Experimental Study on the Physisorption Characteristics of O2 in Coal Powder are Effected by Coal Nanopore Structure

Abstract

Bo tan , Gang cheng ✉ , Xiaoman Zhu & Xianbing Yang coal is a porous medium. oxygen molecules in the air penetrate through the pores of coal and are adsorbed on the coal surface. Low-temperature oxidation of coal then occurs, by which coal spontaneous combustion is promoted. Given this process, the authors analysed the physisorption characteristics of o 2 in pulverized coal from the perspective of nanopore structure. In this study, five different kinds of coal samples (two lignites, one bituminous coal, and two anthracites) were selected, and the surface morphology, pore structure parameters and oxygen physisorption capacity of the pulverized coals were determined by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and oxygen adsorption with chromatography (OAC), respectively. The experimental results of SEM and MIP show that with the development of coal, the surface folds increase, and the pores increase in number and shrink, which leads to the nanopores of anthracite and bituminous coal being smaller and more complex than those of lignite. The experimental results of OAC show that adsorbed oxygen is physisorbed by pulverized coal in the order lignite > bituminous coal > anthracite. Analysis of the oxygen desorption curves shows that the oxygen desorption rates of the anthracites and bituminous coal are slower than those of the lignites. The results show that the amount of oxygen physisorbed by pulverized coal is proportional to the fractal dimension of the coal pores, proportional to the pore volume of the nanoscale pores, and inversely proportional to the number of closed pores in the coal. Based on the results of the analyses mentioned above, it is important to analyse the process of coal-oxygen chemisorption and the mechanism for low-temperature oxidation of coal to prevent coal spontaneous combustion. The confirmed worldwide reserves of coal stood at approximately 1,055 billion tons in 2018. The United States, Russia, Australia and China together accounted for 66.1% of the world's coal reserves 1. During mining, storage and transportation, coal can undergo spontaneous combustion, resulting in a huge waste of resources and economic losses in the United States and China per annum. The initial stage of coal spontaneous combustion involves coal low-temperature oxidation, in which oxygen permeates into the coal through pores, then physisorbs and chemisorbs with the functional groups on the coal surface, and adsorption heat is generated and accumulated 2,3 , as shown in Fig. 1. Coal is a porous medium, and the pore structure of coal varies with coal development 4 ; therefore, oxygen diffusion in coal pores and adsorption on coal surfaces are also different 5. The significance of the coal low-temperature oxidation mechanism in the physisorption, chemisorption and diffusion of oxygen in coal nanopores has been studied. In this paper, all oxygen adsorption involved physisorption. Scholars from various countries have performed much work on the influencing factors of coal low-temperature oxidati...

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