Synthesis Of Dimethyl Carbonate From Oxidative Carbonylation Of Methanol Catalyzed By Copper Complex Immoblized On Mesoporous Sieve

Dimethyl carbonate,?DMC?is a green chemical product,and has attracted considerable interest in recent years.The main methods for the synthesis of DMC contain ester exchange,direct synthesis from carbon dioxide,oxidative carbonylation of methanol and urea alcoholysis method.The oxidative carbonylation of methanol to DMC is the most perspective route for industrial application due to the inexpensive materials,simple process and low pollution.It is found that the copper complex catalysts have obvious advantages in the decrease of the corrosiveness caused by the chlorine ions and improvement of the catalytic activity.However,the separation of catalysts from the reaction is still difficult.The heterogenization of homogeneous catalysts is a good way to solve the problem of separation.In this thesis,a series of pyridines and imidazoles were selected as the second ligands,and the effect of their structures and electronic properties on the catalytic performences of Cu?phen?Br₂ and Cu?phen??NCS?₂?phen = 1,10-phenanthroline?was investigated.Cu?phen??NCS?₂/MCM-41,Cu?phen??NCS?₂/SBA-15 and Cu?phen??NCS?₂/SBA-16 were prepared by the impregnation-exchange method,and further modified by methyl,propyl and phenyl silane to synthesize Cu?phen??NCS?₂/SBA-16-C1,Cu?phen??NCS?₂/SBA-16-C3 and Cu?phen??NCS?₂/SBA-16-ph.All of heterogeneous catalysts were characterized by FT-IR,UV-Vis,BET and SAXRD,and the reasons for influencing their activities were discussed in detail.1.The alkaline and steric hindrance of imidazoles and pyridines as the second ligands affected the catalytic activity of Cu?phen?Br₂,and the effect of the methyl was very outstanding,i.e.,Cu?phen?Br₂ exhibited the highest activity with N-methyl imidazole or2-methyl pyridine as the second ligand,and the turnover number of DMC was up to 57.8mol_DMC/mol_Cu and 52.2 mol_DMC/mol_Cu,respectively.2.The alkaline and steric hindrance of imidazoles and pyridines as the second ligands also affected the catalytic activity of Cu?phen??NCS?₂.Of all imidazole ligands,when N-methyl imidazole was used the second ligand,Cu?phen??NCS?₂ exhibited the highest theturnover number of 50.4 mol_DMC/mol_Cu.For 2-substituted pyridine ligands,the stronger the electron-donating effect of the substituent on pyridine was,the higher the activity of Cu?phen??NCS?₂ was.The turnover number of DMC was the highest,up to 51.3mol_DMC/mol_Cu,with 2-amino pyridine as the second ligand.3.The loaded type catalysts,Cu?phen??NCS?₂/MCM-41,Cu?phen??NCS?₂/SBA-15 and Cu?phen??NCS?₂/SBA-16,were prepared by the impregnation-exchange method,and their average pore diameters were 2.8,6.4,and 4.3 nm,respectively.When they were used in the oxidative carbonylation of methanol,their specific surface areas had a little influence on their catalytic performance,but the effect of their pore diameters was the greatest.Among three catalysts,Cu?phen??NCS?₂/SBA-15 with the largest pore diameter of 6.4 nm exhibited the highest activity,and the turnover number of DMC was 31.9 mol_DMC/mol_Cu.When the loaded catalysts were reused,it was easy for Cu?phen??NCS?₂ to spread out of the molecular sieve cage with the increase of pore diameter,reducing the content of catalysts and resulting in the decrease of catalytic activities.Cu?phen??NCS?₂/SBA-16 with the moderate aperture had the better stability than other two catalysts.4.Cu?phen??NCS?₂/SBA-16-C1,Cu?phen??NCS?₂/SBA-16-C3 and Cu?phen??NCS?₂/SBA-16-ph were synthesized by the modification of Cu?phen??NCS?₂/SBA-16 with methyl,propyl and phenyl silanes,and their pore diameters were 3.8,3.5 and 3.3 nm,respectively.After the modification,the orifices of the catalysts shrank,the loss of Cu?phen??NCS?₂ was reduced significantly,and the stability increased.Among them,the stability of Cu?phen??NCS?₂/SBA-16-ph was the highest.5.The turnover number of DMC was 32.9 mol_DMC/mol_Cu under the optimal conditions of 130 °C,reaction time of 6 h,total pressure of 4 MPa,and ratio of partial pressure of CO to O2 of 19:1?below the explosion limit of CO?.