Ind. Eng. Chem. Res. 1988, 27, 1587-1595 Nishiyama, N.; Saketani, N. Japan Patent 41 892; 1972; Chem. Abstr. 1973, 78,29462~. Pearson, R. G. J. Am. Chem. SOC.1963,85, 3533. Reuben, B., Sjoberg, K. Chemtech, 1981,315. Selegiann, D. Rom. Patent 51196; 1968; Chem. Abstr. 1969, 70, 57457d. Starks, C. M. J. Am. Chem. SOC.1971, 93, 195.
1587
Starks, C. M.; Liotta, C. "Phase Transfer Catalysis, Principle and Techniques"; Academic: New York, 1978. Yeh, M. Y.; Lin, T. B.; Shih, Y. P. J.Chin. Chem. SOC.(Taipei) 1985, 32, 143.
Received for review December 23, 1987 Accepted April 26, 1988
Structural Analysis of Extracts from Spent Hydroprocessing Catalysts John H. K. Choi and Murray R. Gray* Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, T6G 2G6 Canada
Solvent extracts from spent commercial naphtha and gas oil hydrotreating catalysts were examined in order to elucidate the structure of adsorbed poisons. Amides were identified in the extracts and made up 20-30% of the basic compounds. The oxygen content of the extracts was as high as 28% by weight. Some of this oxygen may be associated with metal complexes or present as inorganic material. Infrared spectroscopic analysis revealed very strong absorptions due to carbonyls, suggesting that compounds such as ketones and carboxylic acids were present. The extracted compounds consisted of saturated (paraffinic and naphthenic) structures and aromatic groups, with >50 % boiling a t +343 "C. These results suggest polymerization of species on the surface of the catalyst, rather than condensation of aromatic structures to form coke. The deleterious effect of minerals and heterocyclic compounds on the activity of petroleum-processing catalysts has long been recagnized (Furimsky, 1979). Nitrogenous compounds are particularly undesirable. Since these are catalytic poisons (Mills et al., 1950), they are usually removed first by catalytic hydrogenation prior to further upgrading of the fuel (Dorbon et al., 1984; Stern, 1979). Compounds suqh as pyrrole derivatives also affect recovery and storage by increasing the propensity of the petroleum toward gum/tar formation (Ford et al., 1981). Also, many nitrogen compounds, such as quinolines and pyridines, are carcinogens and form toxic combustion products. Johnson et al. (1986) also observed that both metals and coke deposits decreased the diffusivity of aged Co-Mo/AlpOB catalysts, while metal deposits (Ni, V) were mainly responsible for the reduced activity toward hydrodesulfurization, hydrodenitrogenation, and hydrogenation reactions. The nitrogen compounds usually amount to less than 0.5 wt 90in crude petroleum and 1-2% in shale oil and coal-derived liquids (Burchill et al., 1982; Novotny et al., 1980). The high molecular weight (mw) compounds consist mainly of the di- and polynuclear aza arenes. These pyridine and quinoline benzologues have been detected in shale oils (Simoneitet al., 1971; Uden et al., 1979),bitumen and crude oils (Mojelsky et al., 1986; McKay et al., 1976; Schmitter et al., 1980), and coal liquefaction products (Birchill et al., 1982). In the low MW range, pyridines and quinolines are the major components, while weaker bases like amides and nitriles and nonbasic compounds like pyrroles, indoles, and carbazoles in various amounts have been identified in light virgin gas oil (Albert, 1967),cracked gas oil and straight-run distillates (Snyder and Buell, 1964, 1965), and shale oils (Poulson et al., 1971; Poulson, 1975). Although the catalyst-degrading properties of heterocompounds have long been realized, very little work has been done to determine which heteroatomic compounds are most poisonous (Mills et al., 1950; Dorbon et al., 1984). Mills et al. (1950) studied various nitrogenous bases and
* Author for correspondence.
Table I. Properties of Catalysts surface area, pore vol, % Mo catalyst m2/g cm3/g (as metal) naphtha cat. A and B 160 0.45 12.9 220 0.39 gas oil cat. A 18.0 140 0.46 9.3 gas oil cat. B
size: mm 1.5 1.5 2.2 1.5 %
Ni 3.0 5.3
=The naphtha catalyst was a trilobe extrudate. Gas oil catalysts were cylindrical extrudates.
rated the catalytic poisoning effectiveness in the order, quinaldine > quinoline > pyrrole > piperidine > decylamine > aniline. Furimsky (1978, 1982) examined the extracts of cobalt-molybdate catalysts and suggested that phenols, condensed aromatics, and heterocyclic compounds are the main coke precursors. Yoshimura et al. (1987) found that the THF extract from spent Ni/Mo alumina catalyst was enriched in nitrogen and oxygen relative to the heaviest fractions of the coal-liquid feed. The catalyst in a commercial reactor can adsorb and accumulate trace components during 1 or more years of service and provide high concentrations of the most significant poisons, and their derivatives, from the oil feed. This study used solvents to extract adsorbed material from spent hydrotreating catalysts. The extracts were analyzed by a number of techniques, including UV, IR, and NMR spectroscopies and elemental analysis. Potentiometric titration was used to quantify the concentrations of basic compounds. The objective was to identify the major compound types and functional groups in these extracts (prior to more detailed component identification) and determine the characteristics of the hydrocarbon structures in relation to the oils being processed.
Experimental Methods Materials. The following samples of spent catalyst were provided by Syncrude Canada Ltd.: (1)Naphtha hydrotreating catalysts operated at 280-330 "C and 5.5-6.9 MPa (800-1000 psia). (a) naphtha catalyst A Ni/Mo on alumina, in service for 12-14 months in the first naphtha hydrotreating reactor. (b) Naphtha catalyst B: identical
0 1988 American Chemical Society 0888-58~5/88/2627-~587$01.5Q/Q
1588 Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988
Ni/Mo on alumina, in service for 12-14 months in the second naphtha hydrotreating reactor in series. (2) Gas oil hydrotreating catalysts operated at 360-430 "C and 9.6-11 MPa (1400-1600 psia). (a) Gas oil catalyst A: Ni/Mo on alumina, in service for 1 year. (b) Gas oil catalyst B: Ni/Mo on alumina, in service for 1 month in a pilot reactor. The metal content and characteristics of the catalysts are given in Table I. All of the samples were unloaded cold from the reactors, after purging with inert gas. The catalyst samples were stored in closed containers but were exposed to air during handling and extraction. Lithium tetrahydrodioaluminate (Alfa), silica gel (Terochem Lab. Ltd.; catalog no. 1919),and solvents such as methylene chloride, methanol, acetonitrile (all HPLC grade, Fischer Scientific), benzene, acetic anhydride, perchloric acid, hydrochloric acid, and ethyl ether (all reagent grade, Fisher Scientific) were used as received. Extraction of Catalyst. Approximately 40 g of catalyst pellets was first Soxhlet extracted with 150 mL of methylene chloride for 48 h; the solution was filtered and concentrated to yield an extract designated as extract I. The same catalyst was further extracted with 150 mL of methanol for 48 h to yield extract 11. This extract had a high ash content, so it was then back-extracted with methylene chloride to produce extract I1 and an insoluble residue or precipitate. No difference in yield of extracts was detectable between catalyst which was ground up or in pellets, suggesting no significant mass-transfer limitation to extraction over a 48-h period, and longer extraction times did not increase the yield of extract. Potentiometric Titration of Nitrogen Base. The differentiation of nitrogen compounds in petroleum into classes by potentiometric titration in solvents such as chlorobenzene (Deal et al., 1953), nitrobenzene (Darlage et al., 1978),acetonitrile, and acetic anhydride, either alone or in conjunction with another solvent (Buell, 1967; Fritz, 1953),has been extensively investigated. This classification is based on the linear relationship between the half-neutralization potentials (HNP) of these compounds in nonleveling, organic solvents and their basicity (Fritz, 1973). Deal et al. (1953) studied the moderately strong bases, e.g., piperidines, by comparing titrations with perchloric acid and hydrochloric acid; Darlage et al. (1978) differentiated five classes of nitrogen compounds in asphaltene using nitrobenzene as solvent, while Buell classified the nitrogen compounds into four classes using acetonitrile and acetic anhydride solvents (Buell, 1967). The extracts from the catalyst gave gas chromatograms that were too complex for direct determination of individual compounds by GC-MS, so potentiometric titration was used to identify the main classes of bases. The procedure used for potentiometric titration is similar to that used by Buell(1967), so a brief description here will suffice. About 0.08 g of extract I or 0.04 g of extract I1 was dissolved in a mixture of 10 mL of acetonitrile or acetic anhydride and 20 mL of benzene. The solution was potentiometrically titrated with approximately 0.5 N perchloric acid, prepared in dioxane as described by Fritz (1953) and Wimer (1958). LAH Reduction of Extracts I and 11. Potentiometric titration was used with lithium aluminum hydride (LiAlH4 or LAH) reduction of the petroleum sample for further classification (Okuno et al., 1965; Bezinger et al., 1962). For example, Okuno et al. (1965) identified five classes of nitrogen-containing compounds in crude oils by titration in acetic anhydride with perchloric acid before and after reduction.
Table 11. Yield of Extracts from Naphtha and Gas Oil Catalysts catalvst extract yield, wt % naphtha cat. A I 1.9 naphtha cat. B
I1 I
2.8 1.0
I1 I II'
0.3
gas oil cat. A
I1 I
2.1 8.2
11'
0.7
I1
0.4
gas oil cat. B
9.9
5.7
Extract I (0.5 g) was dissolved in 20 mL of anhydrous ethyl ether. An excess of LAH was added and the solution gently refluxed for 48 h. THF was used to dissolve the more polar extract I1 (0.1 g), which was refluxed for 8 h. After reflux, the solution was cooled in ice, and 5 mL of water was added to react with the excess LAH. Then 50 mL of water and 20 mL of methylene chloride were added to facilitate separation in a separatory funnel. The methylene chloride layer was dried over MgSO, and the solvent evaporated to give the reduced extract. Spectroscopic Analysis. Infrared spectra were recorded on a Perkin-Elmer 621 double-beam grating spectrophotometer, using 10% and 2% solutions of extracts I and 11, respectively, in 0.05-cm NaCl cells. UV analysis was performed with a Shimadzu Model UV-160 doublebeam UV-vis spectrometer. 'H NMR spectra were obtained with a Varian Model 56/60 A 60-MHz spectrometer, while high-field lH NMR and I3C NMR spectra were recorded by a 400-MHz Bruker WH-400 spectrometer. Simulated Distillation Analysis (SDA). The gas chromatographicanalysis (HP Model 5710A, TC detector) of the boiling point distribution of two extracts (naphtha catalyst A, extract 11, and gas oil catalyst A, extract 11)was carried out by using a l/*-in (0.d) X 20-in. (length) nonpolar column of 10% UCW 982 on P-AW, 80/100 mesh. The column was heated at a uniform rate of 8 "C/min from -10 to 350 "C. The He carrier gas flow rate was 60 mL/min. Elemental Analysis. The C, H, N, 0, S, and ash contents were measured by the Microanalytical Lab, Chemistry Department, University of Alberta. PerkinElmer analyzers, Model 240 and 240B, were used for the C, H, N, and 0 measurements. S was analyzed by titration with Ba(C104)2. Structural Group Analysis. The structural group analysis (SGA) for the characterization of petroleum mixtures is based on the premise of choosing a set of groups as representative of the characteristics of the sample. The estimates of the group concentrations were optimized subject to the constraints of the analytical data. The groups chosen are dependent on the source/background of the particular sample and on data from analysis such as elemental analysis, 'H NMR, 13C NMR, IR, and nitrogen potentiometric titration. SGA has been applied for the structural characterization of complex hydrocarbon mixtures such as coal-derived liquids (Allen et al., 1985) and gas oils (Khorasheh et al., 1987) and has been employed regularly in our laboratory for the analysis of petroleum mixtures.
Results and Discussion The yields from solvent extraction of the catalyst samples and the elemental analysis are listed in Tables I1 and 111. Methylene chloride was first used to remove the residual feedstock on the catalytic surface (extract I), which might otherwise interfere with the characterization of the more strongly adsorbed species (extract 11), removed
Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988 1589 Table 111. Elemental Analysis of Extracts from Naphtha and Gas Oil Catalysts sample C H N Naphtha Catalyst A original catalyst 8.17 1.08 0.15 5.55 extracted catalyst 0.91 0.01 11.21 0.00 87.25 extract I extract I1 7.45 3.74 46.50
S
0
ash
7.27 7.81 0.43 8.16
5.76 8.28 1.01 21.68
77.57 77.44 0.01 12.47
7.47 7.25 0.32 9.37
5.35 6.45 0.88 21.42
73.55 73.41
9.63 10.73 0.23 6.66 6.76
7.94 10.90 1.89 28.33 16.80
63.30 72.18
7.78 8.11 2.13 8.74 7.17
5.88 7.34 1.14 28.83 18.04
66.91 80.29
Naphtha Catalyst B original catalyst extracted catalyst extract I extract I1
12.61 12.05 86.91 55.22
0.89 0.75 11.80 8.24
original catalyst extracted catalyst extract I extract 11’ extract I1
16.30 4.79 85.79 44.32 64.21
2.52 1.14 11.90 6.84 8.63
original catalyst extracted catalyst extract I extract 11’ extract I1
16.40 3.11 84.00 37.60 58.22
2.49 0.76 12.25 5.88 7.79
0.13 0.09 0.09 4.02
1.37
Gas Oil Catalyst A
Gas ..
0.31 0.26 0.19 2.34 2.98
11.50 0.62
Oil Catalyst B
subsequently by methanol. The high volatility of the naphtha feedstock is reflected in the lower yields of extract I (1-2%) compared to those of the gas oils (10%). The gas oil catalysts were visibly oil wet before extraction, whereas the naphtha catalysts were dry in appearance. The yields of extract I1 were generally low (0.3% to -2% after back-extraction) and correlate with the service time and conditions of the catalyst. Naphtha catalyst A was in the first reactor and has a higher content of extract I1 (2.8%) compared to naphtha catalyst B which was used in the second reactor. The first reactor would receive the highest concentration of poisons and hence would tend to accumulate more adsorbed polar material. Counter to this, the naphtha catalyst B sample (second reactor) had a higher total carbon content and a lower extraction efficiency (based on carbon removal), suggesting a fundamental difference between the deposits on the two catalysts. Gas oil catalyst A was in service for a year and yielded much more extract I1 (2.1%) than gas oil catalyst B (0.4%) which was in service for a much shorter period. Table I11 presents the normalized data from elemental analysis. The values given for sulfur content of the catalysts include both inorganic metal sulfides (from NiS and MoS) and organic adsorbed species. The balance on carbon before and after extraction was within 7 % , except for gas oil catalyst B which gave a significant loss of carbon on extraction. The balances on nitrogen and sulfur closed to within the error of the elemental analysis. The oxygen and hydrogen analyses of the catalysts may include water evolved by dehydration of the catalyst, particularly where the extracted catalysts may have adsorbed some water from the methanol solvent, as indicated by a net increase in oxygen content of some extracted samples. The metals in the catalyst are an unlikely source for this large amount of oxygen because the molybdenum (85% of the metal by weight) would form Moo3 upon oxidation, not a sulfate. The high hydrogen and oxygen content of the extracts, however, suggests that a substantial portion of the H and 0 content measured for the catalyst was organic in origin. A strong correlation exists between the heteroatom content of the catalyst, particularly 0, and the ash content of the extracts. Part of the ash in extract 11’ can be ascribed to the dissolution of the alumina support during the methanol extraction. For example, in gas oil catalyst A, the ash content decreased from 16.32% to 5.72% after back-ex-
0.54 0.38 0.67 2.63 3.06
16.32 5.72
traction with methylene chloride. Furthermore, there is also a correlation between the heteroatom + ash content and the appearance of the extract, which varied from a yellowish brown oil (extract I), when the heteroatom-ash content was low, to a dark green gum/solid (extract 11), when the heteroatom-ash content was high. These observations, and the high ash content of some samples even after back-extraction, strongly imply the presence of some organometallic complexes which were extracted by the more polar methanol in extract 11. The precipitate/residue from the back-extraction of extract 11’with methanol was analyzed by the ICP method for metallic composition and was found to consist mainly of nickel, plus traces of sodium, vanadium, molybdenum, aluminum, and silicon. Apparently very little aluminum was detected because the alumina residue was not dissolved by fusion with lithium metaborate followed by treatment with hot nitric acid. The amount of nickel removed from each catalyst was estimated from the ICP analysis of the residue and the ash contents of extracts I and 11, which were assumed to contain as much nickel as the residue. Since the spent catalysts contained about 3% nickel by weight (as metal), up to -10% of the nickel was removed from the naphtha catalysts by extraction and up to E 3% from the gas oil catalysts. Some caution is warranted in interpreting the results of the elemental analysis. For example, the accuracy of the N analysis is +=10-20% at these low concentrations. Thus, although no N was detectable in extract I of naphtha catalyst A, a later titration with perchloric acid indicated 0.04% N in the extract. Nevertheless, the high N content in extract I1 (N/C = 0.07-0.08, naphtha catalysts; -0.05, gas oil catalysts) clearly indicates the presence of more polar, nitrogenous compounds. On the other hand, Furimsky (1978) obtained a lower 70N in the pyridine extract of cobalt molybdate catalysts (N/C = 0.019, bitumen feedstock; 0.035, gas oil feedstock), possibly due to the shorter extraction time and shorter service time (up to only 8 h) of the catalysts. Infrared Spectroscopy. The infrared spectra of the gas oil and naphtha extracts are quite similar; thus an example set of extract I and extract I1 is presented in Figure 1. The very intense absorptions from 2960 to 2850 cm-’, due to aliphatic CH2 and CH3 stretching vibrations, and the corresponding weak absorptions at 3100-3000
1590 Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988
1x11 Phenolic
OH
F y r o l ~ cNH
\
4000
3500
3000
Wavenumber, cm-l Figure 2. Infrared spectra of gas oil catalyst, extract 11, in the 3700-3200-cm-' region.
4000
3500
3000
2500
2000
15W
1600
1400
1200
1000
Wavenumber, cm-'
Figure 1. Infrared spectra of catalyst extracts: (a) naphtha catalyst A, extract I; (b) gas oil catalyst A, extract I; (c) naphtha catalyst A, extract 11; (d) gas oil catalyst A, extract 11. 0
cm-', due to aromatic C-H stretchings, suggest a significant amount of saturatedlnaphthenic structures in both extracts. The absorbance ratio of the 1450-cm-' band (CH, asymmetric bending + CH2 scissoring) to the 1375-cm-' band (CH, symmetric bending) remains quite high, indicating long alkyl chains or naphthenic CH2 groups. Furthermore, the 1600-cm-' peak, ascribed to aromatic ring skeletal C==Cstretch, appears to be stronger in extract I1 than in extract I, suggesting an increased aromaticity. Other oustanding features of the spectra are the strong C=O absorptions in the 1800-1650-cm-' region and the intense bands at 1200-1100 cm-' in extract 11. The 1750-1700-cm-' absorptions have been ascribed to acidketone carbonyl, while the 1650-cm-' absorption peak has been assigned to amide (amide I band due to C = O stretch) (Bunger et al., 1979; McKay et al., 1975). This result is quite unexpected, since amide is usually not abundant among the nitrogenous bases (Poulson et al., 1971: Poulson, 1975). Consequently, the 3500-3300-cm-' region of N-H absorption was examined more closely. The 3480-cm-' absorption peak has been ascribed to a carbazole-pyrrole-indole type of N-H stretch (Pozelsky and Kukin, 1955), while the amide N-H band occurs at a slightly lower frequency (3460-3400 cm-'1. However, in the extracts where the 1650-cm-' absorptions are prominent (e.g., extract I1 of gas oil catalyst A and naphtha catalyst A), this region is totally obscured by hydrogen bonding. As a result, the above extracts were diluted with methylene chloride, dried over Na2S04and reconcentrated. The hydrogen bonding remained but the magnitude has decreased sufficiently for a shoulder at 2400 cm-l to be discernible (Figure 2). On the other hand, there is more doubt in the band assignment for the two strong absorptions at 1200 and lo00 cm-'. The fact that these absorptions are prominent in the extracts with high ash content suggests inorganic origins (McKay et al., 1975). The 1200-cm-' absorption can be partly ascribed to C-0-C stretching vibration, while the sulfoxide group is responsible for the 1030-cm-' peak (Bunger et al., 1979), although in some extracts it is par-
l
0
2 - 0 '
5-0002-
(mL)
(mL)
Figure 3. Titration curves of gas oil catalyst A, extract 11, with perchloric acid in acetonitrile (AN) and acetic anhydride (AA) before and after reduction with LAH. Table IV. Titration of Catalyst Extracts in Acetic Anhydride base concn, catalyst extract NP/HNP, mV mmol/a equiv % N naphtha I 7501670 0.035 0.05 cat. A I1 7051570 2.186 3.06 0.024 naphtha I 7601660 0.03 I1 6901594 2.344 cat. B 3.28 gas oil I 7451650 0.116 0.16 cat. A 11 7301595 1.871 2.62 gas oil I 7101620 0.081 0.11 cat. B I1 7251595 1.561 2.18
t i d y masked by a sharp peak at a slightly lower frequency. Nitrogen Titrations. Titration of nitrogenous bases with perchloric acid in acetonitrile and acetic anhydride solvent remains an effective way of characterizing the nitrogen compounds according to basicity, since this can be performed on the whole oil without tedious isolation steps using column chromatography. According to Buell (1967),four classes of nitrogen can be differentiated on the basis of the half-neutralization potential (HNP) and titratability in the two solvents. The results from the naphtha and gas oil catalyst extracts are quite similar (Table IV) in that no discernible inflexion point could be obtained with all the titrations in acetonitrile; however, a comparison with the blank titration clearly indicates some bases which are too weak to
Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988 1591 be titratable in acetonitrile. An example set of titration curves is given in Figure 3. Titrations in acetic anhydride produced only one end point in all cases, at a very high neutralization potential, indicating the presence of very weak bases (vwb) in the extracts. Previous researchers have concluded that nitrogen compounds with these characteristics are mainly amides (Buell, 1967; Wimer, 1958). Sulfoxides are likely present since they also titrate as vwb (Buell, 1967; Okuno et al., 1965; Wimer, 1958) and their absorptions at 1030 cm-' have been observed in the infrared spectra. Furthermore, pyrroles, indoles, and tetrahydrocarbazoles may also titrate as this class but only semiquantitatively due to their instability in acid media (Okuno et al., 1965). In such cases, the different compositions of this group could reasonably account for the slight variation in the neutralization potential of these extracts. LAH Reduction of Extracts. The extracts were reduced with LAH and titrated again in the two solvents with perchloric acid to obtain additional insight into the nature of the nitrogen species. The amides (vwb) would be reduced to the corresponding amines which, being stronger bases, could be readily titrated in acetonitrile where no discernible neutralization point was detected before. Also, the titration in acetic anhydride could produce either one or two end points, depending on the extent of reduction. Since the nitrogen compounds in the extracts appeared to be of similar type, a set of extracts (I and 11) from a naphtha catalyst (naphtha catalyst A) and a set of extracts from a gas oil catalyst (gas oil catalyst A) were chosen for a representative study. Figure 3 shows that the titration of the original and reduced extracts is markedly different. After reduction, the starting potential was much lower, and a very distinct neutralization was observed in acetonitrile where none existed before. The titration in acetic anhydride also started at a lower potential and gave a second inflection point, in addition to the original. These results demonstrate unambiguously the presence of a stronger base in the extracts from both naphtha and gas oil catalysts after reduction. The amides (lactams, imides) (Gaylord, 1956) are the only possible nitrogen compounds that behave in this manner. The titration-reduction study, together with the observation of the relatively strong absorption peak at 1650 cm-' (amide I carbonyl band) and the much weaker absorption at 3400 cm-' (N-H stretch), strongly supports the presence of amide as a major constituent of the extracted nitrogen bases. Also, the 90 N of vwb obtained from titration correlates well with the 1650-cm-' band intensity and the total N content of the sample (from elemental analysis). After 2 h of reduction, the 1650-cm-' band intensity decreased, as did the vwb concentration (from 0.10% to 0.07% N per gram of extract), while the stronger base (0.03% N) appeared. After 48 h, the absorption intensity and the VWB concentration decreased further (to 0.06 90), while the stronger base concentration increased to 0.04% N. THF was used as a solvent for the more polar extract 11, and reduction was stopped after 8 h (bp of THF, 64 OC; diethyl ether, 46 "C). As in extract I, some amides (1650-cm-' absorption peak) remained in the reduced extract. This group of amides could be difficult to reduce due to N substitutions. The amides observed in this study would either result from oxidation of organic nitrogen compounds due to exposure to air or from accumulation of amides in the feed to the reactors. Similarly, the ketones observed by IR would result from oxidation of hydrocarbons or from the
l
I
1400
l
l
1200
I
1
1000
1
1
800
I
l
600
Wavenumber, cm-l Figure 4. Infrared spectra of gas oil catalyst A, extract 11, before and after blank reduction.
feed oil. The extracts clearly show that high oxygen content goes along with high nitrogen content. Previous studies of catalyst extracts (Furimsky, 1978; Yoshimura et al., 1987) also observed elevated oxygen contents, relative to the feed oil. Neither study, however, indicated any special handling of the samples to exclude air. 2Quinolones have been identified in heavy fractions of petroleum and in asphalts (Bezinger et al., 1962; Copelin, 1964; Petersen et al., 1971; Petersen, 1975). The catalysts in this study were exposed to coker distillates, hence coking could cause migration of compounds such as quinolones into the distillate fractions. Amides such as 2-quinolones are very stable under catalytic hydrogenation conditions (Galinovsky and Stern, 1944; Gaylord, 1956) and hence could be retained on the surface of the catalyst. Direct formation of quinolone from quinoline requires fusion with KOH (Jones, 1977). The naturally occurring quinolones in petroleum are not produced by oxidation (Petersen, 1975). The observed amides may be derived from the feed oil, but further studies are required to confirm this conclusion. Furimsky (1982) did not observe carbonyl-ketone signals in IR spectra from Co/Mo catalyst extracts, even though no special handling of the catalyst was reported. Hence, the ketone material observed in this study is more likely a result of feed composition and long time on stream than oxidation of hydrocarbons. Of particular interest was the very low yield of the reduced extract I1 (naphtha catalyst A, 25%; gas oil catalyst A, 40%) which cannot be accounted for entirely by handling loss. Apparently some of the polar reduction products (e.g., RCHPOHfrom reduction of carboxylic acid, acid anhydride, ester, etc.) could be lost to the aqueous layer in the extraction step. However, the intense 1200-1000cm-' absorption bands, observed in extract I1 before reduction, almost completely disappeared. This was accompanied by a decrease of about 50% in the ash extract I1 (all steps repeated without LAH). Infrared spectra of the original and the blank-reduced extract were identical in every respect (Figure 4) except in the 1200-1000-~m-~ region, where the strong absorption bands have disappeared. Thus, the removal of these bands is due to the aqueous extraction step and not the reduction. These ash-containing compounds were extracted in methanol, reextracted in methylene chloride, and very soluble in water. Such behavior defies distinct classification and suggests some metal-inorganic-coordination compounds.
1592 Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988 Table V. Nitrogen-Type Content from Elemental Analyses and Titration catalyst extract naphtha gas oil cat. A cat. A I I1 I I1 0.0 3.74 0.32 3.06 % N in orig. extract ( N J 0.04 3.03 0.18 2.20 titration of orig. extract ( N , ) titration of reduced extract (N3) 0.04 1.21 0.10 1.60 0.02 0.56 0.06 0.81 vwb in acetic anhydride (N3J wb/sb in acetic anhydride (N3b) 0.02 0.65 0.04 0.79 0.02 0.83 0.04 1.07 wb/sb in acetonitrile (N3J Chart I. Classification of Nitrogen-Containing Compounds from Extraction of Spent Catalysts nitrogen compounds
class 1 nontitratable. nonbasic
titratable as vwb
-7 class 2
reducible
non red u ci b Ie
I
1
class 3 nontit rata ble
t i tra table
r - 5 class 4
class 5
nonacetylable acetylable
The greenish blue color of the aqueous phase, obtained from the extraction of extract I1 with NaC1-saturated solution, gradually turned yellow on standing, suggesting some ionic-exchange reaction. This solution also produced a rose-red color upon addition of 6 M NH3 and dimethylglyoxime solution, confirming the presence of nickel. The appearance of strong bases after reduction could possibly be attributed to higher concentration after removal of the metal complexes. A small quantity of material would be more likely to give a detectable inflection point when concentrated. The presence of strong bases before reduction could not account for the magnitude of the changes observed. The total base concentration (mmol/g of reduced extract) would exceed the total amount in the original material, contrary to observation (Table V). Also, the starting potential would be lower in the titration of the reduced extract with lower yield, which was not the case. Nevertheless, the presence of stronger bases in the catalyst extracts cannot be excluded. The concentration must, however, be too low to be detectable by titration analysis. Some threshold quantity would be required to give a recognizable inflection point. Classification of Nitrogen Compounds. The nitrogen contents obtained from the titration-reduction experiments can be used to differentiate the very weak bases into five classes of nitrogen-containing compounds: (1)nontitratables; (2) titratables which can be subdivided into (a) nonreducibles and (b) reducible to nontitratables and those titratables that acetylate in acetic anhydride. A classification scheme is presented in Chart I. The %N in each category can be obtained as follows: N 1 = %N in original extract (before reduction), from elemental analysis; N 2 = %N titratable in original extract, from titration in acetic anhydrides; N3 = %N titratable in reduced extract, from sum of all titratable N in acetic anhydrides = N3a+ N3b where N3a= %N as very weak base, from second end point in titration curve; N 3 b = %N
Table VI. Nitrogen Class Distribution
nitrogen type nontitratable (class 1) titratable base A. reducible (a) to nontitratables (class 3) (b) to titratables (i) as sb-wb (class 4) (ii) acetylables (class 5 ) B. nonreducible (class 2, titrate as vwb)
catalyst extract naphtha gas oil cat. A cat. A I I1 I I1 0 0.71 0.14 0.86 0
1.82 0.08 0.60
0.02 0.65 0.04 0.79 0 0.18 0 0.28 0.02 0.38 0.06 0.53
as strong base, from first end point in titration curve; and N3c= %N as strong base, from titration in acetonitrile. Class 1 is nontitratable = N 1 - N,. This class includes such nonbasic nitrogen compounds as carbazoles,N-phenylindoles, and nitriles. Also included here are compounds which are not completely titrated, such as those with two titratable nitrogens of similar basicity. Class 2 is titratable as very weak base (vwb), but nonreducible = N3a- (N3c- N 3 b ) . Compounds such as pyrroles, indoles, and tetrahydrocarbazoles are not reduced by LAH but were found to titrate in acetic anhydride, although only semiquantitatively due to their instability in acid media (Okuno et al., 1965). Some substituted pyrroles and porphyrins have been reported to titrate as vwb as well (Richter et al., 1952; Neuberger and Scott, 1952). N-Substituted amides could also belong to this class. Class 3 is titratable as vwb and reduced to nontitratable = N2 - N3. Sulfoxides appear to account for this group. Although not nitrogen compounds, they titrate quantitatively as vwb in acetic anhydride (Buell, 1967; Okuno et al., 1965; Wimer, 1958) and are reduced by LAH to the corresponding nonbasic sulfides. Their presence is supported by the corresponding detection of the 1030-cm-l infrared absorption peak. Class 4 is titratable as vwb and reduced by LAH to titratable as stronger bases = N3b. Amides and lactams (cyclic amides) appear to be the only vwb in the extract that are reduced by LAH to stronger bases (Gaylord, 1956). For example, lactams such as 2-pyrones and 2-quinolones could be reduced to 2pyridines and 2-quinolines, respectively, and titrate accordingly in acetonitrile as well as acetic anhydride (Poulson et al., 1971). Imides and carbamates behave likewise, but their presence in petroleum has not been reported and therefore they are unlikely candidates. Class 5 is titratable as vwb, reducible, but acetylable = N3c
- N3b.
Anilides represent a class of compound in the unreduced extract which titrate as vwb in acetic anhydride. They are reduced by LAH to the corresponding aniline. These bases contain an active hydrogen, making them easily acetylable in acetic anhydride solvent and therefore titrate as vwb in acetic anhydride titration. In acetonitrile titration, they remained as weak base (wb). Therefore, their quantity can be obtained from the differenence in the wb values in titration in the two solvents. Also included in this class are the primary and secondary amides which are reduced to the corresponding acetylable amines. The class distributions in % N, of the catalyst extracts are given in Tables V and VI. Amides, as class 4 above, account for 20% (naphtha catalyst A, %N of class 4 = 0.65%, N , = 3.03%) to 30% (gas oil catalyst A, %N of
Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988 1593 Table VII. S t r u c t u r a l Profiles of Feedstock Oils and Catalyst Extracts naphtha cat. A gas oil cat. A feed extract I feed extract I % aromatic C 37.1 14.9 31.0 20.6 70 naphthenic C 45.5 61.9 58.5 61.2 % paraffinic C 17.0 24.3 8.5 17.3 % olefinic C 5.2 0 av ring no. 2.1 1.5 1.2 1.1 av chain length 8.4 7.9 5.8 7.8 0.3 0.3 0.4 0.4 degree of substitution
class 4 = 0.79%,N2 = 2.20%) of the very weak base (vwb), N2, determined in the titration of the unreduced extract. This does not include any primary or secondary amides, which are reduced into the acetylable amines and constitute part of class 5. As mentioned before, stronger bases were not detectable in this titration experiment, probably due to the small quantity. However, their presence has been suggested in some preliminary GC-MS results of the base-enriched fractions (vide infra). Structural Analysis of Gas Oil Catalyst Extract. Structural group analysis was performed on extracts I, and the results are compared with a syncrude coker gas oil (SCGO) and a naphtha fraction (Table VII), with the understanding that the extract would contain a mixture of residual feedstock and processed products that coated the catalyst pellets, and also some polar adsorbed materials. The observed decrease in percent aromatic carbon and increase in naphthenic carbon indicated some degree of hydrogenation, in agreement with the infrared analysis showing a large amount of aliphatic (paraffinic and naphthenic) CH2 and CH3 groups. Some cracking is also evident in the gas oil extract, from the shortening in the average alkyl chain length, and a decrease in the average number of rings per molecule, probably due to the more severe operating conditions. In general, the degree of substitution remains quite constant in comparing the extracts to the feedstocks. The gas oil catalyst A extract resembles the feedstock more because the catalyst was more saturated with oil than gas oil catalyst B before extraction. Structural analysis was not performed on extract I1 due to insufficient samples (for 13CNMR). However, analysis such as infrared and nitrogen titration, as presented earlier, together with simulated distillation, UV, high-field 'H NMR, and gas chromatography, gave an overall picture of the characteristics of the adsorbed compounds. Simulated distillation analysis (SDA, Figure 5) of extract I1 of naphtha catalyst A and gas oil catalyst A indicated a high proportion of heavier fractions. Extract I1 of the naphtha catalyst contained only 10% naphtha but 40% atmospheric residue. This result provides clear evidence for an increase in molecular weight on the surface of the naphtha catalyst, because the naphtha feed to the reactor contained no atmospheric residue and -60% naphtha. Low boiling components of the naphtha would be lost when the extracting solvent was evaporated, so that the fraction of higher boiling material could be overstated. Extract I1 of the gas oil catalyst contained about 50% atmospheric residue, as compared to 65-7570 in the feed gas oil. Apparently the more severe processing conditions used for gas oils suppressed any polymerization reactions, giving an adsorbed material of lower molecular weight than the feed oil on average. Earlier results with the infrared spectra (Figure 1)displayed a large majority of saturated (paraffinic and naphthenic) structures and a small amount of aromatics. The detection of these high boiling, high
A) Naphtha catalyst A
loo
M W
1
t
6 4
2
0 Na htha feed
mS C a t A Extract II
n
3
P
"
Naphtha
Distillate
Atmos. Resid
B) Gas oil catalyst A
80 loo 8 w I
3 0 >
I
I Gas ail feed
Ud Cat. A Extract II
60
40 20 n "
Naphtha
Distillate
Atmos. Resid
Figure 5. Simulated distillation of feedstocks and catalyst extracts (A) naphtha catalyst A feed composition and extract 11; (B) gas oil catalyst A feed composition and extract 11.
molecular weight compounds with low aromaticity suggests the existence of polymers. The high-field 'H NMR result is consistent with the above observations, in that the extracts contained less aromatic but more naphthenic (especially cyclic naphthenic) structures than the feeds. The spectra of all the extracts resemble that of the gas oil rather than naphtha, with undistinct general features indicating the presence of a large amount of higher molecular weight compounds. Due to the high metal/ash content rendering the samples paramagnetic, extracts I1 were aqua-extracted for the NMR analysis. Compared to extract I, extract I1 revealed more signals at 2-4 ppm, due to methyl and methylene hydrogens a to the aromatic ring and polar functional groups, and at 7-9 ppm, due to hydrogen on the heteroatoms, indicating the presence of a high concentration of heteroatomic functional groups. Base Enrichment of Extract 11. A preliminary study was carried out to enrich the nitrogenous base by hydrochloric acid modified silica column chromatography, for the purpose of identification of individual compounds by GC-MS. Gas chromatograms of the acid and base fractions, separated on a DB-1 capillary column, revealed compounds to up to C30,with a majority of compounds in the Cl2-ClSregion. The MS result also indicated that some of the minor peaks may be due to stronger bases such as quinoline. However, no further product could be recovered from the hydrochloric acid extraction of the methylene chloride-methanol extracted catalysts. Further investigation is currently under way.
Conclusions 1. This study indicates that the hydrocarbon portion of the adsorbed molecules consists mainly of saturated paraffinic, naphthenic, and alkyl aromatic structures. About half of these have boiling points >343 "C.
1594 Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988 2. Gad chromatography revealed compounds of up to Cs0,with the maximum occurring at CI2-Cls. 3. The extracted nitrogen compounds comprise both nonbasic and very weak bases (vwb). According to their behavior in LAH reduction and titration in acetic anhydride, five classes of nitrogen could be obtained. 4. This work also confirms the presence of amides/ lactams, which constitute at least 20% (naphtha catalyst A) to 30% (gas oil catalyst A) of the very weak bases. 5. Infrared analysis reveals strong acid-ketone absorptions, suggesting that oxygen compounds may play a role in catalyst deactivation. 6. Preliminary study with GC-MS detected some stronger bases, e.g., quinolines. Apparently their concentrations are too low to be detected in the titrations. Nevertheless, the reduction-titration method offers an effective way of differentiating nitrogen compounds, avoiding cumbersome isolation procedures.
Acknowledgment The authors are grateful to the Alberta Oil Sands Technology and Research Authority for financial support under Agreement 521 and to Dr. Emerson Sanford of Syncrude Ltd. for providing catalyst samples and metals analysis. Registry No. C, 7440-44-0; H,,1333-74-0; N2,7727-37-9; S, 7704-34-9; 02, 7782-44-7; Ni, 7440-02-0; Mo, 7439-98-7.
Literature Cited Albert, D. K. ”Determination of Nitrogen Compound Types and Distribution in Petroleum by Gas Chromatography with a Coulometric Detector”. Anal. Chem. 1967,39, 1113-1117. Allen, D. T.; Grandy, D. W.; Jeong, K. M.; Petrakis, L. “Heavier Fractions of Shale Oils, Heavy Crudes, Tar Sands, and Coal Liquids: Comparison of Structural Profiles”. Ind. Eng. Chem. Process Des. Deu. 1985,24,737-742. Bezinger, N. N.; Abdurakhmanov, M. A.; Gal’pern, G. D. “The Nitrogen Compounds of Petroleum-I. The Nature of Neutral Nitrogen Compounds in Petroleum“. Petrol. Chem. USSR 1962,l , 13-19. Buell, B. E. “Nonaqueous, Differential Titration Applied to a Classification of Basic and Very Weak Basic Nitrogen Compounds in Petroleum“. Anal. Chem. 1967,39,756-761. Bunger, J. W.; Thomas, K. P.; Dorrence, S. M. “Compound Types and Properties of Utah and Athabasca Tar Sand Bitumens“. Fuel 1979,58,183-195. Burchill, P.; Herod, A. A.; Pritchard, E. ”Estimation of Basic Nitrogen Compounds in Some Coal Liquefactions Products”. J . Chromatogr. 1982,246,271-295. Copelin, E. C. “Identification of 2-Quinolones in California Crude Oil”. Anal. Chem. 1964,36,2274-2277. Darlage, L. J.; Finkbone, H. N.; King, S. J.; Ghosal, J.; Bailey, M. E. “Nonaqueous Potentiometry of Coal-Derived Asphaltenes and Model Nitrogen-Containing Compounds in Acetophenone and Nitrobenzene”. Fuel 1978,57,479-484. Deal, V. Z.; Weiss, F. T.; White, T. T. “Determination of Basic Nitrogen in Oils”. Anal. Chem. 1953,25,426-432. Dorbon, M.; Ignatiadis I.; Schmitter, J. M.; Arpino, P.; Guichon, G.; Toulhoat, H.; Huc, A. “Identification of Carbazoles and Benzocarbazoles in a Coker Gas Oil and Influence of Catalytic Hydrotreatment on Their Distribution”. Fuel, 1984,63,565-570. Ford, C. D.; Holmes, S. A.; Thompson, L. F.; Latham, D. F. “Separation of Nitrogen Compound Types from Hydrotreated Shale Oil Products by Adsorption Chromatography on Basic and Neutral Alumina”. Anal. Chem. 1981,53,831-836. Fritz, J. S. “Differential Titration of Amines”. Anal. Chem. 1953, 25, 407-411. Fritz, J. S. Acid-Base Titrations in Nonaqueous Solvents; Allyn and Bacon: Boston, 1973; p 75. Furimsky, E. “Chemical Origin of Coke Deposited on Catalyst Surface“. Ind. Eng. Chem. Prod. Des. Deu. 1978,17, 329-331. Furimsky, E.“Deactivation and Regeneration of Refinery Catalysts”. Erdol Kohle 1979,32,383-390.
Furimsky, E. “Characterization of Deposits Formed on Catalyst Surfaces During Hydrotreatment of Coal-Derived Liquids“. Fuel Proc. Technol. 1982,6,1-8. Galinovsky, F.; Stern, E. “Catalytic Reduction of Several Alkaloids of the Spartein Group Which Contain a Lactam or an a-Pyridone Ring”. Ber. 1944,77B,132-138. Gaylord, N. G. Reduction with Complex Metal Hydrides; Interscience: New York, 1956. Johnson, B. G.; Massoth, F. E.; Bartholdy, J. “Diffusion and Catalytic Activity Studies on Resid-Deactivated HDS Catalysts”. AIChE J . 1986,32, 1980-1987. Jones, G. Heterocyclic Compounds (Quinolines);Wiley: New York, 1977; Vol. 32, p 40. Khorasheh, F.; Gray, M. R.; Dalla Lana, I. G. “Structural Analysis of Alberta Heavy Gas Oils”. Fuel 1987,66,505-512. Mills, G. A.; Boedeker, E. A.; Oblad, A. G. “Chemical Characterization of Catalysts. 1. Poisoning of Cracking Catalysts by Nitrogen 1950, 72, Compounds and Potassium Ion”. J . Am. Chem. SOC. 1554-1560. McKay, J. F.; Cogswell, T. E.; Weber, J. H.; Latham, J. R. “Analysis of Acids in High-Boiling Petroleum Distillates”. Fuel 1975,54, 50-61. McKay, J. F.; Weber, J. M.; Latham, D. R. ’Characterization of Nitrogen Bases in High-Boiling Petroleum Distillates”. Anal. Chem. 1976,48,891-898. Mojelsky, T. W.; Montgomery, D. S.; Strausz, 0. P. “The Basic Nitrogen Compounds in Athabasca Bitumen”. AOSTRA J. Res. 1986,3,25-33. Neuberger, F. R. S.; Scott, J. J. “The Basicities of the Nitrogen Atoms in the Porphyrin Nucleus; Their Dependence on Some Substituents of the Tetrapyrrolic Ring”. Proc. R. SOC.London, Ser. A 1952,A213,307-326. Novotny, M.; Kump, R.; Merli, F.; Todd, L. J. “Capillary Gas Chromatography/ Mass Spectrometric Determination of Nitrogen Aromatic Compounds in Complex Mixtures”. Anal. Chem. 1980, 52,401-406. Okuno, I.; Latham, D. R.; Haines, W. E. “Type Analysis of Nitrogen in Petroleum using Nonaqueous Potentiometric Titration and Lithium Aluminum Hydride Reduction”. Anal. Chem. 1965,37, 54-57. Petersen, J. C. “Quantitative Meth6d Using Differential Infrared Spectrometry for the Determination of Compound Types Absorbing in the Carbonyl Region of Asphalts”. Anal. Chem. 1975, 47, 112-117. Petersen, J. C.; Barbour, R. V.; Dorrence, F. A.; Barbour, F. A.; Helm, R. V. “Tentative Identification of 2-Quinolones in Asphalt and Their Interaction with Carboxylic Acids Present”. Anal. Chem. 1971,43,1491-1496. Poulson, R. E. “Nitrogen and Sulfur in Raw and Refined Shale Oils”. Am. Chem. SOC. Diu. Petrol. Chem. Prepr. 1975,20, 183-197. Poulson, R. E.; Jensen, H. B.; Cook, G. L. “Nitrogen Bases in a Shale-Oil Light Distillate”. Am. Chem. SOC.Diu. Petrol. Chem. Prepr. 1971,16,A49-A55. Pozelsky, A.; Kukin, I. “Group-Type Nitrogen-Hydrogen Analysis of Pyrrole-Indole-Carbazole Type Compounds”. Anal. Chem. 1955, 27, 1466-1467. Richter, F. D.; Ceasar, P. D.; Meisel, S. L.; Offenhauer, R. D. “Distribution of Nitrogen in Petroleum According to Basicity”. Ind. Eng. Chem. 1952,44,2601-2605. Schmitter, J. M.; Vajta, Z.; Arpino, P. J. “Investigation of Nitrogen Bases from Petroleum”. Phys. Chem. Earth 1980, 12, 67-76. Simoneit, B. R.; Schnoes, H. K.; Hang, P.; Burlingame, A. L. “High Resolution Mass Spectrometry of Nitrogenous Compounds of the Green River Formation of Oil Shale”. Chem. Geol. 1971, 7, 123-141. Synder, L. R.; Buell, B. E. “Characterization and Routine Determination of Non-Basic Nitrogen Types in Cracked Gas Oils by Linear Elution Chromatography”. Anal. Chem. 1964,36,767-773. Synder, L. R.; Buell, B. E. “Characterization and Routine Determination of Certain Non-Basic Nitrogen Types in High-Boiling Petroleum Distillates by Means of Linear Elution Adsorption Chromatography”. Anal. Chim. Acta 1965,33,285-302. Stern, E. W. “Reaction Networks in Catalytic Hydrodenitrogenation”. J . Catal. 1979,57,390-396. Uden, P. C.; Carpenter, A. P.; Hackett, H. M.; Henderson, D. E.; Siggia, S. “Qualitative Analysis of Shale Oil Acids and Bases by Porous Layer Open Tubular Gas Chromatography and Interfaced Vapor Phase Infrared Spectrometry”. Anal. Chem. 1979, 51, 38-43.
I n d . Eng. Chem. Res. 1988,27, 1595-1599 Wimer, D. C. “Potentiometric Determination of Amides in Acetic Anhydride”. Anal. Chem. 1958,30, 77-80. Yoshimura, Y.; Hayamizu, K.; Sato, T.; Shimada, H.; Nishijima, A. “The Effect of Toluene-Insoluble Fraction of Coal on Catalytic Activities of Ni-Mo-y-A1203Catalyst in the Hydrotreating of Coal
1595
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Received for review October 19, 1987 Revised manuscript received April 1, 1988 Accepted April 15, 1988
Nickel/Vanadium Interactions on Cracking Catalyst David F. Tatterson and Rodney L. Mieville* Amoco Oil Company, Amoco Research Center, P.O. Box 400, Naperuille, Illinois 60566
Major economic incentives exist for processing resid containing high levels of nickel and vanadium in catalytic crackers. The amount of resid which can be fed to current units is limited by the cracking catalyst’s ability to rapidly deactivate the deposited metals and thus prevent excessive coke and gas formation. Development of more metals-tolerant cracking catalyst would be aided by knowledge of the behavior of nickel and vanadium on the surface of cracking catalyst. Toward this goal, we have investigated the behavior of these metals on a commercially available cracking catalyst. It has been found that nickel can occupy several types of sites on the cracking catalyst surface. Different metal-impregnation compounds and techniques can influence which sites are occupied. Some nickel sites were found to be more active for coke and gas production than others. Vanadium was found to interact with nickel in a manner which inhibits the deactivation behavior of nickel. This result indicates that metals-resistant cracking catalyst must be evaluated in the presence of both nickel and vanadium. In recent years the addition of resid to catalytic cracking feedstocks has increased the level of contaminate metals on cracking catalyst. The metals of primary concern are nickel, vanadium, and, to a lesser extent, iron. A t near atmospheric conditions, these metals when deposited on the Catalyst catalyze dehydrogenation reactions during the cracking process to increase gas and coke yields at the expense of gasoline and other more valuable products. Once deposited on the cracking catalyst, the metals deactivate and lose this dehydrogenation activity. The effects of these metals have been recognized for some time (Connor et al., 1957; Crane et al., 1961). Numerous strategies to deal with the deleterious effects of nickel and vanadium have been developed. These include the addition of nickel passivation agents, hydrotreating to remove metals from the resid FCC feed, and development of metals-resistant catalysts. The extent to which these various strategies have been successful varies with the individual refiner and his operating philosophy and goals. In this paper we report some of our initial experiments aimed at developing a better understanding of the behavior of nickel and vanadium on cracking catalyst. Specific areas we have investigated include the effect of impregnation technique on nickel behavior, possible nickel-vanadium interactions, and the effect of calcination and steaming in these areas. As a reference for this study, we have used the behavior of nickel and vanadium deposited on a catalyst during the cracking of resids. The experimental techniques used to evaluate these areas include Amoco’s microcracking activity test, X-ray diffraction, BET surface analysis, temperature-programmed reduction, and a N20 decomposition rate test.
Experimental Section Catalyst Supports. A commercial equilibriumcracking catalyst from Amoco’s FCU system was used as the base for most experiments; the properties of this catalyst are listed in Table I. The catalyst contains 3800 ppm of iron
* Author to whom
correspondence should be addressed.
Table I. Equilibrium Cracking Catalyst Analysis Catalyst Description cracking activity, % conversn of std feedstock coke yield, w t % feed surface area, m2/g pore volume, cm3/g
73 4.85 75 0.26
Metals Analysis Ni, wppm V, wppm Fe, “Pm alumina content, wt % sieve type
185 135 3800 43.3 RE-Y
Cumulative Pore Volume, cm3/g pore radius, A 550 270 190 115 67.5 42.5 32.5 22.5 median pore radius (based on vol)
cm3/g 0.013 0.062 0.096 0.143 0.188 0.216 0.233 0.253 132
deposited during commercial operation. The source of this iron is rust particles picked up by the gas oil during storage and transport. As such, this iron is not highly dispersed and is inactive for catalyzing dehydrogenation and cokeforming reactions. A large quantity of this catalyst was contaminated with natural metals during the cracking of various atmospheric and vacuum resids in an Amoco catalytic cracking pilot plant. The catalyst, when removed from the unit, contained 3600 wppm of nickel, 6600 wppm of vanadium, and 4500 wppm of iron (wppm is weight parts per million). This catalyst is designated 378 in the following discussion. It was chosen as a standard for the behavior of natural metals on cracking catalyst because it was the only catalyst available with a relatively high concentration of naturally deposited metals. In the discussion that follows, the additional 700 wppm of iron which was added to the catalyst is ignored for its effect on coke formation. Iron is known to be much less active for dehydrogenation on cracking
0S88-5885/88/2621-~595$01.50/0 0 1988 American Chemical Society
