Hydrocracking and Hydroisomerization of Long-Chain n-Paraffins. Reactivity and Reaction Pathway for Base Oil Formation

The formation of base oil components by the hydroconversion of long-chain n -paraffins [i.e., n -octacosane ( n -C 28 ), n -hexatriacontane ( n -C 36 ), and n -tetratetracontane ( n -C 44 )] on a 0.3% Pt/amorphous silica−alumina catalyst in a stirred microautoclave was investigated. The reaction pathway of hydroconversion, formation of base oil components, and kinetics were determined. The reaction can be described by a reaction network in which the conversion of n -paraffins occurs by three competitive reactions that directly lead to the formation of cracking products and two pseudocomponents: iso-C n lube (i.e., lump of isoparaffins with sufficiently low pour points to make them suitable for a base oil) and iso-C n nolube (i.e., lump of isoparaffins with pour points that are too high, making them unsuitable for a base oil). During reaction, the iso-C n nolube fraction is converted into iso-C n lube through subsequent hydroisomerization reactions. Both iso-C n lube and iso-C n nolube pseudocomponents further react to give cracking products. The conversion rate constants showed a significant decrease with increasing chain length, whereas the energies of activation did not display any significant change. A consistent decrease of iso-C n and iso-C n lube selectivity for longer chain lengths was observed, whereas reaction temperature was not found to play a significant role in determining the maximum yields of both iso-C n and iso-C n lube that could be achieved.