in a process for distilling polymerization - prone compounds from liquid mixtures of matter which , apart from the readily polymerizable compound , also contain other components and also polymerization inhibitors , the evaporator is operated in forced circulation and at a pressure which makes possible superheating of the liquid with respect to its boiling point at the pressure within the distillation column . this is achieved by transporting the superheated liquid against a flow restrictor , e . g . an orifice plate . the liquid which is expanded and partially evaporated on passage through the flow restrictor is returned to the distillation column . in this manner the formation of an open vapour space in the evaporator circuit after heating downstream of the heat exchanger is avoided in that , in the design of the evaporator of the prior art , formation of polymer deposits frequently occurs .