Gliperol® is another biofuel integrating glycerol recently patented by the Industrial Chemistry Research Institute of Warsaw (Poland).59 It is composed of a mixture of three molecules of FAMEs and a molecule of glycerol triacetate (triacetin). It can be obtained after the transesterification of a mole of TG with three moles of methyl acetate using lipases or an ion-exchange acidic resin as catalysts.59-61 When ethyl acetate is used, the corresponding FAEEs with triacetin are obtained,62 following the enzymatic process summarized in Fig. 7.4.

In both processes, enzymatic and acidic, glycerol is not isolated as a by-product but utilized in the form of esters with low-molecular weight carboxylic acids as biofuel components. The methodology to prepare this novel biofuel employing heterogeneous catalyst allows the reduction of biofuel production costs by running the reaction without having to remove the catalyst. This allows to run the process in a continuous manner.59 The process patented by the Industrial Chemistry Research Institute of Warsaw also consists of a post-treatment of the reaction

mixture in order to remove, by distillation, excess of ester acidic alcohol used (ethyl acetate). Removal of the reactant from the mixture after reaction allows the reutilization of the reactant and, consequently, reduces the process costs.

In the case of an enzymatic process, immobilized lipases have been normally employed. Methyl or ethyl acetates can be used as acyl acceptors in the interesterification reaction, and the deactivation of enzyme by glycerol is minimized as no glycerol is produced in the reaction. Moreover, the use of ethyl acetate could be interesting because of the production of ethyl esters (an extra carbon atom) that increases the heat content and the cetane number of the final biofuel. Using ethyl esters instead of methyl esters also decreases the cold and pour points as well as increases the flash and combustion points, which improves cold starts and safety in handling the biofuel.63 Modi et al. have obtained over 90% yield in ethyl esters by using 10% Novozyme 435 as lipase (wt/wt to sunflower oil) at 50°C after 12 hours, using an ethyl acetate/oil molar ratio of 11:1.62 The reusability of the heterogeneous enzymatic catalyst (Novozyme 435) was also investigated in the same study, both in ethyl acetate and in ethanol. The stability of lipases after 12 reaction cycles was found to be constant: 91.3% and 93.7% as relative activity for interesterification and ethanolysis, respectively. Under these optimized conditions, Glyperol® production by enzymatic interesterification of vegetable oils could be technically and industrially feasible, nearly as much as the acidic process proposed by the Industrial Chemistry Research Institute of Warsaw.

A closing favourable point is also the good market of triacetin as a by-product. Triacetin has widespread applications in food, feed, printing, tanning, cigarettes, cosmetics, pesticides and pharmaceutical industries as well as in medical field.