Quantification of low‐temperature oxidation of light oil and its SAR fractions with TG‐DSC and TG‐FTIR analysis

Abstract

The oxidation reaction is the key to determining the success of air flooding. In this paper, experimental and theoretical techniques have been developed to identify the low-temperature oxidation (LTO) mechanisms for light oil during air flooding by comprehensively analyzing thermal stability and oxidation process of the crude oil and its SAR (ie, saturates, aromatics, and resins) fractions. Experimentally, both a thermogravimetric analyzer coupled with differential scanning calorimetry (TG-DSC) and a thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG-FTIR) are employed to quantify the LTO process of crude oil and each SAR fraction as well as the corresponding oxidation properties. Theoretically, reaction models have been developed to reproduce the experimentally identified reactions. The results show that the oxygen addition reaction and the bond scission reaction occur simultaneously. The former can be initiated when temperature is higher than 50°C, and it is gradually shifted to the latter with the continuous increase in reservoir temperature. The LTO products of light oil include H 2 O, CO 2 , carboxylic acids, alcohols, phenols, and ethers. Saturates, aromatics, and resins are all the sources of H 2 O, CO 2 , alcohols, and carboxylic acids, whereas ethers are mainly derived from aromatics and resins. At the beginning of an air flooding process, heat is mainly generated from the oxidation of aromatics and resins. Subsequently, oxidizing saturates gradually dominates the air flooding process with an increase in the reservoir temperature. K E Y W O R D Scrude oil, LTO mechanism, oxidation process, SAR fraction, thermal stability How to cite this article: Wang T, Wang J, Yang W, Yang D. Quantification of low-temperature oxidation of light oil and its SAR fractions with TG-DSC and TG-FTIR analysis. Energy Sci Eng. 2020;8:376-391.

In Situ Combustion of Heavy, Medium, and Light Crude Oils: Low-Temperature Oxidation in Terms of a Chain Reaction Approach

“…This stage has been widely investigated, and it is commonly known as low-temperature oxidation. Additionally, the hydroperoxides can decompose into a pair of radicals: this is a branching chain reaction. , In fact, the new radicals initiate the new chains and start new oxidation processes (Figure ). This process self-accelerates and causes the ignition of oil.…”

“…The initial studies of hydrocarbon oxidation show that oxidation always proceeds by breaking the C–H bond, both in the branched-chain and unbranched processes. , Liquid hydrocarbons are resistant to dissociation of the C–C bond up to 473.15 K. So, the initial set of reactions is expressed as follows where R • is the alkyl radical, and the initiation rate at this stage depends on the concentrations according to v 0 = k 1 C sat C O 2 .…”

“…The initial studies of hydrocarbon oxidation show that oxidation always proceeds by breaking the C−H bond, both in the branched-chain and unbranched processes. 39,41 Liquid hydrocarbons are resistant to dissociation of the C−C bond up to 473.15 K. So, the initial set of reactions is expressed as follows…”

Evolution of the Pseudo-Components of Heavy Oil during Low Temperature Oxidation Processes

“…Traditionally, most researchers characterized the reaction kinetics of heavy oil during the ISC process solely according to the content variation of saturates, aromatics, resin and asphaltene (abbreviated as SARA) analysis [10,11]. The degree of LTO was intensified with the oxidation temperature, during which gas compositions and the content of elements, saturates-aromatics-resins-asphaltenes (SARA) fractions, free radicals, and hydrogen groups of oils that were produced changed obviously [12,13]. However, the relationship between variation in the SARA fractions and the reaction kinetics as well as fuel consumption have been studied using qualitative or semiquantitative analysis methods, and the conclusions drawn by different researchers are contradictory.…”