The example process chosen for illustration is transesterification of rapeseed oil to produce rapeseed oil methylester (RME) as the main product and glycerine as a co-product. Therefore, the environmental impacts have to be allocated between these two products, using an appropriate allocation basis. Two allocation approaches are considered here — mass and energy basis — to illustrate the difference in the approach as well as any difference in the LCA results. GHG emissions are used for illustration purposes. This example is based on that found in Fehrenbach et al. (2007).

The process produces 1 kg of RME and 0.092 kg of glycerine. The total GHG emissions from the process are 0.307 kg CO2 eq. The lower heating value (LHV) of RME is 37.2 MJ/kg and of glycerine is 17 MJ/kg.

[2] Mass-based allocation:

Total mass of products in the process: 1 kg RME + 0.092 kg glycerine = 1.092 kg Allocation factor:

RME: 1 kg/1.092 kg x 100 = 91.6%

Glycerine: 0.092 kg/1.092 x 100 = 8.4%