Heat of decomposition

The theoretical energy requirement for the burning of Portiand cement clinker can be calculated from the heat requirements and energy recovery from the various stages of the process. Knowledge of the specific heats of the various phases, and the heats of decomposition, transformation, and reaction then permits calculation of the net theoretical energy requirement of 1760 kj (420 kcal) for 1 kg of clinker from 1.55 kg of dry CaCO and kaolin (see Clays) (8). 

Much information can be understood by a review of certain thermophysical properties of materials and mixtures. In comparing the values of heats of reaction, heats of decomposition and CART to values for known hazardous compounds, an estimation of thermal hazard potential can be made. Table A.2 outlines thermal hazard ranking values that could be used in classifying materials and processes based on heats of reaction and CART determinations (Melhem and Shanley 1997). 

Two standard estimation methods for heat of reaction and CART are Chetah 7.2 and NASA CET 89. Chetah Version 7.2 is a computer program capable of predicting both thermochemical properties and certain reactive chemical hazards of pure chemicals, mixtures or reactions. Available from ASTM, Chetah 7.2 uses Benson s method of group additivity to estimate ideal gas heat of formation and heat of decomposition. NASA CET 89 is a computer program that calculates the adiabatic decomposition temperature (maximum attainable temperature in a chemical system) and the equilibrium decomposition products formed at that temperature. It is capable of calculating CART values for any combination of materials, including reactants, products, solvents, etc. Melhem and Shanley (1997) describe the use of CART values in thermal hazard analysis. 

If the decomposition reaction follows the general rate law, the activation energy, heat of decomposition, rate constant and half-life for any given temperature can be obtained on a few milligrams using the ASTM method. Hazard indicators include heats of decomposition in excess of 0.3 kcal/g, short half-lives, low activation energies and low exotherm onset temperatures, especially if heat of decomposition is considerable. 

Use of oxygen and an inert gas enables the heat of combustion and the heat of decomposition to be evaluated respectively. 

Physical and emical Properties - Physical State at 15 XI and I atm. Liquid Molecular Weight 122.95 Boiling Point at 1 atm 169, 76, 349 Freezing Point -141.7, -96.5, 176.7 Critical Temperature Not pertinent Critical Pressure Not pertinent Specific Gravity 1.66 at 16 °C (liquid) Vapor (Gas) Density 4.24 Ratio of Specific Heats of Vapor (Gas) 1.44 Latent Heat of Vaporization 106, 59, 2.5 Heat of Combustion No data Heat of Decomposition Not pertinent. 

Physical and Chemical Properties — Physical State at 15 T7 and 1 atm. Liquid Molecular Weight Mixture Boiling Point at I atm. Decomposes Freezing Point 17, -8,265 Critical Temperature Not pertinent Critical Pressure Not pertinent Specific Gravity 1.2 at 20 °C (liquid) Vapor (Gas) Density Not pertinent Ratio cf Specific Heats cf Vapor (Gas) Not pertinent Latent Heal of Vaporization Not pertinent Heat of Combustion -15,700, -8750 -366 Heat of Decomposition -50, -28, -1.2. 

Vaporization-. Not pertinent Heai of Combustion-. -10,500, -5,830, -244 Heat of Decomposition Not pertinent. 

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