Evidence for Island Structures as the Dominant Architecture of Asphaltenes

Abstract

Laser desorption laser ionization mass spectra of 23 model compounds and 2 petroleum asphaltene samples are presented. These experiments involved desorption by irradiation with the 10.6 μm output of a CO2 laser followed by single-photon ionization with the 157 nm output of a fluorine excimer laser. The average molecular weight of the asphaltene samples agrees closely with that found previously using multiphoton ionization with the 266 nm output of a Nd:YAG laser. The fragmentation behavior as a function of ionization laser pulse energy is studied to evaluate which families of model compounds fragment differently from asphaltenes and, hence, can be excluded from being dominant in asphaltenes. All model compounds having one aromatic core with and without various pendant alkyl groups show little to no fragmentation, mimicking the behavior observed for the two asphaltene samples, whereas all model compounds having more than one aromatic core show energy-dependent fragmentation. These observations support the contention that the dominant structural character of asphaltenes is island-like.

Elucidation of structural information achievable for asphaltenes via collision-activated dissociation of their molecular ions in MSn experiments: A model compound study

“…Further, only few uses exist for asphaltenes, including 69 expensive upgrading to distillates [12], road construction [13] 70 and recently proposed use in organic electronic materials [14,15] [9] to be especially well suited for evaporation and ionization of 114 asphaltenes since it has no bias to more polar analytes and it pro-115 duces only one ion type, molecular ion (M +Å ), for all asphaltene 116 model compounds studied [9]. In addition, it has been demon-117 strated that laser desorption/laser ionization of analytes relevant 118 to asphaltenes produces molecular ions with minimal fragmenta-119 tion for the majority of analytes studied [33,34]. These methods 120 allow for the determination of the molecular weight and elemental 121 composition of all analytes present.…”

The dynamic Flory-Huggins-Zuo equation of state

“…For example, the proposed molecular weight and island molecular architecture have been strongly supported by L2MS studies [29]. Most importantly, L2MS studies have established the ability to disaggregate asphaltene nanoaggregates, [30] a known problem with some mass spectral techniques.…”

“…1, some bulk decomposition studies of asphaltenes indicate the presence of some molecular populations with two or perhaps more aromatic ring systems [45]. Perhaps this fraction is relatively small, thereby not impacting molecular (not bulk) decomposition measurements, which clearly indicate the dominance of island architecture [29]. In addition, in bulk decomposition studies, asphaltenes are found to form structures with two or more aromatic ring systems; [46] thus, interpretation of these decomposition studies in terms of virgin asphaltene molecular structure is rendered very difficult.…”

Avaliação De Asfaltenos Precipitados Em Diferentes Condições De Composição, Temperatura E Pressão

“…Essa característica é condizente com espectros encontrados em outros trabalhos para amostras de diferentes origens e obtidos por outros métodos da espectrometria de massas. 42,[49][50][51][52][53][54] As massas molares médias dos petróleos obtidas por LDI-MS foram 622 Da e 643 Da para os petróleos P01 e P02, respectivamente. As massas molares médias das frações resultantes das extrações com n-pentano (C5I/ C5S) foram sempre inferiores àquelas com n-heptano (C7I/ C7S): 592/ 579 Da para as frações C5 do P01 e 745/ 621 Da para as do P02 contra 759/ 615 Da para as frações C7 do P01 e 814/ 651 Da para as do P02.…”