Consider the reactor in Example 22.9 using an inlet oxylene partial pressure of 0.0175 bar. Without dilution, this feed concentration leads to a runaway condition in the reactor. Explore the possibility of diluting the catalyst.

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.

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

Data:

which are in the correct range to use Equation (22.51),

The reaction rate can be approximated by a pseudo-firstorder equation:

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, p_B,o = 0.21 bar.

The average heat of reaction for this temperature range −ΔH_r 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, T_cool, 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.

Transcribed Image Text:

C8 H10 +302C8H4O3 + 3H₂O