Ind. Eng. Chem. Res. 1987,26, 483-488 Bretherton, F. P. J. Fluid Mech. 1961,10(2),166. Cameron, A. Principles of Lubrication, Longmans: London, 1966; p 49. Cox, G. B.J . Fluid Mech. 1962,14(1),81. Coyle, D. J.; Macosko, C. W.; Scriven, L. E. J. Fluid Mech. 1986,in press. Coyne, J. C.; Elrod, H. G. J. Lubr. Technol. 1969,91(4),651. Fall, C. J. Lubr. Technol. 1978,100(4), 462. Grovenveld, P.; van Dortmund, R. A. Chem. Eng. Sci. 1970,25(10), 1571. Higgins, B. G. Ph.D. Thesis, University of Minnesota, Minneapolis, 1980. Higgins, B. G. Znd. Eng. Chem. Fundum. 1982,21(2),168.
483
Kistler, S. F.; Scriven, L. E. Znt. J. Num. Meth. Fluids 1984,4(3), 207. Lamb, H. Hydrodynamics, 6th ed.; Dover: New York, 1945;p 464. Morse, P. M.; Feshbach, H. Methods of Theoretical Physics; McGraw-Hill: New York, 1953;Part I, p 210. Pearson, J. R. A. J. Fluid Mech. 1960,7(4), 481. Ruschak, K.J. Ph.D. Thesis, University of Minnesota, Minneapolis, 1974. Taylor, G. I. J. Fluid Mech. 1963,16(4), 595. Wilson, S.J . Fluid Mech. 1969,38(4),793. Received for review June 14,1985 Accepted June 24, 1986
Mass Transfer in Wetted-Wall Column with Cocurrent Laminar Liquid-Liquid Flow Satoru Asai,* Jun’ichi Hatanaka, Toshiya Kimura, and Hidekazu Yoshizawa Department of Chemical Engineering, University of Osaka Prefecture, Sakai, Osaka 591, J a p a n
Film- and continuous-phase mass transfers in liquid-liquid systems were studied using a cocurrent laminar wetted-wall column of a modified form. The film-phase mass-transfer coefficients, obtained by dissolution of MIBK, 1-butanol, and cyclohexanol in water, were in good agreement with the Beek-Bakker model, demonstrating the advantage of this column because of its negligible end effect. The continuous-phase mass-transfer coefficients were measured by the transfer of I2 dissolved in continuous phases of ethylhexyl alcohol, toluene, and n-hexane into the interface, where I2 disappeared by an instantaneous irreversible reaction with Na2S203in the aqueous film phase. These coefficients were in satisfactory agreement with the penetration theory when the driving force of solute I2 was evaluated by the method proposed in this paper. In all fundamental studies for liquid-liquid mass transfer, it is desirable to use an experimental apparatus in which the interfacial area and hydrodynamics are well defined. However, few such apparatus have been available. As one kind of suitable apparatus, cocurrent laminar wetted-wall columns have been used by Maroudas and Sawistowski (1964) and Bakker et al. (1967) for mass transfer in binary and multicomponent liquid-liquid systems. Their data were compared with the penetration theory. However, these types of wetted-wall columns are subject to an end effect caused by accumulation of surface-active impurities near the lower end of the wetted wall, and appropriate corrections for this effect must be made. Otherwise, intentional spilling of the film phase over the edge of the run-off tube into the continuous phase, which is not generally practiced, must be used to prevent accumulation of impurities. Unfortunately, however, a reasonable correction to account for the end effect is unlikely to be possible when the mass transfer is accompanied by chemical reaction, since the equivalent length of the end effect varies in an unpredictable manner with the ratio of the reaction rate to the diffusion rate of the transferring solute (Hikita et al., 1967). Furthermore, in previous studies (Maroudas and Sawistowski, 1964; Bakker et al., 1967), the flow rates of both phases were adjusted so that negligible velocity gradients were produced across the interface in order to demonstrate the application of the penetration theory. Hence, the effects of velocity gradients due to viscous drag created by the adjacent phase have not been established. In addition, the mass-transfer coefficients in the continuous phase have not been directly measured. This work presents individual measurements of filmand continuous-phase mass-transfer coefficients in the 0888-5885/87/2626-0483$01.50/0
presence of any velocity gradient at the liquid-liquid interface, using a cocurrent laminar wetted-wall column similar to the one used for gas-liquid systems by Hikita et al. (1967,1976). It has been shown to have a negligible end effect. The observed mass-transfer coefficients are discussed from the aspect of comparison with the model of Beek and Bakker (1961).
Experimental Section The wetted-wall column used in this work is depicted in Figure la. The falling film was formed on the surface of a vertical glass rod 13 or 14 mm in diameter. The rod had a hemispherical end. The internal diameter of the column was 46 mm. The annular space between the rod and column wall was filled with the continuous phase, presaturated with water. The film-phase liquid entered the column through an annular space between a nozzle of 15.6-mm i.d. and a wetted-wall rod, flowed onto the surface of the wetted-wall rod in a laminar liquid film without rippling, and ran down a slender rod 3 mm in diameter into the run-off tube. The liquid level in the run-off tube was adjusted so that the stagnant film of surface-active impurities, building up from the liquid level, just covered the falling film on the slender rod, as shown in Figure lb. Thus, the end effect due to the presence of the stagnant film could be expected to be negligible. The hemispherical end of the wetted-wall rod was taken to be equivalent to a cylindrical vertical rod with length equal to 0.46 times the diameter of the rod. This has been confirmed theoretically and experimentallyfor gas-liquid systems (Hikita et al., 1967). Physical properties of the systems used are shown in Table I. In the experiments on film-phase mass transfer, the dissolution rates of three organic solvents were measured 0 1987 American Chemical Society
484
Ind. Eng. Chem. Res., Vol. 26, No. 3, 1987
Table I. Physical Properties of Systems Used (25 oC)u system: film phase (1)-solute-continuous phase (2) phase p , kg/m3 103r(,Pa s Film-Phase Mass Transfer 0.894 1 997 water-MIBK-MIBK 2 801 0.592 1 997 0.894 water-1-butanol-1-butanol 2 840 2.86 1 997 0.894 water-cyclohexanol-cyclohexanol 2 955 17.5 Na2S203(aqj-12-ethylhexyl alcohol Na2S,03 (aq)-12-toluene Na2Sz03(aqj-12-n-hexane Na2S203(as) containing sucrose-12-n-hexane (I
C,i, kg/m3
109D,m2/s contact time, s
18.0
0.770
0.11-4.2
73.9
0.650
0.18-1.3
38.6
0.626
0.81-19
0.249
0.45-3.6
2.10
0.73-2.2
4.15
0.58-1.7
4.15
0.62-2.8
Continuous-Phase Mass Transfer 1 997 0.894 2 844 6.78 1 997 0.894 2 862 0.552 1 997 0.894 2 655 0.305 1 1230 12.3 2 660 0.352
Na2S203concentration: -0.01 kmol/m3. I2 concentration: 10-4-10-3 kmol/m3. Sucrose: 50 wt %.
solution containing 0.01 kmol/m3 of Na2S203also was used as the film phase, to vary the viscosity of that phase. The liquid flow rates of both phases were varied independently, ranging from 2.3 X to 2.1 X lo* m3/s and from 5.3 X lo-' to 4.6 X lo* m3/s for the film and continuous phases, respectively. The film length was varied from 0.021 to 0.18 m. Both phases flowed cocurrently in every experiment, and the temperature was controlled at 25 "C. The concentrations of 1-butanol and cyclohexanol in the outgoing water stream were measured with a differential refractometer. The concentrations of MIBK in the outgoing water stream and of I, in the inlet and outlet streams of the continuous phase were determined by means of a spectrophotometer. The calculated contact time, Z/ui, between the phases was estimated by using eq 16. Its derivation is presented below. The density and viscosity of ethylhexyl alcohol were determined by conventional techniques, and the diffusivity of I2 in ethylhexyl alcohol was measured by using a diaphragm cell. All the other properties were taken from the literature (Asai et al., 1983,1985;Perry and Chilton, 1973).
0
9 10
.I L^ Figure 1. (a, left) Schematic diagram of wetted-wall column: 1, film-phase inlet; 2, air vent; 3, water jacket; 4, wetted-wall rod; 5, run-off tube; 6, drain; 7, adjustable screw; 8, flange; 9, nozzle; 10, continuous-phase inlet; 11, continuous-phase outlet; 12, film-phase outlet. (b, right) Main part of wetted-wall column.
to evaluate the mass-transfer coefficients. Each solvent formed a continuous phase, and water was used as the film phase. In most of the runs, a surface-active agent (Scour01 100, Kao Co., Ltd., Japan) was added to water to form a 0.05 vol % solution and to eliminate the rippling on the surface of the liquid film. The liquid flow rates were varied from 2.3 X to 1.5 X lo4 m3/s and from 0 to 2.2 X lo4 m3/s for the film and continuous phases, respectively. These ranges were employed in order to vary the interfacial velocity and velocity gradient. The vertical film length ranged from 0.012 to 0.28 m. In the experiments on continuous-phase mass transfer, on the other hand, aqueous Na2&03solutions at about 0.01 kmol/m3 and organic solvents containing Iz a t 10-4-10-3 kmol/m3 were used as the film and continuous phases, respectively. The continuous-phase mass-transfer coefficients were evaluated by measuring mass-transfer rates of 12,accompanied by an instantaneous irreversible reaction with Na2S203(I2 + 2NazS2O3 2NaI + Na2S4O8)at the liquid-liquid interface. An aqueous 50 wt % sucrose
-
Theoretical Section It was assumed that the streams of both phases were laminar and their velocity profiles were fully developed within a negligible distance from the point at which both phases were brought into contact. The velocity profiles in both phases for the type of wetted-wall column shown in Figure 1 can be obtained by solving the Navier-Stokes equations
subject to the relevant boundary conditions
r=R1
ul=O
(3)
r=R2 u2=0 (5) Here R1,Ri, and R2 refer to the radii of the wetted-wall rod, the interface, and the inside wall of the column, respectively, as shown in Figure 2. The solution of these
Ind. Eng. Chem. Res., Vol. 26, No. 3, 1987 485 where
equations yields the following velocity profiles
242 In 4) In
(Rl Ir IR J (6)
R1
,.a(
F4W = ?[M(
42)+ 2c#1~$MIn 4 - 242) In
‘1
-
RZ
(
(Ri Ir 5 R,) (7)
2 In 4
1-
);
+
$-
+ 1- q2) x 1) -
q2(
$
)]
-1
(15)
where
4 = -Ri RZ
M=
q=-
R24
The liquid-liquid interfacial velocity, ui, is given by
$ = -P1
R1
PZ
1 $In 4 -In q
ui
=
Ullj-=Ri
=
UZlr=Ri
=
(8)
The volumetric flow rates of both phases are
(16)
The analytical results reveal that the interfacial velocity ui is primarily fixed by the flow rate, Q1, of the film phase
and, to a lesser extent, by the continuous-phase flow rate, Q2. This observation is true in the present range of Q2, which was confined to such an extent that the film flow was not visually disturbed by the continuous-phase flow. Furthermore, it can be shown that the circulation existed in the continuous phase, the liquid near the interface flowing downward and the liquid in the core region of the annular space of the column flowing upward as depicted in Figure 2. A similar problem of cocurrent laminar flow with circulation has been treated also by Hikita et al. (1979) for a conventional type of wetted-wall column, in connection with gas-phase mass transfer in gas-liquid systems. The velocity gradients, al and a2,at the interface, directed from the interface to the film and continuous phases, respectively, are evaluated as
486 Ind. Eng. Chem. Res., Vol. 26, No. 3, 1987 p J.
r Liquidfilm
/
-,toc
x
-
N
?
-
-
L L -
5 -
Figure 2. Flow pattern and coordinate system.
In the analysis of the experimental data, the BeekBakker model for mass transfer to a fluid moving with a constant velocity ui and constant velocity gradient a at the interface was applied to both phases. The calculated penetration depths of a solute into both phases seem very small compared with the thickness of the liquid film Ri R1 and the continuous phase R2 - Ri, so that the use of Cartesian coordinates should be justified. Exact solutions for this problem could not be obtained; instead, two asymptotic solutions for a > 0 (Beek and Bakker, 1961) and one asymptotic solution for a < 0 (Byers and King, 1967) have been derived for the local mass-transfer coefficients. Approximate solutions have been proposed by Hatanaka (1984). The corresponding two asymptotic solutions for the average mass-transfer coefficients with a > 0 have been reported by Asai et al. (1985), but here the following more compact single empirical expressions are proposed P5= y02,5+ Ym2.5for a I0 and all B (19)
p.5= y02.5 -
P
/"
1
Figure 3. Film-phase mass transfer-dissolution of MIBK in water.
0 M l B K
n-Butanol
A
61
Figure 4. Film-phase mass transfer-dissolution 1-butanol in water.
of MIBK and
for a < 0 and B < 0.05 (20) Equation 19
where
B = a2DZ/ui3
Y = k(Z/uiD)l/z
Yo = 2 / 7 w
= 1.128
(21) (22) (23)
These expressions are analogous to those for the local mass-transfer coefficients (Hatanaka, 1984), but Yo and Ymcorrespond to the average mass-transfer coefficients for the penetration theory ( B 0) and for the Leveque solution (B m), respectively. Equation 19 agrees well with the previous two asymptotic solutions (Asai et al., 1985) for all the values of B with a maximum deviation of 2.7%. On the other hand, eq 20 for a < 0 accords with the expression derived from the asymptotic solution for the local mass-transfer coefficients (Byers and King, 1967), within an error of 0.4%. However, application of eq 20 is limited to B < 0.05, as expected from the fact that the fluid flow for a < 0 and B (ui 0) cannot be realized.
-
-
0.4
lo-'
2
4
6 8 lo-'
2
Bi Figure 5. Film-phase mass transfer-dissolution water.
4
6
of cyclohexanol in
measurement under conditions free from rippling on the surface of the liquid film. All the data, including that at 2 = 1.2 cm, are seen to be in good agreement with the solid line representing eq 25. This fact indicates that, if the application of the penetration theory is justified, the end effect of this apparatus is negligibly small, in line with previous results for gas-liquid systems (Hikita et al., 1967, 1976). In the film flow under the present experimental conditions, the interfacial velocity gradient, al, was always positive. Therefore, the experimental data were compared with eq 19. The mass-transfer coefficients, A,, were evaluated from
- -
Results and Discussion Film-Phase Mass Transfer. Figure 3 shows the data for dissolution of MIBK in water, which are plotted in terms of the total dissolution rate, W , based on the Higbie penetration theory W = 2aRiZN = 4RiCli(7rDloiZ)1i2
(25)
The data for the comparatively long film length, 2, shown by solid symbols were obtained with the addition of a small amount of a surface-active agent to water. This enabled
The data were taken at various combinations of operating parameters, such as film length 2 and the flow rates Q1 and Qzof both phases. Figure 4 presents the data for dissolution of MIBK in water with and without the surface-active agent described above and for that of 1-butanol in water with the surface-active agent. Theoretical predictions from eq 19 are also shown. The data for both systems are in good agreement with the theoretical line, indicating no end effects. In the region of Bl values indicated, eq 19 agrees
Ind. Eng. Chem. Res., Vol. 26, No. 3, 1987 487 2 /Equation 20
00
p1.0 Keys same as
Key 0 Ethylhexyl alcohol A
2
0.1
OA1'11' 6 8 to-'
- Na2Sp03aq
Toluene
0 n-Hexane
6'
v n-Hexane- Na2S20,aq with Sucrose 8I 'to-' I
I
2
I
I
4
,
I
4 , 1 1 1
6 8 to-'
2
4
6 8 tC3
Bz Figure 6. Continuous-phase mass transfer-transfer of Iz to interface from ethylhexyl alcohol, toluene, and n-hexane. Driving force: inlet concentration, C2,m.
with the penetration theory solution, Yl= Yo,within an error of only 0.9%. Thus, the penetration theory can be applied to both systems. Figure 5 represents the results for dissolution of cyclohexanol in water containing a surface-active agent. The values of B1in this system are significantly larger than those in the foregoing two systems, since cyclohexanol is characterized by a large film-phase velocity gradient aland a small velocity vi at the interface. This results from the high viscosity and a density nearly equal to that for water. Although eq 19 yields Yl values 11% larger than the penetration theory solution at B1= 0.4, the experimental data are in good agreement with the theoretical predictions. Thus, for systems that are more viscous and/or nearly as dense as water, the deviation from the penetration theory may become substantial, requiring the use of the Beek-Bakker model solution rather than the penetration theory solution. Continuous-Phase Mass Transfer. During cocurrent laminar flow at an interfacial velocity much larger than the average continuous-phase velocity, corresponding to the present experimental conditions (vi/Dz = 15.2-249.9), circulation exists in the continuous phase as described above. Therefore, the continuous-phase liquid supplied to the column may mix with the circulating liquid flowing upward through the region Ro < r < R2 shown in Figure 2. Furthermore, two stratified flows move downward in the regions Ri < r < R, and R, < r < Ro. In the bottom part of the column, these flows can mix with each other by the existence of a run-off tube to form the exit stream. Since theoretical predictions of the degree of mixing seem impossible, the representative concentration, C2,, of solute Iz in the continuous phase was evaluated for two limiting cases. In the first case, Cz,Rwas taken to be equal to Cz,h, in accordance with the assumption of no mixing of the supplied stream with the circulating liquid. In the second case, CzRwas evaluated assuming that the liquid supplied was well mixed with the circulating liquid. The latter liquid was assumed to have the outlet concentration Cz,out, resulting from complete mixing of downward flows in the two regions Ri < r < R, and R, < r < Re Then, C ~ , R =CZ,~ can be evaluated by using Q&z,in
Cz,m =
QZ
+ QcirC2,out + Qcir
This definition leads to a reasonable result, C2,, = C2,in, for the continuous-phase flow without circulation. Moreover, note that this simple model differs from that of Hikita et al. (1979) for gas-phase mass transfer in a conventional type of wetted-wall column, because their model allows for radial diffusion in the gas core circulation region and results in a very complicated solution. The radius, Ro, of the inversion plane of flows shown by
1
2
I I l l l l l
I
4
6 8
I
2
I
in Fig.6
,
4
, 1 1 1 ,
6 8
Ib3
Bz Figure 7. Continuous-phase mass transfer-transfer of Iz to interface from ethylhexyl alcohol, toluene, and n-hexane. Driving force: concentration, Cz,m,defined by eq 27.
u2 = 0, can be derived from eq 7 and is given by a root of the expression
@2)
+ 2bZJ/MIn 4 - 24')
] :
In - = 0 (28)
The circulating flow rate Qciris evaluated as Qcir=
s
Ro
R,
2aru2 dr = -
x'
2arv2 dr =
The mass-transfer coefficients
k2 =
k, were evaluated from
Q2(C~,in- C2,out) 2aRiZC2,R
(30)
using C2,R = C2,inor Cz,,. Figures 6 and 7 show the data for the systems composed of ethylhexyl alcohol-aqueous Na2S203,toluene-aqueous Na2S203,n-hexane-aqueous Na2S203,and n-hexaneaqueous Na2S203containing sucrose, plotted as YZvs. B2. The driving forces of solute I2were taken as C2,h and C2", respectively. No surface-active agent was added to any system. The data were taken in various combinations of operating parameters. The solid lines in both figures refer to eq 20, corresponding to the present experimental conditions, u2 < 0 and B2 < 0.05. The transfer rates of I, for the viscous ethylhexyl alcohol system were not high enough to detect reliable differences in the concentrations between the ends of the column, showing essential scattering of the data. Duplicate experiments were performed for each run and the observed mass-transfer coefficients were averaged for the plots. Thus, the values of Yzfor this system are independent of the choice of the driving force. The data are in agreement with the theoretical line on the whole, as can be seen from both figures. However, for any other systems that may be sensitive to the choice of driving force, the assumption of C,, = Cz,i, is not justified. On the other hand, the choice Cz,R= C2,, gives satisfactory agreement between the theoretical predictions and data ranging from Qcir/Q2= 1.2 to 18.4. This lends support to the proposed model, which allows for complete mixing at the top and bottom in the column.
I n d . Eng. Chem. Res. 1987,26, 488-494
488
Note that YZmay be approximated by yoover the whole range of Bz covered in this work. Numerical experiments also were performed for several systems having extremely different physical properties, but appreciable deviation of yz from Yo could not be observed. Therefore, the penetration theory appears always to be applicable for mass transfer when the major resistance is in the continuous phase. Conclusion The improved wetted-wall column used in the present work has been shown to have no appreciable end effects. Film-phase mass transfer could be depicted quantitatively in terms of the Beek-Bakker model. The mass-transfer coefficients for the continuous phase were in satisfactory agreement with the penetration theory when the driving force of the solute was evaluated from eq 27. Acknowledgment We are grateful to Dr. K. Ishimi, Department of Chemical Engineering, University of Osaka Prefecture, for helpful discussions. Nomenclature a = velocity gradient at liquid-liquid interface, l / s B = variable, a2DZ/$, cf. eq 21, dimensionless C = concentration of transferring solute, kg/m3 C2,, = concentration of transferring solute in continuous phase defined by eq 27, kg/m3 C2,R= representative concentration of transferring solute in continuous phase, kg/m3 D = diffusivity, m2/s F1(@)-F4(4) = parameters defined by eq 12-15, dimensionless g = gravitational acceleration, m/s2 k = mass-transfer coefficient, m/s M = parameter defined by eq 8, dimensionless N = mass-transfer flux, kg/(m2 s) p = pressure, N/m2 Q = volumetric flow rate of liquid, m3/s R, = radius of inner plane of core circulation region, m Ri = radius of liquid-liquid interface, m Ro = radius of inversion plane of continuous-phase flows, m R1 = radius of wetted-wall rod, m
R2 = radius of inside wall of column, m r = distance in radial direction, m v = velocity, m/s W = total mats-transfer rate, kg/s = variable, k ( Z / u , D ) 1 / 2cf. , eq 22, dimensionless yo= constant 2/7r1I2,dimensionless Y , = variable equal to (3/8)1/3B1/s/I'(4/3),cf. eq 24, dimensionless 2 = film length, m z = distance in axial direction, m Greek Symbols
r(z) = gamma function radius ratio, Ri/R1, dimensionless I.C = viscosity, Pa s p = density, kg/m3 = radius ratio, Ri/R2,dimensionless $ = viscosity ratio, pl/p2, dimensionless 7 =
Subscripts
cir = circulation i = liquid-liquid interface in = inlet out = outlet 1 = film phase 2 = continuous phase Superscript = average value
-
Literature Cited Asai, S.; Hatanaka, J.; Uekawa, Y. J . Chem. Eng. Jpn. 1983, 16,463. Asai, S.; Hatanaka, J.; Kuroi, M. Chem. Eng. J . 1985, 30, 133. Bakker, C. A. P.; Fentener van Vlissingen, F. H.; Beek, W. J. Chem. Eng. Sei. 1967, 22, 1349. Beek, W. J.; Bakker, C. A. P. Appl. Sci. Res. 1961, A10, 241. Byers, C. H.; King, C. J. AIChE J . 1967, 13, 628. Hatanaka, J. Chem. Eng. J . 1984, 28, 127. Hikita, H.; Asai, S.; Himukashi, Y. Kagaku Kogaku 1967, 31,818. Hikita, H.; Asai, S.; Takatsuka, T. Chem. Eng. J. 1976, 11, 131. Hikita, H.; Ishimi, K.; Sohda, N. J . Chem. Eng. Jpn. 1979, 12, 68. Maroudas, N. G.; Sawistowski, H. Chem. Eng. Sci. 1964, 19, 919. Perry, R. H.; Chilton, C. H. Chemical Engineers' Handbook, 5th ed.; McGraw-Hill: New York, 1973.
Received far review July 22, 1985 Accepted July 2, 1986
Asphaltene Reaction Pathways. 2. Pyrolysis of n -Pentadecylbenzene Phillip E. Savage and Michael T. Klein* Department of Chemical Engineering and Center for Catalytic Science and Technology, University of Delaware, Newark, Delaware 19716
The reactions, pathways, kinetics, and mechanisms of alkyl-aromatic moieties likely present in asphaltenes were probed via the thermolysis of n-pentadecylbenzene (PDB) at temperatures from 375 t o 450 "C. The primary reaction pathway led t o two major product pairs, toluene plus 1-tetradecene and styrene plus n-tridecane, respectively. A complete series of n-alkanes, a-olefins, phenylalkanes, and phenylolefins was also formed in lesser yields. PDB thermolysis was demonstrably first-order, and associated Arrhenius parameters of [E* (kcal/mol), log A (s-I)] = [55.45, 14.041 were determined. Reaction in tetralin-d12indicated that the operative PDB thermolysis mechanism was entirely free-radical. This information permitted speculation into the relevance of the modelcompound results t o asphaltene reactions. The current industrial trend toward processing heavy crude oils and residua has focused increased attention on petroleum asphaltenes, the heptane-insoluble and benzene-solublefraction of such feedstocks. Strictly a solubility 0888-5885/87/2626-0488$01.50/0
class, asphaltenes are a chemically ill-defined and complex mixture of heavy hydrocarbons and heteroatom- and metal-containing hydrocarbon oligomers. The complexity and ambiguity of both asphaltenes and their reaction 0 1987 American Chemical Society
