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support and encouragement. This work was supported under U.S. Department of Energy Contract DE-AI81BC10525. References to brand names were made for identification only and do not imply endorsement by DOE or NRL. Registry No. Dimethylheptylpyridine, 95618-01-2; dimethylnonylpyridine, 95618-02-3; trimethylheptylpyridine, 95618-03-4;dimethyloctylpyridine,95618-04-5;trimethyloctylpyridine, 95647-74-8; trimethylhexylpyridine,95618-05-6; dimethylhexylpyridine, 95618-06-7; trimethylpentylpyridine, 95618-07-8;dimethylpentylpyridine,95618-08-9;methylpropyltetrahydroquinoline,95618-10-3. L i t e r a t u r e Cited Affens, W. A.; Hall, J. M.; Beal, E.; Hazlett, R. N.; Leonard, J. T.; Nowack, C. J.; Speck, G. ACS Symp. Ser. 1981, 163, 253. Bartlck, H.; Kunchal, K.; Swltzer, D.; Bowen, R.; Edwards, R. "The Production and Refining of Crude Shale 011 into Military Fuels", Final Report, Office of Naval Research Report No. N-00014-75-C-0055, 1975. Brinkman, D. W.. Bartlesville Energy Technology Center, personal communication, 1983. Burchill, P.; Herod, A. A,; Mahon, J. P.; Pritchard, E. J . Chromatogr. 1983a, 265, 223. Burchill, P.; Herod, A. A.; Prltchard, E. Fuel 1983b, 62, 11. Burchill, P.; Herod, A. A.; Prltchard, E. Fuel 1983c, 62,20. Cooney, J. V.; Beai, E. J.; Hazlett, R. N. Prepr. Div. Pet. Chem., Am. Chem. SOC. 1983, 28(5),1139. Cooney, J. V.; Beal, E. J.; Hazlett, R. N. Prepr., Div. Pet. Chem., Am. Chem. SOC. 1984a, 29(1), 247. Cooney, J. V.; Beal, E. J.; Hazlett. R. N. Li9. Fuels Techno/. 1984b, 2, 395. Cooney, J. V.; Beal, E. J.; Wechter, M. A,; Mushrush, G. W.; Hazlett, R. N. Prepr., Div. Pet. Chem., Am. Chem. SOC. 1984c, 29(4), 1003. Cooney, J. V.; Hazlett, R. N.; Beal, E. J. Second Annual Report, U.S. Dept. of Energy Report No. DOE/BC/10525-8, 1984d. Coordinating Research Council. "CRC Literature Survey on the Thermal Oxidation Stability of Jet Fuel", CRC Report No. 509; CRC, Inc., Atlanta, GA, 1979. Dahlin, K. E.; Daniel, S. R.; Worstell, J. H. Fuel 1981, 60,477. Daniel, S. R. Colo. Sch. Mines 0.1983, 7 8 , 47.
Dev. 1985, 2 4 , 300-306 Frankenfeld, J. W.; Taylor, W. F.; Brinkman, D. W. First Annual Report, U.S. Dept. of Energy Report No. DOE/BC/10045-12, 1981. Frankenfeld, J. W.; Taylor, W. F.; Brlnkman, D. W. Final Report, U S . Dept. of Energy Report No. DOE/BC/10045-23, 1982. Frankenfeld, J. W.; Taylor, W. F.; Brinkman, D. W. Ind. Eng. Chem. Prod.
Res. Dev. 1983a. 22, 608. Frankenfeid, J. W.; Taylor, W. F.; Brinkman, D. W. Ind. Eng. Chem. Prod. R e s . D e v . l 9 8 3 b , 2 2 , 615 Frankenfeld, J. W.; Taylor, W. F.; Brinkman, D. W. Ind. Eng. Chem. Prod. Res. Dev. 1983c, 22, 622. Goetzinger, J. W.; Thompson, C. J.; Brinkman, D. W. "A Review of Storage Stability Characteristics of Hydrocarbon Fuels, 1952-1982", U S Dept. of Energy Report No. DOE/BETC/IC-83/3, 1983. Hardy, D.; Hazlett, R. N.; Solash, J. Prepr. Div. Fuel Chem., Am. Chem. SOC.1982. 27(2), 201. Hazlett, R. N.; Cooney, J. V.; Beal, E. J. First Annual Report, U S . Dept. of Energy Report No. DOE/BC/10525-4, 1983. Holmes, S.A.; Thompson, L. F. Fuel 1983, 62, 709. Jones, R. A,; Bean. G. P. "The Chemistry of Pyrroles"; Academic Press: New York, 1977. Jones, L.; Hazlett, R. N.; Li, N. C.; Ge, J. Prepr. Div. Fuel, Chem., Am. Chem. SOC.1983, 28(1), 196. Klumpp, G. W. "Reactivity in Organic Chemistry"; Wiley: New York, 1982; pp 167-202. Lowry, T. H.; Richardson, K. S. "Mechanism and Theory in Organic Chemistry", 2nd ed.;Harper and Row: New York, 1981; p 670 ff. March, J. "Advanced Organic Chemistry", 2nd ed.; McGraw-Hill: New York, 1977; many examples appear throughout the text. Sheldon, R. A,; Kochi, J. K. "Metal Catalyzed Oxidations of Organic Compounds"; Academic Press: New York, 1981; Chapter 2. Solash, J.; Hazlett, R. N.; Hall, J. M.; Nowack, C. J. Fuel 1978, 57, 521. Solash, J.; Hazlett,R. N.; Burnett, J. C.; Beal, E.; Hall, J. M. ACS Symp. Ser. 1981. 163, 237. Waslik, N. J.; Robinson, E. T. ACS Symp. Ser. 1881, 163, 237. White, E. W. "Annual Technical Report for the Synthetic Fuel Characterization and Crude Assay Program", FY 1980, David Taylor Naval Ship R8D Center Report No. DTNSRDC-81/040, 1981. Worstell, J. H.; Daniel, S.R. Fuel lg81, 60, 481. Worstell, J. H.; Daniel, S. R.; Frauenhoff, G. Fuel 1981, 60, 485.
Received f o r review August 13, 1984 Accepted December 12, 1984
Pyrolysis of Benzylphenylamine Neat and with Tetralin, Methanol, and Water Solvents Martin A. Abraham and Michael T. Kieln' Department of Chemical Engineering, University of Delaware, Newark, Delaware 197 16
Benzylphenylamine(BPA) pyrolysis was studied neat and in tetralin, methanol, and water solvents. Pyrolyses neat and in tetralin yielded aniline, toluene, and benzalanilineas major low-molecular-weight products, with selectivity to the former two being higher during the slower pyrolysis in tetralin. A reaction pathway that involved unimolecular reaction of BPA to an intermediate species that reacted with either BPA or tetralin to form products was likely operative. Pyrolyses in supercritical methanol and subcritical and supercritical water yielded benzyl alcohol plus methylaniline or benzyl alcohol, respectively, in addition to those products observed from pyrolyses neat and in tetralin. Kinetics were slower than observed in neat pyrolysis, and of three candidate pathways considered, namely (a) reaction of the solvent with the neat pathway intermediate, (b) solvation and subsequent solvolysis of BPA, and (c) direct solvolysis of BPA, only the first two were consistent with experimental observations. The chemically intrinsic utility of reaction with supercritical methanol or water is that these solvents are both hot and dense, which cause solvolysis reaction rates to be high.
Introduction
The dramatic effect of pressure on density and hence solvent power (Paulaitis et al., 1983) of a fluid near its critical temperature has motivated considerable interest in the supercritical fluid (SCF) solvent extraction of volatile products from alternate fuel feedstocks (Whitehead and Williams, 1975). Laboratory experiments with coals (Amestica and Wolf, 1984) and biomaterial (Modell, 1977) collectively suggest that high yields of products and re0196-4321/85/ 1224-0300$01.50/0
duced levels of coke can be attributed to operation in SCF solvents. However, the chemically intrinsic fundamentals underlying advantages attributable to SCF solvents remain obscure and equivocal, largely on account of the complexity of the conversion of actual feedstocks to complex product spectra. Model compounds provide insight into the intrinsic chemistry underlying the reactions of actual macromolecules (Brucker and Kolling, 1965; Benjamin et al., 1978; 1985 American Chemical Society
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Schlosberg et al., 1981; Cronauer et al., 1979). Their comparatively simple structure and product spectra allow deduction of model compound reaction pathways (Klein and Virk, 1983), kinetics (Cronauer et al., 1979)) and mechanisms (King and Stock, 1984; Simmons and Klein, 1985) and also inference of the same fundamentals controlling the conversion of macromolecules (Petrocelli and Klein, 1984). Along these lines, previous analyses of dibenzyl ether (Townsend and Klein, 1984) and guaiacol (Lawson and Klein, 1984) pyrolyses in supercritical water (SCW) revealed chemical reaction between the substrate and solvent to be competitive with fragmentation routes observed from pyrolysis neat (Schlosberg et al., 1981; Klein and Virk, 1981) and in tetralin (Connors et al., 1980; Cronauer et al., 1979; Kamiya et al. 1979). The possibility that such solvolysis reactions might more generally occur between heteroatom-containing solutes and solvents motivated the present investigation of benzylphenylamine (BPA) pyrolysis neat and in tetralin, methanol, and water solvents. BPA pyrolysis neat and in tetralin has been studied previously (Miller and Stein, 1979; King and Stock, 1984). Miller and Stein determined rate constants for both gas and liquid phase (in tetralin) BPA pyrolysis and proposed a free-radical reaction mechanism. King and Stock showed BPA fragmentation in tetralin at 400 "C to be facile and accelerated by additives such as coal, benzylphenyl sulfide, and phenol. The present analysis extends the foregoing to include the influence of subcritical and supercritical methanol and water solvents on product identities, yields, and temporal variations. The latter information was also obtained for pyrolysis neat and in tetralin in order to deduce and discriminate between candidate reaction pathways. We also complement the earlier analyses of pyrolysis in supercritical water that examined (a) the influence of temperature (Townsend and Klein, 1984) above 373 "C, the critical temperature of water; and (b) the influence of solvent density (Lawson and Klein, 1984) by probing the influence of temperature below the solvent's critical temperature. Collectively, these analyses were aimed at the elucidation of both reaction network information and also any unusual benefits of operation near the critical temperature. We present these analyses as follows. Experimental methods are described first. We then delineate experimental results, namely: (a) product identities; (b) the temporal variation of individual product yields; and (c) pseudo-first-order kinetics for BPA disappearance; sequentially for pyrolysis neat, in tetralin, in methanol, and in water. Our discussion concerns the development and scrutiny of plausible reaction pathways.
Experimental Section Pyrolyses of N-benzylphenylamine (BPA) were effected neat, in tetralin, in methanol, and in water. All experiments were at 386 " C except for pyrolyses in water (T, = 373 O C ) a t 340 "C and methanol (T, = 240 "C) a t 250 and 340 "C. The reactant, solvents, and GC standards were all commercially available and used as received. A typical experimental procedure was as follows: BPA, solvent, and the demonstrably inert (Townsend and Klein, 1984)internal standard, biphenyl, were loaded into batch "tubing bomb" reactors comprising one Swagelok port connector and two caps of 'I4-in. nominally sized stainless steel parts. The tubing bombs were sealed and immersed in a constant-temperature sandbath. The reactors reached 90% of the desired reaction temperature in 2 min and the desired temperature in 3.5 to 5 min. Reactions were quenched by placing the tubing bombs in a cold water bath. Spectrophotometric grade acetone was used to collect all material from the reactors in one phase. Product identification was accomplished by GC-MS. Major reaction products were benzyl
0.8
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Figure 1. Temporal variations of the molar yields of major neat BPA pyrolysis products at 386 "C.
n J
$
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e
a
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Figure 2. Temporal variations of the molar yields of major products of BPA pyrolysis in tetralin at 386 "C.
alcohol, aniline, toluene, N-methylaniline, benqalaniline, and additional higher weight oligomers of BPA. Quantitation of individual product yields was by GC. An H P 5880 instrument equipped with a 50-m SE-54 fused silica capillary column and a flame ionization detector was used. Response factors were estimated from analyses of standard mixtures containing all but the oligomeric products; their yields were estimated by assuming a response factor equal to that for biphenyl. Experimental uncertainty was approximately i20%. Quantitative calculation of product yields allowed estimation of an observable product material balance index (MBI) as the sum of the mass of identified products divided by the initial mass of BPA charged.
Results Neat pyrolysis of N-benzylphenylamine (BP4) at 36 "C yielded aniline and toluene as major product along with lesser amounts of benzalaniline. The total iormalized weight of identified products (MBI) decreased with time but always remained greater than 0.75. The temQoral variations of product yields (mol of ilinitial mol of BPA) are shown in Figure 1. Aniline, toluene, and benzalaniline appear with positive slopes in Figure 1 and were thus primary products. Aniline and toluene yields of 0.6 and 0.5 were achieved after 30 min, while a benzalaniline yield of approximately 0.2 was observed in the same time. BPA conversion was essentially 1.0 after 30 min, and a leastsquares estimate of a corresponding pseudo-first-order rate s-l. constant is 2.06 X The major products observed from BPA pyrolysis in tetralin at 386 "C were toluene and aniline; benzalaniline, once again a minor product, was found in lesser yields than in neat pyrolysis. MBI varied slightly but always remained between 0.70 and 0.90. Product yields as a function of time are shown in Figure 2. As for neat pyrolysis, the initial slopes of toluene, aniline, and benzalaniline are positive in Figure 2, indicating that these were primary products.
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Figure 3. Temporal variations of the molar yields of major products of BPA pyrolysis in dense methanol at 386 O C .
Yields of toluene and aniline were 0.5 and 0.4, respectively. Benzalaniline yield reached a constant level of 0.1 after 30 min. A pseudo-first-order rate constant of 2.73 X s-l for BPA disappearance was considerably less than the corresponding value for neat pyrolysis. Comparison of Figures 1 and 2 reveals that neat BPA pyrolysis was more rapid than its reaction in tetralin. Also, the yield of benzalaniline from neat pyrolysis was nearly twice that from pyrolysis in tetralin. This indicates that whereas BPA served as its own source of hydrogen during the fragmentation of the central C-N bond during neat pyrolysis, tetralin served as a competitive but not unique hydrogen source during the BPA pyrolysis in solvent. In addition, MBI was always higher from pyrolysis in tetralin, which indicates that benzalaniline and other hydrogen deficient species likely polymerized during neat pyrolysis. BPA pyrolysis in supercritical methanol a t 250 "C ( T , = 1.02, pr = 1.31) yielded no significant products after 90 min. Recovery of a product spectrum containing predominantly BPA was in material balance. The observed BPA conversion of approximately 0.03 corresponds to a pseudo-first-order rate constant of 6.83 X s-l. BPA pyrolysis in supercritical methanol at 340 "C (TI = 1.20, p r = 1.31) yielded aniline and toluene as major products, along with lesser amounts of benzyl alcohol and N-methylaniline. MBI was 0.65 or higher. Toluene and aniline yields were approximately 0.06 and 0.05, respectively, after 60 min, a t which time the yields of benzyl alcohol and methylaniline were about 0.03. A BPA conversion of 0.50 after 60 min corresponds to a pseudofirst-order decomposition rate constant of 1.92 X s-l. Pyrolysis of BPA in supercritical methanol at 386 "C (TI = 1.29, pr = 1.31) yielded toluene, aniline, benzyl alcohol, and N-methylaniline as major products. MBI decreased with time but remained above 0.70 after 60 min. The time dependence of product yields illustrated in Figure 3 shows that toluene, aniline, benzyl alcohol, and N-methylaniline all have initial positive slopes and thus were all primary products. Benzyl alcohol and N-methylaniline yield coincided for the entire experiment and achieved a yield near 0.2 after 60 min. Toluene yield achieved an asymptotic value of approximately 0.4 after 60 min, at which time aniline had achieved an asymptotic yield of 0.15. BPA conversion was 0.80 and a pseudo-first-order rate constant of 4.88 X s-l characterized its disappearance. Pyrolysis of BPA in water a t 340 "C (subcritical) yielded aniline, toluene, and benzyl alcohol as the major products. MBI was initially near 0.80 (at 0.3 conversion) but fell to approximately 0.50 at 60 min. Product yields as a function of time are shown in Figure 4, which indicates by initially positive slopes that the major products were also primary products. The aniline yield was constant a t 0.4 after 20 min. Toluene yield increased slowly with time, reaching
an ultimate yield of approximately 0.05 after 60 min. Benzyl alcohol achieved a maximum of approximately 0.2 at 15 min and dropped continuously to near zero in 60 min. BPA conversion was about 0.80 after 40 min, and a pseus-l describes this do-first-order rate constant of 2.8 X rate of BPA conversion in subcritical water. Aniline, toluene, and benzyl alcohol were also the major products of BPA pyrolysis in supercritical water (SCW) a t 386 "C (TI = 1.02, pr = 1-09). MBI was generally low, remaining between 0.40 and 0.60. The temporal variation of the yields of these products is shown in Figure 5, wherein initial slopes indicate that these were primary products. The yield of aniline was 0.5 after 50 min, whereas the yield of toluene was only about 0.2 after the same time. The yield of benzyl alcohol decreased after it reached a maximum of 0.1 in 15 min. BPA conversion was near 0.80 after 30 min, and a pseudo-first-order rate constant of 6.60 X s-l characterized the rate of BPA disappearance in SCW. Further scrutiny of the product yields shown in Figures 4 and 5 provides reaction pathway information. A t 340 "C the aniline yield of 0.4 was close to the asymptotic yield of 0.5 a t 386 "C. The toluene yield of 0.2 a t 386 "C was significantly larger than its yield of 0.05 a t 340 "C. The yield of benzyl alcohol, however, was maximum at only 0.1 at 386 "C in contrast to a peak yield of 0.2 at 340 OC. These results can be accounted for by competitive hydrolysis and cracking pathways. Aniline, the yield of which was not affected significantly by temperature, would be a product from both. Toluene, the yield of which increased with temperature, would be a product of the cracking pathway. Finally, benzyl alcohol, the yield of which decreased with increasing temperature, would be a product of the hydrolysis pathway.
Discussion Preliminary reaction pathways that summarize the observed product spectra and kinetics trends would be useful information. Comparative scrutiny of individual product yields provides for this and is accomplished sequentially within the product spectra from pyrolysis neat and in tetralin, methanol, and water solvents. Neat Pyrolysis. Figure 1showed aniline, toluene, and benzalaniline to be the major primary products observed from neat BPA pyrolysis. Independent of mechanistic details, BPA fragmentation to near equimolar proportions of aniline and toluene evidently required additional consumption of BPA to maintain hydrogen balance. The latter led to benzalaniline, in lesser proportions than toluene and aniline, and, presumably, other higher molecular weight carbon-rich products. These results are summarized and interpreted in pathway 1 of Table I. In pathway 1,BPA reacts unimolecularly to some unspecified activated or intermediate species I* that can collapse back to BPA or consume another BPA molecule in the formation of 1 mol each of toluene and aniline and a molar equivalent (relative to BPA) of benzalaniline and other carbon-rich products (CRP). Note that I* is not intended to be of mechanistic significance and might equally well depict either an intermediate in a pericyclic pathway analogous to that proposed by Virk (1979) for benzyl phenyl ether pyrolysis or a benzyl-aniline radical pair (Miller and Stein, 1979;King and Stock, 1984). In any event, pseudo-steady-state kinetics are predicted to be first order in BPA at high BPA concentration and second order at very low concentrations. Pyrolysis in Tetralin. Aniline, toluene, and benzalaniline were also the major primary products of BPA pyrolysis in tetralin. Pseudo-first-order rate constants for
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Figure 4. Temporal variations of the molar yields of major products of BPA pyrolysis in water at 340 "C.
BPA disappearance of 2.06 X s-l and 2.73 X s-l for pyrolysis neat and in tetralin, respectively, indicated that tetralin inhibited BPA decomposition. The initial slopes for aniline, toluene, and benzalaniline appearance in Figures 1 and 2 also showed the rate of formation of these products to be slower in tetralin than for neat pyrolysis. However, the asymptotic selectivity of BPA reaction to toluene was 0.68 and 0.85 (mol of toluene formed/mol of BPA reacted) for pyrolysis neat and in tetralin, respectively, which suggests that tetralin competed with BPA as a hydrogen donor. This rather passive hydrogen donor activity is interpreted in pathway 2 of Table I, which includes neat BPA pyrolysis as a limiting case. Thus, the initial reaction of BPA to I* is followed by its fragmentation to toluene and aniline through reaction with either BPA or tetralin; in the former case benzalaniline and other CRP form, whereas in the latter situation naphthalene forms. The reaction of I* with tetralin reduces the overall rate of BPA disappearance relative to neat pyrolysis kinetics, as is indicated by the pseudo-steady-state solutions of pathways 1and 2 that are listed in Table I. In the limiting case of high tetralin concentrations [and lesser but still high BPA concentrations, i.e., kl(BPA) > k-11, the rate would be halved relative to neat BPA pyrolysis. Pyrolysis in Methanol. BPA pyrolysis in methanol was qualitatively different from its pyrolysis neat or in tetralin. Major primary products included benzyl alcohol and methylaniline as well as the toluene and aniline observed from pyrolysis neat or in tetralin. The rate of disappearance of BPA was intermediate between that observed for pyrolysis neat and in tetralin. These observations allow tentative elimination of only one of the three candidate pathways 3a, b, and c set forth in Table I. In pathway 3a, methanol acts as a passive solvent similar to the role of tetralin discussed above. Methanol could also be a more active solvent that participates in a reaction with BPA and not I*. In this case we consider situations where: (3b) cage effects (Labrecque et al., 1984;Lawson and Klein, 1984) occur to form solvated BPA molecules that undergo subsequent reaction with methanol to methylaniline and benzyl alcohol, or (3c) cage effects are not present and the fragmentation of BPA to methylaniline and benzyl alcohol is a direct bimolecular reaction. Caged or solvated BPA molecules are represented in Table I as BPA*. Two major assumptions were used in the kinetics analysis below. First, solvated molecules (BPA*), prevented from undergoing the neat or intetralin pyrolysis reaction to I*, were considered to be the unique precursors to the methylaniline and benzyl alcohol solvolysis products. Second, the solvation of BPA to BPA* was considered to be rapid and in virtual equilibrium a t reaction conditions. Gas chromatographic (GC) analyses
of quenched product spectra would thus be of the observable BPA" = BPA + BPA*. Pseudo-steady-state analysis of the pathways delineated above yields the corresponding rate expressions (3a, 3b, and 3c) listed in Table I. The rate expression for the case where reaction of methanol with I* is predominant, 3a is functionally identical with the rate expression for pyrolysis in tetralin, and thus correctly indicates the observed inhibition of BPA decomposition relative to its neat pyrolysis. The kinetics of BPA disappearance for the case where cage effects occur (3b) are more complex. At moderate concentrations of methanol its solvation of BPA would hinder BPA decomposition through the neat pyrolysis pathway. This would be in accord with the present experimental results. However, increases in methanol concentration would increase the rate of disappearance of BPA by the solvolysis route to higher values than the neat pyrolysis rate. The rate expression for the superposition of bimolecular solvolysis and neat pyrolysis of BPA (312)predicts that, at a given value of BPA concentration, the solvolysis rate is directly additive to the neat pyrolysis rate. This is in contradiction with the present experimental findings. In summary, our preliminary conclusion derived from BPA disappearance kinetics is that methanol may act either as a passive solvent (3a) or as an active solvent that cages the BPA reactant (3b); a direct solvolysis of BPA by methanol (34 appears unlikely. Pyrolysis in Water. Inspection of BPA pyrolysis in water at 340 and 386 "C provides further details. Aniline, always the major primary product at both 340 and 386 "C, was accompanied by lesser amounts of benzyl alcohol and toluene, with the former being more prevalent a t 340 "C and the latter being more prevalent at 386 "C. Thus, the route to toluene formation was more thermally activated than the pathway to benzyl alcohol, although both led to aniline as a coproduct. BPA decomposition kinetics in water a t 386 "C were slightly slower than observed from neat pyrolysis at the same temperature; kinetics were clearly slower at 340 "C. Finally, the secondary degradation of the benzyl alcohol produced during dibenzyl ether pyrolysis in SCW (Townsend and Klein, 1984) was also observed here. Comparison of this information with pathways 3a, b, and c of Table I is analogous to that for BPA pyrolysis in SCM. We thus consider pyrolysis where: (3a) water is a passive solvent (like tetralin) that reacts only with I*; (3b) water is an active solvent that cages BPA molecules (to BPA*) before subsequent hydrolysis; and (3c) water is an active solvent that participates in a bimolecular fragmentation of BPA to toluene and benzyl alcohol. These candidate pathways were described in detail above and do not merit further elaboration. Substitution of water for methanol in the appropriate rate expressions would allow comparison with experimental results given values for the rate expression parameters, which will, in general, be different for pyrolysis in methanol and water. The present experimental results permit only the tentative elimination of pathway 3c. Observed BPA decomposition kinetics in water were comparable to, but certainly slower than, neat pyrolysis, and, in contradiction, pathway 3c requires faster decomposition. Further investigation where the water concentration is varied is suggested for discrimination between pathways 3a and b. In the foregoing the observed suppression of BPA decomposition kinetics in solvent relative to neat pyrolysis was used to eliminate a direct solvolysis of BPA. These
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= 0.2
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Figure 5. Temporal variations of the molar yields of major products of BPA pyrolysis in dense water at 386 "C.
conclusions are tentative because of the possible influence of pressure on rate constants. Although the present work was at pressures considerably lower than the typically 1-10 kbar required to observe the influence of pressure on liquid phase reaction rate constants (Laidler, 1965; Eckert, 1972) illustrated in the equation
(a In k/aPIT = -AV*/RT
(1)
these effects may nevertheless be present if AV*,strictly a difference in partial molar volumes (Eckert, 1972), is unusually large. Since AV* for the neat pyrolysis pathway to I* would be expected to be positive, kI would be expected to decrease with increasing pressure, and candidate (3c) of Table I is yet strictly possible. We conclude by considering the appeal of operating near the critical region (T, z 1, P, 1, pr = 1). It has been shown previously that guaiacol hydrolysis reactions are continuous in water density, with no discontinuity evident at pr = 1 (Lawson and Klein, 1984),and also that dibenzyl ether hydrolysis is facile at 374 "C (Townsend and Klein, 1984). The present results suggest that the intrinsic chemistry underlying solvolysis reactions are strongly dependent upon absolute temperature and rather insensitive to reduced temperature. To this end, BPA solvolysis in methanol at p = 0.361 g/cm3 (p, = 1.31) was barely discernible at 250 OC (TI= 1.02) but quite rapid by 386 "C ( T , = 1.26). However, BPA hydrolysis was facile at both 340 "C (TI = 0.95) and 386 "C (T, = 1.02). With regard to intrinsic chemical reactivity, it thus appears that supercritical methanol and water are appealing solvents because they are hot and dense. For example, in a simple power law rate expression that is first order in substrate and solvent concentration, the former attribute would enhance the rate through its effect on the rate constant and the latter attribute would increase the rate by increasing the reactant concentration. However, it must be noted that the ability of an SCF solvent to dissolve an ambiently immiscible co-reactant has important thermodynamic and mass-transfer implications that would impact observable but not intrinsic chemical kinetics.
Summary and Conclusions Major new results and conclusions arising from this work are as follows. 1. Neat pyrolysis of BPA yielded aniline, toluene, benzalaniline, and higher molecular-weight carbon-rich products (CRP). Ultimate molar yields of approximately 0.5 f 0.1 for aniline and toluene at essentially complete BPA conversion indicate that BPA was required as a hydrogen source. A reaction pathway involving initial first-order BPA reaction to an intermediate I*, followed
by subsequent second-order reaction of BPA and I* to toluene, aniline, benzalaniline, and other CRP, was set forth in tentative explanation of observed results. 2. Major fragmentation products from BPA pyrolysis in tetralin were aniline and toluene, as well as lesser amounts of benzalaniline than observed from neat pyrolysis. A pathway where tetralin competed with BPA for stabilization of I* to toluene and aniline allowed explanation of the slower BPA decomposition kinetics in tetralin relative to those observed in neat pyrolysis. 3. BPA pyrolyses in subcritical and supercritical methanol and water were qualitatively different from its pyrolysis neat or in tetralin. Methylaniline and benzyl alcohol were new major primary products observed from pyrolysis in methanol, whereas pyrolysis in water generated benzyl alcohol in addition to aniline and toluene. Three candidate reaction pathways were considered. In the first, the solvent (either methanol or water) reacted only with I* in the formation of solvolysis products. In the second, solvent molecules efficiently caged BPA molecules, and subsequent reaction with the caged species yielded observed solvolysis products. The third pathway was a direct bimolecular reaction between the solvent and BPA. The observed inhibition of BPA decomposition kinetics was used to eliminate the third pathway as a candidate, although the presently unelucidated influence of pressure on the neat thermolysis rate constants made this equivocal. Discrimination between the former two pathways was not attempted. 4. The appeal of solvents near their critical temperature and pressure appears to derive from their absolute temperature and density. Intrinsic chemical reaction rates are thus affected through an increase in the rate constant and reactant concentration in an associated rate expression. Other benefits associated with operation in SCF solvents, including their ability to dissolve ambiently immiscible eo-reactants, nonvolatile desired products, and catalysts, are more logically classified as mass transfer or thermodynamic effects.
Nomenclature aniline = PhNHz benzyl alcohol = PhCH20H benzylphenylamine = PhCH2NHPh benzalaniline = PhCHNPh N-methylaniline = PhNHCH3 toluene = PhCH3 Registry No. BPA, 103-32-2. Literature Cited Amestica, L. A.; Wolf, E. E. Fuel 1984, 63, 227. Benjamin, B. M.; Raaen, V. F.; Maupin, P. H.; Brown, L. L.;Collins, C. J. Fuel 1978, 57, 269. Brucker, R.; Kolling, G. Brennst. Chem. 1985, 4 6 , 41. Connors, W. J.; Johanson, L. N.: Sarkanen, K. V.; Winslow. P. Holzforschung 1980, 34, 29. Cronauer, D. C.; Jewell, D. M.; Shah, Y. T.; Modl, R . J. Ind. Eng. Chem. Fundam. 1979, 78, 153. Eckert, C. A. Ann. Rev. Phys. Chem. 1972. 23, 239. Kamlya, Y.; Yao, T.; Oikawa, S . Prepr., Dlv. Fuel Chem., Am. Chem. SOC. 1979, 271. King, H. H.; Stock, L. M. Fuel. 1984, 63, 810. Kleln, M. T.; Vlrk, P. S . Ind. Eng. Chem. Fundam. 1983, 22, 35. Klein, M. T.; Virk, P. S. MIT Energy Lab Report MIT-EL-81-005, 1981. Labrecque, R.; Kallagulne, S.; Grandmalson, J. L. Ind. Eng. Chem. Prod. Res. Dev. 1984, 23, 177. Laidler, K. J. "Chemical Kinetics"; McGraw-Hill: New York, 1965. Lawson, J. R.; Kleln, M. T. Ind. Eng. Chem. Fundam. 1985, in press. Miller, R. E.; Stein, S. E. Prepr., Div. Fuel Chem. Am. Chem. SOC. 1979, 271. Modell, M. "Reforming of Glucose and Wood at the Critical Conditions of Water", presented at ASME Intersociety Conference on Environmental Systems, San Francisco, CA, July 11-14, 1977. Paulaitls, M. E.; McHugh, M. A,; Chal, C. P. I n "Chemical Engineering at Supercrlticai Fluid Conditions"; Paulaitis, M. E.; Penninger, J. M.; Gray, R. D., Ed.; Ann Arbor Science Publishers: Stoneham, MA, 1983; p 139. Petrocelli, F. P.; Klein, M. T. Macromolecules 1984. 77, 161.
306
Ind. Eng. Chem. Prod. Res. Dev.
Schlosberg, R . H.; Ashe, T. R.; Pancirov, R. J.; Donaklson, M. Fuel. 1981, 60, 155. Simmons, M. B.; Klein, M. T. I n d . Eng. Chern. Fundam. 1985, 2 4 , 55. Townsend, S. H.; Klein, M. T. fuel 1984, in press. Virk, P. S. Fuel 1979, 58, 149. Whttehead, J. C.; Williams, D. J. J. Inst. Fuel. 1975, 82, 182.
1985,2 4 , 306-313 Received for review SeDtember 7. 1984 ’Accepted December 17; 1984
We gratefully note the support of the US.Department of Energy (NO.DE-FG-22-82PC50799).
Synthesis of Graft Copolymers from Lignin and 2-Propenamide and Applications of the Products to Drilling Muds John J. Melster’ and Damodar R. Pat11 Department of Chemistry, Southern Methodlst Univers& Dallas, Texas 75275
Harvey Channel1 Messina, Inc., Dallas. Texas 75204
Poly(1ignin-g-( l-amidoethylene)), previously made by reacting Kraft, pine lignin, and 2-propenamide, in oxygenbubbled, irradiated dioxane, can be prepared by combining lignin, 2-propenamide, calcium chloride, cerium (IV), and 1,4dioxane autoxidation products in such solvents as l-methyl-2-pyrrolidlnone, dimethyl sulfoxide, dimethylacetamide, dlmethylformamide, and pyridine. The product, a highly water-soluble brown solid containing 4 to 7 wt % lignin and 70+ wt % l-amidoethylenerepeat units, is purifiable by precipitation in 2-propanone and dialysis against water through a 3500 molecular weight permeable membrane. Poly(lign1n-g+amidoethylene)) and its hydrolyzed derivative, poly(lignin-g-((l-amidoethylene)-co-(sodium l-carboxylatoethylene))),lower yield point, lower gel strength, and lower API filtrate volume in a bentonite drilling mud. After hot rolling at 121 O C for 16 h, the graft copolymer outperformed an equal concentration of chrome lignosulfonate when the compounds were tested as thinners or as filtrate control agents.
Introduction Since over 15 million tons of lignin is produced as waste from Kraft pulp mills in the United states alone (Goheen and Hoyt, 1981), there is a significant economic incentive to find uses for this biomass. One particularly versatile method for derivatizing lignin is to attach a polymeric side chain to the lignin molecule that will produce engineering, interfacial, or solubility properties in the resulting two-part molecule, a graft copolymer, that are needed in commercial products or processes. One method used in research to make these polymers is the irradiation of lignin slurries with y-or X-rays followed by polymerization of a vinyl monomer on the “activated” lignin (Koshijima et al., 1964a,b; Simionescu et al., 1975). This method is hard to control and produces large amounh of side chain ungrafted to lignin. Several chemical reagents have been used to graft side (Mikhailov and chains of 2-0xy-3-0~0-4-methylpent-4-ene Livshits, 1969) or prop-2-enoic acid (Krause et al., 1975), to lignin. These methods are more flexible and syntheti d l y productive, but they fail to produce a graft copolymer of lignin and 2-propenamide (Kobayashi et al., 1971; Phillips et al., 1973). Grafting 2-propenamide to lignin is chemically important because the structure and reactions of this natural product are a major and growing area of current research. It is commercially important because the graft copolymer should have properties which will make it useful in water purification, mineral benefication, and energy recovery. To meet these needs, a method has now been developed to chemically initiate free-radical polym0196-432118511224-0306$01.50/0
erization of 2-propenamide on Kraft pine lignin.
Experimental Section Materials. Lignin, which makes up the backbone of the graft copolymers, is a cross-linked, oxy[3-methoxyphenylenelpropylene polymer which acts as a binder in woody plants. Lignin used in these studies is a commercial product. The material is a Kraft pine lignin prepared in “free acid” form with a number average molecular weight of 9600 and a weight-average molecular weight of 22000. The ash content of the product is 1w t % or less. Kraft pine lignin is essentially insoluble in water at pH 7 but dissolves readily in aqueous solutions at a pH above 9. 2-Propenamide (common name: acrylamide), used in all reactions, was reagent grade monomer which was recrystallized from trichloromethane after hot filtration and dried under vacuum (P< 1mmHg) at room temperature for 24 h. 1,4Dioxane was stabilized reagent grade material which was freshly distilled before use. Calcium chloride and other salts used were reagent grade materials and were used as supplied. Gases used in the syntheses were standard commercial grade cylinder gases. The lignin-acrylamide reaction products were tested for effectiveness in a water-base mud containing 28 lb/bbl (ppb) of Wyoming bentonite and 40 ppb of Revdust, a commercial clay mixture used to represent solids generated by drilling. Methods. Two methods are now available to graft 2propenamide onto lignin. In the first method, autopho0 1985 American Chemical Society
