FORMATION OF THE POROUS STRUCTURE OF BROWN COALS DURING CHEMICAL ACTIVATION AND ITS INFLUENCE ON BENZENE ADSORPTION
Keywords:
brown coal, chemical activation, porous structure, specific surface area, surface morphology, low-temperature nitrogen adsorption, adsorption activity, benzeneAbstract
In this study, a comprehensive investigation was carried out on the thermal and chemical modifications of brown coals of BPK and BR grades (Angren deposit, Uzbekistan) with the aim of establishing the regularities governing changes in their physicochemical and adsorption properties. Thermal analysis of the samples revealed the stages of carbon matrix degradation and the removal of volatile components. It was found that chemical activation leads to a significant decrease in the ash content of the coals, which is associated with the dissolution of mineral impurities during KOH treatment. Dispersion analysis demonstrated changes in particle size accompanied by increased structural fragmentation with higher KOH consumption, which was confirmed by morphological analysis using scanning electron microscopy (SEM). The samples after activation exhibited a substantial development of porosity, the formation of network-like structures, and the expansion of the channel system, indicating intensive etching of the carbon matrix. Particular attention was given to the study of the textural characteristics of the activated coals using the low-temperature nitrogen adsorption–desorption method. It was revealed that increasing the KOH ratio promotes a significant growth in the specific surface area (up to 1371.4 m²/g) and the formation of a predominantly microporous structure in BR coals, whereas BPK coals demonstrate a more developed mesoporous system. It was determined that the variation in pore size exerts a decisive influence on benzene adsorption activity. Despite the high specific surface area of the activated coals, their sorption capacity for benzene does not always increase proportionally. This discrepancy is attributed to the peculiarities of the pore structure: BR coals are dominated by narrow micropores (7–12 Å), which ensure high adsorption capacity due to capillary condensation and molecular interactions, while BPK coals contain a higher proportion of pores in the range of 10–25 Å, which limits the retention of benzene molecules.
References
1. Ahmed, M., Mavukkandy, M.O., Hasan, S.W., 2022. Recent developments in hazardous pollutants removal from wastewater and water reuse within a circular economy. npj Clean Water. doi:10.1038/s41545-022-00154-5.
2. Wójtowicz, B.; Kordyzon, M.; Bąk-badowska, J.; Gregorczyk, M.; Gworek, B.; Żeber-Dzikowska, I. 2022. Chemicals in wastewater and sewage sludge—An underestimated health and environmental threat. J. Elem., 27, 847–859. https://doi.org/10.5601/jelem.2022.27.3.2283.
3. González, S.O.; Almeida, C.A.; Calderón, M.; Mallea, M.A.; González, P. 2014. Assessment of the water self-purification capacity on a river affected by organic pollution: Application of chemometrics in spatial and temporal variations. Environ. Sci. Pollut Res., 21, 10583–10593. https://doi.org/10.1007/s11356-014-3098-y.
4. Tanasa, I.; Cazacu, M.; Sluser, B. 2023. Air Quality Integrated Assessment: Environmental Impacts, Risks and Human Health Hazards. Appl. Sci., 13, 1222. https://doi.org/10.3390/app13021222.
5. Glencross, D.A.; Ho, T.R.; Camiña, N.; Hawrylowicz, C.M.; Pfeffer, P.E. 2020. Air pollution and its effects on the immune system. Free Radical Biol. Med., 151, 56–68. https://doi.org/10.1016/j.freeradbiomed.2020.01.179.
6. T. T. Lim and X. Huang, 2007. Evaluation of kapok (Ceiba pentandra (L.) Gaertn.) as a natural hollow hydrophobic-oleophilic fibrous sorbent for oil spill cleanup, Chemosphere, vol. 66, no. 5, pp. 955–963, .https://doi.org/10.1016/j.chemosphere.2006.05.062.
7. D. Wang, T. Silbaugh, R. Pfeffer, and Y. S. Lin, 2010. Removal of emulsified oil from water by inverse fluidization of hydrophobic aerogels, Powder Technol., vol. 203, no. 2, pp. 298-309, https://doi.org/10.1016/j.powtec.2010.05.021.
8. B. I. Waisi, J. T. Arena, N. E. Benes, A. Nijmeijer, and J. R. McCutcheon, 2019. Activated carbon nanofiber nonwoven for removal of emulsified oil from water, Microporous Mesoporous Mater., vol. 296, no. October, p. 109966, 2020. https://doi.org/10.1016/j.micromeso.2019.109966.
9. F. Al Jabri, L. Muruganandam, and D. A. D. A. Aljuboury. 2019. Treatment of the oilfield-produced water and oil refinery wastewater by using inverse fluidization - A review, Glob. Nest J., vol. 21, no. 2, pp. 204–210. https://doi.org/10.30955/gnj.002975.
10. S. Syed, M. I. Alhazzaa, and M. Asif, 2011. Treatment of oily water using hydrophobic nano-silica, Chem. Eng. J., vol. 167, no. 1, pp. 99–103, https://doi.org/10.1016/j.cej.2010.12.006.
11. Lokteva, E.S.; Golubina, E.V. 2019. Metal-support interactions in the design of heterogeneous catalysts for redox processes. Pure Appl. Chem., 91, 609–631. https://doi.org/10.1016/j.cej.2010.12.006.
12. Nowicki, P.; Gruszczyńska, K.; Urban, T.; Wiśniewska, M. 2022. Activated biocarbons obtained from post-fermentation residue as potential adsorbents of organic pollutants from the liquid phase. Physicochem. Probl. Miner. Process., 58, 146357. https://doi.org/10.37190/ppmp/146357.
13. Koul, B.; Yakoob, M.; Shah, M.P. 2022. Agricultural waste management strategies for environmental sustainability. Environ. Res., 206, 112285. https://doi.org/10.1016/j.envres.2021.112285.
14. Olatunji, K.O.; Ahmed, N.A.; Ogunkunle, O. 2021. Optimization of biogas yield from lignocellulosic materials with different pretreatment methods: A review. Biotechnol. Biofuels., 14, 159. https://doi.org/10.1186/s13068-021-02012-x.
15. Saleem, J., Shahid, U., Hijab, M., Mackey, H., McKay, G. 2019. Production and applications of activated carbons as adsorbents from olive stones. Biomass Conv. Bioref., 9, 775–802. https://doi.org/10.1007/s13399-019-00473-7.
16. Bicil, Z., Dogan, M. 2021. Characterization of activated carbons prepared from almond shells and their hydrogen storage properties. Energy Fuels. 35, 10227–10240. https://doi.org/10.1021/acs.energyfuels.1c00795.
17. Oladimeji, T.E., Odunoye, B.O., Elehinafe, F.B., Obanla, O.R., Odunlami, O.A. 2021. Production of activated carbon from sawdust and its efficiency in the treatment of sewage water. Heliyon 7, e05960. https://doi.org/10.1016/j.heliyon.2021.e05960.
18. Jedynak, K., Charmas, B. 2021. Preparation and characterization of physicochemical properties of spruce cone biochars activated by CO2. Materials, 14, 3859. https://doi.org/10.3390/ma14143859.
19. Shafeeyan, M. S., Daud, W. M. A. W., Houshmand, A., & Shamiri, A. 2010. A review on surface modification of activated carbon for carbon dioxide adsorption. Journal of Analytical and Applied Pyrolysis. https://doi.org/10.1016/j.jaap.2010.07.006.
20. Herawan, S. G., Ahmad, M. A., Putra, A., & Yusof, A. A. 2013. Effect of CO2 flow rate on the pinang frond-based activated carbon for methylene blue removal. The Scientific World Journal, https://doi.org/10.1155/2013/545948.
21. Hesas, R. H., Arami-Niya, A., Wan Daud, W. M. A., & Sahu, J. N. 2013. Preparation and characterization of activated carbon from apple waste by microwave-assisted phosphoric acid activation: Application in methylene blue adsorption. BioResources, 8(2), 2950–2966. https://doi.org/10.15376/biores.8.2.2950-2966.
22. Tan, I. A. W., Ahmad, A. L., & Hameed, B. H. 2008. Optimization of preparation conditions for activated carbons from coconut husk using response surface methodology. Chemical Engineering Journal, 137(3), 462–470. https://doi.org/10.1016/j.cej.2007.04.031
23. Yang K, Peng J, Srinivasakannan C, Zhang L, Xia H and Duan X 2010. Preparation of high surface area activated carbon from coconut shells using microwave heating. Bioresour. Technol. 101 (15) 6163-6169. https://doi.org/10.1016/j.biortech.2010.03.001.
24. Wang J and Kaskel S. 2012. KOH activation of carbon-based materials for energy storage J. Mater. Chem. 22 (45) 23710-23725. https://doi.org/10.1039/c2jm34066f.
25. Paryanto, Wibowo, W. A., Hantoko, D., & Saputro, M. E. 2019. Preparation of Activated Carbon from Mangrove Waste by KOH Chemical Activation. In IOP Conference Series: Materials Science and Engineering. Institute of Physics Publishing., Vol. 543. https://doi.org/10.1088/1757-899X/543/1/012087
26. Srinivasakannan, C., Abu Bakar, Z. 2004. Production of activated carbon from rubber wood sawdust. Biomass and Bioenergy, 27(1), 89–96. https://doi.org/10.1016/j.biombioe.2003.11.002
27. Seitnazarova O., Kalbaev A., Mamataliev N., Abdikamalova A., Najimova N., 2025. Structural features of montmorillonite-surfactant systems: influence of surfactant packing density and montmorillonite surface nature. Journal of Chemical Technology and Metallurgy, 60, 1, 43-62. https://doi.org/10.59957/jctm.v60.i1.2025.5
28. Guy, P. J., Perry, G. J. 1992. Victorian brown coal as a source of industrial carbons: a review. Fuel. https://doi.org/10.1016/0016-2361(92)90088-6
29. Amarasekera, G., Scarlett, M. J., & Mainwaring, D. E. 1998, Development of microporosity in carbons derived from alkali digested coal. Carbon, 36(7–8), 1071–1078. https://doi.org/10.1016/S0008-6223(98)00079-7.
30. Lillo-Ródenas, M. A., Cazorla-Amorós, D., & Linares-Solano, A. 2003. Understanding chemical reactions between carbons and NaOH and KOH: An insight into the chemical activation mechanism. Carbon, 41(2), 267–275. https://doi.org/10.1016/S0008-6223(02)00279-8.
31. Khoshimov Sh., Raxmonaliyeva N., Askarova D., Seytnazarova O., Abdikamalova A. 2024. Changes in the porous structure of carbonizate of carbon containing raw under alkaline activation. AIP Conf. Pro. 11 March; 3045 (1): 030059. https://doi.org/10.1063/5.0197789.
32. Shendrik, T. G., Tamarkina, Y. V., Khabarova, T. V., Kucherenko, V. A., Chesnokov, N. V., & Kuznetsov, B. N. 2009. Formation of the pore structure of brown coal upon thermolysis with potassium hydroxide. Solid Fuel Chemistry, 43(5), 309–313. https://doi.org/10.3103/S0361521909050097.
33. Tamarkina, Y. V., Kolobrodov, V. G., Shendrik, T. G., Kucherenko, V. A. 2009. Properties of adsorbents prepared by the alkali activation of Aleksandriisk brown coal. Solid Fuel Chemistry, 43(4), 233–237. https://doi.org/10.3103/S0361521909040090
34. Tamarkina, Y. V., Kucherenko, V. A., Shendrik, T. G. 2015. Interrelation of gas generation and pore formation on the alkaline activation of brown coal. Solid Fuel Chemistry, 49(2), 91–98. https://doi.org/10.3103/S036152191502010X.
35. Tamarkina, Y. V., Kucherenko, V. A., & Shendrik, T. G. 2012. Nanoporous brown coal adsorbents prepared by alkaline activation with thermal shock. Solid Fuel Chemistry, 46(5), 289–294. https://doi.org/10.3103/S0361521912050114
36. Thommes, M., Kaneko, K., Neimark, A.V., Olivier, J.P., Rodriguez-Reinoso, F., Rouquerol, J., & Sing, K.S.W. 2015. Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report). Pure and Applied Chemistry, 87(9-10), 1051–1069. https://doi.org/10.1515/pac-2014-1117.
37. Salehi R., Dadashian F., Abedi M., Eliassi A. 2025. Adsorption studies of benzene and toluene in gas phase onto activated carbon fabrics in fixed bed column. Heliyon. 11(2). doi:10.1016/j.heliyon.2025.e42071.
38. Mamataliev, N., Abdikamalova, A., ... Eshmetov, I., 2025. The role of hydrocarbon radicals in the formation of structural and adsorption characteristics of the montmorillonite–surfactant system. Adsorption Science and Technology 43. doi:10.1177/02636174251377860.
39. Nandi R., Jha M.K., Guchhait S.K., Sutradhar D., Yadav S. 2023. Impact of KOH activation on rice husk derived porous activated carbon for carbon capture at flue gas alike temperatures with high CO2/N2 selectivity // ACS Omega. 8(5). DOI: 10.1021/acsomega.2c06955.
Published
How to Cite
Issue
Section
License
Copyright (c) 2025 «JOURNAL OF MODERN CHEMISTRY»
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
