===Batch reactor===
The simplest type of reactor is a batch reactor. Materials are charged in a batch reactor, and the reaction proceeds with time. A batch reactor does not reach a steady state, and control of temperature, pressure and volume is necessary. Thus, a batch reactor has ports for sensors and material input and output. Batch reactors are used in small-scale production and reactions with biological materials, such as in brewing, pulping and production of enzymes.
===CSTR (Continuous Stirred-Tank Reactor)===
* It can be demonstrated that an [[Infinity|infinite]] number of infinitely small CSTRs operating in series would be equivalent to a PFR.
The behavior of a CSTR is often approximated or modeled by that of a Continuous Ideally Stirred-Tank Reactor (CISTR). All calculations performed with CISTRs assume [[perfect mixing]]. If the residence time is 5-10 times the mixing time, this approximation is considered valid for engineering purposes. The CISTR model is often used to simplify engineering calculations and can be used to describe research reactors. In practice it can only be approached, particularly in industrial size reactors in which the mixing time may be very large.
A loop reactor is a hybrid type of catalytic reactor that physically resembles a tubular reactor, but operates like a CSTR. The reaction mixture is circulated in a loop of tube, surrounded by a jacket for cooling or heating, and there is a continuous flow of starting material in and product out.
===PFR (Plug Flow Reactor)===