Flow of Petroleum Lubricating Greases Dependence of Apparent Viscosity on Temperature, Rate of Shear, Oil Viscosity, and Soap Content M. H. ARVESON,Standard Oil Company (Indiana), Whiting, Ind.
T
HE first a r t i c l e in this Petroleum lubricating greases are dispensed and the oil in the grease. The series (1) described the following should be noted: (1) and used as lubricants under a variety of condiArveson constant-shear The plot is logarithmic; (2) the tions in which the factors determining the flow viscometer and presented data most important factor in detercharacteristics are of primary importance. o b t a i n e d o n s e v e r a l petromining the apparent visoosity of l e u m l u b r i c a t i n g greases at Data have been obtained at 7 7 O , 50", 25", and the greade a t very high rates of 77" F. (25" C.) in the form of shear is the viscosity of the oil; 0' F. on a variety of greases using the constantapparent v i s c o s i t y us. rate of (3) there is a similarity in the shear viscometer (1). shear d i a g r a m s . These diashape of the curves; and (4)the A l l of the data on greases containing calcium grams show clearly that: (1) percentage change in apparent mixed-fatty-acid soap have been correlated into The apparent viscosity of greases viscosity with change in temone general curve, in which the viscosity of the decreases with increasing perature decreases with decreasr a t e s of s h e a r i n a m a n n e r ing rates of shear. oil in the grease at the temperature in question, characteristic of the particular Figure 1 shows t h a t a t a the soap factor K (determined primarily by the soap used, approaching in the rate of shear of 0.1 reciprocal soap content), and the rate of shear are the limit a value higher than but of second, the increase in apparent primary factors determining the apparent visthe same order of magnitude as viscosity between 77" and 0" cosity of the grease. A relatively small correcthe oil in the grease. (2) At F. is approximately 6 fold; a t any given rate of shear the ap300 seconds-' the increase is 64 tion is required f o r the effect of temperature on parent viscosity increases with fold while the oil in the grease the soap factor. The agreement between the increasing soap content. increases 132 fold. point data and the general curve is shown in the It is the purpose of this paper The literature contains several jgures. t o present d a t a , similar t o references to the i m p r o v e A mechanistic conception of grease structure that p r e v i o u s l y presented, to ment in viscosity-temperature which has been added another characteristics of l i q u i d s b y and its behavior during flow is presented. The important variable, t e m p e r a the addition of small amounts inability of Bingham's equation to apply to the ture, and to present a correlaof c e r t a i n s u b s t a n c e s . An data is demonstrated. tion of all the data obtained on example is the addition of 0.1 commercial greases containing to 1 per cent of rubbcr to mincalcium mixed-fatty-acid soap. era1 oil. Instruments commonly used in measuring visAs previously stated, the apparent viscosity is that figure cosity operate a t variable, but still iow rates of shear. It calculated from Poiseuille's equation : should be apparent from the above data, where the addition of about 4 per cent calcium soap lowered the viscosity change PR between 77" and 0" F. from 132 to 6 fold, that the addition 2L F -nPR' =-of very small amounts of certain substances, plastic in them8LV/t 4V/t -- B selves, to liquids may cause very marked effects of this sort. TR8 Since this addition produces a substance which is no longer where 7 = apparent viscosity, poises P = pressure, dynes/sq. cm. a true liquid, extreme caution should be taken when attemptR = radius of capillary, cm. ing to interpret data obtained with conventional instruments L = length of capillary, cm. on such mixtures. For example, Saybolt data a t 1bO" and V / t = rate of efflux, cc./second 210' F. cannot be safely extrapolated, on the A. S. T. M. visF = stress, dynes/sq. om. cosity-temperature chart for hydrocarbon oils, to obtain the S = rate of shear, seconds-' Subscripts a and Q refer to grease, and subscript o refers to the viscosity of such mixtures at 0" and 300" F. Further, the oil in the grease. conventional instruments will not give a measure of the visThere seems to be some disagreement as to what is the true cosity of these mixtures at the high rates of shear involved value for rate of shear in capillaries when plastics are involved; in fluid film lubrication. therefore, to avoid confusion, the definition of rate of shear GRAPHICAL ANALYSISOF DATAON CALCIUM MIXED-FATTYwill be considered as: ACID SOAP GREaSES S = 4Vjt - seconds-', while stress is F = - dynes/sq. cm. It has been previously indicated that there should be some r R3 general relationship which governs the flow for greases made Low rates of shear are involved in dispensing of lubricants, from the same type of soap, at least when the same general approximately 0.1 to 1000 reciprocal seconds, while leakage method of manufacture is used. from housings and feeding from boxes and cups involves an When the data at three temperatures 77", 25", and 0" F. even lower range. Fluid film lubrication involves rates of on greases VI11 and IX became available, a study was started shear from 10,000 reciprocal seconds to indefinitely large which will be described in the order of the development. values. The soap content of both greases was 4.3 per cent and the oil Figure 1 gives a typical set of data, an apparent viscosity viscosities were 2.61 and 9.69 poises at 77" F. us. rate of shear diagram with three isotherms for the grease After plotting the data in several different ways, it was
if
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d i s c o v e r e d that, if Figure 5 shows the agreement that is obv o / q o was plotted as a function of q.S on tained for greases X logarithmic paper, all a n d XI when t h e points fell in a definite v a l u e f o r K is obnarrow band. Better tained from Figure 3, agreement w a s o b knowing the soap cont a i n e d , however, if tent f r o m analysis. s e p a r a t e isotherms The data for 50" F. were d r a w n . T h e also agree satisfaccurves (isotherms) retorily with this quired o n l y a slight g e n e r a l curve. It additional horizontal was indicated above shift to superimpose. that additional shifts Thus, once the effect would be required to of temperature on oil superimpose t h e viscosity is taken into c u r v e s f o r 25" and account in the O O F . , upon the 77°F. manner i n d i c a t ed , curve. This shift is only a slight addit h e e q u i v a l e n t of tional correction is required to draw one curve which will multiplying the value of K by 1.5, thus: probably apply to all greases containing 4.3 per cent of this Kii = K ~ = o K from greases I to VI K25 = 1.5 X K v particular soap. K O = 1.5 X Kib The data on grease X were treated similarly (soap content 8.5 per cent, oil viscosity 0.25 at 77" F.), and the horizontal This change in the value of K for the lower temperatures shift required to superimpose the curves was found to be the was made, and the data for 25" and 0 " F. were placed in same for the same temperature changes as for greases VI11 Figure 5 . The values for K and the viscosity of the oil used and IX. in the calculations are given in the tabulation on Figure 5 . Figure 2 is a plot of apparent viscosity us. rate of shear Exactly the same general curve is reproduced in Figure 6. for a series of greases in which the oil viscosity and the tem- The data for greases VI11 and IX are shown by the points. perature of measurement are constant and t h e soap content The best value for K for the 77" F. data was taken arbiis the parameter. Using the curve for grease I as a reference trarily, and this value was multiplied by the factors precurve, the horizontal shift required to superimpose each of viously given for the lower temperatures. The value of K the curves was determined by averaging the shift required for 77" F. used was equivalent to 4.4 per cent soap according a t a series of fixed apparent viscosities. The values obtained to Figure 3. (Later precision analyses of these two greases were plotted against the soap percentage of various greases. gave check values of 4.3 per cent.) These data are shown in Figure 3, where the actual value of The data for grease XI1 were fitted to the general curve the shift required is plotted against the percentage of soap in a somewhat different manner and the results are shown on logarithmic scales. The symbol, K , has been assigned in Figure 7 . Knowing the value of T Q / q o for each point, to this factor. It was interesting that a straight line was the corresponding value of ooS/K was read from the general obtained as the best curve through these points. curve. The value of qoS is known from the original data. The smooth-curve values of K were read for the various By dividing the known value of qoS by the value of q,S/K greases from Figure 3. The values of the expressions obtained from the general curve, the value of K for each q,/qo and qoS/K were calculated from the smooth-curve point required to fit the general curve was obtained. The values obtained from Figure 2, and a curve was drawn for mean value of K for each temperature series (rate of shear these data. being the only variable in each of these series) was deterFigure 4 shows the resultant general curve with the points mined. Using this value of K , the values of the expression for the original data on greases I to VI. The values of K v,S/K were calculated for each point and the data Dlaced on used were the smoothFigure 7 toshow the curve values of Figagreement with the ure 3. It a p p e a r s general curve. that a f a i r l y satisThe reason for this factory general curve procedure w a s t h a t has been o b t a i n e d the soap content of which will fit all of this g r e a s e was not these data. T h e known e x a c t l y but values of K in Figure was supposed to be 3 are specific to 77" between 10 and 11 per F. f o r t h e calcium cent. The value of mixed-fatty-acid soap K obtained from these of greases I to VI. d a t a a t 77" F. i s If the relation is equivalent to 11.7 per general f o r g r e a s e cent soap according containing calcium to Figure 3. mixed - f a t t y - a c i d F i g u r e 8 shows soap, the data at 77" variation of the ratio, F. for greases VI11 to K a t the desired temXI1 s h o u l d fall on perature to K a t 77" FIGURE2. APPARENTVISCOSITY us. RATEOF SHEARDIAGRAM FOR SERIES this curve. OF CUP GREASES F., with temperature.
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SIGNIFICANCE OF SOAP FACTOR K
SOAP
CONTENT-%
FIGURE3. SOAPFACTOR, K , FOR 77’ F. us. SOAP CONTENT FOR GREASES CONTAININGCALCIUM MIXEDFATTY-ACID SOAP
K has been shown to be a function of the concentration of soap in the grease and to vary somewhat with temperature. Further, the absolute value of this factor cannot be determined directly. The expression q,/q. is obviously dimensionless, and the dimensions of the product q,S are those of stress in the centimeter-gram-second system. Therefore, if the absolute value of K were known, it would necessarily have the dimensions of stress in order that only two dimensionless groups exist. It is suggested that the factor K is related to the elastic properties of the grease and that its absolute value may correspond to the theoretical yield value, which Bingham (2) and others have promoted, and which does not appear to be directly measurable. The general curve (Figure 4, etc.) appears to be approaching a line with a slope of -1. If this is assumed to be true, it can be shown that, as the expression q,S/K approaches zero, the stress required approaches the value K , times a constant (the factor for converting the units of K to the centimeter-gram-second system). Thus as o,S/K 1 0, FG A aK; then by definition aK is the “yield value,” and’ this yield value is determined by the concentration of soap and the temperature, and is independent of the oil viscosity. Figures 2 and 3 show that, as the soap content increases, the value of K (and therefore the stress required to force the grease through the capillary) increases. K then may be considered as a measure of the resistance of the soap structure to deformation at the particular concentration and temperature in question. If the straight line through the points shown in Figure 3 is extrapolated, the line intersects the 100 per cent soap ordinate at K = 1.6 X lo6. If the conversion factor is 10, the value becomes 1.6 X lo7 dynes per sq. cm. This extreme extrapolation is not justified because of the dependence of the system on the presence of the oil phase. However, the value obtained is believed to be a fair qualitative indication of the modulus of elasticity of the soap, still in a state of dispersion. Since completing this work, it has been noted that Poole (4), in making measurements of elasticity of gelatin gels, obtained nearly straight lines when log elasticity (Young’s modulus) for the gel was plotted against the log concentration (same coordinates as Figure 3) and also found similar variations with temperature.
The d points indicate those calculated from the data on grease XII, and the 0 and points indicate the values used in plotting greases VI11 and I X and grease X, respectively, on the general curve. The curves of Figures 4 to 7 are identical, and the points indicating the actual data are merely superimposed to show the agreement. In the case of both Figures 4 and 5 there is a trend away from the curve a t low values of qoS/K. The general curve has been drawn a t the upper end, in the manner indicated, on a more or less arbitrary basis, since the break away from this curve between the various greases is not a t all in agreement. Other factors are believed to enter the consideration in this region. These points, which in all cases occur at very low values of the product q,S, are in many cases of low precision (pressure, just a few millimeters of mercury). In any event, there is no doubt that at the low values of the expression q4S/K there is a true divergence from the general curve that has been drawn. I n this region slippage in the capillary may have occurred. The statement made in the previous paper (1) to the effect that no slippage occurred in the capillaries in any region where it was possible to check, still holds. Slippage is most frequently discussed in the literature in connection with viscosity measurements of rather highly plastic materials where water is the continuous phase. Water has a viscosity of the order of magnitude of one twenty-fifth of t h e lo we s t oil viscosity recorded in any of this work. A decrease in the viscosity of the continuous phase and a n i n c r e a s e in the c o n c e n t r a t i o n of “solid” i n g r e d i e n t both tend to increase the rate of shear at which slippage would be expected to take place. FIGURE 4. GENERAL CURVEWITH POINTS FROM DATAAT 77’ F. ON GREASESI
+
TO
VI
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APPLICATION OF THE GENERAL CURVE To illustrate the interrelations of variables, assume t h a t a grease, having an oil v i s c o s i t y and soap factor of 10 and 10, respectively, is being sheared a t a rate of 0.1 (condition A). It may be found from the general curve that q G / q o under these conditions is 255; that by arithmetic qQ, the apparent viscosity of I t h e g r e a s e , is 2550 .WWI .mol .oc I .o I I I 10 100 1000 I0,ooo lDqo00 poises; and that the stress, Fo, is 255 FIGURE 5. GENERALCURVE WITH POINTS FROM DATAON GREASES X AND XI dynes per sq; cm. It is obvious that decreasing the value of K from 10 to 1, in- soaps, are run a t the same temperature, that grease having creasing the rate of shear from 0.1 to 1, or increasing the the flattest viscosity us. rate of shear diagram (log-log) will oil viscosity from 10 to 100, will change the value of the exhibit the largest percentage change in viscosity with temexpression q,S/K ten fold from 0.1 to the value 1 (condi- perature a t any given rate of shear, assuming that soap factor K varies with temperature in approximately the same tion B). From the general curve it is learned that the value of manner in both cases. Since it appears that, in general, soap factor K does not vary markedly with the temperature, ~ G / T . is 40 under condition B (q.S/K = 1). Then with other things held constant as in condition A ( q Q -- 2550, FQ = the above statement is good to the first approximation, for the following reasons: It was stated that the same oil would 255), but with: be used in both cases and that we would assume that K qo increased from 10 t o 100, 7~ = 4000,FG = 400 (1) would vary the same in both cases with temperature. In a or S increased from 0.1 to 1, 7Q = 400, FQ = 400 (2) logarithmic plot of the data, both greases would appear in or K decreased from 10 to 1, 70 = 400, FQ = 40 (3) the same relative position whether the plot was qol vs. S diaIt is important to understand clearly that changing the rate gram or a qcr/qdvs. qoS/K diagram. Therefore, any deof shear and changing the viscosity of the oil in a grease, crease in temperature would merely shift the line of constant either by temperature change (neglecting effect of tempera- shear to the right by the same amount for both greases on ture on K ) or change in oil, by the same ratio result in the the latter diagram. The grease having the steeper curve same change in stress or pressure required to force the grease would have the ratio qol/qodecrease most and therefore have through a given capillary. The directions of change are the the least increase in the apparent viscosity of the grease. It has been previously shown that those greases exhibiting same. steep logarithmic viscosity-shear diagrams were the most tender. It seems odd that tenderness and change of visGREASE FROM OTHER SOAPS cosity with temperature should be so related. It has been What may be said relative to grease made from other known that greases containing soda tallow soap, which are soaps? If two greases containing the same oil, but different tough and gutty, containing the same oil as a similar calcium mixed- f a t t y a c i d grease, are not nearly as satisfactory as the calcium soap greases for low-temperature use. The prediction from this toughness is t h a t t h e s o d a t a l l o w s o a p transmission grease would have a flat apparent viscosity us. rate of s h e a r diagram and therefore would exhibit larger changes i n a p p a r e n t viscosity with temperat u r e t h a n calcium soap greases. Experimentally this has been found to be FOR GREASES VI11 ANJI IX true. FIGURE 6. GENERALCURVEWITH POINTS
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excess of t h a t required in the absence of the bristles. G R E A S E XI1 CAPILLARY N O 3 This system would _ SYM T T & require that a mini77 221 0.88 m u m s t r e s s be a p 0 50 274 2.25 plied before any flow A 25 366 7.20 c o 5 4 8 37.2 can take place. The derived curve in Figure 10 illustrates how the general curve, as d r a w n , is approaching a constant stress with decreasing rates of shear, but, a s previously indicated, flow exists a t s t i l l lower stresses. Note the d e v i a t i o n Iooool .OOOl .001 .o I I 1 IO IO0 1000 lO,Ow, 100,000 of p o i n t s a t low FIGURE 7. GENERAL CURVEWITH POINTS FOR GREASE XI1 v a l u e s of mS/K in Figures 4 and 5. CONCEPT OF GREASE STRUCTURE The soap particles are undoubtedly quite irregular in shape, and, therefore, forces perpendicular to the plane of the paper To augment the views on grease structure presented in the in Figure 9 will exist during flow. This would permit reprevious paper (I), $he author wishes to present a highly lease of the bristles or springs occasionally before the maxisimplified mechanistic conception of grease structure and mum deflection of view 1 is reached. Bombardment of the its behavior during flow. particles by molecules (Brownian movement) might also aid The flow of grease, in a capillary for example, consists of in the release of the bristles before maximum deflection. the laminar flow of true liquids in which a maze of small Further, it would be expected that the relative frequency solid bodies of various shapes and sizes interferes with the of this type of release would decrease as the velocity of plane flow. In order that flow exist, these bodies must undergo C increases, and that it would be of higher order at low values elastic deformation. The conditions of flow in the differen- for the viscosity of the medium. Obviously, increasing the tial element may be visualized as similar to two continuous number of bristles in a unit length and/or the degree of overbrushes with bristles overlapping, one moving with respect lapping will increase the resistance. to the other, the space between being filled with a viscous medium. The bristles represent the projections of the maze of soap particles in the grease which interfere with normal viscous flow, and the viscous medium represents the oil. Figure 9, view 0 represents a finite section through the grease during flow made by a plane normal to the planes of constant velocity and parallel with the direction of flow. Lines A to D represent several planes of constant velocity wherein B is moving in respect to A , C in respect to B , and D in respect to C. E and F represent any two bristles associated with planes B and C, respectively. Views 1 to 8 represent only the small area between planes B and C, with bristles E and F only, reproduced. In the absence of any obstructions, normal viscous flow will exist. View 1 represents the conditions when plane C is moving a t a very low rate in respect to plane B. The positions of E and F represented by the solid lines are, as indicated, those of maximum deflection. The next instant release occurs, and, before contact is made 80 70 80 SO 40 30 20 10 0 -10 with the next springs or bristles (not shown), bristles E and F return to the position of minimum deflection indicated by OF TEMPERATURE ON SOAP FIGURE 8. EFFECT the dotted lines. Views 1 to 8 show the effect of progresFACTOR sively increasing velocities of plane B. At first thought it might be felt that the position of maximum deflection a t all In the above model, force on plane Cis analogous to the velocities would be as illustrated in view 1, while the ministress in grease flow, velocity to the rate of shear, and force mum deflection (dotted lines) would progressively increase, until a t very high velocities the position of minimum deflec- divided by the velocity to the apparent viscosity. The above model can represent only a first approximation tion would approach the position of maximum deflection. More careful review of the system will show that even greater of the conditions existing in the differential element in a maximum deflection than in view 1 will result from stresses grease during flow but, in spite of this, agrees qualitatively transmitted by the viscous medium. In either case the with the following points noted in the behavior of greases limiting minimum deflection at high velocity is the maximum during flow: deflection. As velocity approaches infinity, the bristles are 1. Apparent viscosity decreases with increasing rate of shear. laid down against the planes B and C, and the force required 2. Apparent viscosity increases with increasing soap content. 3. Apparent viscosity approaches a limiting value at high to give C a finite, but very high, velocity is only slightly in 0
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rates of shear, higher than, but of the same order of magnitude as, that of the oil in the grease. 4. With decreasing rates of shear the stress tends t o approach a constant value, but 6. A departure of points from the general curve at very low value rates of shear (also a t l o w values of q&'/K in Figures 4 a n d 5 ) exists a n d c a n be explained by a vibrational effect a n d mu1t i di r ec t i on a 1 motion.
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values for f a r e 40, 65, and 100. Group 2 was drawn because it is believed that the derived curve is approaching a value for l/p nearer to 2.61 (qo) than 3.4. It should be clear, therefore, that Bingham's equation as it stands cannot be made to fit the curves for any of the greases reported in this paper.
CONCLUSIONS
1. A curve has been presented covering the flow characteristics of greases prepared from calcium mixed-fattyacid soap. In addition to the rate of shear, the viscosity of The above conception possesses the oil and a new factor, K ,the soap factor, are found to depoints of similarity with both Poole termine the apparent viscosity of the grease. (4) and Green (3). '-4 3 2. Soap factor K has the dimensions of stress and is a measure of the resistance of the soap structure to deformaEQUATION TO FIT GENERAL CURVE tion. It depends upon the concentration of soap and the Figure 10 illustrates the inability temperature, and curves are presented showing these relaof B i n g h a m ' s e q u a t i o n (6) t o tions. The temperature determines the values of the oil apply to the general curve derived viscosity (qo) and the soap factpr (K) used in the general graphically for petroleum lubricat- curve. 3. The agreement of the general curve with a large ing greases c o n t a i n i n g calcium soap. The conventional variables number of point data is adequately demonstrated. 4. It is believed that a general curve, using the same a r e used-rate of s h e a r a s t h e o r d i n a t e a n d s t r e s s as the ab- variables, exists for each kind of soap. 5. It is shown that Bingham's equation cannot be used scissa. Logaritbmic scales are necesto represent the data satisfactorily. sary. 6. A mechanistic conception of grease structure and its Using t h e g e n e r a l curve, the S vs. FG curve for a g r e a s e h a v i n g behavior during flow, which agrees qualitatively with the vo = 2.6 and K = 4.95 has been data, is presented. calculated. This derived curve and a line 1000( f o r t h e oil i n t h e grease a r e s h o w n i n both groups of curves. 1 1001 The original d a t a on 8 grease IX are shown i n g r o u p 2 t o illusFIGURE9. GREASE t r a t e t h e agreement IC( of direct data with the BEHAVIOR DURING derived curve. FLOW Bingham's equation (9) for capillary tubes, 10
--e-
89 I
may be rearranged thus,
and simplified for our purpose thus,
(i)
.S = F
-j
where the constant (l/p) may be called the reciprocal of the mobility but has the same dimensions as viscosity, q, and the constant, f, is the yield value in dynes per sq. cm. Group 1 shows lines f o r a common value for l/p of 3.4, which brings these lines into c o i n c i d e n c e with the general curve at S = 100,000, and with values for f of 40, 65, and 100, which bring the three l i n e s o n e i t h e r side of the general c u r v e . a t S = 0.0001. Group 2 indicates similarly the lines f r o m Bingham's e q u a t i o n w h e n 1 / p = 2.61 a n d
.O
.oc
.OOOl
I 100
-]r((CROUP 1000
2)10,000
I 100,000
Ipoqooo
FIGURE 10. APPLICATION OF BINGHAM'S EQUATION TO THE GENERAL CURVE FOR GREASES CONTAINING CALCIUM MIXED-FATTY-ACID SOAP
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7. It appears that the relations involved in the general Curve cannot be expressed in the form of a simple equation.
LITERATURE CITED (1) h e s o n , IND. Ewo. CHEM.,24, 71 (1932). (2) Bingham,“Fluidity and Plasticity,” McGraw-Hill, NewYork, 1922.
Vol. 26, No. 6
(3) Green, IND.ENQ.CHEM., 15, 122 (1923). (4)Pool’%Trans. F a r a h f fS0C.s 21, l l k 3 7 , esPecidlY 130 (1925).
RZICEIYED September 29, 1933. Presented before the Division of Petroleum Chemistry at the 86th Meeting of the American Chemical Society, Chicago, I11., September 10 to 15s 1933.
Florida Grapefruit Oil Bureau of Chemistry
E. K. NELSON AND H. H. MOTTERN a n d Soils, U. S. Department of Agriculture,
T
Washington,
D. C.
HE complete utilization the oil itself and of the sepaFlorida grapefruit peel oil, prepared by pressof t h e peel f r o m t h e rated limonene as reported by ing the peel between rolls and separating the g r a p e f r u i t c a n n e d in this author do not agree a n d oil in a centrifugal separator, contains approxiFlorida involves the recovery a r e m a n i f e s t l y f a r too low. mately 90 per cent limonene, 2 to 3 per cent of grapefruit peel oil. T h e d e s i r a b i l i t y of a m o r e oxygenated volatile constituents and sesquiterA p p r o x i m a t e l y 2.5 million thorough investigation of t h i boxes or 100,000 tons of grapeoil is therefore apparent. penes, and 7 to 8 per cent waxy materials. fruit a r e p r o c e s s e d annually The oil used in the investigaThe following other constituents are identified: by F l o r i d a canners. The intion r e p o r t e d here was manuOctyl and decyl aldehydes, geraniol and octyl dustry is sufficiently concenfactured by the Pipkin oil maalcohol (bothfree and as acetates), cadinene, and trated so that at least half the chine in which the peel is passed small quantities of citral and methyl anthranilate. peel is readily available for the through knurled rolls under presm a n u f a c t u r e of oil. On the sure, a n d t h e oil c o n t a i n e d Examination f o r pinene, terpineol, and decyl basis of a commercial yield of in the emulsion coming from alcohol gives negative results, though a small o n e p o u n d p e r t o n of fruit, the rolls is separated in a highquantity of nonyl alcohol may be present. 50,000 pounds of oil could readily speed c e n t r i f u g a l separator. Octylic and decylic acids are present in small b e p r o d u c e d if t h e m a r k e t A small machine was used i n quantities, probably as esters. should call for this quantity. the preparation of the laboraThis oil is new t o commerce tory sample. The commercial Analyses failed to show any marked differbut has recently won favor in samples were taken as the oil ences between oils from hot peel and f r o m cold England, where.it is used for came from the centrifuge in the peel. Experiments on the preparation of terplant. Although the fruit used flavoring beverages. peneless grapefruit oil are described. may have been of d i f f e r e n t Previous l i g h t s u p p l i e s of varieties, it was p r i n c i p a l l y grapefruit oil have come from 8p& and the Union of South Africa, but, since the United Florida Common or Duncan type grapefruit. Analyses were made of seven samples of grapefruit oil States produces approximately 90 per cent of the world’s supply of grapefruit, the utilization of cull. and surplus fruit from different runs of peel, some of which were extracted in the manufacture of by-products becomes essentially an from hot peel and some from cold. No great difference was American industry. Commercial manufacture of the oil in found in the results (Table I). Florida started in the spring of 1933. Further developTABLE I. ANALYSESOF FLORIDA GRAPEFRUIT OILS ments toward quantity production depend upon market deOPTICAL I N D E X O F ALDZIHYDE mand. A B OCTYL SP.GB., ROTATION, RH~PBACTION, Two general methods are employed to remove peel from 80UBCZI O F SAXPLE AND D X C Y L ~ n y sa. d% Degrees % grapefruit before canning. The one most commonly used cold peel 0.8562 f93.33 1.4758 1.68 is to put the fruit through a bath of water at 93” to 100” C. Laboratory 1.4753 Commercial cold peel 0.8563 92.88 1.60 1.4760 1.74 hot peel 0.8579 92.90 until the skin puffs and is easily removed. This is called the Commercial 1.4758 1.68 Commercial hot wee1 0.8572 92.96 “hot peel’’ method. A second method, less used now than Commercial hot bee1 1.4758 1.71 0.8558 93.68 1.4760 1.62 hot peel 0.8561 93.83 formerly, is the knife or cold peel process in which the peel is Commercial 1.4760 Commercial hot peel 0.8543 93.35 1.84 cut away with a sharp knife. The first method results in a Average 0.8563 93.28 1.4758 1.67 warm peel for the oil machine while the latter gives a cold U. 9. P.method for citral. peel. There is also available a quantity of cold peel from fruit extracted for juice. EXPERIMENTAL PROCEDURE Grapefruit oil as prepared by the Pipkin process ( I ) is an For the investigation of the constituents of grapefruit oil, amber colored liquid of pleasing odor resembling both orange and lemon oils. On standing or chilling, a yellowish to 16 liters (13,700grams) of the oil were freed from most of the brown flocculent precipitate forms which may entirely dis- limonene by distilling a t 10 mm. Fourteen liters (11,900 grams) of limonene containing aldehydes were obtained. appear upon warming. The only investigation of the composition of grapefruit oil Limonene was characterized by the preparation of the tetradescribed in the latest edition of “Die aetherischen Oele” bromide, melting point 104.5’ C. The residual oil was disis that of Zoller ( 5 ) . His results are open t o criticism because tilled with steam in order to separate the volatile ingredients of the small quantity of material employed (100 grams of from the fatty and waxy constituents. Seven hundred steam-distilled oil), rendering it impossible to obtain exact and twenty grams of volatile material were obtained, from identification of all the constituents. The optical rotation of which a further quantity of limonene was removed by dis0
