Chemical Processes

1.1 Introduction
Chemical processes usually have three interrelated steps:
1. Transfer of reactants to the reaction zone.
2. Chemical reactions involving various unit processes.
3. Separation of the products from the reaction zone using various unit operations.
Processes may involve homogeneous system or heterogeneous systems. In homogeneous system, reactants are in same phase liquid, gases or solids while heterogeneous system include two or more phases; gas-liquid, gas-solid, liquid- solid. Various type reactions involve may be reversible or irreversible, endothermic or exothermic, catalytic or non-catalytic.
Various variables affecting chemical reactions are temperature, pressure, reactants composition, catalyst activity, and the rate of heat and mass transfer.
The reaction may be carried out in batch, semi batch or continuous reactor. Reactors may be batch, plug flow (PFR), CSTR. It may be isothermal or adiabatic. Catalytic reactors may be packed bed, moving bed or fluidized bed.
The most important factors for chemical processes are: basic data, yield, conversion, and kinetics.
Basic data: are the physical and chemical properties of reactants and products.
Yield is that fraction of raw material recovered as the main product.
Conversion is that fraction of material changed to another desired product.
The yield is frequently above 90 percent, whereas the conversion is limited by equilibrium, changing the operating conditions, the equilibrium can be shifted and the conversion enhanced.
Kinetics: is the study of reaction rates. Such information is essential for plant design, since reaction rate determines equipment size. Catalysts are materials that increase reaction speed.