Catalytic Activity, Lifetime And Corrosive Performance Of CuCl/Schiff Base Catalyst In The Homogeneous Oxidative Carbonylation

Catalytic synthesis of carbonates by oxidative carbonylation of alcohols is an important method in the research and development of the C1 chemistry, which reduces the environment pollution and resource consumption in the chemical industry; it is also a main topic in the field of green chemical industry. The oxidative carbonylation catalyzed by CuCl is one of the most effective methods to produce the carbonates, but this catalytic system often has many disadvantages, such as short lifetime, difficult separation from the products and corrosive effect on the reactor materials. The research and development in the field of copper based catalysts for oxidative carbonylation is needed. Development of a new efficient, environmentally friendly and low-corrosive catalytic system has become a research focus in the field of catalysis. Schiff base ligands combined with CuCl, not only improve the catalytic activity but also reduce the corrosion, which have great theoretical significance and potential applications.Effects of various Schiff base ligands on the catalytic activity of CuCl in the oxidative carbonylation of methanol was studied and discussed in this article. The CuCl/Phen catalyst had the highest activity and the yield of dimethyl carbonate increased three times compared with pure CuCl catalyst. The effects of various Schiff base ligands on the catalytic activity of CuCl in the oxidative carbonylation of ethanol were subsequently explored, and the CuCl/Phen/NMI was the best one among these catalysts. The reaction conditions (catalyst concentration, reaction temperature, etc.) were investigated and the kinetic equation was also established according to the experiment datas. The results indicated that the conversion of ethanol could reach to 15.2% and the selectivity of diethyl carbonate could exceed 99.0% under the optimum condition:. the CuCl concentration of 0.2 mol/L, ligand and CuCl molar ratio of 2:1, reaction temperature 393 K, reaction pressure 2.4 MPa, CO and O2 partial pressure ratio of 2:1, reaction time of 3 h. The yield of diethyl carbonate with CuCl/Phen/NMI catalyst increased to 3.5 times as that of CuCl catalyst. The reaction kinetics with CuCl/Phen/NMI catalyst for the synthesis of diethyl carbonate was investigated. The kinetic equation is and the activation energy Ea is 53.4 kJ/mol.Heterogeneous catalytic systems have many advantages compared with homogeneous system in liquid-phase reactions, including easy separation of catalysts from reaction mixtures and low corrosion rate of catalysts. Preparation of organic-inorganic hybrid material (OIH) supported CuCl catalysts by sol-gel technology was further explored. A novel CuCl/Schiff base/OIH supported catalyst with 7.1 wt%Cu loading was synthesized by y-chloropropyltriethoxysilane(CPTES) as a spacer,5-amino-1,10-phenanthroline (NH2-Phen) as an organic ligand and tetraethyl orthosilicate(TEOS) as a silica source of OIH. The structure of intermediates and supported catalyst were characterized by EA, FT-IR and NMR (1H NMR,29Si-MAS-NMR). The effects of preparation conditions on the synthesis of OIH were investigated. The optimum preparation conditions were:the concentration of NH2-Phen 10 mg/ml DMF, molar ratio of TEOS and CPTES to NH2-Phen 6:1.1:1, reaction temperature 343 K, reaction time 72 h. The catalytic activity of CuCl/Schiff base/OIH in the oxidative carbonylation of methanol was studied. The yield of dimethyl carbonate with CuCl/Schiff base/OIH supported catalyst increased 25.0% compared with CuCl catalysts under the reaction conditions of CuCl concentration 0.1 mol/L, reaction temperature 393 K, reaction pressure 2.4 MPa, CO and O2 partial pressure ratio of 2:1, reaction time 2 h. After recycling 5 times, the catalytic activity remained with a average Cu loss rate of 2.2%. These results indicated CuCl/Schiff base/OIH catalyst was superior in the thermal stability and Cu loss rate.The stability of CuCl/Phen catalyst in oxidative carbonylation of methanol was tested in a batch reactor under the condition of 393 K and 2.0MPa. The lifetime of CuCl/Phen catalyst was more than 330 h. The chemical structure of the catalyst used before and after 330 h in the reaction were characterized with EA, XPS, XRD, TG-DTA, AAS. The reason for the deactivation of CuCl/Phen catalyst was the loss of chlorine and the disproportionation of Cu(â… ). The deactivation mechanism of CuCl/Phen catalyst in the oxidative carbonylation was also discussed.Effects of Schiff base ligands on the corrosive performance of CuCl catalyst in the homogeneous oxidative carbonylation of methanol were also discussed. The inhibition effect of Schiff base ligands with CuCl on the alloy material in oxidative carbonylation system was studied by the weight loss method. The results showed that the ligands with CuCl catalyst system had obvious inhibition effect on the corrosive of alloy. On the conditions of [CuCl]=0.2 mol/L, [Phen]=0.1 mol/L, [NMI]=0.1 mol/L, the inhibition efficiency of TK nickel-based alloys were 98.2%. The corrosion rate of 0.0152 mm/a on TK reached the corrosion resistance of four criteria. Furthermore, the corrosion phenomenon of the alloy materials under different conditions was studied by scanning electron microprobe analysis, combining with electrochemical measurements and oxidative carbonylation reaction mechanism. The corrosion mechanism of the nickel-based alloys in the oxidative carbonylation system and the inhibition mechanism of Schiff base ligands were proposed.