Presence Of Calcium Oxide Research Articles

Influence of Temperature and HCl Concentration on Mercury Speciation in the Presence of Calcium Oxide (CaO)

The behavior of mercury and its compounds in the flue gas of a mixed combustion of coal and secondary fuel is investigated. In an experimental entrained-flow reactor for combustion of pulverized fuels, fly ash and gaseous samples were taken and analyzed for their mercury concentrations. In laboratory tests the mechanisms observed in the reactor were studied in detailed investigations with the purpose of confirming and partly quantifying the influence of temperature and HCl concentration on mercury speciation in the presence of CaO particles.

Influence of Temperature and HCl Concentration on Mercury Speciation in the Presence of Calcium Oxide (CaO)

The objective of this investigations was to determine the behavior of mercury and its compounds in the flue gas of a mixed combustion of coal and secondary fuel. In an entrained-flow reactor for combustion of pulverized fuels, fly ash and gaseous samples were taken and analyzed for their mercury concentrations. During co-combustion of coal and sewage sludge as secondary fuel, CaO and HCl were specifically added to simulate variable fuel qualities. Subsequently, in laboratories tests, the mechanisms observed in the entrained-flow reactor were studied in detailed investigations at varying temperature and HCl concentration by using a synthetic gas made of the relevant components. The purpose was to confirm and partly quantify the influence of temperature and HCl concentration on mercury speciation in the presence of CaO particles.

Study on Tar Property from Coal Mild Gasification with Calcium Oxide Catalyst

Tars in both the presence and absence of calcium oxide were analyzed and compared. The results indicated that tar yields reach the maximum at 650 degrees in the absence of calcium oxide. It is in accordance with Tyler's results. But when calcium oxide is added, the temperature of tar maximum yield is only 550 degrees C. It is also demonstrated that the ratio of H/C, BTX, PCX and other light content in tar increase while the ratio of (O+N+S)/C and oxide compound in tar decrease in the presence of calcium oxide. It is noted that the maximum composition of alkanes in tar is C14∼C20 in the presence of calcium oxide while is C8∼C15 in the absence of calcium oxide. The yield of phenolic compounds was higher in the presence of calcium oxide than the raw coal alone. The result disagrees with the reported literature. The difference may arise from differences in temperature and gas or solid residence time, or from the difference of activity of calcium oxide used.

Effect of calcium oxide on pyrolysis of coal in a fluidized bed

The pyrolysis of Shenmu bituminous coal in both the presence and absence of calcium oxide was studied under atmospheric pressure over a temperature range of 450–750°C in a fluidized bed reactor. Calcium oxide significantly increases the gas yield while decreasing the tar yield. Tars produced in both the presence and absence of calcium oxide were analyzed and compared. The results indicated that tar yields reach a maximum at 650°C for coal pyrolysis without calcium oxide, in accordance with Tyler's results. When calcium oxide is added, the temperature of tar maximum yield is reduced to 550°C. It is also demonstrated that the ratio of H/C; benzene, toluene, xylene (BTX); phenol, cresol, xylenol (PCX) and other light components in tar increase while the ratio of (O+N+S)/C and oxide compounds in tar decrease in the presence of calcium oxide. It is noted that the maximum composition of alkanes in tar is C 14–C 20 in the presence of calcium oxide, while it is C 8–C 15 in the absence of calcium oxide. It results from the fracture of alkanes with long chains to alkanes with short chains when calcium oxide is added.

Mechanochemical Reaction of DDT with Calcium Oxide

Evidence is presented that, in the mechanochemical destruction of DDT [2,2-bis(4-chlorophenyl)- 1,1,1-trichloroethane] by ball milling in the presence of calcium oxide, a complex series of reactions occurs along the pathway to a product that appears to be essentially graphitic, though aromatic chloro and hydroxy substituents are retained to some degree. The production of the various intermediates can be understood in terms of processes initiated at both CaO and steel (of the milling device) surfaces. With the exception of DDE [2,2-bis(4-chlorophenyl)- 1,1-dichloroethene], most of these intermediates attain maximum concentrations corresponding to <1 mol % of the original DDT and have been characterized only by their mass spectra. In the case of dichlorotolane [bis(4-chlorophenyl)ethyne], however, yields are sufficient for it to be isolated chromatographically as a pure, crystalline solid and characterized further by NMR spectroscopy. After 12 h of milling, no organic materials volatile enough to be detecte...

Effects of a getter on nio reduction kinetics and metallic nickel particle formation

Studies have been made on the kinetics of nickel oxide powder reduction by hydrogen in the presence of calcium oxide as a water vapor getter. The getter influences the reduction mechanism and the coalescence of the reduced metal as well as the growth of fresh surface. Data are presented on the fresh surface of the nickel powder formed in the presence of calcium oxide and in the absence of it as regards reduction kinetics.

Thermal decomposition of arsenopyrite in the presence of calcium oxide

The thermal decomposition of arsenopyrite in the presence of calcium oxide was studied using TG/FTIR. A fairly pure arsenopyrite mineral and an industrial arsenopyrite concentrate were examined in inert and oxidizing atmospheres. The decomposition takes place below 800°C with the release of arsenic and sulphur in a form that depends on the prevailing atmosphere and on the amount of CaO added. The results also indicated that, with the addition of an appropriate amount of CaO, nearly complete containment of arsenic and sulphur during the decomposition of arsenopyrite may be possible.

The active phase in sodium-doped calcium oxide catalysts for oxidative coupling of methane

The reactivity of pure and sodium-promoted calcium oxide catalysts toward the oxidative coupling of methane at 640°C has been investigated. While the pure calcium oxide was essentially a combustion catalyst, sodium-promoted calcium oxide exhibited significant C 2 productivity. Study of the deactivation of both pure and promoted catalysts demonstrated that the presence of calcium oxide was necessary for both catalysts to be active. This observation, combined with the effects of sodium doping on C 2 selectivity, suggests that the active phase on Na/CaO catalysts toward C 2 formation consists of sodium species associated with calcium oxide. This active phase was destroyed when calcium oxide was converted into calcium carbonate under reaction conditions.

Swelling and plastic behavior of coal devolatilized at elevated pressures of air in the absence and presence of calcium oxide

Swelling and plastic properties of an lv bituminous coal (PSOC 1197) devolatilized at elevated air pressures (at 60 or 150 K/min) were monitored using a high-pressure microdilatometer. It was observed that the maximum swelling parameter ( V 8) of the coal was markedly reduced when devolatilized at elevated air pressures, provided that the heating rate of the coal was sufficiently low (60 K/min to 923 K). In marked contrast, at a relatively higher heating rate (e.g., 150 K/min), the swelling of coal at elevated air pressures was closer to V s obtained in N 2 pressures. An implication of this finding is that coal swelling can be very high at actual utilization conditions (rapid heating of coal in air). The reduction in coal V s at a relatively slow heating rate is attributable, at least in part, to the preoxidation (chemisorption of oxygen to form oxygen crosslinks) of coal during initial heat-treatment in air (before there is significant devolatilization). Devolatilization of coal in the presence of CaO, however, markedly reduced the swelling of coal at various air pressures and heating rates. This reduction in coal swelling is attributed to crosslinking reactions of pyrolyzing coal that have been catalyzed by CaO.

Reduction of cobalt sulphide in the presence of calcium oxide

The recovery of metals from their sulphide ores by hydrogen reduction is frequently limited by the low equilibrium constants of the reactions. However, θ 1 = 4.86 × 10 −5β −1.69H 0.28d p 0.3 exp ( 188 RT ) Metallographic examination of the reaction product showed meta

Leaching of Sodium and Chlorine from Coals

Abstract The presence of sodium and chlorine in coals often causes fouling and corrosion of boiler tubes and downstream equipment in power plants. These elements are also suspected of augmenting materials problems in fluidized-bed combustors and coal-burning gas turbines. Battelle Columbus Laboratories has developed a process to remove the sodium and chlorine from coal. Experiments carried out with Illinois No. 6 coal suggest that substantial reductions in sodium and chlorine levels can be achieved by extracting the coal with water in the presence of calcium oxide under appropriate conditions. The degree of removal is a function of temperature, extraction time, and coal particle size, and is independent of the water-to-coal ratio. The effects of these process variables on removal are discussed. The data are also interpreted to postulate the mode of sodium and chlorine occurrence in coal.

Hydrogen reduction kinetics of nickel sulfide in the presence of calcium oxide

Recovery of pure nickel from nickel sulfide (Ni3S2) was studied by following to completion the hydrogen reduction reaction in the presence of calcium oxide. The effects of reaction temperature, molar ratio of calcium oxide to nickel sulfide, bed depth, and particle size of the nickel sulfide powder on the reaction were experimentally investigated. A simple empirical integrated rate equation describing the relationship among these variables over the temperature range 773 to 973 K was derived. The activation energy for the scavenged reaction was found to be 101.9 kJ from the experimental data. Over the range of experimental conditions, both globular and fibrous forms of metallic nickel were observed.

Structural changes occurring during reduction of hematite and magnetite pellets containing coal char.

The structural changes that occurred during the reduction of hematite and magnetite pellets containing coal char, in the temperature range between 900°C and 1200°C, were studied.The behavior of the pellets was complex. Significant temperature gradients within the pellet were attained during the process, and the reduction was accompanied by catastrophic swelling of the pellets between 900°C and 1000°C, while shrinkage was observed at 1100 and 1200°C. Observed microstructural features such as intragranular porosity and cracking of oxide grains resulted from severe lattice disturbances occurring upon transformation of hematite to magnetite.The catastrophic swelling observed for hematite and magnetite pellets 900 and 1000°C was due to the filamentary or whisker growth of iron outward from the wustite surfaces. The whisker formation appears to be due to a changing reducing potential of the gas phase within the pellet coupled with the presence of calcium oxide on the wustite surface. The shrinkage reported at 1100 and 1200°C is accounted for in terms of sintering of iron filaments.The pellets strength was found to decrease between 900°C and 1000°C, and increased at higher temperatures. The weakness at low temperatures was due to the absence of bonding between iron filaments or whiskers. The high strength obtained at higher temperatures (1100 and 1200°C) was produced by sintering of iron filaments.

A novel synthesis of 2‐substituted oxazolines

AbstractThermal rearrangement of N‐acyl‐2‐oxazolidones in the presence of calcium oxide has been shown to provide a new entry into 2‐substituted oxazolines.

Physico‐chemical properties of by‐product gypsum

AbstractFour samples of by‐product gypsum were analysed by chemical and physical methods and subjected to comparable degrees of calcination in a special rotary furnace. The hydration characteristics of the resulting calcium sulphate hemihydrates were determined in terms of three basic parameters viz. α0, a measure of heterogeneous nucleation in the system; k, a measure of self‐acceleration of the reaction; and θ, the period of induction. Measurements were made of the size distribution of particles, pH, water requirement, the colour and compressive strength of cast gypsums made from the hemihydrates, and comparisons were made with two samples of calcined natural gypsum. Additions of calcium oxide were also made to the by‐product gypsums and the same procedures followed. Hydration of the calcined products resulted in considerable differences in the kinetic parameters. Both differences in nucleation and transport of calcium sulphate from the grains of hemihydrate to the growing crystals of the dihydrate seemed to contribute to variations in reactivity. The by‐product gypsums calcined alone, or in the presence of calcium oxide, yielded hemihydrates with water requirements greater than those of the calcined natural gypsums. The compressive strengths of cast gypsums made from these hemihydrates were somewhat less than those made from the calcined natural gypsums. The colour co‐ordinates were about the same. After treatment with calcium oxide, the by‐product gypsum appears to be suitable for making plaster of Paris.

Gas‐solid reactions II: Reduction of cobalt sulfide in the presence of calcium oxide

AbstractThe results of an experimental program to test the applicability of the grain‐cell model to complex gas‐solid reactions are presented. The hydrogen reduction of solid cobalt sulfide (CO9/8S) in the presence of calcium oxide was chosen for study. Powders of both solids were mixed in a molar ratio of 3.0 (CaO:Co9/8S), compressed into pellet form, then reduced by hydrogen in the temperature range 600‐800°C. The experimental results at different operating conditions were compared with the grain‐cell model, using the Thiele type modulus (H) as an adjustable parameter. In the presence of excess calcium oxide, the structural‐kinetic parameter (γ) was essentially zero, and (H) was found to be the effective parameter, controlling reduction rates. Good agreement between experimental results and model was obtained.

Kinetics of cobalt sulfide reduction in the presence of calcium oxide

Kinetic measurements have been made on the hydrogen reduction of solid cobalt sulfide in the presence of calcium oxide. The cobalt metal yield was compared with that of the direct reduction reaction over the temperature range 600 to 800°C at various hydrogen flow rates, and calcium oxde to cobalt sulfide mixing ratios. It was found that the presence of calcium oxide caused a sharp increase in the reaction rate—for example a 15 fold increase in conversion was achieved at 700°C after 24 min of reaction. Low hydrogen flow rates were found to be desirable, and an optimum mixing ratio of 3.0 established.

The synthesis of certain derivatives of 2-fluoro- D-ribose, 2-deoxy-2-fluoro- D-ribose, and 2-deoxy-2-fluoro- D-arabinose

Addition or trifluoromethyl hypofluorite to 3,4-di- O-acetyl- D-arabinal ( 1) gave three crystalline products. The reaction products (one F,OCF 3 adduct and two F,F adducts) were determined, by spectroscopic and chemical methods, to be trifluoromethyl 3,4-di- O-acetyl-2-deoxy-2-fluoro-β- D-arabinopyranoside ( 2), 3,4-di- O-acetyl-2-deoxy-2-fluoro-β- D-arabinopyranosyl fluoride ( 3), and 3,4-di- O-acetyl-2-deoxy-2-fluoro-α- D-ribopyranosyl fluoride ( 4). Acid hydrolysis of 2 and 3 furnished 2-deoxy-2-fluoro- D-arabinose ( 5); the reaction sequence is particularly well-suited for large-scale preparation of this fluoro sugar. Similarly, hydrolysis of 4 gave 2-deoxy-2-fluoro- D-ribose ( 6). Crystalline 2,3,4-tri- O-acetyl-1,5-anhydro- D- erythro-pent-1-enitol ( 8) was prepared from tri- O-acetyl-β- D-arabinopyranosyl bromide; it gave two adducts on treatment with trifluoromethyl hypofluorite in the presence of calcium oxide; the structures assigned to them, namely, trifluoromethyl 2,3,4-tri- O-acetyl-2-fluoro-β- D-ribopyranoside ( 9) and 2,3,4-tri- O-acetyl-2-fluoro-β- D-ribopyranosyl fluoride ( 10), were confirmed by 90-MHz n.m.r. spectral studies and spin-decoupling experiments.

Thermal reduction of olivine by calcium carbide and by silicon in the presence of calcium oxide

The vapour pressures over the reactants olivine - calcium-carbide and olivine - silicon - calcium oxide have been measured over the temperature ranges 1115 to 1190°C and 1045 to 1165°C, respectively. The equilibrium reactions do not involve olivine since this material readily decomposes in the presence of CaC2 or CaO. In the calcium carbide reduction, the reaction mechanism depends on the ratio of olivine to calcium carbide in the charge. In the silicon reduction, the equilibrium-pressures are essentially the same as those for the corresponding reduction of dolomite. The possible role of an intermediate calcium-silicon alloy in the latter case is discussed. Résumé Les auteurs ont mesuré les tensions de vapeur au-dessus des réactifs olivine - carbure de calcium et olivine - silicium - oxyde de calcium à des intervalles de température de 1115 à 1190°C et de 1045 a 1165°C respectivement. Les réactions de'équilibre n'impliquent pas l'olivine car ce composé se décompose en présence du CaC2 ou du CaO. Dans le cas de la réduction du carbure de calcium, les mécanismes de réaction dépendent de la proportion d'olivine et du carbure de calcium dans la charge. Pour la réduction du silicium, les pressions à l'equilibre sont essentiellement les mêmes que celles pour la réaction équivalente avec la dolomite. Le rôle possible d'un composé intermédiaire calcium - silicium dans le dernier cas est discuté.

Heterocyclic syntheses by high temperature dehydrocyclisation of amines and imines with iodine. Part I. Pyridine

The stoicheiometric reaction of suitable aliphatic amines or imines with iodine at 400–600° produces pyridine. In the presence of calcium oxide, which removes the hydrogen iodide also formed, a yield of pyridine of 65% may be obtained. Addition of oxygen permits the use of less than the stoicheiometric quantity of iodine. A mechanism is proposed.