How carbonation curing influences ca leaching of Portland cement paste: Mechanism and mathematical modeling

Carbonation curing provides a promising method for both CO₂ sequestration and strength improvement of cement-based materials. To date, there is little knowledge about the influence of carbonation curing on Ca leaching resistance of cement-based materials due to the occurrence of both physical and chemical transformation. It was the first time that Ca solid-liquid equilibrium curves were experimentally established for cement pastes with different carbonation degrees in this paper. Experimental results demonstrated that on the one hand, carbonation curing improves the leaching resistance of cement paste by sequestrating Ca in insoluble CaCO₃; on the other hand, potential negative effects may occur due to the accelerated decalcification and increased solubility of C–S–H after carbonation curing. Results of NMR showed that both carbonation curing and Ca leaching can increase the Si chain length and polymerization degree of C–S–H. Additionally, a modified mathematical model was established to simulate the leaching process of carbonation-cured cement paste and it was also verified by energy-dispersive spectroscopy (EDS) results. Therefore, the long-term leaching resistance of cement-based materials is possibly degraded by the carbonation curing treatment.     

Generation of microcellular biodegradable polycaprolactone foams in supercritical carbon dioxide

Microcellular foaming of low‐T_g biodegradable and biocompatible polycaprolactone (PCL) in supercritical CO₂ has been studied. The purpose is to apply microcellular materials to drug containers and medical materials for artificial skin or bone. Effects of a series of variable factors on the foam structures, such as saturation temperature, saturation pressure, saturation time, and depressurization time were studied. The experimental results indicate that, while keeping other variables unchanged, higher saturation temperature leads to reduced bulk densities and different saturation pressures result in different nucleation processes. In addition, saturation time has a profound effect on the structure of the product. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 593–597, 2004     

Study of different effects on foaming process of biodegradable PLA/starch composites in supercritical/compressed carbon dioxide

Microcellular foaming of biodegradable and biocompatible PLA/starch composites in supercritical/compressed CO₂ has been studied. The purpose of this study is to explore the potential application of this kind of materials in medical materials or drug containers. The rate of CO₂ uptake and CO₂ equilibrium concentration in PLA/starch composites were studied by performing sorption and desorption experiments. The effects of a series of variable factors, such as saturation time and saturation temperature on the foaming morphology were studied through SEM observation and density measurement. The experimental results show that, while keeping other variables unchanged, longer saturation time leads to reduced bulk foam densities and different saturation pressures result in different bulk foam densities. The crystallinity of PLA–starch sample was characterized by differential scanning calorimetry. It indicates that the foaming treatment with supercritical CO₂ increased the crystallinity of PLA/starch composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dependency of C–S–H carbonation rate on CO2 pressure to explain transition from accelerated tests to natural carbonation

The use of normalized accelerated carbonation tests is currently limited to the classification of concretes in terms of carbonation resistance and the results are not easily transposable to forecasting concrete carbonation in natural conditions. Common models assume that the kinetics of the carbonation front ingress in concrete is a square root function of the CO₂ pressure but observations in the field generally invalidate this assumption. Based on an experimental program including carbonation tests at several CO₂ pressures, this paper shows that the amount of carbonated product depends largely on the CO₂ pressure. Several experimental analyses of carbonated concrete under different pressures are confronted, to finally propose a new analytical model able to predict carbonation ingress in natural conditions using the results of accelerated tests. The model takes both the cement chemical composition and its amount in concrete into account. The carbonation kinetics dependence on CO₂ pressure is considered through two underlying functions including, for the first, the dependence of the CSH carbonation rate on the pressure and, for the second, the effect of this additional carbonation on the reduction of the CO₂ diffusion coefficient.     

A numerical study of capillary pressure–saturation relationship for supercritical carbon dioxide (CO2) injection in deep saline aquifer

Carbon capture and sequestration (CCS) is expected to play a major role in reducing greenhouse gas in the atmosphere. It is applied using different methods including geological, oceanic and mineral sequestration. Geological sequestration refers to storing of CO₂ in underground geological formations including deep saline aquifers (DSAs). This process induces multiphase fluid flow and solute transport behaviour besides some geochemical reactions between the fluids and minerals in the geological formation. In this work, a series of numerical simulations are carried out to investigate the injection and transport behaviour of supercritical CO₂ in DSAs as a two-phase flow in porous media in addition to studying the influence of different parameters such as time scale, temperature, pressure, permeability and geochemical condition on the supercritical CO₂ injection in underground domains. In contrast to most works which are focussed on determining mass fraction of CO₂, this paper focuses on determining CO₂ gas saturation (i.e., volume fraction) at various time scales, temperatures and pressure conditions taking into consideration the effects of porosity/permeability, heterogeneity and capillarity for CO₂–water system. A series of numerical simulations is carried out to illustrate how the saturation, capillary pressure and the amount of dissolved CO₂ change with the change of injection process, hydrostatic pressure and geothermal gradient. For example, the obtained results are used to correlate how increase in the mean permeability of the geological formation allows greater injectivity and mobility of CO₂ which should lead to increase in CO₂ dissolution into the resident brine in the subsurface.     

Supercritical CO2 Extraction of Essential Oil from Origanum Vulgare L.: Experiments and Mathematical Modeling

In this work, the supercritical CO₂ extraction of essential oil from Origanum Vulgare L. was investigated and modeled. An orthogonal test and ANOVA indicated that extraction pressure, extraction temperature, and extraction time had significant influence on extraction effects. Based on experiments, a mathematical model depended on mass conservation equation was established to describe and simulate supercritical CO₂ extraction of essential oil from Origanum Vulgare L. The mean diameter, accumulation properties, and the inside and outside transfer properties of extracted material particles were considered in the model. The model was solved numerically with the finite difference method and Runge-Kutta method synthetically. Model estimation was validated with small scale experimental data. Moreover, the effects of extraction pressure, extraction temperature, extraction time, concentration, and the flow rate of the entrainer on mass of essential oil were investigated using the model.     

Carbonation kinetics of a bed of recycled concrete aggregates: A laboratory study on model materials

Taking advantage of atmospheric carbonation of recycled concrete aggregates (RCA) seems particularly attractive to partially reabsorb the chemical part of CO₂ emitted during limestone calcination. The purpose of this article is to investigate the carbonation mechanism of a heap of RCA. As a first approximation, the rate of CO₂ absorption is studied on model materials made of sieved grains of cement paste made of CEM I. Carbonation penetration is measured by gamma-ray attenuation and by thermogravimetric analysis. A model is proposed and verified thanks to experiments. It is based on a dual-scale approach, associating CO₂ diffusion through a granular bed and carbonation of the cementitious matrix. Information is provided concerning the influence of the characteristics of the cementitious phase attached to the original aggregates on the CO₂ absorption rate. Moreover a study of the carbonatable amount of hydration products is performed according to the composition of the material and the CO₂ concentration.     

Study of different effect on foaming process of biodegradable bionolle in supercritical carbon dioxide

Microcellular foaming of biodegradable Bionolle in supercritical CO₂ has been produced. The effects of a series of variable factors, such as saturation temperature, saturation pressure, and depressurization time and step on the foam structures and density, were studied through measurement of density and SEM observation. The experimental results show that higher saturation temperatures lead to an increase in bulk densities; and different depressurization time and step result in different product cell morphology. In addition, at some saturation temperature, the orientation of the cells can be found in the product morphology. XRD experimental results show that the foaming treatment with SC CO₂ increased the crystallinity of Bionolle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2901–2906, 2006     

A numerical study of dynamic capillary pressure effect for supercritical carbon dioxide‐water flow in porous domain

Numerical simulations for core‐scale capillary pressure (P^c)‐saturation (S) relationships have been conducted for a supercritical carbon dioxide‐water system at temperatures between 35°C and 65°C at a domain pressure of 15 MPa as typically expected during geological sequestration of CO₂. As the P^c‐S relationships depend on both S and time derivative of saturation ( ) yielding what is known as the “dynamic capillary pressure effect” or simply “dynamic effect,” this work specifically attempts to determine the significance of these effects for supercritical carbon dioxide‐water flow in terms of a coefficient, namely dynamic coefficient (τ). The coefficient establishes the speed at which capillary equilibrium for supercritical CO₂ (scCO₂)‐water flow is reached. The simulations in this work involved the solution of the extended version of Darcy's law which represents the momentum balance for individual fluid phases in the system, the continuity equation for fluid mass balance, as well as additional correlations for determining the capillary pressure as a function of saturation, and the physical properties of the fluids as a function of temperature. The simulations were carried out for three‐dimensional cylindrical porous domains measuring 10 cm in diameter and 12 cm in height. τ was determined by measuring the slope of a best‐fit straight line plotted between (1) the differences in dynamic and equilibrium capillary pressures against (2) the time derivative of saturation (dS/dt), both at the same saturation value. The results show rising trends for τ as the saturation values reduce, with noticeable impacts of temperature at 50% saturation of aqueous phase. This means that the time to attain capillary equilibrium for the CO₂‐water system increases as the saturation decreases. From a practical point of view, it implies that the time to reach capillary equilibrium during geological sequestration of CO₂ is an important factor and should be accounted for while simulating the flow processes, for example, to determine the CO₂ storage capacity of a geological aquifer. In this task, one would require both the fundamental understanding of the dynamic capillary pressure effects for scCO₂‐water flow as well as τ values. These issues are addressed in this article. © 2014 American Institute of Chemical Engineers AIChE J 60: 4266–4278, 2014     

CO2 Capture Performance of Calcium‐Based Sorbents in the Presence of SO2 under Pressurized Carbonation

In order to understand the effect of SO₂ on the CO₂ capture performance under pressurized carbonation conditions, tests by orthogonal design were carried out in a calcination/pressurized carbonation reactor system. The effects of variables such as carbonation temperature, carbonation pressure, SO₂ concentration, CO₂ concentration, and the number of cycles on carbonation and sulfation were investigated. A range method was employed for analysis. Phase structure and scanning electron microscopy images were measured as supplement for a reaction study. Temperature increase enhanced the SO₂ capture, leading to a rapid decay in CO₂ uptake. The carbonation pressure had a stronger effect on the CO₂ uptake than the temperature. SO₂ uptake increased rapidly with increasing pressure while CO₂ uptake decreased.     

Supercritical CO2 Extraction of Chlorophyll a from Spirulina platensis with a Static Modifier

Supercritical CO₂ extraction with a static modifier was applied to extract chlorophyll a from Spirulina platensis. The effects of the process were investigated by single‐factor and response surface analysis experiments. The optimal process parameters for supercritical CO₂ extraction were determined to be: ethanol/water as the modifier, 40 vol.‐% water content in the modifier, 21.2 mL modifier volume, 1 h static soaking time, 2 h dynamic extraction time, 48.7 MPa extraction pressure, 326.4 K extraction temperature, and 10 g min^–1 CO₂ flow rate. The optimized chlorophyll a extraction yield was 6.84 mg g^–1. A comparison of the experimental results suggested that the yield of chlorophyll a by supercritical CO₂ extraction with modifier was higher than that obtained by conventional solvent extraction.     

Preparation of porous PLGA/HA/collagen scaffolds with supercritical CO2 and application in osteoblast cell culture

Biocompatible three-dimensional scaffolds for cell culturing may facilitate methods for the repair of damaged human tissues. A novel hybrid porous scaffold of poly(lactic-co-glycolic acid), hydroxyapatite and collagen was prepared using a supercritical CO₂ saturation technique. Expansion factors of scaffolds with different compositions were studied after supercritical CO₂ treatment to choose the optimal composition for three-dimensional culture. The supercritical CO₂ process conditions, such as saturation temperature, saturation time and saturation pressure were varied to evaluate their influence on pore structure. The results showed that the pore size and porosity of the scaffold could be controlled by manipulating these process conditions. The porous samples were characterized by environmental scanning electron microscopy, energy-dispersive X-ray spectroscope, Fourier transform infrared spectroscopy and X-ray diffractometry. Finally, MG-63 cells were successfully cultured on the porous scaffold as assessed by electron and confocal microscopy, confirming the biocompatibility of this new hybrid porous scaffold.     

Effects of Process Variables on Microcellular Structure and Crystallization of Polypropylene Foams with Supercritical CO2 as the Foaming Agent—A Study of Microcellular Foaming of Polypropylene

The effects of process variables on the microcellular structure and crystallization of foamed polypropylene (PP) with supercritical CO₂ as the foaming agent were investigated in this article. The cell size increased and the cell density reduced with increased foaming temperature. Differently, both the cell diameter and cell density increased as saturation pressure increased. DSC curves showed that the melting peak was broadened when supercritical CO₂ foaming PP. Furthermore, the width at half-height of the melting peak increased, the melting peak moved to higher temperature, and the melting point and crystallinity enhanced as the foaming temperature lowered and the saturation pressure enhanced.     

Solubility of the diarrheic shellfish toxin okadaic acid in supercritical CO2

The solubility of okadaic acid (OA) in supercritical CO₂ was measured using a flow-type apparatus with sequential sampling during dynamic nonrecirculating experiments at saturation conditions. Methanol and water were used as solvent modifiers of CO₂. Collected OA was measured by high-performance liquid chromatography with fluorimetric detection after derivatization with 1-bromoacetylpyrene to obtain the labeled ester of the toxin. Solubility results were obtained with methanol concentrations ranging from 0 to 8.5% volume in the CO₂ density range of 0.495 to 0.913 g/mL at 40, 60, and 73°C. Measured solubility of OA ranged from 0 to 15×10⁻⁶ mol/L, increasing with methanol concentration and fluid density and diminishing with temperature. Experiments with water-modified CO₂ up to 0.3% volume (near saturation) were done at 60°C; solubilities of OA up to 5×10⁻⁶ mol/L were measured. This is the first approach to handle the liposoluble diarrheic shellfish toxins with supercritical CO₂. The study, with pure OA, provides useful information regarding the effects of pressure, temperature, and addition of modifiers on its solubility. Obtained results show that the toxin can be solubilized in this media and potential applications are suggested and being currently investigated.     

Investigation of the carbonation mechanism of CH and C-S-H in terms of kinetics,microstructure changes and moisture properties

The purpose of this article is to investigate the carbonation mechanism of CH and C-S-H within type-I cement-based materials in terms of kinetics, microstructure changes and water released from hydrates during carbonation. Carbonation tests were performed under accelerated conditions (10% CO₂, 25 °C and 65 ± 5% RH). Carbonation profiles were assessed by destructive and non-destructive methods such as phenolphthalein spray test, thermogravimetric analysis, and mercury intrusion porosimetry (destructive), as well as gamma-ray attenuation (non-destructive). Carbonation penetration was carried out at different ages from 1 to 16 weeks of CO₂ exposure on cement pastes of 0.45 and 0.6 w/c, as well as on mortar specimens (w/c = 0.50 and s/c = 2). Combining experimental results allowed us to improve the understanding of C-S-H and CH carbonation mechanism. The variation of molar volume of C-S-H during carbonation was identified and a quantification of the amount of water released during CH and C-S-H carbonation was performed.     

Pressure variation due to heat shock of CO2hydrate desserts

CO₂ hydrate desserts are carbonated frozen desserts in which the CO₂ is trapped in a crystalline water‐carbon dioxide structure called a CO₂ clathrate hydrate. The CO₂ concentration of the dessert enables strong perception of carbonation, but CO₂ hydrate dissociation during heat shock can cause high package pressures during storage and distribution. In this work, a model is developed for package pressure as a function of temperature, CO₂ content, package volume, dessert mass, and recipe. The model is validated by comparison with an experimental measurement of the pressure and mass of a CO₂ hydrate dessert subjected to heat shock. It is shown that during heat shock a sealed package can reach pressures greater than the ice‐CO₂ hydrate equilibrium pressure. At pressures above the ice‐CO₂ hydrate equilibrium pressure, the fraction of water crystallized in the dessert can be increased, potentially mitigating heat shock damage. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Carbonation of calcium-containing mineral and industrial by-products

The use of carbon dioxide (CO₂) and calcium-containing by-products from industrial activities is receiving increasing interest as a route to valuable carbonate materials while reducing CO₂ emissions and saving natural resources. In this work, wet-chemical experimental data was assessed, which involved the carbonation of three types of materials in aqueous solutions, namely, 1) wollastonite, a calcium silicate mineral, 2) steelmaking slag, a by-product of steel production, and 3) paper bottom ash (PBA) from waste paper incineration. Aims were to achieve either a high carbonation degree and/or a pure carbonate product with potential commercial value. Producing a pure precipitated calcium carbonate (PCC) material that may find use in paper industry products puts strong requirements on purity and brightness. The parameters investigated were particle size, CO₂ pressure, temperature, solid/liquid ratio, and the use of additives that affect the solubilities of CO₂ and/or calcium carbonate. Temperatures and pressures were varied up to 180°C and 4 MPa. Data obtained with the wollastinite mineral allowed for a comparison between natural resources and the industrial by-product materials, the latter typically being more reactive. With respect to temperature and pressure trends reported by others were largely confirmed, with temperatures above 150°C introducing thermodynamic limitations depending on CO₂ pressure. The influence of additives showed some promise, although costs may make recycling and reuse of additives a necessity for a large-scale process. When using steelmaking slag, magnetic separation may remove some iron-containing material from the process (although this is far from perfect), while the addition of bicarbonate supported the removal of phosphorous, aside from improving calcium extraction. The experiments with paper bottom ash (PBA) gave new data, showing that its reactivity resembles that of steelmaking slag, while its composition results in relatively pure carbonate product. Also, with PBA no additives were needed to achieve this.     

Application of the random pore model to the carbonation cyclic reaction

Calcium oxide has been proved to be a suitable sorbent for high temperature CO₂ capture processes based on the cyclic carbonation‐calcination reaction. It is important to have reaction rate models that are able to describe the behavior of CaO particles with respect to the carbonation reaction. Fresh calcined lime is known to be a reactive solid toward carbonation, but the average sorbent particle in a CaO‐based CO₂ capture system experiences many carbonation‐calcination cycles and the reactivity changes with the number of cycles. This study applies the random pore model (RPM) to estimate the intrinsic rate parameters for the carbonation reaction and develops a simple model to calculate particle conversion with time as a function of the number of cycles, partial pressure of CO₂, and temperature. This version of the RPM model integrates knowledge obtained in earlier works on intrinsic carbonation rates, critical product layer thickness, and pore structure evolution in highly cycled particles. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Effect of supercritical carbon dioxide dyeing conditions on the chemical and morphological changes of poly(ethylene terephthalate) fibers

Commercially available regular denier poly(ethylene terephthalate) (PET) fabrics were used in this investigation. PET fabric samples were wound on a bobbin and then exposed to supercritical CO₂ under conditions representing a typical supercritical CO₂ dyeing cycle. Infrared spectroscopy, X‐ray diffraction, differential scanning calorimetry, and scanning electron microscopy were used to characterize the chemical and morphological changes of the PET fibers. The results showed that exposure to supercritical CO₂ did not cause chemical changes in the fibers; the crystal size and the T_mp of the PET fabric after treatment in supercritical CO₂ did not significantly change; the crystallinity decreased; and the treatment in supercritical CO₂ at higher temperature caused surface morphology changes (increased oligomer migration). However, there was no pitting, cracking, or crazing on the surface of the treated fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2008–2012, 2004     

铵基循环碳酸化固定CO2

引言由煤等化石燃料燃烧产生的温室气体CO2的捕集与封存已引起国际社会的广泛关注[1-2];其中,模仿自然界钙镁硅酸盐矿物风化过程的碳酸化固定是实现大规模封存CO2的重要途径,与其他封存技术相比,碳酸化固定CO2环境风险性小,并可