This Is AuburnElectronic Theses and Dissertations

Optimization and economics of small-scale, on-farm biodiesel production using oilseed crops and waste vegetable oil




Mullenix, Daniel

Type of Degree



Civil Engineering


Recent concerns over unpredictable fuel prices and desire to reduce farm input costs have warranted producer interest in growing alternative crops for the production of biofuels such as biodiesel. Ideally, biodiesel could be produced with a small-scale, on-farm system allowing a farm to retain full value of an oilseed crop. Similarly, on-farm biodiesel feedstock could be supplemented with waste vegetable oil (WVO) from local sources, which would be an inexpensive input to lower production costs. The objectives of this research were to: 1) evaluate the impact of an irrigation regime on oilseed constituents (oil concentration, oil free fatty acid (FFA), and protein concentration) within three oilseed crops (cotton, soybeans, and canola) grown in a non-traditional rotation; 2) determine a biodiesel production and phosphorus removal procedure that could be economical for Alabama farmers and a storage interval for vegetable oil in which FFA will remain within acceptable limits for base catalyzed transesterification; and 3) assess economics of a current small-scale biodiesel production system in Auburn University’s Biosystems Engineering department with the data collected being used to develop a prediction model for a small-scale, on-farm biodiesel production system scenario. Five different experiments were performed along with a literature review of biodiesel production practices, efficiency analyses of two mechanical oil extruders, and economic assessments of two small-scale biodiesel production systems. An irrigation experiment examined oilseed constituent responses to varying levels of irrigation for biodiesel production. Triglyceride hydrolysis rates and microbial activity of three vegetable oils were studied over time. The third experiment determined differences in methanol recovery efficiency for two methods. The final two experiments investigated phosphorus removal from two crude vegetable oils, quality of biodiesel produced, and phosphorus removed resulting from transesterification. Results from the irrigation experiment indicated that seed and oil yields significantly improved with irrigation and rainfall. As a result, theoretical biodiesel yields increased 380%, 166%, and 200% for soybean, cottonseed, and canola, respectively. Protein concentrations tended to decrease with irrigation, but FFA values showed little response with emphasis on biodiesel production except when seeds were exposed to excessive end of the season moisture. Based catalyzed transesterification with methanol and sodium was determined to be least expensive yielding favorable results. WVO and canola oil oxidized 68% and 43% during storage and no microorganism activity was detected. While soybean oil oxidized 50%, FFA levels remained well under one percent. Vacuum pump assistance increased methanol recovery by 600%. ASTM requirements of phosphorus removal were not met during oil degumming experiments. Bench scale transesterification reactions resulted in higher ester conversion than the Biodiesel Logic, Inc. processor due to increased oil/methanol interaction, but AMBERLITE™ BD10DRY satisfactorily removed free glycerin from biodiesel. A mechanical screw press with fixed components required less operator aptitude to increase oil extraction of canola, however soybean oil extraction proved efficient on the Henan Double Elephant mechanical press. Oil extraction efficiency was heavily dependent on oilseed moisture content and operator ability. WVO biodiesel cost of production was $0.58/L while soybean and canola biodiesel production costs were substantially higher. However in 2010, Alabama soybean farmers could have reduced losses by $24.70/ha when producing biodiesel as opposed to selling crops through traditional market outlets.