The great interest always aroused by activated coal in industry, both for its characteristics and its many applications, has not kept out of the technological advances that improve the quality of the products. In this sense, a research group of the Department of Inorganic Chemistry of the University of Granada works on a project subsidized by the Spanish Ministry of Environmental Issues to obtain activated coal from polymeric waste as raw materials.
Activated coal is a solid with a big specific area, as it presents numerous pores of the order of the nanometres which make that a surface area of a small quantity of coal ranks equally with the area of a football pitch, as points out the coordinator of the group Francisco Javier López Garzón.
It is used to manufacture filters for cigarettes, in catalysis processes, or in the decontamination of the atmosphere, among other applications. This is, precisely, in the ambit of gaseous effluents depuration, where the research group has been working for four years to obtain activated coal with a developed and homogeneous porosity and lower production expenses at the same time. In general, commercial activated coal are obtained from precursors like olive pits, almond shells or coconut shell, natural and heterogeneous products that produce heterogeneous coal, unselective as regards the absorption of pollutant substances.
Scientists have found an alternative to the use of organic polymers as precursors. However, such precursors are very expensive. That is why they have selected a waste polymer like terephthalate of polyethylene, commonly known as PET, a plastic material used in the production of drink containers. Taking into account that such waste is calculated in millions of tons in all Europe, it is an abundant raw material, easily available, because at best, these containers end up in controlled garbage dumps, whose salvage would involve the compliance of the European regulation currently in force.
The transformation of the PET into active coal is carried out by means of a process of pyrolysis, this is, the material is burnt in a special oven and in the absence of oxygen, in such a way that it does not react with coal, which is the desired product. The researchers have obtained a highly porous, selective and uniform active coal, as they have proved through absorption tests carried out with molecules of different sizes, from nitrogen to organic vapours. Faced with the obtained results, the team is experimenting with other polymeric materials, at the same time that they optimize the production process to obtain a performance of 60%, as an important fraction of the PET volatilizes during the process, and it is necessary to recover it and turn it into coal.