The present invention provides an improvement in a process and apparatus for manufacturing acrylonitrile by the vapor phase ammoxidation of a hydrocarbon. The invention comprises contacting the gaseous product stream with a quench fluid in a reverse jet scrubber. The quenching fluid is injected counter-current to the gas flow, and the gas velocity is sufficient to reverse the flow direction of the water, thereby forming a standing wave or froth zone wherein the quench is rapidly achieved. The quench fluid may be obtained from many sources, but is preferably obtained from a waste process stream emanating from a subsequent recovery or purification step. The quench fluid may contain acid to facilitate removal of ammonia from the gas stream. The quench fluid that is not vaporized may be recirculated. Impurities and contaminants may be removed from the quench fluid prior to recycle. In a most preferred embodiment, the quench fluid is not cooled during recirculation, and the cooling process is essentially adiabatic, with the sensible heat of the hot gaseous stream being converted to latent heat in the form of vapor.