Abstract
A mixed product of lithium metasilicate (74%) and minor proportions of calcium carbonate, lithium carbonate and calcium hydroxide was prepared by hydrothermal synthesis from waste green container glass in 4 M lithium hydroxide solution at 125 °C. The reaction product was characterised by powder X-ray diffraction and Fourier transform infrared spectroscopy. The lithium metasilicate product was found to be a successful heterogeneous catalyst for the Knoevenagel synthesis of ethyl trans-α-cyanocinnamate from benzaldehyde and ethyl cyanoacetate.
Highlights
Soda-lime-silica glass (SLSG) containers form a large proportion of the urban waste-stream in every developed nation
These data confirm that the principal reaction product is orthorhombic lithium metasilicate (JCPDS file 29-0828), and that calcite, lithium carbonate and calcium hydroxide, are present in minor proportions
The composition of the impure lithium metasilicate obtained in this study is similar to that reported previously for a hydrothermal reaction product of colourless SLSG synthesised in 4 M lithium hydroxide at 100 °C for 5 days [2]
Summary
Soda-lime-silica glass (SLSG) containers form a large proportion of the urban waste-stream in every developed nation. A number of projects have been carried out to ‘upcycle’ surplus soda-lime-silica glass into potential value-added materials such as ion-exchangers, lightweight aggregates and ceramics [1,2,3,4] In this respect, a recent study reports the hydrothermal synthesis of lithium metasilicate (Li2SiO3) from waste container glass and its potential to act as a carrier for zinc ions [2]. Basic inorganic waste-derived heterogeneous catalysts are currently being considered for various organic reactions [7] These include a wide range of mixed oxide materials from fly ashes, slags and red muds, silica-rich phases from slags and rice husk ash, and calcium-rich phases derived from bones, molluscs and egg shells [7]. Lithium metasilicate, prepared by calcination of rice husk ash and lithium carbonate, has proven successful in the catalysis of the transesterification of soybean oil with methanol to produce biodiesel [8]
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