FRYING OIL RECYCLING WITH DENSE CARBON DIOXIDE

摘要

Waste frying oils are a pollution source that may be eliminated by oil recycling. A possible technology to recycle this oil is extraction with dense gases. In this work we investigate the use of sub and supercritical carbon dioxide to recover the undegraded triglycerides fraction from the waste oil. The experiments have been performed in a semicontinuous extraction system. The effects of pressure (300-400 atm) and temperature (25-80°C) on the extraction yield have been investigated. In order to study the characteristics of the oils recovered under different operating conditions, the concentrations of the polar components coming from the oxidation, hydrolysis, and/or polymerisation of triglycerides have been measured in the extracted oils. The results obtained in the experimental range investigated showed several findings. Extraction yields obtained with liquid CO_2 slightly increased with pressure at constant temperature. With supercritical CO_2 the extraction yields increased with increasing pressure and decreasing temperature (while keeping constant temperature and pressure, respectively); besides, the yield increase with pressure was more significant than with liquid CO_2. As regards to the polar compounds concentrations, it has been found that the effect of pressure and temperature on this variable followed a trend similar to that observed with the extraction yield and that the effect of pressure was also more noticeable with the solvent at the supercritical state.