Effect of Pressure on the Oxidation Kinetics of Asphaltenes

Abstract

This study was carried out with the aim of evaluating the effect of the high pressure on the oxidation kinetics of n-heptane-insoluble asphaltenes, obtained from an extra-heavy crude oil. Thermogravimetric analyses (TGA) were performed under an air atmosphere, at different pressures from 0.084 to 7 MPa, and temperatures from 100 to 600 °C at different heating ramps of 5, 10, and 15 °C min −1 . The effective activation energy and the kinetic parameters were obtained using a first-order kinetic model, which indicated a pressure-dependent behavior. For a better understanding of the asphaltene oxidation under high-pressure conditions, the temperature range in which the oxidation process was carried out was divided in to four main regions according to the TGA profile, namely: (i) oxygen chemisorption (OC), (ii) decomposition of the chemisorbed oxygen (DCO), (iii) first combustion (FC) region, and (iv) second combustion (SC) region. It was observed that the increase of pressure favors the asphaltene decomposition as the percentages of mass loss in the first combustion region are 20% at 0.084 MPa and 50% at 7 MPa. Furthermore, the temperature at which each thermal event ends is reduced by approximately 35, 23, 13, and 51 °C from 0.084 to 7 MPa for OC, DCO, FC, and SC, respectively. Also, by increasing the heating rate, the decomposition of the asphaltene in the second combustion region is increased, indicating that the decomposition follows different mechanisms depending on the exposure time. On the other hand, with the increase in the system pressure, an increase of 53.1 and 71.1% of the effective activation energy values was observed for the thermal events associated to oxygen chemisorption and decomposition of chemisorbed oxygen, respectively, while for the combustion (FC and SC) stages, the activation energy decreases by 61.4 and 75.6%, respectively, indicating that the asphaltene oxidation behavior is controlled by the pressure in the four regions. All of these facts show that the kinetic limiting step for the asphaltene oxidation is the chemisorption of the oxygen, which is favored by the increase of the pressure.

Upgrading of Extra-Heavy Crude Oils by Dispersed Injection of NiO–PdO/CeO2±δ Nanocatalyst-Based Nanofluids in the Steam

“…The selected EHO has an API gravity of 6.4 • , resin and asphaltene contents of 52.0 wt.% and 28.7 wt.%, respectively, and a viscosity of 6 × 10 6 cP at 25 • C. n-Heptane (99%, Sigma-Aldrich, St. Louis, MO, USA) was used to isolate the asphaltenes from the EHO, and chromatographic silica (Sigma-Aldrich, St. Louis, MO, USA) was added to the deasphalted crude oil to separate the resins from the solution. The extraction procedure has been explained in previous studies [30]. The compositions of the isolated asphaltenes and resins are shown in Table 1.…”

Improvement of Steam Injection Processes Through Nanotechnology: An Approach through in Situ Upgrading and Foam Injection

“…Subsequently, the sand was rewashed with 10% HCl to remove impurities and residues from the solvents. Finally, the sand was dried in a vacuum oven for 12 h at 120 • C. A total of 100 g of silica sand were used to carry out each displacement test, its porosity was estimated following the saturation method [54], where a low flow rate of 0.1 cm 3 •min −1 is fixed with the sample holder in a vertical position. The time in which the system saturates itself and the permeability under Darcy's law are recorded [55].…”

“…The tests were conducted at a fixed back pressure of 110 psi, overburden pressure of 700 and 800 psi for basic characterization and steam injection tests, respectively and a temperature of 80 °C. For the basic characterization of the absolute and effective permeabilities, (Kabs and ko) are estimated applying Darcy's law [55] by injecting water and oil at 0.5 mL 3 •min −1 according to previous studies [59]. Then, the steam was injected into the porous medium between 3 and 5 mL•min −1 at 210 °C and 210 psi and a quality of 70% (X = 70%) and the oil recovery curves in the absence of the nanofluids were obtained.…”

“…The evaluation of nanofluid at dynamic conditions was carried out in five stages including (i) basic characterization, (ii) oil recovery after steam injection in the absence of nanofluids, (iii) oil recovery after the injection of nanofluids for in situ upgrading, and (iv) N 2 injection to obtain gas permeability baseline, and (v) oil recovery after the injection of the foaming nanofluid. The tests were conducted at a fixed back pressure of 110 psi, overburden pressure of 700 and 800 psi for basic characterization and steam injection tests, respectively and a temperature of 80 • C. For the basic characterization of the absolute and effective permeabilities, (K abs and k o ) are estimated applying Darcy's law [55] by injecting water and oil at 0.5 mL 3 •min −1 according to previous studies [59]. Then, the steam was injected into the porous medium between 3 and 5 mL•min −1 at 210 • C and 210 psi and a quality of 70% (X = 70%) and the oil recovery curves in the absence of the nanofluids were obtained.…”

“…One of the biggest problems in the use of heavy (HO) and extra-heavy crude oils (EHO) as an energy source is their low quality [1][2][3], which leads to production, transportation, and refining operations that require high energy and economic investments [4][5][6]. HO and EHO generally have a Methanol (99.8% purity), toluene (99.8% purity), and HCl (37% purity) were used for porous media cleaning, and this was prepared with clean silica sand (Ottawa sand, US sieves 30-40 mesh) purchased from Minercol S.A. (Colombia).…”