A total of 18 chars from the pyrolysis of six trios of sugar cane bagasses (SCBs; original, water-washed, and acid-washed) were gasified with CO2 at 900 °C, aiming at a quantitative description of the rate of gasification catalyzed by inherent metallic species and a correlation of the catalytic activity and its change during the gasification with the metallic species composition. The measured kinetics was described quantitatively over a range of char conversion, 0–0.999, by a model that assumed progress in parallel of the catalytic gasification and non-catalytic gasification, together with the presence of a catalytic precursor and three to four types of catalysts having different activities and deactivation characteristics. A series of regression analyses was scrutinized and reached expression of initial catalytic activity as a linear function of Na, K, Ca, Fe, and Si concentrations in the char with a correlation factor (r 2) of >0.98. The catalyst precursor contributed fully by water-soluble Na, K, and Ca. Si was responsible for the catalyst deactivation during the pyrolysis but not during the gasification. The chars produced from original SCBs followed a linear relationship between the initial catalytic deactivation rate and initial activity (r 2 > 0.99), while such a linear relationship was not valid for those formed from the water-washed SCBs. This was explained mainly by more rapid deactivation of the Fe catalyst in the chars from water-washed SCBs than that in the chars formed from the original SCBs. Na and K in char from the original SCBs, originating from the water-soluble SCBs, chemically interacted with the Fe catalyst, slowing its deactivation.

Removal of alkali and alkaline earth metallic (AAEM) species, in particular, that of potassium, is an effective way to upgrade rice husk, because its combustion and gasification often suffer from the formation of potassium silicate with a low softening or fusion temperature. This work has been investigating the leaching of AAEM species with a bio-oil (BO) from the pyrolysis of the parent rice husk. The leaching with BO, which had a pH of 2.59, gave removal rates of K and Na equivalent to or higher than those with an aqueous solution of hydrogen chloride (HCl aqueous) or acetic acid (AcOH aqueous) at pH of 2. The leaching abilities of BO in terms of the removal rates of Mg and Ca were equivalent to HCl aqueous at pH 0 and AcOH aqueous at pH < 2, respectively. Such performances of BO arose from the presence of not only AcOH with a concentration of 6 wt % but also phenolic compounds (phenol, alkylphenols, and methoxyphenols). The phenols permeated into the organic matrix of the rice husk, forming hydrophobic interactions as well as hydrogen bonds with macromolecules, making the matrix more accessible to AcOH and water, and thereby promoting the leaching of organically bound AAEM species. The result of the leaching test with a simulated BO quantitatively demonstrated the role of the phenolic compounds as the leaching promoter.

Binderless briquetting of lignite at 100-200°C and subsequent carbonization produces formed coke with tensile strength (ST) of 5-40 MPa, while the briquetting often requires mechanical pressure over 100 MPa. High reactivity is another feature of the lignite-derived coke, and this arises from highly dispersed metallic species such as alkali/alkaline-earth metallic species and ferrous/ferric ones that catalyze CO2 gasification. This work investigated effects of leaching of those metallic species in aqueous solution of hydrochloric acid, acetic acid or oxalic acid on the reactivity and ST of resulting coke from a lignite. The leaching at pH ≤ 1 removed catalytic metallic species near completely, reducing the coke reactivity by a factor of 8-15. The reduced reactivity was similar to the reactivity of coke from a typical coking coal. The leaching at pH ≤ 2.2 increased ST from 6 to 13 MPa for briquetting at 200°C and 32 MPa. The performance of leaching with oxalic acid, of that solution had pH of 0.75 at 1 mol/L, was much better than that with acetic acid. This work also examined another type of leaching, oxidation of the lignite in aqueous solution of hydrogen peroxide, which produced organic mono-/di-acids in-situ from the oxidation of aromatic carbons of the lignite. The degree of reduction of the coke reactivity was between that for leaching at pH of 1 and 2. The degradation of macromolecules enhanced plasticizability of the lignite under briquetting and increased ST of the resulting coke to 22 MPa.

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