Statistical Distribution Characteristics of Pyridine Transport in Coal Particles and a Series of New Phenomenological Models for Overshoot and Nonovershoot Solvent Swelling of Coal Particles

Abstract

In this study, the solvent-swelling processes of coal particles of Zao Zhuang coal and Taiheiyo coal were investigated using a novel orthogonal microscopy image analysis technique proposed recently by our laboratory. The overshoot swelling and slow-climbing swelling are characteristic of Zao Zhuang coal and Taiheiyo coal particles in pyridine at ambient temperature, respectively. Super-Case II diffusion is dominant in Zao Zhuang coal particles and anomalous diffusion in Taiheiyo coal. The present study shows that the slow-climbing-type solvent-swelling processes of Taiheiyo coal particles can be described using the semiempirical model proposed by Ritger and Peppas. However, overall solvent-swelling processes with an overshoot feature in many coals could not be simulated well by the model. In addition, we observed that both the diffusion mechanism exponent n and proportionality constant k in the model for the two coals have characteristic statistical distributions. The distributions of n and k for Zao Zhuang coal are normal, and those of Taiheiyo coal are doubly exponential. On the basis of these observations, the connotation of the parameters, k and n, in the Ritger and Peppas model was expanded in view of a statistical distribution. On the other hand, based on the analysis of swelling features of Zao Zhuang coal particles in pyridine at ambient temperature, a series of new phenomenological models, a second-order system with a unit-step forcing function in nature, was used to describe the solvent-swelling processes of Zao Zhuang coal particles with or without overshoot features. The simulated overall processes of the coal particles using the new models agree very well with the measured ones and suggest that the viscoelastic properties of pyridine-dilated Zao Zhuang coal, the main features of solvent-swelling and/or solvent transport of the coal particles, can be well characterized by second-order system with the denominator τ2 s 2 + 2ζτs + 1 and a unit-step forcing function (1/s).

Pretreatment of coal by ionic liquids towards coal electrolysis liquefaction

“…Therefore, pretreatment of coal, which can break the coal network, expand the pores and increase the mobility of small molecules trapped in the network of the coal, is essential to CEL. Many studies have reported that in the presence of hydrocarbon solvents, such as tetrahydrofuran (THF), toluene, pyridinium, N-methyl pyrrolidinone (NMP) and other mixed organic solvents, non-covalent interactions within the coal network can be disrupted and relaxed [11][12][13]. However, these traditional solvents are volatile, toxic, and difficult to be recycled [14].…”

The role of volatiles and coal structural variation in coal methane adsorption

“…However, the peak at about 450°C shrank for tetrahydrofuran-and pyridine-treated samples. This indicates that the two extraction methods each removed a portion of the volatile content in the raw coal [46]. This also indicates that the quantity of the volatiles removed was proportional to the observed extraction yield.…”

Damage and deformation control equation for gas-bearing coal and its numerical calculation method

“…On one hand, its volume expansion after gas adsorption will result in expansion stress (Harpalani and Chen, 1997;Gao et al, 1999;Zhou and Lin, 1999;Karacan, 2003Karacan, , 2007Liu et al, 2010). On the other hand, its strength and elastic modulus on the surfaces of coal after gas adsorption will decrease.…”

“…A large amount of experiments on gas-containing coal rock showed that coal rock expands after it adsorbs porous gas and manifests the expansion stress (Harpalani and Chen, 1997;Gao et al, 1999;Zhou and Lin, 1999;Karacan, 2003Karacan, , 2007Liu et al, 2010). The elastic modulus of coal rock lowers with pressure of gas adsorbed by solid skeleton rising (Jin et al, 1991;Liang et al, 1995;He et al, 1996).…”