(3) 0. C. Hatchard and C. A. Parker, Proc. R. Soc. London, Ser. A, 235, 518 (1956). (4) J. Lee, A. S.Wesley, J. F. Ferguson, and H. H. Seliger in “Bioluminescence in Progress”, F. H. Johnson and Y. Haneda, Ed., hinceton University Press, Princeton, N.J., 1986, p 35 ff. (5)J. Lee and H. H. Seliger, Photochem. Photobiol., 15, 227 (1972). (6) C. A. Heller, D. 1.Carlisie. andR. A. Henry, J. Luminescence, 4,81 (1971). (7) A. Fontijn and J. Lee, J. Opt. Soc. Am., 62, 1095 (1972). (8) R. Bezman and L. R. Faulkner, Anal. Chem., 43, 1749 (1971). (9) R. Bezman and L. R. Faulkner, J. Am. Chem. Soc., 94, 6317 (1972). (IO) W. H. Melhuish, J. Opt. Soc. Am., 52, 1256 (1962). (1 1) K. D. Mieienz, R. Mavrodineanu, and E.D. Cehelnik, Appl. O p t , 14, 1940 (1975).
(12) J. Lee and H. H. Seliger, Photochem. Photobiol., 4, 1015 (1965). (13) E. H. White and M. M. Bursey, J. Am. Chem. Soc., 86, 941 (1964). (14) J. W. Hastings and G. T. Reynolds in “Bioluminescence in Progress”, F. H. Johnson and Y. Haneda, Ed., Princeton University Press, Princeton, N.J., 1966, p 45 ff. (15) J. W. HastingsandG. Weber, J. Opt. Soc. Am., 53, 1410 (1963).
RECEIVEDfor review November 10,1975. Accepted April 5, 1976. Presented in part at the 170th National Meeting of the American Chemical Society, Chicago, Ill., August 29,1975. We are grateful to the National Science Foundation for supporting this work through Grants GP-37335X and MPS-75-05361.
Direct Determination of Organic Carbon in Oil Shale R. N. Heistand” and H. 6. Humphries Development Engineering, Inc., Box A, Anvil Points, Rifle, Colo. 81650
A direct determination of organic carbon in oil shale has been developed to replace the normal procedure in which organlc carbon is calculated as the difference betweenthe total carbon and the Inorganic carbon. The direct determination Is obtained by controlled combustion using the Perkln-Elmer Model 240 Elemental Analyzer. Inorganic carbonates are not pyrolyzed when the combustion temperature is lowered to 450 f 10 ‘C. Precislon of the method is f0.10% org. C. The organic carbon data are useful In raw shale characterization, can be related to potential oil yield, and serve as a measure of energy potential, or coke, remaining on the retorted shale.
Oil shale is a complex lamellar mineral. The term oil shale is a misnomer because the inorganic portion is not a shale. Shales are usually mixtures of quartz and mica, while the inorganic components of oil shale are largely carbonates. The minerals present in oil shale are quite complex with the occurrences of many double salts and hydrates. A list of the more common minerals are given in Table I. Some of these tend to concentrate in localized sites while others are widely distributed throughout the formation. Thus, it is difficult to assign relative abundances to any particular mineral species. Also, the organic component is not oil. Oils are liquid hydrocarbons, while the organic component of oil shale is a complex solid called kerogen. Vanderborgh ( 4 ) gave the chemical formula for kerogen as C215H330012N5S. This is in general agreement with the empirical formula, C6Hg.sNo.lsS0.0400.56proposed by Stanfield and others (5). The economic importance of oil shale is related to the potential energy contained in the kerogen. Since the kerogen is a solid organic material embedded in a carbonate mineral matrix, the energy potential cannot be obtained by conventional means. Thermal decomposition is required to break down the kerogen. The mineral matrix is largely carbonates; thus, it too is thermally reactive. Upon heating to sufficient temperature, carbonate decomposition occurs producing carbon dioxide and metal oxides. Carefully controlled thermal decomposition, called pyrolysis or retorting, is needed to convert the kerogen into three products-gas, oil, and coke without causing excessive carbonate decomposition. The relative amounts of these end products depend upon the kerogen content of the raw shale and the retorting conditions. Since carbon accounts for nearly 80% of the kerogen, the organic carbon content is an important characteristic of the oil shale. Normally, organic carbon is not measured directly (6), but is calculated as the difference between the total carbon 1192
ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
and the mineral carbon. Total carbon is measured by conventional pyrolysis techniques. The inorganic (or carbonate carbon) is measured gravimetrically on a separate sample by the collection of the acid-liberated carbon dioxide on a suitable absorbent. Direct determination of organic carbon in oil shale offers several improvements over the calculation by difference.
EXPERIMENTAL To determine total carbon in raw oil shale, it is necessary to conduct the pyrolysis at 1000 O C in pure oxygen. The milder conditions normally used to determine total carbon in organic materials (7) result in incomplete pyrolysis of the mineral carbonates. Material balances made on a Fischer assay show that little or no mineral carbonate decomposition occurs. Direct determination of the organic carbon should be feasible if the pyrolysis temperature of the elemental analyzer were lowered to about 500 O C , the temperature specified for the Fischer assay (8). A series of pyrolysis experiments were carried out using the Paraho raw shale standard. This material, representing a composite of oil shale mined at Anvil Points during January 1975, has been analyzed routinely in our laboratory as an in-housestandard. The Anvil Points mine near Rifle, Colo., is Iocated on the southeast edge of the Piceance Creek formation. The compiled analyses are shown in Table 11. Re-
sults from the pyrolysis experiments are shown in Table 111. These results indicate that the organic carbon is completely pyrolyzed to carbon dioxide while the inorganic mineral carbonates remain unaffected when the temperature is lowered to 450 O C and the pyrolysis time extended by 5 min. Equipment. The Perkin-ElmerModel 240 Elemental Analyzer and Model AM-2 Microbalance were used in the direct determination of organic carbon. This equipment is particularly well-suited for microchemical analysis in a field laboratory where there is little or no control over temperature, humidity, dust, or vibration. Procedure. The procedure followed for the direct determination of organic carbon in oil shale is similar to the normal procedure (7) used to determine total C, H, and N. No solid oxidant or catalyst is used. The k-factors are determined using normal conditions while blank values are determined using the modified conditions. These modifications include lowering the combustion temperature to 450 f 10 O C and increasing the combustion time by 5.0 min.
RESULTS AND DISCUSSION Precision. Repeatability of the direct organic carbon method was determined using replicate analyses of the Paraho standard raw shale. These replicates were made over a three-month period during which many total C, H, and N determinations were made, and carrier gas cylinders and combustion, reduction, and absorption tubes were changed many times. The mean value from these replicate analyses, 12.70% org. C, agrees well with the conventional calculated value given in Table 11. Further evidence of the precision and accuracy of the direct organic carbon method is shown in
Table I. Common Minerals Found in Oil Shale in the Piceance Creek Basin Type
Structure
Carbonates (50%) Dolomite Dawsonite Nacholite Shortite Calcite Siderite Magnesite Ferroan Sands (9%) Quartz Clays (40%) Analcite Albite Microcline Illite. Chlorite. 1 Montmorillite,' Muscovite Plagiclase, Orthoclase Sulfides (1%) Pyrite, Marcasite Fluorides (< 1%) Neighborite
Table 111. Effects of Pyrolysis Conditions on the Direct Organic Carbon DataQ Temperature, "C
Reference Time, min
(Mgl-XFeX )Ca(C03)2 NaAl (OH), CO, NaHCO, Na,CO, 2CaC0, CaCO, FeCO, MgCO 3 (Mg1-x Fex )COS
(3). (2, 3
-
(2)
(1-3) (293) (29 3 ) (2, 3 )
SiO,
(1, 2 )
NaAlSi, 0, .H, 0 NaAlSi, 0 , K,AlSi, 0 ,
2) (2) (2) (.1 , 2 ), ( 11
(K4A14Si,A10zo
1
(CaAl, Si, 0, )
H,O)
17.50
5 min 7.5 min
450
400
12.95 12.57 13.23 12.95
10.04 7.84 11.69 11.76 12.48 12.34
500
12.93 12.82 13.00 12.98 13.43 13.09
QParaho standard raw shale (Total C carbon = 12.70%).
=
17.50%;organic
( 1 9
-
,)
No
1000
Table IV.Repeatability and Accuracy of the Direct Organic Carbon Method
( 11
Organic carbon, w t %
(11 Sample
Total C inorganic C
Direct organic C
A B C D E
2.99 5.78 10.61 14.70 23.69
2.87, 2.78 6.13, 6.17 10.73, 10.69 14.65, 14.75 23.35, 23.96
( 1)
FeS,
(1,2 ) ( 21
NaMgF,
Table 11. The Paraho Standard Raw Shale Mean value
Fischer assay Oil, gal/ton Water, gallton Gas, wt % Mineral CO,, wt % Elemental Total C, wt % Total H, wt % Total N , wt % Organic C, wt % Ash, wt % Moisture, wt %
f 1 .O
std dev
Table V. Direct Determination of Organic Carbon in Retorted Shales
29.2 f. 0.49 3.3 t 0.53 2.33 i: 0.26 17.33 t 0.26 17.50 + 0.08 1.85 t 0.03 0.54 i: 0.02 12.70 * 0.09 66.31 i 0.44 0.28 t 0.03
Table IV where organic carbon values are compared for six oil shales having wide variations in their kerogen content. The average absolute difference between the two methods is 0.18% organic carbon. The standard deviation of the direct method from all replicate data (D.F. = 20) is f0.10% organic carbon. Applicability. The direct organic carbon method is rapid-less than 20 min are required for a single determination. Only 5-10 mg of shale is needed. Including start-up, calibration, and shut-down, a skilled analyst can complete 20 direct carbon determinations in 1 man-day. As pointed out earlier, shale is a complex mixture of thermally reactive minerals. However, no interferences from carbonate decomposition have been noted, even though the shales sampled represented raw shale mined at Anvil Points over a six-month period, core samples obtained from other Piceance Creek sites, and retorted shales. Relationship with Fischer Assay. Although the knowledge of the organic carbon content of oil shale is useful information, it is the oil yield (gal/ton), as determined by the Fischer assay, that is the criterion of the oil shale industry. Since the Fischer assay represents carefully-controlled retorting, the quantities of gas, oil, and coke produced are a direct function of the kerogen content of the shale. Thus, the oil yield should correlate well with the organic carbon. The
Total C (wt %) Min C (wt %)
Org C (wt %) direct
Shale
RSS-1
Q
2.23, 2.24, 2.31 2.22Q 2.22, 2.22 PD-22 1.69 1.57 SA-11 4.75 4.76 PD-21 1.71 1.52 sa-lo 2.00, 2.02 2.11 Mean value calculated from 25 replicate analyses.
equation of the best fit line, as determined by least squares is: Oil (gal/ton) = 2.37 X org. C (wt %)
- 0.80
(1)
The correlation coefficient of the computer-generated equation is 0.998. Equation 1compares fairly well with those developed previously (6, 9-12). Equation 1 was used to calculate the oil yield of the Paraho raw shale standard from organic carbon data. The mean value, 29.07 gal/ton and the standard deviation, f0.46 gallton, compare well with the data given in Table 1. Retorted Shale. The organic carbon, or coke, remaining on retorted shales, is one of the measures of retorting efficiency. The organic carbon content on retorted shales is a measure of wasted energy potential and, possibly, an indication of the ease of compaction and revegetation efforts. Comparison of the direct organic carbon determination with conventional data (obtained by difference) is shown in Table V for five different shales.
CONCLUSIONS The direct determination of organic carbon is superior to the conventional means of calculating the value difference. In addition to eliminating an unnecessary analysis, the needed data are obtained directly. ANALYTICAL CHEMISTRY. VOL. 48,
NO. 8,
JULY 1976
1193
The organic carbon is a useful measure of the energy potential of raw shale. If required, the oil yield (galhon),as determined by Fischer assay, can be calculated from the organic carbon. Finally, the organic carbon content on retorted shale is a useful measure of an energy, or heat source, that is wasted. Although most of the material used in this study was mine-run raw shale (that is, samples were a n aggregate composite of shale from many strata), several of the samples are from cores obtained from the Piceance Creek basin. Some changes in the inorganic matrix may have occurred in these samples, yet the organic carbon data are valid. Since gross changes in the inorganic (mineral) matrix may affect the validity of the direct determination of organic carbon, a thorough study of other shale deposits should be made before applying this method as a routine procedure for organic carbon determinations.
ACKNOWLEDGMENT These studies were conducted a t the ERDA Anvil Points facilities located on the Naval Oil Shale Reserve near Rifle, CO. The authors wish to thank ERDA for permission to publish.
LITERATURE CITED (1) T. F. Yen, “Facts Leading to the Biochemical Method of Oil Shale Recovery’’, Anal. Chem, Pertaining to Oil Shale and Shale Oil, Washington, D.C., June 24-5, 1974. (2) J. W. Smlth, L. G. Trudeii, and W. A. Robb, U S . , Bur. Mines, Rep. lnvest. 7693, 1972. ( 3 ) N. B. Young, J. W. Smith, and W. A. Robb, US., Bur. Mines, Rep. invest. 8008, 1975. (4) N. E. Vanderborgh, “Characterization of Oil Shales by Laser Induced Pyrolysis”, FACSS, Atlantic City, N.J., Nov. 19, 1974. (5) K. E. Stanfield, i. C. Frost, W. S. McAulev, and H. N. Smith, U.S., Bur. Mines. Rep. lnvest4825, 1951. E. W. Cook, Fuel, 53, 16-20 (1974). R. F. Cuimo, Mikrochim. Acta, 175-180 (1969). A. B. Hubbard, U.S., Bur. Mines Rept. Invest. 6676, 1965. K. E. Stanfieid, i. C. Frost. W. S. McAuiey, and H. N. Smith, U.S., Bur. Mines Rep. invest. 4825 (195 1). J. W. Smith, Bull. Am. Assoc. Petrol. Geol., 50, 167-70 (1966). A. W. Decora, F. R. McDonald, G. L. Cook, US., Bur. Mines, Rep. lnvest. 7523, 1971. B. L. Beck, D. Liederman. and R. Bernheimer. Am. Chem. SOC.,Div. Fuel Chem. Prepr., 15, 31-37 (1971).
RECEIVED for review February 2, 1976. Accepted April 8, 1976.
Simplified Kjeldahl Nitrogen Determination for Seawater by a Semiautomated Persulfate Digestion Method J. M. Adamski Suffolk County Department of Environmental Control, 1324 Motor Parkway, Hauppauge, N. Y. 11787
Persulfate digestion in combination with indophenol colorlmetry via a Technlcon AutoAnalyzer II was used as an alternative to the standard Kjeldahl nltrogen method as specified in “Standard Methods”. Application of this method to the analysis of seawater samples demonstrated that a large quantity of samples can be rapidly processed wlth relative ease in a small envlronmental laboratory. A detection limit of 0.06 mg/l. as nitrogen was calculated for the operating range 0-5.6 mg/l. Seawater samples spiked wlth 3.00 mg/l. of ammonia nltrogen were analyzed wlth a precision of f0.25 mg/l. and a spike recovery of 105 f 6.8%. Seawater samples splked with 3.35 mg/l. of Kjeldahl nitrogen contained in raw domestic waste were analyzed with a precision of f0.30 mg/l. and a spike recovery of 100 f 8.1 %. The results of this study indicated that the persulfate method greatly simplifies the determination of Kjeldahl nitrogen in seawater while successfully malntalnlng low level requirements for sensltivity, precision, and accuracy.
low nitrogen levels commonly encountered in marine samples even when large sample aliquots are utilized to increase the sensitivity. The following study proposes the use of an alternative procedure for determining Kjeldahl nitrogen in seawater samples which provides better sensitivity, better precision and accuracy, greater simplicity in sample preparation, and a greater capacity for handling a large quantity of samples with minimal manpower and space requirements. This procedure employs a modified persulfate digestion procedure as described in the routine methods manual of the Ontario Ministry of the Environment (2) in combination with indophenol colorimetry for ammonia nitrogen as described in the works of Rossum and Villarruz ( 3 ) and Weatherburn ( 4 ) . Applying these principles to the analysis of marine samples using an adaptation of the automated Grasshoff and Johannsen ( 5 )procedure as specified by O’Connor and Miloski (6) completes the analytical scheme.
EXPERIMENTAL Although the analysis of Kjeldahl nitrogen has received widespread acceptance as an important parameter for assessing the effects of domestic wastes on receiving waters, its use is often limited by the expensive nature of the analysis, especially in cases where a large data base is necessary to satisfy the statistical requirements of routine monitoring surveys and computer models. Employing the classical Kjeldah1 technique as described in “Standard Methods” ( I ) on a large scale is a tedious and time-consuming proposition which can seriously limit the analytical capabilities of small environmental laboratories, both in terms of manpower as well as bench space requirements. This classical procedure often lacks the necessary precision and accuracy for detecting the 1194
ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
Apparatus. A modified version of the indophenol procedure as described by O’Connor and Miloski ( 6 )was employed using a Technicon AutoAnalyzer I1 system with the appropriate accessories as shown in Figure 1. Sample digestion was accomplished on a hot plate in standard 125-ml Erlenmeyer flasks. Reagents. Phenate reagent was prepared by dissolving 35 g of phenol and 0.4 g of sodium nitroprusside in approximately 250 ml of distilled water and diluting to 11. The phenate reagent was stored in an amber glass bottle to inhibit decomposition and refrigerated when not in use. Preparation of the phenate reagent with fresh reagent grade phenol was necessary for proper color development. Once a bottle of phenol has been opened, reagent quality can be maintained by storing the remainder of the phenol under nitrogen gas. Hypochlorite reagent was prepared by dissolving 20 g of sodium hydroxide and 2 g of sodium dichloro-S-triazine-2,4,6-( lH,3H,5H)-trione (MCB Manufacturing Chemists catalogue number SX503) in approximately 250 ml of dis-
