Process and apparatus to form vinyl chloride monomer from ethylene dichloride in a cracking furnace, including a firebox chamber having a thermal protective layer disposed on refractory walls and/or process tubes disposed within the chamber, a quencher to form vinyl chloride monomer, and fractionator separate products. The thermal protective layer which contains an inorganic adhesive for metal/alloy tubes or colloidal silica and/or colloidal alumina for refractory walls or ceramic tubes, a filler, and one or more emissivity agents.