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L Zeolite Catalyst for Hexanes Aromatization
Guni, L et al. (Editors), New Fronriers k Caialpis P m d i n g s of the 10th International Congress on Catalysis, 19-24 July, 1992,Budapest, Hungary 6 1993 Elsevier Science Publishers B.V. All rights mewed
NEW MODIFICATION METHOD OF Pt/L ZEOLITE CATALYST FOR HEXANES AROMATIZATION
H.Katsuno, T. Fukunaga and M.Sughoto Central Research Laboratories, Idemitsu Kosan Co.,Ltd., 1280 Kamiizumi, Sodegaura, Chiba 299-02, Japan (As a member of Research Association for Utilization of Light Oil [RAULO], Japan.)
Abstract
The treatment of KL zeolite with halocarbons prior to its impregnation with Pt(NH3) C12 improves the activity and selectivity The treatment is also effecfor the aromatization of hexanes. tive for the stability of the catalyst. The halocarbon treated catalyst shows a unique advance in the industrial production of aromatics from hexanes.
.
1 INTRODUCTION
Conventional reforming catalysts have poor activities and selectivities for the aromatization of hexanes and heptanes. Bernard reported that platinum supported KL zeolite is much more active and selective than conventional Pt/A1203 reforming catalyst for the aromatization of n-hexane(1). It has been also demonstrated that acidic sites decrease the selectivity and stability of the Pt/L zeolite for the hexane aromatization (1)(2). In this paper we report that the treatment of KL zeolite with halocarbons prior to its impregnation with Pt(NH3)4C12 improves the activity and selectivity for the hexanes aromatization. The treatment is also effective for the stability of the catalyst. The chemical , physical and catalytic properties of the treated catalysts (Pt/FKL) are evaluated by the application of a variety of techniques. 2.EXPERIMENTAL
Catalyst Preparation KL zeolites used in this study were obtained from Tosoh corporation. Halocarbon treatment was carried out in a fixed bed quartz reactor at 500°C for 2 hours. CF C1, (CF2C1I2, CFC13 were used as a halocarbon,respectively. PZatinum was supported on the halocarbon treated KL zeolite (FKL) by incipient wetness impregnation with an aqueous solution of Pt(NH3I4Cl2. The
2420
impregnated zeolites were dried at 80°C for 3 hours , and then calcined at 300 "C for 1 hour. Surface Property The behavior of surface OH groups was examined by FT-IR spectroscopy after the evacuation of KL zeolites at 500 'C, for 1 hour. Electronic State of Platinum The electronic state of platinum has been studied by means of CO adsorption and infrared spectroscopy. The catalysts prereduced under flowing H were reduced in the infrared cell at 540"C, for 1 hour and &en evacuated at same temperature for 1 hour. CO gas was introduced with 3 torr at room temperature for 30 minutes. The spectra were recorded after evacuation for 1 hour. Catalytic Measurement The aromatization reactions of hexanes were carried out in a continuous flow micro reactor. The catalyst was activated under H2 flow before introducing hexanes. 3.RESULTS AND DISCUSSION
Chemical and Physical Properties of the Zeolites Table 1 lists the BET surface area and the composition of the FKL and KL zeolites. The BET surface area of FKL zeolites are lower than that of KL zeolite. Fig.1 shows X-ray diffraction patterns of KL zeolite and FKL zeolite( CF3C1 and CFC13). CF3C1 treated zeolite retained its crystalinity The decrease of intensity and the presence of AlF3 (29=25.3')in the X-ray spectram of CF3C1 treated zeolite show that some aluminum is removed from the zeolite framework. It is suggested that AlF3 formed by halocarbon treatment plugged a part of channel of the zeolite. Fig. 2 shows IR spectra of KL zeolite and FKL zeolite treate with CF3C1. After the CF3C1 treatment , the band at 3745 cm
.
-9
Table 1 . Chemical Composition and Surface Area of KL and FKL zeolite. Sample Composition Halogen (Molar Ratio) Cont.(wt%) BET Area F c1 (m2/g) K20 A1203 S i O 2 KL FKL(CF Cl) FKL((C$ C1)2) FKL(CFC~~)
1.09 1.06 1.06 1.00
1.00 1.00 1.00 1.00
5.99 5.91 5.96 5.97
0.0 0.5 0.4 6.7
0.0 0.5
0.3
6.4
195 110
133 19
20 25 30 35 26 Figure 1 . X-ray Diffraction Spectra of FKL and KL Zeolites 5
10
15
assigned to terminal OH was considerably decreased,suggesting that the terminal OH groups were replaced with €7 or C1 (3)(4). Transmission electron micrographs of Pt/KL and Pt/FKL(oCF3C1) catalysts showed that platinum particles on $F3Cl (<8A) are smaller than those on untreated catalyst(8-15A). CO/Pt ratios calculated from CO chemisorption uptakes of catalyst treated with CF3Cl and untreated catalyst were 0.50 and 0.39,respectively,also suggesting that platinum particles on FKL(CF3C1) are smaller than those on KL. The electronic state of platinum has been studied by means of CO ads rption and infrared spectroscopy. The bands in the 2060-2075 cm-’ which were attributed to CO linearly adsorbed on platinum (6)were shifted to lower wavenumber after halocarbon treatment(Fig.3). This result suggests that platinum particles on the CF3C1 treated catalyst are electron rich compare with those on untreated one.
PI C
aa VI 0
n
Figure 3. I R Spectra of CO adsorbed on Pt/FKL(CF3Cl) and Pt/KL
I
4000
3800 3600 3 4 0 0 3200 W a v e n u m b e r I cm-’ 1
Figure 2. I R Spectra of FKL(CF3C1) and KL Zeolites
Catalytic Properties The product yields of n-hexane aromatization over Pt/FKL and Pt/KL are compared in table 2. The CF3C1 and(CF2C1)2 treated catalysts have higher aromatization activity and lower cracking activity than Pt/KL. On the other hand, the CFC13 treated Table 2. Product Yield for Aromatization of n-Hexane on Pt/KL and Pt/FKL Catalysts Wt% KL FKL(CF3Cl) FKL((CF2Cl)z) FKL(CFC13) H2 c1-5 C6 Benzene Toluene
6.8 17.7 2.1 72.5 0.9
8.1 8.0 1 .8 81.9 0.2
8.0 10.1 1.2 80.3 0.4
Reaction Fonditions; Skg/cm2G, SOOC WHSV-2hr- ,H2/HC=Smol/mol
0.1 0.6 98.1 1.2
0.0
2422 catalyst has no aromatization activity ,which is due to its small surface area. These data suggest that FKL catalysts adequately treated with halocarbons are much superior to Pt/KL catalyst for the aromatization of n-hexane. The higher aromatization activity and lower cracking activity over FKL catalyts would be attributed to the higher Table 3. dispersion and unique Weight and Deposition Rate of Carbon on Used Catalysts electronic property of Process Carbon platinum on the zeolites. Catalyst Time Weight Deposition Rate The life tests of the (hr) (wtB) (ppm/hr) catalysts were carried out Pt/KL 170 1.4 82 with a hydrogen/hexanes Pt/FKL(CF3Cl) 3200 2.1 6.6 molar ratio of 0.5. As shown in fig.4 ,the U catalyst life of CF3C1 . . ._ treated catalyst was about 15 times as long as that of untreated one. i Elemental analyses of used PA E: llool catalysts indicated that carbon deposition rate on 2 the CF3C1 treated catalyst 3 was much lower than that Time on Stream , hr on untreated one (table 4 ) . ~ ~ electron micro~ Figure ~4. Life Tests ~ of PtlFKL(CF3Cl) ~ and pt/KL i graphs show that platinum Conditions; 5kg/cm G , wnsv.2hr-1, particle size of the both ~ 2 / ~ e x a n e s0.5moi/mol, = Aromatics Yield=COwtB usgd catalysts are less than 25A. These results show that halocarbon treatment is also effective in stabilizing the catalysts and CF3C1 treated catalyst has a good performance for industrial production of aromatics from hexanes. 4. REFERENCES
J. R. Bernard, Proc. 5th Intern. Conf. Zeolites, Heyden London, 686 (1980) T.R. Hughes, Proc. 7th Intern. Conf, Zeolites, Tokyo 725 (1986) B. M. Lok, F. P. Gortsema, C. A. Messina. H. Rastel i and 41 (1983) T. P. J. Izod, ACS Symp. Ser., 18, K.A. Becker and S. Kowalok, J. Chem. SOC., Faraday Trans.1, -8 11 1161 (1985) J. A. Maness, Jr. and K. M. Dooley, J. Catal. 117,3 2 2 (1989) C.Besoukhanova, J.R.Bernard, J. Chem. Soc.,Faraday Trans.1, 77,1595,(1981)
NEW MODIFICATION METHOD OF Pt/L ZEOLITE CATALYST FOR HEXANES AROMATIZATION
H.Katsuno, T. Fukunaga and M.Sughoto Central Research Laboratories, Idemitsu Kosan Co.,Ltd., 1280 Kamiizumi, Sodegaura, Chiba 299-02, Japan (As a member of Research Association for Utilization of Light Oil [RAULO], Japan.)
Abstract
The treatment of KL zeolite with halocarbons prior to its impregnation with Pt(NH3) C12 improves the activity and selectivity The treatment is also effecfor the aromatization of hexanes. tive for the stability of the catalyst. The halocarbon treated catalyst shows a unique advance in the industrial production of aromatics from hexanes.
.
1 INTRODUCTION
Conventional reforming catalysts have poor activities and selectivities for the aromatization of hexanes and heptanes. Bernard reported that platinum supported KL zeolite is much more active and selective than conventional Pt/A1203 reforming catalyst for the aromatization of n-hexane(1). It has been also demonstrated that acidic sites decrease the selectivity and stability of the Pt/L zeolite for the hexane aromatization (1)(2). In this paper we report that the treatment of KL zeolite with halocarbons prior to its impregnation with Pt(NH3)4C12 improves the activity and selectivity for the hexanes aromatization. The treatment is also effective for the stability of the catalyst. The chemical , physical and catalytic properties of the treated catalysts (Pt/FKL) are evaluated by the application of a variety of techniques. 2.EXPERIMENTAL
Catalyst Preparation KL zeolites used in this study were obtained from Tosoh corporation. Halocarbon treatment was carried out in a fixed bed quartz reactor at 500°C for 2 hours. CF C1, (CF2C1I2, CFC13 were used as a halocarbon,respectively. PZatinum was supported on the halocarbon treated KL zeolite (FKL) by incipient wetness impregnation with an aqueous solution of Pt(NH3I4Cl2. The
2420
impregnated zeolites were dried at 80°C for 3 hours , and then calcined at 300 "C for 1 hour. Surface Property The behavior of surface OH groups was examined by FT-IR spectroscopy after the evacuation of KL zeolites at 500 'C, for 1 hour. Electronic State of Platinum The electronic state of platinum has been studied by means of CO adsorption and infrared spectroscopy. The catalysts prereduced under flowing H were reduced in the infrared cell at 540"C, for 1 hour and &en evacuated at same temperature for 1 hour. CO gas was introduced with 3 torr at room temperature for 30 minutes. The spectra were recorded after evacuation for 1 hour. Catalytic Measurement The aromatization reactions of hexanes were carried out in a continuous flow micro reactor. The catalyst was activated under H2 flow before introducing hexanes. 3.RESULTS AND DISCUSSION
Chemical and Physical Properties of the Zeolites Table 1 lists the BET surface area and the composition of the FKL and KL zeolites. The BET surface area of FKL zeolites are lower than that of KL zeolite. Fig.1 shows X-ray diffraction patterns of KL zeolite and FKL zeolite( CF3C1 and CFC13). CF3C1 treated zeolite retained its crystalinity The decrease of intensity and the presence of AlF3 (29=25.3')in the X-ray spectram of CF3C1 treated zeolite show that some aluminum is removed from the zeolite framework. It is suggested that AlF3 formed by halocarbon treatment plugged a part of channel of the zeolite. Fig. 2 shows IR spectra of KL zeolite and FKL zeolite treate with CF3C1. After the CF3C1 treatment , the band at 3745 cm
.
-9
Table 1 . Chemical Composition and Surface Area of KL and FKL zeolite. Sample Composition Halogen (Molar Ratio) Cont.(wt%) BET Area F c1 (m2/g) K20 A1203 S i O 2 KL FKL(CF Cl) FKL((C$ C1)2) FKL(CFC~~)
1.09 1.06 1.06 1.00
1.00 1.00 1.00 1.00
5.99 5.91 5.96 5.97
0.0 0.5 0.4 6.7
0.0 0.5
0.3
6.4
195 110
133 19
20 25 30 35 26 Figure 1 . X-ray Diffraction Spectra of FKL and KL Zeolites 5
10
15
assigned to terminal OH was considerably decreased,suggesting that the terminal OH groups were replaced with €7 or C1 (3)(4). Transmission electron micrographs of Pt/KL and Pt/FKL(oCF3C1) catalysts showed that platinum particles on $F3Cl (<8A) are smaller than those on untreated catalyst(8-15A). CO/Pt ratios calculated from CO chemisorption uptakes of catalyst treated with CF3Cl and untreated catalyst were 0.50 and 0.39,respectively,also suggesting that platinum particles on FKL(CF3C1) are smaller than those on KL. The electronic state of platinum has been studied by means of CO ads rption and infrared spectroscopy. The bands in the 2060-2075 cm-’ which were attributed to CO linearly adsorbed on platinum (6)were shifted to lower wavenumber after halocarbon treatment(Fig.3). This result suggests that platinum particles on the CF3C1 treated catalyst are electron rich compare with those on untreated one.
PI C
aa VI 0
n
Figure 3. I R Spectra of CO adsorbed on Pt/FKL(CF3Cl) and Pt/KL
I
4000
3800 3600 3 4 0 0 3200 W a v e n u m b e r I cm-’ 1
Figure 2. I R Spectra of FKL(CF3C1) and KL Zeolites
Catalytic Properties The product yields of n-hexane aromatization over Pt/FKL and Pt/KL are compared in table 2. The CF3C1 and(CF2C1)2 treated catalysts have higher aromatization activity and lower cracking activity than Pt/KL. On the other hand, the CFC13 treated Table 2. Product Yield for Aromatization of n-Hexane on Pt/KL and Pt/FKL Catalysts Wt% KL FKL(CF3Cl) FKL((CF2Cl)z) FKL(CFC13) H2 c1-5 C6 Benzene Toluene
6.8 17.7 2.1 72.5 0.9
8.1 8.0 1 .8 81.9 0.2
8.0 10.1 1.2 80.3 0.4
Reaction Fonditions; Skg/cm2G, SOOC WHSV-2hr- ,H2/HC=Smol/mol
0.1 0.6 98.1 1.2
0.0
2422 catalyst has no aromatization activity ,which is due to its small surface area. These data suggest that FKL catalysts adequately treated with halocarbons are much superior to Pt/KL catalyst for the aromatization of n-hexane. The higher aromatization activity and lower cracking activity over FKL catalyts would be attributed to the higher Table 3. dispersion and unique Weight and Deposition Rate of Carbon on Used Catalysts electronic property of Process Carbon platinum on the zeolites. Catalyst Time Weight Deposition Rate The life tests of the (hr) (wtB) (ppm/hr) catalysts were carried out Pt/KL 170 1.4 82 with a hydrogen/hexanes Pt/FKL(CF3Cl) 3200 2.1 6.6 molar ratio of 0.5. As shown in fig.4 ,the U catalyst life of CF3C1 . . ._ treated catalyst was about 15 times as long as that of untreated one. i Elemental analyses of used PA E: llool catalysts indicated that carbon deposition rate on 2 the CF3C1 treated catalyst 3 was much lower than that Time on Stream , hr on untreated one (table 4 ) . ~ ~ electron micro~ Figure ~4. Life Tests ~ of PtlFKL(CF3Cl) ~ and pt/KL i graphs show that platinum Conditions; 5kg/cm G , wnsv.2hr-1, particle size of the both ~ 2 / ~ e x a n e s0.5moi/mol, = Aromatics Yield=COwtB usgd catalysts are less than 25A. These results show that halocarbon treatment is also effective in stabilizing the catalysts and CF3C1 treated catalyst has a good performance for industrial production of aromatics from hexanes. 4. REFERENCES
J. R. Bernard, Proc. 5th Intern. Conf. Zeolites, Heyden London, 686 (1980) T.R. Hughes, Proc. 7th Intern. Conf, Zeolites, Tokyo 725 (1986) B. M. Lok, F. P. Gortsema, C. A. Messina. H. Rastel i and 41 (1983) T. P. J. Izod, ACS Symp. Ser., 18, K.A. Becker and S. Kowalok, J. Chem. SOC., Faraday Trans.1, -8 11 1161 (1985) J. A. Maness, Jr. and K. M. Dooley, J. Catal. 117,3 2 2 (1989) C.Besoukhanova, J.R.Bernard, J. Chem. Soc.,Faraday Trans.1, 77,1595,(1981)