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Catalytic experiments for kinetic modeling were carried out in a CREC Riser Simulator (T: 300-400 °C; t: 5-20s). Based on the product analysis of a set of of experiments and on the similar studies by our research group [1-3], a reaction network involving five series-parallel reactions is proposed:
Reaction 1: Dealkylation of MEBs to toluene
Reaction 2: Transalkylation of TMBs and toluene to xylenes
Reaction 3: Disproportionation of TMBs to xylenes and toluene
Reaction 4: Paring reaction of tetramethylbenzenes (TeMBs) to toluene
Reaction 5: Dealkylation of MEBs to xylenes
The intrinsic reaction rates of the individual steps were related to the overall mole balance for the species involved.
Table 1: Estimated Kinetic Parameters |
|||
Parameter |
Value |
Parameter |
Value |
k1,0 |
1.31 ± 0.06 |
E1 |
29.25 ± 2.43 |
k2,0 |
0.03 ± 0.00 |
E2 |
16.82 ± 1.56 |
k3,0 |
0.06 ± 0.01 |
E3 |
11.46 ± 9.14 |
k4,0 |
2.71 ± 0.15 |
E4 |
46.33 ± 3.83 |
k5,0 |
0.98 ± 0.04 |
E5 |
19.54 ± 2.41 |
λ(deactivation) |
0.41 ± 0.15 |
||
ki: units vary; Ei: kJ/mol |
The kinetics parameters (Table 1) were estimated by a least square fitting of the rate equations using the experimental data (120 points). The k0 values for monomolecular reactions were higher than the values for bimolecular reactions. The lowest activation energy required is for transalkylation of TMB with toluene (11.46 kJ/mol), which compares well with the reported value of 11.2 kJ/mol for zeolite β3. Disproportionation of TMBs require somewhat higher activation energy of 16.8 kJ/mol, which is attributed to involvement of two large molecules in this reaction. However, the value of activation energy was much lower than the reported value 29.9 kJ/mol for zeolite β. The highest apparent activation energy (46.3 kJ/mol) was observed for the paring reaction of TeMBs which are the molecules with largest diameter. The catalyst deactivation, estimated as λ = 0.41, indicates a very low coke formation. In conclusion, the hierarchical pore structured composite catalyst is favorable for the conversion of heavy reformate to xylenes. A series-parallel network of five reactions represents the experimental data adequately.
Literature Cited
- S. Ali, K. Al-Nawad, C. Ercan, Y. Wang, Parametric Study of Dealkylation-Transalkylation Reactions over Mordenite-Based Bi-Functional Catalysts, Applied Catalysis A: General, 393 (2010) 96-108.
- S. Ali, F. Almulla, B. Jermy, A. Aitani, R. Abudawoud, M. AlAmer, Z. Qureshi, T. Mohammad, H. Alasiri, Hierarchical composite catalysts of MCM-41 on zeolite Beta for conversion of heavy reformate to xylenes, Journal of Industrial and Engineering Chemistry 98 (2021) 189-199
- Al-Mubaiyedh, S. Ali, S. Al-Khattaf, Kinetic modeling of heavy reformate conversion into xylenes over mordenite-ZSM5 based catalysts, Chemical Engineering Research and Design, 90 (2012) 1943-1955.
Acknowledgements
The authors acknowledge the support of King Fahd University of Petroleum and Minerals for conducting and for permission to present this work.
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