Daniel J. Fauth

Designing adsorbents for CO2 capture from flue gas-hyperbranched aminosilicas capable of capturing CO2 reversibly

Carbon dioxide adsorption from a simulated flue gas stream was successfully performed with a hyperbranched aminosilica (HAS) material. The HAS was synthesized by a one-step reaction, spontaneous aziridine ring-opening polymerization off of surface silanols, to form a 32 wt % organic/inorganic hybrid material. The adsorption measurements were performed in a fixed-bed flow reactor using humidified CO2. The advantage of this adsorbent over previously reported adsorbents is the stability of the organic groups covalently bound to the silica support compared to those made by physisorbed methods. Furthermore, a large CO2 capacity (∼3 mmol CO2/g adsorbent) associated with the high loading of amines was observed.

Performance of immobilized tertiary amine solid sorbents for the capture of carbon dioxide

The capture of carbon dioxide (CO2) from a simulated flue gas stream was achieved by utilizing immobilized tertiary amine solid sorbents. The tertiary amine immobilized in these solid substrates was 1, 8 Diazabicyclo-[5.4.0]-undec-7-ene (DBU) and it has the stoichiometric capability of capturing carbon dioxide at a 1:1 R-NH2:CO2 molar ratio. This is a unique feature compared to other primary and secondary amines which capture CO2 at a 2:1 molar ratio, thus making the immobilized DBU solid sorbents competitive with existing commercially available sorbents and liquid amine-based capture systems. The immobilized DBU solid sorbents prepared in this study exhibit acceptable CO2 capture capacities of 3.0 mol CO2/kg sorbent at 298 K; however, at the critical operational temperature of 338 K, the capacity was reduced to 2.3 mol/kg sorbent. The DBU sorbents did exhibit acceptable stability over the adsorption/desorption temperature range of 298–360 K based on XPS and TGA analyses.

Dry beneficiation of high loss-on-ignition fly ash

Abstract Dry beneficiation of three high loss-on-ignition (LOI) fly ashes were conducted. The combination of two different types of dry separation techniques—ultrasonic sieving and triboelectrostatic separation—were used for this study. The results indicate that a simple separation of unburned carbon from fly ash is achievable at particle sizes of 149, 74 and 44 μm, and screening could be utilized as the rough separation mechanism for fly ash. Subsequently, triboelectrostatic separations were conducted on these different particle size fractions of the fly ash and indicated that the final carbon content in the products, as low as 2.5% or as high as 60%, can be further adjusted with the combination of dry sieving and triboelectrostatic separation.

Dry regenerable sorbents for the separation and capture of CO2 from large point sources

The combustion of fossil fuels generates large quantities of carbon dioxide (CO2), a greenhouse gas most likely to influence global warming and climate change. Large stationary sources that include coal-based electric generating stations are plausible targets for the removal of CO2. Chemical absorption of CO2 is viewed as one option that could be applicable for its separation from both fuel gas and flue gas streams. Processes based on solid regenerable sorbents that efficiently absorb CO2 and release it in concentrated form have the potential to be cost-effective relative to solvent-based practices. This communication summarises a preliminary investigation exploring the reaction of CO2 with a number of calcium-based sorbents using a thermogravimetric (TG) analyser. Upon reaction at high temperature with pure CO2, these materials are converted into metal carbonates. Thermal regeneration of the sorbents was accomplished upon heating spent materials to higher temperature in a nitrogen stream. TG studies show the absorption reaction for Ca-based materials was initially rapid and then entered into a slower kinetic regime. Multi-cycle testing conducted within the TG analyser indicated sorbents could be regenerated and reused. Theoretical conversions ranging from 50–75% were observed for the calcium/zirconia sorbents in comparison to 15–20% for the calcium/lanthanum-doped alumina sorbent. Improved conversion was attributed to the pore size differential between mesoporous zirconia and microporous lanthanum-alumina. TG studies performed at 500°C with lithium zirconate show that the rate of CO2 absorption was continuous with time on stream. Under nitrogen, rapid regeneration of the lithium carbonate product occurred at temperatures greater than 700°C.

Carbon Storage and Sequestration as Mineral Carbonates

The U.S. Department of Energy has identified mineral sequestration as a promising CO2 sequestration technology option, converting anthropogenic CO2 and magnesium silicates into permanent carbonate minerals. Advantages of a mineral CO2 mitigation scheme include (1) enormous deposits of ultramafic rock such as serpentine [Mg3Si2O5(OH)4] and olivine [(Mg,Fe)2SiO4], exist in nature, providing a large potential capacity for CO2 sequestration, (2) resulting magnesite (MgCO3) product is thermodynamically stable and environmentally benign, and (3) overall process is exothermic with potential to be implemented with acceptable economics. High carbonation efficiencies were attained at elevated temperatures and supercritical CO2 pressures employing magnesium silicate ores. However, unlike olivine, serpentine required an additional high temperature pre-treatment step to drive off hydroxyl groups prior to carbonation. X-ray diffraction analysis (XRD) identified magnesite as the primary reaction product. Mechanistic aspects of mineral dissolution/magnesium carbonate precipitation were investigated with the aid of scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) of polished cross sections of solid process grains. Alterations to both thermally pre-treated serpentine and natural olivine grains revealed outer surfaces to be noticeably depleted in magnesium in comparison to its inner core. Formation of silica rims on the reaction surfaces may slow further dissolution of magnesium from silicate grains

Ultrasonic Characterizations of Solids Holdup in a Bubble Column Reactor

An ultrasonic transmission technique has been developed to measure solids holdup in a gas-liquid-solid bubble column reactor. The results presented in this study show that the transit time of an ultrasonic signal is influenced by the variation of solids holdup and the operating conditions in the bubble column. The transit time can be correlated to the solids holdup. The ultrasonic technique is potentially applicable to high-temperature, nontransparent fluids in high-pressure, metallic reactors and, with some modifications for solids holdup measurements, applicable in slurry-bubble column reactors.

Decomposition of Coal Model Compounds During Simulated Chemical Coal Cleaning with Molten Hydroxides

Abstract Coal model compounds, such as dibenzothiophene, its analogs and the hydroxylated derivatives of these compounds. were treated with molten hydroxides to evaluate the importance of nucleophilicity for the different alkali-metal hydroxides. The soluble hydroxylated model compounds were decomposed and desulfurized by RbOH or CsOH at lower temperatures and in less time than when decomposed by KOH or NaOH, indicating that molten hydroxides have varying degrees of nucleophilicity, the progression of nucleophilicity being CsOH > RbOH ≥ KOH > NaOH. The discrepancy of these results with previously published studies, suggesting NaOH is as effective as KOH in desulfurizing coal, is discussed. Increased solubility of the hydroxylated derivatives in molten hydroxide led to faster reaction rates under homogeneous reaction conditions. Aryl ethers decomposed more readily than did aryl sulfides. Sulfur-carbon bond cleavage was more facile in sulfur compounds with conformational mobility.