(650e) Study of Asphaltene Precipitation From Brazilian Petroleum

Petroleum is a complex fluid containing several classes of compounds dispersed or solubilized in a liquid phase. During the petroleum production and processing, changes in pressure, temperature, and composition can decrease the stability of the dispersed systems, causing precipitation of a solid phase, composed mainly by asphaltenes. Asphaltenes are recognized as a mixture of species of high molecular weight, with a reasonable polarity, and different functional classes¹. The aggregative nature of asphaltenes is related to the presence of heteroatoms in its structure that results in a superficial activity for this compounds^2,3. The precipitation and deposition of asphatenes is a serious problem that can affects the production and refining process. Some methods are used to prevent deposit or its removal, but the use of precipitation inhibitors and/or dispersants is a feasible solution⁴. This work presents a kinetic study of asphaltene precipitation in two different types of Brazilian crude oil (P1 and P2). N-heptane was used as precipitant and three different types of precipitation inhibitor or dispersant (I1, I2 and I3) were tested. The efficiency of the additive was accessed by the sedimentation curves of the precipitated asphaltenes followed using a Hewlett Packard spectrophotometer, model 8453. Samples were prepared by weighing 0.1 g of oil, followed by the addition of different concentrations of additive, and approximately 10 g of n-heptane. After homogenizing the solution, 3 mL was placed into a quartz cuvette and the absorbance was monitored at 850 nm for a period of 3600 seconds. All tested additives presented some efficiency on the precipitation of asphaltenes but I2 needed lower concentration to stabilize the system.  

¹ Loh, W., Mohamed, R.S., Ramos, A.C., “Aggregation of asphaltenes obtained from a brazilian crude oil in aromatic solvents”, Petroleum Science and Technology, 17, 147-163, 1999.

² Mohamed, R.S., Loh, W., Ramos, A.C., “Aggregation behavior of two asphaltenic fractions in aromatic solvents”, Energy & Fuels, 13, 2, 323-327, 1999.

³ Mansoori, G.A., “Modeling of asphaltene and other heavy organics deposition”, J. Pet, Sci. Eng., 17, 101-111, 1997.

⁴ Stephenson, W.K., “Producing asphaltenic crude oils: problems and solutions”, Petroleum Eng. International, 24-31, 1990.