- Email: [email protected]
Silicon carbide supported NiS2 catalyst for the selective oxidation of H2S in Claus tail-gas
Studies in Surface Science and Catalysis 130 A. Corma, F.V. Melo, S. Mendiomz and J.L.G. Fierro (Editors) O 2000 Elsevier Science B.V. All rights reserved.
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Silicon carbide supported NiSz catalyst for the selective oxidation of HzS in Claus tail-gas M.J. LEDOUX, C. PHAM-HUU, N. KELLER, J.-B. NOUGAYREDE*, S. SAVINPONCET* and J. BOUSQUET** Laboratoire de Chimie des Mat6riaux Catalytiques, GMI/ECPM/Universit6 Louis Pasteur, 25, rue Becquerel, B P 08, 67087 Strasbourg Cedex 2, France. Tel. (33) 3 88 13 68 81, Fax. (33) 3 88 13 68 80, E-mail: [email protected] * Elf Aquitaine, Groupement de Recherche de Lacq, BP 34, 64170 Lacq, France. ** Centre de Recherche de Solaize, Elf Antar France, BP 22, 69630 Solaize, France. The selective oxidation of H2S into elemental S, in a discontinuous mode (100*C), is reported. A very efficient (100% yield) nickel sulfide catalyst supported on a new type of support, silicon carbide is used. This support avoids reactions with the support during the test or the regeneration cycles, due to its chemical inertness. I. INTRODUCTION Natural gas plants and oil refineries generate acid gases containing hydrogen sulfide, HzS, in large amounts, generally by reduction of the sulfur compounds present in the raw material. I-t2S must be recovered before releasing the gas to the atmosphere, due to its high toxicity, and is usually selectively transformed into elemental sulfur by the Claus-modified process [1,2]. New Claus tail-gas processes have been developed to go above the typical sulfur recovery efficiencies of 90-98% which can be reached with the alone Claus process [36]. This can be done by absorption of H2S in a basic solution or by combustion into SO 2. However catalytic processes are also used either in a continuous mode over sulfur dewpoint temperatures (>180"C) [6,7] or in a discontinuous mode at temperatures lower than 180"C, i.e. Sulfreen or Doxosulfreen processes [5]. The high temperature used in the continuous mode is responsible for the formation of SO2 as side-product by reaction between the initial H2S or the sulfur formed and the oxygen in the feed and consequently, a total selectivity towards elemental sulfur cannot be reached. A total selectivity can be obtained at lower reaction temperatures because of the absence of any secondary reactions [8]. The catalysts are generally supported on oxidic materials, very prone to sulfatation during the test, leading to an irreversible deactivation. The aim of the present article is to report the results obtained for the selective oxidation of H2S in a discontinuous mode (100*C) on a nickel sulfide catalyst supported on a new type of support, silicon carbide which avoids reactions with the support during the test or the regeneration cycles, due to its chemical inertness [8,9]. In addition, several characterization techniques were used during the study in order to obtain further insight into the mode of sulfur deposition on the catalyst during the test.
2. EXPERIMENTAL SECTION 2.1. Support and catalyst Silicon carbide used as support was synthesized by the gas-solid reaction between SiO vapors and preshaped activated charcoal under dynamic vacuumn at temperatures around 1200-1250"C [10,11]. The resulting silicon carbide used, previously ground and sieved, had a
2892
particle size ranging from 0.250 to 0.425 mm. A calcination was then performed at 700~ for 3 h in order to stabilize the textural characteristics and to burn any remaining unreacted carbon. The catalysts were prepared by incipient wetness impregnation of the support with an aqueous solution of Ni(NO3)2.6H20 (Merck). They were dried at 120~ for 14 h and then calcined at 350~ for 2 h in order to decompose the nitrate salt and to form nickel oxide. The nickel concentration measured by atomic absorption spectrocopy (AAS) was 5 wt. %. NiS2/SiC was obtained by sulfidation of NiO/SiC by reaction with a H2S/He flow at 300~ 2.2. Selective oxidation of H2S The analyses of the inlet and outlet gases were performed on-line using a Varian CX3400 gas chromatograph equipped with a Chrompack GSQ capillary column (allowing the separation of 02, H2S, H20 and SO2), a catharometer detector and a calibrated six port loop (500 td-,). Steam was provided by a saturator kept at the required temperature to obtain a partial pressure of steam from 0 to 30 vol. %. Regeneration of the catalyst was carried out in flowing helium at 300~ for 2 h in order to vaporize the sulfur deposited on the catalyst surface during the test. 2.3. Characterization techniques The metal loading was analyzed by AAS performed at the Service Central d'Analyse of the CNRS, Vernaison, France. Structural characterization of the samples was carried out by powder X-ray diffraction (XRD) with a Siemens Diffractometer Model D-5000, using a Cu Ktx monochromatic radiation (7~= 1.5406 A) operating at 40 kV and 20 mA. The pore size and surface area measurements were performed on a Coulter SA-3100 porosimeter using N 2 adsorption at -196"C. The analysis was carried out without any pretreatment in order to avoid any catalyst structural modifications. The morphology of the catalyst, before and after catalytic test was observed by scanning electron microscopy (SEM) using a JEOL Model JSM-840 operating at 20 kV and by transmission electron microscopy (TEM) using a Topcon Model EM200B operating at 200 kV with a point-to-point resolution of 0.17 nm. 3. RESULTS AND DISCUSSION The desulfurization activity expressed in terms of conversion, the selectivity into sulfur and the sulfur weight deposit obtained on the NiSz-5%/SiC catalyst at 100*C in the presence of 20 vol. % of steam are reported in Figure 1. The catalyst exhibited high performances (100% sulfur yield) and was totally efficient during 200 h on stream. No deactivation was apparent even with a sulfur storage of almost 80% in weight. Such a phenomenon was quite surprising for a medium specific surface area catalyst (25 mZ/g), as deactivation is generally observed at relatively lower storage on high surface area catalysts (e.g. activated charcoal) due to pores plugging [12-14]. The original mode of deposition of sulfur, which is presented later, explained this high capacity of storage without rapid deactivatiort The low reaction temperature and the lack of micropores of the support explained the absence of SO2. The only diffraction lines of SiC and of NiS 2 were detected on the fresh catalyst XRD pattern, whereas the lines due to the solid sulfur deposit could be observed on the used catalyst. Regeneration could be performed by submitting the sulfur loaded catalyst to an helium flow at 3000C for 2 h in order to vaporize the sulfur, and the XRD pattern of the regenerated catalyst was similar to the pattern of the fresh catalyst. No nickel oxide or sulfate species could be detected on the fresh, used or regenerated catalysts. The absence of nickel sulfate was due to the low reaction temperature and the absence of hot spots because of the high thermal conductivity of silicon carbide, which allows the dispersion of the heat induced by the high exothermicity of the H2S oxidation reaction. The stability of the catalyst and the total efficiency of the regenerative treatment could be attributed to the chemical inertness of SiC, preventing any reactions between the reactants, the sulfur formed, the active phase and the support itself.
2893
100
80 J
70
~80 60 f
50 ~
o "~60 r~
40 ~ ~
"'~
o ~40
3o'8
m~'~ ~
r~
20 N
20
10 T
'
0
I
'
50
I
'
I
100 150 Time on stream (h)
200
Fig. l. H2S conversion, selectivity into elemental sulfur and % wt. solid sulfur deposit in function of time on stream obtained on the NiS2/SiC catalyst at 100*C in the presence of 20 vol. % of steam. Reaction conditions : H2S = 0,2%, 0 2 = 0,32%, H 2 0 = 20%, balanced He. Space velocity = 1060 h -1. The surface area of the catalyst slowly decreased from 25 m2/g to about 5 m2/g as a function of the sulfur deposition (Figure 2). However, on a large range of sulfur loading (from 10% to 45%), the specific surface of the catalyst, corrected for the sulfur deposit weight, remained stable. This meant that during a large part of the test, the solid sulfur deposition occured without plugging any porosity of the catalyst. 30
I
I
I
i
!
I
I
25 exo t'q
E 20 m2/g of catalyst
u= 10 .,...4 Q.,
m
5
m2/g of catalyst + sulfur I
I
10 20
I
I
I
I
I
30
40
50
60
70
80
% of sulfur (%) Fig. 2. Surface area modification as a function of sulfur deposition. The test was carried out in the presence of 20 vol. % of steam in the feed. Separate experiments have shown that sulfur had no surface area, < 1 m2/g.
2894 SEM micrographs of the sulfur loaded catalyst were in agreement with the previously advanced hypothesis of a peculiar sulfur deposition mode. They showed the presence of several aggregates of sulfur dispersed on the catalyst surface (Figure 3a). However, it was significant to note that even at a high concentration of sulfur, a part of the catalyst surface was still accessible. Large sulfur particles were observed on different zones of the surface, but small particles homogeneousely dispersed on the totality of the catalyst surface could not be formed. This explained why at high sulfur loading the desulfurization activity remained stable at a 100% level. Fig. 3. SEM micrographs of the NiS2/SiC catalyst after catalytic test at 100*C in the presence of 20 vol. % of steam with a 45% wt. sulfur storage. (a) Low magnification image showed the presence of sulfur throughout the catalyst surface, a part of the catalyst surface remaining accessible for the reactants, (b) Some regions of the catalyst completely covered by solid sulfur, (c) High magnification image showed the presence of some highly dispersed melted sulfur inside the catalyst. White bars represent 10 lxm.
Previous work showed that the SiC surface had zones which were partially covered by a 2-3 nm thick silicon oxycarbide and oxide amorphous hydrophilic layer, and zones showing only pure hydrophobic silicon carbide [15]. The hydrophilic part of the support probably covered the internal surface of the pore, due to the high density of crystal defects in these areas. The NiO and thus the NiS 2 particles were located on the hydrophilic parts in the pores of the catalyst, because their salt precursor was impregnated using an aqueous solution. In the
2895 presence of water during the reaction, the formation of a thin water film on the hydrophilic parts of the SiC surface allowed the sulfur particles to be removed from the active sites, as a conveyor belt to the hydrophobic part, where large sulfur particles were stored. The performances of the NiS 2 based catalyst were thus not affected by the high sulfur deposit. The NiS 2 surface was consequently kept clean and free for access as shown in Figure 4. In dry reaction conditions, in the absence of any liquid film on the surface, the sulfur particles could not be mechanically removed from the actives sites, and the resulting blockade of the NiS 2 particles by solid sulfur induced rapid deactivation of the catalyst after only few hours on stream [15a, 16].
Fig. 4. TEM image which shows the sulfur deposition besides the NiS 2 active particles, keeping them free for the reactants. 4. C O N C L U S I O N At a temperature of 100~ the NiS2/SiC catalyst exhibited high performances for the H2S oxidation into elemental sulfur in the presence of 20 vol. % steam (100% selective for a conversion of 100%), even at a sulfur loading of almost 80%. The role of water was evidenced and the formation of a water liquid film on the hydrophilic Si oxycarbide/oxide part of the surface could explain the continuation of a total desulfurization activity even after 200 h of sulfur storage. The absence of microporosity on the catalyst and the low reaction temperature could explain the high selectivity into sulfur. The catalyst remained stable even after many cycles of test and regeneration, because of the chemical inertness of SiC. Work is going on to get more insight on the mode of sulfur deposition and its transport on the catalyst surface. ACKNOWLEDGEMENTS
The present work was financially supported by the Elf Aquitaine Co. Mrs G. Ehret and Dr. CI. Estourn~s (IPCMS, UMR 7504 CNRS) are gratefully acknowledged for performing TEM and S EM. REFERENCES
1. 2. 3.
J. Wieckowska, Catal. Today, 24 (1995) 405. Sulphur, Keeping Abreast ofthe Regulation, 231 (1994) 35. Sulphur, Controlling Hydrogen Sulfide Emissions, 250, (1997) 45.
2896
o
5.
.
7. .
10. 11. 12. 13. 14. 15. 16.
Sulphur, Approaching the Limit: 99,9+% Sulphur Recovery, 257 (1998) 34. S. Savin, J.-B. Nougayr~de, W. Willing and G. Bandel, New Developments in Sulfur Recovery Process Technology, in The International Journal of Hydrocarbon Engineering, p. 54-56 (1998). P.H. Berben and J.W. Geus, U.S. Patent No. 4818740 (1989). M.J. Ledoux, J.-B. Nougayr~de, C. Pham-Huu, N. Keller, S. Savin-Poncet, C. Crouzet, Eur. Pat. Appl. No. 98-11941, assigned to the Elf Aquitaine Production (1998). A. Philippe, S. Savin-Poncet, J.-B. Nougayr~de, M.J. Ledoux, C. Pham-Huu and C. Crouzet, Eur. Pat. Appl. No. 94-013752, assigned to the Elf Aquitaine Production (1994). N. Keller, C. Pham-Huu, C. Crouzet, M. J. Ledoux, S. Savin-Poncet, J.-B. Nougayr~de and J. Bousquet, Catal. Today, 53(4) 1999 535. (a) M. J. Ledoux, S. Hantzer, J. Guille and D. Dubots, US Patent No. 4914070, assigned to the Pechiney Electrometallurgie Co. (1990). (b) M.J. Ledoux, S. Hantzer, C. PhamHuu, J. Guille and M.P. Desaneaux, J. Catal., 114 (1988) 176. N. Keller, C. Pham-Huu, S. Roy, M.J. Ledoux, C. Estoum~s and J. Guille, J. Mat. Sci., 34(13) (1999) 3189. M. Steijns and P. Mars, J. Catal., 35 (1974) 11. A. Trovarelli, F. Felluga, C. de Leitenburg, P. Andreussi and G. Docetti, Proc. 1~ World Congress on Environmental Catalysis, G. Centi et al. (Eds.), p. 667 (1995). A. Primavera, A. Trovarelli, P. Andreussi and G. Dolcetti, Appl. Catal. A: General, 173 (1998) 185. (a) N. Keller, PhD. Dissertation, University of Strasbourg (1999). (b) N. Keller, C. Pham-Huu, M.J. Ledoux, C. Estoum~s and G. Ehret, Appl. Catal. A: General, 187 (1999) 255. (c) PEchiney Recherche, non published results. N. Keller, C. Pham-Huu, M.J. Ledoux, S. Savin-Poncet, J.-B. Nougayr~de and J. Bousquet, Appl. Catal. A: General, in preparation.
2891
Silicon carbide supported NiSz catalyst for the selective oxidation of HzS in Claus tail-gas M.J. LEDOUX, C. PHAM-HUU, N. KELLER, J.-B. NOUGAYREDE*, S. SAVINPONCET* and J. BOUSQUET** Laboratoire de Chimie des Mat6riaux Catalytiques, GMI/ECPM/Universit6 Louis Pasteur, 25, rue Becquerel, B P 08, 67087 Strasbourg Cedex 2, France. Tel. (33) 3 88 13 68 81, Fax. (33) 3 88 13 68 80, E-mail: [email protected] * Elf Aquitaine, Groupement de Recherche de Lacq, BP 34, 64170 Lacq, France. ** Centre de Recherche de Solaize, Elf Antar France, BP 22, 69630 Solaize, France. The selective oxidation of H2S into elemental S, in a discontinuous mode (100*C), is reported. A very efficient (100% yield) nickel sulfide catalyst supported on a new type of support, silicon carbide is used. This support avoids reactions with the support during the test or the regeneration cycles, due to its chemical inertness. I. INTRODUCTION Natural gas plants and oil refineries generate acid gases containing hydrogen sulfide, HzS, in large amounts, generally by reduction of the sulfur compounds present in the raw material. I-t2S must be recovered before releasing the gas to the atmosphere, due to its high toxicity, and is usually selectively transformed into elemental sulfur by the Claus-modified process [1,2]. New Claus tail-gas processes have been developed to go above the typical sulfur recovery efficiencies of 90-98% which can be reached with the alone Claus process [36]. This can be done by absorption of H2S in a basic solution or by combustion into SO 2. However catalytic processes are also used either in a continuous mode over sulfur dewpoint temperatures (>180"C) [6,7] or in a discontinuous mode at temperatures lower than 180"C, i.e. Sulfreen or Doxosulfreen processes [5]. The high temperature used in the continuous mode is responsible for the formation of SO2 as side-product by reaction between the initial H2S or the sulfur formed and the oxygen in the feed and consequently, a total selectivity towards elemental sulfur cannot be reached. A total selectivity can be obtained at lower reaction temperatures because of the absence of any secondary reactions [8]. The catalysts are generally supported on oxidic materials, very prone to sulfatation during the test, leading to an irreversible deactivation. The aim of the present article is to report the results obtained for the selective oxidation of H2S in a discontinuous mode (100*C) on a nickel sulfide catalyst supported on a new type of support, silicon carbide which avoids reactions with the support during the test or the regeneration cycles, due to its chemical inertness [8,9]. In addition, several characterization techniques were used during the study in order to obtain further insight into the mode of sulfur deposition on the catalyst during the test.
2. EXPERIMENTAL SECTION 2.1. Support and catalyst Silicon carbide used as support was synthesized by the gas-solid reaction between SiO vapors and preshaped activated charcoal under dynamic vacuumn at temperatures around 1200-1250"C [10,11]. The resulting silicon carbide used, previously ground and sieved, had a
2892
particle size ranging from 0.250 to 0.425 mm. A calcination was then performed at 700~ for 3 h in order to stabilize the textural characteristics and to burn any remaining unreacted carbon. The catalysts were prepared by incipient wetness impregnation of the support with an aqueous solution of Ni(NO3)2.6H20 (Merck). They were dried at 120~ for 14 h and then calcined at 350~ for 2 h in order to decompose the nitrate salt and to form nickel oxide. The nickel concentration measured by atomic absorption spectrocopy (AAS) was 5 wt. %. NiS2/SiC was obtained by sulfidation of NiO/SiC by reaction with a H2S/He flow at 300~ 2.2. Selective oxidation of H2S The analyses of the inlet and outlet gases were performed on-line using a Varian CX3400 gas chromatograph equipped with a Chrompack GSQ capillary column (allowing the separation of 02, H2S, H20 and SO2), a catharometer detector and a calibrated six port loop (500 td-,). Steam was provided by a saturator kept at the required temperature to obtain a partial pressure of steam from 0 to 30 vol. %. Regeneration of the catalyst was carried out in flowing helium at 300~ for 2 h in order to vaporize the sulfur deposited on the catalyst surface during the test. 2.3. Characterization techniques The metal loading was analyzed by AAS performed at the Service Central d'Analyse of the CNRS, Vernaison, France. Structural characterization of the samples was carried out by powder X-ray diffraction (XRD) with a Siemens Diffractometer Model D-5000, using a Cu Ktx monochromatic radiation (7~= 1.5406 A) operating at 40 kV and 20 mA. The pore size and surface area measurements were performed on a Coulter SA-3100 porosimeter using N 2 adsorption at -196"C. The analysis was carried out without any pretreatment in order to avoid any catalyst structural modifications. The morphology of the catalyst, before and after catalytic test was observed by scanning electron microscopy (SEM) using a JEOL Model JSM-840 operating at 20 kV and by transmission electron microscopy (TEM) using a Topcon Model EM200B operating at 200 kV with a point-to-point resolution of 0.17 nm. 3. RESULTS AND DISCUSSION The desulfurization activity expressed in terms of conversion, the selectivity into sulfur and the sulfur weight deposit obtained on the NiSz-5%/SiC catalyst at 100*C in the presence of 20 vol. % of steam are reported in Figure 1. The catalyst exhibited high performances (100% sulfur yield) and was totally efficient during 200 h on stream. No deactivation was apparent even with a sulfur storage of almost 80% in weight. Such a phenomenon was quite surprising for a medium specific surface area catalyst (25 mZ/g), as deactivation is generally observed at relatively lower storage on high surface area catalysts (e.g. activated charcoal) due to pores plugging [12-14]. The original mode of deposition of sulfur, which is presented later, explained this high capacity of storage without rapid deactivatiort The low reaction temperature and the lack of micropores of the support explained the absence of SO2. The only diffraction lines of SiC and of NiS 2 were detected on the fresh catalyst XRD pattern, whereas the lines due to the solid sulfur deposit could be observed on the used catalyst. Regeneration could be performed by submitting the sulfur loaded catalyst to an helium flow at 3000C for 2 h in order to vaporize the sulfur, and the XRD pattern of the regenerated catalyst was similar to the pattern of the fresh catalyst. No nickel oxide or sulfate species could be detected on the fresh, used or regenerated catalysts. The absence of nickel sulfate was due to the low reaction temperature and the absence of hot spots because of the high thermal conductivity of silicon carbide, which allows the dispersion of the heat induced by the high exothermicity of the H2S oxidation reaction. The stability of the catalyst and the total efficiency of the regenerative treatment could be attributed to the chemical inertness of SiC, preventing any reactions between the reactants, the sulfur formed, the active phase and the support itself.
2893
100
80 J
70
~80 60 f
50 ~
o "~60 r~
40 ~ ~
"'~
o ~40
3o'8
m~'~ ~
r~
20 N
20
10 T
'
0
I
'
50
I
'
I
100 150 Time on stream (h)
200
Fig. l. H2S conversion, selectivity into elemental sulfur and % wt. solid sulfur deposit in function of time on stream obtained on the NiS2/SiC catalyst at 100*C in the presence of 20 vol. % of steam. Reaction conditions : H2S = 0,2%, 0 2 = 0,32%, H 2 0 = 20%, balanced He. Space velocity = 1060 h -1. The surface area of the catalyst slowly decreased from 25 m2/g to about 5 m2/g as a function of the sulfur deposition (Figure 2). However, on a large range of sulfur loading (from 10% to 45%), the specific surface of the catalyst, corrected for the sulfur deposit weight, remained stable. This meant that during a large part of the test, the solid sulfur deposition occured without plugging any porosity of the catalyst. 30
I
I
I
i
!
I
I
25 exo t'q
E 20 m2/g of catalyst
u= 10 .,...4 Q.,
m
5
m2/g of catalyst + sulfur I
I
10 20
I
I
I
I
I
30
40
50
60
70
80
% of sulfur (%) Fig. 2. Surface area modification as a function of sulfur deposition. The test was carried out in the presence of 20 vol. % of steam in the feed. Separate experiments have shown that sulfur had no surface area, < 1 m2/g.
2894 SEM micrographs of the sulfur loaded catalyst were in agreement with the previously advanced hypothesis of a peculiar sulfur deposition mode. They showed the presence of several aggregates of sulfur dispersed on the catalyst surface (Figure 3a). However, it was significant to note that even at a high concentration of sulfur, a part of the catalyst surface was still accessible. Large sulfur particles were observed on different zones of the surface, but small particles homogeneousely dispersed on the totality of the catalyst surface could not be formed. This explained why at high sulfur loading the desulfurization activity remained stable at a 100% level. Fig. 3. SEM micrographs of the NiS2/SiC catalyst after catalytic test at 100*C in the presence of 20 vol. % of steam with a 45% wt. sulfur storage. (a) Low magnification image showed the presence of sulfur throughout the catalyst surface, a part of the catalyst surface remaining accessible for the reactants, (b) Some regions of the catalyst completely covered by solid sulfur, (c) High magnification image showed the presence of some highly dispersed melted sulfur inside the catalyst. White bars represent 10 lxm.
Previous work showed that the SiC surface had zones which were partially covered by a 2-3 nm thick silicon oxycarbide and oxide amorphous hydrophilic layer, and zones showing only pure hydrophobic silicon carbide [15]. The hydrophilic part of the support probably covered the internal surface of the pore, due to the high density of crystal defects in these areas. The NiO and thus the NiS 2 particles were located on the hydrophilic parts in the pores of the catalyst, because their salt precursor was impregnated using an aqueous solution. In the
2895 presence of water during the reaction, the formation of a thin water film on the hydrophilic parts of the SiC surface allowed the sulfur particles to be removed from the active sites, as a conveyor belt to the hydrophobic part, where large sulfur particles were stored. The performances of the NiS 2 based catalyst were thus not affected by the high sulfur deposit. The NiS 2 surface was consequently kept clean and free for access as shown in Figure 4. In dry reaction conditions, in the absence of any liquid film on the surface, the sulfur particles could not be mechanically removed from the actives sites, and the resulting blockade of the NiS 2 particles by solid sulfur induced rapid deactivation of the catalyst after only few hours on stream [15a, 16].
Fig. 4. TEM image which shows the sulfur deposition besides the NiS 2 active particles, keeping them free for the reactants. 4. C O N C L U S I O N At a temperature of 100~ the NiS2/SiC catalyst exhibited high performances for the H2S oxidation into elemental sulfur in the presence of 20 vol. % steam (100% selective for a conversion of 100%), even at a sulfur loading of almost 80%. The role of water was evidenced and the formation of a water liquid film on the hydrophilic Si oxycarbide/oxide part of the surface could explain the continuation of a total desulfurization activity even after 200 h of sulfur storage. The absence of microporosity on the catalyst and the low reaction temperature could explain the high selectivity into sulfur. The catalyst remained stable even after many cycles of test and regeneration, because of the chemical inertness of SiC. Work is going on to get more insight on the mode of sulfur deposition and its transport on the catalyst surface. ACKNOWLEDGEMENTS
The present work was financially supported by the Elf Aquitaine Co. Mrs G. Ehret and Dr. CI. Estourn~s (IPCMS, UMR 7504 CNRS) are gratefully acknowledged for performing TEM and S EM. REFERENCES
1. 2. 3.
J. Wieckowska, Catal. Today, 24 (1995) 405. Sulphur, Keeping Abreast ofthe Regulation, 231 (1994) 35. Sulphur, Controlling Hydrogen Sulfide Emissions, 250, (1997) 45.
2896
o
5.
.
7. .
10. 11. 12. 13. 14. 15. 16.
Sulphur, Approaching the Limit: 99,9+% Sulphur Recovery, 257 (1998) 34. S. Savin, J.-B. Nougayr~de, W. Willing and G. Bandel, New Developments in Sulfur Recovery Process Technology, in The International Journal of Hydrocarbon Engineering, p. 54-56 (1998). P.H. Berben and J.W. Geus, U.S. Patent No. 4818740 (1989). M.J. Ledoux, J.-B. Nougayr~de, C. Pham-Huu, N. Keller, S. Savin-Poncet, C. Crouzet, Eur. Pat. Appl. No. 98-11941, assigned to the Elf Aquitaine Production (1998). A. Philippe, S. Savin-Poncet, J.-B. Nougayr~de, M.J. Ledoux, C. Pham-Huu and C. Crouzet, Eur. Pat. Appl. No. 94-013752, assigned to the Elf Aquitaine Production (1994). N. Keller, C. Pham-Huu, C. Crouzet, M. J. Ledoux, S. Savin-Poncet, J.-B. Nougayr~de and J. Bousquet, Catal. Today, 53(4) 1999 535. (a) M. J. Ledoux, S. Hantzer, J. Guille and D. Dubots, US Patent No. 4914070, assigned to the Pechiney Electrometallurgie Co. (1990). (b) M.J. Ledoux, S. Hantzer, C. PhamHuu, J. Guille and M.P. Desaneaux, J. Catal., 114 (1988) 176. N. Keller, C. Pham-Huu, S. Roy, M.J. Ledoux, C. Estoum~s and J. Guille, J. Mat. Sci., 34(13) (1999) 3189. M. Steijns and P. Mars, J. Catal., 35 (1974) 11. A. Trovarelli, F. Felluga, C. de Leitenburg, P. Andreussi and G. Docetti, Proc. 1~ World Congress on Environmental Catalysis, G. Centi et al. (Eds.), p. 667 (1995). A. Primavera, A. Trovarelli, P. Andreussi and G. Dolcetti, Appl. Catal. A: General, 173 (1998) 185. (a) N. Keller, PhD. Dissertation, University of Strasbourg (1999). (b) N. Keller, C. Pham-Huu, M.J. Ledoux, C. Estoum~s and G. Ehret, Appl. Catal. A: General, 187 (1999) 255. (c) PEchiney Recherche, non published results. N. Keller, C. Pham-Huu, M.J. Ledoux, S. Savin-Poncet, J.-B. Nougayr~de and J. Bousquet, Appl. Catal. A: General, in preparation.