The most researched thermal recycling route is pyrolysis. In this process, the polymer chains are broken purely by thermal energy. Normally, when plastics are heated just in the open air, they start burning, which means that they react with the oxygen to produce CO2 and CO. This can be avoided, if instead of air, pure nitrogen is used. In that case the polymer chains are broken into liquids and gasses that resemble diesel and gasoline, but other chemicals like aromatics can be produced as well. Which products are obtained, depends on the temperature, whether a catalyst is used and other parameters.