Energy Efficient Recovery of Methanol and Glycerol in Biodiesel Production

Abstract

Biodiesel is a renewable fuel that consists of fatty acids methyl esters – currently produced by trans-esterification of glycerides with methanol. After the biodiesel synthesis, the downstream processing steps involve the purification of crude glycerol, as well as the separation of excess methanol (recyclable), glycerol by-product and water (from washing and pre-treatment step). The separation of the ternary mixture methanol-water-glycerol is carried out in a conventional direct sequence that requires two distillation columns and rather high amounts of energy. This study proposes an efficient process intensification method for this ternary separation, namely the use of a dividing-wall column (DWC) that is able to separate all products at high purity, in only one equipment unit. AspenTech Aspen Plus was used as a computer aided process engineering tools to perform the rigorous steady-state simulations, as well as the optimization of the new DWC separation alternative. In order to allow a fair comparison, all designs were optimized using the state of the art sequential quadratic programming (SQP) method. Remarkable, the results show that the proposed DWC system requires 27 % less energy and 12 % lower investment costs, thus having a significant contribution towards inexpensive biodiesel production.