(243g) High Efficient and Recyclable Heterogeneous Catalysts (Ni-modified zeolites) for Reppe Carbonylation to Acrylic Acid

Reppe Carbonylation is undoubtedly one of the most important reactions in acetylene chemistry for yielding acrylic acid and its esters. Although this route had been replaced by propylene oxidation in the past decade owing to the global availability of inexpensive ethylene from petroleum, the desire for diversified feedstock for bulk chemical commodity is steadily on the increase. Because of the traditional homogeneous catalysts shows disadvantages in the catalyst -product separation and the scaling up of the process, more recent works were focused on the development of heterogeneous catalysts.

 The current paper reports, for the first time, a highly efficient heterogeneous catalyst systems for the hydrocarboxylation of acetylene to acrylic acid. The nickel modified Y zeolites with carefully controlled concentrations of metallic and acidic sites were prepared, characterized and tested in acetylene carbonylation performed in a batch reactor. The catalysts were thoroughly characterized by ICP-AES, X-ray diffraction, Temperature-programmed Reduction, Extended X-ray absorption fine structure, Temperature-programmed desorption of NH₃, pyridine-FTIR, SEM, Raman and thermal gravimetric analysis. It was found that all of the exchanged Ni in zeolite were present as charge-compensating cations and remained this state through the overall reaction. The nickel sites play a determinative role in the carbonylation of acetylene, and the acidic sites would interact with acetylene and favor the protonation of acetylene to form active intermediates, but a too high density of acid sites would cause the formation of coke.  Base on these findings, it is necessary to design a catalyst with a proper ratio between nickel ion and acid sites. In addition, promoters such as copper salts were required, and the CuBr₂/Ni-Y-zeolite has been proved to be a highly effective catalyst system in the hydrocarboxylation of acetylene with 1400 h^-1 of average turn over frequency after six times of recycle at 235℃ and 3.6MPa of initial total pressure with 30min of reaction time. The amount of acrylic acids formed with these Ni-exchanged Y catalysts(4~5×10^⁴g/(molNi*h)) was far higher than those reported with Ni supported on silica gel (~3.4 g/(molNi*h)). Furthermore, the coke deposited on the zeolites, locating mainly on the external of external surface of the zeolite, was present as ordered filamentous nature, and much of them was separated from the zeolite crystals and thus keeps the catalysts with a remarkable reusability. The current heterogeneous catalysts system showes the best catalytic activity for synthesizing acrylic acid by carbonylation of acetylene with carbon monoxide and water  to date.