Dielectric characterization of the seeds of invasive Chinese tallow tree

Biofuels have the potential to replace a significant portion of the transportation needs of the USA and the world. Low-cost lipid feedstock (i.e. tallow tree seeds) can be used for production of biodiesel, but these seeds need to be dried. Microwave drying is utilized to dry various seeds and grain, but for this process to be most efficient the dielectric properties of the materials need to be known. This study presents, for the first time, the dielectric properties of the seeds of the Chinese tallow tree. The dielectric constant and dielectric loss factor were determined using a modified free-space method for different moisture contents at frequency ranges centered around 915 and 2450 MHz respectively. The dielectric constant decreased with frequency in those respective ranges, and increased linearly with increasing moisture content, from 1.96 at 0% m.c. to 2.3 at 7% m.c. at 915 MHz, and from 2.08 at 0% m.c. to 2.42 at 7.6% m.c. at 2450 MHz. The dielectric loss factor generally decreased with frequency in both frequency ranges, and increased linearly with moisture content from a low of 0.16 at 0% m.c. to 0.21 at 7.56% at 915 MHz, respectively from a low of 0.13 at 0% m.c. to 0.2 at 7.6% m.c. at 2450 MHz. These results can be used to design microwave processing operations and systems for drying of tallow tree seeds, as well as for non-destructive determination of theses seeds' moisture content.