Macro maceral separation of low-rank coal and the pyrolysis behavior of the maceral-rich fractions

Abstract

An ideal way of clean and efficient utilization of low-rank coal by separating it into different maceral-rich fractions and then choose the appropriate utilizing method based on its composition and structure was proposed. In this paper, the coal sample was successfully separated into vitrinite-enriched coal (VC), inertinite-enriched coal (IC) and mineral-enriched coal (MC) by macro maceral separation method, and the structure and pyrolysis characteristics of different maceral-rich fractions were studied. The XRD analysis revealed that VC exhibited a higher degree of structural disorder, whereas the IC displayed greater aromaticity and graphitization. Raman analysis showed a higher proportion of amorphous carbon structure in VC, indicative of abundant side-chain active components. Conversely, IC contained more ordered aromatic rings and a higher degree of aromatic condensation. FTIR analysis confirmed that VC contained the highest aliphatic hydrocarbon content and aliphatic long-chain structures, while IC showed a lower aliphatic/aromatic ratio. The pyrolysis of different maceral-rich fractions indicated that VC pyrolysis produced the largest amount of tar (15.68 %), which was 4.37 % higher than that of the raw coal’s 11.31 %, and contained a large number of aliphatic hydrocarbons and phenols. In contrast, the tar yield of IC pyrolysis was 1.08 % lower than that of raw coal, and the tar was composed of more polycyclic aromatic hydrocarbons such as biphenyl, naphthalene and benzene series. The maceral macro separation of low-rank coal effectively realizes the separation and enrichment of different type of components in coal, which was beneficial to its subsequent cascade utilization.