Anal. Chem.
-Table V. The Slope and Variance for the Plots of ADM Analyses vs. Direct DCP Analyses for Used Oil Samples no. of element samples slope variance Ag
0.65 0.76 0.84 0.61 0.81 0.91
19 37 35 55 89 50
Al
cr cu Fe ME
1.54 3.75 0.91 6.7 18.95 7.46
Table VI. Comparison of ADM Analyses with Direct DCP (No Acid) ~4nalysesfor Used Oil Samples sample no. elements 1
Cd Ni
Ti 2
Fe C!u
MO 3
Zn Na Pb Si
Sn 4 5 6c
Fe
F'e C!u Ag F'e
cr
C!u Zn O1 Run at 4 0 "C. sample.
concn, ppm no acid
ADM
26.6 6.3 11.6 310 380 3.2 26.1 1.7 933 195 2.4 1.0 3.8 3.5 0.5 3.6 0.5 2.2 1.7
67.5 12.9 16.0 370 560 11.8: 15.5b 33.1 7.8 1670 240 6.2 4.2 15.1 8.6 3.6 23.1 3.4 6.4 3.8
Run at 65 "C.
C
979
1982, 54, 979-985
Hydraulic fluid
that the direct analysis is not quantitatively analyping the oil samples. Therefore, the ADM must be utilized to ensure the quantitative recovery of all wear metal(s) in used lubricating oils. Even Ag, which hm a 75% recovery for simulated wear
metal suspensions, affords much higher concentrations when ADM is used compared to direct analysis (Table V). For spectrometers to detect severe wear at an earlier stage, the samples could be analyzed by direct analysis and the ADM. Any significant difference between the analyses would indicate the presence of large particles limits, predict imminent engine failure even in samples with low wear metal concentrations. Therefore, the defective component can be repaired, avoiding further wear and eventual equipment failure. Three examples which support this proposed approach are samples 4, 5, and 6 in Table VI. In each case the concentration(s) found by either method are within normal operating limits, but the presence of severe wear is indicated by the large difference in concentrations determined by direct analysis and the ADM. The wear debris filtered from the oil samples 4 and 5 were examined by an optical microscope. Metallic particles with sizes up to 70 pm were found in each sample. The engines from which these samples were taken developed gear box failures soon after sampling.
LITERATURE CITED (1) Selfert, W. W.; Westcott, V. C. Wear 1973, 2 3 , 239. (2) tukas, M.; Gierlng, L. P. Symposium No. 95a on Military Technology Oil Analysis 1978"; Materialpruefstelleder Bundeswehr und Bundesakademle fur Wehrverwaltung und Wehrtechnik: Erding, West Garmany, 4-6 July 1978; p 95a.01. (3) Selfert, W. W.; Westcott, V. C. Wear 1972, 2 1 , 27. (4) Kahn, H. L.; Peterson, G. E.; Manning, D. C. At. Absorpt. Newsl. 1970, 9 (3), 79. (5) Saba, C. S.; Rhine, W. E.; Elsentraut, K. J. Anal. Chem. 1981, 5 3 , 1099. (6) Kriss, R. H.; Bartels, T. T. At. Absorpt. Newsl. 1970, 9 (3), 78. (7) Saba, C. S.; Eisentraut, K. J. Anal. Chem. 1979, 5 1 , 1927. (8) Saba. C. S.; Elsentraut, K. J. Anal. Chem. 1977, 4 9 , 454. (9) Brown, J. R.; Saba, C. S.; Rhine, W. E.; Eisentraut, K. J. Anal. Chem. 1980. 5 2 . 2365. (IO) Rhine, W.'E.; Saba, C. S.; Kauffman, R. E.; Brown, J. R.; Fair, P. S. "Research and Development on Wear Metal Analysis"; Report No. AFWAL-TR-81-4184. Materials Laboratory, Air Force Wright Aeronautical Laboratories, Air Force Systems Command, Wright-Patterson Air Force Base, OH, Jan 1982.
RECEIVED for review December 11,1981. Accepted February 16, 1982. Presented in part a t the 180th National Meeting, American Chemical Society, Division of Analytical Chemistry, Las Vegas, NV, Aug 24-29, 1980.
Determination of Low-Rank Coal Liquefaction Light Oils by Chromatography and Nuclear Magnetic Resonance Spectrometry Sylvia A. Farnum" and Bruce W. Farnum Grand Forks Energy Technology Center, U.S. Department of Energy, Box 8213 University Statlon, Grand Forks, North Dakota 58202
Llght oils from Ilquefactlon of lignlte were separated by extraction into dlmethyi sulfoxide (Me,SO) insoluble hydrocarbon, aromatic, phenolic, and basic fractions and by silica gel column chromatography Into 11 fractlons of Increasing polar content. The fradlons were characterizedby 200-MHz 'H NMR, 50-MHr "C NMR, and caplilary gas chromatography. Forty hydrocarbons and six phenolic compounds were Identified, and their quantity was determined. Analysis and comparison of process-derived samples are possible by use of these methods.
Liquefaction of low-rank coal with synthesis gas (carbon
monoxidehydrogen) to produce distillable products is under study at the Grand Forks Energy Technology Center (GFETC) (I). A 30% by weight slurry of as-received Beulah, North Dakota, lignite in redistilled anthracene oil was fed to a 4.55-L continuous stirred tank reactor at 460 "C and 27.5 MPa with a nominal residence time of 1 h. Light oils were condensed from products in the gas phase at 300 OC and 27.5 MPa, along with a water layer saturated with phenol arid cresols. The water layer was separated. An ASTM D-86 distillation of the light oil (atmospheric pressure 98.7 kPa) had an initial boiling point of 60 "C and a dry point of 298 O C with 94% of the oil distilled. The heavy liquid product stream (including mineral matter) from each pass was used
This article not sublect to U.S. CoDvrlaht. Publlshed 1982 by the American Chemical Society
980
ANALYTICAL CHEMISTRY, VOL. 54, NO. 6, MAY 1982 LIGHT OIL IN PENTANE
Table I. Elemental Analysis of Light Oil 28-14 and Distribution of Elements among Solvent Extraction Fractions
HCI
PENTANE
1 NEUTRALIZE
%
1 NEUTRALIZE
I
280L0-14 basic phenolic aromatic hydrocarbon
p" "] i - C 12 [e%P""l I
PENTANE
AQUEOUS
HA-P
HA-M (12 4%)
(154%)
AROMATICS
PENTANE
EVAP BA-P (20%)
BASES
AQUEOUS
EVAP CH,CI, SA-M (13%)
PENTANE
EVAP PH-P (156%)
EVAP PH-M ( 5 9%)
PHENOLS
Flgure 1. Extraction procedure for the separation of light oils
as pasting solvent to prepare a new 30% lignite slurry for 32 subsequent recycle passes through the reactor. The light oil accounted for about 19% of the yield calculated on a moistureand ash-free coal basis (2, 3). The light oil characterized in this study was produced during the 30th recycle pass and represents a lignite-derived material free of the effects of start up solvent (2). To rapidly evaluate liquefaction products, it was desirable to develop characterization methods which could be applied to a large number of light oils with a minimum of sample handling. Since the oil mixtures are extremely complex and contain hundreds of compounds, comparison of similar samples during processing becomes difficult. The goal was to develop a fast, reproducible method for the identification of the major organic compounds in light oils from process streams and the estimation of approximate amounts of these materials present. The usual approach when evaluating soluble coal-derived materials by lH and/or 13C NMR spectrometry was proposed by Brown and Ladner ( 4 ) . The method has been developed and amplified by other investigators (5-12). Average molecular structure parameters based on the percentage integrated hydrogen or carbon types seen in the MMR spectrum are calculated. Due to the complexity of most of the spectra obtained from coal products, detailed assignments are not attempted, especially when conventional spectrometers are used. The increased resolution that can be obtained with the use of superconducting solenoids makes individual assignments possible in many cases. In the present work a simple separation scheme (13) was chosen and modified for lighter samples and the separated fractions were examined by 200-MHz lH NMR and 50-MHz 13C NMR complemented by capillary gas chromatography (GC). A column chromatographic technique was developed which was used to check the results obtained from the extraction procedure. These methods are rapid and yield excellent results with small amounts of sample.
EXPERIMENTAL SECTION Extraction. The light oil as received from the Continuous Processing Unit was fractionated by using a modification of the scheme suggested by Fruchter et al. (13). The modified procedure is shown in Figure 1. A solution of 50 g of sample in 250 mL of pentane was extracted with 100 mL of 2 N NaOH (3X), neutralized to pH 1, extracted with 100 mL of pentane (3X) and reextracted with 100 mL of methylene chloride (3X). The solvent-sample solution was next extracted with 100 mL of 2 N HCl (3X) to remove the bases which, after neutralization to pH 11, were reextracted into 100 mL of pentane (3X) and 100 mL of methylene chloride (3X). The pentane sample was also extracted with dimethyl sulfoxide (MezSO),100 mL (3X). Water (500 mL) was added to the MezSOand the solution was saturated with KCI. The MezSOsolution was then extracted with 100 mL of pentane (3x) and 100 mL of methylene chloride (3X). All of the solvent-oil
%S
H,Oa
84.34 10.69 3.70 0.37 0.22 3.86 0.50 0.21 0.25 0.0 19.15 2.34 3.08 0.01 0.01 19.07 1.83 0.38 0.10 0.13 42.26 5.58 0.03 0.0 0.08
0.23
%C
a
%H
%O
%N
Karl-Fischer titration.
extracts were dried over anhydrous MgS04before recovery with a rotary evaporator operated at less than 30 "C. The pentane and methylene chloride extracts from the MezSOsoluble aromatics were combined for analysis. Column Chromatography. A pentane solution containing 1 g of the light oil was fractionated according to the method of Dooley et al. (14). The procedure was modified in that a simple 1.9 cm X 43 cm neutral silica gel column activated at 260 "C was used. The solvent schedule was adjusted to elute smaller samples. The volumes used were as follows: pentane, 5 X 50 mL, 5% benzenelpentane, 2 X 50 mL, 15% benzenelpentane, 2 X 20 mL, 20% benzene/20% ether/60% methanol, 2 X 50 mL, and methanol, 150 mL. Nuclear Magnetic Resonance. 'H NMR spectra were obtained at 200 MHz with a Varian XL-200 NMR spectrometer. Solutions were prepared by dilution of 25 WLof sample with lo00 gL of CDC13 containing tetramethylsilane (Me4Si). They were pulsed 25 times at a flip angle of 4 5 O at ambient temperature, approximately 22 "C. The "C NMR spectra were also acquired with the Varian XL-200. The instrument was operated at 50 MHz with the 10-mm broad band probe. The solutions were 30% oil M C ~ ( A C A C )The ~ . pulse in CDC13 with 2% MelSi and 5 x angle was 60". The number of pulses varied from 5000 to 15000 with a 5-9 delay, at ambient temperature. Gated proton decoupling was used with the decoupler off during the delay and on during acquisition. All chemical shifts were measured relative to Me4Si. (More recent runs show that with 50% solutions 1500-3000 pulses over a 2-3 h time period yield comparable spectra.) Gas Chromatography. Gas chromatography of the fractions was carried out on a Varian Model 2100 with flame ionization detection using a 6 ft 3% Dexsil 300 on 80/100 Supelcoport column or on a Varian Model 3700 on a 50-m OV-101 glass capillary column utilizing flame ionization detection. Temperature programming was at 4 deg/min from 80 to 240 "C for the capillary column or was varied to give most efficient separation for the packed Dexsil 300 column.
RESULTS AND DISCUSSION Separations. The modification of the Fruchter et al. scheme was chosen to yield fractions in which NMR overlap of key resonances was minimal. The separation used gave several other advantages. The initial 50-g sample when separated gave adequate quantities of each fraction for further investigations. The use of pentane as the principal organic phase enabled the removal of the extracting solvent at a temperature of less than 30 "C. We were thus able to preserve most of the lower boiling materials. Rearrangement in the order of extraction (Figure 1)was essential for the examination of this type of oil in which phenols are present in large amounts (about 20%) and bases in small amounts (
