Immobilization Of Acidic Ionic Liquids On Mesoporous Materials Containing Siliceous And The Catalytic Activities For Biodiesel Production

Biodiesel,as a promising biomass energy to replace conventional fossil fuels,has a prefect market prospect because of the environmental-friendliness and renewable.Heterogeneous catalysts,which would be efficient to the reaction for biodiesel,are the key to realize the industrial production of biodiesel.At present,there are many kinds of heterogeneous catalysts which have been applied to the synthesis of biodiesel,and the supported ionic liquid catalysts are getting considerable attention due to their green and environmental protection.The paper studied the design and preparation of a series of the acidic mesoporous materials and obtained the supported ionic liquid catalysts with double-acid active sites,which were synthesized by immobilizing acidic ionic liquid onto the acidic mesoporous material.The catalytic activities of the resulted catalysts were evaluated through the transesterification of soybean oil with methanol for biodiesel production.First of all,a series of acidic hybrid mesoporous materials(SO₄^2--x/ZrO₂-SiO₂-y)were prepared by a one-step co-condensation technique combined with hydrothermal treatment.The composition and structure of the materials were characterized by FT-IR,29 Si MAS NMR,and XPS,and proved that the materials were synthesized successfully.Wide-angle XRD and physical adsorption of nitrogen were employed to analysis the pore performance of the materials,and found out that the materials had excellent mesoporous structure.Acid-base titration was applied to evaluate the amount of Br?nsted acid on the surface of the hybrid materials,and it turned out that the acidity was determined by the number of active component(SO₄^2-).Secondly,the supported ionic liquid catalysts SO₄^2--x/ZrO₂-SiO₂-y-IL were synthesized by grafting the acidic ionic liquid sulfonic acid functionalized imidazolium hydrogen sulfate（[Ps-im]HSO4）onto the surface of the hybrid mesoporous materials(SO₄^2--x/ZrO₂-SiO₂-y).The catalysts possessed the properties of excellent structure and unique double-acid sites.And the prepared catalysts behaved better than the homogeneous catalysts and the immobilized ionic liquid catalyst SBA-15-IL with one-acid active sites in the transesterification reaction.The structure and composition of the catalysts were investigated through FT-IR,XRD,physical adsorption of nitrogen,TEM,and TG.Additionally,the optimum conditions of transesterification for biodiesel production were studied under the catalytic of SO₄^2--1.2 /ZrO₂-SiO₂-1.0-IL.And the appropriate conditions were showed as follows: reaction temperature,140 ℃;reaction time,4 h;methanol to soybean oil,30:1;amount of catalyst,5%（w/w）.Under the conditions,the yield of biodiesel was more than 96%.But the activity of the catalyst decreased gradually during the recycling and it might be caused by the adsorption of glycerol onto the surface of carrier which is hydrophilic.Finally,the hydrophobicity of the hybrid material was enhanced to increase the reusability of the supported ionic liquid catalyst.And immobilized different dosages of ionic liquid onto the organic-inorganic hybrid material(SO₄^2-/ZrO₂-SiO₂（Et）)which was synthesized by changing inorganosilicon（TEOs）into organosilicon（BTEE）during the preparation of hybrid material.The composition,porosity structure,thermal stability,and acid properties of the catalysts were well characterized by FT-IR,solid-state NMR,XPS,XRD,TEM,N2 physical adsorption,TG,and so on.Besides,the effect of organic modification was researched through the test of contact angle.And the catalysts were applied to the transesterification of soybean oil with methanol for the optimization of reaction conditions by the means of single factors and response surface.It was found that the yield of biodiesel was 99.02% under the following optimized conditions: supported amount of IL at 2.50 mmol·g^-1,catalyst dosage at 5%（w/w）,reaction temperature at 151.0 ℃,reaction time at 3.5 h,molar ratio of methanol to oil at 21:1.Furthermore,the catalyst had good recyclability.