Role Of Calcium Oxide Research Articles

Role of Calcium Oxide in Directional Regulation Microstructure of Coke during High Sulfur Coal Pyrolysis

Role of Calcium Oxide in Directional Regulation Microstructure of Coke during High Sulfur Coal Pyrolysis

Deciphering CaO-induced peroxydisulfate activation for destruction of halogenated organic pollutants in a low energy vibrational mill

• CaO-PDS features high reactivity in low energy vibrational mill. • The CaO addition much enhances 2,4-DCP dechlorination and mineralization. • PDS is activated via electron transfer, base activation, and energy transfer. • CaO both activates PDS and transforms SO 4 •− surf to •OH surf. • CaO-PDS enables destruction of persistent halogenated organic pollutants. Mechanochemical (MC) treatment utilizing calcium oxide (CaO) and peroxydisulfate (PDS) for halogenated organic pollutants (HOPs) has been developed for pure substance degradation and contaminated soil remediation. However, the role of CaO and the mechanism of PDS activation in solid phase reaction remain unclear. This study was dedicated to decipher CaO-induced PDS activation for destruction of typical HOPs such as 2,4-dichlorophenol (2,4-DCP), in a low energy single-cylinder horizontal vibrational mill. With mass ratio of CaO:PDS:2,4-DCP = 6.3:6.7:1, CaO-PDS as co-milling agents destructs 2,4-DCP with much higher degradation and dechlorination rate than CaO (about 13.9- and 121.2-fold) or PDS (about 2.5- and 9.4-fold) only. According to detection of intermediates and measurement of total organic carbon, the CaO addition shifts the degradation pathway into dechlorination and ring-open routes, and increase mineralization efficiency from 64% (PDS only) to 96%. Quenching test suggests •OH surf is the dominant oxidative species with CaO-PDS as co-milling agents, which enables complete oxidative destruction. PDS in such MC system is activated mainly via electron transfer (∼50.6%), followed by base activation (∼40.5%) and energy transfer (＜ 8.9%). CaO plays a dual role in activating PDS and transforming SO 4 •− surf to •OH surf . Finally, CaO-PDS shows high reactivity in destructing persistent HOPs like polybrominated phenols and polychlorinated benzenes, which expands its potential in practical application. This study may guide the selection of effective oxidative co-milling agents for mineralization of solid HOPs by mechanochemistry, facilitating safe disposal of obsolete HOPs.

Role of Calcium Oxide in Nucleation and Microstructure of Geopolymers and Alkali Activated-Based Cements

Role of Calcium Oxide in Nucleation and Microstructure of Geopolymers and Alkali Activated-Based Cements

Thermal conduction mechanism based on microstructural transformations of molten slag: The role of calcium oxide

The built up of the slag layer is a character of the entrained-flow gasifier, and its thickness distribution and heat transfer characteristics affect the stable operation of gasification, which is closely related to the thermal conductivity of molten slag. A non-stationary hot wire experimental method and a reverse non-equilibrium molecular dynamics simulation method were combined to investigate the thermal conductivity of the SiO2-Al2O3CaO-Fe2O3−MgO molten slag with a mass ratio of CaO ranging from 5 to 25 wt.%. The slag microstructure information of the distribution of oxygen and tetrahedron Qn was calculated by molecular dynamics simulation. A good agreement within the deviation of 18% between the measured and calculated thermal conductivity over the entire operating temperature range is observed, and one can find that thermal conductivity decreases significantly as the CaO content increased. The principal pathway for CaO modifying the network structure is the connection between two tetrahedral structures by generation of the Si-O-Ca and Al-O-Ca through the fracture of Si-O-Si and Si-O-Al. The rise of CaO promotes the formation of non-bridging oxygen (NBO) and the decomposition of bridging oxygen. The existence of NBOs leads to an enhancement of anharmonicity and shortens the interatomic distance in the tetrahedral structure, which aggravates phonon scattering to reduce phonon mean free path, thereby decreasing the thermal conductivity. Since the phonon propagation is restricted to short-range tetrahedron separated by structural disorder, the Q4 structure is the most sensitive to the addition of CaO. An equivalent molar concentration of the Q4 tetrahedron (XQ4) is defined and the approximate positive linear relationships between the thermal conductivities and XQ4 are obtained.

The role of CaO in the steam gasification of plastic wastes recovered from the municipal solid waste in a fluidized bed reactor

The worldwide solid waste composition indicates that polymeric materials account for, approximately, 10 % of municipal solid waste (MSW). After sorting, MSW still contains a fraction of plastic (Municipal Plastic Waste - MPW) which is a potential raw material for thermochemical processes. Among the thermochemical processes, combustion, pyrolysis and gasification are the most important. This study reports the steam gasification process of the MPW after the MSW sorting of the selective collection in the municipality of Garibaldi, southern Brazil. The samples were obtained after the separation of materials intended for recycling. A total of 29.8 % of the MSW after sorting was found to be made of polymeric materials incorrectly sent to landfill. The MPW was characterized by gravimetric composition, particle size distribution, ultimate and proximate analyzes. The polymeric materials with the highest participation in MPW are polypropylene (28.77 %), polystyrene (23.53 %) and polyethylene (16.67 %). The gasification experiments were carried out in a fluidized bed reactor at different temperatures (800, 850 and 900 °C), by using steam as gasification agent (0.3 kg/h). Gasification experiments were also performed with calcium oxide (CaO). The remaining ash had its morphology analyzed by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), while gas from steam gasification was evaluated between 0−90 min by Gas Chromatography (GC). The steam gasification of MPW with CaO increased both dry gas yield and hydrogen yield. The maximum dry gas yield (3.12 Nm3/kgMPW) was obtained at 900 °C with CaO, as well as a high H2 yield (104 mol/kgMPW). This energy reuse can help to reduce energy demand bottlenecks, as well as the decrease of landfills.

Viscosity temperature properties from molecular dynamics simulation: The role of calcium oxide, sodium oxide and ferrous oxide

For the long-term stable operation of the entrained flow gasifier in the coal chemical industry, the flux agents are generally adopted to adjust the fusibility of coal ash. Therefore, it is necessary to understand the underlying mechanism for the impact of typical oxide flux agents on viscosity temperature properties of coal ash from structures and thermodynamics. In this work, the role of calcium oxide, sodium oxide and ferrous oxide on viscosity temperature properties is investigated by a combination of molecular dynamics simulations and thermodynamic calculations. The variations of viscosity and temperature of critical viscosity are obtained for different ternary coal ash systems by thermodynamic calculation. Ternary phase diagrams are applied to evaluate the effect of different flux agents, which are also found to cause mineral transformation from high-temperature minerals to low-temperature minerals. Oxygen bond species are employed as the indicator of the structural evolution originating from addition of different flux agents. The sodium atoms may more readily weaken the tricluster oxygen bonds than calcium or ferrous atoms according to the results. Higher content of bridging oxygen bonds in the sodium oxide ternary coal ash system can enhance the stability of the structures and induce higher viscosity. Stability coefficients are defined here and a function to describe the relationship between the viscosity and flux agent content is established. The results from the current work are expected to provide new clues to find strategies controlling the fusion behaviour of coal ash systems.

Coal ash fusion properties from molecular dynamics simulation: the role of calcium oxide

The role of calcium oxide on ash fusion properties was investigated in this work by molecular dynamics simulations and thermodynamics calculations. The variation of volume was used to identify the melting points, which was compared with the liquidus temperature calculated by the FactSage codes. The phase diagram was calculated to explain the variation of melting points with the content of calcium oxide. The radial distribution functions and species of oxygen bonding were employed to characterize the structural evolution with the different fraction of calcium oxide. The melting point of anorthite is lower than that of mullite due to less tricluster oxygen atoms. The content of CaO with high flux efficiency in (SiO2)2-Al2O3-CaO is found from 5.00% to 15.00%. The current modelling work on melting behaviors of minerals containing various amount of CaO may provide new insight into the mechanism of ash fusion influenced by flux.

The enhancing mechanism of calcium oxide on water gas shift reaction for hydrogen production

To figure out the role of CaO (calcium oxide) on WGS (water gas shift) reaction and the related enhancing mechanism, the WGS reaction of absorption enhanced biomass steam gasification with CaO addition was performed with thermodynamic simulation and bench-scale experiment. The results showed that, the experimental WGS reaction was kinetically limited at lower temperature and far from equilibrium without CaO addition. However, much higher H2 concentration could be obtained with CaO addition, as CaO acted not only as a CO2 absorbent, but also a catalyst for WGS reaction. And the enhancing effect showed obvious segmentation feature with the reaction time streamline due to the variation of CaO carbonation performance. Typical product gas composition in stable region (10–70 min) was approximately 71 vol% H2, 22 vol% CO and 7 vol% CO2, with CO2 absorption rate of 87.41%–91.44%, CO conversion rate of above 75.5%, and enhancement ratio of CaO of about 81%. The possible catalytic mechanism for absorption enhanced WGS reaction could be concluded as carboxyl mechanism, while CaO activated H2O dissociation forming H* and OH*, thus further reacted with CO* to generate COOH* and then decomposed to CO2 and H*, and two H* met to form H2. The H2O/CO increasing was favorable for WGS reaction.

Role of calcium oxide in sludge granulation and methanogenesis for the treatment of palm oil mill effluent using UASB reactor

The granulation process in palm oil mill effluent using calcium oxide-cement kiln dust (CaO–CKD) provides an attractive and cost effective treatment option. In this study the efficiency of CaO–CKD at doses of 1.5–20 g/l was tested in batch experiments and found that 10 g of CaO/l caused the greatest degradation of VFA, butyrate and acetate. An upflow anaerobic sludge blanket (UASB) reactor was operated continuously at 35 °C for 150 days to investigate the effect of CaO–CKD on sludge granulation and methanogenesis during start-up. The treatment of POME emphasized the influence of varying organic loading rates (OLR). Up to 94.9% of COD was removed when the reactor was fed with the 15.5–65.5 g-COD g/l at an OLR of 4.5–12.5 kg-COD/m 3 d, suggesting the feasibility of using CaO in an UASB process to treat POME. The ratio of volatile solids/total solids (VS/TS) and volatile fatty acids in the anaerobic sludge in the UASB reactor decreased significantly after long-term operation due to the precipitation of calcium carbonate in the granules. Granulation and methanogenesis decreased with an increase in the influent CaO–CKD concentration.

Effects of CaO on crystallization properties in BaO–SrO–TiO 2–SiO 2 glass–ceramics

The role of calcium oxide (CaO) was investigated in the crystallization of BaO–SrO–TiO 2–SiO 2 glass. The CaO dopant altered the oriented growth facets of crystal unit cells in the glass–ceramics. The crystallites are acicular in micron scale in the samples having as small as 1% CaO dopant, but are long granular in the nanometer scale in the sample without CaO. The glass–ceramics which have nano crystallites are observed with a less crystallization density qualitatively, a higher transmissivity in the wavelength range of 200–2600 nm, and 30% lower piezoelectric coefficient, d 33, at 9.5 ± 0.3 pC/N than those glass–ceramics having CaO in the study.

A simple and rapid method for the isolation of cholesterol from spinal cord of cattle.

A method is described for the large scale isolation of cholesterol from cattle spinal cord. Cholesterol is released from the lipo-protein by drying the wet tissues with calcium oxide. This treatment appears to prevent the extraction of polar lipids with acetone, which reduces the lipophylic properties of the solution and thus provides a method for almost exclusive extraction of cholesterol. The further role of calcium oxide is also discussed. The method evolved is simple, rapid and eliminates several previously required steps.