Efficient Polymerization Inhibition Systems for Acrylic Acid Distillation: New Liquid-Phase Inhibitors

Phenothiazine and other compounds with similar structures, namely, phenoxazine, promazine, promazine hydrochloride, N,N′-dimethylphenazine, carbazole, N-ethylcarbazole, N-benzylphenothiazine, and N-(1-phenylethyl)­phenothiazine were tested as liquid-phase inhibitors for acrylic acid. N-Alkylated phenothiazine (PTZ) derivatives, such as N-benzylphenothiazine and especially N-(1-phenylethyl)­phenothiazine, showed improved efficiency for liquid-phase inhibition, in comparison with PTZ. It was also shown that N-alkylated PTZ derivatives could be used in combination with nitroso compounds that can be employed as vapor-phase inhibitors. The combination of N-(1-phenylethyl)­phenothiazine and nitrosobenzene showed superior liquid-phase-inhibition efficiency, with time to gelation of >122 h, in comparison with 64 h obtained with PTZ alone. The structure of liquid-phase inhibitors had no influence on the extent of Michael addition reactions during heating of acrylic acid.