Chemical Recycling of Cellulose Acetate Eyewear Industry Waste by Hydrothermal Treatment

Cellulose acetate waste from eyewear industry is produced in considerable amounts, and its biodegradability is not straightforward due to the presence of plasticizers and the slow kinetics of deacetylation reactions. In this work, the chemical recycling of cellulose acetate waste coming from eyewear industry is proposed through hydrothermal treatment with the aim of acetic acid and diethyl phthalate recovery. Cellulose acetate was first characterized to determine the acetylation degree which was measured to be 2.45 and the amount of diethyl phthalate which was 30% by weight. Hydrothermal tests were performed in batch 10 mL reactors studying the influence of temperature (190-250 °C) and reaction time (10-240 min). The products were characterized by gas chromatography-mass spectrometry and Fourier transformed IR analysis, in order to determine the acetic acid and diethyl phthalate recovery percentage. The maximum recovery of acetic acid, 90%, was obtained at 250 °C for a reaction time of 30 min; in these conditions, the diethyl phthalate extracted was about 20% by weight, which is 65% of recovery. The diethyl phthalate undergoes a hydrolysis reaction at high temperatures and long reaction times, decreasing its recovery degree. The diethyl phthalate is recovered mainly in the liquid phase extracted with ethanol and for 210 °C and 60 min and 190, 240 min it is almost pure (>97%), with a recovery efficiency of 87%. Cellulose decomposition products, mainly 5-(hydroxymethyl)furfural, were detected in the liquid products with an increase raising the reaction temperature and time. Aspen Plus simulation was performed in order to figure out the whole process including the separation of the products; a preliminary energy balance indicates that combustion of the solid residue can contribute to lower the energy required for the process, which results in 800 MJ/h for a plant capacity of 10 ton day-1