Effects of Zn Addition into ZSM-5 Zeolite on Dehydrocyclization-Cracking of Soybean Oil Using Hierarchical Zeolite-Al2O3 Composite-Supported Pt/NiMo Sulfided Catalysts

Abstract

Zn-exchanged ZSM-5-Al₂O₃ (ZA) composite-supported Pt/NiMo (NM) sulfided catalysts were prepared using the conventional kneading method and were tested for dehydrocyclization-cracking of soybean oil. The effects of Zn addition on the activity and selectivity of products were investigated under moderate-pressure conditions of 0.5 and 1.0 MPa H₂ in the temperature range of 420-580 °C. At the temperature 500 °C and higher, most of the sample soybean oil was converted at both the pressures of 0.5 and 1.0 MPa. At 1.0 MPa and 500 °C, the effects of Zn addition appeared and increased the yields of aromatics, while the catalyst without Zn produced larger amounts of products with more than C18. Further, at 0.5 MPa and 580 °C, the gas formation was inhibited in comparison to the cases of 1.0 MPa and the effects of the Zn addition also appeared and increased the yields of aromatics, while the catalyst without Zn produced larger amounts of products with more than C18. The Pt/NM/Zn(122)ZA test catalyst produced more than 63% of liquid fuels in the range C5-C18, and the yield of aromatics was 13%, the maximum value in the present study. The following reaction routes were proposed. The structure of triglyceride is converted by hydrocracking to three molecules of aliphatic acids and propane on the surface PtNiMo sulfide on Al₂O₃ support. The converted aliphatic acids are decomposed through decarboxylation to hydrocarbon fragments, which are further decomposed by cracking on the acid sites of the catalyst, the surface of NiMo sulfide, Al₂O₃, or ZSM-5. Finally, the formed C3 and C4 olefins are transformed to aromatics through the Diels-Alder reaction on the Zn species of ZnZSM-5. On the other hand, although gases were relatively small in amount, aromatic compounds were formed significantly, suggesting that cyclization might directly occur without conversion to gaseous hydrocarbons to some extent.

Figure 1

XRD patterns of Pt/NM/ZnZSM-5-Al₂O₃ composite catalysts.

Figure 2

NH₃-TPD curves and amount of NH₃ desorbed in Pt/NM/ZnZSM-5-Al₂O₃ composite catalysts. The total amount of NH₃ desorbed is given on the right-hand side of the figure. The amounts of weak acid sites detected in the range of 100–350 °C (left) and strong acid sites detected in the range of 350–650 °C (right) are given in parentheses.

Figure 3

Effect of temperature on the conversion of soybean oil via dehydrocyclization-cracking reaction using Pt/NiMo/ZnZSM-5-Al₂O₃ composite catalysts.

Figure 4

Carbon number distribution of products in dehydrocyclization-cracking reaction of soybean oil using Pt/NiMo/ZnZSM-5-Al₂O₃ composite catalysts.

Figure 5

Reaction routes of aromatics formation of soybean oil via dehydrocyclization-cracking using Pt/NiMo/ZnZSM-5-Al₂O₃ composite catalysts.