Trapping of paraffin and other compounds by asphaltenes detected by laser desorption ionization-time of flight mass spectrometry (LDI-TOF MS): Role of A1 and A2 asphaltene fractions in this trapping
Résumé
Trapping of compounds by asphaltenes in guest-host complexes (GHC) is an important phenomenon relevant to many properties of the system, such as asphaltene structure, swelling and solvent trapping, geochemical impact, as well as the trapping of metalloporphyrins, free radicals, resins, and other crude oil components, such as, e.g., paraffin. Several trapping mechanisms, such as adsorption and occlusion, during asphaltene separation from crude oil can be considered, but most interest is attracted to GHC, in which the guest is firmly bound and cannot be completely liberated from the host by solvent extraction. An example of such trapping is presented, with the guest being paraffinic and other resin-like compounds hereafter called trapped compounds (TCs). TCs were isolated from asphaltenes by the partition of the asphaltene sample in fractions A1 (toluene insoluble) and A2 (toluene soluble). A small quantity (about 8%) of a heptane-soluble TC fraction was isolated along with the A2 fraction. The presence of TCs in asphaltenes and their absence in fractions A1 and A2 were detected by means of laser desorption ionization-time of flight mass spectrometry (LDI-TOF MS) in the 450-600 molecular-mass range. These finding suggests that the TC sample is probably trapped in a network formed by both A1 and A2 fractions.