The optimum reaction temperature

Ammonia s3mthesis is a reversible and exothermic reaction without any side reaction. With the rising of temperature the reaction rate constant increases while the equilibrium constant decreases. For a given reactant composition, the reaction rate is affected by two contradictory factors thus there exists an optimum reaction temperature. 

In a lower temperature range, the equihbrium constant Ky is larger, and the temperature has a marked effect on the reaction rate constant ki. However, as the temperature is gradually increased, the reversible exothermic reaction equilibrium constant Ky is decreased. The value in the square brackets in equation (8.5) is reduced, with the effect of temperature on reaction rate decreased too. When the temperature reaches a certain point, the effect of temperature on reaction rate becomes zero. Under continuously rising temperature, the impact of temperature on the equilibrium constant reverses, the reaction rate reduced when the temperature increases. That is, for a given composition of reactants, at a low temperature range )y 0. When the temperature reaches a certain value with -)y = 0, the reaction rate reaches a maximum, which is the optimum temperature under this certain composition. After that, )y 0 with the temperature continues increasing. 

When the reaction is controlled by process dynamics, the optimum temperature curve of the reversible exothermic reaction (without any side reaction) can be obtained according to the kinetic equation using the common method that for finding the extremum. 

When the composition of the reactants is fixed, differentiating with respect to T, Tm being the optimmn temperatme, leads to the following equation  

In addition, when the reaction reaches equilibrium, = 0, the equilibrium temperature is Te, then, 

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The spent acid strength is maintained at about 90 wt% H2SO4. The molar isobutane/alkene feed ratio ranges from 7 1 to 10 1. Typical operating alkene space velocities (LHSV) range from 0.2 to 0.6 h-1 (corresponding to WHSVs from 0.06 to 0.19 h 1). The optimum reaction temperatures range from 279 to 283 K, but some units are operated at temperatures up to 291 K. 

An even more powerful option is the use of micro flow reactors, which can potentially be automated to provide a complete series of optimisations [49]. For example, a glycosylation reaction was monitored over a series of reaction temperamres. Although the optimum reaction temperature for maximum yield was determined to be — 60°C, it was noted that by increasing the temperature of the reaction to — 35°C the yield only dropped shghtly but the reaction rate increased considerably. It was therefore possible to achieve a ten-fold increase in production rate. The complete optimisation took one afternoon and consumed 2 mg of starting material. 

The rate of addition should be as rapid as possible provided that the proper temperature is maintained. Deviation of more than 5° from the optimum reaction temperature of 95° results in reduced yields. 

The optimum reaction temperature is approximately 30°. A yellow product results at higher reaction temperatures, while lower reaction temperatures lead to an uncontrollable reaction resulting from the base-initiated polymerization of acrylonitrile. 

The initiation of crystallization indicates the optimum reaction temperature for the catalyzed cyanosilylation of p-benzo-quinone. The use of higher temperatures results in excessive darkening of the product and a decrease in yield. 

The optimum reaction temperature of 280 °C is the same as the temperature for the direct reaction of methylene chloride, indicating that... 

The decarbonylation of furfural to give furan is best carried out at rather high temperatures. The following catalysts have been described Pd or Pd on charcoal,30 calcium oxide,31 32 zinc and iron chromite,33 or zinc, chromium, and manganese oxide (from ammonium chromate and manganese nitrate).34 The optimum reaction temperature with... 

The 3,3-dialkyl-l-aryltriazene (0.1 mmol) was treated with TBAF or CsF (0,2 mmol) in the presence of MsOH or TFA (5 mol equiv), or cation-exchange resin (BioRaD AG 50W-X12-hydrogen form), in anhyd MeCN, trichloroacelonitrilc. THF, DMF, DIVlSO. PhBr, toluene, CCI4 or 1,2-dichlorobenzene (3 ml,). The optimum reaction temperature for aromatic triazene decomposition in most solvents was 70-80 C. 

Commercial SCR catalyst used in connection with coal-based power stations are generally composed of base metals, since platinum-group metal catalysts are too readily poisoned and have too narrow an operating temperature window for this application. Favored compositions are titania-based together with active components, normally oxides of vanadium, tungsten, or molybdenum. For these systems the optimum reaction temperature is usually in the range 3(XM00°C. 

Deviation of the reactor temperature from the optimum reaction temperature is directly detected by the on-line Raman FT-spectrometer as shown in Fig. 5. 

A spectacular example of stability enhancement through immobilization has been reported for the enzyme catechol-2,3-dioxygenase.27 This enzyme, isolated from the thermophilic bacterium Bacillus stearothermophilus, catalyzes the conversion of catechol to 2-hydroxymuconic semialdehyde (which can be monitored by absorbance at 375 nm). The soluble enzyme exhibits maximal activity at 50 °C, but following immobilization on glyoxyl agarose beads with a borohydride reduction step, the optimum reaction temperature shifted to 70 °C. At a total protein concentration of 0.010 mg/mL and a temperature of 55 °C, the half-life of the soluble enzyme was 0.08 h, while the enzyme-modified beads had a half-life of 68 h. This represents a 750-fold enhancement of stability that has been attributed to the prevention of subunit dissociation upon immobilization. 

Temperature. The catalyst activity is quite sensitive to temperature changes. As temperature increases, the catalyst activity and the ethylene conversion increase. However, the selectivity to butene-1 production is adversary affected through the increase in by-product, mainly hexenes formation. Another undesirable effect of temperature increase is the extent of polymer formation. The optimum reaction temperature range is generally between 50 to 60°C [141. 

Glyoxylic acid was found to be produced by a vapor-phase oxidative dehydrogenation of glycolic acid over iron phosphate catalysts with a P/Fe atomic ratio of 1.2. The best results were obtained with iron phosphates freshly calcined at 400 to 450°C. Reduced iron phosphates showed a markedly lower activity. The optimum reaction temperature was about 240°C. The selectivity to glyoxylic acid was 74 mol% up to the glycolic acid conversion of about 70% the highest yield of glyoxylic acid was 56.5 mol% at the conversion of 80 %. 

A study of the thermal factors relating to the reduction of nitrobenzene shows that the reaction is distinctly exothermic. It is necessary, therefore, to remove the surplus heat generated while maintaining the reduction at the optimum reaction temperature. When nonvolatile materials are treated, as in the conversion of p-nitroaniline to p-phenylenediamine, flumes of suitable diameter and height are sufficient. When volatile nitro compounds are used, an efficient tubular condenser (vapors pass on outside of water-cooled pipes) gives eminently satisfactory results. 

Synthesized from VgOs and V metal powder under vacuum or Ar. The reactants are kept in AI3O3 crucibles which, in turn, are inserted into small, evacuated quartz tubes. Or. the apparatus described by Ehrlich for the preparation of TiO (p. 1214) may be used. The optimum reaction temperatures lie between 1200 and 1600 °C. A product of greater uniformity is obtained by occasionally interrupting the heating and repulverizing the material. A reaction time of the order of 24 hours at 1200-1300°C is needed, whereas 1 hour is sufficient at 1600°C. 

For a reversible exothermic reaction, the rate increases with temperature when the mixture is far from equilibrium, but at T, the net rate is zero, since the forward and reverse rates are equal. Therefore the reaction rate must go through a maximum at some temperature below T. This is illustrated in Figure 3.16. The reverse reaction increases more rapidly with temperature than the forward reaction because of the differences in activation energies. The temperature for maximum rate is the optimum reaction temperature, which may be a few degrees below or quite far from... 

The optimum reaction temperature proved to be 120 C, whereas at higher values the decomposition of the catalyst prevailed. The most favourable solvent for the reaction was acetonitrile. In alcohols such as ethanol or isopropanol only few amounts of the new C- 3-lactone were obtained and n-pentane or acetone desactivated the catalyst. 

Calcium carbonate precipitates from the calcium hydroxide solution, as it has a lower solubility than that of calcium hydroxide. The optimum reaction temperature is 80 to 90°C. The calcium carbonate is settled, and the overflow is a weak caustic soda, which is concentrated by evaporation. 

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