Integrated technology for supercritical biodiesel production and power cogeneration

A supercritical (SC) fluid technology coupled with power cogeneration is proposed to produce biodiesel fuels without the conventional complex separation/purification steps. The core of the integrated system consists of the transesterification (TE) of various triglyceride sources (i.e., vegetable oils and animal fats) with SC methanol/ethanol. Part of the reaction products can be combusted by a diesel engine integrated in the system, which, in turn, provides the power needed to pressurize the system and the heat of the exhaust gases for the TE process. This article reports laboratory-scale investigations directed to system optimum performance (i.e., near complete conversion in short processing time) in connection with the effects of process operating conditions. TE experiments have been conducted at 100-300 bar, 250-425 °C, and 0.73-8.2 min residence time with soybean/sunflower oils as triglycerides and SC methanol/ethanol at ratios of alcohol to oil from 3 (stoichiometric) to 24. Special emphasis was on reactant phase transitions from liquid to SC states. These transitions were monitored with a high-pressure, high-temperature view cell connected to the reactor outlet for the continuous TE experiments and also serving as a batch reactor. Under selected parameters, near complete oil conversion to biodiesel has been achieved with the glycerol decomposition products included in the fuel. Commercial biodiesel production by this method estimated processing costs as low as $0.26/gal for a plant capacity of 5 million gal/year, significantly lower than the current processing costs of ∼$0.51/gal for biodiesel produced by conventional catalytic methods. The retail cost of biodiesel produced by the proposed method is likely to be competitive with diesel fuel prices.