Ind. Eng. Chem. Res. 1996, 35, 621-626
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RESEARCH NOTES Vanadium-Based Mixed-Oxide Catalysts for Selective Oxidation of Hydrogen Sulfide to Sulfur Kuo-Tseng Li,* Min-Ya Huang, and Wen-Da Cheng Department of Chemical Engineering, Tunghai University, Taichung, Taiwan, Republic of China
The selective oxidation of hydrogen sulfide to sulfur was studied over three vanadium-based mixed-oxide catalysts, including the binary oxides of vanadium-molybdenum, vanadiumbismuth, and vanadium-magnesium. The catalytic reaction was carried out in a fixed-bed reactor in the temperature range 200-300 °C. Strong synergistic phenomena in catalytic activity and selectivity were observed for the binary oxides. Under identical reaction conditions, the performances of the binary oxide catalysts within certain composition ranges were superior to those of the corresponding single-oxide catalysts. These synergistic phenomena suggest that the new compounds Mo6V9O40, BiVO4/Bi4V6O21, and MgV2O formed in the binary oxides are much better than the corresponding single-oxide catalysts for the selective oxidation of hydrogen sulfide. The maximum sulfur yield obtained with the vanadium-based binary mixed-oxide catalysts was 97%, which was much higher than that obtained with pure vanadium oxide (78%). Introduction The petroleum refining industry uses a hydrodesulfurization process to convert the sulfur content of petroleum fractions into hydrogen sulfide. Additionally, natural gas and coal gas also contain 0.3-3 vol % hydrogen sulfide. The highly toxic hydrogen sulfide is often converted to elemental sulfur by the Claus process. However, the recovery of sulfur in the Claus process is not complete (approximately 95-97% of sulfur is recovered) due to the limitation of thermodynamic equilibrium. Therefore, in order to meet the demand of strict environmental regulations, a tail gas treatment system is always needed in conjunction with the Claus process to eliminate the remaining hydrogen sulfide. In 1885, Chance and Claus used iron oxide to catalyze the selective oxidation of hydrogen sulfide to elemental sulfur (Thomas, 1970). Recently, a similar catalytic process (called SuperClaus) have been developed for treating the tail gas from the Claus process by selective oxidation of the remaining hydrogen sulfide to sulfur using a R-alumina-supported iron oxide/chromium oxide catalyst (Lagas et al., 1988; Terorde et al., 1993; Van Nisselrooy et al., 1993). The advantage of this selective oxidation is that it is not equilibrium limited; therefore, complete recovery of sulfur is possible. Selective oxidation of hydrogen sulfide to sulfur can be represented by the following four reactions (Terorde, 1993):
Main reaction: H2S + 1/2O2 f (1/n)Sn + H2O (n ) 6 f 8) (1) Side reactions:
H2S + 3/2O2 f SO2 + H2O
(2)
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(1/n)Sn + O2 f SO2
(3)
(3/n)Sn + 2H2O S H2S + SO2
(4)
An optimum catalyst should be able to achieve the maximum sulfur yield and the minimum sulfur dioxide generation. Vanadium-based mixed-oxide catalysts have been used extensively for the selective oxidation of hydrocarbons. Examples are vanadium-molybdate catalyst for the production of maleic anhydride from benzene (Satterfield, 1991) and for the ammoxidation of toluene to benzonitrile (Chen et al., 1994), vanadium-bismuth catalysts for the ammoxidation of toluene (Lee, 1993), and vanadium-magnesium catalysts for the oxidative dehydrogenation of alkane to alkene (Chaar, 1987). In addition, vanadium-type catalysts are used for the selective oxidation of naphthalene or o-xylene to phthalic anhydride, for the oxidation of SO2 to SO3 (Satterfield, 1991), and for the liquid-phase oxidation of hydrogen sulfide to sulfur (called the Stretford process which was developed by North Western Gas Board in 1959) (Dalrymple et al., 1989). In the Stretford process, the catalyst used for the liquid-phase oxidation of hydrogen sulfide was an aqueous solution containing vanadium salt, sodium carbonate, sodium bicarbonate, and anthraquinone disulfonic acid (ADA). The function of ADA is for the oxidative regeneration of the vanadium catalysts. In addition, Bagajewicz et al. (Bagajewicz, 1988) used an aluminum-supported vanadium oxide as a sorbent for hydrogen sulfide adsorption at 650-700 °C. Although vanadium-based catalysts have been used extensively for the oxidation of organic and inorganic chemicals, there is no information available about the use of vanadium-based mixed-oxide catalysts for the gas-phase selective oxidation of hydrogen sulfide. The paper deals with the use of vanadium-based mixed oxides for the gas-phase selective oxidation of hydrogen sulfide to sulfur, from which we have observed the © 1996 American Chemical Society
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existence of unexpected synergistic phenomena for the binary oxide catalysts. Experimental Section Catalyst Preparation and Characterization. Five single-oxide catalysts (vanadium oxide, bismuth oxide, molybdenum oxide, magnesium oxide, and iron oxide) and three vanadium-based mixed-oxide catalysts (binary oxides of vanadium-molybdenum, vanadiumbismuth, and vanadium-magnesium) were used for the selective oxidation of hydrogen sulfide to elemental sulfur. The single oxides of vanadium and bismuth were prepared by calcination in air of ammonium vanadate (NH4VO3) and bismuth nitrate (Bi(NO3)3‚5H2O), respectively, at 550 °C for 5 h. Molybdenum oxide was prepared by precipitation from ammonium molybdate ((NH4)6Mo7O24‚4H2O) with nitric acid, followed by washing, drying, and calcination at 400 °C for 8 h. Magnesium oxide was prepared by precipitation from a magnesium nitrate (Mg(NO3)2‚6H2O) with ammonium carbonate ((NH4)2CO3), followed by evaporation, drying, and calcination at 700 °C for 3 h. Iron(III) oxide was obtained from Showa Chemicals, Tokyo, Japan. The binary oxides of vanadium-molybdenum and vanadium-bismuth were prepared by mixing ammonium vanadate with ammonium molybdate and with bismuth nitrate, respectively, in a 0.1 N oxalic acid solution at 80 °C, followed by evaporation, drying, and calcination at 500 °C for 8 h. The binary oxide of vanadium-magnesium was prepared by mixing ammonium vanadate and magnesium oxide in the desired atomic proportions in 80 °C water, followed by evaporation, drying, and calcination at 550 °C for 6 h. Chemicals used for catalyst preparation were obtained from the following suppliers: ammonium vanadate, bismuth nitrate, and iron(III) oxide were from Showa Chemicals, Tokyo, Japan; ammonium molybdate was from Riedel-deHaen, Seelze, Germany; manganesium nitrate was from Janssen Chimica, Beerse, Belgium; ammonium carbonate was from Fisher Scientific Co. The phase analysis was performed by X-ray diffraction crystallography (Shimadzu XD-5), and the microscopic aspect of the catalysts was examined under the scanning electron microscope (Banseh & Lomb ARL. Nanol 2100). The specific surface areas of the spent catalysts were determined by nitrogen adsorption with a Micromeritics BET surface area analyzer (Model Gemini). Apparatus and Procedure. A schematic of the apparatus used for the measurements of catalytic properties is shown in Figure 1. Gaseous feed containing hydrogen sulfide, oxygen, and nitrogen in a molar ratio of 1:5:94 was obtained by mixing gases from three gas storage tanks. A rectangular electrically heated furnace in which the temperature could be held to within 1 °C of the desired value was used to house a packed-bed reactor. The reactor was constructed from a 0.8 m long, 0.007 m i.d. Pyrex glass tubing. The amounts of catalysts packed in the glass tubing were between 0.2 and 2 g, which was dependent on the catalyst activities. Ceramic particles were placed in front of the catalyst bed for uniform preheating. Before the measurements of catalytic properties, catalysts were presulfurized in an environment of hydrogen sulfide at 250 °C for over 12 h.
Figure 1. Schematic diagram of the experimental apparatus.
The reactor outlet led to a sulfur condenser, which served to collect the elemental sulfur produced from the selective oxidation of hydrogen sulfide. The glass tubing between the reactor outlet and the sulfur condenser was maintained at 200 °C by wrapping with a heating tape to prevent clogging. The product gas was passed through the sulfur condenser to remove elemental sulfur and was then analyzed for hydrogen sulfide and sulfur dioxide by a HP 5890 gas chromatograph equipped with a 9 m long, 80/100 mesh Propak Q column and a thermal conductivity detector. The column temperature was operated isothermally at 90 °C; the detector temperature and the injector temperature were set at 140 and 120 °C, respectively. Carrier gas was helium at 20 mL/min. The conversion of hydrogen sulfide and the sulfur selectivity were calculated using the following equations: conversion (%) ) (moles of hydrogen sulfide reacted)/(moles of hydrogen sulfide fed) × 100%; sulfur selectivity ) (moles of hydrogen sulfide reacted - moles of sulfur dioxide produced)/(moles of hydrogen sulfide reacted) × 100%. Results Catalytic Properties of Single Oxides. The catalytic properties of five single oxides for the selective oxidation of hydrogen sulfide were studied in order to compare the differences in catalytic performances between binary oxide catalysts and their corresponding single-oxide catalysts. The results obtained are presented in Table 1, which shows that the catalytic activity of the single oxides decreased in the following order: vanadium oxide > iron oxide > bismuth oxide > magnesium oxide > molybdenum oxide. Besides, the vanadium oxide catalyst also had the best sulfur selectivity. That is, vanadium oxide was the best
Ind. Eng. Chem. Res., Vol. 35, No. 2, 1996 623 Table 1. Catalytic Properties of Single Oxides for Selective Oxidation of Hydrogen Sulfide conversion (%) at 200 °C
selectivity (%) at 200 °C
conversion (%) at 220 °C
selectivity (%) at 220 °C
55.7 76 5.6 5.5 7
82.8 100 100 100 100
81 12.2 10.4 9
89 100 100 100
iron oxide (1 g) vanadium oxide (0.5 g) bismuth oxide (0.5 g) magnesium oxide (0.5 g) molybdenum oxide (2 g)
Table 2. Catalytic Properties of Vanadium-Molybdenum Mixed Oxides for Selective Oxidation of Hydrogen Sulfidea temp, (°C) 200 conv. (%) select. (%) 220 conv. (%) select. (%) 240 conv. (%) select. (%) 260 conv. (%) select. (%) 270 conv. (%) select. (%) 280 conv. (%) select. (%) spent catalyst surface area (m2/g)
V/Mo ) 1/0, H2S:O2 ) 1/5
V/Mo ) 5/1, H2S:O2 ) 1/5
V/Mo ) 2/1, H2S:O2 ) 1/5
V/Mo ) 1/1, H2S:O2 ) 1/5
V/Mo ) 2/7, H2S:O2 ) 1/5
V/Mo ) 0/1, H2S:O2 ) 1/5
V/Mo ) 2/1, H2S:O2 ) 1/1
V/Mo ) 1/1, H2S:O2 ) 1/1
49 100
86 66
80 99
43 100
37 100
∼0
71 100
28 100
53 100
90 60
87 83
61 100
45 100
∼0
76 100
38 100
58 100
76 100
59 100
∼0
79 93
52 100
68 95
82 83
74 89
87 83
69 74
73 81
82 70
74 100 84 80
4.4
4.4
3.1
2.0
3.5
7.3
a Reaction conditions: gas flowrate ) 200 mL/min with 1 vol % hydrogen sulfide; catalyst weight ) 0.2 g. conv. represents the converison of hydrogen sulfide; select. represents sulfur selectivity.
catalyst among the five single oxides studied for the gasphase selective oxidation of hydrogen sulfide to sulfur. Since the vanadium oxide had the best performance for the selective oxidation of hydrogen sulfide to sulfur, it was used for the following studies. Vanadium-Based Mixed-Oxide Catalysts. (1) Vanadium-Molybdenum Binary Oxide Catalysts. (a) Catalytic Properties. Six vanadium/molybdenum atomic ratios were studied for the binary oxide catalysts, including V/Mo ) 1/0, 5/1, 2/1, 1/1, 2/7, and 0/1. Table 2 presents the performances of these catalysts for the selective oxidation of hydrogen sulfide. Under the same reaction conditions (reaction temperature ) 200 °C, gas flowrate ) 200 mL/min, and catalyst weight ) 0.2 g), the conversions of hydrogen sulfide at V/Mo ) 5/1 and at V/Mo ) 2/1 were 86% (selectivity to sulfur was 66%) and 80% (selectivity to sulfur was 99%), respectively, which were significantly higher than catalysts with other compositions (conversions were 49% for pure vanadium oxide, 43% for V/Mo ) 1/1, 37% for V/Mo ) 2/7, and neglible for pure molybdenum oxide). The surprising findings suggest that the mixture of vanadium oxide and molybdenum oxide exhibits strong synergistic behavior in the catalytic activity for hydrogen sulfide selective oxidation. Table 2 also shows the performance of the vanadiummolybdenum binary oxide catalysts as a function of oxygen concentration (molar ratio of H2S to O2 ) 1/5 and 1/1). For catalysts with V/Mo ) 2/1 and 1/1, the maximum conversions for 100% sulfur selectivity were between 75 and 80% and were almost independent of the change in reaction temperature and oxygen concentration. For pure vanadium oxide, the selectivity at 73% conversion was only 81%, which was much smaller than the selectivity for the binary oxide catalysts (selectivity
was 100% at 73% conversion). The results suggest that the addition of molybdenum oxide into the vanadium oxide significantly improved the catalyst selectivity. (b) Catalyst Characterization. The X-ray diffractometry patterns of six vanadium-molybdenum catalyst samples are presented in Figure 2, which shows that the catalysts with V/Mo ) 5/1 and V/Mo ) 2/1 contain Mo6V9O40 and V2O5. This is consistent with the XRD studies by Lee and co-workers (Chen et al., 1994), who found that the vanadium-molybdenum binary oxide contained a new compound Mo6V9O40 when the molybdenum concentration in the binary oxide was greater than 16 mol %. As shown in Table 2, catalysts with V/Mo ) 5/1 and V/Mo ) 2/1 had higher conversion than pure V2O5 catalyst; the results suggest that Mo6V9O40 had better catalytic properties than V2O5 for the selective oxidation of hydrogen sulfide. This should be the reason for the observed synergistic phenomena for catalysts with V/Mo ) 5/1 and V/Mo ) 2/1 atomic ratio. When the concentration of molybdenum in the binary oxide was increased further, the XRD patterns in Figure 2 show that the catalysts with V/Mo ) 1/1 and V/Mo ) 2/7 contain largely Mo6V9O40 and MoO3 (the intensity of the V2O5 characteristic peaks becomes much smaller compared to those of Mo6V9O40 and MoO3 characteristic peaks). Since MoO3 is relatively inactive for the selective oxidation of hydrogen sulfide, therefore, the dilution effect of MoO3 in the binary oxides caused the decrease of conversion for catalyst with V/Mo ) 1/1 and V/Mo ) 2/7. Analysis by the scanning electron microscope for catalyst with V/Mo atomic ratio ) 2/1 and 1/1 revealed that Mo6V9O40 crystallized in a relatively large polyhedral form (the platelike material in Figure 3a should be Mo6V9O40 because we did not find such material in
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Figure 2. X-ray diffractometry patterns of catalysts with V/Mo ) (1) 0/1, (2) 2/7, (3) 1/1, (4) 2/1, (5) 5/1, (6) 1/0.
the SEM micrographs of fresh catalysts with V/Mo ) 1/0, 5/1, 2/7, and 0/1); the product obtained after reaction was amorphous (Figure 3b). The same results also can be found in the X-ray diffractometry patterns for catalyst with V/Mo atomic ratio ) 2/1 before the reaction and after the reaction, as shown on Figure 4. Figure 4b shows that the characteristic peaks of Mo6V9O40 disappeared completely after the reaction. These results suggest that the compound Mo6V9O40 was converted to an amorphous compound during the selective oxidation of hydrogen sulfide. (2) Vanadium-Bismuth Binary Oxide Catalysts. (a) Catalytic Properties. Five vanadium/bismuth atomic ratios were studied for the binary oxide catalysts, including V/Bi ) 1/0, 2/1, 1/1, 1/2, and 0/1. Table 3 presents the performances of these catalysts for the selective oxidation of hydrogen sulfide. Under the same reaction conditions (reaction temperature ) 200 °C, gas flowrate ) 100 mL/min, and catalyst weight ) 0.5 g), the conversion of hydrogen sulfide at V/Bi ) 1/2 was 94.52% (selectivity to sulfur was 100%), which was much higher than catalysts with other V/Bi ratios (conversions were 75.56% for pure vanadium oxide, 48.93% for V/Bi ) 2/1, 46.2% for V/Bi ) 1/1, and 5.56% for pure bismuth oxide). The surprising finding suggests that the mixture of vanadium oxide and bismuth oxide also exhibits strong synergistic behavior in the catalytic activity for hydrogen sulfide selective oxidation when the V/Bi atomic ratio was 1/2. It is worth noting in Table 3 that the maximum sulfur yield of 97% was obtained at V/Bi atomic ratio ) 1/1 at 260 °C. Although the catalyst with V/Bi atomic ratio ) 1/1 was much less active than the catalyst with V/Bi ) 1/2 and pure vanadium oxide, its selectivity was the best among the vanadium-bismuth binary oxides.
Figure 3. Scanning electron microscopy of (a) fresh catalyst and (b) spent catalyst with V/Mo ) 2/1.
Figure 4. X-ray diffractometry patterns of (a) fresh catalyst and (b) spent catalyst with V/Mo ) 2/1.
Ind. Eng. Chem. Res., Vol. 35, No. 2, 1996 625 Table 3. Catalytic Properties of Vanadium-Bismuth Mixed Oxides for Selective Oxidation of Hydrogen Sulfidea temp (°C) 200 conv. (%) select. (%) 210 conv. (%) select. (%) 220 conv. (%) select. (%) 230 conv. (%) select. (%) 240 conv. (%) select. (%) 260 conv. (%) select. (%) 270 conv. (%) select. (%) 290 conv. (%) select. (%) spent catalyst surface area (m2/g)
V/Bi ) 1/0
V/Bi ) 2/1
V/Bi ) 1/1
V/Bi ) 1/2
V/Bi ) 0/1
75.56 100
48.93 100
46.2 100
94.52 100
5.56 100
77.96 100
55.91 100
55.26 100
96.78 88.2
12.2 100
80.73 88.6
76.98 100
64.79 100
12.2 100
90.32 100
71.78 100
15.2 100
90.79 86.3
79.09 100
18.9 100
97.0 100
34.2 100
98.2 85.2
47.2 100
2.9
1.44
0.58
0.99
84.6 79.7 0.52
a Reaction conditions: gas flowrate ) 100 mL/min with 1 vol % hydrogen sulfide; catalyst weight ) 0.5 g.
Table 3 also shows that the maximum sulfur yields obtained for the three vanadium-bismuth binary oxides were all over 90%, which was much higher than those obtained for the pure vanadium oxide and for the pure bismuth oxide. The results suggest that the addition of bismuth oxide into the vanadium oxide significantly improved the catalyst selectivity. (b) Catalyst Characterization. Figure 5 shows the powder X-ray diffraction spectra of the fresh catalysts for the three vanadium-bismuth binary oxides, for the pure vanadium oxide, and for the pure bismuth oxide. For catalysts with V/Bi atomic ratio ) 1/2 (curve b), three distinct phases were found to exist in the catalyst, including Bi4V6O21, BiVO4, and Bi2O3. Figure 6 shows the powder X-ray diffraction spectra of the spent catalysts. For catalysts with V/Bi atomic ratio ) 1/2 (curve b), the Bi2O3 phase in the fresh catalyst was converted to Bi2S3, while the phases of Bi4V6O21 and BiVO4 remained unchanged. It is possible that the coexistence of the three phases (Bi2S3, Bi4V6O21 and BiVO4) caused the dramatic increase in the catalyst activity for the catalyst with V/Bi atomic ratio ) 1/2. Figure 7 shows the scanning electroscopy of fresh catalyst (curve a) and spent catalyst (curve b) for the binary oxide with V/Bi ) 1/2. The phase structure of the fresh catalyst was a relatively continuous elongated form, while the phase structure of the spent catalyst was a discrete particle form with some short filaments. The needle-shaped filaments in the spent catalyst might be the condensed sulfur product. Figures 5 and 6 show that all three binary oxides (V/ Bi atomic ratio ) 2/1, 1/1, and 1/2) contained Bi4V6O21 and BiVO4, and Table 3 shows that the maximum obtainable sulfur yields of the three binary oxides were significantly higher than those of V2O5 and Bi2O3. In addition, Figure 5 shows that the binary oxides with V/Bi ) 1/1 had the highest concentration of Bi4V6O21
Figure 5. X-ray diffractometry patterns of fresh catalysts with V/Bi ) (a) 0/1, (b) 1/2, (c) 1/1, (d) 2/1, and (e) 1/0. Symbols 2, 4, O, and b represent the characteristic peaks of Bi2O3, V2O5, Bi4V6O21, and BiVO4, respectively.
Figure 6. X-ray diffractometry patterns of spent catalysts with V/Bi ) (a) 0/1, (b) 1/2, (c) 1/1, (d) 2/1, and (e) 1/0. Symbols 0, 9, O, and b represent the characteristic peaks of Bi2S3, BiS2, Bi4V6O21, and BiVO4, respectively.
and BiVO4 (since it contained little V2O5 and Bi2O3), and Table 3 shows that the catalyst with V/Bi ) 1/1 had the highest sulfur yield (97%). These results suggest that Bi4V6O21 and BiVO4 had much higher selectivity than
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Ind. Eng. Chem. Res., Vol. 35, No. 2, 1996 Table 4. Catalytic Properties of Vanadium-Magnesium Mixed Oxides for Selective Oxidation of Hydrogen Sulfidea temp (°C) 200 conv. select. 210 conv. select. 220 conv. select. 230 conv. select. 300 conv. select. spent catalyst surface area (m2/g)
V/Mg ) 1/0
V/Mg ) 3/1
V/Mg ) 1/1
V/Mg ) 1/3
V/Mg ) 0/1
75.56 100
80.34 100
73.28 100
69.63 100
5.46 100
77.96 100
87.74 100
75.98 100
72.04 89.2
8.65 100
80.73 88.6
90.67 100
78.03 92.3
74.33 85.2
10.43 100
95.09 84
83.87 82.6
75.88 71
12.52 100
23.5
48.11 100 6.6
2.9
1.7
4.6
a Reaction conditions: gas flowrate ) 100 mL/min with 1 vol % hydrogen sulfide; catalyst weight ) 0.5 g.
V/Mg ) 3/1 suggests that MgV2O was better than pure vanadium oxide for catalyzing the selective oxidation of hydrogen sulfide to sulfur. Acknowledgment We gratefully acknowledge the National Science Council of the Republic of China for financial support (Grant No. NSC-84-2214-E-029-002). Literature Cited
Figure 7. Scanning electron microscopy of (a) fresh catalyst and (b) spent catalyst with V/Bi ) 1/2.
pure V2O5, and the former should be the better catalysts for the selective oxidation of hydrogen sulfide than the latter. (3) Vanadium-Magnesium Binary Oxide Catalysts. Five vanadium/magnesium atomic ratios were studied for the binary oxide catalysts, including V/Mg ) 1/0, 3/1, 1/1, 1/3, and 0/1. Table 4 shows the performances of these catalysts for the selective oxidation of hydrogen sulfide. Under the conditions of temperature ) 200 °C, gas flowrate ) 100 mL/min, and catalyst weight ) 0.5 g, the conversion of hydrogen sulfide for the binary oxide catalyst with V/Mg ) 3/1 was 80.34% (selectivity to sulfur was 100%), which was slightly higher than that of pure vanadium oxide. But the catalyst with V/Mg ) 3/1 had a much higher selectivity than pure vanadium oxide (for example, the selectivity at 220 °C was 100% with 91% conversion for the former and was only 88.6% with 81% conversion for the latter). The possible compounds resulting from the reaction between vanadium oxide and magnesium oxide were MgV2O, Mg2V2O, and Mg3V2O8 (Chaar et al., 1987). Therefore, the better sulfur selectivity for catalyst with
Bagajewicz, A. J.; Tamhankar, S. S.; Stephanopoulos, M. F.; Gavalas, G. R. Hydrogen Sulfide Removal by Supported Vanadium Oxide. Environ. Sci. Technol. 1988, 22, 467-470. Chaar, M. A.; Kung, M. C.; Kung, H. H. Selective Oxidation Dehydrogenation of Butane Over V-Mg-O Catalyst. J. Catal. 1987, 105, 483-498. Chen, W. S.; Chiang, H. B.; Lee, M. D. Ammoxidation of Toluene to Benzonitrile on Vanadium-Molybdenum Binary Oxide. J. Chin. Inst. Chem. Eng. 1994, 45-50. Dalrymple, D. A.; Trofe, T. W.; Evans, J. M. An Overview of Liquid Redox Sulfur Recovery. Chem. Eng. Prog. 1989, 43-49. Lagas, J. A.; Borsboom, J.; Berben, P. H. Selective Oxidation Catalyst Improves Claus Process. Oil Gas J. 1988, 86, 68-71. Lee, M. D.; Chen, W. S.; Chiang, H. P. Ammoxidation of Toluene to Benzonitrile Over Vanadium-Bismuth Scheelite. Appl. Catal. 1993, 101, 269-281. Satterfield, C. N. Heterogeneous Catalysis in Industrial Practice; McGraw-Hill: New York, 1991; pp 267-337. Terorde, R. F. A. A.; Van den Brink, P. J.; Visser, L. M.; Van Dillen, A. J.; Geus, J. W. Selective Oxidation of Hydrogen Sulfide to Elemental Sulfur Using Iron Oxide Catalysts on Various Supports. Catal. Today 1993, 17, 217-224. Thomas, C. L. Catalytic Process and Proven Catalysts; Academic Press: New York, 1970; p 184. Van Nisselrooy, P. F. M. T.; Lagas, J. A. SUPERCLAUS Reduced SO2 Emission by the Use of a Selective Oxidation Catalyst. Catal. Today 1993, 16, 263-272.
Received for review July 3, 1995 Revised manuscript received October 23, 1995 Accepted November 14, 1995X IE950403L
Abstract published in Advance ACS Abstracts, December 15, 1995. X
