Abstract
Glycerol carbonate (GC) is a value-added product originating from the valorization of widely available glycerol (Gly), a side stream from the production of biodiesel. Here we approach the production of this chemical comparing two reactions based on the transesterification of Gly with dimethyl carbonate (DMC) and ethylene carbonate (EC). When using DMC, it was observed that the free enzyme CALB (lipase B from Candida antarctica) gave the best results, whereas Eversa Transform (a genetic modification of Thermomyces lanuginosus lipase) performed better than the rest if EC was the reagent. With the selected catalysts, their immobilized analogous enzymes Novozym 435 and Lypozyme TL IM, respectively, were also tested. Observing that the yields for the reaction with EC were significantly faster, other operating variables were evaluated, resulting the best performance using a closed system, tert-butanol as solvent, a concentration of enzyme Eversa Transform of 3% w/w, a molar excess of EC:Gly of 9:1 and a temperature of 60 °C. Finally, several runs were conducted at different temperatures and molar ratios of EC:Gly, fitting a kinetic model to all experimental data for the reaction catalyzed with Eversa Transform. This model included the bimolecular transesterification reaction of Gly and EC catalyzed by the lipase and a reversible ring-opening polymerization of EC.
Highlights
Valorization of glycerol (Gly) is a blossoming topic of research given the need to make good use of the abundant surplus caused by the development of the biodiesel industry [1], which, in the end, has led to a marked decline in the retail prices in spite of its use in the food, healthcare, pharmaceutical, or tobacco industries [2]
The following free enzymes were employed throughout the experimental work: CALB (Candida antarctica lipase B) and Lypozyme TL 100 L (Thermomyces lanuginosus lipase) and Eversa Transform 2.0, which were a kind gift from Novo
The kinetic model fits perfectly to retrieved experimental data, as indicated by the very high values for Fisher’s F parameter, and very low values of SQR and residual mean squared error (RMSE), together with the evident goodness of fit shown by lines and experimental points in the figure
Summary
Valorization of glycerol (Gly) is a blossoming topic of research given the need to make good use of the abundant surplus caused by the development of the biodiesel industry [1], which, in the end, has led to a marked decline in the retail prices in spite of its use in the food, healthcare, pharmaceutical, or tobacco industries [2]. Several reviews have described extensively the methods of production of GC [7,8,9,10], which could be summarized in the following reaction pathways: (i) addition of CO or CO2 to Gly under pressurized conditions; (ii) reaction of urea and Gly under vacuum conditions so as to remove the ammonia generated as by-product; and (iii) transesterification of Gly with organic carbonates (OC) For the latter route, the authors of the present work have conducted extensive research using both dialkyl carbonates like dimethyl carbonate (DMC) [11,12] or cyclic carbonates like ethylene carbonate (EC) [13,14,15,16], or more recently, propylene and butylene carbonate [17]. The advantage of this reaction pathway is that alcohols or glycols can be concomitantly produced when dialkyl or cyclic carbonates, respectively, are used as co-substrates along with Gly
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