1 Introduction
2 Experimental
2.1 Materials and Chemicals
2.2 Synthesis of mesoporous SBA-15 and KIT-6 silica
2.3 Formulation of the composite catalysts
Tab.1 Proportion of components in the formulated composite catalysts |
Composite catalyst | Weight percent of the component/wt % | ||
---|---|---|---|
ZY | ZSM-5 | Mesoporous silica | |
ZY/ZSM-5/KIT-6(35:5:60) | 35 | 5 | 60 |
ZY/ZSM-5/KIT-6(30:10:60) | 30 | 10 | 60 |
ZY/ZSM-5KIT-6(20:20:60) | 20 | 20 | 60 |
ZY/ZSM-5/SBA-15(35:5:60) | 35 | 5 | 60 |
ZY/ZSM-5/SBA-15(30:10:60) | 30 | 10 | 60 |
ZY/ZSM-5/SBA-15(20:20:60) | 20 | 20 | 60 |
ZY/ZSM-5/MCM-41(35:5:60) | 35 | 5 | 60 |
ZY/ZSM-5/MCM-41(30:10:60) | 30 | 10 | 60 |
ZY/ZSM-5/MCM-41(20:20:60) | 20 | 20 | 60 |
2.4 Characterization of materials
2.5 PFG-NMR analysis
2.6 Catalytic cracking
Fig.1 Schematic of the experimental rig for performing the catalytic cracking reaction. 1. pressure regulators for N2 and air; 2. valves; 3. mass flow controllers; 4. bubblers; 5. chiller bath; 6. pressure gauge; 7. pressure relief valve; 8. reactor tube; 9. furnace; 10. glass wool; 11. catalyst bed; 12. glass beads; 13. GC; 14. data collector. |
3 Results and discussion
3.1 Physicochemical properties of the materials under investigation
Tab.2 Textural properties of the mesoporous silicas and the composite catalysts |
Materials | Specific surface areaa)/(m2·g–1) | Specific surface areab)/(cm3·g–1) | Si/Alc) | |||||
---|---|---|---|---|---|---|---|---|
SBETa) | Sextb) | Smicroc) | Vtotald) | Vmicroe) | Vmesof) | |||
KIT-6 | 755 | 559 | 202 | 0.34 | 0.11 | 0.23 | – | |
MCM-41 | 810 | 767 | 42 | 0.33 | 0.02 | 0.31 | – | |
SBA-15 | 755 | 442 | 312 | 0.66 | 0.16 | 0.5 | – | |
ZY/ZSM-5/KIT-6(35:5:60) | 601 | 418 | 183 | 0.30 | 0.1 | 0.2 | 48.4 | |
ZY/ZSM-5/KIT-6(30:10:60) | 585 | 351 | 234 | 0.27 | 0.12 | 0.15 | 47.5 | |
ZY/ZSM-5/KIT-6(20:20:60) | 541 | 331 | 211 | 0.25 | 0.11 | 0.14 | 42.1 | |
ZY/ZSM-5/MCM-41(35:5:60) | 726 | 564 | 161 | 0.31 | 0.08 | 0.23 | 36.7 | |
ZY/ZSM-5/MCM-41(30:10:60) | 705 | 535 | 169 | 0.31 | 0.09 | 0.22 | 36.2 | |
ZY/ZSM-5/MCM-41(20:20:60) | 718 | 583 | 135 | 0.31 | 0.07 | 0.24 | 36.3 | |
ZY/ZSM-5/SBA-15(35:5:60) | 604 | 391 | 212 | 0.30 | 0.11 | 0.19 | 16 | |
ZY/ZSM-5/SBA-15(30:10:60) | 535 | 301 | 234 | 0.25 | 0.12 | 0.13 | 20.4 | |
ZY/ZSM-5/SBA-15(20:20:60) | 577 | 368 | 210 | 0.30 | 0.11 | 0.19 | 26.7 |
a) Total surface area (SBET) by the BET method, external surface area (Sext) = SBET – Smicro, microspore surface area by the t-plot method; b) total pore volume at P/P0 (Vtotal) = maximum pore volume, microspores volume (Vmicro), mesoporous volume (Vmeso); c) by XRF; d) by the BJH method. |
3.2 Catalytic cracking of n-Hptane (n-C7)
Tab.3 Averaged activity and selectivity data of n-C7 cracking over the selected composite catalysts at 550 °C, 0.4 h–1 and atmospheric pressure |
Composite catalyst | Conversion | C2=–C4=a) | C2=/C3= | C2=/C2 | C3=/C3 | C4=/C4 | O/Pb) | HTCc) |
---|---|---|---|---|---|---|---|---|
% | – | |||||||
ZY/ZSM-5/SBA-15(20:20:60) | 84 | 26.2 | 0.8 | 2.5 | 0.6 | 0.4 | 0.7 | 0.7 |
ZY/ZSM-5/KIT-6(20:20:60) | 94 | 26.6 | 0.6 | 2.5 | 0.7 | 0.5 | 0.7 | 0.7 |
ZY/ZSM-5/MCM-41(20:20:60) | 82 | 25.5 | 0.5 | 2.4 | 0.7 | 0.5 | 1.1 | 0.6 |
a) C2=–C4= : averaged total yield of LOs; b) O/P: olefin-to-paraffin ratio; c) HTC = (n-C4 + i-C4)/C4=). |
3.3 PFG-NMR study of self-diffusion of n-C7 within the selected composite catalysts
Tab.4 Relevant diffusion coefficients and calculated tortuosity values by PFG-NMR |
Composite | Dself of n-C7 | D1 (10–10 m2·s–1) | D2 | τ1 | τ2 |
---|---|---|---|---|---|
ZY/ZSM-5/KIT-6 (20:20:60) | 32.4 | 11.2 ± 0.2 | 2.0 ± 0.2 | 2.9 | 16.3 |
ZY/ZSM-5/SBA-15 (20:20:60) | 9.7 ± 0.1 | 2.4 ± 0.2 | 3.4 | 13.7 | |
ZY/ZSM-5/MCM-41 (20:20:60) | 6.9 ± 0.1 | 1.7 ± 0.1 | 4.7 | 19.3 |