Fischer-Tropsch synthesis using H 2/CO/CO 2 syngas mixtures: A comparison of paraffin to olefin ratios for iron and cobalt based catalysts

Yali Yao; Xinying Liu; Diane Hildebrandt; David Glasser

doi:10.1016/j.apcata.2012.04.041

Fischer-Tropsch synthesis using H ₂/CO/CO ₂ syngas mixtures: A comparison of paraffin to olefin ratios for iron and cobalt based catalysts

Yali Yao, Xinying Liu, Diane Hildebrandt, David Glasser

Research output: Contribution to journal › Article › peer-review

40 Scopus citations

Abstract

Fischer-Tropsch synthesis (FTS) using H ₂/CO/CO ₂ syngas mixtures over cobalt and iron based catalysts was carried out in a fixed-bed reactor. CO ₂ rich feeds produce products that are mostly light hydrocarbons with higher molar paraffin to olefin (P/O) ratio, whereas CO rich feeds shift the product composition to an FT type product with higher olefin product selectivity over both iron and cobalt based catalysts. Although the P/O ratio for FTS is strongly dependent on the operating conditions, the experimental evidence shows that the linear relationship between P _(n+1)/O _(n+1) and P _(n)/O _(n) holds for a large number of experiments. It is also shown to be independent of the type of the reactor, the composition of the syngas, reaction conditions and the kind of catalyst. Two features about the ratio of ξ = [P _(n+1)/O _(n+1)]/[P _(n)/O _(n)] for the FT products have been identified: (1) with n > 2, the experimental values of ξ _n>2 are higher than 1, fairly constant and independent of chain length n; (2) with chain length n = 2, the ratio of P ₃/O ₃ to P ₂/O ₂ (ξ _n=2) is significantly different, and shows that ξ _n=2 ξ _n>2. An equilibrium hypothesis is considered in an attempt to explain this experimental phenomenon. A simple vapor-liquid equilibrium (VLE) model indicates that the ratio of P _(n+1)/O _(n+1) to P _(n)/O _(n) changes in a range of (1, 1/β), where β is the variation of the vapor pressure coefficient, which is related to the incremental energy of vaporization per CH ₂ unit of the hydrocarbon chain. Our experimental results support the expression when the chain length n > 2. But with chain length n = 2, this expression is unable to explain the relationship between P ₃/O ₃ and P ₂/O ₂. Another model, based on quasi reaction equilibrium, is developed to explain the linear relationship between P _(n+1)/O _(n+1) and P _(n)/O _(n). We assume that the reaction of C _n+1H _2n+2 + C _nH _2n+2 = C _n+1H _2n+4 + C _nH _2n reaches quasi-equilibrium. Because the experimental results are quite close to the equilibrium calculations, we postulate that the product distribution might be determined by considering reaction equilibrium.

Original language	English (US)
Pages (from-to)	58-68
Number of pages	11
Journal	Applied Catalysis A: General
Volume	433-434
DOIs	https://doi.org/10.1016/j.apcata.2012.04.041
State	Published - Aug 8 2012
Externally published	Yes

All Science Journal Classification (ASJC) codes

Catalysis
Process Chemistry and Technology

Keywords

CO hydrogenation
CO hydrogenation
Fischer-Tropsch synthesis
Paraffin to olefin ratio
Quasi-equilibrium
Vapor-liquid equilibrium

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10.1016/j.apcata.2012.04.041

Cite this

@article{32d6f5d04d53485f8490955ff110dc3a,

title = "Fischer-Tropsch synthesis using H 2/CO/CO 2 syngas mixtures: A comparison of paraffin to olefin ratios for iron and cobalt based catalysts",

abstract = "Fischer-Tropsch synthesis (FTS) using H 2/CO/CO 2 syngas mixtures over cobalt and iron based catalysts was carried out in a fixed-bed reactor. CO 2 rich feeds produce products that are mostly light hydrocarbons with higher molar paraffin to olefin (P/O) ratio, whereas CO rich feeds shift the product composition to an FT type product with higher olefin product selectivity over both iron and cobalt based catalysts. Although the P/O ratio for FTS is strongly dependent on the operating conditions, the experimental evidence shows that the linear relationship between P (n+1)/O (n+1) and P (n)/O (n) holds for a large number of experiments. It is also shown to be independent of the type of the reactor, the composition of the syngas, reaction conditions and the kind of catalyst. Two features about the ratio of ξ = [P (n+1)/O (n+1)]/[P (n)/O (n)] for the FT products have been identified: (1) with n > 2, the experimental values of ξ n>2 are higher than 1, fairly constant and independent of chain length n; (2) with chain length n = 2, the ratio of P 3/O 3 to P 2/O 2 (ξ n=2) is significantly different, and shows that ξ n=2 ξ n>2. An equilibrium hypothesis is considered in an attempt to explain this experimental phenomenon. A simple vapor-liquid equilibrium (VLE) model indicates that the ratio of P (n+1)/O (n+1) to P (n)/O (n) changes in a range of (1, 1/β), where β is the variation of the vapor pressure coefficient, which is related to the incremental energy of vaporization per CH 2 unit of the hydrocarbon chain. Our experimental results support the expression when the chain length n > 2. But with chain length n = 2, this expression is unable to explain the relationship between P 3/O 3 and P 2/O 2. Another model, based on quasi reaction equilibrium, is developed to explain the linear relationship between P (n+1)/O (n+1) and P (n)/O (n). We assume that the reaction of C n+1H 2n+2 + C nH 2n+2 = C n+1H 2n+4 + C nH 2n reaches quasi-equilibrium. Because the experimental results are quite close to the equilibrium calculations, we postulate that the product distribution might be determined by considering reaction equilibrium.",

keywords = "CO hydrogenation, CO hydrogenation, Fischer-Tropsch synthesis, Paraffin to olefin ratio, Quasi-equilibrium, Vapor-liquid equilibrium",

author = "Yali Yao and Xinying Liu and Diane Hildebrandt and David Glasser",

year = "2012",

month = aug,

day = "8",

doi = "10.1016/j.apcata.2012.04.041",

language = "English (US)",

volume = "433-434",

pages = "58--68",

journal = "Applied Catalysis A: General",

issn = "0926-860X",

publisher = "Elsevier B.V.",

}

TY - JOUR

T1 - Fischer-Tropsch synthesis using H 2/CO/CO 2 syngas mixtures

T2 - A comparison of paraffin to olefin ratios for iron and cobalt based catalysts

AU - Yao, Yali

AU - Liu, Xinying

AU - Hildebrandt, Diane

AU - Glasser, David

PY - 2012/8/8

Y1 - 2012/8/8

N2 - Fischer-Tropsch synthesis (FTS) using H 2/CO/CO 2 syngas mixtures over cobalt and iron based catalysts was carried out in a fixed-bed reactor. CO 2 rich feeds produce products that are mostly light hydrocarbons with higher molar paraffin to olefin (P/O) ratio, whereas CO rich feeds shift the product composition to an FT type product with higher olefin product selectivity over both iron and cobalt based catalysts. Although the P/O ratio for FTS is strongly dependent on the operating conditions, the experimental evidence shows that the linear relationship between P (n+1)/O (n+1) and P (n)/O (n) holds for a large number of experiments. It is also shown to be independent of the type of the reactor, the composition of the syngas, reaction conditions and the kind of catalyst. Two features about the ratio of ξ = [P (n+1)/O (n+1)]/[P (n)/O (n)] for the FT products have been identified: (1) with n > 2, the experimental values of ξ n>2 are higher than 1, fairly constant and independent of chain length n; (2) with chain length n = 2, the ratio of P 3/O 3 to P 2/O 2 (ξ n=2) is significantly different, and shows that ξ n=2 ξ n>2. An equilibrium hypothesis is considered in an attempt to explain this experimental phenomenon. A simple vapor-liquid equilibrium (VLE) model indicates that the ratio of P (n+1)/O (n+1) to P (n)/O (n) changes in a range of (1, 1/β), where β is the variation of the vapor pressure coefficient, which is related to the incremental energy of vaporization per CH 2 unit of the hydrocarbon chain. Our experimental results support the expression when the chain length n > 2. But with chain length n = 2, this expression is unable to explain the relationship between P 3/O 3 and P 2/O 2. Another model, based on quasi reaction equilibrium, is developed to explain the linear relationship between P (n+1)/O (n+1) and P (n)/O (n). We assume that the reaction of C n+1H 2n+2 + C nH 2n+2 = C n+1H 2n+4 + C nH 2n reaches quasi-equilibrium. Because the experimental results are quite close to the equilibrium calculations, we postulate that the product distribution might be determined by considering reaction equilibrium.

AB - Fischer-Tropsch synthesis (FTS) using H 2/CO/CO 2 syngas mixtures over cobalt and iron based catalysts was carried out in a fixed-bed reactor. CO 2 rich feeds produce products that are mostly light hydrocarbons with higher molar paraffin to olefin (P/O) ratio, whereas CO rich feeds shift the product composition to an FT type product with higher olefin product selectivity over both iron and cobalt based catalysts. Although the P/O ratio for FTS is strongly dependent on the operating conditions, the experimental evidence shows that the linear relationship between P (n+1)/O (n+1) and P (n)/O (n) holds for a large number of experiments. It is also shown to be independent of the type of the reactor, the composition of the syngas, reaction conditions and the kind of catalyst. Two features about the ratio of ξ = [P (n+1)/O (n+1)]/[P (n)/O (n)] for the FT products have been identified: (1) with n > 2, the experimental values of ξ n>2 are higher than 1, fairly constant and independent of chain length n; (2) with chain length n = 2, the ratio of P 3/O 3 to P 2/O 2 (ξ n=2) is significantly different, and shows that ξ n=2 ξ n>2. An equilibrium hypothesis is considered in an attempt to explain this experimental phenomenon. A simple vapor-liquid equilibrium (VLE) model indicates that the ratio of P (n+1)/O (n+1) to P (n)/O (n) changes in a range of (1, 1/β), where β is the variation of the vapor pressure coefficient, which is related to the incremental energy of vaporization per CH 2 unit of the hydrocarbon chain. Our experimental results support the expression when the chain length n > 2. But with chain length n = 2, this expression is unable to explain the relationship between P 3/O 3 and P 2/O 2. Another model, based on quasi reaction equilibrium, is developed to explain the linear relationship between P (n+1)/O (n+1) and P (n)/O (n). We assume that the reaction of C n+1H 2n+2 + C nH 2n+2 = C n+1H 2n+4 + C nH 2n reaches quasi-equilibrium. Because the experimental results are quite close to the equilibrium calculations, we postulate that the product distribution might be determined by considering reaction equilibrium.

KW - CO hydrogenation

KW - Fischer-Tropsch synthesis

KW - Paraffin to olefin ratio

KW - Quasi-equilibrium

KW - Vapor-liquid equilibrium

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VL - 433-434

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JO - Applied Catalysis A: General

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