Flammability ranges oxidants

An increase in temperature tends to widen the flammable range, reducing the LFL. For example, the LFL for methane in air is commonly quoted as 5%. As the temperature of methane increases to autoignition temperature, the LFL falls to around 3%. Stronger ignition sources can ignite leaner mixtures. Flammability limits also depend on the type of atmosphere. Flammability limits are much wider in oxygen, chlorine, and other oxidizers than in air (NFPA, 1997). 

A refined grade of MTBE is used in the solvents and pharmaceutical industries. The main advantage over other ethers is its uniquely stable structural framework that contains no secondary or tertiary hydrogen atoms, which makes it very resistive to oxidation and peroxide formation. In addition, its higher autoignition temperature and narrower flammability range also make it relatively safer to use compared to other ethers (see Table 3). 

The presence of the catalyst provides a lower-energy chemical path than that offered by a thermal reaction. A catalyst accelerates oxidation of hydrocarbon/carbon monoxide/air mixtures that lie outside the flammability range required for thermal reactions. In the exhaust of the automobile the composition of the pollutants is far below the flammability range yet the oxidation reactions occur by the catalyst providing a lower-energy chemical path to that offered by the thermal reaction. An excellent example is the oxidation of CO with and without a catalyst. Without a catalyst the rate-limiting step is 02 dissociation at 700°C followed by reaction with gas phase CO. In the presence of the Pt catalyst 02 dissociation is rapid and the rate-limiting step becomes the surface reaction between adsorbed O atoms and CO that occurs below 100°C. 

The minimum ignition energy is simply the minimum energy necessary to cause the ignition of a mixture of flammable gas and oxidizing gas within the flammable range. It is usually measured by an electrical spark discharge because of the ease of the test. 

Because CPO reactors are normally operated in the fuel-rich regime, the proper way to shut them down is to remove the oxidant and thus avoid feed compositions that are within the flammable range that could potentially lead to explosions. 

Only the first step differs from the tertiary butyl alcohol conversion scheme. It has given rise to considerable research, particularly by Asahi, Dow, Japan Catalytic, Kureha, Mitsubishi, Montedison, Nippon Kayaku, Nippon Zeon, Sohio, Toyo Soda Ube, etc. It takes place in the vapor phase, between 300 and 40O°C, at 0.1 to 0.5 Pa absolute in the presence of a fixed bed of unsupported mixed oxides based on molybdenum, bismuth, tellurium and various additives. To avoid the flammability range, the isobutene and air feed must be diluted with nitrogen and possibly steam. With a residence time of 2 to 3 s, once-through conversion is better than 95 per cent and the molar yield of methacrolein is up to 85 to 90 per cent... 

If chlorine does not evolve in the gas phase in normal process conditions, an inert gas flush in the reactor gas phase is recommended (see below). If a chlorine flow evolves from the liquid reaction mixture unreacted, enough inert gas flush must be provided in the reactor gas phase to lower the chlorine concentration below the minimum oxidizer concentration (MOC) of the fuel flammable range. 

In diffusion-mixed burners, shown schematically in Figure 1.25 and in a drawing in Figure 1.26, the fuel and the oxidizer are separated and unmixed prior to combustion, which begins where the oxidizer/fuel mixture is within the flammability range (assuming the... 

Turbulence is required for the acceleration of flame front to speeds required to produce the blast overpressure associated with a VCE. In the absence of turbulence, a flash fire will occur without any appreciable overpressure, with the hazard limited to the thermal radiation impacts associated with the burning of the cloud from the ignition point back to the release source, or within the flammable range of the cloud. Flame turbulence is typically formed by the interaction between the flame front and obstacles. The blast effects produced by VCEs vary greatly and are primarily dependent on flame speed therefore, areas of confinement and congestion near the release point can influence the likelihood of a VCE. Additionally the reactivity of the material is an important consideration highly reactive materials such as ethylene oxide are much more likely to lead to a VCE than lower reactive materials such as methane. 

Toxicology LD50 (oral, rat) 4260 mg/kg LC50 (inh., rat, 0.5 h) 253,000 mg/m irritating to eyes, skin, mucous membranes harmful by inh. may affect respiratory tract, liver and CNS may cause sleepiness, muscular incoordination, respiratory depression TSCA listed Precaution Elamm. incompat. with strong oxidizers, strong bases forms flamm. mixts. with air in a narrow flammability range contains may explode in fire... 

AH the pertinent physical and chemical properties of chemical materials should be evaluated in relation to the hazards of fire, explosion, toxicity, and corrosion. These properties should include thermal stability, shock sensitivity, vapor pressure, flash point, boiling point, ignition temperature, flammability range, solubility, and reactivity characteristics (e.g., water reactivity and oxidizing potential). 

Flammable. Flammable gases are defined as those that form a flammable mixture with air at 13 percent or less by volume, or have a flammable range in air of greater than 12 percent by volume regardless of the lower flammable limit [49 CFR 173.300 (b)] (see Section 16.3). The flammable range of a gas is strongly dependent upon the temperature, pressure, or oxidant concentration of or in the vicinity of the gas thus control of physical conditions near the gas is important. An... 

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