Characterization of Fast Pyrolysis of Dry Distiller's Grains (DDGS) and Palm Kernel Cake Using a Heated Foil Reactor: Nitrogen Chemistry and Basic Reactor Modeling

In this paper, two residues of liquid biofuels production were tested: dry distiller's grains with solubles and palm kernel cake. The fuels were tested in a heated foil reactor inserted in a Fourier Transform Infrared spectrometer under fast pyrolysis conditions: a heating rate of 600 degrees C/s and final temperatures ranging from 500 to 1300 degrees C. The fuels were also pretreated by water leaching to remove water-soluble inorganic compounds. A numerical model of the unloaded system was developed to gain better insight into the temperature and velocity profiles in the reactor and on the foil. The model allowed the detection of zones of high temperature and low velocity around the hot foil, indicating that secondary reactions are likely. Moreover, temperature validation with an InfraRed pyrometer indicated that the temperature measured by the control thermocouple is on average about 15% (in degrees C) lower than the actual foil temperature. The product composition and final yields of volatile species were measured at different final temperatures. The main volatile species was CO2 for temperatures lower than 1000 degrees C At higher temperatures CO became the most abundant volatile species, likely because of tar cracking. HCN resulted to be the main volatile-N compound for all samples at all temperatures, while NH3 was detected in minor amounts. The mechanism of decomposition of proteins seems to have changed from deamination, at slow heating rates, to dehydration, followed by the formation of cyclic amides. These structures were released as tar-N and subsequently decomposed into HCN and NH3. The effect of the leaching was not relevant for weight loss and main species release, but it appeared to enhance tar-N decomposition for the DDGS sample.