Science of today -production
tool o f tomorrow
INDUSTRIAL PHOTOCHEMISTRY
Fifteen years ago, I&EC [Vol: 39, page 844 (194711 published an article, "Photosensitization in Chlorination," by William T. Anderson, Jr., o f Hanovia Chemical and Manufacturing Co., n o w Hanovia tamp Division, EngelhardHanovia, Inc., Newark, N. J. Since then, much has been accomplished in the field, and Hanovia i s one o f the principal manufacturers o f equipment for photochemical processing. In 1949 (Vol. 41, page 18121, w e described in detail in an I&EC Staff Industry Collaborative Report, the industrial photochemical operations of Tennessee Products and Chemical C o r p . M o r e recently, w e have been privileged t o publish the original research and design w o r k b y Marcus and Wohlers of the Stanford Research Institute, summarized briefly on page 22. Details of this work w e r e presented in I&EC b y these authors under the titles: "Photochemistry in the Solar Furnace," 51, 1335 (19591 ; 52, 377 (19601. "A N e w Solar Furnace," 52, 825 (1960). Some examples of other recent publications o f interest are:
hotochemistry is emerging as a full-blown science.
P I n the twenties and thirties, it consisted merely of irradiating a compound with ultraviolet light and then analyzing the resulting fragments to find out what had happened. In that sense, photochemistrywas just another weapon in the armament of the kineticist. Now, however, it is developing into the science of delivering precise amounts of energy, useful for precisely known transformations, some of which are now the basis of industrial processes. The future will probably see more of such transformations applied industrially. The number of publications is increasing, on uses of photochemistry other than for photography-for the first time in 10 years, next year's Annual Reviews of Physical Chemistry will publish a review on photochemistry. Interscience is organizing an Advances in Photochemistry Series of monographs, and recently Pergamon Press has started publication of a nmv journal, Photochemistry and Photobiology. Designers working with photochemical processes face many problems :
Boynton, H. G., Lewis, W. E., Watson, A. T., "A High Pressure Photochemical Reactor," Ind. Eng. Chem. 51, 267 (19591. Clingman, H.,Jr., "Photosensitized Oxidation of Propane," Ibid., 52, 915 (19601. Evans, Latimer R., Neligan, R. E., "Vapor Phase Chlorination o f Dimethyl Ether," Ibid., 52, 379 (19601. Gaertner, R. F., Kent, J. A., Ibid., 50, 1223-6 (1958). Mallory, Frank B., Wood, Clelia S., Lindquist, Lois C., "Photochemical Synthesis of Phenanthrenes," 140th Meeting, ACS, Div. O r g . Chem., Chicago, 1961. Sharp, Dexter B., LeBlanc, John R., "Stereospecific Photooxidation of Olefins. Quantum Yield and Olefin Structure," 138th Meeting, ACS, Div. O r g . Chern., N e w York. 1960.
Thus, empirical scale-up is used, but this approach offers serious problems. Important scale-up parameters are not always obvious and, when they are, they are not always properly handled. The result is an evolutionary design which depends on judgment and intuition of the development group. In this article the word '(design" is used in a sense different from scale-up. Design refers to the formulation of a mathematical model to describe the kinetic behavior
AUTHORS T h i s staf feature was prepared with material and personal assistance from Dr. Rudolph J . Marcus, D r . James A . Kent, and D r . G. 0 . Schenck. D r . Marcus is Physical Chemist with Stanford Research Institute, Menlo Park, Calif. D r . Kent is Professor of Chemical Engineering at the Unicersity of West Virginia, and D r . Schenck is at the M a x -
Planck-lnstitut f u r Kohlenforschung Abteilung Strahlenchemie, Miilheim a.d. Ruhr, Germany. For additional material we are indebted to J . F. H u j , D o w Chemical Co., Midland, Mich., C. C. Thomas, University o j Bufalo Research Center, and D r , R. J . CvetanoviE, National Research Council of Canada.
20
I N D U S T R I A L AND ENGINEERING C H E M I S T R Y
-Clear-cut methods are lacking f o r applying physical and kinetic principles to reactor design and selection of light sources -Usually, information on reaction mechanism, rate constants, and light absorption coeflcients is unavailable
I
Photochemical engineering is developing into a precise science of the proposed reactor type, and the use of this model to size a reactor io meet production requirements. Obviously, reliable data and a n understanding of the principles involved are necessary for this approach. Scaleup, on the other hand, implies that some aspects of the system’s behavior are unknown, and the final design is arrived a t by enlarging a prototype reactor without changing values of the important parameters. Actually, values of the design and operating variables are intended to bear the same relation to each other in the prototype reactor as in the scaled up version. By contrast, in a designed reactor interrelation between variables may be quite different than in the prototype but the resulting product stream is the same. The result is a more optimum, better understood system. To some extent, this applies also to the present state of industrial practice in reactor designs for other types of catalysis. Photochemical processes differ only in that more and less familiar principles are involved ( 2 ) . However, only recently have articles appeared on how these fundamental physical and kinetic principles can be used to interpret and predict photochemical reactor behavior (3, 5, 7). Much work remains to be done, but a good example has been published ( 4 ) . Economic Aspects Need Development
If quantum yield of photochemical reactions under operating conditions were known, calculating cost of the product would be reasonably simple. Such cost, however, when compared with that of the same product made by thermochemical techniques often can be higher without making the process uneconomic. I t is possible that photochemical plants, because of difference in raw materials used, may be set up in locations where thermochemical plants cannot exist. Thus, direct comparison is difficult. However, as a first step, the two production methods can be compared in terms of the number of steps required. Before this can be done, the amount of light energy available must be determined as well as that fraction which is useful for production purposes. Throughput, which can be calculated from quantum yields, is important because it indicates the use factor of the photochemical equipment. Consider the case where thermochemical production
Adding the cost of light to that of thermochemical techniques and concluding that photochemical routes are more expensive are insufficient. Instead, several factors such as r a w material cost, yield, throughput, apparatus cost, and number of production steps must be compared separately for photochemical and thermochemical production of the same compound. 22
INDUSTRIAL A N D ENGINEERING CHEMISTRY
requires more steps than photochemical. Cyclohexanone oxime can be prepared photochemically in one step from cyclohexane and nitrosyl chloride. However, it is usually made from these materials in two steps, and from other raw materials in even more steps. In the first step, cyclohexane is converted to cyclohexanone by air oxidation. But the average yield is only about 55%, and therefore other raw materials are often used. In the second step, cyclohexanone oxime is formed from reaction of cyclohexanone with hydroxylamine. Thus, thermochemical production requires at least two steps, each with a reactor and associated equipment, as well as intermediate product isolation and purification. In contrast, photochemical production involves only a single step in a single reactor and also avoids intermediate product isolation and purification. If photochemical production saves considerable capital equipment and processing costs, the saving must be balanced against cost of the photochemical reactor. Photosensitization broadens the scope of photochemistry. I t implies that different light absorbers can be used to photocatalyze a reaction, and where a particular light absorber is unsatisfactory, photosensitizers can always be sought. Oxidation of xylene to phthalic acid is an example. Here oxygen can be used, if a trace of chlorine is added, to absorb light and initiate the reaction. Also ceric ions can be used to absorb light, but in this case, the oxidation is caused by- oxygen atoms, and the ceric ion must be thought of a photosensitizer. Two factors will play an important role in photochemical production and will make more processes economic-high light intensities and flow systems. Concentrated light sources can increase output to the point of industrial practicality and in this area Stanford Research Institute has conducted experiments, using the solar furnace. This apparatus, a cool source of light, focuses the sun’s rays into a small area which receives the entire range of the solar spectrum as received on the earth’s surface. I t can be used for liquid- as well as gas-phase reactions, and is particularly adaptable to flow systems. The focal spot of arc image furnaces can be used in exactly the same manner for 24-hour-per-day operation. I n such devices, the light may be generated by carbon, mercury, or xenon arcs. Using such focused light devices, the production of oxygen from the photoreduction of ceric perchlorate has been increased by factors of lo5 to lo6, and the efficiency of nitrosyl chloride photolysis in solution, a reaction which produces two free radicals (nitric oxide and chlorine atoms), has been increased by a factor of 10. Which Reactions Are Suitable for Photochemical Production?
Halogenation. The only large-scale photochemical halogenation process is the production of benzene hexachloride. Thermal chlorinations, carried out at high temperatures in autoclaves, produce a variety of
PHOTO
THERMAL
I'
ENERGY FROM FARRINQTON DANIELS
Figure 7 . Energv distribution from two sources-from light such as a lamb or arc, and heat. Energy from the heat source is widely distributed, and only a few out of many molecules have enough for chemical reaction. I n contrast, the light source has a narrow distribution, and therefore a much larger percentage of highly energetic molecules are produced. Thus, light sources are im@ortant in industrial firocesses
WAVE NUMBER IN KAYSERS 1400 1300 12001100 loo0
900
800
700
650
0.05
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0.30
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a
1.00 2.00
: $ 0
8
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WAVE LENGTH IN MICRONS
Figure 2 . Infrared spectra of a-hexachlorobenzene and chlorine in carbon tetrachloride (upper curve) and of the same solution after irradiation in a solar furnace (lower curve). Such irradiated compounds may be used as intersecticides, after insects have become resistant to hexachlorobenzene
different molecular species which have to be separated. This results from the broad energy distribution of a thermal source and the different activation energy for each product. I n contrast to this, the photochemical process produces only a single product and also is useful when a low temperature is required. Both of these conditions are useful in making benzene hexachloride. I n addition to this process, it is probable that other photochemical halogenations will be found profitable. Cyclohexanone Oxime. A photochemical process has recently come into prominence for making cyclohexanone oxime which leads to caprolactam, the Nylon-6 monomer. The reaction was reported as early as 1917, and a number of companies have experimented with the process. However, the first large-scale use has been reported by the Toyo Rayon Co. of Japan, which is now building a 30-ton-per-day plant designed to make caprolactam at 20 cents per pound. The company will use 10-kw. mercury arc lamps which seem to be important for two reasons-greater light intensity seems to have an intrinsic effect on the reaction rate and also means that fewer lamps are required. This is important in reactor geometry, because after all, the number of mercury arcs which can be packed into a given size reactor is limited. Photopolymerization. Photochemistry is likely to play a larger part in initiating polymerization, which for the most part occurs by chain mechanisms. Such chains started by light are a particularly cheap way of using light because quantum yields of l o 3 to l o 4 are common. Also there are two other advantages-no remnants or fragments of initiator molecules remain, and production rate by means of the flow process is extremely fast. Photooxidation. Industrial use of this reaction has barely been touched. A large number of oxidation products can be involved, and one which has been experimented with in particular is phthalic acid. I n the future, this method of manufacture may be applied to other oxidation products. I n this area, production of oxygen atoms shows promise of being exceedingly useful. A number of organic compounds, epoxides, aldehydes, and ketones have been produced in the laboratory by reaction of photochemically produced oxygen atoms with olefins. I n terms of chemical feasibility, these reactions are potentially useful on a commercial scale-generally, yields are high and side reactions are minor, at least for terminal olefins. For internal olefins, however, pressure-independent fragmentation is likely to occur. Two methods of generating oxygen atoms involve reactions of nitrous oxide : mercury photosensitized decomposition and direct photolysis. Rather high conversions are obtainable, and the reactions are adaptable to flow or recycling reaction systems. Standard techniques of reactant and product handling can be used. R . J. CvetanoviC of the National Research Council, Ottawa, Canada, has investigated extensively these techniques of organic synthesis.
(Continued on next puge) VOL 54
NO. 8 A U G U S T 1 9 6 2
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Perhalogenated Hydrocarbons. Benzenoid compounds can be produced which carry more than 6 chlorine atoms per ring. For instance, when hexachlorobenzene is dissolved with additional chlorine and exposed to concentrated light, more chlorine atoms add to the ring, producing a compound containing sometimes as many as 9, 10, or 11 per ring. Such compounds will probably find some use as insecticides after insects have become resistant to hexachlorobenzene. Perhaps other uses will be found also. Why i s Photochemistry Not Used More Widely?
A main problem in using photochemical reactions industrially is related directly to insufficient knowledge of the parameters involved and their effect on reactor design. Then added to this are other problems-inadequate flow of information between workers and a limited variety of equipment available. The solution to these two problems is not easy, but several steps in the right direction could be taken : -Release information on reactor design -Develop improved and more adaptable manufacturing equipment -Encourage chemical engineering schools to carry out graduate research, possibly through fellowships jointly sponsored by industry
Kinetic and mechanistic studies appear in the literature, but engineering aspects for industrial uses have not received the attention they deserve. One chemical engineer said that he had worked with more than a dozen processes, but that none reached the commercial stage. Before they emerged from the pilot plant, all were supplanted with more economic methods. It is surprising that any photochemical processes reach the production stage, and success of those that do can probably be attributed to three factors : The reaction is not practical by any other known method ; the production technique is so straightforward that scale-up presents no difficulties; and the development team is particularly expert. I t is interesting that economic advantage is not listed among these three factors which contribute to realization of a commercial process. Reason: Designs for industrial processes have not been developed to the point where they can compete with better understood thermal or peroxide-catalyzed methods. Too often the pilot plant is regarded as a place to “demonstrate” a process conceived in the laboratory. Where the process is routine, this is sometimes practical. However, in photochemical processing, where mathematical models, generalized correlations, and rigorous design procedures are lacking, considerably more than demonstration is needed. The pilot plant should evolve a production model capable of operating on a small scale. Otherwise, the jump to production scale is crucial. And even if the scale-up parameters have been identified, direct scale-up can lead to impractical geometric configurations. In such cases, the most likely 24
INDUSTRIAL AND ENGINEERING C H E M I S T R Y
recourse is use of proved multiple reactors in parallel. O r performance of the reactor can be brought to specification by varying values of the parameters. However, this approach often entails high cost, and as a result the project may be completely abandoned or other processing schemes are sought. Developmental Experience in Industry
Because the literature contains so little data, information on design and engineering had to be gathered from technologists with photochemical processing experience. The usual problems regarding proprietary information arose, but with helpful cooperation of several individuals and approval of their respective managements, a crosssection of current design practices was obtained. One company doing photochlorination reports : “Our research groups determine the effect of waue length anp intensity, agitation, and vessel type on the rate and degree of chlorination. From this information, small scale pilot runs are made to determine the effectiveness of our scale-up methods. W e could design a production unit by using correlations obtained betmen the laboratory and pilot plant operations, and then going to the (lamp) manufacturers and asking them to help us with scale-up. T h e type of lamps, the number, methods of cooling them, and installation of additional lamps would be worked out with the vendor.” Another company doing photochlorination reports : “ I n our company a new process is the responsibility of the research department, which carries it through bench scale, pilot plant, and initial commercial operation. I n the work ( a photochlorination) research developed rather complete information on the photochemical requirements. T h e depth of fluid which would be effectively penetrated by tile light was determined by relating reaction rate to illuminated depth in an apparatus where the light path could be regulated by inserting spool pieces of various lengths. T h e approach to full commercial plant design was by four successive scale-ups including bench scale, large lab scale, pilot plant, large pilot plant, or semiworks followed by the engineering design of the commercial plant. We believe that a design of this nature is still largely an art and can best be handled by a series of moderate scale-ups. T h e depth of solution that can be efectively irradiated is the important design criterion at all stages of process development. At an early pilot plant stage we used a tank-type reactor with the light sources in vertical wells. We were not satisJed with this type of reactor and went to a reactor consisting of the solution in a borosilicate glass pipe unit consisting of pipe and return bends with the light external to the reactor. T h i s reactor is made up from standard borosilicate g l a s s j t t i n g s and was very satisfactory .” Radiation Pebble-Bed Reactor
Because of new technology in fixing waste fission products and fabrication of small spherical radiation sources, interest in a 10-year old pebble-bed concept has been revived. Pebble beds have interesting possibilities, but they are still not a reality and require considerably more experimental work. Furthermore, even if the concept is proved feasible, pebble beds will not cure all problems in the photochemical industry. In thin film graft polymerization they would be useless and handling kilocurie sources of strontium-90 is not without problems.
. -.
.
The principle of pebble beds is simple: Radioisotopes are incorporated in pebbles which then become a source of radiant energy resulting from either beta particleinduced ultraviolet or the beta particles themselves. Thus, each pebble is a miniature fluorescent source that can cause photochemical or radiochemical reactions in the surrounding substance. For present industrial photochemical or radiochemical reactions, ultraviolet from special mercury vapor lamps or electron accelerators which emit ultraviolet are used. Both techniques, however, pose the problem of uniform dosage. Therefore, various mixing, spraying, and multiple-pass techniques are used. Accelerator irradiation of bulk liquids must be done under thm film conditions where film thickness depends on energy of the electrons generated by the machine. This would be true also with flat geometry-type beta sources, but here the whole problem is complicated because beta sources do not emit mono-energetic particles. Consider a typical batch reactor system used today in photochemical processing. A 500-gallon tank contains two 4-foot lengths of ultraviolet-emitting tubes. Assuming the maximum diameter of each tube to be about 1 inch. the total radiant surface area is 302 sauare inches. For the same 4-foot tank half lilled with a bed of '/*-inch diameter beads, the total radiant surface area is 4.2 X lo' square inches. This represents an increase of more than 5 orders of magnitude which may increase reaction rate, decrease dwell time, or decrease reactor size and complexity. Basically, the larger surface area provides shorter absorption paths-Le., it exposes more of the reactants to radiant energy. During the past few years, considerable effort has been expended on methods for disposing of fission product wastes, including adsorption on clay or porous ceramic sponges and subsequent firing and incorporating the material in glass or ceramic systems. Many metho d s produce materials containing a fair percentage of radioactive isotopes in a form that is not leachable. A radioactive pebble, called a microsphere, is commercially available, with or without a stainless' steel cladding and coated with a ceramic material. Such spheres may be suitable for use in pebble beds. Work carried out on waste disposal methods has resulted in systems that could contain as much as 10 curies of strontium-90 per gram of adsorbent. A glass system has been made which contains as much as 15% by weight of calcined fission product wastes. If such glass were made with strontium oxide having a specific activity of 60 curies per gram, specific activity of the final glass would be 9 curies per gram of glass. The pebbles can be coated with a material which produces ultraviolet radiation under electron- or betaparticle bombardment. Many commonly available materials behave thus, and the main ultraviolet wave length varies with the material--e.g., barium chloride shows a band a t 2600 A,, potassium bromide at 3800 A,, magnesium oxide at 3400 A,, zinc carbonate at 3000 A., and cesium chloride at 2250 A.
REACTANT OUT Fiprc 3. A radioisotope pcbble-bed main,tream
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REACTIONS WHERE PEBBLE BEDS MAY BE USEFUL
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Conversion efficiencies for producing ultraviolet by beta irradiation vary with the nature of the phosphorzinc sulfide (silver-activated) with low-energy beta particles has an over-all efficiency of 330 (photons per electron absorbed). However, in this case the phosphor was activated with silver; based on the number of activator atoms in the lattice and the probability of direct interaction by electrons with activator atoms, conversion efficiency is near 100. If the phosphor or fluorescent material has an abundance of activator sites, then conversion efficiency could be considerably higher than the low value of 330 for zinc sulfide. With a material such as strontium-90 in the pebbles, complete utilization of activity to produce ultraviolet is impossible, because a layer of phosphor on the pebble, thick enough to absorb all of the beta energy, would also absorb much of the ultraviolet generated. Assuming a phosphor thickness which optimized energy adsorption VOL 5 4
NO. 8
AUGUST 1 9 6 2
25
us. ultraviolet adsorptive losses, practical conversion efficiencies of IO3 to lo4 might be expected. However, this has to be verified experimentally. The pebble-bed system must respond strongly to a particular wave length of light. With the proper phosphor, it should be possible to get most of the radiation emitted at or near the most effective u-ave length; thus, production efficiency should be obtainable, which is somewhat higher than that for norma! ultraviolet photochemical processes, as well as the inherenr: advantage of minimizing the unirradiated reactanrs. Beta radiation can be used directly. For a I//g-inch pebble containing strontium-90, about 3 to 10% of the energy available should be expended into the medium being irradiated. O n a 5y0 basis, each beta particle should deposit an average of 100 k.e.v. in the medium. For example, where a chemical system ha> a G value (number of molecules formed per 100 e.v. absorbed) of 10, 10,000 molecules per beta particle kvould be formed. This would amount to 3.7 X 10l4 molecules per curie per second of dwell time, -4 IO-kilocurie source would give 3.7 X 1 O I 8 molecules or about 6 X 10-6 mole per second of d ~ l time. l An increase in G would naturally increase production rate from a 10kilocurie strontium-90 pebble bed. Also. using microspheres with diameters of 200 microns in a fluidized bed might improve radiation utilization b>- reducing adsorption processes in ad.jacent pebbles. However, attrition may be a problem. A radiation-induced reaction for which the pebble bed may be used is production of y-hexachlorobenzene. Work carried out with a gamma source indicates that G
varies from about 9.96 X 104 to 5 X 105 (7). Thus G is increased over its previous value by a factor of IO. In other words, with a system of this type (10 kilocuries) production rates of 0.06 to 0.1 moles per second of dwell time might be obtainable. Because dwell time for this type of system is considerably greater than 1 second, production rate from the reactor could amount to as much as 60 to 100 times that quoted per pass through the bed. One interesting possibility in making y-hexachlorobenzene is that amount of gamma isomer produced is an inverse function of temperature. Thus, if temperature of the reactor is controlled to -10” to -20” C., production rate would be pushed toward the higher gamma isomer yield. Operation of the pebble bed at these low temperatures would probably be somewhat easier than trying to operate a normal ultraviolet system.
SUGGESTED READING (1) Black, J. F.; Baxter, E. F., Jr., 2nd Intern. Conf. Peaceful Uses of Atomic Energy, Paper 197, 1758. (2) Doede, C. M., Walker, C . A., Chem. Eng. 62, No. 2, 159-78 (February 1955). ( 3 ) Governale, L. J., Clarke, J. T., Chem. Eng. Progr. 52, No. 7, 281-5 (1756). (4) Huff, J. E., Walker, C. A., Meeting, A. I. Ch. E. Journal 8, 193-200 (1962). (5) Reactor Fuel Proc. 6 (July 1961); Zbid., 4 (October 1761). (6) Schechter, R. S., Wissler, E. H., Appl. Sci. Research A9, 334-44 (1760). (7) Schneider, A , , “Sulfochlorination of Hydrocarbons Induced by Gamma Radiation,” ANL 5863, June 1758. (8) United Kingdom AEA Tech. Radiation Lab., Wantage, Bristol, England.
T H E PRESENT AND FUTURE To what extent does the chemicai i n d w i t y actually use photochemishy in its manufacturing Processes today?
I H E C editors have tried to find an answei t o this question by going to the primary sources: manufactitrers of both chemicals and equiflment. A cloak nf secrecy seems to surround
certain
area r, parlicularly
completeness is not possible.
eyui;Dment, and
Rut the pictuie obtained
shows that photochemical technology, although still not widely used, has better than auerage p i o L $ ~ c t sfor wider use zn the future. 26
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Already, practically all the benzene hexachloride produced in this country (more than 1 million pounds) is made by photochemical processes. This is the only product made OI? such a large scale, but this type of spotty development is typical in the early growth of most technologies-in terms of photochemistry, the reaction is fairly elementary, and commercially produced equipment needed to initiate the reaction is available. Chlorine is readily dissociated by ultraviolet light at wave lengths in the neighborhood of 3650 A., and mercury vapor discharge lamps offered for sale by equipment manufacturers emit these wave lengths. Also, the rays can be directed with aluminum reflectors and transmitted with relatively little loss by special types of glass and quartz. Most photochemical processes which have reached the commercial scale depend on dissociation of chlorine by near ultraviolet light at a wave length near 3650 A. Under this influence, chlorine combines readily with benzene, toluene, and similar compounds to form insecticides and other valuable products. In the photochemical step involved in the process for making capro-
lactam, recently announced by Toyo Rayon Co. of Japan, nitrosyl chloride mixed with cyclohexane is passed under mercury lamps which emit in the 3650to 6000-A. wave length.
WHERE PHOTOCHEMICAL REACTIONS ARE USED
Benzene Hexachloride Companies presently manufacturing
Diamond Alkali, which irradiates petroleum-base compounds on a commercial scale has this to say:
This company does not use extensively light wave energy for promoting chemical reactions. However, considerable development work has been done to optimize the few specific processes where photochemistry is used on a commercial scale. Specifically the field of application is in making organic derivatives from petroleum-base compounds. The wave length and density of light as well as exposure time are usually critical and specific for each type of reaction. However, a guiding principle in all our processes is to attain as short a contact time as possible between the reactants and light source, and also to use continuous rather than batch processing. The basic reason for this approach is to obtain uniform exposure of all parts of the reactants, which in turn leads to optimum quality and efficiency. T o achieve this, minimum depth of reactants is desirable because as light penetrates the mixture, its intensity rapidly decreases. In addition to using photochemistry as a fundamental reaction for making organic derivatives from petroleum-base compounds, this company uses it also in purification techniques-trace contaminants are reacted from main process streams.
Pharmaceuticals. Vitamin D3 is still made commercially from ergosterol by a photochemical process, and some of the anti-inflammatory steroids are made by the side chain degradation of desoxycholic acid. Ascaridole, which is the active principle of wormsees oil, used as an anthelmintic, can be synthesized by a photochemical process. However, there is no evidence of its therapeutic use in this country. Here again the reaction is extremely simple : An oxygen-saturated alcoholic solution of a-terpinene is mixed with spinach or stinging nettle leaves and exposed to sunlight. Equipment. The wave lengths involved in photochemistry range from about 1000 to 10,000 A. I n the electromagnetic spectrum, this includes the range from infrared down to just short of x-rays. Some photochemical processes are commercially feasible with standard fluorescent lamps which supply light in the visible spectrum only (4000 to 7000 A.). More often, however, mercury vapor discharge lamps are used. The spectrum of mercury consists of wave lengths ranging principally from 1850 to 10,000 A. At low pressures, the most powerful radiation is at about 2537 A . As pressure rises from heavier loading of the discharge tube, energy in the longer wave lengths increases. Finally, at extremely high pressures, such as 100 atm. per square inch where heavy walled quartz discharge tubes are required, the long ray lines are stronger and wider and an important background band
D I A M O N D ALKALI STAUFFER C H E M I C A L H O O K E R CHEMICAL Companies which process
F R O N T I E R CHEMICAL COLUMBIA S O U T H E R N CHEMICALS
have discontinued either the product or
TENNESSEE P R O D U C T S & CHEMICAL CORP. PENNSALT CHEMICALS
ETHYL CORP.
Other Products Presently Manufactured Compd.
From
Benzyl chloride, benzal chloride benzotrichloride
Made by
Toluene
Benzyl alcohol, benz- Chlorination aldehyde, benzoyl products chloride, sodium above benzoate, benzoic acid, benzyl benzoate Benzotrichloride, benzoyl chloride, benzoic acid
Toluene
Chlorinated paraffin compounds containing high %chlorine -
Paraffins
Dimethvltetrachloroterephthalate (selective herbicide)
Xvlene
Caprolactam
TENNESSEE P R O D U C T S & CHEMICAL CORP.
H O O K E R CHEMICAL
I
1 D I A M O N D ALKALI
Nitrosyl chloride, cyclohexane
T O Y 0 RAYON (Tokyo)
of energy appears. T h u s , the type of energy from mercury vapor lamps can be controlled by varying the load of the discharge tube. Several models of mercury vapor lamps suitable for industrial photochemical processes are offered by equipment manufacturers. In the following table, note the predominance of wave lengths near 3650 A., which is within the range that readily dissociates chlorine. For oxygen, hydrogen, and other elements, wave lengths shorter than 2967 A. are required. The Pfaudler Co. makes available about 30 types of reactors usable for photochemical reactions. Some are one-pieced vessels and others have a removable, clamp top. Sizes range from 5 to 4000 gallons, and all are lined with a pigment-free borosilicate glass which reflects rather than absorbs light. (Continued on next page) VOL. 5 4
NO. a A U G U S T 1 9 6 2
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General Electric Co. Lamp Model UA-2 UA-3 UA-11 UA-B UA-37 UA-9
3 Principal
Arc
Volts 92 134 450 450 1500 535
Watts
250 360 1200 120Ob 3000 3000
Length, In. 35/16 6 1731~ 17'/r 48 50
Wave Lengths" 3654, 5780, 5461 3654, 3131, 5461 3654> 3131: 5780 3654, 5780, 5461 3654, 3131, 2537 5780, 5461, 4358
Hanovicl lamp Div., Engelhard Industries, Inc. 150 700 7.5 3660: 5461, 285 1200 12.0 3660: 5780, 550 2000 21.0 3660, 5780, 925 3450 48.0 3660, 5780, 1000 4500 58.0 3660, 3130, 960 4500 42.0 3660, 3130, 1250 7500 59.0 1260 5000 46.5 3660> 5780, 1700 7500 59.0 3660, 5780,
67' 189" 78" 47AC 59AC 77'4" 65.4 57A 4013
5780 4358 3130 5461 5461 5780 5461 5461
Quarzlampen Gesellschaft m.b.H., Hanau, Germany Over-all Length, M m,
Q 7000 Q 1200~ TQ 2 0 2 4 ~
144 144
Q 25 Q 81
72 72 110 90 125 125 230 240 650
Q 300 Q 400 Q 600 Q 700 Q 1200 TQ 2024 Q 3000
HOK I
720 1050 2000 2000 7000 25 70 240 120 180 720 1050 2000) 30001
3660, 3130, 4360 3660, 3130, 4360 3660, 5460, 3130 577-9, 5460, 3660 45 3660, 5460$4360 125 3660, 5460, 577-9 240 3660, 3130, 5460
1421
202 3660, 5460, 577-9 346 388 396/ 14651 3660, 577-9, 3130 I
Deutsche Philips G.m.b.H., Hamburg, Germany 550 1200 520) 550 2000 710 I 550 2500 3655, 5780, 5461 1750 1500 1250 3000 14901 1800 5000 1490,
i2k:;
HOG HOQ
HOK HOGK
190 190 550 550 550
700 700 2000 2500 2000
567 567'1 1367) 1504; 780
190 550 550
700 2000 2500
l:;] 1504,
5461, 4358, 5780 3655, 5461, 3130 3630, 5780, 5461 3650; 5461, 3130
a Values in descending order, based on watts of radiant energy. ii This is the UA-11 quartz lamp enclosed in a l'ia-inch diameter tube of heat-resistant plass which transmits middle and near ultraviolet radiation. C l\'ith immersion fitrings.
TRENDS
At its present stage of growth, photochemical technology zs lzttle beyond infancy, and expansion can be in several directions. Seoeral companies are doing developmental woik in photosensitization and processing, both continuous and bafch. One company (Phillips Petroleum Go.) doing such work says: We believe that there is some probability that an investigation of photochemical reactions in the 28
INDUSTRIAL A N D ENGINEERING CHEMISTRY
liquid phase will lead to reactions that can be exploited commercially. In support of this belief, we have a small group in our research laboratories working in this area.
A prime deterrence in developing photochemical technology 2s lack of light sources which supkly the desired waee lengths
with ieasonable economy in electrical power. In this connection it is unfortunate that exchange of information among users and manufacturers of equipment is somewhat guarded. However, other solutions to this problem may be in the offing: the solar or arc image furnace, and the pebble-bed reactor. Regarding the maser principle, although probably of academic interest at the moment, W. D. Williams of the Royal College of Science and Technology, Glasgow, says: For appreciable yields of product, the light source must be of adequate intensity if chain reactions d o not occur, and application of the maser principle for obtaining intense beams of monochromatic light is one method applicable to photochemistry [Pharrn. J . (May 12, 1962)].
Photochemical reactions are promising for preparing rare and expensive chemicals and pharmaceuticals.
Dr. Max Tischler, President of the Research Laboratories of Merck Sharpe & Dohme, says: Aldosterone is a potent steroid hormone which is present in adrenal glands, but only in infinitesimal amounts. Thus, biological studies of this compound were limited because of its inaccessibiliq-, and even though this situation was remedied in part by development of a synthesis technique, the process was long, tedious, and costly. .4 few years ago, however, Dr. Derek Barton, using a photochemical reaction, transformed the 6-11 nitrite ester of compound B to an intermediate oxime which, by normal nonphotochemical reactions, was easily transformed to aldosterone. Thus, if aldosterone becomes important therapeutically, the photochemically produced oxime would also increase in technological importance. Another instance of a potentially important photochemical reaction was uncovered in the early days of cortisone synthesis. Dr. E. R. H. Jones devoted considerable effort to synthesize cortisone by using a peroxide of ergosterol. The peroxide is obtained by photosensitizing oxygen molecules Lvhich are then activated sufficiently to attach themselves to the A5,7 system of ergosterol. These special situations where photochemical activation is useful are rare in synthetic organic chemistry, corn pared to ionic or free-radical reactions, .iz.hich are not onl>- easier to control, but also more suitable to the diverse requirements of the complex structure of current therapeutic a,gents. Nevertheless, as our understanding increases in depth as well as breadth, photochemistry will become increasingly useful in the technology of or g a iiic chemistry.
