Abstract
The chain length and hydrocarbon type significantly affect the production of light olefins during the catalytic pyrolysis of naphtha. Herein, for a better catalyst design and operation parameters optimization, the reaction pathways and equilibrium yields for the catalytic pyrolysis of C5–8n/iso/cyclo-paraffins were analyzed thermodynamically. The results revealed that the thermodynamically favorable reaction pathways for n/iso-paraffins and cyclo-paraffins were the protolytic and hydrogen transfer cracking pathways, respectively. However, the formation of light paraffin severely limits the maximum selectivity toward light olefins. The dehydrogenation cracking pathway of n/iso-paraffins and the protolytic cracking pathway of cyclo-paraffins demonstrated significantly improved selectivity for light olefins. The results are thus useful as a direction for future catalyst improvements, facilitating superior reaction pathways to enhance light olefins. In addition, the equilibrium yield of light olefins increased with increasing the chain length, and the introduction of cyclo-paraffin inhibits the formation of light olefins. High temperatures and low pressures favor the formation of ethylene, and moderate temperatures and low pressures favor the formation of propylene. n-Hexane and cyclohexane mixtures gave maximum ethylene and propylene yield of approximately 49.90% and 55.77%, respectively. This work provides theoretical guidance for the development of superior catalysts and the selection of proper operation parameters for the catalytic pyrolysis of C5–8n/iso/cyclo-paraffins from a thermodynamic point of view.
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Abbreviations
- \({\Delta _{\rm{f}}}H_{\rm{m}}^\theta \) :
-
Standard molar formation enthalpy, kJ
- T :
-
Reaction temperature, K
- C p,m :
-
Molar heat capacity at constant pressure, J·mol−1 ·K−1
- \({\Delta _{\rm{f}}}S_{\rm{m}}^\theta \) :
-
Standard molar formation entropy, J·K−1
- C p,m,i :
-
Contribution value of each group to the Cp,m
- N i :
-
The number of groups
- \({\Delta _{\rm{r}}}H_{\rm{m}}^\theta \) :
-
Standard molar reaction enthalpy, kJ
- \({\Delta _{\rm{r}}}S_{\rm{m}}^\theta \) :
-
Standard molar reaction entropy, J·K−1
- \({\Delta _{\rm{r}}}G_{\rm{m}}^\theta \) :
-
Standard molar reaction Gibbs free energy, kJ
- K θ :
-
Standard equilibrium constant
- R :
-
Molar gas constant, J·mol−1 ·K−1
- G t :
-
Total Gibbs free energy of mixed system, kJ
- n t :
-
Numbers of moles of species i
- μ i :
-
Chemical potential of species i
- λ k :
-
Lagrange multiplier of the kth element
- β ki :
-
Number of atoms of the kth element in a mole of the ith species
- b k :
-
Total moles of the kth element, mol
- \(\Delta G_{i,{\rm{f}}}^\theta \) :
-
Standard mole generation Gibbs free energy of species i, kJ·mol−1
- P :
-
Total hydrocarbon pressure, MPa
- P θ :
-
Standard pressure, MPa
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Acknowledgements
The authors acknowledge the support from the National Natural Science Foundation of China (Grant No. 22021004) and the National Key Research and Development Program of China (Grant No. 2020YFA0210900)
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Liu, D., Zhi, Y., Bai, Y. et al. Thermodynamic analysis of reaction pathways and equilibrium yields for catalytic pyrolysis of naphtha. Front. Chem. Sci. Eng. 16, 1700–1712 (2022). https://doi.org/10.1007/s11705-022-2207-6
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DOI: https://doi.org/10.1007/s11705-022-2207-6