Published March 1998
Asahi Chemical Industry (Asahi) is constructing a 132,000,000 lb/yr (60,000 t/yr) methyl methacrylate (MMA) monomer plant at the site of its Kawasaki plant. The plant employs a new process based on the direct oxidative esterification of methacrolein (MA) obtained from isobutylene (IB). Unlike current MMA routes, which are based on IB, isobutane, or t-butanol feedstock and involve three synthesis steps for MMA production, Asahi's technology consists of only two steps. In contrast with the other C4-based processes, no intermediate production of MAA occurs. Consequently, the Asahi process is simpler than competing commercial technologies. Moreover, the waste streams it generates are easier to dispose of than those from currently used routes. The process does not produce by-products.
In the first step of the process, IB undergoes vapor-phase oxidation in a fixed-bed reactor to produce MA. The catalyst for the reaction consists of a complex metal-oxide containing molybdenum, bismuth, cerium, cobalt, potassium, iron, and cesium, combined in a specific weight-ratio. In the second step, MA is purified and converted directly to MMA in a liquid-phase simultaneous oxidation and esterification reaction in a stirred-tank reactor. The catalyst for the reaction consists of palladium, lead, and magnesium on an alumina support. The process forms only a small amount of methacrylic acid (MAA) as a by-product in the first stage. Using methanol, MA is then oxidized and esterified to MMA in a single step. Asahi claims high conversion rates and good product selectivities for the process.
This Review evaluates the Asahi technology for a plant with a 250 million lb/yr (113,400 t/yr) MMA production capacity. Our estimates indicate that the total fixed capital investment for Asahi's process is the lowest among other commercially successful processes.