a phic Determinatio
rogen, Oxygen,
and C, th in Refine Caroline N. Jones The Standard Oil Co. (Ohio), Research and Development Department, 3092 Broadway Acenue, Clecehnd, Ohio 44115 HYDROGEN-RICH REFINERY gas streams contain hydrogen in amounts varying up to 9 7 x . The balance of the samples are composed of any or all of the following: nitrogen, carbon monoxide, carbon dioxide, ammonia, hydrogen sulfide, C1through C5hydrocarbons, and water. Oxygen may appear if the samples have been contaminated with air. No published work (1-18) described a gas chromatographic procedure which would measure all of the compounds desired. Several (4,9,12) required removal of one or more components such as carbon dioxide, hydrogen sulfide, or water before gas chromatographic analysis. With only two exceptions (9, I ] ) , two or more columns were employed either in series or separately; most common were an adsorption column for the fixed gases and a partition column for hydrocarbons. A separate analysis was required ( 2 , 4, 8, IO, 12, I d , 17) for quantitative determination of hydrogen. A mixed carrier gas on a single column was employed (11) for quantitative hydrogen analysis over a wide concentration range. 0. L,.Hollis described the use of synthesized porous polymer beads as column packing
(1) J. E. Attrill, C. M. Boyd, and A. S. Meyer, Jr., ANAL.CHEM., 37, 1543 (1965). (2) F. L. Boys, J. Gas Chromatog., 4, 20 (1966). (3) M. Cerrone, U. Piatti, and A. Rio, Chim. Ind. (Milan), 46, 1054 (1964). (4) R. Ciola, Anais Assoc. Brasil, Quim.,19, 35 (1960). (5) A. A. Datskevich, A. A. Zhukhovitskii,and N. M. Turkel’taub, Industrial Laboratory, 25, 222 (1959). (6) E. L. Erikson, Instr. Control Systems, 33, 1362 (1960). (7) L. Giuliani and G. Russo, Chim.Ind. (Milan), 46, 1186 (1964) (8) N. Hara, H. Shimada, and M. Oe, J. Chem. SOC.Japan, Znd. Chem. Sect., 64,772 (1961). 32, (9) T. A. McMenna, Jr., and J. A. Idlernan, ANAL.CWEM., 1299 (1960). (10) D. M. Ottenstein, 13th Pittsburgh Conf. on Anal. Chem. & Appl. Spectroscopy, Pittsburgh, Pa., March 5-9, 1962, Program Abstr., p. 53. (11) J. E. Purcell and L. S. Ettre, 9.Gas Chromatog., 3,69 (1965). (12) F. N. Rhoad, Southern Pulp Paper Mfr., 28, GO (1965). (13) E. V. Rouir and J. Sigalla, Riv. Ital. Sostanze Grasse, 41, 91 (1964). (14) D. Sandulescu, Rev. Chim. (Bucharest), 12, 341 (1961). (15) P. G. Sevenster, S. African Znd. Chemist, 12, 151 (1958). (16) N. Takamiya and S. Murai, J. Chetn. SOC.Japan, Ind. Chem. Sect., 63, 1935 (1960). (17) S. Tsudano and M. Kimura, Kagaku No Ryoiki (J. Japan. Chem.), 12, 620 (1958). (18) N. M. Turkel‘taub and A. A. Zhukhovitskii, Zavodsk. Lab., 23, 1120 (1958).
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ANALYTICAL CHEMISTRY
FLOW
CARRIER GAS IN
c2
Figure 1. Flow system
(19). Varian Aerograph literature (20) indicated that Porapak Q would separate fixed gases at subambient temperatures and hydrocarbons through Csat elevated temperatures. Uncoated Porapak Q is ideally suited for this application; retention data are unusually constant, and column life is unlimited. In the proposed analytical method one Porapak Q column was temperature programmed froni subambient to above ambient temperature, using a mixed carrier gas. To utilize existing equipment without subambient programming capabilities, two columns of the same packing were maintained at different temperatures, one subambient and one above room temperature. Previous work (21) on an Aerograph Model A-350-B had utilized a AQW system with two 4-way valves which allowed operation of two columns in series or individually and provided also for backflushing. This instrument and valve system were modified as described below, and a satisfactory analytical procedure was devised for the complete analysis of all desired components from a single sample.
EXPERIMENTAL Apparatus. An Aerograph Model A-350-B dual column programmed gas chromatograph equipped with a gas sampling valve was employed. Two stainless steel, 4-way valves with Teflon seats (Republic Manufacturing Co., Cleveland, Ohio, No. 310-6-1/8-inchdiameter) were used. These valves leaked when tested with helium; stronger springs in the (19) 0. L.Hollis, ANAL.CHEM., 38, 309 (1966). (20) F. Baurnann and J. M. Gill, “Aerograph Research Notes,” Spring, 1966, p. 1. (21) D. A. Wohleber, “The Standard Oil Company (Ohio) Letter Report-Dev. #321,” November 5 , 1962.
valve seats made them leak-free at 50 psig. Stainless-steel fittings and tubing were used exclusively for corrosive gas service. Two columns were prepared using 0.25-inch stainless-steel tubing. A 4-fOOt column filled with SO- to 100-mesh Porapak Q was coiled to fit into the heated oven compartment. A 6-foot column filled with SO- to SO-mesh Porapak Q was coiled to fit into a 1-quart Dewar flask outside the instrument. The lengths and mesh sizes were arbitrarily selected, based on single column retention data at various temperatures obtained on another instrument. The 4-foot column in the oven compartment was designed for adequate separation of saturated hydrocarbons in a minimum amount of time, using elevated temperatures as necessary. The 6-foot column in the Dewar flask was designed for separation of nitrogen, oxygen, and carbon monoxide when immersed in dry ice. The columns and valves were installed in the measuring side of the dual flow system as shown in Figure 1. Dimensions of the fittings and tubing were minimized to prevent large dead spaces. The reference side was left intact. The built-in flow controllers were found inadequate to compensate for the severe changes in backpressure which occurred when the 6-foot column was isolated from the flow system. The flow controller on the measuring side was replaced with a sensitive Millaflow controller and needle valve assembly, which maintained a constant flow rate during the entire analysis with a recovery time of less than 30 seconds. The built-in flow controller was left in place on the reference side because it was adequate for the gradual changes in back pressure of the reference column. An Alltek Peakometer (Alltek Associates, Arlington Heights, Ill.) was employed for peak area measurements. Operating Parameters. The carrier gas used was a mixture of 8.5% hydrogen and 91.5% helium. A plot of thermal conductivity of helium-hydrogen mixtures DS. hydrogen concentration has a minimum at 8 % hydrogen. Use of the mixed carrier gas ensures that the thermal conductivity of the hydrogen in the sample will always be less than that of the carrier, and hydrogen peaks will always be negative. This phenomenon is explained fully by Purcell and Ettre (11). Detector polarity was reversed to record the hydrogen as a positive peak. Identical flow rates of 100 cc/min were established for both measuring and reference sides of the flow system. Matched flows provided the minimum shift in base line when the polarity was changed; a change in either flow rate was thus detectable. Detector cell current was maintained at 200 mA. Synthetic blends and pure compounds were used to determine retention data through the desired columns at various temperatures, Column 2 was cooled in dry ice for separation of nitrogen, oxygen, and carbon monoxide. Column 1 was operated at room temperature in order to achieve adequate separation of methane and carbon dioxide, then temperatureprogrammed to 125" C to hasten elution of the hydrocarbons. The analysis time was further shortened by backflushing the cold column after carbon monoxide was eluted to shorten the retention time of methane, and backflushing the heated column after n-butane was eluted to speed up the elution of Cg material. Samples to be analyzed were supplied in small stainlesssteel bombs at pressures ranging up to 1500 psig so the conventional gas sampling valve could be used. The 10-cc gas sample loop was selected so that miilor components in concentrations as low as 0.1 % could be detected. Procedure. The complete analysis scheme is illustrated by the composite chromatogram in Figure 2. Both columns were in series during sample injection. The hydrogen passed through both columns in less than 1 minute, after which column 2 was bypassed while carbon dioxide, ammonia, water, hydrogen sulfide, and the Cz-C4 saturated hydrocarbons eluted from Column 1 as its temperature increased from ambient to 125" C. Immediately after n-butane eluted,
+
I
;f
a Figure 2. Composite chromatogram Flow changes : A Columns 1 and 2 in series B Bypass column 2 C Backflush column 1 D Columns 1 and 2 in series E Backflush columns 1 and 2
Column 1 was backflushed to remove C b material while Column 2 remained isolated. When all heavy components had eluted, Column 2 was again put in series with Column 1 allowing the nitrogen, oxygen, and carbon monoxide to pass through both columns. Immediately after the carbon monoxide peak emerged, both columns were backflushed in series to speed up elution of methane. Calibration. Quantitative calibration factors were determined for all components from their area response values relative to methane, and used to correct the actual peak areas. Two standard gas blends of known composition (Phillips Petroleum Co.) were analyzed and the corrected areas obtained for each component. The calibration graph was a linear plot of corrected area us. mole %. A separate calibration was formed for hydrogen; peak height was plotted us. mole % in the range from 5 to 100%. The lower portion of the hydrogen calibration is linear, while the upper portion exhibits nonlinearity as reported by Purcell and Ettre (11). RESULTS AND DISCUSSION
Hydrogen content below 70 % was determined from the hydrogen calibration curve. These values were repeatable to =k 5 %. In the range above 70 %, hydrogen content was computed by difference, using the sum of the measured minor Table I. Refinery Gas Streams Analyzed by GC 0-15
Gas feed from contactors Gas feed to contactors Natural gas Furnace effluent High temperature shift Low temperature shift COZabsorber outlet Methanator effluent Makeup hydrogen
Hydrogen, Z 15-30 30-75 75-100 X X
X X X X X X X
Recycle gas
X
Low pressure separator off gas
Stabilizer overhead vapor product Stabilizer reflux Depropanizer overhead vapor product Fuel gas Makeup gas Depropanizer overhead
X
X X
x X X X
VOL. 39, NO. 14, DECEMBER 1967
1859
components. Standard deviation was 1.84% for hydrogen by difference in the range above 70 %. Seven samples were analyzed by both mass spectrometry and gas chromatography; results of single analyses by both methods showed good agreement. Standard deviation of the MS technique is 0.4 % or better for all components. Standard deviation of the GC method is satisfactory at 0.25% for all minor components through n-butane. Sensitivity or limit of detectability was not determined for each individual compound; however, some components in concentrations of 0.1% or less were represented by peaks whose heights were more than 10% full scale. Accuracy may be improved and sensitivity limits extended by more precise calibration techniques. Twenty-two different refinery streams were analyzed successfully by this method; Table I indicates the wide range in
hydrogen content of some samples. Only samples which are in the vapor phase under atmospheric conditions may be analyzed; the method is not applicable to two-phase samples. Small amounts of water may be tolerated, however. No pretreatment of any kind is required to remove acid gases or corrosive gases before analysis. This GC technique is a convenient, low-cost substitute for MS in the analysis of hydrogen-rich refinery streams. ACKNOWLEDGMENT
The instrument modifications described in this paper were completed by Clark Gilbert. Donald A. Wolf and Oleh Lepak performed the calibration and sample analyses. RECEIVED fer review June 8,1967. Accepted August 23, 1967.
R. V. Moen and N.S . Makowski Analytical Research Division and Enja y Polymer Laboratories, Esso Research and Engineering Co., Linden, N . J .
THEREHAS BEEN considerable interest in NMR spectra of bicyclic compounds in recent years. Bicyclo-(Z,Z,l)-heptenes (1-61, bicyclo-(2,2,1)-heptanes (7-10), and bicyclo-(2,1,1)hexanes (11,I.Z) have often been studied. The rigid structure of these compounds allowed the study of the correlation between coupling constant and dihedral angle (Karplus' rule). Unusually large coupling constants have been observed in these systems (11, 12). Williamson studied the effect of substituent electronegativity on the coupling constants in hexachlorobicyclo-(2,2,1)-heptenes (13). Qften only the endo isomer was studied because this is the major product from most Diels-Alder condensations between cyclopentadiene and ethylene derivatives. I n general, the spectra are very complex, and in many cases they have been only partly analyzed. Spin decoupling ( 1 , 5 ) , use of IsCsatellites (31, specific deuterium labeling (5), and selective solvent shift have been used to obtain the complete parameters. We have studied the NMR spectra of 2-substituted-5norbornenes [bicyclo-(2,2,1)-heptenes]. Very little is known (1) J. C . Davis and T. V. Van Auken, J. Am. Chern. Sac., 87, 3900 (1965). (2) R.W. King and P. E. Butler, Abstracts; 142nd Meeting, ACS, Atlantic City, N.J., 1962, p. 84 Q. (3) P. Laszlo and P. von R. Schleyer, Y. Am. Chem. Soc., 85, 27099 (1963). (4) Ibid.,86, 1171 (1964). (5) P. M. Subramanian, M. T. Emerson, and N. A. Le Bel, J. Org. Chem., 30,2624 (1965). (6) E. C. Wong and C . C . Lee, Can. J. Chem., 42,1245 (1964). (7) F. A. L. Anet, Ibid.,39, 789 (1961). (8) J. Meinwald and J. C. Meinwald, 9. Am. Chem. SOC., 85, 2514 (1963). (9) J. Meinwald, J. C . MeinwaId, and T. N. Baker, Ibid.,p. 2513. (10) J. I. Musher, Mol. Phys., 6,93 (1963). (11) J. Meinwald and A. Lewis, J. Am. Chem. SOC.,83,2769 (1961). (12) K. B. Wiberg, B. R. Lowry, and IB. Nist, Ibid., 84, 1594 (1962). (13) A. B. Williamson, Ibid.,85,516 (1963).
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ANALYTICAL CHEMISTRY
07036
about the alkenyl derivatives (14, 1 3 ,and their NMR spectra have not been previously reported. EXPERIMENTAL
All compounds except the alkenyl norbornenes were prepared directly by Diels-Alder condensations between cyclopentadiene and substituted ethylenes. The alkenyl norbornenes were obtained from Witting reactions of 2-formyl-5norbornene and 2-acetyl-5-norbornene with both methylene and ethylidene triphenyl phosphorane. The purity of the compounds (ex0 -/- endo) was greater than 98%. All spectra were recorded on a Varian A-60 NMR spectrometer operating at a radiofrequency of 60 Mc/second. Spectra were measured neat at ambient temperature using tetramethylsilane (TMS) as internal standard. Chemical shifts are reported in cps downfield from TMS. The chemical shifts were considered to be accurate to &0.5 cps and coupling constants to h 0 . 2 cps. Only the values of the coupling constants were determined, and no attempts were made to determine the signs of the coupling constants. Spectra were expanded (100 cps sweep width) and areas measured with a planimeter. The exo and endo isomers were separated on a PerkinElmer Model 226 gas chromatograph with flame ionization detector. A 300-fOOt X 0.01-inch i.d. open tubular column, coated with Carbowax 1540, and a column temperature of 1.50' C were used for most compounds. A column coated with DC-550 silicone oil was used for the four alkenyl derivatives. The column temperature was held at 100"-125" C in this case, The only isomers that could not be separated by GC were those of 2-vinyl-5-norbornene. The agreements between NMR and GC results were good. NMR data showed that the minor isomer with the shorter G C retention (14) A. F. Plate and N. A. Belikova, Zh. Obshch. Khim., 30, 3945 (1960). For English translation, see J. Gen. Chern. U.S.S.R.,30, 3902 (1960). (15) A. F. Plate and N. A. Belikova, Zh. Obshch. Khim., 30, 2953 (1960). For English translation, see J. Gen. Chem. U.S.S.R., 30, 3910 (1960).
