Adsorption in Biodiesel Refining - A Review

CARLOS R. VERA; MARIANA BUSTO; JUAN C. YORI; GERARDO C. TORRES; DEBORA L. MANUALE; SERGIO CANAVESE ; JORGE SEPÚLVEDA

Biodiesel. Feedstocks and Processing Tecnologies

INTECH

Lugar: Rijeka; Año: 2011; p. 427 - 458

Adsorption is a robust and reliable operation for the refining of biodiesel and its feedstocks. Hydrophillic adsorbents seem the best choice, because most of the undesired impurities are polar. In this sense silicas offer a high saturation capacity (10-15%) for glycerol and glycerides, and enough affinity for soaps, FFA, metals and salts. One advantage of adsorption units for the removal of glycerol, glycerides, soaps, phosphatides and metals from biodiesel and its feedstocks, is the reduction in wastewater effluents and the sparing of washing, oil-water separation and wastewater treatment units.  Other advantages are small capital expenditure, robustness and easiness of operation.  Cost-effective means for the scale-up of packed bed adsorbers for biodiesel refining seem to be accurate models for flow and adsorption and scaled-down RSCCTs. Accurate models for flow and adsorption can be solved in their full complexity only with the aid of numerical alculations but analytical solutions for rapid design and sensitivy analysis can be got using approximations, such as the use of square and linear isotherms and LDF models. Further approximations can be obtained for low Biot and high axial Péclet numbers.  The operation of adsorbers should minimize the consumption of adsorbent. From this point of view countercurrent bleaching tank arrays should be used but this mode of operation cannot be exploited in the case of adsorbents with linear isotherms. In the case of packed bed adsorbers common lead-lag setups of 2 or more serial columns are recommended.  Hydrophillic adsorbents seem the best choice, because most of the undesired impurities are polar. In this sense silicas offer a high saturation capacity (10-15%) for glycerol and glycerides, and enough affinity for soaps, FFA, metals and salts. One advantage of adsorption units for the removal of glycerol, glycerides, soaps, phosphatides and metals from biodiesel and its feedstocks, is the reduction in wastewater effluents and the sparing of washing, oil-water separation and wastewater treatment units.  Other advantages are small capital expenditure, robustness and easiness of operation.  Cost-effective means for the scale-up of packed bed adsorbers for biodiesel refining seem to be accurate models for flow and adsorption and scaled-down RSCCTs. Accurate models for flow and adsorption can be solved in their full complexity only with the aid of numerical alculations but analytical solutions for rapid design and sensitivy analysis can be got using approximations, such as the use of square and linear isotherms and LDF models. Further approximations can be obtained for low Biot and high axial Péclet numbers.  The operation of adsorbers should minimize the consumption of adsorbent. From this point of view countercurrent bleaching tank arrays should be used but this mode of operation cannot be exploited in the case of adsorbents with linear isotherms. In the case of packed bed adsorbers common lead-lag setups of 2 or more serial columns are recommended.