McMahan L. Gray

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.

CO2 capture by amine-enriched fly ash carbon sorbents

The capture of CO2 from gas streams has been achieved by the utilization of amine-enriched fly ash carbon sorbent system. The initial fly ash carbon sorbents were generated by the chemical treatment of carbon-enriched fly ash concentrates with a 3-chloropropylamine-hydrochloride (CPAHCL) solution at 25 ◦ C. It was determined that these amine-enriched fly ash carbon sorbents performed at a 9% CO2 capture capacity based on commercially available sorbents. The chemical sorption performance of these amine-enriched fly ash carbon sorbents will be described within this paper.

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.

Amine‐Tethered Solid Adsorbents Coupling High Adsorption Capacity and Regenerability for CO2 Capture From Ambient Air

Silica supported poly(ethyleneimine) (PEI) materials are prepared via impregnation and demonstrated to be promising adsorbents for CO(2) capture from ultra-dilute gas streams such as ambient air. A prototypical class 1 adsorbent, containing 45 wt% PEI (PEI/silica), and two new modified PEI-based aminosilica adsorbents, derived from PEI modified with 3-aminopropyltrimethoxysilane (A-PEI/silica) or tetraethyl orthotitanate (T-PEI/silica), are prepared and characterized by using thermogravimetric analysis and FTIR spectroscopy. The modifiers are shown to enhance the thermal stability of the polymer-oxide composites, leading to higher PEI decomposition temperatures. The modified adsorbents present extremely high CO(2) adsorption capacities under conditions simulating ambient air (400 ppm CO(2) in inert gas), exceeding 2 mol(CO (2)) kg(sorbent)(-1), as well as enhanced adsorption kinetics compared to conventional class 1 sorbents. The new adsorbents show excellent stability in cyclic adsorption-desorption operations, even under dry conditions in which aminosilica adsorbents are known to lose capacity due to urea formation. Thus, the adsorbents of this type can be considered promising materials for the direct capture of CO(2) from ultra-dilute gas streams such as ambient air.

Physical cleaning of high carbon fly ash

An industrial fly ash sample was cleaned by three different processes, which were triboelectrostatic separation, ultrasonic column agglomeration, and column flotation. The unburned carbon concentrates were collected at purities ranging up to 62% at recoveries of 62%. In addition, optical microscopy studies were conducted on the final carbon concentrates to determine the carbon forms (inertinite, isotropic coke and anisotropic coke) collected from these various physical-cleaning processes. The effects of the various cleaning processes on the production of different carbon forms from high carbon fly ashes will be discussed.

Capture of carbon dioxide by solid amine sorbents

The reaction of tetraethylorthrosilcate (TEOS) with y-aminopropyltriethoxysilane (APTS) has produced stable solid amine sorbents for the capture of carbon dioxide. The resulting amine-enriched silicon sorbent (SBA-15) has been proven to be competitive with existing environmental CO2 controlled life sorbents based on the immobilised amine technology. XPS analysis has indicated that the amine groups (N1s Peak) were incorporated onto the surfaces of this amine-based sorbent in the range of 7%. The performance of the SBA-15 was comparable to the commercially available immobilised amine sorbent (IAS).

CO2 Adsorption on Supported Molecular Amidine Systems on Activated Carbon

The CO(2) capture capacities for typical flue gas capture and regeneration conditions of two tertiary amidine N-methyltetrahydropyrimidine (MTHP) derivatives supported on activated carbon were determined through temperature-controlled packed-bed reactor experiments. Adsorption-desorption experiments were conducted at initial adsorption temperatures ranging from 29 degrees C to 50 degrees C with temperature-programmed regeneration under an inert purge stream. In addition to the capture capacity of each amine, the efficiencies at which the amidines interact with CO(2) were determined. Capture capacities were obtained for 1,5-diazo-bicyclo[4.3.0]non-5-ene (DBN) and 1,8-diazobicyclo[5.4.0]-undec-7-ene (DBU) supported on activated carbon at a loading of approximately 2.7 mol amidine per kg of sorbent. Moisture was found to be essential for CO(2) capture on the amidines, but parasitic moisture sorption on the activated carbon ultimately limited the capture capacities. DBN was shown to have a higher capture capacity of 0.8 mol CO(2) per kg of sorbent and an efficiency of 0.30 mol CO(2) per mol of amidine at an adsorption temperature of 29 degrees C compared to DBU. The results of these experiments were then used in conjunction with a single-site adsorption model to derive the Gibbs free energy for the capture reaction, which can provide information about the suitability of the sorbent under different operating conditions.

Parametric study of the column oil agglomeration of fly ash

Abstract A promising oil agglomeration process has been developed for the beneficiation of fly ash using a six-ft agglomeration column. Carbon concentrates have been isolated in recoveries greater than 60% and purities of 55–70%. The parameters studied include agitation speeds, airflow rates, slurry feed rates, solvent/ash ratios, and the use of various solvents as agglomerating agents. The effects of these variables on the quality of separation are discussed.

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.

Cyclic Stability Testing of Aminated‐Silica Solid Sorbent for Post‐Combustion CO2 Capture

The National Energy Technology Laboratory (NETL) is examining the use of solid sorbents for CO2 removal from coal-fired power plant flue gas streams. An aminated sorbent (previously reported by the NETL) is tested for stability by cyclic exposure to simulated flue gas and subsequent regeneration for 100 cycles. Each cycle was quantified using a traced gas in the simulated flue gas monitored by a mass spectrometer, which allowed for rapid determination of the capacity.