MIL-100 (Fe)-based Solid Acid Catalyzed Esterification To Produce Biodiesel Characteristics And Process Simulation

The main constraint to the large-scale application of biodiesel is the high cost of production.Low-grade waste fats and oils,represented by restaurant waste fats and oils,can be used to produce biodiesel not only to greatly reduce production costs,but also to achieve the resource utilization of waste fats and oils.Waste fats and oils often contain large amounts of free fatty acids and the solid bases used in traditional transesterification reactions are not suitable for catalyzing low-grade waste fats and oils.For this reason,waste oils and fats need to be treated with acid reduction.The conversion of free fatty acids into biodiesel by transesterification with solid acids is an effective way to reduce acidity.However,common solid acids suffer from unsatisfactory pore structure,small specific surface area and poor reusability,which limit industrial applications,and there is an urgent need to develop highly stable solid acids.As a typical representative of metal organic frameworks(MOFs),MIL-100(Fe)has the advantages of high porosity,highly ordered structure and large specific surface area.In this study,MIL-100(Fe)and its derivatives were functionalized by both high temperature activation and ambient temperature sulfonation to prepare efficient and stable solid acid catalysts for catalytic esterification of oleic acid and methanol for biodiesel production.In order to elucidate the relationship between structural properties and catalytic activity,the catalysts were characterized.In addition,the CIS catalyzed preparation of biodiesel from oleic acid and methanol was used to simulate the biodiesel production process using Aspen Plus,focusing on the influence of key parameters on the distillation effect and economy of the crude biodiesel distillation process.(1)The solid acid IS and CIS were prepared by loading(NH₄)₂SO₄ onto MIL-100(Fe)and its derivatives under high temperature activation under nitrogen atmosphere.the effect of the preparation conditions such as(NH₄)₂SO₄ loading amount,activation temperature and activation time on the catalytic activity was investigated using the esterification of oleic acid and methanol as the probe reaction.The results showed that the optimum preparation conditions for both catalysts were:(NH₄)₂SO₄loading amount of 150 wt.%,activation temperature of 400?and activation time of 2h.On this basis,the effects of catalyst amount,molar ratio of methanol/oleic,reaction temperature and reaction time on the esterification conditions on the conversion were investigated and optimized by the single factor method.At a catalyst amount of 8 wt.%,reaction temperature of 70°C,molar ratio of methanol/oleic of 8 and reaction time of2 h,the conversion of CIS was 95.68%,and the conversion remained at 87.76%after three reuses.Under the same conditions,IS only achieves 90.95%conversion and the conversion drops to 79.5%after three repetitions.The results of isothermal adsorption and desorption of nitrogen showed that the specific surface area of CIS was higher than that of IS(24.04 m~2/g and 22.73 m~2/g,respectively).The higher specific surface area was favorable for esterification reaction.In addition,CIS is a superparamagnetic material with a saturation magnetization strength of 22 emu/g,which allows the catalyst to be separated by external magnetic fields alone,reducing catalyst losses.(2)The solid acid M-SO₃H was obtained by sulfonating MIL-100(Fe)with chlorosulfonic acid at room temperature.The highest conversion of M-SO₃H was achieved at a catalyst amount of 10 wt.%,reaction temperature of 70°C,molar ratio of methanol/oleic of 10 and reaction time of 2 h,reaching 96.2%,and 82.64%after 5times of reuse.In addition,the catalytic activity of M-SO₃H was not significantly affected when water was added to the reaction system at 5 wt.%,and the conversion remained at 89.57%even when the water addition was increased to 20 wt.%.XRD and FTIR results showed that sulfonic acid groups were successfully introduced into MIL-100(Fe),and the crystal structure of MIL-100(Fe)was well preserved during sulfonation.Compared with CIS and IS,M-SO₃H has larger specific surface area(149.15 m~2/g)and specific pore volume(0.25 cm~3/g),which is an important reason why M-SO₃H has better catalytic activity and stability than CIS and IS.(3)With the aid of Aspen Plus,the whole process of CIS catalytic production of biodiesel from oleic acid and methanol was simulated and the main parameters of the distillation process were optimized using sensitivity analysis:distillation kettle temperature of 120°C;methanol recovery column reflux ratio of 1.5,number of plates of 20 and position of feed plate of the 16th plate;product distillation column reflux ratio of 1.8,number of plates of 59 and position of feed plate of the 29th plate.Under these parameters,a refined biodiesel with a purity of 97.25 wt.%(annual production of7973.6 t)can be obtained,meeting the national standard(purity of not less than 96.5wt.%)with an annual operating cost of 0.331 M$/a.The above results provide basic design data for the industrial application of CIS catalyzed biodiesel production.