Ibid., 13,427-60 (1921). (9) Ibid., 16,121542 (1924). (10) Liddell, D. M.,“Handbook of Chemical Engineering,” New York, McGraw-Hill Book Co., 1922. (11) Little, A. D., in “Twenty-Five Years of Chemical Engineering Progress,” S. D. Kirkpatrick, ed., pp. 1-14, New York, Am. Inst. Chem. Engrs., 1933. (12) McCabe, W.L., and Thiele, E. W., IND. ENG.CHEM.,17,605-21 (1925). (13) Perry, J. H., ed., “Chemical Engineers’ Handbook,” 1st ed., New York, McGraw-Hill Book Co., 1934. (14) Peters, W. A,, Jr., etal., J. IND. ENG.CHEM.,14,476-97 (1922). (15) Sorel, Ernest, Compt. rend., 58, 1128, 1204, 1317 (1880); 68, 1213 (1894); ”Le rectification de I’alcool,” Paris, Dunod, 1893. (16) Stanton, T.E., Trans. Roy. Soc., London, 190,(A),67-88 (1897).
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(17) Stine, C. M. A., Trans. Am. Inst. Chem. Engrs., 21, 45-53 (1928). (18) Walker, W. H.,Lewis, W. K., and McAdams, W. H., “Principles of Chemical Engineering,” 1st ed., New York, McGrawHill Book Co., 1923. (19) Young, Sidney, “Distillation Principles and Processes,” London, Macmillan Co., 1922. (20) Young, Sidney, “Fractional Distillation,” London, Macmillaii Co., 1903.
R. N. SHREVE
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HE great emphasis in the development of chemical engineering came from the origination and expansion of the unit operations concept covering the physical changes that the chemical engineers used. However, chemical changes could not be neglected. When the chemical engineer applied his knowledge of chemical changes or reactions to the plant, there was a very definite separation from the laboratory test tube and beaker stage to that of the factory. I n industry, the chemistry itself, yields, and equipment (including instrumentation), all were of paramount significance. Before and after 1932, a number of people working in the field of chemical processes and noting the succesB of the concept of unit physical operations thought there should be more attention given to these industrial chemical changes. Probably the first man t o associate the unit process term with chemical activity was Groggins ( 1). The Division of Industrial and Engineering Chcmistry came into this picture with a symposium in Denver on August 24, 1932, under the chairmanship of D. B. Keyes. This was titled “The Design, Construction, and Operation of Reaction Equipment” and it included papers descriptive of chemical changes and the equipment needed to commercialize these chemical reactions. Keyes in his introductory comments (3) said: “Much has been written in recent years about unit operations but very little about unit processes. It is strange that this particular subject, which means so much to every chemical engineer, should have received scarcely any consideration at all in our modern chemical literature.” I n 1937 the annual series of Unit Process Symposia was inaugupated, under the sponsorship of the division, with R. N. Shreve as chairman. These have been held each year at the fall meeting of the division. The fifteenth symposium was held in Chicago a t the fall~1950meeting. These symposia have served as a medium for the presentation of papers emphasizing the industrial chemical changes and the necessary equipment. Out of these came the definition of unit processes as chemical changes carried out economically on an industrial scale. A number of suggestions had been made t o name or classify these chemical changes in other ways. However, the concept of unit processes is well established in the literature. Fundamentally, the unit processes involve the study of kinetics, equilibria, and any other conditions that affect the chemical change in the direction of an economical process. The equipment to commercialize these chemical changes becomes an integral part of the concept. Such equipment has been presented not only in the annual Unit Process Symposia but in many specialized symposia, all listed in the annual directory of the Division of Industrial and Engineering Chemistry. Among such symposia, very helpful to the chemical process industries, might be mentioned the following, several of which antedate the more formalized Unit Process Symposia: Automatic Process Control (1922) Combustion (1922) Materials of Chemical Equipment Construction (1923) Industrial High-pressure Reactions (1930)
R. N. Shreve, Purdue University, Lafayette, Ind.
