Repeat Example 22.9 for the case when catalyst is placed in a packed bed without internal cooling,

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Repeat Example 22.9 for the case when catalyst is placed in a packed bed without internal cooling, as shown in Figure 22.8(a). Determine the temperature and conversion profiles within such a packed bed for inlet partial pressures of o-xylene from 0.008 to 0.002 bar.

Assume that the maximum allowable temperature to avoid catalyst sintering is 410°C.


Example 22.9

The synthesis of phthalic anhydride from o-xylene is considered. The following parameters and pseudo-firstorder reaction rate may be used for an approximate preliminary design of a shell-and-tube reactor.C8 H10 +302C8H4O3 + 3HO

The autoignition temperature of o-xylene = 465°C and lower explosion limit (LEL) = 0.9% at room temperature.

Data:= Tube length, L> 1 m; Dtube = 0.0254 m; catalyst is V05 on promoted silica gel; diameter of catalyst

Dtube 0.0254 Dp 0.003 = = 8.467









which are in the correct range to use Equation (22.51),hw,eff Dtube kg (2.03) (127) 0.8 exp[-8.467] = 48.17 (48.17) (0.0469) = 88.9 W/m/K (0.0254) andUhw,eff = 88.9









The reaction rate can be approximated by a pseudo-firstorder equation:(reaction rate) = mol/h/m catalyst Pbulk kPB,0PA

where Component A is o-xylene, k = 4.122 × 108e−13,636/T[K] mol/h/bar2/kg (catalyst), and Component B is oxygen with an initial partial pressure, pB,o = 0.21 bar.

The average heat of reaction for this temperature range −ΔHr is 1150 kJ/mol.

For illustration purposes, it is assumed that cooling takes place by heat exchange with a cooling medium flowing through the shell side at 335°C that vaporizes at constant pressure and temperature. With this assumption, the shell-side temperature, Tcool, is fixed at 335°C.

Determine the temperature profiles in the tube for partial pressures of o-xylene in the feed ranging from 0.01 to 0.02. Assume that the effect of changing pressure is small; that is, assume constant pressure conditions and a process gas inlet temperature of 335°C.Z N T T (a) I I I I I | Packed bed of catalyst Catalyst particles Tube bank Process feed (d) Z N T Cold shot

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Analysis Synthesis And Design Of Chemical Processes

ISBN: 9780134177403

5th Edition

Authors: Richard Turton, Joseph Shaeiwitz, Debangsu Bhattacharyya, Wallace Whiting

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