Unsaturated compounds, particularly vinyl monomers found in hydrocarbon streams, can undesirably polymerize at various stages of their manufacture, processing, handling, storage, and use. Vinyl monomers can undergo self-initiated polymerization at elevated temperatures even in the absence of polymerization promoters. This undesired thermal polymerization can be a problem during the purification of vinyl aromatic monomers and during sudden process shutdowns. Undesirable polymerization results in product loss because the valuable monomer, the end product, is consumed in the undesired side reaction. Moreover, polymerization reduces production efficiency as the polymer is deposited on process equipment. This fouling of process equipment may require unscheduled shutdown to remove the undesired polymer by physical methods.
Currently, there are antipolymerants that are in use, most notably dinitro-substituted aromatic compounds. Despite their antipolymerant efficacy and low cost, dinitrophenols (DNP), which include 2,6-dinitrophenol, 2,4-dinitrocresol, and 2-sec-butyl-4,6-dinitrophenol (DNBP)) compounds, are highly toxic, particularly DNBP. In the case of the purification of styrene, the dominant product in the market is DNBP. In spite of its high antipolymerant performance, DNBP is highly toxic and has a deleterious environmental impact. Consequently, the use of DNBP is becoming highly restricted, for example its usage under the restrictive European REACH legislation. There is a need for alternative antipolymerants that are as efficient as DNBP at reducing polymerization and yet are safe and environmentally friendly.
USPTO Backgrounds
USPTO Backgrounds