INDUSTRIAL A N D ENGINEERING CHEMISTRY
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VOl. 21, No. 9
Transparent Emulsions of Some Essential Oils"z Willet F. Whitmore and Richard E. Linehan3 THEPOLYTECHNIC INSTITUTE, BROOKLYN, N. Y.
emulsions is by no means new, but there is still room f o r considerable improvement and development in this field. Some types of are preparations Of Oil in water containing gum arabic or tragacanth the agent. Their short durat i o n of stability indicates the need of fuller application of the principles of emulsification in the manufacturi n g process. It is well
d i s p e r s i o n medium, well m i x e d , a n d t h e mixture homogenized three t i m e s through the Hurrell homogenizer, a continuous type colloid mill, operating at 2850 r. p. m. I n every ins t a n c e the produced was transparent. A sample of the r e s u l t i n g emulsion was then centrifuged at 1750 r' p* m' for to test its stability. 11 minutes I n order to consider suffi! cient the amount of peptiz7
indices of the two phases at the Same the peptizing agents second, whereas proved unsatisfactory. by employing sugar and 1 part of sucrose in the dispersion mepreparation
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TNDUSTRIAL AND ENGINEERING CHEMISTRY
September, 1929
Although gelatin proved to be an excellent peptizing agent, the emulsions began to grain, or deposit crystals, within 2 or 3 months, presenting an obstacle that had to be overcome before the emulsions could have any commercial value. The graining was due to crystallization of dextrose from the invert sugar constituting the dispersion medium. Experience with sugar products has shown that this crystallization can be overcome by the use of a mixture of 2 parts of invert sugar and 1 part of sucrose, instead of straight invert sugar. Consequently, this mixture was tried in the preparation of these emulsions, and the result was satisfactory. Five per cent emulsions made with the 2 : l mixture and 0.25 per cent of gelatin have shown no indications of graining or breaking over a period of 11 months. Emulsion 60 in the table is an example. Relative Efflciency of Various Peptizing Agents Dispersed phase: Orange oil, 5 per cent b y volume, n~ a t 2 5 O C.,1.4690. Dispersion medium: Invert sugar and water containing peptizing agent; no at 25' C . , 1.4690.
EFFECTOF
CENTRI- DURATION OF OTHEROBSSRVATIONS FUOING STARILITY 2 Stable 2 months Grained slightly Grained slightly Stable 7 weeks 36 Grained heavily Stable 4 weeks 30 Grained heavily Stable 3 weeks 4 . . . . . .. . . . . . . Broke . . 6 Stable 3 months Did not break, but 9 grained Did not break, hut 3 months 0.507, gelatin Stable 10 grained Did not break, but 3 months 0.25% gelatin Stable 11 :rained can l o grain after 11 months 0.267, gelatin Stable 60a 11 months Broke, grained Stable 6 weeks 0.10% gelatin 12 Broke, grained 0.0~. .5'7,eelatin Stable 1 month 13 0.025%-?;gelatin Broke . .. .. 14 0.2570 agar-agar Stable 7 days 21 0 . lOV0 agar-agar Stable 6 days 26 0.05% agar-agar Stable 5 days 26 0.026% agar-agar Stable 3 days 27 . .. . , . . , . . . , 0 0107, agar-agar Broke . ... . 28 Difficult t o homoge0 . 5 0 7 , tragacanth Stable 1 month 22 nize; retained air; broke and grained . , . . , . . . . . .. 0.267, tragacanth Broke . .. . . 23 Graining retarded by employing a mixture of 2 parts of invert sugar and 1 part of sucrose instead of straight invert sugar. No.
PEPTIZING AGENT 5% gum arabic 2.57, gum arabic lY0 gum arabic 0.5% gum arabic 0.257, gum arabic 1% gelatin
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Relation between Amount of Dispersed Phase and Quantity of Gelatin Required as Peptizing Agent
In many instanceq an emulsion of high flavor concentration is desirable. Consequently, a number of experiments were made to determine the relationship between the dispersed phase, the peptizing agent, and the degree to which the dispersed phase may be increased from a practical viewpoint. The emulsions were made up as outlined under General Procedure, employing orange oil as the dispersed phase and gelatin as the peptizing agent. Quantities of gelatin ranging from 0.25 to 1.00 per cent were taken and the amount of orange oil successively increased until a concentration was reached a t which emulsification was no longer complete. With 0.25 per cent of gelatin it was possible to incorporate 15 per cent of orange oil in an emulsion; 0.50 per cent of gelatin, 20 per cent of orange oil; and 1.00 per cent of gelatin, 30 per cent of oil. When these concentrations were exceeded, emulsification was incomplete and there was a tendency for the emulsion to gelatinize and break. Best results were obtained by adding the oil to the dispersion medium in portions of 5 per cent a t a time and homogenizing after each addition of oil. As the concentration of the oil phase increased, the emulsions became more viscous and difficult to homogenize. The results of this part of the work indicate that the relationship between the amount of dispersed phase and the quantity of peptizing agent required for stability is not directly proportional, but the ratio of peptizing agent to dispersed phase increases as the concentration of the oil is increased.
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Properties of Emulsions
I n every instance the emulsions prepared in this investigation proved to be of the oil-in-water types. This was expected, since the peptizing agents employed were all watersoluble and oil-insoluble. Observations on viscosity and viscosity variations disclose that the viscosity of the emulsions varies with the nature and concentration of the peptizing agent employed, the concentration of the dispersed phase, and the percentage of sugar in the dispersion medium. An increase in any one or all of these factors will cause an increase in the viscosity of the emulsion produced. In some cases, notably orange emulsions of high oil content, high viscosity was accompanied with prolonged stability. On the other hand, a 5 per cent emulsion containing 0.05 per cent of gelatin showed a higher viscosity than a 5 per cent peppermint oil emulsion with the same amount of gelatin, but the peppermint emulsion retained stability twice as long as the orange emulsion. Furthermore, emulsions prepared with agar-agar or tragacanth as the peptizing agent were much more viscous than any in which gelatin or gum arabic was. used, but the stability of the former was poor while that of the latter was good. These findings indicate that high viscosity alone does not cause emulsification or account for stability, but is a favorable factor when other conditions are right. Stability towards Temperature Change, Acids, and Alkalies
I n order to determine the susceptibility of these emulsions to changes in temperature and acidity, a number of emulsions were subjected for 4 days to temperatures ranging from 0" to 90" C. Transparency was not much affected within a range of 5 degrees above or below 25" C., a t which temperature the refractive indices of the two phases were equalized, but below 20" or above 30" C. the emulsions gradually became opaque. The stability, however, was not affected over this temperature range, showing that the emulsions will stand up under any range of temperatures likely to be met in storage. A number of samples u-ere taken from the same orange emulsion, and t o them were added 0.03 per cent HCI, 0.05 per cent HC1, 0.59 per cent HC1, 0.05 per cent NaOH, and 0.08 per cent NaOH, respectively. The emulsions containing the alkali rapidly turned brown and broke down. The effect of the acid was not so pronounced, but when the samples began to break the rate of oil separation was proportional to the acidity. The conclusion deduced from these experiments is that a neutral or slightly acid medium is conducive to maximum stability of the emulsions. Alkali must be avoided, since sugars in alkaline solution oxidize rapidly with the formation of highly colored products. Furthermore, alkali tends to destroy the protective gelatin film around the dispersed oil particles. Transparent Emulsions of Essential Oils of High Refractive Index
In the preparation of transparent emulsions of orange, peppermint, and rose oils, no difficulty was experienced in adjusting the refractive index of the dispersion medium so that it was equal t o the refractive index of the oil under consideration. Furthermore, no trouble was experienced in passing the emulsions through the homogenizer, each one flowing freely and giving transparent emulsions of high quality. S o such satisfactory results were attained in adjusting refractive indices when an attempt was made to prepare emulsions of wintergreen, anise, and cinnamon oils. The high refractive indices of these oils require invert sugar solutions of unattainable concentrations to produce transparent emulsions. I n order to attain the high refractive index required for transparency, other dispersion mediums
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I,VDUSTRIAL AND EiVGINEERlNG CHEMISTRY
were tried. A 45 per cent solution of sugar in glycerol was prepared by heating glycerol and sucrose to 130" C. with 0.10 per cent of tartaric acid, and this was tried as the dispersion medium. The refractive index of this solution was 1.4960 a t 25"C., but its viscosity was so high that it stopped the homogenizer when an attempt was made to prepare a wintergreen emulsion. Since no satisfactory dispersion medium of high refractive index was obtained, it was decided to attempt to lower the refractive index of the oil phase by the addition of sufficient quantity of the ethyl esters of coconut oil, prepared by alcoholysis of coconut oil with ethyl alcohol. The essential oils and these esters are mutually soluble. By using a solution of 1 part of oil and 2 parts of ester it was possible to reduce the refractive indices of wintergreen, anise, and cinnamon oils low enough to permit the use of aqueous sugar solution of sufficiently low concentration t o pass through the homogenizer without difficulty. The results of this work have demonstrated that coconut oil ester is a satisfactory material for reducing the refractive index of any essential oil to a value low enough to permit the
5'01. 21, No. 9
use of concentrated aqueous sugar solution as the dispersion medium. Emulsions so prepared were satisfactory from the viewpoint of transparency and stability, but developed a pronounced coconut taste on standing. It is hoped that some other esters more permanent in character than those of coconut oil may serve the same purpose and not develop the objectionable taste on standing. Recommendations
It is recommended to employ 0.25 per cent of gelatin as the peptizing agent for emulsions up to 5 per cent by volume, in order to insure a long period of stability. For higher concentrations of oil, the amounts of gelatin specified in this paper for concentrated orange oil emulsions should be used. Preparation of terpeneless instead of straight oil emulsions is recommended in the case of oils of the terpene variety, such as orange, lemon, and lime. Terpeneless emulsions retain their flavor quality almost indefinitely owing to the removal of the terpenes, which oxidize and produce objectionable taste and odor.
Action of Iron Catalysts on Mixtures of Carbon Monoxide and Hydrogen' Abstract E t i e n n e Audibert a n d Andre Raineau Soc16T6 NaTIoNALE DE RECHERCHES SUR LE TRAITEMENT DES COMBUSTIBLES, VILLERS-SAINT-PAUL (OISE), FRANCE
ABATIER (3) and, more recently, Franz Fischer (2) have studied the catalytic action of the metals of the iron group on mixtures of carbon monoxide and hydrogen. The program of work of the SocibtB Nationale de Recherches has included a study of this catalysis, particularly with a view t o the possibility of its being used for the production of liquid organic products. The present paper is a report of preliminary experiments which, while not presenting a final solution of the problem, do show that this process holds considerable promise. There will be described: (1) The experiments which have led to a selection of the most promising catalysts, (2) the essential properties of these catalysts, (3) an attempt to analyze the mechanism of the catalysis and to discover its defects, (4) the results obtained by the two methods which have been thought most workable.
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Properties of Metallic Iron
In a previous report (1) it was stated that hydrogen a t 150 atmospheres pressure does not rapidly reduce the hydrate or oxide of iron to the metal when the temperature is below about 450" C. If an iron catalyst, whose reduction from the oxide has accordingly been carried out slowly, is used with a mixture of carbon monoxide and hydrogen a t a total pressure of 150 atmospheres, it is found that a reaction starts a t 250" C. with freshly prepared metal and a t 275-300" C. with metal that has been previously used. This reaction is strongly exothermic and the temperature in the catalyst chamber tends to rise rapidly. The following products are formed: Methane, carbon dioxide, and water according to the reactions: (!)
Abstracted from A n n . ofice natl. combuslibles 1 Received May 6, 1929. liquides, 1988, No. 3, by Daviq F. Smith, Pittsburgh Experiment Station, U. S. Bureau of Mines, Pittsburgh, Pa.
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CO 3H2 CHI H?O (1) 2CO 2H2 CHa COz (2) I n the resulting gas the ratio of carbon dioxide to water varies with the composition of the initial gas, the time of contact, and the temperature of the catalyst. (2) Organic acids, principally or exclusively formic acid, in small quantities not exceeding 0.5 per cent of the weight of the water. The formic acid is quite possibly formed by a secondary reaction between water and carbon monoxide. (3) Carbon, according to the reaction 2 c o +c COL (3) Other things being equal, the speed of this reaction varies with the partial pressure of carbon monoxide and with the catalyst temperature.
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It is thus concluded that iron prepared by reduction from the oxide does not induce the formation of liquid organic products in a mixture of carbon monoxide and hydrogen a t 150 atmospheres pressure. Properties of Ferric Oxide
When ferric oxide is used in place of metallic iron, a reaction is again noticed in a mixture of carbon monoxide and hydrogen when the temperature reaches 250" C. However, if the catalyst is well cooled to avoid overheating, a t low space velocities not only methane, carbon dioxide, and water, but also liquid organic products are formed. The yield of these liquid organic products, however, rapidly decreases to zero as the oxide is reduced and only methane, carbon dioxide, water, and eventually carbon are formed. Properties of Iron-Alkali Catalysts
Following the work of Fischer, the effect of alkalizing the iron catalyst was determined. To precipitated iron hydroxide were added 2 parts of potassium carbonate to 98 parts of anhydrous ferric oxide. The resulting mixture
