Catalytic Studies On The Synthesis Of Dimethyl Carbonate Via Liquid-phase Routes

In order to explore more efficient catalysts and catalytic systems for the synthesis of dimethyl carbonate, three parts of work have been done in the thesis. Studies on the organic ligands accelerated CuCl2 homogeneous catalysts and its additivesIt is well known that the catalytic activity and the selectivity of a homogeneous CuCl2 catalyst are much inferior to those of a slurry Cud catalyst system. Hence, it is highly attractive to develop new homogeneous copper-based catalytic systems with significantly improved catalytic properties. Recently, homogeneous transition metallic-complex catalysts have attracted considerable attention because their high activity and selectivity in many reactions by means of the addition of various useful organic molecular ligand or polymeric ligand systems. The enhanced activity and better selectivity are described to the ligand interaction between the molecular or polymeric ligands and transition metallic species. Three types of polymer-bound monometallic catalysts (PEG-CuCl2, PPA-CuCl2. PVP-CuCl2) respectively containing oxygen, amide and lactara group for dimethyl carbonate (DMC) synthesis by oxidative carbonylation of methanol in the liquid-phase reaction were investigated. The PVP-CuCl2 catalyst (PVP = Poly (N-vinyl-2-pyrrolidone)) exhibitsexcellent catalytic performance for the oxidative carbonylation of methanol with carbon monoxide and oxygen to DMC. The catalyst exhibits much higher activity and selectivity than non-supported CuCl2 in the DMC synthesis reaction. It is shown that the variable of reaction conditions including the catalyst composition, temperature, the amount of catalyst and reaction time have a significant influence on the DMC synthesis. The optimized reaction conditions are as follows: total pressure is 3.0 MPa (PO2 = 0. 24 MPa, Pco = 2. 76 MPa), [Cu2+] - 180 mmol L-1, reaction time = 5h, reaction temperature is between 120 ℃ and 160 ℃, and stirring rale is 1000 rpm. XPS data for PVP, CuCl,, and the PVP-CuCl, (N/Cu = 2) complex show that the binding energies of N1s and O1s in PVP-CuCl, are 399. 35 and 531.22 eV, respectively, which are higher than those in PVP. The Cu photoelectron transitions of the PVP-CuCl2 catalyst were observed at 932. 10 eV with a shoulder peak at 934.01 eV. The difference of the Cu2p32 binding energies between PVP-CuCl2 and CuCL. is 2. 9L and 1. 0 eV, respectively, these results suggest that coordination bones may have occurred between N, 0 atom and metal atom. FTIR data show that the carbonyl band of PVP appearing at 1674 cm-1 is due to the stretching band of carbonyl group in PVP, whereas it shifts to 1610 cm"1 with a well-resolved shoulder at 1668 cm-1 in PVP-CuCla complexes. Compared to that of PVP, these bands were shifted to much lower wavenumbers indicating the existence of ligand interaction between carbonyi moiety and Cu(II) species. The XPS and FTIR data provide evidence that the complexation of the amide ligands with CuCl2. The remarkable increase in the conversion and selectivity is attributed to the presence of a strong complexation effect between Cu(II) and the amide ligands in the polymer chains.Many additives such as CaCl2, MnCl2, MgCl2 and PdCl2 and so on had been investigated, the results showed that most of additives did not work well, only the presence of a small amount of base in the polymer-complexed copper catalysts can lead to a remarkable increase in the efficiency for the oxidative carbonylation of methanol to dimethyl carbonate. The dramatic increase in the reaction efficiency upon the base addition in the present case can be understood by a fine tuning of the ligand interaction between the Cu(II) species and the amide moieties in the PVP-CuCl2 complex. Thisis confirmed by FT1R data. It should be noted that the addition of base will decrease the acidity of reaction system, this will be benefit to the decreasing of corrosive, which is very desirable from the practical point of view.2. Studies on the organic-inorganic hybrid mesoporous materials anchored copper chlorides catal...