Convective drying characteristics and moisture transfer properties of Jatropha curcas L. seeds

Abstract

Jatropha curcas L. seeds are good sources of industrial-grade oil for biodiesel production and feedstock for thermochemical conversion to other biofuels. Freshly harvested seeds are wet and susceptible to deterioration due to enzymatic and microbial activities, excess moisture also limits the efficiencies of biofuel production processes. Hence, they require moisture removal by drying pre-treatment before storage and further industrial processing. Drying characteristics and moisture transfer properties of Jatropha seeds are also needed for the design, analysis and optimization of the process. Jatropha curcas seeds were dehydrated in a convective hot-air dryer at 80 - 140 °C using 1.5 m s − 1 air velocity. Dehydration rates and energy consumption were evaluated from the dehydration data. Coefficients of diffusion and mass transfer as well as activation energy were estimated by the Crank, Dincer-Dost, Biot-Lag factor (Bi-G), Biot-Drying constant (Bi-S), Biot-Dincer (Bi-Di) and Biot-Reynolds (Bi-Re) moisture transfer models. The dehydration kinetics of the seeds were also defined by thin-layer dehydration models. The dehydration rate was enhanced by drying at higher temperatures and occurred in the falling-rate phase. The energies needed to dehydrate the seeds were 0.155 – 0.184 kWh/kg fresh seed at 80 – 140 °C. Diffusion coefficients, moisture transfer coefficients and activation energies evaluated by the models were 0.975 – 3.013 × 10−8 m2 s − 1, 0.316 × 10−6 – 4.88 × 10−6 m s − 1 and 16.1 - 26.8 kJ mol−1 at 80 – 140 °C, respectively. Dincer-Dost, Bi-G, Bi-S, Bi-Di and Bi-Re moisture transfer models aptly predicted dimensionless moisture content profile. The Weibull model was the thin-layer drying model that best described the dehydration kinetics of the seeds. Moisture transfer properties and drying rate of Jatropha seeds can be enhanced and energy requirement minimized by drying seeds at higher temperatures, thus reducing the overall cost of processing seeds and boosting the profitability of biofuel production from the seeds.

Keywords

• Drying rate
• Drying energy consumption
• Effective moisture diffusivity
• Mass transfer coefficient
• Thin layer drying models
• Moisture transfer models