Abstract
Various compounds prepared using glycerol, diglycerol (DG), and triglycerol (TG) have been gaining increasing attention due to their wide range of applications. To increase the yield and selectivity of DG and TG syntheses, previous studies investigated a variety of catalysts with different basicity and variable reaction temperatures. In this study, we introduced additives that act as inhibitors to increase the selectivity of the etherification reaction for DG and TG production and depress the formation of higher oligomers by moderating the activity of the catalyst. By adding weakly acidic alkali metal-based inorganic salts (NaHSO4 and KHSO4), the selectivity of DG and TG formation could be enhanced, although the conversion of glycerol decreased due to the reduced activity of catalyst. We found that the decrease in the activity of the catalyst caused by the additives could be recovered and that side reactions were reduced if the reaction was carried out at an increased temperature of 280 °C and if the reaction time was shortened to 2 h to suppress the formation of oligomers. The dependence of the reaction on the amount of the additive, the reaction time, and the reaction temperature was investigated to elucidate the role of the additive.
Highlights
DG and TG prepared by the etherification reaction of glycerol have been used widely in applications including pharmaceuticals, food additives, cosmetics, lubricants, plasticizers, stabilizers, dispersants, and wetting agents [24,25,26,27]
The selectivities of DG and TG in the presence of NaOAc and KOAc were 38.7, 31.9 and 32.8, 25.1%, respectively. This is because DG and TG produced by the etherification of glycerol further reacted to form the oligomers
Glycerol (30 g), the catalyst, and optionally the proton donor were put into a two-necked round bottomed flask (150 mL) that was placed on a heating mantle equipped with a temperature controller
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In 2008, biodiesel and glycerol were produced globally in quantities of 10.1 million and 1.1 million tons, respectively; the consumption of glycerol was only 0.6 million tons [4] For this reason, various studies of the catalytic conversion of glycerol to high value-added commodity chemicals including acrolein [5,6], allyl alcohol [7,8,9], epichlorohydrine [10], glycerol carbonate [11,12], glycidol [13,14], acetins [15,16,17,18], and condensed glycerols such as diglycerol (DG), triglycerol (TG), and polyglycerols [19,20,21,22,23] have been proposed. To the best of our knowledge, this is the first study to increase the selectivities and Catalysts 2021, 11, 1000 yields of DG and TG using inhibitors that lower the activity of the catalysts as additives by suppressing the formation of oligomers in the catalytic etherification of glycerol
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