Phloroglucinol-melamine-formaldehyde Polymeric Nanofibers:Synthesis And Their Gas Adsorption And Separation Properties

The aggravation of greenhouse effect becomes more and more serious due to the rise of the concentration of CO2 in the atmosphere.Capture and sequestration of CO2 is an effective method to reduce its massive emissions.The adsorption technology using solid adsorbents has a lot of merits,such as low energy consumption,avoiding the corrosion problem of equipment,etc.,showing a good application prospect in CO2 capture.Study on high-efficiency CO2 adsorption materials is of great significance for the CO2 capture and separation as well as the recycle of carbon resources.Amine-based porous materials are a kind of CO2 adsorption materials that have been reported in recent years.By virtue of the high affinity of amines groups for CO2,amine-based porous materials show good CO2 adsorption performance.In this thesis,phloroglucinol-melamine-formaldehyde(PMF)polymeric nanofibers were synthesized by hydrothermally polycondensation reaction using melamine,phloroglucinol and formaldehyde as starting materials.The adsorption and separation performance of CO2 on the PMF were studied.The main content consists of two parts as follows:1)Optimization of the synthesis of phloroglucinol-melamine-formaldehyde.The influences of some factors such as reaction temperature,pH value etc.on the synthesis of PMF were investigated.The morphology and structure of PMFs were characterized by scanning electron microscope(SEM),transmission electron microscope(TEM),N2 adsorption-desorption,and Fourier transform infrared spectroscopy(FT-IR)etc.The condensation polymerization of phloroglucinol,melamine and formaldehyde at 298 K,353 K,393 K and 423 K were investigated,respectively.The results showed that PMFs in powder form could be obtained at all investigated temperatures,which presented morphology of fiber.As the temperature increases,the regularity of the fibers increased and the fiber bundles became disassembled.However,when the temperature is further increased to 423 K,the fiber diameter became thicker.FT-IR detected the presence of hydrogen on benzene and triazine ring of melamine in the PMF,indicating that melamine and phloroglucinol entered in PMF by reaction.The PMF sample synthesized at 393 K presented a regular shape and a higher specific surface area(64 m2/g).The effect of pH on the synthesis of PMF was investigated by adding acid or alkali in the reaction system of phloroglucinol with formaldehyde or melamine with formaldehyde,respectively.The results showed that PMF can be synthesized when the reaction system of phloroglucinol and formaldehyde is acidic.The morphology is even more regular and the specific surface area is 70 m2/g when both of the reaction systems of phloroglucinol with formaldehyde and of melamine with formaldehyde were acidic.In addition,the specific surface areas and micropore volumes of the PMF increased significantly,with a specific surface area up to 490 m2/g,after the PMF samples were post-treated at high temperatures in various atmosphere,such as N2,H2,water vapor and ammonia vapor,etc.2)Gas adsorption and separation performance of the PMF materials.Pure gas adsorption equilibrium isotherms of CO2 and N2 on PMF were acquired by volumetric method.Ascribed to the high affinity of amines for CO2,PMF displayed a higher adsorption capacity of CO2(1.83 mmol/g @ 1.2 bar,298 K),while the adsorption capacity of N2 is very low(0.3 mmol/g @ 1.2 bar,298 K).After PMF was thermal treated at 873 K,CO2 adsorption performance is further improved to 2.83 mmol/g(@ 1.2 bar and 298 K).Combined dual-site Langmuir(DSL)model and single-site Langmuir(SSL)model were used to fit the adsorption equilibrium data of CO2 and N2 on PMF at different temperatures,respectively.According to the fitting parameters,the isosteric heat of CO2 adsorption on the PMF was calculated using the Clausius-Clapeyron equation,ranging from 33 to 20 kJ/mol.The separation performance of the mixture of CO2-N2 and CO2-CH4 on the PMF was investigated by the breakthrough column technique.The experiments showed that the mixture of CO2-N2 and CO2-CH4 can be efficiently separated on PMF at 298 K under different pressures.