Development of Pt/Zeolite for Selective Conversion of <i>n</i>-Decane and <i>n</i>-Dodecane to <i>i</i>-C6-7 and <i>i</i>-C7-9

Abstract

Jet fuel production from long-chain n-paraffins obtained by hydroprocessing of vegetable oils and animal fats has attracted immense interest. Isomerization and mild cracking are essential to transform long-chain n-paraffins with chain lengths of 16, 18, or 20 into bio-jet fuels consisting of isoparaffins with carbon numbers ranging from 9 to 15. Bifunctional catalysts consisting of noble metal and metal oxide support with solid acid, such as Pt loaded zeolite, are promising for hydroisomerization and cracking reactions. However, the effect of the specific properties of Pt loaded zeolite on the hydroisomerization and simultaneous mild cracking activity are not understood. We investigated the hydroisomerization and cracking of n-paraffins into isoparaffins with shorter chain length by 3-5 carbons over Pt loaded zeolite. n-Decane was first used as a reactant to simplify the reactions, and the effects of zeolite framework structure, solid acid sites, and Pt loading were investigated. 0.5 wt% Pt loaded MFI with Si/Al of 200 was found to maximize the targeted isoparaffin yield. Further modification of the optimized catalyst was performed for isoparaffin production from n-dodecane. Addition of MgO to the catalyst successfully suppressed overcracking and improved the desired isoparaffin yield.

Characterization and Hydroisomerization Performance of Mg‐Promoted, Pt/ZSM‐23‐Based Catalysts

“…However, the data in Figure 6 indicate that catalyst overloading with Mg can be unfavorable for the best performance. Our results are also in line with recent study of Mg‐promoted Pt/MFI catalysts, where the addition of MgO to the catalyst allowed suppressing overcracking (dodecane as the substrate) and improving isoparaffin yield [20] . Such beneficial effect of Mg is certainly connected with the decreasing of surface acidity (Table 2) and elimination of acid sites on the external surface, which cannot provide shape selectivity for the products.…”

“…Our results are also in line with recent study of Mgpromoted Pt/MFI catalysts, where the addition of MgO to the catalyst allowed suppressing overcracking (dodecane as the substrate) and improving isoparaffin yield. [20] Such beneficial effect of Mg is certainly connected with the decreasing of surface acidity (Table 2) and elimination of acid sites on the external surface, which cannot provide shape selectivity for the products. We have performed auxiliary experiments using 2,2,4trimethylpentane (TMP) as a substrate.…”

“…[18] In this respect, more attractive is tuning surface acidity through addition of Group-II elementsbecause of seeming simplicity of the method. [10,19,20] Parmar et al [21,22] have examined the effect of Ca, Mg and Ba ions on catalytic properties of ZSM-22 and ZSM-12 zeolites in nhexadecane hydroconversion and reported that the ion exchange of H + for Ba 2 + or Ca 2 + was effective for increasing isomerization selectivity, whereas no selectivity improvement was found in the case of Mg-modified samples. Lee et al [23] used impregnation route for promoting and observed an increased isomerization performance for a Pt/ZSM-23/Al 2 O 3 sample with a large MgO loading (3 wt.…”

“…However, such approaches are rather complex and may require additional conditions to be met (e. g., partial blockage of micropores) [18] . In this respect, more attractive is tuning surface acidity through addition of Group‐II elements – because of seeming simplicity of the method [10,19,20] . Parmar et al [21,22] .…”