tert-Butylcatechol (TBC) has been tested under laboratory conditions as an inhibitor of undesired polymerization during the processing of liquid pyrolysis products and has shown high efficiency. Pilot- and industrial-scale tests and evaluation of TBC as an inhibitor in the thermal treatment of styrene have been carried out. It has been shown that this inhibitor operates only in a composition with other co-inhibitors. An inhibitory composition of TBC and copper diethyldithiocarbamate is proposed, which has shown high performance in the thermal treatment of both pyrolysis condensates and styrene. Other TBC formulations with monohydric sterically hindered phenols have been considered.