The Structure-activity Relationship And Mechanism Of The Selective Adsorption Of 5-hydroxymethyl Furfural On Hollow Polymers

Catalytic dehydration of fructose to 5-hydroxymethylfurfural(HMF)is a key step for converting biomass into liquid fuels and high-valued chemicals.Unfortunately,the presence of thermodynamic equilibrium limitation and side reactions(HMF hydration and internolecular condensation)result in low HMF yield.Therefore,a challenging undertaking is to efficiently separate HMF from fructose dehydration system.In this thesis,solid-liquid adsorption technology was employed to separate HMF molecules from acid-catalyzed fructose dehydration mixture.On the basis of differences in physico-chemical properties of each component,a hollow porous aromatic polymer(H-PAP)was designed and synthesized via surface coating and template-etching method.The microstructure,texture properties and surface hydrophilicity/hydrophobicity of H-PAP materials were systematically characterized.Moreover,the structure-function relationship was elucidated.Combining adsorption isotherm model with theoretical calculations,the mechanism toward HMF adsorption on H-PAP surface was revealed.The details as follows:(1)A series of H-PAP materials with different internal cavity sizes were synthesized via surface coating and template-etching method,where Sonogashira carbon-carbon coupling reaction was carried out around silica sphere.The microstructure,texture properties,surface hydrophilicity/hydrophobicity and stability of H-PAP were systematically characterized.The resultant H-PAP material is characterized by hollow structure,in which its internal size can be tuned(228±11 to 464±15 nm)by changing the diameter of SiO2 sphere,and the shell is composed of hydrophobic and microporous aromatic polymer.Moreover,it is found that decreasing cavity diameter results in decreased specific surface area and micropore volume,whereas the total specific surface area increases slightly.The stability tests show that H-PAP material has a favorable thennal stability,but also is tolerant in acid,alkali and oiganic solvents.Beyond this,H-PAP material demonstrates a scalability in laboratory scale from standard scale to 20-fold scale-up.(2)The adsorption behavior of the single-component(fructose,HMF,formic acid and levulinic acid),binary and multi-component aqueous solutions was studied in static batch mode and continuous flow fixed-bed,respectively.In the case of single-component adsorption,H-PAP shows an exclusive adsorption for HMF,without adsorption of fructose,levulinic acid(LA)and formic acid(FA).Decreasing in cavity size and micropore volume,the apparent amount of HMF adsorbed decreases gradually,and its maximum amount of HMF adsorbed reaches to 0.63 ± 0.11 mg/mg.In the multi-component competitive adsorption,the presence of other adsorbate has no effect on selective adsorption of HMF,but the apparent amount of HMF adsorbed decreases when the concentration of levulinic acid increases.In addition,H-PAP adsorbent can be recycled three times without significant loss in adsorption capacity.In the case of HMF adsorption from the real reaction mixture of acid-catalyzed fructose dehydration,H-PAP can still maintain high adsorption capacity,and HMF constituent with high purity(ca.94.4%)ean be recovered via desorption using anhydrous ethanol.Correlating characterization with adsorption results,it is proposed that HMF adsorption capacity is related to textural properties(cavity size,micropore surface area and pore volume),whereas adsorption selectivity is determined by the surface hydrophobicity.The combination of adsorption isotherms with DFT calculation reveals adsorption mechanism that HMF adsorbed on H-PAP proceeds initially via ?-? stacking interaction,and then assembles into regular array around spherical surface to form monolayer coverage following modified Langmuir model,and finally diffuses into interior cavity until adsorption saturation.