Hydroisomerization and hydrocracking of n-alkanes. 1. Ideal hydroisomerization PtHY catalysts

Abstract

The transformation of n-heptane was studied at 250 °C, 1 atm, and PH/Pn-heptane = 9 on a series of PtHY catalysts containing from 0.1 to 1.5 wt % platinum and having Si/AI atomic ratios of 3, 9, or 35. The activities, stabilities, and selectivities of the catalysts are clearly governed by the number of their acid sites (nA) and hydrogenating sites (np,). nA is defined here as the number of acid sites on which the adsorption heat of NH3 is greater than 100 kj mol"1 and zip, as the number of accessible platinum atoms. For nA/n w <10 (i.e., with catalysts with about 1 wt % Pt and Si/AI atomic ratio of 9 or 35) the formation of monobranched, bibranched, and tribranched isomers and cracking products is a step by step process. Such catalysts present the best possible hydroisomerization selectivity, the cracking products appearing only at conversion rates of over 50% and the yield in isomers reaching 65% for a total conversion rate of 75-80%. Thus they can be considered as "ideal hydroisomerization catalysts".

Differences between MFI- and MEL-Type Zeolites in Paraffin Hydrocracking

“…It yields an n-C 4 /C 3 instead of an i-C 4 /C 3 product pair (28,(37)(38)(39). It occurs when there are multiple transformations at acid sites inside pores that significantly limit sorbate mobility (14,28,38,40).…”

“…It has been shown that n-C 7 and n-C 10 share essentially the same hydroconversion mechanism (37,39,44,45,46). The only difference between n-C 7 and n-C 10 is that the latter can hydroisomerize into a tribranched "iii-C 10 " isomer with both geminal and quasi-vicinal methyl groups (i.e., with methyl groups on α,α,γ positions) (39, 44-48) before hydrocracking, whereas the former is too short to form the equivalent iii-C 7 hydrocracking precursor.…”

“…In practice, consecutive hydrocracking and hydroisomerization yield a secondary product slate interfering with a straightforward identification (19). The primary i-C 7 isomers are particularly prone to consecutive reactions, because they are the most reactive (37,39,51) and because they will stay adsorbed longer than the other primary hydrocracking products will (52). By contrast, the C 5 isomers are relatively unreactive (37, 39, 51) and are short enough to desorb rapidly (and stay desorbed) due to competitive adsorption with longer molecules (52).…”

Continuous-Flow Hydroisomerization of C5–C7 Alkanes Using Mechanochemically Synthesized Supported Pt and Pd-SBA-15 Materials

“…n-Heptane was the selected starting feedstock for all processes as widely used in literature [26][27][28] and more reactive raw material as compared to n-hexane or n-pentane [29]. This compound is also present in the gasoline fraction.…”

Hydroisomerization of n-hexadecane: remarkable selectivity of mesoporous silica post-synthetically modified with aluminum

“…16,18 Furthermore, the degree of noble metal dispersion, interplay between hydrogenation/dehydrogenation and acidic sites, and spatial constraints within zeolitic micropores were demonstrated to affect isomerization activity and selectivity. 16,[19][20][21] Even though hydroisomerization process has been extensively studied for decades, there is a need for highly selective catalyst, especially at high temperature conditions. In industrial hydrocarbon conversion settings, high temperature conditions are favored to increase the overall turnover rate of the reactions.…”