A System to Reduce Soot Pollution
May. 10 de 2012
By: Ángela M. Betancurt Jaramillo, Unimedios
Incinerators, industries, heating systems and vehicles are some of the sources of pollution that constantly emit gases into the atmosphere such as carbon monoxide, sulfur dioxide or lead, which are substances that affect people's health as well as the environment.
According to the World Health Organization (WHO), 2 million people die each year due to air pollution, above all in the large cities, which causes heart disease, asthma and lung cancer.
The effects of soot
Soot is a combination of very small particles composed of impure black-colored carbon, which are generated by burning wood, coal and mainly diesel engines used in public transport buses, trains, ships and even construction equipment.
Precisely because of its microscopic size, soot has the ability to be easily introduced into organisms, and its atmospheric concentration contributes towards global warming.
The problem of pollution caused by diesel engines stems from incomplete combustion due to insufficient oxygen to enable the fuel to completely burn, producing soot or coal dust.
Once the particles are created through this process, the soot, which is mainly made up of carbon, has two destinations: part of it is released into the atmosphere through exhaust gases while the rest remains inside the engine, causing internal damage.
An optimum reduction
To contribute towards reducing the coal dust produced by those engines, implemented in this country since 1983, the Chemical, Catalytic and Biotechnological Processes research group at the National University (Universidad Nacional) in Manizales, and the MCMA group at the Universidad de Alicante (Spain) are working on a project aimed at degrading the compound using chemical elements.
The first step taken by the chemists at both institutions was to select the (solid) catalysts to facilitate degradation of the soot. These elements are important because they help to make the chemical reactions more rapid and selective, as they have the ability to affect only the compounds of interest, and their use can be prolonged for a number of cycles for the same operation.
In this case, the chosen solids are birnessite or pyrolusite type manganese oxides – the most important within the manganese–, which are characterized by their low environmental impact because they are analogous to minerals found in natural deposits in various regions of the country.
These oxides are inexpensive, as opposed to titanium or palladium, which are usually used, and have greater structural versatility. Also, their properties can be extensively modified as needed.
"The increase in contaminating emissions from diverse sources makes it necessary to develop new and more efficient, economical and environmentally friendly materials. Manganese oxides fulfill these requirements while also making it possible to generate changes in their states of oxidation, chemical composition, structure, surface and morphology, which significantly affect the metallic oxide making it easy to work with", according to Óscar Hernán Giraldo Osorio, a professor at the National University in Manizales.
Calcination, washing and recalcination
The manganese oxides that are to be adapted in the exhaust pipes of the engine are exposed during a first stage to a three–step method consisting of calcination, washing and recalcination. The process lasts for a total of 48 hours and begins by heating the potassium permanganate to 400ºC; it is then removed to wash away the impurities formed during this stage and reintroduced into the oven, this time at a temperature of 60ºC, to be finally recalcinated at 600ºC.
Giraldo Osorio explains that "this process of synthesis was determined based on previous studies. However, it produced better results for modulating the properties for its specific application as a catalyst for burning soot".
The oxides are adhered to a supporting structure created using a material called alumina, which facilitates impregnation and application of the product in the automotive filter, through which the exhaust gases pass into the atmosphere.
After being impregnated into the filter, the oxides begin their work: to retain the soot and begin its process of degradation, made possible by the temperature of the solid when it comes into contact with the contaminant, and which is different from that of the vehicle itself.
"Without the presence of the catalyst, the coal dust begins to burn at 600ºC, which is a temperature that is difficult to achieve, unlike what happens when the solid is present, because the reaction accelerates, thus lowering the temperature by approximately 200ºC according to the UN researcher.
This makes it possible for the material that contains the carbon particles, so damaging to the environment and humans, to be transformed into carbon dioxide, a gas that does not cause respiratory problems.
The research is now in its third phase of pilot tests, and the results until now lead to the conclusion that it will considerably reduce coal dust production, as Colombian regulations limit opacity in vehicular emissions, depending on the model and year, to between 50% and 35%.