On the mass balance of asphaltene precipitation

In the evaluation of experimental data as well as in calculation of phase e quilibria the necessity of the application of mass balances is obvious. In the case of asphaltenes the colloidal nature of these compounds may highly affect the mass balance. In the present paper several experiments are perfo rmed in order to check the consistency of mass balances within asphaltene p recipitation. Asphaltenes are precipitated in two step processes either by changing temperature or by changes in precipitant with increasing precipita tion power. This has been performed for three different oils. The data indi cates that in temperature experiments as well as in solvent series experime nts the precipitation of heavy asphaltenes affects the following precipitat ion of lighter asphaltenes. In both cases the mass balance using standard s eparation techniques cannot be closed, as less material is precipitated in a two step process than in the direct process either at low temperature or by direct precipitation with one precipitant. The different fractions were subject to HPLC size exclusion chromtagraphy showing that the material rema ining in solution in the stepwise process was of low molecular weight, and that the material in the second precipitation step was often of higher appa rent molecular weight anti had an increased overall absorbance coefficient.