Each year a million tons of used oil/water emulsions have to be disposed alone in Germany. Most of these emulsions are wasted by the metal-working industry. Additional 1.2 million tons of oil sludge with water and solid contents have to be treated. The deposition of such products as hazardous waste becomes more and more expensive. Therefore several classical techniques to split emulsions into fractions of oil and water are in use. It is possible to concentrate the emulsions by ultra-filtration, to separate both components by distillation or to add chemicals like acids to split the emulsions.

Alternatively a separation technique using compressed propane was investigated for splitting oil/water emulsions. In the frame of that research, more than 20 industrially used emulsions could be separated into water and oil fractions successfully by using propane. The new technique is characterized by very fast splitting kinetics (some seconds to a few minutes), compared to the classical processes (hours to weeks).

To investigate the mechanism of splitting and the influence of the main process parameters, model emulsions of mineral oil, water and emulsifiers were used. The main focus of the work lies on the behaviour of the tensides at the boundary of the water and oil phase. The emulsifiers are classified with regard to there stabilizing or destabilizing behaviour of the emulsion, depending on the process temperature. Destabilizing is necessary for the splitting by the use of compressed propane. The splitting experiments and the phase behaviour of oil/water/emulsifier at different temperature are illustrated. In addition measurements of surface tension under high pressure are presented.

The technique is meanwhile used in pilot plant scale with a capacity of 40 kg/h (figure 1). The engineering of a 5000 t/year plant is finished and the first industrial scaled plant is in operation.

Figure 1: Pilot plant 40 kg/h (pictures by courtesy of Minitec Engineering)