Residence experimental determination

Experimental Determination of Residence Time Distribution Functions... 

When 0 k, Eq. 16 reduces to ca(t) =ct0e kt, and the kinetics can be observed unperturbed by the source residence time. However, when this inequality is not fulfilled, (16) predicts an approximately exponential rise of c, which passes through a maximum and then decays away. If 0 is known or can be determined, then (16) can be used to fit data and extract the first-order rate coefficient. The value of 0 could be experimentally determined by introducing an unreactive species into the ion source as a step function. The transient response is given by... 

Fig. 10. Experimentally determined [I2]ss and [I-]ss as a function of flow rate with [IOJ]0 = 1.33 x 10 3M and [HjAsO3]0 = 2 x 10 3M. Arrows indicate transitions from one steady state to the other as the flow rate is varied. (At all ko [I2]ssn is too small to measure ko is reciprocal of the reactor residence time.)...

Fig. 8.16. Schematic flowsheet for the experimental determination of pressure drop, flooding limits, residence time distribution (RTD), and mass transfer.

The extruder flow model suggested by Carley et al. (9) is chosen, by virtue of its simplicity and good agreement with experimentally determined residence time distributions, throughput and power requirements, to illustrate the methodology of this approach. 

However, if the reactor is filled, for example, with a catalyst, the situation becomes more complicated. The Vr would be the empty volume of the reactor, which is then difficult to determine, for instance, using settled apparent densities. The residence time can also be experimentally determined, usually resulting in a residence time distribution however, the experimental effort for such experiments is often large. Therefore, it is useful to apply a modified residence time, as shown in Equation (27), which defines the ratio of the mass of the catalyst and the gas flow, two easily measurable values ... 

The development of the concentration as a function of the residence time was experimentally determined for several different reaction conditions, such as modified residence time, temperature, and feed gas composition. This is shown in Figure 4.1.8. Moreover, it is important to perform experiments adding product to the feed gas stream, to investigate if a product inhibition of the reaction can occur. 

Overall, evaluation of catalysts on resid feedstocks requires sophisticated and well integrated catalyst deactivation, catalyst stripping and cracking systems. It is important to determine not only the coke yield, but each of its components (Catalytic coke, contaminant coke, CCR coke and stripper (soft) coke). This paper provides details on how each of the components of the coke yield may be experimentally determined using catalyst metallation by cyclic deactivation, catalyst strippability measurements and modified catalytic cracking techniques. 

Covell DG, Berman M, DeLisi C. Mean residence time — Theoretical development, experimental determination, and practical use in tracer analysis. Math. Biosci. 1984 72 213-244. 

Arsenic may be assumed to be released according to its own kinetic scheme, independent of the release of other volatile compounds. A simple first order reaction is used to model the arsenic release. The derivation of this kinetic scheme is based on the arsenic releases that were experimentally determined for different combinations of temperature and residence time during the pyrolysis studies (labscale and TGA) [21. 22]. According to the following equations, with mo the mass of As in the pyrolysis residue at time to and m at time t (t is defined as the time that the reactor temperature is 20 °C lower than the pyrolysis temperature, such that in the period [to,t] the pyrolysis process can be classified as nearly isothermal) ... 

Although there are aqua ions still to be identified, many have been characterized as already described. On the other hand, information about the number of water molecules in the second-coordination sphere of metal ions and their residence times is scarce, and the only experimentally determined lifetime of a water molecule exchanging between the 12 H20 of the second-coordination sphere and bulk water is 1.28 x 10-los (Ih o = 7.8x 109s 1) at 25°C for [Cr(H20)6]3+whieh compares with 1.44 x 10-los from molecular dynamics calculations.24 63 Similar calculations show Nd3+, Sm3+, and Yb3+ to have 17.61, 17.13, and 16.74 water molecules in the second-coordination sphere, with residence times of 1.3 x 10-11 s, 1.2 x 10—11 s, and 1.8 x 10 11 s, respectively.211 These studies are consistent with the exchange of water between the second-coordination sphere and the bulk solvent being close to diffusion controlled, as has generally been assumed in mechanistic models for the substitution of water in the first-coordination sphere. 

The HDU can also be experimentally determined by measuring the residence time distribution of the two phases in the extractor unit. 

Fig. 11.1 5 The experimentally determined bifnrcation structure of the chlorite-iodide reaction. The two constraints used here are the ratio of input concentrations, [CIO2 ]o/[I ]o> and the logarithm of the reciprocal residence time, log k(,. Notation filled triangles, supercritical Hopf bifurcations filled circles, saddle-node infinite period bifurcations in the region between these two kind of bifurcations, stable oscillations were observed. Open circles, excitable dynamics the smallest circles correspond to perturbations of 2 x 10 M in NaC102 the next smallest, 6 X 10 M in NaC102 the next smallest, 1.25 x 10 X x oMn - o io-2 1...

Fig. 7. Experimental determination of the mean surface-residence time in the presence of interparticle readsorption.

For confirmation of adequacy of chosen technique for experimental determination of distributions of reagents residence times in tubular turbulent apparatus numerical calculation of three-dimensional turbulent liquid flow with the use of CFD soft PHOENICS was carried out. 

Design equations can be developed for partial mixing in either or both phases. The first step is to experimentally determine the residence time distribution for each phase. But the procedures tend to be quite involved, and are outside the scope of this treatment (see Kastanek et al., 1993, for a comprehensive exposition). 

When drying the protein hydrolyzate from Xi = 4 kg/kg to Xf = 0.05 kg/kg at Tgi = 300°C, Tp = 105°C, and = 100°C, the parameter (p was found to be 0.7 kg/m at dry coat thickness from 0.2 to 0.3 mm. The calculated drying time varied from 60 to 90 seconds, whereas the experimentally determined material residence time was in the order of 200 to 400 seconds. This indicates that several wet coats were dried in this case before dry material was cracked and peeled off from the inert carrier (Kutsakova and Utkin, 1987). 

The second advantage of the quantum-mechanical approach to biochemistry and biophysics resides in the possibility that it offers to precede experimentation in a number of fields in which this experimentation seems to be particularly difficult to carry out. Thus, the calculations frequently permit determining the values (more or less exact values, according to the degree of refinement of the calculations) of a series of physicochemical characteristics of molecular systems which seem to be at present beyond the possibilities of experimental determination, or which are at least very difficult to measure presently. Among these characteristics are e.g., dipole moments, ionization potentials, electron affinities, resonance energies, etc., all of which are fundamental quantities for the understanding of the physicochemical properties of molecules. The calculation of these quantities frequently permits discovery and prediction of new correlations between structure and behaviour, and sometimes completely new aspects of biochemical problems. 

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