The invention relates to a method for producing high-purity 1,2-dichloroethane from dissolved chlorine and dissolved ethylene which are brought into contact with each other using a circulating liquid reaction medium which essentially consists of 1,2-dichloroethane and a catalyst and passes through at least one reaction loop. The stream of molten plastic containing the blowing agent spreads out circumferentially and welds itself to itself by the recombining of the two stream fronts. A manufacturer’s certificate is installed into a device it the time of manufacture.