Synthesis Of Melamine Based Microporous Organic Polymers And Their Gas Adsorption Properties

Melamine based microporous organic polymers (MBMOPs), which were prepared through the Schiff base condensation of melamine and phthalaldehyde analogues, are porous polymer materials comprised of light and non-metallic elements. Ascribed to their robust microporosity and abundant imines, MBMOPs exhibit a good CO2capture properties. In this thesis, MBMOPs have been prepared via one pot Schiff base condensation using inexpensive materials of melamine and phthalaldehyde. The adsorption and separation behaviors of CO2on the prepared MBMOPs were investigated from experimental and theoretical aspects. The thesis consists of two parts as follows:1) Optimization of the synthesis conditions for MBMOPs. The influences of some factors such as the type of phthalaldehyde, heating modes, total reactant concentration, reaction temperature, reaction time, solvent and addition of TPABr etc. on the synthesis of MBMOPs were investigated. Various techniques such as N2adsorption-desorption, SEM, TEM, FT-IR and TG etc. have been used to characterize the porosity, textural structure and stability of the synthesized MBMOPs. The results indicate that MBMOPs are constructed by the connection of benzene and triazine through amine linkage in three dimensions. The synthesized MBMOPs exhibit a high BET specific surface areas, large micropore volume and good thermostability. It is of great importance to control the synthesis system in an appropriate reaction rate for the MBMOPs construction of hierarchical pore system with abundant micropore. Moreover, some MBMOPs with relative low specific surface area were post treated by carbonization, indicating that the porous carbons derived from MBMOPs show a great enhancement of microporosity and specific surface area.2) Gas adsorption and separation performance on MBMOPs. The adsorption equilibrium isotherms of CO2, CH4and N2on MBMOPs were accurately measured via a volumetric method at different temperatures and pressures up to118kPa. Ascribed to the specific affinity of amine groups for CO2and robust microporosity, MBMOPs display a very high CO2adsorption equilibrium amount, up to2.8mmol.g-1at273K and118kPa, while there have been a relatively low CH4and N2adsorption capacity. According to the textural properties of MBMOPs and physicochemical characteristics of the adsorptives, single-site or multisite Langmuir models were used for a combined fitting of above the isotherm data, and can well describes the adsorption behaviors of the adsorptives on MBMOPs. Based on the estimated values from the combined fitting of isotherm data, the isosteric heat of adsorption for CO2, N2and CH4on MBMOPs were calculated by using the Clausius-Clapeyron equation. An ideal adsorbed solution theory (IAST) was adopted to predict the binary mixture adsorption behaviors of CO2-N2and CO2-CH4and thus derive the ideal selectivity of CO2over N2or CH4. At a given temperature (298K) and total pressure (100kPa), the ideal selectivity of CO2increases with the increase of CO2molar fraction, while there is a reversal as increasing the temperature. On the basis of the above theoritical analysis, experimental techniques were used to invesitgate the adsorption and separation of binary mixture on MBMOPs. Breakthrough column technique and thermogravimetry were adopted to study the real separation of CO2from CO2-N2and CO2-CH4binary mixtures and the adsorption-desorption cycles of CO2on the MBMOPs. The experimental results revealed that CO2can be separated from the CO2-N2and CO2-CH4binary mixures through MBMOPs at normal temperature and pressure. The real separation selectivity of CO2over N2and over CH4is still up to15and2, respectively, although the values are lower than those predicted by IAST. The synthesized MBMOPs show a fast CO2adsorption-desorption kinetics. Importantly, CO2adsorbed can easily desorb from MBMOPs. A simple nitrogen purge at298K can regenerate the adsorbent. As a result, MBMOPs exhibit a good CO2adsorption-desorption properties. After thirty consecutive adsorption-desorption test cycles, no decay in the adsorption amount was observed. Moreover, the adsorption and separation of some widely used hydrocarbons in industrial fields such as C2H4, C2H6, C3H6and C3H8on the synthesized MBMOPs have been tentatively explored.