Our Experience of Using Thermally Recycled Silica Gel in a Teaching and Small Research Laboratory Setting

Abstract

Organic synthetic research laboratories generate a large amount of waste. Some of the waste is the silica gel used as the stationary phase in column chromatographic separations. Here, the authors discuss the possibility of recycling silica gel wastes thermally at 600 °C, at which temperature the remnant adsorbed organic material combusts. It could be shown that the recycled silica gel maintains its adsorption characteristics. The process could be repeated 10 times with any discernable deterioration of the separation properties of the silica gel for the product mixture of the reactions used in this research. In those cases where triphenyl oxide remained on the silica gel after the separation of the reaction mixture, such as after Wittig olefination and Appel-type reactions, an increase of phosphorus content was noted in the silica gel after thermal treatment. The original and recycled silica gel was partly analyzed by Brunauer-Emmett-Teller (BET) surface measurements, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and in inductively coupled plasma optical emission spectroscopy (ICP-OES). The process significantly reduced waste production in our laboratory and also led to a reduction in costs associated with acquiring new silica gel and with the management and the disposal of spent silica gel. A simple environmental impact assessment has been carried out.