Maximum reaction temperature

Chemical reactions are sometimes conducted in a dilute solution to moderate reaction rates, to provide a heat sink for an exothermic reaction, or to limit maximum reaction temperature by tempering the reaction. In this example there are conflicting inherent safety goals—the solvent moderates the chemical reaction, but the dilute system will be significantly larger for a given production volume. Careful evaluation of all of the process risks is required to select the best overall system. 

The reactor would be run adiabatically, but the maximum reaction temperature allowable is 400 °C, since above this temperature undesirable by-products are formed. Calculate the minimum reactor volume required to obtain 80% conversion of A. What must the heat transfer rate be in the cooling section of the reactor ... 

The heat of decomposition (238.4 kJ/mol, 3.92 kJ/g) has been calculated to give an adiabatic product temperature of 2150°C accompanied by a 24-fold pressure increase in a closed vessel [9], Dining research into the Friedel-Crafts acylation reaction of aromatic compounds (components unspecified) in nitrobenzene as solvent, it was decided to use nitromethane in place of nitrobenzene because of the lower toxicity of the former. However, because of the lower boiling point of nitromethane (101°C, against 210°C for nitrobenzene), the reactions were run in an autoclave so that the same maximum reaction temperature of 155°C could be used, but at a maximum pressure of 10 bar. The reaction mixture was heated to 150°C and maintained there for 10 minutes, when a rapidly accelerating increase in temperature was noticed, and at 160°C the lid of the autoclave was blown off as decomposition accelerated to explosion [10], Impurities present in the commercial solvent are listed, and a recommended purification procedure is described [11]. The thermal decomposition of nitromethane under supercritical conditions has been studied [12], The effects of very high pressure and of temperature on the physical properties, chemical reactivity and thermal decomposition of nitromethane have been studied, and a mechanism for the bimolecular decomposition (to ammonium formate and water) identified [13], Solid nitromethane apparently has different susceptibility to detonation according to the orientation of the crystal, a theoretical model is advanced [14], Nitromethane actually finds employment as an explosive [15],... 

Once the onset temperature is determined, it is then possible to obtain the maximum reaction temperature by the adiabatic temperature rise and any contribution due to external heat input. The theoretical adiabatic temperature increase is... 

From these expressions, the maximum reaction temperature Tmax is defined by... 

Very recently, a novel microwave-assisted high-temperature UV digestion system for accelerated decomposition of dissolved organic compounds or slurries was developed [95, 96]. The technique is based on a closed, pressurized, microwave decomposition device wherein UV irradiation is generated by immersed electrodeless Cd discharge lamps (228 nm) operated by the microwave field in the oven cavity. The immersion system enables maximum reaction temperatures of up to 250-280 °C, resulting in a tremendous increase in mineralization efficiency. 

Melt index potential means the maximum MI that can be obtained with a catalyst activated at maximum temperature (871 °C), and making homopolymer at maximum reaction temperature (110 °C). Catalystshaving a high-MI potential need not be used to make high MI resins, but they have the capability. Low-MI polymers are typically manufactured more easily with catalysts having a high-MI potential. 

The continuous evolution of carbon dioxide from water-blown foam from the earliest times of reaction is a mechanism for significant heat loss from free-rise foam, the magnitude of which will depend on the scale of foaming. This observation offers an explanation for the departure from adiabaticity, lower than expected maximum reaction temperature, in smaller scale foaming. 

In a first step the isoperibolic and the partially controlled mode of operation shall be investigated more closely because they are common in industrial practice and they have an analogy to a mode of operation for homogeneous cooled tube reactors (c.f. introduction to Section 4.3.1.2). For these two modes the analysis of the heat balance leads to an equation with two unknowns the maximum reaction temperature and the corresponding value for the conversion. 

In daily practice, a frequently asked question looks for the tolerable value of the thermal reaction number if the maximum sensitivity value is fixed. The background to this situation usually is a given plant with a certain instrumentation and a known variability for the coolant temperature under normal operating conditions. Usually more than 5 K variability in the maximum reaction temperature cannot be tolerated in the production of specialties such as those manufactured in the fine chemicals and pharmaceutical industry. This information fixes the value for the maximum sensitivity. 

At this point the remark made in Section 4.1.3.1 about an optimized start-up strategy for the cooled CSTR shall be explained. The safety technical assessment procedure for the cooled isoperibolic SBR has demonstrated that in the case of correct design a prediction of the maximum reaction temperature is easily possible. This can be utilized for the optimization of the start up of the CSTR. The later steady state operating temperature of the CSTR is defined as the set value for the maximum SBR process temperature. In a next step one of the two reactants of the CSTR process is charged initially. Then the reactor is started as a semibatch process by feeding the second reactant. When the maximum temperature is reached, the feed of the initially charged reactant is started, and the feed streams are adjusted in such a way that the Stanton number of the CSTR is established. This way the initial oscillations are elegantly avoided. 

First a 5 kW combined methanol steam reformer-catalytic combustor was built. The reactor was composed of modules ofthree types of plates forming a stack. Instead of microchaimels, fins served as mechanical support and improved heat transfer. A total of 225 plates were incorporated into the reactor. The reactor was designed for a maximum operating pressure of 4bar and 350 °C maximum reaction temperature. The experimental results presented were determined at a partial load of the device [1-2 kW for the lower heating value (LH V) of the hydrogen produced]. At a S/C ratio of... 

Spectroscopic evidence of the seven-membered rings has been found in the preparation of polyimides from pyromellitic dianhydride and methylenediphenyl-diisocyanate (MDI) [105]. The reaction is conducted in solution of aprotic solvents, with reagents addition at low temperature and a maximum reaction temperature of about 130 °C. On the other hand, polyimides of very high molecular weight have not been reported by this method. The mechanism is different when the reaction is accelerated by the action of catalysts. Catalytic quantities of water or alcohols facilitate imide formation, and intermediate ureas and carbamates seem to be formed, which then react with anhydrides to yield polyimides [106]. Water as catalyst has been used to exemplify the mechanism of reaction of phthalic anhydride and phenyl isocyanates, with the conclusion that the addition of water, until a molecular equivalent, markedly increases the formation of phthalimide [107] (Scheme 13). The first step is actually the hydrolysis of the isocyanates, and it has been claimed that ureas are present in high concentration during the intermediate steps of the reaction [107]. Other conventional catalysts have been widely used to accelerate this reaction. Thus, tertiary amines, alkali metal alcoholates, metal lactames, and even mercury organic salts have been attempted [108]. 

Maximum reaction temperature Limited by stability of metal (complexes) and ligand Limited by ionic liquid stability... 

Equation (4.10.53) expresses that if we reach the critical (maximum) reaction temperature, the heat released by the reaction just exactly equals the heat removed by cooling. 

This equation shows that at the location of the critical maximum reaction temperature the heat released by the reaction equals the heat removal by wall-cooling. The... 

The maximum reaction temperature of 450 K was held for two days and was followed by slow cooling to room temperature. A final composition of a-Zr2PdD2,7 was calculated from the total pressure drop, but similar preparation of a nominal a-Zr2PdH2,7 sample showed H2.9 upon NMR spin count. The magnetic susceptibility of a small part of the ribbon pieces was measured between 7 and 300 K with an S.H.E. SQUID magnetometer, as had been done on the original glassy alloy. The NMR sample was prepared... 

Figure 3.7 shows the results obtained in the batch process at 87 °C according to literature procedures [50]. A mixture of water and p-dioxane as a solvent system was chosen to allow for homogenous reaction conditions using a Pd(0) catalyst Reaction times of 8 and Ih were observed for bromo- and chlorobenzaldehyde, respectively, until the (nonisolated) GC yield reached about 90%. The maximum reaction temperature was limited in these experiments by the boiling point of the mixture at ambient pressure. The same reaction was performed in the MMRS, which was equipped with a backpressure controller, so that the reactor could be operated at elevated temperatures and pressures. Conditions could be achieved with temperatures above the boiling point of the mixture under ambient pressure, which are often referred to as superheated conditions. The setup allowed quick variation... 

The boiling point of the solvent has a major influence on the reaction conditions since its presence during the polymerisation dictates the maximum reaction temperature which can be utilised. In turn the reaction temperature will influence the choice and quantities of initiator and modifi used to achieve the desired molecular weight and degree of conversion. Thus solvent combinations are often used to allow the polymerisation to be carried out at a suitable reaction temperature. Often where low boiling solvents are required in the final polymer solution, they are added after polymerisation has been carried out in another solvent. 

These thermal effects associated to the hydrolysis reaction have been studied on a fully dehydrated NaBH4 powder by means of an IR imaging camera and a differential titration calorimeter. Various amounts of solid sodium hydroxide were added to the system (NaBH4 -I- metallic nanoCobalt catalyst) allowing an increase of the maximum reaction temperature (up to 140 °C). The reaction maximum temperature and the hydrogen yield were considerably modified by varying the amount of NaOH and the amount of catalyst (Fig. 11.13). At a temperature of more than 140 °C, it is reasonable to expect the formation of low hydration borate phases. In fact, at temperatures above 105 °C water is expected to participate preferentially in the hydrolysis reaction rather than in the hydration of the... 

Pyrolysis can be divided into two types fast pyrolysis and slow pyrolysis. These reactions are different mainly in terms of heating rates and maximum reaction temperatures (Brown et al., 2011). Heating rates for slow pyrolysis are typically below lOOK/min, whereas fast pyrolysis can achieve heating rates exceeding lOOOK/min. Reaction temperatures are about 300°C and 500°C for slow and fast pyrolysis, respectively. Slow pyrolysis requires several minutes or even hours, while fast pyrolysis is completed within 2 s. This difference in time results in dramatic differences in product distributions. 

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