SEPARATION OF ASPHALTENES BY POLARITY USING LIQUID-LIQUID-EXTRACTION

In order to investigate the nature of petroleum asphaltenes in terms o f polarity a process was developed using initial liquid-liquid extract ion of the oil phase followed by precipitation of the asphaltenes usin g n-heptane. The liquid-liquid extraction was performed using toluene- methanol mixtures with increasing content of toluene. Although large f ractions of the crude oil (Alaska '93) was extracted in the higher pol arity solvents (high concentration of methanol), the asphaltene conten t of the dissolved material was low. As the toluene content increased more asphaltenes were transferred to the solvent phase. The asphaltene s were analysed using FTir, Elemental analysis, and HPLC-SEC with a di ode array detector. With increasing content of toluene in the methanol the molecular weight distribution of the asphaltenes significantly mo ve to higher molecular weights. The content of nitrogen and sulfur of the maltene phase also increase while WC decreases. The content of het eroatoms in the asphaltenes are relatively higher and apparently incre ase with the polarity of the solvent. It is concluded that these aspha ltenes are indeed dominated by high molecular weight substances that c annot be extracted in the high polarity solvents.