Chemical engineers deal with chemical reactions. There are two basic types of problems described here: chemical reactors and reaction/diffusion in a porous catalyst pellet. There are many types of flow reactors, and one-dimensional flow reactors are common, but axial flow reactors are sometimes important in laboratory situations, and reactors with radial variations are sometimes important in nonisothermal problems. These various reactors are solved using the finite difference method, the orthogonal collocation method, initial value methods, and the method of orthogonal collocation on finite elements.
Many chemical reactions occur on catalysts, and the catalysts are usually attached to a porous particle, perhaps of cylindrical or spherical shape. Thus, the diffusion and reaction inside a porous catalyst pellet is an important problem and is solved using orthogonal collocation, orthogonal collocation on finite elements, and the finite difference method.