Coke Yield Prediction Model for Pyrolysis and Oxidation Processes of Low-Asphaltene Heavy Oil

Abstract

Accurate prediction of coke yield is the basis for simulation and operation of the in situ combustion process. In view of the low asphaltene content of heavy oil in China, this study established coke yield prediction models for the pyrolysis and oxidation processes of low-asphaltene heavy oil based on the coking characteristics of the main fractions, including saturates (S), aromatics (A), and resins (R). The models were verified by the experimental coke yields of heavy oils using a fixed-bed reaction system. The prediction model for the pyrolysis process included evaporation rate equations and kinetic equations for coking reactions. Besides the same parts with pyrolysis, the model for the oxidation process included the kinetic equation of coke oxidation. The evaporation rate equations were determined by fitting the mass loss rate in the evaporation range of thermogravimetric analysis (TGA) pyrolysis results with a maximum error of 6%. The kinetic parameters for the conversion of each fraction to the coke precursor were determined by the isoconversional method based on TGA results of the separated SAR fractions. Considering the interactions among fractions during oxidation, this study included mixtures of SAR fractions as the samples and obtained the mass loss results of a single SAR by subtraction. The activation energies of SAR pyrolysis range from 99 to 180 kJ/mol and those of SAR oxidation range from 92 to 130 kJ/mol. The kinetic parameters of coke from the coke precursor were obtained by temperature-programmed coking data of a prepared intermediate, with an activation energy of 177 kJ/mol in an inert atmosphere and 65 kJ/mol in an oxidizing atmosphere. The kinetic parameters of coke oxidation were derived by the isothermal kinetic method in TGA, with an activation energy of 136 kJ/mol. The experimental coke yields of Fengcheng and Hongqian heavy oils under various pyrolysis and oxidation conditions were predicted by this model with an error around 10%, indicating that this model could be successfully applied to the prediction of the coking process of low-asphaltene heavy oil under complex conditions.

Insights into the Morphology Effect of Ceria on the Catalytic Performance of NiO–PdO/CeO2 Nanoparticles for Thermo-oxidation of n-C7 Asphaltenes under Isothermal Heating at Different Pressures

“…Because they are highly polar and present high molecular weights, their proper removal is of significance to enhance crude oil production technologies. , The injection of air or oxygen-rich gases has been used worldwide for producing heavy and extra-heavy crude oils, where the content of asphaltenes ranges between 2 and 30% in a mass fraction. , Nevertheless, limited by the combustion front stability and the efficiency of combustion, pyrolysis, and oxidation reactions, asphaltenes convert mainly into coke. Hence, advanced strategies are needed to circumvent the problem. − The catalytic oxidation of asphaltenes using nanoparticles is attractive, but the synthesized materials tested were far from perfect. The major shortcoming is the reduction of the oxidative asphaltene decomposition temperature. − In most cases, it occurs at temperatures greater than 300 °C. ,− The importance of reducing the oxidative decomposition temperature of asphaltenes lies in the subsequent improvement in the crude oil quality.…”

A Critical Review of Reservoir Simulation Applications in Key Thermal Recovery Processes: Lessons, Opportunities, and Challenges

“…It was found that the coke deposition in pores turned large pores into micropores which deteriorated permeability. A series of experiments were conducted to understand coke formation under different reaction conditions , and the presence of montmorillonites and nanoparticles . Yu et al in 2017 concluded that clay could accelerate reaction rates and improve an ignition process .…”

Exothermal Property and Kinetics Analysis of Oxidized Coke and Pyrolyzed Coke from Fengcheng Extra-Heavy Oil

“…Wei investigated the interactions between the SARA fraction of Xinjiang heavy oil and indicated that the asphaltene components were the main material for sustaining the continuity of the combustion front, and 10.35 wt % coke was formed after the LTO reactions . Liu established coke yield prediction models for the pyrolysis and oxidation processes of low asphaltene heavy oil, and the reliability of the obtained model was verified by Fengcheng (FC) and Hongqian (HQ) heavy crude oils …”

“…37 Liu established coke yield prediction models for the pyrolysis and oxidation processes of low asphaltene heavy oil, and the reliability of the obtained model was verified by Fengcheng (FC) and Hongqian (HQ) heavy crude oils. 25 Based on the extensive literature available for coke formation and its exothermal behavior, we found that regardless of the exothermic property or combustion reactivity, there is little simultaneous research on pure oxidized coke and pyrolyzed coke. Therefore, it is necessary to compare and investigate the characteristics and differences of coke formed in an air or nitrogen atmosphere, including combustion exothermal effects, kinetics analysis, morphological structures, and main elements.…”

“…Free radicals undergo polymerization reactions to produce coke precursors, such as polycyclic aromatic hydrocarbons. These polycyclic aromatic hydrocarbons will convert to coke through polycondensation and high-temperature thermal cracking reactions. − However, when oxygen makes contact with the crude oil in the reservoir, the free radicals generated by early cracking reactions undergo oxygen addition reactions to generate hydroperoxides. These hydroperoxides convert to oxygen-containing derivatives (ketones, aldehydes, carboxylic acids, etc.)…”