Sorbent Reactivity Research Articles

Performance evaluation and sensitivity analysis of polyethyleneimine-based sorbent in a circulating fluidized bed carbon dioxide capture unit

Greenhouse gases, particularly carbon dioxide, have increased the Earth’s average temperature by 1 °C, which has resulted in significant consequences for human life. To prevent further global warming and maintain a stable lifespan, it is imperative to achieve carbon neutrality. Post-combustion capture using an amine-based aqueous solvent is an advanced technology that has gained attention, but there are challenges such as corrosion, environmental impact, and energy consumption associated with it. This study aims to evaluate the performance of a polyethyleneimine-based sorbent in a circulating fluidized bed carbon dioxide capture unit and to determine the optimal operating conditions through sensitivity analysis. Various variables, including carbon dioxide concentration, water vapor content, desorber temperature, and sorbent residence time, were analyzed. The unit was continuously operated for 128 h even under challenging conditions with higher oxygen concentrations than the actual flue gases, and sorbent degradation was negligible. The results showed a 55 % carbon dioxide removal efficiency, a dynamic sorption capacity of 0.041 g-CO2/g-sorbent, and a regeneration heat energy of 4.2 GJ/tCO2. Sensitivity analysis revealed that there was minimal improvement even with changes in the absorber structure and physical properties of the sorbent. Only an increase in the sorbent reaction rate had a significant effect. If the reaction rate were to double, the carbon dioxide removal efficiency would reach 90 %, with a dynamic sorption capacity of 0.068 g-CO2/g-sorbent and regeneration heat energy of 2.9 GJ/tCO2.

Aspen plus-based techno-economic assessment of a solar-driven calcium looping CO2 capture system integrated with CaO sorbent reactivation

Given the gradual nature of the energy transition, retrofitting coal-fired power plants with carbon capture technology is crucial. The calcium looping (CaL) process is a promising solution, with challenges like absorbent deactivation and reduced thermal efficiency mitigated by absorbent reactivation and heat recovery systems. This study evaluated the techno-economic feasibility of integrating a novel wet extraction and precipitation process for absorbent reactivation within a solar-assisted CaL system, alongside an existing coal power plant. The process incorporated a secondary steam cycle and an ammonia absorption chiller for enhanced heat recovery and district cooling. The integrated project could increase daily power generation by 50% and reduce CO2 emissions from 820.4 g/kWh to 54.5 g/kWh. Over its lifespan, the reactivation facility could reduce limestone extraction by 21 Mt with 90% capture efficiency. With a levelized cost of electricity (LCOE) of 116.1 €/MWh and breakeven electricity selling price (BESP) of 56.6 €/MWh, the system demonstrated promising commercial viability, with the reactor and concentrated solar heating (CSH) system making up over 60% of investment costs. CSH cost and solar abundance were identified as key factors, indicating potential feasibility even in higher latitude regions. At CO2 revenues of 150 €/t, a stand-alone capture project can break even based solely on CO2 sales, demonstrating its potential for expansion to other areas. A case study highlighted the benefits of integrating absorbent reactivation and an ammonia absorption chiller, improving both economics and carbon capture efficiency. The study also confirmed the viability of solar-assisted projects in high-latitude regions, with optimistic future CO2 revenues and advancements in carbon capture technology enhancing feasibility.

Synergistic effects of CeO2 and Al2O3 on reactivity of CaO-based sorbents for CO2 capture

The calcium looping (CaL) process, comprising reversible calcination and carbonation reactions with CO2 and CaO-based sorbents, stands out as a highly promising industrial approach for CO2 capture. A significant challenge, however, is the swift degradation of the reactivity of CaO-based sorbents. In this study, CeO2-stabilized and CeO2/Al2O3 co-stabilized CaO-based sorbents were produced via a Pechini technique. Results indicated that incorporating CeO2 enhanced the CO2 sorption performance of CaO-based sorbents. The most effective CeO2-stabilized CaO-based sorbents (a CeO2/CaO mass ratio of 15:85) demonstrated an initial sorption capacity of 0.479 gCO2/gmaterial, undergoing a 41% reduction in its initial reactivity by the 20th cycle. To enhance CO2 sorption stability and reduce the high cost linked with the expensive cerium precursor, Al2O3 was introduced as the second stabilizer into the CeO2-stabilized CaO-based sorbents. When the CeO2/Al2O3/CaO mass ratio was adjusted to 5:10:85, the CO2 sorption capacity of CeO2/Al2O3 co-stabilized CaO-based sorbents reached 0.354 gCO2/gmaterial in the 20th cycle. This represented only a 17.7% reduction in its initial performance, surpassing the CeO2-stabilized counterpart by 26.3%. Comprehensive characterizations, including scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), and electron paramagnetic resonance (EPR), revealed that incorporating Al2O3 into the CeO2-stabilized CaO-based sorbents served a dual purpose: acting as a stable framework to inhibit pore structure deterioration and increasing the concentration of oxygen vacancies. In consequence, the synergistic effect of CeO2 and Al2O3 improved both structural stability and oxygen vacancy concentration of the sorbents, ultimately leading to superior CO2 sorption performance.

New Approach for Sulfidation Process in Packed Bed with Hi-Fuel A310 Sorbent—Thermodynamical Studies

This paper presents tests related to the reactivity of commercial Hi-Fuel sorbent toward H2S (H2S/N2 mixture) in a packed bed at 300 °C. The sorbent used for breakthrough test was characterized before and after test by ESEM-EDX, FTIR-ATR, Raman, and elemental analyses. Testing reveals that the commercial sorbent contains two compounds reacting with H2S: ZnO and ZnCO3. According to thermodynamical studies, the reactivity of ZnCO3 at 300 °C is privileged (KR = 9.5 × 108) than ZnO (KR = 6.6× 106). In addition, the reaction of H2S with ZnCO3 induces a volume decrease, which promotes the movement of gas through the newly formed layer. The properties of this sorbent thus hold a good potential for the desulfurization process of gases polluted with H2S. We observed that the maximum sulfidation rate was reached on the surface of the sorbent and showed a maximum conversion of 27%.

Pelletizing and acid modifying of Zr-stabilized CaO-based sorbent for cyclic high-temperature CO2 capture

The process of calcium looping (CaL), which contained reversible carbonation/calcination periods, was one of the most promising candidates for high-temperature CO2 capture. Herein, kilogram-scale of Zr-stabilized CaO sorbent pellets were granulated via extrusion-spheronized methods, in which Zr species were well scattered into the CaO particles and effectively alleviated the thermal sintering. A typical binder of pseudo-boehmite (PB), with two types of peptizers including nitric acid (NA) and malonic acid (MA), was incorporated to improve the sorption capacity and mechanical strength of the sorbent pellets. The results revealed that the presence of PB, which provided mechanical strength to the pellets due to the binder effect, can promote the cyclic sorption capacity and thermal stability for pure CaO but had an adverse impact on the reactivity of the Zr-doped sorbent. And peptizer was employed to achieve homogeneity and enhance the strength of the pellets, for it can take chemical reaction with the hydroxyl groups on the surface of PB and disintegrate the PB particles into aluminum sol. In particular, the Ca/Zr sorbent pellets modified by MA were superior to the unmodified sorbent both on CO2 capture performance and mechanical strength due to the formation of smaller and dispersed CaO crystal particles.

Understanding the Selective Extraction of the Uranyl Ion from Seawater with Amidoxime-Functionalized Materials: Uranyl Complexes of Pyrimidine-2-amidoxime

The study of small synthetic models for the highly selective removal of uranyl ions from seawater with amidoxime-containing materials is a valuable means to enhance their recovery capacity, leading to better extractants. An important issue in such efforts is to design bifunctional ligands and study their reactions with trans-{UO2}2+ in order to model the reactivity of polymeric sorbents possessing both amidoximate and another adjacent donor site on the side chains of the polymers. In this work, we present our results concerning the reactions of uranyl and pyrimidine-2-amidoxime, a ligand possessing two pyridyl nitrogens near the amidoxime group. The 1:2:2 {UO2}2+/pmadH2/external base (NaOMe, Et3N) reaction system in MeOH/MeCN provided access to complex [UO2(pmadH)2(MeOH)2] (1) in moderate yields. The structure of the complex was determined by single-crystal X-ray crystallography. The UVI atom is in a distorted hexagonal bipyramidal environment, with the two oxo groups occupying the trans positions, as expected. The equatorial plane consists of two terminal MeOH molecules at opposite positions and two N,O pairs of two deprotonated η2 oximate groups from two 1.11000 (Harris notation) pmadH− ligands; the two pyridyl nitrogen atoms and the –NH2 group remain uncoordinated. One pyridyl nitrogen of each ligand is the acceptor of one strong intramolecular H bond, with the donor being the coordinated MeOH oxygen atom. Non-classical Caromatic-H⋯X (X=O, N) intermolecular H bonds and π–π stacking interactions stabilize the crystal structure. The complex was characterized by IR and Raman spectroscopies, and the data were interpreted in terms of the known structure of 1. The solid-state structure of the complex is not retained in DMSO, as proven via 1H NMR and UV/Vis spectroscopic techniques as well as molar conductivity data, with the complex releasing neutral pmadH2 molecules. The to-date known coordination chemistry of pmadH2 is critically discussed. An attempt is also made to discuss the technological implications of this work.

Revealing the mechanism of oxygen vacancy defect for CO2 adsorption and diffusion on CaO: DFT and experimental study

The calcium looping is a promising technology to achieve industrial CO2 capture, and the introduction of oxygen vacancy can promote the CO2 capture reactivity of CaO-based sorbents. In this work, DFT calculations were performed to investigate the CO2 adsorption by CaO in the presence of oxygen vacancy defect. The presence of oxygen vacancy reduces the band gap of CaO surface, which results from the delocalization of Ca 2p orbital. Besides, the electron accumulation at the oxygen vacancy occurs due to the unsaturated Ca-O bonds, and the reaction possibility is promoted neighbouring the defect. The top site of oxygen vacancy defect of CaO is favourable for CO2 adsorption. The adsorption energy of CO2 on CaO with oxygen vacancy achieves − 2.52 eV, which is 1.81 times as high as that on pristine CaO. Due to strong interaction between CO2 and CaO with oxygen vacancy, CO2 migration from this site is more difficult, while the following diffusion is more prone to occur. In the presence of steam, CO2 adsorption energy is enhanced to − 2.70 eV on CaO with oxygen vacancy, and the distance from CO2 radical to surface is intuitively reduced, which results from the electrons donated from defect and neighbouring Ca atoms, while CO2 diffusion difficulty is increased. This work provides an incisive investigation for structural, electronic, and thermodynamic characteristics of CO2 adsorption and diffusion on CaO in the presence of oxygen vacancy defect, and it can shed light on rational synthesis and functional design of surface-active sites of CaO-based sorbents.

Enhanced Sewage Sludge Gasification by Bauxite‐Modified Carbide Slag for Hydrogen‐Rich Syngas Production with In Situ CO2 Capture

Calcium‐looping gasification is attractive to dispose massive sewage sludge for hydrogen‐rich syngas with in situ CO2 capture but still challenged by apparent drop of CO2 sorbent reactivity, sorbent attrition, and uncertainty of sorbent performance during multi‐cycle gasification. Herein, bauxite‐modified carbide slag is prepared as a cheap CaO‐based CO2 sorbent by a simple mechanical mixing method. Based on physical and chemical characterization as well as thermogravimetric analyses, it is found that the bauxite‐modified carbide slag (CS) contained the inert component of mayenite, which is beneficial to improve pore characteristic and promote stability and mechanical strength of sorbent during multi‐cycle CO2 capture. Fluidized bed gasification tests verify that adding carbide slag increases H2 yield and efficiency of sewage sludge gasification. Moreover, appropriate increase in reaction temperature and steam flow rate enhances sewage sludge gasification with bauxite‐modified carbide slag. During multi‐cycle fluidized bed gasification, modified carbide slag CS‐5 (with 5 wt% bauxite) presents more stable performance and better anti‐attrition characteristic in comparison to carbide slag without modification. After five cycles of fluidized bed gasification, the yield and concentration of H2 are increased while the fraction of fine particles produced by attrition is largely decreased for CS‐5 in comparison to ordinary carbide slag.

Highly active mesoporous Co–Al2O3 sorbents for the efficient destructive sorption of NF3

Nitrogen trifluoride (NF3) is widely used as an etching gas and cleaning agent in the microelectronics industry. However, it is a novel and powerful greenhouse gas. The destructive sorption of NF3 over metal oxides is an efficient route to control its emission. Here, several sorbents of homogeneous Co–Al2O3 oxides were prepared via changing the molar ratios of HNO3 to Al(OPri)3 in the raw materials, whose impact on the structure of sorbents and the reactivity for NF3 destructive sorption was investigated. It is found that the destructive reactivity of sorbents is strongly affected by their surface area and pore volume. Impressively, the optimal Co–Al2O3-2.45 sorbent with the largest surface area and pore volume presents the longest time of NF3 complete destruction, which is clearly more active than most of the results in the literature. Furthermore, the F migration over the solid interfaces between Al2O3 and Co oxides in Co–Al2O3 sorbents enhances the efficient destruction of NF3. These findings well explain the better reactivity of Co–Al2O3 complex oxides than bare Al2O3, and are beneficial to develop more efficient sorbents for NF3 destruction.

Magnesite as a Sorbent in Fluid Combustion Conditions—Role of Magnesium in SO2 Sorption Process

This article presents the results of research on magnesites from the Polish deposits of Szklary, Wiry and Braszowice as SO2 sorbents under the conditions of fluidized bed combustion technology. In practice, magnesites are not used as SO2 sorbents, and the role of magnesium in the desulfurization process under the conditions of fluidized bed combustion technology is evaluated differently among researchers. The literature data question the participation of magnesium in the process of SO2 capture from flue gas and prove its high reactivity. Similarly, previous studies referred to the problem of the stability of magnesium-containing desulfurization products under high temperature conditions. This paper analyzes the SO2 binding process and determines the parameters of the sorbent responsible for the efficiency of magnesite sorption. It was shown that MgO, formed as a result of thermal dissociation of magnesite, actively participates in the SO2 binding reaction to form magnesium sulfate phases (MgSO4 and CaMg2(SO4)3) stable in the temperature conditions of fluidized bed boilers. The problem of differentiated reactivity of magnesium-containing sorbents should be associated with the porosity of the sorbents. If the secondary surface of the sorbent is developed based on micropores and smaller mesopores (below 0.1 µm), the sorbent will be characterized by low sorption activity. It was shown that the SO2 binding process is then limited only to the outer part of the sorbent grains. This results in the formation of a massive, SO2-impermeable desulfurization-product layer on the sorbent grain surface. In real conditions, where the reactions of CaCO3 thermal dissociation and SO2 sorption occur almost simultaneously, the inside of the sorbent grains may remain undissociated. The results of experimental research allowed us to trace the dynamics of the SO2 binding process in relation to real conditions prevailing in fluidized bed boilers.

Sorption and oxidation of Co(II) at the surface of birnessite: Impacts of aqueous Mn(II)

The sorption of aqueous Mn(II) (1 mM) and Co(II) (50 and 200 μM) onto hexagonal birnessite (0.1 g L−1) was studied under anoxic conditions at pH 6.5 and 7.5 in binary and ternary experiments using batch kinetic experiments and XRD, ATR-FTIR, and Co K-edge EXAFS analyses. In the binary systems, sorption of Co(II) was accompanied by partial oxidation to Co(III) yielding a mixture of corner-sharing Co(II) and edge-sharing Co(III) complexes at both pH values, while Mn(II)-birnessite interaction resulted in coordination of Mn(II/III) at layer vacancy sites at pH 6.5, and led to reductive transformation of birnessite into feitknechtite at pH 7.5. In the ternary systems, strong mutual interferences between Co(II) and Mn(II) co-sorbates reduced the rate and extent of sorption relative to the binary experiments. The introduction of Mn(II)aq into the high-Co systems (200 μM) halted the slow sorption of Co(II) that was attributed to the incorporation of Co(III) into layer vacancies, while Co(II)aq prevented Mn(II)-driven transformation of birnessite into feitknechtite at pH 7.5. In the low-Co system (50 μM), reductive transformation of birnessite by Mn(II)aq at pH 7.5 produced Co(II)-substituted feitknechtite, a conversion that was accompanied by reduction of sorbed Co(III) to Co(II) which was partially released to solution. The strong effects of co-sorption are attributed to the similarity in sorption mechanisms of Co(II) and Mn(II), which both sorb as a mixture of di- and trivalent species. The results of this work demonstrate that aqueous Mn(II) may significantly affect the reactivity of phyllomanganate sorbents towards dissolved Co(II), and therefore impact the speciation and solubility of this trace metal in anoxic and suboxic geochemical environments.

In Situ XRD, Raman Characterization, and Kinetic Study of CO2 Capture by Alkali Carbonate-Doped Na4SiO4

Sodium silicate, a new type of CO2 sorbent, has a relatively low cost, but its sorption reactivity is not yet good enough. Alkali carbonate doping is commonly used as an effective means to improve the CO2 uptake reactivity of solid sorbents. In this study, sodium orthosilicate, Na4SiO4, was synthesized and mixed with 5, 10, and 20 mol% of Li2CO3–Na2CO3 or Li2CO3–Na2CO3–K2CO3 as CO2 sorbents. The promotion of alkali carbonates on Na4SiO4 in CO2 capture was characterized using thermal analyses in an 80 vol% CO2–20 vol% N2 atmosphere. The phase evolution and structural transformations during CO2 capture were characterized by in situ XRD and Raman, and the results showed that the intermediate pyrocarbonate, C2O52−, which emerged from alkali carbonates, enhanced the CO2 capture of Na4SiO4 to form Na2CO3 and Na2SiO3 from 100 °C. Isothermal analyses showed that 10 mol% of Li2CO3–Na2CO3 was the optimal additive for Na4SiO4 to attain better CO2 uptake performance. The alkali carbonates were effective in reducing the activation energy for both chemisorption and bulk diffusion, improving the cycle stability of Na4SiO4.

Effect of steam addition during calcination on CO2 capture performance and strength of bio-templated Ca-based pellets

Enormous efforts have been devoted to improving the cyclic reactivity of the Ca-based sorbent for cyclic CO2 capture. Steam reactivation is one of the most promising technologies to regenerate the CO2 capture performance of the Ca-based sorbent remarkably. However, the strength of the pellets during the steam reactivation process is insufficiently investigated. This study examined the influences of steam addition during calcination on the CO2 capture capacity and mechanical strength of the bio-templated sorbent over multiple carbonation-calcination cycles. A CO2 uptake of 0.31 g/g was achieved after 20 cycles by adding 30 % steam into the calcination atmosphere, which is 2.2 times higher than the cycles without steam injection. After the long-term test up to 100 cycles with 30 % steam in the calcination environment, a 6-fold increase in the average crushing force of the pellets was observed. The enhancement of the mechanical strength was attributed to the synergy effect of thermal sintering and atmosphere-induced sintering. Generally, steam addition during calcination demonstrated great potential in retaining CO2 capture capacity and improving the mechanical strength of the bio-templated sorbent.

Sr2CeO4 as a robust high temperature sorbent for CO2 capture with near 100% sorbent conversion efficiency

As a typical CO2 capture and storage (CCS) technology, sorbent looping CO2 capture (SLCC) can be incorporated into CO2-related processes to enable potential revenue. The main challenge of the SLCC is the poor reactivity stability and limited operation temperature of sorbent. High temperature sorbent of SrO was prepared with sol–gel method and the carbonation/calcination performance was evaluated in thermogravimetry. The effect of different support materials (Al2O3, Y2O3, MgO, CeO2 and ZrO2) on the reactivity stability was initially evaluated during 25 carbonation/calcination cycles. The CeO2 supported sorbent exhibited super stable CO2 capture performance, whereas other materials could not stabilize the sorbent reactivity over multiple cycles. Afterwards, the effect of CeO2 loading on the sorbent reactivity, microstructure and phase transition was further identified. The results indicate that the Ce-Sr interaction induced new decarbonation path of SrCO3 + CeO2 = Sr2CeO4 + CO2 instead of conventional thermal sorbent decomposition of SrCO3 = SrO + CO2. It promoted the reaction kinetic and enabled the carbonation/calcination at a lower temperature. Also, it improved the microstructure and the sintering resistance, promoting sorbent reactivity stability. The ratio of Ce/Sr higher than 0.5 was necessary to obtain a stable CO2 capture performance with almost 100% sorbent efficiency over multiple cycles.

Effect of the Presence of HCl on Simultaneous CO2 Capture and Contaminants Removal from Simulated Biomass Gasification Producer Gas by CaO-Fe2O3 Sorbent in Calcium Looping Cycles

This study investigated the effect of HCl in biomass gasification producer gas on the CO2 capture efficiency and contaminants removal efficiency by CaO-Fe2O3 based sorbent material in the calcium looping process. Experiments were conducted in a fixed bed reactor to capture CO2 from the producer gas with the combined contaminants of HCl at 200 ppmv, H2S at 230 ppmv, and NH3 at 2300 ppmv. The results show that with presence of HCl in the feeding gas, sorbent reactivity for CO2 capture and contaminants removal was enhanced. The maximum CO2 capture was achieved at carbonation temperatures of 680 °C, with efficiencies of 93%, 92%, and 87%, respectively, for three carbonation-calcination cycles. At this carbonation temperature, the average contaminant removal efficiencies were 92.7% for HCl, 99% for NH3, and 94.7% for H2S. The outlet contaminant concentrations during the calcination process were also examined which is useful for CO2 reuse. The pore structure change of the used sorbent material suggests that the HCl in the feeding gas contributes to high CO2 capture efficiency and contaminants removal simultaneously.

Assessment of the Impact of Modification of Calcium Sorbents and the Possibility of Their Use in Desulfurization for Oxy-Fuel Combustion Process

The paper describes the possibilities of simple and effective modification of calcium sorbents used for flue gas desulfurization with a size between of 125–250 µm. The additives to the sorbents in the amount of 0.5% and 1.0% were inorganic sodium and lithium compounds. The research on the reactivity of sorbents was analyzed in the process of simultaneous calcination and sulfation at the temperature of 850 °C. The type of Na+ or Li+ cations and the inorganic salt anions have an influence on the modification of calcium sorbents in order to improve the efficiency of the calcination and sulfation process. Modification of calcium sorbents by adding inorganic sodium and lithium compounds, regardless of the amount, changes the reactivity coefficient RI [mol/mol] and the absolute sorption coefficient CI [g S/kg sorbent]. In the case of inorganic sodium salt (Additive 1), regardless of the amount of modifier added, there was a visible improvement in the reactivity of the sorbent: 1.0% of the additive caused an increase in the RI coefficient in relation to the raw sorbent by over 14%, and in the case of the CI coefficient by over 24%. Additional research was the analysis of the limestone behavior mechanism during the simultaneous calcination and sulfation (SCS) process under conditions of elevated temperature and with variable CO2 and O2 contents in the flue gas. The behavior of sorbents with a size distribution of 125–250 µm was assessed on the basis of the change in mass of the samples by determining the reactivity coefficient RI, [mol/mol] and the absolute sorption coefficient CI, [g S/kg sorbent]. Using the mercury porosimetry technique, the change in sorbent porosity in the subsequent stages of the simultaneous calcination and sulfation process was investigated. The process was carried out in the temperature range corresponding to the oxy-combustion (i.e., from 850 °C to 1000 °C).

Effect of calcination temperature and extent on the multi-cycle CO2 carrying capacity of lime-based sorbents

This paper investigates the effect of calcination temperature and duration on the cyclic CO2 capture performance of natural lime-based sorbents. Tests showed that increasing calcination temperature considerably reduced the sorbent reactivity over the first few calcination-carbonation cycles. No significant variation in performance was observed when a sorbent remained at the calcination temperature after completing limestone decomposition. On the other hand, incomplete limestone calcination significantly altered the sorbent cyclic utilization and CO2 carrying capacity. A semi-empirical method is proposed to estimate the fast reaction-controlled carbonation extent at different reaction cycles, calcination extents and temperatures. This method is shown to work well for two different naturally-derived limestones exposed to different calcination conditions.

Comparative study of lithium-based CO2 sorbents at high temperature: Experimental and modeling kinetic analysis of the carbonation reaction

Abstract This work focuses on the study of the CO2 capture kinetic properties and reactivity of different alkali-based sorbents. Three samples, K-doped Li2ZrO3, mixed Li2ZrO3-Na2ZrO3, and Li4SiO4, were characterized and evaluated by thermogravimetric analysis under different reaction conditions. The presence of alkali zirconate and silicate phases was confirmed by XRD and Raman spectroscopy. The Li-Na zirconate showed the fastest initial reaction rates and the strongest dependence on the temperature, while the K-doped Li zirconate presented a higher dependence on the CO2 concentration. The activation energies derived from the modeling with the double exponential and the Avrami Erofeev model were consistent with the calculated apparent activation energy. Finally, the phase evolution followed by operando Raman Spectroscopy during the capture process was in agreement with the kinetic analysis, confirming the higher reactivity of the Li4SiO4 and Li-Na zirconate derived samples.

Effect of steam addition during carbonation, calcination or hydration on re-activation of CaO sorbent for CO2 capture

Calcium looping (CaL), based on cyclic carbonation/calcination using lime-based sorbents, is a promising technology for post-combustion CO2 capture. An important obstacle of this technology is the decay of sorbent over multiple cycles. Steam re-activation is a potential approach to improve the sorbent reactivity, however, the effects of both in-situ high-temperature steam (in carbonator or/and calcinator) and ex-situ low-temperature steam (steam hydration in hydrator) are still a matter of debate. Here, a bubbling fluidised bed reactor was used to investigate three steam addition options: steam addition during carbonation stage, or during calcination stage, or intermediate steam hydration after each CaL cycle. A CaO sorbent was tested under varying steam concentrations up to 40 vol.% for 10 CaL cycles (carbonation: 650 °C, calcination: 900 °C). Compared to the dry condition, steam addition during carbonation and intermediate steam hydration were both found effective for CaO re-activation. For the former, the improved sorbent reactivity was mainly attributed to an increased pore volume enhancing the extent of carbonation in kinetic regime; while for the latter, the formation of cracks accelerated the rate of diffusion. Nevertheless, decreasing the hydration temperature was detrimental to sorbent reactivity due to enhanced sintering upon cooling. In case of steam addition during calcination, the sorbent was affected negatively or positively depending on the concentration of steam. At higher steam concentrations (20, 40 vol.%), the sorbent reactivity was significantly decreased due to sintering associated with larger pores and lower surface areas. Overall, steam addition during carbonation was recommended for sorbent re-activation.

The effect of porosity on the reactivity of calcium sorbents

Abstract The current work presents the results of seven sorbent samples investigated with respect to SO2 capture. The sorbents’ reactivity and capacity indexes were determined, and the tests were carried out in accordance with the ‘classical’ procedure for limestone sorbents. The reactivity indexes (RIs) of the tested samples were in the range of 2.57 and 3.55 (mol Ca)/(mol S), while the absolute sorption coefficients as determined by the capacity index (CI) varied between 87.9 and 120.6 (g S)/(kg of sorbent). Porosimetric analysis was also carried out and the specific surface area of the samples was found to be between 0.2 and 1.7 m2/g. The number of micro-, meso- and macro-pores in individual samples was determined from the corresponding pore size distribution histograms, and the values of sorbent RIs and CIs were correlated with the samples’ total porosity and specific surface.