Preparation Of Titanate Solid Base And Its Catalytic Synthesis Of Glycerol Carbonate

The prosperous development of biodiesel industry brought a serious surplus of by-product glycerol（GL）,which lead to the decrease of the economic benefit of the industry.Hence,it is of great significance for sustainable development of biodiesel industry to develop downstream fine chemical synthesis technology with GL as raw material.Among them,the synthesis of glycerol carbonate（GC）from dimethyl carbonate（DMC）and GL by transesterification process is considered to be one of the best choices.Homogeneous base catalysts have high catalytic activity but are difficult to separate from the product,which affects the quality of products.Hence,solid base catalysts have received much attention while most of them have the problem of low activity and poor stability.To solve the problem,alkaline-earth metal titanate were used as solid base catalysts to synthesize GC by transesterification in this thesis.The effects of alkali-earth metal type,morphology and doping modification on the structure and performance of the catalyst were mainly studied.The research conclusions are as follows:（1）The alkali-earth titanate was synthesized by citric acid complexation,which were used in transesterification reaction between DMC and GL.The effects of alkali-earth metal type,preparation temperature and reaction conditions on the catalytic performance were studied.The results showed that the catalytic performance of titanate solid base was as follows:Mg Ti O₃<Sr Ti O₃<Ba Ti O₃<Ca Ti O₃.Among them,Ca Ti O₃synthesised by roasting at 700℃（Ca Ti O₃-700）showed the best catalytic activity in this reaction.The catalyst with a GC yield of 98.63%under the condition of 5.0 wt%catalyst dosage,DMC/GL ratio of 3:1 at 85℃temperature for 3 h.In the kinetic study,the activation energy of the reaction was calculated to be 43.11 k J/mol.The lower the activation energy of the reaction,the higher the activity of the catalyst.The excellent activity of Ca Ti O₃-700 is mainly attributed to its large surface,which facilitates full exposure of basic sites.In addition,Ca Ti O₃-700 shows high thermal stability of perovskite structure and GC yield only decreased slightly after five cycles.（2）The solid base catalysts showed obvious morphology effect in transesterification reaction.Butterfly,cubic,fibrous and spherical Ca Ti O₃were synthesized by different methods and the influence of morphology on the synthesis of GC by transesterification catalyzed by Ca Ti O₃solid base was investigated.The results show that the cubic Ca Ti O₃（CTO-cube）solid base catalyst exhibits excellent catalytic performance,which is attributed to the large specific surface area and abundant alkaline sites.According to the results of alkaline test,the concentration of basic site on the surface of CTO-cube is nearly twice as high as that of irregular Ca Ti O₃.The catalyst with a GC yield of 98.76%under the condition of 3.0 wt%catalyst dosage,DMC/GL ratio of 3:1 at 85℃temperature for 2 h.The activation energy of transesterification was 40.99 k J/mol when CTO-cube solid base was used as catalyst.CTO-cube shows high thermal stability and the GC yield can still reach 85.17%after five cycles.（3）In order to further increase the concentration of basic site on catalyst surface,Ca Ti O₃was doped with alkali metals（Li,Na,K）,the effects of the type and quantities on the structure and properties of the catalyst were investigated.The results show that the catalytic activity of Ca_1-xK_2xTi O₃obtained by K doping Ca Ti O₃is significantly better than that of Li and Na doping Ca Ti O₃.When the K doping amount is0.4,the catalytic activity of Ca Ti O₃is the best.The catalyst with a GC yield of 98.91%under the condition of 2.0 wt%catalyst dosage,DMC/GL ratio of 3:1 at 65℃temperature for 1 h,and the excellent catalytic performance of the catalyst was due to the addition of alkali metal K,which increased the number of strong basic sites,increased the concentration of strong basic sites and enhanced the strength of the catalyst.After5 cycles,the GC yield decreased to 82.41%.