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Currently, the oil sands industry is producing millions of tons of tailings by‐products from the tailings solvent recovery unit (TSRU) into the tailings ponds. TSRU tailings (TTs) consist of water, asphaltene, and minerals, including silica and alumina mixtures. The oil sands sector has expanded efforts to discover solutions to remove the tailings ponds due to growing public concern about the environmental effects of these ponds and stiffer government rules on their disposal. Therefore, this report studied the effect of the different methods for the conversion of the TTs into the activated carbon‐zeolite composite. The TTs were treated with activation followed by hydrothermal, either with or without fusion with NaOH at 800°C for 1 h as a pre‐treatment. Zeolite Na‐P, zeolite A, and zeolite X were identified during the different characterizations, depending on the pre‐treatment of the fusion. The result showed that the fusion with NaOH before the hydrothermal reaction was effective as it increased the porosity and adsorption of the composite. The CO2 capture capacity of the product before fusion was 0.19 mmol/g, and after fusion, it was improved to 0.486 mmol/g. [ABSTRACT FROM AUTHOR]

Calcium looping process is a promising approach for CO2 capture from the flue gas of fossil fuel power plants and the cement industry. Even though the advantages of calcium‐based sorbents are low cost and high uptake capacity, they suffer from low durability during cycles. Modified sorbents were fabricated by adding alumina and zirconia and the mixture of alumina and zirconia to calcium oxide via the co‐precipitation method. The performance of synthesized sorbents in terms of stability and CO2 capture capacity were evaluated using a fixed bed reactor in various CO2 sorption/desorption cycles. The sorbents were fabricated by a co‐precipitation methodology using 10% binders (alumina and/or silica). X‐ray diffraction (XRD), BET/BJH, and scanning electron microscopy (SEM) were conducted for characterization of synthesized sorbents. CaO‐10% ZrO2 showed the best performance among the fabricated sorbents in terms of stability during 5 cycles and CO2 capacity (14 mmol CO2/g sorbent). The formation of CaZrO3 with a perovskite structure and high‐temperature resistance could be attributed to well performance of zirconia‐supported sorbent. On the other hand, no sign of aluminum zirconate formation was approved in XRD analysis for the fabricated sorbent using mixed binders of zirconia and alumina to enhance its stability during cycles. [ABSTRACT FROM AUTHOR]

Carbon capture and utilization/storage is an integral part of a smooth transition to a net‐zero energy portfolio. The distinctive advantages of the calcium looping (CaL) process, including low‐cost and high‐theoretical uptake capacity, make it a promising approach for the decarbonization of fossil fuel power plants and carbon‐intensive industries, including cement and steel. CaL exploits the reversible reaction of CO2 with CaO to capture and release carbon dioxide in a cyclic process. This paper reviews the fundamentals of the CaL process, the kinetics of the carbonation reaction, and extensive research on the development of sorbent materials with high durability for use in the CaL process. Various optimizing strategies for the improvement of the stability and CO2 uptake capacity of materials are outlined. Lastly, an overview of bench‐ and pilot‐scale testing facilities around the world is provided. The characteristics, operating conditions, and the main experimental findings of the testing facilities are summarized. [ABSTRACT FROM AUTHOR]

This study investigated the carbonation behaviour of a calcium‐based sorbent in the calcium‐looping CO2 capture process as a non‐catalytic gas‐solid reaction using a modified grain size distributed (GSD) model. In GSD model, the calcium‐based particle consisted of numerous spherical grains with variable size distribution. The GSD model was modified by considering a variable diffusion coefficient of the gaseous reactant through the development of the product layer. The overall conversion over the reaction time was calculated by a mathematical modelling. The overall sorbent conversion obtained by using the modified GSD model showed better agreement with the experimental data with the average absolute deviation of 4.2 % than the results obtained using the grain model with the average absolute deviation 9.4 %. In the modified GSD model, the physical microstructure of the sorbent particle changes due to the molar volume expansion during the carbonation reaction. The model also predicted accurately the change of particle structural properties such as porosity, molar density, and specific surface area during the carbonation reaction. [ABSTRACT FROM AUTHOR]

In this study, a series of core-shell structured spheriform CO2 sorbents were synthesized by using CaO-based pellets as cores and different mesoporous metal oxides (e.g. alumina, ceria, and yttrium-stabilized zirconia) as shells through a repeated wet impregnation coating process. Cyclic CO2 capture performance of the obtained sorbents was investigated using a thermogravimetric analyzer. Among all the core/shell sorbents under study, the pellets coated with a layer of alumina exhibit the best performance in the retention of CO2 uptake over 20 cycles with the lowest activity loss of only 30.4 %, attributed to the existence of the thermal stable porous alumina shell which prevents the sintering and the aggregation of the CaO grains. Moreover, the attrition study using an air-jet apparatus and a standard test method reveals that such sorbents exhibit enhanced attrition resistance due to the protection of the porous shell providing them with a great potential for application in fluidized bed conditions. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) capture is a process that can significantly reduce the amount of CO2 in the atmosphere. In this study, several solid sorbents were examined for their CO2 capturing performance over 30 carbonation-calcination cycles. The sorbents included natural calcined Cadomin limestone (denoted as CD), hydrated calcined Cadomin pellets (denoted as CP), core/shell sorbets with CD and CP as cores, and mesostructured silica (denoted as CD@Si and CP@Si, respectively) and titania (denoted as CD@Ti and CP@Ti) as shells. The core/shell sorbents were prepared with a protective porous shell using the mesoporous silica and titania layers. The surface morphology and porosity of all sorbents were qualified using scanning electron microscopy and were quantified using nitrogen physisorption. X-ray diffraction was also used to identify the crystal phase composition of the sorbents before and after calcination. The CP@Ti pellets showed the best performance in the retention of CO2 uptake over 30 cycles with an activity loss of 50.9%. This is attributed to the formation of a protective layer of thermally stable mesoporous titania using a sol-gel method, which prevented the aggregation of CaO crystals and sorbent sintering. Although the modified core/shell sorbents exhibited an improvement in maintaining the stability of the cyclic operation compared to natural limestone, further study is needed to understand the core/shell sintering phenomenon at high temperatures using other novel materials. [ABSTRACT FROM AUTHOR]

The intrinsic kinetics of the carbonation reactions for two limestones (Havelock and Cadomin) were studied using an atmospheric thermogravimetric analyzer (ATGA) and a pressurized thermogravimetric analyzer (PTGA). A grain model was applied to measure the kinetic parameters. The order of the carbonation reaction was related to the carbon dioxide (CO2) partial pressure, changing from the first order to the zero order when the CO2partial pressure exceeded ~0.7 atm for both limestones. The rate of carbonation reaction increased with increasing temperature up to 675°C and decreased with further increases. No significant effect of particle size was found on the rate of carbonation reaction. Thermodynamic and kinetic simulations of the carbonation reaction using the Aspen Plus simulator was performed, obtaining the optimal temperature of 650°C. The activation energies were 32.1 and 20.3 kJ/mol for the tested Havelock and Cadomin limestones, respectively. The simulation results from the kinetic model were in good agreement with the experimental data, showing the reversible characteristic of the carbonation reaction. The shift in the mechanism of the carbonation reaction with temperature and the shift in the reaction order with CO2partial pressure were demonstrated by both the experiments and simulation. [ABSTRACT FROM PUBLISHER]

The behavior of the carbonation reactionof the calcined Cadominlimestone used for CO2capture is described using the grainmodel and the changing grain size (CGS) model. To calculate the overallconversion over time, the mathematical modeling was solved semianalytically.The overall sorbent conversion obtained with the CGS model showedbetter agreement with the experimental data than the results obtainedusing the grain model. In the CGS model, the physical structure ofthe sorbent particle changes during the reaction. The CGS model wasmodified by considering a variable diffusion coefficient of the gaseousreactant through the development of the product layer. The modelingresults showed the positive effects of increasing the reaction temperatureand particle porosity on the rate of carbonation reaction. However,the rate of carbonation reaction decreased by increasing the sorbentparticle size. Moreover, the modeling results demonstrated an initialkinetic control stage which was followed by a diffusion control stepin the carbonation reaction of the calcined Cadomin limestone. [ABSTRACT FROM AUTHOR]

Highly stabilized mesoporous core-shell-structured CaO-based spheriform CO2 sorbents are fabricated, for the first time, by a novel repeated impregnation coating process combined with the mesoscopic surfactant-templating method. By adopting our established wet-coating strategy along with a sol-gel process, different mesoporous material-shelled sorbents with various shell thicknesses (1-5 μm) and shell compositions (silica/zirconia or pure zirconia) are synthesized. Cyclic CO2 capture performance is tested in a thermogravimetric analyzer with the core-shell pellet sorbents with a ~1 μm mesoporous zirconia shell exhibiting an unprecedented CO2 uptake capacity of ~7.2 moles CO2 per kg decarbonated sorbent and the lowest activity loss of only 30.8% after 20 cycles. This is attributed to the unique core- shell coating strategy in which the thermally stable Zr species prevent the aggregation and overgrowth of CaO crystals and sorbent sintering. When comparing the core-shell sorbents with Si-contained mesoporous shells, zirconia shelled ones exhibit significantly more outstanding performance. An attrition study using an air-jet apparatus under the standard test method reveals that the mesoporous zirconia shelled sorbent exhibits enhanced attrition resistance, which is also attributed to the novel core-shell design, offering protection for the reactive core. [ABSTRACT FROM AUTHOR]

In this work, CO 2 capture and H 2 production during the steam gasification of coal integrated with CO 2 capture sorbent were investigated using a horizontal fixed bed reactor at atmospheric pressure. Four different temperatures (650, 675, 700, and 750 °C) and three sorbent-to-carbon ratios ([Ca]/[C] = 0, 1, 2) were studied. In the absence of sorbent, the maximum molar fraction of H 2 (64.6%) and conversion of coal (71.3%) were exhibited at the highest temperature (750 °C). The experimental results verified that the presence of sorbent in the steam gasification of coal enhanced the molar fraction of H 2 to more than 80%, with almost all CO 2 was fixed into the sorbent structure, and carbon monoxide (CO) was converted to H 2 and CO 2 through the water gas shift reaction. The steam gasification of coal integrated with CO 2 capture largely depended on the reaction temperature and exhibited optimal conditions at 675 °C. The maximum molar fraction of H 2 (81.7%) and minimum CO 2 concentration (almost 0%) were obtained at 675 °C and a sorbent-to-carbon ratio of 2. [ABSTRACT FROM AUTHOR]

Highlights: [•] CaO-based pellet sorbents were tested for 31 carbonation–calcination cycles. [•] Pellet surface characterization was investigated using BET/BJH, XRD, and SEM tests. [•] Pellet sorbents exhibit lower activity loss than natural limestone. [•] Binders decreased the negative effect of sintering. [•] The core/shell pellets had the highest stability among the sorbents. [ABSTRACT FROM AUTHOR]

Thesteam gasification of biomass in the presence of calcium oxideoffers a viable route for the dual purpose of hydrogen productionand carbon dioxide (CO2) capture. Although previous studieshave dealt with experimental and intrinsic rate constants of carbonationand calcination of calcium looping cycles, the data has not been comparedwith thermodynamic or kinetic simulation. In this study, the thermodynamicand kinetic simulation of the CO2capture process usingtwo calcium-based sorbents (i.e., Imasco dolomite and Cadomin limestone)have been studied using Aspen Plus software. The thermodynamic simulationwas able to predict the overall trend of the CO2adsorptionon dolomite and limestone. However, a kinetic model was also appliedto achieve a more accurate analysis. The results show good agreementbetween the modeling and the experimental data obtained using a thermogravimetricanalyzer (TGA). A shift in the reaction mechanism was observed withrespect to temperature. The experimental data and kinetic model illustratedthat the maximum conversion occurred at 650 °C. [ABSTRACT FROM AUTHOR]

Abstract: The effect of sawdust on the rate of limestone carbonation/calcination reactions was studied in a thermogravimetric analyzer applying a grain model for the calcium-based sorbent, namely Havelock limestone (0.50–1.41mm). Two samples were employed for calcination under N2 at 850°C: one containing limestone, and the other a mixture containing limestone and sawdust. The resulting limestone samples were observed under a scanning electron microscope (SEM), while the quantitative influence of calcination conditions was examined by BET surface areas. The presence of sawdust during calcination caused a significant increase in the initial rate of carbonation, which has been attributed to the enhancement of CaO surface area. The presence of H2 which is emitted from sawdust pyrolysis was assumed to be responsible for reduction of limestone sintering. [Copyright &y& Elsevier]