Briefly introduce the three operating modes of the chemical reactor

The chemical Reactor has three operation modes: batch (batch), continuous and semi-continuous (semi-batch).

1. Intermittent (batch) operation

A reactor that uses batch operation is called a batch reactor, which is characterized in that the required raw materials are loaded into the reactor at one time, and then the chemical reaction is carried out in it. Materials, which are mainly reaction products and small amounts of unconverted raw materials. Next, the reactor is cleaned, and then the next batch of raw materials are charged, reacted, and discharged. Therefore, batch reactor is also called batch reactor. The batch reaction process is a non-stationary process, and the composition of the system in the reactor changes with time, which is the basic feature of the batch process. The batch reactor has neither material input nor material output during the reaction process, that is, there is no material flow, and the entire reaction process is carried out under constant volume. If the reactant system is gas, it will fill the entire reactor space; if it is liquid, although it does not fill the reactor space, the change in liquid volume due to pressure changes is usually negligible, so constant volume treatment is also accurate enough.

Almost all reactors using batch operation are kettle reactors, and the remaining types are extremely rare. Batch reactors are suitable for chemical reactions with slow reaction rates and chemical production processes with low yields. They are particularly suitable for companies with small batches and many product varieties, such as pharmaceuticals and other fine chemicals.

2. Continuous operation

The characteristic of this mode of operation is that the raw materials are continuously fed into the reactor, and the reaction products also continuously flow out of the reactor. The reactor that uses continuous operation is called a continuous reactor or a flow reactor. The various reactors described above can be operated continuously. For certain types of reactors in industrial production, continuous operation is the only mode of operation available. Continuously operated reactors are mostly stationary operations. At this time, the physical parameters of any part of the reactor, such as concentration and reaction temperature, do not change with time, but change with location. Most of the reactors for large-scale industrial production are continuously operated, because it has the advantages of stable product quality, high labor productivity, and easy implementation of mechanization and automation. These are not comparable to intermittent operation. However, once the continuous operating system is established, it is very difficult to change the product variety. Sometimes it is not easy to even change the product output significantly, but the intermittent operating system is more flexible.

3. Semi-continuous (semi-intermittent) operation

As long as one of the raw materials and products is continuous input or output and the rest is batch addition or discharge, they are semi-continuous operations. The corresponding reactor is called semi-continuous reactor or semi-batch reactor. It can be seen that semi-continuous operation has certain characteristics of continuous operation and intermittent operation. There is continuous flow of material, which is similar to continuous operation; there are also materials that are added or discharged in batches, so the production is intermittent, which reflects the characteristics of intermittent operation. For these reasons, the composition of the reactant system in a semi-continuous reactor must change both with time and with the position within the reactor. Tubular, kettle, tower and fixed bed reactors can all be operated in semi-continuous mode.

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