Since the dawn of modern-day science, chemical reactors have been regarded as the heart of chemical processes. A chemical reactor is a piece of enclosed equipment, made from metal (often high resistant alloys or stainless steel) in which chemical reactions are contained and controlled. They vary in size from small test-tubes in the lab to industrial-size reactors, in which complex heat and mass transfers occur amidst computerized provisions of safety and control. Over time, reactor designs have improved to enhance operation efficiency, and reduce significant costs, thereby increasing revenue potential in the long-term. When classified according to the mode of operation, three basic types of reactor models exist that estimate the important aspects of process variables of different chemical reactions. These include the batch reactor, the continuous reactor, and the semi-batch reactor.
These are processing tanks in which a “batch” of chemical reactants are introduced and stirred using a pump-around loop, an internal impeller, or with gas bubbles, after which a fraction of the reactants are separated, removed, and externally re-circulated back into the reactor.
The batch reactor is usually operated and maintained at a particular desired condition. To accomplish this, the reactor has jackets, reflux condensers, cooling surface (like coils or tubes), and a pump-around loop that goes through a heat exchanger regulating the temperature.
Batch reactors are ideal for chemical reactions that require long reaction times to complete, and which require flexibility in campaigning different materials. They are also suitable for small production rates. They are applicable in the fermentation of beverage products and in wastewater management.
In continuous reactors, the initial reactants are introduced into the process and the by-products removed continuously at a consistent rate of mass flow. This type of reactor is suitable for large production rates conducted in continuous equipment. There are three types of continuous reactors, classified according to their modes of operations.
The continuous stirred tank reactor (CSTR) is where reactants are added and removed from the equipment while the contents within are being stirred by internal agitation and recycling. It can be structured in series or parallel and is applicable in breweries, and antibiotic industries.
The plug flow reactor is made up of a hollow pipe, encased in a tank, through which the products pass. Water at a controlled temperature is circulated in the tank to ensure the temperature is maintained. It’s applicable in gasoline production.
Lastly, the tubular flow reactor is a pipe of varying diameter through which reagents flow, react and get converted to the final product. Structured in a continuous gradient, several pipes can be arranged in series or parallel.
In semi-batch reactors, chemical reactants are initially loaded into the reaction chamber and the rest is fed gradually until the reactor is full. Once full, it’s operated in a batch mode until the reaction is complete. Semi-batch reactors are ideal for reactions with large heat effects and limited heat-transfer capabilities or where toxic by-products need to be controlled. The gradual feeding of reactants limits their concentration, thereby helping to control reactions. It’s applicable in a variety of industries including pharmaceutical, and agricultural commodities.
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