An economical and easy to scale up method for glycerol conversion to solketalacetin (i.e., (2,2-dimethyl-1,3-dioxolan-4-yl)methyl acetate) as a valuable fuel additive is described, for the first time. Monoacetin was synthesized by reacting glycerol with acetic acid, and then solketalacetin was produced from the reaction of monoacetin with acetone using Purolite PD 206 as a catalyst. The central composite design was employed for the experimental design and then response surface methodology was used for the optimization of variables for the second stage of the reaction. The optimum operating conditions for the second stage of the reaction were as follows: acetone to monoacetin mole ratio, 5; reaction temperature, 20 °C; pressure, 45 bar; flow rate, 0.2 mL•min −1 ; and catalyst, 2.0 g. Yield of the second stage of the reaction at the experimental design conditions and at the acetone to monoacetin mole ratio of 9 was obtained as 69% and 100%, respectively.

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...

No abstract