A vortex tube has certain advantages as a chemical reactor, especially if the reactions are endothermic, the reaction pathways are temperature dependent, and the products are temperature sensitive. With low-temperature differences, the vortex reactor can transmit enormous heat fluxes to a process stream containing entrained solids. This reactor has nearly plug flow and is ideally suited for the production of pyrolysis oils from biomass at low pressures and residence times to produce about 10 wt% char, 13% water, 7% gas, and 70% oxygenated primary oil vapors based on mass balances. This product distribution was verified by carbon, hydrogen, and oxygen elemental balances. The oil production appears to form by fragmenting all of the major constituents of the biomass. Cyclonic fast pyrolysis, also called vortex fast pyrolysis, separates the solids from the noncondensable gases and returns them to the mixer.