Base-catalyzed Glycerol Etherification To Prepare Diglycerol

Diglycerol is an important chemical raw material and intermediate,and has been widely used in the cosmetics,food,polymer and plastic industries.In this thesis,diglycerol was prepared by glycerol etherification.Research was carried out from three aspects:process and condition optimization,reaction equipment and solid base catalyst.It is desirable to establish a process for industrial production and design a continuous reactor to produce efficiently diglycerol with high purity.（1）Using K₂CO₃ as a catalyst,the effect of reaction conditions on the preparation of diglycerol by glycerol etherification was investigated.In the experimental range,with the increase of the reaction time,the reaction temperature and the amount of the catalyst,the glycerol conversion and the diglycerol yield increased,but the selectivity of the diglycerol declined.The reaction conditions were optimized by orthogonal experiments.The reaction was carried out for 3 hours under the conditions of the reaction temperature of 230°C and the catalyst dosage of 2.7 g/100 g glycerol.The glycerol conversion was 30.4%,the diglycerol yield was 23.0%,and the diglycerol selectivity was 75.6%.After the crude diglycerol product was neutralized by acid,it was subjected to two vacuum distillations.97%glycerol was recovered after the first vacuum distillation（70 Pa,bottom temperature 200°C）.Distillate containing 94.75%diglycerol and bottom residue having an average degree of polymerization of 2.48 could be obtained as two products vis the second vacuum distillation（43 Pa,bottom temperature 220°C）.（2）A continuous ball milling reactor was designed and processed.The effects of reactor wall temperature,cylinder rotation speed,residence time and ball milling media on the synthesis of diglycerol were investigated.When the wall temperature was 310°C,the cylinder rotation speed was 15 r/min,the residence time was 177 min,and the ball milling medium was zirconia pellet,a crude product with a diglycerol content of 15.5%could be obtained.The multi-stage mixing model and the axial diffusion model were used to analyze the residence time distribution and mass transfer performance in the ball milling reactor.The ball milling reactor constructed in this study had channel flow and dead zone,and axial diffusion and backmixing were serious.A one meter long reactor was equivalent to only 7-10 full mixing tanks.（3）The catalytic properties of alkaline earth metal oxides and K₂CO₃/γ-Al₂O₃ solid catalysts were investigated.The effects of alkali strength on the synthesis of diglycerol were investigated.The increase in alkalinity facilitated the synthesis of diglycerol,and could increase the yield and selectivity of diglycerol.（4）The role of acid-base synergistic catalysis was explored by adding activeγ-Al₂O₃ powders with different acidity and alkalinity to K₂CO₃ to catalyze glycerol dimerization.The results showed that the L acid sites ofγ-Al₂O₃ had a synergistic effect on the K₂CO₃ catalysis.Compared with single K₂CO₃ catalysis,acid-base synergy could reduce the reaction activation energy of glycerol dimerization effectively.And the glycerol conversion and the diglycerol yield could be improved without affecting the selectivity of diglycerol.