Reduction maximum rate temperature

Example 5.6 Hydrocarbon cracking reactions are endothermic, and many different techniques are used to supply heat to the system. The maximum inlet temperature is limited by problems of materials of construction or by undesirable side reactions such as coking. Consider an adiabatic reactor with inlet temperature Tm. Then T z) < T, and the temperature will gradually decline as the reaction proceeds. This decrease, with the consequent reduction in reaction rate, can be minimized by using a high proportion of inerts in the feed stream. 

The maximum operating temperature may be evaluated from DTA/DSC curves if the shift of the peak due to reduction of the heating rate to 0.5-1 K min does not exceed 40 K. This corresponds to moderate activation energies of the secondary reactions, i.e. less than 50 kJ/mol for values obtained from the Arrhenius plots . 

Conclusions. In tubular multiphase reactors with an exothermic reaction where one phase with a high throughput serves to carry the heat of reaction out of the reactor, a sudden flow reduction in this phase (whether accompanied by a similar reduction in the other phases or not) can lead to a considerable transient temperature rise, well above the new steady state temperature. The maximum excess temperature depends in a complex way upon the rate of the flow reduction, the flow rates in the different phases, the heat capacities and the reaction rates of the system. 

If the motor operates at temperatures above 40 °C, it will heat up beyond its maximum permissible temperature at its rated power, which can lead to destruction of the motor. For this reason, a derating (power reduction) must be provided for. That means that a more powerful motor has to be used which is not loaded to its power rating and thus never reaches its limit temperature, even at increased ambient temperature. The maximum temperature of a motor is mainly determined by the temperature stability of the insulating paint on the winding. Several classes are distinguished here. The most common classes are ... 

The maximum rate of reduction in weight, which is expressed in terms of the angle from the temperature axis on the strip chart, of the sawdust of wood species relatively easy to heat oxidatively is 30 40° on the other hand, the maximum rate of reduction in weight of the sawdust of wood species relatively hard to heat oxidatively is approximately 50°, except that of Japanese cedar. In other words, it will be permitted to say that, when heated in thermal analysis performed in air, the sawdust of wood species relatively easy to heat oxidatively continues the oxidative decomposition reaction uninterruptedly but lazily from relatively low temperatures on the other hand, although the sawdust of wood species relatively hard to heat oxidatively remains as it is up to relatively high temperatures, once the sawdust begins to decompose oxidatively in the course of time, the oxidative decomposition reaction proceeds more rapidly and actively than the former. 

A third study of the kinetics of lipoamide dehydrogenase has utilized the enzyme isolated from rat liver (9S). At 25°, the temperature of the two previous studies, when dihydrolipoamide was varied at fixed levels of NAD the double reciprocal plots were concave down. At 37° this behavior was not observed. The detailed studies were carried out at the higher temperature. Rates were measured in both directions at pH 8.0, the pH optimum for the reduction of NAD. Under these conditions, initial velocity patterns for the forward and reverse reactions were a series of parallel lines. The Km for NAD was 0.52 mAf, for dihydrolipoamide was 0.49 mAf, for NADH was 0.062 mAf, and for lipoamide was 0.84 mAf. The maximum rate for NAD reduction was 20,700 min- /FAD... 

The experimental results obtained with the different catalysts are summarized in Table 2. In this table, the maximum reduction rate of NO to N2 and the corresponding temperature are given for each catalyst. The temperature range of activity corresponds to the range where the reduction rate is higher than half the maximum rate. In this table Cu-ZSM-5-27.5-100 means that Si/Al = 27.5 and that the Cu exchange level is 100 %. 

Temperature can ultimately be viewed as a thermal stress — one that causes an increase in failure rate (and life if applicable). But how severe a stress really is, must naturally be judged relative to the ratings of the device. For example, most semiconductors are rated for a maximum junction temperature of 150°C. Therefore, keeping the junction no higher than 105°C in a given application represents a stress reduction factor, or alternately — a temperature derating factor equal to 105/150 = 70%. 

Fluoropolymers are, generally, very stable at or below their specified maximum use temperatures. The rate of degradation of these plastics at higher temperatures is a function of their chemical stmc-tures in addition to temperature, time at temperature, and, to some extent, on the pressure and the atmosphere of decomposition. In actual processing, degradation is tracked by indirect measurement of molecular weight. Thermal exposure leads to a reduction in the molecular weight, which can be quantified by an increase in the MFR, heat of fusion of polymer, and in specific controlled measurements. 

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