Characterization of chemical production processes

Production in chemical industry is in many aspects different from common industries. In most industries final products are produced by mechanical transformation processes such as assembling or machining. In contrast, in chemical industry the chemical and/or physical properties of substances are altered. Most chemical production processes rely on chemical reactions aiming at the transformation of reactants into substances of interest. The term chemical reactions refers to changes of the reactants molecular structures. Be- 

Usually, chemical reactions require an initiation, i.e. they only take place under specific circumstances. The list of reaction parameters is vast. Basic physical parameters are pressure, temperature, electricity, or fight. Specific constellations of these parameters influence the reaction rate, i.e. how fest or slow a reaction takes place. If a reaction can only take place by means of auxiliary chemicals, it is called catalytic and such an auxiliary reactant is called catalyst Another important measure of chemical reactions is the conversion rate of a reaction, i.e. how many percent of the input reactants mass is transformed into the substances of interest. This measure is important to decide whether a reaction cam be realized in am economically profitable way. 

The molecular structure of reactants can be changed in numerous ways First the reactants molecules can be combined which is called synthesis. A prominent example is the hydrogenation of carbon dioxide to produce methanol. 

Second, a molecule or molecular fragment can also be split which is called decomposition. To recycle bottles made of polyethylene terephthalate (PET) catalytic depolymerization is used to split the PET in valuable components.  

In a substitution, a molecular fragment of a reactant is replaced by a fragment of another reactant. A prominent example is the alkylation where an alkyl group is transferred from one molecule to another. E.g., the production of Ethylbenzene from Benzene and Ethylene by the so-called Priedel-Crafts alkylation is a standard process in chemical industry.  

---