Early maturation processes in coal. Part 1: Pyrolysis mass balances and structural evolution of coalified wood from the Morwell Brown Coal seam

TL;DR

This study combines experimental and theoretical methods to analyze the structural evolution and hydrocarbon generation during the early maturation of Morwell coal, focusing on kerogen transformation and pyrolysis mass balances.

Contribution

It introduces a molecular dynamic reactive modeling approach to simulate coal maturation and provides detailed structural and chemical insights into kerogen evolution.

Findings

Structural defunctionalization of functional groups during maturation

Generation of hydrocarbons like CH4, C4H8, and C14+ liquids in low yields

Increase in cross-linking within residual kerogen

Abstract

In this work, we develop a theoretical approach to evaluate maturation process of kerogen-like material, involving molecular dynamic reactive modeling with a reactive force field to simulate the thermal stress. The Morwell coal has been selected to study the thermal evolution of terrestrial organic matter. To achieve this, a structural model is first constructed based on models from the literature and analytical characterization of our samples by modern 1-and 2-D NMR, FTIR, and elemental analysis. Then, artificial maturation of the Morwell coal is performed at low conversions in order to obtain, quantitative and qualitative, detailed evidences of structural evolution of the kerogen upon maturation. The observed chemical changes are a defunctionalization of the carboxyl, carbonyl and methoxy functional groups coupling with an increase of cross linking in the residual mature kerogen. Gaseous and liquids hydrocarbons, essentially CH4, C4H8 and C14+ liquid hydrocarbons, are generated in low amount, merely by cleavage of the lignin side chain.