Ind. Eng. Chem. Prod. Res. Dev. 1988, 25,549-553
of the process. Injection of preheated gas to the catalyst has the potential to significantly increase reaction rates and allow the operation of the catalyst system at lower pressures. However, further experimentation will be needed to quantify more fully this potential.
Acknowledgment We thank Gary Neuenschwander, who assisted in the assembly of the reactor system and in its operation. Registry No. Na2C03,497-19-8; H, 1333-74-0; ammonium hydroxide, 1336-21-6; sodium citrate, 994-36-5; cadmium hydroxide, 21041-95-2.
Literature Cited Baker, E. C.; Hendrlcksen. D. C.; Elsenberg, R. J . Am. Chem. SOC. 1980, 702, 1020-1027. Bjurstrom, E. Chem. Eng. 1985, 92(4), 126-158. Bortolini, P. Chem. Eng. Sci. 1958, 9 , 135-144. Casale, L. U S . Patent 1 843 540, 1932. Cheng, C.-H.; Elsenberg, R. J . Am. Chem. SOC. 1978, 700. 5966-5970. Elliott, D. C.; Seaiock, L. J., Jr. Ind. Eng. Chem. Prod. Res. D e v . 1983, 22, 427-431. Elliott, D. C.; Sealock, L. J., Jr. Prepr. Pap.-Am. Chem. Sac., Div. Fuel Chem. 1984, 29(6), 14-21. Elliott, D. C.; Hallen, R. T.; Sealock, L. J., Jr. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 431-435. Gollakota, S. V.; Guln, J. A. Ind. Eng. Chem. Process D e s . D e v . 1984,23, 52-59. Hawker, P. N. Hydrocarbon Process. 1982, 67(4). 183-187.
549
Hill, C. G. An Introduction to Chemical Engineering Kinetics and Reactor Design; Wiiey: New York, 1977. King, A. D., Jr.; King, R. 6.; Yang, D. C. J . Am. Chem. SOC. 1980, 702, 1028-1032. King, A. D., Jr.; King, R. 8.; Yang, D. C. J . Am. Chem. SOC. 1981, 703,
-2699-2704. - - - -. - ..
Mukherjee, P. N.; Basu, P. K.; Roy, S. K.; Chatterjee, S. K. Indian J . Techno/. 1978. 74. 138-141. Seaiock, L. J:. Jr.: Elliott, D. C.; Butner, R. S.“Development of an Advanced Water-Gas Shifl Conversion System”; final report to the U.S. Department of Energy, Morgantown, WV, NTlS PNL-5468, 1985. Singleton, T. C.; Park, L. J.; Price, J. L. Presented at the 177th National Meeting of the American Chemical Society, Division of Petroleum Chemistry, Honolulu. HI, April 1-6, 1979. Ungermann, C.; Landls, V.; Moya, S.A.; Cohen, H.; Walker, H.; Pearson, R. G.; Rinker, R. G.; Ford, P. C. J . Am. Chem. Soc.1979, 707, 5922-5929. Yoneda, K.; Kondo, S.; Abe, R. J. J . Chem. SOC. Jpn. 1941% 44, 385. Yoneda, K.; Kondo, S.; Abe, R. J . Chem. SOC.Jpn. 1941b, 44, 388. Yoneda, K.; Honda, Y.; Momiyana, N.; Abe, R. J . Chem. SOC.Jpn. 19438, 46, 554. Yoneda. K.; Kondo, S.;Abe, R. J . Chem. SOC.Jpn. 1943b, 46, 667. Yoneda, K.; Kondo, S.; Abe, R. J . Chem. SOC.Jpn. 1944a, 47, 5. Yoneda, K.; Kondo, S.;Abe, R., J . Chem. SOC.Jpn. 1944b, 47, 7. Zielke, C. W.; Rosenhoover, W. A.; Gorln, E. Prepr. Pap.-Am. Chem. Soc., Dlv. Fuel Chem. 1978, 27(7), 163-186.
Received for reuiew September 3, 1985 Revised manuscript receioed May 22, 1986 Accepted June 30, 1986 This work was funded through the Advanced Coal Gasification Program of the Morgantown Energy Technology Center of the U.S.Department of Energy.
Fluid Catalytic Cracking Catalyst Demetalation by Converting Metal Poisons to Washable Sulfur Containing Compounds Jln S. Yoo,” J. A. Karch, and E. H. Burk, Jr. Hervey Technical Center, A R C 0 Petroleum Products Company, Harvey, Illinois 60426
The Demet 111 process consists of three steps: a sulfiding reactlon to convert metals to sulfides, a gaseous oxidation of the resulting metal sulfides to washable moieties, and washing steps to remove the metals. This process can rejuvenate the metal-contaminated and deactivated fluid catalytic cracking (FCC) catalyst by ensuring g o d metals removals and by minimizing any deleterious effect on the catalyst structure. The key feature of this process lies in the gaseous oxidation of preactivated metal sulfides to readily washable form by air in the same sulfiding reactor. The effective temperature range was defined to be 550-680 O F . At these temperatures, metal sulfides may be converted to sulfites, thiosulfate, and/or most likely sulfate, which can be removed by simple washing procedures. At temperatures above 700 O F , metal sulfides were most llkely converted to oxkies, which became difficutt to wash off. At temperatures below 500 O F , oxidation of the metal sulfides did not occur to any significant degree.
Introduction It has been widely accepted that principal metal contaminants in various crudes produced today are nickel, vanadium, and iron. A large portion of these metals is present in these crudes as organometallic chelates called porphyrins, having a closed planar structure (Valkomic, 1978). Under fluid catalytic cracking (FCC) operating conditions, almost 100% of these metal contaminants decompose and deposit on the FCC catalyst (Skinner, 1952). In most FCC feeds, the vanadium content is considerably higher than the nickel content. The manner in which vanadium is deposited on the catalyst surface and the *Address correspondence to this author at Amoco Chemicals Co., Amoco Research Center, Naperville, IL 60566. 0196-4321/86/1225-0549$01 S o l 0
deleterious effect that vanadium has on cracking catalyst performance differ distinctly from those of nickel. Recent studies for deposition of these metals on the catalyst with secondary ion mass spectroscopy (SIMS) (Jaeras, 1982; Upson et al., 1982), electron spectroscopy for chemical analysis (ESCA) and atomic absorption spectrophotometry (Lars et al., 1984), electronprobe microanalysis (EMPA), and differential thermal analysis (DTA) (Masuda et al., 1983b) showed that nickel was homogeneously distributed throughout the catalyst surface, but vanadium was preferentially deposited on the zeolitic sites and reacted destructively with zeolite. Thus, vanadium oxide interacts with rare-earth metals exchanged with the zeolite sites to form a eutectic mixture that causes severe loss of catalyst activity. This eutectic mixture formation reaction is catalyzed by sodium oxide (Masuda et al., 1983a). Destruction of the catalyst lattice by vanadium is reflected 0 1986 American Chemical Society
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986
in the decrease in the surface area, pore volume, crystallinity, and cracking activity of vanadium-contaminated FCC catalyst (Occelli et al., 1985). However, the results of the devanadation study (Yo0 et al., 1986) clearly indicate that vanadium poisoning is reversible. The catalytic activity of the vanadium-contaminated FCC catalyst was effectively rejuvenated by selective vanadium removal. Some of the vanadium that is not removed by the devanadation process may be responsible for the permanent activity loss due to zeolite destruction, as reported in the aforementioned literature. I t should be mentioned that the vanadium remaining on the devanadated catalyst is a minor fraction of the total vanadium on the catalyst. Nickel, on the other hand, is primarily responsible for promoting the dehydrogenation activity that produces coke and gaseous products, in particular, hydrogen at the expense of more useful liquid products. A spent residual demetalation catalyst has also been studied by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ESCA, electron microscope, CO and N2 chemisorption, and kinetic analysis (Fleisch et al., 1984). In the course of demetalation, the deposition of metals, sulfur, and coke takes place preferentially at the entrance of pores, causing pore-mouth plugging and leading to its deactivation. Maintaining the proper catalyst activity and selectivity of a FCC catalyst in the FCC unit is a key factor in controlling the quality and yield of the desired liquid products. This requires that the level of these metal contaminants deposited on the catalyst from the FCC feed should be strictly controlled to minimize the deleterious effects by these contaminants. It can be achieved by the makeup of fresh catalyst, but the cost of the makeup catalyst becomes so exorbitant, in particular, for the cracking of residue containing higher levels of metals, that the fresh catalyst makeup operation becomes uneconomical for the current FCC operation. This has led to an alternate method of controlling metal-contaminant levels on the FCC catalyst, namely, selective removal of these metal contaminants from the catalyst. Prior attempts at dealing with removal of metals from the FCC catalysts can be traced back to Atlantic Refining Co.’s Met-X process (Dilliplane et al., 1963; Ozawa et al., 1964), and Sinclair Refining Co.’s Demet process (Sandford et al., 1962) in the 1960s. Also, methods of removing vanadium from the regenerated FCC catalyst (Anderson, 1964) by subjecting the sulfided catalyst to an oxygen oxidation at lo00 O F and a washing with aqueous mineral acids (Anderson, 1965) are in the patent literature. A list of patents covering removal of vanadium as well as total metals including nickel, iron, and vanadium are also referenced (Erickson et al., 1964). Burk et al. (1978, 1981) claimed a process for removal of nickel, iron, and vanadium via chemical methods to ensure higher catalytic activity. In the course of this treatment, the integrity of catalyst structure was maintained, and satisfactory rejuvenation of highly contaminated FCC catalyst was achieved (Burk et al., 1978,1981). The process concept and the pilot-plant data of the process called Demet I11 by Atlantic Richfield have been reported (Edison et al., 1976). The primary objective of this paper is to discuss some of the chemistry involved in three different reaction steps involved in the Demet I11 process. Special efforts have been made to define the optimum range of temperatures for converting the sulfided metal compounds to washable moieties and to provide plausible mechanisms for various reactions of each step. All the experiments reported were carried out with the FCC equilibrium catalyst loaded with very high levels of metals
Table I. Catalytic Activity of Virgin and Metal-Contaminated Catalyst surface catalytic activity area, m2/g MA CPF H2/CH4 N2 zeolite virgin catalyst 80 0.75 8.0 metal-contaminated catalyst 59.1 3.02 20.0 104 29
at Phillip’s Borger, TX, refinery, where the heavy oil cracking process has been used with success since 1964 (Finneran et al., 1974).
Experimental Section The process for the removal of metal poisons such as nickel, vanadium, and iron from a regenerated FCC catalyst includes three steps, i.e., a sulfidation reaction to convert the metal contaminants to sulfides, a separate phase from the catalyst matrix; air oxidation of the resulting sulfides to washable moieties; and finally a washing step to remove the converted metal compounds in an aqueous medium. An equilibrium-regenerated zeolitic catalyst sample consisting of 54% Filtrol catalyst F-100,41% Engelhard catalyst HFZ-20, and 5 % Davidson catalyst CBZ-4 was obtained from the Phillip’s Borger refinery and was exclusively used for this study. The equilibrium catalyst sample was withdrawn from the Phillip’s HOC unit in March 1974. This catalyst was selected because of high metal loadings, 2400 ppm Ni, 7500 ppm V, and 6800 ppm Fe. The original catalytic activity of the virgin catalyst was drastically lowered, as shown in Table I, due to high metal contaminations. Sulfidation. The contaminated catalyst was regenerated under normal regeneration conditions, in air flow at 1200 O F for 4 h, in order to remove any coke present. The resulting catalyst was then heated to 1350 O F in a quartz reactor under fluidizing conditions with an accompanying nitrogen purge. At this temperature, hydrogen sulfide with nitrogen as a diluent (in a ratio of 1:4) was introduced to the catalyst. The flow of hydrogen sulfide was held constant for 4 h. After the addition of hydrogen sulfide was terminated, the catalyst was allowed to cool under nitrogen flow to approximately 500 O F for the subsequent oxidation reaction. The sulfur level on the sulfided catalyst at this point was controlled between 1.0% and 1.5%. Metal oxides existing as a free phase on the regenerated equilibrium catalyst are readily sulfided. It is speculated that metal oxides interacted strongly with the catalyst matrix to form plausible mixed oxides such as FeV03 and LaV03 and spinels such as NiA1204,and FeA1204may also be converted to sulfides under the sultiding conditions. In the case of spinel a free alumina phase may be formed by metal sulfide formation. The sulfidation conditions employed here were established from the previous work in order to minimize the sulfidation of alumina, which exists as the mixed-metal oxide or is in the original FCC catalyst matrix structure. MnOm+ H2S M x S y + H20 MA1204 + H2S LaVO,
+ H2S
-
-
-
MxSy+ A1203 + HzO
V,S,
+ LazO3+ H20
Air Oxidation of Sulfided Catalyst. After the sulfided catalyst had cooled to about 500 O F , it was again heated to a constant temperature of approximately 600 O F under a constant flow of nitrogen. After the temperature had stabilized to within 5 OF, the nitrogen was turned off and air was introduced to the catalyst at a rate of 3.0 L
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986 551 Table 11. Metal Removal as a Function of Sulfur Level of Sulfided Catalystn demetalated catalyst % removal sulfided catalyst, S % 0.17 0.53 0.56 0.74 0.76 0.80 0.98 1.10 1.25 1.46 1.53
run no. 1 2 3* 4 5b 6 7 8 9 10 11'
Ni 38 76 72 86 86 79 79 86 86 86 83
Fe 5 36 35 47 45 40 45 50 55 47 54
V
S
8 18 15 29 29 32 37 42 48 40 52
65 79 79 80 80 80 83 84 42 82 48
catalytic activity
MA
CPF
H2/CH4
70.4
1.17
8.00
69.9 70.5
1.06 1.20
6.20 7.65
66.8
1.47
"Catalyst: Phillip's Borger equilibrium catalyst 02328. Sulfiding conditions: 1350 O F , H,S/N, (1:4), 4 h HN03 treatment: 20% solid slurry, 0.2 g/g of catalyst, 176 O F , 5 min, repeat 3 times. *Air calcination at 1350 O F for 4 h prior to sulfidation. Sulfidation at 1500 O F for 4 h.
min-l (kg of catalyst)-l for 25 min. An exotherm of the reaction raised the reactor temperature from 600 O F to between 630 and 690 O F . The extent of the exothermicity varied depending upon the amount and type of sulfur left on the sulfided catalyst. After the catalyst had cooled under a nitrogen flow of about 3.0 L min-' (kg of catalyst)-', it was transferred under a nitrogen atmosphere into a sample bottle with a tight cover having a rubber seal. The sulfur level on the catalyst at this stage was between 0.7% and 0.9%. The oxidation of the sulfided catalyst is carefully controlled to produce washable oxidized sulfide forms such as metal sulfate, thiosulfate, and sulfite. It may also be speculated that some of the pyritic sulfides convert to simple stoichiometric sulfides which can easily be solubilized in an acid medium. M,S,
+ O2
-
MS2O3 or MS03
MS2 + 0
2
+
02
MSOl
MS
Washing Procedure. The detailed reductive and oxidative washing procedure has fully been described in the patent literature (Burk et al., 1978). The catalyst was slurried with water to give approximately 20 w t % solids. Sufficient sulfur dioxide was purged through the slurry to give an initial pH of 2.5-3.0, and the system was vigorously agitated at 158 O F for 3 min and then filtered. The same aqueous SO2 wash was repeated twice more for a total of three washes. A blue-colored wash solution indicative of V02+was obtained in the sulfur dioxide washing step. The catalyst was thoroughly washed with water until all sulfur dioxide associated with the catalyst surface was completely removed before the hydrogen peroxide wash was applied. The aqueous sulfur dioxide solution is believed to provide three essential functions, acidity, reduction potential, and sulfite anions, which are essential for complete removal of the oxidized metal moieties from the catalyst phase and to keep them in solution. The oxidative wash with an aqueous solution of hydrogen peroxide followed in the same manner. The initial pH of the slurry was kept at about 2.8-5.0, and temperature was maintained at 176 O F . After the wash procedure was repeated twice, the resulting catalyst was filtered and dried under a vacuum; the hydrogen peroxide wash produces a distinctly brown to yellow solution indicative of peroxyvanadium species VOZ3+. Vanadium pentoxide is also soluble in aqueous hydrogen peroxide to yield a similarly yellow solution. Unnecessary prolonged contact of cleaned catalyst with the yellow wash solution of solubilized vanadium pentoxide should be avoided. On standing at room temperature, the yellow vanadium pentoxide solution has
a tendency to make a sol, which in turn redeposits back on the catalyst surface. In the course of washing, solubilized metals in the wash solution were constantly monitored by means of spot tests, i.e., the hydrogen peroxide test for vanadium, the thiocyanate test for iron, the dimethylglyoxime test for nickel, and the morin test for aluminum (Feigl et al., 1972). Analyses of Metals and Sulfur on FCC Catalyst. Metals on the FCC catalyst were determined with the Phillip's Standard 100 KV or PW 1410 X-ray fluorescence spectrograph. The analysis consisted of measuring intensities of Ni, Fe, V, Ce, and Ti related to previously prepared calibration. The nickel concentration was corrected for the iron content. Other elements were not corrected for other metals. The sulfur content on the sulfided catalyst was determined by the sodium peroxide bomb method and/or the Leco method. Mat Test. In the standard microactivity test (MAT) developed by Atlantic Richfield, the catalyst to be tested is pelleted from its powder form by a single punch machine. The pellet is in. in diameter and 'Ia in. long and has 0.5-1 kg of crushing strength. It is calcined in air at 900 O F for 3 h before it is used. One milliliter of the standard feedstock oil is charged automatically over 5 g of pelleted catalyst packed in a reactor made of two concentric glass tubes of 10-mm i.d. at 900 OF. The cracking reaction was performed for 5 min to determine the activity of the catalyst. The activity of the catalyst is defined by volume percent conversion of 430 OF+ material in the feed to 430 OF- product. The liquid product is continuously collected in a calibrated microreceiver while the total gaseous product including the purge nitrogen is collected over water. This product is then injected into the GC unit to determine liquid yield. The spent catalyst is removed from the reactor for determination of carbon content, which then provides the basis for calculating a carbon-producing factor (CPF). The gaseous product, which is sampled in an evacuated gas bomb, is analyzed for hydrogen and hydrocarbons and is used to determine the molar ratio of hydrogen to methane. It was usually obtained at 95%-96% material balance in this test.
Results and Discussion The sulfidation was carried out to produce various sulfur levels of sulfided catalyst under different reaction conditions. The sulfided catalyst was subjected to nitric acid treatment to estimate the maximum extent of metals removal. Both metal removal and catalytic activity of the treated catalyst are correlated with the sulfur level of the
Ind. Eng. Chem. Prod. Res. Dev.. Vol. 25, No. 4, 1986
552
"1
"1
10
I
D
l0O
LGn
IM
600
I.mP.r.rYr*
100
am
I)M
lIxul
0
20
60
60
I Ivlfu.
'I
-
, 80 J",T'd.b
i L 00
1.20
140
I 6o
€.I.lY.t
Figure I. Metal removal aa a function of sulfur level of aulfided catalyst.
Figure 2. Oxidation temperature effect on metal removal and cat-
sulfided catalyst. Resulta are summarized in Table I1 and illustrated in Figure 1. The levels of metals set up as free metal sulfides on the catalyst surface in the sulfidation reaction were determined by the nitric acid treatment without worrying about the possible deleterious effect of the acid on the catalyst matrix structure, in particular, dissolution of alumina from the catalyst. The nitric acid treatment was chosen because the sulfided metal compounds could readily be solubilized in a dilute nitric acid medium and achieve rather effective metal removal to give rejuvenated catalyst, while in a nonoxidative acid medium, such as sulfuric acid, the major fraction of the sulfided metal compounds remained unreacted under the conditions described above. A very limited portion of the metal sulfides was dissolved in sulfuric acid and produced a catalyst whose activity was inferior to that of the sulfided catalyst itself. This clearly shows that the majority of metal sulfides do not exist in the form of standard acid (nonoxidative) sensitive stoichiometric sulfides such as FeS, NiS, etc. When the sulfided catalyst was exposed to a liquid-phase oxidation with an aqueous solution of hydrogen peroxide, metals were easily removed to provide lighter colored low-metal catalyst with excellent catalyst activity. This observation has led to the assumption that the main portion of metal sulfides remain rather unusual forms of sulfides such as V3S4,Ni3S2,NiS,,, NiS2, FeSh, FeS,, etc. (Fleisch et al., 1984). However, the MAT test results shown in Table IX suggest that the nitric acid treating conditions used, 2 g/10 g of catalyst to 20% solid slurry in an aqueous medium at 158 O F for 5 min, do not inflict noticeable damage to the catalyst structure. It is obvious by the comparison of results in Tables I and U that the catalyst performance of the treated catalyst bas improved rather dramatically by the nitric acid treatment. Those remarkably improved results clearly reflect excellent removal of nickel, iron, vanadium, and sulfur, while the integrity of original catalyst structure is maintained. Plots of metal removal vs. sulfur percent on the suBded catalyst illustrated in Figure 1show that there is a defmite limit on sulfur level on the sulfided catalyst to achieve
maximum metal removal. Although in the case of vanadium the best removal of approximately 42%-48% was reached at 1.0%-1.25% sulfur level, iron and nickel were removed 86% and 4770, respectively, at a sulfur level of 0.7%. These removals are very close to the maximum extent possible under the treating conditions employed here. It was also observed that some molten elemental sulfur formation at the cooler part of the sulfidmg reactor became apparent when the sulfur content on the sulfided catalyst was over 1.15%. This has led to the conclusion that a sulfur level in the range 0.7%-1.0% on the sulfided catalyst is sufficient to warrant the best possible removal of all metals, nickel, iron, and vanadium. As long as the level of sulfur on the sulfided catalyst was kept the same, the precalcination of the regenerated catalyst, air calcination at 1350 "F for 4 h under the fluidizing conditions, did not affect the outcome of metals removal. Compare results of runs 2 and 3 and runs 4 and 5 in Table 11. The gas-phase oxidation of the sulfided catalyst with air in the range of 515-725 OF, more preferably 550-680 OF, can convert the metal sulfides to the oxygen-containing moieties, which are removable in the subsequent washing steps. The oxidation reaction was carried out by allowing the sulfided catalyst to contact air or air plus steam in the fluidizing reactor a t various temperatures, 40&900 OF. This was done in order to define the optimum range of oxidation temperatures providing the best metal removals. The identities of metal sulfides and their oxidized washable forms have not been fully characterized. The metal sulfides converted via the oxidation reaction were removed and thoroughly washed in the washing procedure, a combination of a reductive wash with an aqueous solution of sulfur dioxide and an oxidative wash with a hydrogen peroxide solution. The results are summarized in Table 111. Figure 2 is a plot of catalytic activity of treated catalyst, MA, CPF, and H2/CH4,and percentage metal removal of nickel, iron, and vanadium vs. oxidation temperature. It clearly indicates that oxidation temperature in the range 550-700 "F provides the best metal removals and highest
alytic actirity.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986 553
Table 111. Effect of Oxidation Temperature of Sulfided Catalyst on Demetalation and Catalytic washing treatment % oxidation condition removal run no. temp, OF time, min oxidant Ni Fe V S untreated equil catalyst 0 0 0 20 air 1 900 57 19 29 94 2 25 air + steam 800-840' 71 33 31 25 air 3 750-830' 75 41 35 91 4 90 air + steam 700 79 52 41 83 661-717" air 5 82 45 40 85 650-720' air + steam 6 71 52 50 91 650 air + steam 7 86 49 38 83 613-680' air 8b 86 56 41 608-682' air 9b 86 57 43 10 600-650' 30 air t steam 86 56 60 90 559-588' 11 25 air 89 57 31 12 180 air 400 50 31 8 72
Activity of Treated Catalysto catalytic activity of treated catalyst MA CPF H2/CH4 59.1 65.7
3.02 3.26
20.0 23.4
71.2 75.6 74.8 74.4 73.1 73.4
1.48 1.24 1.24 1.25 0.91 1.19
7.41 8.60 9.21 7.24 10.9
74.0
1.66
6.28
"Catalyst Phillip's Borger equilibrium catalyst 02328. Sulfiding conditions: 1350 OF, 4 h controlled to get 0.8-1.0% sulfur on the sulfided catalyst. bSulfided with hydrogen sulfide and hydrogen, H2S:H2 = 1:4; other runs were made with the hydrogen sulfide and nitrogen mixture H2S:N2= 1:4. 'Temperatures raised due to the exothermicity of the oxidation reaction.
catalytic activity. At temperatures higher than 800 OF, the metal sulfides may be converted to metal oxides, which become difficult to remove in the subsequent washing step. The black sulfided catalyst turned brownish via complete oxidation at these elevated temperatures, indicative of iron oxide formation on the catalyst surface. On the other hand, the same metal sulfides were not properly oxidized to form washable compounds at temperatures below 500 O F . Although a significant portion of sulfur was removed from the catalyst in the oxidation reaction, the appearance of the resulting catalyst remained dark. In general, improvement of the catalytic activity of the treated catalyst reflects the extent of metal removals. The catalytic activity, however, is extremely sensitive to the amount, physical state, and, in particular, the oxidation state of unremoved metals. These remaining metals, which have been activated by the sulfidation reaction and are in a well-dispersed state, are extremely active. In many cases, the amount of these unremoved metals is extremely low, so that X-ray fluorescent analytical techniques are unable to detect them. Nonetheless, these trace quantities of well-dispersed activated metals remaining on the catalytic surface affect catalytic activity significantly. It is therefore essential to ensure the complete removal of activated metals by employing a combined procedure of reductive and oxidative washing techniques. Comparison of results in Tables I1 and I11 shows that oxidation of the sulfided catalyst at 550-680 O F provides effective conversion of metal sulfides to allow better metal removals in the washing step than the nitric acid treatment.
Conclusions The Demet I11 process for the removal of metal poisons from FCC catalyst consists of three steps-a sulfiding reaction to set metals free as sulfides from the catalyst matrix, the gaseous oxidation of the resulting sulfides to washable moieties, and a washing step to clean the converted metal compounds. This process can rejuvenate the deactivated metal-contaminated catalyst by ensuring good metal removals without harming the basic catalyst structure. The effect of temperatures on converting metal sulfides produced from the sulfiding reaction to washable forms by the air oxidation reaction under fluidizing conditions was studied and defined. The optimum range of oxidation temperature was found to be 525-700 OF, more preferably 550-680 O F . In this oxidation reaction metal
sulfides may be converted to sulfites, thiosulfates, and/or most likely sulfates. A t higher temperatures, the metal sulfides tend to be converted to metal oxides, which can again intimately interact with the catalyst matrix and become difficult to remove by the washing procedures employed. At lower temperatures, the metals are not adequately converted to removable compounds. Reductive washing of the oxidized catalyst with an aqueous sulfur dioxide solution followed by an oxidative wash with an aqueous solution of hydrogen peroxide ensures good metal removals and high catalytic activity of the treated catalyst. In short, the Demet I11 process can effectively control the metal levels on the catalyst by removing metal poisons while maintaining the integrity of the catalyst structure. Good metal removals result in improved catalytic activity. The makeup rate of fresh catalyst to adjust the catalyst selectivity and activity in the FCC operation can successfully be controlled to increase the yield of the desired liquid products by incorporating this demetalation technology into the FCC operation. Registry No. Ni, 7440-02-0; V, 7440-62-2; Fe, 7439-89-6. Literature Cited Anderson, A. D. U S . Patent 3 150 103, 1964. U S . Patent 3 173 882, 1965. Burk, E. H.; Yoo, J. S.;Karch, J. A.; Sun, J. U.S. Patent 4101444, 1978. U.S. Patent 4 102811, 1978. U S . Patent 4293403, 1981. Designa, W. L.; Foster, R. L. U S . Patent 3252918, 1966. Dilliplane, R. A.; Middlebrooks, G. P.; Hicks, R. C.; Bradley, E. P. Oil Gas J . 1963, 67(31), 119. Edison, R. R.; Siemssen, J. 0.; Masoiogites, G. P. Hydrocarbon Process. 1976, 133. Erickson, H. et ai. U.S. Patent 3 147209, 1964. Feigl, F.; Vlnzena, A.; Oesper, R. E. Spot Tests in Inorganic Analysis; Eisevier: New York, 1972; pp 95, 271, 325, 503. Finneran, J. R.; Muarphy. J. R.; Whittlngton, E. L. Oil Gas J . 1974, 72(2), 52. Fieisch, T. H.; Meyers, B. L.; Hall, J. B.; Ott, G. L. J . Catal. 1984, 86, 147. Jaeras, S.Appl. Catal. 1982, 2 , 207. Lars, S.; Andersson, T.; Lundln, S. T.; Jaeras, S.; Otterstedt, J. Appl. Catal. 1984, 9 , 317. Masuda, T.; Ogata,M.; Yoshida. S.;Nishimura, Y. J . Jpn. Pet. Inst. 1983a, 26(1), 19. Masuda, T.; Ogata, M.; Ida, T.; Takakura, K.; Nishimura, Y. J . Jpn. Pet. Inst. 1983b. 26(5), 344. Occelli, M. L.; Psaras. D.; Suib, S. L. J . Catal. 1985, 36, 363. Ozawa. J. K.; Porter, R. F.; Humble. J. R. Oil Gas J . 1964. 62(6), 101. Sandford, R. A.; Erickson. H.; Gossett, E. C.; Van Petten, S. L. Oil Gas J . 1962, 60(35), 92. Hydrocerbon Process. 1962, 47(7), 103. Skinner, D. A. Ind. Eng. Chem. 1952, 4 4 , 1159. Upson. L.; Jaeras. S.; Dalln, I. Oil Ges J . 1982, 135. Valkomlc, V. Trace Elements in Petrobom; Petroleum: Tulsa, OK, 1978; pp 45, 72-77. Yoo. J. S.; Burk, E. H.; Voss, A. P., unpublished work.
Received f o r review July 31, 1985 Accepted April 21, 1986
