Gas Chromatographic Determination of Fuel Dilution in Lubricating Oils ROGER S. PORTER and JULIAN F. JOHNSON California Research Corp., Richmond, Calif.
b A gas chromatographic method has been developed for measuring fuel dilution in crankcase oil. The apparatus consists of a preheater block which flashes the diluent from the oil into a helium stream, a precolumn which condenses oil entrained in the helium flow, and a gas chromatographic column which resolves and measures the amounts of diluent. Results are based on the use of an interhal standard placed in known concentration in each determination. Extensive calibration tests indicate that the chromatographic method i s the most sensitive and accurate analysis yet available for measuring fuel dilution. Supplementary advantages over distillation analyses are that small samples are used, the test i s simple, the volatility range of the diluent i s indicated, and the chromatographic chart provides a permanent record.
T
HE amount of gasoline found in
crankcase oil may be used as a criterion of automobile engine performance. Dissolved gasoline lowers motor oil viscosity and causes an increase in oil consumption. Section Q-1, Technical Committee B, Committee D-2 of the American Society for Testing Materials has been studying determination of fuel dilution by distillation methods for many years. From extensive cooperative testing of distillation methods in several laboratories (S), it has been shown that: distillation methods give results lower than the true values, analysis is influenced by the nature and amounts of diluent and by the composition of the base oil, and reproducibility and repeatability of the distillation methods are poor. With the aid of a simple attachment for a conventional gas chromatographic apparatus, a method for determining fuel dilution has been developed. The method has good precision, accuracy, and sensitivity. Results also give a n indication of the nature of the diluent fraction, The test is simple and inexpensive. A single analysis requires 1 hour of instrument time and about 0.5 hour of operator time. 866
ANALYTICAL CHEMISTRY
APPARATUS
The sample containing a n internal standard is injected into a preheater block which flashes the diluent and standard into a stream of helium. The gas then goes into a precolumn which removes oil entrained in the helium. The helium plus the vaporized diluent and standard then enter a chromatographic unit where the diluent and standard are resolved and measured. A schematic drawing of the entire apparatus is shown in Figure 1. Preheater Block. A high temperature method has been chosen for removing diluent fractions from oil. Heliurn is used t o sweep volatilized fractions directly into a chromatographic rolumn. A cutaway drawing of t h e heatel block used t o remove fuel fractions from oil is shown in Figure 2. The heater block has been designed with a high thermal capacity to ensure good heat transfer to the sample. Four 125-watt strip heaters are bolted to the sides of the brass block. The heaters are connected in series and are controlled through a variable transformer. Fuel dilution determinations are made a t block temperatures of 315' C. which correspond to a transformer setting of 65 volts. Settings of 110 volts may be used to bring the block quickly up to test temperature. The lowest temperature at which gasoline fraction> are all immediately volatilized is 315' C. No peaks are observed for 0 1 1 fractions or for products due to degradation of oil or polymer additives below this temperature. The threaded plug at the base of the preheater block provides a niethotl of removing solids from the system. In practice, it has been found that small amounts of solids do not affect the method or results. Moreover, solids accumulate slowly so that the block needs to be cleaned out no more than once every 50 runs. The threaded plug makes a tight seal n i t h or without the use of a Teflon gasket. The high operational temperatures for the preheater block require that it be extensively insulated. The block fits conveniently within a 2-liter borosilicate glass beaker. The sides and the base of the beaker are packed m-ith asbestos and glass wool. The top of the beaker has been trimmed so that the valves on the preheater block may be easily operated.
PR RE
Figure 1. tests
Apparatus for fuel dilution
Precolumn. Early research showed t h a t oil samples are carried out of t h e preheater block by entrainment in t h e helium stream. The entrained oil is carried into the column where it condenses and dissolves i n t h e packing, resulting in a marked change in the retention times and in t h e resolving por$er of the column. I n cases of extreme contamination, column blockage occurs. To protect the column packing, a vertical 4-inch precolumn has been installed between the preheater block and the Fractometer. The precolumn traps oil fractions ~thich have been carried from the Hock. The position of the precolumn is shown in Figures 1 and 2. The column is constructed from conventional pipe, inch in outside diameter. The precolumn and adjacent lines arc kept a t a temperature well below that of the block and slightly higher than that of the analyzer column. Sine feet of Fibprglas-covered Xichrome nire (1.55 ohms per foot) is wrapped crenly about the helium line between the preheater block and the Fractometer inlet. A potential of 33 volts, established by a variable transformer, gives a satisfactory precolumn temperature of 175" C. Higher precolumn temperatures allow oil to be carried through into the unit; loner temperatures tend to retard unduly the diluent fractions. To minimize vapor condensation and diffusion, short heated lines are used to connect the block, the precolumn, and the Fractometer. The precolumn packing is the same as that employed in the Fractometer and can hold up to 1.5 ml. of oil without disturbing experimental
3 L,
PIPE PLUGS
NEEDLE VALVE
A HELIUM INLET
-
REFERENCE
: B
BRASS BLOCK, 2.112' x 2 . 1 1 2 " ~ 5-112"
I
e&.
REFERENCE
-2
Figure 3. A.
OIL INJECTION CAPILLARY
B.
SECTION A-A 3 - - 3
48 -1
I HOUR
>\ SAMPLE
5.56
e-4
TIME
GLASS JAR ASBESTOS PAD
TEFLON GASKET BRASS PLUG
SAMPLE
Chromatographic analyses in base oil 0.1 0% premium gasoline, analysis 0.1 1 % 10.00% premium gasoline, analysis 9.78%
SCALE, INCHES
Figure 2.
Preheater block for fuel dilution apparatus
results. Beyond this amount, abnormal retention times and blockage of flow are observed. Therefore, the column packing is systematically replaced every three runs. To repack the precolumn, the helium flow is diverted >by first turning the gas sample valve to vent. The Hoke valves adjacent to the precolumn are then turned off. Next, pipe plugs a t either end of the column are unscrewed. The glass wool is then removed a t each end of the precolumn, and the packing is rammed out by using a small diameter rod. To replace the precolumn packing, glass wool is loosely fitted a t the base of the precolumn. A small funnel is helpful in pouring the packing into the precolumn. A glass wool plug is placed a t the top of t h e lightly packed column. The pipe plugs are then replaced, and the helium flow is again routed through the block and precolumn. Some care must be taken to prevent packing from entering and blocking the side arms. Packing replacement takes about 3 minutes. The heater on the precolumn need not be turned off for this operation. To measure the temperature of the preheater block, a lI8-inch hole is drilled several inches into the top of the brass block. A Chromel-Alumel thermocouple is inserted in the hole to record block temperatures. Another thermocouple is placed against the barrel of the precolumn. Readings taken at this position have been shon-n to represent true piecolumn temperatures. Temperatures of the block and precolumn are rcad from a single potentiometer box which is connected to the thermocouples through a heavy-gage, double-throw, knife switch. Gas Chromatographic Apparatus. A Perkin-Elmer Vapor Fractometer Model 154B was used. Choice of the column packing, length, operating temperature, and other specifications is arbitrary; many variations are possible. The chief reasons for the particular conditions given here are t h a t they give a reasonable elution time (about 1 hour) and some resolution for diluent components.
The column is 2 feet long and is made from copper tubing inch in outside diameter. The column temperature is 150' C. The column packing is 20 to 40 mesh size, Johns-Manville C-22 insulating brick, coated with 15 grams of 128' to 130" F. melting point paraffin wax per 100 grams of brick. The helium valve on the unit is adjusted a t pressures between 10 and 20 p.s.i. to produce rotameter readings between 12 and 15. This corresponds to helium flow rates of 500 to 700 ml. per minute. The high flow rates keep run times below 1 hour. The potential on the detectors is set a t 8 volts. METHOD
An internal standard is used to determine the amount of diluent present. Two reference compounds have been used satisfactorily as standards. Each gives a useful retention time and is readily available in sufficient purity. n-Dodecane has aretention time of about 40 minutes and is used for many samples. When samples contain diluent less volatile than n-dodecane, 2-methylnaphthalene with a retention time of about 1 hour is used. The internal standards are made up in oil so that solid reference compounds may be used and small amounts of the reference may be accurately measured volumetrically. Reference solutions are made up with 10 grams of reference in 100 ml. of base oil plus reference. The base oil is conventional lubricating oil that has been heated under vacuum to remove any low boiling contaminants. Unused samples of some compounded motor oils give a single peak on the recorder chart with a retention time of less than 30 seconds. Presumably this peak is associated with an oil additive. All diluent fractions tested have retention times greater than 30 seconds. Therefore, components which appear a t less than 30 seconds are disregarded. Measurements on unused oils showed
no detectable peaks with resolution times between 30 seconds and 2 hours. The base oil therefore does not interfere with the analysis. A11 species in the gasoline boiling range which are found in used oils are arbitrarily classified as fuel dilution.
A graduated hypodermic syringe is used to blend carefully a 10-ml. aliquot of test oil with 1 ml. of reference solution. The mixture is agitated in a closed bottle a t room temperature for 30 seconds. By using a clean syringe with a long needle of large diameter, 0.25 to 0.5 ml. of sample is removed from the bottle. A 2-ml. B-D Yale syringe with a Luer-Lok fitting is satisfactory for sample handling. The needle on the syringe is detached, and the tip of the syringe is turned up. The plunger is then pushed in until essentially all air is removed and the proper amount of sample remains in the syringe. The syringe is next screwed onto the Luer-Lok fitting on the block. If the entire fuel dilution apparatus has come to thermal equilibrium, the sample may then be injected. To inject a sample, the hypodermic syringe and plunger are held firmly, Tvhile the small valve leading to the block is opened by turning the stem 90". When the valve is open, internal helium pressure tends to push out the hypodermic plunger. When this impulse is felt, the plunger is pushed donn and 0.25 to 0.5 ml. of sample is injected. Kliile the plunger is held down, the inlet valve is closed. The syringe muy then be removed and cleaned. The therniocouples in the block, precolumn, and Perkin-Elmer unit are used to judge n hen the dilution apparatus is in thermal equilibrium. In practice, t8he recorder is the most sensitive indicator for thermal equilibrium. When the pen record is smooth, and without drift with time a t high sensitivity settings, a dilution sample may be injected. The Perkin-Elmer unit is commonly run a t an attenuation setting of one. Any reduction in sensitivity which may be necessary to kcep the pen on VOL. 31, NO. 5 , MAY 1959
0
867
Calibration Runs on Dilution Samples of Known Concentration Gasoline, 50% Made Up Av. for 10 Bottoms Concn., 7oa Runs, % a Bbs. Error Std. Dev. Table 1.
5
0,117 0.107 -0,010 Regular 0.110 0.103 -0,007 Premium 1.003 0.98 -0.023 Regular 0.94 -0.052 0.992 Premium 5.004 5.10 $0.096 Regular 5.006 5.02 + O . 014 Premium 10.02 10,09 +O. 07 Regular Premium 10.07 10.23 + O . 16 1% dilution is 1 gram of diluent in 100 ml. of oil plus diluent. Table 11.
ASTN Sample
Q-1-s Q-1-T Q-1-U
0.034
0.018
0.081 0 092 0.34 0.26 0.26 0.52
RESULTS
ASTM Cooperative Fuel Dilution Samples
Base Oil TT'inter Summer
Y X
Diluent 207, Whole bottoms gasoline
x
Y
S
X Y
Fuel Dilution, Volume in Volume, % MethodMethod I, Method 11, 111, gas steam vacuum chromadistn. distn. tography
2.7 13.8 2.7 9.6
5.2 15.8 4 7 12 2
5.1 10 7 57 12.1
Table Ill. Analysis of Regular Fuel Dilution Samples Gas Chromatography Steam Distn., Difference, Gram/ml. Ml./ml., % MI,/Ml., 7, MI./ml., 2 1 1 2 -0 9 1 68 x 2 77 3 4 2 5 -0 9 12 4 10 2 -2 2 10 17 6 2 5 0 -1 2 5 06 1 1 0 4 -0 7 0 90 0 19 0 6 0 1 -0 5 0 8 Trace -0 8 0 66 7 26 8 9 6 0 -2 9
chart occurs within the first 5 minutes of a run. The highest concentration of diluent fractions is commonly found in this region. From 5 minutes to the termination of the run, operator time may be spent in preparing samples and in integrating areas on the charts from previous determinations. All diluent fractions are integrated as one area. For convenience, the dilution area may be arbitrarily divided up. Of course, where recorder sensitivity has been changed, areas must be integrated separately. Commonly, the base line for a dilution run is identical with the base line on the chart. I n cases where the pen does not start or terminate at zero, careful judgment must be used in drawing the base line. There can be little uncertainty in the base line when the line is drawn through the initial and final pen positions. The pen often returns to the base line a t midrun, which is after the gasoline fractions and prior to the reference. When this is true, the base line for the diluent and reference are the same. However, when diluent fractions dribble out into the dodecane region, the base line for the reference is drawn on a regular descending 868
ANALYTICAL CHEMISTRY
tubing from a vacuum bottle to the Luer-Lok fitting. With vacuum on the sample inlet valve, the valve is opened for about 5 seconds. The oil is sucked up the tubing and is observed as a small amount of froth in the bottle, Only a small fraction of the total oil sample is recovered in this way as most of the oil is entrained in the helium stream. The entrained oil is condensed and recovered in the precolumn packing.
slope of the gasoline peak. S o significant error is caused by this procedure as the distribution of compounds and isomers in the higher molecular weight range is such that there is no resolution in this region. The concentration of diluent in oil is calculated by dividing the area for the diluent by the area of the reference peak. The quotient gives directly the concentration in grams of diluent per 100 ml. of oil; 1 gram in 100 ml. is called 1% dilution. No correction is entered for the differences in the thermal conductivities of the vapors involved. Thermal conductivities of all species in gasoline are known to be very similar. Moreover, calibration of the method with samples of known diluent concentration indicates that conductivities need not be considered as a source of error. The analyses may be easily adapted to other types of detection systems. For example, the carbon dioxide conversion technique would yield results which would be nearly independent of calibration errors. After the final peak for a run has appeared on the recorder chart, the residual oil in the block is removed. This is accomplished by attaching
Three typps of test samples were used in the development of the method: samples of knoivn diluent concentration, ASTN cooperative samples, and randomly selected samples sent in for dilution analyses by distillation. Samples of Known Concentration. Eight synthetic fuel dilution blends of known composition have been tested by the chromatographic method. The base oil for these blends T T ~ Ean unused 10-30 SAE multigrade oil. A standard and premium gasoline were distilled and the'507, bottoms used as diluent. The diluent samples Iyhich were made up a t four concentration levels were analyzed in random fashion. Table I lists these rrsults. I n similar gas chromatographic analyses, peak areas have been found to agree well with known weight percentages. Therefore, the results are presented in units of weight of diluent per volume of oil. For each sample the average deviation of results is larger than the absolute error, which indicates that there are no consistent errors in the determination. Three per cent of all values viere rejected on the basis of probability theory The suspected values in each case differed from the mean of the rest of the array by four times the average deviation. As experience n-ith the method was gained, the number of rejected results diminished rapidly. Figure 3 shows typical results obtained on samples containing 0.1% and 10.0% dilution. The initial peak is caused by a pressure surge and'or air and is disregarded. The numbers under the curves are the planimetered areas for the diluent and reference in square inches, The numbers on the base line are sensitivity settings. The record illustrates the sensitivity and versatility of the method. The planimetered area representing 0.17, dilution is large enough so that it is safe to predict that dilutions can be detected to below 0.03%. ASTM Samples. I n 1957, eight laboratories participated in a cooperative program on eight fuel dilution samples. Two distillhtion analyses were employed: Method I was a conventional steam distillation ( I ) ; Method I1 n a s essentially a reduced
pressure distillation somewhat similar to ASTAI D 1160 ( 2 ) . Two base oils and two types of diluent uere used. One diluent was a nhole gasoline, the other a 207, bottoms fraction from the distillation of gasoline. These samples nere run in quadruplicate by the gas chromatographic method. API gravities reported for the diluent were used to convert the gas chromatographic results to volume-in-volume concentrations to permit direct comparisons. Table I1 lists sample composition and results and > h o w that gas chromatographic values are generally higher than distillation results. Distillation procedures in no case give significantly higher diluent concentrations than chromatography. Results on sample Q-1-S seem abnormally high, and perhaps the sample tcstcd in this work has become contaminated.
It is difficult to remove all diluent by distillation. Sample (2-1-R was heated to 300” F. for 4 hours and all vapors were remox cd which came off TT ith the pressure reduced to 1 mm. of mercury.
After this treatment, about 1% of diluent still was present in the oil. Regular Dilution Samples. Eight randomly selected samples of used lubricating oil, submitted for dilution analysis by ASTM distillation D 32255T ( I ) , were determined by the gas chromatographic method. Using an assumed density for diluent of 0.82, gas chromatographic results were converted to volume-in-volume units. Results for these samples are tabulated in Table 111. The chromatographic charts obtained were similar to those for the synthetic and ASTII samples. ilgain the chromatographic results were consistently higher than those obtained by steam distillation.
run by weighing in the internal stand ard. Therefore, oil dilution samples may be periodically extracted during a continuous engine test without appreciably altering engine conditions. If desired, resolution of the diluent can be increased by use of longer columns and Ion er temperatures than used in this work. This makes it possible to ftudy individual fuel components that appear as diluent. The chromatographic chart also provides a permanent record of the nature and amounts of diluent. This general technique has proved to be very useful for a variety of analytical problems. LITERATURE CITED
CONCLUSIONS
Results indicate that the chrcmatographic technique has improved the sensitivity, precision, and accuracy of fuel dilution analyses. Moreover, there are several additional advantages of this method over distillation procedures. Samples as small as 0.25 ml. may be
(1) Am. Soc. Testing RIaterials, Philadelphia, Pa., “ASTlI Standards,” p. 169, Method D 322-55T, 1958. ( 2 ) Ibid., Appendix I, p. 1076. (3) ASTM Bull., to be published. RECEIVEDfor review July 25, 1958. Accepted October 17, 1958. Division of Petroleum Chemistry, 134th Meeting, ACS, Chicago, Ill., September 1958.
Gas Chroma tog ra phic Dete rmination of DissoIved Oxygen in Lubricating Oil PAUL G. ELSEY Research lobcrafories, Ethyl Corp., Detroit, Mich.
b A rapid quantitative method for the determination of oxygen in lubricating oil, utilizing gas chromatographic techniques, was developed in connection with a program relating engine wear to the amount of oxygen present in lubricating oil.
I
the recently developed chromatographic method for oxygen determination in lubricating oil, a special column effects a preliminary separation of the dissolved gases from the oil. Then the mixture of gases is passed through a llolecular Sieve analyzing column, which separates the individual components so that oxygen can be determined. The total analysis time is approximately 10 minutes. The lower limit of detection of oxygen is 0.01 volume 70. The standard deviation of a single determination is 2.2% of the mean. The method can be extended to include the determination of other dissolved gases, such as nitrogen. The only knon n interference is argon, which has the same retention time as oxygen. N
EXPERIMENTAL
T h e apparatus consists of a commercial gas chromatographic instrument modified with a bypass arrangement. The preliminary column, a glass U-tube, is attached t o t h e bypass arrangement as shown in Figure 1. One leg of t h e glass U-tube is fitted with t1T-o coarseporosity fritted disks 5 inches apart. d sampling port for injection of the oil sample is located midway betn-een the disks. The diameter of the sample chamber is 0.5 inch. The analyzer column, a section of copper tubing 20 feet long and 0.25 inch in outside diameter, is packed with Linde 14 X 30 mesh Type 5,4 Molecular Sieve. The recorder is a 0 to 5 mv. strip chart rvhich is operated a t 60 inches per hour. Procedure. The instrument is thermostatted t o 75’ C. and is operi t e d with a helium carrier gas f l o ~ rate of 50 ml. per minute. The glass TT-tube is wrapped with heating tape and also maintained a t 75’ C. I t is attached t o t h e bypass assembly, and t h e entire assembly is purged with helium. Then t h e stopcocks of the assembly are adjusted so t h a t t h e glass V-tube is in the carrier gas stream of Apparatus.
the instrument. K h e n the instrument has reached equilibrium, as evidenced by a stable base line on the recorder, the oil sample is injected into the YDLECYLA.(I 5 L Y E I*A.L”lE* COLUUli
Til
rrro
0,s-
PORT
61UPLlNO
CONThIW 110 I I L CONE. PLUG
I
1 C(IE6YI
-lr 0“ T
Figure 1 . Preliminary column for separating dissolved oxygen from oil VOL. 31, NO. 5, MAY 1959
869
