Reduction of polycyclic aromatic hydrocarbons from thermal clay recycled oils using technical adsorbents

In Italy recycled oils are obtained by treating exhaust oils by deasphaltation, redistillation and subsequent thermal clay processing. PAH concentrations of intermediate and finished products were found to be 1200, 285, 420, and 275, 126 and 60 A.U. (FDA method, sun test), respectively for light, medium and heavy distillation fractions of intermediate and finished products. The polynuclear fractions of all intermediate products and of the light fraction of finished products from exhaust oils exceeded HSE (Health, Safety, Environment) standards. Because the light distillate intermediate product gave the highest FDA value (1200 A.U.), laboratory purification tests were carried out on it using four technical adsorbing substances (two active carbons, alumina silica gel) with an adsorbent/oil ratio of 5/100. No reduction of the PAH fraction was found after oil percolation at room temperature (26 degrees C). Oil treatment as indicated above for 30 minutes at 100 degrees C gave a reduction of FDA values for the light distillate of about 50% using several vegetal active carbons, PAH content were found to be less reduced with silica gel and alumina (32% and 12% reduction, respectively). In any case, the FDA values of active carbon treated oils remained >200 A.U.. The light product which had already undergone thermal clay processing was treated using between 0.5% and 3% of adsorbent in the mix, at 120-265 C, with oil/adsorbent contact times of up to 2 hours. After treatment, the FDA values of most oils fell to below 200 A.U, and the best PAH reduction (about 70%) was obtained with 3% active carbon at temperatures between 120 and 200 degrees C. On the basis of these results, the light oil fraction obtained from thermal clay processing and its 6 samples after treatment with active carbon were tested for compliance with Health Safety Environment standards (viz, FDA <200 A.U., PAF<2%, Total PAH<100 ppm and M.I.<1.0). The best conditions for reducing residual PAH in light fraction of recycled oils are the treatment with active carbon at concentrations between 1% and 3% with 120 OC temperature contact time of about 1 hour.