Ultrasonic removal of heavy metals from waste oils

A. Fontana et al./ Fuel Processing Technology 48 (1996) 107-113
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iron corresponds a capacity of a waste oil consumption of about 100 ton per day in one blast furnace. The second one consists in coprocessing the treated waste oil in a coal liquefaction or gasification process, or even with coal in a coke oven plant. The third one consists in a copyrolysis of a coal-oil mixture which allows the recuperation of the hydrocarbons with the gas and liquid fractions of the coal, the solid residue of the oil being recovered with the semi coke. This last product is fated to be burned in a power-plant or gasified and has to be free of heavy metals. The high long chain paraffmic content of the waste oil will favor the formation of BTX during the copyrolysis with coal, leading to an important upgrade of the produced tars. The formation of BTX during the thermal cracking of the long chain paraffins is intensively studied in our laboratory on the n-decane, choosen as mode1 compound [ 14-171. This is a true valorization of the waste oils, the absence of contaminants in the residue allows burning it with the semi coke. This project is under assay with the Instituto de Carboquimica, Zaragosa, Spain and supported by the CCE. Preliminary results of lead elimination from waste oil are described hereafter.
University Libre de Bruxelles, Faculte’ des Sciences Appliquies, Service Chimie GMrale SO au. F.D. Roosevelt, cp 165, B 1050, Brussels, Belgium et Carbochimie,
Keywords: Heavy metals; Waste oils; Lead, Oils
1. Introduction
According to the international regulations, waste lubricants are considered as hazardous substances; their transport, disposal and use are regulated. The waste oils amounts generated every year have been evaluated for selected countries, late 1980s or early 1990s (Table 1) [l-4]. The worldwide annual consumption of lubricants is
reaching 40 million tons. One large part of these waste oils are used motor oils which contain mainly paraffinic, naphthenic and aromatic hydrocarbons, additives, degradation products and metals. Among the metal impurities, lead is actually the major one [4,5]. The lead content of the used motor oils is mainly caused by the use of tetraalkyl lead in the fuel, so that a general decrease is observed, from 1% in the late 197Os, down to 0.1% presently. With a content of 1OOOppm of lead, the use of these waste oils causes problems.
Received 15 March 1995; accepted4 March 1996
Abstract
The elimination of lead from used motor oils is performed by ultrasonic lixiviation using nitric acid, the lead being recuperated as lead sulfate during the acid regeneration. Beside the treatment of waste oils by the traditional methods, this new processing way gives alternative routes, not used usually for waste oils, such as introduction through the blowpipes of a blast furnace, addition to the coal in coke oven plants, coprocessing with coal in liquefaction or gasification plants, or even in copyrolysis with coal.
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A. Fontana et al. /Fuel
Processing Technology 48 (1996) 107-I 13
Table 1 Amounts of waste oils generated yearly Country Canada USA Austria Fl-aIlCe West Germany Norway embourg Spain Year 1989 1992 1983 1992 1987 1989 1990 1990 T/year 370000 5000000 650000 290000 860000 55000 10000 300000
FUEL PROCESSING TECHNOLOGY
Fuel Processing
Technology 48 ( 19%) 107- 113
Ultrasonic removal of heavy metals from waste oils
A. Fontana, C. Braekman-Danheux *, C.G. Jung
The major part of the collected waste oils is burned or dumped on the ground. Only a small part is treated, generally for recycling in fresh oil production. The sulfuric acid/Fuller’ s earth process gives a reclaimed oil equivalent to the fresh one in respect of the viscosity index, colour, ash and water content and flash point [6]. But the treatment is very expensive and results in high yield of waste products with high disposal costs (acid tar). The Mohawk/Evergreen Process combines, after a pretreatment, an atmospheric flash evaporation, a vacuum distillation, a.thin film evaporation and a catalytic high pressure hydrogenation. This process yields 65% lube oil and 10% fuels, but also 15% asphalts flux and 10% waste waters [2,‘ 7]. The Entra re-refining process [8] consists in applying a controlled high energy level to the waste oil for an extremely short time so that the hydrocarbon chains pass the stimulated zone intact, while additives are depleted and form a bituminous material. The yield of light yellow lubricant basestock reaches about 85%. For all these processes, the yield of waste material is between 10% and 20% and it contains the major part of the metals. Another way of treatment concerns the total gasification of the waste oil in a fluidized bed [9] to produce a synthetic gas containing about 25% H,, 20% CO and 11% CH,. The metal oxides will have to be mixed with the fluidization product, and separated afterwards. As dumping waste oils causes a dramatic pollution of the water reserves, and furthermore burning waste oils containing lead is dangerous, it is then important to decrease their lead content, especially in countries where the automobile park is rather old, like in southern and eastern Europe, Asia, Africa and Latin America. We develop a new process, now under licence [lo], to decrease the metal content of waste oils. Beside the treatment of waste oils by the traditional methods, we enphasize that our new processing gives three possible alternative routes, not usually used for waste oils. The first one consists in injecting the treated waste oil through the blowpipes of blast furnaces [l l-131, or even, coal-waste oils slurries. The injection of 30 to 35 kg oil per ton of pig iron saves 50 to 60 kg coke. A mass balance shows that the other impurities of the oil does not interfere with the pig iron quality. At a daily capacity of 3000 ton of pig