Edwards, J. B., PhD Thesis, Georgia Institute of Technology, 1962.
Griswold. J.. Wonz. S. Y.. Chem. Ena. Proar. Svmv. Ser.., 48 (3). ” ,, 0 1
“
1
~
18 (1952):
Hankinson, R. W., Langfitt, B. D. Tassios, D. P., presented a t the AIChE-IMIQ Third Joint Meeting, Denver, Colo., 1970. Helpinstill, J. G., Van Winkle, M., Ind. Eng. Chem. Process Des. Develop., 7, 213 (1968).
Kobayashi, R., Chappelear, P. S., Deans, K. H., Ind. Eng. Chem., 59(10), 63 (1967).
Kretschmer, C. B., Nowakowska, J., Weibe, R., J. Amer. Chem. SOC.,70, 1785 (1948).
Martire, D. E., Pollava, L. Z., Advan. Chromatogr., 1, 335 (1965). Myers, H. S., Ind. Eng. Chem., 47, 2215 (1955). Myers, H. S., ibid., 48, 1104 (1956). Myers, H. S., Petrol. Refiner, 36 (3), 175 (1957). Neretnieks, I., Ind. Eng. Chem. Process Des. Develop., 7, 335 (1 968\.
Prausnitz, J. M., Eckert, C. A,, Orye, R. V., O’Connell, J. p., “Com uter Calculations for Multicomponent Vapor-Liquid E a u i l i k k ” Prentice Hall. Enelewood Cliffs. N. J . . 1967. Saun’ders, D’. F.,Spaull, A.’J. g.,2. Phys. Che& (Frankfurt), 28, 332 (1961).
Severns, W. H., Sesonke, A., Perry, R. H., Pigford, R. L., AZChE
J.. 1, 401 (1955).
Sinor, J. E. Weber, J. H., J . Chem. Eng. Data, 5,243 (1960). Tassios, D., presented a t the 62nd Annual Meeting of AIChE, Washington, D. C., November 1969. Weimer, R. F. Prausnitz, J. M., Hydrocarbon Process., 44, 237 (1965).
Wilson, G. M., J. Amer. Chem. SOC,86, 127 (1964). Wilson, G. M., Deal, C. H., Ind. Eng. Chem. Fundam., (1962).
1, 20
Wong, K. F., Eckert, C. A., ibid., 10, 20 (1971). Young, C. L., Chromatogr.Rev., 10, 129 (1968).
\-_.I
Null, H.’R., Palmer, D. A., Chem. Eng. Progr., 65 (9), 47 (1969). Orye, R. V., Prausnitz, J. M., Ind. Eng. Chem., 57 (5), 18 (1965). Pierotti, G. J., Deal, C. H., Derr, E. L., ibid., 51 (I), 95 (1959). Porter, P. E., Deal, C. H., Stross, F. IT, J.Amer. Chem. SOC.,78, 2999 (1956).
RECEIVED for review January 4, 1971 ACCEPTED April 23, 1971
Work supported financially by the Petroleum Research Fund of the American Chemical Society.
Estimation of Ideal Gas Heat Capacities of Hydrocarbons from Group Contribution Techniques New and Accurate Approach Tran-Phuc Thinh, Jean-louis Duran, and Rubens S. Ramalho’ Lava1 University, Department of Chemical Engineering, Quebec 10, Que., Canada
An additive group technique for calculation of ideal gas heat capacities is proposed. Testing with hydrocarbons at several temperatures reveals that this technique is more accurate than any now appearing in the literature.
S e v e r a l methods for predicting C,* values for hydrocarbons are available in the literature. These methods fall into two categories. Category 1 constitutes methods based upon use of theoretical concepts to obtain contributions to C*, from translational, rotational, and vibrational energies. Typical are the methods described by Dobratz (1941), Stull and Xayfield (1943), Crawford and Parr (1948), Souders e t al. (1949), and Lleghreblian (1951). Category 2 comprises additive-group techniques. Methods are empirical and are based upon the assumption that each molecular structural group contributes to the overall heat capacities in a n additive manner. Typical are the methods of Anderson et al. (1944), Johnson and Huang (1957), and Rihani and Doraiswamy (1965). Reid and Sherwood (1966) point out that the methods of Johnson and Huang (1957) and Rihani and Doraiswamy (1965) are the most accurate within category 2 appearing in the literature. If both categories are considered, the methods of Souders et al. (1949) (category 1) and Rihani and Doraiswamy (1965) (category 2) give the most accurate estimations. To whom correspondence should be addressed. 576
Ind. Eng. Chem. Process Des. Develop., Vol. 10, No. 4, 1971
The method proposed in this article falls within the category of the additive-group techniques. This proposed technique of estimation is shown t o be definitely more accurate than any of the existing methods within both categories. In general no single previous method can combine the three following desirable characteristics: good accuracy, applicability over a broad temperature range from cryogenic to very high temperatures, and continuous estimation of C,* as a function of temperature (many of the existing techniques are limited t o point values a t certain temperature intervals). .4 method which could combine these three characteristics is needed since even the extensive compilation of thermodynamic properties of hydrocarbons of the API Research Project 44 (1969) does not include all hydrocarbons known (e.g., naphthalene is not tabulated). Also, no C,* data for hydrocarbons below 273°K (and often below 298°K) are available except for the first few members of the paraffinic series. Of
Additive
Franklin (1949) suggested, by extension of Pitzer’s statistical mechanical treatment for long chain paraffins (1940), that any thermodynamic property P of hydrocarbons could be well approximated by
Table 1. Aliphatic Hydrocarbon Groups
AC,*
=
A + B , ~ - C I / T ~ I-
B,e-C2/Tnz
AC,* in cal/(g mol)(OC) or Btu/(lb mol)(OF) and T in
O K
Group
no.
1 2
20.4410 136.8702
G 1013.8229 788.7739
1,0489 1.0380
0 120.3019
0 832.8313
0 1.0452
-0.6214
75.9952
601.8911
0.9953
61.3229
1013.8229
1.0489
- 2.4690
89.6797
733.9538
1.0396
81.7638
1013.8229
1.0489
3.4382 2.4980 1,6538 1.5307 1.6606
15.3919 24.0973 12.4458 36.4231 31.4786
527.1308 1133.5426 21.3585 321 ,4962 134.8699
0.9644 1.0774 0.5 0.9048 0.8030
0 20.4410 0 30.7839 0
0 1013.8229 0 527.1308 0
0 1.0489 0 0.9644 0
4.9218
62.5821
652.9594
0.9990
40.8819
1013.8229
1.0489
-0.0015
102.8316
51 1,5828
0.9573
81 ,7638
1013.8229
1,0489
2.6362
78.5993
874.4157
1.0464
61.3229
1013.8229
1.0489
H
3.1836
62,2851
1110.9532
1.0843
40.8819
1013.8229
1.0489
H
5.9189
60.2442
990,4639
1.0590
40,8819
1013.8229
1.0489
7.5007
66,6656
578.8631
0.9870
40.8819
1013.8229
1.0489
8.5582
49.9143
700.3515
1.0163
20,4410
1013.8229
1.0489
8.0606
64.5906
949.4988
1.0596
40.8819
1013,8229
1.0489
A
Group
-CHB
B1
4.7366 3.0820
I
nl
B2
CZ
n2
-CH? 3
I
-C-H
I
4
-C5 6 7 8 9
10
11
I I
-CH2 -CE =CH
=C= H
\ C=CH? / \ C=CHZ / \ / C=C
12
/ \ \ / c=c / \
13
H
H
\ / C=C / \ (cis)
14
\
/
/
\
c=c
H
(trans) 15
\ C=C=CHZ / \
16
H 17
= 2
/
\ / C=C=C \ /
H
P
C=C=CH?
H
+
Contribution of molecular structural groups 2: corrections where necessary correction for the symmetry of the molecule
+
(1)
All existing additive-group techniques ignore the correction for the symmetry of the molecule in the estimation of C,* values but include this correction in the estimation of values for AHI*, ASI*, and AF,*.
The technique proposed in this article differs from those existing in the scientific literature by the following refinements: Corrections for the symmetry of the molecule are considered in identical manner, whether the thermodynamic property t o be estimated is Cp*, AH,*, AS,*, or AFf*. This article is only concerned with estimation of C,* values. A careful examination of the recent C,* data from API Project 44 (1969) and comparison with the estimated values led us t o Ind. Eng. Chem. Process Des. Develop., Vol. 10, No.
4, 1971 577
Table II. Aromatic Hydrocarbon Groups Group no.
A
61
c1
nl
Bz
CZ
nz
1.4345
10.8720
1174.9378
1.1387
0
0
0
*r
1.3635
79.6089
1269.0479
1.1387
74.9247
986.1985
1.0928
6 \
2.3297
47.6491
1587 ,2948
1.1915
43.4881
1174.9378
1,1387
Group
18
/
\
19
-c*,
20
--c
Table 111. Ring Formation Correction Correction
no.
Ring
A
01
c1
nl
BL
1 2
3-Membered ring 5-Membered ring, cyclopen t ane 5-Membered ring, cyclopentene 6-Membered ring, cyclohexane 6-Membered ring, cyclohexene
-1 7223 -5 5560
30 1047 86 9988
4304 6037 1281 9257
1 3222 1 1221
32 9162 82 7124
c1 1237 7501 545 5184
1 1173 0 9912
-2 3485
70 5966
1877 9329
1 1852
70 5846
813 0059
1 0604
-1 8728
95 6365
4371 2289
1 3210
99 2549
545 5184
0 9912
-4 7552
91 0076
972 7163
1 1001
87 0564
756 9254
1 0481
3 4
5
include this correction, which although generally small, is not always negligible. The mathematical model chosen in this work for calculating the three terms on the right-hand side of Equation 1 is the exponential model recently proposed by Yuan and Mok (1968a), namely
Previous methods utilized the polynomial model
C,*
= a
+ bT + c T 2 + dT3 + .
. . . .
(3)
for the calculation of the two first terms on the right-hand side of Equation 1 and have always ignored the correction for the symmetry of the molecule. 'Yuan and hIok proved their model, derived from statistical thermodyi;;;,;iic considerations, superior to the empirical polynomial equation within the temperature range of the data used. Furthermore, the exponential model permits accurate extrapolat'ion, \yhich is not feasible with the polynomial model. When experimental C,* data in the commonly available temperature range of 298-1500OIi are used for obtaining the coefficients of Equation 2, this model can be used t o predict C,* values over the range from 200-600OoK, usually within a n average percentage error of 1% as indicated by Yuan and Mok (1968a,b). A comparison between values of C,* obtained by application of polynomial and exponential models has been made. The results are presented in Table VIII, which has been filed with the ACS Microfilm Depository Service. Inspection of this table reveals t'he superiority of the exponential over the polynomial model, particularly for the case of extrapolated values. The upper limit of temperature has actually little meaning in the case of hydrocarbons since they are usually unstable a t temperatures above 1500-2000°K. However, this upper limit might be of interest in the case of other compounds such as carbon monoxide. I n summary the contribution of each structural group and the corrections (including that for the symmetry of the molecule) were represented in our work as 578
Ind. Eng. Chem. Process Des. Develop., Vol. 10,
NO. 4, 1971
nz
ACp* (of molecular structural group or coirection) =
A
+ Ble
-Ci/T"l
- B ~ ~ - C ~ / T "(4) J
The values of the constants in this equation were determined by application of the least-squares method, minimizing the sum of the squares of percentage deviations. Several authors who used,the less accurate polynomial form (Equation 3) employed a conventional least-squares, method, minimizing the sum of the squares of the absolute deviations, which is a procedure less suitable for deriving C,* equations. The C,* data used in this work were those reported from API Research Project 44 (1969). Previous authors used older data (e.g., API Research Project 44 of 1948) which have suffered significant revisions since then. These data are generally tabulated from 298-150O0K a t intervals of 100OK. The exponential model was fit to these data as indicated. From the C,* equations in exponential form of appropriate hydrocarbons, the AC,* of a composing group or corrections as shown in Equation 4 can be determined by assuming additivity of contributions. The overall heat capacity of any hydrocarbon is given by z
Significant improvements in the method proposed in this article over those now available are special corrections which were introduced for the first few molecular structural groups (--CH*) in normal series. This feature permits us to obtain
I
accurate estimates of C,* for short as well as long-chain hydrocarbon compounds. In this work the regular incremental values corresponding to the group (-CH2) from the API Proj-
I
ect (1969) were selected as a starting point. However, from the C,* data the incremental values correspoiiding to the group (-CHz) become uniform only after the first few members of
I
the respective normal series. Other group contribution methods available, such as those of Johnson and Huang (1957)
Table IV. Correction for Branching in Cycloparaffins Correction no.
A
nl
c1
81
82
cz
nz
Branching in five-membered ring 6 7
8 9 10 11
Single branching Double branching, 1,l position 1, cis-2 1, trans-2 1, cis-3 1. trans-3
2.6826 5.4945
102.9302 115.3182
1040.8363 1362.2334
1.0906 1.1394
104.7224 122.2821
1062.1344 951.9636
1.1013 1,0909
5.1851 5.0336 5,0336 5.0336
116.5713 117.2347 117.2347 117.2347
1170.5749 1084.4398 1084.4398 1084.4398
1.1148 1 ,1022 1,1022 1,1022
122.2821 122.2821 122,2821 122,2881
951.9636 951.9636 951.9636 951.9636
1.0909 1.0909 1 ,0909 1.0909
1.5560 4,5367
112.8656 124.6332
2470.4850 3819.4942
1,2344 1,3044
113.1267 130.5289
3061.5552 2405.6012
1,2706 1.2375
3.6537 2.9896 4,7228 3.8571 3.8571 3.4805
126.7920 128.1617 125.9625 127.3311 127.3311 126.8064
2640.9182 2189.0807 3032.2880 2403.6929 2403.6929 2616.9819
1.2462 1.2193 1,2661 1.2294 1.2294 1.2473
130,5289 130,5289 130.5289 130.5289 130.5289 130.5289
2405.6012 2405.6012 2405,6012 2405.6012 2405.6012 2405,6012
1.2375 1.2375 1.2375 1.2375 1.2375 1,2375
Branching in six-membered ring 12 13 14 15 16 17 18 19
Single branching Double branching, 1,l position cis-l,2 trans-l,2 cis-1,3-d trans-l,3 --e cis-1,4 trans-1,4
Table V. Correction for Branching in Aromatics Correction no.
20 21 22 23 24 25
Double branching, 1,2 position 1,3-position 1,4 position Triple branching, 1,2,3-position 1,2,4-position 1,3,5-position
A
61
Cl
nl
62
C2
n2
2.2108
93.1940
1137.6065
1.1076
93.8766
1381.8801
1.1442
0,4109 1,0741 3,2258
94.1667 93.3095 106.7469
1266.8220 1414.2979 1416.3668
1.1287 1.1428 1,1311
93,8766 93.8766 108,0631
1381 ,8801 1381 ,8801 1496.1894
1 ,1442 1.1442 1.1513
3.7823 1.4321
105.6478 107.5030
1513.4331 1482.6086
1.1414 1.1443
108.0631 108,0631
1496.1894 1496.1894
1.1513 1.1613
and Rihani and Doraiswamy (1965), simply took a n average value of the contribution of the group (-CH2). Our approach,
I
introducing special corrections for the first few molecular structural groups (-CH2) before reverting to the regular in-
I
cremental values, results in significant improvement, particularly in the case of short-chain hydrocarbons. Even for longer-chain hydrocarbons, the improvement is significant a t lower temperatures (e.g., 298’K) when C,* values are low; therefore, the correction becomes appreciable. Tabulation of Group Contributions and Corrections
Tables I through VI are needed for the application of the proposed technique. Tables I and I1 present the calculated constants for the exponential model for 17 aliphatic and 3 aromatic hydrocarbon groups, respectively. The contribution of any of the indicated groups toward the value of C*, for a given compound can be easily determined a t any desired temperature. The groups listed in Tables I and I1 are the same considered by Rihani and Doraiswamy (1965) in drawing up their tables for group contributions to values of Cp*, plus group No. 8, which does not appear in these authors’ tables for Cp*, but is included in the tables for estimations of AH,* by Verma and Doraiswamy (1965). The calculations of the parameters listed in these tables were performed as outlined in the previous section of this article. T o construct these
tables, a pair of “typical” compounds must be selected to arrive a t the contribution of a given group toward the total value of C,*, by straightfomard application of the additivity concept. The selection of these “typical” pairs was generally the same employed by Rihani and Doraiswamy (1965). Table I11 presents the corrections indicated by the second term on the right-hand side of Equation 1. Tables IV and V permit us to calculate the symmetry corrections, which had been ignored by the previous techniques for estimation of C,* by group contributions. Finally, Table VI presents the special correction for the first few (-CHJ groups in normal series dis-
I
cussed in the previous section of this article. Estimation of Cp*
A stepwise procedure for the estimation of C,* values by the proposed technique is outlined. Table VI1 presents numerical examples of this sequence of calculation for five typical compounds. The successive steps are as follows: Step 1. Write down the molecular structural formula of the compound. Step 2. Break up the molecular structural formula into appropriate molecular structural groups given in Tables I and I1 to have a minimum number of molecular groups. Then calculate the numerical contributions of the various molecular groups. Samples of selected numerical values for group contributions (corresponding to Tables I and 11) a t eight selected Ind. Eng. Chem. Process Des. Develop., Vol. 10, No.
4, 1971 579
Table VI. Special Correction for First Few (-CHz)
in Normal Series
I Correction no.
A
81
nl
c1
For first three (-CHg)
BZ
cz
nt
in normal paraffins
I
26
1st (-CH2)
- 1.6075
59.4196
653.8562
0.9992
57.8390
779.2506
1.0174
27
1st and 2nd
-0.5942
74.1066
745,5631
1.0220
74.5838
694,6245
1.0053
-0.3156
89.9889
750.0491
1.0258
91.2438
652.7659
0.9996
I
(-CH2)
'I
28
lst, 2nd, 3rd
(--CHd
I
For first three (-CH2) in normal alkyl benzenes
I
29
1st (-CH2)
-0.6231
96.7804
972.3475
1 ,0980
95.8682
1115.4125
1.1162
0.9122
110.6626
1065.8703
1.1084
112.1937
1014.5118
1.0997
1,1845
126.5265
1024.6444
1.1005
128.5645
943.4540
1,0870
I 30
1st and 2nd
(-CH2)
I
31
lst, 2nd, 3rd
(-CHz)
I
For first two (-CHZ)
in normal monoolefins
I
32
1st (-CH2)
1.8693
64.0369
616.9205
0.9973
68.6181
313.8732
0.8983
33
1st and 2nd
3.0142
78.5361
721,9341
1.0225
84,9976
352.8265
0.9180
(-CHz) For first two (-CH2)
in normal acetylenes
I
34
1st (-CH2)
- 1.9514
54.0869
333.3507
0.9005
49.9997
504.9147
0.9628
35
1st and 2nd
-0.2389
66.9791
533.4160
0.9750
66.5609
510.4336
0.9686
956.9970
1,0777
I
(-CH2) For first (-CH2), outside ring, in normal alkyl cyclopentanes
I
36
1st (-CHz)
-7,2831
140.4183
312.1951
0,9010
119,3679
I
For first two (-CHz),
I
37
1st (-CH2)
38
1st and 2nd
0,1936
outside ring, in normal alkyl cyclohexanes
128,1843
2165,9117
1.2143
128.8507
2097,6983
1.2081
147.1091
1465.2225
1.1521
144.9198
1839.8190
1.1870
I
-0,5250
(-CH2)
I
temperatures are given in Table I X , which has been filed with the ACS Microfilm Depository Service. Actually, such numerical values can be obtained a t any desired t'emperature from the respective equations. Similarly, Table X, which has also been filed with the ACS Microfilm Depository Service, presents samples for the corrections indicated in Tables 111-VI a t the same eight selected temperatures. Step 3. If the compound belongs t o the series of 3580 Ind.
Eng. Chem. Process Des. Develop., Vol. 10,
No. 4, 1971
membered ring compounds, cyclopentanes, cyclopentenes, cyclohexanes, or cyclohexenes, a ring formation correction must be added (Table 111). Step 4. If the compound belongs to the series of cycloparaffins or aromatics and there is branching, a correction must be added for the kind of branching shown in Tables IV and V (symmetry corrections). Step 5. If the compound belongs to one of the following
normal series: n-paraffins, n-alkyl benzenes, n-monoolefins, n-acetylenes, n-alkyl cyclopentanes, or n-alkyl cyclohexanes, a special correction must be added for the first few molecular groups (-CH2) (Table VI).
I
Step 6. Summation of the numerical values of the various molecular groups and corrections yields the desired C,* value of the compound. Q,
k-
m
u)
m
M ri
II
*
*ri
xxx
u)
M W
wm0.1 00
0 . 1 W 0 -
2 X
M
Comparison with Other Methods
Q,
X I1 ri
2 3 0
00 CD
X
0 M
N
ii'
L
II 0 m
e 3
8
Tables XI-XI11 present a comparison of C*, values estimated by the proposed technique (for 42 hydrocarbons a t several temperatures between 298.16' and 1500'K) with the experimental values. These three tables have been filed with the ACS Microfilm Depository Service. In Table X I the average percentage error for a total of 68 points is only o.1570. For Table X I I , with a total of 125 points, the average percentage error is only 0.2670. Table XI11 presents similar comparison a t cryogenic temperatures for a few cases when experimental data were available. The lack of experimental C,* data below 298'K limited the testing of this method a t cryogenic temperatures (down to 200'K) to the seven hydrocarbons listed in Table X I I I . Despite the needed extrapolation, the average error is below 1%. Concerning the possibility of extrapolation to higher temperatures (up to SOOO'K), the difficulty in testing the method for the case of hydrocarbons resides in their instability a t temperatures above 1500-2000'K. There are no experimental data above 1500'K to make the comparison possible. These results indicate for all normal series that the values of C,* estimated by the proposed group contribution technique are actually as accurate as those calculated from polynomial equations for which the constants were evaluated based upon the most recent experimental data available. This is a remarkable achievement as far as estimation techniques are concerned.
1
0.1
">
Results
r, 3
$
X
X
00
0.1
a rl
8
c
80.1
cy
0 0 0
*
?
a a z g s:
Reid and Sherwood (1966) present a critical review of the various methods available to estimate C*, values for hydrocarbons. For comparison among methods, these authors have chosen the typical hydrocarbons which are presented in Table X I a t the four indicated temperatures. Table XIV presents the average percentage errors obtained by the use of each method [as reported by Reid and Sherwood (1966)], as well as the average percentage error obtained for these same hydrocarboiis a t the same temperatures, by the method proposed in this article. Because of specific limitations, some of the methods reported in Table XIV cannot be applied to all hydrocarbons. The standard of reference for error calculation, in the case of the data reported by Reid and Sherwood, was the set of API data of 1953. These data are essentially identical to the API (1969) values; therefore, it was unnecessary to adjust them to refer all errors to the latter standard. Table XIV has been filed with the ACS Microfilm Depository Service. Inspection of Table XIV indicates that the proposed technique for estimation of C,* is more accurate than all previous ones reported in the literature. Nomenclature
3
= = AH I* = AS,* =
C,*
AFf*
heat capacity a t zero pressure, cal/(g mol)("K) standard free energy of formation, cal/g mol standard heat of formation, cal/g mol standard entropy of formation, cal/(g mol)('K)
Ind. Eng. Chem. Process Des. Develop., Vol. 10, No. 4, 1971
581
literature Cited
Souders, M., Matthews, C. S., Hurd, C. O., Ind. Eng. Chem., 41,
Anderson, J. W., Beyer, G. H., Watson, K. M., Nut. Petrol. News, Tech. Sec., 36, R476 (July 5, 1944). API Research Project 44: “Selected Values of Properties of Hydrocarbons and Related Compounds,” from TRC Data Distribution Office, Texas A & M Research Foundation (April
Stull, D. R., Mayfield, F. D., Ind. Eng. Chem., 35, 639 (1943). Verma, K. K., Doraiswamy, L. K., Ind. Eng. Chem. Fundam.,
30, 1969).
Crawford, B. L., Parr, R. G., J . Chem. Phys., 16, 233 (1948). Dobratz, C. J., Ind. Eng. Chem., 33,759 (1941). Franklin, J. L., Ind. Eng. Chem., 41, 1070 (1949). Johnson, A. I., Huang, C. J., Can. J . Technol., 34, 405 (1957). Meghreblian, R. V., J . Amer. Rocket Soc., p. 128, September 1951. Pitzer, K. S., J . Chem. Phys., 8,711 (1940). Reid, R. C., Sherwood, T. K., “The Properties of Gases and Liquids,” 2ndEd., McGraw-Hill, New York, N.Y., 1966, Chap. 5., 169.
Rgani, D. N., Doraiswamy, L. K., Ind. Eng. Chem. Fundam., 4, 17 (1965).
1037 (1949).
4, 389 (1965).
Yuan, S.C., Mok, Y. I., Hydrocarbon Process., 47, 3, 133 (1968a). Yuan, S. C., Mok, Y. I., Hydrocarbon Process., 47, 7, 153 (1968b). RECEIVED for review February 10, 1971 ACCEPTED?*lay 18, 1971 The authors gratefully acknowledge the financial assistance of a grant from t)he National Research Council of Canada. Tables VIII-XIV nil1 appear following these pages in the microfilm edition of this volume of the Journal. Single copies may be obtained from the Reprint Department, American Chemical Society, 1155 Sixteenth St., N.W., Washington, D. C. 20036, by referring to author, title of article, volume, and page number. Remit $3.00 for photocopy or $2.00 for microfiche.
Heavy Actinide Element Partitioning by Extraction with Monoacidic Phosphorus Esters-HEPEX Boyd Weaver and Richard R. Shoun Chemical Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tenn. 37830
A process has been developed for separating the heaviest actinides from americium and curium by extraction with di(2-ethylhexyl)phosphoric acid in an aliphatic diluent from hydrochloric acid solutions. Singlestage californium/curium separation factors were -40. The process has been applied successfully to the separation of californium from curium in a continuous multistage operation where the feed solution contained corrosion-product zirconium, iron, and nickel, along with much lithium introduced in previous processing. When zirconium is absent and the concentration of extracted elements is very low, the preferred choice of extractants is 1 -methylheptyl phenylphosphonic acid, which is especially advantageous in extraction from nitric acid solutions. The extractant 2-ethylhexyl phenylphosphonic acid is a second choice for very dilute zirconium-free solutions.
P e p p a r d et al. (1959) first reported that in extractions of the trivalent actinides by di(2-ethylhexy1)phosphoric acid (HDEHP) from hydrochloric acid solutions, the difference between berkelium and curium was much greater than that between curium and americium. A moderately large separation between californium and berkelium was also observed. Later work indicated that the differences could be made still larger by using 2-ethylhexyl phenylphosphonic acid (HEH[@PI) as the extractant (Peppard et al., 1961). When plans were made for producing large quantities of the transplutonium elements a t Oak Ridge National Laboratory, the flow sheet for separating these elements included a process in which berkelium and the heavier elements were to be separated from americium and curium by continuous, countercurrent, multistage extraction from dilute hydrochloric acid by HEH [@PIin diethylbenzene diluent. Preliminary plans for this process were based on a study by Baybarz (1963). After observation by one of us (Weaver, 1968) showed that effects of zirconium on extractions by HEH [@€’I precluded the use of this extractant with feed solutions encountered in the ORXL Transuranium Processing Plant, where corrosionproduct zirconium is indigenous, a much more thorough study of altarnatives was made. This paper reports some basic data 582
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on extraction by HEH[@P] and HDEHP which led to the development and application of a process based on H D E H P . It also suggests possible improvements through the use of a third extractant, 1-methylheptyl phenylphosphonic acid. Experimental
Materials. T h e effect of quality of the HDEHP became a n essential part of the study and is treated in a later section. The d a t a on which standard process parameters were based were obtained with a n unusually pure batch of HDEHP from Virginia-Carolina Corp. (now Mobil Chemical) which was not matched by a large subsequent supply of the material purchased from the same supplier. These data were checked with other much more expensive pure (>99yo) HDEHP from Eastman Chemicals and other material laboriously purified by us. Most supplies of HDEHP contain several percent of mono(2-ethylhexy1)phosphoric acid and small, unknown, but significant amounts of powerfully extracting polyphosphates or pyrophosphates. The HEH [@PI used was from a one-ton supply purchased from Victor Chemical Works for process use but not used for that purpose because of the zirconium effect mentioned above. K e removed phenylphosphonic acid from it by washing with
