Determination of Sludge in Used or Oxidized Motor Oils CLIFFORD G. LUDEBIAh. The Texas Co., h e w Yorh, N. I.
M
A S Y methods have been suggested and used for the determination of sludge in motor oils with consequent, variations of results. Serious discrepancies have been demonstrat,ed in cooperative surveys in which the various workers used the same oils and supposedly the same procedure of sludge determination. Preliminary to other motor oil investigations in this laboratory, t’herefore, a feu- of the more important variables of sludge determination procedures were studied. Based on this study together v i t h other results found in the literature, a coordinated procedure for the det,ermination of sludge and sludge components is presented. -
Sludge and Sludge Components Motor oil sludge is composed of the alteration products of the oil, dust’ and dirt, met’al wearings, emulsions, etc. This study is confined to tlie alt’eration products of t,he oil alone and the term “sludge” as used here applies t’o such alterat’ion products only. The importance of other sludge components, however, is not to be ignored and methods suitable for their estimation are of considerable interest’ and value. The alteration products of motor oils are formed by oxidation and polymerization and may be subdivided into components whose names are derived from the various components of asphalt with which they are identical or n-hicli they closely resemble. hlotor oil sludge components and asphalt components are considered to be formed through oxidation of hydrocarbons in the order of the series: slightly altered hydrocarbons, resins, asphaltenes, carbenes, and carboids. The asphalt components are defined by their solubilities in various solvents or precipitants. The American Society for Testing Materials (1) defines asphaltenes as bitumens soluble in carbon disulfide but insoluble in paraffin naphthas, and carbenes as bitumens soluble in carbon disulfide but insoluble in carbon tetrachloride. Carboids (the names “kerobenes” and “kerites” have also been suggested) are insoluble in carbon disulfide. Ssplialtenes, carberies, arid carboids are more or less insoluble in oil, the insolubility increasing in the order na,med. Resins are “fairly” soluble in motor oils and in petroleum naphtJias. Resins have been defined as asphalt components soluble in petroleum naphthas and absorbed from such solutions by infusorial earth, kieselguhr, etc., from which the resins are removed rather completely by solvents such as carbon disulfide, pyridine, etc. Commercially, resinlike bodies are removed from motor oils during refining by propane precipitation. An excellent analytical application of propane for soluble sludge precipitation from used or oxidized motor oils has been advanced by Hall, Levin, and 1IcMillan (a),mention of which is made below. Hence, since sludge is defined by solubility characteristics, it is exactly defined only by the analytical method of estimation-i. e., the method of establishing solubilities involved in the definitions.
Oils and Solvents Used Sufficient amounts of both oils and solvents or precipitants were obtained, so that the same stock was used in all tests during these studies. Analyses and tests of the solvents are showii in Table 1. The hydrocarbon analyses were made according to the procedure recommended by Tonne (14) wit,h t,he determination of the paraffin-naphthene ratio hy the
aniline point procedure of Orrnandy aiid Craveii (13). Three S. A. E. 30 oils representing a naplithene base, a midcontinent base, and a paraffin base were used and tests on these oils are shown in Table 11. These oils were sludged by blowing n-it’h air a t 175” C. (347’ F.) until sufficient sludge wae formed. The samples of sludged oil were transferred hot, immediately after blowing, by a wide-tipped pipet to the precipitation flasks.
lccuracy All deterininations were run in t’riplicateexcept a few experiments on precipitant selection and ratio. Determinations having an act’ual deviation of more than 0.03 per cent (approximately i per cent of all determinations) were rejected. This maximum allowable error permitted a maximum average error of a single determination of 0.021 per cent, a maximum average error of the arithmetical average of 0.012 per cent, a maximum probable error of a single determination of 0.014 per cent, and a nlaximuni prohable error of t,he ariblimetical average of 0.008 per cent. The chief contributing factor t o errors was electrostatic coiiditioris; it was noticed that a t times a small hair-fine stream of solvent x-as ejected upwards from the crucible during filtration, giving rise to error if sludge were entrained. Such a factor requires \\-(irk untler safe conditions.
Filter Selection Since sludge is somex-liat’ colloidal, an efficient filter of standard porosity is most desirable. Slundum crucibles have been recommended (4, 5, 6, I f ) but have been found unsatisfactory by some members of tlie A. S. T. M. ( 2 ) since inconsistent results due to oil retention were obtained, Woog and Givaudon (15) have recommended a frittedglass disk crucible containing a layer of powdered glass. In this work, filter papers of various types were found to be too slow and ivasteful of solvent. Porous porcelain-bottomed crucibles (both medium and dense) were t o o slo~v.Fritted-glass disk crucibles were suitable if carefully selected for uniform porosity, since retention varied with porosity (as determined by filter rates tvith rr.ater), Properly prepared asbestos-filled Gooch crucibles were easily equal to selected fritted-glass disk carucihles and were chosen for all subsequent JTork.
Standard Experimental Procedure Except when noted, the method of sludge determinatiorl n-as as follows: In an Erleniiieyer flask of 500-cc. capacity iveighed to the closest milligram were pipetted approxiniately 10 cc. of hot, freshly oxidized oil whose weight to the closest milligram was determined by reweighing after cooling (flask !vas stoppered while cooling). The sludge LT-as precipitated by adding solvent with sj$-irlingto ensure complete solution of the oil sample, the sides of the flask being washed down with the remainder of a 200-cc. volume of solvent. The flask was then tightly stoppered and set in the dark for exactly 24 hours at room temperature (approximately 25’ C . ) . Coors KO.4 Gooch crucibles (30-cc. capacity) n-ere filled 1%-itlian asbestos suspension (10 grams of asbestos per 1000 cc. of water), and sucked dry at the vacuum pump, and tht. asbestos mat was n-ell pressed with the forefinger, refilled jyith aFbestos suspension, surked dry, repressed, and n-ell Trashed witli distilled water. The resulting asbestos filtering mat was approximately 3 nim. thick. I t was prepared from Ponminco asbesto. produced by the Powhatan Mining Corporation, Baltimore, >Id. -4fter drying several hours in a hot-air oven at 110” c., the prepared crucible was cooled in a desiccator and then iveighed to the closest 0.1 mg. The contents of the Erlenmeyer flask
ANALYTICAL EDITION
SEPTEMBER 15, 1940
521 .. .. .. .. .. .. .. '.. '..
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%be mmm dm* m "
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TABLE 11. TESTSO Y OILS Oils, all S. A E. 30 Gravity, A. P. I.
Specificogravity, 60°/600 F. Flash, F. Fire, ' F. Viscosity, Saybolt Universal
loo0 F.
130' F. 210' F.
Pour,
\-or,.12, XO. 9
I> DDUSTRIlL .4KD ENGINEERIXG CHEMISTRY
522
O
Saphthene
Md-Continent
21.5 0,9036 395 460
28.3 0.8855 450 520
549 5 Xf.5
481.5 212 5 60
a .I
F.
Color. Lovibond. cell leneth. inches Neutralization No., me. KOH per gram Sulfur, bomb, % Carbon residue, %
0
-5
Paraffin 28.5 0.8844 445
515 415
206 61.5
- 20
255-6"
30-1/?"
n.18
0.085
0.03
0.345 0.08
0.205 0 06
0.18 0 54
150--1/2"
were carefully decanted through the prepared Gooch crucible, which was held in a Gooch crucible funnel in a suction flask connected to a vacuum line and to the atmosphere by a two-way stopcock. Care was taken to get as little sludge into the crucible as possible until toward the end, when an effort was made to transfer the total at one time. The flask and lip of the flask were washed once into the crucible as soon as possible. I t was then essential that the sludge cake be sucked dry and allowed to develop a number of cracks. The crucible was removed from the funnel, the small line of oil which always crept over the edge was washed back into the Erlenmeyer flask, and the crucible was returned to the oil-free funnel. The flask was then washed twice into the crucible, a rubber policeman being used if necessary. The vacuum was shut off, the crucible half-filled with solvent and allowed to stand 1 to 2 minutes, and the vacuum reapplied; this was repeated for a total of three times, when the crucible and contents were oilfree. Approximately 100 t o 150 cc. of solvent are necessary for washing when used from a fine-tipped flask. After a final \\-ashing down of the crucible to remove possible traces of oil, the crucible and contents were dried at 110" C. for an hour, cooled in a desiccator, and reweighed to the closest 0.1 mg. The calculations were as follows: %sludge
=
weight of sludge X 100 weight of oil sample
The character of the sludges or the various sludge components determined as per cent sludge is dependent upon the solvent employed. The above procedure was adopted as the standard method for this study.
Solvent Selection I n Table 111, the relative sludge-precipitating pon ers of various solvents are shown. Each group of results as set apart in the table was obtained with a different sludged oil of the base indicated. I n all cases, isopentane was found to precipitate the greatest amount of sludge. As a basis of comparison, the sludge precipitated by the other solvents is expressed as a percentage of the amount precipitated by isopentane and is termed here '5sopentane sludge". It is not implied that isopentane precipitates 100 per cent of all sludge present in an oxidized oil, since more efficient precipitation solvents have been found. However, it is impossible to use hydrocarbons lover boiling than isopentane for the more or less conventional sludge precipitation procedures without the use of pressure or refrigeration. An excellent application of propane is cited below. Isopentane precipitates asphaltenes, carbenes, and carboids, and since the latter two are usually rather insoluble in oil or very easily precipitable, isopentane may be regarded as an asphaltene precipitant. Isopentane also complies fully with the A. S. T. M. solvent requirement involved by the definition of an asphaltene, since it is a pure "paraffin naphtha". OTHERSOLVENTS.If n-pentane precipitated sludge in a definite ratio to isopentane-i. e., a constant per cent isopentane sludge-the use of mixed pentanes would allow the estimation of isopentane sludge by a conversion factor based
on t'he composition of the mixed pentanes. Unfortunately the ratio v a s found to vary lvvith the oil base used. This v a s also h u e of all other precipitation solvents. It will be noted that 86" BB. gasoline was used as an auxiliary precipitant with each oxidized oil, so affording a check. t'he variation of the isopentane sludge value being, no doubt, partially due to the distribut'ion of the sludge components. 1.S. T. A i . precipitat'ion naphtha has lower sludge precipitat'ion ability than Kahlbaum normal benzine, n.liich is so widely recommended and used in Europe. Kerosene was tried, since it is so widely used as a flushing agent for engines in experimental work from which sludge results are sought. The choice of kerosene for such Jvork seems unfortunate and a better selection might be carbon tetrachloride or benzene which could be later removed to leave essentially unchanged oil. Diethyl ether (dry and ethanol-free) and a 1 to 1 by volume mixture of ether (dry) and ethanol (absolute) were tried, since thesc sol\-ents hare been used by some Tvorkers. The latt'er mixed solvent' was difficult to handle and gave poor reproducibility. A number of sludge procedures recommend precipitation of sludge by naphtha followed by extraction of the sludge with chloroform, carbon tetrachloride; carbon disulfide, or benzene, etc., with recovery and weighing of the extracted material as sludge. These methods appear tedious and indirect and so were not tried except to test the precipitation powers of the solvents recommended therein. RECOMJIENDED SOLVENTS.Evans (7) in an article covering a number of the factors connected wit'h methods of sludge determination has pointed out that small amounts of aromatics and unsaturates as well as the boiling range of the petroleum napht'ha could cause considerable differences in the amount's of sludge precipitated. This is confirmed in part by the results on benzene in Table 111. It is also to be noted that the amount of sludge varies with the different' hydrocarbons. Despite the lower molecular \?-eight of the mixed hexanes as well as a lower boiling range, more sludge Tvas precipitat'ed by pure n-heptane, although possibly this might not be true of the pure hexane components. It is probable that the lower amounts of sludges precipitated by the mixed hexanes are due to the presence of small amount's of unsaturates (4.1 per cent) and aromatics (3.1 per cent) as shon-n by the hydrocarbon analysis presented in Table I. .4n attempt to relate various chemical and physical properties (see Table I) viith the sludge-precipitation ability of T ~ B L111. E SOLVEST SELECTION Saphthene Base 011
IsoSolFent
Sludge
pentane sludge
Mid-Continent Base 011 Isopentane Sludge sludge
Paraffin Rase 011
Sludge
Isopentane sludge
%
%
%
Isopentane 86' Be. gasoline n-Pentane Mixed pentanes Mixed hexanes n-Heptane A. S. T. 11.Dreciuitation naphtha ICahlbaumnormal benzine Kerosene
2.04
2.00 1.56 1.81 1,83 0.74 1.31 0.72
I~ 0 0 . 0
1.80 1.91 1.96 1 35 1.64 1.38
100.0 88.2 93.6 96.1 66.2 80.4 67.6
78.0 90.5 92.5 37.0 85.5 36.0
1.45
71.1
0.83
..
..
0.24
Isopentane 86'RB.gasoline Kerosene Isopentane 8AoBB.gasoline Carbou tetrachloride Carbondisulfide Benzene
1.63 1.41 0.67 2 34 2.05
100.0 86.5 41.1
2.32 1.79 0.48
ion.0 77.2 20.7
2.36 1.69 0.061
100.0 71.G 2.6
1no.o 87.6 4.7
1.61 1.24 0.28
100.0
0.96 0.63 0.066
100 o 6.5.6 6.9
2.6 1.5 100.0 90.1 0.8
0.26 0.24 2.63 2.10 0.61
(1.033 0.04'3
5.5 5.1
26.0
0.73 0.98
15.9 14.6 100.0 79.9 23.2 27.7 37.2
0 . 11
0060 0.036 3.12 2.81 (1.024 0.81 0.61
19.6
%
%
2.95 2.27 2.59 2.66 0.89 1.68 0.91
100.0 76.9 87.8 90.2 30.2 38.7 30.8
41.5
1.01
34.2
12.0
,
70
75.6 17.1
..
5.03 :3,91 1.26 1.48 3.08
..
ion. o
77.7 25.0 20.4 61.2
SEPTEMBER 15, 1 9 E O
ANALYTIC4L EDITION
523
tion, and in some cases slightly out of line with other results. TABLE IV. EFFECT OF TIME
An interval of 24 hours was found to be convenient and was
adopted as standard for this work. T E V P E R I T U R E . The effect of temperature upon the amount of sludge precipitated was studied by following the Solvent Time standard experimental procedure except for the temperature, IroUjs % % % % % 9% during the 24-hour period of standing, which was -25", O", Isopentane 6 1.60 97.6 2.29 94.9 2.31 97.5 12 1.62 98.8 2.31 97.5 2.33 98.3 and 25" C. The results shown in Table J- for 86" BB. gaso2 36 99.6 24 1.63 99.4 2.32 97.9 line are to be compared to those with isopentane at the same 48 1.63 99.4 2.33 98.3 2.37 100.0 120 1.64 100.0 2.37 100.0 2.37 100.0 temperature, the same oil being used for all three tempera86' Be. tures. The amount of sludge increases with decreasing gasoline 6 1.44 88.7 1.80 75.9 1.67 70.5 12 1.43 87.2 1.77 74.7 1.69 71.4 temperatures within the temperature range studied. A l::: ;: ::;! logical speculation is that the maximum amount of sludge 120 1.47 89.6 1.84 77.6 1.71 72.2 would be obtained a t the miscibility temperature of the oil and solvent' a t the particular solvent-to-oil ratio present, although the sludge TABLE 1 ' . EFFECT OF TEMPERATURE so obtained might contain resins. Low temSaphthene Base Mid-Continent Paraffin Base Oil Base Oil Oil Derature techniclue is inconvenient and impractical for routine- analytical work and the more pentane Isopentane IsoSol\-ent Temperature Sludge sludge Sludge sludge Sludge sludge convenient temperature of 25' c. was chosen as C. I". % ' B 4"o 70 R % standard for these studies. 2.18 100.0 Isopentane -25 -13 1.87 100.0 3.72 100.0 DILUTION.Of importance secondary only to 0 i-32 1.84 100.0 2.23 100.0 3.62 100.0 + E +77 1.73 100.0 2.16 100.0 3.49 100.0 the choice of solvents is the ratio of the volume 86' BB. of solvent to the weight of the sample of oil. The gasoline -25 -13 1.69 90.4 1.69 77.6 2.85 76.6 0 +32 1 . 62 88. 0 1.68 75.3 2.80 77.3 groups of results shown in Table VI were obtained +26 f77 '.jO 86.7 76.9 2.62 73.1 ~~.ithdifferent,oxidiaed oils according to the given = experimental procedure in which only the ratio of the solvent volume to the sample weight mas the various solvents (see Table 111) was completely unsucvaried. The amount of sludge obtained increased in most cessful, I t therefore appears that regardless of rigid specicases to a maximum with increasing volumes of solvent for a fications for sludge precipitation naphthas, the possibility of given weight of sample. Only with the mid-continent base the exact reproduction of naphthas, especially from varying and the paraffin base oile precipitated with 86" BC. gasoline crude sources, of identical sludge-precipitation ability is were there failures to obtain sludge maximums. A ratio of small. However, pure chemical compounds are reproducible 25 cc. of solvent t o 1 gram of oil sample n a s necessary in the and their properties and effects are inherent. The recomother cases to obtain maximum precipitation. The results mendation is therefore made to use isopentane, carbon tetrawith isopentane and with 86" BC. gasoline are shown graphichloride, and carbon disulfide as standard solvents for the cally. d maximum also appeared to be attained with both precipitation of sludge from motor oils. The recommendacarbon tetrachloride and carbon disulfide a t the recommended tion of isooentane is based uDon the data so far presented. ratio of 25 to 1. All three solvents comply with the requirements of the ,4.s. T. 11. definitions and those tacitly implied by TABLE VI. EFFECTOF I ) l L U T I O S general usage and practice for the variNap1 ithene Base Oil .\lid-C ontinent Base Oil Paraffin Base Oil ous sludge components. IsoIsoIsoNaphthene Base 011 Isopentane Sludge sludge
Mid-Continent Base Oil Isopentane Sludge sludge
Paraffin Base 011 Isopentane Sludge sludge
~
;:::
2;
pe2i;e
O
Effect of Time, Temperature, and Dilution TIME. The effect of the time of standing of a precipitated sample between addition of the solvent and filtration is small. There is, however, a slight increase in the amount of sludge obtained with increased standing, as shown by Table IT'. The same oxidized oil sample was used with both isopentane and 86" BB. gasoline according to the foregoing experimental procedure, except for the time variation. The increase in sludge is in general positive with increased time in all six serieq arid greater than the permissible divergence or error. The increase in the amount of sludge may be due to the conversion of resins into asphaltenes which occurs with time a t ordinary temperatures, as pointed out by Holde and Eikmann (9). Samples allowed to stand only 6 hours were somevhat difficult to filter, perhaps because of incomplete coagula-
Solrent
Solvent ratio Sludge c /G
Isupentane
86' Ui.. gasoline
Isopentane 86' BB. gasoline Carbon tetrachloride Carbon disulfide Benzcue Isopentane
6 05 9.00 12.0 18.0 24.0 30.0 6.13 9.10 12.1 15.2 24.2 30.2 24 2 24.6 16.3 24.2 30.3 18.1 24.1 30.4 18.1 24.1 30.8
24.3 24.4 Chloroform 18.1 24.1 30.0 Diethyl ether 18.0 24.0 29.9 Ether-alcohol (1 1 8 . 0 t o l b y v o l u m e ) 23.9 29.9 X G O B P . gasoline
1.62 1.59 1.59 1.60 1 61 1.60 1.34 1.38 1.39 1.38 1.38 1.3s 2.34 2.05 0.11 0.11 0.11 0.060 0 . 0lj0 0.061 0 034 0.036 0.037 3.12
2.82 0.024 0.024 0.024 0.78 0.81 0.82 0.64 0.61 0.70
pentane sludge
Solrent ratio
c/C
95.0 99.4 99.4
100.0 100 6 100.0 83.8 86.2 86.9 86.2
86.2 66.2 100.0 87.6 4.i
4.7 4.7 2.6 9.6 2 6 1.5 13 1.6 100.0 90.4 0.76 0.76 0.76 25.0 260 26.3 20.5 19.6 22.4
Sludge (7
/O
6.29
9.4' 12.5 18.7 24 9 31 3 6.39 9 52 12 7 19.0 25.3 :31.6 25.5 25.4 19.0 25.4 31.7 18.9 25.2 31.4 16.9 2.5 2 31.6 25,< 25.a
18.9 25.1 31.4 18.5 25.0 31.2 18.7 25.0 30.9
1.6 3 1.82 1.92 2.03 2.09 2.09 1 22 1 35 1.42 1.52 1.57 1 60 1.64 1.24 0.28 0.2s 0.28 0.26 0.2ti 0.26 0.21 0.24 0.25 2.02
2.10 0.60 0.61 0.60 0.74 0.73 0.79 1.00 0 98 1.02
prntanc sludge
Solvent ratio
78 0 87.1 91.9 97.1 100 0 100 0 58.4 64 ti 67 9 72 7 75 1 iG.l 100 0 73.6 17.1 17.1 17.1 15 0 15.9 15.9 14.6 14.6 14.6 100 0 80.2 22.9 23.3 22.9 28.2 27.9 97.5 38.2 87.4 38.9
0.32 9.46 12.0 16.6 2.3.1 31.3
cc
638
9 51 12.7 19.0 25.2 31 5 25.5 23.7 19 1 25 R 31 9 19.0 25 4 31.5 19.1 25.4 31.7 25.3 25.4 18.9 25.1 31.3 18.8 pS.0 .31.2 18.7 24.9 31.1
Sludee
pentane aludee
70
52
2 72
90 4 93 7 96 0 97 7 100 0 100 3 63 1 66 8 69 4 73 4 75 7 77 7 100.0 GL6 6.7 6.9 6.9 5,3 5.5 5.8 5.0 5,1 5.1 100.0 77.7 25.2 25.0 25.2 28.8 29.4 29.2 62.0 61.2 61.4
2.82 2.89 2.94 3.01 8 02 190 2 01 2.09 2.21 2.28 2.34 0 96 0 63 0 064 0 OG6 0 066 0 051 0 053 0 056 n 048 0 049 0.049 8.03 3.91 1.27 1.26 1.27 1.45 1.48 1.47 3.12 3.08 3.09
ISDUSTRIAL AND ENGINEERING CHEMISTRY
524
Volumetric Sludge Determinations Preliminary experiments were conducted to ascertain if there was any relationship between gravimetric and volumetric methods which would obviously involve a constant density of sludge from all sources. Samples of oil were weighed into 100-cc. conical centrifuge tubes whose tips were graduated to 0.02 cc., precipitated with 90 cc. of solvent (except the straight oil Ramples), stoppered, and thoroughly shaken, the sides were washed down, and the tubes were restoppered and allowed to stand 24 hours in the dark. The tubes were then centrifuged for exactly 60 minutes a t 1900 r. p. m. a t room temperature in a centrifuge having a radius of swing of 25 cm. (10 inches) (axis to tip of tube). After determining the sludge volume, the supernatant oil or oil solution was carefully pipetted off to just above the sludge surface and discarded. The sludge layer was then broken up and washed with 100 cc. of 86’ Be. gasoline except for the isopentaneprecipitated sample, for which isopentane was used. After standing 24 hours, the sludge was filtered through a Gooch crucible and further handled exactly as outlined in the standard gravimetric procedure. The same samples of oil were also analyzed according to the standard gravimetric procedure. The results are summarized in Table VII. It is apparent that the various sludges were not of constant density and that no simple relationship exists between gravimetrically and volumetrically determined sludge according to this preliminary work. Possibly, other time intervals of centrifuging, speeds, or radii of swing might have given closer density values. It is interesting to note that kerosene, so widely used in engine experimentation on motor oil investigations, shows little agreement with the straight oil and in one casethe paraffin base oil-gives a reversal of magnitude for the gravimetric and volumetric sludges.
Discussion The excellent methods of Levin and Towne (IZ),in which undissolved sludge is determined as the difference between sludge precipitated on a filtered and an unfiltered oil sample, and of Hall, Levin, and RlcMillan (8), which determines soluble sludge by propane precipitation of a filtered oil sample,
’RIC SLUDGE DETERYINBTIONS TABLE VII. VOLUJIET
IsoSolvent Naphthene base oil Volumetric procedure sludge, cc. per 100 grams isopentane sludge sludge, grams per 100 grams % isopentane sludge Apparent density of sludge, grams per cc. Gravimetric procedure
8
2
?.ki%ane
sludge
MidContinent base oil Volumetric procedure sludge. cc. per 100 grams isopentane dudge sludge, grams per 100 grains p/ isopentane sludge g p p a r e n t density of sludge, erams Der cc. Grajimetric procedure
t
2 i%:%ane
sludge
Paraffin base oil Volumetric procedure sludge. cc. per 100 grams iaopentane sludge sludge, grams per 100
grams per cc. Gravimetrio procedure
2 $$%tane
sludge
pentane
S6’B& Gasoline
7.64 100.0
73.4
0.67 100.0
77.6
0.0877 0.75
NO Kerosene
Solvent
5.61
1.14 14.9
0.16 2.1
0.52
0.10 14.9
0.042
0.0927
6.3
0.0877
0.2626
...
... ...
100.0
0.60 80.0
8.41 100.0
5.68 67.5
1.72 20.4
15.8
1.35
0.92 68.1
25.9
0 35
0 39 28 9
100.0
.
I
1.33
0.1620
0.2085
0.2932
1.24
,.
75.6
.
...
...
100.0
3.73 63.5
0.50 9.3
0.43 8.0
0.81 100.0
0.44
54.3
0.082 10.1
0.1605
1.64 100.0 5,40
0,1500
0.96 100.0
0.1180 0.63 65.6
0.1640
...
...
...
0.12
14.8
0.2791 .
.
I
...
VOL. 12, NO. 9
in combination with the procedures advanced in this paper, suggest a complete scheme of analysis for used or oxidized oils. It is suggested that the filtration be carried out a t 25’ C., by the use of pressure if necessary, so that the results may be correlated a t a common temperature, the effect of which has been pointed out above. The soluble or dissolved sludge of Hall, Levin, and hIcMillan (8),when corrected for soluble asphaltenes, closely resembles the sludge component defined earlier as resins. Their method being exactly outlined as to technique suggests that the use of the term “resins” be abandoned for the term ‘‘soluble sludge”, exactly defined by their procedure of determination. The combination of results of this study and the two methods mentioned in the foregoing paragraph gives a complete and sound analytical procedure for used or oxidized motor oils. The following determinations are necessary to the complete determination of the various components: (a) Asphaltenes, carbenes, and carboids as well as inorganic materials by isopentane precipitation ( b ) Carbenes and carboids as well as inorganic materials by carbon tetrachloride precipitation (c) Carboids as well as inorganic materials by carbon disulfide (d) Soluble sludge by propane precipitation of the oil obtained by evaporation (preferably under vacuum) of the filtrate from the isopentane precipitation under a ( e ) Dissolved sludge by propane precipitation of an oil sample filtered at 25” C., with or without pressure (f) Inorganic material by ignition of the precipitates obtained in a, b, or c
The individual components are then found as follows: Soluble sludge, determined directly by d Asphaltenes, a - b Carbenes, b - c Carboids, c - f Inorganic material, determined directly by f 6. Undissolved sludge, a - e 7. Dissolved sludge, e
1. 2. 3. 4. 5.
The undissolved sludge is determined according to the specifications of Levin and Towne except for the filtration a t 25’ C. The dissolved sludge, item 7, is in accord with the specifications of Hall, Levin, and McMillan, whereas the soluble sludge contains the asphaltene correction.
Summary Of the filters tested for sludge filtration, the most convenient and reproducible is a carefully prepared asbestosfilled Gooch crucible. The solvent or sludge precipitant employed greatly affects the amount of sludge obtained from an oxidized or used motor oil. Of the solvents investigated, the greatest amount of sludge is precipitated by isopentane. The amount of sludge precipitated is little affected by the time of standing after dilution. Temperature has an appreciable effect on the precipitation of sludge, being inversely proportional over the temperature range investigated. The amount of sludge precipitated increases with increasing dilution, a maximum being attained at 25 cc. of isopentane per gram of sample. Three reproducible solvents, isopentane, carbon tetrachloride, and carbon disulfide, are recommended which precipitate asphaltenes, carbenes, and carboids, respectively. (A fourth reproducible solvent is propane for soluble sludge as recommended by Hall, Levin, and McMillan.) These recommended solvents comply with A. S. T. AI. definitions and general usage in the field. A standard procedure for sludge precipitation of good reproducibility is outlined.
INALYTICAL EDITIOS
SEPTEMBER 15, 1940
An outline for the complete determination of sludge and sludge components is presented and recommended. S o simple relationship between gravimetric and yolumetric sludge appears to exist.
Acknowledgment The recommendations made in this article are the author's and it is not to be implied that the methods are used or recommended by The Texas Company. The author wishes to express his appreciation to The Texas Company for permission to publish the results shown in this article.
Literature Cited (1) Am. Soc. Testing Materials. Glossarv. 1931. i2) A. S. T. M. Committee D-9, sud-committee IV, Section (June 17, 1931).
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(3) Beilstein, "Handbuch der organischen Chemie", Berlin, Julius Springer. (4) Damian, J., Chimie & industrie, Special No., 323-5 (1932); Rev. pholifkre, 61-2 (1933). (5) Damian, J., and Dixmier, G., Ibid., 23, 834 (1930). (6) Dixmier, G., I b i d . , Special No., 283 (1938); Ibid., Special No.. 2 7 2 4 (1929). (7) Evans, E. A., J . Inst. Petroleum Tech., 9, 384 (1923). (8) Hall, F. IT., Levin, H., and hIcMillan, W.A., ISD.ENQ.CHEM., Anal. Ed., 11, 183 (1939). (9) Holde and Eikmann, Mitt.~ ~ ~ l . l a t e r i a l p r ~ ~ ~ ~ Berlin-Lichter1Lgsamt felde West, 25, 148 (1907). (10) International Critical Tables, New York, McGraw-Hill Book Co., 1926. (11) Knutson, B., Tek. Tid., 53, (36), Kemi, (9) 49 (1923). (12) Levin, H., and Towne, C. C., IND.ESG. CHEY.,Anal Ed., 11, 181 (1939). (13) Ormandy, IT.R., and Craven, E. C., J . Inst. Petroleum Tech., 10, 101 (1924). (14) Towne, C. C., Ibid., 17, 134 (1931). (15) Woog, P., and Givaudon, J., B u l l . SOC. chim.,(4) 47, 1419-20 (1930).
Laboratory Uses for Surface-Active Agents CHESTER M .ALTER
AND
DEANE S. THOMAS, J R . l
Boston University, Boston, Mass.
D
U R I K G the past few years a large number of surfaceactive agents have become available ( 2 ) . These substances derive their claim for unusually wide interest from their ability to lower substantially the surface tension of water and aqueous solutions when present in relatively small concentrations. There are doubtless many applications of these materials in the analytical laboratory; one such use has recently appeared in the literature (1). It is the purpose of this paper to call attention to other uses which the authors have made of surface-active agents.
Quantitative Separations by Centrifuging I n the course of some experiments invoking the determination of magnesium by precipitation with 8-hydroxyquinoline, it was difficult to separate the precipitate b y means of the centrifuge. Even with relatively high speeds, small crystals of the precipitate were held at the surface of the liquid in the centrifuge tube, making it impossible to remove the supernatant liquid without removal of some of the solid. It occurred to the authors that this annoying surface phenomenon might be overcome by reducing the surface tension of the liquid. It was necessary to do this without adding any appreciable amount of foreign material that would interfere with the subsequent determination of the magnesium salt, which was to be done colorimetrically. Some of the new surface-active agents were tried and found successful for this purpose. The direct addition of one drop of Tergitol 7 (manufactured b y the Carbide and Carbon Chemicals Corporation) to the centrifuge tube containing 10 ml. of the suspended magnesium salt was sufficient to cause the solid to be completely settled by slight centrifugation. It is apparent that the procedure outlined above is applicable to many analytical methods. It should be especially helpful in microanalytical work where quantitative separation by centrifugation is very often used. One of the authors has found it often applicable in routine separations in semimicromethods of qualitative analysis. 1
Present address, Eastman Kodak Company, Rochester,
N.Y
Creeping Precipitates Certain finely divided precipitates handled in quantitative analysis have a tendency to creep u p the walls of the container causing annoyance and possible error in many analytical procedures. Calcium oxalate is especially offensive in this respect. If the surface tension of the solution is lowered by the addition of a surface-active agent such as one of the Tergitols, this difficulty is remarkably decreased. If the agent is added previous to the time of precipitation, crystal growth is inhibited by the adsorption of the large polar molecule. A precipitate of calcium oxalate thus formed will pass through the ordinary quantitative filter paper. If the agent is added after precipitation and digestion, the particles of precipitate mill remain large and easily filterable, the c r e e p ing tendency is almost completely overcome, and transfer of the precipitate is easily accomplished. The concentration of Tergitol necessary is not great enough t o cause appreciable error in the ordinary determination of calcium if gravimetric methods are to be used. If the volumetric method is used for the determination of the calcium oxalate, no error should be expected.
Stabilizing Suspensions I n nephelometric and turbidimetric analysis one of the experimental difficulties encountered is the settling of the suspensions. Often it is desirable to stabilize such suspensions in order to make consistent determinations. Some of the surface-active agents are particularly well adapted for this purpose, since they are active in such low concentrationsfor instance, the life of a silver chloride opalescence as used in nephelometric measurements is increased twenty fold by the addition of a small amount of Tergitol. There are doubtless many other applications of such materials in the laboratory, but these three mill suffice to indicate that surface-active agents are useful reagents to keep on the laboratory shelf.
Literature Cited (1) Roberts, C. H. M., IND. ENQ.CHEN.,Anal. Ed., 10, 518 (1938). (2) Van Antwerpen, F. J., IND. ENQ.CHEN.,31,66 (1939).
