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Inhibition and Deactivation of Hydrodenitrogenation (HDN) Catalysts by Narrow-Boiling Fractions of Athabasca Coker Gas Oil Will Kanda,† Iva Siu,† John Adjaye,‡ Alan E. Nelson,† and Murray R. Gray*,† University of Alberta, Department of Chemical and Materials Engineering, Edmonton, Alberta, Canada T6G 2G6, and Syncrude Canada, Ltd., Edmonton Research Centre, Edmonton, Alberta, Canada T6N 1H4 Received September 24, 2003. Revised Manuscript Received December 3, 2003
The hydrodenitrogenation (HDN) of quinoline in the presence of narrow-boiling fractions of Athabasca bitumen coker gas oil was studied over a commercial NiMo/γ-Al2O3 hydrotreatment catalyst. The study was conducted to determine whether trends in HDN activity with increasing boiling point were the result of the increased molecular weight of the Athabasca coker gas oil (i.e., changes in hydrocarbon structure) or due to the nitrogen species contained in the feedstocks. In each boiling-point range, the components in the gas oils demonstrated, to a varying degree, both reversible inhibition and deactivation of catalyst activity. The low-boiling gas oil fraction (bp. 343-393 °C) was more inhibitory and deactivated the catalyst to a greater degree than intermediate- (bp. 433-483 °C) or high-boiling (bp. 524 °C+) fractions for the HDN of quinoline. Nitrogen speciation analysis suggested that alkyl-carbazoles and tetrahydrobenzocarbazoles were the primary species responsible for the higher inhibition and deactivation observed in the lightest fraction. In addition, the HDN activity of the narrow-boiling fractions varied with hydrogen partial pressure and sulfur concentration, although these effects were independent of molecular weight. This study suggests that, although Athabasca coker gas oils have higher concentrations of polyaromatics, compared to conventional distillates, non-nitrogen-containing species are insignificant in inhibiting catalyst activity, in comparison to the organonitrogen compounds. Consequently, the resistance of the Athabasca coker gas oils to HDN can be attributed to the organonitrogen compoundssparticularly, alkyl-carbazoles and tetrahydrobenzocarbazolessrather than the aromaticity of the gas oils.
1. Introduction The expanding utilization of heavy oils and bitumens as refinery feedstocks has led to an increased worldwide interest in the characterization of the properties of highsulfur-content and high-nitrogen-content distillates and the resultant effects on hydroprocessing kinetics.1 In this regard, considerable research efforts have been directed toward studying the reaction kinetics of the whole feedstocks from various sources. However, whole oils with similar physical properties can exhibit unique kinetic behavior, because of differences in chemical structures and heteroatom functionality.2 With a wide distribution of chemical and physical properties, the reactivities of components in such mixtures will also vary over a wide range. As a result, it becomes important to examine the physical properties and reaction kinetics as a function of molecular weight and chemical class. By fractionating the whole feedstocks into narrowboiling fractions, the effect of molecular weight on the * Author to whom correspondence should be addressed. E-mail:
[email protected]. † University of Alberta. ‡ Syncrude Canada, Ltd., Edmonton Research Centre. (1) Gray, M. R. Upgrading Petroleum Residues and Heavy Oils; Marcel Dekker: New York, 1994. (2) Trytten, L. C.; Gray, M. R.; Sanford, E. C. Ind. Eng. Chem. Res. 1990, 29, 725-730.
variation in the chemical and kinetic properties can be carefully studied. Further fractionation by chemical type, using column chromatography, allows identification of the refractory compounds. Distillate feedstocks that have been derived from heavy oils and bitumens differ from conventional refinery feedstocks, in that they contain high concentrations of organic nitrogen and are more aromatic in nature.1 These properties, as well as the prior thermal processing by coking or hydroconversion, make these fractions more difficult to process than conventional feeds, thereby increasing the demands on existing hydrotreatment catalysts. The higher concentrations of nitrogen and polynuclear aromatics are believed to result in catalyst inhibition and deactivation, which results in lower hydrotreatment conversions. Inhibition in this context is defined as a loss of activity because of reversible adsorption of some components of the feed. Numerous studies of hydrotreatment kinetics of distillate fractions have shown that the rates and extents of nitrogen compound removal are lower than those for sulfur compounds.3 For high-nitrogen distillates, such as bitumen-derived material, the removal of nitrogen can be more of a concern than the removal of sulfur. (3) For example, see: Kabe, T.; Ishihara, A.; Qian, W. Hydrodesulfurization and Hydrodenitrogenation; Wiley: New York, 1999.
10.1021/ef034063p CCC: $27.50 © 2004 American Chemical Society Published on Web 02/12/2004
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Research investigations that have used whole oils and model compounds have been reported for catalytic hydroprocessing reactions, including hydrogenation,4-6 hydrodesulfurization (HDS),6-8 hydrodenitrogenation (HDN),8-12 and hydrodeoxygenation (HDO).13 The inhibition of HDS by nitrogen-containing species is welldocumented;3 however, the inhibition of HDN by either high-molecular-weight nitrogen compounds or polynuclear aromatics has not been investigated. Studies by Hoog14 and Yitzhaki and Aharoni15 have considered HDS kinetics using narrow-boiling fractions. Their models suggest that the rate of HDS decreases as the boiling point increases. Although previous kinetic investigations have demonstrated that the HDN reactivity of gas oil fractions decreases exponentially as the boiling point (i.e., molecular weight) increases, the causes for this behavior are not clear.2 Quinoline is the most-studied model compound for HDN, and its reaction pathways and kinetics are wellknown. For example, Sundaram et al.16 proposed a detailed model for the HDN of quinoline, using Langmuir-Hinshelwood rate expressions to estimate the reaction rate of quinoline to its various intermediates, and eventually to HDN, when NH3 is produced. The overall reaction rate (and rate of HDN) of quinoline was dependent on the reaction intermediates, such as 1,2,3,4tetrahydroquinoline, 5,6,7,8-tetrahydroquinoline, decahydroquinoline, and o-propylaniline. Sundaram et al.16 suggested that nitrogen compounds such as quinoline, aromatic compounds, and sulfur-containing compounds may compete for the same catalyst sites. However, when combinations of naphthalene and quinoline or dibenzothiophene and quinoline were reacted in a batch reactor, the HDN rate was virtually unchanged, but the hydrogenation rate of the aromatic compounds and the hydrogenolysis of the sulfur compounds were significantly inhibited. This result indicated that these compounds do compete for the same site during reaction; however, in this instance, the quinoline is preferentially adsorbed to the catalyst. This study suggests one additional benefit of using a defined probe compound to explore HDN activity. Analysis of the reacted products not only can give the disappearance of the parent compound, but also can indicate shifts in the selectivity for different pathways in the reaction network. Such shifts would signal preferential inhibition of different types of active sites on the catalyst surface.
Several additional studies have considered the effects of sulfur concentration in the reactor on the conversion of quinoline over hydrotreatment catalysts. Satterfield and co-workers10,11 and Gultekin et al.17 showed that the presence of H2S increases the reaction rate of quinoline. When sulfur-containing species were added to the reactor (i.e., CS2) to form H2S, the removal rate of quinoline increased significantly. Satterfield et al.18 reported that, during the HDN of pyridine, sulfurcontaining compounds increased the rate of HDN at temperatures of >325 °C but reduced the overall rate of HDN at temperatures of 524
S content (ppm)
N content (ppm)
40700 38600 24300 41300 13800 46100 38300
3900 2400 16300 4200 10400 6800 16200
C content (wt %)
H content (wt %)
85.4
10.7
85.1 79.9 85.2 79.3
10.5 8.8 9.3 8.7
Table 2. Coker Gas Oil Narrow Fraction Physical Properties asphaltenes (%, in pentane)
MCR (%)
1.55 0.10 0.20 12.67
1.98 0.07 1.18 19.12
feed Fraction 2 Fraction 4 Fraction 8
Fraction 2 Z
(-5)/(-19) (-7)/(-21) (-9)/(-23) (-11)/(-25) (-13)/(-27) (-15)/(-29) (-17)/(-31)
Fraction 4
total acid number
aromatic carbon content (%, from 13NMR)
2.1 2.5 1.9
38.12 34.25 35.89 43.05
0.003 0.80
Table 3. Percentage of Primary Compound Types in Fractions and Nitrogen Extracts numbersa
ext mat (% Res)
Fraction 8
whole
extract
whole
extract
whole
extract
10.7 9.2 9.0 14.8 14.6 26.1 15.6
10.8 11.6 13.5 20.0 21.4 13.3 9.4
13.6 27.1 16.1 10.3 9.5 11.3 12.1
15.4 15.1 14.3 13.0 13.9 13.8 14.5
14.5 13.2 13.2 14.5 15.8 14.5 14.5
14.4 14.3 13.2 13.9 14.8 14.8 14.6
a The Z numbers correspond to the following compounds: (-5), alkyl-pyridines; (-7), alkyl-naphthenopyridines; (-9), alkyl-indoles, alkyl-dinaphthenopyridines; (-11), alkyl-quinolines; (-13), alkyl-naphthenoquinolines; (-15), alkyl-carbazoles; (-17), alkylacridines; and (-17), tetrahydrobenzocarbazoles.
°C), a middle fraction (#4, bp. 433-483 °C), and a heavy fraction (#8, bp. 524 °C+). The fractions were characterized for elemental composition (Table 1), selected physical properties (Table 2), and primary nitrogen compounds (Table 3) prior to reaction. The nitrogen speciation analysis was performed using mass spectroscopy with N2O chemical ionization and direct injection electrospray ionization.22 Results of both mass spectrometry analyses are tabulated according to Z number and compound types in Table 3. The Z number is a measure of hydrogen unsaturation, based on the formula CnH2n+ZN, and facilitates the identification of alkyl-pyridines, alkyl-naphthenopyridines, alkyl-indoles, alkyl-dinaphthenopyridines, alkyl-quinolines, alkyl-naphthenoquinolines, alkyl-carbazoles, alkyl-acridines, and tetrahydrobenzocarbazoles. The nitrogen speciation analysis indicates that the lightest fraction (bp. 343-393 °C) is dominated by alkyl-carbazoles and tetrahydrobenzocarbazoles, the intermediate fraction (bp. 433-483 °C) is dominated by alkyl-naphthenopyridines, and the heaviest fraction (bp. 524 °C+) has an even distribution of nitrogen compound types. An additional series of gas oils was prepared by concentrating the nitrogenous species in the aforementioned fractions, using retention chromatography. The light fraction (Fraction 2) was separated using a 25-mm inside diameter (id) by 1.2m-long column with activated silica gel (200 g, 100-200 mesh, activated for 20 h at 175 °C), whereas the heavier fractions (Fractions 4 and 8) were separated with activated neutral alumina (200 g, 60-325 mesh, activated for 20 h at 275 °C). Previous work has shown this to be the best method for producing nitrogen concentrates from narrow-boiling fractions.23 Each sample (∼100-150 g) was diluted with 25-100 (22) Qian, K.; Rodgers, R. P.; Hendrickson, C. L.; Emmett, M. R.; Marshall, A. G. Energy Fuels 2001, 15, 492-498. (23) Nowlan, V., personal communication, Syncrude Canada, Ltd., Edmonton Research Centre, Edmonton, Alberta, Canada.
mL of pentane, depending on the initial viscosity, and loaded into the column. The nitrogen concentrate was eluted from the column with 1250 mL (silica gel) and 1500 mL (alumina) of methanol and subsequently characterized for elemental composition (see Table 1). The extracts were further characterized by mass spectroscopy with N2O chemical ionization and direct injection electrospray ionization (see Table 3). In the nitrogen concentrates, the lightest fraction (bp. 343-393 °C) is dominated by quinolines and naphthenoquinolines, with a carbon number in the range of 13-24. The intermediate fraction (bp. 433-483 °C) had an even distribution of nitrogen compound types and a carbon number in the range of 14-32. The heaviest fraction (bp. 524 °C+) also had an even distribution of nitrogen compound types with a carbon number in the range of 19-64. A clean feed, or carrier gas oil, was also used in this study, as a baseline reactant. The clean feed was a heavily hydrotreated gas oil blended with 1 wt % quinoline to give a corresponding total nitrogen concentration of 1080 ppm. This feed was used to assess the catalyst activity before and after reactions with narrow-boiling fractions to characterize catalyst inhibition and deactivation. The catalyst was a commercially available NiMo/γ-Al2O3 hydrotreatment tri-lobe catalyst, which was previously aged in a pilot plant at Syncrude Canada, Ltd., to eliminate the initial period of rapid deactivation that occurs with fresh catalysts. The commercial hydrotreatment catalyst was an extrudate of γ-alumina with 10-15 wt % molybdenum and 2-4 wt % nickel and a BET surface area of 150-250 m2/g. The catalyst was presulfided by loading the catalyst in a batch reactor with 140 µL of CS2 per gram catalyst (140 µL/g cat). The reactor was then pressurized with 900 kPa of H2 (at room temperature) and then placed in a sand bath at 350 °C for 2 h. After the reactor was removed from the sand bath, it was quenched in a water bath and then the product gas was purged. The reactor was then repressurized with H2 and then purged again, to reduce the concentration of H2S potentially in the reactor. The catalyst activity was further characterized in a series of hydrotreatment reactions to ensure experimental repeatability (not shown). Thus, any inhibition or deactivation observed during this study can be attributed to the feedstock and reaction conditions, and not the natural deactivation of the fresh catalyst. As a result, catalyst activity can be largely eliminated as an experimental variable in the HDN kinetic experiments. 2.2. Reaction Experiments. The HDN of quinoline was studied using microbatch reactors. This type of reactor was selected to allow the reaction of very small quantities of material, such as column chromatography fractions. The reactor setup consisted of 15-mL microbatch reactors constructed from stainless-steel tubing and Swagelok fittings. The reactor temperature was controlled and maintained by im-
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mersion in a fluidized sand bath for the duration of the experiment. The reactor was mounted in a vertical position and connected to an external agitator used to mix the reactor at a frequency of 1 Hz. The microbatch reactor has been previously used for hydroprocessing studies and has been described in detail elsewhere.24 The conversion of quinoline was studied under the following reaction conditions: temperature, 350 and 380 °C; total pressure, 8650 and 9000 kPa (at reactor temperature); total nitrogen concentration, 2000 and 3000 ppm; and reaction time, 20 min. The hydrogen partial pressure (PH2) was essentially equivalent to the initial reactor pressure at ambient temperature (4150 kPa). The catalyst:feed loading was constant at 1:25 on a mass basis, with 3.2 g of feed, 0.13 g of catalyst pellets, and 30 µL of CS2 to maintain the catalyst in the sulfide form. CS2 rapidly hydrogenates to produce H2S under reaction conditions.11 Quinoline was used as an internal standard, to determine the absolute catalyst activity using gas chromatography (GC) analysis. The individual microbatch reactions were repeated a minimum of three times to verify the repeatability of data and catalyst stability. The conversion of quinoline, which is defined as the percentage of the reactant quinoline converted to products, is the average for a given composition where statistical outliers (95% confidence) were excluded. The products included nitrogen-free compounds, as well as nitrogen-containing reaction intermediates. Because of analytical limitations in the quantitation of multiple products in the presence of gas oil mixtures, only the concentration of quinoline was measured by GC. Selectivity was studied by reacting DHQ, which is a known intermediate in quinoline hydrotreatment.20 Analysis. The analysis of the feed and product samples was performed with a Hewlett-Packard model 5890 gas chromatograph with an autosampler. The gas chromatograph had a cross-linked methyl silicone gum column with a 0.32 mm id, a length of ∼25 m, and a film thickness of 0.17 µm. The condensed-phase products were detected using a flame ionization detector that was operated at a temperature of 320 °C. The chromatograph also included a 0.32 mm id × 1 m guard column that contained nonpolar fused silica to sacrificially capture heavy component deposits and prevent shortening the active column. However, no column plugging issues arose during this study. Compounds were identified by comparing their respective retention times with the retention times of pure standards (quinoline, DHQ) previously analyzed with the chromatograph. Additional nitrogen concentration analysis was performed with an ANTEK model 9000 NS sulfur/nitrogen analyzer for the detection of chemically bound total nitrogen content. The detection of total nitrogen content allowed for the discrimination between the hydrogenation of nitrogen compounds and complete HDN.
3. Results and Discussion 3.1. Quinoline Conversion. Experiments were conducted mainly with intermediate-boiling material (Fraction 4, bp. 433-483 °C) and high-boiling material (Fraction 8, bp. 524 °C+), with some experiments with a low-boiling fraction (Fraction 2, bp. 343-393 °C). The reactor feed was blended to contain a total nitrogen concentration of ∼3000 ppm nitrogen, with 1080 ppm due to quinoline and 1900 ppm due to the nitrogen species in the different narrow-boiling fractions. The sequence of the feeds was selected to enable a comparison of the levels of inhibition between the different boiling-point fractions, compared to the clean feed. Reactions with the clean feed were also performed (24) Richardson, S., Ph.D. Thesis, University of Alberta, Canada, 1996.
Kanda et al.
Figure 1. Conversion of quinoline at 350 °C and 3000 ppm total nitrogen at 8650 kPa.
before and after the reactions with each fraction, to characterize any catalyst deactivation. Representative quinoline conversions at 350°C and 3000 ppm total nitrogen are shown in Figure 1. The histogram bars represent the average of each feed condition, and the error bars are the 95% confidence levels. The extent of reaction for clean-feed reactions decreased from 51.3% ( 4.8% to 34.9% ( 4.6% quinoline conversion when the Fraction 4 feed was added, and subsequently returned to 51.8% ( 5.7% after the Fraction 4 feed was removed and the clean feed was reanalyzed. This result suggests that, although Fraction 4 has an observable inhibitory effect on quinoline conversion, the inhibition is reversible and no permanent catalyst deactivation was incurred. When the Fraction 8 feed was added, the amount of quinoline conversion decreased to 23.3% ( 5.0%, which suggested more inhibition than that with Fraction 4 at 350 °C. Following the analysis, a clean feed was again reacted and a mean quinoline conversion of 39.1% ( 1.9% was observed. This result suggests Fraction 8 caused slight deactivation, i.e., irreversible inhibition of catalyst activity. An extensive series of 14 repeat reactions were performed (not shown) and this deactivation persisted, with the catalyst giving constant activity within experimental error, which suggests that the reduction in catalyst activity was permanent. The results of the reactions performed at 380 °C and 3000 ppm total nitrogen are shown in Figure 2. The conversion of quinoline in the clean feed was 52.2% ( 3.1% and subsequently decreased to 35.0% ( 3.2% when Fraction 4 was introduced. The conversion returned to 51.3% ( 2.6% after the clean feed was reanalyzed. As observed previously, Fraction 4 demonstrated catalyst inhibition but no permanent catalyst deactivation. When Fraction 8 was added to the feed, the quinoline conversion decreased to 29.2% ( 4.9%. Although this conversion was 5.8% lower than that with the Fraction 4 feed, the reduction was not significant. After Fraction 8 was removed and clean feed was reintroduced, the amount of quinoline reacted increased to 47.3% ( 2.9%, which is similar to the original level of quinoline conversion. The difference in the catalyst inhibition and deactivation in the presence of Fraction 8 be explained by considering the fact that the data presented in Figures
Inhibition and Deactivation of HDN Catalysts
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Figure 2. Conversion of quinoline at 380 °C and 3000 ppm total nitrogen at 9000 kPa.
Figure 3. Conversion of quinoline at 380 °C and 2000 ppm total nitrogen at 9000 kPa.
1 and 2 were obtained under different reaction conditions. It is conceivable during the reaction of the clean gas oil, following Fraction 8 at 380 °C and 9000 kPa H2 (Figure 2), that the higher temperatures and pressures are able to regenerate the catalyst to a certain degree. Consequently, the conversion of quinoline in the carrier gas oil after reaction approaches the conversion before the reaction with Fraction 8. The reaction conditions used in Figure 1 (350 °C, 8650 kPa H2) are not adequate to remove surface contamination and, therefore, indicate a slightly greater degree of deactivation following the reaction with Fraction 8. When the low-boiling material (Fraction 2) was added to the feed, the quinoline conversion decreased from the baseline value of 50.4% ( 4.6% to 17.5% ( 3.7% (see Figure 2). This 32.9% decrease in the amount of quinoline reacted was greater than the 17.2% decrease observed with Fraction 4 and the 22.1% decrease observed for Fraction 8, as noted previously. These results, with a constant total nitrogen content of 3000 ppm, clearly showed that catalyst activity was sensitive to the types of components in the gas oil fractions. When the clean feed was reintroduced following the analysis of Fraction 2, the quinoline conversion only increased to 28.9% ( 6.8%, which indicated severe catalyst deactivation. This low activity continued for an extended sequence of 12 repeat reactions with the clean feed (data not shown). 3.2. Effect of Total Nitrogen Concentration. Although the HDN of gas oils commonly follows apparent first-order kinetics,25 the reactions of quinoline follow the Langmuir-Hinshelwood kinetics that are typical of catalytic reactions.16 To evaluate the role of total nitrogen concentration, the nitrogen concentration was reduced to ∼2000 ppm (1080 ppm due to quinoline and 900 ppm due to the nitrogen species in the different narrow-boiling fractions). The results of the reactions with different feeds and a total nitrogen concentration of 2000 ppm are shown in Figure 3. The initial quinoline conversion in the clean feed was 55.5% ( 4.7% and subsequently decreased to 49.5% ( 6.1% with the addition of Fraction 4. After the reaction with Fraction 4, the quinoline conversion in the clean feed increased
to 60.6% ( 2.7%, which was higher than the starting reactivity of the catalyst. The conversion of quinoline decreased to 40.6% ( 3.4% when Fraction 8 was in the feed, and subsequently recovered to 52.1% ( 2.7% quinoline conversion when the clean feed was reintroduced. The quinoline conversion using Fraction 2 decreased to 18.4% ( 7.6% and only increased to 43.4% ( 4.2% following the reintroduction of the clean feed. Although the observed quinoline conversions using the clean feed were more variable, the relative catalyst inhibition and deactivation behavior due to the narrowboiling fractions was similar to the results with 3000 ppm total nitrogen. The amount of catalyst inhibition and deactivation displayed by each narrow-boiling fraction at the same reaction conditions was different, indicating that inhibition and deactivation is not simply a function of total nitrogen concentration. Fraction 8 demonstrated a higher level of inhibition and deactivation than Fraction 4 at both reaction temperatures and total nitrogen concentrations studied. This result suggests that polyaromatic and higher-molecular-weight compounds are partially responsible for the inhibition of catalyst activity. In residue processing, the amount of coke (i.e., material that will not desorb using solvent extraction) has a tendency to increase as the amount of asphaltene in the feed increases. Although the analysis of the feed (Table 2) indicates that Fraction 8 has a significant amount of asphaltenes, the asphaltene concentration in the reactor is not as dramatic as these data would suggest, because of dilution by the gas oil solvent, and is much lower than that in residue conversion where a decrease in dibenzothiophene HDS has been attributed to asphaltene content.26 In addition, in this study, the HDN activity is quantified using a small model compound (quinoline), which may be less sensitive to the effects of asphaltenes. Because Fraction 2 was the lightest narrow-boiling fraction studied, it was expected that it would affect the catalyst the least. On average, this fraction had the lowest carbon number (13-24) and lowest concentration of aromatic carbon and two- and three-ring nitrogen
(25) Yui, S. M.; Ng, S. H. Energy Fuels 1995, 9, 665-672.
(26) Gray, M. R.; Zhao, Y.; McKnight, C. M.; Komar, D. A.; Carruthers, J. D. Energy Fuels 1999, 13, 1037-1045.
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Figure 4. Conversion of quinoline as a function of CS2 concentration. Reactions were performed at a temperature of 330 °C with a feed:catalyst ratio of 4:1 for 30 min.
heterocycles. Despite these favorable characteristics, Fraction 2 demonstrated a significant amount of catalyst inhibition and deactivation, relative to Fractions 4 and 8, at both 2000 and 3000 ppm total nitrogen concentration at 380 °C. To further study the contributions of the different nitrogen components to inhibition and deactivation, nitrogen-rich extracts were used in subsequent experiments, which are detailed below. 3.3. Effect of CS2 Concentration. CS2 was added to the feedstocks (30 µL) to maintain the catalyst in a sulfided state during the hydrotreatment reactions. Changing the amount of CS2 provided a simple means of exploring the impact of HDS reactions on quinoline conversion, via the generation of hydrogen sulfide and the consumption of hydrogen. The effect of varying CS2 concentrations on the extent of quinoline conversion was initially studied with a feed:catalyst ratio of 4:1 at temperature of 330 °C with clean feed (Figure 4). As the CS2 levels increased above 47 000 ppm S (an addition of 140 µL), the extent of quinoline conversion declined significantly. This decline in activity is consistent with the consumption of H2 by the hydrogenation of CS2 to produce H2S. Because the narrow-boiling fractions already had high levels of sulfur, it is possible that the addition of CS2 to the reactor could affect the apparent catalyst activity. As a result, the effect of adding 30 µL of CS2 to Fraction 4 reactions was investigated at 330 °C and reaction times of 30 min. The average quinoline conversion with Fraction 4 and no added CS2 was 37.6% ( 3.9%, compared to a 36.5% ( 2.2% conversion that is observed with the addition of 30 µL of CS2. The results with and without CS2 with Fraction 4 suggest no impact of CS2 additions of
