The role of hydroquinone monomethyl ether in the stabilization of acrylic acid

Stabilizers prevent the inadvertent polymerization of acrylic acid; they work as scavengers. In practice, hydroquinone monomethyl ether (p-methoxyphenol, MeHQ), among others, has established itself as a standard stabilizer. Under the process conditions of acrylic acid production, MeHQ is required at high temperatures and in the presence of dissolved atmospheric oxygen for polymerization inhibition. Our investigations in air and nitrogen atmospheres confirm that MeHQ is only effective as a stabilizer in the presence of dissolved molecular oxygen. Up to temperatures of 60 degrees C, MeHQ consumption in acrylic acid is practically negligible. At temperatures above 60 degrees C, the stabilizer concentration decreases almost linearly with time. At temperatures above 80 degrees C, degradation accelerates. The consumption ratio of O-2 (in number of moles) to MeHQ (in number of moles) is about 6:1. Based on the degradation kinetics of O-2 und MeHQ that are determined, the amounts of MeHQ required for a reasonable stabilisation can now be calculated.