Ind. Eng. Chem. Res. 1992,31,487-490
487
Reforming Catalyst Made from the Metals Recovered from Spent Atmospheric Resid Desulfurization Catalyst Fu-Ming Lee,* Ronald D. Knudsen, and Dennis R. Kidd Phillips Research Center, Phillips Petroleum Company, Bartlesville, Oklahoma 74004
The metals deposited on spent atmospheric resid desulfurization (ARDS) catalyst can be effectively removed by acid extraction. We discovered that a reforming catalyst can be prepared by impregnating a suitable catalyst support with this metal-laden extraction liquor. Since nickel and iron oxides have a detrimental effect on the performance of the reforming catalyst, aqueous solution of oxalic acid was used to selectively extract vanadium (excluding nickel and iron) from spent ARDS catalyst for the catalyst preparation. Catalyst prepared with the recovered vanadium and other minor elements showed significant dehydrocyclization activity to convert paraffins to aromatics. For example, in a nonoptimized fluidized-bed reactor, this catalyst can improve the research octane number of a paraffinic naphtha from 55 to 87 with approximately 81 wt % liquid yield. Hydrogen pretreatment to reduce vanadium on the catalyst can substantially decrease the catalyst activity and selectivity.
Introduction Vanadium and nickel are the major heavy metal contaminants in the heavy crude oils or residual oils. During hydrotreating of heavy oils in a typical atmospheric resid desulfurization (ARDS) unit to remove metal contaminants and sulfur, the catalysts are gradually deactivated by metal deposits of mainly nickel and vanadium. Regeneration of these ARDS catalysts is attractive from both economic and environmental viewpoints. A number of different approaches for regenerating the ARDS catalysts have been reported. Among these are chlorination and vaporization of the volatile vanadium tetrachloride (Yoshida et al., 1980),extraction with a hetropoly acid such as molybdophosphoric acid (Silbernagel et al., 1981; Mohan et al., 1981), extraction with aqueous ammonium carbonate (Gutnikov, 1971),or extraction with complexing reagents such as oxalic or citric acids (Beuther and Flinn,1963; Farrell and Ward, 1978; Hernandez, 1982). An examination of metals extraction from spent ARDS hydrotreating catalysts provided citric and oxalic acid extracts containing significant amounts of vanadium. A potential, beneficial utilization of these extracts is the subject of this paper. The transition metal oxides (including vanadium oxides) have long been recognized as having dehydrogenation activity for hydrocarbons. However, the activity of supported and unsupported vanadium oxides has been extensively studied mainly as oxidation catalysts. A comprehensive review on this subject was made by Wainwright and Foster (1979). Although there has been some earlier work on the use of vanadium oxides for dehydrogenation and dehydrocyclization (DHC) (Richardson and Rossington, 1969; Wang et al., 1985),these reactions have not been extensively investigated. Only recently, one of the authors of this article made an in-depth study on supported vanadium oxides for DHC reactions (Lee and Schaffer, 1988). The study showed that vanadium pentoxide supported on high-surface area silica has significant dehydrocyclization activity to convert paraffins into aromatics. The purpose of this investigation is to determine if a DHC (reforming) catalyst can be produced by impregnating a suitable catalyst support with the extraction liquor of spent hydrotreating catalyst. The liquor contains significant amounts of vanadium and other transition metals. Experimental Section Metal Extractions from Spent Hydrotreating Catalyst. 1. Citric Acid Extraction. Spent heavy oil hy-
Table I. Metals Content of Acid Extraction Solutions' metal concn, ppm metal concn, ppm metal citric acid oxalic acid metal citric acid oxalic acid Ag 0 7 Mn 12 2 7150 A1 6200 Mo 1530 167 65 As 66 Na 639 489 B 0 6 Ni 15000 111 Ba 0 15 P 123 59 164 Ca 292 Si 715 616 co 692 0 Ti 31 14 Cr 44 31 v 21000 18000 20 Fe 2650 Zn 183 0 41 Mg 96 The metal contents were analyzed by inductively coupled plasma (ICP) spectrometry.
drotreating catalyst was extracted with warm toluene to remove residual oil. After subsequent extraction with hexane and drying in a vacuum desiccator, the spent catalyst was extracted with 10% citric acid for I5 min at 95-100 "C. After catalyst extraction and filtration, the citric acid solution was dark in color and was reduced to one-third of its original volume. The metals content of this liquor is shown in Table I. 2. Oxalic Acid Extraction. Spent heavy oil hydrotreating catalyst was extracted with warm toluene to remove residual oil. After subsequent extraction with hexane and vacuum drying, the spent catalyst was extracted with an 8% oxalic acid solution for 60 min at 100 "C. After filtration, the oxalic acid solution was reduced to one-third of its original volume and used for catalyst impregnation. The metals content of this liquor is also shown in Table I. goth citric acid and oxalic acid extraction liquors had about the same vanadium content, but the oxalic acid extraction liquor contained much lower iron, molybdenum, and nickel. Catalyst Preparation. To prepare a silica-supported contaminant metals catalyst, a high-surface amorphous silica (Davison Grade 62) was impregnated with the citric acid or oxalic acid extraction liquor (see Table I for detailed analyses). The high-surface silica had 340 m2/g surface, 1.15 mL/g pore volume, 0.40 g/mL bulk density, 99.68 wt % SiOz,0.02 wt % Fe203,0.06 wt % Na20, 0.02 wt % CaO, 0.09 wt % TiOz, and 0.03 wt % ZrOP The mixture was slowly dried by heating in a ceramic drying dish. The impregnated silica was then calcined in air for about 2 h to remove any carbon residue. To stabilize the metal oxides on silica, the catalyst was treated under hydrogen at 510 "C and under air at 650 "C for 10 alternating
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488 Ind. Eng. Chem. Res., Vol. 31, No. 2, 1992 Table 11. Physical Properties of the Catalystsa physical property catalyst A catalyst B catalyst C 1.59 1.51 1.50 vanadium content, wt % nickel content, wt % 1.20 0.01 0.00 aluminum content, w t % 0.48 0.59 0.00 iron content, wt % 0.20 0.00 0.00 molybdenum content, wt % 0.09 0.01 0.00 cobalt content, w t % 0.05 0.00 0.00 surface area, m2/g 195 201 236 pore volume, mL/g 0.94 0.99 0.95 "Catalyst A was prepared with citric acid extraction liquor. Catalyst B was prepared with oxalic acid extraction liquor. Catalyst C was prepared with a solution of vanadium oxobis(1-phenyl1,3-butanedionate) dissolved in hot toluene, using the same preparation procedure as for catalysts A and B.
Table 111. Dehydrocyclization Activity of the Catalysts Prepared from the Acid Extraction Liquors (Hydrocarbon Feed = n -Octane; WHSV = 1.6; Catalyst On-Stream Time = 6 min; Reaction Temperature = 560 "C) catalyst A catalyst B reaction product, wt % 4.6 2.8 hydrogen 12.7 4.9 C 1 4 4 olefins 1.2 4.9 C W 8 olefins 1.4 0.9 benzene 1.2 1.5 toluene 2.3 8.4 ethylbenzene 0.6 1.3 p-xylene 2.5 1.3 m-xylene 5.5 12.2 o-xylene 23.4 4.6 coke 59.3 54.5 conversion, wt 9i 20.8 50.0 aromatic selectivity, w t %
produced. No correction was made for this effect. The material balance for the runs to be acceptable had to be within 95 and 105 wt % . All the conversions and aromatic selectivities reported in this study are single-pass results.
FEED VAPORIZATION
u 2 M M CAPILLARY TUBE
I
SYRINGE PUMP
1
MERT GAS
Figure 1. Schematic diagram of the fluid-bed reactor.
cycles each lasting about 5 min. The physical properties of the catalyst used in this study are given in Table 11. Reactor Construction and Procedures. A schematic diagram of the fluid-bed reactor is shown in Figure 1. The reactor was made from quartz and was positioned in a high-temperature electric heated furnace. The catalyst was supported by a porous disk which allowed gas (or feed vapor) to pass through and fluidize the catalyst bed. In a normal run, about 25 g of catalyst was used. Liquid feed such as n-hexane or n-octane was fed by a Sage syinge pump (Model 351) at a controlled rate through a capillary tube into a vaporization chamber where the liquid was vaporized by furnace heat. As shown in Figure 1,reactive or nonreactive gases can be mixed with the feed vapor to control the initial feed concentration and retention time. It should be emphasized that all reactions were studied without oxygen or hydrogen in the feed stream. Also,all experiments were conducted at atmospheric pressure and a catalyst on-stream time of 6 min. Reaction products were collected in a liquid trap at 0 OC and in a gas receiver at room temperature. Liquid and gas products were analyzed by gas chromatography. Coke on catalyst was determined by weighing the reactor plus catalyst before and after regeneration. Since metals on the catalysts such as vanadium are reduced by hydrocarbon feed during a run, the coke yield determined by weighing would be less than the actual amount of coke
Results and Discussion Dehydrocyclization (DHC) Activity of the Spent Metals on Silica. The DHC activities of both catalysts A and B were determined using n-octane as the model feed in a fluidized-bed reactor. As shown in Table 11, Catalysts A contains mainly vanadium, nickel, and aluminum, and catalyst B contains the same amounts of vanadium and aluminum but no nickel. These metals were oxidized by air at 675 "C before experimentations. The reactor conditions and product yields are summarized in Table 111. Both catalysts had similar total conversions (around 55-59 wt %) but the aromatic selectivity (DHC activity) of catalyst B was as high as 50.0 wt 90,which was substantially higher than that of catalyst A. The major products for catalyst B were ethylbenzene and o-xylene (8.4 and 12.2 wt % yields, respectively) produced from straight DHC reactions of n-octane. The presence of mand p-xylenes in the products could be an indication that the feed was isomerized into branched-chain octanes followed by DHC, or that the DHC products, ethylbenzene and o-xylene, were isomerized by the catalyst. The presence of toluene and benzene in the products could be due to the de&lation of C8 aromatics or DHC of the C6 and C7 aliphatic hydrocarbons present among the cracked products. It was also noted from Table I11 that the coke and C1C4 (mainly olefiis) yields of catalyst B were much lower than those of catalyst A. These results imply that the presence of nickel and iron on catalyst A caused significant dehydrogenation and cracking of the feed, producing higher yields of hydrogen, coke, and Cl-C4 olefins, at the expense of aromatic yields in the product. Catalyst B contained basically about 1.5 wt % vanadium and 0.6 wt % aluminum. To find out which of the metal oxides on the catalyst was reaponsible for the DHC activity, we compared the performance of catalyst B with catalyst C which was prepared by impregnating pure vanadium onto the same silica support with the same procedure. The experimental results are presented in Table IV. Under the same reactor condition (1.6 weight hourly space velocity (WHSV) and 560 "C reaction temperature), catalyst B showed the same conversion as and a slightly lower DHC selectivity (50.0 vs 65.7 wt % ) than catalyst C (vanadium only catalyst). In fact, the only differences between these two catalysts were yields of ethylbenzene, o-xylene, and coke, which might be caused by the presence
Ind. Eng. Chem. Res., Vol. 31, No. 2, 1992 489 Table IV. Comparing the Activity of Spent Metals with Pure Vanadium on Silica Support (Hydrocarbon Feed = n-Octane; WHSV = 1.6; Catalyst On-Stream Time = 6 min; Reaction Temperature = 560 O C ; Reaction Pressure = Atmospheric Pressure) catalyst B catalyst C reaction product, wt % hydrogen C 1 4 4 olefins C5-C8 olefins benzene toluene ethylbenzene p-xylene m-xylene o-xylene styrene coke conversion, wt % aromatic selectivity, wt %
2.8 9.1 4.9 0.9 1.5 8.4 1.3 2.5 12.2 0.4 4.6 54.5 50.0
Table VI. Analysis of the Naphtha Used in This Study ~~~
n-butane isopentane n-pentane 2-methylpentane 3-methylpentane n-hexane methylcyclopentane and 2,2-DMP 2,4-dimethylpentane benzene 2,2,3-trimethylbutane 3,3-dimethylpentane 2-methylhexane 2,3-dimethylpentane 3-methylhexane cis-l,3-dimethylcyclopentane trans-1,3-dimethylcyclopentanane trans-l,2-dimethylcyclopentane C7 olefins n-heptane 2,2-dimethylhexane 1,1,3-trimethylpentane methylcyclopentane 2,5-dimethylhexane 2,4-dimethylhexane toluene
2.8 7.6 5.2 1.0 1.5 11.6 1.4 2.8 17.7 0.5 2.0 55.4 65.7
Table V. Effect of Reduction (by Hydrogen) on Dehydrocyclization Activity (Hydrocarbon Feed = n -Octane; Catalyst On-Stream Time = 6 min; Reaction Pressure = Atmosoheric Pressure) catalyst B catalyst C a b a b WHSV 1.6 4.0
~
wt%
~~
0.1 1.3 0.6 0.7 0.5 0.6 2.5 2.5 0.9 0.3 2.0 18.5 7.1 23.2 1.5 3.8 2.0 0.1 22.5 0.6 0.9 0.2 0.2 0.6 6.5
~~
~
reaction temp, OC reaction product, wt % hydrogen C 1 4 4 olefins C 5 4 8 olefins benzene toluene ethylbenzene p-xylene m-xylene o-xylene coke conversion, wt % aromatic selectivity, w t '70
560 2.8 9.1 4.9 0.9 1.5 8.4 1.3 2.5 12.2 4.6 54.5 50.0
1.5 16.6 4.9 1.0 1.3 3.4 1.0 1.8 4.5 2.0 41.6 31.6
510 1.1
5.0 6.9 0.4 0.6 5.1 0.4 0.9 6.9 1.9 29.8 47.8
0.4 3.3 4.3 0.1 0.2 1.2 0.1 0.3 1.6 0.4 15.2 23.0
'Catalysts were fully regenerated under air at 675 OC. bCatalysts were fully regenerated under air at 675 "C and followed by hydrogen reduction at 650 OC for 20 min.
of aluminum oxides in catalyst B or lower surface area of catalyst B (236 vs 201 m2/g). Nevertheless, we concluded that catalyst B, containing mainly vanadium extracted from the spent ARDS catalyst by oxalic acid, can be potentially used as a reforming catalyst because of ita significant DHC activity. Effects of Oxidation and Reduction on Catalyst Activity. Both catalysts B and C were used to study the effects of oxidation and reduction on the catalyst activity. For an oxidation run,the catalyst was fully oxidized before experiment, by fluidizing the catalyst bed with air at 675 "C for 20 min followed by nitrogen purge to remove excess oxygen in the reactor. For a reduction run, the catalyst was first regenerated in air at 675 "C for 20 rnin and then reduced by pure hydrogen at 650 "C for 20 min followed by nitrogen purge. The reaction conditions and product yields are summarized in Table V. As can be seen, the oxidized case for catalyst C (vanadium only) had a significantly higher activity and aromatic selectivity than the pre-reduced case (case a vs case b). This result confirms the observation of a previous investigation (Lee and Schaffer, 1988) that the oxidation state in the pre-reduced catalyst (V")is less active than the oxidation state in the calcined catalyst (predominantly V5+). The effects of oxidation and reduction for catalyst B, however, were much less predominant than that of catalyst
Table VII. Activity of Spent Metals for Improving the Octane Number of a Naphtha Stream hydrocarbon feed
WHSV catalyst catalyst-to-oil ratio catalyst on-stream time reaction temperature reaction pressure reaction products, wt % C 1 4 4 gases C5 and heavier liquid coke hydrogen RON of C5 and heavier liquid
naphtha (with RON of 55; see Table VI for component analysis) 1.7 catalyst B 4.4 6.0 rnin 575 oc atmospheric pressure 9.9 80.6 7.3 2.2 86.5
C. For the most part, the changes were quite similar in direction for both catalysts with the exception of the C1C4 olefin yield. For catalyst B, the Cl-C4 olefin yield, instead of decreasing as for catalyst C, increased substantially from 9.1 to 16.6 wt % upon pre-reduction of the catalyst. This result suggests that DHC reactions, promoted by vanadium oxides, and cracking reactions, promoted by aluminum oxides, are competing reactions on catalyst B. Upon catalyst reduction, the cracking reactions prevail because the DHC reactions are less promoted by the reduced vanadium oxides. Upgrading the Octane Number of a Refinery Naphtha Stream. The performance of catalyst B for upgrading a low-octane naphtha has been investigated. A light naphtha from a west Texas refinery were used for this study. Its boiling range was 36-115 "C, and density was 0.71 g/mL. As shown in Table VI,the detailed component analysis of this naphtha shows that the naphtha contained as high as 85 wt % paraffins and isoparaffins. These paraffii/isoparaffii can be converted to the high-odane aromatics only through very difficult DHC reactions. The reaction condition, product distribution and research octane numbers (RON) of the feed and the product 82eBin Table W. As can be seen, at a reaction temperature of 575 "C and a WHSV of 1.7, the RON of the naphtha increased from 55 to 86.5 with a liquid yield of 80.6 wt % and a coke yield of 7.3 wt %. We found that the spent catalyst can be completely regenerated in air at
490
Ind. Eng. Chem. Res. 1992,31,490-496
675 "C for 20 min. In a continuous fluidized-bed reactor, the coke on spent catalyst can be burned in the catalyst regenerator to provide all or a part of the heat required for the reforming reactions. A better performance of catalyst B can certainly be achieved if the reactor operating conditions are optimized. Although conventional reforming operation is carried out in the presence of hydrogen to maintain catalyst activity, we expect that hydrogen addition to the reactor should actually reduce the DHC activity of catalyst B due to accelerated reduction of vanadium on the catalyst. One of the authors has previously studied the deactivation of vanadium catalyst (catalyst C) in a fluid-bed reactor and found the deactivation is a first-order function of catalyst on-stream time (Lee and Schaffer, 1988). Since the catalyst is deactivated at a much slower rate than the catalytic cracking catalyst, a low-pressure, slow-moving fluid-bed reactor with a catalyst regenerator is recommended for this operation. Conclusions 1. Catalyst prepared with oxalic acid extraction liquor contained mainly vanadium oxides and showed significant DHC activity to convert n-octane to C8 aromatics. Under a nonoptimized reactor condition,this catalyst can improve the research octane number of a paraffinic naphtha (containing 85% paraffins) from 55 to 86.5with about 81 wt % liquid yield. This is a potential reforming catalyst for a fluidized-bed reactor with continuous catalyst regeneration and circulation. 2. Catalyst prepared with citric acid extraction liquor contained vanadium, nickel, and iron oxides. Nickel and iron oxides on the catalyst caused significant dehydrogenation and cracking of the feed, producing higher yields of hydrogen, coke, and light olefins, at the expense of aromatic yields in the product. 3. The DHC activity of catalyst that contains mainly vanadium oxides, depends strongly on the oxidation state of vanadium; e.g., V5+is more active than V3+. To reduce this catalyst, the activity of the minor amount of aluminum
oxides on the catalyst becomes more important in promoting cracking reactions because the predominant DHC reactions are suppressed.
Acknowledgment We thank Phillips Petroleum Company for permission to publish the results. Registry No. V, 7440-62-2;oxalic acid, 144-62-7.
Literature Cited Beuther, H.; Flinn, R. A. Technique for Removing Metal Contaminants from Catalysts. Ind. Eng. Chem. Prod. Res. Dev. 1963,2, 53-57. Farrell, D. R.; Ward, J. W. Method for Rejuvenating Catalysta in Hydrodesulfurization of Hydrocarbon Feedstock. US Patent 4,122,000,1978. Gutnikov, G. Method of Recovering Metals from Spent Hydrorefining Catalysts. US Patent 3,567,433,1971. Hernandez, J. 0. On the Use of Spent Hydrodesulfurization CataDiu. Pet. Chem. 1982,27,679-681. lysts. Prepr.-Am. Chem. SOC., Lee, F.; Schaffer, A. M. Catalytic Activity of Silica-Supported Vanadium for Paraffin Reactions. Appl. Catal. 1988,39,135-151. Mohan, R. R.; Silbernagel, B. G.; Singhal, G. H. Regeneration of Spent Hydrodesulfurization Catalysts with Heteropoly Acids and Hydrogen Peroxide. US Patent 4,268,415,1981. Richardson, P. C.;Rossington, D. R. The Activity of Transition Metal Oxides for Cyclohexane Dehydrogenation. J . Catal. 1969, 14, 175-181. Silbernagel, B. G.; Mohan, R. R.; Singhal, G. H. Regeneration of Spent Hydrodesulfurization Catalysts Employing Presulfiding Treatment and Heteropoly Acids. US Patent 4,272,400,1981. Wainwright, M. S.; Foster, N. R. catalysts, Kinetics, and Reactor Design in Phthalic Anhydride Synthesis. Catal. Rev. 1979, 19, 211-292. Wang, I.; Wu, J. C.; Chung, C. S. Dehydrogenation of Ethylbenzene and Ethylcyclohexane Over Mixed Binary Oxide Catalysts Containing Titania. AppE. Catal. 1985,16,89-101. Yoshida, T.; Ushiyama, M.; Yokoyama, T. Process for Recovering Vanadium Accumulated on Spent Catalyst. US Patent 4,216,118, 1980.
Received for review May 23, 1991 Accepted November 5, 1991
Effects of the Structure of the Polymer Support on the Substitution Reaction in a Triphase Catalysis Maw-Ling Wang* and Ho-Sheng Wu Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan, ROC
The substitution reaction of hexachlorocyclotriphosphazeneand 2,2,2-trifluorethanol in an organic solvent/alkaline solution by triphase catalysis was carried out in the present study. The main purpose of this study was to investigate the effects of the imbibed compositions, which were influenced by the internal structures of the triphase catalyst particles, on the reactivities. The effects of the structure of the polymer support, which can be related t o the factors of the degree of cross-linking, ring substitution (RS), lipophilicty of the polymer, the chloride density, and solvents, on the imbibed compositions were investigated in great detail. It was found that the reaction could be improved to obtain a high reaction rate by using a polar solvent. The experimental results suggest that a 6% degree of cross-linking with 20% RS of the polymer support is recommended to obtain a higher value of the reaction rate. The results obtained from this study provide valuable information in the search for the optimum conditions in preparing the polymer support of the triphase catalyst.
Introduction since J~~~~~~ (1951)carried out experiments to promote the rates of reaction between two immiscible reace
* To whom all correspondence should be addressed. 0888-5885/92/2631-0490$03.00/0
tanb bv addine a small amount of auaternarv ammonium
salt, phae-trak3fer catalysis has &en paidattention by many scientists. It has been considered to be one of the effective tools in the organic svnthesis of mecialitv chemicals (Starks and LiotL, 1978;Dehmlow-and Dihmlow, 1980;Weber and Gokel, 1977). However, the process for 0 1992 American Chemical Society
