1,721,124 research outputs found
The effect of CO2 and salinity on olivine dissolution kinetics at 120 {ring operator} C
No full textThis paper reports the results of an experimental study on the dissolution kinetics of olivine (Mg1.82 Fe0.18 SiO4) at operating conditions relevant to the mineral carbonation process for the permanent storage of CO2. In particular, we investigated the effects of CO2 fugacity (fCO2) and of salinity on the kinetics of olivine dissolution, which is assumed to be the rate-limiting step of the overall carbonation process. Dissolution experiments were carried out at 120 {ring operator} C in a stirred flow-through reactor. Different pH values (between 3 and 8) and solution compositions were investigated by varying fCO2 and by dosing LiOH (for pH control), NaCl, and NaNO3. The specific dissolution rate values, r, were estimated from the experimental data using a population balance equation (PBE) model coupled with a mass balance equation. The logarithms of the obtained r values were regressed with a linear model as a function of pH and compared to the model reported earlier [Hänchen, M., Krevor, S., Mazzotti, M., Lackner, K.S., 2007. Validation of a population balance model for olivine dissolution. Chem. Eng. Sci. 62, 6412-6422] for experiments with neither CO2 nor salts. Our results confirm that, at a given temperature, olivine dissolution kinetics depends on pH only, and that fCO2 and the concentrations of NaCl and NaNO3 affect it through their effect on pH. © 2009 Elsevier Ltd. All rights reserved
The effect of CO2 and salinity on olivine dissolution kinetics at 120 {ring operator} C
No full textThis paper reports the results of an experimental study on the dissolution kinetics of olivine (Mg1.82 Fe0.18 SiO4) at operating conditions relevant to the mineral carbonation process for the permanent storage of CO2. In particular, we investigated the effects of CO2 fugacity (fCO2) and of salinity on the kinetics of olivine dissolution, which is assumed to be the rate-limiting step of the overall carbonation process. Dissolution experiments were carried out at 120 {ring operator} C in a stirred flow-through reactor. Different pH values (between 3 and 8) and solution compositions were investigated by varying fCO2 and by dosing LiOH (for pH control), NaCl, and NaNO3. The specific dissolution rate values, r, were estimated from the experimental data using a population balance equation (PBE) model coupled with a mass balance equation. The logarithms of the obtained r values were regressed with a linear model as a function of pH and compared to the model reported earlier [Hänchen, M., Krevor, S., Mazzotti, M., Lackner, K.S., 2007. Validation of a population balance model for olivine dissolution. Chem. Eng. Sci. 62, 6412-6422] for experiments with neither CO2 nor salts. Our results confirm that, at a given temperature, olivine dissolution kinetics depends on pH only, and that fCO2 and the concentrations of NaCl and NaNO3 affect it through their effect on pH. © 2009 Elsevier Ltd. All rights reserved
Precipitation of Mg-carbonates at elevated temperature and partial pressure of CO2
No full textIn this paper, we present an experimental study on the precipitation of magnesium carbonates (Mg-carbonates) from a solution containing magnesium chloride and sodium carbonate and in the presence of supercritical carbon dioxide. We performed homogeneous (unseeded) batch precipitation experiments at 100bar of CO2 and at 90°C, 120°C, and 150°C. The system was monitored with online temperature and pressure sensors and an online Raman spectroscopy probe. We investigated the effect of temperature and solution composition, i.e., supersaturation ratio, pH, speciation, ionic strength, and water activity on the mechanism and the kinetics of the precipitation of Mg-carbonates. Raman spectroscopy measurements allowed us to follow the temporal evolution of the solution and suspension composition and showed two Mg-carbonates can form under the investigated conditions, i.e., magnesite and hydromagnesite. The precipitation of these two phases occurred between pH 5.5 and 6.5 and was influenced by temperature, supersaturation ratio with respect to magnesite (SM) and hydromagnesite (SH), and the initial concentration of magnesium.At all investigated temperatures, we observed direct precipitation of magnesite while at 120°C and 150°C also simultaneous precipitation of magnesite and hydromagnesite followed by the transformation of the latter into the former. Under highly supersaturated conditions with respect to magnesite, SM as large as 20, magnesite nucleated rapidly when the system was also supersaturated with respect to hydromagnesite, SH as large as 1.5; whereas no nuclei formed within 20h, otherwise. The analysis of the data collected at 120°C and at 150°C highlighted that the change in the type of mechanism was associated with the initial supersaturation ratios and the initial concentration of magnesium in solution. At 120°C, the transformation process lasted for 2h, slowing down the formation of magnesite, despite of the large SM; whereas at 150°C, the transformation process was only 5min long, without affecting magnesite precipitation. © 2013 Elsevier B.V
Dissolution of olivine in the presence of oxalate, citrate, and CO2 at 90 °C and 120 °C
No full textIn this article, we report the results from a study of olivine dissolution kinetics under operating conditions suitable for ex situ aqueous mineral carbonation for CO2 storage. We studied the effect of oxalate and citrate ions on the dissolution of gem-quality San Carlos olivine (Mg1.82Fe0.18SiO4). Flow-through experiments were performed at 90°C and 120°C, at fCO2 between 4 and 81bar, with a solution containing either sodium oxalate or sodium citrate in a molality range between 10-3 and 10-1. The pH was varied between 2 and 7 by adding HCl, LiOH, and adjusting fCO2. At all investigated temperatures and for pH values in a broad range, both sodium oxalate and sodium citrate increased dissolution rate with the strongest effect up to one order of magnitude in presence of 0.1m of oxalate, at 120°C, and above pH 5. The enhancement effect was primarily ascribed to the oxalate or citrate ions that are the dominant species in this pH range. The overall dissolution process was described using the population balance equation (PBE) coupled with a mass balance equation to account for the evolution of the particle size distribution (PSD) of olivine. Far from equilibrium conditions for dissolution were established in all the experiments in order to achieve a surface-reaction controlled mechanism. We described the reaction with a surface complexation model, which assumes adsorption of a proton and of an oxalate (citrate) ions (proton and oxalate) on adjacent sites in order to enhance dissolution, and we derived a dissolution rate equation in presence of oxalate:r=r*1+KHaHn1+ΒKXaX1+KXaX,where r* is the specific dissolution rate commonly used in absence of organic compounds, and KH, KX, and Β are thermodynamic and kinetic parameters. The values of these parameters have been estimated from the experimental data and the agreement between the model results and the experiments is very good. © 2011 Elsevier Ltd
Process design and energy requirements for the capture of carbon dioxide from air
No full textA process to capture carbon dioxide from air to reduce its atmospheric concentration and to mitigate climate change is studied. It is based on the absorption of carbon dioxide in a sodium hydroxide solution, its precipitation as calcium carbonate, and its release as pure gas stream through oxy-fuel calcination. The process utilizes existing commercial technologies wherever possible, particularly in the case of the absorber, whose design is carried out in detail. The analysis allows deriving material and energy balances for the whole process and determining energy demands that can be used for a technical, economical, and environmental feasibility evaluation of the technology. In particular, it indicates that the real specific energy demand is larger than the heat released to emit the same amount of CO2 by the combustion of coal, and smaller than that of methane. (c) 2006 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dissolution of dehydroxylated lizardite at flue gas conditions: I. Experimental study
No full textThe direct mineralization of flue gas CO2 yields serviceable carbonates, thus combining CO2 utilization
with its permanent storage. Such a process requires the rapid dissolution of a magnesium or calcium
source at lean operating conditions. Motivated by its worldwide abundance, we have studied the dissolution
kinetics of a lizardite-type serpentine that was 75% dehydroxylated by thermal pretreatment to
maximize its reactivity. A continuous stirred liquid and gas flow-through setup was designed to perform
far-from-equilibrium dissolution experiments at moderate temperatures ð30 C 6 T 6 120 CÞ; low CO2
partial pressures ð0:1 bar 6 pCO2 6 2 barÞ, using two different particle size fractions, and using a mineral
acid instead of CO2 to vary the solution pH. Dissolution was measured to be non-stoichiometric and did
not reach steady state within 10 h. Up to 83% of the magnesium (Mg) and 72% of the silicon (Si) dissolved
within the first 100 min, where the dissolution rate for both Mg and Si increased with temperature and
pCO2. This fast stage was followed by a period with much reduced dissolution rates. The key observations
are rationalized with regard to the physical morphology and chemical properties of the thermally activated
mineral, and discussed in view of the design of a process that combines CO2 capture and storage
by mineralization
- …
