This study is the first of its kind to report on the transesterification of industrial grade crude glycerol (GLY) to glycerol carbonate (GC) using microwave processing. Pure and two grades of crude GLY at 70% and 86% purity were transesterified with dimethyl carbonate (DMC) using calcium oxide (CaO) as catalyst. A comparison study was made of the conventional and microwave-assisted transesterification process. It was found that 70% purity of crude GLY gave higher yield in both conventional and microwave-assisted transesterification processes with the latter technique showing better energy efficiency. The highest GC yield of 93.4% was obtained from GLY with purity of 70% under microwave irradiation system with 1 wt% of catalyst, 2:1 M ratio of DMC:GLY at 65 degrees C in five minutes reaction time. The yield of GC was observed to increase with temperature, time and molar ratio but not the catalyst loading. The impurities such as methanol (MeOH) and sodium methylate (NaOMe) in the crude GLY were found to increase GC yield by four times. This indicates that the impurities which might not be desirable for the transesterification process under normal circumstances have unconventionally demonstrated positive effects on the performance of transesterification under microwave irradiation. (C) 2015 Elsevier B.V. All rights reserved.