Carbonate decompositions

Carbonate Decomposition. The carbonate content of Green River oil shale is high (see Table 4). In addition, the northern portion of the Piceance Creek basin contains significant quantities of the carbonate minerals nahcoUte and dawsonite. The decomposition of these minerals is endothermic and occurs at ca 600—750°C for dolomite, 600—900°C for calcite, 350—400°C for dawsonite, and 100—120°C for nahcohte. Kinetics of these reactions have been studied (19). Carbon dioxide, a product of decomposition, dilutes the off-gases produced from retorting processes at the above decomposition temperatures. 

Reacting species, predominant, 80 Reaction coordinate, 133 Reaction heat, 135 additivity of, 111 measurement of, 111 Reaction rates, 124 factors affecting, 125 Reactions, 38,129 acid-base, 188 balancing, 42, 217, 219 calcium carbonate decomposition, 143... 

X-ray diffraction confirms linear coordination in Au(PPh3)(C=CC6F5) and Au(H2NCHMe2)(C=CPh) with the short Au-C bonds (1.935-1.99 A) expected for bonds to sp hybridized carbon. Decomposition of these compounds in the vapour above 150°C is a potential route to very pure gold films [162],... 

Metal carbonate decompositions proceed to completion in one or more stages which are generally both endothermic and reversible. Kinetic behaviour is sensitive to the pressure and composition of the prevailing atmosphere and, in particular, to the availability and ease of removal of C02. The structure and porosity of the solid product and its relationship with the reactant phase controls the rate of escape of volatile product by inter-and/or intragranular diffusion, so that rapid and effectively complete withdrawal of C02 from the interface may be difficult to achieve experimentally. Similar features have been described for the removal of water from crystalline hydrates and attention has been drawn to comparable aspects of reactions of both types in Garner s review [ 64 ]. 

The kinetics of carbonate decompositions have been studied for both their technical importance and their theoretical interest. While both isothermal and non-isothermal techniques have been used, data obtained by rising temperature methods may be unreliable where the influence on the reverse reaction of C02 gas present has not been positively characterized. 

Activation energy values for the recombination of the products of carbonate decompositions are generally low and so it is expected that values of E will be close to the dissociation enthalpy. Such correlations are not always readily discerned, however, since there is ambiguity in what is to be regarded as a mole of activated complex . If the reaction is shown experimentally to be readily reversible, the assumption may be made that Et = ntAH and the value of nt may be an indication of the number of reactant molecules participating in activated complex formation. Kinetic parameters for dissociation reactions of a number of carbonates have been shown to be consistent with the predictions of the Polanyi—Wigner equation [eqn. (19)]. 

The presence of impurities can cause a shift in the dissociation point. It implies that the equilibrium temperature and pressure of the carbonate decomposition reaction are shifted. The effect of silica is particularly illustrative in the case of limestone. If silica is present as an impurity, it lowers the decomposition point of limestone. The acid anhydride silica slags combines with the basic calcium oxide according to following ... 

Stage III The decomposition of calcium carbonate to calcium oxide, which is a function of the partial pressure of the C02 in contact with the sample. The endothermal band for the carbonate decomposition is sharply peaked spread over a relatively narrower temperature range in an atmosphere of C02. 

Calcium, in oil, 27 317 Calcium carbonate, decomposition of, dislocations and, 19 377-389 Calcium molybdate, 27 206... 

Combustion temperatures are high enough to ensure carbonate decomposition and full oxidation of the sulphur values to the sulphate form. 

Barium carbonate decomposes to barium oxide and carbon dioxide when heated at 1,300°C. In the presence of carbon, decomposition occurs at lower temperatures. Barium carbonate dissolves in dilute HCl and HNO3 liberating CO2. Similar reaction occurs in acetic acid. The solid salts, chloride, nitrate and acetate that are water soluble may be obtained by evaporation of the solution. Dissolution in HF, followed by evaporation to dryness, and then heating to red heat, yields barium fluoride. 

If the solution is dried for long times over potassium carbonate, decomposition of the oxaziridine sometimes occurs. 

Carbonate decomposition does not become significant until 1000°F and, as would be expected, is greater for longer periods at temperatures above 1000°F. There appears to be a qualitative correspondence be-... 

An alternative method of suppressing carbonate decomposition is possible because the decomposition pressure of calcium carbonate is low enough to be overcome by a trace of carbon dioxide in the gas phase. When 2% carbon dioxide was added to the feed gas (10-psia carbon dioxide), the carbonate decomposition was much less than in the corresponding pure hydrogen runs. 

However, while the carbonate decomposition was repressed, the kerogen recovery was also reduced relative to the pure hydrogen runs. Thus, the net improvement was not as striking as implied by the carbon dioxide repression (Figure 4). 

Figure 4. Correlation of rich shale kerogen recovery and carbonate decomposition in pure hydrogen...

---