Search

First-principles molecular dynamics simulations were carried out to explore the mechanistic and thermodynamic ramifications of the exposure of variably hydrated Ca-rich montmorillonites to supercritical CO2 and CO2-SO2 mixtures under geologic storage conditions. In sub- to single-hydrated systems (⩽1W), CO2 intercalation causes interlamellar expansion of 8-12%, while systems transitioning to 2W may undergo contraction ( ∼7%) or remain almost unchanged. When compared to ∼2W hydration state, structural analysis of the ⩽1W systems, reveals more Ca-CO2 contacts and partial transition to vertically confined CO2 molecules. Infrared spectra and projected vibrational frequency analysis imply that intercalated Ca-bound CO2 are vibrationally constrained and contribute to the higher frequencies of the asymmetric stretch band. Reduced diffusion coefficients of intercalated H2O and CO2 (10-6-10-7 cm2/s) indicate that Ca-montmorillonites in ∼1W hydration states can be more efficient in capturing CO2. Simulations including SO2 imply that ∼0.66 mmol SO2/g clay can be intercalated without other significant structural changes. SO2 is likely to divert H2O away from the cations, promoting Ca-CO2 interactions and CO2 capture by further reducing CO2 diffusion (10-8 cm2/s). Vibrational bands at ∼1267 or 1155 cm-1 may be used to identify the chemical state (oxidation states +4 or +6, respectively) and the fate of sulfur contaminants. [ABSTRACT FROM AUTHOR]

Spatially resolved deep-ultraviolet (UV) Raman spectroscopy was applied to solutions of CO2and H2O or D2O subject to a temperature gradient in a thermally regulated high-pressure concentric-tube Raman cell in an attempt to measure a Soret effect in the vicinity of the critical point of CO2. Although Raman spectra of solutions of CO2dissolved in D2O, at 10 MPa and temperatures near the critical point of CO2, had adequate signal-to-noise and spatial resolution to observe a Soret effect with a Soret coefficient with magnitude |ST| > 0.03, no evidence for an effect of this size was obtained for applied temperature gradients up to 19 °C. In contrast, the concentration of CO2dissolved in H2O was shown to vary significantly across the temperature gradient when excess CO2was present, but the results could be explained simply by the variation in CO2solubility over the temperature range and not by kinetic factors. For mixtures of D2O dissolved in scCO2at 10 MPa and temperatures close to the critical point of CO2, the Raman peaks for D2O were too weak to measure with confidence even at the limit of D2O solubility. [ABSTRACT FROM AUTHOR]

Abstract: Adsorption of CO2 on dehydrated Prussian blue analogue CoII 3[CoIII(CN)6]2 was studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). An infrared peak at 2340cm−1 assigned to adsorbed CO2 was identified and used semi-quantitatively to construct an isotherm at 298K that followed the Langmuir–Freundlich equation in the low-coverage Henry''s law limit with CO2 pressure below about 25kPa. Temperature-dependence at 6.8kPa CO2 was used to determine ΔH ad =−23±3kJmol−1, in this limit as well. Deviation from the Langmuir–Freundlich model was significant at temperatures above 298K and attributed primarily to a loss of reliability of the DRIFT spectra at higher CO2 pressures, particularly at higher temperatures, and the accompanying uncertainties in the difference spectra when correcting for the presence of gaseous CO2. Based on this work, the application of DRIFTS to study CO2 adsorption on Prussian blue analogues and other adsorbents is promising, although the range of conditions over which it can be applied appears to be more limited than with other techniques. [Copyright &y& Elsevier]

Adsorption isotherms of pure gases present in flue gas including CO2, N2, SO2, NO, H2S, and water were studied using prussian blues of chemical formula M3[Co(CN)6]2∙nH2O (M = Co, Zn) using an HPVA-100 volumetric gas analyzer and other spectroscopic methods. All the samples were characterized, and the microporous nature of the samples was studied using the BET isotherm. These materials adsorbed 8-10 wt % of CO2 at room temperature and 1 bar of pressure with heats of adsorpiton ranging from 200 to 300 BtuIlb of CO2, which is lower than monoethanolamine (750 Btuilb of CO2) at the same mass loading. At high pressures (30 bar and 298 K), these materials adsorbed approximately 20-30 wt % of CO2, which corresponds to 3 to 5 molecules of CO2 per formula unit. Similar gas adsorption isotherms for SO2, H2S, and NO were collected using a specially constructed volumetric gas analyzer. At close to 1 bar of equilibrium pressure, these materials sorb around 2.5, 2.7, and 1.2 mmol/g of SO2, H2S, and NO. In particular, the uptake of SO2 and H2S in Co3[Co(CN)6]2 is quite significant since it sorbs around 10 and 4.5 wt % at 0.1 bar of pressure. The stability of prussian blues before and after trace gases was studied using a powder X-ray diffraction instrument, which confirms these materials do not decompose after exposure to trace gases. [ABSTRACT FROM AUTHOR]