Synthesis Of Mesoporous Mesoporous ZSM-5 / MCM-41 Molecular Sieve And Its Catalytic Performance For Polyester Esterification

Micro-mesoporous composite molecular sieves which combine the advantages of microporous molecular sieves and mesporous molecular sieves with large specific suface area, high acid strength and hydrothermal stability are widely used in the fileds of chemical production and environmental protection. In this thesis, ZSM-5/MCM-41 composites were synthesized by a two-step crystallization process, and they were modified by ion exchange process and impregnation. The catalytic activity of the composites was investigated by the reaction of polyhydric alcohols with acetic acid.1. Preparation, characterization and catalytic performance of HZSM-5/MCM-41 compositesZSM-5/MCM-41 composites were synthesized by two-step hydrothermal crystallization process using CTAB as template, Na2SiO3 and the slurry of alkali-treated ZSM-5 zeolite as stuff. The acidity of ZSM-5/MCM-41 composites was modified by ion exchange process, then, HZSM-5/MCM-41 composites were prepared. The catalysts were characterized by X-ray diffraction, infrared spectroscopy, NH3 chemical adsorption and N2 physical adsorption and so on. The results showed that ZSM-5/MCM-41 possess the characteristics of both ZSM-5 and MCM-41, and NH3-TPD results suggested that the acidity of HZSM-5/MCM-41 composites were very strong. Their catalytic activity was evaluated in the esterification reaction of glycerol with acetic acid, and the experimental conditions including reaction time, the dosage of catalyst was investigated. The results indicated that under the optimal conditions of the amount of catalyst was 2.2%, the ratio of acetic acid/glycerol was 6:1, the reaction time was 32h, and during the reaction the water was separated by distillation, the conversion of glycerol and the selectivity of triacetin were up to 100% and 87% respectively.2. Preparation, characterization and catalytic performance of modified ZSM-5/MCM-41The reaction speed is slow and the selectivity of triacetin is low when HZSM-5/MCM-41 composits were used as the catalysts. In addition, because of the strong acidity of HZSM-5/MCM-41 composites, which are easy leading to carbon deposition on catalyst surface and catalyst deactivation. Therefore, SnCl4, Zn(AC)2, Fe(NO3)3 and Fe2(SO4)3 were selected as the active precursor to modify ZSM-5/MCM-41 composits, and Fe-ZM, Zn-ZM, Sn-ZM, ZnO/ZM and Fe2(SO4)3/ZM were synthesized by ion exchange and impregnation methods. The catalysts were characterized by X-ray diffraction, infrared spectroscopy, NH3 chemical adsorption and N2 physical adsorption. The X-ray diffraction and infrared spectroscopy characterization results suggested that the active species are highly dispersed on the surface of ZSM-5/MCM-41 composites. The N2 adsorption-desorption results showed that the impregnation modified has less affected on the structure of mesoporous compared with ion exchange process. NH3-TPD results indicated that the acidity of modified ZSM-5/MCM-41 composites reduced compared with ZSM-5/MCM-41 composites. At last, the reactions of glycerol with acetic acid, and ethylene glycol with acetic acid were selected to evaluate the catalytic activity of modified ZSM-5/MCM-41.The activity of the modified composites was investigated by the esterification of glycerol with acetic acid. The results demonstrated that the catalytic stability of the modified composites improved, but the catalytic activity of the ion exchanged composites didn’t increased significantly. Of all the modified composites, the catalytic activity of the Fe2(SO4)3/ZM composites was the highest. Under the conditions of the molar ratio of acetic acid/glycerol was 5:1, the amount of Fe2(SO4)3/ZM was 1.2%, the reaction time was 14h and the water was separated by distillation during the reaction, the conversion of glycerol and the selectivity of triacetin were 100% and 93%. After regenerating and reusing 7 times, the conversions of glycerol all reached 100%, the selectivities of triacetin stay above 92%.The esterification of ethylene glycol with acetic acid was selected to evaluate the catalytic activity of the modified composites. The results demonstrated that under the investigated conditions, Fe2(SO4)3/ZM was the most active catalyst, followed by H-ZM, Sn-ZM, Fe-ZM. Under the conditions of the molar ratio of acetic acid/ethylene glycerol was 3:1, the amount of Fe2(SO4)3/ZM was 1.2%, the reaction time was 10h and the water was separated by distillation during the reaction, the conversion of ethylene glycol and the selectivity of ethylene glycol diacetate were 100% and 96%. And it was also found that the ether bond of diethylene glycol monoacetin and diethylene glycol diacetate formed in the reaction was easily broken, and then formed ethylene glycol diacetate by reacting with acetic acid.