- Nano Express
- Open Access
Supercritical Water as Nanomedium for Gasification of Lignite-Water Suspension
© Korzh and Bortyshevskyi. 2016
- Received: 21 December 2015
- Accepted: 27 April 2016
- Published: 18 May 2016
The gasification of an aqueous suspension of lignite from Alexandria coalfield (Ukraine) under the supercritical pressure was studied. The initial rates of the formation of hydrogen, carbon dioxide and methane were evaluated. The mutually stimulating interaction of the components of “brown coal-water-mineral matter” system was shown due to the influence of nanoscaled water medium on the formation of dipole-inductive, dispersive and ionic associates. In the temperature range of 300–450 °C, the oxygen source for gaseous products of the lignite supercritical gasification is mainly ion-associative nanoclustered water. The source of hydrogen at the subcritical temperature is the organic part of brown coal. For the supercritical water, the source of H is the nanoscale medium with ion associates. The last ones were responsible for the further transformation of coal.
- Supercritical fluids
- Nanosized clusters
- Ionic associates
- Water-coal suspension gasification
These changes of conditions, medium, and products of the supercritical gasification are caused by the changes of the mechanism of coal converting. The supercritical water gasification of coal is reviewed in [3–6]. The aim of our work was to clear the general scheme of the mechanism gasification of coal water slurry under the supercritical conditions by water. The primary problem was faced while assessing the impact of supercritical water properties on the transformation of organic matter of lignite.
The conditions of the supercritical gasification of lignite aqueous suspension
Lignite (30 %, mass)
Water (70 %, mass)
NaOH, Ca(OH)2, NiO-MoO3-Al2O3 (ANM)
Н2, СО2,СН4, С х Н y , N2, О2
1—feedstock reservoirs; 2—level meter; 3—high pressure pump; 4—back valve; 5—manometers; 6—reactor; 7—condenser; 8—pressure regulator; 9—separator; 10—gas meter; 11—reservoir for liquid and solids
Liquids: organics + water soluble compounds (oxygenates and inorganics)
The experimental results of the gasification of lignite aqueous suspension under the supercritical conditions
Initial rate of gas formation, mg/h
NiO-MoO3-Al2O3 (AMN 10 % to coal)
NaOH (5 % to coal)
Ca(OH)2 (10 % to coal)
The resulting product is divided into three phases: gas, liquid and sludge . The main gaseous products are hydrogen (volume fraction of 30–50 %), methane (15–20 %), carbon dioxide (40–60 %), nitrogen (up to 5 %) and light hydrocarbons (up to 5 %). The gasification is accelerated in the temperature range of 300–350 °C, which is considered as subcritical according to . Notable rate of formation of carbon dioxide, methane and hydrogen can be achieved under the heating to the supercritical temperatures above 400 °C. The addition to the reaction mixture of mineral acid catalysts and alkaline nature increases the rate of formation of hydrogen, methane and carbon dioxide with maximum values for calcium hydroxide (Table 2).
Origin of Elements
According to the calculations, the own hydrogen of coal is ample for the formation all the hydrogen of gas phase at the subcritical temperature from the organic mass of coal. At the supercritical temperature, the own hydrogen of converted coal is not enough to form hydrogen of gas phase. So 70 % of the gaseous hydrogen produces from water and mineral parts.
Combining the two graphs from Fig. 3 shows the trend of the system of “brown coal-water-mineral substance” to the inversion. In the first approximation, the carbon of lignite at the subcritical temperature behaves like an acid and water is like a base; under the supercritical temperature, they switch their roles.
The Influence of Reactive Medium
Special attention attracts the influence of the supercritical water medium and the mineral part of lignite to the coal conversion. The indicative result was no transformation of pure carbon materials like graphite by the supercritical water at temperatures ranging from 300 to 500 °C. Only when the organic, mineral and water components are combined at the supercritical pressure, the carbon is gasified. It allows us to predict the effect of the mutual stimulation (or inter amplification) of reagents in the supercritical conversion.
General Scheme of Lignite Gasification in the Supercritical Water
Comprehensive experimental investigation of the gasification of lignite-water slurry under the supercritical pressure shows the mutually stimulating interaction the components of the “brown coal-water-mineral matter” system due to the influence of nanoscale water medium on the formation of dipole-inductive, dispersive and ionic associates. Oxygen source for the gaseous products of the lignite supercritical conversion in the temperature range 300–450 °C is mainly ion-associative nanoclustered water. The source of hydrogen for the subcritical temperature is an organic part of lignite and for the supercritical temperature is the nanoscale medium with ion associates. Addition of acid-base catalyst accelerates the formation of hydrogen and methane. The acid catalysts under the supercritical temperature twice more attracted to convert oxygen of organic part of lignite. The alkaline catalysts enhance the transition to the gas phase of hydrogen from nanoclustered supercritical water and mineral part of lignite.
The catalytic experiments and laboratory installation assembling have been funding by Target Complex Program of Scientific Research of NAS of Ukraine “Biomass as a fuel” (“Biofuels”), project 24, 2009-2012. http://www1.nas.gov.ua/infrastructures/Legaltexts/nas/2010/regulations/Pages/199.aspx, http://www1.nas.gov.ua/Chronicle/Events/091215biofuel/Pages/default.aspx.
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- Kruse A, Dinjus E (2007) Hot compressed water as reaction medium and reactant. Properties and synthesis reactions. J Supercrit Fluids 39:362–80View ArticleGoogle Scholar
- Gurina DL, Abakumova NA, Antipova ML, Petrenko VE (2010) Hydrogen bonds in sub- and supercritical water near the saturation curve: topological aspect. Vestnik TGTU 16(4):848–57, http://cyberleninka.ru/article/n/vodorodnye-svyazi-v-subi-sverhkriticheskoy-vode-vblizi-krivoy-nasyscheniya-topologicheskiy-aspekt Google Scholar
- Wang S, Guo Y, Wang L, Wang Y, Xu D, Ma H (2011) Supercritical water oxidation of coal: investigation of operating parameters’ effects, reaction kinetics and mechanism. Fuel Process Technol 92(3):291–297View ArticleGoogle Scholar
- Elliot DC, Neuenschwander GG, Hart TR, Rotness LG Jr., Zacher AH, Santosa DM (2009) Catalytic hydrothermal gasification of lignin-rich biorefinery and algae. Final Report. PNNL-18944. http://www.pnl.gov/main/publications/external/technical_reports/PNNL-18944.pdf
- Li Y, Guo L, Zhang X, Jin H, Lu Y (2010) Hydrogen production from coal gasification in supercritical water with a continuous flowing system. Intern J Hydrogen Energy 35:3036–3045View ArticleGoogle Scholar
- Jin H, Lu Y, Guo L, Zhang X, Pei A (2014) Hydrogen production by supercritical water gasification of biomass with homogeneous and heterogeneous catalyst. Adv Condens Matter Phys. http://dx.doi.org/10.1155/2014/160565
- Korzh RV, Bortyshevskyi VA (2014) Conversion of carbonic raw material under the supercritical conditions. Perspectives for fuel and fine chemicals production. In: Advance in petroleum and gas industry and petrochemistry. Proceedings of VIIth intern. sci.-tech. conf. APGIP-7 Ukraine. National University “Lviv Polytechnika”, Lviv, pp 32–35, ISBN 978-617-607-554-7Google Scholar
- Korzh RV, Bortyshevskyi VA, Burdeynyi VG (2012) Catalytic gasification of coal-water suspension under the supercritical conditions. Catalysis Petrochem (Kataliz i neftechimia) 21:63–9. http://nbuv.gov.ua/UJRN/KiN_2012_21_10
- Fulton JL, Chen Y, Heald SM, Balasubramanian M (2004) High-pressure, high-temperature X-ray absorption fine structure transmission cell for the study of aqueous ions with low absorption-edge energies. Rev Sci Instrum 75(12):5228–31. doi:10.1063/1.1813131, http://www.pnl.gov/publications/abstracts.asp?report=202321 View ArticleGoogle Scholar