THERMODYNAMICS OF ASPHALTENE PRECIPITATION AND DISSOLUTION INVESTIGATION OF TEMPERATURE AND SOLVENT EFFECTS

Petroleum asphaltenes have been precipitated in solvent mixtures of n- heptane and toluene at various temperatures, likewise n-heptane asphal tenes have been dissolved in under similar conditions. This give added evidence to apparent hysteresis phenomenon between the two processes. The Asphaltenes have been characterized showing that although data is scattered convergence to certain structural parameters as incipient f locculation is approached. The asphaltenes are seen to consist of an a ssociating and a non-associating part. The solubility of asphaltenes h as been correlated/modelled using the Flory-Huggins equation using two different terms for the Flory parameter. A process for evaluation of best choice of solubility parameter and molar volume for the asphalten es is proposed. Dissolution processes are seen to be best fitted by th e equations. Based on these findings the asphaltenes are proposed to b e formed by a colloidal and a true solution part.