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Batch reactor
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Batch reactor
A batch reactor is a chemical reactor in which a non-continuous reaction is conducted, i.e., one where the reactants, products and solvent do not flow in or out of the vessel during the reaction until the target reaction conversion is achieved. By extension, the expression is somehow inappropriately used for other batch fluid processing operations that do not involve a chemical reaction, such as solids dissolution, product mixing, batch distillation, crystallization, and liquid/liquid extraction. In such cases, however, they may not be referred to as reactors but rather with a term specific to the function they perform (such as crystallizer, bioreactor, etc.).
Many batch processes are designed on the basis of a scale-up from the laboratory, particularly for the manufacture of specialty chemicals and pharmaceuticals. If this is the case, the process development will produce a recipe for the manufacturing process, which has many similarities to a recipe used in cookery. A typical batch reactor consists of a pressure vessel with an agitator and integral heating/cooling system. The vessels may vary in size from less than 1 L to more than 15,000 L. They are usually fabricated in steel, stainless steel, glass-lined steel, glass or exotic alloys. Liquids and solids are usually charged via connections in the top cover of the reactor. Vapors and gases also discharge through connections in the top. Liquids are usually discharged out of the bottom.
The advantages of the batch reactor lie with its versatility. A single vessel can carry out a sequence of different operations without the need to break containment. This is particularly useful when processing toxic or highly potent compounds.
The usual agitator arrangement is a centrally mounted driveshaft with an overhead drive unit. Impeller blades are mounted on the shaft. A wide variety of blade designs are used and typically the blades cover about two thirds of the diameter of the reactor. Where viscous products are handled, anchor shaped paddles are often used which have a close clearance between the blade and the vessel walls.
Most batch reactors also use baffles. These are stationary blades which break up flow caused by the rotating agitator. These may be fixed to the vessel cover or mounted on the interior of the side walls.
Despite significant improvements in agitator blade and baffle design, mixing in large batch reactors is ultimately constrained by the amount of energy that can be applied. On large vessels, mixing energies of more than 5 W/L can put an unacceptable burden on the cooling system. High agitator loads can also create shaft stability problems. Where mixing is a critical parameter, the batch reactor is not the ideal solution. Much higher mixing rates can be achieved by using smaller flowing systems with high-speed agitators, ultrasonic mixing or static mixers.
Products within batch reactors usually liberate or absorb heat during processing. Even the action of stirring stored liquids generates heat. In order to hold the reactor contents at the desired temperature, heat has to be added or removed by a cooling jacket or cooling pipe. Heating/cooling coils or external jackets are used for heating and cooling batch reactors. Heat transfer fluid passes through the jacket or coils to add or remove heat.
Within the chemical and pharmaceutical industries, external cooling jackets are generally preferred as they make the vessel easier to clean. The performance of these jackets can be defined by three parameters:
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Batch reactor
A batch reactor is a chemical reactor in which a non-continuous reaction is conducted, i.e., one where the reactants, products and solvent do not flow in or out of the vessel during the reaction until the target reaction conversion is achieved. By extension, the expression is somehow inappropriately used for other batch fluid processing operations that do not involve a chemical reaction, such as solids dissolution, product mixing, batch distillation, crystallization, and liquid/liquid extraction. In such cases, however, they may not be referred to as reactors but rather with a term specific to the function they perform (such as crystallizer, bioreactor, etc.).
Many batch processes are designed on the basis of a scale-up from the laboratory, particularly for the manufacture of specialty chemicals and pharmaceuticals. If this is the case, the process development will produce a recipe for the manufacturing process, which has many similarities to a recipe used in cookery. A typical batch reactor consists of a pressure vessel with an agitator and integral heating/cooling system. The vessels may vary in size from less than 1 L to more than 15,000 L. They are usually fabricated in steel, stainless steel, glass-lined steel, glass or exotic alloys. Liquids and solids are usually charged via connections in the top cover of the reactor. Vapors and gases also discharge through connections in the top. Liquids are usually discharged out of the bottom.
The advantages of the batch reactor lie with its versatility. A single vessel can carry out a sequence of different operations without the need to break containment. This is particularly useful when processing toxic or highly potent compounds.
The usual agitator arrangement is a centrally mounted driveshaft with an overhead drive unit. Impeller blades are mounted on the shaft. A wide variety of blade designs are used and typically the blades cover about two thirds of the diameter of the reactor. Where viscous products are handled, anchor shaped paddles are often used which have a close clearance between the blade and the vessel walls.
Most batch reactors also use baffles. These are stationary blades which break up flow caused by the rotating agitator. These may be fixed to the vessel cover or mounted on the interior of the side walls.
Despite significant improvements in agitator blade and baffle design, mixing in large batch reactors is ultimately constrained by the amount of energy that can be applied. On large vessels, mixing energies of more than 5 W/L can put an unacceptable burden on the cooling system. High agitator loads can also create shaft stability problems. Where mixing is a critical parameter, the batch reactor is not the ideal solution. Much higher mixing rates can be achieved by using smaller flowing systems with high-speed agitators, ultrasonic mixing or static mixers.
Products within batch reactors usually liberate or absorb heat during processing. Even the action of stirring stored liquids generates heat. In order to hold the reactor contents at the desired temperature, heat has to be added or removed by a cooling jacket or cooling pipe. Heating/cooling coils or external jackets are used for heating and cooling batch reactors. Heat transfer fluid passes through the jacket or coils to add or remove heat.
Within the chemical and pharmaceutical industries, external cooling jackets are generally preferred as they make the vessel easier to clean. The performance of these jackets can be defined by three parameters: