Study On The Synthesis Of Glycerol Carbonate By Heterogeneous Catalysis

Recently, large amount of glycerol as a by-product were produced for the bio-diesel production was continuously increasing. Glycerol carbonate(GC) is one of the promising value-added glycerol derivatives due to its potential and widely used in various fields. This topic with glycerol as raw material, through urea method, dimethyl carbonate method and two-step method to synthesis glycerol carbonate,and rational utilization of byproduct glycerol of biodiesel.The main contents and achievements of this paper are as follows:(1) Synthesis of glycerol carbonate by urea method. Glycerol carbonate was synthesized by glycerol and urea, and the conversion of glycerol was determined by periodic acid oxidation method. Through the screening of various catalysts, results showed that catalytic activity of heterogeneous catalysts (shell solid base,zinc-MMT) were good,and easy separation. The catalysts were characterized by XRD?SEM? TGA and BET.XRD showed that the composition of shell was mainly CaCO3 (Aragonite)before roasting, and the shell solid base solid base was mainly CaO; SEM showed that the surface of the shell solid base had a sheet-like topography,X-ray photoelectron spectroscopy (EDS) showed that the main components of shell solid base were Ca, O and a small amount of C elements; TGA of shell and calcium carbonate showed that the thermogravimetric curves were similar,their weightlessness was accelerated after 600?,and began to maintain weight when the temperature up t0 750 ?, but before 600 ?,calcium carbonate was different from the shell in a state of slow weight loss; BET of shell solid base and calcium oxide showed shell solid base of specific surface area was about 7.7 times of calcium oxide. The orthogonal experiment with temperature, dosage of catalyst, urea, reaction time as a variable, the four factors three levels orthogonal experiments, the experimental results showed that under the condition of the experiment temperature was 15°C, molar ratio of glycerol to urea 1:1.4, the dosage of catalyst was 1%, the reaction time for 2h, and get the optimal experimental conditions, glyceride reaction conversion rate can reach 74.21%. The effects of pressure and water content on the reaction were studied, the decompression was beneficial to the reaction; Adding water, glycerol conversion rate was reduced.(2) Synthesis of glycerol carbonate by dimethyl carbonate method.Glycerol carbonate was synthesized by glycerol and dimethyl carbonate ,the product was determined through gas chromatography analysis. With calcium oxide as catalyst, reaction time and the dosage of catalyst on the reaction was studied, the influences of the optimized conditions were as follows: the reaction time was 3h and the amount of calcium oxide was 1.5%, the conversion of glycerol was 94.53% and the yield of glycerol carbonate was 85.18%. Adding water, it was found that calcium oxide catalyst had a certain water-resistance performance. Calcium oxide catalyst was reused twice, and maintained good catalytic activity. With shell solid base as catalyst, the conversion of glycerol was 95.52% and the yield of glycerol carbonate was 87.03%. The product of the reaction was determined by gas chromatography-mass spectrometry (GC-MS),result found that the product contains peaks of glycerol and glycerol carbonate.(3) Synthesis of glycerol carbonate by two-step method. Two-step method was based on urea method, then add dimethyl carbonate to further improve glycerol conversion. Catalysts for the reaction were shell solid base and calcium oxide, respectively, the conversion of glycerol from shell solid base and calcium oxide was 96.80% and 94.41%, respectively, shell solid base was better than calcium oxide.