Continuous Synthesis of a Green Fuel Additive Mixture with Highest Quantities of Solketalacetin and Solketal and Lowest Amount of Diacetin from Biodiesel-Derived Glycerol

Abstract

This work presents a continuous, easy-to-scale-up system for glycerol conversion to a valuable fuel additive mixture such as solketalacetin ((2,2-dimethyl-1,3-dioxolan-4-yl)methyl acetate), solketal and minimum amount of diacetin with no byproducts. A two-stage reaction was conducted to synthesize the mixture. At first, glycerol was reacted with acetic acid in a continuous system to synthesize monoacetin using a small plug flow reactor and central composite design to optimize the variables related to monoacetin synthesis. Finally, an acetic acid:glycerol mole ratio of 3.7:1, a temperature of 79 °C, a flow rate of 0.9 mL min −1 , and a pressure of 1 bar were determined as the optimum conditions. At the optimum condition, predicted and experimental yields of monoacetin were 63 and 62%, respectively. In the next stage, monoacetin and the residual glycerol were reacted with acetone to obtain a mixture of solketalacetin, solketal, and diacetin with the mole percentage of 62, 30, and 8%, respectively.Keywords: biodiesel additive, monoacetin, solketalacetin, (2,2-dimethyl-1,3-dioxolan-4-yl) methyl acetate, central composite design IntroductionBiodiesel is a renewable energy source that is synthesized via transesterification of the vegetable oil triglycerides.1 In this process, glycerol is produced as a byproduct that accounts for approximately 10 wt.% of the biodiesel produced.2,3 One of the uses of glycerol is its chemical transformation into oxygenated fuel additives. [4][5][6][7][8][9][10] Glycerol can be reacted with acetone to produce solketal. 4,11,12 Moreover, glycerol can react with acetic acid to produce monoacetin (MA), diacetin (DA), and triacetin (TA). 13,18 Although triacetin is one of the best biofuel additives, the process of triacetin synthesis is costly and requires high mole ratio of acetic acid:glycerol, high temperatures, and pressures. 6,13,19,20 Garcia et al. 21 synthesized solketalacetin ((2,2-dimethyl-1,3-dioxolan-4-yl)methyl acetate), whose properties were in some respects superior to those of triacetin as a biodiesel additive, but they used acetic anhydride and triethylamine to synthesize solketalacetin that is not suitable for industrial process due to the cost of these materials, and health and safety problems. They indicated that solketalacetin is a better viscosity improver and does not increase the density as much as triacetin. In our previous work, 22 a novel method was developed for the synthesis of solketalacetin consisting of two stages. In the first stage, a mixture was obtained from the reaction of glycerol and acetic acid in a batch system with the mole percentage of 60, 31, 4 and 5%, for monoacetin, diacetin, triacetin, and the residual glycerol, respectively. In the second stage, solketalacetin was obtained from the reaction of monoacetin with acetone in a continuous system. The final mixture composition changed to solketalacetin, solketal, diacetin, and triacetin with the mole percentage of 60, 5, 31, and 4%, respectively. 22 Among the fuel additives synthesized from glycer...

Isopropenyl Acetate for the Continuous-Flow Synthesis of Triacetin, Solketal Acetate, and Allyl Acetate from Pure or Crude Glycerol

“…TA and acetal acetates (mainly solketal) are among the most attractive derivatives of glycerol, and one of their most studied applications is as additives for biofuels. , This prompted us to investigate the performance of products 3 / 3′ and 6 achieved in this work as additives for a commercial soybean oil-derived biodiesel. Compounds 3 / 3′ and 6 were tested as single components (10 wt % in the biodiesel) or as a 1:1 mixture (5 wt % each) to explore their effects on the biofuel density, viscosity, cloud point, and pour point.…”

Synthesis of solketalacetin as a green fuel additive via ketalization of monoacetin with acetone using silica benzyl sulfonic acid as catalyst

“…Samples were collected in a cold trap and analyzed by GC-FID. The optimum conditions for the reaction of acetic acid and glycerol were obtained in our previous work, i.e., reaction temperature of 78 °C, acetic acid to glycerol mole ratio of 3.7:1, pressure of 1 bar, and the feed flow rate of 0.9 mL·min −1 (Gorji et al, 2018). Reaction of glycerol and acetic acid was conducted under these optimum conditions to obtain a mixture with the following mole percent; remaining glycerol (30%), monoacetin (62%), and diacetin (8%).…”

“…The main heterogeneous catalysts used for ketalization and acetalization reaction include niobium-zirconium oxide catalysts ). In our previous works, a method was developed for economical synthesis of solketalacetin in two stages using a type cation-exchange resin catalyst, namely Purolite PD 206 (Gorji et al, 2016 and2018). More specifically, in the first stage, monoacetin was synthesized through the reaction of glycerol with acetic acid.…”