An investigation of the role of carbon-chain length of precipitating solvent in the precipitation/dissolution of heavy organics

Abstract

An investigation of the role of carbon-chain length of precipitating solvent in the precipitation/dissolution of heavy organics (HO) has been carried out. The heavy organics-rich residue was generated from a medium crude called Qua Iboe blend having an API gravity < 40. The precipitates were obtained from the n-pentane (n-C₅), n-hexane (n-C₆) and n-heptane (n-C₇) solvents using a modified ASTM  D6560 method. Precipitation of heavy organics, Dissolution of heavy organics  precipitates of lower molecular weight n-alkane solvents by higher molecular weight n-alkane solvents and Stirring in of precipitates of the higher molecular weight n-alkane solvents in lower molecular weight n-alkane solvents (i.e. reprecipitation) were the experimental determinations carried out using the named solvents. The following results were obtained from these experiments: Precipitated heavy organics from n-pentane, n-hexane and n-heptane were 8.68%, 7.46% and 6.25%  respectively. The dissolution showed that 95% of n-C₅ ppt. and 96% of n-C₆ ppt. dissolved in n-C₆ and n-C₇ solvents respectively. The re-precipitation results demonstrated that 93% of n-C₆ ppt. and 96% of n-C₇ ppt. were insoluble in n-C₅ and n-C₆ solvents respectively. These findings further reiterate the observation that heavy organics precipitation increases with decrease in carbon-chain-length of the precipitating solvent. It is also shown that HO precipitation from solutions does occur. This same trend is also observed in the precipitation and dissolution.