A biocatalytic synthesis of glycerol carbonate (GlyC), as an added-value product of renewable glycerol, has been developed using a catalytic route in which glycerol (Gly) was reacting with dimethyl carbonate (DMC) in the presence of lipase under solvent-free conditions. The enzyme screening indicated lipase from Aspergillus niger as the most efficient biocatalyst for the GlyC synthesis. After the optimization of the reaction conditions it was established that the best results corresponded to 12% (w/w) Aspergillus nigerlipase, to a glycerol : DMC molar ratio of 1 : 10, to an incubation time of 4 h and to an incubation temperature of 60 °C. Consequently, the glycerol conversion was around 74%, the yield in GlyC of 59.3% and the selectivity to GlyC of 80.3%. Recycling experiments demonstrated that the biocatalyst can be successfully used for several reaction cycles (at least 4 times) and confirmed its very high stability under the reaction conditions.

A new strategy for the preparation of biocatalysts based on enzyme immobilization was explored, leading to cross-linked enzyme aggregate onto magnetic particles (CLEMPA). Lipase enzyme from Aspergillus niger was precipitated from aqueous solution followed by cross-linking of the enzyme aggregates onto magnetic particles using glutaraldehyde as cross-linker. An optimization study has been carried out for the CLEMPA approach to determine the best experimental conditions for both preparation steps (i.e. enzyme precipitation and cross-linking of the enzyme aggregates onto magnetic particles). Type and concentration of the precipitation agent, type and size of magnetic particles, ratio of lipase to magnetic particles, concentration of the cross-linker and growth time of CLEMPA clusters were the experimental factors taken under investigation. Characterization of CLEMPA biocatalyst considering the cluster size and lipase loading was performed using light scattering detection and UV-vis spectrophotometric techniques. The catalytic capacity of CLEMPA biocatalyst was tested with the “green” alternative of glycerol carbonate (GlyC) synthesis. CLEMPA catalyzed the conversion of glycerol to GlyC with an excess of dimethyl carbonate (DMC) providing solvent-free conditions for the reaction. These experiments resulted in encouraging biocatalytic performance with 61% glycerol conversion, 55% GlyC yield and 90% selectivity in GlyC. CLEMPA biocatalyst was also tested in the reaction of “crude” glycerol extracted from the biodiesel process, with similar performance results. Recycling experiments for 20 successive reaction cycles demonstrated the robustness of the prepared CLEMPA structure.