| The synthesis of new Polyoxometalates (POMs) crystal is the main branch of chemistry. POMs, as environmently-friendly catalysts, have high activity and selectivity, mild reaction conditions, and small corrosion that make them attractive in catalysis. Ethylene glycol is an important raw material for chemical engineering. The large quantities of ethylene glycol are imported in China every year. Ethylene carbonate hydrolysis is one of the most promising industrial technology. Ethylene carbonate hydrolysis includes two processes, the first step is that ethylene oxide and carbon dioxide generated ethylene carbonate, which has been industrialized in the fifties, the second step is that ethylene carbonate hydrolysis, which is the bottleneck in the current study. Development and selection of the catalyst is mainly obstacle. Therefore, POMs crystals catalyzed ethylene carbonate hydrolysis, which has theoretical significance and application prospects.The eight novel POMs crystals with tungstates and molybdates have been designed and synthesized under hydrothermal conditions. Synthesis conditions were studied. POMs crystals are characterized by elemental analysis, infrared spectrography (IR), X-ray photoelectron spectroscopy (XPS) and X-ray single crystal diffractometer. Chemical formulas are as follows: [Ni6(imi)6(B-α-H3AsW9 O33)2]·2H2O (HNU1); [Zn6(imi)6(B-α-H3AsW9O33)2]·2H2O (HNU2); [Mn6(imi)6 (B-α-H3AsW9O33)2]·4H2O(HNU3); Cu4(phen)4(HPO4)2(H2O)2(OH)2][HPMo12O40]·H2O(HNU4); [(CuO6)(As3O3)2Mo6O18][imi]2 (HNU5); [Ni(bpy)2(H2O)2]{[Ni(H2O)2] [Ni0.5(MoO2)6(OH)3(PO4)(HPO4)3[Ni(bpy)2(H2O)]2][Ni0.5(MoO2)6(OH)3(PO4)(H2PO4)2(HPO4)]}·14H2O (HNU6); [{Cu(imi)2}3As3Mo3O15]·H2O (HNU7); [Hphen] [NbOF4]·H2O (HNU8)。X-ray single crystal diffraction analyses reveal that HNU1, HNU2 and HNU3 are isostructural, made up of [AsW9O33]12- anions and [M6(imi)6] complex. [M6(imi)6] complex forms hexagonal metallocycles by bridging oxygen atoms (M = Ni, Zn and Mn). HNU4 and HNU6 are consisted of molybdenum phosphate anions, transition metal complexes and water molecules. HNU4 contains the Keggin anion. HNU6 contains reduced molybdenum phosphate unit. HNU5 is derived from Anderson anion. HNU7 is consisted of a new molybdenum arsenate anion [As3Mo3O15]3-, decorated with three [CuI(imi)2] complexes. The [As3Mo3O15]3- is a new member for the POMs family. HNU8 is composed of [NbOF4]- anion, phen ligand and water molecule. The thermal stabilities of eight POMs crystals reveal that their structures are stable at 200℃below, which provides the basic for the catalysis.The POMs crystals as catalyst, water as solvent, and ethylene carbonate hydrolysis are used to prepare ethylene glycol as the target reaction. HNU1, HNU2, HNU3, HNU4 and HNU8 don't catalytic activity, and HNU5, HNU6 and HNU7 have catalytic activity. HNU5 and HNU7 have higher activity and show characteristics of heterogeneous catalysis for the ethylene carbonate hydrolysis. HNU5 and HNU7 are composited of molybdenum arsenate anions and copper- imidazole complexes, respectively. We also studied process conditions of HNU5 and HNU7 catalytic ethylene carbonate hydrolysis, such as reaction temperature, time, amount of catalyst and water-ester ratio.The optimization process condition for HNU5 is ethylene carbonate of 1.2g, temperature of 95℃, time of 8h, HNU5 of 0.04g and H2O of 1.8ml. Conversion of ethylene carbonate is 90.06%.The optimized process condition for HNU7 is ethylene carbonate of 2.0g, temperature of 95℃, time of 4h, HNU7 of 0.04g and H2O of 2.0ml. Conversion of ethylene carbonate is 90.36%.The reaction activation energy of two catalytic systems is 74.70kJ?mol-1 and 47.87kJ?mol-1 through kinetic explored, respectively. This indicates the activity of HNU7 is higher than HNU5, which is consistent with the experimental results.The reaction condition of POMs crystals catalyzed ethylene carbonate hydrolysis is mild and controllable, low energy consumption, and high conversion rate and selectivity, byproducts CO2 were re-used, which has great industrial prospects and laid the foundation for the pilot study.
|
PDF Full Text Request