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Catalysis and compensation effect of K2CO3 in low-rank coal - CO2 gasification

100%

Skodras G.

Open Chemistry

2013

vol. 11

issue 7

1187-1200

The CO2 gasification of a low rank coal catalysed by K2CO3 was studied, at 700–950°C and 1 atm. A two level full factorial design revealed that the gasification reaction was sensitive to the solid residence time, reaction temperature, CO2 partial pressure and catalyst load. K2CO3 was an efficient catalyst at all temperatures studied, particularly during the second stage when the Boudouard reaction dominates. The gasification rate was increased continuously with increasing catalyst load up to a load of ∼20% w/w K2CO3 concentration, following a sigmoid curve. Above this point, limited catalytic effect was observed, possibly due to the saturation of the lignite surface by K+. A correlation was found to exist between the catalytic gasification rate and the Alkali Index, which increased with the impregnation of the inorganic K2CO3 salt. When K2CO3 load increased, the Arrhenius parameters, E and k 0, increased simultaneously exhibiting a compensation effect. The isokinetic temperature was found about 600 to 650°C corresponding to the minimum temperature required for the formation of catalytic active intermediates. At temperatures studied, the catalytic active intermediates seemed to be always present and the catalysis progresses unhindered due to the redox cycle, resulting in high rates and conversion. [...]

Cation exchange capability and reactivity of low-rank coal and chars

51%

Skodras G., Kokorotsikos P., Serafidou M.

Open Chemistry

2014

vol. 12

issue 1

33-43

In this work the C.E.C. and its effect on the reactivity of low rank coal and chars were investigated. The C.E.C. was measured by potentiometric titration and was correlated with the solution pH, the carbonization extent and the oxygen content. Coal and chars presented permanent C.E.C. primarily derived from inorganic sites and was independent of solution pH, and variable C.E.C. derived from organic matter and was increased continuously, and reversibly, as the solution pH increased. The latter is due to the complete dissociation of the carboxylic groups of the organic matter of the coal and, thus, the C.E.C. is directly related with the oxygen content. The C.E.C. of chars decreased with the carbonization extents and its variation was described by a modified cumulative distribution function of the Weibull probability density function. A linear correlation was identified between the C.E.C. and the elemental oxygen conversion, justifying further the direct relation between the C.E.C. and the oxygen functional groups. Following the decrease of the C.E.C., the potassium chemisorption capacity of the chars also decreased. Chars of decreased C.E.C. were less reactive during CO2 gasification and reduced maximum weight loss and CO formation rates were obtained, also shifted at higher temperatures. [...]

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Catalysis and compensation effect of K2CO3 in low-rank coal - CO2 gasification

Cation exchange capability and reactivity of low-rank coal and chars