Triglycerides from lipid rich sources can be converted to biofuels that are directly compatible with existing petro-fuel infrastructure. Pyrolysis is an alternate method for processing vegetable oils for production of fuels and chemicals. Most studies that conduct vegetable oil pyrolysis are carried out in batch reactors at high residence time with low yield of liquid products. At higher vapor residence time, primary products undergo secondary reactions pathway, which results in further cracking of products and formation of more gaseous product. In this study, conversion of vegetable oils was carried out in a novel continuous pyrolysis system equipped with an atomizer to introduce vegetable oils. With this design, we were able to achieve vapor residence times (τvap) of 1-300s, depending upon feed flow rates without preheating the feed and inert gas usage.
Effects of reaction temperature (from 450 to 550 ºC) and vapor residence time (from 1 to 300s) on conversion, products yields and composition were investigated. At T> 475 °C and τvap >6s, nearly quantitative conversion of feed was achieved and we were able to recover nearly 90% of the feed as a liquid product in a downstream condenser. Fatty acids side-chains of the triglyceride molecules degraded to hydrocarbons during pyrolysis and the highest hydrocarbon yields were obtained at T=500 °C and τvap = 60s. Under these conditions, we observed nearly 40% hydrocarbon content in the product (5% C5-C7, 17% C7-C12 and 16% >C12). In addition long-chain (C16-C18, 33% of product) and short-chain (C6-C12; 15% of product) fatty acids were also observed. Overall, our results show that it is possible to produce a wide range of products at high yields (relative to feed) – gasoline, jet or diesel fuel as well as fatty acids for oleochemicals – with integration of conventional downstream separations, such as distillation.