Interactiue Chemistry of Coal-Oil Reactions conditions and in the presence of excess sulfur formed the active catalytic species which is a finely dispersed, high surface area molybdenum sulfide whose stoichiometry has been shown to be MoS2.10 The selected reactants representing coal and petroleum compounds follow distinct and somewhat unique reaction pathways in the presence of molybdenum naphthenate and excess sulfur. The molybdenum sulfide catalyst generated in situ promoted partial saturation of polynuclear aromatic rings but did not saturate single-ring aromatics. For heteroatom removal, two pathways were typically observed one involved saturation of the aromatic ring prior to heteroatom removal producing alkyl alicyclics as end products while the other removed the heteroatom prior to saturation of the aromatic ring producing alkyl aromatics as end products." The effect of the presence of multiple hydrocarbon and heteroatomic species on the reaction of each other with molybdenum naphthenate and excess sulfur is the subject of this investigation.
Experimental Section Model Reactants and Catalysts. The model reactants se-
lected were naphthalene (99%), indan (97%), indene (99%), benzothiophene (97%),quinoline (99%),indole (99%),o-cresol (99%)and benzofuran (99.5%). n-Hexadecane (99%)was used as a solvent. All of the reactants, their hydrogenation products, and the solvent were obtained from Aldrich Chemical Company. Molybdenum naphthenate (MoNaph) containing 6 w t % Mo was obtained from Shepherd Chemical Company. Reaction Procedures and Conditions. Hydrogenation reactions were conducted in 20-cm3stainless steel batch microtubing bomb reactors that were oriented horizontally. The model reactants were reacted both individually and in various combinations. Three different reactions were performed for each reactant set: a thermal reaction, a thermal reaction with excess sulfur, and a catalytic reaction with excess sulfur. For the individual reactant systems, 2 wt % naphthalene or 1wt % of each of the other reactants dissolved in hexadecane was used as the reactant. For the combined reactant systems, combinations ranging from two to six compounds in hexadecane were charged at 2 w t % naphthalene and 1wt % of each of the other reactants. Four grams of reactant solution was charged for each reaction. For the catalytic reactions, MoNaph was premixed at a level of 2850-2950 ppm Mo in the reactant solution and -0.024 g of elemental sulfur was added to generate the active catalytic species. The atomic ratio of S to Mo in the reactor was 6, providing 3 times the sulfur actually required to produce MoS2. For the thermal reactions with sulfur, -0.016 g of elemental sulfur, the approximate amount of free sulfur that would remain in a catalytic reaction after formation of MoSz, was introduced in order to observe the effect of excess sulfur on the reaction. Hydrogen was introduced to the reactor at 1250 psig at ambient temperature prior to the reaction. All of the reactions were performed at 380 O C . The reactors were horizontally agitated at 550 cpm. The system pressure at reaction temperature and hydrogen consumption during reactions were estimated to be 2400-2700 psig and less than 1-12%, respectively, based on the recovered gas amount. After each catalytic reaction, the product solution was recovered and centrifuged for 2-3 h to separate the black catalyst precipitate from the product solution. This recovered solid appeared to be MoSz with rhombohedral crystalline structure.1° All thermal and catalytic reactions were at least duplicated, and the results were summarized in averaged values and standard deviations of X f 6,. Catalytic reactions of the reactants except for nitrogen compounds showed less error (u, 5 1.0 in percent hydrogenation) and higher recoveries of liquid products (over 96% recovery based on the reactants) than thermal reactions with additional sulfur. Catalytic reactions of nitrogen compounds showed low recoveries (-88% recovery of quinoline and -82% (10) Kim, H.;Curtis, C. W.; Cronauer, D. C.; Sajkowski,D. J. Prepr. Pap.-Am. Chem. SOC.Diu. Fuel Chem. 1989,34, 1431-1438. (11) Kim,H.;Curtis, C. W. Energy Fuels, preceding paper in this issue.
Energy & Fuels, Vol. 4, No. 2, 1990 215 of indole) and larger standard deviations with u,, = 1.0-2.0 in percent hydrogenation. Additional Nitrogen Compounds. Reactions were performed to examine the effect of additional nitrogen compounds on the catalytic hydrogenation of naphthalene, o-cresol,quinoline, and indole in the presence of 2850-2950 ppm Mo as MoNaph and 3 timea the required amount of sulfur to produce MoS2. Each model reactant was introduced at 1 wt % except for naphthalene introduced at 2 wt % in hexadecane. The additional nitrogen compounds were introduced at an equivalent molar amount of 3.4 X lo-' mol of quinoline, indole, or pyridine in a total 4-g charge; the ratio of additional nitrogen to metal Mo was kept constant at 2.8 g-atoms of nitrogen/g-atom of Mo. Effect of Sulfur. Reactions were performed to examine the effect of sulfur amount on thermal and catalytic hydrogenations of individual and combined reactants. The reactants used were naphthalene, o-cresol, benzothiophene, and quinoline. The amount of reactants introduced was 1wt % for the heteroatomic species and 2 wt % for naphthalene. Elemental sulfur was added in 3,6,9,12, and 15 times the amount needed to produce MoS2. In a separate set of reactions, benzothiophene was introduced at 1, 2, and 3 wt % in the 4-g reactant solution. Product Analysis. The liquid products were analyzed by gas chromatography using a 30-m fused silica capillary DB-5 column of 0.32-mm inner diameter (obtained from J&W Scientific)with FID detection. p-Xylene was used as the internal standard. Products were identified by using a VG 70EHF mass spectrometer and a Varian 3700 gas chromatograph.
Results and Discussion Individual and combined model systems were reacted both thermally and catalytically to examine the chemical interactions of these systems a t coprocessing conditions. Catalytic reactions were performed with MoNaph and excess sulfur. Thus, in order to differentiate between the effect of the catalyst and the effect of excess sulfur, thermal reactions were performed with excess sulfur and were compared to both the catalytic and the thermal reactions. The effect of different sources of sulfur on the catalytic activity of MoNaph was examined. Two sulfur sources were chosen: carbon disulfide and elemental sulfur. Both of them appeared to quickly sulfide the Mo species in situ and produced equivalent amounts of hydrogenation of naphthalene under the reaction conditions of this study. Elemental sulfur was chosen as the sulfur source because of greater ease of handling and reproducibility. The degree to which hydrogenation and heteroatom removal occurred in each reaction has been summarized by using the defined terms of percent hydrogenation (5% HYD), percent hydrogenolysis (% HYG), percent hydrodesulfurization (% HDS), percent hydrodenitrogenation (% HDN), and percent hydrodeoxygenation (% HDO). Percent hydrogenation is the number of moles of hydrogen required to achieve the final liquid product distribution as a percentage of the moles of hydrogen required to achieve the most hydrogenated liquid product. Percent hydrogenolysis is the summation of the mole percents of products resulting from carbon-carbon or carbon-heteroatom bond cleavage. Percent hydrodesulfurization is the summation of the mole percents of products not containing sulfur. Percent hydrodenitrogenation is the summation of the mole percents of products not containing nitrogen. Percent hydrodeoxygenation is the summation of the mole percents of products not containing oxygen. In the calculation of percent hydrogenation, the most hydrogenated liquid products defined for the systems used in this work were decalin for naphthalene; n-propylcyclohexane and n-butylcyclopentane for quinoline; and cyclohexane for indan, indene, benzothiophene, indole, ocresol, and benzofuran. The moles of hydrogen required to achieve the most hydrogenated product from each
216 Energy & Fuels, Vol. 4, No. 2, 1990 Table I. Thermal Hydrogenation of Individual Model Compounds" % HYDb reactant thermal without S thermal with S 4.5 & 0.7 naphthalene 0.4 f 0.0 indan 0.0f 0.0 0.0 f 0.0 indene 7.4 12.8 f 1.0 8.0 f 1.2 benzothiophene 1.8 f 0.3 quinoline 26.4 f 0.8 28.2 f 0.6 indole 8.8 11.9 o-cresol 0.0 3.0 benzofuran 1.5 6.2
'The most hydrogenated products are decalin for naphthalene, n-propylcyclohexane and n-butylcyclopentane for quinoline, and cyclohexane for the other reactants. % HYD is expressed as the averaged value and standard deviation of X f 6., reactant were 5 mol of H2 for naphthalene; 6 mol for indan; 7 mol for indene; 8 mol for benzothiophene, benzofuran, and indole; 5 mol for o-cresol; and 7 mol for quinoline. Percent hydrogenolysis of benzofuran, quinoline, or indole was the summation of the mole percents of single-ring products, which resulted from a ring opening by carbonheteroatom bond cleavage from each reactant, such as o-ethylphenol, o-propylaniline, o-ethylaniline, or the similar products with a fully saturated ring structure such as 2ethylcyclohexanol, or the single-ring products without heteroatoms such as alkylbenzenes, alkylcyclohexenes,and alkylcyclohexanes. Thermal Reactions. Each model compound species was reacted individually and in combination under thermal reaction conditions to ascertain their individual reactivity and the degree of thermal interaction among the different species. All of the thermal reactions were conducted with and without sulfur. The extent of the thermal hydrogenation of each individual species under both reaction conditions is given in Table I. The only species that showed any substantial thermal reactivity at 380 "C without sulfur were quinoline, indole, and indene. With the addition of sulfur, the hydrogenation of each model compound except for indan was enhanced. When the reactants were combined using two to six of the following species, naphthalene, indan, benzothiophene, quinoline, o-cresol, and benzofuran, the conversion of each species was slightly reduced by the presence of the other species. The exception was quinoline. Quinoline markedly inhibited the reactivity of each species in the thermal reactions with sulfur. The % HYD of the compounds affected by quinoline was reduced as follows: for naphthalene from 5 % to 0; for benzothiophene from 8 to 6%; for o-cresol from 3% to 0; and for benzofuran from 6 to 2 % . The % HYD of quinoline was also reduced from 28 to 15% with the presence of the additional compounds. No enhancement in HYD of any species by the addition of other compounds was detected. Under the reaction conditions used for these thermal as well as catalytic experiments, hydrogen was present in sufficient excess so as not to limit the hydrogenation of the reactants. Catalytic Reactions. The individual and combined catalytic reactions of the model species were performed with MoNaph and excess sulfur. The interactive effect of the chemistry of the different species among the species present in the reaction was examined. Naphthalene Hydrogenation. The catalytic hydrogenation of naphthalene alone and in combination with other species is shown in Table 11. With MoNaph and excess sulfur, naphthalene was nearly totally converted, yielding tetralin as the major product (92%)and decalin as the minor product (6%).
Kim and Curtis Table 11. Catalytic Hydrogenation of Naphthalene in Multireactant Systems' reactantsb % HYD of NAPHe NAPH 42.6 f 0.4 NAPH, IN 43.3 f 0.5 NAPH, INE 42.1 f 0.9 NAPH, BZT 43.7 f 0.2 NAPH, CR 42.2 f 0.4 42.4 f 0.2 NAPH, BZF NAPH, IN, BZT 42.7 f 0.6 42.2 f 0.1 NAPH, IN, BZT, CR 41.2 f 1.6 NAPH, IN, BZT, CR,BZF NAPH, QN 9.3 f 0.5 NAPH, QN, BZT 11.7 f 0.5 NAPH, QN, BZT, IN 10.9 f 0.8 NAPH, QN, BZT, IN, CR 10.8 f 0.2 NAPH, QN, BZT, IN, CR,BZF 10.7 f 0.3
" A key for the abbreviations is given in the Nomenclature section. bThemost hydrogenatedproduct for naphthalene is decalin. % HYD is expressed as the averaged value and standard deviation of X f un. Table 111. Catalytic Hydrogenation of Indan and Indene in Multireactant Systems reactants" % HYDb IN 4.0 f 0.3 IN, NAPH 4.2 f 0.4 IN, NAPH, BZT 3.6 f 0.1 3.8 f 0.1 IN. NAPH. BZT. CR IN; NAPH; BZT[ CR,BZF 2.9 f 1.0 IN, NAPH, QN, BZT 0.0f 0.0 IN, NAPH, QN, BZT, CR -0.2 f 0.P IN, NAPH, QN, BZT, CR, BZF -0.3 f 0.P INE 18.3 f 0.3 INE, NAPH 17.6 f 0.9 "The most hydrogenated product for indan and indene is cyclohexane. % HYD is expressed the averaged value and standard deviation of X f un. Negative values in % HYD represent dehydrogenation of indan to indene.
The effect of additional hydrocarbons or heteroatomic species containing oxygen or sulfur on catalytic naphthalene HYD was small (Table 11). Naphthalene HYD in the presence of all the reactants except quinoline ranged from 41 to 44%. However, in each group of combinations containing benzothiophene, the naphthalene HYD was slightly increased. This difference in naphthalene HYD was the result of increased conversion of naphthalene to tetralin and from tetralin to decalin. Quinoline, however, severely inhibited the catalytic HYD of naphthalene reducing it from 42 to 9 %. This reduction resulted in much less naphthalene conversion, reducing it from -98 to 2 3 % , and no decalin production. Nitrogenous bases have been shown to poison sulfide ~atalysts'~-'~ as appears to be the case with the catalyst generated from MoNaph and excess sulfur. However, when benzothiophene was added to the naphthalene/quinoline systems, an increase in naphthalene HYD from 9.3 to 11.7% was observed. The change observed in the product distribution was 6% more conversion from naphthalene to tetralin. This phenomenon is examined further in a later section. Indene and Indan Hydrogenation. The catalytic hydrogenation of indan and indene is presented in Table 111. Under the reaction conditions used, indene was readily thermally hydrogenated, converting nearly 52% to indan without sulfur and nearly 97% with sulfur. With
-
(12)Shah,Y. T.Catal. Rev.-Sci. Eng. 1979,20(2),209-301. (13) Weisser, 0.; Landa, S.Sulphide Catalysts, Their Properties and Application; Pergamon: New York, 1973; Chapter A-5. (14)Satterfield, C.N.; Yang, S. H. J. Catal. 1983.81,335-346. (15)Rollmann, L.D. J . Catal. 1977,46, 243-252.
Interactive Chemistry of Coal-Oil Reactions
Energy & Fuels, Vol. 4, No. 2, 1990 217 Table VI. Catalytic Hydrodeoxygenation of Benzofuran in Multireactant Systems reactants" %HYDb %HYGb % HDOb BZF 46.3 f 0.1 100.0 f 0.0 79.3 f 2.1 BZF, NAPH 46.8 f 0.4 100.0 f 0.0 79.9 f 1.3 BZF, NAPH, IN, BZT, CR 40.8 f 1.1 100.0 0.0 59.4 f 4.6 BZF, NAPH, IN, BZT, CR, 25.6 f 0.1 92.7 0.8 7.1 1.5 QN
Table IV. Catalytic Hydrodesulfurization of Benzothiophene in Multireactant Systems reactants" %HYDb %HDS 40.7 f 0.9 100.0 BZT BZT, NAPH 40.2 f 0.5 100.0 BZT, NAPH, IN 39.7 0.1 100.0 BZT, NAPH, IN, CR 39.8 f 0.1 100.0 BZT, NAPH, QN 38.2 f 0.1 100.0 38.0 f 0.1 100.0 BZT, NAPH, QN, IN 38.1 f 0.2 100.0 BZT, NAPH, QN, IN, CR
*
* *
" The most hydrogenated product for benzofuran is cyclohexane.
" The most hydrogenated product for benzothiophene is cyclohexane. % HYD is expressed as the averaged value and standard deviation of X f 6,. Table V. Catalytic Hydrodeoxygenation of o-Cresol in Multireactant Systems reactantsa % HYDb % HDOb CR 36.2 f 0.2 86.7 0.6 CR,NAPH 33.7 f 0.7 81.4 f 1.9 CR,NAPH, IN, BZT 29.1 f 0.5 63.8 f 0.1 CR,NAPH, IN, BZT, BZF 26.5 f 1.3 57.5 f 5.7 10.6 f 0.3 4.2 f 0.1 CR,NAPH, IN, BZT, QN 4.1 f 0.2 10.6 f 0.4 CR,NAPH, IN,BZT, BZF,QN
*
" The
most hydrogenated product for o-cresol is cyclohexane. % HYD and % HDO are expressed as the averaged values and standard deviations of X f on.
MoNaph and excess sulfur present, indene was totally converted and yielded indan as the major hydrogenation product. Indan, by contrast, was thermally stable with and without sulfur. With the introduction of MoNaph and excess sulfur, indan as both a reactant and a hydrogenation intermediate from indene was further hydrogenated, forming 9% hexahydroindan and small amounts of other products such as toluene, methylcyclohexane,benzene, and cyclohexane. The addition of other hydrocarbons and oxygen- and sulfur-containingheteroatomic species slightly lowered the amount of indan HYD and HYG observed. The introduction of quinoline, however, severely poisoned the catalyst and eliminated any hydrogenation of indan. Benzothiophene Hydrodesulfurization. When reacted individually in the presence of MoNaph and excess sulfur, benzothiophene was totally converted and completely desulfurized, yielding ethylbenzene as the primary final product. The addition of hydrocarbons (naphthalene and indan) and o-cresol slightly decreased the amount of benzothiophene HYD but did not affect HDS as shown in Table IV. The addition of quinoline also did not affect HDS of benzothiophene but did reduce the amount of fully saturated products such as ethylcyclohexane and methylcyclohexane produced and, hence, lowered the % HYD of benzothiophene. Thus, quinoline appeared to poison the catalytic sites of the in situ generated molybdenum sulfide for hydrogenation but not those for desulfurization. o-Cresol Hydrodeoxygenation. With MoNaph and excess sulfur the most stable isomer of the cresols, o-creso1,16 was not completely deoxygenated a t 380 "C, producing toluene as the primary product and fully saturated isomers of methylcyclohexane and ethylcyclopentane as the secondary products. Both the catalytic hydrogenation and deoxygenation of o-cresol were affected by the presence of other compounds as shown in Table V. The HYD and HDO of o-cresol were reduced from 36.2 and 86.7%, respectively, when reacted alone, to 26.5 and 57.5% with the addition of benzofuran, naphthalene, indan, and benzothiophene. The effect of these added species on the ~
~~
Stiegel! G. J:; Shah, Y. T.; Krishnamurthy, S.; Paulvelker, S. V. Reaction Engineering in Direct Coal Liquefaction; Shah, Y . T., Ed.; Addison-Wesley: London, 1981; Chapter 6. (16)
*
* % HYD, % HYG, and % HDO are expressed as the average values and standard deviations of X f u,,.
Table VII. Catalytic Hydrodenitrogenation of Quinoline in Multireactant Svstems reactants" %HYDb %HYGb % H D N b 90.6 f 1.5 100.0 f 0.0 89.7 f 2.2 QN QN, NAPH 85.1 f 1.3 98.6 f 1.8 82.9 f 1.9 QN, NAPH, BZT 87.2 f 0.9 99.3 f 0.7 84.9 f 1.4 86.5 f 0.4 99.5 f 0.7 83.6 f 0.6 QN, NAPH, BZT, IN 87.6 f 0.1 100.0 f 0.0 84.9 f 0.1 QN, NAPH, BZT, IN, CR QN, NAPH, BZT, IN, CR, 87.7 f 0.1 100.0 f 0.0 84.9 f 0.6 BZF
" The most hydrogenated products for quinoline are propylcyclohexane and n-butylcyclopentane. % HYD, % HYG, and % HDN are expressed as the averaged values and standard deviations of x f 6,. o-cresol product distribution resulted in less o-cresol being deoxygenated and then converted to toluene. When quinoline was added, an even more substantial reduction to 4.2% HYD and 10.6% HDO was observed. Only 10% of the o-cresol was converted. Thus, the addition of quinoline poisoned the active catalytic sites of molybdenum sulfide for both hydrogenation and deoxygenation of o-cresol. Benzofuran Hydrodeoxygenation. Benzofuran was totally converted and deoxygenated in the presence of MoNaph and excess sulfur (Table VI). The primary products were ethylbenzene and ethylcyclohexane. Substantial deoxygenation, -80%, occurred when benzofuran was reacted individually and in combination with naphthalene. However, the addition of compounds containing sulfur and oxygen heteroatoms reduced both HYD and HDO but not HYG. With these additions, the decrease in HDO was mainly due to the sulfur-containing compound; this inhibiting effect was examined further in later experiments. When quinoline was added, the HYD of benzofuran was reduced by half and only 7% HDO occurred. The primary product was the hydrogenolyzed oxygen-containing compound, o-ethylphenol. Quinoline Hydrodenitrogenation. Quinoline showed substantial hydrogenation under thermal conditions. The thermal hydrogenation was adversely affected by the presence of the other compounds. Catalytic reactions with MoNaph and excess sulfur yielded much higher levels of quinoline hydrogenation, regardless of the added species, compared to the thermal reactions. Quinoline HYD ranged from 85 to 90% in the catalytic reactions depending upon reactant composition as presented in Table VII. The primary product produced was propylcyclohexane. A small amount of competition from hydrocarbons and heteroatomic species for the active sites reduced slightly the HYD, HYG, and HDN in most of the reactions with added species. However, the mixtures containing benzothiophene showed slightly higher HYD and HDN than the mixtures without benzothiophene. Effect of Additional Nitrogen Compounds. The effect of the addition of each of the three nitrogen compounds, pyridine, indole, and quinoline, introduced in equimolar amounts on the catalytic hydrogenation of
Kim and Curtis
218 Energy & Fuels, Vol. 4, No. 2, 1990 Table VIII. Effect of Added Nitrogen on the Activity of the Catalyst Generated in Situ from MoNaph and Excess Sulfur+ without nitrogen pyridine indole quinoline NAPH % HYD 42.6 f 0.4 29.2 f 0.4 23.7 f 1.2 7.8 f 0.5 CR % HYD 36.2 f 0.2 9.5 f 1.2 8.4 f 0.2 2.9 f 0.1 % HDO 86.7 f 0.6 22.8 f 2.6 19.6 f 0.7 7.7 f 0.1 QN 70 HYD 90.6 f 1.5 72.5 f 1.2 75.5 f 1.6 66.9 f 0.5 89.7 f 2.2 63.0 f 1.4 67.6 f 1.8 55.0 f 0.9 % HDN % HYG 100.0 f 0.0 82.8 f 2.4 86.8 f 2.2 73.8 f 0.7 IND 40.4 f 0.7 58.5 f 4.0 NP' 70.4 f 2.2 70 HYD 35.7 f 1.3 70.9 f 8.3 N P 96.2 f 4.5 % HDN 91.3 f 0.7 % HYG 100.0 f 0.0 100.0 f 0.0 N P Nitrogen compounds were added on an equivalent mole basis: mol of nitrogen compound in a 4-g charge of reactant solution. * % HYD, % HYG, % HDO, and % HDN are expressed as the averaged values and standard deviations of X f un. 'NP, not performed. 3.4 X
naphthalene, o-cresol, quinoline, and indole was investigated. The results given in terms of 5% HYD, 5% heteroatom removal, and % HYG for each species are presented in Table VIII. A substantial reduction in naphthalene HYD was observed with each nitrogen compound addition. The hydrogenation pathway from tetralin to decalin was eliminated, and the amount of naphthalene HYD to tetralin was reduced. Quinoline was the most detrimental nitrogen-containing species while pyridine was the least. For o-cresol, the amount of HYD and HDO was also substantially reduced by the addition of the organic nitrogen compounds; quinoline showed the most detrimental effect. These decreases in activity manifested themselves as decreased conversion of o-cresol, going from -87% conversion without a nitrogen compound to -23% or less with a nitrogen compound. The effect of additional nitrogen compounds on the catalytic hydrogenation of nitrogen-containing compounds themselves was tested with both quinoline and indole. The nitrogen compounds inhibited the hydrogenation and heteroatom removal of nitrogen compounds themselves. The addition of quinoline was most detrimental to the HYD, HDN, and HYG of quinoline. Indole and pyridine had lesser but nearly equivalent inhibiting effects. For indole, quinoline again showed a much stronger inhibiting effect than pyridine. The inhibiting effect for all of the test compounds occurred in the order of quinoline > indole L pyridine. The order of inhibiting effect of nitrogen compounds did not simply follow the order of basicities of the added nitrogen compounds: pyridine (pK, = 5.3) > quinoline (pK, = 4.9) > indole (pK, = -2.4)."J8 As the reaction occurred, many different nitrogenous species were formed and each had its own basicity, thereby changing the basicity of the system; hence, the basicity of each system at any one time could not be easily determined. Effect of Sulfur. The role of sulfur in the reaction was to form molybdenum sulfide in situ from the MoNaph; the effect of the excess sulfur on the reaction and on the catalytic activity and selectivity of the catalyst was explored. Therefore, the effect of the sulfur amount on individual and combined model reactions was examined in both thermal and catalytic reactions. (17) Albert, A. Heterocyclic Chemistry; Athlone: London, 1968 Chapter 13. (18) Perrin, D.D.Dissociation Constants of Organic Bases in Aqueous Solution; Butterworth London, 1965.
Table IX. Effect of Sulfur Amount on Thermal Hydrogenation of Naphthalene" sulfur amountb NAPH (2 wt % ) NAPH (1 wt %) NAPH, BZT NAPH, BZF NAPH, QN
0
3
12
0.4 0.5 0.0 0.0 0.0
4.0 5.2 2.6 2.1 0.5
3.9 4.3 3.2 3.0 1.2
"As % HYD of naphthalene. bSulfur amount: Multiples of 0.008 g of elemental sulfur (0.008 g of S was the amount of sulfur required to make MoS2).
Although the effect of excess sulfur in the thermal hydrogenation of naphthalene was small as shown in Table IX, sulfur appeared to enhance the hydrogenation of naphthalene to tetralin. However, the amount of sulfur present in the reactor did not affect the degree of hydrogenation substantially: the catalytic role of sulfur itself seemed to be unlikely in these reactions. The role of the sulfur in the thermal reaction was also examined by performing several experiments in which the reactor wall was sulfided prior to reactions. Thermal reactions performed thereafter without additional sulfur showed increased reactivity of naphthalene, which was slightly less than that observed in the thermal reactions with excess sulfur. Thus, the most likely cause for the enhanced HYD was activation of the reactor wall by the added sulfur; however, this catalytic effect was negligible compared to that of MoNaph with excess sulfur. The effect of the amount of sulfur present on the catalytic HYD of naphthalene individually, on naphthalene and benzothiophene combined, on naphthalene and ocresol combined, and on naphthalene and quinoline combined was examined. When the sulfur amount was increased from 3 to 6 to 9 times the stoichiometric amount required for MoS2, the HYD of naphthalene increased from 43 to 44 to 45%, respectively. This change in HYD was significant because it can be translated into a doubling from 5 to 9% of the decalin produced. The HYD of benzothiophene did not change. However, the HDO of o-cresol was reduced from 61 to 59 to 5 5 % , as the sulfur level was increased. This effect was observed in the product distribution of o-cresol as less conversion of ocresol to deoxygenated products. The inhibiting effect of sulfur on the HDO of these same oxygen compounds was confirmed and amplified when a larger reactor was used.1° On the basis of these results, it can be concluded that the catalytic HDO of oxygen compounds, o-cresol and benzofuran, with MoNaph and excess sulfur was inhibited by both sulfur-containing compounds and additional elemental sulfur. A similar inhibiting effect on the HDO of o-cresol by benzothiophene and dibenzothiophene has also been reported with COMO/A~,O,.~~ Catalytic systems with MoNaph and excess sulfur-containing organic nitrogen compounds were positively affected by an increase in the sulfur amount. The additional sulfur suppressed some of the catalyst poisoning by quinoline and allowed greater hydrogenation of naphthalene in a combined quinoline and naphthalene system as shown in Table X. Naphthalene HYD increased from 9 to 22% as the sulfur amount was increased from 3 to 9 times the required stoichiometric amount. Substantial increases were also observed in the HYD and HDN of quinoline. Thus, the presence of sulfur markedly enhanced the catalytic activity of the molybdenum sulfide catalyst (19)Odebunmi, E. 0.;Ollis, D. F.J. Catal. 1983, 80,65-75.
Interactive Chemistry of Coal-Oil Reactions
Energy & Fuels, Vol. 4 , No. 2, 1990 219
Table X. Effect of Sulfur Amount on Catalytic Hydrogenation of Multireactant Systems sulfur amountb NAPH and QN" 3 6 9 % HYD of NAPH 9.3 f 0.5 17.0 21.6 % HYD of QN 90.7 94.4 85.1 f 1.3 % HYG of QN 98.6 f 1.8 100.0 100.0 % HDN of QN 82.9 f 1.9 88.9 94.6 NAPH, QN, sulfur amountb and BZTn 3 6 9 12 15 HYD of NAPH 11.7 f 0.5 19.3 14.3 22.2 23.5 HYD of BZT 38.2 f 0.1 38.1 38.2 38.5 38.0 HYD of QN 87.2 f 0.9 89.7 93.8 94.8 95.1 HYG of QN 99.3 f 0.7 100.0 100.0 100.0 100.0 HDN of QN 84.9 f 1.4 87.3 93.3 95.2 94.7 ~~
% % % % %
" Most hydrogenated product: decalin for naphthalene, cyclohexane for benzothiophene, and n-propylcyclohexaneand n-butylcyclopentane for quinoline. bSulfuramount: Multiples of 0.008 g of elemental sulfur (0.008 g of S was the amount of sulfur required to make MoS,). Table XI. Effect of Benzothiophene Amount on Catalytic Hydrogenation of Naphthalene, Quinoline, and Benzothiophene Combined Using Molybdenum Naphthenate and Excess Sulfur benzothiophene amount, w t % products"sb 0 1 2 3 % HYD of 9.3 f 0.5 11.7 0.5 13.0 f 1.2 18.6 f 1.2 NAPH % HYD of BZT 38.2 f 0.1 38.0 f 0.0 38.3 f 0.1 % HYD of QN 85.1 f 1.3 87.2 f 0.9 89.3 1.3 92.7 f 1.0 % HYG of QN 98.6 f 1.8 99.3 k 0.7 100.0 f 0.0 100.0 f 0.0 % HDN of QN 82.9 f 1.9 83.6 f 0.6 86.2 f 1.6 92.5 f 1.4
*
*
a Most hydrogenated products: decalin for naphthalene, cyclohexane for benzothiophene, and n-propylcyclohexaneand n-butylcyclopentane for quinoline. * % HYD, % HYG, and % HDN are expressed as the averaged values and standard deviations of X f
an.
when quinoline was involved in the reaction. Likewise, in a tertiary system with naphthalene, quinoline, and benzothiophene, the addition of excess sulfur increased the amount of naphthalene HYD observed. In fact, when the sulfur amount was increased from 3 to 15 times the stoichiometric amount of sulfur required for MoS2 production, the HYD of naphthalene increased from 12 to 24%. The HYD of benzothiophene did not change. However, the HYD and HDN of quinoline increased from 87 to 95% and 85 to 95%, respectively, as the sulfur amount increased. The effect of the source of sulfur as well as the amount of sulfur was examined by using various amounts of benzothiophene as the sulfur source instead of elemental sulfur. As shown in Table XI, benzothiophene was completely desulfurized to release sulfur to the system. The released sulfur enhanced the catalytic activity of molybdenum sulfide which had been poisoned by quinoline and the other nitrogen-containing products produced from quinoline. Thus, in both systems regardless of the sulfur
source, the presence of sulfur reduced the inhibiting effect of organic nitrogen compounds on the HYD of hydrocarbons and the HYD and HDN of the nitrogen-containing compounds. Enhancement of HDN of nitrogen-containing compounds by sulfur has also been observed with N ~ M o / A ~and ~ C ~ O~ M ~ O ~ /*A~~ ~~ *~ ~~ . ~~ ~ , ~ ~
Summary Thermal reactions showed little reactivity a t 380 "C. Only quinoline, indole, and indene were hydrogenated. However, the introduction of additional compounds reduced their thermal hydrogenation. Addition of sulfur to the thermal reactions activated the reactor wall and led to higher reactivity, but the sulfur-reactor wall catalysis was minimal compared to the catalytic reactions with molybdenum naphthenate and excess sulfur. In catalytic reactions, the interactions among the different hydrocarbon and heteroatomic species present in multiple reactant systems were complicated. Organic nitrogen compounds severely deactivated the in situ generated molybdenum sulfide catalyst for hydrogenation and removal of oxygen and nitrogen. The nitrogen compounds, however, did not affect sulfur removal. Both the addition of benzothiophene and the addition of excess elemental sulfur reduced catalyst poisoning by nitrogen compounds. However, the presence of increased sulfur amounts reduced deoxygenation of both benzofuran and o-cresol in the presence of MoNaph. Thus, the heteroatomic species influenced the catalyst, which then affected the degree of reactivity of the individual species at coprocessing conditions. Acknowledgment. We gratefully acknowledge the support of the Department of Energy under Contract No. DEFG-2285PC80502, The provision of molybdenum naphthenate from Shepherd Chemical is also gratefully acknowledged. Nomenclature benzofuran benzothiophene o-cresol percent hydrodenitrogenation percent hydrodeoxygenation percent hydrodesulfurization percent hydrogenation percent hydrogenolysis indan indene indole naphthalene quinoline Registry NO.NAF'H, 91-20-3; IN, 496-11-7; N E , 9513-6; BZT, 95-15-8; QN, 91-22-5; IND, 120-72-9; CR, 95-48-7; BZF, 271-89-6; S, 7704-34-9; MoS~,1317-33-5.
BZF BZT CR % HDN % HDO % HDS % HYD % HYG IN INE IND NAPH QN
(20) Yang, S. H.; Satterfield, C. N. J. Catal. 1983,81, 168-178. (21) Olalde, A.; Perot, G. Appl. Catal. 1985,13, 373-384. (22) Goudriaan, F.; Gierman, H.; Vlugter, J. C. J.Inst. Pet. 1973,59, 40-41. (23) Ramachandran, R.; Massoth, F. E. J. Catal. 1981,67, 248-249.
