1026
Ind. Eng. C h e m . Res. 1987, 26, 1026-1033
Catalytic Hydrogenation and Hydrocracking of Fluoranthene: Reaction Pathways and Kinetics Arunas T. Lapinas, Michael T. Klein,* and Bruce C. Gates Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716
Aris Macris and James E. Lyons S u n Company, Marcus Hook, Pennsylvania 19086
Catalytic reaction pathways for fluoranthene hydrogenation and hydrocracking were determined at 310 t o 380 "C and 153 atm of total pressure. Fluoranthene hydrogenation was catalyzed by a presulfided NiW /A1203 catalyst, whereas its hydrogenation and subsequent hydrocracking were catalyzed by a presulfided NiMo/zeolite-Y catalyst. The activities for conversion of fluoranthene were comparable, as the fluoranthene disappearance rate constant k (cm3 of solution/(g of catalyst s)) = 0.28,0.70, and 1.2 at 320,350, and 380 "C, respectively, for the reaction catalyzed by NiW/A1203, suggesting Arrhenius parameters of [log A (cm3of solution/(g of catalyst s)), E,,, (kcal/mol)] = [6.4, 18.71, whereas k = 0.27,0.63, and 1.00 at 310, 350, and 380 "C, respectively, with [log A , Eact]= [4.8, 14.21 for the reaction catalyzed by NiMo/zeolite. Hydrocracking of the five-carbon-memberedring-containing fluoranthene had kinetically significant cleavage pathways distinct from those observed for the six-carbon-membered-ring-containing fused-ring polynuclear aromatic compounds. The former should. therefore. be regarded as a ser>arate class in modeling the conversion of heavy oil feedstocks; the data presented gere provided -a basis for such modeling. Limitations in supplies of petroleum have focused attention on increasingly heavy oils for the production of gasoline, lubricants, and chemicals. Hydrocracking was developed as a process to provide flexibility in refining to make gasoline and light oils from less valuable petroleum stocks such as residua, cycle oils, gas oils, and cracked and straight run naphthas (Sullivan and Scott, 1983), some of which contain high concentrations of polycyclic aromatic compounds, that also may contain heteroatoms (Unzelman and Gerber, 1965; Gould et al., 1967; Ward, 1975; Billon et al., 1978). Fuels derived from blends from coal, shale, and tar sands also provide potential feeds for hydrocracking processes (Guin et al., 1976; Petrakis et al., 1983a-c; Allen et al., 1984). Hydrocracking of polycyclic aromatic compounds to give lower molecular weight species with increased H:C ratios requires bifunctional catalysts having hydrogenation and cracking activity (but in some processes the cracking may actually be thermal). Many commercial hydrocracking catalysts consist of palladium distributed on or in zeolite supports, with the metal providing the hydrogenation sites and the highly acidic support providing cracking activity. Amorphous silica-alumina supports can also be used to provide the cracking activity, but the zeolites are more common and have much higher activity because of their higher densities of acidic sites. The zeolites also have a much higher tolerance for organic nitrogen, NH,, and higher boiling point feed fractions, which are identified as reaction inhibitors and/or coke precursors (Gates et al., 1979). Catalysts for the heavier feedstocks often contain metal sulfides (e.g., of Ni and Mo or Co and Mo) instead of metals and amorphous supports instead of or in addition to zeolites. In general, amorphous catalysts are used for the production of heavy lube oils and for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) pretreatment of the feed, whereas zeolite catalysts are used for hydrocracking of heavy feeds to produce kerosene. jet and diesel fuels, gasoline, and chemicals. The reaction pathway characterizing hydrogenation and hydrocracking of six-carbon-membered-ring-containing aromatic compounds such as naphthalene, anthracene, phenanthrene, and pyrene have been reported (Qader and 0888-5885'I 87 12626- 1026$O1.50/0
Table I. Summary of Catalytic Reaction ExDeriments autoclave agitated tubing bomb reactor autoclave catalyst NiW/A1203 NiMo/ NiMo/zeolite-Y zeolite-Y total 153 153 75 at 25 "C pressure, atm temp, "C 320, 350, 380 310, 350, 380 380 8, 15, 20 reaction 220, 160, 100 350, 60, 35 time. min
Hill, 1972; Qader et al., 1973; Qader, 1973; Wu and Haynes, 1975; Huang et al., 1977; Veluswamy, 1977; Shabtai et al., 1978; Wuu, 1983; Stephens and Chapman, 1983; Stephens and Kottenstette, 1985). Typical hydrocracking pathways proceed through terminal-ring hydrogenation followed by possible isomerization to compounds containing a methylcyclopentyl moiety, ring opening, and dealkylation. Much less attention has been paid to five-carbon-membered-ring-containing compounds, which are, however, present in roughly as high as a mass fraction as the sixcarbon-membered-ring-containingfused-ring aromatics in many crude oils and coal liquids (Petrakis et al., 1983b; Guin et al., 1976). Fluoranthene was therefore chosen as the subject of the present investigation, the goal of which was the elucidation of the hydrogenation and hydrocracking reaction pathways and kinetics. Experiments were aimed at characterization of two catalysts (one amorphous and one containing zeolite) at temperatures and pressures of industrial processes (Unzelman and Gerber, 1965; Ward, 1975). The results include a quantitative model of the hydrogenation/ hydrocracking network of fluoranthene, which is expected to be useful as a basis for process modeling.
Experimental Section Hydroprocessing reactions were investigated isothermally at temperatures ranging from 310 to 380 O C and at a total pressure of 153 atm (2250 psig). Table I is a summary of the conditions of the experiments, including the catalysts, reactors, temperatures, pressures, and holding times. 0 1987 American Chemical Society
Ind. Eng. Chem. Res., Vol. 26, No. 5 , 1987 1027 Table 11. Properties of NiMo/Zeolite-Y and Shell 454 NiW/A1,OI Catalysts Shell 454 NiMo/ amorphous zeolite-Y pellet diameter, cm 0.159 0.318 bulk density, g/cm3 1.03 0.61 surface area, m2/g 133 625 pore vol, cm3/g 0.34 24.45 unit cell size, A composition, wt % Ni 4.36 5.9 W 27.2 Mo 10.9 SiOB 0.11 55.0 4 0 3 58.2 28.2 estd Thiele modulus and 0.36, 0.93 0.33, 0.94 effectiveness factor: 4, q
Materials. The reactant, fluoranthene (Aldrich, 98%), high-pressure hydrogen (Linde, 3500 psi), n-hexadecane solvent (Humphrey Chemical Co., specially distilled), gas chromatography standards, and sulfiding materials such as carbon disulfide (Fisher Scientific) and hydrogen sulfide (Matheson Gas Products; 90% H2/10% H2S) were all commercially available and used as received. The commercial catalysts were a Shell 454 NiW/A1203hydrogenation catalyst and NiMo/zeolite-Y hydrocracking catalyst. Both catalysts were equilibrated over a few months of stream time in hydroprocessing applications at Sun Oil prior to our treatment procedures. This minimized deactivation in the present experiments. The catalyst properites are summarized in Table 11, including the estimated Thiele modulus ($), which suggested the kinetics would be intrinsic. The catalysts were sulfided before use. The extrudates were first ground to 80-100 mesh, and then a 30 cm3/min flow of an H,S/H2 gas mixture (10% H2S)was passed over the catalyst particles as they were heated to and held for 2 h at 400 "C and atmospheric pressure. The sulfided catalyst particles were then introduced into the reactor after cooling for 1 h (Bhinde, 1979). Reactors. Two reactors provided complementary information. Reaction kinetics were measured with a 300cm3 stirred batch reactor (Autoclave Engineers) that allowed for reactant injection at time zero, periodic liquid and gas sampling, efficient liquid- and gas-phase agitation, and precise temperature and pressure measurement and control. This reactor was typically loaded with 150 cm3 of high-purity n-hexadecane solvent, 0.3 g of sulfided catalyst, and 0.07 g of carbon disulfide. After the system had been purged with hydrogen, it was heated to a temperature 5 "C higher than the reaction temperature to allow for some cooling upon injection of reactant. The hot reactor was then pressurized to 102 atm with hydrogen. Concurrently,a loading device containing 35 cm3of solvent and 1.2 g of the fluoranthene reactant was heated to 180-190 "C to ensure that all contents were in the liquid phase. Samples were removed from the reactor before the arbitrary time zero to allow measurement of the degree of the background thermal and catalytic cracking of the nhexadecane. A 0.5-pm pore size filter prevented removal of catalyst during sampling. A 51-atm excess driving force in the loader allowed rapid injection of the contents into the reactor and simultaneous pressurization of the reactor with 153 atm of hydrogen. Stabilization of the reactor temperature was rapid (typically occurring in less than 2 min). Liquid samples were withdrawn periodically for analysis. The reaction of fluoranthene in the absence of solvent was examined in 10-cm3tubing bomb reactors that were
connected to a motorized reciprocator mechanism to permit a vertical agitation at a rate of up to 300 cycles/min with a 7-cm maximum stroke. The reactant-to-catalyst ratio was the same as in the autoclave reactor experiments. A 1.0-cm-diameterstainless steel ball bearing was present in the reactor to ensure good mixing. After the introduction of hydrogen (75 atm at 25 "C), the reactor was heated to reaction temperature in a constant-temperature fluidized sand bath and quenched in a cool water bath after the desired reaction time. Gas sampling was achieved after the quenching by opening the reactor valve to a GC gas sampling valve. The liquid samples were then collected with methylene chloride for analysis. These experiments allowed analysis of the light products (one- and two-ring compounds and light paraffins) of fluoranthene hydrocracking that were obscured by products of n-hexadecane cracking in the autoclave. Analytical Chemistry. Reaction products were identified by GC/MS (with a Hewlett-Packard 5970 mass selective detector at the University of Delaware; by the MS analytical laboratory at Sun Company; and at The Pennsylvania State University Chandlee Laboratory) and by GC with coinjection of standards. Products were analyzed by GC. Condensed-phase products were separated in a 50-m SE-54 fused-silica capillary column and detected by flame ionization in a Hewlett-Packard 5880 gas chromatograph. Gas samples were analyzed by separation in a silica gel column and detection by thermal conductivity. Separately determined GC response factors, relative to the external standard (dibenzyl ether) and the internal standard (nitrogen) for liquid and gas analysis, respectively, allowed determination of product yields. These analyses permitted calculation of the GC-observable products index (OPI), defined as the sum of the mass of all observed products (including reactant) divided by the initial mass of reactant.
Results and Discussion NiW/A1,03 Catalyst. The major products from both autoclave and tubing bomb reactors were 1,2,3,10b-tetrahydrofluoranthene (THFL), 1,2,3,3a,4,5,6,6a,lOb,lOcdecahydrofluoranthene [SS-DHFL], and perhydrofluoranthene (PHFL), along with lesser amounts of 6b,7,8,9,10,10a-hexahydrofluoranthene (HHFL) and 1,2,3,6b,7,8,9,10,10a,l0b-decahydrofluoranthene [SADHFL]. The abbreviation SS depicts the naphthalene moiety of fluoranthene with both rings saturated, and the abbreviation SA refers to that moiety with one ring saturated. Table I11 is a summary of the chemical structures and representative product molar yields (moles of product/initial moles of fluoranthene). An OPI of 1.0 f 0.1 indicated essentially complete accounting of all reaction mass. Cracking was minimal in the presence of the hydrogenation catalyst; the four-ring products constituted approximately 95% of the products at all times. The results of autoclave experiments at 320, 350, and 380 "C are summarized in Table 111. The major products were THFL, SS-DHFL, PHFL, and SA-DHFL at each temperature. The molar yields of these products are plotted vs. reaction time at 320 "C and 153 atm in Figure 1. This plot illustrates that the major product, THFL, initially appeared at a rate closely matched by the rate of fluoranthene disappearance. The other products appear with essentially zero initial slopes in Figure 1, which indicates that THFL was the sole primary product. The THFL yield reached a maximum of 0.67 at approximately 90 min, and its decomposition led to the formation of SS-DHFL, which was detected after 28 min. The molar yield of SS-DHFL reached 0.30 after 250 min, and PHFL
1028 Ind. Eng. Chem. Res., Vol. 26, No. 5, 1987 Table 111. Reaction of Fluoranthene in the Presence of the NiW/A1203Catalyst in the Autoclave temp, "C 320 320 320 350 350 350 time, min 10 50 100 10 100 50 fractional conversion of fluoranthene 0.27 0.75 0.93 0.50 1.0 0.96 Product Molar Yields 0.25 0.07 0.50
fluoranthene
0.73
tetrahydrofluoranthene (THFL)
0.27
0.58
0.61
hexahydrofluoranthene (HHFL)
0
0
(SS)decahydrofluoranthene(SS-DHFL)
0
(SA)decahydrofluoranthene(SA-DHFL)
perhydrofluoranthene (PHFL)
7?
110
O .
nm.
380 100 1.0
0
0.30
0.01
0
0.46
0.67
0.42
0.55
0.26
0.04
0
0
0
0
0
tr
tr
0.06
0.12
0.03
0.27
0.43
0.10
0.59
0.38
0
0
tr
0
0
0.01
0
tr
0.01
0
0
0.10
0
0.01
0.12
tr
0.09
0.17
nu-nth.no
40
380 50 0.99
0.04
+ THFL
0
380 10 0.70
0
¶¶--DCIFL
4
MCL
200
(In,")
Figure 1. Product yields for reaction of fluoranthene catalyzed by NiW/Al,O, a t 320 O C and 153 atm.
was detected after approximately 90 min and reached a yield of 0.24 a t 250 min. THFL was also the sole primary product of the reaction a t 350 "C. The maximum in THFL yield for reaction a t 350 "C was 0.85 and occurred a t 47 min, a t which point
the rate of formation of SS-DHFL was approximately a maximum. SS-DHFL was the major secondary reaction product, and its maximum yield of 0.43 occurred a t 160 min. The yields of PHFL and SA-DHFL were discernible after 63 min, and the former product reached a yield of 0.24 at 160 min, while still increasing, whereas the yield of the latter product approached an asymptote of 0.05. Hydroprocessing at 380 "C was qualitatively similar to that observed a t the lower temperatures. Fluoranthene disappearance was faster than a t 350 "C, and its rate of disappearance was again essentially the same as the rate of THFL appearance. The rate of SS-DHFL appearance was greatest at 17 min, approximately the time a t which the maximum in THFL yield of 0.67 was observed. Secondary reaction of SS-DHFL to give PHFL was observed after 20 min. SS-DHFL achieved a maximum yield of 0.59 after 57 min, and the yield of PHFL reached 0.14 after 94 min. SA-DHFL appeared after 38 min but reached a maximum molar yield of only 0.02. Hexahydrofluoranthene reached a maximum molar yield of only 0.01 after 57 min. The foregoing results suggest that fluoranthene hydrogenation proceeded by the reaction pathways summarized
Ind. Eng. Chem. Res., Vol. 26, No. 5, 1987 1029
f 0.4
4 *A aw
0
nm
Figure 3. Product yields for reaction of fluoranthene catalyzed by NiMo/zeolite a t 310 "C and 153 atm.
Figure 2. Fluoranthene hydrogenation pathways. Table IV. Fluoranthene Hydrogenation and Hydrocracking Rate Constants: Arrhenius Parameters and Values at 380 "C rate const log A , cm3 of (380 "C),cm3 Ea& of soln/(g of soln/(g of reactiona catalvst s) kcal/mol catalvst s) Hydrogenation Pathways Observed with NiW/A1203 1 7.1 20.9 1.43 2 3 4
5 6
11.0 6.5 10.6 6.0 5.1
36.4 20.9 36.4 20.9 20.9
0.072 0.298 0.023 0.101 0.005
Hydrocracking Pathways Observed with NiMo/Zeolite-Y 6.9 20.7 0.935 a b 6.8 20.5 0.90 C
d e
6.9 6.7 8.3
19.5 19.1 26.3
sm
(mh)
2.57 2.11 0.33
in the network of Figure 2. THFL is the major primary product, and its subsequent hydrogenation yields SS-DHFL, the major secondary product. The hydrogenation of THFL also gives SA-DHFL, and subsequent hydrogenation of SS-DHFL and SA-DHFL yields PHFL. The initial rate of HHFL appearance was small but apparently nonzero at 380 "C, which suggests that HHFL was also a minor primary product. Fluoranthene disappearance was essentially first order in fluoranthene. Apparent first-order rate constants for all reactions in Figure 2 were estimated via the multiple search algorithm COMPLEX (Beveridge and Schechter, 1970). Those for fluoranthene disappearance are summarized in Table IV. The activation energies also reported in Table IV are consistent with the range 15-40 kcal/mol reported in the literature for catalytic hydrogenation of polynuclear aromatic compounds (Gates et al., 1979; Qader et al., 1973; Stephens and Chapman, 1983). The activation energies for dehydrogenation were substantially higher than those for hydrogenation,which is consistent with both the exothermicity of these hydrogenation reactions and also the literature (Stephens and Chapman, 1983). The solid lines in Figure 1represent predictions of molar yields of the major products calculated from these rate constants and the network of Figure 2. The rate constants for the reactions in the network other than those numbered 1-6 were assumed to be zero. The agreement between the predictions and experimental results is good. NiMo/Zeolite Catalyst. Reactions in both the autoclave and the agitated tubing bomb reactors with added NiMo/zeolite catalyst led to the major products THFL,
-
-1
0.4
0.1
oa
0. I
0.0
Figure 4. Molar yields of cracked products for reaction of fluoranthene catalyzed by NiMo/zeolite at 310 "C and 153 atm.
1-phenyltetralin, 2-phenyltetralin, 2-phenylmethylindan, tetralin, and benzene. Important minor products were 2-phenylnaphthalene, fluorene, cis- and trans-decalin, indan, toluene, methylcyclohexane, methylcyclopentane, cyclopentane, and light gases. Typical molar yields from reaction in the autoclave at 310,350, and 380 "C and the agitated tubing bomb at 380 "C are listed in Table V. Cracking was significant, as indicated by the decrease in time of the fraction of the OPI representing four-ring compounds. The yields of the major products of reaction in the autoclave at 310 "C are illustrated in Figure 3. THFL was the major primary product, reaching its maximum yield of 0.60 at 52 min. 1-Phenyltetralin appeared after approximately 35 min. 2-Phenyltetralin appeared shortly after 1-phenyltetralin, and its rate of formation was approximately a maximum when the yield of 1-phenyltetralin was a maximum. It is therefore likely that 1-phenyltetralin was the major secondary product and underwent a facile isomerization to 2-phenyltetralin. The minor yields of 2-phenylmethylindan illustrated in Figure 4 appeared shortly after the appearance of 2-phenyltetralin, which reached its maximum yield at approximately 240 min. Tetralin appeared at about 100 min, and its yield increased to 0.1 after 350 min. The OPI was >0.9 for the first 160 min (approximately 0.98 conversion) and >0.7 for the first 240 min. This drop in the OPI in the autoclave reactor was accounted for by the cracked products of fluoranthene in the tubing bomb reactor, which were obscured by the products of n-hexadecane cracking in the autoclave. Reaction at 350 "C gave THFL as the only major primary product, observed in maximum yield of 0.51 at 17 min; its subsequent reaction led to 1-and 2-phenyltetralin in maximum yields of 0.09 at 28 min and 0.33 at 44 min,
1030 Ind. Eng. Chem. Res., Vol. 26, No. 5, 1987 Table V. Reaction of Fluoranthene in the Presence of Reactors A A A reactof 310 310 310 temp, "C time, min 60 10 30 0.82 conversion of fluoranthene 0.24 0.57
NiMo/Zeolite Catalyst, in Both the Autoclave and Tubing Bomb
A 350 10 0.44
A 350 30 0.88
A 350 60 0.97
A 380 10 0.58
A 380 20 0.82
A 380 30 0.96
ATB 380 8
ATB 380
0.60
ATB 380 15 0.89
20 0.94
Product Molar Yieldsb (1)
1-phenyltetralin
0.76 0.24 0
0.43 0.42 tr
0.18 0.53 0.05
0.56 0.37 0.03
0.17 0.40 0.09
0.03 0.02 0.04
0.42 0.38 0.02
0.18 0.30 0.08
0.04 0.11 0.07
0.40 0.35 0.03
0.11 0.16 0.10
0.06 0.09 0.09
2-phenyltetralin
0
tr
0.18
0.02
0.20
0.33
0.03
0.15
0.25
0.03
0.23
0.25
2-phenylmethylindan
0
tr
0.02
0.01
0.03
0.02
0.02
0.05
0.07
0.01
0.06
0.09
tetralin (2) benzene 2-phenylnaphthalene fluorene cis- and trans-decalin methylindan indan toluene methylcyclohexane methylcyclopentane cyclopentane (3) methane ethane propane n-butane isobutane pentane
0
0
0.01
0
tr
0.10
0.01
0.04
0.09
0.01
0.02
0.03
0 0 0 0 0 0 0 0 0 0
0.05 tr tr tr tr 0.01 0.02 0.01 0.04 0.02
0.07 tr tr tr tr 0.01 0.02 0.01 0.05 0.03
0 0 0 0 0
0.02 tr tr 0.02 0.02 0.01
0.01 0.01 0.01 0.04 0.02 tr
fluoranthene
THFL
(I
A = autoclave; ATB = agitated tubing bomb.
t
C
0 Figure 5. Fluoranthene hydrocracking pathways.
0
tr = trace amount.
respectively. Only a minor amount of 2-phenylmethylindan was formed. The tetralin that formed was from the reaction of 1-phenyltetralin. The OPI was at least 0.83 for the first 30 min (0.85 conversion), after which is decreased to as little as 0.45 at 60 min. THFL was also the only major primary product from reaction at 380 "C. Its maximum yield was 0.39 at 13 min. The phenyltetralins were the major secondary products and reached a combined molar yield of 0.3 after 31 min. Tetralin appeared after about 7 min and had reached a molar yield of 0.11 after 31 min. The OPI was at least 0.9 for the first 20 min (0.80 conversion) and dropped to 0.74 after 30 min. The temporal variations of these yields suggest the hydrocracking network of Figure 5. The primary reaction pathway is hydrogenation of fluoranthene to give THFL, with subsequent bond scission leading to 1-phenyltetralin. This product undergoes isomerization to give 2-phenyltetralin, which in turn isomerizes to 2-phenylmethylindan. The major cracking pathway is the reaction of l-phenyltetralin to give tetralin and benzene followed by the reaction of tetralin to give methylindan, indan, alkyl-
Ind. Eng. Chem. Res., Vol. 26, No. 5,1987 1031 1.2
,
:I
1.1
-
1.0 I
0.e 0.a
X
0.8 0.7
0.S
TublnS momb nota: t
Clam. (2)
A
Tot01 1+2+3
0.0
0.0
0.2
0.1
0.4
0.8
1 .o
Fluorantheno Cmnrenlen
Figure 7. Autoclave OPI's compared with agitated tubing bomb OPI's for reaction at 380 "C.
benzenes, benzene, and probably other light products that were not observed. The decrease in OPI with reaction of phenyltetralins and phenylmethylindans indicates that the phenylnaphthenes likely cracked to give both one- and two-ring compounds and probably the other lighter products. Linear regression of the fluoranthene disappearancedata obtained at 310, 350, and 380 "C allowed determination of the pseudo-first-order disappearance rate constant. Parameter estimation through the COMPLEX algorithm yielded the remaining rate constants summarized in Table IV. The reactions are identified in Figure 5; each reaction is approximated as pseudo-first-order in the organic reactant. The kinetics of Table IV provide activation energies within the literature bounds of 15-40 kcal/mol for the hydrocracking of polynuclear aromatic and naphthenic compounds (Gates et al., 1979; Qader et al., 1973; Stephens and Chapman, 1983). Comparison of the solid lines (network predictions) and experimental points in Figures 3 and 4 shows that the data are consistent with this model. However, the network is complex and not unequivocally determined by the available data. The dependence of OPI on conversion is illustrated in Figure 6. The data from the three autoclave reactor experiments show that the OPI was close to unity as long as hydrogenation, isomerization, and ring opening reactions were limited to three- and four-ring compounds. After a conversion of approximately 0.6, when lighter products typically appeared, the OPI decreased to as little as 0.63. The data obtained from the agitated tubing bomb reactors show that this drop in OPI is due to the masking of lighter fluoranthene products arising from the cracking of the n-hexadecane solvent. Values of OPI determined from the autoclave and tubing bomb conversion data at 380 "C are shown in Figure 7. The conversions ranged from 0.22 to 0.94. OPI data are plotted for three product classes, namely, (1)products observed in both the tubing bombs and autoclave, (2) condensed phase products observed in the tubing bombs but not in the autoclave, and (3) gases observed only in the tubing bomb reactors. Thus, four plots of OPI vs. conversion appear in Figure 7. The first plot represents reaction in the autoclave reactor. The second plot represents reaction in a tubing bomb and is of the OPI for only those products that were observed in both the tubing bomb and autoclave reactors. The third plot is of condensed phase products observed in the tubing bombs but not in the autoclave. The fourth plot is of the OPI for gases, observed only in the tubing bomb reactors. OPI data from both reactors agree well for the first class of products. The decrease in total OPI observed at higher conversions in the
. H'
ti
+H*
Q$"
-3" 1,5
"
1 1 . 3 shlfl
shlfl
.H' ." ...
q-a&a Q Figure 8. Postulated mechanism for fluoranthene hydrocracking.
autoclave experiments is closely balanced by the increase in OPI for the second class of products with conversion in the tubing bombs. The sum of all classes of products from reaction in the tubing bomb yields an OPI of at least unity. Reaction Mechanisms. The initial products formed from the reactio'i of fused-ring aromatic compounds with hydrogen in the presence of hydrogenation and hydrocracking catalysts result from simple ring hydrogenation (Lemberton and Guisnet, 1984). The cracking reactions, which occur subsequently, require acidic sites and are limited to the opening of saturated rings formed by hydrogenation (Lemberton and Guisnet, 1984). In the case of fluoranthene, the major initial product also results from simple hydrogenation; this product is THFL. Initial hydrogenation is quite selective because of the relatively high reactivity of the fused Clo naphthalene-like fragment. Further hydrogenation of the remaining, lessreactive aromatic rings proceeds at a far lower rate than intial hydrogenation of the reactive ring in the presence of either catalyst. THFL undergoes facile hydrogenolytic cleavage to give 1-phenyltetralin at a rate greater than the rate of its further hydrogenation in the presence of the NiMo/zeolite catalyst. Protonation of THFL, illustrated in Figure 8,
1032 Ind. Eng. Chem. Res., Vol. 26, No. 5, 1987
produces an intermediate which can relieve considerable ring strain by cleaving to form the relatively stable benzylic carbenium ion. This relaxation of ring strain may provide the driving force for the rapid and selective cleavage reaction. Rapid isomerization of l-phenyltetralin occurs to give the thermodynamically more stable isomer, 2phenyltetralin. These two isomers are the only observed phenyltetralins. A possible mechanism for the isomerization of l-phenyltetralin to give 2-phenyltetralin involves the intermediacy of a nonclassical bridged phenonium ion similar to that proposed to explain some acid-catalyzed Wagner-Meerwein rearrangements and aromatic substitution reactions (Cram and Hammond, 1964). In these reactions, also illustrated in Figure 8, the aryl group is known to have substantial migratory aptitude. Since cracking reactions generally occur by opening saturated rings, it might be expected that the cracking of the phenyltetralins in the presence of the NiMo/zeolite catalyst would proceed by initial ring hydrogenation followed by the hydrogenolytic cleavage of the cyclohexyl ring. However, there was no evidence of cyclohexyltetralins in the product spectra, and the predominant single-ring product was benzene, not cyclohexane or methylcyclopentane. Thus, the major cracking reaction was the direct hydrogenolytic cleavage of phenyltetralin to tetralin and benzene. A possible mechanism for this reaction is illustrated in Figure 8 and involves the protonation of l-phenyltetralin to give a carbenium ion which rearranges to a stable benzylic carbocation by hydride transfer from the saturated ring. Inspection of both the Dreiding and space-filling molecular models of l-phenyltetralin and the possible intermediates of the reaction suggests the extremely facile nature of this conversion. l-Phenyltetralin is sterically crowded and the benzylic hydride which transfers is positioned within bonding distance to the carbocation. The driving force for hydride transfer is the formation of a more stable benzylic carbenium ion. Expulsion of benzene following a 18-hydride shift to ultimately produce tetralin relieves considerable steric strain. Note that 2-phenyltetralin is not capable of acid-catalyzed cleavage via a similar mechanism. It is therefore likely that the eventual depletion of 2-phenyltetralin occurs by facile hydrocracking of the l-phenyltetralin with which it is in equilibrium. In support of this mechanism, it was found that when l-phenylnaphthalenewas reacted over NiMo/zeolite at 380 "C in an agitated tubing bomb reactor, the major products were 1- and 2-phenyltetralin together with equimolar amounts of tetralin and benzene. This product profile is consistent with direct cleavage of the carbon-carbon bond between the aromatic rings of the intermediate 1phenyltetralin and not with prior hydrogenation of phenyltetralins to either phenyldecalins or cyclohexyltetralins since neither decalin nor cyclohexane was a major reaction product. Direct hydrogenolysis of the carbon-carbon bond between two aromatic rings is not a usual hydrocracking pathway and may be dictated in the case of l-phenyltetralin by a structure which permits the facile 1,5-shift shown in Figure 8. Under normal circumstances prior hydrogenation of one aromatic ring followed by acid-catalyzed dealkylation would be the preferred pathway. For example, when biphenyl was reacted over NiMo/zeolite in an agitated tubing bomb reactor a t 380 "C, benzene, cyclohexane, and methylcyclopentane were the major products. The yield of benzene roughly equaled that of the sum of the yields of cyclohexane and methylcyclopentane. A low yield of the presumed primary hydro-
Fiuaanlhsne
+ c4
i
Figure 9. Comparison of fluoranthene hydrocracking pathway with that characteristic of fused-ring aromatic compounds.
genation product, cyclohexylbenzene,was also observed. Thus, except in the case of the particular structure of l-phenyltetralin, which may provide a unique hydridetransfer pathway, the classical hydrocrackingpathway will predominate. Implications to Hydrocracking Processes. The primary reaction in both the hydrogenation and hydrocracking networks of fluoranthene is hydrogenation to give THFL. Although the cracking activity of the NiMo/zeolite catalyst is substantially greater than that of the NiW/ A120, catalyst, the overall activities of the two catalysts for the conversion of fluoranthene are approximately the same. The present results also suggest that both hydrogen consumption and product molecular weight will be different for five-carbon-membered-ring-containingcompounds such as fluoranthene, on the one hand, and sixcarbon-membered-ring-containing compounds such as phenanthrene and chrysene, on the other. This point is illustrated in Figure 9, which is a comparison of the fluoranthene network proposed here and the conventional hydrocracking pathways, involving terminal ring hydrogenation, followed by isomerization and ring opening, and dealkylation, for phenanthrene and chrysene. One mole of fluoranthene consumes 4 mol of H, to produce 1 mol of tetralin and 1 mol of benzene, whereas phenanthrene and chrysene consume 6 and 10 mol of H2, respectively, to produce 1mol of tetralin. Also, whereas hydrocracking of fluoranthene to give tetralin by the major reaction pathway shown in Figure 9 does not include the production of light paraffins (C, or lower), the hydrocracking of phenanthrene and chrysene to give tetralin by the traditional hydrocracking pathways of fused-ring aromatics includes the production of at least 1and 2 mol of gaseous products, respectively. We therefore conclude that fivecarbon-membered-ring-containingcompounds such as fluoranthene should be considered a separate class in the process modeling of heavy oil hydrocracking; the results presented here provide a basis for the modeling.
Conclusions 1. Hydrogenation of fluoranthene catalyzed by NiW/ A1203 yields tetrahydrofluoranthene, 1,2,3,3a,4,5,6,6a,lOb,lOc-decahydrofluoranthene,perhydrofluoranthene, as and 1,2,3,6b,7,8,9,10,10a,l0b-decahydrofluoranthene
Ind. Eng. Chem. R e s . 1987,26, 1033-1037
major products and hexahydrofluoranthene as a minor primary product. The major primary product is tetrahydrofluoranthene,which undergoes further hydrogenation until the ultimate stable product, perhydrofluoranthene, is formed. 2. Hydrocracking of fluoranthene catalyzed by NiMo/zeolite-Y also yields tetrahydrofluoranthene as the major primary product; cracking and isomerization follow. The major cracked products are 1-phenyltetralin, 2phenyltetralin, 2-phenylmethylindan, tetralin, and benzene. 3. The reaction networks for hydrogenation and hydrocracking are modeled as shown in Figures 2 and 5. The COMPLEX multiple search routine was used to estimate the pseudo-first-order rate constants in these networks, and agreement between network predictions and experimental results is good. 4. The cracking of the phenyltetralins may involve hydride abstraction steps; it does not involve ring hydrogenation prior to hydrogenolytic cleavage. This is further evidence that five-carbon-membered-ring-containing fluoranthene possesses kinetically significant cleavage pathways distinct from those observed for the sixcarbon-membered-ring-containing fused-ring aromatic compounds. 5. Five-carbon-membered-ring-containingcompounds should be regarded as a separate class in the modeling of complex heavy oil feedstocks; the data presented here provide a basis for the modeling. Registry No. Fluoranthene, 206-44-0.
Literature Cited Allen, D. T.; Petrakis, L.; Grandy, W.; Gavalas, G. R.; Gates, B. C. Fuel 1984,63,803. Beveridge, G. S. G.; Schechter, R. S. Optimization: Theory and Practice; McGraw-Hill: New York, 1970. Bhinde, M. V. Ph.D. Thesis, University of Delaware, Newark, 1979.
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Billon, A.; Franck, J. P.;Peries, J. P.; Fehr, E.; Gallei, E.; Lorenz, E. Hydrocarbon Process. 1978,May, 122. Cram, D. J.; Hammond, G. S. Organic Chemistry; McGraw-Hill: New York, 1964. Gates, B. C.; Katzer, J. R.; Schuit, G. C. A. Chemistry of Catalytic Processes; McGraw-Hill: New York, 1979. Gould, G. D.; Paterson, N. J.; Rogers, G. B.; Schultz, T. F. Chem. Eng. Prog. 1967,63,60. Guin, J.; Tarrer, A.; Taylor, L.; Prather, J.; Green, S., Jr. Znd. Eng. Chem. Process Des. Deu. 1976,15, 490. Huang, C.; Wang, K.; Haynes, H. W. Liquid Fuels from Coal; Ellington R. T.; Ed.; Academic: New York, 1977;p 63. Lemberton, J.; Guisne, M. Appl. Catal. 1984,13, 181. Petrakis, L.; Allen, D. T.; Gavalas, G. R.; Gates, B. C. Anal. Chem. 1983a,55, 1557. Petrakis, L.; Ruberto, R. G.; Young, D. C.; Gates, B. C. Ind. Eng. Chem. Process Des. Dev. 1983b,22,292. Petrakis, L.; Young, D. C.; Ruberto, R. G.; Gates B. C. Ind. Eng. Chem. Process Des. Dev. 1983c,22,298. Qader, S. A. J. Znst. Petrol. 1973,59,178. Qader, S. A.: Hill, G. R. PreDr.-Am. Chem. SOC..Diu. Fuel Chem. 1972,16, 93. Qader, S. A,; McOmber, D. B.; Wiser, W. H. Prepr.-Am. Chem. SOC.,Diu. Fuel Chem. 1973. 18. 127. Shabtai, J.; Veluswamy, L.; Oblad, A. G. Prep.-Am. Chem. SOC., Diu. Fuel Chem. 1978,23,107. Sullivan, R. F.; Scott, J. W. In Heterogeneous Catalysis Selected American Histories, Davis, B. H., Hettinger, Jr., W. P., Eds.; ACS Symposium Series 222;American Chemical Society: Washington, DC, 1983;p 293. Stephens, H. P.; Chapman, R. N. Prepr.-Am. Chem. SOC.,Diu. Fuel Chem. 1983,28,161. Stephens, H. P.; Kottenstette, R. J. Prepr.-Am. Chem. SOC.,Diu. Fuel Chem. 1985,30,345. Unzelman, G.H.; Gerber, N. H. Petrol. Chem. Eng. 1965,Oct. 32. Veluswamy, L. R. PhD Thesis, Univeristy of Utah, Salt Lake City, 1977. Ward, J. W. Hydrocarbon Process. 1975,Sept, 101. Wu, W.; Haynes, H. W. ACS Symp. Ser. 1975,20,65. Wuu, S.K.PhD Thesis, Univeristy of Alabama, Birmingham, 1983.
Received f o r review March 25, 1986 Accepted November 10, 1986
Kinetics of Extraction of Iron(II1) by Bis(2-ethylhexyl) Phosphate in a Laminar Liquid-Liquid Jet Reactor Sambandham Swaminathan, Tarun R. Das, and Ashok K. Mukherjee* Department of Chemical Engineering, Indian Institute of Science, Bangalore 560 012, India
The kinetics of iron(II1) extraction by bis(Zethylhexy1) phosphate (HDEHP, HA) in kerosene from sulfuric acid solutions has been studied in a liquid-liquid laminar jet reactor. The contact time of the interface in this reacting device is of the same order of magnitude as the surface renewal time in dispersion mixing and much less than that obtained in the relatively quiescent condition of the Lewis cell. Yet the analysis of the data in this study suggested a rate-controlling step involving surface saturation quite in conformity with that obtained in the Lewis cell and not with that in dispersion mixing as reported in the literature. Further, the mechanism suggested a weaker dependence of the rate on hydrogen ion concentration which was reported by other workers. Solvent extraction, in recent years, has become not only an indispensable technology in the recovery and processing of radioactive and rare-earth metals but also the only commercially viable technology to exploit mixed ores and ores of poor metal values, especially those of base metals. In the study of this interesting area, while greater attention has been devoted to the reagent selectivity and to the equilibrium distribution and stoichiometryof the extracted species, the kinetics of extraction has received relatively OSSS-5885/S7/2626-1033$01.50/0
less attention. However, the latter is essential for the proper selection and optimal design of the equipment for extraction. Depending on the situation, the extraction can be affected either by picking the desired metal values from its aqueous mixture with a host of other metals or by the removal of impurities from the aqueous solution. Our present study concerns itself with the latter aspect. We have opted to study the kinetics of extraction of iron(II1) by bis(2-ethylhexyl) phosphate (symbolizedby HDEHP). 0 1987 American Chemical Society
