Carbonaceous materials are rapidly pyrolyzed by feed of the carbonaceous material at a high velocity tangentially to a cyclone reactor-separator while introducing a high velocity stream of a particulate source of heat into the cyclone reactor-separator at an angle inclined to the path of travel of the carbonaceous material. The cyclone reactor-separator induces separation of solids consisting of the particulate carbon containing solid residue of pyrolysis and particulate heat source from a vapor stream which includes condensible and non-condensible hydrocarbon products of pyrolysis. The particulate source of heat and solid particulate carbon containing residue of pyrolysis are transported to a cyclone burner and heated by partial combustion to a temperature suitable for feed to the cyclone reactor-separator. Rapid pyrolysis maximizes the yield of middle boiling hydrocarbons and olefins.