A new procedure allows treating used motor oil to exploit its potential energy
FGUSAL/DICYT Used motor lubricating oils are currently considered one of the most important pollutant liquids in the European Union. Little more than 60% can be recycled, the rest is incinerated with the objective of taking advantage of its energetic power, which entails high environmental contamination risks. Researchers from the University of Salamanca are working to innovate in this field. In particular, they intend to use a very advanced technology, oil gasification with supercritical water, to transform them into other valuable compounds.
"Our group has pioneered in Spain supercritical water research," says Francisco Salvador Palacios, a scientist from the Recognized Research Group (GIR) 'Supercritical Fluids and Activated Carbon', which has more than two decades of experience in this field. "The water, when heated above 374 degrees Celsius and 220 bars of pressure, reaches the supercritical state. In this state, water is not a liquid or a gas, it becomes a more or less dense fluid with very surprising properties. One of the most interesting applications of supercritical water is using it to destroy toxic and dangerous organic pollutants in a very efficient way, "he adds.
His partner in the Department of Physical Chemistry María Jesús Sánchez Montero explains that used motor oil is "one of the most abundant and polluting residues that exist." In fact, it is estimated that about 253,000 tonnes are generated each year in Spain. That is why developing an efficient technology to transform them into "high energy value compounds, such as hydrogen and methane becomes such an important goal".
Until now, the most popular way of re-using these residues was to transform them into fuel in cement kilns, but this practice has proven to be very harmful to the environment, while other alternatives to destroy them and extract the energy they contain have shown very low efficiency.
For this reason, researchers from the University of Salamanca considered the use of supercritical water. The project has been developed thanks to the Proof of Concept call of the General Foundation of the University of Salamanca and the TCUE program, promoted by the Regional Government of Castilla y León, and co-financed with FEDER funds. The tests have taken place in the gasification facilities that the group has at the Department of Physical Chemistry.
Water and oil mixtures are introduced, by means of high-pressure pumps, into a tubular reactor placed inside an oven where they are heated to the desired temperature. "The supercritical water reacts quickly with the oil transforming it into liquid and gaseous products, which are cooled and separated in a liquid-gas separator. The obtained products are continuously analyzed by gas chromatography and mass spectrometry techniques, "says Ana María Sánchez, also a member of the group. Researchers study the conditions of pressure, temperature, reaction time and other variables that may influence the process to optimize it.
New products applications
It is not only important to achieve the maximum transformation of the oils, but also that the obtained products are easily exploitable," emphasizes Carmen Izquierdo Misiego, another researcher involved in the project. Hydrogen and methane are the main derivatives in this process, so thanks to their high calorific value "they could be a cleaner alternative to other fuels that are being used today".
Hydrogen is also obtained during the process but the difficulties of storage and transportation due to its high flammability have yet to be overcome. However, this gas has other applications in different industrial processes, such as the production of synthesis gas and ammonia, the obtaining of methanol and the hydrogenation of oils, among others.