# Effects of functional groups on the energetics of CO and CO2 formation during secondary oxidation of coal following pre-treatment

## TL;DR

This study explores how pre-oxidation affects coal's functional groups and how these influence CO and CO2 release during secondary oxidation.

## Contribution

The paper introduces a quantitative analysis linking functional group composition to activation energies of CO and CO2 formation during coal oxidation.

## Key findings

- The activation energy for CO formation is consistently higher than for CO2 during secondary oxidation.
- Aliphatic and carbonyl groups significantly reduce activation energies for CO and CO2 evolution at specific temperature ranges.
- The effect of functional groups on reactivity varies with secondary oxidation temperature ranges.

## Abstract

To investigate how functional groups introduced in coal during pre-oxidation influence the release behavior of CO and CO2 during subsequent secondary oxidation, experimental characterization was conducted to identify the types and relative abundances of functional groups formed at varying pre-oxidation temperatures. Concurrently, the apparent activation energy (Eα) for CO and CO2 evolution during secondary oxidation was determined via kinetic analysis. A series of multiple linear regression models were then developed to quantitatively assess the relationships between Eα values for CO/CO2 generation and specific functional group contents – or their combinations-in pre-oxidized coal, across distinct temperature intervals of secondary oxidation. The results indicate that, under all pre-oxidation conditions examined, the Eα for CO evolution during secondary oxidation exceeds that for CO2. However, this gap narrows progressively with increasing pre-oxidation termination temperature. Notably, when pre-oxidation is terminated below 140 °C, the Eα for CO formation during secondary oxidation is lower than that observed during initial (unprioritized) coal oxidation – whereas the Eα for CO2 formation remains consistently higher than in the initial oxidation stage. Further, within the secondary oxidation temperature range of 40–170 °C, elevated concentrations and synergistic interactions between aliphatic –CH2/–CH3 groups and carbonyl (C

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Created by potrace 1.16, written by Peter Selinger 2001-2019
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O) groups significantly reduce the Eα for both CO and CO2 evolution. However, as the secondary oxidation temperature interval is refined into narrower subranges, the dominant functional groups-and their interaction patterns-exhibit marked variation, underscoring the context-dependent nature of functional group reactivity.

The FTIR scanning curves of the functional groups in raw coal and coal samples oxidized to different temperatures.