INSTRUCTIONAL RELATIONSHIPS between CHEMISTRY and CHELMICALENGINEERING* HARRY McCORMACK Armour Institute of Technology, Chicago, Illinois
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HE chemist and the chemical engineer have much in common. They have a common origin and their methods of investigation and trends of thought are analogous. The past decade has, more than any other, indicated diversification in their training and in their literature. The belief is still prevalent, however, that a sound fundamental training in the principles and heories of chemistry is essential to the subsequent satisfactory training of the chemical engineer. This has received its due emphasis in the suggested time allotment, in the curriculum promulgated by the
* Contribution to the Symposium on Chemical Engineering Education, conducted by the Division of Chemical Education at the ninety-fourth meeting of the A. C. S., Rochester, N. Y., September 7,1937.
Committee on Chemical Engineering Education of the American Institute of Chemical Engineers, of twentyfive to t h i i y per cent. of the students' time to chemical subjects and twenty to fifteen per cent. to chemical engineering subjects. I t might be wise a t this time to "qualify the witness" -more than thirty-five years a member of the American Chemical Society, a teacher of chemistry for ten years or more and for twenty-five years the director of the chemical engineering option of a school recognized by the Committee on Chemical Engineering Education, to be giving a satisfactory course in Chemical Engineering. Assume that such a witness is testifying and voicing his conceptions as to the contributions which the proper teaching of chemistry can make in the training
of the chemical engineer. The foundation is laid with that subject matter customarily comprised in the term general chemistry. The chemical engineer is going to be interested in the physical as well as the chemical characteristics of the elements and their compounds, so the inclusion of some material of this type will be of distinct value. It is also believed that the student's interest in the course can be stimulated by some citations as to the influence of certain characteristics on industrial uses of the materials and on the processes involved in securing the elements and their compounds. An excellent illustration of the kind of instruction desired is exemplified in a recently built sulfuric acid plant. The student is probably informed that dry sulfur dioxide has no corrosive actiowon the customary iron alloys, but this can be driven home by describing the sulfuric acid system where molten sulfur is atomized with dry air and the combustion gases, like ordinary combustion gases, give up their heat to generate steam in steam boilers, and that more than enough power is obtained from these boilers to operate the entire plant. Some other excellent examples are to be found in the electric or in the blast-furnace production of phosphorus and its compounds. The sulfur and the phosphorus compounds are supposed to be closely related chemically; chemically, therefore, there should be no objections to oxidizing the phosphorus in dry air and utilizing the heat thus produced. The chemical engineer, to date, has not attempted this, being deterred by the constructional and operating difficulties where the oxidation product is a solid rather than a vapor. Instruction in analytical chemistry affords opportunities of other kinds. One of the major laboratory interests of the student consists in the formation of precipitates and the separation of them, by filtration, from the liquids in which they have been formed. Quite analogous is the industrial practice of filtration with the same importance to be ascribed to correct technic. Some precipitates are produced in the cold and filtered cold, others are produced in the cold but heated to boiling and digested for a time prior to filtration; there are a dozen and one diversifications of the cited procedures. Back of all these varieties of procedure are certain fundamentals. Bring them forth for the student's consideration. Tell him something about hard crystals and soft crystals, about conditions favoring increase in crystal size, and a few words in regard to influence of pH on crystal formation will not be out of place. It might also be well to tell him that precipitates are either crystalloid or colloid, that colloids do not filter satisfactorily, hut that certain changes in solution may cause colloids to floc, which permits their filtration. Call attention to the decrease in viscosity of water between 20' and 100" with specific figures cited. The case for industry is even more marked in favor of the heated solution; for example, a petroleum distillatemay have a viscosity of 2.99 a t 15.6' and 0.049 a t 100°. Advantage is taken of this in industrial filtration.
The proper selection of filter paper for the type of precipitate being separated is important, perhaps not on account of the separation, but certainly on account of the time factor. The chemist using only one grade of filter paper for all his filtrations is just as unintelligent as a chemical engineer who might insist on one grade of canvas for all industrial filtrations; therefore, call attention to the existence of various grades of filter paper, indicate the saving in time made possible by the selection of the proper one; then, for the benefit of the chemical engineer, point out the industrial significance of this. The customary way to use a filter paper is to fold it in a certain way and place it in a funnel. This, too, can be taught in a way to be of particular benefit to the chemical engineer. The rate of filtration depends to a considerable extent on (a) pressure differential, (6) free area on the filtrate side, (c) particle size of precipitate, and (d) viscosity of the filtrate. The free area on the filtrate side refers to that portion of the filter paper not in contact with the glass of the funnel. Filtration occurs chiefly, if not entirely, within this area. Then consider what happens when a filter paper is folded in quarters and placed in a sixtydegree funnel. The Coming Glass Company has begun making Pyrex funnels with a few channels; is this the correct procedure? Ask your students, but be sure you have the correct answer for yourself first. All this may well serve as the young chemical engineer's introduction to the unit operation of filtration. The teaching of organic chemistry has little bearing on later instruction in chemical engineering unless there has been some study of the unit processes included in our chemical engineering curricula. Many of us are coming to the conclusion that this is desirable. The organic chemistry should then contribute a knowledge of organic chemical reactions, characteristics, and properties. The laboratory technic acquired had best be forgotten when working with the unit processes; all i t can or should have contributed is an experimental knowledge of organic chemical reactions and something of the conditions under which they occur. What may physicalchemistry contribute to the chemical engineer's basic preparation? Considered solely as a course in a curriculum, much or little depends upon its presentation by the individual instructor. The major portion of our chemical engineering is cross-hatched and paralleled by the facts and fancies of physical chemistry; however, this has been so completely ignored by the authors of most of our texts on physical chemistry that a student pursuing them would complete the subject without knowing that any of the principles and theories presented had any useful application. Few students have much interest in abstract matters. Therefore, i t is believed that the teacher of physical chemistry overlooks an opportunity when attempting to present its topics without calling attention to their useful applications. These applications of physical
chemistry occur essentially in the practice of chemical engineering, not in its formal study. In essence a student can complete the undergraduate study of chemical engineering as embodied in our customary curricula without having studied what is termed pbysical chemistry. A knowledge as elementary as that acquired in general chemistry will suffice. Such topics are involved as the gas laws, Avogadro's hypothesis, Raoult's and Henry's laws, and not much else. An examination of what is involved in practicing chemical engineering yields a different answer. It would be impossible for the chemical engineer to design equipment, to plan and to operate chemical processes without having extended this elementary knowledge to include: rates of reaction, heats of formation, free energy components, and so forth. Referring again to the production of sulfuric acid; the designing engineer must know the rate of oxidation, in contact with a certain catalyst, and the equilibrium constants, through a certain temperature range, before the equipment can be satisfactorily designed. The design and operation of a metallurgical furnace is likely t o involve the heats of formation and the fusion points of some complex silicates. The satisfactory production of a soap involves a knowledge of the solubilities of soap in sodium hydroxide solution, of water in soap, of soap in water, and of soap in sodium chloride solution. This knowledge was once only empirical; now it is theoretical as well, and it is probably conceded that better, more uniform soap has resulted. Many other citations might be given, all of them, however, being connected with the practice of chemical engineering rather than with the formal training pre-
ceding its practice. The subject matter presented naturally leads to the question, "Can the teacher of chemistry present these subjects in the manner indicated unless a t least an elementary knowledge of chemical engineering is possessed?'My own answer is, "The more the teacher of chemistry knows about chemical engineering, the better he will be as a teacher of chemistry to chemical engineers." This should not lead to any particular difficulty, as for several decades many chemists have imagined themselves to. be chemical engineers. There remains another contribution from the chemistry courses, somewhat indefinite, yet very real. This has to do with the evaluation of experimental data and trends of thought arising in any investigation. Here the chemist and chemical engineer meet on common ground so that technic and habits of thought acquired in chemistry courses can and should carry over into the chemical engineering courses. Importance is attached to the sequence of topics in the curricula. A resurvey of the material heretofore presented indicates the following: general, analytical, and organic chemistry t o be presented prior to the subject matter of chemical engineering; physical chemistry to be presented prior to or concurrent with this subject matter. Are there any other chemical subjects of prime importance to the undergraduate chemical engineer? The answer is No; but for the practitioner in chemical engineering a broader and deeper knowledge of chemistry will be very helpful, keeping in mind the fact that the most extensive training in chemistry will never produce a chemical engineer.
