Low-pressure CO2 Adsorption Research Articles

Superior Capture of CO2 Achieved by Introducing Extra-framework Cations into N-doped Microporous Carbon

We designed and prepared a novel microporous carbon material (KNC-A-K) for selective CO2 capture. The combination of a high N-doping concentration (>10 wt %) and extra-framework cations, which were introduced into carbonaceous sorbents for the first time, endowed KNC-A-K with exceptional CO2 adsorption capabilities, especially at low pressures. Specifically, KNC-A-K exhibited CO2 uptake of 1.62 mmol g–1 at 25 °C and 0.1 bar, far exceeding the CO2 adsorption capability of most reported carbon material to date. Single component adsorption isotherms indicated that its CO2/N2 selectivity was 48, which also significantly surpasses the selectivity of conventional carbon materials. Furthermore, breakthrough experiments were conducted to evaluate the CO2 separation capability of KNC-A-K on CO2/N2 (10:90 v/v) mixtures under kinetic flow conditions, and the obtained CO2/N2 selectivity was as high as 44, comparable to that predicted from equilibrium adsorption data. Upon facile regeneration, KNC-A-K showed constant CO2 adsorption capacity and selectivity during multiple mixed-gas separation cycles. Its outstanding low-pressure CO2 adsorption ability makes KNC-A-K a promising candidate for selective CO2 capture from flue gas. Theoretical calculations indicated that K+ ions play a key role in promoting CO2 adsorption via electrostatic interactions. In addition, we found that HCl molecules anchored in N-doped carbon have a similar promotion effect on CO2 adsorption, which contradicts the conventional wisdom that the neutralization of basic sites by acids diminishes the adsorption of acidic CO2 gas.

Characterization of tight gas reservoir pore structure using USANS/SANS and gas adsorption analysis

Small-angle and ultra-small-angle neutron scattering (SANS and USANS) measurements were performed on samples from the Triassic Montney tight gas reservoir in Western Canada in order to determine the applicability of these techniques for characterizing the full pore size spectrum and to gain insight into the nature of the pore structure and its control on permeability. The subject tight gas reservoir consists of a finely laminated siltstone sequence; extensive cementation and moderate clay content are the primary causes of low permeability. SANS/USANS experiments run at ambient pressure and temperature conditions on lithologically-diverse sub-samples of three core plugs demonstrated that a broad pore size distribution could be interpreted from the data. Two interpretation methods were used to evaluate total porosity, pore size distribution and surface area and the results were compared to independent estimates derived from helium porosimetry (connected porosity) and low-pressure N2 and CO2 adsorption (accessible surface area and pore size distribution). The pore structure of the three samples as interpreted from SANS/USANS is fairly uniform, with small differences in the small-pore range (<2000Å), possibly related to differences in degree of cementation, and mineralogy, in particular clay content. Total porosity interpreted from USANS/SANS is similar to (but systematically higher than) helium porosities measured on the whole core plug. Both methods were used to estimate the percentage of open porosity expressed here as a ratio of connected porosity, as established from helium adsorption, to the total porosity, as estimated from SANS/USANS techniques. Open porosity appears to control permeability (determined using pressure and pulse-decay techniques), with the highest permeability sample also having the highest percentage of open porosity. Surface area, as calculated from low-pressure N2 and CO2 adsorption, is significantly less than surface area estimates from SANS/USANS, which is due in part to limited accessibility of the gases to all pores. The similarity between N2 and CO2-accessible surface area suggests an absence of microporosity in these samples, which is in agreement with SANS analysis. A core gamma ray profile run on the same core from which the core plug samples were taken correlates to profile permeability measurements run on the slabbed core. This correlation is related to clay content, which possibly controls the percentage of open porosity. Continued study of these effects will prove useful in log-core calibration efforts for tight gas.

Evaluating metal–organic frameworks for post-combustion carbon dioxide capture via temperature swing adsorption

Two representative metal–organic frameworks, Zn4O(BTB)2 (BTB3− = 1,3,5-benzenetribenzoate; MOF-177) and Mg2(dobdc) (dobdc4− = 1,4-dioxido-2,5-benzenedicarboxylate; Mg-MOF-74, CPO-27-Mg), are evaluated in detail for their potential use in post-combustion CO2 capture via temperature swing adsorption (TSA). Low-pressure single-component CO2 and N2 adsorption isotherms were measured every 10 °C from 20 to 200 °C, allowing the performance of each material to be analyzed precisely. In order to gain a more complete understanding of the separation phenomena and the thermodynamics of CO2 adsorption, the isotherms were analyzed using a variety of methods. With regard to the isosteric heat of CO2 adsorption, Mg2(dobdc) exhibits an abrupt drop at loadings approaching the saturation of the Mg2+ sites, which has significant implications for regeneration in different industrial applications. The CO2/N2 selectivities were calculated using ideal adsorbed solution theory (IAST) for MOF-177, Mg2(dobdc), and zeolite NaX, and working capacities were estimated using a simplified TSA model. Significantly, MOF-177 fails to exhibit a positive working capacity even at regeneration temperatures as high as 200 °C, while Mg2(dobdc) reaches a working capacity of 17.6 wt % at this temperature. Breakthrough simulations were also performed for the three materials, demonstrating the superior performance of Mg2(dobdc) over MOF-177 and zeolite NaX. These results show that the presence of strong CO2 adsorption sites is essential for a metal–organic framework to be of utility in post-combustion CO2 capture via a TSA process, and present a methodology for the evaluation of new metal–organic frameworks via analysis of single-component gas adsorption isotherms.

Bimodal Mesoporous Carbons for CO2Sorption Application

Figure S1. SEM images of BMC-1 (a), BMC-2 (b), BMC-3 (c), and BMC-4 (d). Synthesis of the BMS materials. The homogeneous mixture of 10 wt % CTAOH aqueous solution (5.0 g, 1.66 mmol, TCI) and deionized water (240 g, 13.3 mol) was heated at 353 K under constant stirring for about 1 h (500 rpm). TEOS (4.0 g, 19.2 mmol, Aldrich) was injected rapidly into the mixture. The reaction mixture was stirred at 353 K for 24 h. The as-made BMS-1 was recovered by hot filtration and washed with a copious amount of water. The isolated solid was dried in air overnight. The template-free BMS-1 was obtained via calcination in air at 823 K for 6 h. The BMS-2 material was prepared by adding Brij76 (1.0 g, 1.41 mmol, HO(CH2CH2O)10C18H35, TCI) into the aforementioned reaction mixture. P123 (1.0 g, 0.182 mmol, HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H, Aldrich) was added to the reaction mixture for the preparation of BMS-3. P123 (0.5 g, 0.09 mmol, Aldrich) was added to the reaction mixture for the preparation of BMS-4. Other preparation conditions are same unless otherwise noted. Synthesis of the BMC materials. The preparation of BMC-1 from BMS-1 is described in detail. The BMS-1 (0.5 g) was suspended in 50 mL of 0.5 M of p-toluenesulfonic acid (pTSA) ethanolic solution. The suspension was gently stirred at room filtration and dried at 353 K for 2 h. 1.0 mL of furfuryl alcohol was mixed with the pTSA-loaded BMS-1. The solids were carbonized at 1073 K in N2 flow for 2 h (ramping rate = 2 °C/min). The resulting solids were immersed into 30 mL of 48 wt % HF aqueous solution and maintained at room temperature for 12 h. The silica-free BMC-1 was obtained by filtration and washed with a copious amount of water. The BMC-1 was further dried at 353 K overnight. Physical measurements. The N2 sorption analysis was performed on a Belsorp-miniII at 77 K (BEL Japan). The samples were dried at 423 K under high vacuum for 2 h. Low pressure CO2 adsorption measurements were performed at 196 K (2propanol/dry ice bath), 273 K (ice bath), and 298 K (water bath) on a Belsorp-miniII. All other samples were dried at 423 K for 2 h under high vacuum prior to the measurements. TEM images were obtained by using JEOL JEM-2100F operated at 200 kV. FE-SEM images were obtained using Jeol JSM-7500F.

Changes in reservoir properties from injection of supercritical CO2 into coal seams — A laboratory study

article i nfo Two Australian Permian coals of similar rank but different texture, one predominantly dull and the other predominantly bright, were investigated in laboratory experiments to assess changes in reservoir properties following exposure to supercritical CO2 (SCCO2) and water. Both powdered coal (0.180-0.220 mm) and small cubes (15 mm to a side) were tested in a high-pressure (HP) batch reactor for up to 120 h. Two reaction fluids were used, each on separate sister coal samples: de-ionised water (DH2O) only, and a SCCO2 and DH2O mixture. Properties were measured before and after treatment with: high-pressure CO2 adsorption isotherms (storage capacity); helium pycnometry, mercury porosimetry and low-pressure (LP) CO2 adsorption (density, porosity and PSD effects); leachate chemical analysis for dissolved mineral matter; and water and CO2 permeabilities at in situ conditions during core flood experiments on an 80 mm cube. Micro and meso porosities for both coals showed significant increases after reactions with the SCCO2 and DH2O mixture. The macroporosity decreased significantly for the dull coal, but increased marginally for the bright coal. Total accessible porosity for dull coal showed virtually no change (0.5%); the bright coal exhibited 3.4% increase from a pre-treatment total porosity of 11.0%. On powdered samples reacted with the mixture, 80%+ increases in internal surface areas, measured using LP CO2 sorption at 0 °C, were noted for both coals. The HP CO2 excess adsorption isotherms on both coals increased after treatment, varying with pressure level, coal type and coal texture. The core flood tests indicated the permeability to CO2, after a waterflood stage, increased significantly. The second stage waterflood exhibited an over 600% increase on the pre-CO2 first stage waterflood permeability. These combined results indicate that mineral matter in Permian coals is dissolved and mobilized by the carbonic acid formed during CO2 dissolution in water, leading to increased porosity, permeability and HP CO2 excess adsorption.

Extraction of oil shales with sub- and near-critical water

Desorption is routinely employed for assessing the recoverability of coalbed gas resources. However, desorption behavior is strongly affected by coal structure. Canister desorption experiments on undeformed and mylonitic coals collected from drill holes in the Zhina Coalfield (Southwest China) were conducted to study temporal desorption rates and gas compositional shifts. Low-pressure N2 and CO2 adsorption tests revealed that the micropores, mesopores, and macropores in mylonitic coal have larger pore volumes and greater specific surface areas compared to those of undeformed coal. The “ink-bottle-shaped” pore is the main type of pore structure in mylonitic coal, whereas undeformed coal shows well-developed slit-shaped pores with good interconnectivity. The detailed desorption experiments in this study lasted 61 d and 110 h for undeformed and mylonitic coal, respectively. For undeformed coal, CH4 and C2H6 concentrations steadily increased with desorption time, whereas N2 and CO2 concentrations progressively decreased. The gas compositional shift of mylonitic coal during the entire desorption process could be divided into two stages: an initial stage, when CH4 and C2H6 concentrations in the desorbed gas increased (within the first 12 h), and a later stage, when they decreased rapidly; N2 and CO2 concentrations exhibited the opposite trend. The two-stage gas compositional shifts in mylonitic coal are likely linked to its pore structure. Gases in the “parallel-plate-shaped” pores of undeformed coal are mobile, whereas those in ink-bottle-shaped pores of mylonitic coal have restricted mobility. This is because CO2 and N2 can enter the narrow throats (with diameters of 3.3–3.8 Å) of ink-bottle-shaped pores, which are inaccessible to CH4 and C2H6 because of their larger diameter, causing the late-desorbed gas of mylonitic coal to be relatively enriched in CO2 and N2. The initial desorption rate of mylonitic coal is much greater than that of undeformed coal, which is closely related to developed microfractures in mylonitic coal. The desorption rate of undeformed coal is a power function of time, whereas that of mylonitic coal can be divided into two stages in which the relationship between desorption rate and time is a power function. The results suggest that the two-stage desorption rate is attributable to the molecular sieve effect due to the presence of massive ink-bottle-shaped pores in mylonitic coal.