In a method of treating the reaction product of pyrolysis of 1,2-dichloroethane to form vinyl chloride and hydrogen chloride with multiple stage cooling and distillation separation of the reaction product and recycle of unreacted 1,2-dichloroethane to the pyrolysis step, the improvement comprising direct cooling of the reaction product immediately after leaving the pyrolysis step, within 1 sec from a temperature range of 480.degree. to 540.degree. C. down to 150.degree. to 250.degree. C., charging the cooled product into a quench column, recovering the vapors from the head of the quench column and indirectly cooling the same by heat exchange to at least its condensation point, the heat exchange media being at least one member of the group consisting of (a) 1,2-dichloroethane to be fed in heated condition to the pyrolysis unit, (b) air used as combustion air to fire the pyrolysis zone, (c) the sump of the hydrogen chloride column as defined above, (d) liquid hydrogene chloride to be evaporated and, (e) water, to dissipate heat not used within the measures according to the present invention.