Preparation And Properties Of Core-Shell Carbon-based Solid Acids

As an environmental-friendly catalyst,magnetic solid acid expresses excellent catalytic activity and stability in processes like esterification,transesterification and hydrolysis reaction.What is more,magnetic catalysts can be separated easily from the reaction system by their own magnetism,which simplifies the separation process and assures that the catalyst can be recycled several times.Due to these advantages,magnetic solid acid has been a hot-spot in the researching of catalyst.In this paper,nano-Fe₃O₄ balls were synthesized by using FeCl₃.6H₂O as iron source and glycol as a reducing agent.Afterward,core-shell magnetic carbon-based solid acid Fe₃O₄/C-SO₃H was synthesized during carbonization-sulfonation two-step method by using glucose as carbon source and isethionate as a sulfonating agent.The surface morphology,element distribution and chemical structure of the catalyst were characterized by infrared spectroscopy?IR?,Scanning electron microscope?SEM?,EDS,etc.To test the performance of the prepared catalyst,it was applied in cellulose hydrolysis,esterification,and xylan hydrolysis.The detailed process is listed below:?1?Core-shell magnetic carbon-based solid acid was prepared by carbonization-sulfonation two-step method,and the improved synthesis conditions consist of:carbonization temperature was 200?,carbonization time was 8h,m?glucose?:V?water?was 1:6?g/mL?,sulfonation temperature was 190?,sulfonation time was 8h,m?carbide?:m?isethionate?was1:2.5 and the surface acid concentration was 1.45 mmol/g.?2?The core-shell magnetic solid acid catalyst was used as a catalyst in the hydrolysis of microcrystalline cellulose.The efficiency was indicated by the yield of glucose.The hydrolysis reaction was optimized by single factor experiment and orthogonal experiment,and the result showed that the order of factors affecting cellulose hydrolysis was the mass ratio of catalyst and cellulose>hydrolysis temperature>volume of water>hydrolysis time.When the hydrolysis temperature was 200?,m?microcrystalline cellulose?:m?catalyst?was1:1.5 and hydrolysis time was 90min,m?microcrystalline cellulose?:V?water?was1:62.5?g/mL?,the yield of glucose was 43.8%,and the catalyst can be recycled for three times.?3?The core-shell magnetic solid acid catalyst was used in the esterification of oleic acid with methanol.Factors related to yield of esterification such as the mass ratio of reactants,reacting temperature are considered and the kinetics of acidification were researched.The experiment showed that when esterification temperature was 70?,esterification time was 4h,the mole ratio of methanol and oleic acid as 14:1,and catalyst was added by 5%of the mass of oleic acid,the esterification yield of oleic acid can be as high as 90.5%.The catalyst can be recycled for 3-4 times with a yield higher than 80%.The reaction basically conforms to the second-order reaction kinetic equation,with a pre-exponential factor of 1.89×10⁹and apparent activation energy of 54.8kJ/mol.?4?The core-shell magnetic solid acid catalyst was used as a catalyst in oligomeric xylose hydrolysis.Factors related to the yield of xylose and total reducing sugar,such as hydrolysis time or hydrolysis temperature was researched.The result showed that when the hydrolysis temperature was 180?,hydrolysis temperature was 30min,the ratio of reactants was 1:1 and volume of water were 15mL when initial amount of oligomeric xylose was 0.3g,the yield of xylose can reach 56.4%and the yield of total reacting sugar is 75.2%.The catalyst can be recycled for 3 times.