Elimination of cutting oil wastes by promoted hydrothermal oxidation

Cutting oils are emulsionable fluids widely used in metalworking processes. Their composition is normally oil, water, and additives (fatty acids, surf actants, biocides, etc.) generating a toxic waste after a long use. General ly, 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 fa rms of hydrothermal oxidation that have been proved to be effective process es 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 eno ugh due to the moderate temperatures used. SCWO is a more powerful process since operating temperatures are usually around 600 degreesC, but the use o f severe conditions leads to major disadvantages in the commercialization o f 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 promo ted hydrothermal oxidation have been tested to treat cutting oil wastes in a continuous flow system operating at 300-500 degreesC. Hydrogen peroxide h as 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 decomposi tion, respectively. Organic material is easily oxidized in both cases, obta ining more than 90% TOC reduction in less than 10 s at 500 degreesC. At low er temperatures, the use of promoters clearly enhances the oxidation proces s. Activation energies have beer. estimated for normal and promoted oxidati on processes. (C) 2001 Elsevier Science B.V. All rights reserved.