Anal. Chem. 1981,53, 831-836 (33) Merrltt, C.; Robertson, C). H.; Cavagnaro, J. F,; Graham, R. A,; Nichols, T. L. J. Agric. Food Clbm. 1974, 22, 750. (34) Alshima, T.; Nobuhara, A. Agric. Biol. Chem. 1977, 47, 1841. (35) Tressl, R.; Friese, L.; Fendenck, F.; Koppler, H. J. Agric. Food Chem. 1978. 26. 1422. (36) von Sydow, E.; Anderson, J.; Anjou, K.; Karlsson, G. Lebensem.-Wiss. Techno/. 1970, 38, 11. (37) Galetto, W. 0.; Bednarozyk, A. A. J. Food Sci. 1975, 40, 1165. (38) Parrlsh, M. E.; Higgins, C. T.; Douglas, D. R.; Watson, D. C. HRC CC, J. Hlgh Resolut. Chromatogr. Chromatogr. Commun. 1979, 2 , 551. (39) Schomburg, G.; Husmann, H.; Weeke, F. J. Chromatogr. 1974, 99, 63. (40) Schieke, J. D.; Comlne, N. R.; Pretorius, V, J. Chromatogr. 1975, 772, 97. (41) Hatch, F. W.; Parrlsh, hh. E. Anal. Chem. 1978, 50, 1165. (42) "Eight Peak Index of Meiss Spectra", Mass Spectrometry Data Centre, UK, 1974. (43) Guilford, J. P. "Psychometric Methods", 2nd ed.; McGraw-HIII: New York, 1954.
(44) (45) (46) (47) (48) (49) (50)
83 1
Thurstone, L. L. Am. J. Psycho/. 1927, 38, 368. Helm, E.; Trolle, B. Wallefstein Lab. Commun. 1946, 9, 181. Frljters, J. E. R. Br. J. &th. Stat. Psycho/. 1979, 32, 229. Gridgeman, N. T. J. Food Sci. 1970, 35, 87. Byer, A. J.; Abrams, D. Food Techno/. (Chicago) 1959, 7, 185. Peryam, D. R.; Food,Techno/.(Chicago) 1958, 72, 231. Atkinson, W. 0. Proceedings of the Tobacco and Health conference"; University of Kentucky: Lexlngton, KY, Feb 1970 Conference Report No. 2, p 28.
RECEIVED for review August 25,1980. Accepted February 9, 1981. This paper has been presented in part at a Symposium on Advances and Applications of High Resolution Chromatography a t the 31st Pittsburgh Conference on Analytical Chemistry and Applied Spectrscopy in Atlantic City, NJ, March 11, 1980.
Separation of Nitrogen Compound Types from Hydrotreated Shale Oil Products by Adsorption Chromatography on Basic and Neutral Alumina C. D. Ford,' S. A. Holmes," L. F. Thompson, and D. R. Latham Laramie Energy Technology Center, Department of Energy, P.O. Box 3395, Laramle, Wyoming 82071
The nltrogen compounds In hydrotreated shale oll products derived from Paraho shale oll are separated Into speclflc nitrogen-type fractions by using baslc/neutral alumina adsorption chromatographly. The separatlon scheme, whlch gives fast and reproducilble results, Is successfully applled to shale oil products produced under dlfferent hydrotreating condltlons. These products vary In the level of nltrogen and/or In the dlstillation range. Infrared spectrometry of the fractlons identified three major nltrogen compound types: pyrldlne-type nitrogen, pyrrole-type nltrogen, and amide-type nitrogen. The distribution of these nitrogen types In varlous hydrotreated shale oil products Is shown,,
The detrimental effect of nitrogen-containing compounds in transportation fuels and in fuel oils is demonstrated by relatively high NO, emisriions and by fuel product instability. Separation and characteriizationprocedures used in identifying nitrogen compound types can be used to help design refining processes that eliminate these detrimental compounds. A study of the nitrogen types in fuel products derived from shale oil requires a suitable separation scheme to selectively concentrate nitrogen compound types and to facilitate their characterization. The separation scheme should give rapid results and clean fractiondl of specific nitrogen compound types and should apply to samples independent of nitrogen level or distillation range. Numerous separation methods have been used in the analysis of nitrogen compounds in shale oil (1-4). Earlier work using ion-e rchange and coordination-complex chromatography by Holmes et al. (5) indicated difficulty in adequately separating anjd concentrating nitrogen compound types present in hydrotreated shale oil products. This work suggested that sample alteration occurring during any par'Present address: University of Utah, Salt Lake City, UT.
ticular separation is a primary concern when analyzing hydrotreated shale oil products. Snyder et al. (6) and Schiller et al. (7) successfully employed alumina adsorption chromatography to separate various compound types in petroleum and coal liquids, respectively. More recently Guerin (8) developed a separation scheme to effectively isolate nitrogen compound types from petroleum substitutes utilizing acidbase extraction, alumina and silica adsorption chromatography, and Sephadex LH-20 column chromatography. The latter separation schemes involve a considerable amount of time and effort and generate numerous fractions that in this study are not necessary for characterization. This work presenk a useful scheme incorporating basic and neutral alumina adsorption chromatography for separating the nitrogen compound types present in hydrotreated shale oil products. The separation scheme is applied to several hydrotreated shale oil products produced under different refining conditions. These products vary in boiling range and in total nitrogen. The composition of the fractions collected by the separation and the stability of the hydrotreated shale oil products are discussed. The separation procedure is also applied to a crude shale oil sample with poor results.
EXPERIMENTAL SECTION Hydrotreated Shale Oil Products. Five hydrotreated shale oil products produced by the Standard Oil Co. of Ohio (Sohio), Toledo, OH, and two hydrotreated shale oil products produced by Chevron Research Co., Salt Lake City, UT, were studied in this work. All products were derived from Paraho crude shale oil containing about 2.2 w t % nitrogen. Details regarding the hydrotreating conditions can be found elsewhere (9,lO). In the Sohio operation, the crude shale oil was allowed to settle, run through an alumina guard bed to remove particulates and metals, and then catalytically hydrotreated over a nickel-molybdenum catalyst. The hydrotreabd whole product was distilled into four fractions: gasoline (11vol %),jet fuel (26 vol %), diesel fuel marine (31 vol %), and residuum (32 vol %). The Sohio products studied in this work include the following: the hydrotreated whole product which included recycled bottoms; two jet
This article not subject to U.S. Copyrlght. Published 1981 by the Amerlcan Chemical Society
832
ANALYTICAL CHEMISTRY, VOL. 53, NO. 6, MAY 1981
HYDROTREATED SHALE OIL PRODUCTS (Jet and Diesel Fuels)
I
BASIC ALUMINA (Gravity. or pumped-flow)
1
-
I
n-C6
IFRA;llONpEUTRALj
1% CzH50H/ CHC13
I
,, FRACTION
L sL ~ B -J 1 1
BASIC ALUMINA (Pumped-flow)
I
-
I
I Figure 2. Separation scheme for the fractionation of hydrotreated
Figure 1. Separation scheme for the fractionation of hydrotreated shale oil products (jet and diesel fuels). Subfraction 1 is denoted as fraction 1*, and subfraction 2 combined with fraction 2 is denoted as fraction 2' in Tables I-V.
whole shale oli and residuum. Subfractions 1 combined and denoted as fraction 1*, and subfractions 2 combined and denoted as fractlon 2' in Tables I-V.
fuels, JP-5 and JP-8, having a boiling range from 163 to 249 OC; a diesel fuel marine, DFM, having a boiling range from 245 to 343 "C; and a 345 "C+ residuum. None of these products was fully refined; therefore, the nitrogen content ranged from 0.3 to 0.5 wt %. Sulfur content was low-less than 20 ppm for each of these products. The two hydrotreated whole products refined by the Chevron Research Co. were produced over a proprietary ICR-106 nickel-tungsten catalyst. The boiling range for each of these two hydrotreated whole products was about 50-500 "C. The samples contained 0.048 and 0.095 wt % nitrogen. Again, very little sulfur (less than 20 ppm) was present in these products. Gravity-Flow Separation Procedure Using Basic Alumina. A gravity-flow column chromatographic method was employed to separate compound types from the two jet fuel products and the diesel product produced by the Sohio operation. Each sample was separated into four fraotions. An accurately weighed sample, approximately 8 g, was diluted with 80 mL of n-hexane. The solution was charged onto 16 g of basic alumina in a 100-mL buret by gravity flow. The flow rate of charge and elution was 3-4 mL/min. The charge volume plus an additional 120 mL of n-hexane were used to elute fraction 1from the column. Fraction 2 was then eluted with 250 mL of 5 vol % methylene chloride in n-hexane. Fraction 3 was eluted with 250 mL of methylene chloride; finally, 100 mL of methanol/benzene (40:60 v/v) was employed to remove fraction 4 from the basic alumina. The elution volumes were determined by analyzing infrared spectra of the fractions collected. Figure 1 (left-hand side) displays this separation scheme. Pumped-Flow Separation Procedure Using Basic Alumina. The gravity-flow procedure used in the separation of the shale oil jet fuel and diesel samples was adapted for use with a pumped-flow system. An accurately weighed sample of jet fuel or diesel fuel, approximately 8 g, was diluted with 80 mL of n-hexane. This solution was charged at 3 mL/min onto an 0.9-cm i.d. X 25-cm glass column containing 14 g of basic alumina. The charge volume plus an additional 120 mL of n-hexane pumped through the column constituted fraction 1. Fraction 2 was collected by pumping 150 mL of 5 vol % methylene chloride in n-hexane through the column, fraction 3 was collected by pumping 200 mL of methylene chloride through the column, and fraction 4 was backflushed from the column by pumping 100 mL of methanol/benzene (4060 v/v) through the column.
The procedure for the residuum sample and hydrotreated whole shale oil samples used a 0.9-cm i.d. X 50-cm glass column containing 30 g of basic alumina to separate the nitrogen compound types present in these samples. An accurately weighed sample of a residuum or a hydrotreated whole shale oil-approximately 3 g for the residuum and Sohio samples, 10 g for the Chevron samples-was diluted with 150 mL of n-hexane and charged onto a column containing basic alumina at a flow rate of 3 mL/min. Fraction 1included the charge eluate plus an additional 210 mL of n-hexane pumped through the column. Fraction 2 was collected with 300 mL of 5 vol % methylene chloride in n-hexane and fraction 3 with 400 mL of methylene chloride. Fraction 4 was backflushed from the column by pumping 100 mL of methanol/benzene (4060 v/v). This separation procedure is presented in Figure 2 (left-hand side). Gravity-Flow Separation Procedure Using Neutral Alumina. Infrared spectrometric analysis indicated that fraction 1 from each jet fuel and diesel fuel sample separated on basic alumina contained nitrogen compound types similar to those types in fraction 2. Therefore, it was necessary to remove these nitrogen compound types from fraction 1and combine them with fraction 2. To achieve this goal, we employed a gravity-flow column containing 15 g of neutral alumina. Figure 1 (right-hand side) shows this separation scheme. Fraction 1 was diluted with 80 mL of n-hexane and charged onto the neutral alumina column. Subfraction 1was eluted with an additional 150 mL of n-hexane. Subfraction 2 was desorbed from the column with 100 mL of 1 vol % ethanol in chloroform. Subfraction 2 and fraction 2 from each sample were combined and denoted as fraction 2* in Tables I-v. Fractions 1 and 2 from the residuum and total hydrotreated samples also contained overlapping compound types, and each was separated on 15 g of neutral alumina adsorbent into subfractions 1 and 2. After either fraction 1 or 2 was diluted with n-hexane (1:30), an additional 50 mL of n-hexane and 100 mL of 5 vol % methylene chloride eluted subfractions 1. The subfractions 2 were desorbed from the column with 100 mL of 1vol % ethanol in chloroform. This separation is shown in Figure 2 (right-hand portion). Subfractions 1 were combined for each sample and denoted as fraction 1*, and subfractions 2 were combined for each sample and denoted as fraction 2* (Tables I-V). The solvents were stripped from each fraction with a Buchi rotary evaporator. The fractions were quantitatively transferred
ANALYTICAL CHEMISTRY, VOL. 53, NO. 6, MAY 1981
833
Table I. Results of the Separation of Nitrogen Compounds by GravityFlow and the Pumped-Flow Systems wt 74 distribution of M compounds diesel jet fuel (JP-8) __-
fraction
gravity
2*
60
3 4
43 7
pump 47 44 9
gravity 41 44 15
Pump 40 47 13 FRACTION 2
to weighed 10-mL glass %vialswith three washes of methylene chloride. Each fraction was carefully dried to constant weight with a nitrogen evaporator. Reagents. All solvents employed in the work were HPLC grade and were helium degassed prior to use. The basic alumina was Bio-Rad AG-10 with an average particle size of 0.254-0.127 mm (100-200 mesh). The neutral alumina was Bio-Rad AG-7 with an average particle size of 0.254-0.127 mm (1W200 mesh). Both of the alumina adsorbents were factory-activated Brockmann activity I and were used as received. Apparatus. The chromatographic columns employed for the gravity-flow system were 100-mLburets, which were 1.5 cm i.d. X 65 cm. An FMI lab pump and either a 0.!3 cm i.d. X 25 cm or a 0.9 cm i.d. X 50 cm Altex glass column were employed for the pumped system. Infrared spectra were obtained with a Perkin-Elmer Model 621 grating infrared spectrophotometer. The spectra were recorded in the absorbance mode with a matched pair of sodium chloride infrared cells, 0.5-mm cell pathlength. All fractions were diluted with methylene chloride and run against methylene chloride in the reference cell. Elemental nitrogen determinationswere made by using an HP-185 F&M CHN analyzer or by chemiluminescence using an Antek Model 7'11 pyroreactor and Antek Model 720 digital nitrogen detector.
RESULTS AND DISCUSSION T h e Basic a n d Neutral Alumina Separations. A flow diagram for the separation of the nitrogen compound types in jet fuel products and the diesel fuel product using the gravity-flow system and the pumped-flow system is presented in Figure 1. Only slight modifications in elution volumes were necessary to adapt the gravity-flow system to a pumped-flow system for the separation of the nitrogen compound types in these shale oil products. Results from the separation of these products by either technique were complementary and reproducible. A comparison of these data for the diesel and jet fuel (JP-8) is shown in Table I. The pumped-flow system offered more control of parameters such as flow rate and required less overall attention than the gravity-flow system; the pumped-flow system was the method choice. The separation of the nitrogen compound types from the residuum and the three hlydrotreated whole shale oil products was accomplished by using the pumped-flow system. Essentially the same separation scheme employing basic alumina was used for all these product separations. Because these products contained higher molecular weight materials and/or a wider range of molecular weights than the distillate or fuel products, more basic alumina and eluting solvent were required to produce a similar separation. Figure 2 shows the flow diagram for the separation of the nitrogen compound types from the residuum and hydrotreated whole shale oil products. The neutral alumina separation was necessary to remove nitrogen compounds from fraction 1in the jet fuels and diesel fuel and to remove these similar compounds from fractions 1 and 2 in the residuum and whole hydrotreated shale oil samples. Both infrared analysis and percent nitrogen data indicated that these fractions contained mixtures of hydrocarbons and nitrogen compounds. Therefore, to concentrate the nitrogen, the separatilon schemes shown on the right-hand
9
Y
n
WAVENUMBER (cm-')
Flgure 3. Partlal infrared spectra of the fractions from the JB-8 fuel product.
portion of Figures 1 and 2 were undertaken. A complete separation using the procedure as outlined in the Experimental Section can be completed within an 8-h working day. Identification of Nitrogen Compound Types by Infrared Spectrometry. Infrared spectra were obtained for each of the fractions collected from basic and neutral alumina. Infrared absorption bands identified in the spectra have been shown to originate from particular nitrogen compound types (11). For example, infrared absorption due to N-H stretch at 3460 cm-l is generally indicative of pyrrole-type nitrogen. A doublet absorption due to C=N stretch at 1598 and 1557 cm-l originates from pyridine-type nitrogen, and infrared absorptions due to N-H stretch at 3450 cm-l and absorption due to C=O vibrations at 1698, 1665, and 1638 cm-l are characteristic of amide-type nitrogen. Typical infrared spectra are shown in Figure 3 for fractions 1*to 4 from the JP-8 product separated by basic and neutral alumina adsorption chromatography. The spectral regions shown are only those of interest; i.e., the 3600-3300 cm-' and 1700-1500 cm-l regions where nitrogen compound types characteristically absorb infrared radiation. Fraction I* exhibits no significant absorbance in these regions. The weak absorption at 1590 cm-l is due to aromatic hydrocarbons present in this fraction. Fraction 2* exhibits little absorbance from 3600 to 3300 cm-l but shows very strong absorbance at 1597 and 1557 cm-l characteristic of pyridine-type nitrogen. The infrared spectrum of fraction 3 shows strong absorption bands at 3460, 1612, and 1598 cm-l and weaker absorption bands at 3375 and 1550 cm-l. The band at 3460 cm-l is characteristic of N-H stretch from pyrrolic-type nitrogen compounds. This fraction also apparently contains other types of nitrogen compounds that have not yet been positively identified. However, preliminary work in this laboratory has indicated that aromatic amines may be responsible for the absorbance at 3375 and 1612 cm-l. Fraction 4 exhibits infrared absorbance at 3450,1687, and 1590 cm-l. The former two absorbances are characteristic of amide-type nitrogen in which the 3450-cm-l absorbance is due
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ANALYTICAL CHEMISTRY, VOL. 53, NO.
6,MAY 1981
Table 11. Results of Compound-Type Separation of Hydrotreated Shale Oil Products wt
compound-type fractions
JP-8
DFM
residuum
of sample
-
hydrotreated (Sohio)
hydrotreated* (Chevron)
hydrotreatedC (Chevron)
1* (hydrocarbon fraction) 2* (pyridine fraction) 3 (pyrrole fraction) 4 (amide fraction) total recovery
93.1 93.1 89.1 d 1.70 2.05 2.69 2.84 0.24 0.61 1.49 1.85 6.57 5.90 0.62 1.47 0.43 0.35 0.47 0.45 0.17 0.28 96.7 97.4 98.8 Average of duplicate separations determined within t0.05 wt %. Total nitrogen at 0.048%. Total nitrogen at 0.096%. Reliable data unavailable because of the high volatility of hydrocarbon fractions.
FRACTION 3
- LA FRACTION 4
3500
3300
1700
I500
WAVENUMBER (cm-']
P3500P 3300
1700
I500
WAVENUMBER (cm-'J
Flgure 4. Partlal Infrared spectra of the fractlons from the hydrotreated shale oil residuum.
Flgure 5. Partlal Infrared spectra of the fractions from the hydrotreated whole shale oil.
to the N-N stretching frequency and the 1687-cm-' absorbance is due to the carbonyl stretching frequency for amides. Absorbance at 1590 cm-l is again due to aromatic C=C stretching frequency. Figures 4 and 5 show the infrared spectra of the fractions derived from the 345 "C+ residuum and Sohio hydrotreated whole shale oil samples, respectively. Arguments similar to those used for the JP-8 infrared spectral analysis also apply to these two products. The infrared spectra of the fractions from the diesel product were similar to those presented in Figure 3; whereas the infrared spectra of the fractions collected from the separation of the Chevron hydrotreated whole shale oil products were similar to those spectra presented in Figure 5. Weight Distribution of t h e Chromatographic Fractions. Table I1 gives the results of the compound-type separation of hydrotreated shale oil products using alumina. These data show the relative weight distribution of the chromatographic fractions isolated from the shale oil products. The major compound type identified in each fraction is identified by infrared spectrometry. Percentage weight recovery data were obtained only for the JP-8, diesel, and residuum samples since the other samples contained light ends consisting of the gasoline distillate that were easily lost during
solvent stripping and fraction drying. The percentage weight recoveries for the JP-8, diesel, and the residuum were 96.7, 97.4, and 98.8%, respectively. These data indicate that the recovery was good using this separation scheme and that in all probability irreversible adsorption was a minor problem. Nitrogen Balance Data. Elemental nitrogen analyses were obtained for each basic/neutral alumina fraction, and these data are compiled in Table 111. These determinations for fractions 2*, 3, and 4 are within f0.05wt % nitrogen. The data demonstrate that the separation scheme was applicable to samples with different average molecular weights. The average molecular weight of the compounds in the fuel products was about 200 amu; whereas the average molecular weight of the compounds in the residuum and hydrotreated whole shale oil products was about 400 amu as determined by low-voltage mass spectrometry. The differences in average molecular weight of these products are reflected in the elemental nitrogen analysis data in Table I11 because fractions containing lower average molecular weight compounds would be expected to have larger percent nitrogen values. By use of the data compiled in Tables I1 and I11 the nitrogen recovery results were calculated for each sample separated on alumina. The results presented in Table IV were obtained by multiplying the fraction weight percent of sample/100 in
ANALYTICAL CHEMISTRY, VOL. 53, NO. 6, MAY 1981
Table 111. Elemental Nitrogen Content of Basic/Neutral Alumina Fractions nitrogen, wt %" of fraction hydrotreated compound-type fractions JP-8 DFM residuum (Sohio) I * (hydrocarboi~)~ 2" (pyridine type) 3 (pyrrole type) 4 (amide type)
0.0009 7.37 8.52 7.79
0.0002 6.51 7.18 7.38
0.0044 3.48 4.77 3.91
hydrotreated (Chevron)
hydrotreatedC (Chevron)
0.0002 3.94 5.15 6.40
0.0004 2.80 4.13 4.00
0.0006 4.51 4.94 5.99
835
a Measurements are within iO.0002 wt % nitrogen for fractions 1* and within iO.05 wt % nitrogen for fractions 2*, 3, and 4. Total nitrogen 0.048%. Total nitrogen 0.095%. Measurements were made by a chemiluminescence detector.
Table IV. Nitrogen Balance Results on Fractionated Hydrotreated Shale Oil Products nitrogen, wt % a of sample hydrotreated compound-type fractions JP-8 DFM residuum (Sohio) 1* (hydrocarbon) 2* (pyridine type) 3 (pyrrole type) 4 (amide type) cumulative N recovery N in original sample N balance
hydrotreated (Chevron)
hydrotreated (Chevron)
