Building of a Heterogeneous Catalysis Reactor
by: Jake Smith
Introduction
to Heterogeneous Catalysis:Catalysis is the acceleration of a chemical reaction induced by the presence of material that is chemically unchanged at the end of the reaction. Catalysis is one of the largest industries in the world. In the United States alone, catalyst technologies yield an annual revenue in excess of $1 trillion. Catalysis research is central to the science of modern chemical processing. It controls more than 90% of the world's chemical manufacturing processes. Modern society, as we know it, would be impossible without catalysis. It is used in almost every aspect of life: production of materials, such as plastics, fuel production, and food production.
Catalysis can be divided into two types: (1) homogeneous reactions and (2) heterogeneous reactions. In homogeneous reactions, the reaction occurs between similar species, e.g. liquid-liquid reactions. In heterogeneous reactions, the reaction occurs between different types of species, e.g. gas-solid, liquid-solid, and liquid-gas. The most common of these groups is the gas-solid reaction. Most catalytic reactions follow the simple multi-stage process in the following diagram:
Image from The Basis and Applications of
Heterogeneous Catalysis by Michael Bowker.
Catalysis research is never ending. New catalysts are constantly being developed to make old processes much more efficient. To test the new catalyst developments, testing reactors must be built. In our research group, we designed and built a reactor for the testing of the catalysts being created in our labs.
Moon Reactor:
A reactor must be
built to properly test a catalyst. The construction of these
reactors can be difficult and expensive due to the several variables
which must be precisely controlled in order to obtain accurate data
about catalyst performance. The reactor designed and built by the
research group is unique for catalyst testing because it is able to
perform several different tests in the same reactor without
necessitating
serious modifications to the reactor design. Temperature,
pressure, back flow pressure, and feed gas content can all be
controlled
simply and quickly within the reactor. The major improvement on
reactor efficiency is due to the fact that the reactor can test
both
the product
and feed gas for the same reaction without reloading a catalyst. This
operation is performed by the use of a complicated, yet easy to use
control system. Next, the processes of gas testing for both the
product and feed gases will be explained in detail.
Image of Reactor Moon with gas chromatograph: click on photo for reactor schematic
Background
on the
Reactor Schematic Diagram:
The parts of the schematic (found by clicking on the reactor photo) correspond to the parts in the picture by numbers. In the schematic, there are three circular symbols with dots on them. They are called switching valves. These valves can be turned in two different directions. When turned in one direction, the gas which flows through the reactor passes through the solid lines in the valve. When the valve is then turned in the other direction, the gas flows through the dotted line path. Each of the three switching valves in the reactor has its own important purpose. Valve 2-A is known as the PRODUCT/FEED valve. This valves determines the gas which will eventually be tested. When in product mode, the gas is passed through the reactor and then the product is tested. In feed mode, the feed gas bypasses the reactor and is directly analyzed. Valve 2-B is the LOAD/INJECT valve. The load direction creates a flow either product or feed gas (determined using valve 2-A) through the sample loop. Then when the valve is switched to inject, a flow of Helium gas sweeps the content of the sample loop to the Gas Chromatograph (GC) for analysis. The final switching valve, valve 4, determines which of the two columns of the GC will test the product or feed gas. Column A uses a Thermal Conductivity Detector to test for large molecules and Column B uses a Flame Ion Detector for the analysis of smaller molecules. For these tests, whether valve 4 is set as Column A or Column B has no effect on the reaction, only the manner of testing. So for the following gas analyses, specification of valve 4 position will be unspecified.
Product Gas Analysis:
Product gas analysis allows for the determination of the overall effectiveness of the catalyst being tested. This is the most important function of the entire reactor. The product gas is analyzed by using the following process:
First, the gas flow amounts are chosen by using the gas flow valves illustrated in (1). The chosen gas mixture is then sent to the switching valve box (2) and travels through valve 2-A in the PRODUCT position. The gas then continues to the reactor where it reacts with the catalyst being tested. After reaction, the product gas is returned to valve 2-A only to turn around and continue to valve 2-B set in the LOAD position. The product gas is then vented into the hood (5). Once a continuous flow is reached and pressure is constant, valve 2-B is switched to INJECT. At this point, the product gas remaining in the sample loop is swept out by a flow of Helium from the GC. Helium gas is used as a sweep because the GC does not detect the amounts of He2, and only the product gas is analyzed. When the gas is tested in the GC (6), the results are printed for analysis (7).
Feed Gas Analysis:
Feed gas analysis is important to provide a basis for the results of the product gas analysis. With this reactor, the testing of the feed gas is done simply by changing the orientation of the PRODUCT/FEED valve. The feed gas analysis follows this path:
Just as in product gas analysis, the gas flow mixture is set by using the gas flow valves (1). The feed gas then enters the reactor box, but rather than entering the reactor to interact with the catalyst, the flow continues to valve 2-B. The gas continues through the sample loop just the same as the product gas. Upon returning to valve 2-A, the feed gas flows through the reactor. At this point, it does not matter whether there is any catalyst in the reactor because the gas is vented immediately after. Since the sample loop was filled in the same manner, the rest of the process is identical to the product gas analysis except no reaction has taken place.
Application for Moon Reactor:
The moon reactor is currently being used to test catalysts created on site at the Department of Chemical Engineering of the University of South Carolina.
The parts of the schematic (found by clicking on the reactor photo) correspond to the parts in the picture by numbers. In the schematic, there are three circular symbols with dots on them. They are called switching valves. These valves can be turned in two different directions. When turned in one direction, the gas which flows through the reactor passes through the solid lines in the valve. When the valve is then turned in the other direction, the gas flows through the dotted line path. Each of the three switching valves in the reactor has its own important purpose. Valve 2-A is known as the PRODUCT/FEED valve. This valves determines the gas which will eventually be tested. When in product mode, the gas is passed through the reactor and then the product is tested. In feed mode, the feed gas bypasses the reactor and is directly analyzed. Valve 2-B is the LOAD/INJECT valve. The load direction creates a flow either product or feed gas (determined using valve 2-A) through the sample loop. Then when the valve is switched to inject, a flow of Helium gas sweeps the content of the sample loop to the Gas Chromatograph (GC) for analysis. The final switching valve, valve 4, determines which of the two columns of the GC will test the product or feed gas. Column A uses a Thermal Conductivity Detector to test for large molecules and Column B uses a Flame Ion Detector for the analysis of smaller molecules. For these tests, whether valve 4 is set as Column A or Column B has no effect on the reaction, only the manner of testing. So for the following gas analyses, specification of valve 4 position will be unspecified.
Product Gas Analysis:
Product gas analysis allows for the determination of the overall effectiveness of the catalyst being tested. This is the most important function of the entire reactor. The product gas is analyzed by using the following process:
First, the gas flow amounts are chosen by using the gas flow valves illustrated in (1). The chosen gas mixture is then sent to the switching valve box (2) and travels through valve 2-A in the PRODUCT position. The gas then continues to the reactor where it reacts with the catalyst being tested. After reaction, the product gas is returned to valve 2-A only to turn around and continue to valve 2-B set in the LOAD position. The product gas is then vented into the hood (5). Once a continuous flow is reached and pressure is constant, valve 2-B is switched to INJECT. At this point, the product gas remaining in the sample loop is swept out by a flow of Helium from the GC. Helium gas is used as a sweep because the GC does not detect the amounts of He2, and only the product gas is analyzed. When the gas is tested in the GC (6), the results are printed for analysis (7).
Feed Gas Analysis:
Feed gas analysis is important to provide a basis for the results of the product gas analysis. With this reactor, the testing of the feed gas is done simply by changing the orientation of the PRODUCT/FEED valve. The feed gas analysis follows this path:
Just as in product gas analysis, the gas flow mixture is set by using the gas flow valves (1). The feed gas then enters the reactor box, but rather than entering the reactor to interact with the catalyst, the flow continues to valve 2-B. The gas continues through the sample loop just the same as the product gas. Upon returning to valve 2-A, the feed gas flows through the reactor. At this point, it does not matter whether there is any catalyst in the reactor because the gas is vented immediately after. Since the sample loop was filled in the same manner, the rest of the process is identical to the product gas analysis except no reaction has taken place.
Application for Moon Reactor:
The moon reactor is currently being used to test catalysts created on site at the Department of Chemical Engineering of the University of South Carolina.