Ind. Eng. Chem. Process Des. Dev. 1986, 25, 618-626
618
Catalytic Hydroprocessing of SRC-I I Heavy Distillate Fractions. 6. Hydroprocessing of the Bases and Neutral Resins Sanjeev S. Kattl and Bruce C. Gates' Center for Cata&Uc Sclence and Technolcgy, Department of Chemical Engineering, UnlversHy of Delaware, Newark, Delaware 19716
Leonklao Petrakis' Gulf Research end Development Company, PmSbwgh, Pennsylvania 15230
Heavy distiltate obtained by hydroliquefactlon of Powhatan No. 5 coal in the SRC-I I process was separated into nine fractions by liquid chromatography. The very weak bases, strong bases, and neutral resins were used as feeds in hyboprocessingexperiments with suffided N1-Mo/y-A1203 catalyst. Analysis by gas chromatography/mass spectrometry led to identification of some of the major components, many being high-molecular-weight aromatic nitrogen-containing compounds. The major reactions were hydrogenation, hydrodenhogenation, and ,hydrodeoxygenation. The reactivity for hydrodenitrogenation decreased with increasing base strength of the coal-liquid fraction, typical fractional conversions at 0.1 (g of feed/(g of catalystah)), 400 OC,and 131 atm being 0.48, 0.38, and 0.26 for the nitrogen in neutral resins, very weak bases, and strong bases, respectively. Quantitative kinetics data are presented for conversion of some individual compounds in the strong base fraction.
In earlier parts of a systematic investigation of the catalytic hydroprocessing of well-defined fractions of a heavy distillate obtained from Powhatan No. 5 coal by the SRC-I1hydroliquefaction process, we have reported reaulta for the neutral oils (Katti et al., 1984) and the acidic fractions (Li et al., 1985; Grandy et al., 1985). Here, we consider the basic and neutral resins fractions, which contain most of the organonitrogen components of the coal liquid. The details of the preparation and characterization of the fractions have been reported in the first papers of this series (Petrakis et al., 1983a, 1983b). The strong, weak, and very weak base fractions account for about 10% of the total heavy distillate. In a typical compound, nitrogen is present in -NH2 groups or in sixmembered rings. Since the weakly basic fraction has such a low solubility in all relatively unreactive solvents (Katti, 1984), the hydroprocessing experiments were carried out only with the more soluble strongly basic fraction and the very weakly basic fraction; cyclohexane was used as the solvent. The strong base fraction accounts for more than half of the bases and 5.7% of the heavy distillate. It contains much less oxygen (1.8%) and much more nitrogen (4.85%) than the other two basic fractions. The infrared spectrum has only weak bands indicating -OHand -NH groups and no bands indicating other heteroatomic functional groups. Only trace quantities of sulfur could be detected by gas chromatography with a sulfur-specific Hall detector. This fraction has an "-determined aromaticity of 0.67 and appears to be made up primarily of substituted benzoquinolines and quinolines with few structures containing NH or OH groups. The very-weak-base fraction accounts for 2.6% of the total heavy distillate, containing 7.8 wt % oxygen, 0.52 wt % sulfur, and 1.27 wt % nitrogen. The infrared spectrum shows that some -OH and -NH groups are present. The aromaticity is 0.79; the fraction contains aminophenols or structures containing two or more aromatic rings. Hydroaromatic structures and alkyl substituents are present, 0196-4305/86/1125-0618$01.50/0
but only in low concentrations. The neutral resins fraction amounts to about 1% of the heavy distillate, containing 5.9 wt % oxygen and 0.8 wt 9% nitrogen. The infrared spectrum shows tightly hydrogen-bonded groups and a strong carbonyl band. Further details of these fractions are available elsewhere (Petrakis et al., 1983a, 1983b; Katti, 1984). Individual compounds identified in the fractions are mentioned below. Since these fractions have high concentrations of organonitrogen compounds, the reactions expected to be of most interest are hydrodenitrogenation and hydrogenation, which typically precedes C-N bond breaking. The conditions required for hydrodenitrogenation are more severe than those required for hydrodesulfurization. Individually measured pseudo-first-order rate constants for pure nitrogen-containing compounds are roughly equal for conversion of two-membered to five-membered ring compounds (Katzer and Sivasubramanian, 1979). The reaction networks characteristic of several basic compounds containing nitrogen in six-membered rings have been established to various extents: pyridine (McIlvried, 1970; Sonnemans, 1972);quinoline (Shih et al., 1977; Satterfield et al., 1978;Bhinde, 1979; Satterfield and Cocchetto, 1981; Sundaram et al., unpublished results); acridine (Zawadski et al., 1981);5,6-benzoquinoline (Wiser, 1980);isoquinoline (Landa et al., 1969); and 7,8-benzoquinoline (Shabtai et al., 1978). The reaction network for quinoline is typical, showing that hydrogenation of the aromatic rings is required prior to the breaking of the carbon-nitrogen bond; both hydrogenation and hydrogenolysis are kinetically important. The networks are consistent with low overall rates of hydrodenitrogenation and large hydrogen consumptions. The catalytic conversion of these organonitrogen compounds with hydrogen has typically been reported in terms of pseudo-first-order kinetics (Shih et al., 1977; Bhinde, 1979; Stern, 1979). Some workers (McIlvried, 1970; Sonnemans, 1972; Goudriaan, 1974; Shih et al., unpublished results; Bhinde, 1979; Satterfield and Cocchetto, 1981) 0 1986 American Chemical
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Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 3, 1986 619
have proposed Langmuir-Hinshelwood rate expressions, indicating strong adsorption of the reactant and self-inhibition of the reaction. The hydrodenitrogenation of nonbasic compounds like pyrrole, indole, and carbazole also proceeds through ring hydrogenation (Hartung et al., 1961; Flinn et al., 1963; Bhinde, 1979; Stern, 1979). These nonbasic compounds, upon hydrogenation, give strongly basic intermediates. For example, pyrrole (&, = 10-l~) gives pyrrolidine (& = and the more basic compounds are evidently the strongest reaction inhibitors.
Experimental Section Materials. The catalyst was a commercial NiOMo03/7-A120, (American Cyanamid, HDS 9A), crushed and sieved to 149-178-pm (80-100 mesh) particle size and sulfided in situ. The catalyst composition is given elsewhere (Houalla et al., 1978). Alundum RR (Fisher Scientific, Blue Label-approximately 90 mesh) was used as an inert reactor packing and as a diluent for the catalyst. Cyclohexane (Aldrich, reagent grade) (peroxide free by the test of Gordon and Ford (1976)) was used as a solvent. Hydrogen was obtained from Linde as 3500 psi grade; traces of moisture and oxygen were removed in copper oxide and zeolite traps. H2S was supplied by Linde in a custom mixture with H2 with a concentration of 10 mol ?% H2S. Procedures. A high-pressure, packed-bed, isothermal, plug-flow microreactor (described in detail by: Eliezer et al., 1977; Broderick, 1980) was used for the catalysis experiments. The catalyst (50-200 mg) was mixed with alundum in a 2:l catalyst/diluent ratio and placed in the central isothermal zone of the reactor, and the ends were filled with the inert alundum. The catalyst was presulfided in the reactor for 7.2 X lo3 s, being subjected to a flow of approximately 5 x IO-' m3/s of 10 mol % H2S in H2 at atmospheric pressure and 400 "C. A 0.25 wt % solution of the appropriate coal-liquid fraction in cyclohexane was prepared and loaded into an autoclave. The low concentration of the organic reactant was chosen to provide a large excess of hydrogen in the reactant mixture-this procedure prevented a significant conversion of hydrogen and the complications in data interpretation that would ensue. Hydrogen was bubbled slowly through the feed solution at ambient pressure for 7.2 X lo3 s to purge out air. After purging, 0.1 wt % CS2 was added to the feed. The hydrogen partial pressure was then raised to the desired value, and the autoclave was stirred for 7.2 X lo3 s to allow saturation of the solution with hydrogen. Approximately 20% of the strongly basic fraction was insoluble in cyclohexane. The solids were removed by filtration, dissolved in a 50-50 wt % mixture of methylene chloride and chloroform, and injected into the gas chromatograph; only two peaks were observed, at very long retention times. The gas chromatographic analysis of the cyclohexane-soluble part of the fraction and that of the whole fraction in methylene chloride/chloroform gave virtually indistinguishable results except for the peaks mentioned above. The cyclohexane-soluble part of the fraction was used in the catalytic reaction experiments, being judged to be representative of the whole fraction. The other coal-liquid fractions were used whole. Immediately after sulfiding of the catalyst, the reactor was cooled to the desired temperature, and flow of the reactant solution was started. The pressure was controlled with a back-pressure regulator to ensure that no gas formed in the reactor-all the hydrogen was present in solution, as shown by thermodynamic estimates (Katti, 1984).
Time-averaged samples of the product were taken every 2 h. Steady state (determined by constancy of the analysis for three successive time-averaged samples) was achieved in about 10-12 h. A typical run lasted for about 30 h. Each run was started with freshly sulfided catalyst. Analysis of Feeds and Products. Routine analysis of the feed and product samples was carried out with gas chromatography; a 30-mSE 54 fused silica capillary column with a 0.25" i.d. was used. A Tracor 560 gas chromatograph was equipped with a flame ionization detector (FID) and a nitrogen-specific Hall electrolytic conductivity detector. A splitter at the outlet of the column directed the effluent stream to the two detectors; two traces were recorded simultaneously. The column temperature was ramped from 100 to 300 "C at 0.033 O C / s and held at 300 "C for 600s. The pyrolysis reador temperature was 875 "C. The liquid sample size was 5 pL. The other conditions were the same as those reported for analysis of the neutral oils fraction (Katti et al., 1984). For accurate analysis, it was necessary to concentrate the 0.25 wt % samples of products of the very weak bases and neutral resins; solvent was evaporated at room temperature by slowly blowing nitrogen over the sample. The samples were concentrated quantitatively about 2-4 times for gas chromatographic analysis and 7-10 times for total nitrogen analysis. The response of the nitrogen-specific Hall detector of the gas chromatograph could not be stabilized even for a simple mixture of four compounds (quinoline, acridine, phenanthridine, and pyrene). This detector was therefore used only for qualitative identification of peaks on the FID trace indicative of organonitrogen compounds. The quantitative analysis was done with an external standard (a mixture of pyrene and quinoline in cyclohexane) added quantitiatively to the sample; from the FID peak areas normalized to the peak area of pyrene on the trace, the amount of any component was calculated by standard methods, described elsewhere (Katti, 1984). The reproducibility of the gas chromatographic analysis was f5-10%. Products of the fractions were analyzed by chemical ionization and electron impact gas chromatography/mass spectrometry at the Pennsylvania State University and at Gulf. Details of the equipment and experimental conditions are given elsewhere (Katti, 1984). The conditions of the gas chromatography were the same as those stated above, and the solvent was a mixture of methylene chloride and chloroform rather than cyclohexane. Analysis of the feed and product samples for C, H, N, 0, and S was carried out by Microanalysis, Inc., Wilmington, DE. The solvent was removed completely to ensure accurate results. A total nitrogen analyzer, a combination of a pyroreactor (Antek, Model 771) and a digital nitrogen detector (Antek, Model 720), was used to determine the nitrogen contents of the liquids. Since this instrument was highly sensitive, it was necessary to remove only part of the solvent. The feed and product solutions of the basic fractions were characterized by infrared spectroscopy. The samples were placed in cells with sodium chloride windows and analyzed with a Nicolet 7199 Fourier transform spectrometer. The absorption of solvent (cyclohexane) in the range of 3000-4000 cm-' was subtracted from the spectra. There were significant complications due to interference from N-H groups and possibly hydrogen bonding.
Results and Discussion The Strong Bases. Characterization by Gas Chromatography and Mass Spectrometry. Chromatograms
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Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 3, 1986
?
ELUTION TIME, min ELUTION TIME, min
Figure 1. Flame ionization detector trace of the strongly basic fraction. The numbers next to the peaks are the retention times in minutes. f X f 4 2
h
ELUTION TIME, min
Figure 2. Nitrogen-specificHall detector trace of the strongly basic fraction. The numbers next to the peaks are the retention times in minutes. E
100
200
300
400
500
SCAN NUMBER
Figure 3. Total ion chromatogram (chemical ionization mode) of the strongly basic fraction. The numbers next to the peaks are molecular weights.
determined with the flame ionization and Hall detector are shown in Figures 1and 2, respectively. The large peak at 50.76 min in the former is indicative of pyrene, added as an external standard. The fact that almost as many peaks were detected with the nitrogen-specific Hall detector as with the unspecific flame ionization detector shows that most of the compounds in the fraction contain nitrogen, as expected from the separation chemistry (Petrakis et al., 1983a, 1983b). A trace of the strongly basic fraction determined with the gas chromatograph/mass spectrometer (in the chemical ionization mode) is shown in Figure 3. The odd numbers next to most of the peaks (which correspond to molecular weights) indicate nitrogen-containing compounds. The peak identifications were carried out by spiking the fraction with authentic compounds and determining the retention time in the gas chromatograph and by chemical ionization and/or electron impact mass spectrometry. The identifications of individual compounds by gas chromatography/mas spectrometry are summarized in the supplementary material, which is a table listing each compound, the retention time, molecular weight, number of isomers, the basis for identification, E1 confirmation, and detection in product by GC/MS and/or retention time and/or spiking with pure compounds. These results confirm that the strongly basic fraction contains organo-
Figure 4. Flame ionization detector trace of a product of hydroprocessing (run SB4) of the strongly basic fraction. The numbers next to the peaks are retention times in minutes.
nitrogen compounds with the nitrogen in six-membered rings or -NH2 groups. The major constituents are benzoquinolines, naphth[2,1,8-deflisoquinoline,biphenylamines, and their substituted derivatives, mono-, di-, tri-, and tetramethylquinolines. Unless exact positions of substituents are specified, they are not known. Further, isomers have often not been resolved, for example, a tetramethyl-substituted compound might instead have a normal or isobutyl group, or methyl and propyl groups, or two ethyl groups, etc. Also, quinoline and isoquinoline isomers of the substituted quinoline have not been resolved; for simplicity, the compounds are reported as quinolines. Qualitative Product Analysis. One product sample was analyzed in detail by gas chromatography/mass spectrometry. The flame ionizatioq detector trace of this sample is shown in Figure 4. It is evident from a comparison with the trace for the feed (Figure 1) that light compounds are products of hydroprocessing. The peaks appearing before the dimethylquinoline peak are primarily indicative of products, compounds not present in the feed. Most of these products have been identified by mass spectrometry as hydrocarbons, including tetralin, naphthalene, methyltetralins, methylnaphthalenes, cyclohexylbenzene, biphenyl, and ethylnaphthalene. Some methylquinolines and tetrahydromethylquinolines,but no decahydromethylquinolines,were deteded. One of the 132 peaks resolved on the mass spectrometer trace may be indicative of tetrahydroquinoline; a peak for tetrahydrodimethylquinoline was also observed. The next section of the chromatogram (16.15-34.25 min, representing compounds with molecular weights of 157 to 183) includes some of the compounds present in the feed, namely, dimethylquinolines, trimethylquinolines, tetramethylquinolines, (1,l’-biphenyl)amine, and methyl( 1,l’biphenyllamine. Some new organonitrogen compounds were also detected and are identified as products, but the identifications are made with less confidence here because of the lack of reference compounds for comparison by spiking: tetrahydrotrimethylquinolines,hexahydro(1,l’biphenyl)amine, tetrahydrotetramethylquinolines,hexahydromethyl(1,l’-biphenyl)amine, tetrahydromethyl(1,l’-biphenyl)amine, dihydrobenzoquinolines, and tetrahydrobenzoquinolines. Some denitrogenated products were also detected: bicyclohexyl (this might instead be fluorene), methylbiphenyl, isopropylnaphthalene, methylfluorene, and tetramethylnaphthalene. The third section of the trace (from 34.25 min to the end) (molecular weights 1183) shows an absence of denitrogenation products. Most of the organonitrogen compounds present in the feed were detected in this section of the trace, including methyl(1,l’-biphenylbine, benzoquinolines, their methyl and dimethyl derivatives, dimethyl(1,l’-biphenyllamine (or possibly tetrahydromethylbenzoquinoline),and naphth[2,l ,&deflisoquinoline and its methyl derivatives. The acridine peak overlaps
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 3, 1986 621 Table I. Hydroprocessing of Strongly Basic Fraction Catalyzed by Sulfided Ni-Mo/yAl2Oa
WHSV, g of run no. SB4 SB5 SB6 SB7 SB8 SB9
temp, "C 400 400 400 400 375 350
Hzconcn,
saturation pressure, atm 117 117 117 117 117 117
pressure, atm 142 142 142 142 142 142
mol/L 0.184 0.184 0.184 0.184 0.205 0.225
feed/(g of catalyst-h) 0.0516 0.0258 0.103 0.387 0.0516 0.0516
% removal
of total N 21 f 3 37 f 5 26 f 3 38 f 5 17 f 5 15 f 5
Table 11. Conversion of Individual Organonitrogen Compounds in the Strongly Basic Fraction' % conversion of the reactant 7,8-benzoquinoline or 5,6-benzoquinoline methylbenzorun no. 9H-fluorene-9-imine acridine or phenanthridine quinoline naphth[2,1,8-deflisoquinoline 33 f 4 41 f 4 19 f 5 SB4 44 f 4 49 f 3 SB5 72 f 3 38 f 5 52 f 5 50 f 5 64 f 5 SB6 43 f 5 22 rt 5 42 5 20 f 5 34 f 5 SB7 66 f 3 35 3 47 f 4 28 f 6 55 f 3 SB8 38 f 5 b b 5f5 43 f 3 34 f 5 22 f 3 5f5 SB9 33 f 4 34 f 5
*
Reaction conditions given in Table I.
*
Steady-state conversion could not be determined.
those of tetrahydrobenzoquinoline and tetrahydromethylbenzoquinoline; however, the latter peak appears to be smaller than the acridine peak on the trace, and the kinetics reported below for acridine may be assumed to be correct with negligible error. Some of the new organonitrogen products are tetrahydromethylbenzoquinolines, dihydrobenzoquinolines, tetrahydronaphth[2,1,8deflisoquinoline, dihydrodimethylbenzoquinolines,and di- and tetra-hydromethylnaphth[ 2,1,8-defl isoquinolines. The absence of any compound with molecular weight 205 confirms that the structure of the compound with molecular weight 203 in the feed (and product) is
eN \ /
i.e., naphth[2,1,8-deflisoquinoline, and not
The former structure, upon hydrogenation, is expected to give a tetrahydro product,
having a molecular weight of 207,whereas the latter would be expected to give a dihydro product,
qp
having a molecular weight of 205. All these results indicate that virtually all the denitrogenated products formed are much lighter than the reactant. Infrared spectroscopic analyses were carried out for the feed and a few product samples. The feed spectrum (shown by Katti, (1984))lacks bands around 3610 and 3480 cm-l, indicating the absence of O-H- and N-H-stretching vibrations. The product spectra (Katti, 1984)show new bands a t 3035, 3070, and 3090 cm-'; we lack sufficient
information to assign these bands; they might be indicative of aliphatics. Kinetics of Catalytic Hydroprocessing. Catalytic reaction experiments with the flow reactor were carried out under reaction conditions summarized in Table I. Conditions were markedly more severe than those required for significant conversion of the neutral oils (Katti et al., 1984) and acidic fractions (Li et al., 1985). Conversions were determined from peak areas in the chromatograms determined with the flame ionization detector. Eleven well-resolved peaks were monitored, each representing an organonitrogen compound in the feed. Difficulties such as interference by product peaks made integration less than highly accurate for all but five of these compounds; the results for these (obtained after steady state had been attained in the flow reactor) are shown in Table II. Other, less accurate data are available in a thesis (Katti, 1984). The conversions of these five compounds at steady state at 400 "C and 142 atm are plotted as a function of inverse space velocity in Figure 5. The results indicate that pseudo-first-order kinetics does not provide a good approximation of the removal of the various nitrogen-containing compounds. The temperature dependence of the conversions of each of the compounds at 142 atm with a weight hourly space velocity of 0.0516 g of feed/(g of catalyst-h) is shown in Table 11. These data were influenced by the change in hydrogen concentration with temperature. Although the saturation pressure and saturation temperature (and hence hydrogen mole fraction) and the total pressure were held constant, the concentration of hydrogen [estimated from thermodynamic properties (Katti, 1984)]decreased from 0.23 to 0.18mol/L as the temperature increased from 350 to 400 OC. Some data indicating the increase in conversion with increasing hydrogen concentration at a given temperature are shown in Tables I and 11. The nitrogen content of the products was determined with the total nitrogen analyzer as a function of the time on stream (Katti, 1984). Steady-state data are shown in Table I. The total nitrogen removal is shown as a function of inverse weight hourly space velocity in Figure 6. The shape of the curve is similar to those indicating conversion of the individual organonitrogen compounds. Discussion. The products identified in this work are in agreement with the ones expected from hydro-
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Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 3, 1986 I O
0 8
06 0
w
0 5
a W
5
04
0
z 03
ELUTION TIME, min
Figure 7. Flame ionization detector trace of the very weakly basic fraction. The numbers next to the peaks are retention times in minutes.
0 !W
q (r
LI
02
-
01
ELUTION TIME, min
1
SIrong ~ o s e s
0
-
-
r..
Nilrogen Removol
Neulrol Resins
(120 otm I
I
0
1
Oxygen Removol
I T 02
-
I
I
,
J
10
20
30
40
I N V E R S E W E I G H T H O U R L Y SPACE V E L O C I T Y , [ g o f c a t a l y s t h ) / g of f e e d
Figure 6. Hydrodenitrogenation (determined by total nitrogen analysis) of the strong bases, very weak bases, and neutral resins at 400 O C and hydrodeoxygenation (determined by total oxygen analysis) of the very weak bases at 400 O C . The catalyst was sulfided by Ni-Mo/y-A1203.
denitrogenation of the compounds identified in the feed. The nonlinearity of the kinetics plots (Figure 6) suggests that the organonitrogen compounds react by complex reaction networks, such as those determined for quinoline and hydrogen (involving rapid hydrogenationfdehydrogenation preceding carbon-nitrogen bond breaking) (Shih et al., 1977; Sundaram et al., unpublished results). Using the values for the pseudo-first-order rate constant in the quinoline network of Sundaram et al. (unpublished results) typical of the conditions of our experiments, we calculated curves for a pseudo-first-order kinetics plot by obtaining a shape closely similar to those of the lower curves of Figure 5 (Katti, 1984). This result suggests that the organonitrogen compounds in the strongly basic fraction react by similar networks, but the data are insufficient to determine any rate constants in the networks. The curve for total nitrogen removal (Figure 6) is similar to those typical of the removal of the individual compounds (not removal of nitrogen from them) (Figure 5 ) . The observation is in agreement with the results of Hara et al. (1979),who found that the removal of the NH group
Figure 8. Nitrogen-specific Hall detector trace of the very weakly basic fraction. The numbers next to the peaks are retention times in minutes.
in SRC coal liquids (as determined by infrared spectroscopy) did not follow pseudo-first-order kinetics at 399 OC and 136 atm. The total nitrogen removal observed in experiments with pure compounds [e.g., quinoline (Bhinde, 1979)] or whole fuels is usually represented well by pseudo-first-order kinetics. (We emphasize that our results represent conversion of individual compounds as well as total nitrogen removal from the mixture.) The differences may be associated with differences in hydrogen concentrations. In the batch and trickle-bed reactor experiments that have been used to generate the literature data, the hydrogen concentrations have been much higher than those of the experiments reported here. The equilibrium conversions are then higher, and much higher conversions may be necessary for the nonlinear behavior associated with equilibrium limitations of the reactions preceding C-N bond breaking. T h e Very Weak Bases. Characterization by Gas Chromatography and Mass Spectrometry. Gas chromatograms of the very weak base fraction determined with the flame ionization and nitrogen-specific Hall detector are shown in Figures 7 and 8, respectively. The large peak in Figure 7 at 51.57 min indicates pyrene added as an external standard. The peaks in this chromatogram appear in bunches of three or four; there are many large peaks indicating compounds much heavier than pyrene. There are many compounds containing nitrogen (Figure 8). The large peak at 8.75 min indicates quinoline, added as an external standard. The organonitrogen compounds are distributed over the entire boiling range of the fraction. It was difficult to match the peaks determined in the gas chromatography/ mass spectrometry traces with those of Figures 7 and 8, in part because of the lack of reference compounds. Similarly, the peak identifications using computer searches of gas chromatographyfmass spectrometry data (with techniques described by Katti (1984)) failed to give definitive identifications of any of the compounds in this fraction. Therefore, the identifications stated in the next few paragraphs should be considered only tentative.
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 3, 1986 623 Table 111. Hydroprocessing of Very Weakly Basic Fraction Catalyzed by Sulfided Ni-Mo/y-A1203 WHSV, g of saturation H2 concn, pressure, feed/ (g of run no. temp, "C pressure, atm mol/L atm catalystah) 141 0.10 VWBl 400 117 0.184 350 86 0.157 120 0.20 VWB2 400 86 0.126 120 0.20 VWB3 VWB4 375 86 0.139 120 0.21 400 86 0.126 120 0.10 VWB5 VWB6A 400 86 0.126 120 0.40 400 86 0.126 VWB6B 120 0.70
From its weakly basic nature, the fraction was expected to contain aminophenols (Petrakis et al., 1983a, 1983b). But aminophenol and its methyl derivatives were not observed. However, peaks observed with molecular weights 159 and 173 could be considered to be indications of aminonaphthol and its methyl derivatives; the dimethyl derivative, however, was not observed. The corresponding three-membered ring compound containing -NH2 and -OH groups and its methyl derivatives were not detected. Another likely candidate is hydroxyindole, but the identification by mass spectrometry is uncertain. Compounds detected with molecular weight 145 could be quinolinol (hydroxyquinoline) or dimethylindolizine or dimethylindole. A series of compounds [similar to the ones observed in the neutral oils (Grandy et al., in press) and strong bases], namely, mono- and dimethyl derivatives, were observed in the feed. They have molecular weights of 131,145, and 159; 170,184, and 198; 168,182, and 196; and 200 and 214. Some electron ionization spectra match, at least in part, the reference spectra of the following compounds: 2- or 4-methylquinoxaline 1-oxide
9i removal
total N 64 f 4 22 f 2 30 f 4 28 f 3 38 f 3 22 f 2 10 f 2
total 0 93 54 >99 87 94 I7 58
Some electron ionization mass spectra of products match in part or in full the reference spectra of the following compounds;compounds with these molecular weights were observed in the feed spectra also, and hence these compounds are likely to have been present in the feed: 9Hpyrido[3,4-b]indole
I H
benzo[c]cinnoline 5-oxide
lH-phenanthro[9,lO-d]imidazole H N ,-,
0 I1
0;)CH3
4,5-dihydr0-4-methyl-2-phenyl-lH-imidazole
3-methylcinnoline
1-methyl-2-phenoxybenzene
0:
O H- 3P h C
carbazole
I
H
N-methylcarbazole
I CH3
Kinetics of Catalytic Hydroprocessing. The flow reactor experiments were carried out under conditions summarized in Table 111. A t 400 "C and 141 atm, many light products were formed; most individual compounds containing nitrogen were completely converted, and high total nitrogen removal was observed. Most of the experiments were done at lower temperatures with lower conversions. Steady-state conversions determined with the total nitrogen analyzer are summarized in Table 111. The total nitrogen removal is plotted as a function of inverse weight hourly space velocity in Figure 6. Again as for the strongly basic fraction, the total nitrogen removal does not follow pseudo-first-order kinetics; the plot suggests equilibrium limitations in the reaction networks. The effect of hydrogen concentration on conversion is shown by the data of Table 111. The effect of temperature is also indicated by these results, but again, the interpretation is complicated by the decrease in hydrogen concentration with increasing reaction temperature. The compounds listed in Table IV were identified in one product sample analyzed in detail by gas chromatography/mass spectrometry. The mass spectra show that many light products were formed. Most are hydrocarbons; there were no nitrogen-containing compounds among the light organic products. Because of the difficulties in determining definitive identifications of reactants, the conversion data for individual compounds are omitted here; they are available in a thesis (Katti, 1984). Most of the organonitrogen compounds reacted readily, and some were almost completely converted. The very weak base fraction contains 7.8 wt 70 oxygen, and conversion of the organooxygen components was de-
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Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 3, 1986
Table IV. Compounds Identified by Gas Chromatography/Mass Spectrometry in the Product of the Very Weak Base Fraction Following Hydroprocessing compound' M,d 2,3-dihydro-x-methyl-1H-indeneb 132 2-methylbenzimidazole 3-oxideb 148 naphthaleneb 128 1,2,3,4-tetrahydro-2-methylnaphthaleneb 146 2,3-dihydro-x,y-dimethyl-1H-indeneb 146 cyclohexylbenzeneb 160 160 dihydro-x,y,z-trimethyl-1H-indeneb methylnaphthaleneb 142 x-ethyltetrahydronaphthaleneb 160 biphenylb 154 ethylnaphthaleneb 156 1-cyclohexyl-x-methylbemeneb 174 fluoreneb 166 9-methylfluoreneb 180 x-ethyl-1,l'-biphenyl (two isomers)b 182 1-methylfluorene 180 phenanthreneb 178 carbazoleb 167 dimethylbenzene" 106 trimethylbenzeneC 120 quinolinol' 145 145 dimethylindolizinec dimethylindoleC 145 butyl- or tetramethyl-1H-benzimidazole' 174 x-ethylquinazoline y-oxidec 174 methylbiphenyl' 168 9H-pyrido[3,4-b]indolec 168 1-cyclohexyl-x-methylbenzenec 174 3,4-dihydro-x,y-dimethylnaphthalen~ne~ 174 isopropylnaphthalenec 170 2-phenyl-lH-pyrrolo[2,3-b]pyridinec 194 192 methylphenanthreneC benzo[c]cinnoline 5-oxidec 196 phenazine 5-oxidec 196 194 x-methylbenzo[c]cinnolineC 2-phenylna~hthalene~ 204 202 fluoranthenee 218 (phenylmethyl)naphthaleneC 218 1H-phenanthro[9,10-d]imidazolec methylfluoranthene or methylpyrene' 216 'Unknown substituent positions are denoted by x , y, and 2. Accuracy of identification is high. Accuracy of identification is low. dRelative molecular mass.
termined by elemental analysis of all the product samples. The data are shown in Figure 6; they are well-represented by pseudo-first-order kinetics for overall oxygen removal, with a rate constant of 2.01 X L/(g of catalyst-s) at 400 "C and 120 atm. Discussion. These results indicate that the hydrodenitrogenation of the very weak bases occurs much more readily than that of the strong bases. For example, at 400 "C and 142 atm with a concentration of hydrogen of 0.184 mol/L and an inverse weight hourly space velocity of 0.1 g of feed/(g of catalyst-h),the total nitrogen removal was 64 f 4% for the very weak bases (Table 111) and 26 f 3% for the strong bases (Table I). The hydrodenitrogenation of benzylamine (Ph-CH2NH2) is much faster than that of aniline (Ph-NH2) (Doelman and Vlugter, 1963; Katzer et al., 1982). In aniline, the amino group is stabilized by resonance with the aromatic ring, and ring hydrogenation is required before nitrogen removal. It appears that the aminophenols in the very weakly basic fraction undergo rapid hydrodenitrogenation. We infer that the -OH group, an electron donor, reduces the resonance stability of the amino group and facilitates the hydrodenitrogenation. The literature provides no data concerning the reactivities or reaction networks of the several types of compounds (e.g., indolizines, cinnolines, imidazoles, etc.)
suggested by the mass spectra of the very weakly basic fraction. The phenolic compounds in the very weakly basic fraction are apparently intermediate in reactivity to those of the weak-acid fraction (Li et al., 1985) and the dibenzofuran of the neutral oils fraction (Katti et al., 1984), but this suggestion is tentative because the experiments were done at different temperatures and because the organonitrogen compounds (especially those formed as intermediates) are strong reaction inhibitors (Krishnamurthy and Shah, 1982). The Neutral Resins. Characterization by Gas Chromatography and Mass Spectrometry. The results of the gas chromatography (obtained with both detectors) and the gas chromatography/mass spectrometry (shown by Katti (1984)) indicate that only about a third of the compounds in the neutral resins fraction contain nitrogen. A major component was the plasticizer di-2-ethyl hexylphthalate (an impurity) (Petrakis et al., 1983a, 1983b; Katti, 1984). From its nature, this fraction is expected to contain neutral organonitrogen compounds such as carbazole (Petrakis et al., 1983a). Carbazole, methylcarbazole (three isomers), dimethylcarbazole (four isomers), trimethylcarbazole (three isomers), and tetramethylcarbazole (one isomer) were indeed observed by chemical ionization mass spectrometry. The presence of carbazole at a retention time of 37.53 min was confirmed by (1)comparison with the retention time of the authentic compound and (2) spiking the neutral resins with pure carbazole and observing the increase in flame ionization and Hall detector responses. However, some other likely candidates such as diphenylamine and its mono-, di-, etc., methyl derivatives and indole and its mono-, di-, tri-, etc., methyl derivatives were not observed. A series of variously substituted compounds (similar to the ones observed in the other fractions) and their monomethyl derivatives were observed in the neutral resins, e.g., with molecular weights 153 and 167, 157 and 171 (these could be tetrahydro derivatives of the former compounds), and 220 and 234. Some electron impact mass spectra match in part or in full the reference spectra of the following compounds, but the identifications are less than definitive (Katti, 1984): 2(1H)-quinoxalinone
H
3,4-dihydro-3-methyl-l(2H)-naphthalenone
7-(or 8-)ethylquinoline
/
C2H5
diethyldimethylbenzene C H5
p
p
3
AA C,H5
CH3
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 3, 1986 825 Table V. Hydroprocessing of the Neutral Resins Fraction Catalyzed by Sulfided Ni-Moly-AlzOS run no. NR1 NR2 temp, OC 400 350 saturation pressure, atm 86 86 H2 concn, mol/L 0.126 0.157 pressure, atm 120 120 WHSV,g of feed/(g of cata1yst.h) 0.1 0.1 % removal of 48*5 33i4 total N 100 77 total 0
The following compounds are suggested tentatively on the basis of the chemical ionization mass spectra: dimethyl-1-indanone 0
CH3 CH3
2-ethylquinoxaline 1,6dioxide
,U. It
sions of individual compounds. The data do show conclusively that the conversion of the plasticizer impurity was more than 98% in each experiment. The flame ionization detector trace shows the formation of a large number of light products, none containing nitrogen. The Hall detector trace shows that all the nitrogen-containing compounds eluted before carbazole were converted completely. Most of the nitrogen-containing compounds underwent detectable conversion. Discussion. There are too few data to determine the shape of the kinetics plot (Figure 6), and the curve shown for the total nitrogen removal from the neutral resins has been assumed to be similar in shape to those of the other fractions. The comparison is sufficient to demonstrate clearly that the hydrodenitrogenation of the neutral resins is more facile than that of the very weak bases, which is more facile than that of the strong bases. This result points to a correlation between the basicity of the organonitrogen reactants and the hydrodenitrogenation reactivity: the greater the base strength, the less is the reactivity of the class of compounds for hydrodenitrogenation. The correlation might be explained by the differing hydrogen requirements for opening the nitrogen-containing rings, the less basic compounds already being partially hydrogenated.
Acknowledgment We thank S. K. Starry and S. K. Banerjee for help with the experiments. This work was supported by the US Department of Energy.
0
Registry No. Naphth[B,l,8-deflisoquinoline, 193-98-6;tetralin, 119-64-2; naphthalene, 91-20-3; methyltetralin, 31291-71-1; methylnaphthalene, 1321-94-4;cyclohexylbenzene,827-52-1;biphenyl, 92-52-4; ethylnaphthalene, 27138-19-8; (1,l'-biphenyl)amine, 41674-04-8; methyl(1,l'-biphenyl)amine,79869-61-7;hexahydro(1,l'-biphenyl)amine, 99796-99-3; hexahydromethyl(1,l'-biphenyl)amine, 99880-89-4;tetrahydromethyl(1 ,l'-biphenyl)amine, 99880-90-7; methylbiphenyl, 28652-72-4; isopropylnaphthalene, 29253-36-9; methylfluorene, 26914-17-0; dimethyl(1,l'-biphenyl)amine, 99797-00-9; tetrahydromethylbenzoquinoline, 99808-47-6; bicyclohexyl, 92-51-3; fluorene, 86-73-7; tetrahydronaphth[ 2,1,8-deflisoquinoline, 99797-01-0; dihydromethylnaph[2,1,8-deflisoquinoline, 99797-03-2; tetrahydromethylnaphth[2,1,8-deflisoquinoline, 99797-04-3; aminonaphthol, 42884-33-3; methylaminonaphthol, 99797-05-4;2,3-dihydromethyl-lH-indene, 27133-93-3; 2-methylbenzimidazole 3-oxide, 16007-52-6;1,2,3,4tetrahydro-2-methylnaphthalene,3877-19-8; 2,3-dihydrodimethyl-1H-indene, 53563-67-0; dihydrotrimethyl-1H-indene, 36541-18-1; ethyltetrahydronaphthalene, 99797-06-5; l-cyclohexylmethylbenzene, 26590-33-0; 9-methylfluorene, 2523-37-7; ethyl-1,l'-biphenyl, 40529-66-6;phenanthrene, 85-01-8; carbazole, 86-74-8; acridine, 260-94-6.
3-methyoxy-9H-carbazole
H
2-phenylindole
I H
tetramethylbenzothiazole
Literature Cited C" 3
diphenylfuran
Ph
Ph
Kinetics of Catalytic Hydroprocessing. Only two catalytic reaction experiments were done, with the conditions listed in Table V. One run was carried out under the standard conditions used with the strongly basic fraction, the other at a lower temperature and otherwise the same conditions. Steady-state conversion was attained after 15-20 h onstream. The steady-state data for total nitrogen conversion are given in Table V and Figure 6. Difficulties in the analysis of products (such as overlapping peaks) made it impossible to determine conver-
Bhinde, M. V. Ph.D. Thesis, University of Delaware, Newark, 1979. Broderick, D. H. Ph.D. Thesis, University of Delaware, Newark, 1980. Doelman, J.; Vlugter, J. C. "Proceedings of the Slxth World Petroleum Congress"; The Hague: The Netherlands, 1963; Section 111, p 247. Eliezer, K. F.; Bhinde, M.; Houalia, M.;Broderick, D. H.; Gates, B C.; Olson, J. H. Ind. Eng. Chem. Fundam. 1977, 16, 380. Flinn, R. A.; Larson, 0. A.; Beuther, H. Hydrocarbon Process. Pet. Refin. 1983 42 (9), 129. Gordon, A. J.; Ford, R. A. "The Chemist's Companion"; Wiiey Interscience: New York, 1976. Goudriaan, F. Ph.D. Thesis, Twente Technical Institute, The Netherlands, 1974. Grandy, D. W.: Petrakis, L.; Katti, S. S.; Gates, B. C., unpublished results. Grandy, D. W.; Petrakis, L.; Li.. C.-L.; Gates, B. C. Ind. Eng. Chem. Process Des. Dev. 1988, 25, 40-48. Hara, T.; Tewari, K. C.; Li, N. C.; Fu, Y. C. Prepr.-Am. Chem. Soc., Div. fuel Chem. 1979, 24 (3), 215. Hartung, G. K.; Jeweii. D. M.; Larsen, 0. A,; Fllnn, R. A. J. Chem. Eng. Data 1981. 6 ,477. Houalla. M.: Nag, N. K.; Sapre, A. V.; Broderick, D. H.; Gates, B. C. AIChEJ 1978, 24, 1015. Katzer, J. R.; Sivasubramanian, R. Catel. Rev.-Sci. Eng. 1979, 20, 155. Katzer, J. R.; Stiles, A. B.; Kwart, H. US Department of Energy Report 78 ET-1 1429-Fina1, 1982.
626
Id.Eng. Chem. Process Des. Dev. 1986, 25, 626-630
Kattl, S.S. FhD. Thesls, University of Delaware, Newark, 1984. Kattl, S. S.; Westerman, D. W. B.; Qates, B. C.; Youfigless, T.; Petrakis, L. Ind. Eng. Chsm. Recess Des. Dev. 1984, 23, 773. Krlshnamvthy, S.; Shah, Y. T. Chem. Eng. Commun. 1902, 16, 109. Landa, S.; Kafka. 2.; QalL, V.; Safar, M. Collect. Czech. Chem. Commun. 1969, 3 4 , 3987. Ll, C.-L.; Xu, 2.4.; Gates, 8 . C.; Petraks, L. Ind. Eng. Chem. Process Des. h v . 1985, 24, 92. McIlvried, H. G. Rep.-Am. Chem. Soc.,Div. Petrol. Chem. 1970, 15(1), A33. Petrakis, L.; Ruberto, R. G.; Young, D. C.; Gates, B. C. Ind. Eng. Chem. Process Des. Dev. 1983a, 2.2, 292. Petrakis. L.; Young, D. C.; Ruberto, R. G.; Gates B. C. Ind. Eng. Chem. Process Des. Dev. 1983b, 22, 298. Satterfield, C. N.; Modell, M.; Hltes, R. A.; Dederck, C. J . Ind. Eng. Chem. Process Des. Dev. 1978, 17, 141. SatterfW. C. N.; Cocchetto, J. F. Ind. Eng. Chem. Process Des. Dev. 1*81.20,53. Shabtal, J.; Oblad. A. 0.; Wlser, W. H., paper presented at the Fifth Annual DOE Fossll Enecgy Conference on University Coal Research, Aug 23-24, Loulsvllle KY. 1978.
Shih, S. S.; Katzer, J. R.; Kwart, H.; Stiles, A. B. Prepr.-Am. Chem. Soc.. Dlv. Petrol. CY”. 1977, 22, 919. Shih, S. S.; Katzer, J. R.; Kwart, H.; Stiles, A. B.; Mathur, K. N., unpubllshed resutts. Sonnemans, J. Proceedings of the Fifth International Congress on Catalysis, Palm Beach, FL, 1972, p 1085. Stern, E. W. J . Catal. 1979, 57, 390. Sundaram. K. M.; Blschoff. K. B.; Katzer, J. R., unpublished results. Wiser, W. H. U.S. Department of Energy, Quarterly Progress Report DOE/ ETl14700-2, Aug 1980, pp 21-25. Zawadski, R.; Shlh, S. S.;Katzer, J. R.; Kwart, H., unpublished results.
Received f o r review March 21, 1985 Accepted September 13, 1985
Supplementary Material Available: Table containing the identification of compounds in the strong-base fraction by GC/MS (4 pages). Ordering information given on any current masthead page.
Kinetics of Combustion of Carbon and Hydrogen in Carbonaceous Deposits on Zeollte-Type Cracking Catalysts Guang-xun Wang, Shi-xlong Lin, Wel-Jlan Mo, Chun-Ian Peng, and Guang-hua Yang East Chlna Petroleum Institute, Oongying, Sttandong, People‘s Republic of China
The kinetics of combustion of carbon and hydrogen in carbonaceous deposits, or “coke”, on zediitype cracking catalysts at high temperatures up to 800 OC and resldual coke contents down to 0.05% of cracking catalysts were investigated with both the continuous-flow technique and p u b f l o w technique. The problem of a very short reaction period (of the order of seconds) at a high temperature of regeneration was overcome by a high-sensitivity, quickqesponse thermoconductivity ceH, and the problem of strong adsorption of one of the reaction products, water, on the cracking catalyst and on the reactor system was solved by means of a pulse technique and a model reactor
technique. Kinetic equations of the combustion of carbon and hydrogen in coke on the cracking catalysts obtained fit the experimental data satisfactorily.
The mechanism and kinetics of the regeneration of carbonaceous deposits on cracking catalysts has been extensively investigated since the 1940s. Fundamental works had been done by Hagerbaumer and Lee (1947), Pansing (1956), Dart et al. (1949), Weisz and Goodwin (1966), Massoth (1967), and others. However, their works were concerned mainly with the regeneration of amorphorous bead catalysts at a comparatively low temperature, mostly below 600 “C,and a rather high residual coke content, >0.5%. The kinetic data and rate expression concerning the burning of hydrogen in the coke appeared very few times in the literature. The introduction of zeolite cracking catalysts with their high activity and thermal stability permits the operation of a regenerator of a cracking unit a t temperatures as high 800 OC and a low residual coke content down to 0.05% after regeneration. Therefore, in the design and operation of this type of modern catalytic cracking unit, it is quite essential to acquire the kinetic data for the combustion of carbon and hydrogen in coke on cracking catalysts. An attempt has been made to throw light on this problem by Wang et al. (1982). The present work is a continuation of that effort. Experimental Work The experimental difficulty of determining the kinetics and the mechanism of carbon and hydrogen combustion in coke at high temperatures arises from the high speed of reaction; so it is important to develop an in-line detection device which has a quick response to the reaction 0196-4305/86/ 1125-0626$01.50/0
signal and high precision of measurement. In the case of measuring hydrogen reaction velocity, the problem is even more strenuous because the reaction product-water-is readily adsorbed on the reactor wall and on the cracking catalyst. To circumvent this difficulty, special techniques were developed and will be described below. Experimental Technique for Measuring Reaction Kinetics of t h e Combustion of Carbon The flow diagram of the experimental setup for the determination of the combustion kinetics of carbon in coke on the cracking catalyst is shown in Figure 1. A quartz reactor, 7-mm inside diameter, was designed to meet the various strict requirements for a good flow pattern, isothermal reaction, small pressure drop across the catalyst bed, differential oxygen consumption in the reactor, and absence of mass transport limitations between coke and oxygen. In accordance with the aforementioned requirements, a limited amount (several milligrams) of coked cracking catalyst was placed on the sintered quartz plate fused to the reactor wall, and a sufficient quantity of coke-free inert of the same particle size was then added to mix with the coked catalyst as a diluent for the isothermal reaction. Air in the reactor was expelled with a stream of nitrogen, purified by passing through two deoxygenators connected in series. The reactor was then heated by submerging its reaction zone into a fluidized bed filled with silica gel microbeads to ensure even temperature distribution. 0 1986 American Chemical Society
