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The performance of a custom-designed, multimode 2450 MHz laboratory-scale, batch type-converted to continuous microwave-assisted extraction (CMAE) system was investigated and the optimization results obtained were used to develop and test a pilot-scale 5 kW, 915 MHz focused cavity CMAE system. Oil was extracted from soy flour and rice bran at various time–temperature combinations with an ethanol: feedstock ratio of 3:1. Both processes were optimized to minimize extraction time while maximizing the quantity of oil extracted. Extraction yields were compared to conventional (CE) and Soxhlet extraction. Yields in the laboratory-scale system for soybean oil were highest at the highest temperature (73 °C) and longest exposure time (21 min), while for rice bran oil, the highest yields were obtained at 73 °C and 17 min. Using the pilot-scale extraction system, greater than 93.0% of total recoverable oil was extracted from both feedstock at all tested flow rates and extraction times, more than the oil recovered by the laboratory-scale unit. Time of extraction and flow rate did not have a significant influence on extraction yield at tested temperatures for the pilot-scale process for soybeans. For rice bran, extraction yield decreased slightly with increasing flow rate (from 0.6 to 1.0 l/min) and extraction time also influenced oil yields. Analysis of oil quality indices (IV, AV, FFA content, wax and phospholipids) extracted by both CMAE processes indicate that the oil meets prescribed biodiesel feedstock quality standards, further justifying use of microwaves as a rapid tool for oil extraction. |
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