August 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY LITERATURE CITED
(1) Aldrich, E. \TT., and Robie, N. P., S.A.E. Journal, 30, 198-205 (1932). (2) Am. SOC.Tasting il.lateriaZs, Standards, 111-A,210-13 (1946). (3) Bridgeman, 0. C., Oil Gas J . , 31, No. 3,55-7 (1932). (4) Brooks,B. T., IND.ENG. CHEM.,18, 1198-1203 (1926). (5) Casaar, IT. A , ,Ihid., 23, 1132-4 (1931). (6) Coordinating Research Council, “Report on 1943 Desert Storage Tests on 80 Octane Number All Purpose Gasoline,” September 1944. (7) Ihid., “Report on Gasoline Gum Tolerance of Ordnance Material,” July 14, 1945. (8) Downing, F. B., Clarkson, R. G., and Pederson, C. J . ,Oil Gas J . , 38,KO.11, 97-101 (1939). (9) Flood, D. T., Hladky, J. W., and Edgar, G., IND. ENG.CHEM., 25, 1234-9 (1933). (10) Hunn, E. B., Fischer, €1. G. M., and Blackwood, A. J., S . A . E . Journal, 26, 31-7 (1930). (11) Larsen, R. G., and Armfield, F. A , , IND. ENG.CHEM.,35,581-8 (1943). (12) Morrell, J. C., Dryer, C. G., Lowry, C . D., Jr., and Egloff, G., Ihid., 26, 497-503 (1934). (13) Naphtali, M., Chem. Ztg., 54, 371 (1930).
1729
(14) Rogers, T. H., and Voorhees, V., IND.ENG.CHEM.,25, 520-3 (1933). (15) Shell Oil Co. Inc., Wood River Resed.ch Laboratory, private
communication. (16) Velde, H. von, Oel u. Kohle, 40, 10-15 (1944). (17) Vellinger, E.; and Radulesco, G., Proc. W o r l d Petroleum Congr., 11, 103-7 (1933). (18) Wagner, C. R., and Hyman, J., J . Inst. Petroleum Technol., 15, 6‘74-80 (1929). ~. (19) Walters, E: L i U . S. Patent 2,361,337 (Oct. 24, 1944). (20) Walters, E. L., -Yabroff, D. L., and Minor, H. B., IA-D.EA-G: CHEM.,39, 987 (1947). (21) Walters, E. L., Yabroff, D . L., Minor, H. B., and Sipple, H. E., A n a l . Chem., 20,423 (1948). (22) White, E . R., snd Walters, E. L., U. S. Patents 2,300,998 (Nov. 3, 1942); 2,361,339 (Oct. 24, 1944). (23) Windle, Q. S., Petroleum Refiner, 23,No.2, 83-7 (1944). (24) Yabroff, D. L., and Walters, E. L., IND. ENG.CHEM.,32, 83-8 (1940). (25) Yabroff, D. L., Walters, E. L., Nixon, A . C., and Minor, H. B., NatZ. Petroleum ’Vews, 32,R-445-8 (Dee. 11, 1940). RECEIVEDApril 2 , 1948. Presented before the Division of Petroleum Chemistry a t t h e 113th Meeting, of t h e AMERICANCHEMICALSOCIETY, Chicago, Ill.
Fluid Catalyst Cracking with Silica-Magnesia J
R . W. RICHARDSON, F. B. JOHNSON, AND L. V. ROBBINS, J R . Esso Laboratories, Esso Standard Oil Company, Louisiana Division, Baton Rouge, La. T h e development and pilot plant testing of synthetic silica-magnesia catalyst for use in fluid catalyst cracking have been carried out in various pilot plants, including the 100-barrel-per-day unit. The over-all results show that this catalyst is superior to synthetic silica-alumina and treated natural clay with respect to gasoline yield. The gasoline octane numbers are, however, lower than those obtained with silica-alumina, but approach those obtained with natural catalyst. Silica-magnesia is indicated to be superior from the standpoint of activity maintenance and is now in commercial production.
0
S L Y two types of catalysts have been employed t o any
appreciable extent commercially in the fluid catalyst cracking process-namely, natural clay and synthetic silica-alumina. The latter was especially adapted for the production of high octane and volatile gasoline plus large yields of butanes arid butenes, and it was used extensively during the war period for making aviation gasoline. -4 new type of catalyst, designed primarily for motor gasoline product, is a synthetic silica-magnesia composition of the gel type. The purpose of this paper is to describe the pilot plant results obtained with this catalyst and t o point out some of the possible advantages in cracking operations primarily directed toward obtaining high yields of motor gasoline. The fluid catalyst cracking process has been accepted for wide commercial application during the past few years ( 7 ) . Previous articles discussed the process ( 5 ) and its pilot plant development ( 3 ) in considerable detail. The nominal 100-barrel-per-day feed capacity pilot plant a t Baton Rouge was relied on for the major part of the process data and engineering studies required for the commercial designs, and this pilot plant has been used also t o test a variety of catalysts. Since the 100-barrel-per-day pilot plant was first described ( S ) , it has been modified by an improved downflow design for fluid catalytic cracking. Engineering and mechanical features
of the commercial downflow design have already been reported ( 6 ) . A brief description of the present 100-barrel-per-day unit follo!w. Figure 1 is a general view of the plant, and Figure 2 is a flow diagram of the equipment. The reactor coiisists of a vessel with a bottom section of 15 feet of 17-inch-diameter pipe which enlarges to a 22S/8-inch-diameter top section 18 feet high. The regenerator is 32 inches in diameter and 34 feet high. The general scheme of cat,alyst and oil flows described previously (6) for commercial downflow units is essentially the same for the 100-barrel-per-day pilot plant. Catalyst testing and development are also carried out, a t the Baton Rouge laborat,ory in several snialler units-i.e., 200-cc. testing units, 2-liter fixed-bed units, and 4-barrel-per-day feed capacity pilot plant. The 200-cc. units are fixed-bed catalyst reactors with a capacity of 200 cc. of pilled catalyst (4).Tests are conducted with a standard gas-oil feed stock a t fixed feed ratme and cracking conditions. Although these units are desirable for test’ing small quantities of cat,alysts prepared in the laboratory, the amount of data t’hat can be obtained is limited to (a)initial catalyst activity, ( b ) carbon- and gm-forming tendencies, and (c) stability t o heat and t’o stcam in conjunction with accelerated laboratory tests. I n the larger units of 2-liter cat,alyst capacity, the cat,alyst is tested in pilled form in the fixed-bed reactors. These units give sufficient product to allow octane numbers to be determined and t o define product distribution. The downflow design fluid catalyst pilot unit has a nominal feed capacity of 4 b a r d s per day. The reactor is 4 inches in diainet,er and 25 feet long, and the regenerator is 8 inches in diamet,er and 18 feet long. A similar plant has been described in detail ( 1 ) . LABORATORY AND SMALL PILOT T E S T S
The two widely used types of commercial catalysts (synthetic silica-alumina and acid-treated montmorillonite clay) are cited as
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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VoL 41, No. 8
Tests of silica-magnesia in the 200-cc. units indicated that its initial cracking activity and carbonand gas-forming tendencies are equivalent to those of silica-alumina. The silica-magnesia compared well with silica-alumina in stability to heat and was superior in stability t o steam in accelerated laboratorj- tests. Another major advantage for silica-magnesia type catalysts is the high yields of gasoline and heat,ing oil. The gasoline i s not so high quality as that produced with silica-alumina synthetic catalyst hut, approaches that from natural clay. Table I summarizes results of te on one of the fixed-bed units of 2-liter capacity. Operating rceult>s from various catalysts are usually compared a t a given level of feed stock conyersion, and the relative yields of various products are noted. Feed stock conversion is arbitrarily talien as 100 minus the volume peroent,age of cycle gas oil. Cycle gas oil is the product having a higher boiling point than gasoline, as determined by distillation of the gasoline to a 330" F. final vapor temperature wit,h good fractionation. Although this expression is not an esact measure of feed stock destruction, it does furnish a convenient means for correlating the yields of various products. The silica-magnesia catalyst mas next tested in the 4-barrel-per-day unit, and the data substantiated the trends in the fised-bed unit (Table 11). The results indicate nearly 25% greater gasoline yield n-ith less butanes-but,enes and less dry gas for silica-magnesia than for silica-alumina. CarFigure 1. General I-iew of 100-Barrel-per-Day Fluid Catalyst bon forniation was the same for both. The octane Cracking Unit numbers of the motor gasoline produced with silica-magnesia were two t o three points lower than those obtained with silica-alumina. The volatility of the standards of comparison for the newer types of catalysts. The gasolifie was lower with silica-magnesia. general procedure in evaluating a new catalyst has been t o test it in progressively larger equipment t o obtain more complete data in each step as long as the catalyst gives proniising results. After this selective screening process, the development tests are conT A B L E 1. COMPARISON OF CATALYSTS I N L 4 B O R A T O R Y FIXEDBED CRACKING U N I T S AT 65% COhrvERSION O F EAST TEXAS firmed by actual operation in a commercial fluid catalyst cracking LIGHTGas-OIL FEED unit. Katural CYCLONE SEPARATOR
ELECTRICAL PRECIPITATOR
1'1 \ 1
REGENERATOR
CATALYST FINES RETURN
Catalyst Reaction temp., O F. Yields on feed Gasolinea, vol. Yo Total butanes-butenes, vol. %b Gas oil, voi. Yo D r y gas. Ca a n d lighter. Rt. % ' Carbon, wt. Yo Gasoline quality Motor octane No. Research octane Yo. Same with 1.5 cc. tetraethyllead/ gal. a 10-pound Reld Tapol piesswe.
SiOn-NgO
975
Si02-4120a
900
Clay
900
900
48.0 10.0 35 0 10 1 3.4
52 9 35 7 4
0 2 0 6 0
42.0 18.3 35 0 9.5 4.8
46.2 13.4 35.0
79.2 90 2
78.2 86 5
80.8 92 2
78,O
95.7
94.2
96.5
95.0
7.8 6.5 87.5
T.4BLE 11. CollPARISOA O F C41'ALYSTS I N 4-BARREL-PER-DAY UNIT AT 65% CONTERSION O F !JyIDE-CUT P A R A F F I h I C GAS-OIL FEEDAT 975" F.
CYCLONE SEPARATOR
CatalSst
KT,. space relocity
\\-t ratio catalvstioil Cat'aiyst actiyitji, 70 D ~a Yields on feed 10-lb. gasoline. vol. Vo Total butanes-butenes, vol. 53 Gas oil, 1-01, "c Dry gas (Cr a n d lighter), n-t. 70 Carbon. wt. c%
+
STANDPIPES VENTURI METER
PiOrIIgO 23 10 60
S10~-.41n03 17 10 44.5
59 0 12 6 36 0 6 6 3.6
47.6 18.2 3.5.0 10.0 3.6
RECYCLE -HEAT EXCHANGER
PREHEATED OIL--' LAIR
Figure 2.
Flow Diagram of 100-Barrel-per-Day Cracking Unit
+
+
%D L (dist.illation loss) is used in laboratory tests as a measure of catalyst activity under fixed cracking conditions. Roughly, i t is t h e volume per cent of gasoline produced; this test has already been described in det,ail Q
(4).
August 1949
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
1731
T E S T S IN 100-BARREL-PER-DAY PILOT PLANT
Two 1000-hour demonstration runs were made in the 100-barrel-per-day unit to evaluate silica-magnesia for motor gasoline production. The feed stock was a wide-cut paraffinic gas oil obtained by distilling in a commercial pipe still a mixture of Baton Rouge-Olla, Nebo, and South Louisiana crudes (Table 111). The silica-magnesia was prepared in a commercial catalyst plant, and exhibited high specific surface and good heat and steam stability in accelerated laboratory stability tests: Catalyst Sp. surface sq. m./g. Activity aiter heat treatment (1400' F., 3 hr.) % D La Activi'ty after steam treatmentb, % D L
+
SiOz-MgO 543
+
56 42
AcidTreated Clay 315
SiOn&Os 555
50 25
36 33
a Defined in Table 11. b Steamed for 24 hours a t 1050' F. under partial pressure of 60 pounds per squaie inch gage
Table IV summarizes results obtained in the 100-barrel-per-day plant under comparable conditions with the three catalysts. It is evident that silica-magnesia yields considerably mole 10-pound gasoline (56.2%) than either silica-alumina (45.5%) or natural (47.80j0) catalysts. Motor octane number and research leaded octane number approach those for natural clay catalyst operation; however, the reseahh octane (clear) is about two numbers lower for silica-magnesia, The gasoline yield and quality comparison from a wide-cut paraffinic gas-oil feed are show? graphically in Figures 3, 4, and 5. The yields of isobutane and butanes as well as of total butanes-butenes with silica-magnesia are less than those with silica-alumina or natural clay. The volatility of the 10pound gasoline produced with silica-magnesia is somewhat lower than that with silica-alumina and natural clay-for example, under the conditions shown, 60% conversion of gas oil at 975" F. cracking temperature, the A.S.T.M. distillation points (% D L) are as follows:
+
Temp.,
F.
SiOn-MgO 25 0 46.0 61 0
158 212 257
SiOz-AlnOa 32.0 54.0 65.5
Natural Clay 27 5 52.0 64.5
Silica-magnesia produces a larger yield of heating oil stock than silica-alumina. Inspection data indicate t h a t the quality of the heating oil fraction produced over silica-magnesia is about the same as that over silica-alumina. COMPOSITION OF GASOLINE
In view of the high yield and lower octane number of the gasoline produced over silica-magnesia catalyst, a closer study of the characteristics of comparable gasolines from silica-magnesia and silica-alumina appeared desirable. Figure 6 compares the volume percentage and octane number of 50" F. boiling range
TABLE 111. TYPICAL INSPECTION DATAOF FEED STOCKox 100BARREL-PER-DAY UNIT Gravity, A.P.1 29.4 Aniline point, F. 197 Diesel index 57.9 Color, Tag-Robinson 1 /? Flash point, Pensky-Martens, ' F. 283 Viscosity a t 210° F., Baybolt Universal see. 38.1 Carbon, Conradson, wt. yo 0.294 Sulfur, Braun-Shell, wt. 7o 0,202 Pour uoint. A.S.T.N.. O F. 85 Boil& rangea Initial h.p., F. 444 5% over, F. 499 50% over, F. 701 95% over, F. 994 Final b . p . , F. 1008 Recovery, 70 97.0 a Corrected t o atmospheric pressure from d a t a obtained a t 10 mm. plessure.
TABLE IV. COXPARISON OF CATALYSTS IK 100-BARREL-PER-DAY 60% COKVERSIOii O F WIDE-CUT P4RAFFIiiIC GAS-OIL FEEDAT 9i5' F.
USITS AT
Catalyst Ratio. catalvst-oil Yields on fekd 10-lb. gasoline, vol. 7o Total butanes-butenes, 5.01. Butenes, vol. yo Isobutane, vol. % Heating oil base, vol. % Heavy gas oil, vol. % D r y gas wt. 7 Carbon.'wt. 'ZG Gaioline--&ualiti" Motor octane No. Research octane No. S a n e , with 1.5 cc. tctraethyllead/gal. Volatility, A.S.T.M. distn., % D L A t l58O F. A t 212O F. A t 257O F. Quality of heating oil base Gravity A.P.I. Cetane No. (estd.) Initial b.p., F . 50% over, F. Final b.p., F.
+
6102-AIgO 6-10
SiOz-hl~03
Satural Clas
9-12
7-10
50 2 10.0 6.4 2.6 22.3 17.7 6.2 2.9
45.5 16.0 9.0
47.8
21.51 18.5~ 9.0 2.9
9.2 4.0 40.0 8.7 3.1
79.2 91.5 96.3
81.6 95.0 98.7
79.8 93.6 97.2
25.0 46 0 61.0
32.0 54.0 65.5
27.5 52.0 64.5
29.5 36 455 514 577
30.0 32 470 517 589
*.
5 4
14.0
.. .. .. ..
fractions of the product from comparable cracking operations with both of these catalysts. The upper field (research octane number us. boiling range) shows the reason for the lower octane number of the total motor gasoline produced over silica-magnesia. Although the light fractions from silica-magnesia catalyst operation are slightly higher in octane number than those from silicaalumina, the heavier fractions (over 200' F. mid-boiling point) are appreciably lower. I n this range the gasoline octane numbers for silica-alumina operation increased with increasing boiling point, whereas those for silica-magnesia decreased with increased boiling point. Table V gives typical composition data on the light and heavy gasoline fractions from silica-magnesia and silicaalumina operations at about 60% conversion level at a 975' F. cracking temperature.
TABLE V. TYPICAL COMPOSITION DATA Light Naphtha, 65Heavy N a p h t h a , 250250° F. Vapor Temp. b 430' F. Vapor-Te_mp. -b Compositiona Si02-XIgO SiOz-AlzOs %On-MgO SiOn-AlzOa Aromatics 2 5 30 67 Naphthenes 13 25 26 21 Acyclics 86 70 44 12 Olefins 68 64 45 26 I n the analysis of catalytically cracked naphthas, t h e practice was adopted of reporting one composition giving t h e acyclic-cyclic division a n d another giving the olefin-nonolefin division. F o r example, unsaturated naphthenes are determined both a s olefins a n d a s naphthenes. When t h e olefin content exceeds the acyclic content, the presence of diolefins or unsaturated naphthenes is indicated; diolefins have, in general, been found only i n small amounts in catalytically cracked gasolines. b Vapor-temperature-cut points in a 15-plate-efficiency laboratory distillation column a t 5 t o 1 reflux ratio.
k
t
89
60
a?
5hJg 0 2
OF6
55
cdcc
50
8
45
>
0-82 ?O
40 45
50 60 70 VOLUME % G A S O I L C O N V E R S I O N
Figure 3, Motor Gasoline Yields at 975' F. Reactor Temperature in Large Pilot Plant
The silica-magnesia light naphtha contains less aromatics and less naphthenes, but slightly more olefins than the silica-alumina
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 8
nearly those for silica-alumina catalyst a t high conversion 1evels. The high gasoline yield with silica - m a g n e s i a catalyst is obtained at, the expense of light hydrocarbons, as noted above on b u t , a n e- b u t e n e y i e l d s ; coiiseyuently, the dry g a s (C, and lighterj yield with silica - m a g n e s i a eatal,) st is roughly 25% less than that nith silica-aluNATURAL CLAY milia catalyst,. SI LICA-MAGNES IA The 100-barrelI per-day plant re4' I I I sults at optimum 50 60 70 operating condiV O L U M E To GAS O I L C O N V E R S I O N tions indicate that Figure 4. Alotor Gasoline Octane Numbers silica - m a g n e s i a at 975" F. Reactor Temperature in Large and silica-alumina Pilot Plant g ive approxiI 1 1 I I mately the same 60 70 50 carbon yields on light naphtha. The aromatic content of the heavy V O L U M E 70 G A S O I L C O N V E R S I O N feed. These renaphtha from the silica-magnesia catalyst is conFigure 5. \lotor Gasoline J-olatility at 975" F. sults are in agreesiderably Ion-er arid the olefin content appreciably Ileactor Temperature in Large Pilot Plant ment with other higher than that of the naphtha produced over experimental data silica-alumina catalyst. These data support very ~. well the octane number-boiling range data of Figur? 6. obtained on this catalyst in Iahorat,ory fixed-tied and 4-barrel-perday units. The lon-er section of Figure 6 illustrates the product yield I n the 2-liter fixed-bed unit XT-ith tt high-sulfur \Yest Texas gastrends shon-ti in Table IT and discussed previously. The cracked oil feed stock, the silica-magnesia catalyst was subject to teriipoproduct from silica-magnesia operation, compared with that ntry poisoning which resulted in higher carbon formationin the abfrom silica-alumina, contains less gas and light fritctioiis boiling sence of steam. The use of a noiniiial amount of steam x i t h the below 150" F., more gasoline and heating oil boiling bet\vecn 1j O D feed prevented sulfur poisoning of the catalyst and also restored and 600" F., and less heavy gas-oil boiling over 600" F. Thus it catalyst quality following periods of operation without steam. appears that with silica-magnesia catalyst there is a greater destruction of heavy material : however: the shift in boiling range is not so great as wit,h silica-alumina, arid less light, niatprial is ENGINEERING DATA produced. I t also seems that the chain rupture with silica-niagIn the evaluation of any new catalyst it is desirable to obtain nesia is relatively mild, since the low yield of light gaees iiidiciLlcs criyineering data that will affect plant, design and operability. only a small amount of fragtneritatioii to C1,C2, or Ca fractions. Therefore, so far as it was possible to do so during tests in t,he 100barrel-per-day unit with silica-magnesia, data were obtained on GENERAL PRODUCT DISTRIBUTIOh~ catalyst attrition, regeneration: and coilcentration in the vessels The high liquid product yields n-i th silica-magnesia catalyst are and standpipes. The silica-magnesia catalyst vias generally satattractive, particular1)- in instances where butane-butene requireisfactory with regard to operation in the fluid cata1,yst unit. ment is not of major importance. The silica-magnesia catalyst Silica-magnesia catalyst gave att,ritioii rates comparable t n makeP less tot,al butanes and butenes; hon-cvcr, the trend in those !or catalysts ivhich have performed satisfactorily in conitotal butane-butene yield Jvith conversion is essentially thesamefoi. iiiercial plants. both synthetic catalysts. The composition of this fraction with Carbon burning rates during rcgcneration of silica-magnesia silica-magnesia changes less with conversion than n-i th silicain the 100-hnrrel-per-day plant were equivalent, to those obtained alumina : ivith silica-alumina and natural clay. However, the ratio of carSiO?-AlsOi S102-;\IgO bon dioxide to carbon monoxide i n the regeneration flue gas for 50 75 50 75 silica-magnesia (1.6 to 2.0) TTas higher than that for silica-aluniiria 12,s 23 0 7 0 142 (1.0) and roughly thc samc as that for natural clay (1.7 to 2.2). 24 13 26 21 44 30 n-Butenes 43 37 This would mean additional ail. requirenients for silica-magnesia 44 21 31 24 Isobutane and natural clay catalysts t o obtain the same carbon burning 10 11 8 13 n-Butane capacity found with silica-alumina. However, t h e higher ratio obtained niay be beneficial in some cases because more heat is With increasing conversion the iso- and n-butene concentration evolved per unit of carbon burned, and thus less extraneous hestn the total fraction changes less with silica-magnesia catalyst so ing of the oil feed is required for a given reactor temperature. hat the yield on feed of these constituents approaches more
August 1949 $110 W
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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SI LICA-ALUMINA
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300
400
500
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shown in Figure 7 to illustrate the dat'a for the first 403 hours of the first run with silica-magnesia. During this period no fresh catalyst was added and a smooth curve was obtained. Tnese data show that silica-magnesia in the 100-barrel-per-day unit maintained a much better surface activity than wasobtained under comparable conditions with silica-alumina. From the decline curves established as shown in Figure 7 , the effect cf periodic, nominal, fresh cat'alyst addition rates on "equilibrium" specific surface can be calculated. By "equilibrium" specific surface is meant the essentially constant activity which will be maintained in a fluid catalyst unit a t a given replacement rate under constant operating conditions; the loss in specific surface each day is balanced with the incremental increase in specific surface contribut,ed by the fresh catalyst additions. The calculations involved are rather specific to a given unit; therefore, the equilibrium values given in the following tabulation are intended merely t,o indicate the approximate relative difference between silica-magnesia and silica-alumina catalyst's. These calculated values are valuable in giving the relative rates of decline; however, actual values in commercial practice might be very different owing to variat,ioiis in deactivation conditions encount,ered:
B O I L I N G TEMPERATURE,OF.
Figure 6.
Distribution of Products from Large Pilot Plant
vI: 800 $ 500 W
u
2
300
*
200
CL
u
k
U
2 Vl
100 lo
Figure 7.
30 40
60 80 -200 R U N , HOURS
400
Comparison of Specific Surface Decline
The catalyst concentration or density in the regenerator o€ the 100-barrel-per-day unit was 2 to 5 pounds per cubic foot higher than the densit>yt,hat would be obtained with silica-alumina under comparable conditions. Pressure surveys also indicated that the standpipe height required to build a given pressure was about 20y0 lower than the requirements for silica-alumina and natural clay cat,alysts. These differences appear to be in direct relation to the bulk densit'ies of the catalysts, 0.66 for silica-magnesia and 0.55 for silica-alumina. I n t'his regard, the density of silica-magnesia is subject to a considerable degree of control by properly regulating catalyst manufacturing variables. Catalysts have been made in t'he laboratory which are equivalent in density to normal silica-alumina. Therefore, this density difference is apparently not a significant factor, inasmuch as the silica-magnesia catalyst can be manufactured so that it will have any density desired within a normal range.
Fresh catalyst addition, % of inventory per day Esuilibrium sp. surface, sq. m./g. Silica-magnesia Silica-alumina
0.5
1 ,O
1.5
295 160
320 180
33: 195
Although specific surface is not an exact criterion of the relative cracking activity which will be shown by catalysts of greatly different chemical composition, the pilot plant data also indicate that silica-magnesia will maintain a considerably better fluid unit activity than silica-alumina a t a given inventory replacement rate. The better activity maintenance shown for the silica-magnesia catalyst is felt to be a result of the better steam stability of this catalyst, as shown earlier by data obtained in a fixed-bed catalyst test under accelerated conditions. CONCLUSIONS
The over-all results obtained with silica-magnesia in laboratory and in large-scale fluid catalyst pilot plants indicate that this catalyst is superior to silica-alumina and natural clay catalysts with respect t o gasoline yield. The gasoline octane numbers are, however, lower than those obtained with silica-alumina catalyst, but approach those obtained with natural clay catalyst. Carbon formation is equivalent t o that with silica-alumina, but dry gas and butane-butene yields are lower. Silica-magnesia is superior to silica-alumina from the standpoint of activity maintenance. Satisfactory fluid catalyst operation was shown for silica-magnesia with regard t o other properties such as carbon burning rate, attrition rate of catalyst, and catalyst concentration and pressure build-up in vessels and standpipes. I n general, the use of silica-magnesia seems warranted for cominercial fluid catalyst cracking, especially in those cases where high liquid product yields are desirable and where yields of low boiling unsaturates are not of major importance. Furthermore, the better activity maintenance should result in some economic advantage since less fresh catalyst replacement would be necessary to maintain a constant level of catalyst activity. LITERATURE CITED
.MAINTENANCE OF CATALYST ACTIVITY
I n the fluid catalyst cracking units, as in other catalytic processes, the majntenance of the catalyst activity is of prime importance, for this factor determines the rate a t which the spent material must be replaced with fresh catalyst t o maintain a constant activity with respect to conversion of the gas-oil feed. In the fluid catalyst process the specific surface of the catalyst ( 2 ) , measured as square meters per gram by nitrogen adsorption, has been a highly satisfactory measurement of catalytic activity. I n the 100-barrel-per-day unit specific surface is normally measured daily on samples of the circulating catalyst stream, and the values found may be plotted against the time of use of the catalyst. Thus specific-surface-area decline curves are constructed as
(1) Anonymous, PetroEeum Processing, 2, 518 (1947). (2) Brunauer, I., Emmett, P. H., and Teller, E. J., J . Am. Chem. SOC., 60, 305 (1938). (3) Carlsmith, L. E., and Johnson, F. B., IND. EKG.CHEM.,37, 451 (1945). (4) Conn, M . E., and Connolly, G. C.,,I b i d . , 39, 1138 (1947). ( 5 ) Murphree, E. V., Brown, C. L., Fischer, H. G. M., Gohr, E. J., and Sweeney, W. J., I b i d . , 35, 768 (1943). (6) Murphree, E. V., Brown, C. L., Gohr, E. J., Jahnig, C. E., Mart'in, H. Z., and Tyson, C. W., Oil Gas J . , 43,64 (1545). (7) Murphree, E. V., Gohr, E. J., and Kaulakis, A. F., Pacific Chemical Exposition, Tech. Paper, 1947. RECEIVEDM a y 17, 1948. Presented before the Division of Petroleum Chemistry a t the 113th Meeting of the AMERICAIVCHEMICALS o r m n , Chicago, Ill.
