Catalytic effects temperature, time

Product Quality Considerations of product quahty may require low holdup time and low-temperature operation to avoid thermal degradation. The low holdup time eliminates some types of evaporators, and some types are also eliminated because of poor heat-transfer charac teristics at low temperature. Product quality may also dic tate special materials of construction to avoid met hc contamination or a catalytic effect on decomposition of the product. Corrosion may also influence evaporator selection, since the advantages of evaporators having high heat-transfer coefficients are more apparent when expensive materials of construction are indicated. Corrosion and erosion are frequently more severe in evaporators than in other types of equipment because of the high hquid and vapor velocities used, the frequent presence of sohds in suspension, and the necessary concentration differences. 

Temperature. The temperature of the reaction is important, for it is only above 180°C. that all catalysts and catalyst combinations are fully effective. W ith a reaction temperature of 160°C. and the use of an aluminum-sodium combination, for instance, the esterification, as compared to that of the purely thermal procedure, is 4.5 times faster it is 20 times faster at 200°C. In order fully to use the catalytic effectiveness of aluminum hydroxide in case of alcohols with a boiling point below 180°C., it is necessary to work with the appropriate high pressure. 

During the appropriate tests phthalic anhydride was smoothly esterified with 2-ethylhexanol in the mole ratio 1 4. The reaction temperature rose to 200°C. after about 15 minutes, then rose slowly up to 210°C. till the end of the esterification. Table I shows the esterification time in hours after 99.9% conversion, while continuously removing the reaction water, according to the acid number relative to monooctyl phthalic acid. Furthermore, it indicates the ester colors according to the iodine scale in milligrams iodine/100 ml., whereby 1 mg. iodine/100 ml. can be more or less compared with a dye number of 120 APHA. Since, the values are obtained with the same starting materials, it is possible to compare the color numbers. They show that with the same times, the amphoteric catalysis achieves better colors than in the reaction course containing catalytically effective acids. 

Unless carried out very carefully, data from flow reactors may be influenced by experimental uncertainties. Potential problems with the flow reactor technique include imperfect mixing of reactants, radial gradients of concentration and temperature, and catalytic effects on reactor walls. Uncertainties in induction times, introduced by finite rate mixing of reactants, presence of impurities, or catalytic effects, may require interpretation of the data in terms of concentration gradients, rather than just exhaust composition [442]. 

Special care has to be taken, however, that the quinoline titer truly represents the minimum amount of catalyst poison. In most cases this type of base is adsorbed by inactive as well as active sites. Demonstration of indiscriminate adsorption is furnished by the titration results of Roman-ovskii et al. (52). These authors (Fig. 13) showed that introduction of a given dose of quinoline at 430°C in a stream of carrier gas caused the activity of Y-zeolite catalyst (as measured by cumene conversion) to drop with time, reach a minimum value, then slowly rise as quinoline was desorbed. The decrease in catalytic activity with time is direct evidence for the redistribution of initially adsorbed quinoline from inactive to active centers. We have observed similar behavior in carrying out catalytic titrations of amorphous and crystalline aluminosilicates with pyridine, quinoline, and lutidine isomers. In most cases, we found that the poisoning effectiveness of a given amine can be increased either by lengthening the time interval between pulse additions or by raising the sample temperature for a few minutes after each pulse addition. 

Commercially available 85% MCPBA is generally employed in chlorinated hydrocarbon solvents at room temperature. Reaction times are typically a few hours to several days. Buffers utilized include disodium hydrogen phosphate, sodium acetate and sodium bicarbonate, the catalytic effect of which has been occasionally noted. Acid catalysis with sulfuric acid or Nafion-H are alternatives. Oxidations have been performed at elevated temperature with the aid of radical scavengers. "... 

More pyrolysis oil was produced from treated than untreated wood at 400 °C at 200 s. of pyrolysis time. CCA showed a significant influence on the thermal behavior of wood. The metals may have a catalytic effect on the thermal decomposition of the wood, resulting in more pyrolysis oil [6]. According to the thermal analysis study, thermal decomposition of hemicellulose is shifted to lower temperatures in the presence of CCA resulting in a higher release of volatile compounds [7],... 

In principle, treated wood behaves similar to the untreated with respect to the yields of pyrolysis products. However, more pyrolysis oil was produced from treated than from untreat wood at 400 °C potemially caused by the catalytic effect of CCA. The gas yield at low temperature is increased markedly by prolonging the pyrolysis time. A lower content of arsenic in oil was obtEuned at higher temperature. Although TBAH was used to trap arsotic con xiunds from the gases losses of almost 20 % were measured. 

Both effects, addition time and temperature, are illustrated [47] by the reaction of geranyl acetate with /j-butylmagnesium bromide in THF in the presence of a catalytic amount of Li2CuCl4 [Eq. (45)]. 

Fig.2 Deactivation of calcined dolomites-Effect of the type of dolomite(SW = Swedish Sala SP= Spanish Norte I) and of the temperature in catalytic reactor (space-time of this catalytic reactor Q.lS-0,24 kg,h/kg)...

A particularly strong browning-effect is achieved when ammonia is applied, because e reaction time is shortened and the reaction temperature decreased. - " Aliphatic primary and secondary amines and diamines may replace ammonia in these reactions, because of their catalytic effect, but they are not on the list of permitted additives. Thus, Gow Chih Yen studied such reactions from the point of view of produdng the most inten-... 

The tabulated reaction times are those required to cause a 90% or more decrease in CsN infrared absorbance at a reaction temperature of 165°C and demonstrate the marked catalytic effect of each additive. The powerful base, benzyl trimethylammonium hydroxide was employed as the solvent free solid and is by far the most powerful catalyst, however, it gave no detectable quantity (less than one part per million) of phthalocyanine. This is consistent with the proposed mechanistic criteria and dramatically demonstrates that in the absence of a viable redox pathway, reactions other than phthalocyanine formation can occur very rapidly. All other entries gave substantial amounts of phthalocyanine hydroquinone being superior in this regard. 

Gladkii(16) at the State Scientific Research Institute of Industrial and Sanitary Gas Cleaning at Moscow did work on the three-phase calcium sulfite slurry oxidation system, finding that the liquid phase oxidation (pH 3.6-6) is first order with respect to the sulfite species. He pointed out, on the basis of pH versus time data from his semi-batch reaction, that the slurry oxidation had different periods in which either reaction kinetics or solid-liquid mass transfer controlled the oxidation rate. He also presented an omnibus empirical correlation between pH, temperature, and the liquid phase saturation concentration of calcium sulfite solution for predicting the slurry oxidation rate. The catalytic effect of manganese... 

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