The Effect of Compositional Changes of Binary Mixtures of n-alkane solvents on the Precipitation of Heavy Organics from a Solution of Crude Oil Residue

Abstract

The effect of precipitant compositional changes on the precipitation of heavy organics (HO) from a solution of crude oil residue using binary mixtures of n-alkane solvents was studied. Heavy organic precipitates were generated using different ratios of C₅:C₆, C₆:C₇ and C₅:C₇ n-alkane solvents. The result obtained showed that for binary mixtures at 1:0, 3:1, 2:1, 1:1, 1:2, 1:3 and 0:1 ratios, the weight percentage precipitates of C₅:C₆ were 11.19±0.45, 8.56±0.80, 5.62±0.58, 8.53±0.80, 5.83±1.29, 5.45±0.57 and 5.24±0.32; C5:C7 were 11.19±0.90, 5.63±0.52, 2.12±0.25, 4.51±0.65, 2.11±0.37, 1.67±0.40 and 0.97±0.05; and C₆:C₇ were 5.24±0.32, 3.37±0.08, 1.94±0.03, 3.39±0.60, 1.48±0.03, 1.43±0.03 and 0.97±0.05 respectively. The results have shown that the quantity of HO precipitate decreases with increasing quantity of higher carbon number of n-alkane solvent to a minimum value at 2:1 ratio. From the minimum value, it rises to a maximum at 1:1 ratio as the proportion of C_n+x to Cn (where C is carbon atom, n and x represent the number of carbon atom) increases. The quantity of HO precipitate decreases again to a minimum at 1:2 ratio as the proportion of C_n+x increases further, and finally to the lowest value at pure C_n+x. The conclusion is that the components of the crude oil residue undergo a three-stage phase transition as the volume ratios of the n-alkane solvents vary. This study can lead to a better  understanding of the phase behavior of heavy organics under compositional changes and hence the prediction of heavy organic precipitation.

Keywords: Heavy Organics, Precipitates, crude oil, binary mixtures, n-alkane.