Skip to main content
Log in

Effects of Organic Micromolecules in coal on its Pore Structure and Gas Diffusion Characteristics

Transport in Porous Media Aims and scope Submit manuscript

Abstract

Coal has complex pore structures including micro-, meso-, and macropores and cracks, and contains organic micromolecules. To in-depth study the effects of organic micromolecules in coal on the pore structure and gas diffusion characteristics, organic micromolecules were extracted by tetrahydrofuran using microwave-assisted method from anthracite and bituminous coal samples to obtain the residual coal samples at 50 \(^{\circ }\)C and atmospheric pressure. Changes in raw and residual coal samples were explored using a series of methane desorption and low-temperature nitrogen adsorption experiments and their pore structure parameters were compared using samples with same granule size (0.180–0.250 mm). The results showed that (1) although the micropores of both raw and residual coal granules are characterized by fractal, residual coal has lower fractal dimension than raw coal; (2) residual coal samples have higher gas emission amount and rate than the raw coal samples and lower gas diffusion resistance, indicating that gas in residual coal is easier to flow from micropores through mesopores into macropores and cracks. Based on the fractal theory and the diffusion model, extraction of organic micromolecules increased the number and diameter of pores and cracks and dredged the rawly clogged pores and cracks, all of which decreased the resistance of gas diffusion in the coal matrix. In addition, extraction of organic micromolecules has the most obvious effect on diffusion pores. After extraction, the proportion of meso-/macropores increased, while that of micropores reduced, thereby reducing the resistance of gas flowing from micropores through mesopores into macropores and cracks, and subsequently increasing the amount and rate of gas emission. The study is of great significance for pushing forward the boundary of our recognition of the influences exerted by micromolecules on gas diffusion.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Fig. 1
Fig. 2
Fig. 3
Fig. 4

References

  • Busch, A., Gensterblum, Y.: CBM and CO2-ECBM related sorption processes in coal: A review. Int. J. Coal Geol. 87(2), 49–71 (2011)

    Article  Google Scholar 

  • Cai, Y., Liu, D., Yao, Y., Li, J., Liu, J.: Fractal characteristics of coal pores based on classic geometry and thermodynamics models. Acta Geol. Sin. Engl. Ed. 85(5), 1150–1162 (2011)

    Article  Google Scholar 

  • Cai, Y.D., Liu, D.M., Pan, Z.J., Yao, Y.B., Li, J.Q., Qiu, Y.K.: Pore structure and its impact on CH4 adsorption capacity and flow capability of bituminous and subbituminous coals from Northeast China. Fuel 103, 258–268 (2013)

    Article  Google Scholar 

  • Chen, H., Ge, L.M., Li, J.W.: Optimization of microwave-assisted extraction coal and analysis of soluble fraction and residue. J. China Coal Soc. 4, 022 (2009)

    Google Scholar 

  • Chen, X., Cheng, Y., He, T., Li, X.: Water injection impact on gas diffusion characteristic of coal. J. Min. Saf. Eng. 30(3), 443–448 (2013)

    Google Scholar 

  • Cheng, Y.P.: Theories and engineering applications on coal mine gas control. China University of Mining and Technology Press, Xuzhou (2010)

    Google Scholar 

  • Clarkson, C., Bustin, R.: The effect of pore structure and gas pressure upon the transport properties of coal: a laboratory and modeling study. 1. Isotherms and pore volume distributions. Fuel 78(11), 1333–1344 (1999a)

    Article  Google Scholar 

  • Clarkson, C.R., Bustin, R.M.: The effect of pore structure and gas pressure upon the transport properties of coal: a laboratory and modeling study. 2. Adsorption rate modeling. Fuel 78(11), 1345–1362 (1999b)

    Article  Google Scholar 

  • Clarkson, C.R., Marc Bustin, R.: Variation in micropore capacity and size distribution with composition in bituminous coal of the Western Canadian Sedimentary Basin: Implications for coalbed methane potential. Fuel 75(13), 1483–1498 (1996)

    Article  Google Scholar 

  • Day, S., Sakurovs, R., Weir, S.: Supercritical gas sorption on moist coals. Int. J. Coal Geol. 74(3), 203–214 (2008)

    Article  Google Scholar 

  • Fang, P.H., Wong, R.: Evidence for fullerene in a coal of Yunnan, Southwestern China. Mater. Res. Innov. 1(2), 130–132 (1997)

    Article  Google Scholar 

  • Harpalani, S., Chen, G.: Influence of gas production induced volumetric strain on permeability of coal. Geotech. Geol. Eng. 15(4), 303–325 (1997)

    Google Scholar 

  • He, X.: The effect of alternative electromagnetic field on adsorption of gas by coal. J. China Coal Soc. 21(1), 63–67 (1996)

    Google Scholar 

  • He, X., Nie, B.: Diffusion mechanism of porous gases in coal seams. J. China Univ. Min. Technol. 30(1), 1–4 (2001)

    Google Scholar 

  • Hu, S., Li, M., Xiang, J., Sun, L., Li, P., Su, S., Sun, X.: Fractal characteristic of three Chinese coals. Fuel 83(10), 1307–1313 (2004)

    Article  Google Scholar 

  • Iino, M., Takanohashi, T., Ohsuga, H., Toda, K.: Extract ion of Coals with \(\text{ CS }_{2}\) -N-methyl-2-pyrrolidinone mixed solvent at room temperature: effect of coal rank and synergism of the mixed solvent. Fuel 67, 1639–1647 (1988)

    Article  Google Scholar 

  • Ji, H.J., Li, Z.H., Peng, Y.J., Yang, Y.L., Tang, Y.B., Liu, Z.: Pore structures and methane sorption characteristics of coal after extraction with tetrahydrofuran. J. Nat. Gas Sci. Eng. 19, 287–294 (2014)

    Article  Google Scholar 

  • Jiang, W.: Study on features comparison and mechanism of methane adsorbed by coal before and after solvent extraction. Coal Sci. Technol. 41(3), 114–119 (2013)

    Google Scholar 

  • Krooss, B., Van Bergen, F., Gensterblum, Y., Siemons, N., Pagnier, H., David, P.: High-pressure methane and carbon dioxide adsorption on dry and moisture-equilibrated Pennsylvanian coals. Int. J. Coal Geol. 51(2), 69–92 (2002)

    Article  Google Scholar 

  • Laxminarayana, C., Crosdale, P.J.: Role of coal type and rank on methane sorption characteristics of Bowen Basin, Australia coals. Int. J. Coal Geol. 40(4), 309–325 (1999)

    Article  Google Scholar 

  • Li, Y.H., Lu, G.Q., Rudolph, V.: Compressibility and fractal dimension of fine coal particles in relation to pore structure characterisation using mercury porosimetry. Part. Part. Syst. Charact. 16(1), 25–31 (1999)

    Article  Google Scholar 

  • Liu, B., Xiong, D., Xian, X.: Adsorption and seepage characteristics of coal to methane under electric field. J. Chongqing Univ. (Nat. Sci. Ed.) 29(2), 83–85 (2006)

    Google Scholar 

  • Mandelbrot, B.B.: The fractal geometry of nature. Macmillan (1983)

  • Marzec, A.: Towards an understanding of the coal structure: a review. Fuel Process. Technol. 77–78, 25–32 (2002)

    Article  Google Scholar 

  • Mathews, J.P., Chaffee, A.L.: The molecular representations of coal—a review. Fuel 96(1), 1–14 (2012)

    Article  Google Scholar 

  • Moore, T.A.: Coalbed methane: a review. Int. J. Coal Geol. 101, 36–81 (2012)

    Article  Google Scholar 

  • Nie, B., Guo, Y., Wu, S., Zhang, L.: Theoretical model of gas diffusion through coal particles and its analytical solution. J. China Univ. Min. Technol. 30(1), 19–22 (2001)

    Google Scholar 

  • Qin, Y., Fu, G.: Study on fractal characteristic of pore in coal and moisture absorbing property of coal. J. China Coal Soc. 25(1), 55–59 (2000)

    Google Scholar 

  • Qin, Z., Gong, T., Li, X., Li, H., Zhang, D., Sun, h: TEM analysis of coal extract ion and coal inbuilt state structural model. J. China Univ. Min. Technol. 37(4), 443–449 (2008)

    Google Scholar 

  • Qin, Z., Li, H., Zhang, D., Ding, S., Sun, h, Jiang, C.: Characteristics of micropore-inbuilt form of micromolecules in coal and their solubilization rules. J. China Univ. Min. Technol. 36(5), 586–591 (2007)

    Google Scholar 

  • Ruckenstein, E., Vaidyanathan, A.S., Youngquist, G.R.: Sorption by solids with bidisperse pore structures. Chem. Eng. Sci. 26(9), 1305–1318 (1971)

    Article  Google Scholar 

  • Rus’ ianova, N., Maksimova, N., Jdanov, V., Butakova, V.: Structure and reactivity of coals. Fuel 69(11), 1448–1453 (1990)

  • Shi, J.Q., Durucan, S.: A bidisperse pore diffusion model for methane displacement desorption in coal by CO2 injection. Fuel 82(10), 1219–1229 (2003)

    Article  Google Scholar 

  • Takanohashi, T., Terao, Y., Iino, M.: Sorption behaviors of methanol vapor by coal extracts and residues. Fuel 79(3), 349–353 (2000)

    Article  Google Scholar 

  • Wang, E., He, X.: Fractal descript ion of coal seam porosity and crack system and its application. J. Fuxin Min. Inst.(Nat. Sci.) 15(4), 19–23 (1995)

    Google Scholar 

  • Wang, F., Zhang, D.J., Li, X.P., Yang, Ml: Adsorption behaviors for nitrogen by coal, its extractions and residues. J. Fuel Chem. Technol. 31(5), 395–399 (2003)

    Google Scholar 

  • Xie, K.: Coal structure and its reactivity. Science Press, Beijing (2002)

    Google Scholar 

  • Yang, Q., Wang, Y.: Theory of methane diffusion from coal cuttings and its application. J. China Coal Soc. 8(3), 87–93 (1986)

    Google Scholar 

  • Yang, Q., Wang, Y.: Mathematical simulation of the radial methane flow in spherical coal grains. J. China Univ. Min. Technol. 4, 44–48 (1988)

    Google Scholar 

  • Yang, R.T.: Gas separation by adsorption processes. Butterworth Publishers, Buffalo (1987)

    Google Scholar 

  • Yuan, W., Pan, Z., Li, X., Yang, Y., Zhao, C., Connell, L.D., Li, S., He, J.: Experimental study and modelling of methane adsorption and diffusion in shale. Fuel 117, 509–519 (2014)

    Article  Google Scholar 

  • Zeng, F.: The fractal surface of coal. Coal Convers. 18(2), 7–13 (1995)

    Google Scholar 

  • Zhang, D.J., Wang, F., Li, X.P., Xian, X.F.: Effect of solvent extraction on pore character and granularity of bituminous coal. J. Fuel Chem. Technol. 32(1), 18–22 (2004)

    Google Scholar 

  • Zhu, Z., Gao, J.: Coal chemistry. In., pp. 194–198. Shanghai science and Technology Press, Shanghai (1984)

Download references

Acknowledgments

This study is supported by the National Basic Research Program of China (973 Program) (No. 2011CB201200) and the National Natural Science Foundation of China (No. 51304189).

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Zenghua Li.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Ji, H., Li, Z., Yang, Y. et al. Effects of Organic Micromolecules in coal on its Pore Structure and Gas Diffusion Characteristics. Transp Porous Med 107, 419–433 (2015). https://doi.org/10.1007/s11242-014-0446-9

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s11242-014-0446-9

Keywords

Navigation