Contact time plots

The time required for a system to reach equilibrium can be determined by shake-out tests, as described in earlier sections. Contact times are varied between about 0.5 and 15 min, at suitable intervals, and the extraction coefficient for each contact time plotted as a function of time. With this method, there is a lower practical limit on the contact time of about 0.25 min. These data will not be directly applicable to a continuous process because the rate of metal extraction is a function, in part, of the type and degree of agitation. However, a good idea of whether the extraction rate is sufficiently fast for the system to be suitable for use in a large contactor can be obtained. For example, if equilibrium is attained in less than 1 min, almost any type of contactor may be used. 

U. Single water drop in air, liquid side coefficient / jy l/2 ki = 2 ), short contact times / J 1 lcontact times dp [T] Use arithmetic concentration difference. Penetration theory, t = contact time of drop. Gives plot for k a also. Air-water system. [lll]p.. 389... 

Adsorption for gas purification comes under the category of dynamic adsorption. Where a high separation efficiency is required, the adsorption would be stopped when the breakthrough point is reached. The relationship between adsorbate concentration in the gas stream and the solid may be determined experimentally and plotted in the form of isotherms. These are usually determined under static equilibrium conditions but dynamic adsorption conditions operating in gas purification bear little relationship to these results. Isotherms indicate the affinity of the adsorbent for the adsorbate but do not relate the contact time or the amount of adsorbent required to reduce the adsorbate from one concentration to another. Factors which influence the service time of an adsorbent bed include the grain size of the adsorbent depth of adsorbent bed gas velocity temperature of gas and adsorbent pressure of the gas stream concentration of the adsorbates concentration of other gas constituents which may be adsorbed at the same time moisture content of the gas and adsorbent concentration of substances which may polymerize or react with the adsorbent adsorptive capacity of the adsorbent for the adsorbate over the concentration range applicable over the filter or carbon bed efficiency of adsorbate removal required. 

The comparison of calculated solubilities by Equation 13 with the values from experiment (12 months contact time). The values are plotted as a function of the concentration of free hydroxide ion at solubility equilibria (cf. Figure 6). 

The reaction was performed over the iron phosphate catalyst by changing the feed rate of oxygen from zero to 350 mmol/h, while fixing the sum of feed rates of oxygen and nitrogen at 350 mmol/h. The feed rate of pyruvic acid was fixed at 10.5 mmol/h. The yields of citraconic anhydride obtained at a temperature of 230°C and a short contact time of 0.52 s (amount of catalyst used = 2 g) are plotted as a function of the feed rate of oxygen in Figure 3. 

Fig. 11 Plot of the 13C signal intensity as a function of contact time for two distinct methyl resonances of two polymorphic forms of a developmental drug substance.

Effect of Space Velocity The data are given in Table VI, and the conversion and selectivities are plotted against 1/WHSV in Figure 3. +Clearly, at longer contact time (or lower space velocity), C decreased and C KL increased. Thus the latter appear to be rormed as a sequentail reaction product. 

Various adsorption parameters for the effective removal of Pb + and ions by using new synthesized resin as an adsorbent from aqueous solutions were studied and optimized. Time-dependent behavior of Pb + and ions adsorption was measured by varying the equilibrium time between in the range of 30-300 min. The percentage adsorption of Pb + plotted in Fig. 26.2 as a function of contact time... 

Time-depended behavior of Cu + ion adsorption was measured by varying the equilibrium time between in the range of 0.5-72 h. The percentage adsorption of Cu + ions plotted in Fig. 28.2 as a function of contact time. The percentage adsorption of Cu + indicates that the equilibrium between the Cu + ions and sumac leaves was attained 4 h. Therefore, 4 h stirring time was found to be appropriate for maximum adsorption and was used in all subsequent measurement. The effect of temperature and pH the adsorption equilibrium of Cu + on sumac leaves was investigated by varying the solution temperature from 283 to 303 and pH from 6 to 10. The results are presented in Fig. 28.3. The results indicated that the best adsorption results were obtained at pH 8 at 293 K. 

Experiments 3-5 show a small trend toward more 1-alkene as the alumina becomes more basic. From a plot of product composition versus contact time and extrapolation to zero time Pines and Haag (49)... 

Fig. 2. Hexane cracking with HZSM-5 (Si/AI = 35) at 538°C. a. First order rate constant determined at different hexane pressures, b. First order plot of conversion (e) at different contact times, hexane pressure = 10 torr.

Fig. 4. Autocatalysis in hexane cracking (HZSM-5 Si/AI = 35, 370°C, 150 torr hexane), a. Conversion vs. contact time. b. First-order plot.

Effect of temperature. The reaction was conducted by changing the temperature and the contact time, while fixing the other conditions. In order to compare the selectivity at the same level of the toluene conversion, the yields of benzaldehyde are plotted as a function of the conversion in Fig. 3. The selectivity increases with raising the temperature. This finding is in conformity with that obtained with V- and Mo-P-based oxide catalysts [19-21]. 

FIGURE 23. Contour plots of the 2D H-29Si correlation experiments on silica gel obtained with a 22.0 ms contact time, a 3.0 s repetition time and a 4.0 kHz sample spinning rate. The vertical axis represents the proton chemical-shift scale and the horizontal axis the 29Si chemical-shift scale. The spectra above and at the side of the figures are the one-dimensional projections. The 2D spectrum was obtained from 64 individual experiments (a) unwashed silica gel, 80 scans for each individual experiment (b) D2O washed sample, 200 scans for each experiment. Reprinted with permission from Reference 137. Copyright 1988 American Chemical Society... 

Predicted conversion profiles for a particular case are plotted in Fig. 9.19. For contact times such as those used in industrial practice (up to 30 s), they are extremely sharp. There is a moving conversion boundary, generated by the high value of the activation energy of the novolac-hexa reaction. 

Figure 7.30 shows dependencies of 1/r on 1/[S], which indicate a satisfactory description of plots from Figure 7.29 (with the exception of two points, corresponding to contact times equal 1.9 and 3.1 s) by equation (7.16). The high deviation of two points from the appropriate lines can be explained by the shortcomings of the Linuver-Berk equation, the use of which at low substrate transformations leads to overestimated values of r. 

Figure 3 shows the yields of MTBE plotted against the contact time, observed at 345 K, 360 Kand 371 K, respectively. The yield in C8 products at 360 K, which is also reported in this figure, did not exceed 1.5 C-atom % at high contact times. At die reaction temperatures tested, the production of dimethyl ether (DME) and other hydrocarbons was practically negligible (less than 1 C atom %). Lower production of DME was also observed by Chang... 

Figure 2 A) Yield of MTBE versus contact time. (O) = 345 K, ( ) = 360 K and (A ) =371 K at short contact times. B) Arrhenius plot.

In Figure 5 the curves of differential adsorption heat of NH3 for the fresh catalyst and the catalyst used for 2 and 12 h have been plotted for a reaction temperature of 350 °C and a contact time of 0.05 h. It is concluded that there is a severe decrease in total acidity (total amount of base used in the neutralization) and that the strongly acidic sites are those that are mostly affected by deactivation. The quality of the total acidity measurement obtained following the calorimetric technique has been contrasted with the desorption technique at programmed temperature (TPD), using the FTIR analysis for measurement of desorbed NH3. 

Figure 1.5 (A) Dependence of rate on contact time r W is the weight of catalyst F is the flow-rate. (B) Arrhenius plot showing change from kinetic control to mass-transport control.

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