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
510
ACKNOWLEDGMENT
( A S ) T = change in entropy of vapor at constant temperature,
The authors wish to express their appreciation to K. R. Ericson, B.B. Bohrer, and H. W. Rogers for their aid in obtaining and compiling the data presented in this study; t o C. A. Porter of The Pure Oil Go. and L. F. Stutzman and G. M. Brown of Northwestern University for their suggestions and encouragement in presenting this work; and to The Pure Oil Co. for permission to publish this report. NOMENCLATURE
C'i = heat capacity a t zero pressure, B.t.u. per
R.
temperature T , B.t.u. per pound ( ~ H ) T= change in enthalpy of vapor a t constant temperature from the datum pressure of 2.46 pounds per square inch absolute to pressure P , B.t.u. per pound H L ~= enthalpy of saturated liquid a t datum temperature, B.t.u. per pound (assumed to be 0 a t 32" F.) ( A H ) L V ~= latent heat of vaporization a t 32" F., B.t.u. per pound HT.P = enthalpy of vapor a t temperature T and pressure P , B.t.u.- per pound = H L ~ (AH)Lv., (AH)P (AH)T P = absolute messure. uounds ver sauare inch ( & S ) p = change in entcopy of-the capor a t constant datum pressure from datum temperatureo of 491.7" R. to temperatmureT , B.t.u. per pound, R.
+
from the datum pressure of 2.46 pounds per sqyaie inch absolute to pressure P, B.t.u. per pound, R S L ~ = entropy of saturattd liquid a t datum temperatures, B.t.u. per pound, R. (assumed to be 0 a t 32" F.) ( A S ) L V ~= entropy of vaporization a t 32" F., B.t.u. per pound, ' R. S T P = entropy of vapor a t temperature T and pressure I', B.t.u. per pound, R. = S L ~ ( AS)LVO ( L$')P ( AS)T 2' = absolute temperature, R. T7 = specific volume, cubic feet per pound
+
pound,
( A H ) p = change in enthalpy of vapor a t constant datum preasure from the datum temperature of 491.7' R. to
+
Vol. 43, No. 2
+
+
O
+
LITERATURE CITED
(1) Beattio, J. A . , and Bridgeman, 0. C., Proc. Am. Acad. Arta S c i . , 6 3 , 2 2 9 (1928).
12) Clapeyron, P. B. E.. J . &cole polytech., 14, 143 (1834). (3) Cross, P. C., J . Chem. Phys., 3, 825 (1936). (4) Hodgman, C.D., ed., "Handhook of Chemistry and Physics." 30th ed., Cleveland, Ohio, Chemical Rubber Publishing C o , , 1948. (5) International Critical Tables, New York, McGraw-Hill Hook Co., 1927. (6) Kolley, K. K., U. S.Bur. Mines, Bull. 383 (1935). ( 7 ) Maron. R. H., and Turnbull, D., IND. ENG. CHEX.,33, 408 (1941). (8) Spencer, 11. M., and Flannagan, G. RI., J . Am. Chem. Soc., 64, 2511 (1942).
du, G.-J., IND.ENG.CHEM.,38, 923 (1946) (10) Watson, K. M., I h i d . , 35, 398 (1943). (9)
RECEIVED ,July 14, 1950.
rolysis of Te er
Qp
B
AUGUST STURZENEGGER' AND HERMANN STURM Friedrich Steinfels A k t . - G e s . , Zurich, Switz;erland T h e cleavage of fats a t temperatures above 220" C. is continually assuming greater technical importance. Furthermore, in this temperature range, the solubility relationships of fat and water are considerably different from those pertaining to the temperatures usually employed. There are no published data on reaction time and mechanism of autoclave fat splitting. The hydrolysis of three different types of fats has been investigated a t 225' to 280' C. and 30 to 70 atmospheres. A t 225" and 280' C. hydrolysis attains equilibrium after 2.5 hours and 0.5 hour, respectively, The presence of a
catalyst (zinc oxide) accelerates the reaction considerably. The reaction velocity is almost independent of the oil-water ratio as Lascaray (4, 5 ) has also found for the lower temperatures. The influence of the oil-water ratio on the degree of hydrolysis a t equilibrium was measured and the results agreed with calculations of Sturm and Frei (9). The reversibility of the process was demonstrated by hydrolysis and esterification. Fat splitting shows no heat of reaction between 150" and 280' C. These results might be helpful in the design of fat splitting equipment.
T
tially a homogeneous reaction occurring between fat and watt.r dissolved in the oil phase. Although all publications deal with the problem of fat splitting a t relatively low temperatures (up t o 220' C.), the cleavage of fats a t high temperatures assumes continually greater importance, and, further, a t very high temperatures the solubility relationships of fat and water are considerably different from those pertaining to the usually employed temperatures (6). Consequently, the study of the hydrolysis of fats in this region was undertaken. The investigation was carried out a t temperatures between 225 and 280' C. The objects were:
HERE are numerous theoretical and experimental investi-
gations of the splitting and hydrolysis of fats, which make it clear that the reaction proceeds stepwise from the triglyceride to fatty acid and glycerol through the di- and monoglycerides (a, 7, 8, 11-13). The reaction may thus be formulated as fo1lo-m:
C,H,(OCOR)s
TIOH
HOH
+ RCOOH P HOH + RCOOH eC3H,(OH)S + RCOOH
C,Hs(OH)(OCOIt)n
C,H,(OH)2(0COR)
where RCOOH represents any fatty acid and CsH5(OH),, glycerol. According to Lascaray ( 4 ) only a minor part of this splitting reaction occurs at the oil-water interface and hydrolysis is essenPresent address, Hoffmann-La Roche, Inc., Nutley, N. J.
1. Determination of the course of the fat cleavage reaction. 2. Measurement of the dependence of reaction velocity on temperature (temperature gradient).
February 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
3. Investigation of the influence of the oil-water ratio on the position of the hydrolysis equilibrium. 4. Determination of the dependence of the degree of hydrolysis on temperature. EXPERIMENTAL METHOD
The course of the fat splitting reaction was followed by removing samples at specific time intervals from a fat-water mixture held a t constant temperatures. Analyses gave the acid number and saponification number and hence the corresponding degree of hydrolysis.
8
Figure
1. Schematic of Apparatus
Drawing
I n evaluating the effect of temperature on the equilibrium point, it was important t o avoid disturbance of the equilibrium by premature sampling; therefore, the time t o reach equilibrium was determined in trial runs a t the appropriate temperature. The same conditions were used in determination of the dependence of degree of hydrolysis on the oil-water ratio. T o permit measurement of the high initial reaction velocities, an apparatus was devised for mixing the components under pressure at the reaction temperature, which was controlled t o *lo C. The samples were immediately chilled to -10" C. and time was measured t o the nearest second. The apparatus was nitrogen-filled. The amount of water vapor above the liquid phase was included in the estimation of hydrolysis water. All weighings were made to the nearest gram. APPARATUS *
xr
The electrically heated autoclave of 1-liter capacity was made of Type 316 stainless steel and designed for a maximum working pressure of 80 atmospheres. It was equipped with a stirrer and two valves for filling and emptying (Figure 1). . The exhaust valve was fitted with a chrome tube of 1.5-mm. bore reaching to the bottom of the autoclave. A stainless steel tube (150 cm. X 25 mm.) was screwed onto the second valve and fitted with a manometer at its upper end. A pressure capillary was screwed onto a threaded steel tube welded near this point. A thermometer-pocket was inserted in the lower third of the tube. As the lower end of the tube narrowed t o 2 mm., the fat could flow through this cone into the autoclave without blowback. The electric heating enabled a temperature of 250' C. t o be reached in 1.5 hours, and wrtst hermostatically controlled. All thermometers were calibrated against Anschutz thermometers. REACTION VELOCITY O F FAT HYDROLYSIS AS A FUNCTION O F TEMPERATURE
The experiments were carried out with beef tallow, peanut oil, and coconut oil, representing three different types of fats. Tables I, 11, and I11 give the properties of the fats.
511
OF BEEFTALLOW TABLE I. HYDROLYSIS
(Acid value, 5.5; saponification value, 195; iodine value, 46.5, distilled water, 70%) Reaction Time, i, Min. Acid Reaction Time, t , Min. Acid Interval Total Value Interval Total Value 279' = 1' C.; Vapor Pressure of Water, 63.3 Atrn: Working Pressure, 70 'Atrn. 1.00 14.0 1.00 2.00 22.5 1.00 33.4 3.05 1.05 44.0 4.05 1.00 57.7 5.05 1.00 97.8 8.07 3.02 125,3 11.05 2.98 147.2 3.00 14.05 171.1 5.00 19.05 179.0 24.05 5.00 180.7 29.05 5.00 181.9 34.05 5.00 180.8 39.05 5.00 179.8 54.05 15.00 239O t lo C.; Vapor Pressure of Water, 33.0 Atm.; Working Pressure, 38 Atm. 2.00 7.8 2.00 4.00 9.9 2.00 2.00 6.00 13.5 24.2 5.00 11.00 16.00 36.5 5.00 54.3 5.00 21.00 91.1 31.00 10.00 124.6 41.00 10.00 150.2 51.00 10.00 61.00 165.4 10.00 174.4 72.00 11.00 177.1 82.00 10.00 92.00 177.6 10.00 177.2 10.00 102.00 260° * l o C ' Vapor Pressure of Water, 46.3 Aim.; Working Pressure. 55 Atrn.; Catalyst. 0.2oJ, ZnO 1.00 11.2 1.00 2.00 20.2 1.00 45.9 1.00 3.00 121.9 6.00 3.00 167.4 11.00 5.00 177.9 5.00 16.00 183.1 21.00 5.00 183.1 31.00 10.00 181.9 36.00 5.00
260° = 1' C.; Vapor Pressure Workingof Water, 40.3 Atrn Pressure, 5 6 ',tm. ~ 1.00 1.00 7.1 1.00 2 00 9.4 11.1 1.00 3.00 14.2 1.00 4.00 27.6 3.00 7.00 58.0 5.00 12.00 10.02 22.02 136.9 162.2 5.02 27.04 175.2 5.02 32.06 180.4 5.00 37.00 181.3 5.00 42.06 182.0 5.00 47.06 182.1 5.00 52.00 180.6 5.00 57.06 180.7 5.00 62.06
.
.
224O + 2O C Vapor Pressure of Water, 25.i' Atm.: Working Pressure, 30 Atm. 3.00 3.00 8.7 6.00 3.00 10.7 21 .oo 20.3 15.00 16.00 45.3 37.00 76.8 51.00 14.00 66.00 15.00 111.8 81.07 139.7 15.07 96.00 159.9 14.93 170.9 15.00 111.00 177.8 126.00 15.00 181.0 142.00 16.00 182.7 156.00 14.00 180.9 181.00 25.00 180.3 196.00 15.00 260° il o C ' Vapor Pressure of Water, 46.3 A&: Working Pressure, 55 Atm.; Distilled Water, 150% 1.00 8.7 1.00 2.00 11.0 1.00 3.00 13.5 1 .oo 8.00 34.5 5.00 13.00 66.7 5.00 23.00 128.3 10.00 33.00 169.7 10.00 38.00 182.0 5.00 5.00 43.00 189.5 48.00 191.4 5.00 53.00 193.7 5.00 58.02 192.1 ,5,02
OF COCONUT OIL TABLE 11. HYDROLYSIS (Acid value, 2.8; saponjficstion value, 258; iodine value, 8.6; distilled water, 90%) Reaction Time, t , Min. Acid Rraotion Time, 1. Min. Acid Interval Total Value Interval Total Value
.
279' rh lo C.; Vapor Pressure of Water, 63.3 Atm.; Working Pressure, 70 Atm. 1.00 11.8 1 .oo 19.0 2.00 1.00 30.1 3.00 1.00 40.5 4.00 1.00 84.7 7.00 3 .OO 129.6 IO.00 3.00 169.2 13.00 3.00 213.2 18.00 5.00 233.0 23.00 5.00 236.0 28.00 5.00 238.8 33.00 5.00 235.7 38.00 5.00 236.6 43.00 5.00
260° * 1' C Vapor Pressure of Water, 40.3' Atrn.; Working Pressure, 55 Atm. 1 .oo 1 .oo 4.8 5.9 1.02 2.02 8.1 3.02 1 .oo 16.6 6.02 3.00 38.7 11.02 5.00 60.2 16.02 5.00 102.4 21.02 5.00 158.6 26.02 5.00 31.02 5.00 200.9 223.2 36.02 5.00 41.02 231.5 5.00 230.1 46.02 5,oo 236.2 51.02 5.00 235.1 56.02 5.00
240° f 1" C: Vapor Pressure of Water, 33.0' Atm.; Working Pressure, 38 Atm. 1.00 5.0 1.00 3.00 8.6 2.00 8.00 17.4 5.00 13.00 31.4 5.00 18.00 50.6 5.00 23.00 74.1 5.00 33.00 129.7 10.00 43.00 184.5 10.00 53.00 214.1 10.00 64.00 232.4 11.00 74.00 234.4 10.00 84.00 235.9 10.00 94.00 237.0 10.00 104.00 288.4 10.00
223O * lo C.; Vapor Pressure ;f Water, 28.1 Atrn.; Working Pressure. 30 Atm. 3.00 5.4 3.00 7.8 8.00 5.00 23.00 24.3 15.00 39.00 61.4 16.00 104.2 53.00 14.00 156.8 68.00 15.00 195,6 83.00 lij.00 221.1 98.00 15.00 230.2 113.00 15.00 232 0 128.00 15.00 235.6 158.00 30.00 173.00 234.3 15.00 238 1 16 00 188.00
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512
Vol. 43, No. 2
TABLE 111. HYDROLYSIS OF PEANUT OIL (Acid value, 0.28;saponification value, 187; iodine value, 89; distilled water, 50%) Reaction Time, t , Min, Acid Reaction Time, t , &fin. Acid Interval Total Value Interval Total Value
280' * '1 C
' Vapor Pressure of Working Pressure, 70 Atm.
Water, 6 3 . i ' Atm.;
5.18 4.25 3.10 2.92 3.03 4.75 4.00 5,42 5.08 5.15 5.30 5.60 5 08
5.18 9.43 12.53 15.45 18.48 23.23 27.83 33.25 38.33 43.48 48.78 54.38 59.46
* 1' C.; Vapor Pressure of Water, 46.3Atm.; Working Pressure, 55 Atm.; Distilled Water, 260'
49.0 92.8 107.1 138.0 151.2 163.5 164,4 169.8 167.9 168.9 169.7 170.7 167,s
.
* 1' C Vapor Pressure Water, 33.0'Atm.; Working Pressure, 38 Atm.
240'
2.18 3.00 6.00
4.98 5.00 5.28 9.98 10.00 10.00
10.03 10.02 10,02 9.98
2.18 5.18 10.18 15.16 20.16 25.44 35.42 45.42 55,42 65.45 75.47 85.49 95.47
13.7 22.6 46.0 63.3 81.1 101.9 131.1 149.8 158.0 163,5 165.2 166.4 168.0
0.88 1.93 3.11 6.07 8.87 11 .a4 16.81 21.88 26.87 31.90 36,93 41,92 46.97
14.3 21.2 33.4 53.4 73.0 89.8 106.8 126.8 143.9 152.8 158.5 160.2 162.3 162.8 163.0
.
* 1' C Vapor Pressure of Water, 25.i'Atm.; Working Pressure. 30 Atm.
224'
8.02 3.08 14.98 16.17 13.83 15,OO 15.00 15.12 14.91 30.00 15.02 29.98 45.00
Test for Reaction Order: Initial Acid Value, 50.7; 260° * 1' C.: Vapor- Pressure of Water, 46.3 Atm.; ,Working Pressure, 55 Atm.
0.88 1.05 1.18 2.96 2.80 2.97 4.97 5.07 4.99 503 5.03 4.99 5.05
45% 2.00 3.17 5.27 8.22 11.24 14.21 17.51 22.64 27.67 32.70 37.60 42.63 47.63 52.63 57.65
2.00 1.17 2.10 2.95 3.02 2.97 3.30 5.13 5.03 LO3 4.90 5.03 5.00 5.00 5.02
3.02 6.10 21.08 37.25 51.08 66.08 81.08 96.20 111.11 141.11 156.13 186.11 231.11
5.8 11.9 34.5 68.2 101.2 128.4 145,s 155.7 162.3 164.8 165.9 165.8 163.7 0
52.4 58.6 65.5 87.3 107.4 127.0 146.4 160.0 165.1 169.2 169.8 170.0 169.8
EXPERIMENT. I n ' deter mining the charge, allowance was made for the holdup of fat in the pressure tube and for the water present in the vapor phase. The amount of water used was about ten times theory-i.e., 3O-mole proportions. For every 100 parts of f a t there were 70 of water (for beef tallow) or 90 of water (for coconut oil). For peanut oil 50 parts of water R-ere used. I n the autoclave 354 grams of water (including 4 grams of vapor) were placed, the air was displaced by nitrogen, and the apparatus heated t o 280" C. The pressure tube was brought as near as possible to the reaction temperature with an oxyacetylene torch, charged with preheated fat (500 grams of beef tallow plus 4 grams to allow for holdup), and closed. A pressure of nitrogen somewhat greater than that in the autoclave ( a p proximately 70 atmospheres) was applied. When the exact temperature was reached, the valve to the reaction chamber was opened, while the necessary pressure was maintained. The end of the filling process, which required 10 t o 20 seconds, was shown clearly by a sudden rise in the autoclave pressure after the initial fall owing to mutual solution of the reaction components. The valve was then shut and the stopwatch started. From the beginning the contents were stirred a t 120 r.p.m.
TABLEIlr. Tpp., C.
DESCRIPTION
INFLUENCE O F TEMPERATURE ON
Time to Reach Equilibrium, Nin. Coconut Peanut Beef tallow oil oil
225 240 260 280 260 (catalyst, 0.2% ZnO)
O F AN
SPLITTINGTIME
Half-Life Time, 7 , Min. Beef Coconut Peanut tallow oil oil
156 82 47 34
158 84 46 33
156 85 53 33
62 34 18 8
21
...
...
4
58 33
23 10
50 25 16 10
...
...
i
9 m
-
MinU&S /WhU&S
50
7m
750
Figure 2. Hydrolysis of Beef Tallow ( t o p ) Coconut Oil (center), and Peanut Oil (bottom) versus Temperature S A m L I x G . , Shortly before sampling a small portion waq run out to wash the tube; the sample was run into an Erlenmeyer flask cooled to -15" C., whereupon the fat rapidly solidified. The time of sampling was taken as t h a t of opening the valve. AX-ALYSIS. The sample was melted and then mashed with water to remove traces of glycerol. According to Trauth (IO) and Hilditch ( 1 ) and the present authors' own experiments, loss of mono- and diglycerides is not to be feared. Drying was achieved by solidification of the fat and finally by fusion over anhydrous sodium sulfate. The weighed sample was titrated with 0.1 N potassium hydroxide and phenolphthalein. Runs were made a t 225O, 240°, 260°, and 280" C. The results of the experiments are in Tables I, 11, and 111 and Figure 2. The times to reach equilibrium and the half-life times for different runs are presented in Table IV. RESULTS. Table IV shows that fat hydrolysis is not instantaneous even a t 280' C. but that half an hour is required t o reach equilibrium. The reaction velocities of the three fats studied are similar. Figure 2, in which the acid number and degree of
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1951
- - -e
+
caicu/a/ed
Foond
poles 40 0
30 50
Figure 4.
M/i/u/es 24
36
ffl
Figure 3. Dependence of Reaction Rate on Oil-Water Ratio for Beef Tallow
*
hydrolysis are plotted against time, shows an induction period. Degree of hydrolysis is defined by the authors as the ratio of free t o total fatty acids, both measured on the same sample. TO simplify Tables I, 11, and I11 saponification values have been omitted. The induction period is very short a t high temperatures (260' t o 280' C.) and becomes more marked a t lower temperatures (240' to 225" C.). The initial delay in reaction, which is small in the case of peanut oil, is clear with tallow and particularly pronounced with coconut oil. Here, however, one must remember that coconut oil contains considerable quantities of water-soluble fatty acids--e.g., about 9% of caproic acjd, 0.079% water soluble -which dissolve in the hydrolysis water and thus are not estimated in the assay by acid number. Although the later washing with water was omitted in these experiments, the acid numbers at the beginning of the reaction are a few units too low. Actually the induction periods are not so pronounced as shown in the curves of Figure 2, center. The curves approach the equilibrium state asymptotically. Theoretically, equilibrium is reached only after infinite time. I n practice, however, i t is attained when the changes in the acid numbers have become small. The determination of the time to achieve equilibrium is strongly dependent on the accuracy of the analyses. As the accuracy of these is a t most 0.5010, Table IV includes the half-life times which are more readily estimated from the curves owing to the steeper gradient a t this point. IKFLUENCE of CATALYST on RATE of CLEAVAGE.According t o a theory of Lascaray (6), the action of a splitting reagent is explained by the increase in the solubility of water in the fat phase. Thus, 1.39% of water dissolves in fatty acids a t 100" C. in absence of a splitting agent, but 2.43% in presence of 0.517' zinc oxide. The report of Mills (6) that tallow fatty acids dissolve approximately 16% water a t 260' c. was confirmed by
TABLE V.
720
30
I
260 O
72
60 700
725
750
MD wf % 4 0
250
Dependence of Degree of Hydrolysis at Equilibrium on Oil-Water Ratio
experiments in glass pressure tubes, using various fat-water mixtures and determining the temperature where complete miscibility occurs. This quantity suffices for the hydrolysis. I n the authors' opinion, if the action of a catalyst lies merely in the increase in the solubility of water, its addition should have no great influence on the reaction velocity a t this temperature. However, a n experiment with 0.2Oj, zinc oxide as splitting reagent at 260' C. showed that the time of cleavage is reduced from about 47 minutes to approximately 20 minutes (Table I and Figure 2, top). Therefore, the action of the catalyst cannot simply be the increasing of the fat solubility of water. DEPENDENCE OF HYDROLYSIS VELOCITY ON THE QUANTITY OF WATER
Table V and Figure 3 show that the reaction velocity is almost independent of the amount of hydrolysis water, as Lascaray has also found. Figure 3 shows that the curves are almost identical in the main portion of the reaction and differ only in the final phases. DEPENDENCE OF DEGREE OF HYDROLYSIS AT EQUILlBRIUM ON QUANTITY OF WATER
According t o the law of mass action the degree of hydrolysis of fats varies with change in the amount of water and the glycerol concentration. Table VI and Figure 4 illustrate the dependence of the degree of hydrolysis a t equilibrium of beef tallow on the quantity of water.
TABLEVI. DEPENDENCE OF DEGREEOF HYDROLYSIS AT EQUILIBRIUM ON &*WATER RATIO Beef Tallow a t 260° C. Degree of Hydrolysis, r?, I Y
Moles
1 2 3 6 10 18 33.6 60 120 300 600
Water
Wt. % 2.08 4.16 6.25 12.5 20.9 37.5
70 125 250 625 1250
Acid value 59.1 82.1 100.4 129.5 146.8 165.7 181.9 189.7 192.4 196.5 200
Saponification value 193 193 193 195.3 198.3 200 202 202 202 203 204
Found
Calod. by formula of Sturm and Frei (9)
DEPENDENCE OF REACTION RATEON THE OIL-WATER' RATIO
Water, Wt. % of F a t 70 150
Beef Tallow a t 260' C. Degree of Time to reach Acid value hydrolysis, % equilibrium, min. 182.1 90.2 47 193.7 94.5 53
The reaction time was fixed a t 260" C. To avoid disturbance of the oil-water ratio, samples were removed only after reaching equilibrium. I n this case the water vapor was included in the calculation. All experiments were a t least duplicated and all tables contain mean values. At low water concentrations the
INDUSTRIAL AND ENGINEERING CHEMISTRY
514
pressure drop caused by solution was as much as 17 atmospheres. An example is given as follows: Experiment with 1 mole of water plus 1 mole of fat a t 260' C. Water vapor pressure, 46 atmospheres; observed pressure, 29 atmospheres. Pressure drop observed, 17 atmospheres; calculated (Raoult'E law), 15.3 atmospheres.
Vol. 43, No. 2
In Table VI and Figure 4 the measured degrees of hydrolysis are compared with those calculated by the above formula. The equation of Sturm and Frei corresponds to a hyperbola with an asymptote y = 100, and is useful because of its simplicity. ils is clear from the table, the calculated values are about 2 units t,oo high in the technically interesting region. The curves cross at 66.5%. DEF'ENDENCE O F DEGREE O F HYDHOLYSIS AT EQUILIBRIUM ON TEMPERATURE
The hydrolysis of glycerides proceeds without detectable heat of reaction in the 150' to 220' C. range ( d , 6 ) . A series of experiments over a temperature range as large as possible is desirable to detect a heat of reaction and results for the 150' t o 280" C:. range are collected in Table VII.
DESCRIPTION OF EXPERIR;IENTS. Weighed quantities of water and fat %'ere placed in the autoclave and the air displaced by nitrogen. Samples were removed after stirring a t the desired temperature until equilibrium was attained. All values are the mean of two independent'runs.
CONCLUSION. The reaction is temperature independent. heat of solution could be detected on mixing fat and water.
So
ESTERIFICATION OF FATTY ACIDS WITH GLYCEROL-WATEH
20
7U
30
lz?
If the cleavage of fats is a truly reversible process it must be possible to approach the equilibrium from both sides; therefore, the opposing reaction-via., the esterification of fatty acids with glycerol a t 260' C.-was investigated. The runs were arranged so that in the equilibrium state t,hc concentrations of fatty acid, water, glycerol, and fat would b~ the same as if the runs had been started with fat and water. For example, a run of 500 grams of beef t,allow and 380 grams of water is 90% hydrolyzed at, equilihrium and the equilibrium mixture has the following composition :
50
Figure 5. Hydrolysis of Beef Tallow and Esterification of Beef Tallow Fatty Acids
RESULTS. The plot of degree of hydrolysis against quantity of water approaches 100% asymptotically-Le., an infinite quantity would be required to achieve total cleavage of fat. In practice, however, the maximum for a good commercial grade of tallow lies near 99%. The curves rise steeply a t first and become flatter at 70% water (33 moles) and 90% hydrolysis. If the corresponding molar proportions are substituted for the weight per cent of water the relationships hold for different fats. They hold for all temperatures as the hydrolysis has no heat of reaction. APPROXIMATION FORMULA for DEGREE of HYDROLYSIS CURVE. Sturm and Frei (9) have described a method for calculating from the quantity of water the obtainable degree of hydrolysis of a chosen fat. The equation and example of its use follows: Degree of hydrolysis, % 31
=
3100 X %jyater value of triglyceride
x % waterfsaponification
3100 X 70 Degree of hydrolysis = -____ = 91.5y0 31 X 70 202
+
Temp., a
c.
150 226 260 280
INFLUENCE
OF TEMPERATURE
HYDROLYSIS AT EQUILIBRIUM
ON
DEQREEO F
(Peanut oil, 50%; distilled water, 50%) Time of Acid Degree of Reaction, Hr. Value Hydrolysis, % 37 163.1 83.7 3 161.1 82.6 1 163.8 83.9 0.5 161.0 83.0 Mean
162.4
Esterification run: Beef tallow fattv acids, 476 grams Glycerol (100%-pure), 53.5 grams Water, 318.7 grams Total, 848.0 grams As usual the water in the vapor phase and the oil remaining in the pressure tube were taken int>oconsideration. The fatty acids were inject,ed into the autoclave a t the reaction temperature. The results are collected in Table VIII. Figure 5 shows hydrolysis of beef tallow and esterification of beef tallow fatty acids as A reversible process.
TABLEVIII.
ESTERIFICATION OF BEEF TALLOW FATTY ACIDS
[Acid value, 204; saponification value, 204; fatty acids, 100 parts; $lycerolwater, 78 parts (14.3% plyrerol content)] Reaction Time, t , Min. Acid Value Interval Total 280' 1' C.; Vapor Pressure of Water, 63.3 Atm.; Working Pressure 70 Atm. 1.00 199.3 1.00 2.50 196.6 1.50 193.3 3.50 1.00 187.3 5.00 8.50 183.2 13.50 5.00 18.50 5.00 182.0 182.1 23 50 5.00
-
Beef tallow, saponification value 202; water 70%
TABLEVII.
Composition at equilibrium: Fatty acids, 428.2 grams Fat, 50.0 grams Glycerol, 48.0grams'~ i.e., 13% glycerol in Water, 321.8 grams/ water Total, 848.0 grams
83.3
260'
*
l o C.;
Vapor Pressure of+Wat,er, 46.3 Atm.; Working Pressure, JJ
2.00 1.00 5.00 6.00 10.00 5.00 6.00
Atm.
2.00 3.00 8.00 14.00 24.00 29.00 36.00
199.3 197.1 190.5 185.0 182.5 182.0 182.4
February 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
KINETNAPPROXIMATIONS. Although in the hydrolysis of fats several reactions are taking place simultaneously, some kinetic data were calculated assuming a roughly first order reaction for which the following relations hold:
515
brought to reaction temperature and then, by means of a special device, introduced into the reaction vessel under pressure. The three fats do not show considerable differences. The hydrolysis at 280' C. is completed after about 0.5 hour, while at 225' C. the same reaction takes 2.5 hours. From these data, the temperature gradient of fat hydrolysis was determined.
where k = reaction velocity constant t = time in minutes cg = initial concentration of ester at time zero c = ester value a t time t 7 = half life 1
The values thus obtained might be of some practical use, although the theoretical basis is questionable.
P
Reaction Rate Constants, k, for Peanut Oil at Various Temperatures Temp.,* C. L 0.0732 A 30 280 0.0422 15 260 0.0270 * 12 240 0.0141 * 10 225
.
The following values for the hydrolysis activation energies and the temperature gradients were obtained. Activation Energy, E , Calories 14.500 += 800 15,400 * 800 15,600 800
Fat Beef tsllow Cooonut oil Peanut oil
Tern erature GraJent, &IO 1.29 1.33 1.33
A Ql0 value of 1.33 means that the reaction rate increases by a factor of 1.33 for every 10" CJ. rise in temperature. From these data the following Arrhenius equations were derived. They merely represent approximations neglecting any induction periods. The smaller the latter are, the more exactly do the calculated velocity constants agree with the measured ones. Reef tallow: log k
=
3367 -~
T
TESTING AND APPLICATION OF THE EQUATIONS. The applicability of the equations was tested with the hydrolysis of peanut oil a t 150' C. (Note extrapolation from temperature range 225' t o 280' C. for which equations are calculated.) The results were :
klz$
=
M O O
2500
MOO
Temperature, ' C .
Figure 6. Hydrolysis of Peanut Oil; Half Life as Function of Temperature
3170 4.663 - T
Coconut oil: log k = 5.062 -.
*
750
The reaction velocity is almost ihdependent of the oil-water ratio used. The results of Lascaray (4,6)are confirmed. The influence of the oil-water ratio on the degree of hydrolysis at equilibrium was measured, and the results agreed with calculations according to Sturm and Frei (9). The reversibility of the process was demonstrated by the results of hydrolysis and esterification experiments. F a t splitting shows no heat of reaction between 150' and 280' C. This is in agreement with other authors who worked at lower temperatures (9, 6).
0.00092 LITERATURE CITED
Calculated degree of reaction after 24 hours (1440 minutes), as per cent of initial concentration of fat = 100 c =
100(e--0.0009**1440)
=
26,6y0
Hilditch, T. P., Industrial Chemistry of Fats and Waxes, pp. 274, 406, London, Baillibre, Tindall & Cox, 1941. (2) Kaufmann, H. P., and Keller, M. C., Fette u . Seifen, 44, 4 2
(1)
(1937).
Expected degree of hydro1 isis after 24 hours = 73.4y0 Acid value, 147.0: saponiication value, 193.0 (average of two independent runs): Measured degree of hydrolysis = 76.1% The above equation gives satisfactory results.
Kellner, J., Chem.-Ztg., 33, 453, 661, 993 (1909). Lascaray, L., Fette u. Seifen, 46, 628 (1939). (5) Lasoaray, L., IND.ENG.CHEM., 41, 786 (1949). (6) Mills, V. (to Procter and Gamble Co.), U. S. Patent 2,156,863
In Figure 6 the half life of the hydrolysis of peanut oil was plotted as a function of temperature. Values calculated with the given formula for the hydrolysis of peanut oil hold within less than 574.
(7)Paquot, Ch., and Richet, H., Compt. rend., 226, 925 (1948). (8) Schlenker, E., and Gnaedinger, J., J . A m . OiE Chemist's SOC.,24,
SUiMMARY
The mechanism of autoclave fat splitting was investigated in the temperature range of 225O to 280' C. for commercial grade beef tallow, coconut oil, and peanut oil. I n order to follow the considerably fast reaction from the beginning, the two components, fat and water, were separately
(3) (4)
(1939).
239 (1947).
Sturm, H., and Frei, J., Fette u . Seifen, 45, 219 (1938). Trauth, J. L., Oil & Soap, 23, 137 (1946). Treub, J. P., J . chim. phys., 16, 173 (1918). Wegscheider, R., Monatsh., 29, 84 (1907). , (13) Yamasaki, E., J . Am. Chem. Boc., 42, 1456 (1920); 44, 426 (9) (10) (11) (12)
(1922).
RECEIVEDJuly 25, 1949. Presented before the Division of Industrial and CHEMICAL Engineering Chemistry at the 118th Meeting of the AMBRICAN SOCIETY, Chioago, Ill.
