Chemical recycling of phenol resin by supercritical methanol

Thermosetting resin is one of the most difficult substances to be recycled, because it includes a highly cross-linked structure which gives the polymer chemical and thermal resistances. A preliminary study on the technique to recycle phenol resin was conducted in the present study, which was intended to be achieved by the use of a supercritical fluid. Supercritical methanol was employed because it has the following advantages over supercritical water: i.e., it allows milder reaction conditions and easier operation for the separation of the products from the solvent. The reaction of phenol resin in supercritical methanol was studied by varying the temperature in the range of 300-420 degrees C or changing the reaction time 30-150 min to understand the effects of the reaction temperature and of the reaction time. The conversion increased rapidly above 350 degrees C to give 94% at maximum at 420 degrees C, and the gas fraction also increased at the same time. When a longer reaction time was employed for the reaction at 400 degrees C, the conversion increased without giving additional gas product. From the point of view of liquefaction, the longer reaction at lower temperature would give better results. A gas chromatographic study revealed that the liquid product included phenol and its methylated derivatives. The carbon content of the solid product was higher than the initial phenol resin, showing that some carbonization took place during the reaction.