Research On The Preparation And Shaping Of Imidazolate Metal-Organic Framework

Zeolitic Imidazate Frameworks (ZIFs) are metal organic frameworks with excellent aqueous and thermal stability, which display wonderful prospect in the field of gaseous separation, gaseous storage and catalyst. However, newly synthetic ZIFs are nanometer fines, the process of shaping can cause great effect on their structures and properties. It is a bottleneck that has to be solved. Thus, the article lauched research on optimization of synthetic conditions and the process of shaping. Adsorption separation effect of small hydrocarbons by ZIF-8powders and shaping products was explored.Based on the solvothermal reaction, the method of synthesizing ZIF-8on a large scale was explored. By investigating order of charging, time of crystallization, temperature of crystallization and molar ratio of raw materials measured by amount of substance, combined characterization method of XRD, analysis of N2adsorption-desorption and SEM, the optimized synthetic conditions are obtained. That is, charging2-methylimidazole first, then adding Zn(NO3)2·6H2O, reacting at140centigrade for24hours, the molar ratio for Zn(NO3)2·6H2O and2-methylimidazole is1to3.ZIF-8powders were shaped with sesbania powder, methylcellulose, hydroxyethyl cellulose, kaolin as binders and distilled water, dilute nitric acid, trichloroacetic acid, acetic acid, glycerol as peptizer. The mass of binders are10percent of original powder. Through tests of XRD, BET, strength, shaping conditions are optimized. The loss of specific surface areas can be minimized with methylcellulose and sesbania as binders and trichloroacetic acid as peptizer.Adsorption of pure methane, ethane/ethane, propane/propene mixtures in ZIF-8is simulated by GCMC method. The conclusions are as follows:the process of adsorption is dominated by enthalpy effect and entropy effect. The amount of alkanes adsorbed is higher than the amount of alkenes in case of lower pressure, while it is on the contrary when the pressure is high. The research on adsorption site illustrates that two sites exist. The first one locates around the C=C bound of imidazate, the second one locates at the center of six-membered ring.Adsorption properties of ZIF-8powders and shaping products are explored by constant volume method. The results shows that shaping product is able to adsorb propane and propene to4.81mmol per gram and4.09mmol per gram, which means the amount of adsorption decreases by around15percent by adding10percent of binder. Experiment results are consistent with the simulation result basically.