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Novel catalyst for liquid phase fischer-tropsch synthesis
Applied Catalysis, 47 (1989) Ll-L6 Elsevier Science Publishers B.V.. Amsterdam -
Printed in The Netherlands
Novel Catalyst for Liquid Phase Fischer-Tropsch Synthesis Potassium-Promoted Copper-Iron Ultrafine Particles Prepared by Liquid-phase Chemical Deposition
H. ITOH*, H. TANABE and E. KIKUCHI Department of Applied Chemistry, School of Science and Engineering, Waseda University, 3-4-l Okubo, Shinjuku-ku, Tokyo 160 (Japan) (Received 18 October 1988, revised manuscript received 28 November 1988)
INTRODUCTION
Although the liquid phase Fischer-Tropsch (FT) synthesis has conventionally been accomplished using pulverized catalyst, it is interesting to use much smaller catalyst particles to enhance the gas-liquid-solid interfacial contact. In our previous work [ 11, iron ultrafine particles (Fe UFP) prepared by the gas evaporation method were used as a catalyst for liquid phase FT synthesis. The activity of the UFP catalyst was shown to be greater than that of an ordinary precipitated iron catalyst, although the BET surface areas of the two catalysts were almost equal. The addition of alkali metal and copper to iron catalysts is known to be very effective in FT synthesis [ 21. The effect of alkali promotion of the Fe UFP catalyst has been discussed elsewhere [ 1,3]. The purpose of the present work is to prepare alkali-promoted Cu-Fe UFP and to determine the catalytic activity and selectivity of this catalyst for liquid phase FT synthesis. The procedure for preparation of ultrafine alloy particles by reduction in aqueous solution, by means of chemical deposition in the liquid phase (CDL ), has been reported by Van Wonterghem et al. [ 41, who have also mentioned the potential application of amorphous alloy UFP as a catalyst.
L2 EXPERIMENTAL
Apparatus
and procedure
The catalytic study was carried out in a high-pressure flow system using a suspension of a catalyst in hexadecane as the liquid medium (80 ml). The liquid phase (slurry) reactor was a stainless steel autoclave, having an internal volume of 300 cm3, equipped with a stirrer. Syngas with a hydrogen-to-carbon monoxide molar ratio of 1 was fed to the bottom of the reactor through a nozzle and was allowed to react on the suspended catalyst. After passing through a pressure regulator and an ice-cooled receiver, the flow-rate of the gaseous products stream was measured. The distribution of products and the level of carbon monoxide conversion were determined by analyzing the products collected in the three sections of the apparatus: in the aqueous and oil phases in the receiver, in the effluent stream, and in the reaction medium. Concentrations of hydrogen, carbon monoxide, methane and carbon dioxide were determined using a TCD gas chromatograph and other products were analyzed by means of FID gas chromatography. The procedure employed for the addition of potassium to UFP was described in detail elsewhere [ 5 ] : A prescribed amount of colloidal potassium metal was added to the UFP catalyst, suspended in a liquid medium. An ultrasonic generator was used to prepare a suspension of UFP prior to the reaction [ 51. Catal.ysts
Fe and Cu-Fe UFP catalysts listed in Table 1 were prepared by the CDL method: An aqueous solution of KBH, was added dropwise to an aqueous solution of FeCl, alone or to aqueous solutions containing FeC$ and CuCl, with a copper-to-iron weight ratio of 5:95,10:90 and 20:80. The solution was stirred, and the resulting precipitate was washed with water and then with methanol. TABLE 1 Composition of catalysts prepared by the CDL” method Catalyst
Fe Cu( 5%)-Fe Cu ( 10% ) -Fe Cu (20% ) -Fe
Composition (wt.-%) Fe
CU
B
95.6 84.3 83.2 74.3
-
4.0 8.6 4.2 7.9
“Chemical deposition in liquid phase.
4.0 9.6 14.8
K
Others
-
0.4 3.1 3.0 3.0
Fig. 1. Transmission
electron micrograph
of Cu
(10%)-Fe UFP.
The catalyst was dried in vacua and crushed to a fine powder in a nitrogen atmosphere. As can be seen in Table 1, chemical analysis of the Cu-Fe UFP showed that the ratios of copper-to-iron were identical to those in the parent aqueous solutions. Transmission electron micrographs of the catalysts showed typical flakeand sphere-shaped particles, as can be seen in Fig. 1. The size of the sphereshaped particles was about 40-80 nm. Only broad diffraction peaks due to metallic iron and copper were detected by X-ray diffraction analysis of these catalysts. RESULTS
AND DISCUSSION
Liquid phase hydrogenation of carbon monoxide was investigated at 300 “C and 30 atm using the UFP catalysts listed in Table 1. The products distribution and the average space time yields (STY) in the initial 6 h of the runs are summarized in Table 2. It was reported in our previous paper [3] that the promotion by potassium enhances the activity of Fe UFP catalysts prepared by the gas evaporation method at relatively high temperatures ( - 300” C), at which unpromoted Fe UFP or an ordinary potassium-promoted iron precipitation catalyst significant.ly deteriorated due to oxidation. Similarly, the addition of potassium promoted the catalytic activity of Fe UFP prepared by the CDL method, as shown in Table 2. Fig. 2 illustrates the variation in the catalytic activities of potassium-pro-
L4 TABLE 2 Space time yield and product distribution over UFP prepared by the gas evaporation method and by chemical deposition in liquid phase Reaction conditions: temperature, 300°C; pressure, 30 atm; HJCO, 1 mol/mol; W/F, 50 g-cat*min/ CO-mol. Catalyst
Gas Evaporation
CDL”
Cu content (wt.-%)
0
0
K content (wt.-%)
3
0
STY. 10” (C-mol/g-cat-h) Hydrocarbons Oxygenates Carbon dioxide
145 32 209
3
122 9 22
239
11 274
5
10
20
3
3
3
246 10 281
366 10 244
115 13 313
53.0
13.6
60.1
55.6
51.1
62.4
Product distribution (C-%) Hydrocarbons 10.1 C, 9.6 C2 12.8 C:, 10.4 C, 8.3 C, 22.5 G-C,, 9.0 c,,-Cl, 7.6 CKG, CPI+ 9.7
14.3 9.4 15.0 12.5 10.4 28.6 5.9 2.7 1.1
7.4 6.9 11.8 11.3 9.3 22.1 11.9 10.8 8.7
7.6 7.3 12.5 11.5 9.4 23.2 14.1 7.1 7.1
5.0 4.3 7.5 6.6 5.3 15.5 23.1 17.4 15.3
8.8 9.0 14.8 12.5 10.0 23.0 10.3 5.8 5.8
(7.4) 5.4 1.4 0.7
(16.7) 7.0 8.5 0.1 1.1 (83.3) 7.9 30.5 20.1 14.9 9.9 -
(14.7) 3.1 9.8 1.8
(23.0) 9.4 11.8 1.8
(12.6) 2.0 8.4 2.4 -
(6.3) 6.5 27.0 26.6 17.4 7.8 -
(17.0) 6.0 30.0 22.6 12.1 6.3 -
(87.4) 4.7 19.7 21.3 12.1 6.2 17.5
Carbon monoxide conversion ( % )
0 lxygenates Alcohols C, C, C:, C Aldihydes + Ketones C, C:, C, C, C,; C7+
(9.8) 3.9 3.9 1.2 0.8 (90.3) 9.8 18.6 15.2 13.1 8.8 24.8
“Chemical deposition in liquid phase.
(92.6) 6.9 40.7 23.0 11.4 10.6
L5
0
I
I
1
1
I
I
1
2
3
4
5
6
Time on strecm
(hr)
Fig. 2. Catalytic activities of Fe UFP prepared by the gas evaporation method ( o ) and by chemical deposition in liquid phase (A). Reaction conditions: temperature, 3OO;C; pressure, 30 atm; H.JCO, 1 mol/mol; W/F, 50 g-cat*min/CO-mol.
moted Fe UFP prepared by the gas evaporation method and the CDL method. Although the catalytic activity of UFP prepared by the gas evaporation method increased remarkably with time-on-stream [ 31, that of UFP prepared by the CDL method was fairly high from the start of the run, and barely changed for a period of at least 6 h. The activity of the potassium-promoted Cu (10% )-FeUFP catalyst listed in Table 2 was significantly higher than that of the other UFP prepared by either method. The STY of hydrocarbons on the Cu (10% )-Fe UFP catalyst corresponds to 5 kg/kg-cat * h, which is about twenty times as great as that reported for ordinary iron catalysts. In addition, the selectivity of this UFP catalyst for liquid-fraction hydrocarbons was extremely high (ca. 75% on the basis of carbon) even at 300” C which is higher than the ordinary FT synthesis temperature. The carbon number distribution of the hydrocarbon products was analyzed based on the dual-site model, as proposed previously [ 11. The chain growth probabilities and contributions of each kind of site were estimated to give the best fit for the obtained data by means of a nonlinear least-squares method, and the simulated product distributions corresponded satisfactorily with the experimental results. The estimated chain growth probabilities on each kind of site (cy*, cre) and their contributions (C,,Ce) are listed in Table 3. Both chain growth probabilities on the potassium-promoted Cu( 10% )-Fe UFP catalyst were fairly great. Furthermore, the contribution of site B, which was assigned to the potassium-promoted site [ 11, was exceptionally large. This effective promotion of the Cu-Fe UFP with potassium explains the excellent selectivity of this catalyst for liquid fraction hydrocarbons. These results indicate that potassium-promoted Cu-Fe UFP prepared by the CDL method is a promising catalyst for liquid-phase FT synthesis to produce liquid fuels.
L6 TABLE 3 Estimated chain growth probabilities and contributions” Reaction conditions: temperature, 3OO’C; pressure, 30 atm; Hz/CO, 1 mol/mol; W/F, 50 g-cat*min/ CO-mol. Catalyst
Gas evaporation
CDL*
Cu content (wt.-%)
0
0
K content (wt.-%)
3
0
aA
0.60
:: Ca
0.72 0.85 0.28
5 -
10 -
20 -
3
3
3
3
0.58
0.58
0.67
0.73
0.68
0.86 0.81 0.14
0.87 0.71 0.29
0.85 0.73 0.27
0.24 0.87 0.76
0.89 0.90 0.11
“Based on the dual-site model. ‘Chemical deposition in liquid phase. ACKNOWLEDGEMENT
This work was supported by a Grant-in-Aid for Scientific Research, No. 63603005, from the Ministry of Education, Science and Culture, Japan.
REFERENCES H. Itoh, H. Hosaka, T. Ono and E. Kikuchi, Appl. Catal., 40 (1988) 53. M.E. Dry, in J.R. Anderson and M. Boudart (Eds. ), Catalysis: Science and Technology, Vol. 1, Springer, Berlin, 1981, p. 159. H. Itoh, T. Ono, S. Nagano and E. Kikuchi, Sekiyu Grakkaishi, submitted for publication. J. van Wonterghem, S. Marup, C.J.W. Koch, SW. Charles and S. Wells, Nature (London), 322 (1986) 622. H. Itoh, E. Kikuchi and Y. Morita, Sekiyu Gakkaishi, 30 (1987) 324.
Printed in The Netherlands
Novel Catalyst for Liquid Phase Fischer-Tropsch Synthesis Potassium-Promoted Copper-Iron Ultrafine Particles Prepared by Liquid-phase Chemical Deposition
H. ITOH*, H. TANABE and E. KIKUCHI Department of Applied Chemistry, School of Science and Engineering, Waseda University, 3-4-l Okubo, Shinjuku-ku, Tokyo 160 (Japan) (Received 18 October 1988, revised manuscript received 28 November 1988)
INTRODUCTION
Although the liquid phase Fischer-Tropsch (FT) synthesis has conventionally been accomplished using pulverized catalyst, it is interesting to use much smaller catalyst particles to enhance the gas-liquid-solid interfacial contact. In our previous work [ 11, iron ultrafine particles (Fe UFP) prepared by the gas evaporation method were used as a catalyst for liquid phase FT synthesis. The activity of the UFP catalyst was shown to be greater than that of an ordinary precipitated iron catalyst, although the BET surface areas of the two catalysts were almost equal. The addition of alkali metal and copper to iron catalysts is known to be very effective in FT synthesis [ 21. The effect of alkali promotion of the Fe UFP catalyst has been discussed elsewhere [ 1,3]. The purpose of the present work is to prepare alkali-promoted Cu-Fe UFP and to determine the catalytic activity and selectivity of this catalyst for liquid phase FT synthesis. The procedure for preparation of ultrafine alloy particles by reduction in aqueous solution, by means of chemical deposition in the liquid phase (CDL ), has been reported by Van Wonterghem et al. [ 41, who have also mentioned the potential application of amorphous alloy UFP as a catalyst.
L2 EXPERIMENTAL
Apparatus
and procedure
The catalytic study was carried out in a high-pressure flow system using a suspension of a catalyst in hexadecane as the liquid medium (80 ml). The liquid phase (slurry) reactor was a stainless steel autoclave, having an internal volume of 300 cm3, equipped with a stirrer. Syngas with a hydrogen-to-carbon monoxide molar ratio of 1 was fed to the bottom of the reactor through a nozzle and was allowed to react on the suspended catalyst. After passing through a pressure regulator and an ice-cooled receiver, the flow-rate of the gaseous products stream was measured. The distribution of products and the level of carbon monoxide conversion were determined by analyzing the products collected in the three sections of the apparatus: in the aqueous and oil phases in the receiver, in the effluent stream, and in the reaction medium. Concentrations of hydrogen, carbon monoxide, methane and carbon dioxide were determined using a TCD gas chromatograph and other products were analyzed by means of FID gas chromatography. The procedure employed for the addition of potassium to UFP was described in detail elsewhere [ 5 ] : A prescribed amount of colloidal potassium metal was added to the UFP catalyst, suspended in a liquid medium. An ultrasonic generator was used to prepare a suspension of UFP prior to the reaction [ 51. Catal.ysts
Fe and Cu-Fe UFP catalysts listed in Table 1 were prepared by the CDL method: An aqueous solution of KBH, was added dropwise to an aqueous solution of FeCl, alone or to aqueous solutions containing FeC$ and CuCl, with a copper-to-iron weight ratio of 5:95,10:90 and 20:80. The solution was stirred, and the resulting precipitate was washed with water and then with methanol. TABLE 1 Composition of catalysts prepared by the CDL” method Catalyst
Fe Cu( 5%)-Fe Cu ( 10% ) -Fe Cu (20% ) -Fe
Composition (wt.-%) Fe
CU
B
95.6 84.3 83.2 74.3
-
4.0 8.6 4.2 7.9
“Chemical deposition in liquid phase.
4.0 9.6 14.8
K
Others
-
0.4 3.1 3.0 3.0
Fig. 1. Transmission
electron micrograph
of Cu
(10%)-Fe UFP.
The catalyst was dried in vacua and crushed to a fine powder in a nitrogen atmosphere. As can be seen in Table 1, chemical analysis of the Cu-Fe UFP showed that the ratios of copper-to-iron were identical to those in the parent aqueous solutions. Transmission electron micrographs of the catalysts showed typical flakeand sphere-shaped particles, as can be seen in Fig. 1. The size of the sphereshaped particles was about 40-80 nm. Only broad diffraction peaks due to metallic iron and copper were detected by X-ray diffraction analysis of these catalysts. RESULTS
AND DISCUSSION
Liquid phase hydrogenation of carbon monoxide was investigated at 300 “C and 30 atm using the UFP catalysts listed in Table 1. The products distribution and the average space time yields (STY) in the initial 6 h of the runs are summarized in Table 2. It was reported in our previous paper [3] that the promotion by potassium enhances the activity of Fe UFP catalysts prepared by the gas evaporation method at relatively high temperatures ( - 300” C), at which unpromoted Fe UFP or an ordinary potassium-promoted iron precipitation catalyst significant.ly deteriorated due to oxidation. Similarly, the addition of potassium promoted the catalytic activity of Fe UFP prepared by the CDL method, as shown in Table 2. Fig. 2 illustrates the variation in the catalytic activities of potassium-pro-
L4 TABLE 2 Space time yield and product distribution over UFP prepared by the gas evaporation method and by chemical deposition in liquid phase Reaction conditions: temperature, 300°C; pressure, 30 atm; HJCO, 1 mol/mol; W/F, 50 g-cat*min/ CO-mol. Catalyst
Gas Evaporation
CDL”
Cu content (wt.-%)
0
0
K content (wt.-%)
3
0
STY. 10” (C-mol/g-cat-h) Hydrocarbons Oxygenates Carbon dioxide
145 32 209
3
122 9 22
239
11 274
5
10
20
3
3
3
246 10 281
366 10 244
115 13 313
53.0
13.6
60.1
55.6
51.1
62.4
Product distribution (C-%) Hydrocarbons 10.1 C, 9.6 C2 12.8 C:, 10.4 C, 8.3 C, 22.5 G-C,, 9.0 c,,-Cl, 7.6 CKG, CPI+ 9.7
14.3 9.4 15.0 12.5 10.4 28.6 5.9 2.7 1.1
7.4 6.9 11.8 11.3 9.3 22.1 11.9 10.8 8.7
7.6 7.3 12.5 11.5 9.4 23.2 14.1 7.1 7.1
5.0 4.3 7.5 6.6 5.3 15.5 23.1 17.4 15.3
8.8 9.0 14.8 12.5 10.0 23.0 10.3 5.8 5.8
(7.4) 5.4 1.4 0.7
(16.7) 7.0 8.5 0.1 1.1 (83.3) 7.9 30.5 20.1 14.9 9.9 -
(14.7) 3.1 9.8 1.8
(23.0) 9.4 11.8 1.8
(12.6) 2.0 8.4 2.4 -
(6.3) 6.5 27.0 26.6 17.4 7.8 -
(17.0) 6.0 30.0 22.6 12.1 6.3 -
(87.4) 4.7 19.7 21.3 12.1 6.2 17.5
Carbon monoxide conversion ( % )
0 lxygenates Alcohols C, C, C:, C Aldihydes + Ketones C, C:, C, C, C,; C7+
(9.8) 3.9 3.9 1.2 0.8 (90.3) 9.8 18.6 15.2 13.1 8.8 24.8
“Chemical deposition in liquid phase.
(92.6) 6.9 40.7 23.0 11.4 10.6
L5
0
I
I
1
1
I
I
1
2
3
4
5
6
Time on strecm
(hr)
Fig. 2. Catalytic activities of Fe UFP prepared by the gas evaporation method ( o ) and by chemical deposition in liquid phase (A). Reaction conditions: temperature, 3OO;C; pressure, 30 atm; H.JCO, 1 mol/mol; W/F, 50 g-cat*min/CO-mol.
moted Fe UFP prepared by the gas evaporation method and the CDL method. Although the catalytic activity of UFP prepared by the gas evaporation method increased remarkably with time-on-stream [ 31, that of UFP prepared by the CDL method was fairly high from the start of the run, and barely changed for a period of at least 6 h. The activity of the potassium-promoted Cu (10% )-FeUFP catalyst listed in Table 2 was significantly higher than that of the other UFP prepared by either method. The STY of hydrocarbons on the Cu (10% )-Fe UFP catalyst corresponds to 5 kg/kg-cat * h, which is about twenty times as great as that reported for ordinary iron catalysts. In addition, the selectivity of this UFP catalyst for liquid-fraction hydrocarbons was extremely high (ca. 75% on the basis of carbon) even at 300” C which is higher than the ordinary FT synthesis temperature. The carbon number distribution of the hydrocarbon products was analyzed based on the dual-site model, as proposed previously [ 11. The chain growth probabilities and contributions of each kind of site were estimated to give the best fit for the obtained data by means of a nonlinear least-squares method, and the simulated product distributions corresponded satisfactorily with the experimental results. The estimated chain growth probabilities on each kind of site (cy*, cre) and their contributions (C,,Ce) are listed in Table 3. Both chain growth probabilities on the potassium-promoted Cu( 10% )-Fe UFP catalyst were fairly great. Furthermore, the contribution of site B, which was assigned to the potassium-promoted site [ 11, was exceptionally large. This effective promotion of the Cu-Fe UFP with potassium explains the excellent selectivity of this catalyst for liquid fraction hydrocarbons. These results indicate that potassium-promoted Cu-Fe UFP prepared by the CDL method is a promising catalyst for liquid-phase FT synthesis to produce liquid fuels.
L6 TABLE 3 Estimated chain growth probabilities and contributions” Reaction conditions: temperature, 3OO’C; pressure, 30 atm; Hz/CO, 1 mol/mol; W/F, 50 g-cat*min/ CO-mol. Catalyst
Gas evaporation
CDL*
Cu content (wt.-%)
0
0
K content (wt.-%)
3
0
aA
0.60
:: Ca
0.72 0.85 0.28
5 -
10 -
20 -
3
3
3
3
0.58
0.58
0.67
0.73
0.68
0.86 0.81 0.14
0.87 0.71 0.29
0.85 0.73 0.27
0.24 0.87 0.76
0.89 0.90 0.11
“Based on the dual-site model. ‘Chemical deposition in liquid phase. ACKNOWLEDGEMENT
This work was supported by a Grant-in-Aid for Scientific Research, No. 63603005, from the Ministry of Education, Science and Culture, Japan.
REFERENCES H. Itoh, H. Hosaka, T. Ono and E. Kikuchi, Appl. Catal., 40 (1988) 53. M.E. Dry, in J.R. Anderson and M. Boudart (Eds. ), Catalysis: Science and Technology, Vol. 1, Springer, Berlin, 1981, p. 159. H. Itoh, T. Ono, S. Nagano and E. Kikuchi, Sekiyu Grakkaishi, submitted for publication. J. van Wonterghem, S. Marup, C.J.W. Koch, SW. Charles and S. Wells, Nature (London), 322 (1986) 622. H. Itoh, E. Kikuchi and Y. Morita, Sekiyu Gakkaishi, 30 (1987) 324.