Structures of Aromatic Clusters of Different Coals Based on Benzene Carboxylic Acids from Coal via Oxidation

Abstract

Benzene carboxylic acids (BCAs) are considered to be an important group of chemicals and widely used in the chemical industry. The generation of BCAs from coal via oxidation is widely studied, indicating that the distributions of BCAs are various with different coals and the yields of BCAs with lower numbers of carboxyl groups increase in the process of coalification. However, the relationship between distributions of BCAs and the aromatic clusters of coal is unclear. In this work, combined with the results of distributions of BCAs and 13 C NMR, the most probable aromatic clusters in different coals were proposed. The result indicates that, in the process of coalification (from lignite to anthracite), the aromatic cluster size and the degree of condensed aromatic rings both increase with an increase in carbon content or coal rank, but the substituted degree of aromatic rings decreases. When the carbon content of coal is lower than 87%, the aromatic rings in coal are arranged in a linear catenation manner. When the carbon content of coal is more than 87%, aromatic rings in coal are arranged in a circular catenation manner. The substituents of aromatic clusters are distributed uniformly on the aromatic rings. With the increase of coal rank, the average substituted carbon chain length (L n ) decreases; namely, more and more aromatic clusters tend to be directly connected to others. These structural features make the yields of benzene dicarboxylic acids and benzene tricarboxylic acids (BTAs) increase with coal ranks from lignite to anthracite via oxidation. The highest yield of BCAs is benzene tetracarboxylic acids from Xiaolongtan lignite to Xuanzhong bituminous coal via oxidation. With further increasing coal rank, the highest yield of BCAs is BTAs from Pingdingshan bituminous coal to Taixi anthracite via oxidation. The proposed aromatic clusters well explain the reasons that the yields of BCAs with lower numbers of carboxyl group are significantly increased with increasing coal rank.

Characterization of woodstove briquettes from torrefied biomass and coal

“…However, the 13 C CP/MAS spectra indicated that the organic structure of biomass and coal is different. Anthracite contains a great amount of hydrogenated polycyclic aromatic rings arranged in a linear catenation order, whereas biomass samples are rich in polysaccharides, proteins, lipids and other abundant compounds [82,83]. The high moisture content in original woodchips and olive stones could also have a strong impact on the calorific value of torrefied biomass briquette, confirming the previous results of Demirbas [84].…”

Molecular Modeling and Reactivity of Thermally Altered Coals by Molecular Simulation Techniques

“…The parallelogram-shaped aromatic fragments are not the actual structure of aromatic units in coal but only a method to enrich the structural diversity of coal. 22 The linear and circular catenations were also proposed by Solum et al 56 and exploited in the models by Yang et al 57 Previous studies indicated that certain polycyclic aromatic hydrocarbons in coal affected by igneous intrusions, such as fluoranthene and benzofluoranthene, contained a certain number of pentagonal aromatic rings, 58 which may be caused by tectonic stress 59,60 or high temperature. 61 Considering that the three thermally altered coals in this study were affected by igneous rock intrusions, the pentagonal aromatic rings were incorporated into the aromatic units of thermally altered coals by removing a protonated aromatic carbon from the outside hexagonal aromatic ring and creating an aromatic carbon− carbon covalent bond for aromatic ring closure.…”

“…The parallelogram-shaped aromatic fragments are not the actual structure of aromatic units in coal but only a method to enrich the structural diversity of coal . The linear and circular catenations were also proposed by Solum et al and exploited in the models by Yang et al…”

New Insights into the Primary Reaction Products of Naomaohu Coal via Breaking Weak Bonds with Supercritical Ethanolysis

“…The coal resource is abundant in the world. Studying the coal structure not only has important theoretical significance but also has important guiding significance for coal processing and utilization, such as oxidation, thermal dissolution, pyrolysis, , and liquefaction. − More importantly, understanding the structure of coal or the composition of its primary reaction products can provide information for its pyrolysis and liquefaction reaction, which are two essential ways to obtain valuable chemicals and fuel oil from coal. As a basic reaction of coal utilization, pyrolysis can break the coal structure to form gas, tar, and char at temperatures above 500 °C, while the pyrolysis products can reflect some aspects of the coal structure. , For direct coal liquefaction, coal can be converted to liquid fuel by hydrocracking in the presence of hydrogen, solvent, and catalyst at high pressures and temperatures.…”