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A flow reactor continuously creates products by adding raw materials to a series of tubes, with temperature control and mixing methods such as coils, packings, and baffles. Catalysts can be added to aid reactions and ensure consistent product quality. Tube design and flow rates are important for achieving plug flow conditions.
A flow reactor is a chemical process in which raw materials are added to a reaction vessel, usually a series of tubes, to create products continuously. This is different from a batch process, where all materials are added and reacted, then removed and machined. Flow reactions continue until raw materials are added at one end and can be used for both liquids and gases.
A flow reactor design is typically a series of tubes within a temperature controlled enclosure. Heat or coolant can be added to the shell to provide temperature control of the reaction within the tubes. The reactor can be constructed of metals, plastics, or composites as needed to prevent feedstock from attacking it.
Tube designs for a flow reactor can vary greatly depending on the desired reactions. Tubes are rarely empty, because mixing will not occur in empty tubes; the materials will remain separate within the tubes and will not react. Coils of smaller tubes, small shapes called packings, or internal barriers called baffles are all used to mix the reactants or raw materials together.
Placing coiled tubes within a flow reactor can help with mixing or heat transfer. Coils add distance for chemicals to travel in the reaction section, providing more time for the chemical process. The heating or cooling liquids can also be inside the batteries, with the reagents on the outside, for better temperature control. The size of the tube, which changes the inside diameter or cross section, can be varied to change the flow rates of the reactants.
Pipes can be packed with various materials according to the reactions needed. Some chemicals require a catalyst, a material that speeds up reactions without being consumed in the process. The catalysts can be added to glass ceramic beads or other materials and packaged in the tubes. Non-catalyst packing can also be used to help mix the reactants, which is often necessary if heat or cooling is applied to the outside of the tubes. Without mixing, the material closest to the pipe walls will be too hot or cold, which will affect the quality of the product.
Baffles can vary greatly in design, but all aid mixing by creating eddies or swirls of turbulence within the tube. These can be layers of mesh installed in pipes or grooves made in the walls of pipes. Catalysts can also be coated on the baffle surfaces, providing control of the reaction in addition to mixing.
The flow reactor design also takes into account the reaction rate of the chemicals. The movement of chemicals through all tubes must be the same, otherwise the quality of the finished product can be different from each tube. Designing flow rates to achieve plug flow conditions ensures a consistent product. Plug flow is a feature of tube design and flow control in which the time the reactants spend in the reactor is the same regardless of which tube is observed.
