
The continuous stirred-tank reactor (CSTR), also known as vat- or backmix reactor, mixed flow reactor (MFR), or a continuous-flow stirred-tank reactor (CFSTR), is a common model for a
chemical reactor in
chemical engineering
Chemical engineering is an engineering field which deals with the study of the operation and design of chemical plants as well as methods of improving production. Chemical engineers develop economical commercial processes to convert raw materials ...
and
environmental engineering
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. A CSTR often refers to a model used to estimate the key unit operation variables when using a continuous agitated-tank reactor to reach a specified output. The mathematical model works for all fluids: liquids, gases, and
slurries.
The behavior of a CSTR is often approximated or modeled by that of an ideal CSTR, which assumes
perfect mixing. In a perfectly mixed reactor, reagent is instantaneously and uniformly mixed throughout the reactor upon entry. Consequently, the output composition is identical to composition of the material inside the reactor, which is a function of residence time and reaction rate. The CSTR is the ideal limit of complete mixing in reactor design, which is the complete opposite of a
plug flow reactor (PFR). In practice, no reactors behave ideally but instead fall somewhere in between the mixing limits of an ideal CSTR and PFR.
Ideal CSTR
Modeling
A continuous fluid flow containing non-conservative chemical reactant ''A'' enters an ideal CSTR of volume ''V''.
Assumptions
* perfect or ideal mixing
*
steady state , where ''N
A'' is the number of moles of species ''A''
* closed boundaries
* constant fluid
density
Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...
(valid for most liquids; valid for gases only if there is no net change in the number of moles or drastic temperature change)
*
nth-order reaction (''r'' = ''kC
An''), where ''k'' is the reaction rate constant, ''C
A'' is the concentration of species ''A,'' and ''n'' is the order of the reaction
*
isothermal conditions, or constant temperature (''k'' is constant)
* single, irreversible
reaction (''ν
A'' = −1)
* All reactant ''A'' is converted to products via chemical reaction
* ''N
A'' = ''C
A'' ''V''
Governing equations
Integral mass balance on number of moles ''N
A'' of species ''A'' in a reactor of volume ''V'':
1.