DESIGN AND DEVELOPMENT Correlation Courses for Instruction in Unit Processes and Operations FRANK C. VILBRANDT Virginia Polytechnic Institute, Blacksburg, Va.
H E level of accomplishment achieved by the application of science to industry since the World War has emphasized the need for a similar high level of training in all grades of professional curricula, for the bachelor, master, and doctorate graduates. The industrialists have demanded engineering and science graduates of a caliber unthought of twenty years ago. The age is specialization, and the industrialists expect the students t o be specialized. An emphasis resulted for certain course work to fill the gaps left in the old order of professional curricula. One of the results of this emphasis has been the splitting up of some of the fundamental courses and the addition of numerous advanced courses, especially in the curricula of chemistry and chemical engineering. One trend has been along the lines of specialization for specific industries such as petroleum, gas, heat, cellulose, rayon, ceramics, etc. The merits or faults of this trades specialization are not the subject of this paper. The other trend has been along the lines of specialization according to functional concepts. This started with the introduction of the group of physical functional operations known as chemical engineering unit operations about twenty years ago and mas closely followed by the chemical functional operations known as unit processes. The rapid advancement of chemical engineering education can be traced to the introduction of the physical or engineering functional concept, in the teaching of fundamentals of chemical engineering. More recently the addition of many advanced courses of specialization dealing with specific unit operations has been apparent through a study of catalogs of colleges and universities. The products of this method of teaching are individualists, and seemingly they are well versed in the fundamentals of each unit operation but not in the correlation of these functions to production of commodities. And the leanings have been away from the chemical and towards the physical side. As a result of the strenuous efforts of R. N. Shreve, Harry McCormack, and D. B. Keyes, the chemical functional concept has been kept alive but has not received as hearty cooperation from all concerned as it should. But the first symposium on unit processes ( g ) , held a t the Rochester CHEMICAL SOCIETY, and the present Meeting of the AMERICAN symposium are indications of the new interest taken in this vital phase of instruction. The unit process group has benefited through the errors of the unit operation by avoiding isolation of functions. This may be intentional or may have been due to the conditions surrounding chemical processing. But the results have been to bring back to the attention of chemical engineers their close relation to chemistry and to bring to Ihe attention of chemists their close relation to chemical engineers.
T
MARCH, 1939
I N T H E teaching of unit processes it is necessary t o use the unit-operation terminology. The chemical engineer who has not forgotten his chemical background finds the unit processes as correlated steps, a tying together of several unit operations in the carrying out of an isolated chemical-type reaction. The chemist, on the other hand, finds it necessary to learn the new terminology in its application to specific processes. The time is a t hand when chemists also need to have some elementary training in the unit operations. When industrialists complain of our graduates as being well trained technically but lacking a sense of proportion, of application, and of living, we must feel that there is still something lacking in our training of students for their professional careers. And it seems that the overemphasis in specialization, either the isolated physical or chemical functional concepts, may contribute something to this condition. If that is so, then correlation is essential-correlation of unit processes and unit operations. Just how this can be accomplished is subject to argument, but the application of principles taught in lecture by laboratory practices seems to have its merits. Not everything is worthless because it is old; sound fundamentals are always good bases upon which to build. Many of you were given industrial chemistry laboratory practice, consisting in preparing some chemical commodity, carrying this through a batch experiment, ending with an economic study of its production on a definite large-scale basis, and sometimes designing a plant to carry out this process. A large number of institutions have held t o this practice and have improved the old course considerably, because the students are better qualified to handle more detailed and more intricate processes than formerly. Senior students in the curricula of chemical engineering usually have a training based upon the application of the fundamentals of chemistry, physics, mathematics, mechanics, engineering, English, and economics acquired in the first three years. At this stage students have completed all laboratory work in unit operations and have had four quarters of unit-operations theory, completed all junior courses in chemistry, organic and physical. By the winter quarter they will have had a t least one quarter of industrial chemistry lecture and industrial stoichiometry, and an introduction to literature review. The student is now capable of studying a process problem involving economics of processes, personnel, materials and heat balances, unit operations, thermodynamics, kinetics, stoichiometric calculations, report writing, and drawing of process equipment assemblies. Such a correlation course should be essentially on development and may be named design, or development, or both. In this course the reaction kinetics are presented from the engineering point of view, taking up where physical chemistry
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left off, treating experimental data by graphical calculus to predict optimum conditions of operation for pilot-plant and plant-scale performance. Also, the course should deal with the visualization of processes in terms of equipment, men, materials, and money. AT THIS point the one phase of work that the general run of students lacks is a correlation of design principles to actual cases in one’s own professional field. Often this is accomplished by invoking the practice of applying the principles in report writing for junior chemical engineering unit-operation assignments. If not, then some time should be devoted t o assigning simple problems for the practice of calculation, sketching, and report writing, including detailed sketches of assemblies of available chemical engineering pilot or commercial plant equipment. Bills of materials should also be included in such assignments. The next step probably should involve the selection of problems on the preparation and production of some marketed chemical commodity. Whether t o give individual or group problems depends upon the size of the class. A class of five to ten can be taught individually, but the difficulty increases with the larger classes, and it may be necessary to assign two to a topic or as many as four. The problem should be solvable with a fair degree of ease and should be on some commodity already on the market that is produced by several correlated unit processes and unit operations. Following the assignment of the process topic or commodity should be the preliminary survey. A review of the literature on many approved processes by which the commodity can be made should then be undertaken, the chemistry involved carefully scrutinized, preliminary flow sheets drawn, and some preliminary costs figured. Then a decision of the particular process to be undertaken may be arrived a t by weighing all known facts. The order of procedure in the preliminary survey to select most feasible process reaction or reactions may be as follows: 1. Literature review 2. Raw materials considerations (theory, all possible re-
actions)
3. Market considerations (curves for all products and all
possible raw materials, for 15 years) 4. Lowest possible costs (based on all possible raw materials and theoretical yields) 5. Selection of one or more basic processes The next step should be acquisition of experimental data through laboratory studies. The course work in the laboratories can be considered as development. In this laboratory work the students should prepare the commodity according to the process selected, for the purpose of acquiring necessary data for plant design. All thermal, chemical, and physical data not available for literature reviews must be acquired. A material balance should be made. In order to obtain yield and other general data on process reactions studied, the students should follow this order of procedure: 1. Probable costs (yield and reaction study on one-pound 2.
batch) Materials and equipment requirements Observations essential are : a. Type of reaction b. Quality of product c. Quantity of product d. General solubility e . Separation characteristics f. Heat considerations g. General operations required
Following the laboratory- or beaker-scale experimentation when the students are satisfied as to feasibility of the prepara254
tion and have enabled themselves to acquire sufficient information to undertake a large batch operation, such as 2 to 10 pounds, a “pail-and-tub” process laboratory study should then be undertaken; attention should be paid to the engineering considerations involved in the production of the commodity. In order t o obtain engineering data essential for the design of pilot-plant investigation of the production of commodity selected, the following considerations may be important : 1. Procedure essentials
2. Raw material characteristics 3. Chemical flow sheet
4. a.
6.
7. 8. 9. 10.
Corrosion characteristics Effect of impurities Heat considerations Unit operations required Material handling Storage Engineering flow sheet
A GENERAL departure from unit process studies is that which involves laboratory data first in pilot-plant design. Immediately following the acquisition of laboratory data from the beaker and the 2-10 pound batch experimentation, a review of pertinent facts on the process should be undertaken, using some kind of check list ( 1 ) . I n order to design a pilot plant for the production of 100 pounds per day, the following considerations may be important: 1. Equipment flow sheets 2 . Selection of equipment 3. Selection of materials
4. 5. 6. 7.
Procedure necessary Labor requirements Plan Elevation
Then should follow commercial unit design calculations. The detailed calculations necessary to obtain quantitative considerations for the design of the commercial unit should require the major attention and application of mental energy in the design course. The sequence of this phase of the study may be according to the following outline: 1. List of laboratory and plant data 2 . Quantitative reaction calculations 3. Equipment calculations 4. Flow of materials
5. Material balance 6. Thermal balance 7 . Quantitative flow sheet
The final step in the study should be the coordination of all chemical and engineering data obtained and their translation into a definite organized unit. Access must be had t o trade literature for selection of types and specific pieces of equipment. Capacities and performance should be studied. Preliminary layouts should be attempted, and the best flowing arrangement obtained. Organization of the equipment by means of templates will give the student a better picture of the possibilities of different layouts. After arriving a t the most desirable layout, actual drawing of the plan and elevation of the assembly should be undertaken followed by preconstruction costing. I n order to design a commercial unit, including housing for the production of the specified commodity, the following considerations may be important: 1. Specifications of equipment Specificationsof materials 3. Selection of commercial equipment 2.
4. Plan 5. Elevation 6. Location of plant
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7. Operating instructinn for labor
8. Selection of personnel 9. Preconstruction costing
10. Production costs per unit of material
Notebooks must be kept with a daily log of all observations and data. Each page should have a title and date, and a t the end of each period a brief resume must be written of the day's work, signed by initials of the worker and someone who was with him in the laboratory. Notebooks should be deposited with the instructors. Weekly reports to the class are essential, and weekly written reports should be made. The student should receive practice in presentation. calculations and reasons for making certain decisions should be presented concisely to the class for criticism. The discussions should be informal. At the end of the year a complete report should be turned in which includes all calculations, flow sheets, material balances, plans, and layouts, and a carefully executed drawing on plans and elevation of the completed plant, with such detailed drawings as may be necessary to clarify the drawing.
Thus t h e unit operations and unit processes are correlated not only yfth each other but also with economic and design considerations of unit process. This is the old i n d u s t r i a l c h e m i s t r y laboratory dressed up to conform to present-day demand.
IS THIS the type of course work that will fulfill the need of the students and of the industrialists? And will the industrialist want a man so trained and start him in his plant with only the necessity of teaching him the details ofihis own process?
Literature Cited (1) Chem. & Met. Eng., 43,58-82 (1936). (2) IND. ENG.CHEM.,29, 1329-64 (1937). RECEIVED n'ovember 2, 1938.
MANUFACTURE OF ISOAMYL CHLORIDE An Example of Chlorination
Using Thionyl Chloride AUBURN A. ROSS AND FRANCIS E. BIBBINS Eli Lilly and Company, Indianapolis, Ind.
I
N THE manufacture of 5,5'-dialkyl barbituric acid, it has been the practice for many years to use an alkyl bromide as a means of introducing the desired alkyl group into the 5 position of the barbituric acid nucleus. Several years ago it was found a t this plant that, by means of the correct technique and proper equipment, ethyl chloride could be satisfactorily substituted for ethyl bromide in this procedure. Such a change resulted not only in a substantial savings but also eliminated the undesirable, but economically necessary, recovery of the by-product sodium bromide which is used in the manufacture of more halide. The next step was to substitute for the bromide the chloride of the other alkyl group in the 5 position-namely, the isoamyl. The manufacture of this chemical and the chemical engineering involved in its production is t o be discussed in this paper. Thionyl chloride (SOClJ has long been known as a valuable chlorinating agent, but not until the development of new catalytic methods for making it from carbon monoxide, chlorine, and sulfur dioxide in recent years, has its cost been lowered enough to permit its use in large-scale manufacture (2). The fact that it is a low-boiling liquid (boiling point, 78.8" C.) and that the side products of its reaction are gases which can be easily eliminated from the reaction mixture are its two great advantages. Its main disadvantage is its sharp, penetrating odor which irritates the eyes, nasal passages, and throats of workers and thus requires ample ventilation and utmost care in its handling. MARCH, 1939
Stahler and Schirm (1) made a rather comprehensive study of the action of thionyl chloride on methyl, ethyl, propyl, and isobutyl alcohols, and concluded that this reaction proceeded according to the following equations :
+
ROH SOClz = RO-SOC1 RO-SOC1 = RCl SO2
+
+ HC1
(1)
(2)
The chlorosulfinyl ester formed in Equation 1 is very unstable and decomposes readily upon heating, as shown in Equation 2. By taking advantage of these reactions, isoamyl chloride can now be produced in the plant economically by the process described below and shown in Figure 1.
Equipment The equipment for the manufacture of this halide consists of a glass-lined, steam-jacketed kettle, to the vapor outlet of which is connected a 12-foot lead reflux column packed with 1-inch stoneware Raschig rings. Down the outside of this column flows a spray of water for cooling it. This external cooling method has two advantages: ( a ) Should a leak develop in the column, due to corrosion, it will be immediately discovered because the gases evolved from the reaction will fume when in contact with water. (b) Since the pressure is always outward, there is no chance, with the development of a leak, for water t o enter the column and perhaps spoil the reaction within the kettle.
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