Demetallation of Used Oil to Facilitate Its Utilization as a Fuel

Abstract

Used oil invariably contains soluble and insoluble metal-bearing compounds. The presence of these compounds complicates the recycling of used oil as a fuel, by causing boiler maintenance problems and by making it difficult to comply with paniculate emission standards and Resource Conservation and Recovery Act (RCRA) regulations. Demetallating a used oil before its burning minimizes maintenance problems and facilitates meeting the regulatory requirements controlling its burning. Different physical and chemical methods can be used to demetallate used oils. In this work, a chemical demetallation agent was used to convert entrained nonfilterable metals into a form that could be effectively removed by filtration. Two different types of chemical demetallation agents were used: metallic borohy-drides (NaBH4 and KBH4) and diammonium phosphate (DAP). The activity and selectivity of these demetallation agents under different reaction conditions in various types and sizes of reactors (thereby varying mass transfer rates) were compared. Several types of used oils having different metal contents were examined. It was observed in this study that metallic borohydrides were highly selective with regard to the types of metals they removed. The accompanying sludge formed also made the separation operation inefficient. On the other hand, results obtained with DAP were extremely favorable. The presence of water during the reaction was found to play an important role as a carrier for the DAP, aiding in its dispersion and reducing the importance of mass transfer. This study, which also evaluated different separation techniques, found the use of both sedimentation and filtration to be practical, with filtration rates being significantly accelerated by the addition of low percentages of No. 2 fuel oil.