Additives can be classified in various ways based on their properties and effects. They can be categorized as liquid additives or solid additives, depending on their physical state. Another classification is based on the phase state of the reaction system, which divides additives into homogeneous additives and multiphase additives.
Homogeneous additives are those that are uniformly dispersed in the reaction system. This category includes acids, bases, soluble transition metal compounds, and peroxide additives. On the other hand, multiphase additives are those that exist in a different phase from the reaction system. Examples of multiphase additives include solid acid additives, organic alkali additives, metal additives, metal oxide additives, complex additives, rare earth additives, molecular sieve additives, biological additives, and nano additives.
Furthermore, additives can also be classified based on the type of reaction they participate in. This classification includes additives used in polymerization, polycondensation, grafting, esterification, acetalation, hydrogenation, dehydrogenation, oxidation, reduction, alkylation, isomerization, and various other reactions.
The size of the additive's action can also serve as a criterion for classification. Main additives refer to those that play a critical role in the reaction and directly affect its outcome. On the other hand, co-additives are substances that work in conjunction with the main additives to enhance their effects or provide additional functionality.
In summary, additives can be divided based on their physical state (liquid or solid), the phase state of the reaction system (homogeneous or multiphase), the type of reaction they participate in, and the magnitude of their impact on the reaction.