Disclosed is a pyrolysis reaction process. The process can be advantageously accomplished using a pyrolysis reactor that has a primary reaction zone comprised of bed packing having multiple passages through the bed packing and a secondary reaction zone having an open flow arrangement. The process includes a step of injecting a pyrolysis feed comprising a first hydrocarbon into the primary reaction zone to produce a primary pyrolysis product containing unsaturated hydrocarbon. A reactive feed comprising a second hydrocarbon is injected into the secondary reaction zone to mix with the primary pyrolysis product and produce a secondary pyrolysis product.