Solid Calcium Oxide Research Articles

Efficient mineralization of organic pollutants in water via a phenol-responsive catalytic ozonation process

Background: Catalytic ozonation process has become one of the most promising technologies in organic wastewater treatment industry due to its high efficiency and rapidity. Some researchers have found that alkaline earth metal oxides can be used to promote the ozonation process to removal organic compound in wastewater. And some of them believe that calcium-based catalysts can effectively catalyze the ozonation reaction, but there are few reports about its reaction mechanism.Methods: In this work, calcium oxide was used as catalyst to study their effect in phenol wastewater and the mechanism of catalytic reaction process. In the catalytic ozonation process, the surface hydroxyl of solid CaO-based catalyst can react as the reaction active sites to promote the formation of free radicals, and the Ca2+ solutes in this system can promote the decomposition of H2O2 to produce free radicals. At the same time, the addition of calcium oxide-based catalyst also increases the pH of the reaction system, which is conducive to the decomposition of ozone to produce hydroxyl radicals. Owing to the presence of •OH, 1O2 and •O2−, phenol and by-product are decomposed effectively.Significant findings: The experimental results show that the COD removal rate of phenol reached ∼100% in 20 min. And in this study, the mechanism of CaO-based catalysts used in the ozonation process was studied. We found that both of Ca2+ in solution and solid calcium oxide promoted the formation of active free radicals in catalytic ozonation process.

Solid Catalyzed Reaction of <i>Jatropha Curcas</i> Seed Oil with Methanol

Production of biodiesel by transesterification method from renewable feedstock has come to stay. Biodiesel usage in internal combustion engines is gradually gaining ground due to its ability to produce less carbon (iv) oxide gas than fossil diesel during combustion. The production of less carbon (iv) oxide fumes will help to reduce environmental pollution that causes climate change. Jatropha curcas seed oil is a viable renewable feedstock for biodiesel production. Transesterification of Jatropha curcas seed oil with methanol using solid calcium oxide as catalyst was carried out. The free fatty acid of the oil used was 1.4%, while the molar ratio of methanol to oil, reaction temperature and time were 8:1, 65 °C, and 1hour respectively. The biodiesel produced was analyzed with gas chromatography mass spectrophotometer and the methyl ester content was 87.25%. The fuel properties of the biodiesel produced in a reaction time of about 1 hour 30 minutes are within the range of the values given by ASTM D6751 standard.

Oil majors invest in CO2 capture company

Venture investment arms of Chevron and Occidental Petroleum have invested an undisclosed sum in Carbon Engineering, a Canadian firm that is developing a chemical method of capturing CO2 from the atmosphere. In the process, CO2 reacts with calcium hydroxide to create a calcium carbonate solution. Carbonate pellets are formed, then decomposed into concentrated CO2 and solid calcium oxide. The CaO is then hydrated to regenerate the hydroxide. Carbon Engineering raised about $8 million in July.

Optimization of Biodiesel Production over Chicken Eggshell-Derived CaO Catalyst in a Continuous Centrifugal Contactor Separator

Solid calcium oxide (CaO) catalyst was prepared via the calcination of chicken eggshells as an environmentally friendly waste resource and incorporated in a continuous centrifugal contactor separator (CCCS) for intensified biodiesel synthesis. Biodiesel or fatty acid methyl esters (FAME) were produced via the transesterification of sunflower oil (containing 5 wt % tetrahydrofuran as a cosolvent) with methanol under 60 °C and separated from the glycerol and catalyst phases continuously in the CCCS. The influence of reaction parameters on biodiesel production was well modeled by response surface methodology. At an oil flow rate of 9 mL/min, an alcohol to oil molar ratio of 11:1, and a weight hourly space time (defined as the catalyst weight over the oil mass flow rate) of 0.050 h, an optimized FAME yield of 83.2% with a productivity of 638 kgFAME/(m3reactor·h) was achieved. CaO catalyst was reused without significant activity loss for at least four cycles.

New kinetic model for the rapid step of calcium oxide carbonation by carbon dioxide

Carbonation of solid calcium oxide by gaseous carbon dioxide was monitored by thermogravimetry. A kinetic model of CaO carbonation is proposed in order to interpret the first rapid step of the reaction. By taking into account, the existence of large induction period as well as the sigmoidal shape of the kinetic curves in this kinetic-controlled region, a surface nucleation and isotropic growth kinetic model based on a single nucleus per particle is proposed, and the expressions of the fractional conversion and the reaction rate versus time are detailed. The induction period is found to have a linear variation with respect to temperature and to follow a power law with respect to CO2 partial pressure. The areic reactivity of growth decreases with temperature increase, and increases with CO2 partial pressure increase. A mechanism of CaCO3 growth is proposed to account for these results and to determine a dependence of the areic reactivity of growth on the temperature and the CO2 partial pressure.

Sintering of calcium oxide (CaO) during CO2 chemisorption: a reactive molecular dynamics study

Reactive dynamics simulations with the reactive force field (ReaxFF) were performed in NVE ensembles to study the sintering of two solid calcium oxide (CaO) particles with and without CO(2) chemisorption. The simulated sintering conditions included starting adsorption temperatures at 1000 K and 1500 K and particle separation distances of 0.3 and 0.5 nm. The results revealed that the expansion of sorbent particles during CO(2) chemisorption was attributed to the sintering of two CaO-CaO particles. Increasing the adsorption temperature resulted in more particle expansion and sintering. The shorter the distance between two particles, the faster the rate of sintering during CO(2) adsorption. A detailed analysis on atom spatial variations revealed that the sorbent particles with a larger separation distance had a larger CO(2) uptake because of less sintering incurred. The chemisorptions of CO(2) on CaO particles sintered at high adsorption temperatures were also simulated to mimic the process of sorbent regeneration. It was found that regeneration would be more difficult for sintered particles than for fresh particles. In addition, a possible sintering barrier, magnesium oxide (MgO), was introduced to prevent CaO particles from sintering during CO(2) chemisorption. It was found that the MgO particles could reduce the sintering of CaO particles during CO(2) chemisorption. Simulation results from this study provided some guidelines on synthesizing or selecting sorbents with less sintering effect for multiple CO(2) adsorption-regeneration cycles.

Thermal behavior of calcite as an expansive agent

In this paper, thermal behavior of calcite as raw material of CaO-based expansive agent was investigated. The products were characterized by using differential thermal analysis (DTA), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD). DTA curves show that calcite has endothermic peak and impurity affects the onset of reactions. The more the impurity increases, the more energy changes increase. At 800-900?C, calcite was decomposed into solid calcium oxide (CaO) and gaseous CO2. Lime (CaO) used as the base of expandable material is the ultimate product of heated calcite. The calcium oxide phase, in reaction to water forms portlandite, at an onset temperature of about 900?C was also characterized by the appearance of the FT-IR mode at 867,3424 and 3644 cm-1. XRD results show that quartz impurity in calcite samples at 900?C forms larnite phase (Ca2SiO4). The expansions are mainly generated from the hydrations of CaO in the CaO-type expansive agent.

A novel method for producing hydrogen based on the Ca–Br cycle

The Ca–Br cycle is a promising method for efficiently producing hydrogen from water; however, it suffers from limitations inherent to gas–solid reactions. The cycle depends on the repeatable transformation of calcium bromide to calcium oxide and back to calcium bromide. The use of pure solids for these reactions would lead to rapid particle degradation and slow reaction kinetics. To circumvent these problems, a new reactor concept based on molten calcium bromide with dissolved calcium oxide has been proposed and developed. Preliminary experimental results indicate that the solubility of calcium oxide in calcium bromide at 800 °C is at least 1.2 wt%, a level that is expected to be high enough to make the proposed process work as designed. Early attempts to hydrolyze molten calcium bromide indicated that solid calcium oxide formation may inhibit reactivity, and thus injection of the moisture into the salt must be optimized.

Effect of Residual Chlorine on Ir-Catalyzed Reaction of Solid CaO with Gas Mixtures of Methane and Water Vapor

The effect of residual chlorine on the metal-catalyzed reaction of solid calcium oxide with a gas mixture of methane and water vapor (CaO + CH4 + 2H2O → CaCO3 + 4H2) is investigated at temperatures in the range 613–713 K, using solid samples of Ir/CaO prepared by TPR of Ir/CaCO3 with different chlorine contents below 1.1%. Chlorine-containing samples exhibit anomalous reaction curves characterized by the initial slow and linear progress followed by abrupt acceleration, while chlorine-free samples react more rapidly from the beginning to give simple curves without any acceleration. In both cases, apparent activation energy of 170–190 kJ/mol and reaction order of 0.8–1.0 with respect to methane pressure are determined, demonstrating that the presence of chlorine does not affect the kinetics of the reaction. Thus, the large difference in initial rate is considered to reflect the inhibiting role of residual chlorine. Based on these findings together with the data on surface properties of Ir/CaO, a model is proposed to explain the accelerative progress observed when residual chlorine is present.

Kinetic study of metal-catalyzed reaction of solid calcium oxide with gas mixtures of methane and water vapor to form hydrogen

With noble metal catalysts (Pd, Pt, Rh, Ir) present, hydrogen is formed by the interaction of solid calcium oxide with gas mixtures of methane and water vapor, according to CaO + CH4 + 2H2O → CaCO3 + 4H2. Among the metals, Ir and Rh are so active that the reaction takes place at temperatures as low as 600 K. Rate data obtained with these metals show a nearly first order with respect to CH4 pressure, while a negative order with respect to H2O vapor pressure. The apparent activation energies are 171 and 217 kJ/mol for the Ir- and Rh-catalyzed reactions, respectively. On the other hand, Ni does not catalyze the reaction below 733 K, probably due to its strong interaction with H2O vapor.

Mechanism of Formation of Colloidal Particles of Calcium Thiophosphates in an Organic Medium

The reaction of calcium oxide, P4S10, and water in the presence of calcium alkylarylsulfonate as a surfactant and tetrahydrofuran and xylene as solvents leads to a mixture of calcium mono-, di-, and trithiophosphate as colloidal particles stabilized by the surfactant in a hydrocarbon medium. A mechanism of the formation of the colloidal particles is proposed on the basis of systematic studies of the reaction medium and the characterization of the colloidal particles performed by means of chemical analyses, 31P NMR and SAXS. The initial step is a reaction of a water-in-oil microemulsion with solid calcium oxide. The resulting reverse micelles containing water and solubilized calcium hydroxide further react with solid P4S10 to yield colloidal particles of calcium thiophosphates. The influences of the surfactant concentration, water, and THF contents have been investigated. THF acts as a cosurfactant and is absolutely required in order to obtain thiophosphates instead of phosphates.

Kinetics of the reaction between gaseous sulfur trioxide and solid calcium oxide

Tiny particles (diameter < 100 µm) of porous CaO have been reacted with SO3 in inert N2 at atmospheric pressure and temperatures between 600 and 900 °C. These particles of CaO were well characterized by BET analysis and mercury porosimetry. Conditions were such that the kinetics of the reaction: CaO + SO3→ CaSO4, whereby one solid gives another, controlled the rate of production of CaSO4. Thus it was established that, for the initial stages of reaction, the diffusion of SO3 to a particle of CaO in the thermogravimetric balance used was relatively rapid, as was the diffusion of SO3 both inside the pores of a particle of CaO and through the layer of product, CaSO4. The reaction is first order in SO3, the rate constant (defined per unit area of solid CaO) being 3.2 ± 0.3 × 10–6 exp(–746 ± 108/T) m s–1. Thus the apparent activation energy is only 6.2 ± 0.9 kJ mol–1. The rate constant is almost identical to that for SO2 reacting with CaO to give CaSO3; in each case the steric factor is extremely low, being ca. 2 × 10–8. The diffusivity for SO3 through the product, CaSO4, is ca. 2 × 10–13 m2 s–1.

Reaction between gaseous sulfur dioxide and solid calcium oxide mechanism and kinetics

Sulfur dioxide has been reacted with tiny (diameter 35–85 µm) particles of porous CaO in a thermogravimetric balance. Kinetic measurements, together with infrared studies of the products, indicate that two reactions, viz: CaO + SO2→ CaSO3 and CaO + SO2→ 3/4CaSO4+ 1/4CaS occur. In the presence of both SO2 and O2, when CaSO3 and CaS both oxidise to CaSO4, these two reactions of SO2 provide the rate-determining steps for the initial stages of reaction for such tiny particles. Thus, the conditions used in this study succeed in preventing the rates of either of these reactions being controlled by the diffusion of SO2. The rates of both reactions per unit surface area of CaO have the general form: k([SO2]–[SO2]e), where [SO2]e is the concentration of SO2 for the reaction concerned being at equilibrium and k is the rate constant. Measurements of initial rates indicate that k= 7.2 × 10–6 exp(–1443/T) m s–1 and 1.2 × 10–6 exp(–481/T) m s–1 for the two reactions, respectively, correct to 25%. However, CaSO3 is unstable above ca. 1123 K, so that only the slower (second) reaction occurs above ca. 1123 K. That the rates of these reactions are independent of the concentration of oxygen confirms that SO3 plays no part in them. Measurements for large extents of reaction showed that the diffusion coefficient of SO2 through the solid products of reaction (mainly CaSO3) was Ds= 1.9 ± 0.5 × 10–14 m2 s–1. However, at high temperatures (> 1160 K) when only CaSO4 and CaS are produced, Ds falls to 2.3 × 10–15 m2 s–1.

Sulfur solubility in iron-carbon melts coexistent with solid CaO and CaS.

Experimental data are presented for the solubility of sulfur in liquid Fe-C alloys coexistent with solid calcium oxide, calcium sulfide and carbon monoxide of known pressures at 1 600°C. The equilibrium constant is determined for the sulfur reaction in terms of the activities of sulfur and carbon in iron for composition ranges 0.005 to 0.4% S and up to 3% C. The extrapolation of the data to hot metal compositions predicts for unit activities of calcium oxide, calcium sulfide and carbon monoxide, the equilibrium sulfur content of 4ppm for 1 600°C and 8ppm for 1 400°C. In relation to ladle desulfurization of hot metal, selected data are presented on some slag-metal reaction equilibria.

The role of various flame constituents in the production of atoms in the air—acetylene flame

Atom-formation processes in the premixed air—acetylene flame used in atomic absorption spectrometry are examined. Flame profiles of copper, indium and calcium atoms for five flames of differing acetylene: air ratios are compared with the flame profiles of temperature and the natural flame species C 2, CH and H. The flame profiles of the metals bear little resemblance to the temperature profile. C 2 and CH radicals are shown to be confined to the lower region of the flame (approximately to the region of the reaction zone), whereas H radicals persist far beyond the reaction zone. The strong resemblance of the profile of indium atoms to that of H radicals suggests the participation of H radicals in indium atom formation. Experiments on the action of the flame on solid calcium oxide similarly suggest the involvement of H radicals in the reduction of calcium oxide.