Ind. Eng. Chem. Process Des. Dev. 1985, 24, 320-325
320
Hd = gap between wedge shaped disks at R = Rd, m L = length of parallel plates, m m = power law model parameter, N sn/m2 N = frequency of disk rotation, rev/s n = power law model parameter (exponent) P = pressure, N/m2 pw = specific power, J/m3 Pw = power, J/s q = volumetric flow rate per unit width, m2/s Q = volumetric flow rate, m3/s Qd = drag flow rate in parallel disk chambers, m3/s Qh = drag flow rate in wedge shaped chamber, m3/s Q = pressure flow rate in parallel disk chambers, m3/s QFP = pressure flow rate in wedge shaped chambers, m3/s R = radius, m R , = shaft radius, m Rd = disk top radius, m s = l/n f = mean residence time, s V, = plate velocity, tangential disk top velocity, m/s (Y = R , / & i. = rate of deformation tensor, AP = pressure rise, N/m2 (discharge pressure less inlet pressure) AT, = adiabatic temperature rise, K t = fraction of chamber circumference filled with liquid = my”-l, non-Newtonian viscosity, N s/m2 0 = angular coordinate, rad
p T T
= Newtonian viscosity, N s/mz = torque, N-m = shear stress tensor, N/mZ
Literature Cited Bouchez, D.; Faure, A.; Scherer, G.; Tranie, L. A.; Antonini, G. “COM: The French Program; Preparation, Stabilization and Handllng of COM”, 4th International Symposium on Coal Slurry Combustion, Orlando, FL, 1982. Edelist. Y. M.S. Thesis, Department of Chemical Engineering, Technion, Israel Institute of Technology. Haifa, Israel, 1982. Edelist, Y.; Tadmor. 2. folym. Process €178. 1983, 1 , 1. McKelvey, J. M. “Polymer Processlng”. John Wiley 8 Sons, New York, 1962. Hold, P.; Tadmor, 2. US. Patent 4207004, 1980. Tandmor, 2. US. Patent 4 142 805, 1979. Tadmor, 2. U.S. Patent 4 194841, 1980. Tadmor. 2.; Gogos, C. G. ”Principles of Polymer Processing”, 1st ed.;Wifey: New York, 1979. Tadmor, 2.; Hold, P.; Valsamis, L. “A Novel Polymer Processing MachineTheory and Experimental Results”; 37th Annual Technical Conterence of the Society of Plastic Englneers, New Orleans, 1979a; pp 193-204. Tadmor, 2.; Hold, P.; Valsamis, L. “Plastics Englneering”, Part I, Nov 1979b; pp 20-25; Part 11, Dec 1979b; pp 34-37. Tadmor, 2.; Klein, I. ”Engineering Principles of Piasticating Extrusion”; Van Nostrand-Relnhold Co.: New York, 1970. Tadmor, 2.;Vaisamis, L.; Mehta, P.; Rapetski, W. “Mixing of Coal Slurries in Plastics and Rubber Processing Machinery, Principles and Applications”; SME-AIME Annual Meetlng: 5th InternationalSymposium on Coal Slurry Fuels, Atlanta. 1983b; pp 75-99. Tadmor, 2.; Vaisamis, L.; Yang, J. C.; Mehta, P. S.;Duran, 0.; Hinchcliff. J. C. folym. Eng. Rev. 19830. 3(1), 29. Valsamiu. L. U S . Patent 4 213 709, 1980.
Received for review September 2 , 1983 Accepted May 7 , 1984
Influence of Compositfon Modulation on Product Yields and Selectivity in the Partial Oxidation of Propylene over an Antimony-Tin Oxide Catalyst Peter L. Sllvedon’ and Michel Forrlsler Institut
de Recherches sur L Catalyse, Centre NaNonal de /a Recherche Scientifique, Villeurbanne, Lyon, France
Composition modulation has been studied by the oxidation of propylene to acrolein over a catalyst composed of a solid solution of antimony oxide in tin oxide. Modulation consists of periodically varying the partial pressures of propylene and oxygen in a square wave pattern so as to maintain a constant time-averaged feed composition. Half-periods were of equal duration. Selectivity to acrolein was found to increase substantlalty, but dependence of the increase on amplitude and period coukl not be ascertained. Yield of acrolein decreased with,composition modulation compared with steady-state operation at the same mean feed composition. Amplitude of the square wave was found to be important, but period affected the results just slightly. Product changes with time following a composition switch are used to comment critically on reaction pathway and rate-controlling step proposals in the literature.
Introduction The object of the exploratory research described in this note was to examine a reaction system yielding a variety of products probably via different pathways to see if composition modulation could alter rates and selectivity. Composition modulation is the intentional periodic variation of feed composition to the reactor. The reaction chosen for our study was the partial oxidation of propylene (e3=) to acrolein (primary product) over a tin-antimony (Sb-Sn) oxide catalyst. Oxidation to acrolein over this
*Addresscorrespondence to this author at the Department of Chemical Engineering,University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. 0196-4305/85/1124-0320$01.50/0
catalyst is thought to proceed via a redox mechanism (Trifiro et al., 1971; Crozat and Germain, 1973; Sala and Trifiro, 1976; Sokolovskii and Bulgakov, 1977). Unni et al. (1973) and Abdul-Kareem et al. (1980) have demonstrated that composition modulation raises the activity of vanadia catalysts in single reactions believed to proceed via redox mechanisms. Indeed, Belousov and Gershingorina (1968) working with the partial oxidation of C3=over various metal oxides demonstrated that catalyst activity was higher in a pulsed reactor than in a reactor operating at steady state. Trifiro et al. (1971) reported a similar observation with an Sb-Sn oxide catalyst. Up to the initiation of our work, selectivity effects of composition modulation had not been explored for complex catalytic reactions proceeding via redox pathways. Renken et al. 0 1985 American Chemical Soclety
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 2, 1985 321
(1976) and Baiker and Richarz (1976) demonstrated a substantial improvement in the yield of ethylene oxide through composition modulation of ethylene oxidation over a silver catalyst. It is not certain, however, that this partial oxidation proceeds via the redox mechanism. Later studies of the selectivity effects of composition modulation (Bilimoria and Bailey, 1978; Al-Taie and Kershenbaum, 1978) employed hydrogenation reactions with metal catalysts.
Experimental Section Composition modulation of continuously operating catalytic reactors is described in adequate details by Abdul-Kareem et al. (1980). One feed composition is sent to the reactor in one half-period, while in the second halfperiod a second composition is used. The half-periods are of equal length to force the system with symmetrical square waves. This type of composition modulation permits an assessment of the effect of wave amplitude on selectivity. Both Unni et al. (1973) and Abdul-Kareem et al. (1980) have found an amplitude effect on rate. Only a single mean composition was employed for the periodic composition changes used. This composition was 50 mmHg C3=, 50 mmHg 02,and 600 mmHg N2. By controlling the flow of reactants in a half-period, square wave amplitudes were varied from 15 mmHg to 50 mmHg. Amplitude is expressed as the difference in partial pressure of one component from its mean partial pressure. For example, an amplitude of 15 mmHg meant that in one half-period, the propylene flow was adjusted to give 65 mmHg C3=in the reactant feed while in the other halfperiod, it was adjusted to give 35 mmHg C3=.The maximum amplitude employed, 50 mmHg, corresponded to 13.2% O2in N2 in one half-period and 13.2% C3=in N2 in the other. It represents, of course, the extreme case of composition modulation. The modulation periods employed ranged from a low of 30 min to a maximum period of 7.4 h. The lower limit was imposed by the maximum retention time of the chromatograph used to measure reaction products. The main product, acrolein, eluted from the column after about 14 min. The longest period used was dictated by gas supply and equipment limitations. In general, to obtain a stationary modulating system, at least 2 full cycles had to be employed, and in this study at least 4 cycles were used. With a period of 8 h, an experiment extended over at least 32 h. Experiments showed that breakdowns caused by either gases running out or equipment malfunction occurred at about a 2-day frequency, making it difficult to efficiently perform experiments at periods greater than 8 h. Feed modulation experiments were supported by measurements made at steady state and by transient measurements to establish the response to a step change in feed composition. The purpose of the former was to provide a comparison basis for the feed modulation results, while the intent of the latter measurements was to assist interpretation of the modulation results. All experiments were carried out at a reaction temperature of 400 "C and atmospheric pressure. A differential fixed bed reactor and an automated feed and sampling system was used. Composition of the feed to the reactor was programmed by a perforated drum turned by a constant-speed motor. Perforations in the drum controlled flows by opening and closing solenoid valves. Each component of the reaction mixture could be fed through six individual lines, each of which was fitted with a solenoid valve and a capillary set to permit a different flow of gas. Through choice of one or more of the lines, composition of the feed could be closely set and the
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space velocity of the feed in the reactor could be kept constant. The length of the perforation in the drum controlled the time which the valve was open and, thus, the half-period length. The revolving drum also initiated a timer controlling the automatic sampling valves which provide samples for the multiple chromatographic columns at points within the half-period. Columns employed were a Poropak Q, a Carbowax 20M-Chromosorb, and a 5A molecular sieve. Both FID and TC detectors were available. Peak areas were measured and peaks were identified by a microprocessor. First injection was timed to occur between 1and 10 min after a composition change. Most injection were made about 5 min after a composition shift. Details of the automation are given by Forissier et al. (1976). For the step-change observations, an infrared spectrophotometer was connected downstream of the GC sampling point. This instrument was used to qualitatively examined the behavior of the C02 signal. It was not calibrated. The catalyst, a solid solution of the oxides of tin and antimony containing 10% Sb on an atomic basis (as % of the metal), was prepared and conditioned as described by Boudeville et al. (1979).
Influence of Period and Amplitude on Reactor Yield and Reaction Selectivity The means of the partial pressure of acrolein and ethanol measured in the gas leaving the reactor are shown in Figure 1. The mean of the modulated partial pressure of propylene in the feed was about 50 mmHg. Conversions to acrolein were thus less than 1%. Though not shown, COz conversions were also about 1%. Ethanol conversions were less than 0.2%. Conversions to the minor products-acetone, propylene oxides, and propanol-were an order of magnitude lower. Space velocity was held constant for all periods and amplitudes employed. Partial pressures of the acrolein and ethanol produds in Figure 1,therefore, represent the yields of these two products. Acrolein yields are well below those reached under steady-state operation. As the amplitude increases, the yield drops until at the extreme case of cycling between mixtures containing only one reactant (A = 50 mmHg), the yields of the two products become very small. A slow decrease in yield with increasing modulation peribd is also discernible in the figure. Results for ethanol
322 Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 2, 1985 -DE
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resemble those for acrolein, although composition modulation depresses yields more severely. Measurements for COz were similar. Selectivity to acrolein, defined as the yield of acrolein per mole of C3=fed to the reactor divided by the conversion of propylene per mole fed, appears in Figure 2. Trends are not indicated in the figure. It is evident, however, that most of the data lie above the steady-state selectivity of about 40%. The average selectivity under composition modulation is about 55%, representing an increase in selectivity of the order of 35%. Some points show selectivity of about 75%, suggesting an almost doubling of this key performance parameter. Scatter in Figure 2 arises from variability of the C02 measurements. Thus, low selectivity at 7 = 2.12 occurred because C02yield was high for these runs. Unfortunately, the scatter obscures the existence of any trends with modulation period. Selectivity to ethanol under steady state ran about 4%. Selectivity under composition modulation can be calculated by taking the ratio of the ethanol to acrolein partial pressures in Figure 1 and multiplying the respective acrolein point in Figure 2. Inspection of the figures shows that ethanol selectivity under modulation is poorer than steady-state selectivity for most of the data points. The selectivity-yield results are intriguing from a process standpoint. Partial oxidation is exothermic and heat removal is a major reactor design consideration. Composition modulation by reducing rate and increasing selectivity, leads to longer reactors or larger tubes easing the heat transfer problem, but without a loss in selectivity. Al-Taie and Kershenbaum (1978) found yield based on feed was reduced by modulation, while selectivity was increased (also by about 30%). Thus, our observations are not unique. The steady-state selectivity to acrolein at just over 42% is low for Sb-Sn oxide catalysts. A catalyst with a low activity was chosen deliberately so as to provide ample room to show selectivity improvement through modulation. Boudeville et al. (1979) find that the selectivity of the 10% Sb catalyst used can be improved to about 75% by calcination. This improvement corresponds to the maximum found in our study. Evidently, composition moduIation should be viewed as an alternative to catalyst modification by conditioning or moderate changes in the cation mix. The facile explanation of the yield-selectivity relation that oxidation of C3=to acrolein to C02 is a consecutive reaction so that selectivity drops from 100% as the conversion increases is not supported by the data. Modulation at X = 50 mmHg seems to give the poorest selectivity as well as the lowest acrolein yields, whereas at X = 15 mmHg, selectivity is highest while the drop in acrolein yield from
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steady state is the smallest observed. Thus, other explanations must be sought. Interpretation of Results Interpretation is assisted, although not altogether resolved, by examining product concentrations within the periods. Figures 3 and 4 show these concentrations. In the former figure, the feed composition cycles between 65 mmHg C3=/35“ H g O2and 35 “ H g C3’/65 mmHg OF Consideration of the C3=/02ratio indicates that this is a sharp variation in composition. Nonetheless, there is virtually no change in conversion to acrolein between the two half-cycles. Although not shown, conversion to C 0 2 also remained about constant. The ethanol yield on feed to the reactor increases by about 50% on passing from the O2 rich to the C3’-rich half-period. Acetone appears only in the latter half-cycle. Propanol and propylene oxides were also formed, but they were difficult to detect. Note that there are two scales in the figure: the left ordinate for acrolein, and the right for the other products. In Figure 4, the results for a modulation amplitude of 35 mmHg are shown. A t this amplitude, there is a more than 5-fold change in the concentration of each reactant between half-cycles. The figure now shows a shift in acrolein level, but the shift is not commensurate with the large changes in O2 or Cs=concentrations in the feed. Measurements at 7 = 2.2 and 6.3 h showed a larger difference in the half-cycles and a more pronounced decay in the C3‘-rich half-cycle. A large change in ethanol concentration, of the order of 4-fold, occurs on switching from the 02-rich to the C3=half-cycles. As in Figure 3, acetone is seen only in the C3’-rich half-cycle. Trace amounts of propylene oxide and propanol, when detected, were found only in the same cycle. For A = 50 mmHg, large differences in acrolein partial pressures between the half-cycles were detected at low T .
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 2, 1985 323
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Acrolein levels were about 2-fold higher in C3'-rich halfcycles. At a larger 7 , the partial pressure declines with time i n both half-cycles as Figure 5a shows, but the decline is considerably more rapid in the C3=-richhalf-cycle. Ethanol appears only in the C3=-rich half-cycle and its partial pressure declined with time (Figure 5b). Acetone, propanol, and propylene oxide were not detected. The rather small variation of acrolein between half-cycles suggests a low dependence on the rate of acrolein formation on C3= and O2 concentrations. A zero-order dependence of acrolein formation on O2partial pressure is documented for the Sb-Sn oxide catalysts (Godin et al., 1968; Trifiro et al., 19711, but the C3- dependence has been found to vary as the C3=/02ratio (Trifiro et al., 1971). Lankhuyzen et al. (1976), observed a zero-order dependence on reactants for ammoxidation of C3=on a bismuth molybdate catalyst. His interpretation was that the catalyst surface was essentially covered by chemisorb C3=, N H , and acrylonitrile. Krenzke et al. (1978) demonstrated that the surface of an SbSn oxide catalyst is indeed covered by propylene and acrolein or one of its surface precursors. Desorption of acrolein was identified by them as the rate-controlling step. If the surface species is primarily propylene and/or the allylic intermediate rather than acrolein, the observations of Krenzke et al. (1978) could be interpreted by a diffusional rate-controlling step such as surface diffusion of allyl species from an Sb6+/Sb4+site associated with a nucloephilic oxygen were dehydrogenation of C3=has occurred to a site associated with an electrophilic oxygen probably as a covalent bonded oxygen. This sequence has been proposed at different levels of detail by Godin et al. (1968), Crozat and Germain (19731, Sala and Trifiro (1976), and Sokolovskii and Bulgakov (1977). Indeed, the constant acrolein yield across the two half-cycles can be explained by rate control through the diffusion rate of the allylic intermediate between surface sites, as well as by acrolein desorption. Desorption or surface diffusion control alone do not explain the amplitude effect seen in Figure la. The mean C3=and O2levels in the feed are the same at all X and T
conditions shown in the figure. A possible explanation of the 7 and X effects as well as the decline in acrolein partial pressure in the C3'-rich half-cycle at X = 50 mmHg is reduction of the catalyst. Working with an Fe-Sb oxide catalyst, Gelbshtein et al. (1976) found yields of acrolein higher in pulsed operation than in a batch reactor at the same total C3=converted and reasoned that the oxidation state of the surface was higher because of diffusion of O2 ions from the catalyst bulk to the surface. If the oxidation and reduction steps in a redox system occur at different intrinsic rates, varying 7 and X should alter the degree of reduction of the surface. The effect of X (Figure lb) on yield and the different pattern of ethanol partial pressure in the half-cycle (Figures 3-5) suggests that ethanol is formed in parallel with acrolein and is not a further oxidation product. The ethanol mechanism may well involve O2 adsorbed on the surface and ethanol could be an intermediate in the formation of C02. This would account for the low yields in the 02-rich half-cycle at large X and the disappearance of EtOH in this half-cycle when C3=is not in the feed (i.e., at X = 50 mmHg). Acetone formation, unlike ethanol, is found only in the C3=-richhalf-cycle. It is not seen when one of the reactants is removed from the feed (A = 50 mmHg). By the reasoning used for ethanol, it is likely that specific sites are involved and that acetone forms via a reaction sequence operating in parallel with the one giving acrolein. It is unlikely that acetone is a precursor of EtOH, although the sensitivity to oxygen suggests that acetone is a step in an alternate sequence leading to C02. Evidently, acetone or its precursor on the surface must be readily oxidizable to COP The carbonium mechanism of Moro-Oh et al. (1971) seems incapable of explaining the strong O2 dependence. The half-cycles in Figure 3 and 4 represent time spans of over 2 h. It is perhaps surprising that there is no change with time except for a slight drop in acrolein yield in the first portion of the C3'-rich half-cycle at X = 35 mmHg. Substantial decreases in conversion with time occur, however, at X = 50 mmHg corresponding to cycling between a feed with 13.2% C3=in N2 and a feed with 13.2% O2 in this carrier as Figure 5 shows. The presence of acrolein after 3.5 h in the absence of O2 or of C3=in the feed appears remarkable. A careful check, however, indicated that small amounts of oxygen and propylene leaked through the solenoid valves. It is this leakage which amounts for the tail region in Figure 5. Nonetheless, the initial decay should represent the catalyst response to removing a reactant from the feed. On the assumption of a first-order process leading to an exponential decay, it is possible to estimate time constants from Figure 5. These are the times corresponding to a 63% change from the initial partial pressures. Using just the early portions of each half-cycle, the acrolein time constant is about 90 min in both the C3=-and the 0,-rich half-cycles. The ethanol time constant is about 50 min. Using similar data taken at lower values of 7,the average time constant of acrolein in the C3'-rich half-cycle is about 90 min, while in the 02-richhalf-cycle, the average is about 200 min. The average time constant for EtOH was about 70 min. Unfortunately, the variation of the individual calculated time constants from the average is large. This, as well as the shapes in Figure 5, raises the question of whether or not exponential decay actually occurs. Observations discussed further on suggest that the decay should be treated as consisting of more than one process. The time constant measured in a changing system should reflect the rate-controlling process during the
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 2, 1985
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change. These time constants are too long for acrolein desorption or surface diffusion control, particularly if we are dealing with transport between nearby catalyst sites in a two-dimensional adsorbate. The measured time constants point to catalyst oxidation and reduction. The decay in the C3=half-cycle shown in Figure 5a would then occur through reduction of Sb5+. Reduction by olefins is well documented (Sala and Trifiro, 1976; Gelbshtein et al., 1976; Trifiro et al., 1971; Germain and Perez, 1975). In the O2 half-cycle (no C3=present in the feed), the decay is slow because oxidation of Sb3+and increased activity are offset by depletion of C3=from the catalyst surface. A comparison of the time constants indicates reduction is much faster than oxidation; Trifiro et al. (1971) reach the same conclusion from different evidence. As a result, increasing 7 and X causes longer exposure to C3=or exposure to higher concentrations which should lead to greater reduction of the catalyst. A lower oxidation state of antimony, according to Crozat and Germain (1973) and Sala and Trifiro (1976), decreases activity and thus forces acrolein yields downward. Keulks (1970) contends that diffusion of reticular oxygen is rate controlling for BiMo-0 catalysts. It may be that it is this process which controls catalyst reduction and thereby the decay observed in Figure 5a. The ethanol time constant is close enough to that measured for acrolein to conclude that the rate-controlling step is the same for both products. This observation lends credence to Germain’s view (1978) that ethanol is formed from acrolein or its surface precursor rather than via a separate mechanism. The mechanism is discussed by Cathala and Germain (1971). Response of C02yield to a step change in feed composition was measured in a separate set of experiments using an IR spectrophotometer because of fluctuations for the GC measurements. In addition, the feed system was modified by adding tight on-off valves to eliminate leakage. A step change between 13.2% C3=and 13.2% O2was used. Acrolein and EtOH concentrations were determined by GC
sampling; however, in contrast to the modulation experiments, sampling began a minute after the composition switch. Step change results are shown in Figure 6. The IR measurements show a large, narrow C02 peak just after the C3=containing feed is introduced. After 2 min, the conversion to COBcontinues, but now much more slowly. COz appears in the reactor off gas up to and apparently after 100 min even though there is no O2 in the feed. Oxygen for COz formation can only come from the catalyst bulk. The time constant for the tail region is evidently much longer than those for acrolein and ethanol. This may reflect slow further oxidation of an acrolein precursor on the surface by reticular oxygen. The rapid increase in C02and subsequent sharp decline (time constant ca. 1 min) may be explained by the displacement of C02 by the more strongly bound allyl1 derivative of C3=or by rapid, total oxidation of the freshly adsorbed C3=by 0- or 02-species laid down in the O2 pretreatment of the catalyst. Haber (1978) predicts the presence of the sorbed O2 on metal oxides and suggests that the total oxidation step is rapid. Acrolein GC data are also shown in Figure 6a. Sampling in this run was initiated 1 min after the switch to C3=. A sharp decay is now evident with a time constant of about 10 min. This observation is probably explained in the same way as the C02measurements: either by displacement of acrolein by C3=or by initial rapid oxidation of CB=to acrolein by the catalyst in its most oxidized state. Results suggest that acrolein cannot be strongly adsorbed on the surface supporting a view held by Haber (1978). After the initial rapid decay, the slower process becomes dominant which has a time constant of about 100 min in good agreement with the X = 50 mmHg cycling results. Ethanol measurements also agreed closely with the cycling time constant of 70 min. Figure 6b shows the yield of C02 after a switch to 13.2% O2 in N2from a several hour pretreatment with 13.2% C3=. A small COz peak is evident, followed by rapid decline in C02 concentration with a time constant of about 1 min. A slower decline with a time constant of 15 min follows. Propylene is depleted after about 30 min. The figure certainly indicates oxidation by adsorbed 02,but from the size of the peak this process would seem to be less important than the COzformation through reticular oxygen. Acknowledgment Research on which this contribution was based was performed while one of the authors (P.L.S.) participated in the Franco-Canadian Exchange of Scientific Personnel program organized by the N.R.C. (Canada) and C.N.R.S. (France). Support provided by this program is gratefully acknowledged. Research guidance was provided by Drs. Figueras, Portefaix, and de Mourgues. Equipment was operated by Mr. Foujol. The authors are indebted to these gentlemen for their assistance. Registry No. Acrolein, 107-02-8; antimony oxide, 1327-33-9; tin oxide, 1332-29-2; propylene, 115-07-1.
Literature Cited Abdui-Kareem, H. K.; Silveston, P. L.; Hudgins, R. R. Chem. Eng. Sci. 1980, 35,2077. Ai-Taie, A. S.; Kershenbaum, L. S. ACS Symp. Ser. 1978, 6 5 , 518. Baker. A.; Richarz, E. Chimia 1978, 3 0 , 502. Belousov, V. M; Gershingorina, A. V. Trans. Fourth Int. Congr. Catal. Moscow 1968. 260. Bilimoria. M. R.; Bailey, J. E. ACS Symp. Ser. 1978. 65, 526. Boudeville, Y; Figueras, F.;Forissier, M.; Portefaix,J.; Vedrine, J. C. J . Catal. 1979, 58, 52. Cathala, M.; Germain, J. E. Bull. SOC.Chim. F r . 1971, 414. Crozat, M.; Germain, J. E. Bull. Soc. Chim. Fr. 1973. 1125. Forissier, M.; Larchier, A,; De Mourgues, L.; Perrin, M.; Portefaix. J.-L. Rev. Phys. Appl. 1976, 1 1 , 639.
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Received for review September 18, 1981 Revised manuscript received May 21, 1984 Accepted June 1, 1984
Thermal Conductivity of Coal-Derived Liquids and Petroleum Fractionst Monlca E. Baltatu Fluor Engineers, Incorporated, Advanced Technology Division, Irvine, Califomia 92730
James F. Eiy and Howard J. M. Haniey* Chemical Engineering Science Dlvlsion. National Engineering Laboratory, National Bureau of Standards, Boulder, Colorado 80303
Mlchael S. Graboski, Richard A. Perkins, and E. Dendy Sioan Department of Chemical Engineering and Petroleum-Refining, Colorado School of Mines, Golden, Colorado 8040 7
Thermal conductivity coefficients of coal-derived liquids and petroleum fractions are calculated by an extended corresponding states, conformal solution technique. The method requires as input pseudocritical parameters, molecular weight and acentric factor, and a pseudddeal gas heat capacity for each pseudocomponent or fraction. These quantities are estimated here from the mean average boiling point and specific gravity of the fractions using the techniques proposed by Riazi-Daubert, Kesler-Lee, and Winn: the relationship between the estimated conductivity and the choice of the method is noted. Predicted thermal conductivities are compared with data for three coal liquid samples measured at the Colorado School of Mines and with literature data. Agreement between prediction and experiment is generally within 10%, depending on the method used to calculate the input parameters. Some literature petroleum fractions data are also compared with the model. Again, agreement is within 10%.
Introduction This paper follows the work reported by Baltatu (1981, 1982), who applied the extended corresponding states conformal solution transport property model (CST) proposed by Ely and Hanley (1981,1983) to the viscosity of petroleum fractions and coal liquids. Specifically, the object of this report is to complement the viscosity studies by applying the CST model to thermal conductivity. This task was not possible until recently: limited data were available for petroleum fractions (Mallan et al., 1972; Jamieson et al., 1975) but none for coal liquids. Recently, however, Gray (1981) presented results on SRC-I1 coal liquids, and independent experiments have been carried out at the Colorado School of Mines on three liquids: two distillation cuts boiling in the naphtha range produced by Work carried out in part at the National Bureau of Standards. Because of the intended audience, this manuscript sometimes departs from the usual NBS policy to use only SI units. 0 196-4305/85/ 11 24-0325$01 .50/0
the SRC-I and SRC-I1 processes, and a distillate from a Utah coal via the COED processes. An attractive feature of the new data is that they were obtained for liquids which are well characterized so that one can make a quantitative comparison between theory and experiment. The CST procedure is very flexible. It predicts the transport properties-over the phase range from the dilute gas to the dense liquid-for pure species and for mixtures with, in principle, an unlimited number of components. Input parameters required are: the temperature (T), pressure (p), and (for a mixture) mole fractions (xi);the critical temperature, pressure, and volume, molecular weight (M), and acentric factor ( w ) for each species of interest. An estimate of the dilute gas heat capacity at constant pressure is required for each species for the thermal conductivity calculation. To be consistent with our previous work, we will obtain the input parameters from the mean average boiling point T b and specific gravity SpG, but we stress that this step introduces considerable uncertainty into the prediction 0 1985 American Chemical Society
