Solvent Selectivity for Hydrocarbons with Close Molar Volumes Walter A. Spelyng and Dirnitrios P. Tassios* Newark College of Engineering, Newark, New Jersey 07102
Solvent selectivity for hydrocarbons of very close molar volumes has been investigated. Binary isothermal (90°C) vapor-liquid equilibrium data for n-octane and isooctane were obtained in nitrobenzene, butyronitrile, cyclopentanone, and diethyl oxalate. Literature dat.a for three other solvents were also utilized. It is concluded that in spite of the close molar volumes, the main contributions to selectivity result from physical effects, especially dispersion forces. Furthermore, an increase of the solubility parameter for isooctane by 0.7 is required for successful correlation of the results.
Introduction Separation of mixtures where the relative volatility of the key components is very close to unity, or equal to unity for azeotropic mixtures, is often accomplished through extractive distillation. A compound, called the solvent, is added near the top of the distillation column and effects a change in the relative volatility of the key components. The solvent effect is quantitatively expressed by the selectivity S 2 3 (the subscripts are dropped after eq 1for simplicity). sj3
=
[E]
SOl\e"t
The solvent selectivity is the result of two effects: physical and chemical (Prausnitz and Anderson, 1961). The Physical effects result from polar, dispersion and induction contributions. The selectivity for a hydrocarbon pair a t infinite dilution in a solvent is given by
RT In S
=
P
+D +I
(2)
where
- VJ) V'(X1 - A?)' - V,(X1 - A,)' I = 2v,q13 - 2v2q12 P
D
=
= Ti'(V1
(3) (4)
(5)
Weimer and Prausnitz (1965) and Helpinstill and Van Winkle (1968) improved eq 2 by the addition of an entropy term E
between the solvent (electron acceptor-Lewis acid) and each of the hydrocarbons (electron donors-Lewis bases). If the stability varies between the two complexes the selectivity will be enhanced by chemical effects theory. For a hydrocarbon pair with close molar volumes (V2 N V3),eq 3 and 9 indicate that the polar and induction contribution are very small. Also eq 4 becomes in this case
D
1
=
~v,[A,- 2(x2 + x,,)][x, - h21
(4a)
indicating that the despersion effects are also small. For such systems it has been recommended (Prausnitz and Anderson, 1961) that selectivity could be enhanced through chemical effects. To explore this approach the selectivity of the n-octaneisooctane (2,2,4-trimethylpentane) pair with different solvents was investigated in this study because the difference in molar volumes between the two hydrocarbons is very small, 1.73% a t 90°C. Chemical effects could be relatively significant since there is a difference in ionization potentials of 3.6% (9.84 eV for isooctane and 10.2 eV for octane). Infinite dilution selectivities were determined by obtaining vapor-liquid equilibrium data, at 90°C, for each of the above hydrocarbons in the following solvents: nitrobenzene, butyronitrile, cyclopentanone, and diethyl oxalate. Also the literature data presented in Table I were used.
Equipment and Procedure An Othmer (1948) vapor recirculating still, with Teflon(6) stemmed valves replacing the greased stopcocks, was used in this study. Heat inputs to the liquid and vapor phase and eq 2 becomes were controlled by individual Variacs. Temperatures, RT In S = P D E I (7) measured with calibrated thermometers, were maintained a t 90 h 0.1"C by a manostat. Pressures were measured by For the induction term, Weimer and Prausnitz proposed a mercury manometer and a cathetometer with a reading I = 2(VjK13/ - V2K1?')T12 (8) precision of h0.05 mm. Analysis of the vapor and liquid phases was done by gas-liquid chromatrography with a Helpinstill and Van Winkle obtained better results by reproducibility of better than 0.001. The operation of the using still was checked by measuring the vapor pressure of niP = Vz(T1 - T?)' - Vj(T1 - T J ) ' (3a) trobenzene at 99.3"C. A value of 20.1 mm was observed I = 2[VdK11(T1 - T j ) ' - V,KII(rl - T ~ Y I (8a) compared to 20.0 in the literature (Perry, 1963). All the chemicals in this study were of 99% mole minimum purity and these expressions will be used in this study. The and were used without further purification. Measurements value of K12', K13', K l z , and K13 were obtained by reof the refractive indices of the materials gave results to gressing available binary data. For the saturated hydrowithin 0.0002 of the literature values except for butyronicarbons, as in this study, K l z = K13 = 0.399, even though trile. which was within 0.0006. most of the data used were for straight-chain hydrocarbons (Helpinstill and Van Winkle, 1968). Also for octane Results and isooctane 72 = r3 = 0 and eq 5 becomes Tables I1 through IX present the experimental results I = K(V, - V,)T,? = -0.798(V2 - V,)r,? (9) for the eight binary systems. Activity coefficients were calculated from the following expression (Van Ness, 1964) Chemical effects result from the formation of complexes
+ + +
328
Ind. Eng. Chem., Process D e s . Develop., Vol. 13, No. 4 , 1974
Table I. Sources of Vapor-Liquid Equilibrium Data System
Reference
Benzene-Isooctane Benzene-n-Octane Toluene-n-Octane Toluene-Isooctane E thanol-n-Octane Ethanol-Isooctane
Weismman and Wood (1960) Ellis (1952) Bromiley and Quiggle (1933) Thornton, et al. (1951) Pierrotti, et al. (1958) Kretschner, et al. (1948)
Table 11. Vapor-Liquid Equilibrium Data. System: Octane (1)-Nitrobenzene (2)
X
Y
P, mm
Y1
Y2
0.791 0.675 0.585 0.521 0.472 0.392 0.298 0.033
0,970 0.957 0.946 0.945 0.945 0.934 0.934 0.694
211.8 184.3 182.2 162.3 151.3 141.3 131.2 42.3
1.051 1.061 1.196 1.199 1.235 1.374 1.664 3.669
2.293 1.850 1.810 1.410 1.196 1.168 1.088 1.043
~
Table 111. Vapor-Liquid Equilibrium Data. System: Isooctane (1)-Nitrobenzene (2)
X
Y
P, mm
Y1
Y2
0.808 0.717 0.635 0.554 0.454 0.358
0.980 0.979 0.976 0.975 0.974 0.974
480.3 453.0 450.7 437.2 402.8 351.5
1.020 1.097 1.215 1.352 1.521 1.693
3.479 2.383 2.116 1.741 1.406 1,053
Table VI. Vapor-Liquid Equilibrium Data. System: Octane (1)-Cyclopentanone (2) X
Y
P, mm
YI
Y2
0.882 0.671 0.573 0.434 0.324 0.240 0.236 0.175 0.078
0.789 0.621 0.568 0.508 0.439 0.391 0.391 0.336 0.205
297.3 309.7 304.9 297.2 268.6 260.2 260.2 246.7 225.3
1.006 1.148 1.211 1.394 1.465 1.700 1.735 1.905 2.377
2.646 1.768 1.530 1.283 1.108 1.039 1.033 0.990 0,970
Table VII. Vapor-Liquid Equilibrium Data. System: Isooctane (1)-Cyclopentanone (2)
X
Y
P, mm
YI
Y2
0.858 0.684 0.510 0,352 0,342 0.241 0.156 0.073
0.872 0.779 0.697 0.669 0.669 0,602 0,517 0.328
584.5 570.2 515.9 457.2 457.2 411.8 352.5 281.6
1.031 1.127 1.232 1.526 1.573 1.817 2.082 2.265
2.536 1.935 1.554 1.145 1.127 1.062 0.996 1.014
Table VIII. Vapor-Liquid Equilibrium Data. System: Octane (1)-Diethyl Oxalate (2) X
Y
P, m m
Y1
Y2
0,933 0.856 0,713 0,629 0.494 0.325 0.155
0,986 0,973 0.959 0,953 0.947 0.939 0.897
241.4 231.9 214.9 212.7 206.6 186.3 117.3
1.030 1.065 1.170 1.305 1.606 2.185 2.784
3.533 3.068 2.157 1.890 1.514 1.183 1.014
Table IV. Vapor-Liquid Equilibrium Data. System: Octane (1)-Butyronitrile (2)
X
'I'
P, mm
Y1
Y2
0.926 0.770 0.637 0.533 0.425 0.347 0.280 0.162
0.733 0.568 0.493 0.454 0.415 0.394 0.361 0.272
309.7 355.2 376.1 383.4 376.2 366.3 360.3 341.1
0.982 1.044 1.157 1.295 1.454 1.648 1.843 2.268
3.515 2.096 1.649 1.408 1.205 1,072 1.008 0.938
Table IX. Vapor-Liquid Equilibrium Data. System: Isooctane (1)-Diethyl Oxalate (2) X
Y
P, mm
YI
Y1
0,931 0.799 0,704 0.550 0,505 0.380 0.258 0.181
0,994 0,984 0.981 0.977 0.977 0.969 0.963 0,953
546.2 513.8 468.4 448.5 441.1 386.7 312.5 256.0
1.015 1.105 1.143 1.398 1.498 1.740 2.069 2.402
3.448 2.755 2.055 1.611 1.442 1.343 1.089 1.024
Table V. Vapor-Liquid Equilibrium Data. System: Isooctane (1)-Butyronitrile (2)
X
Y
P, mm
Y1
Y2
0.904 0.736 0.587 0.475 0.355 0.269 0.203 0.152
0.844 0.728 0.660 0.608 0.573 0.532 0.486 0.409
644.5 648.3 637.1 606.7 590.8 589.1 544.7 497.5
1.038 1.106 1.235 1.342 1.650 2.011 2.256 2,324
3,200 2.041 1.608 1.394 1.207 1.166 1,091 1.081
where 812 = 2B12 - BII - B 2 2 . Values for B11, &, and BIZ were calculated according to the methods of O'Conne11 and Prausnitz (1967). For isothermal data the Gibbs-Duhem relationship becomes (Van Ness, 1964)
Hence a plot of In (y1/y2) us. XI should give two areas, a positive (Ip)and a negative ( I N )whose sum for isothermal data should be very close to zero. Table X presents values for the consistency index (C.1.) defined by (Hanson and Van Winkle, 1967)
(12) This quantity represents a measure of the thermodynamic consistency of the data. The experimental results can be considered satisfactory with some question for the cyclopentanone systems. Infinite dilution activity coefficients were calculated from plots of In (y 1/y2) us. XI. These plots provide more reliable y o value than plots of y us. x where the curvature is significant and extrapolation is more difficult (Tassios and Van Winkle, 1972). Ind. Eng. C h e m . , P r o c e s s D e s . D e v e l o p . , Vol. 13, No. 4, 1974
329
Table X. Consistency Index Data
Table XII. Pure Component Data
System n-Octane-Nitrobenzene Isooctane-Nitrobenzene n-Octane-Butyronitrile Isooctane-Butyronitrile n-Octane-Diethyl Oxalate Isooctane-Diethyl Oxalate n-Octane-C yclopentanone Isooctane-C yclopentanone
C.I. -0.09 -0.06 -0.04 -0.11 +0.04
-0.05 -0.12 -0.17
Table XI. Infinite Dilution Activity Coefficients Solvent
7 2 Oa
7 2 Ob
Toluene Benzene Nitrobenzene Butyronitrile Cyclopentanone Diethyl oxalate Ethyl alcohol
1.34 1.80 5.95 3.27 2.83 3.71 10.40
1.37 1.62 3.95 3.44 2.90 4.41 14.0
Y*Z O C
m o d
1.37 1.39 6.56 3.86 3.58 4.28 15.72
1.32 1.15 3.47 4.43 3.13 4.37
~~~
5
Isooctane in solvent.
isooctane.
d
n-Octane in solvent. Solvent in n-octane. b
~~
c
Ind. Eng. Chem., Process
(tal/
7.
v,
Compound
T,."C
CC)';~
CC)'/~
Octane Octane Octane Octane Isooctane Isooctane Isooctane Isooctane Nitrobenzene Diethyl oxalate Cyclopentanone Butronitrile Benzene Ethanol Toluene
50 80 90 110.6 50 80 90 110.6 90 90 90 90 80 50 110.6
7.27 6.97 6.82 6.51 6.57 6.24 6.12 5.84 8.78 7.48 8.24 7.48 8.50 7.58 8.06
0 0 0 0 0 0 0
cc/mol 169.0 175.3 177.9 182.3 171.8 178.6 181.0 187.0 108.4 146.2 97.0 95.6 96.0 60.4 118.6
0 4.4 6.11 4.90 5.65 0 8.86 0.46
Table XIII. Contributions to Selectivity
Solvent in
Table XI presents the y o values for all the systems used in this study. Values for the parameters X and T were calculated according to the method of Weimer and Prausnitz (1965). The results, along with values for the molar volumes, are presented in Table XII. Table XI11 presents values for the polar, dispersion, entropic, and inductive contributions calculated from eq 3, 4, 6, and 9, respectively. The difference between observed and calculated (eq 7 ) selectivites, presented in Table X N , is apparently unacceptable. Hildebrand (1950) observes that paraffins in solutions behave with a solubility parameter larger by about 0.6 from the value obtained from heat of vaporization data. Increasing, however, the solubility parameter values a t n-octane and isooctane by 0.6 leads again to erroneous results. For example, such an increase leads to selectivity, with benzene as solvent, of 1.65. Kyle and Leng (1965) in a study of hydrocarbon-polar solvent solutions reached the same conclusion observing that while increasing the value of X for isooctane by 0.5 gave better results, a similar increase of the value for n-heptane gave poorer results. They found that good results were obtained by increasing only the value of X for isooctane. A similar approach was employed in this study. The value of X z (isooctane) was increased by 0.7 to fit the data for the practically nonpolar solvents benzene and toluene. Dispersion contributions calculated with this new value for X z ( D )are presented in Table XIII; the corresponding selectivities (SBcalcd) are presented in Table X N and the resulting improvement is obvious. To explain the differences between S & s d and Scam chemical effects were considered since the difference in ionization potential of the two hydrocarbons (3.6%) is larger than the difference in molar volumes (1.73%) On the other hand, since the value of K in eq 8a was obtained by repressing data where the physical contributions were in general larger than the chemical effects, the quantty Q = RT [In S o b s d - In Scaled] was taken to reflect the contribution to selectivity of the chemical effects. Since these effects result from the solvents' ability to accept electrons, the relative Lewis acidity ( K x ) for the solvents are presented in Table XV. The values were obtained from the work of Harris and Prausnitz (1969) and refer to the squalane-squalene system. Since all the solvents listed in Table XV are not covered in the paper of Harris and Prausnitz, estimation was employed in certain cases. The 330
x. (tal/
Des. Develop., Vol. 13, No. 4 ,
1974
Solvent Nitrobenzene But yronitrile Diethyl oxalate Cyclopentanone Benzene Toluene Ethanol a
Da E -
P D 60 99 116 75 0 1 220
12 24 2 6 25 -6 13
578 278 258 455 501 485 159
I.
I
a
7 10 2 10 12 7 20
- 48 - 79 - 92 - 59 0 -1 - 194
218 - 169 - 246 - 109 36 - 19 -413
Da:calculated from eq 4 with the adjusted value for
XZ.
Table XIV. Experimental and Calculated Selectivities Solvent
Sobsd
Nitrobenzene Butyronitrile Diethyl oxalate Cyclopentanone Benzene Toluene Ethanol
Scdcda
1.51 0.95 0.84 0.98 1.11 0.98 0.74
Saealcdb
SbealcdC
1.04 1.08 1.04 1.05 1.05 1.00 1.10
0.96 0.94 0.88 0.94 1.05 1.00 0.79
2.29 1.53 1.48 1.95 2.08 1.91 1.38
a Calculated from the original model. Calculated by evaluating D with the adjusted value for As. c Calculated as SBcaicd but using eq 13 for the inductive effects instead of eq 9.
values of Q for the different solvents are also presented in Table XV. A plot of Q us. K x shows no interdependency, suggesting that chemical effects do not contribute significantly to selectivity even for systems of very close molar volumes. Following the failure of chemical effects to explain the discrepancy between predicted and observed selectivity, the model describing the physical contributions, and more specifically the inductive effects ( I ) , was investigated. Values for la = [RT In &bsd - P - D - E ] are presented in Table XI11 and are plotted us. ( Vz - V,) ~~2 in Figure 1 while a similar plot, based on the unadjusted values of X for isooctane, gave very poor results. The following expression for F is obtained from Figure 1
I"
= -1.84(V2
-
I/,)T,?
(13)
Selectivities obtained by expressing inductive effects through eq 13 are presented in Table XIV and are in excellent agreement with the experimental values. The only exception corresponds to the selectivity for nitrobenzene which falls off the graph and was not included in the correlation. A probable explanation for this lies with the uncertainty involved in obtaining the yzo value in nitroben-
IS0
I
@
1
100
50
0
C
0
1
I
too
so cv,-
I60
200
-60
V)1?,*
t
1
0
Figure 1. Inductive effects. Correlation for adjusted values of X z for the system octane-isooctane (I = RT In S o b s d - P - DB E). T a b l e XV. Relative Lewis Acid Strength (K,) Based on the Squalane-Squalene System at 80 "C
Q - 18
Solvent Toluene Benzene Diethyl oxalate C yclopentanone Ethanol Butynonitrile Nitrobenzene
2
I
3
T?(Va-V,)X
5
4
102
Figure 2. Inductive effects. System: pentane-pentene at 45°C. The Weimer-Prausnitz correlation, Y(W) = RT In S o b s o - ( P + D + E). 0
K* 0.15 0.18 0.27 0.45 0.55 0.48 0.55
36 154 - 50 134 - 90 226
-
-4
-8
Table XVI. Functions Related to Selectivity. System: Pentane (2)-Pentene (3)
Solvent Tetrahydrofuran Diethyl ketone Diethyl carbonate Methyl ethyl ketone Pentadione Cyclopentanone Acetone Butyronitrile Acetophenone Pyridine Diethyl oxalate Propionitrile Dimethyl acetamide Dimethyl formamide Furfural Acetonitrile Butyrolactone Ethylene Nitromethane
113.1 90.5 117.1 122.0 120.9 104.4 94.2 52.6 157.3 132.9 98.4 71.0 6.9 14.0 1.0 9.1 39.9 -65.4 41.1
13.8 19.7 20.2 28.4 32.4
28.8 37.7 39.4 13.6 13.8 35.3 51.4 59.1 65.1 58.1 80.6 64.2 88.4 89.1
Y ( W ) = [RTIn S - P - D S - D .- S - (Vz7i2 - Val 71 -
Y(H)*
Y(W)a
71
- SI. b Y(H) 731
*) I.
- 644 - 731 - 830 -1016 -1115 -1034 -1254 -1322 - 590 - 628 -1304 -1541 -1693 -1784 -1700 -2003 -1750 -2015 -2007 =
[RTIn
zene where extensive extrapolation is involved as seen from the data in Table III. (Lowest concentration for isooctane is 0.358.) Discussion and Conclusions The large difference between Sobsd and Scaled, Table X N , clearly demonstrates the failure of the WeimerPrausnitz and the Helpinstill-Van Winkle models to predict the results of this study. Attempts to explain the differences in terms of chemical effects were completely un-
-20
I
0
I
8
4
[vp;
-v3
c
TI
I
1
I2
16
-
7,121
20
x 10 2
Figure 3. Inductive effects. System: pentane-pentene at 45°C. The Helpinstill-Van Winkle correlation, Y(H) = RT In Sobsd (P+D + E). successful. On the other hand, adjustment of the X value for isooctane, following the findings of Hildebrand (1950) and especially of Kyle and Leng (1965), gave much better results as seen from the values for P c a l c d . Again chemical effects could not explain the differences between SBcalcd and Sobsd while adjustment of the inductive contributions, Figure 1, resulted in excellent results as the values of Sbcalcd, Table X N , indicate. This interpretation is further supported by the correlations for the inductive contributions in Figure 2 and 3 from the data on the pentane -pentene system (Gerster, et al., 1960). Figure 2 employs the Weimer-Prausnitz (W) model and Figure 3 the Helpinstill-Van Winkle (H) model. The data are also presented in Table XVI. Two important points can be made. First the improved performance of the (H) model resulting from the incorporation of the small value of 7 3 = 1.0 (cal/mol)1/2 for pentene, similar to the adjustment of the X value for isooctane. This and the large difference in the values for the inductive contributions between the two models demonstrate the sensitivity of the physical model. Ind. Eng. Chem., Process Des. Develop., Vol. 13, No. 4 , 1974
331
Second, the very small contribution of chemical effects, as demonstrated by the very close location in Figure 3, of the points for nitromethane (the cross) and ethylene diamine (the triangle), which differ drastically in acidity. It is concluded, therefore, that (i) chemical contributions to selectivity are negligible in comparison to physical contribution even for pairs with very small difference in molar volumes. (ii) Caution should be exercised in using the W and H models. (iii) The improvement resulting by adjusting the value of A 2 to fit the data for benzene and toluene only indicate that use of available data for a few solvents to adjust the X value of one of the hydrocarbons and determine the value of K in eq 13 could lead in better prediction for the others. Nomenclature 6, = second virial coefficient '2.1. = consistency index D = dispersion contributions to selectivity E = entropic contributions to selectivity I = inductive contributions to selectivity Kx = Lewisacidity P = polar contributions to selectivity P = total pressure P," = vapor pressure R = gas law constant S = selectivity at infinite dilution T = absolute temperature V = molar volume x = mole fraction in liquid phase y = mole fraction in vapor phase
Greek Letters y = activity coefficient A = nonpolar solubility parameter $ = polar-polar and polar-nonpolar induction energy T = polar solubility parameter A = volume change of mixing
Subscripts 1 = solvent 2,3 = hydrocarbon
Superscripts = infinite dilution O
Literature Cited Bromiley, E. G . , Ouiggle, D., Ind. Eng. Chem., 25, 1136 (1933). Ellis, S. R . , Trans. Inst. Chem. Eng., 30, 58 (1952). Gerster, J. S . , Gorton, J. S.,Eklund, R. B., J. Chem. Eng. Data, 5, 423
(1960). Hanson, D . O., Van Winkle, N., J. Chem. Eng. Data, 12, 319 (1967). Harris, H. G., Prausnitz, J. M., Ind. Eng. Chem. Fundam.. 8, 180 (1969). Helpinstill, J. G., Van Winkle, M., lnd. Eng. Chem., Process Des. Develop., 7,213 (1968). Hildebrand, J . H., J. Chem. Phys., 18, 1337 (1950) Kretschner, C. B., Nowakowska, J., Wiebe, J . , J. Amer. Chem. Soc.. 70,
1785 (1948). Kyle, B. G., Leng, D . E., Ind. Eng. Chem., 57,43 (1965) O'Connell. J. P., Prausnitz, J. M., lnd. Eng. Chem., Process Des. Develop., 6,245 (1 967). Othmer, D . F., lnd. Eng. Chem., Anal. Ed., 20, 763 (1948). Perry, R . H., Chilton, C. H., Kirkpatrick, S. D., "Chemical Engineers Handbook," 4th ed, 1963. Pierotti, G. I . , Deal, C. H.. Derr, E. L., Document No 5782, American Documentation Institute, Washington, D . C.. 1958. Prausnitz. J. M., Anderson, R.,A.l.Ch.E. J., 7, 96 (1961). Tassios, D. P., Van Winkle, M., Preprint, A.1.Ch.E. National Meeting, Dallas, Texas, 1972. Thornton, J. D . , Garner, F. H., J. Appl. Chem., 1 (Suppl. l), S-74
(1951). Van Ness, H. C., "Classical Thermodynamics of Non-Electrolyte Solutions," p 131,Macmillan, New York, N. Y., 1964. Weimer, R . F., Prausnitz, J. M., Hydrocarbon Process., 44 (9),237
(1965). Weisman, S..Wood, S. E., J. Chem. Phys., 32, 1 1 53 (1 960)
Receioed for reuieu! M a r c h 23, 1973 Accepted M a r c h 26,1974 Presented a t t h e D i v i s i o n of I n d u s t r i a l a n d E n g i n e e r i n g C h e m i s try, 163rd N a t i o n a l M e e t i n g of t h e A m e r i c a n C h e m i c a l Society, Boston, Mass., April 1972.
Thermogravimetric Analysis Kinetics of Jordan Oil Shale Radi A. Haddadin* and Fathi A. Mizyed Department of Chemistry, University of Jordan, Amman, Jordan
By the use of an automatic thermogravimetric apparatus, weight loss vs. time data were collected for the pyrolysis of Jordan oil shale at temperatures ranging from 280 to 518°C. A first-order rate equation using the integral method of analysis fitted the entire range with an activation energy of 9.80 kcal/mol. A mass transfer controlled mechanism of the organic matter through the carbonate matrix was postulated. Kinetics of weight loss on decarbonated shale samples were also studied and the results compared with the untreated shale. The Arrhenius plot of these data had slight curvature and was resolved into two straight lines. DTA tests on both materials under the same N 2 atmosphere show a strong exotherm at about 345°C.
The large deposits of shale energy reserves throughout the world have been of considerable interest to researchers.,The kinetics of decomposition have been studied during the past few years (Zimmerly, 1923; Hubbard and Robinson, 1950; Allred, 1966; and Hill, et al., 1967). The complex nature of the volatile matter within the rock has complicated the pattern of data and led to no straightforward kinetics. Zimmerly (1923) measured the rate of bitumen formation from kerogen. He calculated an energy of 332
Ind. Eng. C h e m . , Process D e s . Develop., Vol. 13, No. 4 , 1974
activation of 40.0 kcal, which was in agreement with the work conducted in the U. S. Bureau of Mines. Hubbard and Robinson showed that the reaction rates of Colorado shale pyrolysis were complex. In their work, they measured the various component concentrations (oil, gas, and residue) us. time. The measured weight loss data correlated as a function of time resembled an S-shaped curve with respect to time, with bitumen formation as the rate-determining step. Allred (1966) working with the same shale of
