Gasification catalysts, either intrinsic to the feed or added, are discussed as to their advantages, disadvantages, and interactions.

9Catalytic gasification is a method of converting biosolids, the solids created during wastewater 10 treatment, into a valuable gaseous stream. One of the challenges with this process is that the 11 components in the ash of the biosolids can interact with the gasification catalyst(s) -in 12 particular, calcium and potassium. In this study, the behaviors of different combinations of 13 switchgrass (the source of potassium), biosolids, ash-free carbon black, and mixtures of each 14 feed with added calcium and/or potassium were observed with a thermogravimetric analysis unit. 15The results were consistent with calcium preferentially reacting with components in the ash, 16preventing the deactivation of potassium. Any additional calcium available may form bimetallic 17

By focusing the power of sound, acoustic stimulation (i.e., often referred to as sonication) enables numerous “green chemistry” pathways to enhance chemical reaction rates, for instance, of mineral dissolution in aqueous environments. However, a clear understanding of the atomistic mechanism(s) by which acoustic stimulation promotes mineral dissolution remains unclear. Herein, by combining nanoscale observations of dissolving surface topographies using vertical scanning interferometry, quantifications of mineral dissolution rates via analysis of solution compositions using inductively coupled plasma optical emission spectrometry, and classical molecular dynamics simulations, we reveal how acoustic stimulation induces dissolution enhancement. Across a wide range of minerals (Mohs hardness ranging from 3 to 7, surface energy ranging from 0.3 to 7.3 J/m2, and stacking fault energy ranging from 0.8 to 10.0 J/m2), we show that acoustic fields enhance mineral dissolution rates (reactivity) by inducing atomic dislocations and/or atomic bond rupture. The relative contributions of these mechanisms depend on the mineral’s underlying mechanical properties. Based on this new understanding, we create a unifying model that comprehensively describes how cavitation and acoustic stimulation processes affect mineral dissolution rates.

The disposal of highly concentrated brines from coal power generation can be effectively accomplished by physical solidification and chemical stabilization (S&S) processes that utilize fly ashes as a reactant. Herein, pozzolanic fly ashes are typically combined with calcium-based additives to achieve S&S. While the reactions of fly ash–(cement)–water systems have been extensively studied, the reactivity of fly ashes in hypersaline brines (ionic strength, I m > 1 mol/L) is comparatively less understood. Therefore, the interactions of a Class C (Ca-rich) fly ash and a Class F (Ca-poor) fly ash were examined in the presence of Ca­(OH)2, and their thermodynamic phase equilibria were modeled on contact with NaCl or CaCl2 brines for 0 ≤ I m ≤ 7.5 mol/L. At low ionic strengths (<0.3 mol/L), reactivity and stable phase assemblages remain effectively unaltered. However, at high­(er) ionic strengths (>0.5 mol/L), the phase assemblage shows a particular abundance of Cl-AFm compounds (i.e., Kuzel’s and Friedel’s salts). Although formation of Kuzel’s and Friedel’s salts enhances the Class F fly ash reactions in both NaCl and CaCl2 brines, NaCl brines compromise Class C fly ash reactivity substantially, while CaCl2 results in the reactivity remaining essentially unchanged. Thermodynamic modeling that accounts for the fractional and noncongruent dissolution of the fly ashes indicates that their differences in reaction behavior are provoked by differences in the prevalent pore solution pH, which affects phase stability. The outcomes offer new insights for matching fly ashes, Ca additives, and brines, and accounting for and controlling fly ash–brine interactions as relevant to optimizing physical solidification and chemical stabilization applications.

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.