Recycling of waste artificial marble powder using supercritical methanol

Waste artificial marble powder (AMP), a composite material of poly(methyl methacrylate) (PMMA) and aluminum tri hydroxide (ATH; Al(OH)(3)), was recycled using supercritical fluids, in which the depolymerization and thermal decomposition of organic materials and the dehydration of inorganic substances occur simultaneously. For PMMA depolymerization in AMP, higher temperatures are required than for PMMA alone, because of the ATH in AMP. Moreover, as Al( OH)(3) transforms to alumina (Al2O3), the generated water influences the methyl methacrylate (MMA) yield. In supercritical methanol, MMA is a major product, whereas in sub- and supercritical water, methacrylic acid (MAA) is the main product. The highest yield of MMA was obtained at 573 K in supercritical methanol. The excess methanol in supercritical methanol suppresses the hydrolysis of MMA to MAA, a reaction that reduces the yield of MMA in sub- and supercritical water. MMA was depolymerized in supercritical methanol, but when the reaction proceeded further, the yield of MMA decreased due to thermal decomposition and/or other chemical reactions. While ATH was converted to boehmite (AlOOH) in sub- and supercritical water, the transformation of ATH was minimized in supercritical methanol. (C) 2020 Published by Elsevier B.V.

Automated summary

The waste artificial marble powder (AMP) composed of PMMA and ATH was recycled using supercritical fluids, showing that higher temperatures are required for PMMA depolymerization in AMP due to the presence of ATH. The transformation of ATH to alumina influences the yield of MMA, with supercritical methanol yielding the highest MMA production. The reaction conditions also affect the products obtained, with MMA as the major product in supercritical methanol and methacrylic acid as the main product in sub- and supercritical water.