Catalysts and Initiators

Catalysts and initiators start or promote chemical reactions that are used to produce organic chemicals, polymers and adhesives. A chemical catalyst is a substance that increases the rate at which a chemical reaction occurs; however, the catalyst itself does not undergo chemical change. An initiator is a chemical compound that helps start a chemical reaction such as polymerization. Unlike a catalyst, an initiator is usually consumed in the reaction. Substances such as organic peroxides are commonly used as initiators. According to some estimates, more than half of all petrochemical processes use catalysts and initiators. In heterogeneous catalysis, a chemical catalyst provides a surface on which reactants become adsorbed temporarily, and where chemical bonds in the reactants are weakened, allowing new bonds to be created. Because the bonds between the products and the catalyst are weaker, the products are released from the chemical catalyst. Continuous process catalysts (CPC) are used to process industrial chemicals such as solvents, plasticizers, monomers and intermediates. Catalytic solutions include a variety of specialized catalyst products.

There are two basic types of catalysis: homogeneous catalysis, in which both the catalyst and reactants are in the same phase (for example, liquid or gas), and heterogeneous catalysis, in which the catalyst and reactants are in different phases (for example, solid catalysts and gaseous reactants). Metal catalysts and initiators are made from precious metals such as gold, iridium, osmium, palladium, platinum, rhodium, ruthenium and silver. They are used as heterogeneous catalysts for reactions such as hydrogenation and isomerization. Zeolites, minerals with a porous structure, can also be used as catalysts. Synthetic zeolites are the most important catalysts in petrochemical refineries. The proper selection of catalysts and initiators is an important consideration. For example, using rhodium or platinum as catalysts can produce different products depending on whether methane or ethane are used.

ASTM International (formerly called the American Society for Testing and Materials (ASTM), maintains standards for catalysts such as ASTM D3766, standard terminology relating to catalysts and initiators. Some catalysts and initiators must be handled as hazardous materials. The National Fire Protection Association (NFPA) maintains NFPA 432, a standard which covers the catalyst organic peroxide.