Analysis of the reasons for negative values in calculating the activation energy of heavy oil oxidation reaction based on Friedman method
In this work,the variations in temperature and the volume fraction of CO+CO2 produced during the oxidation reaction of heavy oil were obtained at different heating rates.The activation energy of the heavy oil oxidation reaction was calculated using Friedman method,and an analysis was conducted to understand the reasons for the appearance of negative values in the activation energy.The results indicate that the average activation energy of the heavy oil oxidation reaction is 189.44 kJ/mol.The activation energy gradually increases to 271.16 kJ/mol in the conversion range of 0 to 0.36(temperature range 245～305 ℃).However,in the conversion range of 0.585 to 0.695(temperature range 365～395 ℃),the activation energy becomes negative.Beyond a conversion rate of 0.625,the reaction's activation energy rapidly increases to 468.64 kJ/mol.The occurrence of negative activation energy is attributed to the diminishing trend in the oxidation reaction rate of heavy oil with increasing temperature.At the same conversion rate,the reaction rate at a higher heating rate(2.92 ℃/min)is lower than that at a lower heating rate(1.64 ℃/min).The logarithm of the reaction rate at three different heating rates in heavy oil oxidation shows a deteriorating linear relationship with the negative reciprocal of temperature,resulting in a negative slope.This study analyzes the reasons for the calculated negative activation energy in the process of heavy oil oxidation reaction.This study analyzed the reasons for calculating the negative activation energy during the heavy oil oxidation reaction,the results are of great significance to the kinetic characteristics of heavy oil oxidation reaction.
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