Low and Moderate Pressure Liquefied-Gas Aerosols LYLE D. GOODHUE Phillips Petroleum Company, Bartlesville, Oklu. Liquefied-gas propellents to produce insecticidal aerosols at lower pressures than that of dichlorodifluoromethane have made possible the use of lighter, less expensive containers. These tin-can type containers can now be used to hold pressures up to 40 pounds per square inch gage at 70' F., and with properly formulated solutions effective aerosols can be produced. A propellent composed of a high and a low pressure liquefied gas appears to give a better dispersion than one pure liquid at the same pressure. Highly effective insecticides and only enough auxiliary solvent to dissolve them should be used in the formulations so a maximum percentage of liquefied gas will remain to produce the dispersion.
Some of the material in this paper was used by the Compressed Gas Manufacturers Association, Inc., in preparing the request for this increase in pressure. The dispenser and the aerosol-producing solution as modified for use in the moderate pressure household aerosol are described. The economics and marketing of these aerosols are beyond the scope of this paper, but were discussed in a recent article by Stoddard (18). THE DISPENSER
Even though the common beer can was available as a container, the development of a practical dispenser unit with a suitable valve and nozzle was not an easy problem t o solve. P a s t experience with leakage, faulty valves, and clogged nozzles on t h e HE principle of producing insecticidal aerosols by spraying high pressure dispenser was of considerable value, but the same solutions in liquefied gases has been the subject of numerous difficulties had t o be overcome in the lighter units. Special comarticles (3, 4,6). The aerosol dispenser has satisfied a need for a pounds had t o be found for the seams, t o withstand the solvent convenient and efficient way of applying a household insecticide action of the aerosol solution, and greater accuracy in the seaming for the control of flies, mosquitoes, roaches, and many other comoperation was necessary. The valves used on the high pressure units were either too expensive or not dependable, so cheaper and mon insects. Premium prices have been paid, but with the element of novelty diminishing, manufacturers have considered better valves, combined with nozzles t o aid in the dispersion of the many ways t o reduce t h e high cost of production and pass t h e insecticide at lower pressures, had t o be developed. The use of saving on t o the consumer. For the most part, efforts t o econolighter containers has already been discussed (8). Figure 1 shows mize have been directed toward reducing the cost of the container the types of cans now in u8e. A is a drawn steel containcr with a which has often been higher than the cost of the contents. A wall thickness of 0.015 inch. It is manufactured in special, high much less expensive container was being manufactured by the speed machinery designed for the production of beer cans and can industry t o hold beer under pressure, b u t it was not strong having a capacity of about 300 per minute. The shape of the top enough t o hold safely the common high pressure aerosol with of the aerosol dispenser was changed to eliminate any similarity about 70 pounds per square inch gage at 70" F. To use lighter to a beer can. One aerosol manufacturer modified unfinished containers, a lower pressure was necessary, and t h e result has cans of this type at the top t o accommodate a special valve. A been the development of the low and moderate pressure aerosols. more recent development is a completed can, lacquered inside and At first attempts were made without much success t o produce out, and lithographed with the aerosol manufacturer's label. T h e an effective dispersion a t 25 pounds per square inch gage. T h a t bottom is seamed on a t the can factory, but an opening 1 inch legal limit for light containers was raised on July 28, 1947, to in diameter is left a t the top. A special type of closure is provided, about 40 pounds gage (exactly 55 pounds per square inch absobut the dispensing valve and nozzle are left t o the aerosol manufacturer. lute) a t 70" F. after Can B had both the safety of the ends concave, b u t container was demonan attempt is bestrated and data were ing made t,o use presented t o show a special flat bottom. the much greater It is made from effectiveness of the tin plate by high aerosol a t the higher speed can machinery pressure. A e r o s o l s and furnished t o produced a t 25 aerosol manufacpounds gage or lower turers complete with are commonly known a dispensing valve as low pressure aeroa n d nozzle. The sols, but i t appears bottom is left open more appropriate to for filling. A better use the term "moderlabel can be proate pressure aerovided with this can sols" for those probecause i t is lithoduced by propellents graphed while flat. in the higher range These light disA . Drawn steel d r u m B . Three-piece tin plate up t o 40 pounds pensers have several container Figure 1. Moderate Pressure Aerosol Containers advantages over t h e
T
1523
1524
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
type used for the high pressure aerosol. They can be obtained complete with valve for about one fifth the cost of the high pressure dispenser. Lithographing PI ovides an attractive and permanent label which is not damaged by small amounts of the insecticide that may be spilled on it. T h e tin plated or lacquered containers resist corrosion which was commonly caused by DDT in the unprotected, high pressure dispenser. The) are lighter to ship and easipi for the consumer to handle. The valve IS an important part of the dispenser and has been the S O U I C ~ of most of the trouble in all types of qerosol bombs Leakage was frequent and Figure 2. Typical Aerosol often developed after inD i s p e n s e r ValFe spection. After storage, A . Synthetic rubber valve seat B . Push button some valves could not b(y C . Cap opened and some would not D . Ruhher diaphragm E . Activator pin close. The demand by thc F . v a l v e body 6. Met.31 ball consumer for an easily opera. Spring ated valve required the use of Valve attachment nipple I. one or more synthetic riibbei party and the wrong choice of these was often responsible for the trouble. Figure 2 shows a typical valve. l'alve seat B is composed of two layers of Buna N ; one thicker layer of a rather hard rubber for durability is bonded t o a soft layer to form a gastight seal. Metal ball G is held against the valve seat by spring H , arid the valve remains closed unless opened by pressure from the top. Sometiniee a small inverted cup or a special part is used in place of the ball. An ordinary tire valve with a special valve seat and gasket was employed by one manufacturer with success. A resilient valve seat is used in all push-button type valves because less pressure against the valve seat is required t o form a gastight seal. The valves on the lower pressure dispensers are similar, but have been modified t'o facilitate mass production and to overcome the difficulties previously encountered. It appears that dependable valves can now be produced in quantity, and no trouble should be encountered if a wise choice of propellent and auxiliary solvent. is made. The nozzle for low pressure aerosols requires a more careful design than that for high pressures. Something more than a simple orifice or capillary is needed, especially if the pressure is below 30 pounds per square inch gage, I n the design of a nozzle some means of inducing turbulence and the formation of small bubbles of gas is important. A good way to accoflplish this is to use a constrict.ion about 0.015 inch in diameter, leading into a mixing chamber immediately preceding a 0.020-inch-diameter orifice. This causes a slight drop in pressure t o aid in the formation of many small bubbles that act as nuclei to accelerate the boiling of the propellent when i t is reduced to atmospheric pressure. Turbulence caused by an abrupt change in the direction of the liquid stream through various sized passages aids in the formation of nuclei. Between 35 and 40 pounds gage it is easy to obtain a good dispersion with a properly formulated liquefied-gas solution, but at pressures below 25 pounds gage even the best nozzles d o not give an effective aerosol. Some types of valve mechanisms that change the direction of flow or cause turbulence aid in the formalion of nuclei.
Vol. 41, No. 7
T h e first low pressure aerosol dispensers were filled b y adding t,he ingredients in two parts. Those materials that could be handled without much loss a t atmospheric pressure and teniperature were measured into the open container, and the lid was seamed on. Dichlorodifluoromethane was then forced in through the dispensing valve. This method is relatively slow and introduces more errors in measurement,. Because of t,he construction of some of Lhe newer valves, liquid cannot be added through them. Therefore, the liquefied gas must be cooled below its boiling point and measured into the open container. This may be near - 10' F. for some solutions, but the temperature should be regulated so that' just enough propellent is evaporated t o displace the air that would otherwise be entrapped in the container. Entrapped a.ir adds t o the pressure, but, does not help produce the a.eroso1 and may cause the pressure t.0 exceed the legal limit,. Figure 3 is a flow sheet for the filling of these dispensers. The cold propellent is added first, and the solution of insect,icides is run in on top of this heavy liquid. When a complete formula cont'aining DDT is refrigerated, t,here is a tendency for crystals to form if the solution contains more than 1% of this compound. If more DDT is desired, it, can be added t o the container separately as a pellet or weighed in with a small machine. Filling by refrigeration is desirable because it utilizes high speed automatic machinery that will fill 25,000 dispensers in one 8-hour shift running a t about 80% capacity. Under the new regulation each filled container must be heat'ed to 130" F. and not show evidence of leakage or distortion. THE PROPELLENT
The choice of a propellent for low pressure aerosols requires the saine considerations as for the higher pressures and some others in addition. -4 single propellent or a combination must be nonflaininable, nontoxic, and nonirritating t o man, nearly odorless, chemically inert, and a fair solvent. The vapor pressure must be high enough to expel the liquid forcibly from the container and cause it t,o boil violently at ordinary atmospheric temperature and pressure. A low heat of vaporizat,ionfavors rapid boiling, which gives a good dispersion. Such other properties as density, viscosit>y, and surface tension have some influence on t,hc performance, b u t these are generally good enough to be ignored in a propellent that meets t,he major requirements. M o s t ' of the mechaiiical energy to form a n aerosol from a liquefied-gas solution is drawn from the atmosphere in the form of heal t o produce rapid boiling of the propellent. \\'hen the pressure is much below 40 pounds gage, it is especially important t o use a nozzle that will induce the formation of large numbers of small bubbles in the solution to act as nuclei at the time i t is reduced to atmospheric pressure. With other conditions constant, more bubbles are formed with a mixed propellent containing one high pressure component than with one pure liquid ( 5 ) . For esample, a mixture of dichlorodifluoromet,hane and trichlorofluoromethane in proportions to give 40 pounds gage pressure provided x highly effective insecticidal aerosol; chlorofluoromethane ( 1 5 ) , a pure compound with the same vapor pressure, produced a poor, ineffective dispersion. Bubble formation which prevents sriperheating is initiated by the heat pressure component, and a better dispersion is produced with the mixture even though the low pressure component may add little to the total energy of tmhesystem. If rapid boiling does not occur a t the instant the solution is ejected, the heat energy absorbed from the atmosphere is not utilized in the dispersing process. Assuming the desired pressure will be obtained by using a mixture of a high and a low pressure liquefied gas, it should be pointed out t'hat some change in composition of the propellent will take place as the solution is withdrawn from the dispenser. The change is similar to that already shown to occur in the concentration of a nonvolatile substance in a liquefied-gas solution ( 1 6 ) . The vapor phase above the liquid is richer in the component with the higher vapor pressure, and as the liquid is withdrawn, the
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1949
1525
sol solution (9070 propellent) giving a pressure of only 25 pounds gage a t SCALES MIXER~ 70" F. The results were submitted to SOLVENTS the Aerosol Committee of the Compressed Gas Manufacturers Association, Inc. (14). Because pressure varies with temperature, the efficiency of a low pressure aerosol would be expected to vary in the same manner. At 60' F. or lower nothing better than a wet sprav, . . . or at t,imes a solid stream, was produced. The efficiency against houseflies was determined a t 70°, SO", and 90" F. by the method already reported ( 7 ) . Caged flies were exposed to three different dosages of the aerosol a t each temperature in a 650 cubic foot chamber with an oscillating fan to provide air circulation. The average mortality and knockdown results from three complete series run on different days were plotted on log-probability paper. As measured a t the 50% point, Table I1 gives the increase in dosage necessary t o obtain the Figure 3. Flow Sheet for Filling Moderate Pressure Aerosol Dispensers same effect when the pressure is reduced from 38 pounds gage at 90" F. through The labor requirement is seven m e n to fill 10,000 units per 8-hour shift. 32 at 80" F. to 25 at 70" F. The effect of pressure is marked and shows the space occupied b y it is filled by vapor which evaporates largely necessity of the higher limit for the low pressure aerosols. from the higher pressure component. This causes a loss in pressure of about 5 pounds per square inch when a small dispenser is AUXILIARY SOLVENT nearly empty. If the initial pressure is near 40 pounds per square inch, this drop is inconsequential. With larger shipping conhinMost of the propellents for lower pressure aerosols are better ers, however, which are used to transport liquefied-gas mixtures, solvents for insecticides than dichlorodifluoromethane, and a supsome means of compensation must be used to maintain a constant plementary solvent is not so important as in high pressure aerocomposition as the liquid is withdrawn in the process of filling sols. However, it is better t o dissolve the solids and other active aerosol dispensers. This can be accomplished easily after the first ingredients in a n auxiliary solvent so t,hat foreign matter can be drum has been emptied of liquid by pumping the gas remaining in removed by filtering. Solutions are also easier to handle during the first drum into the second when about half of the liquid has t,he filling process, and suppliers are enabled to sell ready-mixed been withdrawn. This method of controlling the composition can solutions of the active ingredients, t,hen be continued indefinitely, Another means of correcting for No entirely satisfactory auxiliary solvent with no undesirable this change is to maintain a constant pressure of the higher presproperties has yet been found. Some fract,ions of alkylated arosure component through a reducing valve. matic hydrocarbons fulfill most of the necessary requirements, Although there are numerous liquids or mixtures of liquids that but cause synthetic rubber parts of valves t o swell and give a prohave the desired vapor pressure, most of them are not suited for nounced odor, aerosol propellents. Dichlorodifluoromethane in combination with trichlorofluoromethaze is satisfactory and is being used in most of the moderate pressure aerosols. A mixture containing TABLE I. PROPELLENT COMBINATIOKS 54y0of the former and 46% of the latter gives a pressure of about B. P., Pressure a t 70" F., 37 pounds gage at 70 F. in the aerosol solution. Hydrocarbons F. Lb./Sq. I n . Gage such as pentane or butane can be used with the above nonflam1. Dichlorodifluoromethane -21.7 70.1 mable propellents in amounts not exceedirfg the point of flammaTrichlorofluoromethane 74.7 0.0 hility, determined by Jones and Scott (11) to be about 25% by 2. Dichlorohifluorornethane -21.7 70.1 Trichlorofluoromethane 74.7 0.0 volume. n-Pentane 97.2 0.0 Another propellent combination, consisting of dichlorodifluoro3. 1 1-Difluoroethsne -12.5 62.5 methane and methylene chloride, has been under consideration, Triohlorofluoromethane 74.7 0.0 but the high solvent action'and ease of hydrolysis of methylene 4. Dichlorodifluoromethane -21.7 70.1 1-Chloro-1,Ldifluoroethane 15.1 30.2 chloride are serious disadvantages. Other liquids such as chloro5 . Dichlorodifluoromethane -21.7 70.1 difluoromethane, chlorofluoromethane, 1,l-difluoroethane, l-diMethylene chloride 104.2 0.0 chloro-1,l-difluoroethane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, and other halogenated ethanes can be used in certain combinations that produce the correct, pressure. Some of these combinaTABLE I1. IN OF -4 -4BR0SOL AGAINST HOUSEFLIES AS PRESSURE Is REDUCED BY tions are shown in Table I. LOWERING TEYPERATUBE Methyl chloride ( 1 7 ) is too toxic for household aerosols b u t is fiow widely used to disperse toxic insecticides where adequate Dosage a t 50% Point, Grams Loss i n Effectiveness, 5% Temp,, Gage Mortality Knockdown Mortality Knockdown F. safety precautions can be taken. These and other propellents 38 1.3 1.3 .. 90 have been discussed b y Goodhue et al. (6)and b y Fulton ( 2 ) . 80 32 1.7 1.6 32 io Before the pressure limit of 40 pounds per square inch gage at 70 25 2.1 1.8 61 38 70" F. was allowed, a study was made of the effectiveness of aeroINSECTICIDES
--
(1
O
~!f/r:';;,
O
1526
INDUSTRIAL AND ENGINEERING CHEMISTRY
If the solvent is not chemically inert,, it can c a s e serious trouble. During storage the container may corrode, color may develop, and the solvent may react with the propellent or the insecticide. Furthermore, the solvent may polymerize to form resins and tars that precipitate from the solution. Such conditions have been encountered when cyclohexanone was used as an auxiliary solvent, especially if acid entered the dispenser a t the time the fusible metal safety device was added. Also acid may be liberated from DDT and other halogen-containing insecticides. Small amounts of stabilizers, such as propylcne oxide ( 9 ) and ndodecyl mercaptan ( 1 9 ) , have been shown'to reduce greatly the changes that take place during storage of such liquefied-gas solutions. hlost good solvents for solid insecticides cause swelling and dcteriorat'ion of the synthetic rubber valve parts in an aerosol dispenser. Much effort has been made to find a rubber or plastic valve material to resist the action of some chosen solvents, and the results have been reasonably successful. Synthetic rubber of the Buna K type is affected and has given good service in certain nonswelling compounds. Among the plastics, nylon, saran, and Teflon are resistant to solvents but are generally not resilient enough to form a good valve seat. Plastics, fabrics, paint, and other finishes are so commonly encount,ered in the appli~at~ion of aerosols that no active solvent for these materials can be used safely. The alkylated naphthalenes are least destructive, but not all of the great variety of plastics are resistant-for example, polystyrene is badly damaged. Volat,ility helps reduce possible damage where the solution comes in contact with such surfaces, but a t'oo rapid rate of evaporation causes crystalline residues to form in the orifice of the nozzle. With some dispensing devices the residual solution is almost completely discharged from the nozzle, and not enough is left t.o cause stoppage even though crystals are formed. -4more volatile solvent can be used under these conditions, but unsightly crystalline residues collect around the orifice and on the dispenser. When the solvent is sprayed on a surface in a t,hin layer, i t must evaporate completel~.and leave no colored residue. Some solvents develop color in the dispensernandsome darken when exposed t,o light. Wallpaper and fabrics are permanently stained with the solvent,s used in some aerosol dispensers. Many of the particle size data obtained on auxiliary solvents with dichlorodifluoromethane give an indication of what to expect when lower pressure propellents are used. For example, hydrocarbons such as alkylated naphthalenes dispersed too easily to form too many particles below the most effective insect,icidal range, which is 5 to 20 microns in diameter. Therefore this solvent in a lower pressure propellent with less energy should give a particle-size dist,ribution in a higher, more efficient range. Usually oxygenated solvents do not disperse easily and should be avoided in the lower pressure aerosols. A highly viscous liquid requires more energy for dispersion than one with a low viscosity. The auxiliary solvent must be completely soluble in the propellent. An aerosol-producing solution should be homogeneous although some attempts have been made to use a two-phase system, such as a paint or a wax emulsion. Agitation of a dispenser during spraying is necessary with heterogeneous solutions, and even this cannot be depended upon t o overcome the difficulties with settling and coagulation. A solvent with a mild odor is difficult,to find because a fine dispersion of a liquid accentuates the odor. This is the principal objection to the alkylated naphthalenes, and perfumes have been used to cover the odor. Cyclohexanone as used in the army formula was unpleasant t o most people and was later modified with perfume by some manufacturers who filled dispensers with this formula for civilian use. A low toxicity to man and animals is essential for a solvent in a household aerosol. This excludes those causing photosensitivity or other irritations of the skin. Solvents no more toxic than cyclohexanone (IS)or the refined alkylated naphthalenes are con-
Vol. 41, No. 7
sidered safe. It is important to determine the toxicity of any new solvent under consideration. Sometimes it is desirable to add an oil that has little solvent action €or the purpose of controlling the particle size and other physical properties. Sesame oil ( 3 ) was first used, mainly because i t contained sesamin, a synergist for pyrethrum, but it also increased the particle size and rendered the aerosol more effective. Lubricating oil (12) was employed in one army formula with cyclohexanone because it increased the effectiveness and reduced the solvent action of the cyclohexanone on plastics and finishes. Deodorized kerosene has sometimes been used. Bny of these is less expensive than the propellent and, as a diluent, helps to reduce the total cost, but only small amounts can be used in the lowcr piessure aerosol formulations. ACTIVE INGREDIEhTS
Although the auxiliary solvent and oils are considered active for labeling purposes, the materials discussed here are the highly effective ones without which the aerosol would be of little value. The aerosol method works best with sma!l amounts of very potent materials because a higher percentage of liquefied gas remains to produce the dispersion. Such highly effective insecticides as pyrethrum, DDT, DDD, methoxychlor, benzene hexachloride, and chlordan are examples. In choosing an insecticide, however, several points must be considered, assuming first that the chemical is soluble in the liquefied gas and auxiliary solvent. It must be chemically inert and stable under the conditions of use and storage. If it is not inert, it may corrode the container or may lose its effectiveness. For example, polymers and other reaction products may form or highly colored substances may be produced. The odor may change and an inoffensive compourid may become irritating or toxic. The metal container may act as a catalyst during storage and cause undesirable changes. Some of these difficulties have been encountered in commercial aerosol dispensers now on the market. D D T , commonly used in aerosols, tends to liberate hydrochloric acid which forms metal chlorides; these, in turn, accelerate the dehydrohalogenation. A sinall amount of propylene oxide acts as an effective stabilizer by combining with any free hydrochloric acid (9). A good technical grade of DDT appears to be as stable as the aerosol grade. Low toxicity to man and animals is essential for an insect cide in a general-purpose aerosol. Pyrethrum with a synergist from the class containing a piperonyl group has the l o ~ e s ttoxicity, but moderate amounts of DDT have been regarded as safe (IS). The manufacturers of pyrethrum extract are offering several good insecticide formulations to mix with the moderate pressure propellents. Chlordan is an easily formulated liquid insecticide and more effective than DDT against resistant insects such as roaches. Its toxicity to warm blooded animals is in the order of D D T ( I O ) , but it is more irritating to the eyes and nose in aerosol form. Chlordan should be stabilized with propylene oxide to prcvent dehydrohalogenation in the aerosol solution. The odor of the insecticide must be mild. The musty odor of benzene hexachloride, for example, is the limiting factor for its use in household aerosols. Pyrethrum extract when properly refined imparts a pleasant odor, and D D T is odorless. Most of the odor in the commercial aerosols comes from thc auxiliary solvent rather than from the insecticides. OTHER APPLICATIONS
While this discussion is concerned mainly with insecticides, numerous materials useful for other purposes can be dispersed by this method, as suggested by Dietz ( 1). Germicidal, deodorant; and perfume aerosols have already been marketed. Soluble substances useful in aerosol form are easy to apply by this method, and most of the general considerations for the formulation of .a liquefied-gas solution of an insecticide can be applied. Since inex-
July 1949
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
pensive dispensers have now been made available for insecticidal aerosols, the liquefied gas method will be expected to expand into many fields where an aerosol or a wet spray is useful. LITERATURE CITED (1) Dietz, W., and Shepherd, H. H., Soap Sanit. Chemicals, 22, (12) 137-9 (1946). (2) Fulton, R. A., IND. ENG.CHEM.,40, 699-700 (1948). (3) Goodhue, L. D., Chem. Inds., 54, 673-5 (1944). (4) Goodhue, L. D., IND. ENa. CHEM., 34, 1456-59 (1942).
(5) Goodhue, L. D., Fales, J. H., and McGovran, E. R., Soap Sunit. Chemicals, 21, (4) 123, 125, 127 (1945). (6) Goodhue, L. D., and Hazen, A. C., IND.ENG.CHEM.,ANAL. ED., 19,248-50 (1947). (7) Goodhue, L. D., Schultr, F. S.,Innes, Neva, and Stansbury, Roy, Soap Sanit. Chemicals, 23, (9) 119-21 (1947). (8) Goodhue, L. D., Schultz, F. S., and Wilkins, P. H., Chem. Inds., 60, 602-4 (1947). (9) Hazen, A. C., and Goodhue, L. D., Soap Sanit. Chemicals, 22, (8) 151, 153, 155 (1946).
1527
(10) Ingle, Lester, J . Econ. Entomol., 40, 264-8 (1947). (11) Jones, G . W., and Scott, F. E., U. S. Bur. Mines, Rept. Invest. 3908 (1946). (12) Madden, A. H., Schroeder, H. O., Knipling, E. F., and Lindquist, A. W., J. Econ. Entomol., 39,620-3 (1946). (13) Neal, P. A., yon Oettingen, W. F., Dunn, R. C., and Sharpless, N.E., Suppl. Pub.Health Rept. No. 183 (1945). (14) Rhodes, W. W., and Goodhue, L. D., Soap Sanit. Chemicals, 23, (10) 122-3, 151 (1947). (15) Rotheim, Erik, U. S. Patent 2,128,433 (Aug. 30,1938). (16) Smith, C. M., and Goodhue, L. D., IND. ENG.CHEM.,ANAL.ED., 16,355-7 (1944). (17) Smith, W. W., Baldwin, Yvonne, and Grenan, Marie, J. I n d . HDg. Tozicol., 29, 185-9 (1947). (18) Stoddard, R. B., Soap Sanit. Chemicals, 24, (7) 147, 149 (1948). (19) Young, E. G., Ibid., 23, (11) 116-17, 152A (1947). RECEIVED June 11, 1948. Presented as part of the Symposium on Aerosols before a joint session of the Divisions of Physical and Inorganio Chemistry and Colloid Chemistry a t the 113th Meeting of the AMERICAN CRE:X.CAL SOCIETY, Chicago, Ill.
Composition of a Synthetic
Gasoline ALFRED CLARK, ANTHONY ANDREWS,
AND
HAROLD W. FLEMING
Phillips P e t r o l e u m Company, Burtlesvills, Oklu.
T h e percolation through silica gel of eight fractions from a gasoline synthesized from carbon monoxide and hydrogen with a fluidized iron catalyst of the synthetic ammonia type has accomplished the breakdown of each fraction into the following four types: paraffins, olefins, aromatics, and oxygenated compounds. As a result of the segregation of these types, the following additional information was obtained on the character of the gasoline fractions: (1) Forty to fifty per cent by volume of the Cg, Ce, and C7 fractions consist of straight chain 1-olefins. (2) Fifteen different aromatic compounds were identified by infrared absorption as being present in the first six gasoline fractions. (3) There is fairly conclusive evidence of the presence of small amounts of diolefins in most of the fractions.
T
HE efficacy of silica gel in separating mixtures containing different types of hydrocarbons is now well known. Mixtures containing paraffins, naphthenes, olefins, and aromatics may be separated by percolation through silica gel. Several analytical methods using silica gel have been developed for determining the, volume of the various types in hydrocarbon mixtures. Mair (3) outlined a procedure for determining the aroinatic content of a straight-run petroleum distillate, as in the gasoline or kerosene boiling range. Lipkin et al. ( 2 ) describod a method for the determination of aromatics in petroleum fractions boiling above 400" F. A method for the analysis of small samples of shale oil naphthas was developed by Dinneen and eo-workers (1). The present report describes in part the results of large-scale laboratory silica gel percolations in the analysis of eight fractions of a synthetic gasoline prepared by reacting carbon monoxide and hydrogen in the presence of a fluidized iron catalyst of the synthetic ammonia type a t approximately 600" F. I n addition, reaults are given for the precision fractionation of some of the segregated percolates. Since this paper is concerned with separa&ionson one representative synthetic gasoline, no discussion or conclusions concerning other types of gasolines are intended.
MATERIALS AND METHODS
MATERIALS.The synthetic gasoline was first debutanised and then separated into eight fractions by an Oldershaw glass bubbleplate column. Table I summarizes the boiling ranges of the eight fractions and the chemical tests carried out on each fraction. TABLE I. PROPERTIES OF SYNTHETIC GASOLINE FRACTIONS Bromine Hydroxyl No. No. c6 59-104 80.6 183 10.7 C6 104-165 80.8 154 14.5 c7 165-219 81.3 133 21.8 cd 219-279 78.4 112 17.9 Ce 279-324 79.5 101 15.3 ClO 324-369 81.4 93 12.0 Cti 369-394 84.7 88 9.9 c 1 2 394-428 85.0 81 9.3 a As determined by bromide-bromate method.
Fraction
Boiling Range,
F.
Olefin",
%
Carbonyl No.
Acid NO.
2i:o 20.4 23.8 14.7 7.9 5.3 9.1
1.1 2.8 2.5 2.6 1.7 0.7 2.6
...
The silica gel, purchased from the Davison Chemical Corporation, graded as follows when screened by a Roto-Tap: Mesh Size 150 150-200 200-250
Wt. % 19 23 8
Mesh Size 250-325 > 325
wt. % 20
30
Regeneration of the silica gel was not attempted; a new batch of silica gel was used for each percolation. Absolute ethyl alcohol was the desorbing liquid in each of the percolations. CHEMICAL TESTS. Whenever needed, the following group of chemical tests was carried out: Hydroxyl number determination involves the esterification of the hydroxyl group by a 1 to 4 acetic anhydride-pyridine mixture. The excess acetic anhydride and the acetic acid resulting from the esterification a m titrated by a standard potassium hydroxide solution. The hydroxyl number is calculated as the number of milligrams of potassium hydroxide required for a 1-gram sample. The hydroxyl number must be corrected for any acids present in the sample.
