The Symposium on Chemical Processes was a presentation o f the Chemical Processes Subdivision, ACS Division of Industrial and Engineering Chemistry, at the 726th Meeting o f the American Chemical Society, New York, N. Y.
CHEMICAL PROCESSES CHEMICAL PROCESSES-FROM SYMPOSIA TO SUBDIVISION R. Norris Shreve VAPOR-PHASE AIR OXIDATION OF CYCLOHEXANE William F. Hoot and Kenneth A. Kobe OXIDATION OF CYCLOHEXANE TO ADIPIC ACID WITH NITROGEN DIOXIDE William F. Hoot and Kenneth A. Kobe MONONITRATION OF 0 - AND p-NITROTOLUENE Kenneth A. Kobe, Charles G. Skinner, and Hershel 6. Prindle. SYNTHESIS OF PYRIDINES Sherman L. Levy and Donald F. Othmer. CONTINUOUS ESTERIFICATION OF CITRIC AND ACONITIC ACIDS Robert C. Canapary and Paul F. Bruins PYRIDINE-N-OXIDE F. E.Cislak
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Chemical ProcessesFrom Symposia to Subdivision R. NORRIS SHREVE Purdue University, Lafayetfe, Ind.
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H E newly created Chemical Processes Subdivision of the Division of Industrial and Engineering Chemistry makes permanent the work that has been carried on for many years by the eighteen Unit Process Symposia that have been sponsored by the division. The first of these symposia, “Design, Construction, and Operation of Reaction Equipment,” was presented a t the ACS meeting in Denver, August 1932, under the chairmanship of D. B. Keyes. The other symposia have been held a t the fall meetings of the ACS each year from 1937 to 1953 with the writer as chairman. The Chemical Processes Subdivision is a result of a new policy on the part of the officers of the Division of Industrial and Engineering Chemistry to afford, under their organization, a means for the prgsentation of reports and discussions in fields that are allied to the chemical industry and that have been demonstrated to receive the continuing interest of chemists and chemical engineers. The basic interest behind the Unit Process Symposia and this new Subdivision of Chemical Processes is to provide the 774
same service in various phases of the industrialization of chemical change. The annual growth of the chemical industry currently is 10% compared with 3% for all American industries. There are many reasons for this faster growth, but certainly one of the more important is the emphasis that has been placed on chemical processes with consequent reduction of chemical costs and broadening of markets. Chemical processing stresses the study of conditions designed to give the highest possible conversion and the highest possible yields. High yields mean fewer side reactions. A chemical conversion of 100% in comparison to a similar conversion of 50% signifies that equipment of one half the capacity is required. Consequently an important aspect of reports on chemical processing should be the studies directed toward improvement of chemical conversions and yields. This means a thorough study of conditions to control the chemical reaction and to lessen byproducts when possible.
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CHEMICAL PROCESSES Any phase of the study of chemical change that affects cost of manufacture of chemicals or allied products-synthetic fibers, rubber, or plastics, for example-has been considered and welcomed to the predecessor symposia under the heading of unit processes. “Chemical processing” is a broader term and in many minds embraces a wider concept of conditions than did the term, “unit processes.” It also seems to include more readily the actual manufacture of chemicals or allied products, and thus includes engineering activities. Both concepts, unit processes or chemical processes, translate the reaction from the laboratory into conditions prevailing in the factory. The various phases involved in a chemical process or the commercializing of a chemical change are pertinent, as suggested in the following list (4, 6, 7 ) : (Note that a dollar sign is connected with each of these divisions when they are applied to factories.) 1. Knowledge of basic chemical change - in products la) ConveFsions b) Yields or equilibrium (proportion of reactants) c) Rates or kinetics ( d j Catalysis (e) By-products (f) Influence of temperature (g) Influence of pressure 2 . Energy changes 3. Correlation with unit physical operations-eg., agitation, heat transfer 4. Corrosion by chemieal reactants OP products 5 . Design or adaptation of chemical change to equipment 6. Instrumentation 7. Pilot plant 8. Transition from batch t o continuous processing 9. Flow sheets as an integrated entirety of all changes (chemical and physical) from raw materials to salable products 10. Labor savings 11. Over-all costs Under item 1, there is no need with either unit processes or chemical processing to make any sharp distinction between the inorganic and organic fields. To illustrate this, a decade or so ago a large chemical company changed hydrogenation from inorganic ammonia to organic methanol. Both these operations, being aspects of hydrogenation, have so many conditions in common that much of the same equipment, operated under somewhat analogous conditions, was successful for both. Classifying, as we do, unit processes according to the chemical reaction (1, 2, 4, 6, 8),there will be very much in common if we continue this classification by the chemical change for chemical processing. In considering chemical change, the most important consideration is savings of raw materials, because in the average cost of chemicals the raw materials comprise between 30 and 70% of the total cost. This illustrates also the importance of yields and conversions and of any other variable that increases these two aspects of the chemical change. Much of chemical processing is applied physical chemistry. In commercializing any reaction, the energy change (item 2 ) must be known even if only approximately. Many AH’S are given in “Chemical Process Industries” (4). Where such energy changes are not known exactly, they can often be approximated by a rough calculation or by analogy. Here again the classification of both unit processes or chemical processing by the chemical reaction, by bringing allied reactions together, provides a basis for more accurate approximations. Kith knowledge of energy changes, heat transfer can be handled quantitatively. In considering heat transfer in any process, the fouling of the interfaces must be included in the definite quantitative calculation. Some of the better chemical engineering process designs in use in America are concerned with better heat transfer. An interesting example of this is the work of the American Potash and Chemical Corp. of Trona, wherein the fouling of its heat transfer surfaces was greatly reduced by better engineering involving the removal of the heating coils from large evaporators, where evaporation and consequent salt encrustation had interfered with the heat transfer. The heaters were placed outside and at April 1955
a lower level so that no evaporation took place during heating. The hot brines were flashed into the evaporating area. Another excellent example of avoiding fouling through better design in this same processing is extensive use of evaporation under vacuum for cooling and crystallizing liquors. Similarly further correlation of the unit physical operations with the unit chemical processes is particularly necessary in mixed phase reactions where contact is of utmost importance. Much research needs to be done along this line particularly in the change from batch to continuous processing (item 8 ) . After almost 50 years in the chemical industry, the author has never observed a chemical reactor that failed because of lack of material strength based on a physical stress alone. However, in countless instances corrosion (item 4) of the equipment by the chemical contained therein haa caused expensive failures. With the newer materials available for process equipment, such wearing away by corrosion can be minimized and often prevented. By classifying various individual manufacturing processes under chemical change-e.g., nitration or hydrogenationmany observations become available on the behavior of materials of construction. The present-day chemical engineer does not often realize the importance in corrosion prevention of some of the newer materials such as Karbate carbon, tantalum, synthetic rubber, and plastics. Proper design (item 5) to obtBin the best equipment available, either new or converted, is of the utmost significance in chemical processing. Certainly an important contributing factor to the growth of the chemical industry is reduction of the cost of chemicals through large scale manufacturing. The simple rule that the capacity of a reactant vessel batchwise or of piping in a continuous process varies as the cube of the corresponding dimension, while the surface varies as only the square has been applied to advantage by designers in many instances. Factors of design also influence safety to workmen and safety to equipment. The American designer has shown a great amount of daring. Some of us, however, do remember the trepidation during World War I when the dyestuff industry, growing vigorously, started nitrating benzene in 1000-gallon quantities. This was done safely even though modern sparkproof motors were not available, and many precautions were necessary to prevent explosions which might have resulted by a reaction getting only slightly out of control. Instrumentation (item 6) has been developed extensively in processing, and much labor has been saved. On the other hand, in this new Subdivision of Chemical Processes, the application of instruments, particularly to chemical processing, will be one of the striking features of the future. As more and more data become available, the design chemical engineer can be more certain in transitions from laboratory to factory scale. However, pilot plants (item 7) are still necessary to check the transitions and in many new processes, wise managers still insist on sparing no expense in the pilot plant in order to carry out the philosophy of the old saying, “Make your mistakes in the pilot plant so that more profit can be realized in the factory.” As the American chemical industry grows, the change in processing from batch to continuous (item 8) is more striking (3). It is surprising how much material can go through even a small pipe if it is possible to run the reaction steadily for 24 hours. One of the contributions of the petroleum industry to processing has been the demonstration of the advantages of continuous processing in pipes or enlarged pipes, as bubble cap towers might be called. Fifty years ago a flow sheet (item 9) was used only in a very occasional manner. On the other hand, a t the present time, when a process is scaled from laboratory to plant, the flow sheet is the best method of recording the exact conditions necessary to Round commercial operation. In many such developments, numerous flow sheets are prepared as knowledge of the process
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progresses in the’laboratory and design room. We may conclude that a flow sheet is a necessity as an integrated expression of all changes with optimum conditions both chemical and physical for processing from raw material to salable product ( 7 ) . Flow sheets naturally include the equipment needed. Labor costs for chemicals (item 10) have not advanced proportionately as much as they have for many manufactured articles in other fields largely because continuous processing, controlled by instruments, has replaced small batch operations. Also the backbreaking labor of the past decade has been eliminated by mechanical devices in modern processing. We are sure this Subdivision of Chemical Processing will give, in future years, much attention to the reduction of costs in many ways but particularly by saving labor and labor costs through better design. While the Unit Process Symposia are being adsorbed into the broader concept of chemical processing, the unifying aspect of unit processes is too well established in the literature and too useful to be dropped from the thinking of chemical engineers. For example, flow sheets as summations of the unitary changes to which raw materials are subjected to give finished products are firmly established. These unitary changes are either the unit chemical process or the unit physical operation. It is recognized that both these divisions often function simultaneously (10). It has been written ( 1 ) that the “chemical” in “chemical engineering” refers to “unit processes.” The Subdivision of Chemical Processes will sustain and enlarge this assertion. Much improvement has resulted in the past from the classification of chemical change within the framework of the unit process-e.g., oxidation, hydrogenation, pyrolysis. Here similarities become apparent, and general principles are established for guidance of future technology. The history and advantages of, the unit process unitary concept have been described by several authors who have applied this classification of knowledge to chemical change (9, 5, 7 , 9, 11). The Subdivision of Chemical Processes will permanently enlarge this aspect of the parent division of Industrial and Engineering Chemistry and will also permit an extension of the scope of symposia for the various ACS meetings under this division. The majority of papers presented in past unit process symposia
have originated in university research laboratories. However, some of the best presentations have come from industry and from government institutions. It is expected that the change from chemical process symposia to the permanent Subdivision of Chemical Processes will enlarge the contributions from industry as well as from universities. It would be helpful if some of these contributions would report on the following:
1. Investigations of conditions to furnish both the highest and most economical chemical conversions and yields 2. Results of research to indicate the conditions for the close connection required by the chemical change on the part of unit physical operations t o facilitate the chemical change; this is particularly necessary in mixed-phase reactions 3. Researches for conditions to furnish more satisfactory chemical reaction rate (kinetics) 4. Study of catalysts to enhance an otherwise slow reaction rate 5 . Design conditions checked by pilot plants to ensure low cost factory procedures
Literature Cited (1) Groggins, P. H., in “Unit Processes,” Chem. Eng., 58, No. 3, 129 (1951). (2) Groggins, P. H., “Unit Processes in Organic Synthesis,” 4th ed., McGraw-Hill Book Co., New York, 1952. (3) Larian, M. G., “How Batch Unit Processes are Made Continuous,” Chem. Eng., 52, No.5, 114 (1945). (4) Shreve, R. Norris, “Chemical Process Industries,” McGrawHill Book CO., New York, 1945. (5) Shreve, R. Norris, “Chemistry-Key to Better Living,” Unit Processes, p. 60, ACS, Washington 6,D. C., 1951. (6) Shreve, R. Norris, “Classification of Unit Processes,” IND. ENQ.CHEM., 29, 1329 (1937). (7) Shreve, R. Norrjs, in “Encyclopedia Americana,” Chemical Engineering, Americana Gorp., New York, 1954. (8) Shreve, R. Norris, in “Unit Processes,” Chem. Eng., 58, E o . 3, 129 (1951). (9) Shreve, R. Norris, “Unit Processes,” IXD. ENG.CHEM.,35, 263 (1943). (10) Shreve, R. Norris, “Unit Processes in Chemical Processing,” Ibid.,46, 672 (1954). (11) Shreve, R. Norris, “Unit Processes in Retrospect and Prospect,” Ibid.,40, 379 (1948).
Vapor-Phase Air Oxidation of Cyclohexane WILLIAM F. HOOT’
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KENNETH A. KOBE, University o f Texas, Austin, Tex.
Vapor-phase air oxidation of cyclohexane was studied with and without catalysts. Without catalysts, aldehydes were the principal products before the end products of carbon dioxide and water. The maximum yield of aldehydes reported a s formaldehyde was 1.4 moles per mole of cyclohexane reacted at 360” C., a residence time of 1.7 seconds, and a feed ratio of 3 moles of air per mole of cyclohexane. Process variables studied were temperature, residence time, oxygen content of feed gases, and surface-to-volume ratio of the reactor. Intermediate products detected were formaldehyde, acetaldehyde, acrolein, pentanal, and cyclohexanone. Use of metallic and metallic oxide catalysts resulted in the end products carbon dioxide and water.
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HE petrochemical industry produces industrial quantities of oxygenated compounds by direct oxidation of hydrocarbons. Oxidation of cyclohexane is of interest because possible oxidation products include six-carbon aldehydes and ketones. The purpose of this study was possible synthesis of chemicals through vapor-phase oxidation of cyclohexane with air. These studies 1
Present address, Pan American Refining Go., Texas City, Tex.
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are presented as the vapor-phase air oxidation of cyclohexane using no catalyst, vapor catalysts, and solid catalysts.
Prior Work I n the noncatalytic vapor-phase oxidation, Estradere ( 4 ) passed a mixture of cyclohexane and oxygen (mole ratio 4:l) through a glass tube filled with 3-mm. glass rods. She found
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