The effect of small micropores on methane adsorption of coals from Northern China

Abstract

In this study, the effect of coal micropores on the adsorption properties, especially the Langmuir pressure (P L ), was investigated by testing 11 coal samples from Northern China. The adsorption of CO 2 at 273 K was utilized to analyze the pore size distribution. The results of these coals show that micropore volume and micropore surface area are the major factors affecting the Langmuir volume (V L ) but have weaker effects on P L . Micropore filling theory considers that some smaller micropores with an obvious overlapping adsorption force cause volume filling adsorption. These micropores firstly reach saturated adsorption, controlling the adsorption volume at the low-pressure stage and thus have a great effect on P L . Four times the methane molecular diameter, 1.5 nm, was assumed as the critical pore size with obvious overlapping adsorption force. The relationship between P L and the proportion of the pore volume below 1.5 nm to the micropore volume was investigated, and it was found that the higher the volume proportion of these small micropores was, the smaller the P L was, though two data points deviated from this trend. The reason for the anomalous coal samples could be the deviation from the assumed critical pore size of 1.5 nm for volume filling and the effects of the various micropore surface properties, which await further study.The micropore surface increases with increasing coal rank, as does V L . The proportion of pore volume below 1.5 nm increases with coal rank, and P L reverses. However, these relationships are discrete.Keywords Langmuir volume · Langmuir pressure · Micropore filling theory · Pore size distribution · Coal rank Notation V L : Langmuir volume [mL/g] P L : Langmuir pressure [MPa] P : Pressure [MPa] V : Volume [mL] ad: air dried basis daf: dry ash-free basis R o,max : Mean maximum reflectance of vitrinite [%]

Effects of coal rank on physicochemical properties of coal and on methane adsorption

“…Proximate analysis of coal (Mahajan and Walker 1971;Bhattacharyya 1972;Reucroft and Patel 1986;Banerjee 1988, Barker-Read andYalçin and Durucan 1991;DeGance et al 1993;Chaback et al 1996;Clarkson et al 1997;Ö zgen Karacan and Okandan 2000;Laxminarayana and Crosdale 2002;Qin et al 2007;Saghafi et al 2007;Dutta et al 2008;Yu et al 2008a, b, c;Pini et al 2009;Pone et al 2009;Battistutta et al 2010;Gensterblum et al 2010;He et al 2010;Pan et al 2010;Kim et al 2011;Zheng 2012;Wang 2012;Jiang et al 2012;Kutchko et al 2013;An et al 2013;Hao et al 2013;Xiao et al 2016) consists of moisture, ash, volatile, fixed carbon. The widely-used index are: air dried basis (ad), dry basis (d), dry ash-free basis (daf).…”

“…The maceral (Ceglarska-Stefańska and Brzóska 1998; Crosdale et al 1998;Laxminarayana and Crosdale 2002;Busch et al 2003;Mastalerz et al 2004;Chang et al 2006;Busch et al 2006;Qin et al 2007;Majewska and Ziętek 2007;Siemons et al 2007;Chang et al 2008;Day et al 2008;Mazumder and Wolf 2008;Pone et al 2009;Majewska et al 2009;Radliński et al 2009;Battistutta et al 2010;Gensterblum et al 2010;Day et al 2011;Kim et al 2011;Jiang et al 2012;Maphala and Wagner 2012;An et al 2013;Cai et al 2013a, b;Lin et al 2013;Dutka et al 2013;Xiao et al 2016) include Vitrinite, Inertinite, Exinite. The common indicators are: moist mineral matter basis, and moist mineral matter-free basis (mmf).…”

“…According to the structure and morphology of cell, Inertinite is divided into fusinite, half fusinite, fungus, secretion, coarse grain, particles, debris of inertinite, etc. Figure 10 shows the Chang et al 2006;Qin et al 2007;Chang et al 2008;Jiang et al 2012;Lin et al 2013;Xu and Pan 2015;Xiao et al 2016)-159, English Nelson et al 1980;Giuliani et al 1991;Crosdale et al 1998;Laxminarayana and Crosdale 2002;Busch et al 2003;Mastalerz et al 2004;Hildenbrand et al 2006;Busch et al 2006;Siemons et al 2007;Busch et al 2007;Faiz et al 2007a, b;Majewska and Ziętek 2007;Yu et al 2008a, b, c;Astashov et al 2008;Day et al 2008;Mazumder and Wolf 2008;Pone et al 2009;Majewska et al 2009;Radliński et al 2009;Battistutta et al 2010;Gensterblum et al 2010;He et al 2010;Kim et al 2011;Day et al 2011;Le Gal et al 2012;Maphala and Wagner 2012;Sakurovs 2012;An et al 2013;Cai et al 2013a, b;Dutka et al 2013)-292) relationship between inertinite and Vitrinite reflectance (R o;max ). Figure 10 shows that the relationship betw...…”

“…A small amount of carbon is present in carbonate and carbon dioxide, and the content of carbon in coal is higher than that in any other element. Therefore, the Chang et al 2006;Qin et al 2007;Faiz et al 2007a, b;Chang et al 2008;Jiang et al 2012;Lin et al 2013;Xiao et al 2016)-233, English Crosdale et al 1998;Laxminarayana and Crosdale 2002;Busch et al 2003;Mastalerz et al 2004;Busch et al 2006;Hildenbrand et al 2006;Busch et al 2007;Majewska and Ziętek 2007;Siemons et al 2007;Astashov et al 2008;Day et al 2008;Yu et al 2008a, b;Mazumder and Wolf 2008;Pone et al 2009;Radliński et al 2009;Majewska et al 2009;Gensterblum et al 2010;Battistutta et al 2010;He et al 2010;Day et al 2011;Kim et al 2011;Maphala and Wagner 2012;Sakurovs 2012;An et al 2013;Cai et al 2013a, b;Dutka et al 2013)-169) Effects of coal rank on physicochemical properties of coal and on methane adsorption 139 metamorphism degree of coal is often referred to as carbonization degree. In order to reduce the impact of ash, moisture and other content, we use ash-free basis Dry indicator, Fig.…”

“…Scholars at home and abroad have already done a lot of research work in the coal rank impact on physicochemical properties of coal and coal methane adsorption characteristics Faiz et al 1992;Levy et al 1997;Ceglarska-Stefańska and Brzóska 1998;Laxminarayana and Crosdale 1999;Zhang and Yang 1999;Clarkson and Bustin 2000;Ö zgen Karacan and Okandan 2000;Fu et al 2005;Chalmers and Marc Bustin 2007;Faiz et al 2007a, b;Crosdale et al 2008;Day et al 2008;Mares and Moore 2008;Pan et al 2010;Chen et al 2011;Pini et al 2011;Yao et al 2011;Xiao and Wang 2011;Hao et al 2012;An et al 2013). Resulting shows that coal methane adsorption characteristics is affected by many kinds of factors, including coal rank, coal type that can be expressed in terms of many physicochemical properties, e. g. proximate analysis, maceral composition, ultimate analysis, moisture content.…”