2708
INDUSTRIAL AND ENGINEERING CHEMISTRY
hydrogen flow rate of 10 cubic feet per litcr of oil charged, s h o w better desulfurizing efficiency and more efficiency in reforming the heavy material than it shows a t atmospheric pressure VI ithout hydrogen. Co-110-Raux demonstrated the greatest efficiency for desulfurization by reducing the sulfur content of the crude oil from 2.06 to 0.179;b by weight. Zn-hlo-Baux gave the greatest conversion by increasing the gasoline content of the oil from 31.4 t o .!19.97~ by volume. D 875 analyses of some gasoline blends from Hempel distillations show that the use of hydrogen pressure tends t o increase the percentage of paraffins and decrease the percentage of olefins as indicated by the bromine number. CONCLUSION I t is evident that the sulfur content of a crude oil can be reduced greatly by catalytic desulfurization. This preliminary sulfur reduction would aid in the prevention of corrosion in the subsequent steps of refining the oil. The products would be of higher quality and thus more valuable. However, t o be eco-
nomical, morc study ~ o u l dbe the coke formation during the of lower iron content or one of be possible to reduce the coke ment of the process is deemed of the Bureau of Mines.
Vol. 41, No. 12
required to find a way to reduce desulfurization. With a bauxite the synthetic catalysts, it should formation; but further developoutside the scope of the actlvity
ACKNOWLEDGMENT The authors wish to express their indebtedness to H. >I. Smith and C. C. Ward, under whose supervision the work was performed. LITERATURE CITED (1) Dean, E. W., Hill, H. H., Smith, N , 9. C., and Jdcobs, W. A.,
Bur. X i n e s Bull. 207 (1922). ( 2 ) Guthrie, Boyd, and Simmons, M. C., Bur. Mines, Rept. Invest. 3729 (1943). ( 3 ) Kraemer, A . J., a n d Lane, E. C , Bur. Milines Bull. 401 (1937). (4) Ryan, J. G., IND. ESG.C H E Y . , 34, 894-32 (1942). RECEIVED March 24. 1949.
Desulf urization-Hydrogenation of High-Sulfur Catalytically Cracked Cycle Stock ALEXIS VOORHIES,JR., AND W. M . SMITH Esso Laboratories, Esso S t a n d a r d Oil C o m p a n y , B a t o n Rouge, La. H y d r o g e n a t i o n a t 750 p o u n d s per s q u a r e i n c h pressure of a h i g h - s u l f u r , refractory, catalytically cracked cycle stock r e s u l t s i n p a r t i a l conversion of condensed-ring a r o m a t i c s t o single-ring a r o m a t i c s a n d virtually complete removal of s u l f u r . Hydrogenation catalyst activity is m a i n t a i n e d , hydrogenated product yield is 100 v o l u m e 70,a n d little change i n boiling r a n g e occurs. Catalytic cracking characteristics of t h e cycle s t o c k a r e improved by hydrogenation t o t h e point where it is a t least a s desirable a cracking stock a s t h e original virgin gas oil. S u l f u r removal prior t o cracking of a h i g h - s u l f u r stock is necessary for t h e production of a gasoline m e e t i n g s u l f u r specifications without further treating.
I
N A previous article ( 1j the hydrogenation of cycle stocks derived from the cat,alytic cracking of gas oils was discussed. I n that paper it was shown that cycle stocks from catalytic cracking contain refractory aromatic-type conipoiients which resist further cracking, and that hydrogenation of these aromatic-type components t,o naphthene ring derivatives provides an improved catalytic-cracking feed stock which is superior in quality even to the original virgin gas oil from which the cycle stock was derived. In comparing the quality of unhydrogenated and hydrogenat,ed cycle stocks as catalytic cracking feed stocks it was shown that, with a hydrogenated cycle stock, high conversions are obtaincd under similar cracking conditions; that, for a given degree of cracking, less carbon and more gasoline result; and that gssolines derived from the cat'alytic cracking of a hydrogenated cycle stock are a t least as good in quality (as evidenced by octane numbers) as the gasolines derived from the catalytic cracking of the virgin gas oil from which the cycle stock was originally obt,ained. Hydrcgenation conditions used for the conversion of aromatics
t o naphthenes ( 1 ) involved the use of a sulfur-resistant cat,alyst a t the high pressure of 3000 pounds per square inch. The use of high pressure was necessary in order to obtain complete hydrogenation of aromatics to naphthenes with the sulfur-resistant catalyst employed. Inasmuch as all feed stocks investigated contained appreciable amounts of sulfur, the use of a sulfur-resistant catalyst was required for the maintenance of a constant degree of catalyst activity and thereby a continuous and practicable hydrogenation process. Under these conditions, yields of hydrogenated cycle stock were 100 volume % or more in all cases, with little change in boiling range and virtually complete removal of sulfur. I n the previous article it n-as also shown t h a t under milder hydrogenation conditions (750 pounds pcr square inch instead of 3000), partial saturation of aromatics in catalytically cracked cycle stocks to naphthenes n-as obtained instead of the rather complete saturation u-hich resulted with the use of the higher pressure. Under these milder hydrogenation conditions catalyst activity was maintained and, in addition, rather complete sulfur removal resulted, even when the cycle stock used contained a large quant]ity of sulfur. This degree of desulfurization is especially notable because the sulfur-containing molecules in cycle stocks are very refractory, and sulfur removal from this type of material is difficult by ordinaiy methods. The present paper discusses further this lower pressure hydrogenation of high-sulfur catalytically cracked cycle stocks. Under low pressure hydrogenation conditions suitable for t,he maintenance of catalyst activity it is shown that: Despite only partial saturation of the cycle st,ock,it is superior t o the virgin gas oil in cracking characteristics, giving less carbon at equivalent conversion. However, this superiority is not as great as in the case of the completely saturated cycle stock. The
December 1949
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
partially saturated cycle stock gives almost the same conversion as the virgin feed at equivalent cracking conditions, whereas the completely saturated cycle stock gives higher conversion. Partial saturation of cycle stocks from high-sulfur virgin oils gives sufficient desulfurization so t h a t t h e catalytic3:; cracked gasoline produced therefrom is well below established sulfur specifications; whereas the unhydrogenated cycle stock, on subsequent cracking, gives a high-sulfur gasoline requiring further treatment for desulfurization. DESULFURIZATION-HYDROGENATION O F CYCLE S T O C K FROM WEST TEXAS WIDE-CUT GAS OIL The laboratory equipment used for the desulfurization-hydrogenation work has been described (1). The previously reported lower pressure hydrogenation data (1) obtained on a cycle stock produced from fluid catalyst cracking of a high-sulfur West Texas wide-cut gas oil are presented in Table I. It will be noted t h a t extensive sulfur elimination is obtained (1.42 weight % sulfur in cycle stock vs. 0.15 weight 7 0 sulfur in hydrogenated product) with a high yield and little reduction in boiling range. Under the conditions used, satisfactory catalyst activity was maintained for over 26 days without any increase in temperature required for maintenance of product quality.
2709
T a b l e I. Desulfurization-Hydrogenation of Cycle S t o c k from F l u i d C a t a l y s t C r a c k i n g of West Texas W i d e - C u t G a s Oil w i t h N a t u r a l C a t a l y s t Unhydrogenated Cycle Hydrogenated Stock Cycle Stock .. Sulfur resistant .. 750 .. 700
Catalyst Pressure, Ib./sq. inch gage Temperature O F. Feed rate, v&/vol./hour Yield, vol 7 on feed A?P.I. a t 60° F. Gravity Distillahon F. Initial b.;. 5% over
..
'
23:3 470 510 520 550 590 640 700 700a
10%
30% 50% 70% 90% Final b. p. Color (Robinson) Aniline point, ' F. Diesel index Bromine No., cg./gram Sulfur wt. % Hydrdgen, wt. % Refractive index; n %o Specific dispersion a t 20' C. (np
;G
-
30 18 1.42 11.2 1.5174
1
100 27.3 430 480 500 540 580 630 700 700a 8 133 36 9 0.15 12.0 1.5012
n,) X 104/d 180 145 Aromatic rings wt. % b 27 24 Hydrogen co&mption, cubic feet/bbl. feed 360 a 90% over. b Calculated according to method of Vlugter, Waterman, and van Westen
..
($1.
A
CRACKED C Y C L E STOCK CYCLE STOCK HYDROGENATED
N O T E : NUMBERS A 1 POINTS REFER TO PERCENT SULFUR IN T H E CRACKED GASOLINE FRACTION
20
VOLUME % C O N V E R S I O N (100-VOL.% GAS OIL YIELD)
50
Figure 1. C a r b o n Yield VI. Feed Conversion
per molecule, whereas aromatics containing two or three condensed rings contain ten or fourteen aromatic carbon atoms per molecule, respectively. Catalytic cracking results on both the unhydrogenated a n d hydrogenated cycle stocks are presented in Table 111; included for comparison are catalytic cracking results on West Texas widecut virgin gas oil itself. These catalytic cracking tests were made in small k e d - b e d units with the same catalyst and cracking temperature employed originally for the initial production of the cycle stock (natural catalyst, 900" Fa). I n addition, a range of conversion was covered by variation of feed rate. One of the conversion levels covered on the virgin gas oil approximated the conversion level previously employed for the initial production of the cycle stock which was later hydrogenated (52 volume %). Conversion is here expressed as 100% minus the volume percentage of liquid distilling above the motor gasoline boiling range.
Fixed-bed catalytic cracking of West Texas wide-cut gas oil with n a t u r a l catalyst
I n Table I, the various indexes of aromaticity (aniline point, Diesel index, hydrogen content, specific dispersion, weight per cent aromatic rings) indicate appreciable hydrogenation of aromatic rings. Changes in product composition with desulfurieationhydrogenation a t 750 pounds per square inch are further amplified in Table 11, which presents data obtained on the separation of both the unhydrogenated and hydrogenated cycle stocks into aromatic and nonaromatic fractions by means of extraction with silica gel. The nonaromatic raffinate yield is higher with the hydrogenated cycle stock. Sulfur compounds are concentrated in the aromatic-rich extracts from each material, although the extract from the unhydrogenated cycle stock is very much higher in sulfur. Aromatics in the unhydrogenated cycle stock appear t o exist mainly as condensed ring aromatics (two or more rings per molecule). Hydrogenation a t 750 pounds per square inch has apparently resulted in the conversion of some condensed-ring aromatics t o single-ring aromatics. This may be seen from the values of 11.5 and 8.8 aromatic carbon atoms per molecule for the aromatic extracts from the unhydrogenated and hydrogenated cycle stocks, respectively. It is obvious from structural considerations that single-ring aromatics have six aromatic carbon atoms
T a b l e 11. Silica Gel Analysis of Cycle S t o c k from F l u i d Catalyst C r a c k i n g of West Texas W i d e - C u t G a s Oil w i t h Natural Catalyst Unhydrogenated Cycle Stock
Hydrogenated Cycle Stock
Silica gel extraction Rafinate wt. Yo 43 48 Extract, ht. % 57 52 Raffinate inspection Sulfur, wt. Yo 0.005 0,005 Specific dispersion a t 20' C. (nF - nc) X 104/d 97 97 Extract inspection Sulfur wt. Yo 2.7 0.36 Specidc dispersion a t 20' C. (nF - nc) X in4/a 254 193 M&&r wt. 208 209 Hydrogen, wt. % ' 8.6 9.8 88.4 Carbon wt. % 90.0 15.3 Carbon'atoms per molecule 15.7 Aromatic carbon atoms per moleculea 8.8 11.5 Nonaromatic carbon atoms per moleculea 6.9 3.8 a Calculated according to method of Deanesly and Carleton (8).
Prior to the catalytic cracking tests, the unhydrogenated cycle stock had been redistilled t o remove a few per cent bottoms. Inspections obtained on this material after distillation were not ex-
2710
INDUSTRIAL AND ENGINEERING CHEMISTRY
actly the same as the inspections on the undistilled cycle stock which was the material actually hydrogenated (Table I), but these slight differences would not be expected t o make any noticeable differences in a comparison of the catalytic cracking results. Comparison of the data of Table I11 may be made on either of two bases: (1) variation in ease of crackiiig or conversion level a t equivalent cracking conditions, and ( 2 ) variations in product distribution and quality (carbon formation and sulfur content) a t the same conversion level.
Vol. 41, No. I2
Table 111. Fixed Bed Catalytic Cracking of Feed Stock Derived from West Texas Wide-Cut Gas Oil Unhydrogenated Cycle Stock
genated Cycle Stock
24.1
24.7
27.8
0
0
67
98
0 90
665 169 41 1.8 12.0
580 126 31
580 133
41.5
36 0.15 12.0
175
143
1.1
0
Cravoking conditions Catalyst Cracking period, hours Temperature, 0
Hydro-
Virgin Gas Oil
Natural (acid-treated montmorillonite) 7-.-2 __._
F.
..q)(,...-... ~
~-_
~
Feed rate vol./ vol./ho& Pressure, 1L./sq.
2.0
1.2 0 . 9
inch gage Yields Conversion. vol
%
~
22
Gas oil, vol. % 78 Gas, wt. c/o 5,5 Gas, cubic, feet./ bbl. feed 910 Carbon, wt. '7; 1.6 Gasoline Sulfur, v t . yo 0.27 a T o o dark iii color.
Figure 2. Fixed-Bed Catalytic Cracking Equipment Used t o Determine Cracking Characteristics of Cycle Stocks
C'onversions obtained a t equivakrit cracking coiiditioris indicate that, the hydrogenated cycle stock is less refractory than the unhydrogenated cycle stock and almost equivalent iii crackability to the virgin gas oil (49 volume conversion vs. 41 and 50 volume 7 0 for the hydrogenated cycle stock, the unhydrogenated cycle stock, and the virgin gas oil, respectively, a t 0.6 volume/volunie/ hour feed rate). [Previous work involving complete bydrogena,tion of the aromatics in a cycle stock to naphthenes at, a higher pressure of 3000 pounds per square inch ( I ) showed that,, under these conditions, the hydrogenated cycle stock \vas even move readily cracked than the virgin gas oil itself. ] Comparison of carbon formation and sulfur content of the gasoline fraction a t a given conversion level is not too readily made from the method of data preseri1,atiori in Table 111. These data. are plotted, however, in Figure 1,which gives the relation between carbon production and feed conversion for each of the three feed stocks. From this plot it is readily evident. that, rtt a given conversion level, the hydrogenated cycle st,ocli is not only greatly superior to the unhydrogenatcd cycle stock but is also superior to the virgin gas oil in having a lowcr carbon-forming t,endcncy. &-umbers a t t,he various points representing t.he sulfur contents of the gasoline fractions indicate that, for a given feed stock, the sulfur cont'ent of the gasoline tends, in gencrnl, to decrease with increasing conversion. This is due, presumably, t o the more severe degree of cracltirig i'rom ivhich the higher conversions result,. I n no case, howcver, is the rcduction in gasoline fraction sulfur content that is brought about by an increased cracking severity level, comparable to the reduction in sulfur content, that is accomplished by hydrogenation of the cyclc stock prior t;o catalytic cracking. I t is especially noteworthy that only the gasoline produced by the catalytic cracking of the hydrogenated cycle stock is of a low enough sulfur content t o meet established sulfur specifications without any subsequent treating.
0.G --
1.2
0.6
0.6
1.2 .
(J
34 66 7.9
41 5C: 59 50 9 . 3 11.9
6.5
13 73
41 59 10.5
32 6R 6.6
360 4.0
420 4.9
520 G.9
2Y0 4,O
460 7.4
290 2 9
0 . 2 1 0 . 2 4 0.19
0.22
0 . I9
0.0Y
-~
0.09
Judged h> previous noilc ( I ) , no difYerericc>sin deai octane number M ould be expected for the catalytically cracked gasolines produced from the vaiious feed stocks. The gasolines produced from the hydrogenated cycle stock would be expected, h o ever, ~ to have wperior lead susceptibilitier in view of their lowcr sulfur contents.
CONCLUSION Simple hj drogenation of a high-sulfur clatalytically clacked cycle stock at 750 pounds per square inch pressure improves the quality of this material to the point where it is a t least as dcsirablt. a cracking stock as the original virgin gas oil. In the hydrogcnation step, catalyst activity is maintained, product yield i i loo%, little change in boiling range occur&,and mlfur is virtuall, completely removed from a refractory material which resists desulfurization by other methods. Sulfur reduction prior to the oiiginal cracking of a high-sulfur virgin gas oil or the recracliing of LL high-sulfur cycle stock derived therefrom is shown to br nccr5sary in order to alloir the production of a gasoline nhlch nied,i established sulfur specifications without any further trraf ing
LITERATURE CITED (1) B r o w n , C . L., Voorhies, A., J r . , a n d Sniith, i V . M . , 1x0. Em,.
CHEM.,38, 136-40 (1946). (2) Deanesly, R . M . , and Carleton, L. T., IN). EXG. C a ~ x .A, N ~ L . ED.,14,2 2 0 ~ - 6(1942). (3) Vlugter, J. C . , Watermnn, H. I , , and TYentcari, E l . A van, .T. Ins$. Petrolelam Technol., 21, 661-76 (1935).
