Effect of calcium and barium on potassium-catalyzed gasification of ash-free carbon black

Abstract

Gasification of carbon black, an ash-free carbon feed, was performed with K2CO3 and either CaCO3 or BaCO3 as catalysts to examine their interaction. Mixtures were prepared by low-energy ball-milling, and then gasified with CO2 at 750-850 °C in a thermogravimetric analyzer. At temperatures below 800 °C, the presence of calcium had little impact on the potassium-catalyzed gasification of carbon black. At higher temperatures, calcium promoted the activity of potassium up to ~50 % conversion through the formation of a eutectic phase that increased the diffusivity of the potassium. At higher conversions, the tendency of CaCO3 to sinter and limit diffusion of CO2 to the carbon inhibited the reaction. BaCO3 also formed a eutectic phase with K2CO3 confirming that the phase change was beneficial. In contrast to CaCO3, however, BaCO3 does not sinter at 850 °C, such that gasification was promoted to complete conversion.

CO2 Gasification of Sugarcane Bagasse Char: Consideration of Pyrolysis Temperature, Silicon and Aluminum Contents, and Potassium Addition for Recirculation of Char

“…The char samples containing K/Al ratios of 0.5, 1.0, and 1.25 had, respectively, 19-, 30-, and 13-fold increase in the maximum rate compared to the original ball-milled char (with a K/Al ratio of 0.2, Table 2). These maximum rates occurred before 50% conversion, in agreement with previous gasification studies with potassium-catalyzed ash-free carbon black, 46 Genesse raw coal, 47 and switchgrass char. 25,26 The char with a K/Al ratio of 0.5 had a maximum rate at ∼20% conversion, but the rate was relatively constant between 0 and ∼50% conversion.…”

“…The char samples containing K/Al ratios of 0.5, 1.0, and 1.25 had, respectively, 19-, 30-, and 13-fold increase in the maximum rate compared to the original ball-milled char (with a K/Al ratio of 0.2, Table ). These maximum rates occurred before 50% conversion, in agreement with previous gasification studies with potassium-catalyzed ash-free carbon black, Genesse raw coal, and switchgrass char. , The char with a K/Al ratio of 0.5 had a maximum rate at ∼20% conversion, but the rate was relatively constant between 0 and ∼50% conversion. In contrast, the samples with K/Al ratios of 1.0 and 1.25 had more distinct maxima at 30 and 10% conversion, respectively, and, after gasification, the remaining solids (ash including the added K) were stuck to the cooled crucible.…”

Impact of particle size and catalyst dispersion on gasification rates measured in a thermogravimetric analysis unit: Case study of carbon black catalyzed by potassium or calcium

“…CaCO3 and K2CO3 (>99% purity, Sigma-Aldrich, St. Louis, MI) were the calcium and potassium sources, respectively. The atomic ratio between each metallic element (Ca or K) and carbon was 0.1 for consistency with previous publications [35,36]. The high catalyst loading ensured that the number of available catalytic sites was not a limiting factor in the gasification rates.…”

“…In all three cases, the rate of reaction was significantly below that of CB-CaCO3 ball-milled together (XII) from 10-99% conversion. The propensity of CaCO3 to sinter above 850 °C has been shown in previous publications [36,44]. Ball-milling the components together more effectively dispersed the CaCO3 and reduced the extent of sintering.…”

“…2b) are an order of magnitude higher than those observed in the literature for feeds such as coal [47] and biomass [16,48]. Rates greater than 0.1 min -1 have been observed in our previous studies with CB [35,36], suggesting that the extremely high rates are due to the properties of the CB, including the absence of ash, the highly amorphous nature, and the low porosity (18 m 2 /g by CO2 physisorption). These high rates, however, are likely mass transfer limited.…”