Materials may be depolymerized in this way during waste management, with the volatile components produced being burnt as a form of synthetic fuel in a waste-to-energy process.
[2] For most polymeric materials, thermal depolymerization proceeds in a disordered manner, with random chain scission giving a mixture of volatile compounds.
In comparison to simply incinerating the starting polymer, depolymerization gives a material with a higher heating value, which can be burnt more efficiently and may also be sold.
Incineration can also produce harmful dioxins and dioxin-like compounds and requires specially designed reactors and emission control systems in order to be performed safely.
As the depolymerization step requires heat, it is energy-consuming; thus, the ultimate balance of energy efficiency compared to straight incineration can be very tight and has been the subject of criticism.
The presence of PVC can be problematic, as its thermal depolymerization generates large amounts of HCl, which can corrode equipment and cause undesirable chlorination of the products.
[9] Plastic-to-fuel technologies have historically struggled to be economically viable due to the costs of collecting and sorting the plastic and the relatively low value of the fuel produced.
In many countries, incineration with energy recovery remains the most common method, with more advanced technologies being hindered by technical and cost hurdles.
Lignin has been the subject of significant research for the potential production of BTX and other aromatic compounds,[21] although such processes have not yet been commercialized with any lasting success.
Thermal depolymerization is similar to other processes which use superheated water as a major phase to produce fuels, such as direct hydrothermal liquefaction.
[28][29] A demonstration plant due to start up in the Netherlands is said to be capable of processing 64 tons of biomass (dry basis) per day into oil.
Condensation polymers bearing cleavable groups such as esters and amides can also be completely depolymerized by hydrolysis or solvolysis; this can be a purely chemical process but may also be promoted by enzymes.