Removal of greases and lubricating oils from metal parts of machinery processes by subcritical water treatment

• Environmentally benign solvent, subcritical water, can be used as a degreaser.
• More than 90% of degreasing efficiency was obtained by subcritical water treatment.
• Degreasing efficiency was highly dependent on the physical property and chemical composition of grease.
• Subcritical water degreasing was more effective than the conventional degreasing agents.

Toxic or persistent solvents have been widely used to remove greases and lubricants from various machine elements in the washing processes. In this study, an alternative degreasing method that employed subcritical state water was assessed. This environmentally benign solvent has significant potential for various degreasing applications. The operation time and temperature and flow rate of subcritical water had markedly positive impacts on the degreasing efficiency. However, the effect of pressure of subcritical water flow was minimal. The degreasing efficiency was also highly dependent on the physical characteristics and chemical composition of grease. The subcritical water treatment demonstrated a better degreasing efficiency than conventional degreasing methods. Only minor physical damage was observed on the metal parts after the subcritical water treatment. Conclusively, it was found that the subcritical water degreasing system can be used as an effective degreasing technology for machinery operations.

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