Molten Salt Oxidation: A Reassessment of its Supposed Catalytic Mechanism and Hence its Development for the Disposal of Waste Automotive Tires

Abstract

Molten Salt Oxidation, MSO, is a thermal, non-flame process that destroys completely organic compounds and retains non-volatile inorganic species in the molten salt. Hydrocarbons are converted to CO2 and steam but rubber tires leave much unreacted carbon. In the EU tire burial will soon be prohibited. MSO uses a carbonate at up to 1200°C with air constantly bubbling through it and into which waste is added below the melt surface. However, the carbonate is not a catalyst, it dissolves oxygen chemically, forming peroxide and superoxide species. But nitrate is a catalyst, increasing the active species, via recycled nitrite. For complete oxidation of used automobile tires devulcanisation was first required. We used a phosphorus compound not used before. Molten carbonate with 5% nitrate now completely oxidized scrap rubber, leaving no carbon in the melt. The off-gases were CO2, H2O, N2 and excess O2. More tests are needed to optimize the system.