I
S. R. BETHEA, R.
L. HEINRICH, A. M. SOUBY, and L. T. YULE
Humble Oil and Refining Co., Baytown, Tex.
Production of Aromatics by Hydrodealkylation Here is a useful illustration of the application of fluid-solids technique to heat control in an exothermic reaction
IN
VIEW OF increasing demands for simple aromatic hydrocarbons of relatively low molecular weight, such as benzene, toluene, and naphthalene, production from various petroleum fractions has been studied. One phase of this program has been directed toward utilization of kerosine extracts which contain high concentrations of alkylsubstituted benzenes and naphthalenes. Exploratory and pilot unit studies on the dealkylation of pure alkyl-substituted benzenes and the aromatics contained in kerosine extract in the presence of cylinder hydrogen or reformer tail gas are presented here. Aromatic compounds at high temperatures tend to decompose into benzene or its immediate homologs and these
undergo a characteristic reaction to form aromatic compounds of higher molecular weight and hydrogen (70). Exploratory Work The first experiments were carried out with pure toluene in a quartz tube a t atmospheric pressure with 5000 standard cu. feet of hydrogen per barrel of toluene, a feed rate of 1 liquid v./v./hour (volume of liquid at 60' F. per gross reactor volume per hour), and temperatures of 1050' to 1300' F. The catalysts were molybdena on alumina (Harshaw MO-220) ; silver on pumice, chromia-alumina,; copper on pumice; calcium molybdate on alumina; tungsten trioxide on alumina, ferric molybdate, and pilled fresh 3A cracking catalyst (12/82 A1203/Si02). Although benzene yields of up to 16% based on the feed were obtained the carbon yield was generally about equal to that of benzene. As the low-pressure quartz reactor proved unsuitable for hydrodealkylation, all subsequent experimental studies were conducted in pressure equipment. Equipment. The bulk of the experimental work was carried out in stainless steel (Type 304 or 347) equipment at pressures of 200 to 620 p.s.i.g. and temperatures from 1085' to 1335' F. The majority of the runs (E, T, and X) were carried out in a 300-ml. reactor
immersed in a lead bath (Figure 1). The,charge stock was stored in blow cases under nitrogen pressure and pumped with a Hills-McCanna pump ahead of the feed was mixed with rogen was obtained pressure cylinders and charged a Fischer-Porter rotameter. The hydrogen-naphtha mixture was vaporized and preheated to the desired reaction temperature before entering the top of the catalyst bed and passing downflow through the reactor. A water
Table 1.
cooler at the bottom of the reactor condensed a portion of the product, and the total product passed to a separator which also served as liquid product receiver. The noncondensable gases from the receiver flowed through a back-pressure regulator which controlled reactor pressure. The gases, at atmospheric pressure, were metered with a wet-test meter and then vented to the atmosphere. A gas gravitometer was used to obtain the specific gravity of the product gas at intervals. The liquid product was collected in the receiver at room tempera-
Inspections on Hydrodealkylation Feed Stocks
Toluene, CS aromatics, and highly aromatic kerorlne extracts were hydrodealkylated Mixed Mixed CS Kerosine Kerosine Feed Toluene Aromatics Extract Extracts Gravity, OAPI 32.3 31.7 26.8 16.6 ASTM distillation data 5% off, O F. 227 275 333 464 228 276 364 471 10% off, O F. 50% off, O F. 228 277 422 484 230 279 515 508 230 280 550 519 0.2 0.2 5.5 5.1
A
romatics
+ olefins)
99.1
99
1.49418 Density
9,g./ce.
Sulfur, wt. % u l analyses~ ~ wt. % ~
1.49701
1.51492
1,51723
1,52814
0.8637
0.8662
0.8922 1.30
~
cs aromatics
81 6 1.50803
~ 99.1
~ 0.9 98.10
Naphthalene Methylnaphthalenes naphtha1enes IR analysis, est, wt. % as benzene rings Low voltage mass spectrometer analyses, wt. % Benzenes Indanes Indenes Nnphthalenes Acenaphthenes Acenaphthalenes Phenanthrenes
88
0.98
~ 0.3 3.2 0.9 3.9 15.2b 32.2
30.2 40.2
11.1 20.2 8.1 45.3 2.8 0.3 0.2
19.2, 18.3, 44.2, and 18.4 wt. %, respectively, ethylbenzene, pxylene, nt-xylene, and oxylene. b Estimated as wt. % naphthalene.
VOL. 50, NO. 9
SEPTEMBER 1958
1245
.-+K 2
f-
t L 0 2
0 2
I E
i i
I 1246
INDUSTRIAL AND ENGINEERING CHEMISTRY
AROMATICS B Y HYDRODEALKYLATION ture and the total product for an entire run was withdrawn through a cooler. The amount of coke remaining in the reactor at the end of a run was determined by converting the carbon to carbon dioxide, absorbing the carbon dioxide in standard sodium hydroxide, and back-titrating with standard hydrogen chloride. Nitrogen was circulated through the catalyst bed by means of a Norge Rollator compressor and air was added slowly enough to prevent the reactor temperature from rising more than 100' F. above that of the preceding run. A quantity of recycle gas equivalent to the air added was bled through a back-pressure regulator and passed over copper oxide to convert carbon monoxide to carbon dioxide. The gas then was dried and the carbon dioxide absorbed in sodium hydroxide. At the end of regeneration, the gases remaining in the system were also passed through the converter-absorption train. The F runs were carried out in a Type 347 steel reactor 1 inch in diameter and 16l/2 inches long, immersed in an electrically heated fluidized sand bath (7). Other equipment was similar to that used in the E, T, and X runs. However,
Pertinent Literature Benzene passed through porcelain tube heated to dull redness gave diphenyl, chrysene, and resinous substance. Toluene gave benzene, naphthalene, etc. Xylenes gave principally toluene, also benzene, naphthalene, anthracene Hydrogen promoted decomposition of toluene over red hot coke to benzene and methane. Benzene was obtained in 90% of theoretical yield, when mixture of xylene and hydrogen was passed through refractory-lined tube at 1140O F. and 200 p.s.i.g. Solvent xylenes were converted to benzene and toluene in presence of hydrogen at atmospheric pressure and 1380Oto 1430' F. At 932O F. and up to 245 atm. toluene gave benzene and mixture of diphenyl derivatives. Xylenes gave benzene, toluene, and complex mixture of liquid and solid hydrocarbons Methylnaphthalene in presence of hydrogen at 30 to 40 p.s.i.g. and 1200° to 1400O F. over ceramic beads (40% voids), at average liquid space velocity of 0.62 v./v./ hour with Hz/feed mole ratio of 8, gave naphthalene 55 and 59% of theoretical at 1300' and 1400' F.,respectively Hydrodealkylation of alkylated benzenes and naphthalenes Over aluminum phosphate Over promoted iron oxide Over supported metal catalysts
the amount of carbon laid down on the reactor contents was determined by combustion on a representative sample that was removed after a 3-hour run was completed . Feed Stocksand Analyses. The hydrodealkylation of essentially pure toluene, mixed CSaromatics, and the monocyclic and bicyclic aromatic compounds contained in kerosine extract fractions was investigated. Inspections on the feed stocks are shown in Table I. Nitration grade toluene which contained 99 weight yo toluene and 1% nonaromatics and mixed Cg aromatics were hydrodealkylated over both Harshaw MO-220 catalyst and 4- to 8-mesh quartz chips. The olefin contents of the products were determined from their bromine numbers (77). Total aromatics plus olefins were determined by absorption in 98% sulfuric acid and aromatics distributions were Table II.
determined by mass spectrometer analysis. The kerosine extract resulted from commercial sulfur dioxide extraction a t -20' F. of a kerosine distillate and had an aromatic content of approximately 80%. Only thermal hydrodealkylation operations were carried out with this extract. Total naphthalenes and benzenes were determined by ultraviolet and infrared analyses, respectively (Table 11). A mixture of high-sulfur and sweet kerosine extracts was used in a limited number of runs to determine if bulk copper (copper filings) catalyzed the hydrodealkylation. The feed to and products from these runs were analyzed for hydrocarbon types by low voltage mass spectroscopy techniques similar to those described by Hastings and Field (73) (Tables I and 111).
Inspections on Feed to and Product Fractions from Thermal Hydrodealkylation of Kerosine Extract Hydrodealkylation of kerosine extract produced high purity aromatic fractions Run No.
(600 p.s.i.g., 6000 SCF of Hz/bbl.) E-23
Av. reactor temp., O F. Lead bath temp., O F. Yields based on feed Benzene, vol. % Toluene, vol. yo CS aromatics, 001. % Naphthalene, wt. % Liquid yield, POI. % Inspections on cuts from distillation at 20/1 reflux ratio Type of cojumn IBP ZOOo F. cut (UV anal. data) Yield, vole % Benzene, vol. % Thiophene, vol. % 200-250' F. cut (UV anal. data) Yield, vol. % Benzene, vol. % Toluene, vol. % 250-300° F.cut (mass spectrometer data) Yield, vol. % Toluene, vol. Yo Ca aromatics, vol. % 300-400' F. cut (mass spectrometer data) Yield, vol. % Total aromatics, vol. % 400-430° F. cut (UV anal. data) Yield, wt. % Naphthalene, wt. % 1-methylnaphthalene, wt. % 2-Methylnaphthalene, wt. %
1200
1225 8.6 14.8 8.8 11.4 61.3
Hypercal
Melting point of 400-430' F. cut, O C. 430-450' F. cut (UV anal. data) Yield, wt. % Naphthaleneb, wt. % 1-Methylnaphthalene, wt. % 2-Methylnaphthalene, wt. % 450-480O'F. cut (UV anal. data) Yield, wt. % 1-Methylnaphthalene, wt. % 2-Methylnaphthalene, wt. yo I B P -300' F. out. Includes benzothiophene.
E-28 1250 1320 17.5 10.0 1.9 14.5 55.9
Oldershaw
(Feed)
...
... ...
0.3 3.2 0.9
...
Oldershaw
14.5 97.3 1.0
32.6 98.6
24.7 1.3 98.0
18.6 1.8 97.3
... ... ... ... ... ...
15.1 3.2 96.0
3.9 8.8 90.8
4.7 6. la 51.3"
5.8 85.5
1.6 79
4.7 72
18.3 99.2
25.0 99.2 0.8
0.6
...0.8
...
79.5
79.0
15.9 5.5 0.1 0.1
...
2.0
0.5
10.7 5.3 80.5
67.9 7.1 17.6
6.9 0.7 0.4 1.0
... ... ...
... ... ...
13.4 11.7 16.2
VOL. 50, NO. 9
SEPTEMBER 1958
1247
2(
8
02250 CU.FT. H d B B L . e5000 CU. FT. H2/BBL.
jI!
P
g 1( W
N z w ! m
15
chips, and in the empty reactor. T o determine if the quartz chips exerted any catalytic action, the conditions of runs X-1 and X-2 were duplicated in runs X-3 and X-4, respectively, but no reactor filler was employed and the feed rate was adjusted so that comparable contact times were obtained. Comparison of the data obtained indicates little difference in conversion, selectivity, or yield of the dealkylated aromatics. I t was concluded that the quartz chips exerted no appreciable catalytic effect on the hydrodealkylation reaction. The bulk of the experimental runs were carried out with the kerosine extract which contained approximately 32 weight % of benzene homologs (calculated as benzene) and 15 weight % of naphthalenes (calculated as naphthalene). This petroleum fraction was thermally hydrodealkylated over quartz chips in admixture with 2250 or 5000 standard cu. feet of hydrogen per barrel of feed a t temperatures ranging from 1095' to 1330" F., pressures from 105 to 620 p.s.i.g., and feed rates corresponding to 0.5 to 2.0 liquid v./v./hour. Continuous runs of up to 24 hours were made without appreciable operating difficulty (Table V). Except for the first runs at low pressures or low gas rates, the runs are arranged in order of increasing severity, as indicated by decreasing yields of liquid products, which is primarily the effect of increasing tem-
wi
z
10
Table 111. Hydrodealkylation of Mixed Kerosine Extracts over 10- to 20Mesh Quartz Chips and 20- to 100Mesh Copper Filings Gave Similar Results
4 i
s
5
0
Figure 2. Yields of benzene, toluene, CS aromatics, and naphthalene by hydroddalkylaiion of kerosine extract can be correlated with liquid product yikld'
Results. Preliminary work indicated that the hydrodealkylation reaction could be catalyzed by a number of contact materials, but use of catalysts at atmospheric pressure resulted in marked degradation of the feed to gas and coke. A number of runs (T-11 to T-14) then were made with 5000 standard cu. feet of hydrogen per barrel of toluene over the Harshaw MO-220 catalyst, the most active catalyst tested in the preliminary experiments, a t 1100' to 1210' F. and pressures from 200 to 350 p.s.i.g. a t 1 liquid v./v./hour (Table IV). Toluene conversions ranged from 36 to 74%. The mole per cent selectivity of toluene to benzene which corresponds to the moles of benzene produced per mole of toluene reacted decreased with increasing conversion and averaged about 66%.
1 248
Coke production averaged 2.8%. I n runs T-1 to T-3, inclusive (Table IV), the hydrogen-toluene mixture was passed over 4- to 8-mesh quartz chips a t 1200' and 1300" F. at 200 to 350 p.s.i.g.; toluene conversions ranged from 19 to 72%. At 350 p.s.i.g. the selectivity of toluene to benzene was 95% a t 25% conversion and 91% at 72% conversion. The latter may be compared to a selectivity of 51% a t 74% conversion when the Harshaw MO-220 catalyst was employed a t the same pressure. Much less degradation of the aromatic ring was obtained in the thermal operations (over the quartz chips) than with the molybdena on alumina catalyst. Table IV also summarizes the results obtained when mixed Cg aromatics were hydrodealkylated over the Harshaw MO-220 catalyst, over 4-8 mesh quartz
INDUSTRIAL AND ENGINEERING CHEMISTRY
(1235OF., 600 p.s.i.g., 5000 SCF Hi/bbl., 26second contact time, 3-hour runs) Run No. F-1 F-2 Reactor filler 20- to 100- 10- to 20mesh mesh copper quartz filings chips Yield of liquid 71 71 product, wt. % on feed Inspections on liquid product 10.0 10.5 Gravity. OAPI AbsorpGon in 99 f 99+ 98% HxSO4, vol. % Low voltage mass spectrometer analyses, wt. % 23.4 23.4 Benzenes 4.8 5.5 Indanes 7.2 6.2 Indenes 58.8 59.8 Naphthalenes 3.8 3.5 Acenaphthenes 1.1 0.9 Acenaphthalenes 0.9 Phenan0.7 threnes 0.23 0.13 Carbon on reactor filler, wt. %
AROMATICS B Y H Y D R O D l A L K Y L A T l O N tures from 1095' to 1330' F. indicates that when the reactor temperature was increased from 1095: to 1330' F., the yield of benzene was increased a t the expense of toluene and CS aromatics. Naphthalene yield increased with increasing reactor temperature. Essentially equivalent Ce plus C, plus CS aromatics yields (expressed as equivalent benzene) were obtained at 1200' to
perature. No conversion figures are shown for these runs, because the amount of unchanged feed in the product was not known. However, conversion was assumed to be inversely proportional to the total liquid product yield. Comparison of runs E-21, E-23, E-25, E-27, and E-29, carried out at 1 liquid v./v./hour, 600 p.s.i.g., 5000 cu. feet of hydrogen per barrel, and tempera-
Table IV.
1330' F. Inasmuch as the hydrodealkylation reaction is accompanied by evolution of a large amount of heat, the indicated reactor temperatures may not, in the small scale equipment used, reflect the average or the maximum temperature of the reacting gases. The average temperature probably lies between the indicated reactor and lead bath temperatures.
Hydrodealkylation of Toluene and Mixed Xylenes Thermally and over Harshaw MO-220 Catalyst.
Thermal hydrodealkylation of toluene and mlxed xylenes results in high selectivities to lower molecular weight aromatics (5000 SCF Ho/lb. feed. 3-hour reaction periods) Run No. T-1 T-2 T-3 T-11 T-12 T-13 T-14 X-1 X-2 X-3 X-4 X-11 X-12 Feed stock Toluene Mixed Xylenes Reactor filler 4- t o 8- mesh Harshaw MONone 4- to 8-mesh quartz chips Harshaw 1MO-220 catalyst quartz chips , 220 catalyst _. Av. reactortemp., F. 1200 1200 1300 1100 1200 1100 1210 1300 1200 1300 1200 1200 1085 Pressure, p.s.i.g. 200 350 350 200 200 350 350 350 600 360 600 200 355 Feed rate, liquid v./v./ 1.0 1.0 1.0 2.0 1.0 hour Yields based on feed Benzene, vol. Toluene, vol. % Liquidproduct,vol. % Gas, wt. % Carbon, wt. %
13
20
94.3 4.7
4.9 0.1
0.1
Conversion of feed (toluene or xylenes), %
54
23 34 ... ... 89.5 73.6
... ... 82.4 93.8
... 19
16.1 0.2
25
8.1 1.5
72
36
29 e..
20.0 5.2
82.4 16.3 0.5
63
49
Selectivities wt. % to Benzene 73 81 77 63 56 61 Toluene Gas 25 19 23 22 32 33 Carbon 0.7 0.5 0.3 4 8 1 Mole % to Benzene 85 95 91 74 66 71 Toluene e.. e.. Benzene plus toluene 85 95 91 74 66 71 0 10% MOOSon silioa-stabilized (approx. 5 % SiO,) high surface alumina.
...
...
... ...
...
...
...
Table V.
... ...
..*
32 ... 58.0 37.0 3.9
49 21.2 73.8 24.4 0.1
41 27.8 76.0 22.6 0.1
55.9 13.4 73.5 24.3 0.1
41.5 23.6 74.0 24.6 0
23.3 21.4 60.2 34.6 5.2
12.4 37.3 72.6 24.8 2.5
74
98
93
98
92
85
80
44 ... 50
52 21 25 0.1
46 29 25 0.1
60 13 25 0.1
47 25 27 0
28 25 41 6
16 46 32 3
70 25 95
62 34 96
81 15 96
64 29 93
38 28 66
22 53 75
5
... 51
51
Thermal Hydrodealkylation of Kerosine Extract over 4- to 8-Mesh Quartz Chips
Higher severities (lower liquid product yields) result in greater production of completely dealkylated aromatics E-1 E-2 E-11 E-12 E-13 E-21 E-22 E-23 E-24 E-25 E-26 E-27 E-28 E-29
Run No.
Average reactor temp., F. 1290
E-30
E-31
1275
1125
1150
1175
1095
1195
1200
1260
1250
1280
1305
1250
1330
1300
12811
1300
1320
1125
1140
1190
1105
1225
1225
1270
1285
1305
1305
1320
1325
1360
1310
105
195
605
615
605
595
600
620
605
600
595
610
615
Lead bath temp., O
F.
Pressure, p.6.i.g.
Feed rate, liquid v./v./hour +--l.O-+
-60-
-1.-
-1.5-4
1.0
1.0
1.7
1.0
2.0
1.0
2.0
1.9
HZrate, SCF/ bbl.
Cycle length, hours c-3Yields based on feed Benzene, vol. % Toluene, vol.
%
aromatics, vol. % Naphthalene, CI
h: %
Liquid yield, VOI.
%
Gar, at. % Carbon,wt. %
5000
-225-
+-5000-+
4.5
1.5
1.5 -3-+
24
3
24
3
t
24
12
3
7
4
3.8
4.7
1.3
2.6
2.8
1.0
4.6
8.6
9.6
13.1
12.6
18.4
17.5
19.9
19.9
19.8
9.6 10.5
10.5
3.7 9.3
7.1
7.8 12.0
4.1 10.0
11.7
14.8 8.8
15.6 7.4
13.2 3.0
11.3 4.1
11.1 0.7
10.0 1.9
9.1 1.3
5.6 0.4
7.0
11.5
11.4...
14.1
11.613.3
14.5...
15.2
15.1
61.3 35.2 0.3
57.7 38.3 0.3
57.5 38.1 0.3
55.9 39.7 0.2
53.6 41.0 0.6
43.8 0.9
9.7
14.2
..................... 65.4 28.2 1.3
62.0 31.9 0.9
81.2 15.3 0.4
70.3 24.2 0.9
70.3 24.2 0.8
78.6 19.2 0.2
64.1 32.6 0.2
58.4 37.5 0.5
56.1 40.0 0.3
VOL. 50, NO. 9
54.9 40.5 0.6
SEPTEMBER I958
0.9
51.7
1249
il
REFORMER T A I L GAS
WA7
i,
COMPRESSOR
I
c
COKE SCRAPER
i '
HIGH PRESSURE SEPA RAJOR
-
I
,,--TUBE
-
ORlFJGE
FEED PUMP
I
FEED PREHEATER ( L E A D 0AJHl
UT
'
STEAM
Figure 3.
The fluid hydrodealkylation pilot unit provided for needed temperature control
Yields of pertinent aromatics can be correlated with the yield of liquid product. In Figure 2, benzene, toluene, Cg aromatics, and naphthalene yields have been correlated with liquid product yield for the runs at 600 p.s.i.g.: Maximum benzene, toluene, CS aromatics, and naphthalene yields are obtained at liquid product yields of about 55, 60, 64, and 53 volume yo, respectively. The yields of benzene, toluene, Cg aromatics, and naphthalene, when operating to produce maximum quantities of each, are indicated in Table VI. At a severity level corresponding to a liquid yield of 55%, 90% of the alkylsubstituted benzenes were converted to to CS aromatics and over 95% of the naphthalenes were converted to naphthalene. Runs E-I, E-2, E-24, and E-27 were carried out at approximately the same temperature, which averaged about 1280' F., at 1 liquid v./v./hour, with 5000 standard cu. feet of hydrogen per barrel and pressures from 105 to 605 p.s.i.g. Although the increase in contact time which accompanied increase in pressure increased benzene production at the expense of toluene and CS aro-
1250
matics and also the higher total c6-C~ aromatics yield, carbon production decreased with increasing pressure, and averaged only 0.470 at 600 p.s.i.g. Several pilot unit runs were carried out at a hydrogen-feed ratio of 2250 cu. feet per barrel; feed rates were adjusted so that a residence time about equivalent to that in the 1 v./v./hour runs at 5000 cu. feet of hydrogen per barrel resulted. Comparison of runs E-11; E-12, and E-13, made a t the lower hydrogen dilution, with runs E-21 and E-22 (see Figure Z), indicates approximately equal yields of Cb-CS aromatics at the two hydrogen dilutions, but higher coke yield at the lower hydrogen-feed ratio. The simpler aromatics such as benzene and toluene, produced by hydrodealkylation of the monocyclic aromatics in the kerosine extract, boiled below the initial boiling point of the feed; consequently, one would expect to obtain aromatic concentrates of extremely high purity by simple distillation of the total hydrodealkylated products. I n runs E-23 and E-28, carried out at relatively high severities, the benzene and thiophene contents of the IBP-200' F. cuts averaged
INDUSTRIAL AND ENGINEERING CHEMISTRY
98 and 0.8%, respectively (Table 11). Although 1 to 2% benzene was contained in the 200' to 250' F. cuts, the benzene plus toluene contents of these fractions averaged over 997,. The toluene plus CS aromatic contents of the 250" to 300' F. cuts averaged over 99%. The 400' to 430" F. cuts contained over 99% naphthalene plus benzothiophene; sulfur analyses indicated that about 570 of these fractions was benzothiophene. The remainder of the material was indicated to be methylnaphthalenes. The work of Yukhnovskii (20) might be interpreted to indicate that copper filings catalyze hydrodealkylation. To determine if this were true, hydrodealkylation runs in which the reactor was packed with (1) 10- to 20-mesh quartz chips, and (2) 20- to 100-mesh copper filings were carried out under identical conditions. The mixed kerosine extract was charged at a space velocity of approximately 1.I liquid v./v./hour a t 1235' F. As somewhat more void space tras present in the reactor packed with copper filings, feed rates for the two runs were adjusted to give 26-second contact time in each case. The yield of liquid product was identical
AROMATICS BY HYDRODEALKYLATION
,
and inspections on the two products were essentially the same (Table 111). Not only were the concentrations of the major hydrocarbon types such as benzene and naphthalenes essentially equal, but data not tabulated show that this similarity extended to the compounds of various molecular weights in the different homologous series. I t was concluded that the copper filings exerted no catalytic effect on the hydrodealkylation reaction.
Fluidized Solids Pilot Unit The exploratory work indicated that the normal hydrodealkylation process had considerable promise for the production of benzene and/or naphthalene from highly aromatic feed stocks. Consequently, a larger scale pilot unit was designed and built for development studies. Tail gas from a catalytic reforming unit was used as a source of hydrogen. Temperature Control. The exploratory work had been carried out in srrallscale tubular reactors under essentially isothermal conditions. However, the reaction of hydrodealkylation is highly exothermic, and can result in temperature increases of the order of 400' F. under adiabatic conditions. For example, the heat of reaction for the hydrodealkylation of methyl-substituted aromatics at 1300' F. is about 21,000 B.t.u. per lb. mole of hydrogen consumed-sufficient to increase the temperature of the reactants involved by 300' to 600' F. The reaction is slow at lower temperatures, and may not be initiated until the temperature is raised to around 1100' F. Under these conditions, the problem of removing the heat of reaction without allowing the reactor to be subjected to excessive temperatures (especially considering the operating pressure of 600 p.s.i.g.) is very serious. For such a situation, use of a fluid bed of an inert heat transfer medium for conducing the reaction seemed ideal. The feed mixture could be preheated to about 800' F. and then introd,uced into a fluidized sand bed maintained at about 1300' F. by the heat of the reaction. The hot sand would continually initiate reaction, and then serve as a heat transfer medium to absorb the heat of reaction and -transfer the heat to the incoming feed, to increase its temperature to reaction level, without allowing excessive temperatures at any point. Consequently, for larger scale studies, a fluidized solids reactor was designed and constructed. Because the relatively long reactor of small diameter, (1.9 inches in inside diameter X 7 feet long) had a length to diameter ratio (L/D) of
44, much greater than would be used in a commercial reactor, it was not possible to obtain sufficient back-mixing of the fluidized sand for adequate temperature control. Consequently the entire reactor was housed in a metal shell in which another fluidized sand bed was maintained slightly below the desired reaction temperature, in order to approach isothermal conditions. In spite of the dual fluidized bed system, temperature gradients were somewhat greater than would be expected in a commercial sized unit in which an L/DJ of 2 to 4 would be used. A flow diagram of the fluid hydrodealkylation pilot unit is shown in Figure 3. Representative Operations. The fluid pilot unit was operated over a narrow range of conditions. The total
feed rate was limited by the necessity of maintaining a fluidized bed without excessive carry-over of sand. Little information is available on fluidization under the high temperature and high pressure conditions used for hydrodealkylation; it appears that entrainment and carry-over will become much greater for a given superficial velocity as the pressure is increased because of increased fluid density and as the temperature is increased because of increased viscosity. Thus, allowable velocities in a high pressure, high temperature fluid unit may be much lower than in a conventional catalytic cracking unit, though sufficient data for quantitative calculations do not appear to be available. In these pilot unit studies, operations at superficial velocities between
Table VI.
Effect of Severity on Product Distribution when Hydrodealkylating Kerosine Extract Yield of benzene, toluene, Cs aromatics, and naphthalene may be maximized by varying severity
(4- t o 8-mesh quartz chips, 800 p.s.i.g., 5000 cu. ft. Hg/bbl.) Production of Maximum Cs aromatics Naphthalene Benzene Toluene Approx. reactor temp., F. lJOO+ 1230 1195 1300+ Yields, based on feed Liquid product, vol. % 55 60 63.5 53 20 8.4 5.0 20 Benzene, vol. % Toluene, vol. % 9.1 16.3 12.5 7.0 CS aromatics, vol. % 1.5 7.6 14.2 1.0 15.0 Naphthalene, wt. % ' 14.4 12.0 8.6' I
-
-
a
-
From extrapolation of correlation.
Table VII.
Fluid Pilot Unit Hydrodealkylation of Mixed Kerosine Extracts Gives High Yield of Naphthalene' Reactor temp., F. Bottom (inlet) 925 Center 1325 Top (outlet) 1280 Liquid feed rate, gal./hour 0.83 Superftcial liquid space velocity* 0.80 600 Pressure, p.s.i.g. Product inspections FeedC Gravity, "API 10.1 16.6 0.59 0.98 Sulfur, wt. % 99.9 88 Aromatics (acid abs.), vol. % Product yields, vol. % of feed 0 150-20O0 F. (benzene) 6.8 0 200-250' F. (toluene) 3.9 250-410" F. 0 1.4 410-435' F. (naphthalene) 34.5 1.8 435480' F. 38.3 3.6 480-525" C. 40.0 0.8 5.6 525' F. 19.9 100.0 56.6 Total Naphthalene fraction Yield, wt. % of feed 36.7 Melting point, 'C. 78.9 Estimated purity, mole yo 97.5 Sulfur, wt. % 0.64 Estimated naphthalene yield, 78.0' C. m.p., wt. % of feed 37.3 Mixture of high-sulfur kerosine extract and sweet kerosine extract. Volumes of oil feed per hour per volume of reactor. See Table I.
+
*
VOL. 50, NO. 9
SEPTEMBER 1956
1251
0.1 and 0.25 foot per second gave fairly satisfactory operation without excessive entrainment except during upsets in operation. The pressure was 600 p.s.i.g., about the maximum allowable working pressure in the reactor; earlier fixed bed studies had indicated that high pressure resulted in better selectivity and reduced coke formation. The temperatures were purposely high to ensure high conversions. Operations a t 1325' F. maximum reactor temperatures with an oil feed rate of 0.83 gallon per hour charging mixed kerosine extracts (Table VII) gave a naphthalene yield of 36.7 weight % of the feed. The melting point of the naphthalene was 78.9' C. Widening the naphthalene cut to give a 78.0' C. melting point would increase the yield to 37.3 weight % or more. The reactor temperature (Table VII) was controlled by adjusting the electric heaters on the 12-inch metal shell containing the fluidized bed in which the reactor was suspended to maintain the maximum measured reactor temperature a t the desired level. The outer heating bath was 50' to 100' F. lower than the reactor. The temperature was low a t the reactor inlet, and increased rapidly as the reaction progressed, reaching a maximum somewhere around the reactor center, and then decreased as the rate of reaction became slower and heat was lost to the surroundings. Product Quality. The total liquid products from pilot unit operations conducted at 1200' F. and above had aromatic contents of 99f % as deterTable VIII. Inspections on Naphthalene Samples Prepared from Fluid Pilot Unit Products High purity naphthalene may be produced by fractionation of the hydrodealkylated product Sample No. 1 2 3 Feed stock High sulfur Sweet extract extract Melting point, c. 79.2 78.3 79.3 Naphthalene, 98.0 96.4 98.2 mole % Impurities, wt. 0.0
...
0.0
...
%
I-Methylnaphthalene %-Methylnaphthalene Benzothiophene Sulfur, wt. % Residue on ignition Solubility in water Solubility in alcohol
1252
... ... ... ... ... ,,, ... . ..
... . I .
1.8
0.8
0.43
0.18 None Insoluble Completely soluble
mined by absorption in sulfuric acid. There was no matcrial found in the products during Hypercal distillations below the boiling point of benzene. The benzene fractions (150 O to 200 O F. nominal cut points) usually contained about 95% benzene and 3 to 47, toluene, the remainder presumably being thiophene. Several analyses of benzene fractions from high-sulfur kerosine extract indicated about 0.5 weight % sulfur, which corresponds to about 1.3 weight % thiophene. The toluene fraction (200' to 250' F.) usually contained about 94% toluene, 4% benzene, and 2% CS aromatics. The yields of aromatics in the boiling range of 250" to 410' F. were low. The naphthalene fractions (410' to 435' F.) contained about 95 to 99% naphthalene, the major impurity being benzothiophene. The methylnaphthalene fraction (435' to 480' F.) usually contained about 70 to 90% methylnaphthalenes, with naphthalene as the major impurity. The 480' to 525' F. fraction usually contained about 55% total naphthalenes, presumably dimethylnaphthalenes. The material boiling above 525' F. was not analyzed, but must have been composed to a large extent of highly condensed aromatic materials, judging by its specific gravity of about 1.16. The amount of material boiling above 525' F. decreased with severity from 19.9% in the feed to 5.6% (based on the feed) in the run shown. Thus very little material heavier than the feed could have been produced. The naphthalene fractions from the routine Hypercal distillations of the pilot unit products normally had melting points ranging from about 77.6' to 79.7' C., corresponding to purities of 95 to 99 mole % naphthalene. (The melting point of pure naphthalene is 80.3' C.) Some of the variation in melting points was due to differences in feed stocks and operating conditions, but the major difference was apparently due to variations in fractionation or in cut points during the Hypercal distillation. However, naphthalene of 78.0' C. melting point grade was readily producible by fractional distillation of the hydrodealkylated product. With proper fractionation, the major impurity in the naphthalene was benzothiophene, which has a boiling point so close to that of naphthalene (429' F. compared with 424' F.) as to make separation by fractional distillation rather difficult; however, careful fractionation reduced the sulfur content of the naphthalene appreciably. I n a number of cases, naphthalene of 79.0' C. melting point or higher was produced, apparently suitable for refined grade naphthalene. I n three cases, relatively large quantities of naphthalene were prepared by large scale distillation of the composite products of several pilot unit runs (Table VIII). Two samples were pro-
INDUSTRIAL AND ENGINEERING CHIiMlSTRY
duced from high-sulfur kerosine extract and the other from sweet aromatic kerosine extract. During each distillation, a number of small cuts were taken and their melting points determined. The cuts with high melting points were composited to produce the total sample. I n the high-sulfur extracts, some naphthalene cuts had melting points as high as 79.2' C. (only the high melting cuts were used in sample 1); in the sweet extract approximately half of the cuts had melting points of 80.0' C., indicating a naphthalene purity of about 99.5 mole %. Acknowledgment The authors wish to thank die Humble Oil and Refining Co. for permission to publish the information and to acknowledge the assistance of J. A. Anderson, Jr., H. G. Corneil, E. J. Hoffmann, C. J. G. Leesemann, W. D. Seyfried, G. R. L. Shepherd, I. G. Thompson, and H. L. Wilder in planning and carrying out the experimental work. The operating, mechanical, and analytical personnel who participated in the program are so numerous as to preclude individual mention. literature Cited
Adams, C. E., Gernand, M. O., Kimberlin, C. N., Jr., TND. ENC. CHEM.46, 2458 (1954).
Beckberger, LaV. H., U. S. Patent 2,653,176 (Sept. 22, 1953). (3) Zbid., 2,674,635 (April 6,1954). Berthelot, P. E. M., Bull. SOC. chem. (4) 7 (2), 217 (1867).
Bradley, M. J . , Parr, S. W., Chem. @ Met. Eng. 27, 741 (1922).
Clough, H., U. S. Patent 2,709,193 (May 24,1955). Cobb, J. W., Hollin s, H. S., J. Gas Lighting 126, 917 f1914).
Coonrodt, H. L., Gutzeit, C. L., U. S. Patent 2,689,266 (Sept. 14, 1954).
Doumani, T. F., Zbid., 2,734,929 (Feb. 14, 1956). Ellis, C., "Chemistry of Petroleum Derivatives," p. 89, Chemical Catalog, New York, 1934. Friedman, B. S., U. S. Patent 2,700,638 (Jan. 25, 1955). Haensel, V., Ipatieff, V. N., Ibid., 2,422,673 (June 24,1947). Hastings, S. H., Field, F. H., Anal. Chem. 28, 1248 (1956).
Heinemann, H., U. S. Patent 2,692,293 (Oct. 19, 1954). Hetzel, S. J., Ibid., 2,698,869 (Jan. 4, 1955). (16) Kennedy, D. H., Hetzel, S. J., Ibid., 2,431,940 @ec. 2, 1947). (17) Lewis, J. B., Bradstreet, P. B., IND. ENQ. CHEM.,ANAL.ED. 12, 387 (1940). \ - -
.-I.
(18) Oda, von R., J. SOC.Chem. Znd. Japan 34,142B (1931). (19) Rittman, W. F., Byron, O., Egloff, G., J., IND.ENO.CHEM.7,1019 (1915). (20) Yukhnovskil. G . L.. Ukraimkii. Khem. Zfzur. 3, NO. 2, Pt. Tech. 65 (1928). .
I
RECEIVED for review October 11, 1957 ACCEPTED April 2, 1958 Division of Petroleum Chemistrv. 132nd Meeting, ACS, New York, N. Y,,' September 1957.
