Thermal Diffusion Separation of Petroleum Diamondoids and\t\t\tProtodiamondoids

Abstract

Diamondoids were separated from protodiamondoids (precursors of diamondoids)\t\t\t\t\tin a saturated fraction (150–350°C) of crude oil by thermal diffusion. It was\t\t\t\t\tfound that in the course of thermal diffusion separation,\t\t\t\t\t\tC10–C13 adamantanes\t\t\t\t\t\t(tricyclo[3,3,1,13,7]decanes) and\t\t\t\t\t\tC14–C16 diamantanes\t\t\t\t\t\t(pentacyclo[7,3,1,14,12,02,7,06,11]tetradecanes)\t\t\t\t\tare separated from the corresponding protoadamantanes and protodiamantanes and\t\t\t\t\tdescend to the lower sections of the thermal diffusion column. In contrast to\t\t\t\t\tadamantanes and diamantanes,\t\t\t\t\t\tC18–C19 triamantanes\t\t\t\t\t\t(heptacyclo[7,7,1,13,15,01,12,02,7,04,13,06,11]octadecanes)\t\t\t\t\tare not separated from prototriamantanes and are concentrated in the lower\t\t\t\t\tsections of the thermal diffusion column. Catalytic isomerization of this\t\t\t\t\tthermal diffusion fraction with aluminum bromide was carried out to further\t\t\t\t\tconfirm that the numerous compounds that have the same characteristic ions as\t\t\t\t\ttriamantanes but elute later are polycyclic (most likely bridged) hydrocarbons,\t\t\t\t\tspecifically prototriamantanes. As a result, all these polycyclic compounds were\t\t\t\t\tisomerized into triamantanes. Similarly, in the course of isomerization of\t\t\t\t\tthermal diffusion fractions containing protoadamantanes and protodiamantanes,\t\t\t\t\tall of these turned into adamantanes and diamantanes, respectively.