Temperature requirements, for

The use of an unnecessarily hot utility or heating medium should be avoided. This may have been a major factor that led to the runaway reaction at Seveso in Italy in 1976, which released toxic material over a wide area. The reactor was liquid phase and operated in a stirred tank (Fig. 9.3). It was left containing an uncompleted batch at around 160 C, well below the temperature at which a runaway reaction could start. The temperature required for a runaway reaction was around 230 C. ... 

Hence it is necessary to measure the heat capacity of a substance from near 0 K to the temperature required for equilibrium calculations to derive the enthalpy as a fiinction of temperature according to equation (B1.27.15f... 

The autoignition temperature is the minimum temperature required for self-sustained combustion in the absence of an external ignition source. The value depends on specified test conditions. Tht flammable (explosive) limits specify the range of concentration of the vapor in air (in percent by volume) for which a flame can propagate. Below the lower flammable limit, the gas mixture is too lean to burn above the flammable limit, the mixture is too rich. Additional compounds can be found in National Fire Protection Association, National Fire Protection Handbook, 14th ed., 1991. 

Thermally activated initiators (qv) such as azobisisobutyroaittile (AIBN), ammonium persulfate, or benzoyl peroxide can be used in solution polymeriza tion, but these initiators (qv) are slow acting at temperatures required for textile-grade polymer processes. Half-hves for this type of initiator are in the range of 10—20 h at 50—60°C (13). Therefore, these initiators are used mainly in batch or semibatch processes where the reaction is carried out over an extended period of time. 

The extremely high peak power densities available ia particle beams and lasers can heat the small amounts of matter ia the fuel capsules to the temperatures required for fusion. In order to attain such temperatures, however, the mass of the fuel capsules must be kept quite low. As a result, the capsules are quite small. Typical dimensions are less than 1 mm. Fuel capsules ia reactors could be larger (up to 1 cm) because of the iacreased driver energies available. 

K. C. Lee, J. L. Hansen, and D. C. Macauley, "Predictive Model of the Time-Temperature Requirements for Thermal Destmction of Dilute Organic Vapors," 72nd nnual 4PCA Meeting, Cincinnati, Ohio, June 1979. 

Because of the relative instabiUty of FeO, the reduction to metallic Fe occurs at a much lower temperature and appreciable CO2 is present in the product gas. The high temperature required for the reaction of MnO and C results in the formation of essentially pure CO the partial pressures of CO2 and Mn are <0.1 kPa (1 X 10 atm). The product of this reaction is manganese carbide (7 3) [12076-37-8J, Mn C, containing 8.56% carbon. Assuming immiscibility of the metal and carbide, Mn should be obtainable by the reaction of MnO and Mn C at 1607°C. However, at this temperature and activity of Mn, the partial pressure of Mn vapor is approximately 10 kPa (0.1 atm) which would lead to large manganese losses. 

Tertiary phosphine oxides are stable. The temperatures required for thermal decomposition are approximately 300°C higher than the corresponding amine oxides (96). Trimethyl phosphine oxide is stable to 700°C. 

The boiling point of ammonium nitrate—water solutions, given in Table 5, indicates the temperatures required for removing water (18). 

Measurements of stress relaxation on tempering indicate that, in a plain carbon steel, residual stresses are significantly lowered by heating to temperatures as low as 150°C, but that temperatures of 480°C and above are required to reduce these stresses to adequately low values. The times and temperatures required for stress reUef depend on the high temperature yield strength of the steel, because stress reUef results from the localized plastic flow that occurs when the steel is heated to a temperature where its yield strength is less than the internal stress. This phenomenon may be affected markedly by composition, and particularly by alloy additions. 

At least two catalytic processes have been used to purify halogenated streams. Both utilize fluidized beds of probably noimoble metal catalyst particles. One has been estimated to oxidize >9000 t/yr of chlorinated wastes from a vinyl chloride monomer plant (45). Several companies have commercialized catalysts which are reported to resist deactivation from a wider range of halogens. These newer catalysts may allow the required operating temperatures to be reduced, and stiU convert over 95% of the halocarbon, such as trichlorethylene, from an exhaust stream. Conversions of C-1 chlorocarbons utilizing an Englehardt HDC catalyst are shown in Figure 8. For this system, as the number of chlorine atoms increases, the temperatures required for destmction decreases. 

Ceramic bond formation and grain growth by diffusion are the two prominent reactions for bonding at the high temperature (1100 to 1370°C, or 2000 to 2500°F, for iron ore) employed. The minimum temperature required for sintering may be measured by modern dilatometry techniques, as well as by differential scanning calorimetry. See Compo et al. [Powder Tech., 51(1), 87 (1987) Paiticle Characterization, 1, 171 (1984)] for reviews. 

Temperatures required for corrosion by naphthenic acids range from 450 to 750°F, with maximum rates often occurring between 520 and 535°F. Whenever rates again show an increase with a rise in temperature above 650°F, sueh increase is believed to be caused by the influence of sulfur compounds which become corrosive to carbon and low alloy steels at that temperature. 

The chlorine present results in a self-extinguishing polymer. It also leads to a polymer which has a high rate of decomposition at the temperatures required for processing. 

The high temperatures required for phenolic cure are generally viewed as positive characteristics, as they insure that the phenolic does not cure at normal room-temperature storage conditions. This keeps the adhesive soft so that it retains the desired adhesive properties. 

Assume that in Example 7-10, the overall cycle time for a batch reaction is 8 hrs. The cycle time will include 2 hrs for heat-up and 3 hrs for cool-down. The batch will be heated from 20°C to the reaction temperature of 60°C, then cooled to 35°C. Using a hot-water jacket temperature of 80°C, it took 15 min to heat the batch from 20°C and 30°C. Calculate the jacket temperatures required for heat-up and cool-down. 

The jacket temperature required for a 2 hr heat-up can be obtained from Equation 7-104 as ... 

A Microsoft Excel spreadsheet (Example 7-ll.xls) was developed for predicting the jacket temperature required for either heating up or cooling down reactants in a batch reactor. 

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