Ind. Eng. Chem. Process Des. Dev.
does not require much detail about the properties of the reactive mixtures, and can be recommended for guiding the design of such columns.
1073
1985,2 4 , 1073-1080
Registry No. m-Xylene, 108-38-3;p-xylene, 106-42-3;sodium p-xylene, 91862-16-7.
Literature Cited Fieser, L. F.; Fieser, M. “Reagents for Organic Synthesis”;Wiley: New York, 1967; Vol. 1, p 848. Gau, C.; Marquez, S. J . A m . Chem. SOC.1976, 98, 1538.
Acknowledgment We thank the engineering Foundation (grant No. RCA-79-1) for providing financial support.
Received for review May 29, 1984 Accepted March 19, 1985
Weeping from Distillation/Absorption Trays Samuel 0. Fasesan Department of Chemical Engineering, University of Ife, Ile-Ife, Nigeria
The rate of weeping from distillation/absorption trays was measured simultaneously from two identical trays in a 24 in. diameter absorption column by using air-water system. The data were acquired via two independent methods-weepage catch tray and dye trace technique. Models of dynamic response of dye solution pulse were developed and employed to evaluate the data acquired from the latter technique. The measurement covered a wide range of operating conditions. Both sieve and valve trays were investigated. The data obtained compare favorably with some reliable data in the literature.
A recent survey Fasesan (1980) on weeping rate from separation trays reveals the scarcity of adequate quantitative information on weepage from most of the common trays especially sieve and valve trays. Consequently,it has been rather difficult to obtain adequate empirical formulas for confident prediction in design. Existing correlations follow sets of assumptions and mechanisms. The approach adopted by Kupferberg and Jameson (1970) was to define pressure drops and hydrostatic loss
h L = PlgS
(3)
From these, a criterion known as the dumping number was introduced:
Kharbanda and Chu (1970) obtained an empirical equation of the form Umin
= 46.4[5.37(12dh)z”6p1-12(adh)]
(5)
Discarding the surface tension term in Kharbanda’s equation for minimum vapor velocity and expressing it in terms of the F value, Eduljee (1972) derived the expression (for the air-water system)
F b = 13.48~lhO.~~
(6)
Similarly, the equation of Kupferberg and Jameson subjected to the same treatment becomes
Fhm=
1.103dho.5p10.625p,-0,125
(7)
Though it has been remarked by Raper et al. (1977) and
Table I. Tray Specifications valve trays (Koch sieve trays Flexitray) hole diam, mm 6.35 38.1 14.29 82.55 hole pitch (triangular), mm tot hole area, m2 0.027 0.0274 0.1907 0.1907 plate active area, m2 3’% hole-free area 14.2 14.3 valve diam, mm 48 3.23 max valve clearance, mm height of chimney, m chimney diam, mm height of chimney cap, mm
chimney tray 31.75 57.15 0.0275 0.1907 14.4 0.2 25.4 28.58
Other Specifications tray thickness, mm 3.0 500.0 tray spacing, mm weir height, mm 50.8 weir length, mm 0.465 0.0372 cross-sectional area of downcomer (segimental), m2 cross-sectional area of column shell, m2 0.2798
also by Porter and Jenkins (1979) that no one satisfactory correlation exists in the literature, the expression of hydrodynamics phenomena occurring at an orifice according to Kupferberg and Jameson is perhaps preferred and mostly adopted by a number of investigators. The empirical equation of Kharbanda has also been shown by Eduljee to be comparable to that of Kupferberg and Jameson. However, for the development of improved correlations, better weeping-rate data are required. The primary objective of the study, therefore, was to generate new reliable data on weeping from both sieve and valve trays and to test such data against results that had been proven acceptable in the literature.
Experimental Section The test rig constitutes essentially a 24 in. diameter
0196-4305/85/1124-1073$01.50/00 1985 American Chemical Society
1074
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 4, 1985
n
Sample Tray
LJ
4 ,
d-
-
15'
Dye inlet
1
Top test liqui sampler
I
--
--(1.
Middle sample tray
I
liquid
sample 3.93
1 .E
0.95 rQ-:actry
3ottom
15
m sec-'
Ik:pim3iT
Figure 2. Weeping rate measurement in the predominantly weeping regime.
SIEVE
TEST TBAY TOP 90"
e
0
0.96
A
b
1.125
d
a
1.71
v
v
m
0
in dia.
hole
m/.(k+7/m3+
Ps-FACMB
3
.R6
7.21
Figure 1. Column configuration.
absorption/hydraulic column, bottom vessel 3Il2 f t by 4'12 ft, flameproof centrifugal pump, liquid coolers, and flameproof gas blower. The column configuration included two test trays and three sample trays equally spaced a t 20-in. spacing. This configuration is represented in Figure 1. All relevant tray specifications are given in Table I. Weepage Catch Tray. The bottom sample tray, which is a chimney tray, designed and employed in this investigation provides direct volumetric measurement of the weeping rate from the bottom test tray. The chimney tray was designed so that (1)the collected volume or mass of liquid represents the magnitude of the weeped liquid, (2) the reentrainment of the collected weeped liquid is minimal, and (3) the flow of gas arriving at the region beneath the test plate is uniform in order to prevent maldistribution of gas flow which may lead to localized weeping from the test tray. Determination of the Weeping Rates. For set operating condition, the rate of weeping from the bottom test tray was measured by collecting the quantity of liquid discharged per minute and per constant head of liquid on the chimney tray floor repetitively. It was also measured by the dye trace technique. Models of dynamic response to dye solution pulses (Fasesan, 1980) were employed to
-2
1
I
1
5.0
LI ,VI9
I 10
I.I,ALIlN';.
I
I 13
Kg/s*c, m
Figure 3. Weeping rate vs. liquid-loading F, factor parameter (sieve trays).
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 4, 1985 1075 Table 11. Weeping Rate Data from Sieve and Valve Trays liq weeping rate W, % loading F, factor chimney bottom flooding L, v, (p,'I2) tray tray top tray sieve trays 40 50 60 70 80 90 100
100 90 80 70 60 50 40 35
7.15 8.95 10.72 12.50 14.29 16.08 17.90 4.28 5.36 7.15 10.72 8.95 5.36 8.95 4.28 5.36 6.45 7.15 7.88 10.72 11.44 10.72 12.50 14.29 8.95 8.95 10.72 7.15 12.50
1.13 1.33 1.62 1.88 2.21 2.42 2.67 0.96 0.96 0.96 0.96 0.96 1.13 1.13 1.71 1.71 1.71 1.71 1.71 1.88 1.88 2.21 2.21 2.42 1.62 1.04 2.13 1.17 1.58
1.03 0.91 0.60 0.27 0.0 0.04 0.0 0.85 0.90 1.18 0.90 2.09 0.82 1.05 0.19 0.22 0.35 0.38 0.44 0.13 0.24 0.0 0.0 0.0 0.52 1.202 0.07 0.91 0.94
1.29 0.357 0.68 0.393 0.075 0.47 0.0 0.81 0.98 1.327 1.966 1.89 0.76 1.22 0.201 0.253 0.290 0.323 0.358 0.22 0.36 0.0 0.043 0.0 0.593 1.25 0.071 1.09 1.02
2.27 0.706 1.23 0.73 0.178 0.097 0.0 1.673 1.952 2.57 3.91 3.01 1.41 2.52 0.38 0.502 0.59 0.627 0.706 0.33 0.56 0.0 0.08 0.0 1.11 2.42 0.14 2.08 1.96
3.60 5.40 6.45 7.15 8.96 10.75 12.50 14.33 16.12 17.90 19.70 21.50 5.40 7.15 8.98 12.50 19.70 21.50 3.60
valve trays 0.96 0.06 0.96 0.04 0.96 0.12 0.96 0.14 0.96 0.17 0.96 0.44 0.96 0.24 0.96 0.28 0.96 0.33 0.96 0.40 0.96 0.42 0.96 0.47 1.13 0.05 1.13 0.06 1.13 0.103 1.13 0.18 1.13 0.42 1.13 0.43 1.88 nil
0.051 0.068 0.122 0.144 0.175 0.287 0.218 0.27 0.35 0.42 0.452 0.504 0.054 0.067 0.111 0.227 0.427 0.455 0.0
0.080 0.124 0.222 0.274 0.344 0.504 0.424 0.478 0.593 0.744 0.783 0.906 0.096 0.107 0.193 0.397 0.784 0.854 0.0
7.15 10.75 14.33 17.90 21.50 21.50 19.35 17.05 15.05 12.90 10.75 8.60 7.52 10.75 10.75 10.75 10.75 10.75 10.75 12.50 12.50 12.50 12.50
valve trays 1.88 nil 1.88 0.01 1.88 0.08 1.88 0.12 1.88 0.16 3.45 nil 3.35 nil 2.78 nil 2.45 nil 2.10 0.02 1.74 0.04 1.39 0.05 1.23 0.17 1.13 0.07 1.33 0.066 1.50 0.013 1.63 0.053 1.96 0.004 2.21 0.0 1.25 0.167 1.67 0.061 1.88 0.031 2.21 0.002
0.0 0.011 0.084 0.129 0.152 0.0 0.0 0.0 0.0 0.033 0.064 0.068 0.250 0.080 0.07 0.021 0.061 0.004 0.0 0.181 0.063 0.034 0.002
0.0 0.016 0.151 0.219 0.267 0.0 0.0 0.0 0.0 0.064 0.12 0.122 0.35 0.144 0.124 0.038 0.116 0.006 0.0 0.360 0.105 0.057 0.003
Table 111. WeeD Fraction at F,, of 1.6 bottom test tray liq feed rate top test tray L,(bottom) = lia feed rate LJtOP) - W,(tOP), L,(t&), kg/(s m) % W, kg/(s m) 7.15 (200 L/min) 5.0 6.8 (189.7 L/min) 10.72 (300 L/min) 5.1 10.2 (285.1 L/min) 12.5 (350 L/min) 6.0 11.75 (328.8 L/min)
%
w,
2.9 3.0 3.7
analyze the system for its dynamic response to indicate the tracer concentration in the liquid stream across the column sections as a result of the change in inlet-stream tracer composition per element of time.
Results and Discussion Weeping Rate from Sieve Trays. As mentioned previously, the experimentalwork conducted was primarily aimed at generating reliable weeping rate data from two of the common vapor or gas-liquid contacting trays and to examine the validity of the assumption of equal weeping rate from tray to tray. To investigate the latter aspect, the experimentalrig have been operated with two test trays as shown in Figure 1. These trays have been designed to be of the same parameters. The first set of test trays were . . in. diameter hole sieve trays. To maintain uniform gas flow pattern through the two test trays, the middle sample tray has been designed to have the same design parameters as the two test trays. Operating conditions have been varied over as large a range as possible within the technically feasible limits. Table I1 shows the cross section of the operating conditions for weeping rate determination. The percent flood listed in Table I1 was determined as a linear fraction of both the gas and liquid rates required to flood the column. The column flood point was determined by slowly increasing first the gas rate and then the liquid rate (to the column) by increments until excessive liquid backup occurred in the downcomer. At the same time, the froth level on each plate rose to the plate above (observed through the windows in the column wall), the liquid level indicator on the bottom vessel became erratic, and a large rise in the total column pressure drop was observed. To obtain the maximum weeping rate possible with the column configuration in Figure 1,the gas throughput was set at an F, factor of 0.96 with liquid load over the range 5.36-10.72 kg/(s m) weir length for the in. diameter sieve trays. At this F,factor, the weeping rate of 3.91 kg/(s m2)of the plate-active area for a liquid load of 10.72 kg/ (s m) weir length was recorded as the highest. The effect of gas or vapor throughput on the weeping rate is illustrated in Figure 2. This clearly shows the reduction in weeping rate which occurs with increasing F, factor. Further, it is seen that the weeping rate from the top test tray is higher than the weeping rate from the bottom test tray. Due to the withdrawal of the weeped liquid from the top test tray from the column through the middle sample tray, the overflow to the bottom test tray from the top test tray is reduced by the amount of liquid weeped from the latter. Inspection of the present data from each tray reveals that about 30% reduction in weeping rate resulta from a 15% drop in liquid overflow rate. The weeping rate data of Lemieux and Scott (1969) from l/z in. diameter hole sieve
r
TEST TR4Y
mop
-2 IO
LXQ. LOAD Kc/sEc,
Bo"
0
0
7.15
A
II
10.75
A
A
12.50
I
0.5
SIEYE
1
1
1.0
F*-FACTOR m.sec'-'
4" dia.
hole
n
I 1.5
I
I
1
2.6
( Q/m3)*
Figure 4. Weeping rate va. F, factor liquid load as the parameter (sieve trays).
trays with an air-water system indicated about 93% reduction in the weeping rate for a 26% drop in liquid rate. A reduction of 30% in weeping rate due to unequal liquid flow rates on both test trays is considered realistic. Consequently, the weeping rate data collected from the bottom test tray in the predominantly weeping region are subjected to a correction factor relative to the drop in the liquid rate and are represented by brokenlines in Figure 2. These results clearly indicate that weeping rate from identical trays increases from stage to stage in the direction of the column top section. In Figure 3, weeping rate values from sieve trays have been plotted against liquid loading with the F factor as the parameter. From this figure, it is seen that the graph strongly deviates from the straight line with increasing F,
factor. This indicates that weeping rates increase linearly with increasing liquid loading at very low gas or vapor flow rates. Comparison of the Data with Existing Data on the Sieve Tray. To provide a basis for comparison between these results and those reputed few in the literature, the weeping rate values obtained from liquid loading over the range 7.15-12.50 kg/(s m) weir length have been plotted against the values of the F, factor covering operations in the weeping and phase inversion regimes as illustrated in Figure 4. The data of Kupferberg and Jameson (1970) and that of Kharbanda (1970) were defined by Eduljee (1972) for minimum velocity at the weep point by eq 6 and 7 . The in. divalue of Fh calculated from both equations for
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 4, 1985
I
I
I
1
I
I
I
I
WLW
PYdT PRAY
1077
TRAY
2
MP
B ~ U M
LW. i($sec
0
0
8.95
J,
LY A
10.75
A
m
12.5
Figure 5. Weeping rate vs. F, factor liquid loading as the parameter (valve trays).
ameter holes corroborated rather closely, producing corresponding F, values with an average of 1.6 at the weep point. From Figure 4,the values of the weeping rate at the F, value of 1.6 for different liquid loadings are read, and the closeness of the corresponding weepage fractions to 0 suggests the deviation from the prediction of the minimum vapor velocity given by a F, of 1.6 at the weep point, Table 111. The weepage fractions recorded for the data from the top test tray show a maximum deviation of 6%, while that of the bottom test tray shows a maximum deviation of 3.7 %. This comparison suggests a reasonable agreement between this experimental data and that of Kupferberg and Jameson and that of Kharbanda on minimum velocity at the weep point. It has become obvious from these results and earlier results that minimum velocity at the weep point increases with increasing liquid loadings-the least devi-
ation from the weep point at a F, of 1.6 is recorded on the bottom test tray, having less liquid load than the top test trays. Weeping from Valve Trays. Figure 5 is the plot of the weeping rate from the valve tray against the F, factor for the same operating conditions as those presented in Figure 3 for sieve trays. These experimental results indicate insignificant weeping rate from the valve tray at a F, factor of more than 1.88. Further, the linear relation between the weeping rate and the liquid loading at a low F, factor on the sieve trays is not obvious in the case of the valve trays. Nevertheless, these data from the valve trays compliment the earlier results from the sieve tray on the progressive increase in weeping rate from stage to stage in the direction of the top of the column. For a slight increase in gas rate, the valve trays show a higher decline in weeping rate than the sieve trays given
1078
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 4, 1985
1
I
I
I
I
TEST TRAY
I
I
I
VALVE TRAY
I 1
I-
r
t-
t I 0,O
I
I
I
4 L I ! J J I D L0AD"o
I
15
10
I
I
iI
20
Kl>/SEC. M
Figure 6. Weeping rate vs. liquid-loading F, factor as the parameter (valve trays).
the same liquid loading, Figure 6. The comparison of the data collected fromthe valve trays with literature published data cannot be pursued, due to the absence of relevant data in the open literature. The results of Grocott (1961) from valves having a clearance of 3/8 in. and weir height of 3 in. in a rectangular column could not be compared with the present data because of the fundamental differences in the design variables. Reliability of the Data of the Chimney Tray. The experimental program was moreover aimed at establishing the reliability of the data collected via the designed chimney tray (also known as weepage collection tray). These data are compared with the results obtained through dynamic response of dye solution pulses in absorber. The latter have been shown to be comparable with the few reliable data in literature. In Figure 7, experimental values of the weeping rate collected via the two independent data have been plotted against the column capacity ratio for both sets of sieve and valve trays. When a statistical procedure was used, the extent to which the weeping rate data collected via the chimney tray are related to the data collected via the pulse technique measured on bottom test tray has been determined for 25 different measurements
covering a wide range of operating conditions for both sieve and valve trays, Table 11. A coefficient of correlation of +0.85 is obtained. This suggests that the result obtained through the weepage collection tray is substantially comparable to that obtained via the pulse technique. This comparison can be observed from the plots in Figure 7 for sieve and valve trays over a range of column-capacity operating conditions. Figure 7 also clearly shows that the problem of excessive liquid weepage at low-capacity operating conditions and at low vapor or gas rates conditions is not present on Koch valve trays. At 35% flooding condition, a weep fraction of less than 3% is obtained. This corroborates the result of Todd and Van Winkle (1972) who reported a very small amount of tray weepage even at 15% column capacity for their set of valve trays.
Conclusion The scale of these experimental studies is comparable to an industrial scale. Subsequently, the data obtained are of direct relevance to most of the industrial units. Most of the operational problems associated with equipment of
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 4, 1985
Bottom Sieve tray
Chimney tray
e
0
1079
Bottom Valve tray Chimney tray
A
h
1.5
cil
E
0
9d
1.0
W
w e: < 0
H z
a
k i 0.5
0. % Flooding
Figure 7. Weeping rate vs. column-capacity operating condition.
this dimension have been encountered and successfully resolved. Reliable weeping rate data have been obtained from both sieve and valve trays over a wide range of operating conditions. When two identical test trays in the column configuration were used, results have shown that weeping rate varies from tray to tray, increasing in the direction of the column top section. This conclusion is strongly supported by the results of independent measurements of weeping rate from sieve and valve trays. Results of this experimental work have indicated that, on the sieve tray, weeping rate increases linearly with increasing liquid loading, within the weeping regime (below the weep point). When a weepage catch tray is designed correctly, it has been shown that its results are comparable to the reputed few results in the literature.
Fhm= F value at minimum gas velocity through the hole, Uhmbg''')
Nomenclature
F, = energy factor based on active area, U,(P,'/~) g = acceleration due to gravity hL = height of liquid head on tray, mm L , = mass flow rate of liquid/unit length of weir, kg/(s m) Nd = dumping number s = vertical distance of center of bubbles from the plate, mm hpD= dry-plate pressure drop, mm of liquid U = total gas flow per unit time/hole area = velocity of gas through the hole, m/s uho = instantaneous velocity of gas through orifice, m/s uhm = minimum hole velocity, m/s umin = minimum gas or vapor velocity, m/s W , = weeping fraction (i.e., weeping rate/liquid flow rate) W , = mass rate of weeped liquid/active area of plate, kg/(s m2) pg, pI = densities of gas and liquid, respectively, kg/m3 u = surface tension, dyne/cm
dh = hole diameter, mm Fh = energy factor based on velocity through the hole, uh(pp'/2)
Eduljee, H. E. Chem. Eng. 1972, 123.
Literature Cited
1080
Ind. Eng. Chem. Process Des. Dev.
Fasesan, S. 0. Ph.D. Thesis, University of Manchester Institute of Science and Technology. Manchester, England, 1980. Grocott, G. J., Masters (Technical) Thesis, University of Manchester Institute of Science and Technology, Manchester, England, 1961. Kharbanda, 0. P.: Chu, J. C. Br. Chem. Eng. 1970, 15 (6), 792. Kupferberg, A.; Jameson, G. J. Trans. Inst. Chem. Eng. 1970, 4 8 , T140. Lemieux, E. J.: Scottl, L. J. Chem. Eng. Prog. 1969, 65(3),52. Porter, K. E.; Jenkins, J. D. Inst. Chem. Eng. Symp. Ser 1979, No. 56, 3.2/21.
1985, 2 4 , 1080-1087
Raper, J. A.; Phuong, T. V.; Fell, C. J. D. Paper presented at the 5th Australian Chemical Engineering Conference, Canberra, Sept 14-16, 1977. Todd, W. G.; Van Winkle, M. Ind. Eng. Chem. Process Des,Dev. 1972, 7 7 , 578.
Received f o r review October 13, 1983 Accepted October 29, 1984
Pyrolysis of Volatile Aromatic Hydrocarbons and n-Heptane over Calcium Oxide and Quartz Danlel L. Elllg, Chlu K. Lal, David W. Mead, John P. Longwell,' and Wllllam A. Peters' Energy Laboratory and Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02 139
Benzene, toluene, 1-methylnaphthalene, and n-heptane pyrolysis was studied over the temperature range 550-950 OC, by passing the vapor of the pure compound (initial concentration 2.4-3.9 mol % in helium) through -5.5 cm deep packed beds of calcium oxide/quartz mixtures, or of quartz in control experiments. The total pressure was 1 atm, and contact times were 0.9-1.3 s. The calcium oxide significantly increased the rates and extents of pyrolysis of the aromatics, reducing the temperature for a given percentage conversion by around 140, 140, and 170 OC for benzene, toluene, and 1-methylnaphthalene, respectively. In contrast, CaO decreased the comparable temperature for the aliphatic n-heptane by only -40 'C. Coke was the major product from pyrolysis of the aromatics over both beds. Minor amounts of coke deposition slightly increased the CaO activity for benzene and toluene pyrolysis, but continued coking produced a strong acthmy decay that was fitted to an Elovich model. Oxygen burn-off regenerated 75% and 100% of the initial CaO activity for these two compounds, respectively. A generic stone chemical property, rather than specific BET surface area, is believed responsible for the CaO pyrolysis activity.
-
Coal pyrolysis or gasification frequently generates coproduct tars. Opinions differ on the industrial value of these products. They are usually rich in aromatic compounds, phenols, mutagens, and carcinogens and, depending on operating conditions, can account for 5 to 20 wt 5% of the coal. They thus can place significant burdens on product recovery and waste stream clean-up equipment as well as reduce carbon utilization and hence degrade process thermal efficiency. Poor handling and storage behavior including viscosity increases, phase separations, and incomplete miscibility with petroleum products are related problems. On the other hand, these products are high-energy content liquids (typically 16 000-18 000 Btu/lb) readily and economically recoverable from coal. Redemption of these values, by controlled handling procedures such as in-plant or over-the-fence combustion or refining, is therefore worthy of consideration. The technical and economic feasibility of such utilization strategies, as well as the design and operating requirements of waste stream clean-up equipment, will depend on the amounts and composition of the tars exiting the primary conversion reactor. Previous work in this laboratory (Yeboah et al., 1980) demonstrated yield reductions and quality improvement when fresh coal pyrolysis tars were treated with calcium oxide (CaO or calcined dolomite), at temperatures above 400 "C at contact times of about 1s. Pyrolysis of Illinois No. 6 bituminous coal or a 5545 (w/w) mixture of Texas lignite and Illinois No. 6 coal over CaO and a temperature range of 425-760 "C produced tars lower in yield and oxygen content and higher in H/C ratio than those from pyrolysis in the presence of sand. Major
reductions in the evolution of vapor-phase sulfur compounds including thiophenic species were also observed (Yeboah et al., 1982). These results were interpreted in terms of CaO-enhanced cracking of aromatic compounds, and similar effects are believed to be attainable under gasification conditions. Literature data to assess the role of CaO were unavailable, although there have been several studies of the homogeneous and heterogeneous cracking of aromatics (see reviews by: Madison and Roberts, 1958; Johns et al., 1962; Fitzer et al., 1971) and of CaO-facilitated reactions of aliphatics below 400 "C. A brief review of the latter is given by Mead (1979). Research was therefore undertaken to determine the effect of CaO on pyrolysis of aromatics. The present paper presents results for low boiling pure aromatic compounds. Results for phenolic compounds, less volatile aromatics, and fresh coal pyrolysis tars will be reported on later. Specific questions here addressed include the following: (1)What are the effects of calcium oxide on the rates and extents of thermal cracking of pure aromatic compounds and on the yields and compositions of the resulting products at temperatures from 550 to 950 "C? (2) How does CaO activity depend on its extent of utilization, and can deactivated CaO be conveniently regenerated? (3) Are the observed CaO effects primarily due to its moderately high surface area? Experimental Section Apparatus and Procedure. Pyrolysis of n-heptane, benzene, toluene, and 1-methylnaphthalene over CaO was
0196-4305/85/1124-1080$01.50/00 1985 American Chemical Society
