Energy & Fuels 1994,8,823-829
823
An Investigation of Hydrogen Transfer from Naphthenes during Coprocessing Ruth M. Owens and Christine W. Curtis* Chemical Engineering Department, Auburn University, Alabama 36830 Received May 18,199P
Hydrogen transfer from naphthenes to aromatics,coal,resid, and coal plus resid has been investigated at 430 "C in a N2 atmosphere. The reaction of perhydropyrene (PHP) with anthracene (ANT) resulted in the formation of pyrene (PYR) and dihydroanthracene. The weight percents of the products formed varied according to the ratio of ANTPHP used with a minimum appearing at a 2:l weight ratio. Longer reaction times and high ANTPHP ratios also yielded tetrahydroanthracene. Reactions of Illinois No. 6 coal from the Argonne Premium Coal Sample Bank with PHP, ANT, and PYR resulted in higher coal conversion with PHP and lower with ANT and PYR. Reactions of PHP with resid resulted in less retrogressive reactions occurring in the resid than with either PYR or ANT. Apparent hydrogen transfer from coal or resid to ANT was observed. Combining PHP with ANT or PYR with coal, resid, or coal plus resid yielded higher conversions and less retrogressive reactions than with ANT or PYR alone. Hydrogen transfer occurred from PHP to ANT or PYR and to the coal and resid as evinced by the increased conversion and the reaction products obtained from the model system.
Introduction Coprocessingld of coal with petroleum resid involves the reaction of two materials that have quite different compositions. Since the goal in coprocessing is to upgrade both materials simultaneously, it would be advantageous to the process if the H-rich petroleum resid could transfer hydrogen to the H-deficient coal.6 H transfer from solvent molecules to coal has been shown to be beneficial to the conversion of coal to liquefied p r o d ~ c t s . ~ ~ ~ Coal is a complex material which undergoes many reactions. Derbyshire and Whitehurst8 postulated that coal dissolution in a non-hydrogen donor solvent such as pyrene occurred because pyrene acted as a H-shuttling agent. Derbyshire et al.gevaluated reaction pathways by which H transfer occurs in coal liquefaction. These reaction pathways included H transfer from a donor and H transfer between a donor and an aromatic species, in which the hydrogenated aromatic can then transfer hydrogen to coal. A number of researchers have postulated different mechanisms for H transfer. The traditional mechanism for H transfer was described by Curran et al.l0 in which thermally generated free radicals in coal were
* Author to whom correspondence should be addreseed.
Abstract published in Advance ACS Abstracts, May 15,1994. (1)Moechopedis, S.E.; Hawkins, R. W.; Fryer, J. F.; Speight, J. G. Fuel 1980,59,647-653. (2)Mochida, I.; Iwamoto, K.;Tahara, T.; Korai, Y.; Fujitau, H.; Takeahita, K.Fuel 1982,61,603-609. (3)Yan, T. Y.;Eepenschied, W. F. Fuel Process. Technol. 1983,7 , 121-133. (4)Curtis, C.W.;Hwang, J. 5. Fuel Process. Technol. 1992,30,47-67. (5) Ting, P. S.;Curtis, C. W.; Cronauer, D. C. Energy Fuels 1992,6, 511-518. (6)Olson, K.W.; Bedell, M. W.; Curtis, C. W. Fuel Sci. Technol. Int. 1993,11,1517-1538. (7)Bockrath, B. C. Chemistry of Hydrogen Donor Solvents. In Coal Science; Academic Press: New York, 1982;Vol. 2. (8) Derbyshire, F. J.; Whitehurat, D. D. Fuel 1981,60,656662. (9)Derbyshire, F. J.; Varghese, P.; Whitehurat, D. D. Fuel 1982,61, 859-861.
(10)Curran, G.P.;Struck, R. T.; Gorin, E. Ind. Eng. Chem. Process Des. Dev. 1967,6,166-173. 0887-0624/94/250&0823$04.50/0
stabilized by abstraction of hydrogen from a donor molecule. Virk and c o - ~ o r k e r s ~postulated ~-~3 a concerted pericyclic pathway for H transfer in which two hydrogens are simultaneously transferred from a H donor to an acceptor molecule. For these reactions to occur, the rules of conservation of orbital symmetry developed by Woodward and Hoffman had to be followed. King and Stock14 evaluated H-transfer reactions using the 1,2- and 1,4isomers of dihydronaphthalene and concluded that a concerted mechanism of H transfer was not supported by their data. McMillen et al.l6J6 have postulated the mechanism of radical H transfer in which hydrogen atoms are transferred from cyclohexadienylradical intermediates generated in the solvent to the ipso position in the substrate. In the mechanism, the solvent becomes an active agent in causing bond cleavage in coal liquefaction. In the coprocessing of coal with resid, petroleum resid MNW as the solvent and is composed primarily of saturated and naphthenic components,although some aromatics and hydroaromatics are present as well. The naphthene structures are H-rich and have the potential for transferring hydrogen to coal. Reactivity of cycloalkanes in liquefying coal was evaluated by Clarke et al.17 Cycloalkanes were used either alone or in conjunction with an aromatic species. The reactions of cycloalkanes, decalin, and perhydropyrene (PHP) alone with Annesley coal gave low conversionof coal and no conversion of the cycloalkanes to less saturated products. A mixed solvent of perhy(11)Virk, P.S.Fuel 1979,58,149-151. (12)Baas, D. H.; Virk, P. S. Prepr. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1980,25,17. (13)Virk, P.5.; Baas, D. H.; Epping, C. P.; Ekpenyong, D. J. Prepr. Pap.-Am. Chem. SOC.,Div. Fuel Chem. 1979,H (2),144-154. (14)King,H. H.; Stock, L. M. Fuel 1981,60,748-749;1982,61,1172-
1174; 1980,59,447-449. (15)McMillen, D. F.; Malhotra, R.; Hum, F. P.; Chang, S. J. Energy Fuels 1987,1,193-198. (16)McMillen,D.F.;Malholtra,R.;Chang,S. J.;Ogier,W. C.;Nigenda, S . E.; Fleming, R. H.Fuel 1987,66,1611-1619. (17)Clarke, J. W.; Rantell, T. 0.; Snape, C. E. Fuel 1984,63,14761478.
0 1994 American Chemical Society
Owens and Curtis
824 Energy & Fuels, Vol. 8, No. 4, 1994
drophenanthrene and octahydrophenanthrene yielded higher conversion of coal and conversion of octahydrophenanthrene to less saturated products, but the concentration of perhydrophenanthrene remained unchanged. Further experiments were performed with cycloalkane and aromatic mixtures where the aromatic species were phenanthrene and pyrene (PYR). These combinations resulted in higher coal conversions than did either component of the mixture reacted alone with coal. The cycloalkanes were converted to their hydroaromatic and aromatic analogues. McMillen and co-workers18 interpreted the results of Clarke et al.17 by examining the beneficial effect of combining polynuclear aromatic specieswith cycloalkanes on coal conversion. These authors claimed that the conventional coal liquefaction mechanism, where donor molecules provide hydrogen to cap free radicals, does not account for interactive effects. In these type of systems, both hydrogen Udonor"and 'acceptor" species are required. If the cycloalkanes used by Clarke et al.17 are considered representative of resid structures, McMillen et al.l8 suggested the following explanation for the observed activity of the combined cycloalkane/aromatic system. The thermally generated coal radicals abstracted hydrogen from the cycloalkanes and generated a cycloalkyl radical which underwent a bimolecular H transfer to a polynuclear aromatic acceptor by radical H transfer. The presence of polynuclear aromatics in the system can utilize hydrogens from perhydroaromatics into bond cleavage reactions in the coal system. The current research investigated H transfer from naphthene-type compounds that would be present in resids to H acceptors that would be present in coprocessing systems, such as aromatic compounds, coal, and resid itself. The concept being tested is whether naphthene molecules donate their hydrogen when hydrogen acceptors are present at the high-temperature conditions of coprocessing. If this type of H donation occurs, then the naphthene molecules present in resid could serve as an important source of hydrogen in coprocessing. Elucidation of this mode of H donation could provide valuable information concerning the mechanism of H transfer in resid-coal coprocessing reactions. In the current research, systematic sets of experiments were performed to evaluate whether hydrogen can be transferred directly from saturated naphthenic compounds to coal and resid during coprocessing. The initial experiments were performed using polynuclear aromatic species, anthracene (ANT)and PYFt, as acceptors for the hydrogen that could be abstracted from the naphthenes, PHP, or perhydroanthracene. These reactions were conducted at coprocessing temperatures of 430 "C in a Nz atmosphere. Reactions with Illinois No. 6 coal were then conducted to evaluate the effect of (1)PHP; (2)aromatics, ANT, and PYR and (3)PHP and each aromatic on coal conversion. The same set of reactions was performed with Maya resid: PHP with resid, each aromatic with resid, and PHP with each aromatic and resid. The final set of reactions performed involved PHP, an aromatic, coal, and resid. The analysis of each system consisted of evaluating the amount of hydrogenation and dehydrogenation that occurred from the H acceptor and H donor, respectively. In addition, coal, resid, and coal plus resid conversions were determined as appropriate and as defined in the (18)McMillen, D.F.; Malhotra, R.; Tee, D. S. Energy Fuels 1991,5, 179-187.
Table 1. Properties Illinois No. 6 Coal 8.0 c, % moisture, % 15.5 H, % ash, % volatile matter, % Btu
36.9 10999
0, %
s,%
77.1 5.0 13.7 4.9
Table 2. Properties of Maya Resid source of resid Mexico specific gravity, g/cm3 1.0535 Ramsbottom carbon, wt % 26.38 e,wt% 83.7 H,w t % 9.8 s, wt% 5.4 N, wt% NDo Ni, ppm 118 V,ppm 680 hexane solubles, wt % 71.8 hexane insolubles, wt % 28.2 toluene insolubles, wt % 0 a
ND = not detected.
Experimental Section. Base-line experiments were also performed with each individual reactant to evaluate the effect of the reaction conditions on the products produced from the individual species.
Experimental Section Materials. The chemicals used in this study included pyrene and anthracene from Aldrich Chemical with a purity of 99% or higher and perhydropyrene from Pfaltz and Bauer at a purity of 97% . Perhydroanthracene was synthesized by hydrogenating 1.0 g of hexahydroanthracene(obtained from Aldrich) at 380 O C for 60 min in the presence of 1.0 g of presulfided NiMo/AlpOa. Analysis of the synthesized perhydroanthracene by GC showed no contaminantsand that only perhydroanthracenewas present; no partially hydrogenated anthracenes were detected in the chromatogram. The coal used was Illinois No. 6 fromthe Argonne Premium Coal Sample Bank and resid was Maya resid from Amoco. The coal properties are given in Table 1and the resid properties in Table 2. The solvents used for the extraction analyses were toluene (TOL)and tetrahydrofuran (THF)from Fisher Scientific. Procedure. Model compound and coproceesingreactions were conducted in 20-cm3stainless steeltubular microreactors.The conditions for the model compound reactions were a reaction temperature of 430 "C, Nz at 400 psig at ambient temperature, and reaction times of 60,90, and 180 min. The reactor was well agitated at 450 cpm. For the single-component model reactions, 0.1 g of reactant was charged. For the binary component model reactions, the amount of individual reactant used ranged from 0.1 to 0.6g with the total amount of reactants charged ranging from 0.4 to 1.0 g. Following the reaction, the products were extracted with THF and analyzed by gas chromatography. The gaseous products from the reaction were analyzed using a Varian 3700 GC equipped with a thermal conductivity detector and a molecular sieve column. However, the amounts of gaseous hydrogen generated during the reaction were so low that the hydrogen was not detectable. The liquid productswere analyzed by using a Varian 3400 GC equipped with a HT-5 fused silica column from SGE and flame ionization detection. The internal standard method with biphenyl as the internal standard was used for quantitation. Identification of the producte was accomplished by GC mass spectrometry using a VG 70 EHF spectrometer. Recoveries of model compoundsfrom the reactions varied with the particular reaction but were usually between 80 and 100%. The reactante containingcoal and/or resid with model naphthene, aromatic, or both were reacted at the same conditionsas the model reactionsexcept that the reactionswere conducted for 60min. Each reactant was charged at a level of 1 g for the singlecomponent reactions, while for the two-, three-, and fourcomponent coprocessing reactions, the total amounts charged were 2.0, 3.0,and 4.0 g, respectively. After reaction the liquid
-
Hydrogen Trcrmfer from Naphthalenes
and solidproductswere eltractedwith TOLtoyieldTOL solubles and with THFto yield THFsolubka and IOM,which wasdefied as insoluble organic matter and was ash-free. The model compound apeciee introduced as reaktanta and their reaction productewerereaweredintheTOCeolublefractionand~ by GC using the same qualihtiie and quantitative methods as were used for the model compoundstudy. The recoveries from the coal reactions uauaUy ranged from 85 to 105% while thw from the reaid m c t i 0 1 usually ~ ranged from 80 to 100%. Definitionr for Model Syrtemr. The following defiitione of hydrogenation, dehydrogenation, and H efficiency were employed for this work in order to compare readily the results of the different reaction conditions. Percent hydrogenation is defied as the moles of hydrogen required to produce the liquid product as a percentage of the moles required to produce the mosthydrogeumted producttimea100%. Themost hydrogenated product from anthracene was defied as 1,!2,3,4-tetrahydroanthracene. One hundered percent hydrogenation is defiid as anthracene hydrogenating to a 100% yield of tetrahydroanthracene. One hundred percent dehydrogenationis defined 88 perhydropyrene dehydrogenating to yield 100% pyrene; thus, the percent dehydrogenation is equal to the percent yield of pyrene. H efficiency is the moles of hydrogen accepted by the acceptor to form partially eaturated speciesdivided by the moles of hydrogen donated by the donor times 100%. For every mole of pyrene f d from perhydropyrene,8 mol of hydrogen were donated; for every mole of dihydroanthracene formed from anthracene, 1mol of hydrogen was accepted;and for every mole of tetrahydroanthracene formed from anthracene, 2 mol of hydrogen were accepted. The amount of hydrogen present in the product gam was the difference in the amount donated and the amount accepted. Definitienr for Coal and h i d Syrtemta. For this study, coal conversion is defied as
whereIOMistheinsolubleorganicmattsrandmafcoalismoisture and ash free coal. Resid conversion is defied as
[
% resid conversion = 1-
gofloM ] X100% g of resid charged
(2)
Hence, resid conversion is that portion of the resid that remains THF soluble under the reaction conditions. Coal and resid conversion where both species are present is defied 88 % coal
+ resid conversion = of IOM I1 - of m a f d + g of resid charged] x 100% (3) g
Liquid to solid (L/S) ratio is defied as of toluene solublee = g of &IF solubles + g of IOM
,
Energy & Fuels, Vol. 8, No. 4, 1994 826
(4)
A term,degree of upgrading to toluene aolubles,was defied to
describe the degree of upgrading or degrading of the system in tern of the amountof toluene aolublespresent after the reaction. Degree of upgrading is defied as
degm of upgrading = of toluene eolubles M products - g of toluene eolubles as reactants g of upgradable materiale (5)
Upgradable materials are defied as maf coal for coal reactions, resid for resid reactions, and maf coal plus resid for coprocessing reactions. A positive number tor the degree of upgradingindicatea that upgrading o c d while a negative number indicah that retrogressive reactions occurred. Therefore, the value obtained
."."
liydrugemtion of ANT (percent) Y
* m
8.0{
6*O/#f 4.0
,)*?
~
2.0
~
0
.
0
*
o
_I
m
0
~
~::=","~ 0
60 Mln
0.0 0.0
2.0
4.0
6.0
8.0
10.0
12.0
ANTiPHP
Figure 1. Hydrogenation of anthracene as a function of anthracene to perhydropyrene ratio and time.
for degree of upgrading provided a means of comparimnamong the different reactions with coal, reeid, and coal plus resid.
Results and Discussion Hydrogen Transfer in the Model Reactions. Evaluation of H transfer in the model systems at coprocessing conditions included binary combinations of ANT or PYR with PHP and PYR with perhydroanthracene. When PHP, PYR, or ANT was reacted individually at 430 OC in nitrogen, none of them showed any reactivity; however, when perhydroanthracene was reacted under these conditions,-20% ANT was formed. Binary combinations of PHP and PYR were performed using a 1:lweight ratio of naphthene to aromatic. The only species present after reaction were the reactants; therefore, no net change was observed in the reaction products. Rsactions were also performed with perhydroanthracene as the naphthene and PYR as the aromatic in a 4:l ratio of aromatic to naphthene. Since only a small amount of perhydroanthracene was synthesized, the number of reactions performed was quite limited. When the same reaction conditionswere used as in the base-line reactions, less than 10% anthracene was formed from perhydroanthracene. This yield of anthracene was less than when perhydroanthracene was reacted alone. No hydrogenated forms of pyrene were detected in the products; hence, acceptance of hydrogen by pyrene from perhydroanthracene was not evident. A set of experiments was performed with the combination of PHP and ANT to determine if H transfer occurred between these two species at 430 OC in a N2 atmosphere. The measure used to determine H transfer was the production of hydrogenated anthracene speciesand of less saturated hydropyrenes or PYR. The initial experiment was performed with a 1:lweight ratio of ANT to PHP in Nz. Reactivity of both the donor and acceptor species was observed: dihydrotmthracenewas produced from ANT and PYR from PHP. The H transfer that occurred between the naphthene and aromatic in this reaction was unexpected since the previously mentioned reaction systems did not show any reactivity and since mixtures of naphthenes and aromatics teated by Clarke et al." did not produce any hydrogenated or dehydrogenated products. In order to verify the reactivity of the system and to determine if this reactivity was observed at different ratios of acceptor to donor, three seta of experiments were performed at 60, 90,and 180 min with weight ratios of ANT to PHP ranging from 0.14 to -10. H transfer between PHP and ANT occurred over the entire range of weight ratios. The results from these reactions are plotted in Figures 1and 2 as the hydrogenation of ANT and the dehydrogenation of PHP versus the weight ratio of ANT to PHP, respectively. At all three
826 Energy & Fuels, Vol. 8, No. 4,1994
Owens and Curtis
Dehydrogenatlonof PHP (percent)
I
Y
x 18.0
Table 3. Product Distributbn for Anthracene and Perhydropyrene Reactions
ANT/PHP 180 Min 90Miri
10.0 8.0 4.0 0
0.0
2.0
0
4.0
6.0
ao
10.0
ANT/PHP
Figure 2. Dehydrogenation of perhydropyrene as a function of anthracene to perhydropyrene ratio and time.
reaction times, 4-7 75 hydrogenation of ANT was observed at low ANT to PHP ratios of X1.5. A minimum was observed at ANTPHP ratios between 2.0 and 4.0 where 2% hydrogenation of ANT wae observed for all three reaction times. At higher ANTPHP ratios, increased hydrogenation of ANT was observed,particularly at longer times. The range of hydrogenation was between 4 and 10% with the 10% occurring at 180 min. The reaction product observed at low concentrations of ANT was dihydroanthracene. At higher ANT to PHP weight ratios, approximately 5 for 60 min, 4.5 for 90 min, and 4.0 for 180 min, production of tetrahydroanthracene was also observed (Table 3). Cronauer et al.lgevaluated the reverse reaction, dehydrogenation of 1,2,3,4-tetrahydroanthracene, in the presence of bibenzyl and found the formation of two products dihydroanthracene and anthracene. Hence, under thermal hydrogenation conditions the production of both dihydro- and tetrahydroanthracene is likely. Bermejo et aL20evaluated the hydrogen donoracceptor behavior of 9,10-dihydroanthracene in thermal reactions uaing coal. Reactions performed with mixtures of anthracene, dihydroanthracene, and coal yielded tetrahydroanthracene which was produced by either consecutive H transfer or concurrent thermal reactions involvingdihydroanthraceneand/or anthracene. Billmers et aL21have determined the kinetics of H transfer from 9,lO-dihydrophenanthrene to anthracene to form dihydroanthracene and found that the amount of dihydroanthracene present affected the rate of reaction. Dihydroanthracenewas the predominant product in the thermal H transfer to ANT from PHP. When the concentration of ANT and dihydroanthracene increased relative to PHP (weight ratios of 4 and 5)) tetrahydroanthracene was most probably formed from dihydroanthracene as would be indicated by a consecutive hydrogenation reaction. At higher weight ratios of ANTPHP increasing amounts of tetrahydroanthracene were formed, particularly at longer reaction times. This production resulted in increased ANT hydrogenation which is represented in Figure 1 as an upward slope of the curve at higher ANT:PHP weight ratios. Perhydropyrene dehydrogenated when reacted with ANT yielding PYR as the sole product. The hydrogen released in the reaction was transferred to ANT or to the gas phase. Figure 2 presents the dehydrogenation of PHP which increased almost 1inearlywithANTPHP ratio. The (19)Cronauer, D.C.; Jewel, D. M.;Modi,R. J.; Seahadri, K. 5.;Shah, V. T. Isomerization and Adduction of Hydroaromatic System at Conditione of Coal Liquefaction. In Coal LiquefactionFundamentals; ACS Symposium Series 139;Washington: DC,1980;pp 371-392. (20)Barmejo, J.; Canga, J.; Guillen, M.; Gayol, 0.;Blanco, C. f i e 1 Process. Technol. 1990.24.157-162. (21)Billmere, R.;Brown; R. L.; Stein,5. E. Int. J. Chem. Kinet. lS89, 21,375-388.
weight ratio
product distribution (mol %) ANTO
DHA
THA
PHP
PYR
tlomin 12.8 0.0 99.7 0.3 13.3 0.3 99.7 0.0 13.4 100.0 0.0 0.0 12.2 0.0 99.9 0.1 10.8 100.0 0.0 0.0 11.0 99.8 0.0 0.2 9.5 0.0 99.8 0.2 9.4 0.0 99.3 0.7 11.7 0.0 99.6 0.5 10.1 0.0 98.8 1.2 6.9 98.8 1.2 0.0 0.55 98.8 7.0 0.0 1.2 7.9 0.56 0.0 1.1 98.9 1.01 97,2 6.4 0.0 2.8 98.4 5.1 1.03 0.0 1.6 1.05 98.1 6.0 0.0 1.9 1.91 4.7 97.1 0.0 2.9 2.02 96.6 3.9 3.4 0.0 2.02 97.1 3.3 0.0 2.9 4.3 2.10 97.0 0.0 3.0 3.56 98.0 3.9 0.0 2.0 4.26 3.4 0.0 98.5 1.5 4.99 93.0 5.7 trace 7.0 5.02 93.7 6.6 1.5 6.3 5.3 5.89 94.3 0.0 5.7 5.4 5.94 90.3 trace 9.7 6.00 89.7 6.1 trace 10.3 92.4 6.7 6.20 trace 7.6 6.3 6.36 2.0 90.8 9.2 6.54 5.0 1.0 92.3 7.7 8.16 6.1 2.4 87.9 12.1 9.25 4.2 0.8 92.8 7.2 9.98 86.3 13.7 5.3 1.5 90min 0.52 93.5 6.5 0.0 98.4 1.6 0.53 93.5 6.5 0.0 100.0 1.0 92.1 0.53 7.9 0.0 2.1 97.9 94.9 1.02 5.2 2.5 97.5 0.0 95.3 1.02 4.7 97.1 0.0 2.9 94.5 1.03 97.8 5.5 0.0 2.2 92.9 1.06 7.1 0.0 2.2 97.8 1.93 93.3 97.0 6.7 0.0 3.0 96.7 2.02 3.3 0.0 3.4 96.6 95.7 2.06 4.3 0.0 3.5 96.5 96.1 3.97 3.9 0.0 92.2 7.8 4.53 93.6 6.2 1.2 94.5 5.5 91.9 6.1 4.99 2.0 87.2 12.8 90.3 7.5 5.52 91.2 2.2 8.8 92.1 5.5 6.50 2.4 83.3 16.7 95.7 7.10 1.1 3.2 89.5 10.5 91.5 6.0 8.00 13.2 2.5 86.8 8.52 96.8 3.2 94.1 0.0 5.9 180 min 0.51 89.6 10.4 0.0 98.1 1.9 2.08 96.3 3.7 0.0 93.7 6.3 96.7 3.3 0.0 3.00 4.5 95.5 93.1 3.94 5.4 1.5 6.0 94.0 95.9 5.26 4.1 0.0 10.1 89.9 93.4 6.52 5.4 1.2 6.9 93.1 85.8 6.97 9.0 5.2 21.2 78.8 87.8 7.54 8.3 3.9 23.5 76.5 91.3 8.52 16.1 83.9 6.9 1.8 a ANT = anthracene; DHA = dihydroanthracene; THA = tetrahydroanthracene;PHP = perhydropyrene; PYR = pyrene. 0.14 0.17 0.17 0.17 0.21 0.24 0.25 0.32 0.33 0.60 0.51
87.2 86.7 86.6 87.8 89.2 89.0 90.5 90.6 88.3 89.9 93.1 93.0 92.1 93.7 94.9 94.0 95.3 96.1 96.7 95.7 96.1 96.6 94.3 91.9 94.7 94.6 93.9 93.3 91.7 94.0 91.5 95.0 93.2
stoichiometric weight ratio for H transfer of ANTPHP is 6.63:l. Since PHP donated 8 mol of hydrogen for every mole of PYR formed and ANT accepted 1mol of hydrogen for every mole of dihydroanthracene formed, the H efficiency, which is the amount of H accepted divided by the amount of H donated, varied according to the ANT PHP weight ratio. Higher levels of H efficiency of 80-
Hydrogen Transferfrom Naphthalenes
Energy & Fuels, Vol. 8, No. 4, 1994 827
Table 4. Product Distributions for Anthracene and Perhydropyrene Reactions at Different Reaction Times
reaction time (min) 5 5 15 15 30 30 60 60 90 90 120 120 180 180
ANT/PHP weight ratio 4.00 6.11 3.95 6.13 3.99 5.26 4.26 6.00 3.97 6.50 4.53 6.52 3.94 6.97
product distribution (mol %) ANTb 97.3 98.0 97.0 96.4 95.4 95.8 96.6 93.9 96.1 92.1 92.3 89.3 93.1 85.8
DHA 2.7 2.0 3.0 3.6 4.6 4.2 3.4 6.1 3.9 5.5 6.5 7.3 5.4 9.0
THA 0.0 0.0 0.0 0.0 0.0 0.0 0.0 trace 0.0 2.4 1.2 3.4 1.5 5.2
PHP 100.0 100.0 100.0 100.0 100.0 100.0 98.5 89.7 92.2 83.3 93.4 85.0 94.0 78.8
PYFZ 0.0 0.0 trace trace trace trace 1.5 10.3 7.8 16.7 6.6 15.0 6.0 21.2
Reaction conditions: 430 "C,Nz. b ANT = anthracene;DHA = dihydroanthracene; THA = tetrahydroanthracene;PHP = perhydropyrene; PYR = pyrene.
100% occurred at higher weight ratios which were in the range of the stoichiometricweight ratio. Hence, PHP was a more efficient H donor when higher concentrations of ANT were present. Hence, H donation by the naphthene, PHP, was influenced by the type and amount of acceptor present. Both factors made a significant difference in achieving H transfer. Once some ANT was hydrogenated to the primary product dihydroanthracene, dihydroanthracene could serve as an acceptor for additional hydrogen released from PHP,20thereby forming tetrahydroanthracene. The effect of reaction time on H transfer from PHP to ANT was examined further (Table 4). Nominal ANT PHP weight ratios of 4 and 6 were used at six different reaction times of 5, 15, 30, 60, 120, and 180 min. The reactions, performed at 430 "C in N2, showed that with increasing reaction times, the amount of H transfer increased. Dihydroanthracene was the only detected product at reaction times of 30 min or less. At longer reaction times of 60 min or more, both tetrahydroanthracene and PYR were observed as reaction products. The weight ratio of ANTPHP as well as the reaction time influenced the amount of H transfer occurring. At equivalent reaction times,the amount of hydroanthracenes formed was greater at the higher weight ratios of 6.0-6.5, which was in the range of stoichiometric weight ratio for H transfer. Hydrogen Transfer in Coal and Resid Reactions. H transfer between naphthenes and aromatic species was
evaluated in the presence of coal, resid, and coal plus resid. The reaction conditions used for these reactions were the same as those used for the model reactions: 430 OC and a N2 atmosphere. Therefore, the only hydrogen that was available resulted from reactions of the reactants. Twelve different reaction systems were employed to evaluate H-transfer between naphthenes and aromatics as shown in Tables 5 and 6. The reactions were at least duplicated and the error observed is presented as standard deviations in these tables. In addition, Illinois No. 6 coal and Maya resid were reacted individually to provide a base line for their conversion and reactivity under the coprocessing conditions employed. It should be noted that the product distributions in terms of TOL solubles, THF solubles and IOM are dependent upon the totalnumber of Components used in a reaction system. The product distributions should only be used for comparison among the seta of components with the same number of reacting species. Coal Reaction Systems. The binary coal systems ranked in reactivity in terms of coal conversion to THF solubles as coal/PHP > coal/PYR > coal/ANT. The reaction of coal with PHP gave the highest coal conversion of 86% as compared to the coal systems with PYR and ANT, which yielded 38 and 13%, respectively. Coal conversion obtained with coal alone, without either naphthene or aromatic present, was 30 % ;therefore,neither ANT nor PYR promoted coal conversion to any extent. The coal used was Illinois No. 6 from Argonne Premium Coal SampleBank. The coal samples had limited exposure to air, so that only very mild oxidation of the coal samples should have occurred. Derbyshire and Whitehurste have shown that unoxidized coals with C contents ranging from 82 to 88%reacted with pyrene yielded increased conversion because H shuttling. Although only a small increase in coal conversion from 30 to 38% was observed with PYR in this study, H shuttling by PYR may account for the increased conversion over the reaction with coal alone. Anthracene did not participate in H shuttling and increased the amount of IOM produced substantially. When the naphthene PHP was reacted with coal, the substantial coal conversion observed in the coal/PHP system resulted in part from hydrogen transfer from PHP to coal. The aromatic dehydrogenation product PYR was produced during the reaction (Table 6). Both the amount of THF and TOL solubles produced during the reaction ranked the systems in the same order as the coal conversion (Table 5 ) . The THF solubles were similar for the three systems, ranging from 14.0 to 17.5% ,
Table 5. Coal and Resid Reaction Products from Thermal CoDrocessing - Reactions. system coal/PHPb CoaVANT COaVPYR coal/ANT/PHP coal/PYR/PHP resid/PHP resid/ANT resid/PYR resid/ANT/PHP resid/PYR/PHP resid/ANT/PHP/coal resid/PYR/PHP/coal coal resid
TOL solubles ( % ) 75.5 2.F 50.0 f 3.1 58.4 f 1.6 83.8 f 1.0 07.7 1.3 92.3 0.3 77.8 f 1.0 79.5 f 3.6 96.1 f 2.1 94.8 0.5 83.1 1.2 85.5 0.8 4.0 1.6 43.0
*
* *
* * **
THF solubles (% ) 17.5 0.7 14.0 f 1.7 15.2 f 2.7 8.2 f 0.9 7.1 0.7 6.2 f 0 9.4 0.2 12.6 f 3.2 3.0 f 2.1 4.1 0.3 6.9 f 0.9 6.5 f 0.5 31.2 f 0.7 35.2
* *
* *
IOM (% ) 7.0 f 1.5 36.0 f 1.3 26.4 f 1.1 8.0 f 0.1 5.2 f 0.5 1.5 0.2 12.8 f 0.8 7.9 f 0.5 0.9 f 0.1 1.1 f 0.2 10.0 0.4 8.0 f 0.4 64.8 2.3 21.0
*
* *
"Reaction conditions: 430 "C, 60 min, Nz.*ANT = anthracene; PHP = tetrahydrofuran. Standard deviation.
degree of liquid to upgrading (7%) solid ratio 24.0 f 3.4 3.1 -9.0 f 1.1 1.0 7.6 4.6 1.4 26.8 f 19 5.2 29.1 h 8.7 7.2 -47.6 f 1.9 12.0 -69.1 f 2.8 3.5 -55.4 f 4.1 4.0 -46.5 f 1.3 24.6 -45.1 f 9.7 18.4 -6.4 f 6.5 5.0 6.7 18 5.9 4.3 1.7 0.4 80.8 -61.8 f 2.4 0.8 perhydropyrene; PYR = pyrene; TOL = toluene; THF = conversion ( % ) 85.8 3.2 13.4 7.3 38.3 f 3.7 73.0 f 1.3 83.4 1.2 97.4 f 0.5 78.7 1.7 85.5 1.3 97.6 97.1 f 0.5 80.6 f 0.1 83.6 f 0.9 30.4 f 3.8
* *
~
*
**
*
~~
Owens and Curtis
828 Energy &Fuels, Vol. 8, No. 4, 1994
Table 6. Reactive Products from Model Donor and Acceptor Reactions in Thermal Coprocessing. system coal/PHP coal/ANT coal/PYR coal/ANT/PHP coal/PYR/PHP resid/PHP resid/ANT resid/PYR resid/ ANT/PHP resid/PYR/PHP resid/ ANT/PHP/coal resid/PY R/PHP/coal coal resid
DHA
ANTb
THA
C
-
-
89.6f 0.1
-
7.3 f 0.1
-
-
56.2 f 1.0
19.2f 2.3
24.7
3.1 f 1 1.4
PHP 89.8f 2.2
-
84.3 f 0.9 55.4 f 8.0 93.0 f 1.5
PYR 10.2 f 2.4
-
100.0f 0 15.7 f 0.8 44.6 f 8.0 7.0 f 1.4
-
-
82.8 f 4.2
-
3.8 f 0.2
-
-
-
-
-
66.5
-
17.4
-
16.1
-
64.5f 0.4
-
14.0 f 0.4
-
-
89.6 47.8f 5.3 69.7 f 1.5 52.5 f 13.3
100.0 f 0 10.4 52.4 f 5.4 30.3 f 1.6 47.5 f 13.3
-
-
-
-
13.4 f 4.4
-
21.5 f 0.1
-
-
-
hydrogen efficiency NAd NA NA 49.7 NA NA NA NA 60.6 NA 22.0 NA NA NA
0 Reaction conditions: 430 O C , 60 min, N2. b ANT = anthracene; DHA = dihydroanthracene; THA = tetrahydroanthracene; P H P = perhydropyrene; PYR = pyrene. e None of the compound is present. NA = not applicable.
but the TOL solubles varied considerably, ranging from 50.0% for the coal/ANT system to 75.5% coal/PHP system. Since PYR, an aromatic, should have a higher solvating power for coal than PHP, a naphthene, the substantially higher conversion obtained with PHP, compared to PYR, must have involved H transfer. In the PHP/coal reaction, more than 10% PYR was produced (Table 6) from dehydrogenation of PHP. This PYR originated from the PHP since the GC chromatogram of the coal reacted alone did not show any PYR peak. Likewise, the coal/PYR system did not show any reaction products from the PYR, indicating that, since an increase in coal conversion occurred, that PYR served as a H-shuttling agent rather undergoing hydrogenation (Table 6). Production of dihydroanthracene and tetrahydroanthracene in the coal/ ANT system indicated that hydrogen was transferred from coal to anthracene, since the coal was the only source of hydrogen. The ternary systems combined a naphthene and an aromatic with coal and were reacted under equivalent reaction conditions as the binary systems. Comparison of ternary systems showed higher coal conversion for the system of coal/PHP/PYR of 83.4% than for coal/PHP/ ANT of 73.0%. The coal/PHP/ANT system yielded somewhat lower TOL solubles than did the system with PYR. Lower coal conversion with ANT in the system may have resulted from ANT having a lower solvating power for coal than pyrene, a higher propensity for retrogressivereactions or alesser amount of hydrogen being available to coal since substantial ANT hydrogenation occurred (Table 6). The binary coal/PYR system indicated that pyrene may be acting as a H-shuttling agent. Pyrene may be acting as a H shuttler in the ternary system as well, although the exact source, whether the hydrogen came from coal or PHP, could not be determined. An equal weight amount of each reactant was charged to the reactor, but no net change in their amounts was observed after reaction. The error observed in the amounts of PYR and PHP present after reaction was much higher than in other ternary and binary systems, indicating some variability in the products produced and some possible changes in the amounts of each compound. The chemistry of this ternary system with PHP present was conducive for coal conversion while the coal/PYR system was not. Hence, the presence of PHP increased coal conversion possibly by shuttling hydrogen through PYR to coal. The addition of PHP to coal/ANT effectively blocked some of the retrogressive
reactions of ANT and increased coal conversion from 13% for the binary system to 73% for the ternary system. This same synergism between a naphthene and aromatic for increasing coal conversion was observed by Clarke et al." Substantial hydrogenation of ANT occurred in the coal/ PHP/ANT system resulting in 19.2 % dihydroanthracene and 24.7% tetrahydroanthracene. More than 15% pyrene was formed from PHP during the reaction (Table 6). Hence, PHP transferred hydrogen to both coal and ANT. Rasid Raaction System. The binary reactions of the model reactants with resid showed a substantial influence of the different reactants on the solubility of the resid. The resid prior to reaction was totally soluble in THF. Without added reactants in the N2 atmosphere, the resid underwent retrogressive reactions causing 20% of the resid to become THF insoluble. The addition of PHP resulted in 97 % of the resid remaining THF soluble. Neither the addition of ANT nor PYR blocked the retrogressive reactions occurring in the N2 atmosphere. However, the binary system with PYR kept more of the resid THF soluble (-86%) than did ANT at 79%. Hence, a difference in system reactivity between PYR and ANT was observed in thereaid system as it was in the coal system. Pyrene was more effectual in keeping resid THF soluble than ANT, possibly because PYR might have served as a H-shuttling agent among the different resid molecules. These binary systems yielded less THF solubles but substantially more TOL solubles than the resid did alone. The ranking of the binary systems in terms of maintaining THF and TOL solubles was resid/PHP > resid/PYR > resid/ANT. In the binary system, PHP transferred hydrogen to the resid with 7% pyrene being formed. In the resid/PYR system, neither the resid nor pyrene showed anyreactivity. But in the resid/ANT system, anthracene underwent substantial hydrogenation, accepting hydrogen from the resid and formingboth dihydro- and tetrahydroanthracene at 13.4 and 3.8%, respectively. The amount of the hydrogenated products present showed some variability in the two replicate reactions, but regardless, even in the reaction with lower extent of reaction, more than 13% hydrogenated products were formed. Of the three binary resid reactions, resid/ANT yielded the least amount of TOL solubles, intermediate amounts of THF solubles, and the most THF insolubles. The resid, in releasing some of its hydrogen to ANT, underwent changes that resulted in less solubility. In both the binary reactions with coal and with resid, ANT was a very active acceptor for hydrogen since both materials participated in H transfer to ANT.
Hydrogen Transfer from Naphthalenes
Ternary systems involving resid had similar resid conversions: 97 % for resid/PHP/PYR and 98 % for resid/ PHP/ ANT. These conversions were nearly equivalent to resid conversion obtained with the binary system of resid with PHP. Hence, regardless of the aromatic additive in the ternary system,the addition of PHP to resid enhanced resid upgrading in the Nz atmosphere and helped to inhibit retrogressive reactions. The amount of TOL and THF solubles produced during these reactions was quite similar (Table 5 ) . In resid/ANT/PHP reaction more than 30% of the ANT hydrogenated yielding 17.4% dihydroanthracene and 16.1% tetrahydroanthracene as products (Table 6). More than 10% PYR was produced. The H efficiency for this ternary system was quite high at 60.6% compared to the binary system at 49.7 % and quaternary system with resid/coal/ANT/PHP at 22.0%. Since ANT accepted -60% of the hydrogen released by PHP, 40% of the hydrogen released was available to the resid. A high level of TOL solubleswas produced from this reaction which may have been partially caused by the uptake of hydrogen by the resid. The resid/PYR/PHP system, however, showed no net change in the quantity of PYR and PHP present, although substantial variability in these amounts was observed. Since the level of resid conversion in the ternary system with PYR was similar to that obtained with ANT, H-transfer reactions or H shuttling have occurred between PYR and PHP; however, because the reactant and product compositions were the same, it was not possible to delineate the interactions between the reactants. Coal plus Resid Reaction System. Quaternary mixtures of resid/coal/PHP and PYR or ANT yielded similar coal conversions as the ternary system although the coal conversion in the reaction with ANT did increase somewhat. The amount of TOLand THF solublespresent in both quaternary reactions was nearly identical (Table 5). Substantial hydrogenation of ANT to dihydroanthracene at 14.0% and tetrahydroanthracene at 21.5% occurred while substantial dehydrogenation of PHP occurred,yielding 30 % PYR (Table 6). Anthracene only accepted 22% of hydrogen released by PHP, thereby leaving substantial hydrogen for uptake by coal and resid. These materials showed a relatively high combined conversion,indicating that hydrogen was accepted by coal and resid. In the quaternary systems with PYR and PHP, no net change in weight percents of PHP and PYR present after reaction was observed; however, a large variability in the quantities was again observed, which leaves open the possibility that H transfer or H shuttling occurred during these reactions. Degree of Upgrading. The effect of the different added species on the system performance was evaluated by comparing the degree of upgrading occurring in each system (Tble 5). The highest degree of upgrading occurred in coal systems in which PHP was present and the lowest with ANT present. Likewise, since the resid formed IOM in a Nzatmosphere at 430 OC, the least amount of degrading occurred in those resid systems that contained PHP and the most with ANT present. However, for the ternary systems with either coal or resid with PHP and PYR or ANT, the degree of upgrading with PYR or ANT was similar. For reactions with both coal and residuum, combined with either PYR or ANT, PYR had a slightly positive effect on the system compared to ANT. Pyrene acted like a H-shuttling agent while ANT was an active acceptor of hydrogen.
-
Energy & Fueb, Vol. 8, No. 4, 1994 829
Summary and Conclusions The H-donor and -acceptor ability of both coal and resid
has been demonstrated in this study. In a NZatmosphere and when no other donor was present, both coal and resid transferred hydrogen to anthracene, yielding 10.4 % conversion of anthracene to partially saturated products with coal and 17.2% conversion of anthracene with resid. Reactions of perhydropyrene alone did not show any conversion but perhydropyrene released hydrogen when reacted with H acceptors such as anthracene, coal, and resid in a N2 atmosphere. The amount of pyrene produced when reacted with anthracene depended upon the ratio of anthracene to perhydropyrene. In the coal reactions, 10.2% pyrene was formed, while in the resid reactions 7.0% pyrene was formed. Hence, a H acceptor was required in order for perhydropyrene to act as a donor. H transfer from perhydropyreneto aromatics, coal, and resid occurred as demonstrated by their respective conversions. Again the amount of anthracene converted to partially saturated compounds depended upon the ratio of the reactants, anthracene to perhydropyrene. Under the reaction conditions of this study, 85.8 5% conversion of coal was achieved with perhydropyrene compared to low conversions -38% with pyrene and -13% with anthracene. The resid retained nearly all of its solubility in THF when reacted with perhydropyrene while resid solubility in THF was less with aromatic species. The aromatic compounds, anthracene and pyrene, appeared to react differently in N2 at coprocessing temperatures. Anthracene reacted with the hydrogen released from perhydropyrene, coal, or resid producing primarily dihydroanthracene and a smaller amount of tetrahydroanthracene. Although hydrogen donation from these partially saturated anthracenes was possible, anthracene appeared to serve as a hydrogen sponge. Anthracene accepted donated hydrogen from perhydropyrene but did not appear to shuttle that hydrogen to coal or resid. By contrast, pyrene did not accept hydrogen from perhydropyrene as shown by the absence of partially saturated compounds. However, the coal and resid conversionsin the reactions indicated that pyrene shuttled hydrogen, released by perhydropyrene, coal, or resid, to achievethose conversions. Under the conditions employed in this study, H transfer was observed from the naphthene perhydropyrene to an aromtic,Illinois No. 6 coal and Maya resid.
Acknowledgment. We gratefully acknowledge the support of the Department of Energy under Contract No. DE-AC22-88PC88801 and UKRF-4-24351-90-84. The extensive help given by Tom Autrey on an earlier version of this manuscript is greatly appreciated. His comments and suggestionsconcerninghydrogen-transfermechanisms greatly strengthened this paper. We also appreciate the editorial support and wordprocessing skills given by Patricia Sandlin. Nomenclature ANT = anthracene IOM = insoluble organic matter maf = moisture and ash free PHP = perhydropyrene PYR = pyrene THF = tetrahydrofuran TOL = toluene
