Oxidation of n-Alkane (n-C8H18) under Reservoir Conditions, in Context of Gas Mixture Injection (CO2/O-2): Construction of a Kinetic Model

International audienceCO2 geosequestration or enhanced oil recovery (EOR) by CO2 injection in hydrocarbon reservoirs is suggested as a short-term solution for limiting CO2 atmospheric accumulation. In the case of oxy-combustion CO2 capture, the main annex gas associated with CO2 is O-2 in important proportion (=7%). Even if hydrocarbon oxidation processes by O-2 are well-known in high-temperaturelow-pressure (HT-LP) conditions, scarce data are available under reservoir conditions (high-pressurelow-temperature, HP-LT). To predict the hydrocarbon evolution in the presence of O-2 in an oil-depleted reservoir, it is necessary to investigate their reactivity. As a matter of fact, a double approach combining experimentation and modeling was performed in this study. Experiments were carried out on a model compound (n-octane), by injecting O-2/N-2 gas mixtures in a HP-LT titanium reactor. In parallel, a detailed kinetic model for n-octane, generated by the software EXGAS, was applied. Several reactions were added, and some rate parameters have been adjusted to adapt the model to reservoir conditions. The modified model was validated by experiments performed at different reaction temperatures and O-2 concentrations. The consistency between experimentations and modified oxidation model is promising for the development of a tool allowing the prediction of hydrocarbon reservoir stability

Real time monitoring of slow pyrolysis of polyethylene terephthalate (PET) by different mass spectrometric techniques.

In the context of waste upgrading of polyethylene terephthalate (PET) by pyrolysis, this study presents three on-line mass spectrometric techniques with soft ionization for monitoring the emitted decomposition products and their thermal dependent evolution profiles. Pyrolysis experiments were performed using a thermogravimetric analyzer (TGA) under nitrogen atmosphere with a heating rate of 5 degrees C/min from 30 degrees C to 600 degrees C. Single-photon ionization (SPI at 118 nm/10.5 eV) and resonance enhanced multiple photon ionization (REMPI at 266 nm) were used with time-of-flight mass spectrometry (TOF-MS) for evolved gas analysis (TGA-SPI/REMPI-TOFMS). Additionally, the chemical signature of the pyrolysis products was investigated by atmospheric pressure chemical ionization (APCI) ultra high resolution Fourier Transform ion cyclotron resonance mass spectrometry (FT-ICR MS) which enables assignment of molecular sum formulas (TGA-APCI FT-ICR MS). Despite the soft ionization by SPI, the fragmentation of some compounds with the loss of the [O-CH = CH2] fragment is observed. The major compounds were acetaldehyde (m/z 44), benzoic acid (m/z 122) and a fragment of m/z 149. Using REMPI, aromatic species were selectively detected. Several series of pyrolysis products were observed in different temperature intervals, showing the presence of polycyclic aromatic hydrocarbons (PAHs), especially at high temperatures. FT-ICR MS data showed, that the CHO4 class was the most abundant compound class with a relative abundance of 45.5%. The major compounds detected with this technique corresponded to m/z 193.0495 (C10H9O4+) and 149.0233 (C8H5O3+). Based on detailed chemical information, bulk reaction pathways are proposed, showing the formation of both cyclic monomer/dimer and linear structures

Oxidation of <i>n</i>‑Alkane (<i>n</i>‑C₈H₁₈) under Reservoir Conditions in Response to Gas Mixture Injection (CO₂/O₂): Understanding Oxygenated Compound Distribution

CO₂ geosequestration [carbon capture and storage (CCS)] and enhanced oil recovery (EOR) by CO₂ injection in hydrocarbon-depleted reservoirs could limit the CO₂ atmospheric accumulation. In the case of CO₂ capture by oxy-combustion, the main annex gas associated with CO₂ is O₂. O₂ that remains in the flue gas for injection can induce the oxidation of the hydrocarbons contained in the reservoirs. The effect of O₂ must be studied in terms of benefit and/or risk for CCS or EOR. To investigate the mechanism of hydrocarbon oxidation, it is essential to analyze the distributions of the formed oxygenated compounds. That is why experiments have been performed with a model compound (<i>n</i>-octane) in a closed reactor under high pressure at different temperatures and with different oxygen concentrations. The product distribution suggests two pathways of <i>n</i>-alkane oxidation, with (i) the preservation of the aliphatic chain length of the initial <i>n</i>-alkane, which generates oxygenated products with the same number of carbon, and (ii) the breakdown processes of the initial <i>n</i>-alkane, which generates low-molecular-weight oxygenated products. The new understanding of the mechanism of <i>n</i>-alkane oxidation could be incorporated into the detailed kinetic model of our previous study, which is specific to the reservoir conditions