Basic metallosilicate catalysts from waste green container glass

摘要

Environmental imperatives to conserve natural resources and to divert waste streams have stimulated significant interest in mineral recycling. This study illustrates that waste green container glass cullet is a suitable feedstock material for the facile synthesis of basic metallosilicate minerals that have potential as heterogeneous catalysts for industrially significant organic reactions. The target product phases, tobermorite (Ca5Si6O16(OH)(2)center dot 4H(2)O), lithium metasilicate (Li2SiO3) and hydroxycancrinite (Na6Ca(AlSiO4)(6)(OH)(2)center dot 2H(2)O) were synthesised by hydro thermal treatment of waste green cullet in alkaline media at 125 degrees C for 14 days. The reaction products were characterised by powder X-ray diffraction analysis, Fourier transform infra-red spectroscopy and scanning electron microscopy. Phase-pure tobermorite (TB) was prepared from a mixture of glass and lime in sodium hydroxide solution. Impure lithium metasilicate (LS) containing minor proportions of portlandite and calcite was synthesised from the glass in lithium hydroxide solution. A mixed product of hydroxycancrinite (HC), with minor proportions of hydroxysodalite, tobermorite and hydrogarnet, was produced from the glass in a solution of aluminium and sodium hydroxides. All three glass-derived metallosilicate products were found to be effective catalysts for the Knoevenagel synthesis of ethyl (2E)-2-cyano-3-phenylacrylate from ethyl cyanoacetate and benzaldehyde. The order of catalytic efficacy followed the trend in basicity of the metallosilicate products, LS TB HC.