Formation Of CaC2 Research Articles

High-efficient acetylene synthesis by selective electrochemical formation of CO2-derived CaC2

Acetylene can be used as feedstock for various chemical products, but its raw material has been a fossil fuel, which poses an environmental challenge. One way to address the challenge is to form CaC2 from CO2, which reacts with water to form acetylene. This study demonstrated the selective formation of CaC2 from CO2 by an electrochemical process in NaCl-KCl-CaCl2-CaO melt at 823 K to produce C2H2 with high current efficiency. The CaC2 was formed through two reactions: the carbon electrodeposition from CO2-derived CO32− (Step 1) and the electrochemical reduction of Ca(II) ion on the carbon (Step 2). These two reactions could be controlled by conducting potentiostatic electrolysis under CO2 and Ar atmospheres, resulting in acetylene synthesis with a maximum current efficiency of 92 %. Each electrochemical reaction agreed with the thermodynamic electrode potential. The electrolysis on carbon electrodes revealed that the higher the crystallinity of carbon, the more selectively CaC2 was formed. The CaC2 formation was induced by the reduction of Ca(II) ions on the basal plane of the graphite layer rather than the edge plane. The unique interfacial phenomenon between high-temperature melt and a carbon electrode surface will contribute to realizing a highly efficient CO2 conversion process to acetylene.

SiO2 Promoted CaO Diffusion to C Phase at 1500 and 1700 °C

To better understand the mass transfer behaviors in CaC2 production from CaO and coke, this paper studies the diffusion behaviors of CaO and graphite, with or without ash, at 1500 and 1700 °C. CaO and graphite are pressed into tablets and heated alone or in close contact. Physical and chemical changes in these tablets are analyzed by XRD and SEM+EDX. In some experiments, thin Mo wires are placed between the closely contacted CaO and graphite tablets to identify the diffusion direction. It is found that the diffusion between CaO and low-ash graphite is very limited. SiO2 in a high-ash graphite diffuses into CaO tablet and reacts with CaO to form Ca2SiO4, which then diffuses into the graphite tablet easily and leads to CaC2 formation at 1700 °C.

Heterogeneous Phases Reaction Equilibrium in an Oxy-Thermal Carbide Furnace

This work focuses on revealing the chemical reaction equilibrium behaviors of gas–liquid–solid heterogeneous phases in an oxy-thermal carbide furnace. From a CaC2 formation mechanism investigation, it was determined that a one-step mechanism occurs when there is an excess of C and a high CO partial pressure, which inhibits the formation of Ca in the system, and a two-step mechanism occurs when there is insufficient C and a low CO partial pressure, which promotes the formation of Ca. Based on the calculated results of the equilibrium compositions at 100 kPa and different temperature conditions, the chemical reaction equilibrium behaviors of gas–liquid–solid heterogeneous phases in an oxy-thermal carbide furnace were analyzed at conditions of excess C and insufficient C.

Dense carbon film coated 316L via in-situ synthesized CaC2 in FLiNaK molten salts and its high performance of anti-corrosion property

Dense carbon film coated on 316L stainless steel was achieved by electrochemical deposition in molten fluoride salt (LiF-NaF-KF 46.5–11.5-42.0 mol%, FLiNaK, m.p. 727K) using C22- as the C source. The C22- source was in-situ synthesized in the high temperature eutectic salt by adding mixed Ca/C powders. Results of cyclic voltammetry confirmed the formation of CaC2 and the obtained C coated 316L samples demonstrate satisfactory electrochemical deposition via synthesized C22-. SEM images show that a dense and tunable thickness of C film can be fabricated in this FLiNaK–Ca/C–CaC2 system in the range of 2.0–6.0 μm by optimizing the deposition conditions such as concentrations of Ca/C, deposition potentials, temperatures and times. Characterizations of the as-prepared C film by Raman spectroscopy imply that deposited films are predominantly composed of low degree crystallization structures. The anti-corrosion behavior of this coated material was verified by potentiodynamic polarization. Compared to bare 316L material, corrosion rate suppression by a factor of more than 16 was determined for a 4.0 μm C coated 316L sample in 0.1M HCl+0.5M NaCl solution, indicating the coating provides extremely high anti-corrosion performance.

Conversion of bio-char to CaC2 at low temperatures-morphology and kinetics

The conversion of bio-char to CaC2 is a potential way to achieve the production of high-value-added chemicals from biomass. The unique properties of bio-char, such as its fine particles, high activity, and low ash content, provide a high reaction rate, low reaction temperature, and high CaC2 purity, which increase the feasibility of converting bio-char to CaC2. This work investigates the morphological behaviors of the solid reactants and the products, as well as the reaction kinetics, in terms of changes in activation energy and the particle size of the reactants. The experiments were carried out using a thermal gravimetric analyzer coupled with a mass spectrometer (TG-MS) at temperatures lower than 1700 °C using corncob char and CaO as the starting materials. The TG-MS data and kinetics modeling show that at temperatures of 1400–1700 °C, the reaction of corncob char and CaO with a particle size of 22–114 μm is predominantly under reaction control, but is slightly affected by the size of the reactants. During the course of the reaction, the reacting solids agglomerate via the formation of CaC2 without apparent melting.

Reaction kinetics of CaC2 formation from powder and compressed feeds

The production of CaC2 from coke/lime powders and compressed powder pellets are low cost and fast processes. A number of studies have reported the reaction kinetics of these reactions but they are still not well understood and the proposed kinetic models are not comparable due to differences in the reaction conditions. Therefore the reaction behavior of CaO/C powders (0.074 mm) and cubes (5 mm × 5 mm × (4.6–5.1) mm) compressed from a mixture of powders have been studied using thermal gravimetric analysis (TGA) at 1700–1850 °C. Kinetic models were obtained from the TGA data using isoconversional and model-fitting methods. The reaction rates for the compressed feeds were lower than those for the powder feeds. This is due to the reduced surface area of the compressed samples which inhibits heat transfer from the surrounding environment (or the heating source) to the sample. The compression pressure had little influence on the reaction rate. The reaction kinetics of both the powder and the compressed feeds can be described by the contracting volume model f(α) = 3(1–α)2/3, where α is the conversion rate of reactant. The apparent activation energy and pre-exponential factor of the powder feed were estimated to 346–354 kJ∙mol–1 and 5.9 × 107 min–1, respectively, whereas those of the compressed feed were 305–327 kJ∙mol–1 and 3.6 × 106 min–1, respectively. Open image in new window

Transformation of silicon-bearing minerals during CaC2 production and its effect on CaC2 formation

Silicon carbide (SiC) and ferrosilicon are the main solid by-products in the production of calcium carbide (CaC2) from coke and lime. Both of these silicon compounds are formed from silicon-bearing minerals in the raw materials but the routes of their formation are unclear. This paper presents a detailed study about transformation of the silicon-bearing minerals in a CaC2 furnace and its influence on CaC2 formation. The research was carried out in a thermogravimetric analyzer coupled with a mass spectrometer. It is found that the silicon-bearing minerals transform to SiC via reduction by C when the raw materials are large in size or to calcium silicates via reaction with CaO when the raw materials are pulverized and well mixed. The main calcium silicate, Ca3SiO5, reacts further with coke to form SiC and CaC2 via an intermediate Ca2SiO4. At exhaustion of coke, the calcium silicates react with CaC2 to form SiC. SiC may react with Fe to form ferrosilicon which is the main route for ferrosilicon formation in industrial furnaces. Low-temperature eutectics are formed from calcium silicates and CaC2. Calcium silicates inhibit the reaction of C and CaO to CaC2.

Solid-State Synthesis of Calcium Carbide by Using 2.45 GHz Microwave Reactor

A simple solid-state method has been described for the synthesis of CaC2 from CaO and graphite powders by using a 2.45 GHz microwave reactor. The reaction mechanism of CaC2 formation in the microwave environment is explained and compared with that of the conventional method. The whole microwave process completed within 180 min because of efficient coupling of microwaves with graphite powder. X-ray diffraction quantitative analysis results revealed 71.8% CaC2 formation at 1700 °C for 30 min of microwave exposure, whereas conventional heat treatment at 1700 °C for 30 min showed 14.1% CaC2 and 1750 °C for 60 min showed 62.8% CaC2. The X-ray photoelectron spectroscopy quantitative chemical state analysis based on C 1s spectra indicated 54.02% CaC2 in microwave heat-treated samples and 30.75% CaC2 in conventional heat-treated samples. The preliminary experimental results suggest that synthesis of CaC2 by microwave reactor is fast because of rapid volumetric heating.

The effect of CaO on emissions of nitric oxide from a fluidised bed combustor

The effects of adding particles of CaO to a hot bed of quartz sand, fluidised by N2, often containing small amounts of NO and CO, were investigated, especially to study the reduction of NO to N2. These observations indicate that surfaces of CaO are efficient catalysts in the presence of NO of the Boudouard reaction: 2 CO → Cs + CO2. In addition, CaO catalyses the reaction: NO + CO → ½ N2 + CO2. The kinetic parameters describing the nett rate constant for the overall conversion of NO to N2 were measured for the first time with CaO as catalyst; the activation energy is 27 ± 8 kJ/mol. This reaction was found to be more important for removing NO than: NO + Cs → CO + ½ N2 with graphite as the carbon, Cs. It also appears that CaO in a fuel-rich, fluidised bed containing graphite and NO at ∼1000 K produces CaC2, which is demonstrated here to react readily and very exothermally with NO in: CaC2 + 5 NO → 5/2 N2 + CaO + 2 CO2, thereby quickly removing NO and producing CO2. The production of CaC2 from CaO and carbon continues for a long time; the mechanism is discussed and probably involves catalysis by NO. In a bed with excess air, NO can be produced by CaC2 fixing atmospheric N2 to give CaCN2, which is oxidised later, i.e.: CaC2+N2→CaCN2+C, CaCN2+5/2O2→CaO+2NO+CO2. Thus the conspicuous interaction between CaO and NO in a fluidised bed is complicated by the continued formation of CaC2, whose subsequent reaction depends on whether conditions are fuel-lean (oxidising) or rich (reducing).

CaC2 Production from Pulverized Coke and CaO at Low Temperatures—Influence of Minerals in Coal-Derived Coke

Compared to the traditional electric arc process for the production of CaC2 from coke and CaO, the autothermal process requires less energy. However, the coke used for in situ heat generation results in more minerals in the reactor, because of the presence of minerals (or ash) in coke. This paper studies the influence of minerals (Fe2O3, MgO, SiO2, and Al2O3) commonly found in coal-derived coke on the formation of CaC2. The effect of CaF2, which is an additive used in some of the electric arc processes, on CaC2 production is also evaluated. The results show that Fe2O3 and MgO have little influence on CaC2 formation. SiO2 and Al2O3 do not react with coke at temperatures lower than 1460 °C, but they do react with CaO to form Ca3SiO5 and Ca2Al2O5, respectively, or calcium aluminosilicates in the presence of the both. All these Ca-containing compounds are able to react with C to form CaC2 but at rates lower than that of CaO and consume more C (to form CO). CaF2 has little influence on CaC2 formation in terms ...

CaC2 Production from Pulverized Coke and CaO at Low Temperatures—Reaction Mechanisms

CaC2 production with pulverized feeds was proven viable at temperatures about 400 °C lower than that required by the current electric arc technology (2100–2200 °C), which led to development of an autothermal process. For the purpose of reactor design, the reaction mechanism of coke (C) with CaO at temperatures up to 1750 °C is studied in a thermogravimetric analyzer (TGA) coupled with a mass spectrometer (MS). Results indicate that the reaction of C with CaO generally proceeds in three stages, starting at 1460 °C for CaC2 formation, followed by reaction of CaC2 with CaO and by decomposition of CaC2. The second stage is observable only at the complete consumption of C while the third is controlled by surface evaporation of Ca. Reaction behavior at the surface of coke and CaO particles is proposed, including the three-stage reactions and the role of CaC2–CaO eutectics, that promotes CaO diffusion and CaC2 production.

The influence of oxygen on the inoculation process of cast iron

The role played by oxygen during the inoculation of cast iron was investigated. It was found that oxygen is not desirable when commercial and pure Ca inoculants are employed. Consequently, the cast iron exhibits inferior mechanical strength, with increasing chilling susceptibility and hardness. It is shown that depending on the degree of oxidation of the molten iron, CaC2, or CaC2-CaO mixtures are formed. The negative effect of oxygen in iron inoculation can be explained by its effect on reducing the likelihood of CaC2 formation. Relatively large contents of oxygen in the inoculated melt lead to a reduced cell count. Hence, under these conditions, high degrees of undercooling and relatively high chill tendencies are expected during the eutectic transformation.

Revision of the enthalpies and gibbs energies of formation of calcium oxide and magnesium oxide

Major revisions in the enthalpies and Gibbs energies of formation of calcium oxide and magnesium oxide are presented. In free-evaporation experiments over the temperature range of 1830 to 2070 K, the kinetics of vaporization of calcium oxide and magnesium oxide have been studied. Conditions of local equilibrium were established. The results lead to new values for the standard enthalpies of formation of CaO and MgO. The ΔfH298 0 of CaO is ≈33 kJ/mol more positive than the currently tabulated value, whereas that for MgO is ≈34 kJ/mol more negative. The currently tabulated values could not account for these observations nor for other recent studies. These significant changes result in a reversal of the relative thermodynamic stabilities of CaO and MgO, with MgO now indicated as the more stable oxide at lower temperatures on Ellingham diagrams. These results are consistent with recent work on the formation of CaC2, solubility product measurements in liquid iron, and with theoretical models based on ionic radii.

Determination of standard gibbs energies of formation of CaC2, SrC2, and BaC2

Determination of standard gibbs energies of formation of CaC2, SrC2, and BaC2

Influence of Iron oxide, Aluminum oxide, Silicon dioxide and Potassium hydroxide in the Formation of Calcium Carbide

In continuation of the study on reactivity of carbon in the formation of CaC2, the effect of the addition of small amounts of some inorganic substances, such as Fe2O3, Al2O3, SiO2 and KOH, upon the reaction between carbon and CaO in solid phase was studied at 1, 800°C by means of a vacuum electric furnace.Generally, no acceleration could be observed throughout the reaction in the rates of the formation of CaC2. In the earlier stage of the reaction, it was rather likely that the presence of inorganic substances decreases the rates of the formation of CaC2.It is likely that these experimental results attributed to the following reasons that the inorganic substances disturb the mutual diffusion between carbon and CaO, and more-over, that they react respectively with carbon and CaO forming metal-carbides and CaO-metal oxides compounds, such as calcium-silicate, aluminate and ferrite.Accordingly, it was suggested that the inorganic substances have negative effect in the formation of CaC2.

(9)炭化カルシウムに關する研究.補遺(第1報)新製法と融解前後の反應,反應性,石灰よりの生成機構

(9)炭化カルシウムに關する研究.補遺(第1報)新製法と融解前後の反應,反應性,石灰よりの生成機構