Recycling of used PEG solutions by vacuum drying

This study investigates whether high molecular weight polyethylene glycol (PEG) solutions used for waterlogged wood impregnation can be purified using microfiltration and solidified by vacuum or conventional oven drying. Three used PEG solutions were purified with microfiltration and activated carbon, and analysis of total ash content, pH, conductivity, and spot tests for selected ions were performed before and after. Solidification treatments were carried out on new PEG (both solid and in solution) at different temperatures to find optimal process conditions and to assess PEG degradation during treatment. The latter was done by melting point determinations, thinlayer chromatography (TLC), ATR-FTIR spectroscopy, and MALDI-TOF. It was found that the combined microfiltration and activated carbon treatment only removed limited amounts of impurities from the used PEG solutions. Analysis of total ash content and spot test for selected ions were shown to be well-suited, simple, and low-cost methods for determining inorganic impurities. Vacuum drying was found to be the most efficient way to solidify PEG and from the results, it is clear that the solidification process should be terminated at the point where no more water is left, and that the temperature should be kept below 120°C to avoid degradation. Before implementation, the optimal drying time needs to be established individually for each workshop wanting to solidify used PEG to secure optimal PEG quality and minimize energy consumption. Melting point determination was shown to be an efficient way to assess the degradation of PEG and it is advised
to use this method when deciding if the quality of PEG solutions is high enough to be reused.