Conversion Of CaCO3 Research Articles

Thermal Conversion of Coral Waste and its Utilization as Low-Cost Catalyst for Biodiesel Production

This study investigates the thermal conversion of waste coral and its utilization as a heterogeneous catalyst for biodiesel production from soybean oil. In this work, waste coral is calcined at varied temperatures of 800, 900, and 1000°C, and the effect of the calcination temperature on the physicochemical character of the solid is evaluated through Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and basicity measurement. The results show that the higher temperature facilitates the conversion of CaCO3 of the aragonite and calcite phases in raw waste coral into CaO, achieving a complete conversion at the temperature of 1000°C. Thermal conversion influences the increased surface basicity of the solid, which is associated with the higher activity for biodiesel production. Further studies on the obtained CaO as a catalyst demonstrate the catalyst dosage and the methanol-to-oil ratio as significant factors for fatty acid methyl ester production. The highest yield of 98.7% is achieved after a 3 hours reaction with 8 wt.% catalyst dosage and 9:1 methanol-to-oil ratio. The catalyst exhibits stability with an insignificantly decreased yield until the fifth usage cycle. The optimum conditions and reusability features of the calcined waste coral suggest that waste coral is a favorable CaO catalyst source for biodiesel production.

Reaction mechanism of Ca(OH)2-based carbon storage suitable for the production of building materials

The development of CaCO3 oxyfuel combustion and calcium looping techniques offers opportunities for Ca(OH)2 production with near-zero CO2 emissions. This study investigated the viability of Ca(OH)2-based CO2 storage for use in the production of building materials. To resolve the deficient strength gain of Ca(OH)2 carbonation, siliceous materials, using fly ash as a model compound, were introduced into the raw mixture, and hydrothermal curing was applied to promote the pozzolanic reaction. Two microstructural features, i.e., inner and outer CaCO3 formations, were identified during Ca(OH)2 carbonation via backscattered electron imaging. Inner CaCO3 formation is characterized by Ca(OH)2–CaCO3 conversion within the edge of Ca(OH)2 particles. Outer CaCO3 formation is characterized by the dissolution of Ca(OH)2 and the precipitation of CaCO3 in capillary pores, which generates hollow microstructures. The hollow space can be further filled by Al-tobermorite during hydrothermal curing. The prepared materials are capable of storing up to 16 % CO2 by the mass of the raw mixture. Furthermore, the pore structure influenced by inner and outer CaCO3 formation demonstrates the feasibility of adjusting the material's mechanical and CO2 storing properties by controlling the carbonation and hydrothermal curing schemes.

Insights into the thermally induced calcium carbonate oligomers solidifying heavy metals of MSWI fly ash and the mechanism of zinc on crystallization

The preparation of calcium carbonate (CaCO3) oligomers in municipal solid waste incineration fly ash (MSWI FA) is an efficient and low-carbon method for solidifying FA. This study investigated the effects and mechanisms of thermal induction on heavy metal solidification in CaCO3 oligomer fly ash (COFA). Ca in FA formed CaCO3 chains that crystallized into calcite after thermal induction, effectively solidifying heavy metals. The thermal induction temperature rather than induction time, heating rate, or cooling rate was found to be the most significant factor influencing solidification. As temperatures increased (200 °C∼400 °C), CaCO3 in COFA was transformed into calcite, improving the solidification efficiencies of Cu, Pb, and Zn from 70.02 %, 99.91 %, and 71.68 % to above 99.99 %. However, Cr’s efficiency decreased from 96.04 % to −19.66 % due to oxidation. Switching the thermal induction atmosphere from air to nitrogen reduced Cr leaching by 62.9 %. Optimal results were achieved at 300 °C for 30 minutes, with leaching concentrations below China’s reuse standard (HJ 1134–2020). Zn in FA formed oligomer networks with Ca, and then decomposed into stable ZnO during thermal induction. Additionally, Zn promoted the conversion of CaCO3 to calcite. This study provides scientific and theoretical guidance for disposing of MSWI FA using CaCO3 oligomers.

Nitrate-promoted gas–solid reactions of H2 and CaCO3 for mid-temperature integrated CO2 capture and methanation

Integrated CO2 capture and methanation (ICCM) technology has attracted increasing attention for Carbon Neutrality. However, in the mid-temperature ICCM studies dominated by MgO, which involves the gas–gas catalytic pathway, the problems of high CO2 escape and low CH4 yield are common. Replacing MgO with CaO reduced CO2 escape because the reaction proceeded via the gas–solid pathway. However, the lower CaCO3 conversion rate limits its further applications. Here, we present an ICCM process with efficient CaCO3 conversion using alkali metal nitrates (KNO3, LiNO3, and (Li-K)NO3) to promote Ru/CeO2-CaO. The results showed that the doping of nitrates led to a decrease in the specific surface area of CaO, thus losing part of the CO2 capture performance. On the other hand, forming the molten liquid layer facilitated the gas–solid reaction between CaCO3 and H2, which improved the CaCO3 conversion. Compared with the Ru/CeO2-Neat CaO without nitrate promotion, the CaCO3 conversion of Ru/CeO2-KNO3/CaO was increased by 42% and CH4 yield by 52% after five ICCM cycles. Furthermore, kinetic analysis and in situ DRIFTS experiments demonstrated that molten KNO3 facilitated mass transfer in the diffusion-controlled stage of direct CaCO3 hydrogenation.

Comparison of calcium carbonate production by bacterial isolates from recycled aggregates.

The new technology of microbially induced calcium carbonate precipitation (MICP) has been applied in construction materials as a strategy to enhance their properties. In pursuit of solutions that are more localized and tailored to the study's target, this work focused on isolating and selecting bacteria capable of producing CaCO3 for posterior application in concrete aggregates. First, eleven bacterial isolates were obtained from aggregates and identified as genera Bacillus, Lysinibacillus, Exiguobacterium, and Micrococcus. Then, the strains were compared based on the quantity and nature of calcium carbonate they produced using thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. Bacillus sp. dominated the cultured isolates and, along with Lysinibacillus sp., exhibited the highest CaCO3 conversion (up to 80%). On the other hand, Exiguobacterium and Micrococcus genera showed the poor ability to MICP (21.3 and 20.3%, respectively). Calcite and vaterite were the dominant carbonate polymorphs, with varying proportions. Concrete aggregates have proven to be a source of microorganisms capable of producing stable calcium carbonates with a high conversion rate. This indicates the feasibility of using microorganisms derived from local sources for application in construction materials as a sustainable way to enhance their characteristics.

Promotion of active H-assisted CaCO3 conversion for integrated CO2 capture and methanation

Carbonate hydrogenation is a new path for the conversion of metal carbonate with potentially lower energy consumption and CO2 emissions comparing to the traditional thermal decomposition, and the integrated CO2 capture and utilization (ICCU) represents its latest development. However, the slow hydrogenation rate of carbonate at low temperatures is one key scientific challenge for applications. Herein, we report an acidity regulation approach to prepare ZrO2-doped Ni/CaO dual-function material with good CO2 capacity, fast and highly selective conversion below 600 °C for integrated CO2 capture and utilization by methanation (ICCU-methanation). Experiments and DFT calculations show that the introduction of ZrO2 as acid sites effectively strengthens *H adsorption and reduces the formation barrier of intermediate *COOH during carbonate hydrogenation. Thus, Ni10(ZrO2)10CaO80 exhibits a CH4 STY of 14.1 mmol∙min−1∙gNi−1 at 550 °C, 6 times higher than the reference DFM. Furthermore, the presence of O2 in flue gas is observed to have no effect on ICCU-methanation, but steam could delay the in-situ methanation. Long-term cyclic test shows that the optimal Ni10(ZrO2)5CaO85 has a stable CO2 capacity of 7.5 mmol ∙gDFM−1, 98 % CO2 conversion and 95.5 % CH4 selectivity under flue gas containing both steam and O2 at 600 °C, suggesting a good potential to be applied in ICCU-methanation.

Integrated operation and efficiency analysis of CaCO3/CaO in a fixed-bed reactor for thermochemical energy storage

Calcium-based thermochemical energy storage (TCES) has attracted much attention in solar energy utilization and storage. However, the investigations of the CaCO3/CaO system are incomplete and poorly integrated at the reactor scale. In this work, a fixed-bed reactor for calcium looping (CaL) is used to conduct the integrated operation of energy storage and release. The decomposition conversion of CaCO3 in N2 at 850 °C for 8 h is 63.8% and the carbonation conversion of the corresponding decomposition product is 67.2% in CO2 at 750 °C for 4 h. The lower reactor filling increases overall thermal energy storage efficiency but decreases released energy. Furthermore, a simulation model is built to study the key operation parameters that greatly affect reactor performances. According to the orthonormal design, the high calcination temperature and porosity of 0.6–0.7 are key factors to improve both high thermal energy storage efficiency and released energy. The carbonation temperature and thermal conductivity are less important factors than decomposition temperature and porosity, which can be adjusted flexibly to meet the needs of heat utilization and cost reduction. This work provides valuable guidance for optimizing reactor operation and modifying materials to achieve high overall efficiency and released energy in fixed-bed reactors.

Comparative study of a low phosphorous co‐polymer inhibitor with commercial scale inhibitors used in cooling water systems

AbstractTo reduce the economic loss caused by scale formation and corrosion of equipment and pipelines, a low phosphorus polymer scale inhibitor is synthesized and characterized, the ability of the polymer to mitigate the calcium scale and the influences of operating conditions on CaCO3 scale are investigated by static tests. X‐ray diffraction (XRD) and scanning electron microscope (SEM) studies are performed to understand the morphological changes of the scales in the presence of the polymer. The interaction between polymer molecules and calcite crystal surface is studied by molecular dynamics simulation. The synthesized polymer is compared with the commercial product such as hydrolysis polymaleic acid (HPMA), polyacrylic acid (PAA), and 1‐hydroxy ethylidene‐1,1‐diphosphonic acid (HEDP). The experimental results show that the polymer shows better inhibition of calcium scale than the commercial product. The scale inhibition efficiency of the polymer is 92% at 10 mg/L for CaCO3 scale, 83% at 14 mg/L for Ca3(PO4)2 scale, and 98% at 6 mg/L for CaSO4 scale. SEM and XRD analysis show that the polymer induces the conversion of CaCO3 from calcite to arachite and crystal. The interaction of the polymer with both 104 and 1–10 calcite crystal surfaces are more stable than that of commercial product. The experimental results are in good agreement with those of molecular dynamics simulation.

Newly Generated Ca-Feldspar during Sintering Processes Enhances the Mechanical Strength of Coal Gangue-Based Insulation Bricks.

Coal gangue is a solid waste with low carbon content discharged during the course of the coal mining process. The resource utilization of coal gangue could solve environmental problems caused by its excessive production, such as soil contamination and land occupation. This study proposed to produce high-strength thermal insulation bricks using coal gangue as the primary material and three other mineral powders as auxiliary materials, including K-feldspar, CaCO3 and fly ash. A systematic analysis was conducted to explore the optimum raw material addition ratio and optimum sintering temperature; then, the intrinsic structure of thermal insulation bricks and their sintering formation mechanisms were revealed. The results showed that the optimal ratios of coal gangue, K-feldspar, CaCO3 and fly ash were 65 wt%, 15 wt%, 10 wt% and 10 wt%, respectively; the compressive strength of the thermal insulation brick produced under this ratio was 22.5 MPa; thermal conductivity was 0.39 W m-1 k-1. During sintering processes, mineral powders sufficiently fused to form a skeleton, and the CO2 derived from CaCO3 formed pores. The optimum sintering temperature was 1150 °C, because at this temperature, K-feldspar had the best effect in promoting the conversion of CaCO3 to Ca-feldspar. The high level of the relative crystallinity of Ca-feldspar (about 76.0%) helped raise the Si-O network's polymerization degree (NBO/T = 1.24), finally raising the compressive strength of thermal insulation bricks. The innovative method of using coal gangue to make thermal insulation bricks not only solved the environmental pollution caused by coal gangue but also provided excellent construction materials with high practical application value.

Hydrogenation of calcium carbonate to carbon monoxide and methane

The current cement, steel, refractory and calcium carbide industries rely on thermal decomposition of calcium carbonate (CaCO3) that forms calcium oxide (CaO) and carbon dioxide (CO2). Hydrogenation of CaCO3 may reduce or eliminate CO2 in CaO generation and simultaneously generate carbon monoxide (CO) and/or methane (CH4). This work mainly investigates CaCO3 hydrogenation conditions for CO and CH4 and establishes the kinetics for these reactions. It is found that CH4 forms at temperatures lower than that of CO2 but higher than that of CO. The rates of CO and CH4 formation increase with increasing hydrogen pressure (PH2) but that of CO peaks at PH2 of 0.05–0.10 MPa. The CO2, CO and CH4 yields are 17.7%, 81.4% and 0.9% at the PH2 of 0.10 MPa while 1.2%, 20.0% and 78.8% at the PH2 of 6.00 MPa. The kinetics of CaCO3 conversion and CO and CH4 formation can be better modeled by the shrinking core model (SCM) than the volume reaction model (VRM) and the gas reaction model (GRM). The activation energy (Ea) for CaCO3 conversion and CO and CH4 formation by SCM is 165.8, 156.4 and 211.9 kJ·mol−1, respectively, with the order of PH2 of 0.108, 0.005 and 0.673, respectively.

Influence of firing temperature on selected mechanical properties of alluvial clay blended with a limestone and kaolin mixture

ABSTRACT The present study investigated the feasibility of low-energy and low-cost production of ceramic products from widely available alluvial clay in Batchenga, Cameroon, using low firing temperatures. A mixture consisting of 70% kaolin and 30% limestone was prepared and used as an additive in fired alluvial clay bricks. A series of samples was prepared in which the additive made up 5, 10 or 15% of the clay products, and the samples were heated at 700, 750, 800, 850 or 900 °C. The raw materials and ceramic products were characterised using x-ray diffractometry, scanning electron microscopy, bulk density, porosity, thermogravimetry and differential scanning calorimetry analysis. The results revealed that products with 10% additive showed improved mechanical performance and densification after heating at all tested temperatures. A compressive strength of 28 MPa was recorded when the product was heated at 800 °C. A drastic decrease in performance was observed for all samples heated at above 800 °C; this was likely due to the conversion of CaCO3 into CaO, resulting in the appearance of voids within the matrix that weakened the structure. This is in line with the high-water absorption and porosity values recorded. The resultant ceramic products have potential for use in engineering applications.

A novel SAXS model for multi-texture systems: application to CaCO3 calcination using in-situ USAXS-SAXS-WAXS

SAXS models, used to calculate the micro-textural properties (porosity, specific surface, correlation length, correlation function) of porous materials, are especially relevant for in-situ material characterization. Certain classes of porous materials, including those generated during solid decompositions, are characterized by distinct regions with different micro-textures. Classical SAXS models cannot be applied directly to such multi-texture systems, thus a novel SAXS model for multi-texture systems is proposed in this work and validated by using measurements of micro-textural properties of a calcined CaCO3 powder, obtained using time-resolved in-situ synchrotron radiation USAXS, SAXS and WAXS data. The proposed model, in contrast to the direct application of classical SAXS models, is capable of correctly predicting the expected linear trend of the particle internal porosity with respect to the CaCO3 conversion and provides a complete description of the micro-textural properties, in very close agreement with experimental data available in the literature. In the reaction product region the correlation function, as well as the other micro-textural properties, is essentially constant during the solid decomposition, and is accurately represented by a two-parameter model. Based on the proposed SAXS model, a simplified expression of the differential scattering cross section, as a product of the CaO mass fraction times a time-independent function of the correlation function, is obtained; such expression can reliably predict the experimental scattering intensity profiles over time.

Modelling and design of a novel calcination reactor integrated with a CO2 capture process for intensified hydrogen production

Sorption enhanced steam methane reforming (SE-SMR) is an advantageous process for the production of H2 and simultaneous CO2 capture with solid sorbents. Aiming at implementing a continuous SE-SMR process, it is necessary to foresee a regeneration step of the sorbent via its calcination, to make it available for further CO2 capture in the reforming reactor. This work focused on the design of a calcination reactor for the regeneration of a dolomite sorbent to couple with a methane reformer/carbonation reactor. Calcium carbonate (CaCO3) calcination in CO2 atmosphere was studied via thermo-gravimetric analysis (TGA) using naturally occurring dolomite, and kinetic parameters were extrapolated (pre-exponential factor Aapp = 6.28 E+25 s−1 and activation energy Eapp = 6.41 E+5 J/mol). A preliminary design of the calciner was defined and its performance was investigated with Computational Particle-Fluid Dynamics (CPFD) simulations. A first preliminary Geometry 1 showed some limitations in the CaCO3 conversion, due to insufficient particle residence time. An optimized Geometry 2 was developed with an internal tube (jacket tube) acting as obstacle for increasing the average residence time of the particles. A further simulation of this new geometry showed higher residence time and increased conversion rate of approximately 95% after 220 s of simulation.

Experimental investigation of CaCO3/CaO in a spiral coil reactor for thermochemical energy storage

Simultaneously offering sufficient heat and mass transfer is a significant challenge for the reactor design in the field of thermochemical energy storage owing to either a low thermal conductivity or a low permeability of the solid reactants. This paper proposes a spiral coil reactor based on combination of pneumatic transmission and secondary flow for thermochemical energy storage. The CaCO3/CaO is selected as reaction medium. The gas-solid flow behavior, energy charging and discharging are investigated by the experimental methods. The results show that CaCO3 conversion is around 2–5% during the energy charging experiments and CaO conversion is around 60–68% during the energy discharging experiments. The CaO conversion is a little higher than that in the fluidized bed under the same condition. Both the unstable gas velocity and the fluctuation of pressure drop in the spiral coil reactor due to particles agglomeration and sintering at high charging reaction temperature account for the low CaCO3 conversion. In addition, the energy discharging experiments also indicate that the flow rate and reaction temperature have large effects on the CaO conversion. An increase in the gas velocity relieves CaO sintering, consequently resulting in a higher CaO conversion. Moreover, the reaction rate can be improved at higher energy discharging temperature which leads to enough residence time and higher CaO conversion. Overall, this paper provides a novel insight for gas-solid reactor design in the field of thermochemical energy storage.

Effects of steam on the kinetics of calcium carbonate calcination

The effects of the fraction of steam in the reactive gas atmosphere on the decomposition thermodynamics and kinetics of calcium carbonate are reported by systematic assessment of various combination of steam, nitrogen and carbon dioxide. The concentrations of steam, nitrogen and carbon dioxide were varied in the range of 10–90% while assessing the decomposition temperature of the calcium carbonate by means of thermogravimetric analysis. Two commercial samples of stock–lime (96.76% of CaCO3) and Type C sand (85.26% of CaCO3) were compared to investigate the effects of impurities and particle size on decomposition temperature. The effects of temperature and CO2 partial pressure on reaction conversion of CaCO3 were investigated for different concentrations of steam from 70% to 90% in various temperature ranges (830 °C–900 °C). This was used to obtained new kinetic parameters for the calcination reaction with steam and nitrogen at CO2 partial pressure of 0.1–0.4 and temperatures between 830 °C and 900 °C. The activation energy of 161.7 kJ mol−1 and 194.1 kJ mol−1 for calcination of CaCO3 with steam and N2, respectively, imply that steam has a catalytic effect on the calcination reactions. This is confirmed with XRD measurement, which show that no further products are formed after the calcination reaction with steam.

Immobilization and migration of arsenic during the conversion of microbially induced calcium carbonate to hydroxylapatite

Coprecipitation with calcium carbonate (CaCO3) could decrease the bioavailability of arsenic (As). However, in a phosphate-rich environment, some CaCO3 will be converted to hydroxylapatite (HAP). Currently, the behavior of carbonate-bound As during conversion is unclear. Therefore, we prepared bio-induced CaCO3 in an As solution and converted it to HAP. The results showed that a high concentration of arsenate promoted vaterite precipitation and the conversion of CaCO3 to HAP. The dissolution data verified the low solubility of As in HAP, though its As-bearing CaCO3 precursor released up to 88.19% As during the conversion. Furthermore, HPLC-ICP-MS data showed partial oxidation of arsenite to arsenate, suggesting that CaCO3 and HAP's structure favored the incorporation of arsenate. Our results demonstrated that the stability of heavy metal-bearing CaCO3 should be considered, and the role of HAP in the immobilization of heavy metals such as As should not be overestimated.

Indirect integration of thermochemical energy storage with the recompression supercritical CO2 Brayton cycle

Dispatchability is a major technological obstacle for concentrated solar power (CSP) plants. Calcium looping (CaL) is a potential solution for storing solar energy for long periods using raw materials (e.g., natural limestone or dolomite) which are high energy density, widespread availability, and low cost. This study aimed to propose a CSP-CaL plant indirectly integrated with the recompression supercritical CO2 Brayton cycle to realize carbonation under atmospheric pressure. To understand this indirect integration, the thermodynamic models are developed in Aspen and Matlab. The results show that the considered system can achieve storage exergy efficiency in the range of 8.26–16.34%, and power exergy efficiency in the range of 13.6–23.85%. In addition, a sensitivity analysis reveals that the storage exergy efficiency is largely determined by reaction temperature and conversion. Its value decreases with calcination temperature, and increases with carbonation temperature and CaCO3 conversion. Besides, it is found that the power exergy efficiency increase with an increase in power conditions (cycle low pressure, intermediate cycle pressure, and cycle high pressure) initially. However, above a certain pressure (80, 170, 210 bar, respectively), further increase leads to a decrease in power exergy efficiency. The results also indicate that high reaction temperature has a positive effect on power exergy efficiency. Compared to the molten-salt-based and direct integration, this CSP-CaL indirect integration offers competitive performance and promising potential for the commercialization of CSP-CaL systems in the near future.

Formation of calcium carbonates from Ca(OH)2-H2O-supercritical CO2 using a rapid spraying method

Particle formation techniques using supercritical fluid are simple processes that can control particle size and morphology, although high-pressure is required. The purpose of this study was to investigate how the experimental conditions affect the extent and rate of CaCO3 conversion and the size and morphology of the precipitated CaCO3 from the carbonation tests with rapid spraying of reactants causing rapid depressurization of supercritical fluid. The relatively low temperature and pressure conditions (35 °C and 7.5MPa) resulted in low CaCO3 conversion efficiency (41.4–51.9%), high vaterite content (70–78%) of CaCO3, and smaller-sized particles. The relatively high temperature and pressure conditions (80 °C and 12.0MPa) resulted in high CaCO3 conversion efficiency (66.8–73.2%), high calcite content (50–80%) of CaCO3, and larger-sized particles. The particle size of solid products ranged between 20 and 180nm with approximately a peak of 100 nm in the particle size distribution (PSD) curve, irrespective of the test conditions; however, shorter reaction times led to smaller particles. The optimal conditions under which the extent of CaCO3 conversion and calcite content were maximum were 50 °C, 9.0MPa, and 1 h of reaction time (CaCO3 conversion: 92.9%; calcite content of CaCO3: 87%).

Asian dust observed during KORUS-AQ facilitates the uptake and incorporation of soluble pollutants during transport to South Korea

The air quality of South Korea was the focus of the NASA/NIER KORean -United States Air Quality (KORUS-AQ) mission of 2016. KORUS-AQ was planned for the period after the spring peak in outbreaks of Asian dust. Regardless of this strategic planning, quantifiable dust was still observed via instrumentation on the NASA DC-8 in early May. A novel analysis of supermicron dust and associated supermicron ionic relationships was completed using two size dependent instruments. This supermicron dust provided surface area for heterogeneous chemistry between CaCO3, the gases HNO3, NO2, and SO2, and particulate (NH4)2SO4. Uptake of the pollutant gases is greatly enhanced by formation of an aqueous layer on the surface of the dust particles. More water is attracted to particles where uptake of HNO3 has replaced surface CaCO3 with Ca(NO3)2 generating a dynamic aqueous layer on the dust particle. We propose that particulate (NH4)2SO4 coagulated with dust to form (NH4)2Ca(SO4)2 on the particle surface, which rapidly formed CaSO4 and NH4+ in a Ca(NO3)2 facilitated aqueous layer. A conceptual model is proposed to explain these dust uptake chemical processes. We define the nanoequivalent concentration of supermicron SO42− plus NO3− over the nanoequivalent concentration of supermicron NH4+ plus Ca2+ as the Dust Pollution Index (DPI), used to quantify the extent to which carbonate dust has been modified. DPI values range from 0 (pure dust) to 1 (completely reacted); thus, it represents the conversion of CaCO3 into secondary salts. This mechanism should be used to better predict chemical dynamics in atmospheric models while also helping to further explain the importance of dust and secondary coating on cloud formation processes and dust optical properties. Air masses containing dust that traversed industrial China while mixing with polluted southern air had significantly higher DPI values (average = 0.82, 1σ = 0.10) compared to air masses that limited interaction with such pollution (average = 0.51, 1σ = 0.13).

Experimental investigation and mathematical modeling of the reaction between SO2(g) and CaCO3(s)-containing micelles in lube oil for large two-stroke marine diesel engines

Sulfur dioxide, formed in combustion of sulfur-rich fuels in diesel engines, may oxidize and react with water to form corrosive H2SO4. However, the SO2 may also be absorbed in the lube oil and consume CaCO3-containing reverse micelles. In this study, the CaCO3 + SO2 reaction was investigated in a batch reactor setup at temperatures and pressures similar to those on the cylinder liner in an engine. The conversion of CaCO3 and the formation of products were determined by Fourier Transform Infrared Spectroscopy (FTIR). CaSO3 was the main product, but CaSO4 was observed at extended residence times and increased temperature. The SO2-CaCO3 reaction exhibited only a small temperature dependence; the increase in the rate constant with temperature was partly off-set because the absorption of SO2 in the lube oil emulsion decreases at increased temperature. The reaction rate increased slightly with the initial water concentration due to increased SO2 absorbance. A mathematical model for the batch reactor was set up and kinetic parameters were determined by fitting predictions to the experimental data. The model was then used to predict the CaCO3 conversion in lube oil from SO2 for conditions relevant to a full-scale engine application. Simulations showed that consumption of CaCO3 from SO2 is insignificant in a two-stroke marine diesel engine application and that the H2SO4-CaCO3 reaction is far more important than the SO2-CaCO3 reaction.