Pollutants formation, distribution, and reaction mechanism during WT pyrolysis: A review

Waste tires (WT) rubber is non-biodegradable material, tires manufacturing is rapidly increased to meet the demand due to growth in population. Even though it is potential source of resource recovery for various applications such as paving roads, civil engineering severing as insulation material for building construction or costal protection. Its large amount still needs to final disposal. Considering its nature of degradation (thermal), the pyrolysis of WT is regarded as one of the most prominent technology to reduce waste volume as well as production of fuel in different forms. Although pyrolysis reduces the amount of pollutants emission but also resulted in generating various kinds of pollutants. Among those pollutants Polycyclic aromatic hydrocarbons (PAHs), sulfur-based and nitrogen-based pollutants are the major ones. Therefore, many researchers investigated the yield and composition of pyrolysis products but no review has been published till now which mainly discussed on the pollutant's formation and distribution in WT. This review is mainly focused to provide profound knowledge for PAHs, sulfur and nitrogen-based pollutants generation and distribution in the pyrolysis products. The influence of process parameters (final temperature, heating rate, carrier gas, type of reactor), composition of feed has tremendous effects on pollutants formation. Among them, temperature gradient and heating rate are largely known as influencing parameters. As lower temperature favors the formation of aliphatic compounds whereas higher temperature is associated with the production of complex aromatic compounds. Similarly, heating rates from lower to higher result in more PAHs concentration in oil products. This present manuscript will also clarify the reaction pathway/mechanism for degradation of tire rubber. The formation and distribution of these pollutants in liquid, gas and char product with various reaction has been briefly explained. This review will also help for selection of proper process parameters to hinder these reactions. Understanding proper mechanisms for their formation is helpful for designing pyrolysis process and developing better strategy for waste management and producing more eco-friendly fuel.

Automated summary

Waste tire rubber can be reduced in volume and converted into fuel through pyrolysis technology, but it generates various pollutants. Process parameters such as temperature and heating rate affect the formation of pollutants.