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The technical and economic feasibility of an alternative process for biodiesel production from residual oil and fats (ROF) was compared to two cases of the conventional two-step alkali-catalyzed process. A reliable set of thermophysical properties, kinetic data, and a rigorous thermodynamic modeling were used in the simulations. The alternative process employed liquid−liquid extraction to separate the free fatty acids from triacylglycerols, with methanol as the solvent. Both processes were found to be technically feasible based on a design specification of 99.65% esters for the product. The alternative process proved to be slightly more economically viable than the conventional process based on the selected economic indicators and thus is a promising alternative for biodiesel production from ROF.

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In order to provide new isobaric vapor−liquid equilibrium (VLE) data for ethanol-biodiesel systems, experimental boiling points for mixtures of ethanol + biodiesel from soybean oil (SB) and frying oil (FB) were measured. UNIFAC and NRTL models were used to predict and correlate the data, in order to better represent the VLE in process simulation. VLE data were measured with a Fischer type ebulliometer. Reliability and reproducibility were evaluated with VLE data for ethanol + water system at 101.32 kPa. These data also proved to be thermodynamically consistent based on the area test. The boiling temperatures for ethanol + biodiesel systems agreed with other results reported at same pressure for SB and for biodiesel from sunflower seed oil (SSB). The thermodynamic modelling using the NRTL model obtained lower AAD values than those from UNIFAC, assuring better safety in the design and simulations steps of a biodiesel production plant.

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The liquid-liquid extraction of free fatty acids (FFA) from residual oils and fats for biodiesel production, employing methanol as the solvent, has been optimized using process simulation and response surface methodology. The parameters investigated were temperature, number of stages and solvent-to-feed ratio (S/F). Responses evaluated were FFA mass fraction in the oil-rich phase (wFFA B ) and total cost, using yellow and brown greases as the raw materials. Quadratic and linear models were fitted for wFFA B and cost responses, respectively. The optimal conditions satisfying technical (wFFA B ≤ 0.5%) and economic (minimum cost, including capital and operation costs, except for raw material cost) criteria were 321 K, 6 stages, S/F = 1.27, wFFA B = 0.41%, cost = $84.93/ton (yellow grease), and 318 K, 6 stages, S/F = 1.32, wFFA B = 0.49%, cost = $102.89/ton (brown grease).

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