Study On The Preparation And Properties Of 3D Hollow Hydrotalcite-Like Compounds Microspheres

As a biomass energy source,the application of biodiesel（fatty acid methyl ester）can effectively reduce the dependence on fossil energy and contribute to the achievement of the goal of“carbon neutrality”.However,the process of biodiesel production by transesterification produces a large amount of glycerol as a by-product.Therefore,making full use of the by-product glycerol resources and developing the whole utilization process of the transesterification products are of positive significance to promote the application of biodiesel.Transesterification catalyzed by solid base posssesses the advantage of fast reaction rates,but the catalyst usage is large.Thus,it is very necessary to develop highly active catalysts to reduce the catalyst dosage.Hydrotalcite-like compounds（HTLCs）microspheres with 3D structures have the characteristics of large specific surface area and diverse material morphologies,and can obtain abundant basic sites and maintain their 3D structures after being loaded.In this paper,3D hollow Ca-Mg-Al HTLCs microspheres（MS）self-assembled from hydrotalcite-like nanosheets were synthesized in one step by hydrothermal method,and hollow KF/Ca-Mg-Al HTLCs MS catalysts were prepared using MS as the support loaded with KF to catalyze the transesterification reaction of soybean oil and methanol for the preparation of biodiesel.The influence of preparation parameters on the catalyst activity was investigated,and the optimum catalyst preparation conditions were obtained as follows:hydrothermal time of 24h,Ca/Mg ion feeding molar ratio of 1:1,KF/HTLCs loading mass ratio of 1:1,and roasting temperature of 500°C.The yield of biodiesel in 30 min reached 92.2%when the addition amount of the optimum catalyst was 2%of the oil mass.The analytical test results of the catalysts showed that the catalysts possess abundant basic sites and the structural characteristics of the catalysts were also favorable for the oil macromolecules to participate in the reaction on the surface of the catalysts.K₂CO₃ was loaded on the surface of Ca-Mg-Al HTLCs MS using the excess impregnation method to obtain K₂CO₃/Ca-Mg-Al HTLCs MS,and calcined K₂CO₃/Ca-Mg-Al HTLCs（K₂CO₃/Ca-Mg-Al CHTLCs）MS catalysts were prepared after roasting and were applied to catalyze the ester exchange reaction of glycerol（GL）and dimethyl carbonate（DMC）for the synthesis of glycerol carbonate（GC）.The catalyst had the best catalytic activity when the molar ratio of Ca/Mg was 2:1 and the impregnation concentration was 4×10^-3 g/m L（carrier weight0.4 g）.The effects of the reaction process conditions on the GC yield were investigated.The optimum process conditions were as follow:90℃,GL/DMC molar ratio of 1:3,catalyst addition of 4%of glycerol mass,and reaction time of 6 h,at which the GC yield reached 91.8%.The characterization results showed that the prepared catalyst had mesoporous structure and high specific surface area.The reusability of catalyst was tested,and the catalyst showed high catalytic activity after being utilized four times.To reduce the catalyst cost,Na₂CO₃ was loaded on Ca-Mg-Al HTLCs MS by similar method,and Na₂CO₃/Ca-Mg-Al CHTLCs MS catalysts were finally synthesized to investigate their activities for the catalytic synthesis of glycerol carbonate.The results indicated that the maximum yield of GC was 85.6%when the Na₂CO₃ impregnation concentration was 4×10^-3g/m L,the catalyst dosage was 4%,and the reaction time was 6 h.