A simple method for analysis of nitrogen and phenolic compounds in

A simple method for analysis of nitrogen and phenolic compounds in synthetic ... Energy Fuels , 1991, 5 (2), pp 299–303 ... Cite this:Energy Fuels 5...
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Energy & Fuels 1991,5, 299-303 cropores of the synthesis carbons. Further, several quantitative analyses of reaction and diffusion during Spherocarb oxidation indicate that reactant penetration is complete and that the reaction rate is strictly kinetically limited. The accessible total surface area for Spherocarb is expected to be the 640 m2/g measured by carbon dioxide adsorption, and the intrinsic kinetics for oxidation of Spherocarb in 0.21 atm of O2 are given by rate (g/(s m2) = 3.0 X lo3e*IRT, where R is in kcal/(gmol K). The value 36 kcal/mol is a typical activation energy for a low-temperature char or carbon but is substantially lower than activation energies measured for oxidation of some graphites,'l the difference presumably arising from the different degrees of purity and ~rystallinity.'~This level of understanding of diffusional processes is necessary for the fundamental treatment of many aspects of carbon gasification, including a pore structure modeling effort recently undertaken in this lab~ratory.'~ There is evidence for sucrose carbon, on the other hand, that reactant penetration is incomplete. The nature of the effect of particle size on sucrose char reactivity is consistent with restricted diffusion limitations in microporous grains with radii of 27 pm. The severity of diffusion limitations scales as L2/Dand depends, therefore, on the local microporous diffusivity,

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a parameter determined by micropore size, and the characeristic size of the microporous regions, a parameter determined by macroporosity. The major difference between the behavior of the two synthetic carbons in this study is thought to arise from a difference in the characteristic size of microporous grains in the two carbons. Hippo et aL3' have also emphasized the importance of feeder pores to determine the likelihood or severity of microporous diffusion limitations. The severity of microporous diffusion limitations for most chars should lie between that for the highly macroporous Spherocarb and that for the essentially nonmacroporous sucrose carbon. It is therefore expected that the carbon dioxide surface area will be the appropriate total surface area for the gasification of many pure carbons, although restricted diffusion limitations may be important during low-temperature gasification of chars with little or no macroporosity. Acknowledgment. Support of this research by Exxon Research and Engineering Co. is gratefully acknowledged. This paper is based on work supported also under a National Science Foundation Graduate Fellowship. (37) Hippo, E.; Walker, P. L. Jr. Fuel 1975,54 245.

A Simple Method for Analysis of Nitrogen and Phenolic Compounds in Synthetic Crude Naphtha Tadashi Yoshida,**+Pierre D. Chantal, and Henry Sawatzky Energy Research Laboratories, CANMET, 555 Booth Street, Ottawa K 1 A OG1, Canada Received June 5, 1990. Revised Manuscript Received October 9, 1990

A simple and rapid analytical method for trace amounts of nitrogen and phenolic compounds in hydroprocessed Boscan naphtha has been developed by combined use of column adsorption chromatography with basic alumina and GC technique. Based on the breakthrough curves of total nitrogen and total sulfur on basic alumina, an optimal condition was chosen for separating selectively nitrogen and phenolic compounds from the naphtha. The nitrogen compound fraction was further subdivided into groups of pyridine, pyrrole, aniline, and indole types on GC column. The main components in the nitrogen and phenolic compound fractions were identified by gas chromatography-mass spectrometry and determined by gas chromatography. The amount of nitrogen compound fraction in the naphtha was 2.0 wt '% and pyrrole type was most abundant. The amount of phenolic compound fraction was less than 0.4 wt '% and oxygen compounds other than phenols were not found.

Introduction The synthetic crude naphthas derived from coal, heavy oil, tar sand bitumen, etc. generally contain trace amounts of polar compounds. These materials often bring about the deposition of insoluble sediments and g u m s during the storage of naphtha'9 ahd are also harmful environmentally when naphtha is used. Therefore, these polar compounds should be removed from naphtha and the development of a new analytical method will be required for the charac-

terization of polar compounds present in synthetic crude naphthas. Although many studies on the separation and characterization of polar compounds from petroleum?" coal-

'Present address: Government Industrial Development Laboratory,Hokkaido 2-17-2-1Tsukiiu-Higashi, Toyohira, Sapporo 004, Japan.

(1) Cooney, J. V.; Beal, E. J.; Hazlett, R. N. R e p r . Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1984,29(3), 247-255. (2) Mayo, F. R.; Lan,B. Y.Ind. Eng. Chem. R o d . Res. Dev. 1986,25, 333-348.

Table I. Ultimate Analysis of Boscan Naphtha ultimate analvsis. w t % naphtha Boscan

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H

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N

84.7

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0.97

0.35

0887-0624/91/2505-0299$02.50/00 1991 American Chemical Society

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Yoshida et al.

300 Energy & Fuels, Vol. 5, No. 2, 1991 140 r

Basic alumina

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Figure 1. A schematic diagram for separation of nitrogen and phenolic compounds in synthetic crude naphtha.

derived and shale oillOJ1by column adsorption chromatography and ligand exchange chromatography have been reported, most of them were for the distillable fractions higher than 200 "C and not for naphtha fraction.12 Polar compounds in the naphtha fraction are present in very small quantities and consist of numerous isomers and low boiling point compounds. These aspects make the separation and determination of polar compounds in the naphtha fraction difficult. The objective of the present work is to develop a simple analytical method for trace amounts of nitrogen and phenolic compounds in synthetic crude naphthas. Experimental Section Analysis of Naphtha Sample. Boscan naphtha (bp < 200 "C) produced by the CANMET hydroprocess was used as a sample. The ultimate analysis of the naphtha is given in Table I. The naphtha showed high nitrogen and sulfur contents. The total nitrogen of the naphtha was determined by means of a Dohrmann total nitrogen analyzer equipped with a chemiluminescence detector and the total sulfur by an X-ray fluorescence sulfur analyzer. The total oxygen was determined by neutron activation method. Breakthrough Curves of Total Nitrogen and Total Sulfur. The breakthrough curves of total nitrogen and total sulfur for Boscan naphtha were measured to get the information on the adsorption behavior of nitrogen and sulfur compounds on basic alumina. A given amount of the naphtha was upflowed at a flow (3) McKay, J. F.; Weber, J. H.; Latham, D. R. Anal. Chem. 1976,48, 891-898. (4) Schmitter, J. M.; Vajta, Z.; Arpino, P. J. In Aduances in Organic Geochemistry 1979, Physical Chemistry of the Earth; Douglas, A. G., Maxwell, J. R., Eds.;Pergamon Press: Oxford, UK, 1980, Vol. 12, p 67-76. (6)Vogh, J. W.; Dooley, J. E. Anal. Chem. 1975,47, 816-821. (6) Later, D. W.; Lee, M. L.; Bartle, K. D.; Kong, R. C.; Vassilaros, D. L. Anal. Chem. 1981,53, 1612-1620. (7) Boduszynaki, M. M.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1982,54,375-381. (8) Sato, M.; Tanabe, K.; Uchino, H.; Yokoyama, S.; Sanada, Y. Bull. Chem. SOC. Jpn. 1984, No.12, 1964-1973. (9) Nishioka, M.; Campbell,R. M.; Lee, M. L.; Castle, R. N. Fuel 1986, 6.5. - -, 27n-272. - . - - .-. (10) Ford, C. D.; Holmes,S.A.; Thompson,L. F.; Latham, D. R. Anal. Chem. 1981,53,831-836. (11) Holmes, S.A.; Thompson, L. F. Fuel 1983, 62, 709-717. (12) Poirier, M. A.; Smiley, G. T. J. Chromatogr. Sci. 1984, 22, 304-309.

rate of 0.5 mL/min into a stainless column (0.94 cm i.d. X 15 cm) with basic alumina. Samples of the effluent were collected every 4 mL and then subjected to nitrogen and sulfur analyses. Separation of Nitrogen and Phenolic Compounds from Naphtha. A schematic diagram of the method for the separation of nitrogen and phenolic compounds from the naphtha is shown in Figure 1. Basic alumina (Brockman activity I, 80-200 mesh, Fisher Scientific, No. ,4941) was used as an adsorbent to separate nitrogen and phenolic compounds from the naphtha. About 21 g of basic alumina gel was dried a t 150 "C overnight under air prior to use and then packed into a stainless column (0.94 cm i.d. X 40 cm). About 30 g of the naphtha was directly pumped upflow at a flow rate of 0.5 mL/min into the column without solvents. After the percolation of the naphtha, 100 mL of pentane was passed through the column at a flow rate of 1.5 mL/min to flush hydrocarbons and sulfur compounds. The nitrogen compounds adsorbed on basic alumina were selectively recovered from the column by the backflush with 450 mL of methylene chloride, and phenolic compounds still remaining on basic alumina were recovered by the back-flush with 200 mL of methanol/chloroform (60/40~ 0 1 % solvent. ) The fractions recovered were concentrated on a rotary evaporator at 40 "C, followed by the evaporation of solvents under nitrogen gas to a constant weight. Special attention was paid to minimize the weight loss caused by the high volatility of samples. The fraction was then subjected to gas chromatographic (GC)and GC-mass spectrometric (GC-MS) analyses. The nitrogen compound fraction was further subdivided into groups of pyridine, pyrrole, aniline, and indole types on GC column. GC and GC-MS Analyses of Nitrogen and Phenolic Compound Fractions. The nitrogen and phenolic compound fractions were analyzed by a Varian 6000 gas chromatograph equipped with a flame ionization detector (FID), a nitrogen-selective detector (thermionic specific detector, TSD), and a sulfur-selective detector (flame photometric detector, FPD). A Supelcowax 10 fused silica capillary column (0.25 mm i.d. X 60 m, film thickness 0.25 pm) was used for GC analysis. The oven temperature was programmed from 50 OC to a final temperature of 270 "C at a rate of 5 "C/min and held for 10 min. The sample injected was split into two detectors of FID and TSD or FPD after the column and the FID and TSD or FPD chromatograms of the sample were simultaneously recorded. The components in the nitrogen and phenolic compound fractions were identified by using a JMS-DX 303 double-focusing mass spectrometer (Jeol Ltd.). Ions were collected through an electrical detector interfaced to a data system, JMA-DA 5000. The measurement conditions were as follows: ionization mode, electron impact; ionization voltage, 70 eV; acceleration voltage, 3.0 kV; resolution, 500; scan range, m / z 35-300; cycle time, 0.6 s/scan. Mass spectra obtained were identified by comparison with available library data.

Results and Discussion Breakthrough Curves of Total Nitrogen and Total Sulfur on Basic Alumina. When polar compounds in

Energy & Fuels, Vol. 5, No. 2, 1991 301

Analysis of Nitrogen and Phenolic Compounds ( c ) FPD Atten.x 16

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naphtha are separated by column adsorption chromatography, a knowledge of their adsorption behaviors is required for their quantitative separation. The adsorption of polar compounds on basic alumina shows different behaviors among nitrogen, phenolic, and sulfur compounds and these compounds show competitive adsorption when they coexist in naphtha. Phenolic compounds are generally adsorbed more strongly on basic alumina than the other two types. Therefore, the breakthrough curves of total nitrogen and total sulfur, which show the change in the concentration of them remaining in the effluent from the column, in the presence of phenolic compounds provide information on the adsorption behaviors of nitrogen and sulfur compounds on basic alumina. Figure 2 shows the breakthrough curves of total nitrogen and total sulfur on basic alumina for Boscan naphtha. The numbers on the abscissa indicate the weight ratio of naphtha sample to adsorbent (R). The concentration of total nitrogen in the effluent was 3 4 % of the original value up to the breakthrough point of R = 2.4, indicating that most of the nitrogen compounds including pyrrole type which is a very weak base are efficiently adsorbed on

basic alumina in this range of R. Its breakthrough capacity (defined by the adsorption amount of nitrogen up to the breakthrough point) was 8.5 mg of N/g, although it depends on the concentration of nitrogen in the naphthas. On the other hand, the breakthrough curve of total sulfur showed that the concentration of totd sulfur in the effluent reached 100% rapidly at the initial stage of elution and the desorption of sulfur compounds was observed after the saturation point. This is probably due to the replacement of sulfur compounds by phenolic and nitrogen compounds. The desorption area was roughly equal to the adsorption area, indicating that most of the sulfur compounds adsorbed on basic alumina are eventually desorbed during the percolation of the naphtha. Thus, it was found that nitrogen and phenolic compounds alone were selectively separated from the naphtha on basic alumina. Gas Chromatograms of Nitrogen and Phenolic Compound Fractions. Figures 3 and 4 show the FIDTSD-(FPD) gas chromatograms of the nitrogen and phenolic compound fractions recovered from the basic alumina column. The TSD and FPD are highly sensitive to nitrogen and sulfur compounds, respectively, and the

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302 Energy & Fuels, Vol. 5, No. 2, 1991

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Yoshida et al.

Table 11. Identified Compounds and Their Concentrations in Nitrogen Compound Fraction" molecular molecular RT, min formula weight compound concn, ppm 112 10.90 pyrazole, 4,5-dihydro-3,4,5-trimethyl515 11.12 83 pyridine, 2,3,4,5-tetrahydro- or 1,2,4-triazole, methyl245 83 70 190 11.56 cyanamide, dimethyl- or oxazole, trimethyl111

4 5 6 7 8 9 10 11 12

13 14 15 16 17 18 19 20 21

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

11.81 12.15

97

12.46 13.14 14.72 15.27 16.20 17.29 17.75 18.66 18.99 19.73 19.88 20.06 20.41 20.71 20.89 21.26 21.74 21.94 22.44 22.73 23.10 23.26 23.92 24.14 24.66 25.01 25.50 25.71 26.25 26.41 26.82 27.00 27.73 28.10 30.94 31.33 32.07 33.27 33.53 33.89 34.29 34.63 35.12 35.99 36.45 36.60 37.97 38.29 38.91 40.47 46.97 48.07 48.67 48.89 49.27

114

1,2,4-triazole, ethyl?

1,2,4,5-tetrazine, 2,3,4,5-tetrahydrodimethyl?

83 93 107 107

135 95 95 95 95 95 109 133 147 107 121 121 121 121 135 135 129 135

pentanenitrile pyridine, methylpyridine, dimethylpyridine, ethylpyridine, ethylmethylpyridine, dimethylpyridine, dimethylpyridine, dimethyl- or ethylpyridine, trimethylpyridine, dimethylpyridine, trimethylpyridine, propylpyridine, ettylmethylpyridine, ethyldimethylpyridine, trimethylpyridine, ethyldimethylpyridine, ethyldimethylpyridine, ethyldimethylpyridine, ethylmethylpyridine, ethylmethylpyrrole pyridine, trimethylpyridine, ethyldimethylpyrrole, methylpyrrole, methylpyridine, ethyldimethylpyrrole, dimethylpyrrole, dimethylpyrrole, ethylpyrrole, dimethylpyrrole, dimethylpyrrole, trimethylquinoline, tetrahydro1-naphthalenamine, 5,6,7,8-tetrahydroaniline, methylaniline, dimethyl- or ethylaniline, ethylaniline, dimethylaniline, dimethylaniline, ethylmethylaniline, propylquinoline aniline, ethylmethyl-

122 122

phenol, ethylphenol, ethyl- or dimethyl-

122

phenol, ethyl- or dimethylindole indole, methylindole, methylindole, methylindole, methyl-

121

107 107 107 121 107 121 121 121

135 121 135 135 135 121 121

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260 235 240 85 65 170 145 60 135 105 235 135 255 95 170 65 115 165 80 75 70 90 150 375 555 205 80 2175 1340 115 385 235 155 360 115 140 155 . 155 450 400 155 130 135 155 75 215 270 140 125 230 165 145 695 280 90

115 110 "Peak numbers refer to FID chromatogram in Figure 3. Position of alkyl substituents is not identified. Concentration of compound in original naphtha.

use of these detectors is very useful to discriminate between the contaminants in the fractions. Supelcowax 10 capillary column used has a very high resolution for various types of nitrogen compounds such as pyridine, pyrrole, aniline, and indole, and phenols. Therefore, small amounts of phenols contaminated in the nitrogen compound fraction can be easily distinguished from others in the FIDTSD gas chromatograms of the fraction. The FID-TSD chromatograms of the nitrogen compound fraction in

Figure 3 indicate that most of the components can be assigned to nitrogen compounds because of their strong TSD responses. The FPD analysis of the fraction was also made to check the contamination with sulfur compounds, but the FPD response was not observed. This shows that all of the sulfur compounds were eluted from the basic alumina column. The FID-TSD chromatograms of the phenolic compound fraction in Figure 4 show that components in the

Analysis of Nitrogen and Phenolic Compounds Table 111. Identified a m p o u n d s and Their Concentrations in Phenolic Compound Fraction" peak RT, molecular molecular concn, no. min formula weight compound PPm 1 36.46 C7HB0 108 phenol, methyl275 650 2 36.56 C&O 94 phenol phenol, ethyl- or 60 3 37.99 CBH;oO 122 dimethylphenol, dimethyl340 4 38.35 CBHloO 122 phenol, methyl250 5 38.55 C7H80 108 phenol, (1-methylethyl-) 95 6 38.91 C&IzO 136 phenol, ethylmethyl136 7 39.53 CJ3lzO 40 phenol, dimethyl55 8 39.86 C8HloO 122 benzene, ethylmethoxy45 9 40.20 CBHliO 136 phenol, (1-methylethyl-) 55 136 10 40.26 C&lzO 125 phenol, ethyl11 40.47 C8HloO 122 phenol, ethyl12 40.64 CBHloO 122 60 phenol, trimethyl13 41.56 CBHliO 65 136 benzene, ethylmethoxy14 42.12 CBHlZO 35 136 phenol, ethylmethyl15 42.48 CsH120 55 136 ? 60 16 43.00 a Peak numbera refer to FID chromatogram in Figure 4. Position of alkyl substituenta is not identified. Concentration of compound in original naphtha.

fraction were limited to phenols and the contamination with nitrogen compounds was negligibly small. Thus, the nitrogen and phenolic compound fractions were found to be satisfactorily resolved from each other. Identification of Nitrogen and Phenolic Compounds. The main components of the nitrogen compound fraction identified by GC-MS analysis are listed in Table 11. The concentration of individual components in the naphtha was calculated from their FID peak intensities and the yield of the nitrogen compound fraction. As shown by the retention time of components in Table 11, the elution of nitrogen compounds from the GC column was virtually dependent on their compound types and the extent of steric hindrance by alkyl substituents. Therefore, nitrogen compounds were eluted in the order of pyridine, pyrrole, aniline, and indole types and these groups were well resolved from each other, as shown in Figure 3, although some exceptions were involved. Multi-nitrogen compounds were eluted earlier than pyridine type. Trace amounts of sterically hindered alkylated phenols such as 2,6-dimethylphenol were contaminated in the fraction. Although adsorption chromatographic separation with various adsorbenta has often been used for the subdivision of nitrogen compound fraction into specific compound types, such methods are generally tedious and time-con-

Energy & Fuels, Vol. 5, No. 2, 1991 303 Table IV. Amounts of Various Types of Nitrogen ComDounds and Phenols in Boscan NaDhtha compound types concn, w t % nitrogen comDound fraction 2.0 milti-nitrogen 0.2 pyridine 0.4 pyrrole 0.7 aniline 0.35 indole 0.1, others 0.2 phenolic compound fraction C0.4 phenols C0.4

~

suming. However, the present method using GC technique provides a rapid and more accurate analysis for the determination of various compound types as well as individual components in the fraction. The components identified in the phenolic compound fraction are listed in Table 111. Most of the components were assigned to alkylated phenols. The main components were phenol and methyl-, dimethyl-, or ethylphenols. Oxygen compounds other than phenols were not found in the nitrogen and phenolic compound fractions. The amounts of various types of nitrogen and oxygen compounds separated from Boscan naphtha are summarized in Table IV. The total amounts of the nitrogen and phenolic compound fractions were fairly close to the values calculated from the contents of nitrogen and oxygen a t o m in Table I and the distribution of compounds in Tables I1 and 111. Therefore, the nitrogen and phenolic compounds in the naphtha seem to be quantitatively separated by the present method. The amount of nitrogen compound fraction was 2.0 wt 9% and was exceptionally high compared to other n a ~ h t h a s . ' ~Pyrrole type was most abundant in the fraction. It is noteworthy that no more than 0.2 wt % of multi-nitrogen compounds such as pym o l e and triazole homologues was found in the naphtha. The naphtha contained only small amounts of saturated nitrogen compounds. The amount of the phenolic compound fraction was less than 0.4 wt %.

Acknowledgment. We are grateful to the staff of the Analytical Section of the CANMET Energy Research Laboratories for the ultimate analysis of naphtha samples, and to Mr. G. T. Smiley for his technical assistance. (13) Chantal, P. D.; Yoshida, T.; Ahmed, S. M.; Sawatzky, H. h o c . 37th Can. Chem. Eng. Conf., Montreal, Quebec 1987,470-472.