CO2 H2O System Research Articles

Experimental study on carbamate formation in the AMP–CO2–H2O system at different temperatures

Carbamate formation in the 30wt% of 2-amino-2-methyl-1-propanol (AMP) system at different CO2 loadings and temperatures was studied via nuclear magnetic resonance (NMR) spectroscopy. The results indicate that the main species in this system are AMP/AMPH+, AMPCO2− and HCO3−/CO32−. The carbamate was also observed at low loadings and the apparent carbamate stability constant was estimated based on the experimental concentrations of the species from NMR analysis. Carbamate formation was found to have weak temperature dependence in the range tested (25–45°C). To distinguish within the AMP/AMPH+ and HCO3−/CO32− pairs, the amine protonation constant, the dissociation constant of carbonic acid from literature, and pH measurements for different ionic strengths were all employed. All the data were correlated with ionic strength and temperature.The accuracy of the carbamate stability constant determined from the concentration measurements will depend on pKa, ionic strength (I) used to calculate the speciation and on the uncertainty in the species concentration determinations from NMR, particularly for the carbamate species at low CO2 loadings and high temperature.

Fluid-mineral equilibria and thermodynamic mixing properties of fluid systems

The paper presents a review of an experimental method to quantitatively constrain thermodynamic mixing properties of fluid systems at high temperature T and pressure P. The method is based on bracketing equilibrium parameters of simple fluid-mineral reactions. Experimental data obtained with this technique for the H2O-CO2, H2O-N2, and H2O-H2 binary systems were utilized to calculate mixing parameters corresponding to the simplified van Laar model W12VL, according to which the equation for the integral excess Gibbs free energy of a binary mixture Gex is Gex =X1X2W12VL/(X1V10 + X2V20), where Xi is the mole fractions of the components, and Vi0 are pure species molar volumes at given P and T (in cm3). The W12VL for the three mixtures correspond to 202, 219, and 331 kJ cm3/mol. The empirical correlation \(W_{H_2 O - X}^{VL}\) (kJ cm3/mol) = 887.012 QX − 16.674, where Q = Pc (critical pressure, bar)/Tc (critical temperature, K) for gas X (where X = CH4, CO, H2S, O2, Ar, and NH3) is used to evaluate the van Laar parameters for a number of petrologically important water-gas mixtures. The H2O-H2 system is characterized by the greatest positive deviation from the ideal mixing and can thus decompose into two immiscible fluid phases under the P-T parameters typical of deep lithospheric zones. The exsolution of the H2O-CO2 and H2O-N2 systems is expected to occur only under high pressure and low temperature. This combination of parameters may be expected only in the environments of cold subduction. Salts (highly soluble simple salts and/or silicates) should significantly expand the exsolution regions in petrologically important fluids.

Metamorphic CO2 production from calc-silicate rocks via garnet-forming reactions in the CFAS–H2O–CO2 system

The type and kinetics of metamorphic CO2-producing processes in metacarbonate rocks is of importance to understand the nature and magnitude of orogenic CO2 cycle. This paper focuses on CO2 production by garnet-forming reactions occurring in calc-silicate rocks. Phase equilibria in the CaO–FeO–Al2O3–SiO2–CO2–H2O (CFAS–CO2–H2O) system are investigated using P–T phase diagrams at fixed fluid composition, isobaric T–X(CO2) phase diagram sections and phase diagram projections in which fluid composition is unconstrained. The relevance of the CFAS–CO2–H2O garnet-bearing equilibria during metamorphic evolution of calc-silicate rocks is discussed in the light of the observed microstructures and measured mineral compositions in two representative samples of calc-silicate rocks from eastern Nepal Himalaya. The results of this study demonstrate that calc-silicate rocks may act as a significant CO2 source during prograde heating and/or early decompression. However, if the system remains closed, fluid–rock interactions may induce hydration of the calc-silicate assemblages and the in situ precipitation of graphite. The interplay between these two contrasting processes (production of CO2-rich fluids vs. carbon sequestration through graphite precipitation) must be considered when dealing with a global estimate of the role exerted by decarbonation processes on the orogenic CO2 cycle.

Experimental study on phase change solvents in CO2 capture by NMR spectroscopy

2-(Diethylamino)ethanol (DEEA) and 3-(Methylamino) propylamine (MAPA) in combination may represent a promising absorbent system for CO2 capture due to high CO2 loading capacity, high equilibrium temperature sensitivity, low energy requirement for regeneration and relatively high reaction rate.Three different systems: DEEA–CO2–H2O; MAPA–CO2–H2O and DEEA–MAPA–CO2–H2O were studied quantitatively by NMR spectroscopy and the data are reported in the present work. The main products quantified for these systems are: carbonate-bicarbonate for the DEEA–CO2–H2O system; primary, secondary carbamate, dicarbamate for the MAPA–CO2–H2O system, and primary/secondary carbamate, dicarbamate, carbonate/bicarbonate in blended DEEA–MAPA–CO2–H2O. The speciation data of the three systems were measured and reported in the present work. The blended system of 5M DEEA–2M MAPA can form two liquid phases after being loaded with CO2 and both phases were analyzed quantitatively by NMR spectroscopy. The experimental data shows that the lower phase is rich in CO2 and MAPA while the upper phase was lean in CO2 and rich in DEEA. The ratio DEEA–MAPA in the lower phase increases with increasing partial pressure whereas for the upper phase the opposite is true.

Selective hydrogenation of benzonitrile in multiphase reaction systems including compressed carbon dioxide over Ni/Al2O3 catalyst

Selective hydrogenation of benzonitrile was studied with Ni/Al2O3 in compressed CO2, hexane–CO2, ethanol–CO2 and H2O–CO2 systems. The phase behavior and the effect of CO2 on the conversion of benzonitrile and the yield of benzylamine were discussed. The reaction rate was retarded in solventless, hexane and ethanol, but accelerated in water in the presence of compressed CO2. The decrease in reaction rate was mainly ascribed to the formation of carbamate from benzylamine and the intermediate 1-aminodibenzylamine reacting with CO2, and it precipitated out to coat on the surface of catalyst in solventless and hexane, and the dilution effect of compressed CO2 in ethanol. But the yield of benzylamine was increased in solventless, hexane and ethanol due to the following nucleophilic addition of benzylamine and benzylimine to N-benzylidenebenzylamine was inhibited. Although, the reaction rate increased in water for the enhanced solubility of H2 and benzonitrile in H2O and decreased mass-transfer resistance in the presence of compressed CO2, the yield of benzylamine decreased because of the acidic nature of H2O–CO2 favorites the elimination of NH3 and the formation of NH4HCO3. Accordingly, the possible reaction pathway of benzonitrile hydrogenation was proposed for all the studied systems.

Development of a rate-based model for CO2 absorption using aqueous NH3 in a packed column

A rigorous rate-based model for CO2 absorption using aqueous ammonia in a packed column has been developed and used to simulate results from a recent pilot plant trial of an aqueous ammonia-based post-combustion capture process at the Munmorah Power Station, New South Wales, Australia. The model is based on the RateSep module, a rate-based absorption and stripping unit operation model in Aspen Plus, and uses the available thermodynamic, kinetic and transport property models for the NH3–CO2–H2O system to predict the performance of CO2 capture. The thermodynamic and transport property models satisfactorily predict experimental results from the published literature. The modelling results from the rate-based model also agree reasonably well with pilot plant results, including CO2 absorption rate, NH3 loss rate, temperature profiles and mass transfer coefficients in the absorber. To gain insights into absorption performance, we used the rate-based model to analyse the species concentration profile, temperature profile, mass transfer rate and coefficient in the gas and liquid bulk phase along the packing height.

Characterization of light and heavy hydrated magnesium carbonates using thermal analysis

Upon heating, hydrated magnesium carbonates (HMCs) undergo a continuous sequence of decomposition reactions. This study aims to investigate the thermal decomposition of various commercially produced HMCs classified as light and heavy, highlight their differences, and provide an insight into their compositions in accordance with the results obtained from thermal analysis and microstructure studies. An understanding of the chemical compositions and microstructures, and a better knowledge of the reactions that take place during the decomposition of HMCs were achieved through the use of SEM, XRD, and TG/differential thermal analysis (DTA). The quantification of their CO2 contents was provided by TG and dissolving the samples in HCl acid. Results show that variations exist within the microstructure and decomposition patterns of the two groups of HMCs, which do not exactly fit into the fixed stoichiometry of the known HMCs in the MgO–CO2–H2O system. The occurrence of an exothermic DTA peak was only observed for the heavy HMCs, which was attributed to their high CO2 contents and the relatively delayed decomposition pattern.

Raman spectroscopic characterization on the OH stretching bands in NaCl–Na2CO3–Na2SO4–CO2–H2O systems: Implications for the measurement of chloride concentrations in fluid inclusions

Raman spectroscopy has been demonstrated to be an in situ and non-destructive method for the qualitative and quantitative analyses of fluid inclusions, especially for those fluid inclusions with high CO2 densities and/or small size (i.e., <5μm). Here we addressed this issue by studying the Raman spectra of fluids of the NaCl–H2O, Na2SO4–H2O, Na2CO3–H2O, CO2–H2O, NaCl–Na2SO4–H2O and NaCl–Na2CO3–H2O systems. Their characteristics in fused silica capillary capsules (FSCCs) or a high-pressure optical cell (HPOC) were collected at ~22°C. The Raman OH stretching bands were fitted using two Gaussian sub-bands near 3220cm−1 and 3450cm−1. It is found that the peak height and width of the two Gaussian sub-bands can be used to construct the calibration curve for the calculation of chloride concentrations in aqueous NaCl solutions. Our results indicate that (1) this method can be applied to chloride-dominated fluids because the presence of other anions, such as CO32− and SO42−, will result in an overestimation of the calculated chloride concentrations; (2) the presence of CO2 does not have an obvious influence on the Raman OH stretching bands and, thus, this method can be applied to CO2-bearing fluid inclusions; and (3) each Raman spectroscopic system should be calibrated before the application, and reference standards can be easily prepared in fused silica capillary capsules.

Phase equilibria in the H2O–CO2 system between 250–330 K and 0–1.7 GPa: Stability of the CO2 hydrates and H2O-ice VI at CO2 saturation

Although carbon dioxide is of interest in planetary science, few studies have been devoted so far to the H2O–CO2 system at pressures and temperatures relevant to planetary interiors, especially of the icy moons of the giant planets. In this study, new sapphire and diamond anvil cell experiments were conducted in this binary system to constrain the stability of the CO2 hydrates and H2O-ice VI at CO2 saturation in the 250–330K and 0–1.7GPa temperature and pressure ranges. Phases and equilibria were characterized by in situ Raman spectroscopy and optical monitoring. The equilibrium between the CO2 sI clathrate hydrate and the H2O-rich liquid phase was constrained over the entire pressure range of stability of the hydrate, up to 0.7–0.8GPa, with results in agreement with previous studies at lower pressures. Above this pressure and below 1GPa, our experiments confirmed the existence of the new CO2 high-pressure hydrate reported recently. Finally, the melting curve of the H2O-ice VI at CO2 saturation in the absence of CO2 hydrates was determined between 0.8 and 1.7GPa. Using an available chemical potential model for H2O, a first assessment of the solubility of CO2 along the H2O-ice VI melting curve is given. Consistent with these new results and previous studies of the H2O–CO2 system, a P–T–X description of the binary system is proposed. The evolution with pressure of the Raman signatures of the two CO2 hydrates is detailed, and their stability is discussed in light of other clathrate hydrate-forming systems.

A mass transfer model of absorption of carbon dioxide in a bubble column reactor by using magnesium hydroxide slurry

A bubble column reactor was tested and evaluated for carbon dioxide removal from flue gases by using magnesium hydroxide slurry. The study showed that a high CO2 removal efficiency could be achieved. An absorption model was developed for system analysis and CO2 removal data analysis. The overall mass transfer coefficients for CO2-H2O and CO2-Mg(OH)2-H2O systems have been calculated. The chemistry of the system, temperature effects, and changes of equilibrium constants also have been discussed.

13C NMR as a method species determination in CO2 absorbent systems

This paper discusses the main parameters to be considered when using Nuclear Magnetic Resonance Spectroscopy for speciation in liquid phase CO2 capture absorbents and how accurate measurements can be obtained. Liquid phase speciation is one of the most important experimental data for thermodynamic and kinetic modeling of absorption systems. A comprehensive standard method for liquid phase speciation in amine and amino acid–CO2–H2O systems by Nuclear Magnetic Resonance Spectroscopy is presented and validated against measurements on monoamine, diamine and amino acid systems. The CO2 loadings calculated from NMR and titration methods are shown to be in good agreement with an AARD less than 1%. The most important factor for a quantitative measurement with 13C NMR is delay time which is required to be ≥5 times the relaxation time (T1) and 300 numbers of scans. The relaxation times (T1) of carbon nucleus of several amines commonly used in CO2 capture, i.e. monoethanolamine (MEA), diethanolamine (DEA), ethylenediamine (EDA), 2-amino-2 methylpropan-1-ol (AMP), N-methyldiethanolamine (MDEA) and piperazine (PZ) as well as for loaded aqueous solutions of MEA–amino acids salt systems of Glycine, Taurine, l-Alanine, l-Serine, l-Proline and Sarcosine are determined and reported in the present work.The relaxation time for the carbon nuclei of HCO3−/CO32− in monoamine systems increases in this order: AMP (3.5s)=DEA (3.5s)<DEEA (8.0s)<MDEA (9.3s)<MEA (10.2s). In diamine systems we have: PZ (4.6s)<EDA (7.7s). The same trend is also observed for carbon nuclei in carbamate formation of monoamine systems: AMP (4.2s)<DEA (5.4s)<MEA (9.7s). Relaxation time for carbon nuclei in diamine dicarbamate formation systems is in this order: PZ (6.5s)<EDA (6.9s). The relaxation times for unloaded systems are not shown because the carbamate and carbonate/bicarbonate species are formed only in the loaded aqueous systems.

Uncertainty in geochemical modelling of CO2 and calcite dissolution in NaCl solutions due to different modelling codes and thermodynamic databases

A prognosis of the geochemical effects of CO2 storage induced by the injection of CO2 into geologic reservoirs or by CO2 leakage into the overlaying formations can be performed by numerical modelling (non-invasive) and field experiments. Until now the research has been focused on the geochemical processes of the CO2 reacting with the minerals of the storage formation, which mostly consists of quartzitic sandstones. Regarding the safety assessment the reactions between the CO2 and the overlaying formations in the case of a CO2 leakage are of equal importance as the reactions in the storage formation. In particular, limestone formations can react very sensitively to CO2 intrusion. The thermodynamic parameters necessary to model these reactions are not determined explicitly through experiments at the total range of temperature and pressure conditions and are thus extrapolated by the simulation code. The differences in the calculated results lead to different calcite and CO2 solubilities and can influence the safety issues.This uncertainty study is performed by comparing the computed results, applying the geochemical modelling software codes TheGeochemist’s Workbench, EQ3/6, PHREEQC and FactSage/ChemApp and their thermodynamic databases. The input parameters (1) total concentration of the solution, (2) temperature and (3) fugacity are varied within typical values for CO2 reservoirs, overlaying formations and close-to-surface aquifers. The most sensitive input parameter in the system H2O–CO2–NaCl–CaCO3 for the calculated range of dissolved calcite and CO2 is the fugacity of CO2. Hence, the largest range of dissolved calcite is calculated at high fugacities and is 210mmol/kgw. The average deviation of the results using the databases phreeqc.dat and wateq4f.dat in combination with the code PHREEQC is lowest in comparison to the results of the specific model of Duan and Li, which represents the experimental values at best. Still, the solubility of CO2 is overestimated in the formation water using these two databases. Therefore, the model results calculate a larger retention capacity, defined as the quantity of CO2 dissolved in the formation water, than the Duan and Li model would do.

Simulations of vapor–liquid phase equilibrium and interfacial tension in the CO2–H2O–NaCl system

Direct interfacial molecular dynamics simulations are used to obtain the phase behavior and interfacial tension of CO2–H2O–NaCl mixtures over a broad temperature and pressure range (50°C ≤ T ≤ 250°C, 0 ≤ P ≤ 600 bar) and NaCl concentrations (1–4 mol/kg H2O). The predictive ability of several existing water (SPC and TIP4P2005), carbon dioxide (EPM2 and TraPPE), and sodium chloride (SD and DRVH) models is studied and compared, using conventional Lorentz–Berthelot combining rules for the unlike‐pair parameters. Under conditions of moderate NaCl molality (∼1 mol/kg H2O), the predictions of the CO2 solubility in the water‐rich and CO2‐rich phase resemble those in the CO2–H2O system [Liu et al., J Phys Chem B. 2011;115:6629–6635]. Consistent with our previous work, the TraPPE/TIP4P2005 model combination gives the best overall performance in predicting coexistence composition and pressure in the water‐rich phase. Critical assessments are also made on the ranges of temperature and pressure where particular model combinations work better. The dependence of the interfacial tension on temperature and pressure is better predicted by the TraPPE/TIP4P2005 and EPM2/SPC models, whereas the EPM2/TIP4P2005 model overestimates this property by 10–20%, possibly due to the inadequacy of the combining rules. It is also found that the interfacial tension increases with salt concentration, consistent with experimental observations. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3514–3522, 2013

No discernible effect of Mg2 + ions on the equilibrium oxygen isotope fractionation in the CO2–H2O system

Equilibrium oxygen isotope fractionation factors (αCO2g–H2O, αHCO3–H2O and αCO3–H2O) are fundamental geochemical parameters that characterize 18O partitioning in the CO2–H2O system. These constants were established in laboratory experiments using deionized H2O (e.g., Beck et al. (2005) and references therein). The applicability of these constants in environmental waters, including natural seawater, appears questionable due to potentially strong ionic interactions in such aqueous media. For instance, considerable portions of carbonate ions in seawater exist as cation–CO32− ion complexes such as MgCO30. In this study, quantitative BaCO3 precipitation experiments were performed to examine the effect of Mg2+ concentrations on the oxygen isotope equilibrium between dissolved inorganic carbon (DIC) species and H2O. Our results from Mg2+-free control experiments in which BaCO3 samples were precipitated from simple NaHCO3 solutions were in good agreement with empirical results from three independent studies and with theoretical calculations. BaCO3 precipitations from solutions with Mg2+ concentrations higher than 2.5mM caused intolerable quantities of Mg(OH)2 co-precipitation, which interfered with δ18O measurements. Within the limit of 2.5mM of [Mg2+], the MgCO30 abundance in the total carbonate ions ([CO32−]T) and [DIC] was varied over approximately 0 to 40% and 0 to 36%, respectively, by manipulating solution chemistry. Despite such chemical treatment, there was no effect of Mg2+-addition on αBaCO3–H2O. These results suggest that the presence of Mg2+ in solutions has a negligible effect on the oxygen isotope equilibrium in the CO2–H2O system. In seawater, Mg2+ is the most important cation that forms complexes with CO32−. Hence, if our results also hold at higher [Mg2+] and higher ionic strength, they imply that the applicability of freshwater-based equilibrium fractionation factors is not compromised by ionic interactions in seawater.

The effect of carbonic anhydrase on the kinetics and equilibrium of the oxygen isotope exchange in the CO2–H2O system: Implications for δ18O vital effects in biogenic carbonates

Interpretations of the primary paleoceanographic information recorded in stable oxygen isotope values (δ18O) of biogenic CaCO3 can be obscured by disequilibrium effects. CaCO3 is often depleted in 18O relative to the δ18O values expected for precipitation in thermodynamic equilibrium with ambient seawater as a result of vital effects. Vital effects in δ18O have been explained in terms of the influence of fluid pH on the overall δ18O of the sum of dissolved inorganic carbon (DIC) species (often referred to as “pH model”) and in terms of 18O depletion as a result of the kinetic effects associated with CO2 hydration (CO2+H2O↔H2CO3↔HCO3−+H+) and CO2 hydroxylation (CO2+OH−↔HCO3−) in the calcification sites (so-called “kinetic model”). This study addresses the potential role of an enzyme, carbonic anhydrase (CA), that catalyzes inter-conversion of CO2 and HCO3− in relation to the underlying mechanism of vital effects. We performed quantitative inorganic carbonate precipitation experiments in order to examine the changes in 18O equilibration rate as a function of CA concentration. Experiments were performed at pH 8.3 and 8.9. These pH values are comparable to the average surface ocean pH and elevated pH levels observed in the calcification sites of some coral and foraminiferal species, respectively. The rate of uncatalyzed 18O exchange in the CO2–H2O system is governed by the pH-dependent DIC speciation and the kinetic rate constant for CO2 hydration and hydroxylation, which can be summarized by a simple mathematical expression. The results from control experiments (no CA addition) are in agreement with this expression. The results from control experiments also suggest that the most recently published kinetic rate constant for CO2 hydroxylation has been overestimated. When CA is present, the 18O equilibration process is greatly enhanced at both pH levels due to the catalysis of CO2 hydration by the enzyme. For example, the time required for 18O equilibrium is nearly halved by the presence of 3.7×10−9M of CA used for the experiments. Despite its significant influence on the oxygen isotope exchange kinetics, the equilibrium oxygen isotope fractionation between individual DIC species and H2O is unaffected by CA. Because many CaCO3-secreting organisms possess active CA, our findings imply that 18O equilibration of the CO2–H2O system is possible within realistic timescales of biogenic calcification.

13C NMR Spectroscopy of a Novel Amine Species in the DEAB–CO2–H2O system: VLE Model

In the present work, ion speciation studies in solutions of the novel amine 4-(diethylamine)-2-butanol (DEAB), at various CO2 loadings (0–0.8 mol of CO2/mol of amine) and amine concentrations (0.52–1.97 M), were determined by 13C nuclear magnetic resonance (NMR) spectroscopy. In addition, the dissociation constant K of DEABH+ was determined at 24.5, 35, and 45 °C using a pH meter. The ion speciation plot, which contains various sets of concentrations of DEAB, protonated DEAB, bicarbonate, and carbonate, was successfully generated. Because DEAB is a novel solvent, this is the first time that the ion speciation plots of the DEAB–CO2–H2O system have been developed. It is also the first time that the 13C NMR calibration technique was applied to develop the vapor–liquid equilibrium (VLE) model for an amine–CO2–H2O system. The results obtained from the present work can be a great help for the further analysis of the DEAB VLE model, as well as CO2 absorption and kinetics studies. Furthermore, it was found that t...

Coexisting serpentine and quartz from carbonate-bearing serpentinized peridotite in the Samail Ophiolite, Oman

Tectonically exposed mantle peridotite in the Oman Ophiolite is variably serpentinized and carbonated. Networks of young carbonate veins are prevalent in highly serpentinized peridotite, particularly near low-temperature alkaline springs emanating from the peridotite. An unusual feature in some samples is the coexistence of serpentine and quartz, which is not commonly observed in serpentinites. This assemblage is unstable with respect to serpentine + talc or talc + quartz under most conditions. Serpentine in the carbonated serpentinites in this study is more iron rich than in most serpentinites reported in previous studies, and samples with co-existing quartz contain the most iron-rich serpentines. Calculations of thermodynamic equilibria in the MgO–SiO2–H2O–CO2 system suggest that serpentine + quartz may be a stable assemblage at low temperatures (e.g., <~15–50 °C) and is stabilized to higher temperatures by preferential cation substitutions in serpentine over talc. Based on these calculations, serpentine + quartz assemblages could result from serpentinization at near-surface temperatures. Clumped isotope thermometry of carbonate veins yields temperatures within error of the observed temperatures in Oman groundwater for all samples analyzed, while the δ18O of water calculated to be in equilibrium with carbonate precipitated at those temperatures is within error of the observed isotopic composition of Oman groundwater for the majority of samples analyzed. As groundwater geochemistry suggests that carbonate precipitation and serpentinization occur concomitantly, this indicates that both hydration and carbonation of peridotite are able to produce extensive alteration at the relatively low temperatures of the near-surface weathering environment.

From ammonium bicarbonate fertilizer production process to power plant CO2 capture

Ammonia-based CO2 capture technology has attracted wide research interest. Substantial work has been reported that includes theoretical evaluation, laboratory tests, pilot plant tests and economic analysis. Alstom and PowerSpan have conducted a few MW level demonstration tests. However, three inherent hurdles with this potential CO2 capture technology have not been fully solved yet: ammonium bicarbonate solid formation in the absorption tower which may plug the tower packing, high ammonia vapor pressure that results in ammonia slip into the cleaned flue gas, and low CO2 absorption rate resulting in large absorption equipment. Industrial ammonium bicarbonate fertilizer production processes are proven technology and have been optimized both technologically and economically for decades. This technology is also based on the chemistry and physics of the NH3–CO2–H2O system. In the ammonia synthesis plant, CO2 in shifted gas from the syngas obtained by gasification of coal is absorbed into partly carbonated aqueous ammonia in a liquid bubbling column to produce ammonium bicarbonate solid as fertilizer. Using this process, ammonium bicarbonate has been sustainably produced with low ammonia slip into the shifted gas after the CO2 was captured. In this report, the ammonium bicarbonate fertilizer production process is described and analyzed. The advantageous aspects of the fertilizer production technology are compared with the current widely studied ammonia-based CO2 capture technology for power plant applications. Insights into the modifications required for the flue gas CO2 capture application are discussed. New designs of ammonia-based CO2 capture processes are presented.

Selective reduction of nitroarenes to N-arylhydroxylamines by use of Zn in a CO2–H2O system, promoted by ultrasound

The promoting effect of ultrasound on the selective reduction of nitroarenes to N-arylhydroxylamines by use of Zn in an environmentally benign CO2–H2O system has been demonstrated. The yield of N-phenylhydroxylamine reaches 95 % when the reaction is carried out with a Zn-to-nitrobenzene molar ratio of 2.2 under ultrasound (40 kHz) at 25 °C and normal pressure of CO2 for 60 min. Application of ultrasound to the reaction has the advantages of higher yield of N-arylhydroxylamines, shorter reaction time, and consumption of less Zn.

Climate-driven deposition of water ice and the formation of mounds in craters in Mars’ north polar region

This paper explores the origins and evolution of ice-rich interior mounds found within craters of the north polar region of Mars. We present a systematic study of impact craters above 65°N, and identify 18 craters that have interior mounds. At least 11 of these mounds are composed of water ice and geometric similarities suggest that dune-covered mounds may also have a water ice core. The mounds are found in the deeper craters in the north polar area and we suggest that these form a specific microclimate favorable for mound initiation and growth. It is likely that at least seven of the mounds have evolved as individual outliers, rather than conterminous with the main polar cap. Our observations suggest that the mounds are built up by atmospheric deposition, similar to that of the north polar layered deposits. Using a combination of remote sensing techniques enabling topographic, spectral, radar and image data analyses, we have documented the morphology, composition and stratigraphy of selected mounds. We advance and test four hypotheses for formation of these mounds: artesian outpouring from a deep aquifer, hydrothermal activation of ground ice, remnants of a more extensive polar cap, and atmospheric deposition on ice caps in meteorologically isolated locations. We propose that during periods when the perihelion was located in northern summer (most recently 10–25ka before present) the microclimate in these craters retarded the sublimation of CO2 and water ice in northern spring, thus creating a cold trap for volatiles released as the seasonal cap retreated. This created a thick enough deposit of water ice to withstand sublimation over the summer and initiate a positive feedback leading to mound-building. Mounds without complete dune-cover may be in dynamic equilibrium with the ambient climate and show evidence of both present-day and past periods of erosion and aggradation. We conclude that the water ice mounds formed in deep impact craters in Mars’ north polar region may contain sensitive records of past polar climate that may enhance our understanding of the CO2–H2O system in the polar regions.