Page 399 - Chemical process engineering design and economics

Reactor Design 379

coolant is chilled water. Size the reactor, determine the heat exchanger type and
area, and calculate the mixer power.

Data
3
3
Methanol volumetric flow rate 800ft /h(22.7m /h)
3
Propylene oxide volumetric flow rate 800 fWh (22.7 m /h)
3
3
Acid solution volumetric flow rate 4000ft /h(l 13 m /h)
Feed inlet temperature 75°F(23.9°C)
Reaction temperature 100°F(37.8°C)
Chilled water inlet temperature 5°C(41°F)
Chilled water exit temperature 15°C(59°F)
Required propylene oxide conversion 0.37
Thermodynamic properties are summarized in Table 7.1.1, and reaction
properties are given below. Fogler [16] estimated the heat capacity for propylene
glycol using a rale-of-thumb. The rule states that the majority of low-molecular-
weight, oxygen-containing organic liquids have a heat capacity of 0.6 cal/g °F
±15%(35Btu/lbmol-°F)

Reaction Properties
Pre-exponential factor, A 16.96 xlO 12 h' 1
Activation energy, E 32,400 Btu/lbmol (75,330 kJ/kgmol)

Follow the calculation procedure outlined in Table 7.5. Using the equations
listed in Table 7.4, first calculate the reaction volume. Then select a standard reac-
tion volume (rated capacity) from Table 7.3. The actual capacity (reactor volume)

Table 7.1.1 Thermodynamic Properties for Proplyene Glycol Synthesis

Component Molecular Density 3 Heat Capacity 13 Standard
Weight g/cm 3 Btu/lbmol-°F Enthalpy
of Reaction c>d
Btu/lbmol

Propylene Oxide 58.08 0.859 35 -66,600
Water 18.02 0.9941 18 -123,000
Propylene Glycol 76.11 1.036 46 -226,000
Methanol 32.04 0.7914 19.5
a) To convert g/cm to kg/m multiply by 1000.
b) To convert Btu/lbmol-°F to kJ/kgmol-°K multiply by 4.187.
c) At 25 °C (77 °F)
d) To convert Btu/lbmol to kJ/kgmol multiply by 2.325.

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