The Influence Of The Molybdenum Contents
THE INFLUENCE OF THE MOLYBDENUM CONTENTS
OF DESONOX CATALYST
A. Marcewicz-Kuba, D. Nazimek
Faculty of Chemistry, Maria Curie-Sklodowska University,
Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland,
e-mail: amarcewi@hermes.umcs.lublin.pl
The method proposed for the removal of SO2 from combustion gases, described in this paper, is quite different from wet classical desulphurization methods. This paper reports the studies on the influence of molybdenum and vanadium concentration on the catalytic activity of DESONOX catalysts (in the course of DESOX reaction). It also investigates the influence of the total surface area and other physicochemical properties of the catalyst on their behaviour.
The investigated DESONOX catalysts were obtained by co-precipitation of hydroxides from the aqueous solutions of salts, (NH4)2Mo7O24×4H2O (0,01M) and Mg(CH3COO)2×4H2O (1 M). All prepared precursors of the catalysts were dried at 423K in air for 12 hours then calcined at 773K in the atmosphere of air for 4 hours [1]. The investigated hard coal comes from KWK "Bogdanka" (BI) – table 1. The total surface area of the catalysts examined was determined by the BET method [2]. The concentrations of molybdenum, vanadium and other compounds in the examined catalysts were determined by the XRF method [3]. The results that have been achieved were used to measure the degree of sulphur removal (SE) in combustion gases coming from burning the hard coal with catalyst and the degree of nonafterburning of the hard coal (N %).
Table1. The physicochemical properties of the hard coal samples used for the measurements
Code of hard coal
Calorific value, Qri,
kJ/kg
Sulphur concentration in the hard coal, St
wt. %
Concentration of the ballast in the hard coal, Ar
wt. %
B1
23674
1,19
19,66
The total surface area is increasing with decreasing of contain molybdenum in catalysts. The highest degree of the sulphur removal is obtained during the burning of hard coal samples with catalyst that includes molybdenum from 0,123 to 0,332 weight percents. The degree of the sulphur removal for the samples mentioned above equals 0.80 weight percents. The degree of nonafterburning in samples with catalyst includes from 0,17 to 0,82%. The obtained results of investigated DESONOX catalysts specific activity changes show a clear maximum in the concentration of the mole fraction molybdenum reaches about 0,3 (figure 1).
Figure1.Changes of the degree of the sulphur removal with the gases as a function the mole fraction molybdenum in catalyst
The addition of the molybdenum to the DESONOX catalysts causes a specific activity value increase of the catalysts for all samples hard coals. Probably this effect is caused by increase in basity of Levis sites in the ashes of hard coal [4]. Basing on preparation methods described in paper [1] large consignment of DESONOX catalyst was used to remove the SO2 from combustion gases that came from industrial boiler in ZEC "Wieluń". As it is shown, the introduction of 0.4 kg of the DESONOX catalyst into 1000 kg of hard coal removes 75 % of SO2 from combustion gases [5].
References
1. A. Marcewicz-Kuba, D. Nazimek, Ads.Sci.&Technol. 16(1998)803.
2. J. Ościk, Adsorpcja, PWN, Warszawa 1983.
3. A. Cygański, Metody spektroskopowe w chemii analitycznej, PWN, Warszawa 1993.
4. K. Tanabe, Solid Acids and Bases, Academic Press, Tokyo 1970.
5. Sprawozdanie z prób wdrożeniowych katalizatora DESONOX-p na kotle WR-25, ZEC "Wieluń", Wieluń, 1999.
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