Macro kinetics

In addition to microkinetics, macrokinetics is a branch of reaction kinetics . In contrast to microkinetics, it not only deals with the time sequence of a reaction, but also with macroscopic influences such as heat and material transport. Macrokinetics describes the physical and chemical processes in a reactor . It serves on the one hand to predict the behavior of the system described, on the other hand to learn and recognize the procedures and processes in a reactor.

For this, knowledge of the reactor shape, the transport and substance conversion processes and their mathematical mapping is required. This mathematical formulation is mostly done using differential equations ( reaction-diffusion equations , general mass balance ).

Transport processes

Advection

The advection (also convection ) the material transport through flow . The continuity equation must be fulfilled for the entire system . This means that the difference between the inlet and outlet must be in the reactor. The theory of advection is provided by hydrodynamics . ${\displaystyle {\frac {\partial \rho }{\partial t}}+\nabla \cdot (\rho {\vec {u}})=0}$

diffusion

Under diffusion refers to the transport of substances whose driving force is a concentration gradient is. The mass transport is greater, the greater the concentration gradient and a descriptive quantity, the diffusion coefficient . The quantitative description is provided by Fick's laws:

One-dimensional: and Multi-dimensional: and ${\displaystyle J=-D{\frac {\partial c}{\partial x}}}$ ${\displaystyle {\frac {\partial c}{\partial t}}=D{\frac {\partial ^{2}c}{\partial x^{2}}}}$
${\displaystyle J=-D\cdot grad(c)}$ ${\displaystyle {\frac {\partial c}{\partial t}}=div(D\cdot grad(c))}$

See also

• Diffusion equation
• Convection-diffusion equation