The catalytic performance and corrosion inhibition of CuCl/Schiff base system in homogeneous oxidative carbonylation of methanol

A homogeneous catalytic system, CuCl/Schiff base, was studied in the synthesis of dimethyl carbonate (DMC) by oxidative carbonylation of methanol. It was found that among a number of Schiff bases studied, 1,10-phenanthroline (phen) was the most effective promoter in terms of both the catalytic activity and the corrosion inhibition. The catalytic performance of CuCl was enhanced dramatically and the corrosion of the reaction system was effectively inhibited when phen was used as a ligand. At a reaction condition with a catalyst concentration of 0.2 mol/L, n(Cu/)/n(phen) = 2:3, temperature = 120 degrees C, time=2h, P=2.4 MPa and P-CO/P-O2 = 2 : 1, the conversion of methanol is 23.7%, the selectivity to dimethyl carbonate is 98.3% and the TON is 14.4. The catalytic activity increased by about 270% and the lifetime increased by greater than threefold relative to the CuCl catalyst without addition of phen. The corrosion rates to the HC276 and HC686 stainless steels by the CuCl/phen catalyst are 0.0282 and 0.0071 mg/h. In comparison with CuCl catalyst, the inhibition efficiencies (IE) on HC276 and HC686 stainless steel are 95.4% and 98.5%, respectively, under the same reaction conditions. Scanning electron microscopy (SEM) showed that the pitting corrosion was not observed on the HC686 stainless steel surface after adding phen. The adsorption layer of phen on the surface of the corrosion specimen can prevent the pitting corrosion of the material. (c) 2005 Elsevier B.V. All rights reserved.