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Figure
1
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A continuously
stirred tank reactor (CSTR) is an adaptation of a batch reactor in which
the substrate is added continuously to the reactor while the reaction mixture
is removed at the same rate. Since it is possible in such a system that
some substrate molecules can move through the reactor unchanged, the product
yield will usually be lower than in a batch process. These reactors are
sometimes used in series with the reactant stream from one reactor passing
into another so there is a stepwise increase in product formation on going
from one reactor to the next. Figure 1 shows one of our low pressure reactors
set up as a CSTR. We have the capability of running three such reactors
in series, if necessary.
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Figure
2
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In Figure 2
is pictured one of our high pressure autoclaves set up as a CSTR. In this
arrangement there is a liquid level controller (A) which is monitored by
the computer. When the liquid input reaches a set level an exit valve (B)
is opened to drain some of the reaction liquid to maintain the liquid level
in the reactor. With such a system there is no need for a second pump to
remove the product stream.
One problem with this type of continuous reactor is the potential for catalyst
loss during the removal of the reaction liquid. With a powdered catalyst
this loss can be minimized by the use of an appropriate filter on the exit
line inside the reactor. Catalysts made from granular or extruded supports
can be placed in a basket inside the reactor with the reaction liquid circulated
through the catalyst bed by the proper mode of agitation. In this way the
catalyst remains in place during the reaction.
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Figure
3
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Figure 3 is
a picture of a fixed basket adaptation we have made to our standard low
pressure reactor heads. The basket is made up of two concentric mesh walls
a few millimeters apart with space in the center. The catalyst is placed
between the mesh walls of the basket. With good agitation by an efficient
stir-bar on the bottom of the reactor this arrangement allows the reaction
liquid to circulate through the catalyst during the reaction.
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Figure
4
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Figure 4 shows
the fixed bed reactor we have constructed at the Center. This is a small
scale unit capable of being used with different sized reactors: The standard
reactor is a half-inch stainless steel tube, but other reactors ranging
in size from one-quarter inch to one inch in diameter can also be used.
This system is fully automated with all aspects controlled by a computer.
Once the proper parameters are entered into the set-up screen, the computer
takes over operation and cycles the system through purge, pre-hydrogenation,
reaction and shut-down modes. Figure 5 depicts the computer screen which
indicates which mode is presently in progress and displays all pertinent
reaction parameters.
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Figure
5
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The reactor
has three-stage controlled heating with the computer monitoring these temperatures,
the inlet and outlet pressures, the liquid flow rate and inlet and outlet
reactor gas flows. All parameters have set limits which when exceeded automatically
trigger complete system shut-down. After leaving the reactor, the reaction
mixture goes through a gas-liquid separator with the gas going through the
exit gas flow meter and the liquid through an automatic sampler and then
into a product storage container.
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