Study On Adsorption And Pervaporation Separation Of Furfural Based On COF-300 And Green Preparation Of PDMS Membrane

As an important platform compound,furfural can be directly or indirectly used to produce more than 1,600 organic chemicals.When furfural is produced with corn cob as raw material,the furfural concentration in hydrolysate is only 1-6 wt%.The traditional distillation method consumes high energy,which increases the production cost of furfural.Therefore,developing high-efficient methods for furfural separation has important practical significance.Adsorption and pervaporation are two important methods for separating low-concentration organics from aqueous solutions.Meanwhile,porous materials with excellent adsorption performance for organics generally also serve as important raw materials for preparing high-performance pervaporation mixed matrix membranes.Therefore,this study aims to develop a porous material with excellent adsorption performance for furfural,and on this basis,prepare a mixed matrix membrane with high pervaporation performance;further,propose a strategy for continuous preparation of pervaporation membranes.This study mainly includes the following contents.Firstly,in view of the problem that current adsorbents have long adsorption time and low adsorption capacity for furfural,we synthesized COF-300,which has rich aromatic rings in its structure.The adsorption and desorption performances of COF-300 for furfural were investigated.The results show that the adsorption process reached equilibrium within 10 s,which is 2-3 orders of magnitude faster than the reported values(1-24 h),and COF-300 exhibited the maximum adsorption capacity of 567.8 mg g-1 for furfural,which is higher than the reported highest value(536 mg g-1).Thermodynamic study demonstrates that the adsorption process was a spontaneous,exothermic and physical adsorption process.COF-300 displayed outstanding performance in desorption and regeneration.The adsorbed furfural can be completely desorbed from COF-300 by being vacuumed at 85℃ for 2 h.After 5 consecutive adsorption/desorption experiments,COF-300 exhibited no loss in furfural adsorption capacity.In addition,COF-300 also showed excellent adsorption performance for volatile organic compounds such as aniline,phenol,butanol and ethanol.The ultrafast and ultrahigh adsorption of COF-300 for furfural is confirmed to be mainly related to the unique pore structure of COF-300 and its π-π interaction and hydrophobic interaction with furfural molecules.Secondly,in view of the difficulty in recovering COF-300 after adsorption due to the low density of COF-300,we introduced magnetic Fe3O4 nanoparticle into COF-300 particle and prepared Fe3O4@SiO2@COF-300 core-shell composite.The composite can be recovered within 3 s under a magnetic field.In addition,the adsorption of this composite for furfural reached equilibrium within 10 s,and its adsorption capacity for furfural,aniline,phenol and butanol were 256.7 mg g-1,288.3 mg g-1,269.9 mg g-1 and 189.9 mg g-1,respectively.Similar to COF-300,the adsorption capacity of the composite for furfural experienced no loss after five adsorption/desorption experiments.Thirdly,in view of the phenomenon that improving the organic permeability of PDMS membrane by doping with hydrophobic porous particles also increases the water permeability of PDMS membrane,and based on the mass transfer law of water molecules in the confined space,we prepared a mixed matrix membrane that exhibited a characteristic of"promoting organic permeability and inhibiting water permeability" via doping porous particles with excellent adsorption capacity for organic but also with hydrophilic action sites in structure.The N2 adsorption/desorption experiments,FT-IR spectra,X-ray photoelectron spectra,water adsorption experiments and furfural adsorption experiments confirmed the presence of hydrophilic sites in the COF-300 and COF-300 had an excelleent furfural adsorption capacity of 525.3 mg g-1 at 80℃.The COF-300/PDMS membrane exhibited a reduction of 20%in water permeability for pervaporation separation of 1.0 wt%furfural aqueous solution at 80℃ compared to PDMS membrane,while the water permeability of mixed matrix membranes in literature dispaly an increment of 21.4-396%compared to PDSM membrane,and an increase of 14.1%in furfural permeability.As a consequence,the COF-300/PDMS membrane achieved an increment of 42.7%in selectivity,which confirmed the feasibility of the strategy and thus provides a new idea for designing mixed matrix membranes for pervaporation separation of organics from aqueous solutions.Finally,in view of the current difficulty in continuous preparation of PDMS membranes that caused by a long curing time,we proposed a strategy via separately controlling the reaction process before and after coating the casting solution.The rheological methods were used to explore the influence of temperature,dibutyltin dilaurate,water and ethanol on the reaction process before and after coating the casting solution.According to the viscosity-time curves of PDMS casting solutions prepared under different conditions,a mathematical model containing double activation energy was established.The model can be used to predict the coatable time of PDMS casting solution with an error below 2.7 min.An identation method was designed to characterise the curing degree of PDMS membrane,and used to determine the time appropriate for winding membrane.The coatable time of PDMS casting solution was 88.3 min using the above strategy,and the winding time was 11 min,which is only 1/19-1/289 of those in literature(3.5-53 h)and can meet the requirements of continuous industrial production.