Poly(methyl methacrylate) catalytic depolymerization to methacrylic acid

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Polymethyl methacrylate (PMMA) has excellent mechanical and physical properties and is a raw material for surface coating resins, plastics, back lights of automobiles, and electronics, particularly LED-TVs. The world market for the polymer is growing but, like other thermoplastics, recycling technologies are inadequate. Off-spec cast sheets are depolymerized in molten lead baths to recover the monomer but it has environmental concerns and is incapable of treating end-of-life finished products. Primary and secondary (mechanical) recovery methods produce a poor quality polymer. Here we consider tertiary recovery methods combining thermochemical and catalytic processes to convert PMMA to the monomer methacrylic acid. In the first process, we inject PMMA particles directly into a catalytic fluidized bed operating above 300 oC. The polymer melts and contacts both a solid catalyst and hydrogen peroxide to produce gaseous methacrylic acid that we recover at the top of the reactor. The second technology relies on feeding polymer to an extruder operating at high temperature together with radical initiator (like hydrogen peroxide). We recover the gaseous methacrylic acid along the length of the extruder. These technologies may also be combined. Besides understanding the reaction kinetics to design a commercial reactor, we must also identify how to transport fibre glass and other fillers imbedded in the polymer matrix. We will test the technologies in a 610 mm pilot scale fluidized bed.**********************