Presence Of CaO Research Articles

Mineral sulphide-lime reactions and effect of CaO/C mole ratio during carbothermic reduction of complex mineral sulphides

Mineral sulphide (MS)-lime (CaO) ion exchange reactions (MS + CaO = MO + CaS) and the effect of CaO/C mole ratio during carbothermic reduction (MS + CaO + C = M + CaS + CO(g)) were investigated for complex froth flotation mineral sulphide concentrates. Phases in the partially and fully reacted samples were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The primary phases during mineral sulphide-lime ion exchange reactions are Fe3O4, CaSO4 Cu2S, and CaS. A complex liquid phase of Ca2CuFeO3S forms during mineral sulphide-lime exchange reactions above 1173 K. The formation mechanisms of Ca2CuFeO3S liquid phase are determined by characterising the partially reacted samples. The reduction rate and extent of mineral sulphides in the presence of CaO and C increase with the increase in CaO/C ratio. The metallic phases are surrounded by the CaS rich phase at CaO/C > 1, but the metallic phases and CaS are found as separate phases at CaO/C 1 and the reacted samples are excessively sintered.

CaZrO3-based powders suitable for manufacturing electrochemical oxygen probes

Abstract Calcium zirconate powders doped with a small amount of CaO were synthesised using the Pechini method. X-ray analysis revealed that solid solution was formed in the concentration up to 51.5% mol CaO. For synthesis of stoichiometric CaZrO3, the highest temperature was required (1150°C), but introduction of excess CaO from 50.5 to 51.5% mol enabled us to lower the synthesis temperature to 800°C. The sintering behaviour of such samples under non-isothermal conditions was studied by dilatometric methods. Deviations were found in stoichiometry; by increasing the CaO concentration in CaZrO3 sinterability improved in comparison to CaZrO3 with stoichiometric composition. The presence of CaO as second phase caused deterioration of the sinterability of the CaZrO3-based samples. Pellets sintered at 1500°C for 2 h reached 96–98% of theoretical density. SEM and TEM observations were used to characterise the microstructure of the prepared samples. The electrical properties of CaZrO3-based samples were investigated by the AC-impedance spectroscopy method. It was found that introduction of excess CaO into the CaZrO3 structure caused an increase in ionic conductivity up to the solubility limit. The possibility of using CaZrO3-based samples for constructing prototype electrochemical oxygen probes to determine activity of oxygen dissolved in molten copper is also demonstrated.

Comparison of yield and fuel properties of thermal and catalytic Mahua seed pyrolytic oil

In this work, the production and evaluation of fuel properties of pyrolytic oil from one non-edible oil seed Mahua was reported. Both thermal and catalytic pyrolysis using CaO was carried out. The aim of the study was to detect the optimum temperature to produce maximum pyrolytic oil and to increase the quality of oil using catalyst. It was observed that thermal pyrolysis of Mahua seed at 525°C produced maximum yield of liquid. Hence the influence of catalyst was examined at the optimum temperature (525°C) on liquid yield and its properties.The catalytic effect of CaO, on Mahua seed pyrolysis at a feed to catalyst ratio of 2:1, 4:1 and 8:1 was studied. The pyrolytic liquid collected was separated into two phases. The top phase (organic) was considered as oil phase where as the bottom phase as aqueous. Maximum yield of 40.71wt.% of oil with better fuel properties was obtained as Mahua seed pyrolyzed in the presence of CaO at the ratio of 2:1. The result confirmed that catalyst (CaO) not only increased the heating value (41–43.15MJkg−1), viscosity (0.033–0.018Pas) and cold flow properties but also altered the pH (4.86–8.58) significantly when compared with thermal pyrolysis.

Novel bi-functional Ni–Mg–Al–CaO catalyst for catalytic gasification of biomass for hydrogen production with in situ CO2 adsorption

Catalytic gasification of biomass in the presence of CaO is a promising route for CO2 capture and thereby high yield hydrogen production. However, the instability of the CaO sorbent for CO2 adsorption is a challenge for the process. A novel bi-functional Ni–Mg–Al–CaO catalyst has been prepared with different contents of CaO by integration of the catalytic and CO2 adsorbing materials to maximise hydrogen production. The prepared catalysts were tested for hydrogen production via the pyrolysis-gasification of wood biomass using a two-stage fixed-bed reaction system. The carbonation/calcination results using thermogravimetric analysis (TGA), in an atmosphere of N2 or CO2, showed that the reactivity of CaO with CO2 decreased even after several cycles of carbonation/calcination, while the Ni–Mg–Al–CaO catalyst showed a comparatively stable CO2 adsorption even after 20 cycles. Adding CaO to the Ni–Mg–Al catalyst leads to an increase in hydrogen production and selectivity due to the enhancement of the water–gas shift reaction by in situ CO2 adsorption. An optimal content of CaO was suggested to be 20 wt% (weight ratio of CaO/Ni–Mg–Al) which gave the highest hydrogen production (20.2 mmol g−1 biomass) in the presence of the Ni–Mg–Al–CaO catalyst. Temperature-programmed oxidation (TPO) showed that carbon deposition was significantly decreased with the addition of CaO in the Ni–Mg–Al catalyst, and with the increase of CaO content, coke deposition on the reacted catalyst was further decreased.

Liquidus and phase equilibria in CaO-Al2O3-FeOx-SiO2 system under intermediate oxygen partial pressure

Phase equilibria of silicate slags relevant to the copper smelting/converting operations have been experimentally studied over a wide range of slag compositions, temperatures and atmospheric conditions. Selected systems are of industrial interest and fill the gaps in fundamental information required to systematically characterise and describe copper slag chemistry. The experimental procedures include equilibration of synthetic slag at high temperatures, rapid quenching of resulting phases, and accurate measurement of phase compositions using electron probe X-ray microanalysis (EPMA). The effects of CaO, Al2O3 and MgO on the phase equilibria of this slag system have been experimentally investigated in the temperature range 1200 to 1300 oC and oxygen partial pressures between 10-5 and 10-9 atm. It was found that spinel and silica are major primary phases in the composition range related to copper smelting/converting slags. In addition, olivine, diopside and pyroxene also appear at certain conditions. The presence of CaO, MgO and Al2O3 in the slag increases the spinel liquidus and decreases the silica liquidus. Liquidus temperatures in silica primary phase field are not sensitive to Po2; Liquidus temperatures in spinel primary phase field increase with increasing Po2. At 1300?C and low Po2, the spinel (Fe2+,Mg2+)O.(Al3+,Fe3+) primary phase field can be replaced by wustite (Fe2+,Mg2+)O.

Effects of CaO, Al2O3 and MgO on liquidus temperatures of copper smelting and converting slags under controlled oxygen partial pressures

Phase equilibria of silicate slags relevant to the copper smelting/converting operations have been experimentally studied over a wide range of slag compositions, temperatures and atmospheric conditions. Selected systems are of industrial interest and fill the gaps in fundamental information required to systematically characterise and describe copper slag chemistry. The experimental procedures include equilibration of synthetic slag at high temperatures, rapid quenching of resulting phases, and accurate measurement of phase compositions using electron probe X-ray microanalysis (EPMA). The effects of CaO, Al2O3 and MgO on the phase equilibria of this slag system have been experimentally investigated in the temperature range 1200 to 1300 oC and oxygen partial pressures between 10-5 and 10-9 atm. It was found that spinel and silica are major primary phases in the composition range related to copper smelting/converting slags. In addition, olivine, diopside and pyroxene also appear at certain conditions. The presence of CaO, MgO and Al2O3 in the slag increases the spinel liquidus and decreases the silica liquidus. Liquidus temperatures in silica primary phase field are not sensitive to Po2; Liquidus temperatures in spinel primary phase field increase with increasing Po2. At 1300 oC and low Po2, the spinel (Fe2+,Mg2+)O.(Al3+,Fe3+) primary phase field can be replaced by wustite (Fe2+,Mg2+)O.

Recovery of glass fibers from glass fiber reinforced plastics by pyrolysis

Fiber-reinforced plastic sheets containing unsaturated polyester cross-linked with styrene, CaCO3 and glass fibers as fillers were pyrolyzed in a helium and steam atmosphere in order to recover glass fibers and valuable organic pyrolysis products. Glass fibers were separated from CaCO3 and CaO by dissolving calcium salts in hydrochloric acid. Residual organic material was burnt afterwards. Best results were obtained at a pyrolysis temperature of 600 and 700 °C, resulting in a large liquid fraction high in styrene, leaving little residual organic material on the surface of the glass fibers. At a pyrolysis temperature of 500 °C, the degradation of the polymer matrix was incomplete, and at 900 °C, glass fibers were destroyed in the presence of CaO, leaving CaSiO3 as a product.

A combined thermodynamic and experimental study on chemical-looping ethanol reforming with carbon dioxide capture for hydrogen generation

SUMMARY Chemical-looping ethanol reforming with carbon dioxide capture is proposed. It combines chemical-looping reforming and carbon dioxide capture for pure hydrogen generation from ethanol with inherent separation of carbon dioxide. A thermal analysis of the process using NiO oxygen carrier is performed by simulating reactions using the Gibbs energy minimization method. The promising systems are investigated further with respect to temperature, NiO/C2H5OH molar ratio, CaO/C2H5OH molar ratio and pressure changes as well as possible carbon formation in the reformer. Favorable operation conditions in the presence of CaO are: pressures around 3 atm, reactor temperatures around 850 K, NiO/C2H5OH molar ratio = 3 and CaO/C2H5OH = 3. The H2 yield and thermal efficiency with CaO addition are higher than that without CaO addition, showing that the addition of a CO2 sorbent in the process increases the H2 production. Copyright © 2012 John Wiley & Sons, Ltd.

Microstructure and properties of sintered mullite developed from Indian bauxite

Dense mullite aggregates with 72% Al2O3 have been synthesized by reaction sintering of two varieties of Indian bauxite and silica sol. The bauxites used are of inferior grade with different levels of accessory impurities such as Fe2O3, TiO2, CaO. The phase and microstructure development of sintered samples were investigated by XRD and SEM. It was found that morphology of the sintered grain is very much dependent on the impurity level. Mullite formed from bauxite-1 with low impurity is mostly equiaxed, whereas mullite developed from bauxite 2 with higher impurity particularly CaO is needle shaped. Presence of CaO in bauxite was found to be more detrimental than TiO2 and Fe2O3.

Photodegradation of Rhodamine B in Presence of CaO and NiO-CaO Catalysts

A CaO catalyst was prepared by mild calcination (650°C) of facilely precipitated Ca(OH)2and compared to an NiO-CaO catalyst obtained from an Ni(OH)2/Ca(OH)2coprecipitate as a precursor. Both catalysts degraded rhodamine B (RB) effectively when exposed to ultraviolet light but exhibited slower degradation under visible light conditions. Under UV light, CaO was more effective than NiO-CaO, while in visible light, the opposite was observed. A mechanistic study revealed no influence of the specific surface area of the catalysts on RB degradation, no adsorption of RB on the positively charged surfaces of the catalysts, and only incomplete degradation of RB. Consequently, both materials represent nonconventional photocatalysts.

CaO-catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate: Isolation and characterization of an active Ca species

The transesterification of dimethyl carbonate (DMC) with glycerol to produce glycerol carbonate was investigated in the presence of CaO under various reaction conditions. CaO was completely dissolved in the reaction mixture of glycerol and DMC in 5 min at 75 °C and at the molar ratio of glycerol/DMC/CaO of 1/2/0.01. The isolation and the characterization of the dissolved Ca species by means of TOF-SIMS, elemental analysis, and FT-IR revealed that an active species, Ca(C 3H 7O 3)(OCO 2CH 3) is generated from the interaction of CaO with glycerol and DMC. The mechanistic pathways to the formations of Ca(C 3H 7O 3)(OCO 2CH 3) and glycerol carbonate are discussed on the basis of experimental and spectroscopic results.

Effect of Additives on Decomposition of Sodium Carbonate: Precombustion CO2 Capture Sorbent Regeneration

The effect of various additives on the decomposition of sodium carbonate (Na2CO3) was evaluated using temperature-programmed desorption, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Incorporation of additives, CaO and Ca(OH)2, had a significant effect on lowering the decomposition temperature of Na2CO3, while CaCO3, SiO2, and Al2O3 had no effect. The amount of additive, sweep gas flow rate, and heating rate were also found to play a significant role in altering the decomposition temperature of Na2CO3. The formation of a carbonate-type intermediate in the presence of CaO and Ca(OH)2 may have promoted the decomposition of Na2CO3.

Hydrolytic degradation of poly(ethylene terephthalate) in a pyrolytic two step process to obtain benzene rich oil

AbstractPoly(ethylene terephthalate) (PET) was degraded in a two step process to obtain a valuable oil, consisting mainly of benzene. First, PET was hydrolyzed in a steam atmosphere at 450°C, and the resulting terephthalic acid was decarboxylized in the presence of CaO. By separating the two fundamental reactions of this degradation process, the hydrolysis reaction and decarboxylation, the amount of residue was reduced, and the amount of benzene obtained increased. It was found that the best results were obtained at a decarboxylation temperature of 700°C, with a yield of 48% benzene. At lower temperatures, the terephthalic acid was adsorbed at the catalyst without decarboxylation; at higher temperatures, large amounts of char were formed due to pyrolytic reactions. Unlike solvolysis processes, no solvent is used in this process; in effect eliminating the expense of processing waste liquids. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Deoxygenation of Bio-oil during Pyrolysis of Biomass in the Presence of CaO in a Fluidized-Bed Reactor

The direct deoxygenation effect of CaO on bio-oil during biomass pyrolysis in a fluidized-bed reactor was studied. Bio-oils were produced from white pine in the presence and absence of CaO at 520 °C and a carrier gas flow rate of 50 L/min (standard temperature and pressure). The results showed that the oxygen content of the organic components in the bio-oils was 39, 39, 39, 36, 32, and 31 wt % for white pine alone and white pine accompanied with CaO at CaO/biomass mass ratios of 1, 2, 3, 4 and 5, respectively. At a CaO mass ratio of 5, the relative reduction of oxygen content in the bio-oil reached 21%. Detailed gas chromatography−mass spectrometry analysis showed that the relative abundances of high oxygen content laevoglucose, formic acid, and acetic acid were highly reduced by CaO, indicating direct fixation of “the active quasi-CO2 intermediates” produced during biomass pyrolysis. Furthermore, the relative abundances of furfural, furfuryl alcohol, etc., mainly derived from dehydration reactions, all i...

Chemical recycling of polyhydroxyalkanoates as a method towards sustainable development

Chemical recycling of bio-based polymers polyhydroxyalkanoates (PHAs) by thermal degradation was investigated from the viewpoint of biorefinery. The thermal degradation resulted in successful transformation of PHAs into vinyl monomers using alkali earth compound (AEC) catalysts. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s (PHBVs) were smoothly and selectively depolymerized into crotonic (CA) and 2-pentenoic (2-PA) acids at lower degradation temperatures in the presence of CaO and Mg(OH)(2) as catalysts. Obtained CA from 3-hydroxybutyrate sequences in PHBV was copolymerized with acrylic acid to produce useful water-soluble copolymers, poly(crotonic acid-co-acrylic acid) that have high glass-transition temperatures. The copolymerization of CA derived from PHA pyrolysis is an example of cascade utilization of PHAs, which meets the idea of sustainable development.

Microstructure and high temperature transport properties of Ca‐doped nickel oxide

The high temperature microstructure of Ca-doped NiO single crystals was analysed to clear the experimental data on electrical conductivity, Seebeck's effect, diffusion and kinetic demixing. Combined transmission light microscopy and transmission electron microscopy examinations coupled with EDS analyses revealed the presence of CaO precipitates in localized (eutectic-like) zones for a wide range of analysed oxygen partial pressure. Their presence in the structure was confirmed for equilibrium (air) conditions in NiO-CaO system at about 1700 degrees C (approximately 42 mol% CaO), according to phase diagrams (Smith et al., 1969). For the wide range of oxygen partial pressure and high temperature (1000 / 1200 degrees C) the spinel phase was not observed, which is opposite to our previous results obtained for Ca-doped CoO single crystals (Kusinski et al., 2006). The chemical diffusion and electrical field kinetic demixing experiments have been combined to prove that the presence of Ca leads to an increase of the chemical diffusion coefficient of NiO. This unexpected result (D(Ca) > D(Ni)), confirmed during electrical conductivity experiment, indicates that correlation effects between Ni and Ca cations play a decisive role in diffusion processes in (Ni,Ca)O.

An investigation into steam gasification of biomass for hydrogen enriched gas production in presence of CaO

Biomass steam gasification could be an attractive option for sustainable hydrogen production. Biomass, regarded as carbon neutral emitter, could be claimed as carbon negative emitter if carbon dioxide produced is captured and not allowed to emit to the environment during the process. Thus here an experimental study is carried out to find out the potential of hydrogen production from steam gasification of biomass in presence of sorbent CaO and effect of different operating parameters (steam to biomass ratio, temperature, and CaO/biomass ratio). Product gas with hydrogen concentration up to 54.43% is obtained at steam/biomass = 0.83, CaO/biomass = 2 and T = 670 °C. A drop of 93.33% in carbon dioxide concentration was found at CaO/biomass = 2 as compared to the gasification without CaO. Mathematical model based on Gibbs free energy minimization has been developed and is compared with the experimental results.

Synthesis of Functionalized Spiroaziridine‐oxindoles from 3‐Ylideneoxindoles: An Easy Route to 3‐(Aminoalkyl)oxindoles

AbstractNovel potentially bioactive spiroaziridine‐oxindoles have been prepared by treatment of easily accessible 3‐ylideneoxindoles with N‐{[(4‐nitrophenyl)sulfonyl]oxy}carbamate (NsONHCO2Et) in the presence of CaO. These compounds gave new 3‐(aminoalkyl)oxindole derivatives through easy and regioselective reductive aziridine ring‐opening reactions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Chemical recycling of polyhydroxyalkanoates as a method towards sustainable development

Chemical recycling of bio-based polymers polyhydroxyalkanoates (PHAs) by thermal degradation was investigated from the viewpoint of biorefinery. The thermal degradation resulted in successful transformation of PHAs into vinyl monomers using alkali earth compound (AEC) catalysts. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s (PHBVs) were smoothly and selectively depolymerized into crotonic (CA) and 2-pentenoic (2-PA) acids at lower degradation temperatures in the presence of CaO and Mg(OH)(2) as catalysts. Obtained CA from 3-hydroxybutyrate sequences in PHBV was copolymerized with acrylic acid to produce useful water-soluble copolymers, poly(crotonic acid-co-acrylic acid) that have high glass-transition temperatures. The copolymerization of CA derived from PHA pyrolysis is an example of cascade utilization of PHAs, which meets the idea of sustainable development.

Hydrogen production and CO 2 fixation by flue-gas treatment using methane tri-reforming or coke/coal gasification combined with lime carbonation

The production of hydrogen and the fixation of CO 2 can be achieved by treatment of flue gases derived from fossil fuel fired power plants via catalytic methane tri-reforming or by coal gasification in the presence of CaO. A two-step process is designed to be carried out in two reactors: a) a catalytic gasifier or steam-reformer, operating exothermally at 900–1000 K, with inputs of the flue gas, a carbonaceous source, steam and air, as well as CaO from the calciner, and outputs of H 2, and of “spent” CaCO 3 to the calciner; b) a calciner, operating endothermally at 1100–1300 K, with inputs of spent CaCO 3 from the gasifier, make-up fresh CaCO 3, and outputs of CO 2, as well as of CaO, partly recycled to the gasifier and partly processed in a cement plant. Thermochemical equilibrium calculations along with mass/energy balances indicate that for flue-gas treatment by tri-reforming, CO 2 emission avoidance of up to ∼59% and fossil fuel savings of up to ∼75% may be attained when concentrated solar energy is supplied as high-temperature process heat for the calcination step, all relative to conventional H 2 production by coal gasification. If instead fossil fuel would be used to drive the calcination step, the CO 2 emission avoidance and the fuel savings would be only 20% and 67%, respectively. Estimated annual H 2 production from a coal-fired 500 MWe burner by the proposed flue-gas treatment using either CH 4-tri-reforming or coal gasification would amount to 0.7 × 10 6 or 0.6 × 10 6 metric tons H 2, respectively. Estimated fossil fuel consumption for H 2 production by tri-reforming or coke gasification would be 149 or 143 GJ fuel/ton H 2.