EFFECT OF PRECIPITATION TEMPERATURE ON THE COMPOSITION OF N-HEPTANE ASPHALTENES .2.

Petroleum asphaltenes precipitated by n-heptane at temperatures betwee n ambient and 80 degrees C from two crude oils have been characterized regarding hydrocarbon structures using H-1 and C-13 nmr, and fluoresc ence spectroscopy. This indicates a very complex and apparently very s mall change in structural features except for a molecular weight incre ase as more material stays in solution at elevated temperature. Aromat icity increase and apparently alkyl chains diminish. The latter trend is however affected by the structural equation used. According to the fluorescence spectroscopy the content of large and complex chromophore s increases but a significant effect of the presence of porphyrins on the spectra is also observed. The data is analyzed in combination with previous characterizations of the same asphaltenes presented in the f irst part of this work (Andersen, 1994). This indicates that as smalle r molecules are extracted at elevated temperature the precipitated asp haltenes tend to associate more. This implys that these small molecule s block association sites which therefore become available for further association at elevated temperature. For Boscan part of the smaller e asy to extract porphyrins may have this behavior.