NOVEL CATALYSTS FOR THE ENVIRONMENTALLY FRIENDLY SYNTHESIS OF METHYL-METHACRYLATE

The development of a process for the synthesis of methyl methacrylate (MMA) from coal-derived syngas can alleviate the environmental hazards associated with the current commercial MMA technology, the acetone cy anohydrin (AGH) process. A three-step syngas-based process consisted o f synthesis of a propionic acid, its condensation with formaldehyde, a nd esterification of resulting methacrylic acid (MAA) to form MMA. The first two steps, propionic acid synthesis and condensation, are discu ssed here. The low-temperature, low-pressure process for single-step h ydrocarbonylation of ethylene to propionic acid is carried out using a homogeneous iodine-promoted Mo(CO)(6) catalyst at pressures (30-70 at m) and temperatures (150-200 degrees C) lower than those reported for other catalysts. Mechanistic investigations suggest that catalysis is initiated by a rate-limiting CO dissociation from Mo(CO)(6). This diss ociation appears to be followed by an inner electron-transfer process of an I atom from EtI to the coordinately unsaturated Mo(CO)(5). This homogeneous catalyst for propionate synthesis represents the first cas e of an efficient carbonylation process based on Cr group metals. The condensation of formaldehyde with propionic acid is carried out by aci d-base bifunctional catalysts, As a result of screening over 80 cataly tic materials, group V metals (V, Nb, and Ta) supported on an amorphou s silica are found, to be most effective. A 20% Nb/SiO2 catalyst appea rs to be the most active and stable catalyst thus far. Preliminary rel ations among the reaction yield and catalyst properties indicate that a high surface area and a low overall surface acidity (<50 = mol of NH 3/g), with a high proportion of the acidity being weak (<350 degrees C desorption of NH3), are desirable. Long-term deactivation of V-Si-P, Nb-Si, and Ta-Si catalysts suggests that carbon deposition is the prim ary cause for activity decay, and the catalyst activity is partially r estorable by oxidative regeneration.