Selective production of a jet fuel fraction through hydrocracking of n-heptadecane using Pt-supported β-zeolite-Al2O3 composite catalysts

Abstract

Hydrocarbon fuels can be produced from a wide range of carbonaceous materials, including biomass and waste plastics, through the Fischer-Tropsch (FT) process. As sustainable aviation fuel (SAF) becomes increasingly important, selective production of a jet fuel fraction from FT wax is required; however, this has not yet been achieved. In this study, hydrocracking of n-heptadecane (n-C17) as a model diesel fuel fraction of FT wax was estimated to obtain a jet fuel fraction selectively using Hβ-zeolite-Al₂O₃ composite-supported Pt catalysts. The Hβ-zeolite (25 wt%, SiO₂/Al₂O₃ = 100)-Al₂O₃ (60 wt%)-binder (alumina-sol, 15 wt% as Al₂O₃) composite-supported Pt (0.5 wt%) catalyst (0.5Pt/β(100)60A) was tested for hydrocracking of n-heptadecane using a fixed-bed flow reactor under the following conditions: 0.5 MPa H₂ pressure, H₂ 300 mL min^-1, WHSV 2.3 h^-1 and 2 g catalyst weight. After hydrocracking of n-C17 to form gaseous hydrocarbons at 300 °C without pre-reduction of 0.5Pt/β(100)60A, the reaction was performed at 250 °C. A conversion of 97% and a selectivity of 79% for the C8-C14 fraction of the jet fuel range were achieved. The sum of the selectivity for the C7 and C8 fractions was higher than 50%. To confirm reproducibility, when the hydrocracking of n-C17 using the catalyst pre-reduced at 270 °C was performed at 300-304 °C, a conversion of 93% and a selectivity of 55% for C8-C14 were achieved at 302 °C, with high selectivity for C8 and C9, although significant amounts of gaseous products were observed simultaneously. Finally, when the hydrocracking of n-C17 using a catalyst pre-reduced at 310 °C was performed at 300-308 °C, a conversion of 99% and a selectivity of 63% for C8-C14 were achieved at 308 °C, and the selectivity for gaseous products reduced to 16%. However, the high selectivity for C8 and C9 was lost, and the same amount of each fraction of C8-C12 was simultaneously observed. It was suggested that the high selectivity of the β-zeolite-containing catalyst for the C8 and C9 fractions could be attributed to C-H bond activation of the carbon at position 9 of n-C17 on reduced Pt within the micropores of β-zeolite.

Fig. 1. Carbon number distribution of products in hydrocracking of n-heptadecane using 0.5Pt/β(100)60A without pre-reduction H₂ pressure 0.5 MPa, gas flow rate 300 cm³ min⁻¹, WHSV 2.3 h⁻¹, catalyst 2.0 g.

Fig. 2. Carbon number distribution of products in the second hydrocracking run of n-heptadecane using pre-reduced 0.5Pt/β(100)60A. Transfer order in reaction temp.: 270 → 300 → 304 → 303 → 302 → 301 °C. H₂ pressure 0.5 MPa, gas flow rate 300 cm³ min⁻¹, WHSV 2.3 h⁻¹, catalyst 2.0 g.

Fig. 3. Carbon number distribution of products in the fourth hydrocracking run of n-heptadecane using pre-reduced 0.5Pt/β(100)60A. Transfer order in reaction temp.: 310 → 308 → 306 → 304 → 302 → 300 °C. H₂ pressure 0.5 MPa, gas flow rate 300 cm³ min⁻¹, WHSV 2.3 h⁻¹, catalyst 2.0 g.

Fig. 4. Carbon number distribution of products in hydrocracking of n-heptadecane using pre-reduced 0.5Pt/β(100)35A. Transfer order in reaction temp.: 250 → 255 → 260 → 245 → 250 °C. H₂ pressure 0.5 MPa, gas flow rate 300 cm³ min⁻¹, WHSV 2.3 h⁻¹, catalyst 2.0 g.

Fig. 5. Carbon number distribution of products in hydrocracking of n-heptadecane using pre-reduced 0.5Pt/β(100)35A. Transfer order in reaction temp.: 260 → 250 → 251 → 252 → 253 → 254 °C. H₂ pressure 0.5 MPa, gas flow rate 300 cm³ min⁻¹, WHSV 2.3 h⁻¹, catalyst 2.0 g.

Fig. 6. Reaction mechanism for selective production of C8 and C9 fractions on 0.5Pt/β(100)60A in the second run.

Fig. 7. Hypothetical reaction routes on 0.5Pt/β(100)60A at 303 °C in the second run.

Fig. 8. Reaction mechanism on 0.5Pt/β(100)60A in the fourth run.