Regeneration of Spent Resid Fluidized Catalytic Cracking Catalyst by

Jan 22, 2003 - The average amounts of metal poisons in the LC3R E-cat were 5700 ppm for V, 4250 ppm for Ni, and 3650 ppm for Fe. Some coke remains on ...
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Ind. Eng. Chem. Res. 2003, 42, 736-742

Regeneration of Spent Resid Fluidized Catalytic Cracking Catalyst by Removing Metal Poisons Such as V, Ni, and Fe Sang Ku Park,† Hee Jung Jeon,† Kwang Seop Jung,‡ and Seong Ihl Woo*,† Department of Chemical and Biomolecular Engineering & Center for Ultramicrochemical Process Systems (CUPS), Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea, and Fuel Research Team, Daeduck Central Research Center, LG-Caltex Oil Corporation, 104-4 Munji-dong, Yuseong-gu Daejon 305-380, Republic of Korea

Modified Demet III and Demet IV processes were studied to regenerate the spent resid fluidized catalytic cracking (RFCC) catalyst by removing metal poisons. A total of 33.1 wt % of V, 89.2 wt % of Ni, and 67.7 wt % of Fe were removed by modified Demet III, and 37.3 wt % of V was selectively removed by modified Demet IV. The results of a microactivity test (MAT) showed that the activity and selectivity of the regenerated catalysts were considerably enhanced. It was proven by the results of MAT, unit cell size of zeolite, and Brunauer-Emmett-Teller surface area and pore volume that the severe condition for the removal of poisonous metals such as sulfidation and calcination at excessively high temperature and washing with only oxalic acid caused destruction of catalyst structure and consequently did not rejuvenate the spent RFCC catalysts though lots of metal poisons were removed. The regenerated catalysts by Demet IV were tested in a Davison circulation riser (DCR), and the results showed that the conversion and gasoline yield of regenerated catalysts were increased without causing any operating problem. 1. Introduction The fluidized catalytic cracking (FCC)/resid fluidized catalytic cracking (RFCC) process is used to obtain high value added product gasoline by cracking residual oil. The worldwide demand of FCC/RFCC catalysts is roughly estimated to 438 000 ton/year in 2000. Generally, residual oil has a lot of heavy metals such as V, Ni, and Fe that cause deactivation of catalysts. Under the RFCC operating conditions, almost 100% of these metal contaminants deposits on the catalyst surface. Vanadium and nickel are particularly noticed because they are present in high concentrations and have the most detrimental effects on the cracking performance of the RFCC catalyst. Nickel deposits on the catalyst surface and promotes dehydrogenation reactions, consequently increasing yields of coke and hydrogen while decreasing gasoline production, but it has no effect on the stability or life of the zeolite component of the catalyst. Nickel on a FCC catalyst exists in two primary structures, dispersed nickel oxide and nickel aluminate. The oxide structure is favored initially as Ni is deposited on the catalyst, but aluminate formation occurs with catalyst aging. Ni-promoted dehydrogenation activity is decreased with decreasing nickel oxide concentration. Vanadium also deposits on the catalyst surface, but unlike nickel, it migrates through the catalyst and undergoes detrimental reactions. Steam in the regenerator converts V2O5 to vanadic acid (H3VO4), which easily destroys the zeolites by forming vanadate complexes such as Na2OV2O5, Na2OV2O4‚5V2O5, and NiOV2O5 with zeolite and the rare-earth metals. The zeolite is destructed by formation of a low-melting * Corresponding author. Telephone: +82-42-869-3918. Fax: +82-42-869-8890. E-mail: [email protected]. † Korea Advanced Institute of Science and Technology. ‡ LG-Caltex Oil Corp.

eutectic mixture with sodium at the regenerator condition. Catalysts containing vanadium in the reduced +4 state make much less coke and more gasoline than the same catalysts in the oxidized +5 state. Vanadium contamination reduces conversions 3-4 times as much as an equivalent amount of nickel, also reduces gasoline yield about 1.2 times as much as nickel, and increases hydrogen and coke yields 0.5-0.4 times as much as nickel. Also, Cu, Fe, and Ca increase yields of gas and coke.1 Most of the spent catalysts were discarded for landfill or reutilized for cement, wastewater-filtering agent, soil improver, asphalt, and lagging material.2 A demetallization process, namely, the Demet process, which regenerates FCC/RFCC catalysts by removing metal poisons on the catalysts, has been developed. Atlantic Richfield in 1969 developed the Demet II process that consisted of three main steps: sulfidation of the metal contaminants with H2S, reductive chlorination of the resulting metal sulfides, and washing of the metal chlorides remaining on the catalyst off the catalysts. The chlorination process causes an environmental problem, giving off HCl and SO2 in the regenerator and causing corrosion of the RFCC unit. Therefore, the Demet II process was altered to Demet III and IV processes to cope with those problems at the cost of good metal removal efficiency by ARCO Petroleum Products Corp. The reductive chlorination step in the process was replaced with a simple air-oxidation reaction in the Demet III process. The metal sulfides resulting from the first step are oxidized to readily washable moieties such as sulfate, thiosulfate, and dithionate by the air-oxidation reaction, which are subsequently washed off the catalyst, and then a more environmentally friendly demetallization process named Demet IV was developed, which consisted of two steps, air calcination and simple washing.3 The most deleterious metal, vanadium, is selectively removed by the Demet IV process. A total of 48 wt % of V, 86 wt % of

10.1021/ie020515u CCC: $25.00 © 2003 American Chemical Society Published on Web 01/22/2003

Ind. Eng. Chem. Res., Vol. 42, No. 4, 2003 737 Table 1. Regeneration Conditions and Removal Rates of Metals in Demet IIIa removal rate (%) DMIII#1 DMIII#2 DMIII#3 DMIII#4 DMIII#5 DMIII#6 DMIII#7 DMIII#8 DMIII#9 DMIII#10 DMIII#11 a

sulfidation

washing

V

Ni

Fe

Al wt %

H2S (9.69%, H2 balance)/730 °C/4 h H2S (9.69%, H2 balance)/730 °C/4 h H2S (9.69%, H2 balance)/800 °C/4 h H2S (9.69%, H2 balance)/730 °C/4 h H2S-CO (8:2)/730 °C/4 h H2S-CO(8:2)/730 °C/4 h H2S-CO (8:2)/730 °C/4 h H2S-CO (8:2)/760 °C/4 h H2S-CO (8:2)/780 °C/4 h H2S-CO (9:1)/760 °C/4 h H2S-CO (7:3)/760 °C/4 h

oxalic acid oxalic acid + H2O2 oxalic acid oxalic acid + Al impregnation + H2O2 oxalic acid + H2O2 SO2 + H2O2 oxalic acid oxalic acid + H2O2 oxalic acid + H2O2 oxalic acid + H2O2 oxalic acid + H2O2

12.7 21.9 19.2 20.9 26.2 23.4 24.4 28.9 33.1 26.6 29.6

62.9 66.7 69.2 67.5 71.8 71.3 57.2 82.8 89.2 74.5 84.0

41.5 42.0 67.2 39.7 53.8 19.6 52.6 57.5 67.7 53.8 55.1

15.9 15.7 15.9 16.8 15.2 16.5 15.2 15.5 15.3 15.5 15.4

Oxidation condition: air/360 °C/25 min.

Ni, and 55 wt % of Fe were removed by Demet III, and 50-70 wt % of V was removed by Demet IV. The demetallization procedure remarkably improved the catalytic activity and selectivity, which was close to that of the virgin catalyst.2 This study was intended to develop the optimum condition for regeneration that can be applied to LC3R E-cat (equilibrium catalyst) used in LG-Caltex Oil Corp. by modifying the Demet III and IV processes. 2. Experimental Section LC3R E-cat withdrawn from the RFCC unit of LGCaltex Oil Corp. was used for these studies. The average amounts of metal poisons in the LC3R E-cat were 5700 ppm for V, 4250 ppm for Ni, and 3650 ppm for Fe. Some coke remains on the E-cat though hydrocarbon and coke are removed in the regenerator of the commercial unit. Therefore, it was removed from the E-cat under air flow at 640 °C for 4 h before sulfidation. A fluidized-bed-type quartz reactor was used for all solid-gas reactions including coke removal, sulfidation, and air oxidation. A total of 15-40 g of E-cat was used. 2.1. Modified Demet III Process. 2.1.1. Sulfidation. The sulfiding step was conducted with changing gas composition, flow rate, and temperature to find the optimum condition. A total of 9.69% H2S (H2 balance) and 70-90% H2S (CO or N2 balance) were used as sulfiding gas in the temperature range of 730-800 °C at a flow rate of 100 cm3/min for 2-4 h. 2.1.2. Air Oxidation. After sulfidation and cooling to room temperature under N2, oxidation was performed in the temperature range of 300-400 °C at a flow rate of 100 cm3/min for 15-35 min. This reaction was carefully controlled because it is exothermic and excessive oxidation converts the metal sulfides to metal oxides that act as poisons and are nonwashable compounds in the washing medium. 2.1.3. Washing. Oxalic acid, SO2 + H2O2, and oxalic acid + H2O2 were tested as washing media to remove the converted metal poisons formed by the solid-gas reaction. “A + B” means washing with A and then with B. A total of 1 wt % of an oxalic acid solution, a SO2saturated solution formed by purging SO2 gas into deionized water, and a H2O2 solution with 1 g of H2O2/ 100 g of catalysts were used as washing media, respectively. Washing was conducted two to three times at 70-80 °C for 2-5 min in the individual washing step. After washing, filtering and drying in an oven at 110 °C for 24 h were done. 2.2. Modified Demet IV Process. 2.2.1. Calcination. Vanadium oxides exist in various oxidation states

during the RFCC process. Only vanadium pentoxide has a good solubility in washing media such as water or weak acid. Vanadium oxides with various oxidation states are converted to vanadium pentoxides during the calcination under O2. This reaction was conducted with 21-100% O2 (N2 balance) in the temperature range of 730-815 °C at a flow rate of 100 cm3/min for 1-4 h with and without steam. 2.2.2. Washing. Deionized water, oxalic acid, deionized water + SO2 + H2O2, and deionized water + H2O2 were tested as washing media to remove vanadium pentoxide formed by calcination. Concentrations of each solution were the same as those of the Demet III method. Washing was conducted two to three times at 70-80 °C for 2-5 min. After washing, filtering and drying in an oven at 110 °C for 24 h were done. 2.3. Characterization. Metal contents on the regenerated catalysts were analyzed with X-ray fluorescence (XRF; Rigaku, RIX-200, Japan). The X-ray diffraction (XRD) results were obtained using a Rigaku D-MAXRC diffractometer and Cu KR radiation (λ ) 1.5405 Å) to measure the unit cell size (UCS) of zeolite, the main active site of the catalyst according to ASTM D-394291. A microactivity test (MAT; Xytel Automat modified at LG-Caltex Oil Corp.) was performed to estimate the catalytic activity and selectivity. The catalysts were pretreated under air at 700 °C for 20 min before MAT. The catalyst-to-oil ratio was 5.0 (5 g of catalyst and 1 g of O/M feed). A fluidized-bed-type stainless steel reactor was used at a reaction temperature of 530 °C. The catalyst was contacted with a preheated feed at 150 °C that was injected into the reactor at 36.5 bar. The reacted catalysts were regenerated at 700 °C with air, and the amount of coke on the reacted catalysts was calculated with CO2 analyzer during the regeneration. The sulfur contents of the catalysts after sulfiding in Demet III were analyzed with an elemental analyzer (EA; EA1110-FISONS). The automatic volumetric sorption analyzer (Micromeritics ASAP 2000) was used to determine the surface area and pore volume of the catalysts. A Davison circulation riser (DCR; Grace Davison), which is a type of circulation riser, was performed at LG-Caltex Oil Corp. to estimate the catalytic properties of the regenerated catalysts more accurately than MAT. A total of 4 kg of catalysts is used in DCR. 3. Results and Discussion 3.1. Modified Demet III Process. The representative regeneration conditions and the removal rate of metal poisons were shown in Table 1. The optimum

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Figure 1. Effect of the sulfiding temperature on the removal of metals.

Figure 2. Effect of the washing medium on the removal of metals.

oxidation condition was at 360 °C for 25 min with air flow, which was determined by way of comparing the amounts of removed metal poisons with a changing oxidation temperature from 315 to 370 °C for 15-40 min at the same sulfiding and washing conditions. This oxidation condition was fixed during the whole Demet III process. The maximum removal rates of metal poisons with sulfidation under 9.69% H2S (H2 balance) at 730 °C for 4 h merely were 12.7 wt % of V, 62.9 wt % of Ni, and 41.5 wt % of Fe by washing with oxalic acid and 21.9 wt % of V, 66.7 wt % of Ni, and 42.0 wt % of Fe by washing with oxalic acid + H2O2. The mixture of H2S and reducing gas such as hydrogen and carbon monoxide was used for more effective removal of metal poisons.4 For the purpose of increasing the removal rate, the sulfiding gas was changed to a mixture gas of H2S (70-90 mol %) and CO, and the sulfiding temperature was increased to 800 °C. As shown in Table 1 and Figure 1, the removal rate of poisonous metals was increased by sulfiding with 8:2 H2S-CO at higher temperature. Higher sulfur contents in the sulfided catalysts in Table 2 showed that sulfidation with 8:2 H2S-CO at higher temperature more effectively converted poisonous metals to metal sulfides which could be oxidized to washable

Table 2. Sulfur Level and the UCS of Zeolite after Sulfidation sulfidation condition

sulfur (wt %)

UCS (Å)

H2S (9.69%, H2 balance)/730 °C/4 h H2S (9.69%, H2 balance)/800 °C/4 h H2S-CO (8:2)/730 °C/4 h H2S-CO (8:2)/760 °C/4 h H2S-CO (8:2)/780 °C/4 h

0.26 0.53 0.48 0.52 0.64

24.270 24.166 24.269 24.253 24.238

moieties such as sulfate and thiosulfate by an oxidation step. However, as shown in Table 2, the UCS of zeolite was reduced as sulfiding temperature increased above 730 °C regardless of the sufiding gas. Namely, sulfidation at excessively high temperature caused a reduction of the UCS of zeolite. The UCS of zeolite was measured to estimate the degree of destruction of the regenerated catalysts indirectly. The UCS shows the number of acid sites of the zeolite, and a larger UCS value means a higher number of acid sites on the zeolite. The average number of acid sites per unit cell is 3.5, 4.6, 5.8, and 7.0 respectively as UCS changes to 24.22, 24.23, 24.24, and 24.25 Å in Y zeolite.5 That is, the reduced UCS indicates that zeolite was destroyed because of sulfidation at excessively high temperature though the removal rate of metal poisons was increased. Therefore, the

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Figure 3. MAT results of regenerated catalysts by Demet III. Table 3. Surface Area and Pore Volume of Regenerated Catalysts by Demet III

fresh E-cat (LC3R) DMIII#2 DMIII#4 DMIII#5 DMIII#6 DMIII#7 DMIII#8 DMIII#9

BET surface area (m2/g)

micropore area (m2/g)

micropore volume (cm3/g)

BJH desorption cumulative pore volume of pores between 17 and 3000 Å diameter (cm3/g)

209.2 154.1

151.5 110.4

0.0696 0.0492

0.1085 0.1243

166.6 158.7 178.8 152.9 185.7 182.2 191.2

113.3 110.8 118.2 107.4 105.1 120.1 117.8

0.0506 0.0488 0.0523 0.0476 0.0473 0.0527 0.0524

0.1438 0.1313 0.1463 0.1312 0.1672 0.1513 0.1602

optimum sulfiding temperature exists to remove more poisonous metals without damaging the structure of catalysts. Three types of washing media, SO2 + H2O2, oxalic acid, and oxalic acid + H2O2, were tested to find out the most effective one. Figure 2 showed that oxalic acid + H2O2 could remove more poisonous metals than the others. Oxalic acid was not effective for the removal of Ni, and SO2 + H2O2 was not suitable for the removal of Fe. However, oxalic acid removed aluminum at the same time, as shown in Table 1. The results of BET surface area and pore volume in Table 3 showed that the catalytic structure of the regenerated catalysts by Demet III was changed in comparison with fresh and E-cat, especially in the case of washing with oxalic acid and sulfidation at higher temperature. The BET surface area and pore volume were increased by removing the metal compounds blocking the pore of the catalyst and simultaneously by forming new large pores resulting from the removal of aluminum in the catalytic structure. However, in the cases of DMIII#4 that washed with

oxalic acid + Al impregnation + H2O2 and DM#6 that washed with SO2 + H2O2, the BET surface area and pore volume were similar to those of E-cat after poisonous metals were removed. That is, removal of poisonous metals by washing with oxalic acid caused the change of pore distribution of the catalysts by simultaneously removing some aluminum included in the catalytic structure. It is known that metal compounds such as vanadium pentoxide, nickel and iron aluminate (spinel structure), and metal oxides cause pore-mouth plugging and lead to its deactivation.6 Increased micropore area and volume that are regarded as those of zeolites indicated that those compounds which had caused poremouth blocking were removed by the Demet III process. The results of MAT in Figure 3 showed the activity and selectivity of the regenerated catalysts by a modified Demet III method. In the cases of DMIII#2, DMIII#4, DMIII#5, DMIII#6, and DMIII#8, the catalytic properties were considerably improved. The conversion and gasoline yield were increased by about 6-9% and 5-7% individually, and the reduction rates of the coke factor and residual oil (640 °C + bottoms) which was not cracked were about 30-45% and 40-60%, respectively. As known from the results of the UCS of zeolite and BET surface area and pore volume, the regenerated catalysts, DMIII#9 sulfided at 780 °C and DMIII#7 washed with only oxalic acid, were not rejuvenated, though lots of metal poisons were removed, but rather the catalytic activity and selectivity got worse; that is, the gasoline yield was decreased to about 4-6%, and conversions were not improved because of destruction of the zeolite structure. Especially, DMIII#7 washed with only oxalic acid produced hydrogen significantly. Those Demet conditions should not be used as regeneration processes of spent RFCC catalysts because the purpose of the Demet process is not to remove lots of

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Figure 4. MAT results of regenerated catalysts by Demet IV. Table 4. Regeneration Conditions and Removal Rates of Metals in Demet IV

DMIV#1 DMIV#2 DMIV#3 DMIV#4 DMIV#5 DMIV#6 DMIV#7 DMIV#7-1 DMIV#7-2 DMIV#7-3 DMIV#7-4

calcination

washing

removal rate of vanadium (%)

800 °C/air/1 h 800 °C/35% O2/1 h 730 °C/air/4 h/5% steam 815 °C/O2/4 h 800 °C/air/1 h 800 °C/air/1 h 800 °C/air/1 h 800 °C/air/1 h, DM#7 twice 800 °C/air/1 h, DM#7 three times 800 °C/air/1 h, DM#7 four times 800 °C/air/1 h, DM#7 five times

oxalic acid oxalic acid oxalic acid oxalic acid H 2O H2O + SO2 + H2O2 H2O + H2O2 H2O + H2O2 H2O + H2O2 H2O + H2O2 H2O + H2O2

20.6 23.2 23.4 30.9 18.1 23.4 23.1 30.5 34.3 36.2 37.3

metal poisons as much as possible but to rejuvenate the spent catalysts and reuse them. The washing with oxalic acid + H2O2 in DMIII#5 under the same sulfidation and oxidation conditions could remove more iron, about 34 wt %, than that with SO2 + H2O2 in DMIII#6 but also removed about 1% aluminum simultaneously. Aluminum exists as the forms of zeolite structure, extraflamework alumina, alumina, silica-alumina, and nickel and iron aluminate on the matrix.7 The results of BET surface area and pore volume and MAT showed that a small portion of the removed aluminum by washing with oxalic acid + H2O2 came from the zeolite structure of the catalysts; namely, washing with oxalic acid + H2O2 did not destroy the zeolite structure as known from the fact that the catalytic performance was enhanced. The activity and selectivity of DMIII#5 and DMIII#6 were similar to each other, but the H2/CH4 selectivity was better in DMIII#5 than in DMIII#6 because of more removed Fe. DMIII#4 including three washing steps, washing with oxalic acid, adding alumina that was removed because of washing with oxalic acid, and washing with H2O2, can be selected as one of the

desirable Demet III methods because the catalytic activity and selectivity of DMIII#4 were significantly enhanced as shown in Figure 3 and the alumina on the catalyst can play an important role as the metal trap of Ni, Fe, and V during the RFCC process. Additional studies to estimate the stability of the regenerated catalysts and to add metal traps such as alumina and MgO into the regenerated catalysts have been conducted. 3.2. Modified Demet IV Process. The experimental study was performed to optimize the Demet IV process by changing the conditions of calcination including temperature, time, volume percent of O2, and steam and washing media. The representative regeneration conditions and removal rate of metal poisons in the Demet IV process were shown in Table 4. As known, nickel and iron were little removed; namely, only vanadium was removed by the Demet IV process. It was observed by the results of DMIV#1, DMIV#2, and DMIV#3 in Table 4 that a higher volume percent of O2 and 5% steam at the calcinations step could increase the removal rate of vanadium by about 3-4 wt %. However, if the process-

Ind. Eng. Chem. Res., Vol. 42, No. 4, 2003 741 Table 5. Surface Area and Pore Volume of the Regenerated Catalysts by Demet IV BJH desorption cumulative pore BET volume of pores surface micropore micropore between 17 and area area volume 3000 Å diameter (m2/g) (m2/g) (cm3/g) (cm3/g) fresh E-cat (LC3R) DMIV#4 DMIV#6 DMIV#7 DMIV#7-2 DMIV#7-4

209.2 154.1 168.0 151.0 152.9 154.5 149.6

151.5 110.4 108.3 108.4 108.0 107.0 106.2

0.0696 0.0492 0.0478 0.0483 0.0488 0.0477 0.0475

0.1085 0.1243 0.1466 0.1286 0.1278 0.1239 0.1223

Table 6. UCS of Zeolite of the Regenerated Catalysts by Demet IV E-cat UCS (Å) 24.242

DMIV#2 DMIV#4 DMIV#6 DMIV#7 DMIV#7-4 24.256

24.247

24.275

24.266

24.247

Table 7. DCR Results of Regenerated Catalysts by Demet IV

conversion coke factor dry gas (H2+C1+C2) gasoline yield 640 °C + bottoms

LC4R E-cat

5:5 mixture of regenerated catalysts by Demet IV and LC4R E-cat

69.89 9.43 3.79 44.84 13.80

74.23 9.56 3.73 47.04 10.79

ing cost is considered, the calcination with air at 800 °C for 1 h was more economical than the others.8 H2O, oxalic acid, H2O + H2O2, and H2O + SO2 + H2O2 were tested to determine the most effective washing medium. As shown by the results of DMIV#1, DMIV#5, DMIV#6, and DMIV#7 in Table 4, the removal rate of vanadium by washing with H2O + H2O2 was similar to that with H2O + SO2 + H2O2, and the regenerated catalysts by the two washing media also had catalytic properties similar to those shown in Figure 4. Therefore, H2O + H2O2 not using the hazardous SO2 was more environmentally friendly and economical than H2O + SO2 + H2O2 in the Demet IV process. A total of 30.9 wt % of vanadium was removed by the single Demet IV process of DMIV#4. Though lots of vanadium was removed, the UCS of zeolite was 24.247 Å, which was a reduced value in comparison with those of DMIV#2, DMIV#6, and DMIV#7 as shown in Table 6, which indicates that the calcinations at 815 °C for 4 h caused destruction of the zeolite structure. There was a limit to the removal of vanadium by a single Demet IV process because equilibrium exists between washable V2O5 and nonwashable moieties, V2O3 and V2O4 (2V2O4 T V2O5 + V2O3).3 After removal of vanadium by the first Demet IV method, the remaining vanadium on the regenerated catalysts reaches another equilibrium among the vanadium oxides during the calcination step of the repeated Demet IV process and can be additionally removed by the washing step. Practically, the procedure of DMIV#7 was repeated five times to remove vanadium additionally. A total of 37.3 wt % of vanadium was removed by five repetitions, but the additional removal rate of vanadium was gradually reduced as the number of times of repetition was increased, which means that it is difficult to remove vanadium over 50 wt % by the Demet IV process. This is because a stronger vanadium trap than before such as MgO exists in recent RFCC catalysts. The UCS of the zeolite of DMIV#7-4 was the same as

that of DMIV#4, which also indicates that the zeolite structure was destroyed by five repetitions of the DMIV#7 process. It was observed, as shown in Table 5, that the BET surface area and pore volume of the regenerated catalysts by the Demet IV method were little changed except DMIV#4 including washing with oxalic acid in comparison with E-cat. It was proven again that washing with oxalic acid simultaneously removed aluminum and consequently made some larger pores. The results of MAT in Figure 4 showed that the catalytic activity and selectivity of the regenerated catalysts by the Demet IV method were enhanced as good as those by the Demet III process despite the fact that only vanadium was removed; that is, the conversion and gasoline yield were increased to about 4-5% and 2-9% individually, and the reduction rates of the coke factor and residual oil (640 °C + bottoms) were about 20-25% and 20-30%, respectively, which proved that vanadium is the most detrimental poison to the catalysts and nickel and iron oxides are converted to nickel and iron aluminates, which are inert to the catalytic performance during the calcinations in the Demet IV process.9 Though the amounts of removed vanadium of DMIV#6 and DMIV#7 were 7-14% less than those of DMIV#4 and DMIV#7-4, the catalytic activity and selectivity were very similar to each of them as shown in Figure 4, which indicates that severe regeneration conditions of DMIV#4 and DMIV#7-4 destroyed the zeolite structure at the cost of more removal of vanadium as shown by the results of the UCS of zeolite. Like Demet III, additional research is required to estimate the deactivation rate and stability of the regenerated catalysts before using them as the replacement of fresh catalysts. The 5:5 mixtures of the catalysts regenerated by the Demet IV process and LC4R E-cat and full LC4R E-cat were tested in DCR. The fluidized-bed-type quartz reactor was utilized to calcine 600 g of spent catalysts under air flow at 800 °C for 1 h, and the calcined catalysts were washed with H2O + H2O2. As a result, 18.9 wt % of vanadium was removed. The DCR results in Table 7 showed that the replacement of 50 wt % of E-cat with regenerated catalysts provided an increase of the conversion of about 4.34% and an increment of the gasoline yield of about 2.20%, and dry gas and coke production were similar to each other without causing any operating problems. 4. Conclusion The experiments to optimize the regeneration condition that can be applied to LC3R E-cat were conducted. Sulfidation at higher temperature was effective to convert metal poisons on the catalysts into metal sulfides, and oxalic acid + H2O2 was the most effective washing medium in Demet III. H2O + H2O2 not using the hazardous SO2 was a more environmentally friendly and economical washing medium than H2O + SO2 + H2O2 in Demet IV. It was proven that the severe conditions for the removal of metal poisons such as sulfidation and calcination at excessively high temperature and washing with only oxalic acid caused destruction of the catalytic structure though lots of metal poisons were removed. The results of DCR showed an increase of the conversion of about 4.34% and an increment of the gasoline yield of about 2.20% by replacing half of E-cat with generated catalysts by Demet IV. Consequently, the activity and selectivity of E-cat could be enhanced without damaging the catalytic

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properties by removing metal poisons such as V, Ni, and Fe through the Demet process. However, additional research is required to evaluate the stability and deactivation rate of the regenerated catalysts, which can provide a clue to determining whether the regenerated catalysts can be used in the commercial process as the replacement of fresh catalysts or not. Acknowledgment This research was funded by LG-Caltex Oil Corp. as Project BK 21 and by Center for Ultramicrochemical Process Systems (CUPS) sponsored by KOSEF. Literature Cited (1) Otterstedt, J. E.; Gevert, S. B.; Ja¨ra˚s, S. G.; Menon, P. G. Fluid Catalytic Cracking of Heavy (Residual) Oil Fractions: A Review. Appl. Catal. 1986, 22, 159. (2) Yoo, J. S. Metal Recovery and Rejuvenation of Metal-Loaded Spent Catalyst. Catal. Today 1998, 44, 27. (3) Yoo, J. S.; Burk, E. H.; Karch, J. A.; Voss, A. P. Demetalation Chemistry: Control of Vanadium on Fluid Cracking Catalyst. Ind. Eng. Chem. Res. 1990, 29, 1183.

(4) Burk, E. H., Jr.; Yoo, J. S.; Karch, J. A.; Sun, J. Y. Catalyst demetallization by converting the metal poisons to a sulfur containing metal compound having a defined low amount of sulfur. U.S. Patent 4,293,403, 1981. (5) Pine, L. A.; Maher, P. J.; Wachter, W. A. Prediction of Cracking Catalyst Behavior by a Zeolite Unit Cell Size Model. J. Catal. 1984, 85, 466. (6) Yoo, J. S.; Karch, J. A.; Burk, E. H., Jr. Rejuvenation process for Fluid Cracking Catalyst. Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 549. (7) Elvin, F. J.; Otterstedt, J. E.; Sterte, J. In Processes for Demetalization of Fluid Cracking Catalysts; Occelli, M. L., Ed.; ACS Symposium Series 375; American Chemical Society: Washington, DC, 1988; p 17. (8) Cho, S. I.; Jung, K. S.; Woo, S. I. Regeneration of spent RFCC catalyst irreversibly deactivated by Ni, Fe, and V contained in heavy oil. Appl. Catal. B 2001, 33, 249. (9) Woolery, G. L.; Farnos, M. D.; Quinones, A. R.; Chin, A. In Fluid Cracking Catalyst; Ocelli, M. L., O’Connor, P., Eds.; Marcel Dekker: New York, 1997; p 51.

Received for review July 15, 2002 Revised manuscript received December 3, 2002 Accepted December 3, 2002 IE020515U