Biodiesel Production From Continuous Double Transesterification Over Solid Base

In order to solve the low reaction rate and glycerol by-product involved in the transesterification process for biodiesel production,a new method for no-glycerol biodiesel production has been established by integrating the traditional transesterification with the transesterification of glycerol and dimethyl carbonate（DMC）.In this study,the catalytic activity of CaO derived from different kinds of calcium salt roasting for biodiesel production in the continuous double transesterification was investigated and discovered that the CaO derived from 900℃ roasting calcium carbonate exhibits an excellent catalytic performance.The experimental result showed that the yield of fatty acid methyl ester（FAME）exceeded 96.4% over CaO derived from 900 ℃ roasting calcium carbonate at the oil/DMC/methanol ratio of 1:1:8,the amount of catalyst 15% under 65℃ in 7h.Compared with the traditional transesterification reaction,only 0.0196% free-glycerol contained in the biodiesel prepared by continuous double transesterification.the physicochemical properties of CaO was evidenced by TGA,BET,CO₂-TPD and IR.Combined with the structure characterization of calcium oxide from different kinds of calcium salt roasting,it was discovered that the surface basicity of the catalyst is not the only factor and the specific surface area is also affect the activity of the catalyst.In order to further improve the catalytic activity of calcium oxide solid base,a series of CaO supported alkali metal chloride solid bases were prepared by impregnation and their catalytic performance for biodiesel prepared in a continuous double transesterification system were investigated.The experimental result showed that the KCl/CaO and NaCl/CaO catalysts with 15% precursor loading have higher catalytic activity.Under the optimum condition,the biodiesel yield is close to 95.0% after reaction time of 2h catalyzed by KCl/CaO and the biodiesel yield is close to 97.1% after reaction time of 1h catalyzed by NaCl/CaO.Compared with commercial CaO,the reaction time is shortened 5-6h.The catalysts were characterized and discovered that the high catalytic activity of NaCl/CaO is probably due to the isomorphic substitution between NaCl and CaO during calcination.A series of γ-Al₂O₃ supported potassium salts solid bases were prepared by wet impregnation and their optimum preparation parameters and reaction conditions for biodieselproduction in the continuous double transesterification were investigated.The experimental results show that K₂CO₃/γ-Al₂O₃ exhibits an excellent catalytic performance.Under the optimum condition,the biodiesel yield could reached over 99.0% at catalyst amount of 30%after 30 min.The regenerate catalyst was reused in continuous double transesterification.The biodiesel yield can still be above 85.0% reused catalyst.The catalysts were characterized and discovered that the high activity of catalyst is mainly due to the generation of new phase K-O-Al with strong alkaline by the interaction between K+ and-OH on the surface of γ-Al₂O₃ during calcination,when the K₂CO₃ loading amount is more than 15%.Potassium carbonate as the active component,a series supported potassium carbonate solid bases were prepared by impregnation and the catalytic performance of catalysts for biodiesel production in continuous double transesterification was investigated.The experimental results show that K₂CO₃/CaO exhibits an excellent catalytic performance.Under the optimum condition（reaction temperature 65℃,oil/dimethyl carbonate/ methanol molar ratio 1:1:8,loading amount of K₂CO₃ 5%）,the yield of biodiesel could reached 97.9% after 1h at catalyst amount of 15%.The content of free glycerol in biodiesel is only 0.0196%.After supported K₂CO₃,the pore size and pore volume of catalyst are increased and is beneficial to the reactive molecules better access to the active sites of the catalyst.