Comparison of biodiesel production scenarios with coproduction of triacetin according to energy and GHG emissions

A solution for the limited fossil oil resources could be biodiesel. However, the future of biodiesel is threatened by the use of vegetable oil as biodiesel feedstock and the low economic value of the byproduct glycerol. The use of algal oil as feedstock and triacetin instead of glycerol as byproduct could be a solution. Triacetin can be used as a biodiesel additive, so more biofuel will be produced. However the net energy gain and the greenhouse gas (GHG) reduction for this changed biodiesel production process needs to be analyzed. To this end, we compared conventional biodiesel production from algal oil with three scenarios to produce biodiesel and triacetin: catalytic and enzymatic interesterification, and catalytic esterification of glycerol. The energy content of the produced biofuel from the same mass of algal oil increases, when triacetin is formed. The increase compared with conventional biodiesel production is 11.0, 2.8 and 5.6% for the catalytic and enzymatic interesterification reactions and the catalytic esterification of glycerol respectively. However, the energy required for the production increases with a similar, even higher, value, leading to no improvement in the net energy. The energy demand is mostly depending of the reactant production from fossil fuel. Therefore the influence of changing the reactant production process to an alternative process from biomass was assessed. The results showed that the net energy values of all the scenarios increase and that interesterification scenarios and the biodiesel scenario have a similar net energy value. Regarding the GHG emissions, conventional biodiesel scores best. Here, too, the production of the reactants plays an important role. In conclusion, the reactant production from fossil sources leads to a lower net energy value for the scenarios with triacetin coproduction in comparison with the conventional biodiesel production. However, when the production process is changed to a biomass based process the interesterification scenarios and conventional biodiesel scenarios have similar results. © 2014 Published by Elsevier Ltd