Ind. Eng. Chem. Process Des. Dev. 1085, 2 4 , 97-107
07
in the laboratory. The work was supported by the U.S. Department of Energy.
deoxygenation of dibenzofuran is strongly inhibited by 7,8-benzoquinoline (Krishnamurthy and Shah, 1982), and we expect that basic nitrogen-containing compounds inhibit conversion of phenolic compounds as well. The reactivities of the individual organooxygen compounds in the acidic fractions are all roughly the same (Table 11, Figure 8), the greatest difference being a ratio of 5.4 for 4-cyclohexylphenol and 2-hydroxyphenylbenzene. These results are in good agreement with the pure compound data of Krishnamurthy et al. (1981) (obtained at about 350 OC and 104 atm with an Ni-Mo/y-A120, catalyst). We suggest that the small differences in the observed reactivities reflect subtle steric and electronic effects. For process modeling, it may be a good approximation to use one rate constant to represent all the substituted phenols and partially hydrogenated naphthols. The relative rapidity of the conversions of these oxygen-containing compounds implies that they may be largely converted in hydroprocessing of coal liquids (and other fossil fuels), with relatively high hydrogen consumptions being expected. Water is a product of the hydrodeoxygenation reactions, and we might expect it to have an effect on the catalyst structure and activity. The data of Figure 3 indicate that-at least in the presence of excess H2S and hydrogen-the effect is small, being reflected only in the break-in period. These results are in agreement with those observed in experiments with 1-naphthol (Vogelzang et al., 1983). Acknowledgment We thank S. S. Starry and S. K. Banerjee for assistance
Registry No. Ni, 7440-02-0;M o , 7439-98-7;5,6,7,8-tetrahydro-1-naphthol,529-35-1;4-cyclohexylphenol,1131-60-8;3(3-methylphenyl)phenol,9325486-5;2-hydroxyphenylbenzene, 90-43-7.
Literature Cited Ellezer. K. F.; Bhlnde, M.; Houalla, M.; Broderlck, D. H.; Gates, B. C.; Katzer, J. R.; Olson, J. H. Ind. En Chem. Fundem. 1977, 16, 380. Furimsky, E. Fuel 1978,57, 194. Gates, B. C.; Katzer. J. R.; Schult. G. C. A. "Chemistry of Catalytic Processes"; McGraw-HIII: New York, 1979. G r a m , D. W.; Petrakls, L.; Young, D. C.; Gates, B. C. Netwe (London) 1884, 308, 175. Hara, T.; Tewarl, K. C.; Li, N. C.; Fu, Y. C. Prep., Dlv. Fuel Chem., Am. Chem. Soc. 1979,24(3), 215. Houalla, M.; Nag, N. K.; Sapre. A. V.; Broderick, D. H.; Gates, B. C. A I C E J . 1978,2 4 , 1015. Kattl, S. S. Ph.D. thesis, University of Delaware, Newark, DE, 1984. Kattl, S. S.; Westerman, D. W. 8.; Gates, B. C.; Youngless, T.; Petrakis, L., Ind. Eng. Chsm. Proc. Des. Dev. 1884,2 3 . 773. Katzer. J. R.; Slvasubramanlan, R. Catel. Rev.-Scl. Eng. 1878, 2 0 , 155. Krishnamwthy, S.; Panvelker. S.; Shah, Y. T. A I C E J . 1881,2 7 . 994. Krishnamurthy, S.; Shah, Y. T. Chem. Eng. Commun. 1862. 16, 109. Landa, S.; Mmkova, A.; Bartova. N. Sci. Pap. Inst. Chem. Tech. Prague 1868,D 16, 159. Li, C.4.; Xu, 2.43.; Cao, L A . ; Gates, B. C.; Petrakis, L. AIChEJ. 1885,in press. Petrakls, L.; Ruberto, R. G.; Young, D. C.; Gates, B. C. Ind. Eng. Chem. Process. Des. D e v . 1983a,2 2 , 292. Petrakis, L.; Young, D. C.; Ruberto, R. G.; Gates, B. C. Ind. Eng. Chem. Process D e s . D e v . 1983b,22, 298. Socrates, 0."Infrared Characteristlc Group Frequencies"; Wlley-InterscC ence: New York. 1480. Vogelzang, M. W.; Ll, C.-L.; Schult, G. C. A.; Gates, B. C.; Petrakls, L. J . Catel. 1983,84,170.
.
Received for review M a y 13, 1983 Accepted April 9,1984
Thermophysical Properties of Coal Liquids. 3. Vapor Pressure and Heat of Vaporization of Narrow Boiling Coal Liquid Fractions James A. Gray' Gulf Research and Development Company, Pittsburgh, Pennsylvania 15230
Gerald D. Holder University of Pittsburgh, Pittsburgh, Pennsylvania 1526 1
C. Jeff Brady, John R. Cunningham, John R. Freeman, and Grant M. Wllson Wlttec Research Company, Provo, Utah 8460 1
Coal liquids produced from SRC-I1 processing of Pittsburgh Seam bituminous coal from Powhatan No. 6 Mine were distilled into a number of narrow boiling cuts. Vapor pressure measurements were performed on 6 heart cuts at temperatures from 267 to 788 K and pressures to 3.6 MPa with both batch still and flow apparatuses. Heats of vaporization were measured in a flow calorimeter on these same fractions at temperatures from 366 to 755 K. After a number of correlation methods were reviewed, it was found that the modified BWR equatbn-of-state developed by Brul6 and co-workers specifically for coal fluids gave the best representationof vapor pressure data. An empirical method InvoMng a simple boiling point relatlonship combined with the Watson equation gave the best predictions of the latent heat data.
Introduction In the design of coal processing plants, in many instances one must accurately estimate thermodynamic properties such as vapor pressures and heats of vaporization of coal 0196-4305/85/ 1124-0097$01.50/0
liquid fractions. Although a number of generalized methods have been published (Reid et al., 1977; MI, 1976) and are widely used for paraffinic petroleum-derived fractions, there has been some concern (Newman, 1981, 0 1984 American Chemical Society
98
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985
Wilson et al., 1981, Recon Systems, Inc., 1981) about the suitability of these correlations for highly aromatic coalderived fractions which contain significant quantities of polar heterocyclic compounds. Although experimental vapor pressure data on pure compounds typical of those found in coal liquids can be used to derive new correlations or check the accuracy of existing correlations, confirmatory experimental data are also needed on fractions of real process streams from coal conversion plants. These data can be used to verify that calculated critical points lie on the vapor pressure curve and can also be used to check the applicability, for coal liquid pseudocomponents,of fugacity coefficient models. Vapor pressure and heat of vaporization data on well-characterized fractions are practically nonexistent. Background Vapor pressure data on six liquid fractions from the Exxon Donor Solvent (EDS) coal liquefaction process (Furlong et al., 1976) were reported by Wilson et al. (1981) at temperatures to 755 K. Using specific gravity and mid-boiling point (50 w t % distilled temperature) as input parameters to the correlation proposed by Maxwell and Bonnell (19571, Wilson et al. noted an average deviation between experimental and predicted vapor pressures of 10.4%, an overprediction of the vapor pressure by 10% on the average, and a maximum deviation of +39%. Consequently, Wilson et al. developed a corresponding states correlation, based on a form of the Riedel (1954) vapor pressure equation and the Pitzer acentric fador, that reduced the average and maximum deviations by half and reduced the positive bias by a factor of 4. This same type of correlation was developed by Lee and Kesler (1975) for heavy petroleum fractions, and although not explicitly stated by Wilson et al., it apparently was less accurate than the version developed specifically for coal liquids. Brul6 et al. (1982) have proposed a modified Benedict-Webb-Rubin (BWR) equation for application to coal liquids. In their approach, Brul6 and co-workers replaced the acentric factor with a third corresponding states parameter, called the orientation parameter, that is similar to the acentric factor but also takes into account limited nonideal effects, such as weak polarity and steric anisotropy. New constants were derived for the BWR equation from a data base that included over 5000 data points for petroleum and coal chemicals. The overall absolute average relative deviation for predicting the vapor pressure data base was quoted as 1.78%. For a single pseudocomponent at saturated conditions, the Grayson-Streed (1963) vapor-liquid equilibrium calculation simplifies to an iterative solution for vapor pressure such that the fugacity coefficient of the saturated vapor equals that for the pure pseudocomponent liquid at system conditions. The latter quantity is calculated by using Grayson and Streed's correlation. The critical temperature and pressure are estimated by using the Cavett (1962) correlations with specific gravity and boiling point as the input parameters. The critical pressure is then adjusted for coal liquid fractions as follows P, = PJCavett) X [ L O - 0.56(SG - 0.9)] (1) as proposed by Antezana and Stephenson (1979). Vapor pressure and heat of vaporization data on six well-characterized liquid fractions from the Solvent Refined Coal I1 (SRC-11)process (Moschitto, 1978; Schmid and Jackson, 1976) were reported by Gray et al. (1983) at temperatures to 755 K. The vapor pressure data were shown to be well correlated by the Wilson et al. (1981) vapor pressure equation provided critical temperature and acentric factor were derived as adjustable parameters if
not experimentally available. The critical point was observed for only two of six fractions. Heats of vaporization were accurately predicted from the slopes of the vapor pressure curves using molecular weight as an adjustable parameter. The latter molecular weight was generally somewhat higher than that calculated from a correlation which was based on experimental molecular weight data (Gray et al., 1983). A modified Kistiakowsky equation, relating the molar heat of vaporization at the normal boiling point to the boiling point, and the Watson relationship (Reid et al., 1977) were shown to give satisfactory predictions of latent heat. In the present investigation, vapor pressure and heat of vaporization data were measured on six additional wellcharacterized liquid fractions obtained from SRC-I1 process streams and include the observed critical points for three of the fractions. These fractions were produced from the same wider boiling samples previously reported (Gray et al., 1983). Several methods for estimating the vapor pressures and heats of vaporization of the fractions are examined and compared. Since critical temperature, critical pressure, and acentric factor are needed in most of the correlations as basic input properties, several methods of deriving these properties from the experimental vapor pressure data are evaluated. The derived critical properties were then compared to values obtained from correlations that require minimal characterization data such as specific gravity, boiliig point, and molecular weight (Newman, 1981). Experimental Section In earlier work (Gray et al., 1983; Gray, 1981), several large batches (568 L) of full boiling range coal liquids, generated from SRC-I1 processing of Pittsburgh Seam Powhatan No. 5 Mine coal on Process Development Unit P-99 (located a t Gulfs Research Center, Harmarville, PA), were prepared and distilled into 19 narrow boiling fractions having mid-boiling point temperatures from 340 to 794 K. Characterization measurements on these fractions included molecular weight, pour point, elemental analyses, water content and solubility, and hydrocarbon types. Secondary fractionations were performed on six cuts that were spaced, to a good approximation, uniformly over the full boiling range yielding a minimum of 2 L each of six "heart cuts" having boiling ranges that were 4 to 26 K wide. These cuts were used for the previously reported (Gray et al., 1983) vapor pressure and heat of vaporization measurements at temperatures to 755 K. In the present work, secondary fractionations were performed on six more of the original 19 distillate cuts, yielding heart cuts having boiling ranges that were 2.8 to 14.4 K wide. Approximately one year had elapsed from the time the primary cuts were first stored in standard carbon steel drums under nitrogen blanket until the second series of heart cuts was distilled from the primary cuts (Gray and Holder, 1982). Although the freshly distilled heart cuts appeared visually clear, except for the highest boiling fractions which, at room temperature, typically contained stratified crystalline material or were completely solid, the effect of aging on the subsequent measurements is unknown. Table I lists the basic characterization data for the six heart cuts as well as the same data for the earlier set of six heart cuts. The boiling ranges of the fractions, obtained from the secondary distillations, compare well with boiling points derived from the vapor pressure data. Several of the distillations were performed a t low pressure, and the vapor temperature data were corrected to atmospheric pressure using a Watson characterization factor of 10 and the Maxwell-Bonnell vapor pressure correlation (APITechnical Data Book, 1976). Two methods were used for measuring vapor pressure and have been described in some detail elsewhere (Wilson et al., 1981; Gray, 1981). Vapor pressure at temperatures to 589 K were determined in a high pressure, static, boiling point apparatus in which the time at temperature was 60 min or less, thus avoiding significant sample decomposition. At temperatures to 783 K, a flow apparatus was used in which approximately 50% of the sample va-
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985
QQ
Table I. Properties of Coal Liquid Fractions Used in Vapor Pressure and Heat of Vaporization Measurements secondary distillation vapor temp, K" fraction 5HC 8HC llHC 16HC 17HC 19HC-A
init cut point 433.2 520.9 609.8 650.9 693.7 765.9
final cut point 438.7 525.4 623.2 668.7 704.8 791.5
cut width, K 5.5 4.5 13.4 17.8 25.6
bp, Kb 433.2 519.8 612.6 658.7 692.6 776.5
5P gr, 288.7 K1288.7 K 0.8827 0.9718 1.0359 1.0910 1.1204 1.1792
mol wtc 116 158 212 237 258 315
4HC-A 6HC 7HC-B 10HC-B 15HC-B 18HC-B
405.4 464.3 490.9 570.4 629.3 745.9
410.9 469.8 494.8 573.2 640.9 754.3
5.5 5.5 3.9 2.8 11.6 8.4
409.5 467.6 492.6 572.0 632.0 741.5
0.8160 0.9507 0.9672 1.0021 1.0830 1.1760
110 127 140 188 218 285
11.1
"At 101.3 kPa. bFrom vapor pressure data. 'From correlation of Gray et al. (1983) Table 11. VaDor Pressure Data for Narrow Boiling Coal Liauid Fractions cut 4HC-A cut 6HC cut 7HC-B cut 10HC-B cut 15HC-B cut 18HC-B vapor vapor vapor vapor vapor vapor temp, K press., kPa temp, K press., kPa temp, K press., kPa temp, K press., kPa temp, K press., kPa temp, K press., kPa 324.8 5.17 267.1 3.31 395.4 4.69 466.2 6.21 508.9 4.83 589.3 4.48" 480.4 9.79 11.72 9.65 395.4 10.00 423.7 13.79 339.0 537.5 617.5 8.89" 367.0 28.27 423.7 28.89 452.0 34.54 508.9 22.75 561.2 23.72" 645.6 15.79" 480.4 395.4 68.8 452.0 67.57 75.43 566.1 25.44 537.5 47.50 673.9 31.51" 423.7 146.2 480.4 139.3 508.9 146.9 566.1 90.32 589.3 41.58" 702.3 49.92" 589.3 144.8" 452.0 284.8 508.9 262.7 537.5 269.6 594.8 49.30 730.6 86.18 480.4 496.4 537.5 453.7 561.2 429.5" 617.5 236.5" 617.5 72.05" 759.0 130.3" 561.2 508.9 815.6 693.6" 566.1 453.0" 645.6 645.6 378.5" 121.4" 787.5 189.6" 533.1 1187" 566.1 740.5 589.3 673.6" 673.9 559.2" 210.3" 673.9 537.5 1266 589.3 617.5 985.3" 702.3 1045" 702.3 833.2" 314.4" 1713" 1448" 561.2 617.5 645.6 730.6 1560" 465.4" 730.6 1164" 2565" 645.6 589.3 673.9 2068" 759.0 2206" 717.0" 759.0 1651" 603.4 3110" 673.9 702.3 2820" 3161" 787.5 2381" 1112" 787.5 608.9 720.0 3302b 682.4 3385" 3523b 685.5 3585b Measured in flow apparatus.
Observed critical point.
porized while the pressure was accurately measured at a given temperature. At the estimated contact time of 10 s in the flow apparatus, sample decomposition was only noticeable on a few samples a t 755 K or above. Heat of vaporization measurements were performed in the flow apparatus shown schematically in Figure 1. In this apparatus, the sample stream was vaporized isothermally by throttling the stream from a pressure slightly above the vapor pressure to a pressure below the vapor pressure so that none of the stream vaporized before throttling, and all of the stream vaporized after throttling. Then a correction based on extended corresponding states was made to correct the enthalpy of the liquid and the vapor to the measured vapor pressure. This correction was very small at low vapor pressures and increased in proportion to the vapor pressure so that the correction amounted to 5-10% at temperatures close to the critical temperature. Isothermal conditions were maintained in the calorimeter by electrically heating the vaporization block. By this method the heat of vaporization was calculated from the measured electrical power input divided by the flow rate of the sample. At low pressures the sample flow rate was measured by the change in liquid level in a graduated glass receiver. At high pressures, the flow rate was determined by weighing the liquid that was drained over a measured time period such that the liquid level in the windowed separator was constant. The insulated adiabatic shield eliminated the need for heat leak corrections, so the measured enthalpy change corresponded to the enthalpy change of the fluid through the calorimeter. The overall experimental accuracy based upon the accuracy of the temperature, pressure, flow rate, and power measurements is estimated to be 1 3 % .
Results of Measurements The experimental vapor pressure data are listed in Table I1 and a r e plotted vs. inverse absolute t e m p e r a t u r e i n
DOWN.STREAM PRESSURE
UP.STREAM PRESSURE
CONDENSER HEATED VAPORIZATION BLOCK
BALLAST TANK
GRADUATED RECEIVER AT LOW PRESSURES OR WINDOWED SEPARATOR AT n i G n PRESSURES
Figure 1. Schematic of flow calorimeter used for heat of vaporization measurements. Figure 2. The data from the previous set of six heart cuts are also shown in Figure 2 for reference and indicate good consistency with t h e new data. Figure 2 also illustrates t h e excellent consistency between t h e static a n d t h e flow measurements, in agreement with results obtained on EDS coal liquid fractions b y Wilson e t al. (1981). T h e critical points were observed o n fractions 4HC-A, 6HC, a n d
7HC-B. T h e heat of vaporization data for t h e six heart cuts are listed in T a b l e I11 a n d a r e illustrated in Figure 3 a s a function of temperature. As should be t h e case, latent heats decrease with increasing temperature a n d approach
100
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985
Table 111. Heat of VaDorization Data for Narrow Boiling Coal Liauid Fractions heats of vaporization, kJ/kg temp, K 4HC-A 6HC 7HC-B 10HC-B 332.6 366.5 284.5 341.4 422.0 351.4 449.8 247.3 319.6 325.5 477.6 192.0 278.6 288.7 277.4 533.2 144.2 229.3 236.8 236.8 588.7 151.9 179.1 212.5 644.3 102.1 672.0 107.1 175.7 699.8 128.0 755.4 10,000-,
,
,
,
,
1
1
I
15HC-B
265.7 230.5 222.6 196.6
,
I
18HC-B
220.1 207.5
,
A
RIEDEL EQUATION STILL APPARATUS FLOW APPARATUS
0
CRITICAL POINT FROM WILSON
0
-
( 1 9 8 1) CORRELATION
m
n X
w a
2
100 I
v)
W
Ef K
B
U
>
10
-
L
1.0
0.8
1
1.0
1
1
1.2
1
1
1.4
1
1
1.7
1
1
1
1.8
I/T
1
2.0
x
1
1
2.2
1
1
2.4
1
1
2.6
1
1
2.8
1
3.0
~
1
3.2
103,k-1
Figure 2. Vapor pressure data for narrow boiling coal liquid fractions.
TEMPERATURE. K
Figure 3. Heat of vaporization vs. temperature for Narrow boiling coal liquid fractions.
zero as the temperature approaches the critical point. The previous data are also shown in Figure 3 and demonstrate good consistency with the new data, although the experimental scatter in the data is evident. In addition, cuts 6HC and 7HC-B tended to have higher latent heats than the other cuts at temperatures below 550 K, suggesting that the large organic oxygen content of these fractions as reported by Gray et al. (1983) may have influenced the results. The heat of vaporization at the normal boiling point for each of the cuts (except 19HC-A) was determined by smoothing all the latent heat data for each cut using either a cubic, quadratic, or linear equation, depending upon the number of data points for a given cut, and interpolating to the normal boiling point. These results were converted to a molar basis using the molecular weights in Table I, and both sets of values are listed in Table IV. The molar
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985
I
Table IV. Heat of Vaporization at the Normal Boiling Point for Narrow Boiling Coal Liquid Fractions 9"
fraction 4HC-A 5HC 6HC 7HC-B 8HC 10HC-B llHC 15HC-B 16HC 17HC 18HC-B
K 409.5 433.2 467.6 492.6 519.8 572.0 612.6 632.0 658.7 692.6 741.5
Th.
I
I
I
I
I
I
I
I 5w
I 550
1
WO
I 650
I 7W
I 750
" 9
kJlke 295.2 313.0 322.5 317.6 281.9 253.5 269.8 250.3 243.8 244.5 210.6
kJla-mol 32.47 36.31 40.96 44.46 44.26 47.66 57.20 54.56 57.05 62.84 60.02
heats of vaporization at the normal boiling point appear to correlate linearly with normal boiling point as shown in Figure 4, although there is some apparent scatter in the results. Estimation of Critical Properties Using Vapor Pressure Data Correlations exist in the literature which allow calculation of critical pressures (P,),critical temperatures (T,), and acentric factors (w) from boiling point and specific gravity. For example, Wilson et al. (1981) used the following set of equations critical temperature log (1.8TJ = 1.1569 + 0.38882 log sc
I
101
+ 0.66709 log (1.8Tb) (2)
critical pressure log (PJ6.8948) =
+
(
3
2.22066 - 0.05445KW 3.12579 1 - -
(3)
acentric factor
lo 403
450
50 WT% OFF TEMPERATURE, K
Figure 4. Heat of vaporization at the normal boiling point vs. normal boiling point for narrow boiling coal liquid fractions. Table V. Characterization Parameters for 5HC crit crit set temp. K mess.. kPa acentric factor 3509" 0.342O 1 645.7" 2 645.7 3509 0.340 3 645.0b 3254b 0.322b 3540 0.342 4 645.0 5 649.2 3707 0.332 6 645.7 3568 0.340
Experimental results.
= -1% (PR)TR.,,, - 1.0
(4)
From correlations in text.
factor so obtained are likely to be more reliable estimates of the true properties of the fluid. In the present study, this adjustment was done with mixed results. In (PR) = f" w f l (5) We found that many seta of characterization parameters correlate the experimental vapor pressures with equal with accuracy; the experimental vapor pressures could not be used to determine a unique set of parameters. Table V f"(TR)= shows six sets of parameters which correlate the experi5.671485 - 5*809839- 0.867513 In (TR) + 0.1383536T~~ mental results with nearly equal accuracy. For higher TR boiling cuts the range of properties obtained was even (64 greater. Note that the parameters from set (3) of Table V are not based upon vapor pressure measurements, but f(TR) = 12.439604 - 12*755971- 9.654169 In (TR) + only on the correlations (eq 2-4). Hence, we conclude that TR the experimental vapor pressure measurements are not 0.316367TR6 (6b) particularly useful in determining a unique set of charHere TR and P R are the reduced temperature (TIT,) and acterization parameters. Their value lies primarily in pressure (P/P,),respectively, K, is the Watson characevaluation of vapor-liquid equilibrium models and correterization factor, and Tb is the boiling point in kelvins. lations. Using the properties from the above correlations,eq 5 gives When vapor pressure data are available, a given set of the vapor pressure curve. empirical correlations may not result in a critical point (T,, Clearly, if experimental vapor pressure data are availP,) which lies on the extrapolated experimental vapor able, the ability of eq 5 to predict those vapor pressures pressure curve. A unique set of characterization paramis a measure of the reliability of the parameters used in eters can be obtained, if T, is calculated using an empirical correlation, and then the acentric factor ( w ) and the critical the vapor pressure equation. If the parameters used are from the correlations given by eq 2-4, the accuracy of the pressure (P,) are "fitted" by forcing agreement between vapor pressure predictions is a measure of the efficacy of calculated and experimental vapor pressures using the the correlations. appropriate vapor pressure equation. This is superior to the variation where P, is calculated from a correlation Conversely, the characterization parameters can be adjusted in order to improve the accuracy of vapor pressure followed by a regression of the vapor pressure data for T, predictions using eq 5. The critical properties and acentric and w. where
+
102
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985
Table VI. Estimated Critical Properties, Acentric Factor, and Orientation Parameter Based on Fraction Boiling Point and Specific Gravity Brul6 et al.* (1982) Wilson et al. (1981) Grayson and Streed" (1963) VC, fraction Tc,K P,,kPa W T,, K cm3/mol Y T,,K P,,kPa w 4HC-A 602.9 2876 0.3162 610.4 372.7 0.3459 603.4 3425 0.3586 3303 0.3200 645.0 391.8 0.3505 641.3 3547 0.3518 5HC 645.2 428.1 3572 0.3352 691.0 0.3727 689.9 3505 0.3614 6HC 698.9 0.3604 718.4 476.0 0.4011 717.6 3392 3269 0.3887 7HC-B 728.5 3084 0.3938 744.9 534.6 0.4449 743.7 0.4282 2937 8HC 756.5 2787 0.4464 798.8 637.6 0.5208 796.2 2458 0.4910 10HC-B 816.1 842.7 719.6 2685 0.4805 0.5668 837.5 2176 0.5360 llHC 865.3 2900 0.4791 871.7 745.6 0.5530 864.4 2181 0.5347 15HC-B 898.9 2722 0.5081 897.1 804.2 0.5975 0.5812 886.9 1966 16HC 926.7 2666 0.5335 934.5 875.8 0.6281 919.4 1799 0.6318 17HC 968.2 0.5606 992.6 994.9 0.6412 968.5 1659 0.7130 2695 1032 18HC-B 1025 I1071 0.7040 2464 0.6018 994.0 1486 0.8276 1066 19HC-A
"P,= P, (Cavett) X [LO - 0.56 (SG - 0.911. bMolecular weight and specific gravity are used in a correlation to estimate V, rather than P,. Z, is calculated directly from the Bruk et al. modified Benedict-Webb-Rubin equation of state, and P, is calculated from P, = ZJ?T,/ V,. Prediction and Correlation of Vapor Pressure Data Two general approaches have been used to correlate vapor pressure data, empirical correlations and equations of state. Of particular interest are the Wilson et al. (1981) correlation (eq 2-6), the modified Benedict-Webb-Rubin (BWR) equation proposed by Brul6 et al. (1982) for application to coal liquids, and the Grayson and Streed (1963) extension of the Chao and Seader (1961) correlation. In the previous section, the prediction of critical properties and acentric factor from vapor pressure data of coal derived liquids was discussed. The major conclusion of that analysis was that it was difficult to use vapor pressure data for accurate estimation of critical parameters. In this section, an alternative approach is reviewed; correlations from the literature are used to estimate critical properties which in turn are used for calculating vapor pressures. Such an approach is useful in that it serves to evaluate methods developed for predicting vapor pressures of coal liquids from a minimum of experimental characterization. Usually only boiling point, specific gravity, and possibly molecular weight will be known. The basic characterization properties of the coal liquids in this study are given in Table I. Molecular weights, boiling points, and specific gravities are used to obtain critical properties, the acentric factor, and the orientation parameter using the correlations of Wilson (eq 2-4), Brul6 et al. (1982), and Cavett (1962). In the approach suggested by Wilson and by Lee and Kesler (19751, the critical temperature and pressure are determined from correlations. Next, the acentric factor is found by solving Wilson's vapor pressure correlation (eq 5) for the w at the known boiling point. Vapor pressures are then predicted from the vapor pressure correlation as a function of the reduced temperature, TR. In the approach suggested by Brul6 et al. (1982), the critical temperature and critical volume are calculated from correlations. In order to use their three-parameter equation of state (3P-EQS), the third parameter, designated as the orientation parameter (61,must also be determined. In this study, the orientation parameter is determined in a manner analogous to determination of the acentric fador. It is calculated from the known boiling point so that equation of state predicts the known atmospheric vapor pressure exactly. In the Grayson-Streed approach, the critical temperature and pressure are estimated using the Cavett (1962) correlations, and the Antezana and Stephenson (1979) correction is applied to the critical pressure. The acentric factor is calculated by using the Edmister equation as
recommended by Grayson and Streed. At a given temperature, the fugacity coefficient of the saturated vapor calculated from the Redlich-Kwong equation is set equal to the fugacity coefficient correlation for the pure pseudocomponent liquid at system conditions and solved iteratively for the vapor pressure. The results of these three calculations are shown in Tables VI-VIII. It is clear that the 3P-EQS was somewhat better than the methods of Wilson et al. and Grayson and Streed, and, in many cases, produced roughly half the average absolute deviation which is defined as
Near the critical point ( T R> 0.97), where gas and liquid densities approach each other, the Brul6 et al. 3P-EQS does not converge to a solution very easily, and consequently, 14 points were not included in the comparison. However, this problem of noncovergence is due to the numerical procedure used to find the vapor pressure and not to any deficiencies in the equation itself. Note that the critical pressure can be calculated from
pc = ZCPPT, which provides a means of extrapolating the vapor pressure curve to the critical point. Even though a previous study (Holder and Gray, 1983) showed that the 3P-EQS did not predict liquid densities as well as other models, the densities (including the critical density) must be calculated from the 3P-EQS in the vapor pressure calculations to ensure consistency and minimum error. Convergence near the critical point (TR> 0.94) is a problem with the Grayson and Streed method also, resulting in 18 points not being included in the comparison. Estimated critical pressures for cuts 10 HC-B and heavier were significantly lower than those calculated from the Wilson et al. (1981) correlation. Critical temperatures were in good agreement with values estimated by the Brul6 correlation except for the four highest boiling fractions. The Grayson and Streed method had the highest overall deviation of the three methods considered and tended to overpredict vapor pressures by an average of 4.1 % . In the method of Brul6 et al. (1982),there is no separate correlation for critical pressure, but rather a correlation for critical volume, which is used as the density reducing parameter in the equation of state. Critical pressures can only be calculated from the critical compressibility factor and critical volume using eq 8. The critical compressibility factor is obtained from the equation of state by using the
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985
103
Table VIII. Overall Comparison of Three Methods for Predicting Vapor Pressures with Fraction Boiling Point and Specific Gravity as the Only Input Properties method % AARD %BIAS % MD Wilson et al. (1981) 6.33 -1.65 31.06 Brul6 et al. (1982) 4.39 -1.46 -21.87 7.19 4.11 58.54 Grayson and Streed (1963) Y
&0 !
Y
0
Table IX. Comparison of Average Absolute Deviations in Vapor Pressures with Source of Orientation Parameter ( y ) Using Brul6 Equation of State cut no. yo % AARDb % AARDc 4.1 3.8 5HC 0.3443 8HC 0.4372 3.4 2.9 0.5394 5.0 4.8 llHC 16HC 0.5648 6.8 1.6 17HC 0.5895 8.6 2.5 19HC-A 0.6496 20.8 4.9 0.3426 4.7 4.9 4HC-A 6HC 0.3628 8.0 7.0 7HC-B 0.3946 5.6 5.1 10HC-B 0.5014 3.9 1.8 15HC-B 0.5328 6.1 4.7 18HC-B 0.6108 7.5 7.2 a From correlation. Based upon the y shown in this table which is from the Brul6 correlation. Based upon the y given in Table VI which is determined using the boiling point.
di Lo
E
2
aE
3 8 E
'f wx a .-0 Y
f+ sz P 6 s0
nI 5
critical volume and critical temperature. However, the analysis in the previous section indicated that the 3P-EQS of Brul6 et al. predicts lower critical pressures than eq 3, and eq 3 predicts critical pressures that are lower than experimental values. Therefore, it is not desirable to use the 3P-EQS for estimating critical pressures. In comparing the predicted critical temperatures in Table VI with the experimentally observed values for five cuts the correlation of Burl6 et al. (1982) was found to predict the critical temperature much more accurately than Wilson's correlation (eq 2). It is interesting to note that if Brul6's correlation for molecular weight is used in place of the molecular weights in Table I, the results are not significantly different from those presented in Table VI1 (Brul6 et al. approach only). However, if the Brul6 correlation for the orientation parameter is used instead of determining the orientation parameter from the boiling point, the results for the Brul6 approach are not good for the heavier cuts; for cut 19HC-A, the average absolute deviation goes up to 20.8%. It is clear that using the boiling point to determine the orientation parameter can result in much better accuracy for the equation of state approach. Table IX compares the average deviations for the two methods used to obtain the orientation parameter. Correlation of Heats of Vaporization Five methods were studied for correlating the heat of vaporization and are listed in Table X. Method 1 was essentially a rough consistency check in which the molar heats of vaporization were calculated from the slopes of the vapor pressure curves and molecular weight values were derived such that the errors between calculated and measured values were minimized. The molecular weights were then compared to values calculated from a correlation (Table I) which is based on experimental molecular weight data. Method 2 involved calculating the molar heats of vaporization from the experimental data and the molecular weights in Table I and comparing these to the molar heats of vaporization from the slopes of the vapor pressure curves. In method 3, the corresponding states equation of Carruth and Kobayashi (1972) was used to calculate the molar heats of vaporization, and these values were com-
104
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985
Table X. Comparison of the Accuracy of Several Methods for Predicting Experimental Heats of Vaporization fraction ~
4HC-A
5HC
6HC
7HC-B
8HC
5
5
6
6
5
10HC-B
llHC
15HC-B 16HC
~~~
17HC
~~~~
18HC-B 19HC-A
no. of data points 5
5
4
4
3
2
1
%AARD % MD %BIAS mol wt
5.00 8.84 1.48 124
3.38 5.83 -0.14 126
5.60 10.99 1.06 142
9.09 18.77 4.62 150
2.67 -5.25 -0.86 169
Method l a 5.47 1.27 12.42 -3.58 1.95 -0.50 218 214
2.23 5.99 1.36 242
1.47 3.52 0.29 258
2.25 -3.59 -0.14 275
0.09 0.18 0.09 336
25.93b 25.93 --350
% AARD
5% MD %BIAS
13.94 22.21 13.94
8.64 15.16 8.64
12.69 23.76 12.69
12.43 26.86 11.74
6.42 9.94 6.42
Method 2 1.43 17.90 30.00 -2.84 17.90 0.26
12.72 17.87 12.72
10.44 14.00 10.44
6.91 10.25 6.91
17.84 17.95 17.84
39.76 39.76 ---
%AARD % MD % BIAS
10.12 15.59 10.12
5.66 9.12 5.66
7.27 14.82 7.27
7.64 16.02 6.64
4.82 -6.46 1.64
Method 3 12.12 3.56 19.80 -9.56 12.12 -3.56
6.86 12.28 6.86
6.45 9.09 6.45
4.46 6.21 3.01
14.32 15.14 14.32
37.26 37.26 ---
%AARD % MD %BIAS
12.57 19.65 12.57
5.98 10.50 5.98
5.54 13.94 5.31
7.75 16.82 4.94
3.74 -6.48 -0.16
Method 4 13.32 5.43 23.05 -10.11 13.32 -5.43
6.40 11.45 6.40
3.14 5.92 3.14
2.82 -4.97 -0.50
13.26 13.83 13.26
30.20 30.20 - -
Method 5 6.45 6.93 9.86 --15.15 11.43 -16.74 -5.07 6.93 -9.86
2.53 6.71 1.17
1.97 -5.15 -1.67
5.26 -10.43 -5.26
7.73 8.71 7.73
24.54 24.54 ---
%AARD % MD %BIAS
7.33 10.19 7.33
3.27 4.90 2.32
2.43 3.50 -1.22
4.32 6.44 -0.94
~
a Method 1, from slope of vapor pressure curve, molecular weight adjustable. Method 2 , from slope of vapor pressure curve and molecular weight correlation of Gray et al. (1983). Method 3, Carruth and Kobayashi (1972) correlation. Method 4, Kistiakowsky equation and Watson relationship. Method 5, normal boiling point correlation and modified Watson equation in this work. Single experimental measurement questionable.
pared to the values calculated from the data and the molecular weights in Table I. The critical temperatures and acentric factors derived as adjustable parameters in fitting the Riedel equation to the vapor pressure data were used as input to this correlation. In method 4, the Kistiakowsky equation and the Watson relationship were used to predict latent heats. Method 5 constituted deriving modified versions of the latter equations that minimized the relative deviation between calculated and measured heats of vaporization. The heats of vaporization were calculated based on the slopes of the vapor pressure curves and the Clapeyron equation as follows d(ln P ) AH^ = R P A Z dT where AHv is the latent heat on a molar basis, T is the absolute temperature, A2 is the compressibility factor of vapor minus that for the liquid, and d(ln P)/dT is the slope of the vapor pressure curve, determined from eq 5. The compressibility factor of the vapor was calculated from a modified Redlich-Kwong equation of state as described by Wilson et al. (1981), and the compressibility factor of the liquid was calculated by the procedure of Hwang et al. (1982) and Wilson (1981). Since the calculated heats of vaporization are on a molar basis, while the measured heats of vaporization are on a weight basis, the ratio of the two values gives the molecular weight of the fraction. When molecular weight was used as an adjustable parameter to obtain the best match of measured and calculated results, the average deviations for each cut were as shown for method 1 in Tables X and XI. The percent absolute average relative deviation for each fraction ranged from 0.09 to 9.09%, excluding the questionable data point previously reported for Cut 19HC-A. The overall AARD, bias, and maximum deviation were 3.98%, 1.00%, and 18.77%, respectively. Comparison of the molecular weight
Table XI. Overall Comparison of Accuracy of Several Methods for Predicting Experimental Heats of Vaporization" methodb 70 AARD % BIAS % MD 1 3.98 1.00 18.77 10.63 30.00 2 10.83 3 7.32 6.08 19.80 5.12 23.05 4 7.16 -0.14 -16.74 5 5.18 "Excludes questionable point for Cut 19HC-A, 50 data points total. *Method 1, from slope of vapor pressure curve, molecular weight adjustable. Method 2, from slope of vapor pressure curve and molecular weight correlation of Gray et al. (1983). Method 3, Carruth and Kobayashi (1972) correlation. Method 4, Kistiakowsky equation and Watson relationship. Method 5, normal boiling point correlation and modified Watson equation in this work.
values in Table X with those calculated by the correlation of Gray et al. (1983) in Table I indicates that the experimentally derived molecular weights are on the average 10-11 % higher than the values calculated from the correlation. Thus, it is possible to accurately predict the experimental heat of vaporization data from measured vapor pressure data provided that the molecular weight values from the correlation are adjusted upward about 10-11 % . This comparison provides a rough consistency check between the measured vapor pressure data and the measured latent heat data, even though it was necessary to use molecular weight as an adjustable parameter. A consistency check, that is independent of the molecular weight adjustments needed above, can be made by converting the experimental data in Table I11 to a corresponding states basis, as illustrated by Figure 5. The molecular weights in Table I were used to convert the measured heat of vaporization data to a molar basis. The correlation that was used to calculate these molecular weight vslues was based on molecular weight data for the same coal liquids used in the vapor pressure and heat of
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985 105
10.0
boiling point of the cuts, it can be used as an additional correlating parameter in Figure 6 to generate one general curve applicable to all six fractions. In Figure 5, the experimental data points are more scattered than in Figure 6 and do not show the orderly variation in molar heat of vaporization as the boiling point of the cuts increases. The above method of comparison is essentially the same as the indirect approach of comparing molecular weights. When both the experimental latent heat data and those calculated from eq 9 are on a corresponding states basis, an independent correlation can be used to estimate the reduced latent heat. Carruth and Kobayaski (1972) extended the tabulated entropy of vaporization functions developed by Pitzer and co-workers (see Reid, Prausnitz, and Sherwood, 1977) to lower reduced temperatures, and constructed the following analytical representation of the reduced heat of vaporization over the range 0.6 < TR C 1.0
L
Figure 5. Reduced latent heats from calorimeter data vs. reduced temperature for narrow boiling coal liquid fractions. 12'0
10.0
d 0
F
4HC-A
0 6HC h
0
7HC-B 10HC.B
1
1
REDUCED TEMPERATURE, TTT,
Figure 6. Reduced latent heats from slopes of vapor pressure curves vs. reduced temperature for narrow boiling coal liquid fractions.
vaporization measurements. The critical temperatures that were derived as adjustable parameters in fitting the vapor pressure data with the Riedel equation were used to calculate reduced latent heats except when the critical point was available directly from the measurements. The same type of plot is known in Figure 6 for the reduced heat of vaporization values obtained from eq 9. A comparison of the data in Figures 5 and 6, as well as data for the six heart cuts reported previously, shows that the overall AARD was 10.8% and the bias was 10.6%. Method 2 in Tables X and XI summarizes the comparison for all twelve cuts. Thus, the heats of vaporization calculated from the slopes of the vapor pressure curves were nearly always higher than the measured values by 10.6% on the average. The deviation was as high as 30% on one data point for cut 10HC-B. The experimental error in the heat of vaporization measurements is very noticeable when the data points in Figures 5 and 6 are compared. In Figure 6, the molar heat of vaporization increases in a very orderly fashion with the boiling point of the cut (increasingcut number). Since the acentric factor increases monotonically with increasing
Molar heats of vaporization were calculated corresponding to all the data points of the 11 heart cuts (cut 19HC-A excluded) by using eq 10 and were compared to both the measured values and the values calculated using eq 9. As summarized under method 3 in Tables X and XI, eq 10 predicted the experimental latent heat data with an absolute average deviation of 7.32% and a bias of 6.08%. Thus, the corresponding states correlation nearly always predicted latent heat values that were higher than the measured values, similar to the calculations using the slopes of the vapor pressure curves. The maximum deviation was 19.8% for the same cut 10HC-B data point that yielded the 30% deviation previously. The heat of vaporization values calculated from the slopes of the vapor pressure curves yielded an absolute average deviation of 4.05% and a bias of -4.03% when compared to the values predicted by eq 10. Thus, the corresponding states correlation nearly always predicted latent heat values that were lower than the values derived from the vapor pressure curves. The maximum deviation was 8.54% on one of the data points for cut 7HC-B. These comparisons show that the corresponding states equation (eq 10) predicts molar latent heat values that lie between the measured values and the values derived from the vapor pressure curves. Considering the scatter in the experimental data, eq 10, therefore, represents a viable alternative for reasonably accurate calculation of molar heats of vaporization. When combined with the molecular weight correlations of either Gray et al. (1983), Wilson (1981), or Riazi and Daubert (1980), the molar values can be accurately converted to a mass basis. The heat of vaporization for petroleum fractions is often calculated using an equation based on Trouton's rule such as the Kistiakowsky equation (Cavett, 1962; Reid et al., 1977) mVNB -- [8.75 -I-1.987 In ( T b ) ]
4.184 x
(11)
Tb
where T b is the normal boiling point of the fraction in K and AH- is the molar heat of vaporization at the normal boiling point in kJ/g-mol. The heat of vaporization at other temperatures is calculated from the Watson equation
where n = 0.375, T i s the temperature of interest in K, T, is the pseudo-criticaltemperature of the fraction in K, and
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Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 1, 1985
AHVTis the heat of vaporization at T. Heats of vaporization calculated from eq 11and 12 were compared to the measured values, and the results are listed as method 4 in Table X. The AARD ranged from 2.82% for cut 17HC to 13.32% for cut 10HC-B. The overall AARD, bias, and maximum deviation were 7.2%, 5.1%, and 23.0%, respectively. This method was more accurate than the method using the slope of the vapor pressure curve, and was about equivalent in accuracy to the Carruth and Kobayashi (1972) correlation. In order to improve the fit of the Watson equation to the measured heats of vaporization, the experimentally derived values of AHvNB and the data were regressed to find the exponent which yielded the lowest overall deviation between measured and predicted latent heats. For five of the fractions, the observed critical temperature was used in these calculations. The remaining critical temperature were those derived as adjustable parameters from the vapor pressure data and eq 2,3, and 5. The values of T, calculated in this manner are very close to the values listed in Table VI. The optimized Watson equation exponent was 0.419 and resulted in an overall AARD of 3.23%, a bias of -0.05%, and a maximum deviation of 16.06%. This correlation is excellent considering the scatter in the latent heat data (Figure 5). The exponent value is also very reasonable and is not much different from that in eq 12. With the curvature of the latent heat-temperature correlation set by the new exponent in eq 12, the correlation for the molar latent heat at the normal boiling point was improved by fitting the data in Table IV to the folowing simple linear equation as shown in Figure 4 AHVNB= 0.08894Tb - 1.5 (13)
This equation yielded an AARD of 3.68%, a bias of -0.08%, and a maximum deviation of 7.01%. Forms of eq 13 with higher order boiling point terms did not lead to further improvement. Method 5 in Table X summarizes the comparison between measured and calculated latent heats for the twelve fractions and when only the boiling point is specified and both eq 12 and 13 are used. The AARD deviation for the combined equations ranged from 1.97% to 9.86%, and the maximum deviation was -16.74% for cut 11 HC. Table XI shows that method 5 predicted the data best yielding an overall AARD of 5.18% and a bias of -0.14%. Although the heats of vaporization of the heart cuts can be calculated from the vapor pressure data, these estimates contain, in addition to the normal experimental error, uncertainties due to the estimation of the compressibility factors of the liquid and gas that are needed in the Clapeyron equation, and error introduced in differentiating the vapor pressure equation. In each of the estimation methods summarized in Table X, the variation of the percent bias with fraction boiling point was similar suggesting that some of the differences in AARD were due to the values used for the critical temperature and acentric factor of each fraction in the correlations. For example, a 10-15% reduction in the acentric factor values used in eq 10 would reduce the bias and the AARD significantly. A similar reduction of the compressibility factor difference in eq 9 would also improve that method. Thus, corresponding states methods of estimating the latent heats can be significantly reduced in accuracy if characterization parameters such as the critical properties and acentric factors are not optimized. More empirical methods such as eq 1 2 and 13 are desirable in this situation. In most cases the deviation increased as the reduced temperature increased.
Conclusion Experimental data on vapor pressures and the heat of vaporization have been presented for coal liquids whose boiling points range from 410 K to 776 K. These data are consistent, reproducible, and well correlated when using empirical equations which have been derived for use with coal liquids. Vapor pressures are well correlated by using the equations of Wilson or Grayson and Streed, but the equation of state of Brul6 and co-workers was more effective in reproducing experimental results than either of the two former methods. The emprical equations of Brul6 for critical temperature and critical volume provide good characterization parameters for use in the equation of state. For effective use of the Brul6 equation for prediction of vapor pressures, liquid densities must be determined from the equation of state and the orientation parameter ( y ) must be obtained by solving the equation at the boiling point with y as the unknown. Caution must be used in using Brul6's equation for independent prediction of critical pressures. Tentatively, the use of Wilson's correlation (eq 3) and the Cavett-Antezana-Stephenson method (eq 1) appear to be somewhat more accurate. The best method of calculating heats of vaporization is the modified Watson equation together with the normal boiling point correlation. In these calculations the critical temperature is that calculated by the correlation of Wilson et al. (1981) or Brul6 et al. (1982). Acknowledgment This work was supported under U S . Department of Energy Contract No. DE-AC01-79ET10104. Wiltec Research Company performed the vapor pressure and heat of vaporization measurements under subcontract to Gulf Research and Development Company. The suggestions of Drs. F. J. Antezana and J. L. Stephenson during the vapor pressure data correlation work are kindly acknowledged. Nomenclature AHv = Heat of vaporization, kJ/g-mol K , = (1.8T,)113/SG,Watson characterization factor P = pressure, kPa SG = specific gravity (288.7 K/288.7 K) R = gas constant, kJ/(g-mol K) T = temperature, K 2 = compressibility factor Greek Letters w p
= acentric factor
= molar density, g-mol/cm3 y = orientation parameter
Subscripts b = boiling point property
c = critical condition property NB = normal boiling point property R = reduced property T = temperature of property Literature Cited Antezana, F. J.: Stephenson, J. L. Gulf Research and Development Co. (Harmarviiie, PA), personal communication, 1979. American Petroleum Institute, "API Technical Data Book-Petroleum Refining". 3rd ed.;Washington, DC, 1976: Voi. I and 11. Brul6, M. R.; Lin. C. T.; Lee, L. L.: Starling, K. E. AIChEJ. 1982, 28, 616. Carruth, G. F.; Kobayashi. R. Ind. Eng. Chem. Fundam. 1972, 1 1 , 509. Cavett, R. H. Physical Data for Distillation Calculations-Vapor-Liquid Equllibrla". paper presented at the 27th Miyear Mwtlng of the American Petroleum Institute's Division of Reflnlng, San Francisco, CA, May 15, 1962. Chao, K. C.; Seader, J. D. AIChE J. 1961, 7, 598. Furlong, L. E.: Effron, E.; Vernon, L. W.: Wilson, E. L. Chem. Eng. Prog. 1976, 72 (8), 69. Gray, J. A. "Selected Physical, Chemical, and Thermodynamic Properties of Narrow Boiling Range Coal Liquids from the SRC-I1 Process", Report for
Ind. Eng. Chem. Process Des. Dev. 1085, 24, 107-111
the period March 1980-Feb 1981, DOE/ET/10104-7. April 1981. Gray, J. A.; Holder. G. D. “Selected Physlcal, Chemical, and Thermodynamic Properties of Narrow BolHng Range Coal Liquids from the SRC-I1 Process. Supplementary Property Data”, DOE/ET/10104-44, April 1982. Gray, J. A.; Brady, C. J.; Cunningham, J. R.; Freeman, J. R.; Wilson, G. M. Ind. Eng. Chem. ProcessDes. Dev. 1983, 22, 410. Grayson, H. 0.; Streed, C. W. “VLE for High Temperature, High Pressure Hydrogen-Hydrocarbon Systems”, Slxth World Petroleum Congress, Frankfurt/Main, 1963; Sec. 111, p 233. Holder, 0.D.; Gray, J. A. Ind. Eng. Chem. Process D e s . D e v . 1983, 22, 424. Hwang, s. C.; Tsonopoulos. C.; Cunningham, J. R.; Wilson, G. M. Ind. Eng. Chem. Process D e s . Dev. 1982, 21, 127. Lee, B. I.; Kesler, M. 0.AIChE J . 1975, 21, 510. Moschltto. R. D. ”Operation of the Ft. Lewis, Washington Solvent Refined Coel (SRC) Pibt Plant In the SRCI and SRC-I1 Processing Modes”,paper presented at 13th Intersoclety Energy Conference, San Diego, CA, Aug 1978.
107
Maxwell, J. B.; Bonneli, L. S. Ind. Eng. Chem. 1957, 49, 1187. Newman, S. A. k&drocarbon Process. 1981, 60(12), 113. Recon Systems, Inc. “Fundamental Data Needs for Coal Conversion Technology”, Final Report No. TID-28152, US. DOE Contract No. EY-76C-02-4059, Jan 1981. Rledel. L. Chem. Ing. Tech. 1954, 26, 83. Reid, R. C.; Prausnttz, J. M.; Sherwocd, T. K. “The Properties of Gases and Liquids”, 3rd ed. McGraw-Hill: New York, 1977; p 57. Riazl, M. R.; Daubert, T. E. Hydrocarbon Process. 1980, 59(3), 115. Schmid, B. K.; Jackson, D. M. “The SRC-I1 Process”, paper presented at the 3rd Annual Inter. Conf. on Coal Gas.and Llq., University of Pittsburgh, Plttsburgh, PA, Aug 3-5, 1976. Wilson, G. M.; Johnston, R. H.; Hwang, S. C.; Tsonopolos, C. Ind. Eng. Chem. Process Des. D e v . 1981, 2 0 , 94.
Received for review May 17, 1983 Accepted February 17, 1984
Vapor-Liquid Equilibrium for a Methane-Simulated Coal-Derived Liquid System Srlnlvasan Ramanujam, Stuart Lelprlger, and Sanford A. Well Gas Engineering Depettment, Institute of Oes Technology, Illinois Institute of Technoey, Chicago, Iliinois 606 16
Vapor-liquid equilibrium data for methane-highly aromatic multicomponent mixtures were obtained in a recirculation type equilibrium apparatus. The liquid mixture was a simulated, coal-derived light oil. Liquid- and vapor-phase compositions were measured over a temperature range of 400-550 K and a pressure range of 2.03-1 1.1 MPa (20-110 atm).
Introduction Design of coal conversion processes under development today is complicated by high-temperature and high-pressure operating conditions. Because of the enormous size of the commercial installation of these processes, there is a strong economic incentive to provide a good data base to minimize expensive safety factors in the design. The design of a coal gasification reactor and subsequent downstream synthesis gas processing units requires multicomponent phase equilibrium data in systems containing light gases and a variety of hydrocarbons ranging from benzene to heavy polyaromatics and appreciable quantities of 0-,S-, and N-substituted aromatics. For example, Table I provides a condensed version of the composition of a typical recovered light oil sample from the Hygas coal gasification pilot plant. Thermodynamic and thermophysical property needs for emerging coal conversion processes have been treated in detail by Lin et al. (1980) and in the Coal Conversion Systems Data Book (1978). Considerable binary and ternary gas-liquid equilibrium data for methanearomatic hydrocarbon systems have been published recently and reviewed by Sebastian et al. (1981). Multicomponent data for systems which are useful in coal conversion processes are rare except for the work of Li et al. (1981), who studied methane-ethane-propane-toluene-l-methylnaphthalene
VLE, and Henson et al. (1982), who measured the solubility of methane in a creosote oil and an SRC recycle solvent. As a result, this work was initiated to provide multicomponent high-pressure VLE data at elevated temperatures. Table I1 provides the composition of the liquid
* Chemical Engineering Department, Rose-Hulman Institute of Technology, Terre Haute, IN 47803. 0196-4305/85/1124-0107$01.50/0
Table I. Typical Composition of a Light-Oil Mixture from the Hygas Pilot Plant component mass fraction benzene 0.588 toluene 0.148 xylenes 0.062 other two-ring aromatic hydrocarbons 0.028 naphthalene 0.048 other two-ring aromatic hydrocarbons 0.035 three-ring aromatic hydrocarbons 0.012 four-ring aromatic hydrocarbons 0.0019 five-ring aromatic hydrocarbons (34.4 ppm) aliphatics 0.011 0-substituted hydrocarbons 0.046 N-substituted hydrocarbons 0.004 S-substituted hydrocarbons 0.016 Table 11. Composition of the Simulated Aromatic Oil Used in this Investigation component mass fraction mole fraction benzene 0.458 0.548 toluene 0.183 0.186 n-octane 0.0037 0.003 p-xylene 0.092 0.081 o-xylene 0.027 0.024 mesitylene 0.011 0.009 n-decane 0.131 0.086 naphthalene 0.055 0.040 1-methylnaphthalene 0.014 0.009 biphenyl 0.0055 0.0034 acenaphthene 0.0046 0.0027 fluorene 0.0046 0.0026 1-phenylnaphthalene 0.0055 0.0025 phenanthrene 0.0046 0.0024 fluoranthene 0.0018 0.0008 chrysene 0.0014 0.0006
used. The chemical and physical characteristics of this simulated mixture is fairly close to that of Table I without 62 1984 American
Chemical Society
