Elimination of cutting oil wastes by promoted hydrothermal oxidation

• Published in: Journal of hazardous materials 2001-11, Vol.88 (1), p.95-106
• Main Authors: Portela, Juan R., López, J., Nebot, E., Martı́nez de la Ossa, E.
• Format: Article
• Language: English
• Subjects: Applied sciences; Cutting fluids; Cutting oils; Dilution; Environmental Pollution - prevention & control; Exact sciences and technology; Fossil Fuels; Free Radicals; Hot Temperature; Hydrothermal oxidation; Industrial Waste; Industrial wastes; Industrial wastewaters; Kinetics; Lubricating oils; metal-working fluids; Metallurgy; Organic Chemicals; Oxidation; Oxidation-Reduction; Pollution; Promoted oxidation; Refuse Disposal - methods; Supercritical water oxidation; Toxicity; Waste disposal; Waste management; Wastewaters; Water treatment and pollution; Wet oxidation
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/S0304-3894(01)00295-3

Cutting oils are emulsionable fluids widely used in metalworking processes. Their composition is normally oil, water, and additives (fatty acids, surfactants, biocides, etc.) generating a toxic waste after a long use. Generally, it is a waste too dilute to be incinerated and it is difficult to treat biologically. Other conventional treatment methods currently used are not satisfactory from the environmental point of view. Wet air oxidation (WAO) and supercritical water oxidation (SCWO) are two forms of hydrothermal oxidation that have been proved to be effective processes to treat a wide variety of industrial wastes, but hardly tested for oily wastes. In the case of refractory wastes, WAO process is not efficient enough due to the moderate temperatures used. SCWO is a more powerful process since operating temperatures are usually around 600°C, but the use of severe conditions leads to major disadvantages in the commercialization of the technology. In order to enhance WAO and SCWO efficiency at mild conditions, the use of free radical promoters has been studied in this work. Both normal and promoted hydrothermal oxidation have been tested to treat cutting oil wastes in a continuous flow system operating at 300–500°C. Hydrogen peroxide has been used both as a source of oxygen and as a source of free radicals by introducing it into the reactor with or without previous thermal decomposition, respectively. Organic material is easily oxidized in both cases, obtaining more than 90% TOC reduction in less than 10 s at 500°C. At lower temperatures, the use of promoters clearly enhances the oxidation process. Activation energies have been estimated for normal and promoted oxidation processes.