The relation of cool flames and auto-ignition phenomena to process safety at elevated pressure and temperature.
The cool-flame phenomenon can occur in fuel-oxygen (air) mixtures within the flammable range and outside the flammable range, at fuel-rich compositions, at temperatures below the auto-ignition temperature (AIT). It is caused by chemical reactions occurring spontaneously at relatively low temperatures and is favoured by elevated pressure. The hazards that cool flames generate are described. These vary from spoiling a product specification through contamination and explosive decomposition of condensed peroxides to the appearance of unexpected normal (hot) flame (two-stage ignition).
Explosive decomposition of ethylene oxide at elevated condition: effect of ignition energy, nitrogen dilution, and turbulence.
Experimental and theoretical investigation of explosive decomposition of ethylene oxide (EO) at fixed initial experimental parameters (T=100 degrees C, P=4 bar) in a 20-l sphere was conducted. Safety-related parameters, namely the maximum explosion pressure, the maximum rate of pressure rise, and the Kd values, were experimentally determined for pure ethylene oxide and ethylene oxide diluted with nitrogen. The influence of the ignition energy on the explosion parameters was also studied. All these dependencies are quantified in empirical formulas. Additionally, the effect of turbulence on explosive decomposition of ethylene oxide was investigated. In contrast to previous studies, it is found that turbulence significantly influences the explosion severity parameters, mostly the rate of pressure rise. Thermodynamic models are used to calculate the maximum explosion pressure of pure and of nitrogen-diluted ethylene oxide, at different initial temperatures. Soot formation was experimentally observed. Relation between the amounts of soot formed and the explosion pressure was experimentally observed and was calculated.
The Structure of Electronically Excited Organic Molecules
Publisher Summary This chapter focuses on the structure of electronically excited organic molecules. The total number of stable organic molecules whose spectra have been analyzed sufficiently to characterize at least one electronically excited state is only of the order ten or twelve. They include the prototypes of most chromophores of special interest in organic chemistry, so that the information implied should be of value in studies of the complex rearrangements that occur when large molecules are exposed to radiation. An electronic state is characterized by the resultant electron spin S and by the symmetry species of the complete electronic wavefunction. Electronic excitation invariably leads to some changes in bond lengths and angles, the magnitude of the change depending on the extent to which the excited electron participates in bonding. It is common to find a different geometry in the ground and excited states of a polyatomic molecule. Two band systems of methylene have been observed by photolysis of diazomethane in presence of excess nitrogen. The radical is short-lived (no absorption is detected 50 μsec after the photolysing flash) and appears to be formed in an excited state from which it decomposes unless deactivated by collisions with the inert gas.