Page 411 - Chemical process engineering design and economics

Reactor Design 391

Table 7.2.1 Heat-Transfer Coefficients for a Batch Reactor

Heat-Transfer Source Remarks
Coefficient 3
2
Btu/h -ft -°F
hi 250 Reference 10 assuming the worst case
hw 1,700 Reference 10
0 the inside surface is cleaned after
h fi
each batch
1/hfo 0.001 Reference 24
h 0 360 Reference 24 condensing Dowtherm A
k b 113 forSS316
2
a) To convert to W/m -K multiply by 5.678.
2
b) Units of the thermal conductivity are Btu-in/ft -h-°F.

PACKED-BED CATALYTIC REACTORS
Catalysts change the reaction mechanism and therefore the rate of the reaction. If
the reaction rate increases, the reaction volume will decrease, reducing the cost of
the reactor. Many chemical syntheses are impractical without using a catalyst.

Catalytic Pellet Selection

If a pure catalyst is structurally weak and cannot be formed into a pellet or is too
expensive to use as a pellet, then the catalyst is deposited as a thin film on an
inert support. Because the reaction rate is proportional to the catalyst surface
area, the pellet must be porous to achieve a large surface area.
Besides chemical properties of the catalyst, the mechanical properties of
the support material must also be considered when selecting a catalyst. Support
materials are mostly alumina, silica, activated carbon or diatomaceous earth, but

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