INDUSTRIAL
AND
ENGINEERING CHEMISTRY
A N A L Y T I C A L E DITI 0 N PUBLISHED
BY
THE
AMERICAN
CHEMICAL
SOCIETY
0
HARRISON
E.
HOWE,
EDITOR
Chemical Factors in the Determination of Water in Insulating Oil A New Electrical Method R. N. EVANS, J. E. DAVENPORT, A N D A . J. REVUKAS Consolidated Edison Company of New York, Inc., Brooklyn, N. Y. products of combustion and the free water were absorbed in microchemical absorption tubes and weighed as carbon dioxide and gross water. The net water was obtained by applying an empirical correction ratio of water t o carbon dioxide. The accuracy of the method depends on the use of the correct ratio of water to carbon dioxide and the weight of carbon dioxide obtained in each experiment. Some knowledge of the former was obtained by continuing the experiment for 1 liter of nitrogen after the water weight had fallen to a minimum. The latter factor was greatly reduced by a change in procedure which is described in this paper. The ratio adopted for the mineral oil type of transformer oil was 0.3 and for the noninflammable synthetic oil 0.2. Carbonaceous material vaporized from a mineral oil which would be retained by the solid-carbon dioxide trap would be expected theoretically to have a water-carbon dioxide ratio of between 0.2 and 0.5. The higher than theoretical ratio (0.1) for the synthetic noninflammable oils may be due to partially chlorinated compounds below C2,H,CI, or to organic impurities absorbed in the operation of the transformer.
The presence of small quantities of water in insulating oil seriously impairs its usefulness in electrical equipment. The need for an accurate as well as rapid method for its determination cannot be overemphasized. The present paper describes the experimental modifications of the combustion procedure directed toward lowering the hydrocarbon correction. The influence of temperature in the removal of the water from oil and the limitations of the Grignard procedure are experimentally demonstrated. An electrical method is briefly described and its application to a field determination of water is pointed out.
I
N RECENT years several chemical procedures have been advanced which claim specificity for the estimation of water in organic liquids.
Apparatus The modifications in the apparatus were directed toward the reduction of the amount of carbonaceous material entering the combustion furnace. It was found that the magnitude of the correction was greatly reduced by means of an oil scrubber in the train where preferential solution of the oil vapors took place. The change in procedure for the determination of water in oil is apparent from a description of the new section of the apparatus as shown in Figure 1. This section replaces D and F in Figure 1 of (4). (In 6, page 301, in the description of the apparatus, “cell E” should read “cell
The Fischer method (6),worked on extensively in this country by Smith, Bryant, and Mitchell ( l a ) ,depends on the oxidation of sulfur dioxide by iodine in the presence of water. The latter authors first worked out the estimation of water by acetyl chloride, which was adapted by Clark to the determination of water in transformer oil. Because of the color of an insulating oil and the probable presence of interfering substances in the original oil sample, it appears likely that in any chemical procedure the water first must be removed from the oil, as, for example, in the procedure described by the authors (4). The chief difficulties with the Fischer method and the acetyl chloride method in their application bo oils are the estimation of peroxides in the former method and the estimation of volatile acidit,y in the latter. Two additional methods involve the use of a-naphthoxydichlorophosphine (9), which is not specific to the OH group of water, and of benzoic anhydride (11). The Grignard reagent has also been suggested by Larsen ( 7 ) as a possibility for determination of traces of water in oils,
D”). One hundred milliliters of oil were introduced into C through the serum rubber fitopper and stopcock D after the residual water in the train had been removed. Approximately 10 ml. of Apiezon oil (an oil of low volatility used in high vacuum practice) were also added to cell B. Purified nitrogen gas in small bubbles formed by the porous fritted disk, A , carried the water from the oil sample into the solid carbon dioxide trap, E. Durin this period, scrubber B was maintained at a temperature of 100’C. When the removal of water was complete, the Dewarflask was removed and the nitrogen was directed around the oil sample cell by means of the three-way stopcock G. In this manner the
I n the method (4) which the authors have described, the volatile carbonaceous material and the free water, after being trapped out by the use of a Dewar flask containing solid carbon dioxide, were carried into a combustion furnace. The
589
590
INDUSTRIAL AND ENGINEERING CHEMISTRY 3
Vol. 13, No. 9
TABLE 11. EFFECTOF TIMEOF HEATING A N D TEMPERATURE OK REMOVAL OF W.4TER FROM SAMPLE 6 (1@c OIL)" Expt. 3-0,
1 2 3
Oil Sample Tempera- Weight of ture Sample ' C. Grams
4 4 (con-
125 125 25 25 125
4 4 (con(con-
125 125
tinued)
tinued)
56 87 87 87
.. ..
Gross
Xet,
3-z Litera 1 1.5
HzO CO2 HzO P . p . 111. P. p . I I ~ . P . p . 111.
4 17 4 additional
59 99 29 34 112
20 17
li
51 90 23 29 i107 n.7 .
18 additional
34
11
31
26
31
Total water found in E x p t . 4 1 6 i a
Scrubber of hpieaon oil a t room temperature.
3d, '4-16, and A-I) without the scrubber even where large FIGURE
amounts of carbon dioxide were obtained. The correction due to the solubility of water in the Apiezon oil is negligible, as was indicated by continuing the experiment until an additional liter of nitrogen had passed through the train (experiment 3-4).
1. ISTERCHANGEARLE A i P P h R I T U S FOR DETERMISIXG iy.4TER IK INSCL.\TING OIL
A . Porous fritted disks B . Aplezon oil cell C. Oil samule flask D. Serum rubber stopper and stoprock E . Dry Ice t r a p F . External spiral coiled heater G. Three-way stopcock
Effect of Temperature on Removal of Water from Oil
trapped water in E , together with any volatile products, was carried through scrubber B , which was maintained at room temperature, into the combustion furnace. An external coiled heater, F , prevented frothing in either B or C. When the nil was of the halogenated type a spiral tube containing silver oxide maintained at a temperature of 400" C. was put in place at the exit end of the combustion furance. As is shown below, the temperature of the oil sample must be considered in connection with the removal of water. A safe maximum temperature would appear to be the average operating temperature of the oil. One may also be guided by the condition of the oil as revealed by chemical tests. Unless otherwise stated, a new mineral oil or the average nonflammable synthetic oil was heated to 105' C. during the passage of 2 liters of nitrogen, whereas for a used mineral oil the passage of 5 liters of nitrogen was carried out at 50" C. or at room temperature.
Efficiency of Apiezon Scrubber in Diminishing Carbon Dioxide Correction In Table I is illustrated the reduction of the carbon dioxide correction by the use of the Apiezon-oil scrubber. ,When the oil scrubber was maintained at a n elevated temperature, it was apparently ineffective in retaining carbonaceous material (experiments 3 and 3-4). However, when the scrubber was maintained a t room temperature it lowered greatly the quantity of oil vapor entering the combustion furnace. The adopted carbon dioxide-water correction apparently would have enabled one to obtain the correct results (experiments 3,
The experimental results on many oil samples indicated that if a n oil sample were heated lvhile the water was being removed into the solid carbon dioxide trap high results \yere obtained which depended in magnitude on the time of heating. This effect mas more evident in the mineral oil than in the nonflammable synthetic oil. Furthermore, the used transformer oils exhibited this efiect t o a greater degree than the new oils. I n Table 11, the results on a sample of used transformer oil (mineral oil type) are given. When experiments 1 and 2 are compared with experiment 3 (Table 11,last column) the magnitude of the error involved is clearly illustrated. Thermal decomposition of oxygenated compounds was responsible for the formation of the additional water, although the residual dissolved oxygen gas in the sample might have played a minor part. I n experiment 4 after 17 liters of nitrogen had passed through the oil sample at room temperature a very large increase in water content occurred when the temperature of the oil sample n-as raised to 125" C. Further heating yielded comparatively little additional water, indicating that oxygenated compounds were present in a limited amount. The completeness of removal of water at room temperature \vas indicated by the fact that the 4-liter run (experiment 3) yielded very little less than the 17-liter run (experiment 4). Thus by continued heating at 125" C. for a period involving the passage of 22 liters of nitrogen, an oil sample actually containing 30 p. p. m. of water vias shown to behave as if 165 p. p. m. of water mere present.
Behavior of Grignard Reagent in Determination of Water in Oil O F APlEZOX SCRUBBER IN DNINI~HISC THE TABLE I. EFFICIENCY DIOXIDE CORRECTIOK
ExDt. N o .
Oil Tvue
Temperature Oil Oil scrubber samule 25 110
...
0
h
Absent 25 Absent 25 Mineral oil type of transformer oil Kunflamniable synthetic oil.
125 125
...
25 25
125 125
GI'089
CARBON
H20
con
Net,
COS
3.58 1,35 4 . 7 5 8.00 0.14 0.43
...
33 62
13 105
29 31
108 50 116
187 21 96 15
52 43 97 99
H20
3.34 2.14 11,57 3.87
5.80 0.91 9.55 0.58
102
...
HnO
The application of Grignard reagent to the determination of water in oils showed that after making allowance for the acid content determined on a duplicate oil sample the residual active hydrogen content of the oil sample is too large to be neglected. The term "residual active hydrogen" may be conveniently applied to the active hydrogen other than that of nater and acids. Alcohols, amines, phenols, and acids too weak to be titrated may be considered to be the source of the residual active hydrogen.
September 15, 1941
ANALYTICAL EDITION
591
tween the calculated methane from the water obtained a t 125' and 25' C. (54 - 21 = 33 p. p. m.). Except for the possibility of oxidafBingle oil sample a t 25' a n d 153' C.) tion a t the elevated temperature due to disCombustion Seut,raliGriguard Equivasolved oxygen initially present in the oil sample, zatlOn Methane Evolved Calculated" lent Tru:perarure a probable explanation of the anomaly was remethane IVater Ivater l u m b e r Found C0rr.h C)il Sample P. p , , , i , 1' p . I l l . P p . l , , . P . p. i r i . P. p . c. lated to the facts that ketoneb may enolize a t 21 6:) 1l j 123 ''2 0.36 22Bc the elevated temperature and that alcohols may l'j Distillare 0.04 95 67 35 .. split off water which under optimum conditions Residue 0.31 175 92 52 mould yield t n o moles of methane as compared Total 1.59 90 30 54 to a yield of but one mole of methane from the lHnO = 2CHd. Acidity deducted using relation 1YH) = 1CHa. b Blank deducted. Acidity deducted using relation l{H) = 1Cdi. original alcohol. c Grignard reaction carried out i n a mixture of 3053 ether and 70({ 1OC oil. It was concluded that the results of the Grignard test when expressed as evolved methane-may be used only as an index of the stage of oxidation of an insulating oil. Based on experiIt \vas first observed that the character of the oil sample mental results with the microgravimetric procedure devel(petroleum origin or chlorinated aromatic) influenced greatly oped in this laboratory, it mas considered extremely uncertain the yield of the reaction. This phenomenon has been to ascribe the evolved methane to any particular chemidescribed by Hibbert and co-workers (8). It could be minical reactive group or compound after an acidity correction mized by maintaining a large ratio of isoamyl ether to the had been applied. Results of even greater uncertainty may oil sample. An attempt was made to analyze Lvith t,he Grigbe expected in the estimation of the Grignard added. T h e nard reagent the two fractions formed in the combustion establishment of an oxygen balance by means of the results procedure. The material which was condensed in the solid of the Grigiiard test did not appear to be of general applicacarbon dioxide trap (cell 2 ) is referred t'o in Table I11 as the tion in the light of experimental work. distillate and that which remained in the oil cell (cell 1) as the residue. I n a separate experiment, the acidity of the distillate and residue was determined by titration by means of a capillary syringe without removing either from the analytical brain. The results bring out several points of int'erest. The large increase in water resulting from its removal from the oil sample at an elevated temperature (30 p. p. m. as compared to 16 p. p. m.) confirmed the results reported in Table 11. The major portion of the acid for this particular mineral oil sample was nonvolatile. I n experiments with nonflammable synthetic oil carried out in a similar manner, the entire acid content remained in the residue. The residual active hydrogen appeared to a limited extent in the distillate (cf. 54 and 67 p. p. m. methane). After due allowance was made for the influence of the solvent and after the methane equivalent to the acid had been deducted, there was an apparent increase in the active hydrogen content of the oil sample as a result of heating to 125' C. (cf. 123 with 67 92 = 159 p. p. m. methane). This discrepancy (159 - 123 = 36 p. p. ni.) was in good agreement a i t h the difference beTIBLE111.
~ O M P h R I S O SOF
RESULTS OF GRIGSARD ASD METHODS
---
ijf
COUBUSTIOS
---
if,.
11
+
eI c! FIG
IN
POROUS
B
ELECTRICAL
C
COLD
D,SX
HYGROMETER
TRAP
D
WASTE
OIL
E
SERUM
R U B B E R STOPPER
F
STOPCOCI(
G
STOPCOCK
TRAP
2
OIAGRAM OF APPARATUS FOR ELECTRICAL DETERMINATION OF WATER
FRITTED
A
INSULATING
OIL
3. RELATION BE I W E E S ELECTRICAL RESIST~NCE OF HYGRONETER AXD KATER COXTEXT OF INSCLATI~;G OILS
FIGURE
~
TABLE Iv. SOLUBILITY OF WATER I N NEWINSULATING OILS AT
ROOMTEMPERATWE ,.
gxpt No.
A-17 A-15-a A-15-b A-16-a
Vol. 13, No. 9
INDUSTRIAL A N D E N G INEERING CHEMISTRY
592
Temperat"le of Oil Sample
Oil Type 1CC 1CC 1CC
oc.
N. 6. 0.
25 25 125 25
COS
Grass
H,O Net
P.p.m.P.p.m.P.p.m. 7 46 44 21 50 43 32 51 47 6 IC3 102
15 IC2 A-16-b N. 9.0. 125 A-12 5314. 125 7 54 * Mineral oil t y p e of high-voltage cable oil.
99 52
Clark's "sl"e8 at 25" C. P.P.rn.
... 75
izo
(Pyranol)
...
70
Solubility of Water in Insulating Oils a t Room Temperature In a paper hy Clark (9) the solubility of water in new Pyranol, transformer oil, and high-voltage cahle oil was given. In connection with checking the precision of analytical trains, the authors prepared stock saturated solutions of the oils with respect to water a t room temperature, which for purposes of comparison may he considered to be between 20' and 25" C. The saturated values determined together with Clark's values are listed in Table IV.
Electric H y g r o m e t e r The need of an apparatus for the determination of water in oil which would operate satisfactorily in the field is very apparent. With this in mind, the electric hygrometer described by Dunmore (3) was adapted to a procedure which removed the water from the oil a t a temperature not greater than the normal operating temperature of the oil. In Figure 2, a schematic drawing of the apparatus is shown. The oil was introduced by syringe through E, spraying into the evacuated chamber through the porous fritted disk, A. During this operation, the stopcock above D remained closed and the
cold trap, C, was surrounded by a bath of dry ice. Stopcocks F and G were then closed and the contents of the trap and coil raised t o some convenient temperature. The resistance of the film was measured either by a General Radio megohm bridge, as extended by Balshaugh d al. (l), or a modified Jones and Joseph bridge (IO) with a cathode ray tube as a null detector with three s t a p of amplification. In Figure 3 is shown a plot of the logarithm of the resistance against the water content of the oils as determined by the combustion procedure. The drift in the resistance readings is illustrated by the insert curves. The change in resistance with time, although of a larger magnitude a t the higher measured resistance, in terms of water content, is approximately the same as a t the lower measured resistance. The resistance readings on the main curve were taken in each caae after a $minute delay period. Experiments are in progress on the simplification of the hygrometer construction and the selection of a more mgged alternating current resistance bridge of a suitable range. The method shows every promise of working out satisfactorily in the field.
Acknowledgment The electrical bridges described in this paper were constructed in this laboratory under the direction of W. F. Davidson, director of research. Literature f10%\ (1) Balsbaugh snd Onoley. IND.ENa. CH~X.,-1 (2) Clark. Eke. Ewr.. 59,433 (1940). (3) Dunmore. BUT.S h d m d s J . Resemch, 7.3, 701 (1939). (4) Evans. Davenport. and Revukas. IND. Eaia. CHSX.,ANAL.ED.. 11. 553 (1939). (5) r b x ; 12, $01 (i940). (6) Fischer, Angew. C h a . , 48, 394 (1935). (7) L%rB.rSen,IND. ENa. CHBM.. ANAL.ED., 10, 195 (1938). . OLIL. \ " , . , ,%, (8) Lid. Wright, and Hibbert, J . Am. C h a . UYL.. c os, OYY ILZYD,. (9) Lindner. Z.oml. C h a . . 86.141 (1931). (id, Luder. I . Am. Chem. Soc., 62,89 (1940). (11) Ross, J . Soe. Cham. Id.. 51, 121T (1932). (12) Smith. Bryant. and Mitchell. J . Am. Chen. Soc., 57.841 (1935); 61,2407 (1939); 62, 1, 3504 (1940). "^_
P R & B ~ Tbefore B D the Conference D. C.
0x1 Eieotrioal
Insulation. Washington.
A Laboratory Condenser MILTON T. BUSH, Vanderbilt University Sohool of Medicine, Nashville, Tenn.
C
OOLING agents more effective than tap water are often needed in the laboratory condenser. I n the ordinary straight condenser it is not convenient to use ice or other such refrigerant. The single-spiral condenser, suitable for downward distillation, does not usually have su5cient capacity for refluxing. The douhle-spiral condenser shown was designed primarily to 6ll the need of an ice condenser which could he used for both downward distillation and refluxing. The coils are made from Pyrex glass tubing 9 mm. in inside diameter, and are carefully wound so that there are no traps in which liquid can accumulate. It is apparent from the figure that tap water, ordinary ice, or solid carbon dioxide can he used as cooling agents.
This condenser nas oeen particularly useful in this laboratory during the summer, when the tap water is often ahove 30' C. It has been very effectivein the preparation of such products as acetaldehyde, hydrogen cyanide, and diazomethane. The ascending coil is an effective barrier against the evaporation of condensate. T h e specimen shown was fahricated by the Scientific Glass Apparatus Company, Bloomiield, N. J.
