Calcination Heating Research Articles

A novel Ca-Ni looping with carbonation heat thermochemical regeneration method for post-combustion CO2 capture: System integration, energy-saving mechanism, and performance sensitivity analysis

Thermal coupling between the calcium looping (CaL) process and chemical looping combustion (CaL-CLC) offers advantages to avoid electricity consumption of air separation, and the CaL-CLC has presented superior performance realizing CO2 capture. However, in these CaL-CLC and CaL configurations for post-combustion CO2 capture, the carbonation heat is recovered for steam generation with a significant temperature difference, leading to considerable irreversible loss. To prevent the temperature mismatch during carbonation heat recovery, this paper proposes the concept of Ca-Ni looping with the carbonation heat thermochemical regeneration method. Additionally, a novel system integrating with a combined cycle is introduced to effectively decarbonize flue gas. Results show that the proposed system has superior performance compared with the reference system based on the Ca-Cu looping method. The specific energy consumption for CO2 avoided (SPECCA) decreased from 2.13 MJ/kg CO2 in the reference system to 1.43 MJ/kg CO2. Exergy analysis indicates that a total 6.3 % exergy destruction reduction is realized by replacing the Cu-based chemical looping combustion with the Ni-based oxidation reaction for calcination heat supply. Furthermore, the energy utilization diagram (EUD) reveals the mechanism of exergy destruction reduction caused by the thermal coupling between reaction processes. Besides, the impact of key operating parameters on the proposed system performance is investigated. Overall, the proposed Ca-Ni looping with carbonation heat regeneration method enhances the utilization of mid-temperature carbonation heat by converting it into high-grade thermal energy suitable for combined cycles, thereby offering a promising alternative for low-energy-consumption CO2 capture.

The effects of calcination heating rate on phase formation and structure of zircon sand-derived zirconia

Abstract Phase formation and structure examination has been conducted to study the effects of thermal treatment and heating rates on zircon (ZrSiO4) sand-derived zirconia (ZrO2). A preliminary investigation of the elements present in the sand using XRF revealed that Zr was the major element, corresponding to 92.4% of the sample. The zirconia precursor was synthesized through a three-stage process that involves purifying zircon powder, alkali fusion, and co-precipitation method. The zirconia crystal was obtained by heating the sample to 700, 800 and 900 °C with heating rates of 5 and 10 °C/min, respectively. The formation of tetragonal zirconia (t-ZrO2) with space group P42/nmc is shown in a qualitative study of all sample XRD patterns. Furthermore, Rietveld analysis was used to determine crystal structure parameters including lattice parameters and tetragonality. The calcination temperature and heating rate decide the phase, t-ZrO2 crystallite size, and tetragonality. Furthermore, calcining to 700 and 800 °C created t-ZrO2, however, elevated temperature to 900 °C lead to t→m transformation. The t-ZrO2 size increases with temperature between 700 and 900 °C, range of 9 and 15 nm. Meanwhile, the tetragonality of t-ZrO2 tends to decrease due to m-ZrO2 being present.

Structural characteristics of Zn-MOFs and derived zinc oxide by X-ray diffraction peak analysis fabricated by mechanical and hydrothermal methods

In this work, the Zn based MOFs were synthesized from cyanoguanidine and zinc acetate source precursors via two hydrothermal methods and high energy ball milling technique and also the free salt and bimetallic samples have been synthesized. Then, the fabricated Zn-MOFs were heat for calcination at 550 °C for 110 min. The synthesized nanostructures were examined by XRD, SEM and FTIR analysis to gain insight about structure, morphology and functional groups properties. The results confirm that it is possible to prepare Zn MOFs using high energy ball milling methods. Besides, the fabricated MOF and complex structures can be converted to porous zinc oxide (ZnO) by a simple thermal annealing in air. Then, the line broadening of ZnO from mechanochemical and hydrothermal methods was showed due to the small crystallite size and lattice strain. The broadening was studied by the Scherrer formula and Williamson Hall (UDM, USDM, UDEDM) and Size-strain plot techniques. In addition, undesirable phases may affect the synthesized part during thermal cycles. We demonstrate the potential of using high-energy X-ray diffraction for detailed analysis of minority phases in ZnO-derived components.

High-Entropy Oxide of (BiZrMoWCeLa)O2 as a Novel Catalyst for Vanadium Redox Flow Batteries.

In this study, new fluorite high-entropy oxide (HEO), (BiZrMoWCeLa)O2, nanoparticles were produced using a surfactant-assisted hydrothermal technique followed by calcination and were used as novel catalytic materials for vanadium redox flow batteries (VRFBs). The HEO calcined at 750 °C (HEO-750) demonstrates superior electrocatalytic activity toward V3+/V2+ and VO2+/VO2+ redox couples compared to those of cells assembled with other samples. The charge-discharge tests further confirm that VRFBs using the HEO-750 catalyst demonstrate excellent Coulombic efficiency, voltage efficiency, and energy efficiency of 97.22, 87.47, and 85.04% at a current density of 80 mA cm-2 and 98.10, 74.76, and 73.34% at a higher current density of 160 mA cm-2, respectively. Moreover, with 500 charge-discharge cycles, there is no discernible degradation. These results are attributed to the calcination heat treatment, which induces the formation of a new single-phase fluorite structure, which facilitates the redox reactions of the vanadium redox couples. Furthermore, a high surface area, wettability, and plenty of oxygen vacancies can give more surface electroactive sites, improving the electrochemical performance, the charge transfer of the redox processes, and the stability of the VRFBs' electrode. This is the first report on the development of fluorite structure HEO nanoparticles in VRFBs, and it opens the door to further research into other HEOs.

Structural and mechanical optimization of porous alumina structures fabricated by carbon sacrificial template

The Taguchi method is used to optimize the manufacture of porous alumina made through reactive spark plasma sintering and carbon sacrificial template. The goal is to design a new versatile procedure that allows the fabrication of porous alumina with tailored physical properties. The structural and mechanical properties taken as target parameters were the subtle combination of porosity and Young’s modulus of the human cortical bone: typical pore size ¿100μm, and Young’s modulus in the range of 3–30 GPa. The input factors of the Taguchi method are wt.% of carbon, sintering time, calcination heating rate, and final heat treatment. Hg porosimetry, electron microscopy, uniaxial compression and computer aided tomography were used for the characterization of the porosity, pore size distribution, pore interconnectivity, and Young’s modulus. Finally, according to the conclusions of the Taguchi analysis, the parameters of the process were changed for the fabrication of the new samples with optimized properties. Highly porous structures with 90% interconnectivity, Young modulus of 5.5 ± 1.1 GPa, and compression strength of 49 ± 20 MPa, were obtained, successfully emulating the targeted properties.

Thermodynamic analysis of a sorption-enhanced gasification process of municipal solid waste, integrated with concentrated solar power and thermal energy storage systems for co-generation of power and hydrogen

A system of coupled CO2 capture and gasification has led to a new concept entitled sorption-enhanced gasification (SEG) which can increase H2 concentration in the syngas composition. This study proposed a novel configuration of the SEG system comprising concentrated solar power and thermal energy storage systems. Calcium looping (CaL) is utilized as the CO2 capture process. Unlike conventional SEG systems in which calcination heat demand is supplied by an oxy-combustion process, this study considers a heliostat field to provide heat for sorbent regeneration. The solar and thermal energy storage systems are simulated dynamically to achieve accurate results. A steam Rankine cycle is also designed to recover the released heat sources through the SEG system. The overall system performance is explored through energy and exergy analyses. Based on the results, the proposed system managed to produce 0.58 kg/s pure hydrogen in addition to 13.96 MW of net electrical power. Meanwhile, CO2 is captured from syngas composition with capturing efficiency of 95%. The energy analysis shows cold gas efficiency and the annual total energy efficiency of 87.76 and 70.74%, respectively. Based on exergy analysis results, the carbonator reactor exhibits the highest permeance compared to the gasifier and calciner reactors, with an exergy efficiency of 88.74%. Parametric study results show an increase in the cold gas efficiency, hydrogen production rate, and electrical energy efficiency with enhancing steam-to-biomass ratio. An increase in CO2 capture efficiency also improves both the electrical energy efficiency and H2 concentration of the syngas composition. CO2 capture efficiency and S/B ratio are inversely related to the exergy efficiency of the system.

Evaluation of pozzolanic reactivity of maize straw ash as a binder supplement in concrete

Cementitious materials, irrespective of their sources, play a vital role in cement hydration reaction in concrete. Hence, it is critical to understand how each supplement affects the early and later age properties of concrete. Maize Straw Ash (MSA), being a material with minimal consideration as a pozzolan for partial replacement of cement, was evaluated based on different researcher’s reports. A range of outcomes involving the use of maize straw ash as replacement materials in concrete were examined based on their impact on concrete in the early and later stages, and the findings were presented in addition to assisting in their future use. The impact of pozzolanic material on both mechanical and durability property were analysed, and how certain treatment methods influence the property of concrete in the early and later period. The data revealed that maize straw ash has comparable behaviour when given the same treatment technique before use, ability to increase strength over a long duration compared with other Agricultural waste (agro) materials, and likewise act as a void filler when concrete hardens to improve durability, with the usage of these materials for optimal strength not exceeding 20% replacement, shrinkage control not exceeding 30%, and 10–15% for good workability. At (500–800 °C calcination heat), the pozzolanic reaction produces good results.

Enhancement of Ammonia Sensors Using In2O3 Sensing Electrode by Adjusting Particle Size and NiCo2O4 Reference Electrode

A mixed potential ammonia sensor using In2O3 sensing electrode was prepared, and its sensing performance was enhanced by adjusting particle size with calcination heating rate as well as the utilization of NiCo2O4 reference electrode. It was found that the sensor with a calcination heating rate of 2 °C min−1 had the best performance, with a sensitivity of −61.27 mV decade−1 at 525 °C, and the TEM results showed that the average particle size was 70.36 nm. Furthermore, the sensor exhibited good stability against oxygen concentration fluctuation. The results also indicated that the mixed potential has a linear relationship with the logarithm of NH3 concentration, suggesting that the ammonia sensors in this study conform to the mixed potential theory. To address the issue that most ammonia sensors are susceptible to NO2 interference, NiCo2O4 was used as reference electrode to replace the Pt reference electrode, which could greatly offset the response of NO2 and improve the sensors selectivity. In summary, the developed In2O3/YSZ/NiCo2O4 sensor exhibited a great potential for NH3 monitoring in SCR systems.

Deposition of Li/Al layered double hydroxides on the graphite felts for the performance improvement of an all-vanadium redox flow battery

Porous graphite felts (GFs) play an important role in all-vanadium redox flow batteries (VRFBs) because a redox reaction occurs on the surface of the graphite’s fibers. In order to enhance the electrochemical performance of the GFs, a novel method is developed to modify the surface of GFs by decorating layered double hydroxides (LDHs) with Ni or NiO nanoparticles. For a comparative study, GFs treated with acid and heat are also prepared as porous electrodes of the VRFB. The performance of VRFBs with GFs treated with various methods and investigated the characteristics of these GFs. The results show that GFs decorated with LDH (including Ni and NiO nanoparticles) can improve the energy efficiency of the VRFB by 5% compared with acid- or heat-treated GFs. X-ray photoelectron spectroscopy measurements indicate that the improvement in the heat-treated graphite fibers’ wettability is due to a reduction in the O/C ratio and an increase in the C–O/C = O ratio on the graphite fibers. An H2 reduction treatment formed the metallic Ni on the LiAlO platelets. The calcination heat treatment in the air created NiO to improve the active surface area and therefore enhance the redox reaction.

Novel Fluidized Bed Particle Classifier for Application in Calcium Looping With Indirect Heat Transfer – Experiments and Simulations

This article summarizes a detailed scientific study of a particle classification system to be used in a fully integrated regenerative calcium looping (FICaL) system for CO2 capture. In conventional calcium looping, the required calcination heat is provided by a separate oxyfuel combustor, which needs an air separation unit (ASU) to provide the required oxygen for the process. The ASU demands a considerable amount of power, which gives an energy penalty of typically 5 % to the power plant. However, in the FICaL system, the required heat for the calcination is instead supplied indirectly from the main combustor in the power plant, so there is a no need for an ASU in the system. Based on process simulation studies done with Aspen Plus®, this may reduce the energy penalty to values in the order of 1-2 %. The indirect heat transfer is done by using inert heat transfer (HT) particles that are heated up in the combustor and then transferred to the calciner where the sorbent material is heated up after mixing with the hotter inert particles. Thereby the sorbent material is calcined. However, after calcination, the sorbent and heat transfer particles have to be separated. Hence, an efficient classifier is required. The current work has therefore focused on designing, constructing and doing experiments in a novel particle classification system. A novel cross-flow fluidized bed classifier was designed, using computational fluid dynamics (CFD) simulations as a tool, in order to separate the sorbent and HT particles exiting from the calciner. The classifier, which has no mechanical moving parts exposed to very high temperature, can be operated under the required high-temperature conditions prevailing in a full-scale plant. Two different cold-flow lab-scale versions of the classifier was built and used for a large number of experiments. In the classification, the aim is to minimize the loss of sorbent particles via the bottom exit from the classifier, and also to minimize the loss of HT particles via the top exit from the classifier. The second and improved version was able to classify very well a mixture of down-scaled sorbent particles (zirconia) and down-scaled HT particles (steel). The experiments with the improved classifier version gave particle losses in the order of 2-3 %, values that are close to what can be seen as acceptable in a full-scale hot-flow system. Extensive CFD simulations were carried out with the commercial software Barracuda® 17.1 to investigate in detail how the different particle types behave in the classifier. Even if the exact particle losses were not well predicted, Barracuda was able to predict the general gas-solids flow behavior and proved to be a useful tool in the design process. Different drag models were used to reproduce the experimental findings and validate the CFD model. Barracuda was also used to simulate the classification process under hot-flow conditions and indicated that the classifier will also perform well under such conditions. The results of the corresponding research work are promising as the classifier is able to give a high degree of purity of the particle streams leaving the classifier. The iterative design and modelling effort from this research work has produced a functional, high-efficiency classification concept.

Preliminary calciner

In the former years, the total amount of heat indispensable for clinker formation was obtained in the kiln burner, which determined the maximum of this heat, thus the kiln efficiency was simultaneously determined. The kiln has the double role: the hearth and the chemical reactor. The diminishing of the heat loading of the kiln can be obtained only by emitting the calcination heat of raw materials from the kiln. At the same time, it gives the possibility of significant increase of the kiln productivity, which was already no longer limited by the heat quantity, linked to the kiln burner. In this technology, the kiln burner was only applied to heat the material in the kiln from the temperature of 1100°C to 1450°C, which was fulfil about 15% of the heat, from the entire heat demand of clinker burning. It will be 3050 x 0.15 equal to about 480 kJ/kg of clinker. As is known in the clinker formation process, radical changes of the properties of the roasting material occur, which are started at the temperature of 1260°C and are linked with the liquid phase appearing. After the liquid phase appears, the process cannot be conducted in the fluid reactor, because the material can form the roasting formation on the reactor walls, which can cause its plugging. From these reasons, the best technological solution was the division of the process into two operations, applied in two different equipments: (a) heating and calcining conducting in the fluid heater, which was the preliminary calciner, and (b) sintering and clinker formation in the rotary kiln. This technological division caused the high kiln capacity, because the quantity of heat needed in the kiln was low and the heat charge of the zone of fuel burning in the kiln burner was also low

Utilization of cement rotary kiln waste heat for calcination of phosphogypsum

The cement industry nowadays is giving thrust to replace and reduce fossil fuel-based energy through recovery of waste heat, utilization of wastes (Alternative fuels) and adoption of renewable energy sources like wind energy, solar PV systems etc.In cement plants, high temperature heat is released into the atmosphere through exhaust flue gases, radiation and convection heat from hot and exposed surfaces like rotary kiln. A lot has already been explored about recovery of waste heat from exhaust hot flue gases. Many Indian cement plants have installed Waste Heat Recovery Systems (WHRS) at their facility for generating electricity by using heat energy in hot flue gases. At present cumulative generation capacity is estimated as ~344 MW from such WHRS facilities in Indian cement plants.Indian cement industry is facing issues about limited availability of the mineral gypsum. This is going to be more critical with possible restrictions over mineral gypsum import in India. On the other hand, the huge inventory of phosphogypsum is a challenge for phosphoric acid manufacturing plants. Phosphogypsum can’t be used without processing in the cement production process due to adverse impact on cement properties. Processing of Phosphogypsum requires high temperature and if the temperature is raised through fossil fuel combustion then it will add to extra cost and associated Green House Gas (GHG) emissions. Heat recovery from kiln hot shell surfaces can be explored for phosphogypsum calcination purpose here. A feasibility concept of phosphogypsum calcination through kiln waste heat recovery is discussed in this paper.

Effect of calcination process on performance of 3DOM CeMnO3 catalysts

A series of 3DOM CeMnO3 perovskite catalysts were prepared by poly(methyl methacrylate) hard-templating-excessive impregnation method at calcination temperature of x °C (x = 600, 700, 800) and the heating rate of y °C/min (y = 1, 2, 5, 10). The samples were characterized by Brunauer-Emmett‐Teller method, scanning electron microscopy, transmission electron microscopy, H2‐temperature programmed reduction, X‐ray photoelectron spectroscopy, X‐ray diffraction, moreover, the effect of the calcination process on the catalytic activity of the samples were discussed by the catalytic combustion of toluene. The results show that the 3DOM CeMnO3 catalysts calcined at 600 °C promote the formation of a perovskite structure, inhibit the reduction of the Mn4+ species in the catalyst with high temperature. The catalyst expresses the complete macroporous structure, large specific surface area (38.8 m2/g), higher adsorption oxygen concentration and Mn4+ substance concentration, with a low T90%=172 °C. By preparing the catalysts at different calcination heating rates, it can be concluded that the catalyst possesses a high concentration of adsorbed oxygen and a low reduction temperature and a large specific surface area (40.42 m2/g) greatly promotes adsorption stage catalytic oxidation reaction and catalytic combustion of toluene at low temperature under the heating rate of 5 °C/min. When the heating rate is 1 °C/min, the catalyst has a complete macroporous structure (>250 nm), which is beneficial to the exchange of macromolecular substances during the catalytic reaction and the catalyst has a high concentration of lattice oxygen suitable for the catalysis of toluene in high temperature flue gas combustion.

Niobium Pentoxide Nanorods for the Determination of Dissolved Oxygen in Aqueous Media

Niobium oxides are a group of materials with great potential for applications within various research fields. The wide variety of Nb-O bonds, structures and allotropic forms results in unique properties, extensively described in literature as catalyst for various chemical reactions. Since this material has shown itself promising for catalytical applications, the goal of this study was to investigate its performance for the fabrication of a sensor device for the electrochemical determination of dissolved oxygen, which is of fundamental importance in areas such as environmental monitoring. Thus, a hydrothermal synthesis was used to obtain the niobium oxide and samples that, beyond the hydrothermal process, underwent calcination heat treatment, were compared. The obtained niobium oxides were morphologically analyzed through SEM and Raman spectroscopy. The hydrothermal synthesys produced amorphous niobium pentoxide nanorods, while the calcination heat treatment resulted in crystalline niobium pentoxide. The electrochemical behavior was studied through cyclic voltammetry and the pH effect over the oxygen reduction reaction was taken into consideration. The amperometric response of the sensor between the working electrode and a saturated calomel reference electrode was measured in a 0,5 M lithium perchlorate (LiClO4) solution. Results have shown that the synthesized niobium pentoxide is a promising material for the determination of the dissolved oxygen in aqueous media since it showed and electrocatalytic activity towards the oxygen reduction reaction. The amperometric response has shown itself linearly related to the concentration of the dissolved oxygen and detected concentrations below 1mg/L.

An environment-friendly process for limestone calcination with CO2 looping and recovery

Abstract Lime production represents the second largest contributor to industrial CO2 emission in China, but it has not been well addressed. Herein, an efficient and environment-friendly Limestone Calcination Process with CO2 Looping and Recovery (LCPCLR) is established to solve the associated environment issue. CO2 serves as heat carrier in the LCPCLR system, which provides heat for the limestone calcination. The limestone calcination occurs in pure CO2 environment, and the calcination temperature is around 900 °C when CO2 pressure (PCO2) is at ∼1 atm. CaCO3 decomposition is inhibited when PCO2 exceeds the CO2 equilibrium pressure (PCO2eq), and the inhibition can be solved by increase of temperature. PCO2/PCO2eq is suggested to be kept below 0.25 to achieve an efficient calcination process. Both higher temperature and larger gas-solid water equivalent ratio (ηg/s) can enhance the limestone calcination. To replace the pure CO2 with CO2/H2O(g) mixture as the carrier gas is a promising way to enhance efficiency of the calcination process. Through the LCPCLR, more alternative fuels can be used to reduce the operating cost, and CO2 emission is reduced by around 780 kg per ton of lime manufacturing.

In situ construction of yolk-shell zinc ferrite with carbon and nitrogen co-doping for highly efficient solar light harvesting and improved catalytic performance

In this work, carbon and nitrogen co-doped yolk-shell ZnFe2O4 nanostructures (CN-ZnFe2O4) were successfully synthesized through a facile self-templated method with in situ doping strategy. A series of characterizations were processed to present a comprehensive properties of the as-prepared photocatalyst samples. Doping amount could be moderated by the addition mass of dopamine, which was regarded as both the carbon and nitrogen source. And the void space between yolk and shell could be adjusted by heating rates in the calcination process of precursors. With an excellent separation efficiency of photogenerated electron-hole pairs and transfer efficiency of photogenerated electrons, the obtained CN-ZnFe2O4 sample exhibited an enhanced visible light response than ZnFe2O4. And their photocatalytic performances towards gaseous 1, 2-dichlorobenzene (o-DCB) was also systematically studied. The results demonstrated that the CN-ZnFe2O4 sample with 100 mg dopamine addition and 20 °C/min calcination heating rate exhibited the best o-DCB degradation efficiency. In situ Fourier Transform infrared (FTIR) spectroscopy was also recorded to give a detailed information of intermediate products and reveal the mechanism of photocatalytic degradation towards o-DCB. Particularly, density functional theory (DFT) calculation was used to further study the electronic structure of prepared samples to support the experimental results and especially explain the mechanism of enhanced photocatalytic activity through a proposed lattice junction. Additionally, electron paramagnetic resonance (EPR) technique was carried out to prove the reactive oxygen species involved in the photodegradation process. This work not only presents a promising strategy in photocatalyst fabrication but also provides a new sight of enhanced photocatalysis mechanism.

Synthesis of photoluminescent β-Ga2O3 nanostructures using electrospinning method, and control of length-diameter ratio by calcination heating rates

Nanofiber precursors of PVP-Ga(NO3)3 were synthesized through the electrospinning technique, and monoclinic β-Ga2O3 patterns were later obtained through the calcination method. During the annealing process, the nanofibers’ pores decreased, and their lengths were uniform up to several micrometers due to the surface-to-core extension that comprises the crystallization through Ostwald ripening process. Synthesis on the structure and morphology of materials were investigated using scanning and transmission electron microscopy equipped with an energy dispersive spectrometer, X-ray diffraction, Raman and Fourier-transform infrared (FTIR) spectroscopies. The β-Ga2O3 optical properties disclosed very broad and intense photoluminescence emission spectrum in the blue region of the wavelength, whose driving force was the presence of oxygen vacancies in the structures. Two types of Ga3+ ions (GaO6 octahedral and GaO4 tetrahedral chains) were demonstrated to come from different vibrations of Ga–O bonds in the Raman and FTIR spectra. And Ga3+–CO adducts formed on coordinatively Ga3+ ion located at edges and corners of β-Ga2O3 crystallites. Thus, successful results of this work included the control of length-diameter ratio by calcination heating rates, as well as the broad blue emission band, representing a strong potential of β-Ga2O3 materials in optoelectronic applications.

Dispatchability of solar photovoltaics from thermochemical energy storage

Solar photovoltaic plants are today a competitive alternative to power plants based on fossil fuels. Cost reduction in photovoltaics modules, scalability and ease of installation of these plants are enabling a rapid worldwide expansion of the technology. Nevertheless, dispatchability still remains as the major challenge to overcome due the intrinsic variability of solar energy. Most of the current solar photovoltaic facilities at large scale lack energy storage while those with storage systems rely on expensive batteries. Batteries are based on elements such as nickel, lithium or cadmium whose scarcity hinder their sustainability for storing energy in the large scale. This manuscript presents a novel concept to integrate thermochemical energy storage in photovoltaic plants. Furthermore, the concept is also directly adaptable to wind power plants to store surplus energy. The paper analyses the suitability of the Calcium-Looping process as thermochemical energy storage system in solar photovoltaics plants. The system works as follows: part of the power produced in the solar plant provides electricity to the grid while the rest is used to supply heat for calcination of calcium carbonate. After calcination, the products of the reaction – calcium oxide and carbon dioxide- are stored separately. When power production is required, the stored products are brought together in a carbonation reactor wherein the exothermic reaction releases energy for power production. The overall system is simulated to estimate the process behaviour and results show that storage efficiencies of ∼40% can be achieved. Moreover, an economic analysis is developed to compare the proposed system with batteries. Due to the low price of natural calcium oxide precursors, such as limestone, and the expected longer lifetime of equipment as compared to batteries, the Calcium-Looping process can be considered as a potential alternative for improving dispatchability in solar photovoltaic plants.

The effect of calcination rate on the structure of mesoporous bioactive glasses

Mesoporous bioactive glasses (MBGs) are designed to have high specific surface area. They are formulated by a sol–gel process to formulate the glass followed by calcination. This study evaluates how calcination heating rate influences the porous architecture, and thereby the specific surface area, of MBGs. MBGs of molar ratio 80:15:5 for SiO2:CaO:P2O5 were calcined using both low (1 °C/min) and high (20 °C/min) heating rates, termed as L-MBG and H-MBG, respectively. The results obtained from small-angle X-ray diffraction (SAXRD) confirm that the MBGs possess 2D hexagonal (P6mm) spacing groups and wide-angle XRD confirms the amorphicity of both MBGs. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirm that both batches of MBGs have similar chemical composition. Fourier transform infrared spectroscopy identifies the same functional groups present in both batches. However, transmission electron microscopy indicates that H-MBG samples exhibited discontinuities in their ordered channel structure, confirmed by the lower SAXRD peak intensity of H-MBG compared to L-MBG. These discontinuities led to a reduced surface area. L-MBG exhibits more than quadruple the surface area and double the pore volume (373.87 m2/g and 0.27 cm3/g) of H-MBG (85.91 m2/g and 0.13 cm3/g), measured through Brunauer, Emmett, and Teller nitrogen adsorption analysis. This higher surface area resulted in a significant (p < 0.05) increase in the quantity of ion release from the L-MBGs compared to the H-MBGs. It is concluded that the application of a low heating rate during calcination, of the order of 1 °C/min, is more likely to result in ordered mesoporous bioactive glasses with high surface area and pore volume than MBG samples processed at a higher heating rate.

Thermo-chemically tuning of active basic sites on nanoarchitectured silica for biodiesel production

In the design of catalysts, an extremely important point is to determine, control and increase the availability of active sites on the surface. In the present work, active sodium oxide species have been identified and it is demonstrated how its dispersion can be suitably improved by combining sodium loading degree and calcination heating rate in order to increase the catalyst basic character and consequently, its performance. The different synthesized materials were characterized by: small-angle X-ray scattering (SAXS), high angle X-ray diffractions (XRD), atomic absorption spectroscopy (AA), BET method (specific surface determination), Fourier-transform infrared spectroscopy (FT-IR), carbon dioxide temperature programed desorption (CO2 TPD) and X-ray photoelectron spectroscopy (XPS). The obtained catalyst using 10 wt% of sodium loading followed by calcination at 500 °C, employing an 8 °C/min heating rate, showed the highest activity towards the transesterification of sunflower oil reaction (5 h, 60 °C, 14:1 methanol to oil molar ratio, 2 wt% catalyst, vigorous magnetic stirring), achieving a 90% biodiesel yield.