Alkanes Induced Asphaltene Precipitation Studies at High Pressure and Temperature in the Presence of Argon

Abstract

The continuous increase of petroleum production under adverse subsea conditions and the preeminent need for adequate operational conditions and efficient use of additives to warrant flow assurance makes it interesting to set up experimental procedures to carry out n-alkane precipitation studies under high-pressure (p) and high-temperature (T) conditions. In this contribution, some preliminary experimental studies developed to characterize asphaltene precipitation in model systems consisting of asphaltene solutions in toluene or mixtures of hydrocarbons by the addition of propane, n-heptane, or other alkanes at various pressures and temperatures, using a commercial compact equipment, are reported. In general terms, it was established that these tests follow the same pattern described at ambient p and T conditions and the one single study reported in the literature for a stock tank oil sample at 3000 psi and room T. Four crude oils of different characteristics were tested, using diluted or undiluted samples, and it was possible to detect the asphaltene precipitation onset. However, these results cannot be used to infer the stability of the crude oils because results correlating onset and stability at high p and T are not yet available. The effect of pressure at high pressures was not entirely resolved because argon, used as an assumed inert gas to pressurize the system, dissolves in the hydrocarbons and displaces the precipitation onset toward lower values. The need to develop compact equipment to assess the effect of solvents, inhibitors, and other additives on the phase behavior of crude oil at high pressure and temperature and in the presence of CO2 and other gases, representing a valuable contribution to the petroleum industry in the area of flow assurance, still persists.

An Enhanced-Solvent Deasphalting Process: Effect of Inclusion of SiO2Nanoparticles in the Quality of Deasphalted Oil

“…Table 4 shows the DAO yield and quality from both processes when conducted with n-pentane and at 25 ∘ C a dosage of 5 wt% of SiO 2 nanoparticles. Comparing these results with those obtained when using n-heptane as the solvent (Figure 2), it is observed that reducing the carbon number of solvent reduced the DAO yield and hence increased the pitch or precipitated fraction yield [78][79][80][81][82]84]. This is because increasing the molecular weight of the solvent allows it to solubilize heavier hydrocarbons [78,84], as reflected in the solubility parameter of asphaltenes in different solvents [80].…”

“…The DAO is removed from the HO or EHO by solvent extraction using paraffinic hydrocarbons in which there is no chemical reaction between the crude oil feed and the paraffinic solvent [70,[78][79][80][81][82]. Researchers have evaluated the effects of the chemical nature of the solvent [70,[78][79][80][81][82][83][84][85][86][87][88][89], temperature [82,90,91], operating pressure [83-85, 90, 92, 93], and solvent to oil ratio [77,79,81,[94][95][96] on the yield of DAO and/or pitch, as well as the DAO quality in some studies. Improvements of the SDA through the addition of macro-and microadsorbent materials have been reported in the literature, showing improvements in the DAO yield and quality [97,98].…”

Characterization of the Solid Residue and the Liquid Extract Separated by Propane-Induced Crude Oil Fractionation

“…In this case, the trace of the translucence–dilution curve presents more than one maximum. Results reported earlier for other crude oil samples at different temperatures and pressure presented similar profiles, and, considering that asphaltenes is the only crude oil fraction prone to precipitate by dilution with low-molecular-weight alkanes, the asphaltenes precipitation onset was identified as the dilution corresponding to the first translucence maximum. The secondary peaks in Figure were preliminarily attributed to the particle growing and agglomeration process that would induce changes in light intensity registered by the FT5 probe in which both the incident and the transmitted radiation are broad-band white light.…”

“…The asphaltenes precipitation onset of the petroleum sample was measured by titration of 25 g of the oil with n -heptane at ambient conditions as described elsewhere . The precipitation onset was also measured at 40 bar and 68 °C using the FT5 flocculation titrimeter (PSL Systemtechnik GmbH, Clausthal-Zellerfeld, Germany), following the procedure described in a previous publication . The crude oil sample was too dark and exceeded the equipment detection level, and it was diluted to 50 wt % with cyclohexane prior to titration.…”

“…In a first report, the solution behavior of the solid and liquid phases separated by liquid propane in the fractionation process was examined and compared to the asphaltenes and other crude oil components. In a subsequent article, a commercially available high-pressure high-temperature compact flocculation device was used to identify the precipitation onset of model system consisting of solutions of asphaltenes, dissolved in toluene or in mixtures of hydrocarbons and dead oil samples titrated with propane or n -heptane, at 25 bar and 56 °C.…”