Residence time results

Pressure and residence time have relatively Htde effect on reaction selectivity, at least within the ranges normally encountered. Poor mixing and excessive residence time result in increased carbonization of the reactor. 

The high temperature pyrolysis of sulfonyl fluonde results in the elimination of sulfur dioxide, although secondary reactions also occur, depending on the residence tune With perfluorooctanesulfonyl fluonde, long residence times result in perfluoro(Cg-Cig) compounds, and shorter residence times lead to perfluoro-hexadecane [98] (equation 65)... 

The heat stability of 2,3,7,8-tetrachlorodibenzo-p-dioxin is shown in Table II. The material is quite stable to 700°C with 50% decomposition obtained at this temperature. More than doubling the residence time resulted in only slightly more decomposition. However, decomposition of 2,3,7,8-tetrachlorodibenzo-p-dioxin is complete at 800°C. 

These thin-film evaporators are equipped with rotating elements that create a thin, liquid film of high turbulence along the inner surface of the heated tube (see Figure 1). Consequently, favorable heat and mass-transfer conditions (I), (2) and short residence times result owing to the small holdup (3,4). 

Table 4.4 compares the residence time results obtained with the characteristic function given by the original equation (4.201) and with the simplified form (4.224). We can notice that the values obtained with the simplified form are good enough. 

CO2, and has an average residence time in the atmosphere of 5-10 years. Carbon monoxide has an atmospheric residence time of only a few months. Its low concentration, —0.1 ppm, and its short residence time result from its chemical reactivity with OH radicals. Carbon monoxide is not a greenhouse gas, but its chemical reactivity affects the abundances of ozone and methane which are greenhouse gases. Non-methane hydrocarbons, another unstable form of carbon in the atmosphere, are present in even smaller concentrations. The oxidation of these biogenic trace gases is believed to be a major source of atmospheric CO, and, hence, these non-methane hydrocarbons also affect indirectly the Earth s radiative balance. 

The next step is to evaluate the adsorption residence time resulting from a series of encounters. Evidently, the number of short displacements, and also the adsorption events in a sequence, has the discrete geometric probability distribution... 

These reactor types also inevitably suffer from side reactions. Specifically, when alkylate concentrations are high, as is the case in any well-mixed reactor, alkylation of the Cg products causes product degradation and catalyst deactivation. The rate of this reaction is comparable to the rate of olefin addition to isobutane, since both are isoparaffins. Long residence times result in cracking of alkylate into undesirable light components, further reducing product yield. 

For comparison with the data in Fig. 7-28, it is instructive to calculate tropospheric residence times resulting exclusively from dry deposition. We confine the calculation to the size range 0.05-1.0 xm, where the deposition velocity is roughly size-independent. For continental aerosols this size region contains approximately one-half of the total mass of all aerosol particles. The residence time is then given by the tropospheric column content of such particles divided by their flux to the ground,... 

Methane formation is also relatively easy to interpret. Increasing temperatures and increasing residence times result in increased methane formation. The slope of the dashed lines in Figure III gives the apparent rate of methane production at the various temperatures studied. The dependence of this production rate on temperature is used later in this section to estimate the activation energy for methane formation. Efforts to elucidate the mechanism of methane formation (most probably the pyrolysis/hydro-genation of higher hydrocarbons) are presently underway. 

Centurione and Tonhi (1995) in a laboratory study stated that increases in burning temperature or residence time resulted in larger alite alite crystal length-to-width ratio increased with heating rate. 

Integration of the PFR expression for the same feed point and residence time results in an effluent concentration C = [0.1493, 4.8507] mol/L. Observe that in this instance it is still possible to solve for the CSTR expression, although its solution is more complex. Solving for the PFR exit concentration is the same as that performed in Question 1. 

The form of Equation 5.10 is identical to the equation describing the linear mixing law for concentrations developed in Chapter 2. The process of combining two parallel reactors (or reactor networks) of different residence time results in a linear mixing law as well. This implies that residence time may be used in the construction of candidate ARs in a similar manner to that for concentration. 

The total amount of a nonreactive tracer injected as a Dirac pulse at the reactor entrance is given by q. The Bodenstein number, Ho, is defined as the ratio between the axial dispersion time, = L /D, and the mean residence time, t = r = L ju, which is identical to the space time for reaction mixtures with constant density. For Bo - 0 the axial dispersion time is short compared to the mean residence time resulting in complete backmixing in the reactor. For Ho oo no dispersion occurs. In practice, axial dispersion can be neglected for Ho > 100. 

A glass MSR was used to perform the dehydration of ethanol. The microchan-nel of size 200 X 80 pm deep X 30 mm (in a Z shaped configuration) was produced by photohthographic etching [71]. A sulfated zirconia catalyst immobihzed over the surface of the top cover block. In addition, a NiCr wire was immobilized in the reactor cover as a heating device. At a reaction temperature of 155 °C and a flow rate of 3 plmin the main products were 68% ethylene, 16% ethane, and 15% methane. A further increase of the residence time resulted in a reaction progress beyond dehydration to almost complete cracking of the ethanol to methane. 

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