Process for the manufacture of vinyl chloride

In the process for the manufacture of vinyl chloride by pyrolytic decomposition of 1,2-dichloroethane in a furnace with a coiled up reaction tube, the furnace having a convection, a vaporization, a heating and a cracking zones from top to bottom and having a plurality of burner rows from top to bottom, both the convection zone and the vaporization zone being above the top row of burners and both the heating zone and the cracking zone being in that part of the furnace where the burner rows are situated, separating high-boiling constituents from 1,2-dichloroethane in a column preceding the furnace, passing the 1,2-dichloroethane through the reaction tube from top to bottom, carrying out the pyrolysis at a temperature of 480.degree. to 510.degree., separating hydrogen chloride and subsequently vinyl chloride from the cracked gas by distillation, recycling the sump product of the vinyl chloride separation to the column preceding the furnace while adding gaseous chlorine in the absence of a catalyst to the recycled sump product, the improvement which comprises using a reaction tube having an internal diameter of from 12 to 16 cm, and supplying through the rows of burners in the heating zone an amount of heat that is 1.8 to 2.2 times the amount of heat supplied through the rows of burners in the cracking zone whereby rapdi clogging by carbonization is prevented and operating periods are prolonged.