I
B. B. CORSON, W. J. HEINTZELMAN, and F. J. PAVLIK Mellon Institute, Pittsburgh, Pa.
Shallow and Deep Catalytic Dehydrogenation of Petroleum Cs-Aromatic Fraction
Tm
petroleum CS-aromatic fraction has two valuable components-ethylbenzene for dehydrogenation to styrene and xylenes for oxidation to phthalic acids. o-Xylene (boiling point, 144.4' C.) is separable from the Cs-aromatic fraction by distillation but ethylbenzene (boiling point, 136.2' C.) and m- and p-xylenes (boiling points, 139.1 and 138.3' C.) are nonseparable (4). This exploratory study demonstrates that o-xylene-free petroleum Cs-aromatic fraction can be dehydrogenated under such conditions that ethylbenzene is converted to styrene and m- and p-xylenes survive to give a catalyzate from which high purity styrene can be recovered by distillation. The Ca-fraction must be free from o-xylene because o-xylene is nonseparable by distillation from styrene (boiling point, 145.2' C.). The apparatus was similar to that described previously (3). The reactor was a Vycor tube (19-mm. inside diameter) with an integral vaporizer-preheater packed with 4- to 8-mesh Vycor chips. The catalyst charge was 60 ml. The catalyst temperature was measured by a chromel-constantan thermocouple sheathed in a thermocouple well which extended down through the center of the vaporizer-preheater to the middle point of the catalyst bed. Each dehydrogenation experiment was run a t atmospheric pressure for 22 hours, but the production data for the first 4 hours are not included in the tabulations. T h e 4-hour induction period usually gave high yields of benzene and toluene and a low yield of
Table II.
styrene. For example, the yields of benzene, toluene, and styrene during the first 4 hours of operation at 650' C. and 3 seconds contact time were 6, 15, and 25 wt. %, respectively, whereas during the next 18 hours the corresponding yields were 2, 6, and 35 wt. %. Product yields remained constant within experimental error during the 18 hours following the induction period. Liquid catalyzates which were distilled were inhibited with 1% of tertbutylcatechol prior to distillation. Two hydrocarbon feeds were tested: 1. A synthetic mixture containing 65% of ethylbenzene, 24% of m-xylene, and 11yoof p-xylene. 2. A sample of actual Cs-aromatic fraction from the Standard Oil Co. of Indiana from which o-xylene had been separated by distillation, containing G8% of ethylbenzene, 12% of m-xylene, 10% of p-xylene, and 10% of paraffins.
A commercial dehydrogenation catalyst (4- to 8-mesh) was used in all experiments-1707 dehydrogenation catalyst-whose composition was 72.4% magnesium oxide, 18.4% iron oxide, 4.G% potassium oxide (present as carbonate), and 4.6% copper oxide ( 2 ) . The 1707 catalyst is a self-regenerative catalyst, the carbonaceous deposit which would otherwise deactivate it being continuously removed by the water gas reaction. An index of the self-regenerative ability of the catalyst is the regenerative ratio, defined as the weight of carbon in oxides of carbon divided by the weight of carbonaceous deposit on the catalyst.
The regenerative ratio increases with increase in temperature and decreases with increase in contact time. Paraffin in the feedstock seems to decrease the regenerative ratio at 575' and increase it at 700' C. The material balances for all the experiments averaged 96%. The composition of the liquid catalyzate was determined by infrared spectrometry. The over-all reliability of the data was evaluated by making three dehydrogenation experiments under as nearly identical conditions as possible and analyzing three duplicate samples from each experiment. The feed in this case was the paraffin-contaminated Cs-fraction. The data (Table I) apparently
BQ 2 2 2 2 2
Table I. Reliability of Data TQ EB" S" m-X' p-Xu Pa 9
1 8 5 4 7 23 49 10 4 55 4 2 5 2 1 7 55 1 8 0 56 3 6 18 54 2 7 0 5 7 1 8 2 5 3 Zb 6b 8b 54b 0.6c 2 . 9 8.gC 2.4O
a B, T, EB, S, m-X, p-X, P = benzene, toluene, ethylbensene, styrene, m- and p xylene, paraffin. Mean. d2 liZ 0 Standard deviation, f ; .. d , difference from mean: n, number of determinations.
(m)
Dehydrogenation of Cg-Fraction over 1707 Catalyst-Conditions
and Yields
Products, Wt. % Xylene
Expt. 1 2 3 4 5
Conditions Gas Carbon TOC. CT" HzO/CS Ht HC B T EB S m- p-P Cat. COZ CO Hydrocarbon feed: 65% ethylbenzene, 24% m-xylene, 11% p-xylene 575 650 650 700 700
1
1 3 1 3
10 10 10 10 10
1.5 0 . 0 3.8 0.1 4 . 7 0.1 6,9 0.2 11.6 0 . 5
0 2 2 2 2
2 2 6 6 8
34 19 17 1 2
29 36 35 45 31
21 20 17 18 13
10 10 9 9 7
0 0 0 0 0
0.3 0.5 2.8 0.8 2.t
9 8 0 10 7 2 9 8 12 7 9 2 4 11 8 16 10 8 17 10 9 0 6 9 1 9 9 9 1 8 gb 8b lZb 1.6c 0.8c 9 . l C
1.9 5.6 5.0 8.6 15.6
0.1 0.6 0.9 1.7 6.0
Res.* 0.2 0.4 0.5 0.8 0.6
Styrene Yield, Wt. % Based on C8 EB PP Ult. PP Ult. 29 36 35 45 31
61 51 47 45 32
45 55 54 69 48
94 78 73 70 49
Hydrocarbon feed: 68% ethylbenzene, 12% m-xylene, 10% p-xylene, 10% paraffin 6 7 8 0
46 94 31 64 0.6 1 . 6 0.0 0.1 11 9 8 35 31 1 1.7 0.0 1 65 82 44 56 6.3 0.6 0.5 7 7 0.3 1 5 14 44 9 4 . 0 1.3 60 64 41 7 10 0.3 11.0 3 . 2 1.0 41 43 4 4 8 5.8 2 . 7 2 CT, HzO/Cs, Gas HC, B, T, EB, 8 , P, Carbon, Res., PP, Ult. = contact time in seconds, water/Cs-hydrocarbons mole ratio, gaseous hydro575 650 700
1 1 1
10 15 10
carbons, benzene, toluene, ethylbenzene, styrene, para5n, carbon on catalyst and in COz and CO, residue, per pass, ultimate. Amount of high boiling residue in liquid catalyzate determined by topping a 26-g. sample at 1mm. with distilling tube at 4 5 O C. and condensing tube at - 78' C. 1
VOL. 50, NO. 4
APRIL 1958
621
Table Ill. Dehydrogenation of C8-Fraction over 1707 Catalyst-Xylene-EthyIbenzene-Paraffin Survival Survival. Wt. 97, Stvrene Yield. wt. %" Conditions EthylExpt. T o C. CTb HzO/Cs Xylene benzene Paraffin PP Ult. Hydrocarbon feed: 65% ethylbenzene, 24% m-xylene, 11% p-xylene I "
~
~
1 2 3 4 5
575 650 650 700 700
1 1 3 1 3
10 10 10
88 86 74
10 10
77 57
52 29 26 2 3
... ... ... ... ...
45 55 54 69 48
94 78 73 70 49
Hydrocarbon feed: 68% ethylbenzene, 12'3 m-xylene, 10% p-xylene, 10% paraffin 80 46 94 77 52 575 1 10
6 7 8
650 700
1 1
73 68
15 10
21 6
70 100
65 60
82 64
Based on EB. CT, HzO/Cg, EB, PP, Ult. = contact time in seconds, viater/Cg-hydrocarbons mole ratio, ethylbenzene, per pass, ultimate. (I
are reliable (at least reproducible) for all the components except paraffin and ethylbenzene. The unreliability of the paraffin values is understandable inasmuch as no authentic spectrometric standard was available, the composition of the paraffin contaminant being unknown. I n the case of ethylbenzene there is no good analytical band that does not suffer serious interference from other components of the catalyzate. The per pass yields of styrene, based on relatively accurate determination of styrene, are more reliable than the calculated ultimate styrene yields, rendered questionable by uncertainty of analytical values for ethylbenzene. The purity of the distilled styrene was determined cryoscopically by the method of Glasgow, Streiff, and Rossini (7), t, being the freezing temperature determined by extrapolation of the freezing curve. The temperatures were measured by a platinum resistance thermometer and a G-2 Mueller bridge, certified by the National Bureau of Standards and checked prior to use at the triple point of water and with a NBS benzoic acid cell. Dehydrogenation of EthylbenzeneXylene Mixture, Dehydrogenation of this mixture at 575" C. gave a 45% per pass and a 94% ultimate yield of styrene based on ethylbenzene (Table 11). The
survival of ethylbenzene was 52%, that of xylene 88yo (Table 111). One possibility is to distill the styrene from the liquid catalyzate and recycle the recovered ethylbenzene-xylene. Another possibility is to operate under such conditions that all the ethylbenzene is consumed in a single pass. The best temperature for once-through operation was 700' C., the yield of styrene being 69% (based on ethylbenzene), the survival of ethylbenzene and xylene being 2 and 77%, respectively (Table 11). T o determine if high purity styrene can be separated from the dehydrogenation catalyzate, the liquid product from experiment 4 was distilled through a 50-plate column a t 40 mm. and 20 to 1 reflux ratio. The composition of the distillation charge was 57% styrene, 2% benzene, 7% toluene, 1% ethylbenzene, 22% m-xylene, and 11% p-xylene. Fifty-four per cent of the styrene content of the charge was obtained in 98.8 mole purity (ti, -31.16' C.). Redistillation of the 98.8 mole % material under the same conditions gave a 93% re' purity covery of styrene of 99.2 mole % (t,, -30.99' C.), As the severity of dehydrogenation increased, the hydrogen content of the off-gas decreased, the carbon monoxide content increased but the carbon dioxide content remained fairly constant,
and the ethylene and gaseous paraffin production increased but remained small. Dehydrogenation of EthylbenzeneXylene-Paraffin Mixture. The styrene yields from paraffin-contaminated feed were similar to those obtained from parafin-free feed. At 575' C. the styrene yields (based on ethylbenzene) were 46y0 per pass and 94% ultimate for paraffin-contaminated feed, and 45% per pass and 94y0 ultimate for paraffin-free feed (Table 11, expts. 1, 6). At 700' C. the styrene yields were 60% per pass and 64% ultimate for paraffincontaminated feed, and 69% per pass and 70% ultimate for paraffin-free feed (Table 11, expts. 4, 8). The catalyzate from the 700' C. run (Table 11, expt. 8; composition 54% styrene, 3% benzene, 5y0 toluene, 5% ethylbenzene, 11% m-xylene, 9% 6xylene, and 13% paraffin) was distilled through a 50-plate column at 40 mm. and 20 to 1 reflux ratio to give a 68% recovery of styrene of 97 mole % purity (ti. -31.36' C.), Redistillation of this material through same column and 30 to 1 reflux ratio yielded a 68% recovery of styrene of 99.5 mole 7 0 purity (t,, -30.85" C.).
Acknowledgment Thanks are expressed to Gilbert Atwood for styrene cryoscopic determinations, Mary Farquhar for gas and carbon analyses, and C. H. Beebe and Robert Mainier for the spectrometric work. Literature Cited (1) Glasgow, A. R., Streiff, A. J., Rossini, F. D., J . Research Natl. Bur. Standards 35, 355 (1945). (2) Kearby, K. K. (to Jasco, Inc.), IJ.S. Patent 2,395,875 (1946). (3) Nickels, J. E., Webb, G. A., others, IND. ENC.CHEM.41, 563 (1949); Wcbb, G. A., Corson, B. B., Ibid., 39, 1153 (1947). (4) Rossini, F. D., others, "Selected Values of Physical and Thermodynamic Properties of Hydrocarbons and Related Compounds," pp. 71-5, Carnegie Press, Pittsburgh, Pa., 1953. RECEIVED for review May 27, 1957 ACCEPTED July 22, 1957 Work was done by hionomers Fellowship, Koppers Co., Inc.
Dehydrogenation of C8-Fractionover 1707 Catalyst-Off-Gas Composition Composition on CO- and COz-Free Basis, Vol. % Conditions ilctual Composition, Vol. % Paraffin ToC. CTa H%O/Cs Hz co con C2H4 CnHzniz Ha C2H4 CnHnn+z Indexb Hydrocarbon feed: G5% ethylbenzene, 24% m-xylene, 11% p-xylene Table IV.
E@. 1 2 3 4 5
575 650 650 700 700
1 1 3 1 3
6 7
575 650
1 1
10 10 10 10 10
79.8 74.5 75.5 73.4 68.0
0.8 2.8 2.7 4.2 7.8
18.9 21.2 19.6 21.1 21.7
0.2 0.2 0.4 0.5 0.4
0.3 1.1 1.9 1.1 2.5
99.3 98.3 97.4 97.8 96.2
0.4 0.2 0.3 0.7 0.5
0.3 1.5 2.2 1.5 3.3
0.0
1.5
1.0 1.9
1.5 2.0 1.3
Hydrocarbon feed : GS% ethylbenzene, 12% m-xylene, 10% p-xylene, 10% paraffin a
10
82.5
0.2
15.9
0.0
1.4
98.5
15 76.3 1.8 20.0 1.1 0.8 97.6 1.4 1.0 Average number of carbon atoms per molecule. CT, H20/Cs = contact time in seconds, water/Cs-hydrocarbons mole ratio.
622
INDUSTRIAL AND ENGINEERING CHEMISTRY
1.6 1.6
