Abstract
Glycerol is one of the most crucial by-products in the production of biodiesel, and owing to its oversaturation in the market, several synthetic strategies have been developed to transform it into other higher value-added products such as glycerol carbonate, epichlorohydrin, 1,3-propanediol, etc. Amongst them, glycerol carbonate is considered to be the most valuable product. Considering the facile separation and reusability of catalyst, heterogeneous base catalysts have attracted considerable attention due to the obvious advantages over Brϕnsted acid and homogeneous base catalysts in the transesterification of glycerol. Herein, we will give a short overview on the recent development of the heterogeneous catalysis in the transesterification of glycerol with dialkyl carbonate. Focus will be concentrated on the heterogeneous base catalysts including alkaline-earth metal oxides (MgO, CaO, and mixed oxides), hydrotalcites, zeolites, clinoptilolites, organic bases, etc. Their catalytic mechanisms during the heterogeneous process will be elucidated in detail.
Highlights
IntroductionWith the increasing demand for energy sources and environmental safety, biodiesel as a clean and rWeniethwtahbeleinecnreeragsyinigs dcoemnsaidnedrefodrteonbeergaypsootuerncteisalalyndhiegnhvairlotenrmnaetnivtael esnafeertgyy, boifotdraiedsietlioansaal fculeealns
The results showed that the higher yield of product was attributed to the higher total basic sites and the Brunauer–Emmett–Teller (SBET) surface area of the catalyst
Catalysts with different molar ratios are generally synthesized via a co-precipitation methodology followed by decomposition and calcination at different temperatures
Summary
With the increasing demand for energy sources and environmental safety, biodiesel as a clean and rWeniethwtahbeleinecnreeragsyinigs dcoemnsaidnedrefodrteonbeergaypsootuerncteisalalyndhiegnhvairlotenrmnaetnivtael esnafeertgyy, boifotdraiedsietlioansaal fculeealns. In order to gain further insight into the mechanism, a series of experiments were conducted with CaO employed as a catalyst by Lee and Kim’s group (Table 2, entries 7–15) [61] They have successfully isolated an active homogeneous Ca species in the CaO-catalyzed transesterification of glycerol with DMC and characterized it as Ca(C3H7O3)(OCO2CH3) (II). Green, and environmentally friendly methodology for CaO preparation and can be used as an inspiration to various applications of CaO catalyst
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